Lachlan floodplain wetlands: adaptive water management framework, final report

��

��

Lachlan Floodplain Wetlands: Adaptive Water Management Framework.

Final Report.

Resource Analysis Unit

NSW Department of Land and Water Conservation

ii

��

��

Lachlan Floodplain Wetlands: Adaptive Water Management

Framework. Final report

Authors: Patrick Driver, Chris Higgins, Peter Lloyd-Jones, Alastair Mackenzie-McHarg, Greg Raisin,

Suzanne Unthank and Paul Wettin, Resource Analysis Unit, NSW Department of Land and Water

Conservation

Project Funded by: National Heritage Trust (project LA1039.97) & the NSW Department of Land and Water

Conservation.

Published by: Resource Analysis Unit, Central West Region, NSW Department of Land and Water

Conservation. June 2002. ©NSW Government. ISBN 0 7347 5433 7

iii

Executive summary

This report focuses on:

• Modelling Lachlan Valley wetlands responses to river flow regulation and changes in

flow rules (scenarios within the 2002 draft Water Sharing Plan); and

• Historical changes that have influenced wetland flows.

Lachlan wetland inundation modelling

• This objective of this part of the project was to identify the inundation regime required

to sustain the Lachlan wetlands (assumed for now to be the flow regime that would

currently be occurring if the long-term effects of human activities, such as flow

regulation and abstraction, had not occurred), primarily by considering hydrological

data. The project focussed on reference hydrological models, which partly or largely

represent the natural flow regime of the Lachlan River or the natural inundation

patterns of Lachlan River wetlands.

• Field studies of twelve riparian wetlands were undertaken to determine the river flows

at which wetlands start to fill (commence to flow, CTF) and how long the wetlands

tended to hold water before water levels dropped below the level required for aquatic

plant growth (Tw). This information was used for the riparian wetland-IQQM.

• Literature, archival and field studies were undertaken to determine the CTF and

bankfull discharge for Lachlan River for seven effluent creeks (which are also

'wetlands') This information was used for the effluent creek-IQQM.

• IQQM 'reference' flow models are not precise models of 'natural' or pre-regulation

flows. The IQQM reference models 'remove' the effects of current flow-regulating

structures. They do not incorporate various changes that would have also affected river

hydrology such as alterations in river geomorphology, loss of in-stream vegetation and

alterations in stream sediments. However, checks of the effluent-creek reference run

results with pre-regulation flow records indicated that the modelled current/reference

volume ratio for the period of 1915 to 1920 is within 1% of the annual observed value.

iv

• The wetland-IQQM indicated that:

• The flows of the Lachlan River at the 'end of system' at Oxley are 53% of annual

reference flows. Oxley flows are a surrogate for Great Cumbung Swamp inflows;

• Variability of river flows has been reduced among days, seasons and years, and this

is likely to impact upon the seasonal inundation of wetlands;

• The Lachlan River wetlands are currently full 71 percent of the time they would

have been full before river regulation;

• In spite of the above finding some wetlands closer to the river (e.g., billabongs near

Condobolin) are inundated more often under flow regulation;

• Nationally significant wetlands such as Booligal swamp and the 'Reed Bed' of the

Great Cumbung Swamp are full for 51 and 62 percent of the time they would have

before flow-regulation respectively;

• Wetland impacts are seasonal. Mid-Lachlan wetlands that typically require large

winter-spring flows to fill (e.g., Bocabidgle Creek near Forbes) are most impacted

in June because of reduced frequency of inundation. In contrast, Booligal swamp is

most impacted by reduced flows during the March-to-May dry period;

• Flows of the Lachlan effluent creeks have been severely modified. Lower

Willandra, Middle and Merrowie Creeks currently have a greater annual volume of

flows than they did before flow regulation. In contrast, the creeks further

downstream, Merrimajeel, Muggabah and Cabbage Garden creeks now have a

smaller annual inflow; and

• One of the reasons for the reduced flows in Merrimajeel, Muggabah and Cabbage

Garden creeks is that the offtakes of Willandra Creek, and to a lesser extent Middle

and Merrowie Creeks, are taking relatively more of the flows under the current

regulated flow regime;

• We also provided one example of how biological responses can be modelled using

these IQQM models. This model indicated that the frequency of small ibis breeding

events (about 16,000 nests or less) in Booligal swamp has been reduced because of

v

river regulation.

• The information produced for this document has, and will continue to be of use for

river and wetland management, particularly with regard the Lachlan Environmental

Flow Rules and the Lachlan Regulated River Water Source Water Sharing Plan.

Historical changes that have influenced wetland flows

• It was intended that this document would be a resource for wetland and ecosystem

management in the Lachlan catchment. Many of the findings have broad relevance for

water and other resource management. A lot of the detail is very specific, however, and

has been written for locals with the community and local officers within resource

management agencies.

• A detailed understanding of ecosystem interactions is required for effective

management and rehabilitation of species diversity and ecosystem function in the

Lachlan catchment. Accordingly, a synthesis of major influences on wetland flows

and, to a lesser extent, water quality was provided as a 'first cut', using scientific

literature to conversations with landholders to understand how Lachlan wetland flows

have changed. It is hoped that this synthesis will stimulate more detailed studies, and

help fine-tune resource management decisions. It was concluded that:

• Catchment and riverbank erosion, degradation of native vegetation

communities and carp have caused the degradation of the water quality within

wetlands; and

• Flow regulation and a diversity of works on the floodplain have severely

modified spatial and temporal patterns of wetland inundation.

��

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Lachlan Floodplain Wetlands: Adaptive Water Management Framework.

Final Report.



2

��

��

Lachlan Floodplain Wetlands: Adaptive Water ManagementFramework. Final report

Project team: Patrick Driver, Chris Higgins, Peter Lloyd-Jones, Alastair Mackenzie-

McHarg, Greg Raisin, Suzanne Unthank and Paul Wettin

Project Officer: Patrick Driver1,

Project Manager: Greg Raisin

1Author for correspondence


Central West Region


PO Box 136, Forbes NSW 2871

Phone: 02 6853 9024, Fax: 02 6852 3419

Project Funded by:

National Heritage Trust (project LA1039.97)

Published by:


Central West Region


June 2002

©NSW Government

ISBN 0 7347 5433 7

Picture on cover page:

Charlie’s Point in the Great Cumbung Swamp at sunset

(Photo: Peter Lloyd-Jones)

3

Table of Contents

EXECUTIVE SUMMARY.......................................................................................................................... III

LACHLAN WETLAND INUNDATION MODELLING ............................................................................................ III

HISTORICAL CHANGES THAT HAVE INFLUENCED WETLAND FLOWS ...............................................................V

SECTION 1. OVERVIEW........................................................................................................................... 11

1.1 WHY WETLANDS NEED TO BE CONSERVED ......................................................................................... 11

1.2 WETLANDS OF THE LACHLAN VALLEY AND THE IMPORTANCE OF RIVER-FLOW MANAGEMENT......... 11

1.3 KEY STAKEHOLDERS.......................................................................................................................... 14

SECTION 2. AIMS OF THIS PROJECT .................................................................................................. 14

SECTION 3. METHODS............................................................................................................................. 16

3.1 ACQUIRING LANDHOLDER KNOWLEDGE............................................................................................. 18

3.2 WETLAND COMMENCE TO FLOW AND IQQM .................................................................................... 19

3.3 MODELLING WETLAND INUNDATION USING REMOTE SENSING ........................................................... 25

SECTION 4. LONG-TERM CHANGES IN THE LACHLAN RIVER THAT HAVE AFFECTED

FLOWS ................................................................................................................................................. 27

4.1 NATURAL AND REGULATED FLOWS OF THE LACHLAN RIVER............................................................. 27

4.2 LARGE ENGINEERING WORKS ............................................................................................................. 28

4.3 LEVEES .............................................................................................................................................. 29

4.4 CHANGES IN WATER CLARITY AND THE SHAPE OF THE LACHLAN RIVER AND ITS CREEKS ................. 30

(a) Changes in water clarity over time............................................................................................... 30

(b) Observed changes in river shape and water clarity ..................................................................... 31

(c) The role of riparian vegetation in bank stabilisation ................................................................... 34

(d) Carp impacts on water clarity and riverbank erosion.................................................................. 35

4.5 CHANGES IN AQUATIC AND RIPARIAN VEGETATION ........................................................................... 40

(a) Aquatic vegetation........................................................................................................................ 40

(b) Riparian vegetation ...................................................................................................................... 41

(c) Interactions between vegetation change, turbidity and river flows.............................................. 42

(d) Snags, debris dams and river pools.............................................................................................. 43

4.6 CHANGES IN THE FAUNA OF THE LACHLAN RIVER ............................................................................. 45

(a) Changes in fish communities ........................................................................................................ 45

(b) A general loss of biodiversity ....................................................................................................... 46

SECTION 5. CURRENT AND HISTORICAL FLOWS OF THE LACHLAN VALLEY WETLANDS

................................................................................................................................................. 48

5.1 ECOLOGY AND FLOWS OF THE MID-LACHLAN RIVER ......................................................................... 48

(a) Introduction.................................................................................................................................. 48

4

(b) The creeks and anabranches of the mid-Lachlan ......................................................................... 49

(1) Mandagery Creek.....................................................................................................................................49

(2) Bundaburrah Creek / Bundaburrah Cowal...............................................................................................51

(3) Bumbuggan Creek ...................................................................................................................................52

(4) Goobang Creek ........................................................................................................................................53

(5) Island, Wallamundry and Wallaroi Creeks ..............................................................................................55

(6) Kiargathur Creek / Borapine Creek and Big Brotherony Swamp ............................................................55

(7) Booberoi Creek........................................................................................................................................56

(c) The Bogandillon swamp – Lake Cowal system............................................................................. 57

(1) Lake Cowal – Bogandillon Creek –Lachlan River hydrology .................................................................57

(2) Lake Cowal landscape and ecology .........................................................................................................62

(3) Bogandillon Creek/Bogandillon Swamp..................................................................................................64

(4) Bogandillon Creek and Lake Cowal – problems with salinity.................................................................67

(d) Smaller floodplain wetlands of the mid-Lachlan.......................................................................... 68

(1) Smaller floodplain wetlands ....................................................................................................................68

(2) Gum Swamp ............................................................................................................................................70

(3) Lake Forbes .............................................................................................................................................71

5.2 THE LOWER LACHLAN AND ITS EFFLUENT CREEKS ............................................................................ 73

(a) Torriganny Creek ......................................................................................................................... 80

(b) Merrimajeel and Muggabah Creeks............................................................................................. 81

(1) Works in the Merrimajeel and Muggabah Creeks....................................................................................81

(2) Construction of blockbanks .....................................................................................................................82

(3) Flow into Merrimajeel and Muggabah Creeks.........................................................................................83

(4) Plant growth in Merrimajeel and Muggabah creeks and their effect on flow ..........................................84

(c) Cabbage Garden Creek................................................................................................................ 85

(d) Pimpara Creek/Five Mile Creek................................................................................................... 85

(e) Island Creek and other small lesser-known creeks ...................................................................... 85

(f) Merrowie (Marrowie) and Box Creeks ........................................................................................ 85

(g) Middle (Middle Billabong) and Moolbong Creeks....................................................................... 87

(h) Flow modelling of Middle and Merrowie Creeks......................................................................... 88

(i) Willandra Creek ........................................................................................................................... 89

(1) Willandra Creek - overview.....................................................................................................................89

(2) History of works and flows in Willandra Creek .....................................................................................90

(3) The loss of pools along Willandra Creek, and the possible importance of Morrison’s Lake and weir

pools as a refuge.................................................................................................................................................92

(4) Current land and water use along Willandra Creek .................................................................................92

(5) Willandra Creek flow modelling .............................................................................................................93

(6) Effects of Willandra extraction on downstream effluents........................................................................93

(7) Groundwater flow in Willandra Creek.....................................................................................................94

SECTION 6. CURRENT AND HISTORICAL FLOWS OF THE LOWER LACHLAN STORAGES:

LAKES BREWSTER AND CARGELLIGO.............................................................................................. 95

6.1 THE LOWLAND STORAGES OF THE LACHLAN RIVER - OVERVIEW....................................................... 95

5

6.2 LAKE CARGELLIGO ............................................................................................................................ 96

(a) Overview....................................................................................................................................... 96

(b) Regulation .................................................................................................................................... 97

(c) Flooding sequence........................................................................................................................ 97

6.3 LAKE BREWSTER ............................................................................................................................. 101

(a) Overview..................................................................................................................................... 101

(b) Current and historical flows....................................................................................................... 103

(c) Water quality .............................................................................................................................. 103

(d) Bird breeding and bird mortality in Lake Brewster ................................................................... 104

SECTION 7. DISCUSSION: THE ‘WATER REQUIRED TO SUSTAIN THE LACHLAN

WETLANDS’............................................................................................................................................... 106

7.1 WATER REQUIRED TO SUSTAIN THE LACHLAN WETLANDS............................................................... 106

7.2 THERE IS A COMPLEX RELATIONSHIP BETWEEN LAND AND WATER MANAGEMENT, AGRICULTURAL

SUSTAINABILITY AND WETLAND HEALTH .................................................................................................. 106

7.3 HOW THE FLOODPLAIN COMPONENTS OF THE LACHLAN RIVER HAVE CHANGED ............................. 107

7.4 HOW WATER QUALITY HAS CHANGED .............................................................................................. 109

7.5 HOW ‘HEALTHY FLOW REGIMES’ FOR WETLANDS HAVE CHANGED .................................................. 111

7.6 THE INTERFACE BETWEEN LAND AND WATER MANAGEMENT – WEEDS AND EXCESSIVE PLANT

GROWTH .................................................................................................................................................... 111

7.7 INDICATORS OF ‘HEALTH’ FOR LACHLAN WETLANDS ...................................................................... 112

7.8 CONCLUSION.................................................................................................................................... 113

SECTION 8. ACKNOWLEDGMENTS AND REFERENCES.............................................................. 114

8.1 ACKNOWLEDGMENTS ...................................................................................................................... 114

8.2 REFERENCES .................................................................................................................................... 114

8.3 REFERENCES – PERSONAL COMMUNICATIONS.................................................................................. 122

SECTION 9. APPENDIX 1. COMMENCE-TO-FLOW VALUES FOR LACHLAN VALLEY

WETLANDS ............................................................................................................................................... 124

9.1 METHODS FOR DETERMINING WETLAND CTF USED IN THIS STUDY ................................................. 124

9.2 OTHER APPROACHES FOR DETERMINING WETLAND CTF.................................................................. 128

SECTION 10. APPENDIX 2. CURRENT STATUS OF THE LACHLAN VALLEY WETLAND

DATABASE ............................................................................................................................................... 131

10.1 EXPLANATORY NOTES FOR THE WETLAND DATABASE................................................................. 132

10.2 TIER 1: SUMMARY OF WETLAND DATA BY WETLAND MANAGEMENT DIVISIONS ........................ 133

(a) Wetland value............................................................................................................................. 136

(i) Vegetation..............................................................................................................................................136

(ii) Fauna .....................................................................................................................................................137

(iii) Social .....................................................................................................................................................137

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(b) Wetland Management Capability ............................................................................................... 137

(i) Water Management Capability ..............................................................................................................137

(ii) Land Management Capability................................................................................................................137

10.3 TIER 2 GENERAL INFORMATION FOR INDIVIDUAL WETLANDS.................................................... 138

(a) New fields added in this edition of the LVWD............................................................................ 138

(b) Location...................................................................................................................................... 139

(c) Wetland Values........................................................................................................................... 140

(i) Description ............................................................................................................................................140

(ii) Fauna .....................................................................................................................................................140

(iii) Social Values .........................................................................................................................................141

(d) Wetland Management Capability ............................................................................................... 142

(i) Water Management................................................................................................................................142

(ii) Land Management Capability................................................................................................................145

10.4 TIER 3. SPECIFIC AND DETAILED INFORMATION FOR SOME WETLANDS ...................................... 146

SECTION 11. APPENDIX 3. STANDARD QUESTIONS USED FOR PHONE INTERVIEWS ............

............................................................................................................................................... 149

11.1 GENERAL DETAILS ...................................................................................................................... 149

11.2 LIST OF QUESTIONS FOR PHONE INTERVIEWS FOR ‘ECOLOGY AND FLOWS OF THE LOWER LACHLAN

RIVER AND ITS WETLANDS AND DISTRIBUTARIES’ ..................................................................................... 149

11.3 LIST OF QUESTIONS FOR PHONE INTERVIEWS FOR ‘ECOLOGY AND FLOWS OF THE MID-LACHLAN

RIVER AND ITS WETLANDS AND ANABRANCHES’ ....................................................................................... 150

SECTION 12. APPENDIX 4. IQQM’S OF CURRENT AND UNDEVELOPED LACHLAN

EFFLUENT CREEK FLOWS. .................................................................................................................. 151

12.1 INTRODUCTION............................................................................................................................ 151

12.2 METHODS.................................................................................................................................... 153

(a) The effluent creek IQQM............................................................................................................ 153

(b) Controlled versus uncontrolled flows......................................................................................... 155

(1) Controlled flows ....................................................................................................................................155

(2) Uncontrolled flows ................................................................................................................................155

(c) Willandra Creek ......................................................................................................................... 156

(1) Undeveloped flows ................................................................................................................................156

(2) Regulated flows .....................................................................................................................................156

(d) Middle and Merrowie Creeks..................................................................................................... 156


(2) Regulated flows .....................................................................................................................................156

(e) Merrimajeel and Muggabah Creeks........................................................................................... 157


(2) Regulated flows .....................................................................................................................................157

(f) Cabbage Garden Creek.............................................................................................................. 157

12.3 RESULTS ..................................................................................................................................... 158

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(a) Accuracy check for the undeveloped Lachlan River model ........................................................ 158

(b) Effects of river development on effluent creek flows .................................................................. 158

12.4 DISCUSSION ................................................................................................................................ 165

SECTION 13. APPENDIX 5. FLOW EVENT ANALYSIS OF RIPARIAN WETLAND

INUNDATION IN THE LACHLAN RIVER VALLEY.......................................................................... 166

13.1 INTRODUCTION............................................................................................................................ 166

13.2 METHODS.................................................................................................................................... 166

(a) Wetland inundation frequency.................................................................................................... 166

(b) Event duration analyses ............................................................................................................. 168

13.3 RESULTS ..................................................................................................................................... 169

13.4 DISCUSSION ................................................................................................................................ 177

SECTION 14. APPENDIX 6. DETERMINING WETLAND AREA-RIVER FLOWS

RELATIONSHIPS IN THE LACHLAN VALLEY ................................................................................. 178

14.1 OVERVIEW .................................................................................................................................. 178

14.2 METHODS.................................................................................................................................... 178

(a) Imagery Selection....................................................................................................................... 178

(b) Classification.............................................................................................................................. 178

(c) Defining wetland areas .............................................................................................................. 180

(d) Relating wetland areas to river flows......................................................................................... 180

14.3 RESULTS ..................................................................................................................................... 181

14.4 DISCUSSION ................................................................................................................................ 182

(a) Mid-Lachlan wetland inundation-river flow relationships......................................................... 182

(b) Lower-Lachlan wetland inundation-river flow relationships ..................................................... 182

(c) Challenges in further developing wetland inundation-river flow relationships ......................... 183

8

List of Figures

Figure 1 The flood inlet (or commence-to-flow) channel into Erin’s billabong (north of Hay, Photo: Patrick Driver,

July 1999)......................................................................................................................................................21

Figure 2 Peaks of wetland flow events in 1999 for Lachlan wetlands. Approximate upper and lower boundaries to

wetland Commence to Flow are also provided..............................................................................................22

Figure 3 Duration of inundation of Booligal swamp in relation to the number of breeding pairs of ibis (log-scale).

The line with the 1991 data removed ‘omitting 1991’ is the preferred relationship (see text).......................23

Figure 4 The number of days per month that Lachlan riparian wetlands are inundated at or above the depth required

for aquatic plant growth under four flow scenarios: pre-regulated conditions (N09), the original flow rules (E151),

current regulated conditions (E73a) and proposed flow rules (E179)............................................................25

Figure 5 Regression model predicting the area (km2) of wetland inundation in the mid-Lachlan (KM2) in relation to

log10 (maximum discharge (ML/day) at Cotton’s weir in the last 60 days) (L10FBFLOW). Cotton’s weir is a

Lachlan River flow gauge at Forbes. .............................................................................................................26

Figure 6 Channel changes in the Willandra Creek attributed to the effects of carp (HD). The cross-section

dimensions are exaggerated vertically to illustrate the change. Similar changes in channel morphology are reported

for Bumbuggan and Wallaroi Creeks (FD, LA). ...........................................................................................34

Figure 7 Erosion in the middle reaches of the Lachlan catchment (the 'mid-Lachlan catchment') as reported by

landholders. The minimum number of years that erosion or stability has been observed ('years') is indicated.

Where no number is provided the values for 'years' is not known. The extent of the erosion is also indicated.37

Figure 8 The Lachlan River at Oxley (Photo: David Walker, May 2001). The island shown has not been stocked,

indicating that other effects have contributed to the loss of understorey vegetation (McB). Such vegetation loss is

commonly attributed by landholders to the direct effect of carp feeding.......................................................40

Figure 9 The number of days per month that mid-Lachlan riparian billabongs are inundated at or above the depth

required for aquatic plant growth under four flow scenarios: pre-regulated conditions (N09), the original flow rules

(E151), current regulated conditions (E73a) and proposed flow rules (E179)...............................................49

Figure 10 Direction of surface water flow in the Jemalong Irrigation District and extent of the 1990 flood. Map

compliments of Jemalong Irrigation. .............................................................................................................66

Figure 11 Simulation of flows in the Lachlan River at Oxley under the current flow rules and without regulating

structures. ......................................................................................................................................................74

Figure 12 Wetlands and effluent creeks of the lower Lachlan Valley............................................................75

Figure 13 Simulation of inflow into Willandra Creek under the current flow rules and without regulating

structures. ......................................................................................................................................................77

Figure 14 Simulation of inflow into Middle and Merrowie Creeks (flows combined under the current flow rules

and without regulating structures...................................................................................................................77

Figure 15 Simulation of inflow into Merrimajeel, Muggabah and Cabbage Garden Creeks (flows combined) under

the current flow rules and without regulating structures................................................................................78

Figure 16 Seasonal alterations in effluent flows shown as a percentage of current inflows over undeveloped

inflows .......................................................................................................................................................78

Figure 17 The number of days per month that lower Lachlan (a) billabongs and (b) swamps are inundated at or

above the depth required for aquatic plant growth under four flow scenarios: pre-regulated conditions (N09), the

original flow rules (E151), current regulated conditions (E73a) and proposed flow rules (E179).................79

Figure 18 Lake Cargelligo with White-bellied sea-eagle nest in background................................................95

Figure 19 The Lake Cargelligo system prior to river regulation ....................................................................99

9

Figure 20 The current Lake Cargelligo system ............................................................................................100

Figure 21 Lake Brewster (formerly Lake Ballyrogan) under current conditions .........................................102

Figure 22 Conceptual model for the interactions between management, land and water use and the integrity of the

Lachlan floodplain wetlands........................................................................................................................108

Figure 23 Response of the Great Cumbung Swamp (water height (m) in Australian Height Datum to river flows

measured at Booligal weir (using data from Brady et al. 1995). .................................................................127

Figure 24 Flow in Muggabah Creek in relation to flow in Merrimajeel Creek during uncontrolled flows. Based on

flow recordings (DLWC data, OB)..............................................................................................................155

Figure 25 Modelled percentage of time for given discharges (ML/day) at the offtake of Willandra Creek under the

current flow rules and without the effects of current flow-regulating structures. ........................................159

Figure 26 Modelled percentage of time for given discharges (ML/day) for the combined flows of the Merrowie and

Middle Creek offtakes under the current flow rules and without the effects of current flow-regulating structures.

.....................................................................................................................................................159

Figure 27 Modelled percentage of time for given discharges (ML/day) for the combined flows of the Muggabah,

Merrimajeel and Cabbage Garden Creek offtakes under the current flow rules and without the effects of current

flow-regulating structures............................................................................................................................160

Figure 28 Frequency of duration times for Cotton’s weir (Forbes) flows above 13000 ML/day under modelled

regulated (E73a, E151, E179) and undeveloped (NO9) conditions. ............................................................171

Figure 29 Frequency of duration times for Booligal weir flows above 3000 ML/day under modelled regulated

(E73a, E151, E179) and undeveloped (NO9) conditions.............................................................................172

Figure 30 Frequency of duration times for Booligal weir flows above 2500 ML/day under modelled regulated

(E73a, E151, E179) and undeveloped (NO9) conditions.............................................................................173

Figure 31 Classified wetland image (based on Landsat TM imagery) with a 40 m boundary along the Lachlan

River .....................................................................................................................................................179

Figure 32 Wetland area inundated in the mid-Lachlan versus the maximum Lachlan River peak in the last 60 days

at Forbes (Cotton’s weir). ...........................................................................................................................186

Figure 33 Wetland area inundated in the mid-Lachlan versus the maximum peak in the last 60 days at Forbes

(Cotton’s weir) effects. 1990 data not removed. LFW method shown only. ...............................................186

Figure 34 Wetland area inundated in the lower Lachlan versus the maximum peak in the last 60 days at Lake

Cargelligo weir. ...........................................................................................................................................187

10

List of Tables

Table 1 Benefits of maintaining wetland health...............................................................................................13

Table 2 Approximate 95% prediction intervals for the number of ibis nests at Booligal swamp in relation to the

duration of flows above 2500 ML/day at Booligal weir. ...............................................................................21

Table 3 Impact of flow regulation on the number of days that Lachlan wetlands are inundated. ....................24

Table 4 Common and scientific names of plant species discussed in this document .......................................39

Table 5 Volumes of floodwaters entering flood corridor and Lake Cowal from Lachlan River breakouts (1943 –

1976, Rankine and Hill 1979). Highlighted rows indicate years of major flooding events. ..........................61

Table 6 Record of Significant Floods at Jemalong Weir where the river height would have exceeded the banks and

entered the 21-Mile Break Out (7.31 m, DLWC data). .................................................................................62

Table 7 Dates when Booligal Swamp filled (Commence to Flow, OB) based on flows starting at the Merrimajeel

off-take on Torriganny Creek. .......................................................................................................................83

Table 8 Flows through Willandra weir in early July 1998. ..............................................................................92

Table 9 Physical dimensions of Lakes Brewster and Cargelligo......................................................................96

Table 10 Abundance of waterfowl of Lake Brewster, 1977-1985 (BJ)............................................................104

Table 11 Working values for commence-to-flow of Lachlan wetlands and effluent creeks. ...........................129

Table 12 Management divisions used in the wetland database (part 1) ...........................................................134

Table 13 Management divisions used in the wetland database (part 2) ...........................................................135

Table 14 Flow responses of effluent creeks for regulated and unregulated flow periods.................................153

Table 15 Averages of annual effluent flows under current flow conditions and without flow-regulating structures.

.....................................................................................................................................................158

Table 16 CTF and Duration of wetland inundation (Tw) for the wetlands ......................................................167

Table 17 Average wetland inundation days per year during 1898-2000 ..........................................................168

Table 18 Average wetland inundation days per year during 1898-1920 ..........................................................169

Table 19 The modelled average number of days during which the CTF was exceeded per year for 1898-2000 ...

.....................................................................................................................................................170

Table 20 Modelled monthly frequency of wetland inundation days for selected wetlands of the Lachlan Valley under

modelled regulated (E73a, E151, E179) conditions and without flow-regulating structures (NO9)............174


modelled regulated (E73a, E151, E179) conditions and without flow-regulating structures (NO9) (contd.) ....

.....................................................................................................................................................175


modelled regulated (E73a, E151, E179) conditions and without flow-regulating structures (NO9) (contd.) ....

.....................................................................................................................................................176

Table 23 Pixel values used for determination of wetland area .........................................................................179

Table 24 Comparisons of wetland areas calculated from vegetation mapping (DLWC 1997a) and this report. ....

.....................................................................................................................................................182

Table 25 Wetland inundation areas in the mid-Lachlan for given dates determined from classification of Landsat TM

imagery .....................................................................................................................................................185

Table 26 Wetland inundation areas in the lower Lachlan for given dates determined from classification of Landsat

TM imagery.................................................................................................................................................185

11

Section 1. Overview

1.1 Why wetlands need to be conserved

Wetlands, and particularly healthy wetlands, perform numerous functions that benefit the

human community. In global terms, the minimum dollar value of the functions performed

by wetlands has been estimated at 27 percent of the sum of all gross national products

(Costanza et al. 1997). A summary of these benefits for inland Australian wetland is

shown in Table 1. Although wetlands are of great value, the full extent of their worth to the

community does, however, depend on numerous factors. Local land use, the types of

wetlands and the extent of wetland degradation will all influence which benefits of

wetlands have the greatest effect. For example, in a farmland environment, blue-green

algae blooms in weir pools and billabongs, river and dryland salinity are all influenced by

how well the river’s wetlands are managed. In this context wetlands are often referred to as

the ‘kidneys’ of a catchment, because healthy wetlands can reduce the high nutrient levels

that cause algal blooms. Moreover, wetland trees such as river red gums (Eucalyptus

camaldulensis) and black box (E. largiflorens) will help lower groundwater tables, thereby

reducing the risks of salinity. In contrast, in an urban environment the removal of toxic

hydrocarbons by constructed wetlands (eg the Forbes constructed wetland) could be a

more important wetland function.

In most human-modified environments wetlands need to be actively managed so that the

signs of an unhealthy ecosystem do not become more apparent and intractable. It is far

more cost-effective and achievable to prevent the symptoms of unhealthy ecosystems (eg

salinity, erosion, blue-green algae blooms and loss of biodiversity) than to ‘fix’ these

problems when they arise. Hence, the dollar value of ‘ecosystem services’ to the

community is estimated to increase exponentially the more ecosystems are degraded, and,

as a consequence of environmental degradation, values such as agricultural production are

also reduced (Costanza et al. 1997).

1.2 Wetlands of the Lachlan Valley and the importance of river-flow management

In order to maximise the benefits of the wetlands in the Lachlan Valley a detailed

understanding of how these wetlands function and respond to land and water management

12

needs to be developed. This is a large task in the Lachlan Valley as this valley is renowned

for a number of nationally significant and relatively pristine wetlands, and the Lachlan

wetlands are among the most important wetland environments in the Murray-Darling

Basin (EA 2001). Local rural communities also value these wetlands. A remote-sensing

study found that these wetland and floodplain forests cover approximately 3,500 km2

(DLWC 1997a). That is, about four percent of the entire Lachlan catchment (84,700 km2,

DLWC 1997a). These wetlands display great diversity in form and in biota ranging from

river red gum-lined, deeply incised billabongs in the east (eg, around Forbes) to open

swamps dominated by lignum (Muehlenbeckia cunninghamii) or Cumbungi (Typha

species) in the west (north of Hay).

This study, the Lachlan Floodplain Wetlands: Adaptive Water Management Framework

project (LFW, DLWC 1998, DLWC 2000a), concentrates on the implications of water

resource management on the Lachlan Valley wetlands. This focus is primarily because this

study was conceived at the start of a statewide effort to implement the Council of

Australian Governments (COAG) water reform process. It was specified that (CWRTF

1995, p.1):

“ The major goal of water resource management is to achieve the highest and best value of the

limited resource for community benefit whilst ensuring that use of the resource is ecologically

sustainable … Highest value use refers not only to economic returns from consumptive water use,

but also includes the value to society from environmental and other non-consumptive uses of the

resource”.

13

Table 1 Benefits of maintaining wetland health (adapted from Timms and Moss 1984, Scheffer 1990,DWR 1992a, Brady and Riding 1996, Binney et al. 2001, McMahon and Caskey 2001). The section onagricultural benefits applies to the preservation of wetlands and other ecosystems (eg woodlands) infloodplain environments.

Water quality and erosion Plants provide erosion protection and water clarity improvements because of

sediment trapping, buffering of flows and stabilising of banks and riversediments.

Nutrient trapping helps control toxic blue-green algae blooms Improvement of water clarity The removal of pathogens (eg,. from sewerage) The removal of toxins associated with human activities (eg,. lead, pesticides and

various hydrocarbons) Control of dryland salinity

Hydrological Flood mitigation Storm and flood storage Groundwater recharge and discharge (the latter helps prolong water retention

during droughts). Global-scale climatic effects

Carbon sinks and oxygen sources Regulation of atmospheric and climatic fluctuations

Biological Habitats for reproduction, feeding, nurseries and refuge from predators and dry

periods (including drought) for wildlife; including birds and recreational andcommercial fish stocks.

Biodiversity: freshwater ecosystems are being pushed towards less species-rich andless natural systems because of wetland degradation. Degraded freshwaters arecommonly in a ‘turbid and too-nutrient-rich state’.

Benefits for agricultural enterprises Control of insects by insectivorous bats, birds and mammals and therefore also

control of agricultural pests and some forms of die-back Native grasses provide a drought reserve for stock feed and can produce high-

quality wool from a low-cost/low-input fodder source Improvement of soil fertility (through nitrogen fixation) and structure Pollination of plants by insects and birds (and enhanced honey production in some

areas) Shelter and shade (when provided by the wetland) protects stock, reduces heat and

cold stress and feeding requirements, increases live-weight gain, wool growth,fertility and birth weights. Crop yields increase in response to shelter-belts by20% on average.

Suppression of agricultural (and environmental) weeds Remnant vegetation can increase capital value of the property Bio-geochemical cycling (the availability of N, C, S and Fe and other elements

required for production can be reduced because of the degradation of wetlands) Other

Other commercial values (eg timber harvesting Recreation (fishing, duck shooting, bird watching etc.) Open space, aesthetics and ‘life-fulfilment’ Scientific and educational. This includes the storage of genetic material (‘gene

banks’), and other potential useful information used in medical and other research Spiritual and cultural significance for indigenous peoples. Other cultural values: archaeological and historical

14

These aims are pertinent for the Lachlan Valley wetlands as the water-regulating structures

have the capacity to regulate a large proportion of the water resource. The main upstream

regulating structure on the Lachlan River, Wyangala Dam, has a capacity of 1,220,000 ML

(DLWC 1997a). Carcoar Dam (36,000 ML) regulates flows in the Belubula River. Lakes

Cargelligo (36,000 ML) and Brewster (153,000 ML) are en-route, off-river storages

located in the lower section of the river which are used to supplement irrigation flows in

the lower Lachlan river. The combined capacity of these dams (1,445,000 ML) is larger

than the long-term average annual flow into the Lachlan River (1,282,000 ML, Driver et

al. 2000a). Hence, in the Lachlan the response to the broad COAG aims (CWRTF 1995)

has been to develop the ‘Flow Rules for Regulated Streams in the Lachlan catchment’

(LRMC 1999) which are designed to meet the needs of both the environment and water-

users. Developing a conceptual model for understanding the implications of currently

proposed, as well as future, alterations to these flow rules (cf. LRMC 2002) for the

Lachlan Valley wetlands is one of the key aims of this project.

1.3 Key stakeholders

The key stakeholders, those most affected by and interested in the management of the

Lachlan wetlands and Lachlan River flows, are the:

1. Water-users and landholders in the Lachlan river floodplain;

2. Lachlan River Management Committee (LRMC);

3. Indigenous peoples of the Lachlan River Valley – the Wiradjuri people;

4. Lachlan Catchment Management Board;

5. Landcare and environmental groups of the Lachlan catchment.

Section 2. Aims of this project

The overall health of the wetlands of the Lachlan Valley (hereafter referred to as the

Lachlan wetlands) rely on appropriate water and land management practices. In response

to this need, the NSW Department of Land and Water Conservation (DLWC) and the

LRMC initiated this project. Moreover, the DLWC and the National Heritage Trust have

15

funded this project. The project objectives for the LFW are (DLWC 1998, DLWC 2000a)1:

1. To identify the water required to sustain the Lachlan wetlands . This regime is

assumed to be the natural inundation regime2 that would currently be occurring if

the long-term effects of human activities, such as flow regulation and abstraction,

had not occurred. Hence, for wetlands to be healthy (high in diversity and

delivering ecosystem functions, cf. Table 1) we are assuming that wetland flows

must be:

a) Of a quality that does not interfere with growth, reproduction and survival

of native wetland biota more than the range of water quality conditions that

existed before European-human effects on the catchment were established

(not addressed in detail in this document);

b) in terms of the rainfall-river flow and rainfall-wetland inundation

relationships, similar to what occurred before European-human effects on

hydrology were established (i.e. pre-1850’s).

2. The incorporation of these requirements into an overall water-sharing policy

This document actually focuses on the first aim, as information on wetland-flow

relationships aid in meeting aim 2. Additionally, it is not the role of NHT projects such as

this to develop water-sharing plans. Notwithstanding, much of the information presented in

this document has been submitted to the LRMC and been a critical part of the supporting

information used to develop the Water Sharing Plan (LRMC 2002).

1 The original proposal DLWC (1998) was partially modified after negotiations between DLWC and the commonwealth.

The original proposal also included biological, physical and chemical monitoring of the wetlands. These monitoring

activities are now taking place as part of the IMEF program (see DLWC 2001a and DLWC 2001b).

2 We use the term ‘regime’ to describe the patterns of inundation for 100 years or more (cf. Section 3.2).

16

Section 3. Methods

The following sections attempt to provide an overview of the most important Lachlan

wetlands, and their hydrological responses to changes in land and water management3. In

doing this, it is hoped a conceptual model can be developed that describes the water

required to sustain the Lachlan wetlands.

This project has been split into two wetland areas:

• The mid-Lachlan (Mandagery Creek to Lake Cargelligo);

• The lower Lachlan (Lake Cargelligo to McFarland’s State Forest).

This split was mostly for convenience. Nonetheless, these areas are reasonably distinct in

terms of their ecology, hydrology and geomorphology. For example riparian wetlands

differ markedly. The mid-Lachlan is characterised by billabongs and anabranches that tend

to be more clearly defined and deeper-channelled, and are found in river red gum forest.

Lower Lachlan billabongs are characterised by river red gum and black box woodlands in

a flatter landscape. The lower Lachlan is also characterised by effluent creeks and back-

swamps that are typically poorly defined and large, typically with lignum, Typha and/or

Phragmites, in very flat and open country (DLWC 1997a, Driver et al. 2000b).

This project deliberately excludes some wetland areas such as the Great Cumbung Swamp,

which is being considered in a separate study. Additionally, many areas that straddle the

Murrumbidgee and Lachlan River catchments are excluded4.

There have been numerous works that have altered the flows in the Lachlan River. These

changes started to take effect since pastoralism started in the mid-1800’s (Roberts and

Sainty 1996, DLWC 1997a). Although some effects on flow such as abstraction and flow

regulation are clearly dominant, it is, however, very difficult to determine the relative

importance of all the changes that have occurred in the Lachlan catchment. Ideally, a

3 This document does not, however, provide information on DLWC licensing agreements, policy or implementation of

the flow rules.

4 But see DLWC (1997) for Mirrool Creek and Pressey et al. (1984) for a general description of the Lachlan-

Murrumbidgee confluence

17

dedicated technical study would be undertaken to resolve this question (cf. Young 2001).

As a compromise, this document describes the various interrelated changes in ecology,

geomorphology, river and wetland flow and management that have occurred in the

Lachlan River. Additionally, a preliminary conceptual model for the changes in the flows

of Lachlan wetlands is proposed. This approach, at the very least, provides a more detailed

basis with which to develop a conceptual model for the changes that have occurred in the

Lachlan River. Information from the various methods below are incorporated where

appropriate in this discussion.

To identify the water required to sustain the Lachlan wetlands the following methods were

utilised:

1. Acquiring landholder knowledge;

2. Wetland inundation data and wetland-IQQM’s;

3. Remote sensing techniques for determining wetland area-stream flow relationships.

18

3.1 Acquiring landholder knowledge

The value of community knowledge for developing conceptual models of landscape and

ecosystem functioning is becoming increasingly recognised as an important tool in wetland

and other forms of resource management (Roberts and Sainty 1996, Cullen 2002). In this

study, the use of community knowledge cannot be referred to as oral history (unlike the

information in Roberts and Sainty 1996, 1997), as oral history involves structured face-to-

face interviews. Nearly all interviews were made over the phone, to save time. Information

was not tape-recorded, but was written down only. Questions asked in the phone

interviews targeted perceived knowledge gaps.

Selection of the interviewees was potentially quite biased as it was determined from

DLWC and landholder knowledge of community members likely to have a long-term

memory of landscape changes for the wetland areas of interest. The questions asked are

shown in Section 11. Interviews for the lower Lachlan and the mid-Lachlan took place in

1998-2000 and from 1999-2002 respectively. The sampled populations were biased in

terms of age, gender, race and culture. Most of the interviewees were male landholders 50-

75 yrs old (estimated) of European descent. Ideally, the interviewed population would

have also involved representatives of other components of the community, but resources

made this difficult and further studies (eg interviews of Wiradjuri people) would be

required to address this gap.

For the sake of brevity, the identities of the interviewees are indicated in this document

using a two or three-letter code starting with the first letter of the surname, and ending with

the first one or two letters of the first name (see Section 8.3 for codes). For example, if

John Smith said the “bank had many trees” this document would report ‘The bank had

many trees (SJ)’.

19

3.2 Wetland Commence to Flow and IQQM

The commence-to-flow value (CTF) of a wetland is the river height at which a wetland just

starts to fill (often through a well-defined CTF channel, as shown in Figure 1). Wetland

CTF’s allow for the determination of the temporal sequence of wetland fill as flood peaks

progress down the river, and also approximate determination of whether a flow of a given

size at Wyangala Dam will fill certain wetlands (Figure 2). For some wetlands the duration

of flows above the CTF can provide some reasonable predictive capacity for the size of a

biological response. For example, the size of an ibis (Threskiornis spp. and Plegadis

falcinellus) breeding event can be predicted from the time that Booligal swamp flows stay

above the CTF (Figure 3, Table 2). ‘The lower threshold’ for wetland CTF (Figure 2) is,

for a given point along the river, is the lowest river flow at which wetlands will start to fill.

The upper threshold for wetland is the highest point for wetland fill, beyond which only

duration of flows above the upper threshold is important for further wetland filling. The

determination of Lachlan wetland CTF’s is described in more detail in Section 9.

Ultimately this information on wetland hydrology can be used to determine the biological

responses to river regulation. Quantitative descriptions of biological responses are,

however, mostly beyond the scope of this document. Complementary monitoring programs

(the results of which are in Driver et al 2000, DLWC 2001 a, b, Moore et al. 2002,

Chessman et al, in prep.) aim to predict such biological responses. Nonetheless, to achieve

this ultimate aim, a large amount of data on both wetland hydrology and biology must be

available. Accordingly, the revision of the Lachlan wetland database (Bennett et al. 1988)

was also a small part of this study (Section 10).

CTF values can also be used to estimate the effect of river regulation on wetland

inundation when used in conjunction with DLWC’s IQQM (Integrated Quality and

Quantity Model) river flow runs (eg Table 3, 12.4). The IQQM uses a single set of

climatic data (ie. rainfall, evaporation, ungauged catchment inflow) for the years 1898-

2000, and therefore comparisons between different IQQM runs (e.g., without flow-

regulating structures versus regulated) are based on the same inputs of climatic data but

different river regulation and management rules scenarios. Hence, comparisons between

‘without flow-regulating structures’ (hereafter also referred to as ‘undeveloped’) versus

regulated IQQM runs are not confounded by the pronounced changes in rainfall that have

20

occurred over the last century (cf. Riley 1988). IQQM also predicts how the river flows

will change under different flow management scenarios (for more detail on IQQM see

Podger et al. 1994, DLWC 1999a and 12.4). Many assumptions underlie these runs and

therefore they should be not be seen as precise indicators. In relation to this project the

assumption most concern is probably that the undeveloped river can be modelled simply

by removing the effects of current structures. This limitation is understandable, because

IQQM has mostly been calibrated for current conditions, as the primary purpose of IQQM

is to compare the effects of flow rule changes under current conditions. As outlined in

detail in the numerous sections below, the Lachlan River and its catchment has undergone

radical changes in geomorphology, sediment composition and vegetation. Therefore

streams, rivers and, possibly even floodplains and wetlands, now transmit flow differently.

In particular, many of the channels of the Lachlan have become wider5 and a huge biomass

of in-stream vegetation has probably been lost. It seems likely therefore that the Lachlan

River channel probably provides far less resistance to flow. Moreover, as discussed in

Appendix 5, IQQM probably underestimates the loss of flow variability. Notwithstanding

these concerns, IQQM can provide indications of the relative effects of flow-management

decisions and the impact of flow regulation on rivers and wetlands. The IQQM runs

presented in this report include three regulated river scenarios: E73a, the current flows

plan; E151, a modification of E73a and E179, the new rules as currently proposed. The

details of these runs are discussed in LRMC (2002). A undeveloped flow run N09 is also

presented. The undeveloped run for the effluent creeks, N011, discussed in Section 12 is a

modification of N09.

5 It is also possible that parts of the Lachlan River have been straightened, which would also increase flow rates, but this

document and DLWC (1997) do not provide evidence for this.

21

Figure 1 The flood inlet (or commence-to-flow) channel into Erin’s billabong (north of Hay, Photo:

Patrick Driver, July 1999).

Table 2 Approximate 95% prediction intervals for the number of ibis nests at Booligal swamp inrelation to the duration of flows above 2500 ML/day at Booligal weir.

No. days > 2500 19 52 78 93 96 120 155 186

lower limit 217 3278 8230 11474 12126 17251 24350 30364

upper limit 5174 16274 30666 43165 46128 76262 144090 232418

22

L.CargelligoCondobolin

Forbes

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

22000

150 250 350 450 550 650

Downstream distance from Wyangala Dam (km)

Peak

flow

(Ml/d

ay)

Environmental Flow 15/8/99

Environmental Flow 5/10/99

Spill and airspace release 25-31/10/99

Upper wetland CTF

Lower wetland CTF

Booligal

L. Brewster Bocabidgle (wet river)

Wilga (dry river)

Morgan's

Robsar

WhealbahHazelwood Erin's/Cumbung fill

Thomson'sBooligal/Cumbung

CM738 Gum swamp gully

Hillston

Lake Cowal

Willandra Ck. before weir installationCM Bottom lagoon @ Willanthery

Bocabidgle (dry river)Torig Park CM416

CM738A

CM612 Wyuna Park

CM601 Worrongorra

EstimateCM511 Sanderson's

Figure 2 Peaks of wetland flow events in 1999 for Lachlan wetlands. Approximate upper and lower boundaries to wetland Commence to Flow are also provided.

23

log (number of days exceeding 2500 ML/day)

log

(num

ber o

f nes

ts +

1)

0 1 2 3 4 5 6

02

46

810

omitting 1991

robust regressi

on

all d

ata

Figure 3 Duration of inundation of Booligal swamp in relation to the number of breeding pairs of ibis (log-scale). The line with the 1991 data removed ‘omitting 1991’ is

the preferred relationship (see text).

24

Table 3 Impact of flow regulation on the number of days that Lachlan wetlands are inundated. An average value of 0.64 indicates that the wetland was ‘full’ 64 percentof the time that it would have been without flow regulating structures. These values were determined using IQQM and wetland CTF’s. Effects of regulation weredetermined using the regulation IQQM run E073a and the undeveloped flow run N09 (see Section 3.2 for further explanation).

Bocabidgle Robsar Wilga Morgan's ML

billabongs

Hazelwood Thomson's Whealbah Erin's LL

billabongs

Booligal

swamp

Marrool

Lake

Reed Bed Lignum LL

swamps

All

wetlands

Month Jan 0.83 1.17 0.67 0.71 0.80 0.50 0.44 0.82 0.33 0.67 0.50 0.50 0.50 0.47 0.49 0.63

Feb 1.00 1.00 0.71 0.83 0.85 1.00 0.40 0.88 0.00 0.74 0.50 0.60 0.50 0.50 0.54 0.68

Mar 1.00 1.00 0.80 1.36 1.13 0.00 0.50 0.85 0.00 0.65 0.33 0.64 0.33 0.44 0.49 0.71

Apr 0.75 1.25 0.80 1.56 1.18 0.50 0.25 0.50 0.00 0.41 0.33 0.54 0.40 0.41 0.45 0.65

May 0.75 1.00 0.80 1.56 1.14 0.50 0.50 0.44 1.00 0.50 0.33 0.46 0.40 0.47 0.44 0.66

Jun 0.67 1.00 0.67 1.18 0.93 1.00 0.75 0.63 0.50 0.71 0.67 0.38 0.60 0.50 0.48 0.69

Jul 0.69 1.00 0.54 0.88 0.76 0.71 0.71 0.70 0.67 0.70 0.80 0.53 0.60 0.44 0.56 0.68

Aug 0.71 1.08 0.67 0.91 0.83 0.83 0.77 0.69 0.50 0.72 0.50 0.72 0.76 0.56 0.67 0.75

Sep 0.75 1.07 0.74 1.00 0.89 0.85 0.82 0.84 0.50 0.78 0.53 0.88 0.86 0.50 0.74 0.80

Oct 0.79 1.08 0.75 1.05 0.92 0.90 0.83 0.91 0.56 0.83 0.53 0.85 0.86 0.47 0.71 0.81

Nov 0.73 1.13 0.62 0.94 0.84 0.57 0.67 0.91 0.57 0.75 0.50 0.71 0.88 0.50 0.66 0.74

Dec 0.70 1.14 0.58 0.81 0.78 0.50 0.64 0.87 0.40 0.72 0.60 0.59 0.71 0.47 0.59 0.68

Average 0.78 1.08 0.69 1.07 0.92 0.66 0.61 0.75 0.42 0.68 0.51 0.62 0.62 0.48 0.57 0.71

Median 0.75 1.08 0.69 0.97 0.87 0.64 0.65 0.83 0.50 0.71 0.50 0.60 0.60 0.47 0.55 0.69

Minimum 0.67 1.00 0.54 0.71 0.76 0.00 0.25 0.44 0.00 0.41 0.33 0.38 0.33 0.41 0.44 0.63

Maximum 1.00 1.25 0.80 1.56 1.18 1.00 0.83 0.91 1.00 0.83 0.80 0.88 0.88 0.56 0.74 0.81

25

0

5

10

15

20

Jan

Feb

Mar

Apr

May

Jun Jul

Aug

Sep

Oct

Nov

Dec

Month

Wet

land

fills

per

mon

th(L

achl

an w

etla

nds)

N09

E73a

E151

E179

Figure 4 The number of days per month that Lachlan riparian wetlands are inundated at or above the

depth required for aquatic plant growth under four flow scenarios: pre-regulated conditions (N09), the

original flow rules (E151), current regulated conditions (E73a) and proposed flow rules (E179).

3.3 Modelling wetland inundation using remote sensing

Several studies (eg Green et al. 1998, Shaikh et al. 1998, Frazier 1999) have used remote

sensing techniques to determine the relationship between the areal extent (eg in hectares)

of wetland inundation and river flows. This method is still in the development stage in the

Lachlan Valley. Studies so far indicate that remote sensing estimates of wetland area

concur with wetlands areas estimated with vegetation mapping. Additionally, a wetland

inundation-river flow relationship has been developed for the mid-Lachlan (Mandagery

Creek to Lake Cargelligo, Figure 5). The remote sensing analyses developed so far are,

however, not reported in the remainder of the document (except in 13.4). Difficulties in

this method, and suggestions for further improvement are discussed in greater detail in

13.4.

26

3.0 3.5 4.0 4.5 5.0 5.5L10FBFLOW

0

200

400

600

800

1000

KM

2

Figure 5 Regression model predicting the area (km2) of wetland inundation in the mid-Lachlan (KM2) in

relation to log10 (maximum discharge (ML/day) at Cotton’s weir in the last 60 days) (L10FBFLOW).

Cotton’s weir is a Lachlan River flow gauge at Forbes.

27

Section 4. Long-term changes in the Lachlan River that have affected

flows

4.1 Natural and regulated flows of the Lachlan River

Natural stream-flows in the Lachlan are generally highest between June and October and

lowest in late summer (February-March). Although summer and winter flows of the

Lachlan River downstream of Wyangala Dam have been greatly affected by river

regulation, this seasonality persists (DLWC 1997). This seasonality is also reflected in the

patterns of wetland fill (Figure 4)

It is generally held by landowners in the lower Lachlan that less water now reaches the

lower end of the Lachlan River (eg FI, McB, SB). It could be argued that such

observations are biased by a relatively wet period since the mid-1940’s, that included

several floods (Riley 1988). Nonetheless, IQQM runs that allow an estimate of the effects

of river regulation support these assertions, indicating that the end of the Lachlan River (at

Oxley) now receives about 53 percent of undeveloped flows on average. Moreover, a study

in the lower Lachlan (Sims 1996) has indicated that the size and duration of large spring

floods (greater than 3777 ML/day) and smaller (greater than 315 ML/day) floods have

decreased for the Lachlan River at Booligal6. Modelling of the lower Lachlan flows (Sims

1996) indicated that the frequency of smaller flows (about 200 ML/day) at Booligal weir

increased. Additionally, inter-annual variability in flows has probably been reduced.

Wyangala and Carcoar Dams and Lakes Cargelligo and Brewster allow water to be saved

from year to year so that water delivery is more reliable, particularly after 1935 (Lloyd

1988, cf. LRMC 2002).

Various IQQM runs, wetland CTF’s and estimated time of wetland drying have been used

to estimate that the Lachlan River wetlands are currently full 71 percent of the time they

would have been full before river regulation (Table 3, 12.4). This estimate, however,

6 The model by Sims (1996) compares regulation flow data against flow data when flow regulation was much less

intense. It should also be noted that hydrological models are calibrated using real data, and the data used for calibration

can have a large influence on flow-rainfall relationships in the final models.

28

averages and oversimplifies the responses of fundamentally different wetlands. For

example, the wetland-IQQM indicates that two billabongs close to the river near

Condobolin (Robsar and Morgan’s) fill at frequencies greater than 100 percent times

undeveloped, suggesting over-wetting is occurring (discussed in Section 5.1(a)). In

contrast, nationally significant wetlands such as Booligal swamp and the Reed Bed of the

Great Cumbung Swamp are full for 51 and 62 percent of the time they would have before

flow-regulation respectively. It is also of ecological significance that these patterns vary

seasonally, and that these seasonal differences vary depending on the wetland. Mid-

Lachlan wetlands that typically require large winter-spring flows to fill are most impacted

in June or July. In contrast, Booligal swamp is most impacted in during the typically dry

period that extends from March to May. In the latter case, this may be largely affected by

the diversion of waters for irrigation into Willandra and Merrowie Creeks (Section 5.2).

4.2 Large engineering works

There have been a number of engineering works in the Lachlan River. The weirs at Lake

Cargelligo (many spellings have been used for this lake, eg Lake Cudgelligo or Cargellico)

and Booberoi Creek were funded under the Water and Drainage Act of 1902, and

completed about this time (Lachlander 1902, Lloyd 1988, DLWC 1997a). Wyangala Dam,

the main storage for the Lachlan, was completed in 1936 (Lloyd 1988), although it did not

fill until the early 1940’s (DLWC 1997a). A combination of the growth in irrigation and a

dry period in the late 1950’s and 1960’s which required a water rationing scheme in the

lower Lachlan, led to pressures for further storages. This resulted in the enlarging of

Wyangala Dam, which finished by 1971, and the construction of Carcoar Dam on the

Belubula River by 1970 (Lloyd 1988, DWR 1972, 1989). Together, Wyangala and Carcoar

Dams control about 70 percent of the run-off from the Lachlan catchment (DLWC 1997a).

Wyangala Dam reached full capacity in 1971 (DLWC 1997a). In 1936 a weir was built at

Jemalong where the Lachlan River narrows as it passes through the Jemalong Range

(DLWC 1999b). Lake Ballyrogan was fully modified to become Lake Brewster in 1950

(DWR 1972), with construction starting in 1946. The Hillston and Booligal weirs were

built at around the turn of the century for town water supplies. These are both fixed crest

structures. Hillston weir was rebuilt in the 1950’s. The Booligal weir was rebuilt with a

slight relocation sometime during 1931 to 1945. These various works throughout the

Lachlan River have allowed large-scale irrigation projects to be established (irrigation

29

accounts for most water usage, eg 93% in 93/94, DLWC 1997a).

Aside from the major water storages there are a variety of small structures that alter

impediment to stream flow. The DLWC’s weir inventory database lists about 340 water-

related structures in the Lachlan catchment. Weirs have environmental impacts such as the

reduction of flow variability, trapping of sediments, nutrients and pollutants, reducing

water quality, obstructing the migration of native fish and creating pools that favours

introduced species over native ones (Thoms and Walker 1992, Walker and Thoms 1993,

DLWC 1997a, Driver et al. 1997, Harris 2001). Lesser-known forms of abstraction include

the use of farm dams in many of the creeks in the upper catchments. The cumulative effect

of these on the flows on the Lachlan River is unknown, but could be quite large. There is

also some evidence that a number of unregulated streams such as Mandagery Creek,

Burrangong Creek and Goobang Creek have a high level of extraction relative to other

unregulated streams in the Valley (DLWC 1997a) mainly because of agricultural, mining,

urban and rural residential requirements. The combined effect of large and small

structures, irrigation, stock and domestic supply, extraction for mining and also urban

domestic, urban industrial and rural residential requirements, have all produced changes in

the volume and patterns of flows over time in the Lachlan River.

4.3 Levees

Numerous levees and irrigation channels exist along the Lachlan River (eg Brady et al.

1998). In particular, landholders in the mid-Lachlan attempt to keep the floods off their

valuable agricultural land by use of levees. Levees in the mid-Lachlan are larger and more

prevalent compared to the upper and lower Lachlan because of frequently larger-sized

floods. Nonetheless, larger floods (eg 1974 and 1990) top most levee banks. Irrigation

channels on the floodplain also divert floodplain waters. In the lower Lachlan even very

low (eg 10 cm high) structures can have fundamental effects on floodplain flows, because

of the flat landscape. The overall effect of these structures would be to generally increase

the amount of water delivered to the lower Lachlan, and such effects can lead to increased

channel erosion (Warner and Bird 1988). However, this effect is unlikely to increase the

volume of flows to the lower Lachlan, at least during non-flood flows, as it is dwarfed by

irrigation diversions. The construction of levees to prevent inundation by floodwaters can

have significant impacts on wetlands by (Warner and Bird 1988, DWR 1992a):

30

• Decreasing the frequency and depth of inundation in wetlands outside the floodway;

• Increasing the depth and velocity of flows passing through wetlands inside thefloodway;

• Encouraging the clearing of wetland vegetation outside the floodway;

• Altering flow distribution and frequency upstream and downstream of the levee;

• Contributing to changes in vegetation distribution and health;

• Increasing bed and bank erosion within the river and, consequently, increasingsediment delivery to wetlands.

4.4 Changes in water clarity and the shape of the Lachlan River and its creeks

(a) Changes in water clarity over time

Various causes of erosion, vegetation loss and carp effects (all discussed below) are likely

to have contributed to the reductions in water clarity in the Lachlan River and its wetlands,

tributaries and distributaries, and erosion is one of the more important processes. The

Lachlan River has probably always carried a high amount of suspended fine sediment7,

and has consequently often had low water clarity. The turbidity (‘muddiness’ of the

water8) of the Lachlan River and its tributaries and distributaries is now, however,

generally higher than it was before the 1960’s, particularly during low flows (Roberts and

Sainty 1996, 1997). The historical changes in water clarity can be partly attributed to

catchment and riverbank erosion processes that have increased the amount of fine

sediment (clay and silt) in the Lachlan River. The link between erosion and turbidity is not

simple. Firstly, turbidity is only partly affected by the sediments within the river because it

is primarily the fine sediments that scatter light primarily that increase turbidity.

Nonetheless, the floodplain sections of the Lachlan River tend to have low energy flows

and therefore many of the suspended river sediments are clays and silts. Hence, in the

7 The amount of sediment suspended within the whole river water column should not be confused with the bedload. The

bedload is the amount of sediment that moves along the streambed (Young 2001), and tends to be comprised of heavier

particles.

8 Turbidity and other processes reduce water clarity. In the Lachlan the other important processes are the leaching of

tannins from Eucalypts, which causes ‘black water’ (eg see Roberts and Sainty 1996) and the development of algal

blooms.

31

discussion below it is argued that the erosion of the Lachlan Valley catchment and riparian

zones, which lead to the input of fine sediments into the river, and water clarity are closely

connected.

(b) Observed changes in river shape and water clarity

The Lachlan River is naturally turbid, but it has become more turbid over time. The shape

of the Lachlan River channel, particularly the lower Lachlan channel, is characteristic of

rivers which carry much of their sediment load in suspension: tree-lined banks of high

stability, steep sided, narrow, and highly sinuous (winding). Widths to depth ratios are low

on the plains (eg 5.0 to 1 at Forbes), higher upstream (12.4 to 1 at Cowra) (DLWC 1997a)

and generally increasing along the Lachlan River (LM). Hence, landholders currently

report highly turbid water throughout the Lachlan River during high and low flows

(Roberts and Sainty 1996). Similarly, Oxley (1820) observed that the Lachlan River was

commonly turbid, particularly below Hillston (cf. Roberts and Sainty 1996). Nonetheless,

late 1800’s and early 1900’s newspaper reports and landholder accounts indicate that prior

to the 1960’s the waters of Lachlan River were often clear, except after heavy rain or large

river flows (Roberts and Sainty 1996, 1997). Moreover, during low flow periods the river

would often become black with tannins, and large fish kills were consequently observed

(Roberts and Sainty 1996).

The main processes contributing to the sediment load within the Lachlan River are various

forms of erosion, turbid outflows from Lake Brewster (Thurtell et al in prep, Section

6.3(c)), carp and loss of instream and riparian vegetation (Sections 4.4(c)-4.5). Erosion

includes riverbank scouring, undercutting and slumping, incision of the streambed and

gully erosion. Causes of riverbank erosion are complex, depend on the local river

conditions and operate on many time-scales. A 1995/1996 survey found that most of the

worst areas for erosion along the Lachlan River occurs in mid-Lachlan and upland sections

(DLWC 1997a, Massey 1998). This survey recorded that the stability of the riverbank

along the headwaters, the middle sections of the Lachlan and the lower reaches9 were

9 The headwaters include the Lachlan headwaters to Wyangala Dam, Boorowa and Hovells Creek and Crookwell and

Abercrombie Rivers.

32

respectively rated by as ‘moderate to good’, ‘moderate to poor’ and ‘good’10. Accordingly,

landholder accounts provide evidence for a concentration of riverbank erosion in the

middle reaches of the Lachlan (Figure 7). Scouring of the walls of the river channel is

common in the upper Lachlan. Erosion occurring away from watercourses, particularly

gully erosion in the upper catchment where the landscape is steep would also contribute to

the sediment load of the Lachlan River. In the mid and lower Lachlan, particularly

between Cowra and Forbes, periods of prolonged wetting, particularly those followed by

rapid drops in water level, lead to bank collapse (‘slumping’, Gordon et al. 1992).

Slumping is generally associated with steep and unvegetated banks subject to sharp drops

in river levels, occurring during large floods (eg during 1990) or when releases from the

Wyangala storage have been stopped abruptly rather than tapering off (DLWC 1997a,

LM). This process of slumping is exacerbated the undercutting of banks. Permanent low-

discharge stream-flow in the Lachlan River has undercut banks, and has also been

associated with the simplification of channel form. Flow regulation, by extending and

dampening the release of flood events, and de-synchronising upper river and tributary

flows, usually keeps flows within the channel (Walker et al. 1995, DLWC 1997a).

Furthermore, between Cowra and Forbes the river has incised into the floodplain, reducing

the connection between the river and the floodplain (DLWC 1997a). Such channel incision

immediately below dams, and a loss of floodplain connection, is a commonly observed

phenomenon (Ligon et al. 1995).

Although rivers do change shape because of natural processes, the shape of many sections

of the Lachlan River channel have been fundamentally altered because of the erosion

processes described above, and also because of grazing impacts on riparian vegetation

(Section 4.4(c)). Such changes have been observed by many landholders. In some sections

of the mid-Lachlan River banks have widened eight to ten meters on straight reaches, and

up to approximately 15 m on the outside of bends (WL). Sections of the undeveloped

lower Lachlan River are similarly described as considerably deeper and narrower, with a

hard bottom that had little sediment (PL, near Lake Brewster). Lowland sections of

regulated Murray-Darling Basin rivers with a similar floodplain terrain (eg the

Murrumbidgee River) also tend to develop wider and shallower channels, usually in

10 ‘Poor’, ‘moderate’ and ‘good’ are respectively defined as between 30 and 49%, 50 and 69% and 10 and 29% of theupper and lower banks in a particular subsection were unstable or actively eroding.

33

association with an increase in bedload and discharge (Young et al. 2001). The pre-1960’s

Lachlan River also had more pools in the rivers and creeks, which once were the point of

collection of flows from upstream during dry periods (Lloyd 1988, Roberts and Sainty

1996, FI, WR). It is also worth noting that flow regulation effects, particularly a decrease

in flow variability, can lead to the loss of multi-level benches (Young et al. 2001),

although it is not clear whether this process has occurred in the Lachlan River.

Increases in channel width and reduced channel depth have also been observed in many of

the Lachlan creeks. In these streams increased flow, and possibly carp, cause channel

widening. In some of these streams a dominance of instream vegetation probably also

contributes to channel widening because flows are pushed towards the banks (LM, eg.,

Wallaroi and Willandra Creeks). For example, Wallaroi creek at the “Kimaori” irrigation

pump site was about 1.5 m deep about 20 years ago, but is now less than 0.6 m deep, and

parts of the Wallaroi creek have increased in width by about 2 m (FD). Similarly, since the

1960’s, the lower reaches of Bumbuggan creek have become wider and shallower, with

large sand and mud banks forming on the inside bends and large trees falling into the creek

on the outside bends (LA, Massey 1998). These changes in Bumbuggan Creek have

coincided with increases in flows (Massey 1998), and the arrival of carp (LA). Similarly,

after 1972 the shape of Willandra Creek changed with the holes in the upper ends of the

creek filling up, and changes in the creek shape occurred as shown in Figure 6 (HyD). The

shape of the creek has not changed over this same period in the middle to lower reaches.

This part of this creek remains open and flat, with very shallow banks (LaP). Comments

associated with DLWC gauging records in the upper reaches of Willandra Creek (‘Road

Bridge’ site 412012) similarly indicate these changes in channel shape, because they report

problems in gauging flows because of the build-up of silt and aquatic plants since the early

1900’s. Moreover, the bank at this site has a number of river red gums where the bank has

fallen away from the roots, indicating the channel has increased in width (McK)11.

11 Channel cross-section data in the upper reaches (at Tocabil and Road Bridge stations) of Willandra Creek also suggest

this pattern of channel shape change, but the comparisons over time are not completely valid because they are at different

locations.

34

Figure 6 Channel changes in the Willandra Creek attributed to the effects of carp (HD). The cross-

section dimensions are exaggerated vertically to illustrate the change. Similar changes in channel

morphology are reported for Bumbuggan and Wallaroi Creeks (FD, LA).

Unimpacted riverbanks of the lower Lachlan are described as having been much more

gently sloping (CS, McB, respectively near Booligal and Oxley). In some instances, such

descriptions could be misleading because there is not a linear relationship between bank

slope and the degradation of a bank. Field observations indicate that the steepest state is

where stock impacts are relatively low and riparian vegetation holds the top of the bank

together. In this instance, the bank is steep because of constantly regulated low flows, and

possibly also carp, which undercut the toe of the bank. The most impacted state, which is

associated with heavy stock impacts and flow regulation, is a very gently sloping bank

with widely separated riparian trees, very little understorey and a groundcover of grasses.

It is likely that pre-1850’s banks had an intermediate slope and less undercutting, because

of a healthy cover of riparian vegetation and no stock, carp and flow regulation effects

(LM).

(c) The role of riparian vegetation in bank stabilisation

The impacts of flows on riverbank erosion would be exacerbated by the loss of riparian

vegetation, particularly in the upper and middle sections of the Lachlan. At present,

insufficiently vegetated banks resulting from impacts of clearing and grazing, have

reduced the amount of riparian vegetation that consolidates riverbank soils (Massey 1998,

35

LM). Stock impact, however, would vary throughout the catchment and may decrease

along a westerly gradient because stocking rates correspondingly decrease. Accordingly,

the impact of stock on properties at Oxley and Booligal is considered to be minimal (CS,

McB), whereas stock impact on the river near Lake Brewster is reported to be significant

(PL).

The rate of riverbank erosion is dependent on the riparian vegetation. Well-vegetated

banks can maintain steeper banks because of the reinforcement effect of deep roots

penetrating the shear plane of otherwise non-vegetated banks (Abernathy and Rutherford

1999). In particular, banks with a well-developed herbaceous understorey, in addition to

trees such as river red gums, provide flow resistance and reduce stream velocity

(Frankenberg 1997). Stems and branches of riparian vegetation direct the higher velocity

flow towards the centre of the stream. The lower velocity of flow near banks reduces

erosion scour during high flow events, and well-vegetated reinforced banks resist slumping

after the high flow has passed. Moreover, the slower receding flow of a well-vegetated

stream allows slower drainage of the banks, thereby also reducing the slumping effect of a

rapid drop in water level (LM, Gordon et al. 1992). Therefore, loss of vegetation leads to a

greater amount of erosion and sediment input into a river.

The common reed Phragmites australis (see Table 4 for common and scientific plant

names), found in wetlands and along lake and river margins, is widely recognised for its

role in bank stabilisation. Banks are protected by an underground mass of rhizomes that

can grow to depths of 1.5 m (Frankenberg 1997). Although this species persists in many

places along the Lachlan it would have been more common in the past, because it is very

susceptible to the effects of grazing and drainage. The reversal of the annual pattern of

flows, common under flow regulation, may also prevent re-establishment of vegetation on

eroding banks during warmer months (Frankenberg 1997). The evidence for the former

abundance of common reed is the current abundance in riverine sections of the lower

Lachlan that are fenced off from cattle and/or sheep eg at Oxley bridge and travelling stock

reserves at Condobolin (DP). Explorer accounts also indicate the abundance of ‘reeds’

along the lower Lachlan and similar rivers (Oxley 1820, Benson and Redpath 1997).

(d) Carp impacts on water clarity and riverbank erosion

The historical changes in water clarity and riverbank erosion can also be attributed to the

36

invasion and impacts of carp (Cyprinus carpio). It is very difficult, however, to disentangle

the reported effects of carp and changed river flows on bank erosion and water clarity.

Various landholder observations in the Lachlan and elsewhere (eg AJ, CS, McB, MCMC

1994, MDA 1995, DLWC 1997a), and scientific research (eg Fletcher et al. 1985, Roberts

et al. 1995) demonstrate that carp can have localised and possibly also large-scale effects

on aquatic vegetation, sediment mobilisation and turbidity. Furthermore, it is known that

carp impacts are likely to be more evident in floodplain compared to flowing-water

habitats (eg Lake Cargelligo, see Roberts and Sainty 1996). Nonetheless, the relative

impacts of carp and regulated river flows are difficult to discern, particularly as there are

likely to be complex interactions between carp, river flows and land-management practices

that lead to the loss of riparian vegetation.

Landholder accounts of changes in water clarity and increases in bank erosion that

coincide with the invasion of carp in the mid-Lachlan are numerous. For example, in the

lower sections of Bundaburrah Creek silt carried by floodwaters that used in settle into

river pools is now continuously resuspended by carp (GR, WK, WM). The heavy build up

of silt and loss of water clarity in the Wallamundry and Wallaroi Creeks (Roberts and

Sainty 1996, FD) is attributed to carp. In areas where the Wallaroi Creek width has

increased, carp have often been observed ‘chewing’ at the bank-edge and ‘sieving the mud

and undercutting the bank’ (FD). In sections of Wallaroi Creek where the bank is lined

with cumbungi, however, the level of erosion is minimal compared to the open banked

areas. Observations indicate the carp can not easily reach the bank through the cumbungi

under these circumstances (FD). However, erosion may also be low in such areas because

cumbungi reduces flow velocities, thereby reducing the erosive power of stream flows, and

therefore allowing silt to fall out of suspension (cf. Roberts and Sainty 1996).

37

Figure 7 Erosion in the middle reaches of the Lachlan catchment (the 'mid-Lachlan catchment') as reported by landholders. The minimum number of years that erosion or stability

has been observed ('years') is indicated. Where no number is provided the values for 'years' is not known. The extent of the erosion is also indicated.

Carp are also reported to have depleted aquatic vegetation in the mid-Lachlan. In the lower

reaches of Bumbuggan creek, in-stream vegetation is in ‘very poor’ condition (Massey

1998, LA), whereas before carp became prevalent there were many water plants

(especially ‘ribbon weed’ Vallisneria gigantea) in the creek (LA). Carp are also considered

to have reduced the variety of aquatic vegetation’, mainly ribbon weed, in Wallaroi Creek.

Such impacts of carp in Wallaroi Creek were suggested by the consequences of a fence

construction. In response to sticks and turtles (Emydura macquarii) being sucked up, an

area around the suction pipe of the irrigation pump at “Kimaori” was fenced off. Soon

after the fence was constructed ribbon weed started to grow in the fenced off area (FD).

39

Table 4 Common and scientific names of plant species discussed in this document

Common name Scientific name

(African) boxthorn Lycium ferocissimum

(common) reed Phragmites australis

azolla Azolla spp.

Bathurst burr Xanthium spinosum

bimble or poplar box Eucalyptus populnea

black box Eucalyptus

blackberry Rubus fruticosus

bladder saltbush Atriplex versicaria

bull oak, river oak, belah, drooping she-oak Casuarina spp.

cane grass Eragrostis australasica

common green algae Spirogyra spp.

(other green algae taxa exist, but only this is discussed)

cumbungi or bulrush Typha domingiensis and T. orientalis

cypress (pine) Callitris spp.

eastern cottonbush Maireana microphylla

floating pondweed Potamogeton tricarinatus

grey box Eucalyptus microcarpa

lignum Muehlenbeckia cunninghamii

lippia Phyla canescens

nardoo Marsilea mutica

noogoora burr X. occidentale

pink water speedwell Veronica catenata

red azolla Azolla spiciloides

ribbon weed Vallisneria gigantea

river cooba Acacia stenophylla

river red gum Eucalyptus camaldulensis

roly poly Salsola spp.

rosewood Heterodendum oleifolium

Rushes Juncus sp.

sea barley Hordeum marinum

umbrella sedge, dirty dora, nutgrass etc. Cyperaceae species

water milfoil Myriophyllum sp.

water primrose Ludwigia peploides

willows

yellow box Eucalyptus melliodora

40

Accounts of carp impacts are similar in the lower Lachlan (HyD, McB, Figure 8). The

introduction of carp into Willandra Creek is considered to be the reason for the changes in

channel shape and reduction of intensive weed growth (HyD). Accordingly, before the

introduction of carp Willandra Creek was considered to be unsuitable for carrying

irrigation flows because of intensive weed growth (Whitehead 1994).

Figure 8 The Lachlan River at Oxley (Photo: David Walker, May 2001). The island shown has not been

stocked, indicating that other effects have contributed to the loss of understorey vegetation (McB). Such

vegetation loss is commonly attributed by landholders to the direct effect of carp feeding.

4.5 Changes in aquatic and riparian vegetation

(a) Aquatic vegetation

A common observation by landholders and fisherman of the Lachlan is that the river once

had an abundance of aquatic vegetation. Currently there is very little in-stream vegetation

within the Lachlan River (Massey 1998). For example, the main channel of the Lachlan

River above Lake Brewster during the 1930’s is described as very vegetated, by floating

pondweed (Potamogeton sp.), ribbon weed, red azolla (Azolla spiciloides) and a common

green algae Spirogyra. There were also numerous tree martins, which would have fed off

the insects that lived amongst the aquatic vegetation (PL). This loss of vegetation is

commonly attributed to the introduction of carp into the Lachlan. Loss of aquatic

vegetation and water quality appear to coincide with the large floods of the mid-1970’s

when carp spread in great numbers from the Murrumbidgee River (eg CS, FD, LA, McB,

MJ, PL, SB, see also quotes in Roberts and Sainty 1996, 1997).

41

Although most aquatic vegetation has been lost in the middle and lower Lachlan reaches

some species have benefited from land and water use changes. In the reaches above

Forbes the abundance of aquatic vegetation has been low over the past 50 years compared

to sections of the river below Forbes (MaB), and this may have been the case for centuries

because of the higher energy flows in the upper river. The middle and lower reaches have,

however, clearly had their biomass of aquatic plants reduced. The current dominant in-

channel and riparian plant taxa in the middle reaches of the Lachlan are common reed

(Phragmites australis), cumbungi, various Cyperaceae species, willows, lignum, Azolla

and other rushes and sedges (Massey 1998). In the 1960’s the aquatic vegetation along the

Lachlan River west of Forbes was dominated by stands of water reeds (presumably P.

australis) and a type of ‘lily’ species (MJ, probably not a true lily, but pondweed

(Potamogeton tricarinatus) or ribbon weed). Landholder accounts indicate that during the

1970’s and 1980’s ribbon weed was greatly reduced in abundance, to almost non-

existence (Roberts and Sainty 1996, 1997). Landholder accounts indicate that cumbungi

has probably increased dramatically along the Lachlan River as a consequence of human

activities (Roberts and Sainty 1996, 1997). Similarly, a study in the Great Cumbung

Swamp (Sims 1996) attributed the increasing dominance of cumbungi, and the subsequent

reduction in the common reed and river red gums, with an increased incidence of low-

discharge flow events. Additionally, there is now excess growth of lignum and cumbungi

at the middle and lower ends of the Merrimajeel and Muggabah Creek system that

substantially impedes delivery of stock and domestic flows (DP, Section 5.2(b)).

(b) Riparian vegetation

It seems likely that the amount of understorey in riparian areas, particularly vegetation

such as shrubs, has been reduced for the whole Lachlan. These changes have taken place in

conjunction with an overall depletion of native vegetation across the Murray-Darling

Basin. A nationwide study described the upper and lower sections of the Lachlan River as

respectively part of the ‘Riverina’ and ‘NSW South Western Slopes’ Bioregions, which

were respectively estimated to have lost about 48 and 34 percent of their cover (ha) of

native vegetation (NLWRA 2001). As a general rule, perennial grasses, herbs and shrubs

in the Lachlan River catchment have been replaced by introduced grasses and herbs, many

of which are annuals (Porteners 1993, DP).

42

It is difficult, however, to assess the loss of the extent of the river red gums which line the

creeks and river channel. Loss of trees is generally associated with agricultural activity

(Porteners 1993, Hobbs and Yates 2000). For example, the ‘NSW South Western Slopes’

are estimated to have lost 66 percent of the cover of Eucalypts (NLWRA 2001). Moreover,

the vegetation communities in the mid-Lachlan most detrimentally affected by clearing are

the riparian communities (which include river red gum and box woodlands), as these

communities tend to occupy prime agricultural land (Sivertsen and Metcalfe 1995).

Although the density of trees in the lower Lachlan catchment has probably always been

low, because of the fire regime managed by the aborigines (eg accounts by Suttor 1857 in

Lloyd 1988, p.15, Ryan et al. undated) and dominance of shrub-lands (formerly dominated

by bladder saltbush, Atriplex versicaria), the density of river red gums along a watercourse

was probably reasonably high along the both the mid and lower Lachlan (cf. Porteners

1993). The current extent of river red gum occur as narrow bands along the major river

corridors, often only as a single line of trees on either side of the channel (Porteners 1993,

Sivertsen and Metcalfe 1995, DP).

Grazing has had the greatest impact on riparian communities. Early farm-machinery (eg

river pumps) and heating relied on wood fuel, and therefore may have been responsible for

some forest depletion. Moreover, river red gum remains one of the more desirable timbers

for wood fires as it leaves behind little ash. In recent history, there has also been extensive

river red gum loss because of selective logging for red gum railway sleepers (DP, PL). The

greatest pressure placed on riparian vegetation, however, is from grazing pressure by

domestic stock (Massey 1998, DLWC 1997a). Hence, observations of grazing exclusion

plots in the riparian zone of wetlands in the mid-Lachlan have resulted in higher survival

rates of regenerating river red gums (DP, LlP). The level of riparian regeneration has been

observed to vary between sheep and cattle properties. Sheep have been noted to

preferentially graze ‘softer’ grasses (presumably this indicates a higher proportion of

pasture grasses), whilst cattle also graze upon Eucalyptus seedlings and reeds (GB, WL).

(c) Interactions between vegetation change, turbidity and river flows

Vegetation growth is both affected by, and can alter flow regimes. For instance, the

changes in riparian vegetation communities, described above, have implications for water

management, because a reduction of water storage potential of the riparian zones has been

associated with the reduction of perennial understorey. Observations by the early explorer

43

Oxley (1820), in his travels through the rivers of the central west provides strong evidence

that the understorey of riparian corridors has been substantially altered. In particular he

noted that the resemblance of plains near the river to sheets of water. The soil within a few

feet of the rivers was so wet and spongy that ‘the water sprang from even the pressures of

our feet’. Later Thomas Mitchell, making reference to these accounts by Oxley ‘observed

the hardening of the spongy soil by the cattle’s feet, which increased the run off and

impeded water storage’ (Lloyd 1988, similar accounts in Bauer and Goldney 2000). The

loss of the ‘sponge’ effect of forest and wetlands on flows, in conjunction with the

extensive network of levees along the length of the river would probably have increased

the rate of flow of water from one end of the catchment to the other. Moreover, the large

biomass of in-stream aquatic vegetation that once existed (eg PL) must have had a

considerable dampening effect on the velocity of flows in the lower Lachlan. Associated

with this (probable) increased rate of surface, sub-surface and channel flow has been

considerable catchment and channel erosion, and therefore increased mobilisation of

sediments. Part of this channel erosion process has involved channel straightening, and

therefore also shortening, in the upper sections of the catchment which further speeds up

the within channel flows. The combined effect of these processes on the hydrograph of the

lower Lachlan is, however, not clear. Although these processes should increase total

volumes going down the Lachlan, the current hydrograph is probably more affected by

abstraction and increased diversion of flows into the distributaries (see sections on

Merrowie and Willandra Creeks).

The increases in sediment suspension that have occurred in the Lachlan would also deprive

temporarily or permanently inundated plants of light for growth. This effect is likely to be

important for both aquatic vegetation and probably increases the prevalence of algal

blooms (cf. Timms and Moss 1984, Scheffer 1990).

(d) Snags, debris dams and river pools

Although extensive de-snagging of major inland rivers has occurred for over a century

(Roberts and Sainty 1996, Mac Nally et al. 2002) it is commonly stated by landholders that

the Lachlan River was never de-snagged, at least for river navigation. Although there was

limited navigation in the river, steamers were generally not used for trade in the Lachlan

River (Lloyd 1988). Ad hoc removal of snags by landholders is likely to have occurred,

44

because of concerns about snags impeding flows and causing in-stream erosion, but the

extent to which this has occurred is unknown.

Snags and debris dams would have always occurred in the lower Lachlan. Before

European settlement, gum trees would have fallen into the river and formed snags and

debris dams in proportion with natural rates of bank erosion and tree mortality. Snags on

the Lachlan near Lake Brewster were at a low density of about one snag every 100 m of

river channel in the 1920’s (PL). Snags and debris dams, and conditions associated with

these (eg biofilm for invertebrates, pools and refuge from high velocities) are critical

habitat for native fish and their prey (Treadwell et al. 1999).

It is likely that pools and debris dams were often found together in the pre-regulated lower

Lachlan times (before the memory of our best local historians) and up to the mid-1970’s.

Pool formation can occur because of debris dams diverting flows downward into the

streambed and scouring sediments (LM, Treadwell et al. 1999). Pools also form from other

processes, such as from flows on the outside of river bends. Pool density was considered to

be much higher before the mid-1970’s in the lower Lachlan (landholder accounts in

Roberts and Sainty 1996).

The processes associated with snags, debris dams and pools have changed since the mid-

1970’s. Landholder accounts in Roberts and Sainty (1996) suggest snag formation may

have exceeded natural levels in the Oxley area since the mid-1970’s; owing to greater rates

of channel collapse (ultimately because of processes associated with losses of aquatic and

riparian vegetation, changes of flows, grazing and carp). Pool formation is no longer

associated with debris dams because the abundance of silt ensures that pools remained

filled up.

It is unlikely the amount of snags in the lower Lachlan has a substantial affect on flows in

the lower Lachlan. A number of landholders maintain that these snags obstruct flows and

cause erosion. The extent to which snags obstruct flows and cause erosion is highly

variable, however, and is commonly overestimated (Treadwell et al. 1999).

45

4.6 Changes in the fauna of the Lachlan River

(a) Changes in fish communities

Native fish communities were reasonably healthy up until the 1940’s. Historical accounts

from 1915 and 1918 describe the abundance of native fish such as catfish (Tandanus

tandanus), Murray cod (Maccullochella peeli), golden perch (Macquaria ambigua),

Macquarie perch (Macquaria australiasica), and river blackfish (Gadopsis marmoratus)

encountered by fisherman (Roberts and Sainty 1996). Similarly, during the 1950’s the

majority of the fish caught within the middle reaches of the Lachlan River were catfish and

golden perch with the occasional large Murray cod, often as heavy as 70 to 80 pounds

(MaB, MJ, WL). In the 1940’s the fish usually caught in Mandagery Creek were ‘bony

carp’ (possibly Bony Bream, Nematolosa erebi); this species has declined and the common

carp is now prevalent (GT).

Carp has been in the Lachlan River at least since the 1950’s (Roberts and Sainty 1996,

Reid et al. 1997), but oral history indicates the dominance of fish communities by carp did

not occur until the 1970’s (Roberts and Sainty 1996, 1997). Commercial fish catches in the

some Lachlan Valley lakes indicate the first catches where carp dominated (defined here as

50% or more of the fish catch) occurred at Lake Cargelligo in 1965/66 (66% of the catch,

Reid et al. 199712). Large numbers of carp were observed arriving in Lake Cowal, and also

into Bogandillon swamp, after the flood in 1974 (DBA). Moreover, the abundance of

native fish within Wallaroi Creek is reported to have dropped dramatically since the early

1970’s. 30 years ago one could place a drum net in the creek at dusk, and catch 40 to 50

edible fish the next morning. The fish caught were generally golden perch, redfin, and

catfish (FD).

Introduced fish species such as carp, and to a lesser extent, redfin perch (Perca fluviatilis)

and mosquito fish (Gambusia spp.) now dominate the Lachlan River (PL, Harris and

Gehrke 1997). For example, carp are reported to currently dominate the Goobang,

Booberoi, Bumbuggan and Mandagery Creeks, although species such as redfin, yellow

belly, silver perch (Bidyanus bidyanus), and cod, and less commonly, catfish and silver

12 These values are not corrected for catch effort or the extent to which some fish species were targeted more than others.

46

perch, are still observed (FD, GB, GT, HH, NA, RF, WK, WL, Roberts and Sainty, 1996).

The Lachlan is not unique in this respect as alien fish, especially carp, now dominate the

fish communities of southerly inland rivers of NSW, usually in association with human

impacts (Harris and Gehrke 1997). The Lachlan River has, however, some of the highest

estimates of carp density among all NSW sites (Driver et al. 1997). Nonetheless, recently

(1998-2002) the numbers of carp are considered by some observers to have declined

slightly, with an increase in the numbers of Murray cod (HN, MaB, MJ, WL).

(b) A general loss of biodiversity

Biodiversity has generally been reduced in the Lachlan River valley, and this pattern is

also evident in the aquatic ecosystems. Many native vertebrate species have been reduced

substantially or are now locally extinct (Dickman 1994, Bauer and Goldney 2000). Oral

history indicates that the water rat (Hydromys chrysogaster), platypus (Ornithorhynchus

anatinus), and some tortoise, frog and bird species have decreased in abundance (Roberts

and Sainty 1996). Nevertheless, not all observers report the same patterns. For example,

one landholder’s (FD) observations in the Wallaroi Creek over the past 30 years suggest

that the numbers of water rats (Hydromys chrysogaster) and turtles has not dropped. Loss

of native fish has coincided with a general change in freshwater communities. An increase

in the dominance of redfin was observed in 1937-39, with a concurrent reduction in the

abundance of aquatic invertebrates (eg snails and dragonflies) and their predators such as

native fish and tree martins (PL). The presence of mosquito fish in 1944-45, and a

reduction in the abundance of aquatic vegetation (see Section 4.5) and the small shells of

mollusc species13 coincided with the invasion of carp in 1965/66. Crayfish also used to be

more common in the lower Lachlan (Roberts and Sainty 1996). Similarly, over the past 30

years the numbers of leaches, yabbies and mussel shells has declined in Wallaroi Creek

(FD). There has also been a loss of snags, aquatic vegetation and pool-riffle sequences;

habitat which this in-stream fauna would have utilised (see previous sections and

McDowall 1996). A variety of pressures are responsible for the changes that have occurred

13 These included a number of shapes of mollusc shells all of which were observed at high density (ca. 1:1 soil versus

shell) on the river substratum among the river plants : spiral, elongate and a small bivalve shell associated with the

‘young of black mussels’ (PL).

47

in the Lachlan River freshwater ecosystem. The major pressures identified are (from

DLWC 1997a):

• Flow Regulation: persistently high flows, or alternatively, low flows rather than

frequent, natural fluctuations; reduction in high flows to stimulate native fish migration

and breeding; thermal pollution from cold water releases.

• Barriers to fish passage: the construction of dams and weirs across waterways,

impeding migration and spawning opportunities of natives.

• Reduced in-stream and floodplain habitat: river regulation, the removal of riparian and

floodplain vegetation, lakebed cropping, bank erosion, stock access and river

engineering.

• Reduced water quality: insecticides, heavy metals and other toxic substances, water

temperature, increased turbidity and low levels of dissolved oxygen can all directly or

indirectly affect fish survival, growth and reproduction.

• Increased fishing pressure: uncontrolled recreational fishing and increased competition,

predation and habitat changes because of introduced species.

48

Section 5. Current and historical flows of the Lachlan Valley wetlands

In the two sections (5.1 and 5.2) below a picture of the recent history and health of the

Lachlan River and its wetlands is presented. This impression has been constructed using

the knowledge of landholders, DLWC on-ground experience and the literature. Sometimes

these different sources of information contradict, and where they do we have attempted to

objectively represent both points of view and, additionally, to explain (where possible)

why these different perspectives could have arisen.

5.1 Ecology and flows of the mid-Lachlan River

(a) Introduction

This section provides an overview of the history and current status of the ecology and

flows of the mid-Lachlan channel (defined in this document as Mandagery Creek to Lake

Cargelligo), its anabranches and wetlands. Such wetlands are numerous, because the mid

Lachlan is characterised by a floodplain that is flat and wide, favouring the formation of

numerous anabranches and billabongs (WRC 1986).

According to DLWC flow (IQQM) modelling (12.4) the mid-Lachlan wetlands are

primarily dependent on winter-summer flows to fill (July-November, Figure 9). As

discussed in Section 3.2, some wetlands have been deprived of these spring flows whereas

other wetlands are now subject to over-wetting (Table 3). This finding is consistent with

the known effects of river regulation. That is, small flows are more common, whereas

small to medium size flood events are less common under regulated flow conditions

(Walker et al. 1995). Hence, low-lying wetlands that are close to the river get too

frequently inundated (e.g., Morgan’s billabong). In contrast, wetlands typically filled by

intermediate-sized flows (e.g., Wilga Lagoon) are filled less frequently by regulation. It

should also be noted for this part of this river that the river channel is much deeper at

Forbes compared to Condobolin. Hence, low-lying wetlands at Condobolin such as

Morgan’s billabong are more likely to be subjected to over-wetting.

49

02468

101214161820

Jan

Feb

Mar

Apr

May

Jun Jul

Aug

Sep

Oct

Nov

Dec

Month

Wet

land

fills

per

mon

th(m

id-L

achl

an b

'bon

gs)

N09

E73a

E151

E179

Figure 9 The number of days per month that mid-Lachlan riparian billabongs are inundated at or above

the depth required for aquatic plant growth under four flow scenarios: pre-regulated conditions (N09),

the original flow rules (E151), current regulated conditions (E73a) and proposed flow rules (E179).

(b) The creeks and anabranches of the mid-Lachlan

(1) Mandagery Creek

Mandagery Creek is the last of the major Lachlan tributaries, with the capacity of the river

decreasing downstream of the confluence (DLWC 1997a). The long-term average yearly

flow of Mandagery Creek, upstream of Eugowra is approximately 80,000 ML (LVSWMP

1996). Landholder accounts state that prior to 1928 the occurrence of flooding in the

Mandagery creek was rare to non existent, since this time it is estimated that the creek

floods once every seven or eight years (GT). The changes in flow during this period could

be a result of the level of clearing occurring in the upper reaches and the subsequent

increase in the speed and volume of run-off.

Over the last seven years (1996-2002) the creek has had at least a small flow during the

summer months which is unusual for the Mandagery creek because during the previous

60 years the creek was usually dry after Christmas (TD, HD). The reason for the recent

changes in flows is thought to be a result of regeneration of remnant vegetation and

changed management techniques (ie, pasture improvements) in the upper reaches. This has

slowed run-off and the water is moving through the system more slowly (HD).

Landholders of the lower reaches of the Mandagery creek describe the riparian vegetation

as healthy, whereas Massey (1998) considers the riparian vegetation to be in poor

50

condition. There are a variety of overstorey species and generally a ‘good cover’ of grasses

(TD, HD, GT). In some areas the riparian vegetation is considered to have improved

because of regeneration over the past 50 to 70 years (GT). In contrast, Massey (1998) rated

the riparian vegetation as 89 percent ‘very poor’ within the Mandagery catchment, which

includes the lower reaches mentioned above. In these areas agriculture and/or clearing had

occurred on both sides of the stream. In some stream sections riparian vegetation was

dominated by exotics, such as willows or blackberry (Rubus fruticosus), with native trees

rare or completely absent. Such differences in opinion on the state of the riparian zone

could be a result of different definitions of ‘healthy’ riparian vegetation. Massey (1998)

defines a ‘healthy’ riparian zone as comprising greater than 50 m of native trees with a

diversity of species, ages, heights and understorey species. Whereas, in contrast, the

landholders could classify a ‘healthy’ riparian zone as one with a single row of trees plus

high levels of exotics, as long as minimal bank erosion is occurring.

The banks of the Mandagery Creek were considered by Massey (1998) to be mostly stable,

with small unstable areas in the very upper reaches of the catchment. Similarly landholders

consider that the banks have been very stable over the past 50 years (GT, HD, TD), with

the exception of small areas of erosion occurring on the outside of bends in the reaches

near Manildra (CT).

The Mandagery stream is an ephemeral stream in reasonable health. The bed and bar

stability within the Mandagery catchment as ‘good’14 in the lower reaches but ‘very

unstable’15 in most parts of the upper catchment, but the vegetation within the channel is

naturally low in abundance (Massey 1998). In the reach just above Eugowra the creek bed

is currently mobile because of the amount of sand moving downstream from the tributaries

such as Reedy Creek (GT). This shows the possible movement of sand from areas (eg

Reedy Creek, Gumble Creek, Boree Creek, Coates Creek and Manildra Creek) identified

by Massey (1998), down to the lower reaches of the system. Massey (1998) observed a

low cover of aquatic vegetation in this creek and therefore described most of the aquatic

vegetation to be in ‘very poor’ or ‘poor’ condition (Massey 1998). The amount of in-

14 streams with no bars and stable beds were rated ‘very good’ to ‘good’

15 streams with aggrading or eroding beds were given ‘poor’ to ‘very poor’ rating

51

stream vegetation is, however, typically low in such streams because of their ephemeral

nature.

(2) Bundaburrah Creek / Bundaburrah Cowal

1) Overview

This creek system is a high-flow anabranch of the Lachlan, which is lined with river red

gums containing peripheral grey (Eucalyptus microcarpa) and yellow box (E. melliodora)

(WRC 1986). The creek receives the majority of its flows from floodwaters that break out

of the Lachlan opposite the “Southern Cross” breakaway (approximately 16 km upstream

of Forbes). This water crosses the Forbes-Cowra Road at Dukes Crossing and covers

extensive areas of flood country, eventually meeting up with the Bundaburrah Creek (SES

1983). The flows start when the river reaches a height of 8.9 - 9.0 m at the Forbes Iron

Bridge gauge, which is a minor flood event (RG, WK).

2) Upper and Middle Bundaburrah Creek

Upper and Middle Bundaburrah Creek is an almost perennial stream with stable banks that

often attract wetland birds, particularly ducks. In 2002 landholder stated that the section of

creek between Forbes and Garema near the area known as ‘Dog ‘n’ Duck’ had been dry on

only occasion (1982) since the Williams family moved into the area in 1878. Previously

large rainfalls would provide a lot of run-off to the creek from as far as Red Bend Silos,

recently though, the table drains have impeded the natural flow of the run off, diverting

into road reserves or adjacent paddocks (WK, WR). According to landholders in the upper

reaches of the lower Bundaburrah creek the river shape has not changed much over time.

Bank erosion is report to be not a problem because of the amount of grasses and river red

gums, and the regular germination of river red gum after floods (WK). The creek provides

a good habitat for a variety of bird species, particularly ducks (WK).

52

3) Lower Bundaburrah Creek

Lower Bundaburrah Creek is an actively eroding stream that contains Bundaburrah Cowal,

a natural, albeit hydrologically modified, wetland. As the creek flows westward it is

obstructed by Jemalong Ridge, which causes floodwater to spill out of the creek. This

inundates the shallow basin of Bundaburrah Cowal. The shallow basin occasionally

receives inflows from Ooma Creek that drains from a small catchment around Grenfell

(WRC 1986). In the lower sections of Bundaburrah Creek bed movement or erosion has

always been a regular occurrence in the creek (WK, GM). Bundaburrah Cowal is vegetated

by scattered river red gums and a ground layer of pasture grasses. Its floor has been

modified by drainage channels, which aid in the rapid removal of floodwaters. The north-

west section has been protected by levees to allow for irrigated cropping. During large

floods, an area of scattered river red gums to the south of Bundaburrah Cowal is also

inundated (WRC 1986). Outflow from Bundaburrah Cowal proceeds down Jemalong

Creek, back to the Lachlan River, just upstream of Jemalong Weir and forms part of the

weir pool. This weir, under normal operating conditions does not create any spread of

backwater into Bundaburrah Cowal, with the backwater remaining in Jemalong Creek

(WRC 1986). In high river flows of 5.96 m or above the water backs up to Bundaburrah

Cowal (RG).

(3) Bumbuggan Creek

The Bumbuggan is only a small creek, approximately 15 kilometres long, and very similar

to the lower reaches of the Goobang Creek in terms of stream dimensions, morphology and

vegetation (eg both have many willows, HH, WDa). It is located between Forbes and

Condobolin on the north side of the Lachlan River, and it has been substantially modified

to divert water to Goobang Creek, which flows back into the Lachlan at Condobolin.

Historically, this creek would have transported no water or very small volumes of water

between the Lachlan and the Goobang Creek. Currently, Bumbuggan Creek starts to flow

when the Lachlan River reaches about 200 ML/day. At the Lachlan River offtake

Bumbuggan Creek is known as the ‘Little Lachlan’, as a greater volume of water flows

down the anabranch system than the river itself. The Lachlan River often diverts about 85

percent of its flows down Bumbuggan Creek (WRC 1986). Because of these high-volume

53

diversions, a low-level fixed-crest weir in Bumbuggan Creek at the offtake maintains flow

in the Lachlan River during low flow periods.

Bank erosion, channel modification and loss of in-stream vegetation have altered

Bumbuggan Creek. Over the past 50 years landholders along the creek have observed a

considerable amount of bank erosion, with the stream width doubling and the bed

flattening out. Along some sections the tree lines that once lined the bank are located in the

creek, 20 m from the bank. In other reaches small islands have formed making two

channels of water (HH, RB). Bank erosion is most evident when the flows are rising and

falling, as the wetting and drying of the bank causing slumping. Furthermore, stock are

damaging the banks, particularly immediately after water levels have dropped (HH). The

banks along the majority of the creek are quite steep and hence there is a high probability

that stock watering causes further erosion. There are still places where water reeds are

present, but the abundance of aquatic plants has been reduced markedly. During dry times

in the 1960’s the creek was so full of reeds that the property owners were shovelling a path

through the reeds to allow the creek to keep flowing (HH). The wildlife levels along the

creek is considered by locals to be ‘very healthy’, because it has a variety of bird species

present (RB).

The Bumbuggan Creek has a reasonable cover of trees, but the understorey has been

substantially modified. Riparian vegetation is considered by landholders to be ‘quite

healthy’ even although bank erosion is occurring, as there is often a width of 6 to 9 m of

mature trees from the top of the bank (HH, RB). The riparian vegetation varies, with

properties that have less grazing pressures having more ‘healthy’ (ie, vigorous) perennial

grasses and understorey species (GB). In spite of these landholder observations, however,

Massey (1998) reported that the riparian vegetation was ‘very poor’ for most of the reach.

Such differences in interpretation between Massey (1998) and landholders may arise from

landholders equating ‘healthy’ with a relatively extensive cover of tree overstorey

irrespective of the species composition, whereas Massey (1998) would have rated a bank

poorly if the undercover was poor.

(4) Goobang Creek

Goobang Creek is fed largely by run-off from its catchment north east of Parkes and a

number of creeks, mainly Gunningbland and Yarrabandai creeks. There are two large

54

storages in the upper catchment around Parkes (Lake Endeavour and Beargamil), as well

as 16 irrigation licences and 16 other high extraction licences that affect the water flow

(DLWC 1999c). As discussed, Bumbuggan Creek is regulated to contribute water to the

Goobang Creek further downstream by taking water from the Lachlan River. During larger

floods (eg the 1974 flood, SES 1983) water often flows from the Lachlan River

downstream of Forbes near ‘Carrawabitty’, and passes through a gap (Gunning Gap),

which is adjacent to the Gunning Ridge, to join the Creek (Brady 1989).

Goobang Creek is only moderately healthy, because although the banks are generally

stable there are only small sections of healthy riparian vegetation. Most of the creeks’

banks have ‘very good’ or ‘good’ stability, but 17 percent are ‘very unstable’ (Massey

1998). The middle to upper reaches of the Goobang creek are stable, whereas banks are

very unstable below the Bumbuggan creek confluence (Massey 1998). The riparian

vegetation is dominated by river red gums and perennial, tussocky grasses. The only

‘healthy’ riparian vegetation in the catchment is in the middle to lower sections of the

Goobang creek. The other 95 percent of the creeks’ riparian vegetation is ‘very poor’ or

‘poor’ (Massey 1998). The condition of the aquatic vegetation in the Goobang catchment

is not known. Although 100 percent of the Goobang catchments’ aquatic vegetation was

rated as ‘poor’ to ‘very poor’, many of the streams were dry at the time of the survey

(Massey 1998).

The middle reach of the Goobang Creek (Newell Highway to Bumbuggan confluence) is

an ephemeral stream with little evidence of bank erosion (GB, RF, Massey 1998). The

creek only flows after substantial rain in the upper reaches around Parkes. The creek varies

in shape throughout this reach with areas of defined steep banks, some sections of 27-46 m

wide and quite flat, to broad wetland areas like after it passes through Culgan’s Gap (just

north of Gunning Gap, GB, RF). There are not many deep holes along the creek, and hence

this area is not considered by locals to be a fish breeding ground. Where erosion does

occur, it is often observed where water is swirling around snags and gouging the banks. It

has been observed that on the inside of some of the creek bends and along slow-flowing

sections, a thick stand of reeds (Phragmites australis) and bulrushes (Typha spp.) are

present (GB).

Flows down the Goobang Creek below Bumbuggan creek are now consistently large (LA).

This section of the Goobang Creek is also more likely to cause flooding at high flows, and

55

therefore flooding is now more common in this area than it usually has been over the

lifetime of many landholders. The creek system once had bigger flows throughout the

spring with a very reliable half-full flow, and channel capacity was at about 90 percent of

the rest of the year. Now the creek runs full 90 percent of the year with the occasional very

low-flow period (LA).

(5) Island, Wallamundry and Wallaroi Creeks

This division is the most complex anabranch system in the Lachlan. It consists of a series

of interconnecting channels that include Island, Wallamundry, Wallaroi and Nerathong

Creeks. Island creek is an anabranch of the Lachlan, splitting approximately 1 km west of

the Forbes/Condobolin shire boundaries. A weir on Island Creek immediately upstream of

its confluence with the Lachlan (along side Erronwallong Mountain) diverts up to 100

ML/day of regulated flows into Wallamundry Creek. During unregulated high flows the

distribution of water reverts to the natural regime with some 30 percent of Island Creek

flows entering Wallamundry Creek. At flows above 1000 ML/day the Wallamundry takes

about 10 percent of Island Creek flows. The waters of Wallamundry Creek return to the

Lachlan via Nerathong Creek and Wallaroi Creek.

The Wallamundry and Wallaroi Creek system has some natural and unnatural wetland

features. The area is generally considered to be of conservation value, as it contains

extensive floodplain habitat. Moreover, many small weirs have been constructed by

landholders along the creeks over the years to conserve water for stock and domestic

purposes. One of these weirs, Woolshed Weir, causes widespread inundation of about 10

ha when the weir is closed. This inundation provides habitat for wildlife, including the

endangered species the brolga (Grus rubicunda, DWR 1992a). Moreover, during moderate

flooding, Wallaroi Creek flows into an adjacent wetland area, Banar Lake. Banar Lake is

also filled by Humbug Creek. When inundated, Banar Lake forms an extensive area of

shallow open water which provides habitat for large numbers of waterbirds (DWR 1992a),

which also includes the brolga (LlP).

(6) Kiargathur Creek / Borapine Creek and Big Brotherony Swamp

Kiargathur and Borapine Creeks are formerly ephemeral anabranch creeks that have been

modified for water supply. Under natural conditions these were both high flow flood

56

runners. The downstream portion of Borapine Creek now has more persistent flows,

because of an improved channel from Booberoi Weir pool (WRC 1986). Both Kiargathur

and Borapine Creeks are vegetated by large river red gum and black box, the former

assuming dominance where water supplies are more persistent (WRC 1986).

Big Brotherony Swamp is downstream of Borapine Creek. The swamp has an area of

1250 ha, and is usually inundated by moderate flooding (of the magnitude of the 1984

flood) but is occasionally inundated by local run-off. Flows within the swamp may,

however, be largely influenced by levee developments (DWR 1992a). When fully

inundated, to a depth over one metre, this area forms a haven for ducks (WRC 1986). The

area is vegetated by river red gum and scattered black box (WRC 1986).

(7) Booberoi Creek

Booberoi Creek is an anabranch creek that, although the in-stream vegetation has been

substantially modified, has stable banks and continues to provide habitat for some bird

species. Water leaves the river and flows west via the regulator at Booberoi weir pool. The

regulator has been there since about 1901 and is used for the continuous supply of water

for stock and domestic purposes. About five percent of river flows enter the anabranch

when the regulator is fully open (DWR 1992a). Although bank stability and erosion levels

are in ‘good’ to ‘very good’ condition, the riparian vegetation and aquatic vegetation are

generally in ‘poor’ to ‘very poor’ condition. The riparian vegetation along the middle

section, however, is rated in moderate condition, (Massey 1998). In the 1920’s the creek

had a variety of water plants like ribbon weed, floating pondweed (Potamogeton

tricarinatus) and cumbungi through it (Roberts and Sainty 1996). Now the vegetation is

dominated by large stands of cumbungi throughout the length of the creek, which has

slowed the water down and increased the silt levels (NA).

A series of small weirs can be found along the creek, which are densely vegetated by

cumbungi, willows, river red gum, black box and river cooba (Acacia stenophylla, DWR

1992a). The weir pools and cumbungi provide habitat for a variety of bird species. Many

bird species can be seen, including pelicans, swans, various species of ducks, cormorants

and even brolgas.

57

A current problem, according to landholders along the creek, is that the creek is not getting

enough flow. Just downstream of the intake a build up of silt has restricted the flow. The

regulator isn’t large enough to take flows that could flush the silt downstream. For the

creek to get major flows, a break out from the river upstream from the weir occurs that

follows a flood runner across to the creek (NA).

(c) The Bogandillon swamp – Lake Cowal system

(1) Lake Cowal – Bogandillon Creek –Lachlan River hydrology

1) Hydrology of the Lake Cowal system

Lake Cowal receives water from either local run-off in the Bland Creek catchment or from

overland flood flows. The Lake flows back to the Lachlan River through Manna Creek and

Nerang Cowal (Vestjens 1977, Figure 10). Bland Creek flows enter Lake Cowal at its

southern extremity, and these flows fill Lake Cowal much less frequently than flooding

from the Lachlan (Vestjens 1977). The only times a major flood occurred solely because of

run-off from the Bland Creek catchment during the last 100 years was in 1962, 1969 and

1970 (DLWC data).

The direction of the flows that reach Lake Cowal during large-scale flooding from the

Lachlan River is reasonably predictable. The sequence of flooding is as follows (Rankine

and Hill 1979, Hatton 1991, DWR 1992b, cf. Figure 10):

• Floodwaters break out of the Lachlan River at two locations downstream of Jemalong Gap

known as the 17 and 21 mile breakouts (17 and 21 miles west of Forbes respectively).

Breakout flows begin when the Lachlan River flows are about 15,000 ML/day at Jemalong

Weir. Floodwaters spill to both the north and south of the river over a large area;

• To the north much of this water finds its way into natural depressions and effluent channels,

some returning to the river downstream;

• On the southern side, flows from the two breakouts travel in a south-west direction through a

partly leveed floodway, and these flows merge approximately 11 km from the river. These

floodwaters flow westwards along the 24 km-long leveed flood corridor through the Jemalong

and Wyldes Plains Irrigation District and enter Lake Cowal (during the 1990 flood it took five

days for the flood peak to travel from Jemalong Weir to Lake Cowal);

58

• At a storage level of 205.56 AHD16, which corresponds to the level of the saddle separating the

lakes, floodwaters start to flow into Nerang Cowal. The volume stored in Lake Cowal at this

elevation is 152,000 ML and its surface area is 10,500 ha. Nerang Cowal fills rapidly (because

of its small size). When both lakes are filled, water commences to flow over the outlet at the

northern end of Nerang Cowal to Manna Creek;

• Once filled to capacity Lake Cowal takes from two to three years to empty by evaporation and

seepage, provided that no further inflows occur. Water losses are slow with an evaporation rate

of 8.5 m3/s;

• Outflows from the lake system discharge over a bar located at the northern end of Nerang

Cowal and flow down Manna Creek and via Bogandillon Swamp, Wallamundry and Wallaroi

Creeks to the Lachlan River.

When filled to capacity the total volume of the water stored in both Lake Cowal and

Nerang Cowal is about 194,000 ML, of which 162,000 ML is in Lake Cowal (84%) at a

maximum water depth of 4.2 metres. The remaining 32,000 ML is stored in Nerang

Cowal, at a maximum depth of about 1.5 metres. At capacity storage, the surface area of

Lake Cowal and Nerang Cowal are 10,800 ha and 3,800 ha respectively.

Over recent decades Lake Cowal landholders have pressed for the partial drainage of Lake

Cowal (cf. DWR 1992c). Partial drainage is argued to be necessary to compensate for the

increased volumes of floodwaters directed towards the lake from the Lachlan River by

modifications to the floodplain downstream of the two breakout points. A number of

embankments have been constructed downstream of the two breakout points to limit the

spread of floodwaters in the area.

2) Inundation history of Lake Cowal and Nerang Cowal

A rough flow history can be constructed for Lake Cowal. There were breakouts from the

Lachlan River between 1943 to 1976 (Table 5) and 1976 to 2001 (Table 6). Not all of

these breakouts would have reached Lake Cowal on account of losses through evaporation

and depression storage en route to Lake Cowal. During the period 1904 to 1931, Nerang

16 AHD = Australian Height Datum. Within Australia an AHD of 1 m in any location is at the same height as a point with

an AHD of 1 m in any other location.

59

Cowal was dry, although some minor floods occurred in the main lake. A major flood

occurred in 1931, which filled both lakes followed by a smaller flood in 1939, after which

the lakebed remained dry until 1950. On several occasions, floodplain flows from the 17

and 21-mile breakouts have not reached Lake Cowal as they been completely swallowed

up by depression storage (transmission losses) in the flood corridor, which is mainly

contained in the Wilbertroy State Forest area. However, for major floods such as those of

the years 1950, 1956 and also September-October 1974, losses account for a small

percentage of the breakout volume, and the amount of water entering the lake can be

several times its storage capacity. In 1990, the 17 and 21 mile breakouts commenced to

flow on the 21 April and reached Lake Cowal on the 26th of April, filling it by the 27th. In

1998 the flow reached 7.41 m at Jemalong weir on the 26th of July. Hence, Lake Cowal

started filling in mid July (DBA), and later flows in August-September (for ca. 1 month)

resulted in Cowal being half filled.

Lake Cowal has been dry on numerous occasions. According to Vestjens (1977) this

included a period of 20 years and one ‘dry period’ in the 1920’s. From 1904 to 1931, and

from 1939 to 1950 Lake Cowal was dry for ‘most of the time’ (Gourley et al. 1996). Since

1950, this situation was reversed and Lake Cowal was inundated for most of the time,

although the lake completely dried out in the 1981/82 drought, and was considered by

landholders to be ‘dry’ in 1988 (Gourley et al. 1996). The Lake also dried out at the end of

1997 (DBA).

3) Bogandillon Creek and Bogandillon Swamp

Bogandillon Creek is the main surface drainage line for the Jemalong District. Normally

the creek is ephemeral, carrying run-off from the Manna Range, the Bland Catchment

(overflow from Lake Cowal) and floodwaters from the Lachlan River which travel through

the floodway system of the Jemalong Plain (HR, DWR 1990). The creek then discharges

into the Bogandillon Swamp, where the water ponds and then evaporates (Figure 10). In

the event of large floods the creek drains Lake Cowal to the south, flows through to the

Wallamundry-Wallaroi Creek system to the north (DWR 1994b) and ultimately flows back

to the Lachlan River below Condobolin (as also described above).

The last time Bogandillon swamp filled was after the 1993 flood (HR). Bogandillon

Swamp fills about every five to seven years after floods from the Bland system and/or

60

Jemalong Irrigation District. In the larger floods the water flows into the Wallamundry

Creek system draining a small area of the swamp. The remaining water takes about 12 to

18 months to evaporate depending on what time of the year it fills, as it takes longer to

evaporate during the winter months (HR).

61

Table 5 Volumes of floodwaters entering flood corridor and Lake Cowal from Lachlan River breakouts(1943 – 1976, Rankine and Hill 1979). Highlighted rows indicate years of major flooding events.

Volumes Entering Flood Corridor GL Duration of Inflows

21 Mile Break 17 Mile Break

Volume Entering Lake

Cowal (GL)

22/5/43 - 30/5/43 5.4 1.0 -

28/6/45 - 30/6/45 3.1 1.4 -

22/3/50 - 16/4/50 148.4 120.4 236.2

27/5/50 - 4/9/50 234.8 107.8 302.9

28/9/50 - 2/11/50 126.0 94.5 196.4

18/7/51 - 3/9/51 101.4 43.0 114.3

29/10/51 - 12/11/51 25.2 9.2 12.6

20/5/52 - 9/9/52 376.7 457.9 795.5

24/10/55 - 3/11/55 16.8 6.4 -

15/3/56 -29/3/56 36.7 19.1 36.6

18/4/56 - 8/11/56 547.9 290.9 760.6

4/4/59 - 12/4/59 13.7 5.4 -

24/7/59 - 7/8/59 9.2 1.3 -

18/7/60 - 11/10/60 116.5 54.1 134.3

22/11/61 - 30/11/61 10.2 3.6 -

31/8/63 - 16/9/63 30.3 12.4 22.0

2/10/64 - 22/10/64 64.6 33.7 73.2

13/11/66 - 23/11/66 20.5 8.8 8.7

24/7/69 - 2/8/69 7.6 1.7 -

27/9/70 - 8/10/70 10.2 2.7 -

11/7/74 - 2/11/74 161.9 103.9 220.3

3/10/75 - 12/11/75 39.5 14.1 28.9

24/1/76 - 3/2/76 16.7 5.8 -

8/10/76 - 3/11/76 33.1 12.5 24.0

62

Table 6 Record of Significant Floods at Jemalong Weir where the river height would haveexceeded the banks and entered the 21-Mile Break Out (7.31 m, DLWC data).

Date Gauge Height Discharge ML/day

Jul-1978 7.69 17900

Sep-1978 7.87 28500

Aug-1984 7.68 17800

Sep-1984 7.65 17500

Sep-1988 7.49 16000

Apr-1989 7.73 18600

Aug-1989 7.62 17200

Apr-1990 8.00 49300

Jun-1990 7.63 17200

Aug-1990 8.23 103800

May-1990 7.53 16291

Jun-1990 7.63 16000

Aug-1990 8.23 101743

Feb-1992 7.56 16883

Oct-1992 7.53 16291

Nov-1992 7.57 16684

Jul-1993 7.43 15262

Sep-1993 7.65 17475

Sep-1993 7.60 16684

Oct-1993 7.82 19794

Sep-1996 7.34 15172

Oct-1996 7.53 16042

Oct-1996 7.73 18720

Jul-1998 7.45 15700

Nov-1999 7.32 15144

Nov-2000 7.52 15649

(2) Lake Cowal landscape and ecology

Lake Cowal is the largest natural lake in the Lachlan catchment (26 km in length and

6-7 km across). When full, Lake Cowal is about 17 km long by 9.5 km wide and

covers 150 km2 (Vestjens 1977). The lake forms two sections separated by a low

saddle and a hill known as Bogies Island. The northern and shallower portion of the

lake is known as Nerang Cowal (or Little Lake) and the larger deeper southern section

is called Lake Cowal (Figure 9). Nerang Cowal is a large woodland area to the north

63

of Lake Cowal which is frequently dry but fill during floods. The chain of wetlands

which includes Lake Cowal, Nerang Cowal and Bogandillon swamp is about 29,000

ha (Resource Strategies 1998).

Lake Cowal has many values. The name Lake Cowal (Cowal literally meaning

‘Lake’) and archaeological evidence demonstrates that the Lake was occupied by

aboriginals, and, in particular, the Wiradjuri people (Vestjens 1977, Gourlay et al.

1996, Resource Strategies 1998). The Lake is used for wheat cropping, pastures and

fishing (Vestjens 1977, Resource Strategies 1998). Lake Cowal has also been the

subject of an extensive study into the viability of a gold mining operation on the

western side of the lake (Resource Strategies 1998).

Lake Cowal is predominantly fringed with cane grass (Eragrostis australasica) and

occasional river red gums. The northern half of the lake is shallow, dominated by

lignum and contains a thicker stand of river red gums. The southern half is deeper and

is mainly open water. In the centre of the lake, however, there is a stand of lignum

commonly used by water birds (see Vestjens 1977, Resource Strategies 1998). There

are at least 321 native and 90 exotic plant species in the Lake Cowal area (Clements

and Rodd 1995).

Lake Cowal supports a large number of waterbirds and waterbird species (AHC

1992). The Lake has been listed on the register of the National Estate since 1992

(Resource Strategies 1998). Large bird breeding events occur in response to floods.

For example, in 1998 after several flood events an extremely large breeding event

occurred, which was the biggest seen since 1983 (DBA). Breeding avifauna observed

on the eastern side of the lake in 1998 included swamp hens, great-crested grebe,

royal spoonbill, mountain duck, pink eared duck, 35-40 hard-heads, night-herons,

Australasian shovellers, wood ducks, grey teals and swans (DBA).

Many animals of conservation significance are found in Lake Cowal. Regionally

endangered animal populations occur in Lake Cowal (eg the giant burrowing frog,

Heleioperus australiacus, Gourlay et al. 1996). Vestjens (1977) recorded 11

(including 5 introduced) fish, 162 plant, 11 amphibian, 30 reptile, 17 mammal and

172 bird species. A number of animal species have outlying or disjunction populations

at Lake Cowal (eg the eastern golden plover, Gourlay et al. 1996, DBA). The freckled

64

duck is listed on the threatened fauna schedule 12 of the National Parks and Wildlife

Act of 1974. The peregrine falcon, magpie goose, brolga, grey falcon and the great

egret, all of which are observed in Lake Cowal, are also listed on this schedule as

either ‘rare’, ‘vulnerable’ or of ‘special concern’ (Gourlay et al. 1996). International

bird treaties on migratory birds with Japan and China (JAMBA and CAMBA

respectively) are designed to protect cattle egrets, great egrets, glossy ibis, painted

snipe, Caspian tern and the red-necked stint, all of which occur in Lake Cowal

(Resource Strategies 1998).

Although Lake Cowal is considered to be an important drought refuge for birds (AHC

1992), occasional incidents that involve the deaths of many birds may arise with Lake

Cowal drying. In late 1997 the lake dried up and was subject to high temperatures (up

to 45°C). These conditions are extremely conducive for botulism. A large number

fish, mainly carp, died and a large number of birds were observed dying on the eastern

side of the Lake (DBA). About 2000 grey teals, 400 swans, 300 black ducks and the

occasional mountain duck and stilt were observed dead (DBA). Moreover, a similar

assemblage of botulism-sensitive bird species was observed to have died under

comparable conditions in Booligal swamp in the 1998/1999 summer (DP).

(3) Bogandillon Creek/Bogandillon Swamp

1) History of Bogandillon Creek

Bogandillon creek has been used as a source of stock water since early settlement. In

the early 1950’s licenses were granted to build four weirs along the creek to form a

chain of ponds in order to provide a more reliable source of water. Over the years the

quantity and quality of this water supply was maintained by additions of 100-

200 ML/year of irrigation water via supply channel escapes from the irrigation district

(Williams 1994). The existing weirs are in various states of disrepair and there has

been some discussion as to whether they should be removed to reduce pressures on

the groundwater system (Williams 1994).

Levee banks have altered flows in this system. Water travelling from Lake Nerang

Cowal once travelled down Manna Creek into the Manna Swamp which, when full,

would supply the upper reaches of Bogandillon Creek. Levee banks now isolate

65

Manna Swamp from Manna Creek, making Manna Creek and Bogandillon Creek the

one entity (WJ). Clearly, Manna Swamp would have been degraded by a lack of water

under these conditions. Moreover, the speed of flows along the upper sections of

Bogandillon creek has increased noticeably because of these levee banks. In spite of

these high flows, the upper reaches of these creeks have stable banks with healthy

riparian vegetation and little to no bank erosion. The only environmental issue

observed by landholders is the occasional tree death after floods, but these are

generally replaced by regrowth (WJ).

2) Bogandillon Swamp

The Bogandillon Swamp occupies an area of approximately 39 km2 (Williams 1994).

In 1977 the swamp was nominated as a “natural place” on the Australian Heritage

Commission Register because of its capacity for supporting bird life when it fills

(Lyal and Macoun Consulting 1995). Various species of waterbird have been

observed in the swamp, such as yellow spoonbills and pelicans (DLWC wetland

database). Additionally, the plum-headed finch, which is typically associated with a

thick cover of wet vegetation (Pizzey 1987, SN), has been observed in the Jemalong

area, including within Bogandillon Swamp, although these haven't seen any for ‘some

years’ (SN). Lippia (Phyla canescens) hasn’t become a problem within the swamp.

However, in the small part that is drained by the Wallamundry Creek, Lippia is

present (HR).

66

Lachlan River

Newell Hwy

Lake Cowal

Extent of 1990 Major Flood

Lachlan Valley WayBogandillon Swamp

Manna Ck

Bogandillon Ck

Island Ck

6 0 6 12 18 24 Kilometers

FloodwayLakesBogandillon SwampRoadsRiver & Creeks

N

EW

S

Direction Surface Water Flow in the Jemalong Irrigation District and Extent of the 1990 Major Flood

Figure 10 Direction of surface water flow in the Jemalong Irrigation District and extent of the 1990

flood. Map compliments of Jemalong Irrigation.

67

(4) Bogandillon Creek and Lake Cowal – problems with salinity

The Bogandillon Creek area has significant problems with salinity. Before the 1950’s

floods the middle and lower reaches of Bogandillon Creek contained two or three

rows of ‘healthy’ river red gums with grasses, and rates of erosion were low (HoD).

Since this time extensive salt scalds have appeared along the broader meanders of the

main creek bed and in drainage depressions that feed into the creek. A study of the

irrigation district found that groundwater has been moving south towards Lake Cowal,

and is expected to intersect the bed of the lake within 10 years (therefore by 2004,

NPJ 1994). According to this report salinity had already killed vegetation along parts

of Bogandillon creek and swamp by 1994. Tree deaths along and in the drainage

depression have occurred over many years and mature trees are continuing to show

signs of stress. Understorey species are virtually non-existent except for salt-tolerant

grasses and roly-poly (Salsola spp., DWR 1994b). In some areas the adjacent slopes

show severe dry-scalds because of exposed sodic subsoils (DWR 1994b).

Nonetheless, bank and bed erosion levels over the last ten years have been at a

constant level, with most erosion occurring during flood times (HoD).

Salinity effects are a consequence of land management practices, but are now being

addressed. The adverse groundwater effects in Bogandillon creek and swamp were the

consequence of inefficient irrigating practices and leaking irrigation channels (NPJ

1994). Rising saline groundwater mounds are a general management problem in the

Jemalong-Wyldes plains (bordered by Jemalong and Corridgerry Ridges to the east,

and the Bogandillon-Lake Cowal system to the west), and therefore land management

practices need to address this risk (Gourley et al. 1996). Up until the early 1990’s

farmers in the Jemalong Irrigation District channelled their excess irrigation water off

their properties into Bogandillon Creek or Lake Cowal. These problems have,

however, been addressed by the Bogandillon Landcare Group, which re-established a

corridor of riparian vegetation to reduce groundwater levels in the vicinity of the

creek (Lyall and Macoun 1995). The Jemalong Land and Water Management Plan

(DLWC 1999b) is also addressing these various management issues.

The local geology and topography also affect observed salinity levels in the

Bogandillon Creek catchment. The Manna Mountain Range constricts the floodplain

width, the flow of surface water and also the flow of shallow and deep groundwater

68

(DWR 1990). As a result, there is a groundwater mound under the Jemalong Irrigation

district. Since 1983, 23 piezometers in the vicinity of the creek have been used to

monitor groundwater levels. The monitoring results show that significant groundwater

rises of 1 to 1.5 m over the whole Bogandillon creek area in the ten years prior to

1995 (Lyall and Macoun Consulting 1995). Bogandillon creek has EC values that

occasionally reach about 20,000 µS/cm17 during low flow periods (DWR 1994b).

Conductivity is highest in the lower reaches. Marked increases in creek conductivity

begin approximately 1.5 km downstream from the Driftway Bridge (which is in the

lower part of the middle reach, Sturgess et al 1993, Figure 10). For example,

conductivity just upstream of the Driftway Bridge was 1,500 µS/cm during a dry

period (March 1993), whereas conductivity was recorded as 18,260 µS/cm in the

lower reaches during the same dry period (Sturgess et al 1993). In spite of these

trends, however, the water within the swamp is reported to be unaffected by the major

salt problem upstream. When flows reach the swamp the salt tends to be diluted. In

contrast, during periods of low flows the high salt concentrations within the creek

generally do not reach the swamp, because these flows usually evaporate before

arriving (HR).

(d) Smaller floodplain wetlands of the mid-Lachlan

(1) Smaller floodplain wetlands

There are many floodplain wetlands throughout the mid-Lachlan region, most of

which are considerably smaller than wetlands such as Bogandillon swamp. Most

landholders describe some form of wetland on their property, but most of these are

undescribed. It is known, however, that breakout floodwater escaping from the

Lachlan River feed a series of wetlands in the Jemalong and Wyldes Plains before

reaching Lake Cowal. These consist of five main forms: natural floodplains fringed

with river red gum associations; drainage depressions; ephemeral oxbow lagoons and

small floodplain lakes; intermittent creeks with semi-permanent water holes and

17 ANZECC guidelines recommend a maximum of 14,925 µS/cm for sheep and 7,463 µS/cm for beef cattle or loss

of animal condition and health would be expected. (ANZECC, 2000).

69

floodplain-woodland associations of river red gum, lignum and black box (King

1994). One example of the floodplain-woodland association is the Wilbertroy State

Forest area which, like Lake Cowal, fills from the 17 and 21-mile breakouts (King

1994). The most extensive wetland type in the district are natural floodplains which

are characteristically fringed with river red gum or associated with open perennial

wetland species, such as black box and bimble box (also known as ‘Poplar box’,

Eucalyptus populnea) on the open floodplain (King 1994, DP).

There are a variety of management practices that have affected the flow to these

wetlands. For example, on a property approximately 15 km east of Forbes

(“Walangle”) the billabongs received water from moderate and major flood events

before the 1950’s. After the 1950’s floods the owners constructed a levee bank to

prevent regular inundation. This levee bank is now only topped during major flood

events (eg 1990), with the more regular moderate flood events not filling the

billabongs. During large flood events the majority of the water drains off the property,

either though natural or constructed channels (installed in the 1950’s), leaving

approximately two-to-three feet of water in most billabongs. During such events, a

variety of birds, predominantly ducks and ibis, are seen breeding in these billabongs

(MaB).

On other properties such as those along the Bumbuggan Creek, periods of inundation

are occurring in increasing regularity because of the increased supply of water for

irrigation in the lower Lachlan and, more recently, from environmental flows. The

floodplain and billabongs through this area (Bumbuggan Ck and Lower Goobang Ck)

that once contained lignum and a variety of grasses are now dominated by an

extensive cover of Lippia (LA, RB).

Weed invasion is a common problem for mid-Lachlan wetlands. For example,

wetlands adjacent to the Lower Goobang that receive regular fills, but little to no

grazing or weed control, are infested with a variety of weeds such as lippia, Bathurst

burr (Xanthium spinosum), noogoora burr (X. occidentale) and African boxthorn

(Lycium ferocissimum, LA).

Another example of changes to the frequency of riparian wetland inundation is the

installation of weirs. For example, under natural conditions Carrawabitty Creek (a

70

large billabong) filled during high flows; from the offtake at “Lucerndale”, or when

floodwaters broke out at “Kaloola” (which flows when the iron bridge in Forbes is

8.9 m). Currently, because of the installation of Jemalong weir Carrawabity Creek is

affected by the Jemalong weir pool and is consequently rarely dry (MJ).

(2) Gum Swamp

Gum Swamp is a formerly ephemeral floodplain depression that has been modified to

meet the demands on a sewage treatment plant and a travelling stock reserve. The

swamp is south of Forbes and covers an area of approximately 80 ha. Gum Swamp

was originally an ephemeral river red gum woodland up until the 1920’s when a

sewage treatment plant was established. The plant then began discharging secondary

treated effluent into the swamp. Currently treated effluent is discharged into the

swamp at approximately 2.8 ML/day (DLWC 2002). A small percentage of effluent is

used for selective irrigation. These regular flows ensure that water levels in the

swamp remain high over summer and drought periods. Over winter these flows can

cause some overflow into the nearby properties. The swamp is situated beside a

travelling stock route and the vegetation surrounding the swamp is subject to some

grazing, although the vegetation cover is monitored by a Rural Lands Protection

Board ranger to ensure overgrazing does not occur. Along the south-west boundary of

the swamp areas of vegetation have been fenced off to reduce stock impact.

Although modified the swamp has much of the original flora and considerable

conservation value, particularly for local natural history enthusiasts. In particular, the

proximity of this wetland to Forbes and an active field naturalist group (National

Parks Association) and Landcare group (Forbes Urban Landcare Group) has ensured

this area has received considerable attention. River red gum and grey box (Eucalyptus

microcarpa) dominate the upper storey around the swamp. The understorey present is

consists of juvenile canopy species, eastern cottonbush (Maireana microphylla) and a

large cover of introduced grasses and herbs. Wetland plant species are common in the

riparian zone and include cumbungi (Typha orientalis) and Juncus sp. As the swamp

is relatively permanent water it provides a refuge for waterbirds, especially in summer

and over drought periods. Over 160 species of birds have been identified using the

swamp area; six of these are listed as threatened species and have been observed in

the area over the last thirty years (Mullins and Carden 1999). 14 mammals, 3 reptiles,

71

2 frogs and 2 fish species (carp and mosquito fish, Gambusia holbrookii) have also

been recorded. A threatened species of bat has been tentatively identified in the area

as well (Mullins and Carden 1999).

(3) Lake Forbes

Lake Forbes is an anabranch and flood-runner of the Lachlan River, which lies in the

centre of the Forbes township and runs (very roughly) parallel to the river. It is about

seven kilometres long, 30-60 m wide and has an average depth of 1.5 metres (DWR

1994a). The lake was almost certainly once ephemeral, but now the Forbes Shire

Council using local groundwater to maintain the lake as a permanent waterbody.

Floodwaters which overflow at the ‘southern cross breakout’ 15 kilometres upstream

of Lake Forbes flow across low-lying country and into Lake Forbes (DWR 1994a).

During the flood in 1990, floodwaters from Lake Forbes broke into the Battye Street

floodway and isolated a high area of land around Court and Harold Streets. A

pronounced northerly flow-path from the Lachlan River to Lake Forbes also existed

around Ferry, Flint and Hill Streets (DWR 1992d).

There have been a number of works on Lake Forbes. Three weirs are located on the

lake and form three individual water bodies. These weirs are superficially like a

‘chain of ponds’ because they overflow from one to the next with a drop of 1 to 2 m at

each location. A temporary weir exists at the railway crossing. The first weir to be

constructed is located at Wambat Street and was constructed in the 1880’s to provide

water for sluicing of gold (DWR 1994a). The weir at Salisbury Road was the most

recently constructed in the 1980’s. Additionally, since 1964 the lake bed has been de-

silted and deepened and work has been carried out to align the banks (Killingbeck

1982). There has also been a small wetland built for improving water quality at the

north end of Lake Forbes. This filters water from a catchment area of about 10 ha

(ESU, 1997). The constructed wetland was the result of an initiative of the Forbes

Urban Landcare Group and the Forbes Shire Council.

The Forbes Shire actively manages the aquatic vegetation community of Lake Forbes.

Ribbon weed has the tendency to dominate this lake, but now the abundance of this

plant tends to be actively controlled. The ribbon weed has been considered a nuisance

and various methods of control have been used. During 1965-67 a herbicide

72

(‘Aqualin’) was used, however it did cause fish kills (Killingbeck 1982). Manual

removal methods have also been deployed. Between 1939 to 1951 water hyacinth was

also a problem species and spread prolifically through the lake. It was treated with the

herbicide ‘Methoxone” (Killingbeck 1982). Killingbeck (1982) also reports that

filamentous green algae that attach to water plants and submerged surfaces are also

common. Persistent blooms of potentially toxic blue-green algae have been recorded

in the lake. Moreover, the native and harmless fern Azolla commonly dominates the

edge of Lake Forbes, however, and by virtue of its tendency to form mats is often

misunderstood to be harmful algae. Nevertheless, there is a risk that such mats of

plants or algae can block out light that allow (other) aquatic plant species to thrive

(Mitsch and Gosselink 1986), and therefore Azolla requires some level of

management.

It is also apparent that the terrestrial vegetation surrounding Lake Forbes has been

substantially modified. As would be expected in an urban environment lawn grass

dominates. The riparian edge of Lake Forbes alternates between being dominated by

large rocks, open grass, willows, a few concrete structures and some native

vegetation. There is some invasion of Lippia, and, in some places the dominance of

salt tolerant taxa, in particular sea barley (Hordeum marinum) in areas where

groundwater discharge is probably occurring.

Catfish, carp, redfin, bream, some golden perch and many water rats have been

observed, or caught by fishermen, in the lake along with the numerically dominant

aquatic birds that comprise black swans (Cygnus atratus), black ducks (Anus

superciliosa), darters (Anhinga melanogaster) and pelicans (Pelecanus conspicillatus)

(Killingbeck 1982, DP). Numerous other bird species frequent the lake, but there has

been no formal bird survey to fully document these.

73

5.2 The lower Lachlan and its effluent creeks

The lower Lachlan contains a number of wetlands of national importance including

Merrowie Creek (from Cuba Dam to Chilichil Swamp), the Booligal wetlands (on

Merrimajeel and Muggabah Creeks), Lake Merrimajeel and Murrumbidgil Swamp

(on Merrimajeel Creek), the Great Cumbung Swamp and the Waljeers wetlands (or

the ‘Lachlan swamp’, EA 2001). All of these wetlands are part of an interconnected

flow network comprising of creeks, flood-runners, wetlands and the lower Lachlan

River channel (Figure 12). In order to further our ecological knowledge of this

complex wetland system this section specifically aims to list each effluent creek in the

lower Lachlan River catchment, and to outline how people have changed the flood

distribution pattern from the natural state18.

An effluent creek is a creek that takes water away from the main river under high flow

conditions (DLWC 1997a). Similarly, an effluent is defined a stream that flows out of

another body of water’ (definition 2, Collins Dictionary 1991). During high flows

under both current management and undeveloped conditions, the effluent creeks of

the Lachlan River have acted as distributaries, that is, outlet streams that drain the

river (Collins Dictionary 1991).

There is a close connection between the Lachlan effluent creeks and the changes in

the Lachlan River. John Oxley made reference to this connection in 1820 when he

stated that the body of water running into its tributaries would have been:

“… fully sufficient to have constituted a river of magnitude, if it had constantly maintained

such a supply of water, and had not been separated into branches, and lost among the

immense marshes of this desolate and barren country, which seems here to form a vast

concavity to receive them”.

The volume of flows of the river in lower Lachlan have been fundamentally altered by

river regulation, and also land and water management practices associated with river

regulation. The flows of the Lachlan River at Oxley, which are a reasonable surrogate

18 Information from landholder interviews in this lower Lachlan section originates from landholder interviews

conducted in 1999.

74

for flows in the Cumbung swamp, are 53% of modelled annual undeveloped flows

(based on modelling described in Section 12, Figure 11). Flow variability (measured

using standard deviations) is 80% of undeveloped, dipping to 53% in March. In the

usually dry months of summer/autumn (Jan-May) the river now receives 41% of

undeveloped flows. During the wetter winter/spring rainfall months (June-December),

the high flow period, the creeks currently receive 56% of undeveloped flows (Figure

11). Similarly, the Lachlan River at Booligal (near the Booligal swamp) generally

have higher flows in the undeveloped flow run. The modelled daily flows for the

Lachlan River at Booligal, averaged over a year, are:

Undeveloped (N011) = 1008 ML/day

EFR (E109) = 559 ML/day (about 56% of undeveloped).

Flow of the Lachlan River at Oxley

0

200

400

600

800

1000

1200

Jan

Feb

Mar

Apr

May Ju

n

Jul

Aug

Sep Oct

Nov

Dec

Month

Ave

rage

d m

onth

ly in

flow

s (M

l/day

)

Natural

Current

Figure 11 Simulation of flows in the Lachlan River at Oxley under the current flow rules and

without regulating structures.

75

Figure 12 Wetlands and effluent creeks of the lower Lachlan Valley. ‘BB’ indicates the blockbank at Booligal swamp.

77

Flow of Willandra Creek

0

50

100

150

200

250

300

350

400

450

Jan

Feb

Mar

Apr

May Ju

n

Jul

Aug

Sep Oct

Nov

Dec

Month

Ave

rage

d m

onth

ly in

flow

s (M

l/day

)Natural

Current

Figure 13 Simulation of inflow into Willandra Creek under the current flow rules and without regulating

structures.

Combined flow of Middle and Merrowie Creeks

050

100150200250300350400450500

Jan

Feb

Mar

Apr

May Ju

n

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Aug

Sep Oct

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Ave

rage

d m

onth

ly

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ws

(Ml/d

ay)

Natural

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Figure 14 Simulation of inflow into Middle and Merrowie Creeks (flows combined under the current flow

rules and without regulating structures.

78

Combined inflows into Merrimajeel, Muggebah and Cabbage Garden Creeks

0

20

40

60

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100

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n

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rage

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onth

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s (M

l/day

)

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Natural

Figure 15 Simulation of inflow into Merrimajeel, Muggabah and Cabbage Garden Creeks (flows

combined) under the current flow rules and without regulating structures.

0%

20%

40%

60%

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100%

120%

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160%

Jan

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n

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0%

500%

1000%

1500%

2000%

2500%

Merrimajeel, Muggebahand Cabbage GardenCreeks (left axis)

Middle and MerrowieCreeks (left axis)

Willandra Creek (rightaxis)

Figure 16 Seasonal alterations in effluent flows shown as a percentage of current inflows over

undeveloped inflows.

79

02468

101214161820

Jan

Feb

Mar

Apr

May

Jun Jul

Aug

Sep

Oct

Nov

Dec

Month

Wet

land

fills

per

mon

th(lo

wer

-Lac

hlan

b'b

ongs

) N09

E73a

E151

E179

(a)

02468

101214161820

Jan

Feb

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Apr

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Jun Jul

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Sep

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Month

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land

fills

per

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th(lo

wer

-Lac

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sw

amps

)

N09

E73a

E151

E179

(b)

Figure 17 The number of days per month that lower Lachlan (a) billabongs and (b) swamps are inundated

at or above the depth required for aquatic plant growth under four flow scenarios: pre-regulated

conditions (N09), the original flow rules (E151), current regulated conditions (E73a) and proposed flow

rules (E179).

Willandra Creek (Figure 13) and Middle and Merrowie Creeks (Figure 14) currently have a

greater annual volume of flows than they did before flow regulation. In contrast, the creeks

further downstream, Merrimajeel, Muggabah and Cabbage Garden creeks now have a

smaller annual inflow. The combined annual inflows into are now 55% of undeveloped

(Figure 15). The variability (measured by the standard deviation) in flow for these creeks is

currently 77% of undeveloped (dipping to 35% in March). In the usually dry months of

summer/autumn (Jan-May) the creeks now receive 47% of ‘undeveloped flows. During the

wetter winter/spring rainfall months (June-December), the high flow period, the creeks

80

currently receive 55% of undeveloped flows (Figure 15). One of the reasons for the reduced

flows in Merrimajeel, Muggabah and Cabbage Garden creeks is that the offtakes of

Willandra Creek, and to a lesser extent Middle and Merrowie Creeks, are taking relatively

more of the flows under the current regulated flow regime (Figure 16). These patterns in

flows are, however, also likely to be strongly influenced by the abstraction of flows in the

upstream sections of the Lachlan (cf. Section 4). Additionally, there have been a number of

works, channel modifications and changes in water use in the effluent creeks, as discussed

in the following sections.

These changes in flows in the Lachlan River and its effluents have had effects on the

inundation of riparian wetlands. Although Sims (1996) found a large reduction in spring

flows in the lower Lachlan (Section 4.1), the IQQM runs (12.4) do not indicate large

changes in seasonality in the riparian wetlands (Figure 17, Table 3). IQQM runs of riparian

wetland inundation indicate that swamps of the lower Lachlan, represented by three Great

Cumbung Swamp wetlands and Booligal swamp, are re-filled at 57% of undeveloped under

regulation (Table 3). Additionally, the greatest impact on these wetlands is during the

typically dry months from January to May with re-fill getting down as low as 44% of

undeveloped for all wetlands, or 33% of undeveloped for individual wetlands. The lower

Lachlan billabongs are marginally less affected by regulation overall at 68% of

undeveloped. At a seasonal level, however, the modelled impacts of regulation are extreme

with zero percent of undeveloped fill occurring during the drier months. It is probable that

these impacts on the lower Lachlan swamps and billabongs are partially a consequence of

the irrigation diversions into Merrowie and Willandra Creeks, as discussed above.

(a) Torriganny Creek

Torriganny Creek is an anabranch of the Lachlan River, which diverts from the Lachlan

downstream of Hillston and rejoins upstream of Booligal. Merrimajeel Creek and

Muggabah Creeks are distributaries of Torriganny Creek.

On this creek is the Torriganny Weir, a drop board structure owned by the Torriganny,

Muggabah and Merrimajeel Creeks Water Trust. This trust was established in 1907, and a

weir was proposed, and presumably built soon after this date (Lee 1907). Many works took

place in the area during this time (PK). A new weir was built in the financial year ending

1936 (Anon 1936), and further improved by a contractor in 1939 (White 1939). This

81

wooden structure was replaced by a concrete structure by 1958 (PK). Total height of the

current weir is 3.2 metres. The primary function of the weir is to control the diversion of

replenishment flows for stock and domestic purposes during autumn/winter for the water

trust district along Merrimajeel and Muggabah Creeks. The weir has been maintained by

the Water Trust. For example, £142.7.8 was spent on repairing the weir in the financial year

ending 30/6/1940, £140.7.8 was spent on extending the weir to prevent ‘percolation of

water and consequent soil erosion’ in the financial years ending 30/6/1939 (Anon 1939,

Anon 1940). This weir is operated to divert flows in the order of 50-100 ML/day through

the creeks. The flows cease about when Merrimajeel Creek reaches Murrumbidgil swamp

and Muggabah Creek reaches Little Lake (DLWC 1992).

(b) Merrimajeel and Muggabah Creeks

(1) Works in the Merrimajeel and Muggabah Creeks

Clearing out and grading of Merrimajeel and Muggabah Creeks seems to have been a

management strategy occasionally implemented by the Torriganny, Muggabah and

Merrimajeel Creeks Trust (the ‘Water Trust’). Records on this are patchy and so such

works may have been more frequent than is documented. Such works were proposed in

1907 (Lee 1907), and presumably carried out about this time. Similarly, the Water Trust

Annual Report for 1939 states “Arrangements are being made to clean out lignum growth

in the Merrimajeel Creek to the Mossgiel Road (Cobb Highway) which is affecting the

flow of water” (Anon 1939). In these early days bullock-teams were used to clear these

channels. In the mid-1970’s an earth moving plant cleared the silt and lignum bushes in

both these creeks. About 3-4 km of each creek (following the meandering of these creeks)

was cleared, from the Torriganny Creek off-takes to the Cobb Highway (PK). Merrimajeel

Creek, but not Muggabah Creek, was particularly silted up before these works (PK).

Various historical statements of receipts and payments also suggest that the Water Trust has

had an ongoing program of ‘creek cleaning’.

In early 1999 landholders within, or nearby to, the Water Trust and DLWC were in

discussion regarding a channel clearing program that aimed to help landholders receive

their stock and domestic water entitlement. This issue is still in the process of being

resolved. Currently, a lot of flow travels down these creeks during the warmer months

when it is not required for stock and domestic delivery. Most of these flows result from

82

upstream rainfall rejections spilling from Torriganny Creek, but such flows can also occur

because of environmental flows for bird breeding. Hence, there has been discussion about

the construction of small regulators at the offtakes of Muggabah and Merrimajeel Creeks.

Moreover, there is also ongoing discussion about the best time to deliver stock and

domestic flows, because of the enhanced plant growth during warmer months. Accordingly,

in 1998 the Water Trust and DLWC agreed that replenishment flows should commence in

May (OB). When flows occur in warmer months lignum, cumbungi and other plant growth

results, and the creeks are overgrown. This plant growth impedes the delivery of water that

takes place in later cooler months to properties along these creeks. Hence, landholders have

been the driving force in these discussions because they seek the delivery of relatively

unimpeded flows. The reduction of plant growth in these effluent creeks would also be

desirable from an environmental point of view. Prior to active management of these creeks

they would not often be running during the warmer months (commence-to-flow of

Merrimajeel Creek is at 250-300 ML/day at Booligal weir; see Figure 15). Currently,

natural flows to the terminal wetlands of Merrimajeel and Muggabah Creeks, in particular,

Murrumbidgil Swamp and Lake Merrimajeel, are impeded. Murrumbidgil Swamp and

Lake Merrimajeel are listed in the Directory of Important Wetlands (EA 2001).

(2) Construction of blockbanks

A temporary block bank was constructed in Merrimajeel Creek in 1985 to arrest water loss

from a colonial bird-breeding event. This was re-activated and relocated downstream

during the 1989 and 1990 colonial bird breeding events by a construction of a temporary

weir downstream of the original bank. Subsequently, a permanent blockbank with a

telemetered19 regulator was constructed in 1991 (DLWC 1992). The current block-bank is 1

km long, 4 m wide, up to 1.2 m high and contains a drop board regulator (DLWC 1992).

The use of releases from Lake Brewster to sustain flooding, flood recession management

and construction of a block bank on Merrimajeel Creek downstream of the ibis rookery site

in Booligal swamp was adopted by the DLWC as the most efficient approach for

controlling water level in the swamp. The delivery of flows to the nationally significant

Booligal Swamp (EA 2001) is an important component of the Lachlan Environmental Flow

19 Telemetered gauging stations record flow data can be down-loaded remotely using a telephone line.

83

Rules, and, in particular, the use of the Environmental Contingency Allowance (ECA,

LRMC 1999). Water management options for managing and improving colonial bird

breeding in this wetland using the current regulator are discussed in Magrath et al. (1991)

and Moore (1992).

(3) Flow into Merrimajeel and Muggabah Creeks

Merrimajeel and Muggabah Creek receive an annual stock and domestic replenishment

flow. As discussed above, many landholders in the lower sections report that they rarely

receive all their water because of the proliferation of aquatic plants in the upper reaches of

the creeks in the last few years (ca. 1995-1998; cf. Section 5.2(b)(1)). For example, one

landholder (TK) reports that it used to take 14 days from Torriganny Weir to Murrumbidgil

Swamp, and now it takes twice as long because of weed growth.

Booligal swamp (on Merrimajeel Creek) is one of the first wetlands in the Booligal area to

fill. When flows are not managed and flow at Booligal Weir is at 0.48 to 0.51m (250-300

ML), the creeks begin to flow. Booligal swamp drowns out at about the time that Moon-

Moon Swamp starts to fill (OB; ca. 1000 ML/day at Booligal weir). Moon-Moon Swamp is

on the property Euragabah, just north of Booligal. Since 1984 breeding events in Booligal

Swamp occurred in 1984, 1989, 1990, 1992, 1993, 1996, 1998 and 2000 (LRMC Flow

Rules Appendix A 1998, DP).

Table 7 Dates when Booligal Swamp filled (Commence to Flow, OB) based on flows starting at theMerrimajeel off-take on Torriganny Creek.

Year Date of

Commence to Flow

Flows on that date

(ML)

Flows the next day

(ML)

1988 27 Sept 180 525

1990 17 April 199 275

1993 23 July 213 260

1996 1 August 359 (it was 267 the day before) 480

1998 14 July 94 346

When Torriganny weir is has no boards in it, and therefore is not being used to direct flows

up the Merrimajeel and Muggabah creeks, flows of 250-300 ML/day at Booligal weir will

cause water to spill from Torriganny Creek into the Merrimajeel and Muggabah off-takes

(OB). When flows exceed 800 ML/day these two creeks are joined by flood-runners

(Dwyer and Bennett 1988). During these uncontrolled flows more water flows down

84

Merrimajeel Creek than Muggabah Creek (but the reverse is true during controlled flows)

Nevertheless, one landholder (BH) states that the block-bank on Merrimajeel Creek makes

the flow tend to go down Muggabah Creek to a greater degree.

Merrimajeel Creek ‘disappears’ and reappears to flow into Baconian Swamp, which is a

riparian wetland of the Lachlan River near Oxley. The creek route is not marked on

topographic maps, but is marked by infrequent occurrences of black box. Muggabah Creek

runs into the wetlands around Lake Waljeers and Peppermint Swamp downstream of

Booligal; this area is also known as Lachlan Swamp and is listed in the Directory of

Important Wetlands (EA 2001). These terminal sections of Merrimajeel and Muggabah

Creeks only run during very large flood events (eg 1990).

(4) Plant growth in Merrimajeel and Muggabah creeks and their effect on flow

Plant growth during flows varies along the length of the creeks. In most places lignum

dominates. When areas such as Booligal swamp become very wet, water milfoil

(Myriophyllum sp.) and lignum dominate with various other wetland plants such as Cyperus

sp. (probably nutgrass, C. bifax, SB), Pondweed (Potamogeton spp.), cumbungi, water

primrose (Ludwigia peploides) and nardoo (Marsilea mutica). In Murrumbidgil Swamp

river red gums dominate. Along most of the length of these creeks many annual low-lying

herbs and grasses would appear during rain and/or creek flows. For example, a species of

Veronica can grow prolifically along the Merrimajeel Creek channel upstream of the block

bank. This is quite likely to be pink water speedwell (Veronica catenata) which is recorded

as “a plant of wet places, recorded for the region (and for New South Wales) only for a

swamp in the Booligal district” (Cunningham et al. 1981).

Impediments to flow in these creeks are likely to be a combination of factors. Flows at

‘Angora’ (the area with Murrumbidgil swamp and Lake Merrimajeel) were slowed by a

‘mix of pin rush, lignum, kangaroo dung and grass - like a beaver dam’ (TK). Annuals

would combine with perennial plants and dung to produce an abundance of organic matter

to create these dams. Additionally, the lignum is very dense within parts of these creeks. It

is likely that the high density of lignum growth may have been mitigated by past channel

clearing. “Burning and other forms of control which have been used by landholders ... to

remove lignum appear to be successful in the short term but regeneration is usually rapid

and dense following subsequent flooding or wet years” (Cunningham et al. 1981).

85

(c) Cabbage Garden Creek

Cabbage Garden Creek is an unregulated creek, which runs from about ‘Riverview’ at

Hillston to the Cobb Highway near Goonawarrah Nature Reserve (south of Booligal). It is a

significant wetland area dominated by black box and nitre goosefoot (DLWC 1997a). This

creek runs at higher flows than the nearby Moon-Moon and Booligal swamps (SB, Moon-

Moon swamp is north of Booligal, on the property ‘Euragabah’).

(d) Pimpara Creek/Five Mile Creek

Pimpara Creek starts at the McFarland’s State Forest near ‘Corrong’ and finishes at about

‘Toopuntal’ on the Murrumbidgee River. This creek is unregulated. The dominant

vegetation is black box and river red gum (DLWC 1997a). This creek flows only in flood

events.

(e) Island Creek and other small lesser-known creeks

There are probably many small creeks, which could be considered to be distributaries, and

are poorly known in terms of their hydrology, vegetation and management history. One

example of this is Island Creek. Island Creek runs near ‘Hunthawang’ into Gum Swamp (a

river red gum swamp). In the 1990 floods there was concern it may have inundated the

‘Griffith Road’ and run into Hillston. This creek is known to start running when Brewster is

at about 4000–5000 ML/day (HyD).

(f) Merrowie (Marrowie) and Box Creeks

Merrowie Creek is a system of dams, weirs, braided channels and streams (Figure 12). At

its off-take from the Lachlan River at Gonowlia Weir the creek starts as a large channel

with numerous billabongs and flood-runners. The mouth of Merrowie is a big lignum

swamp, which is known locally as the “River lignum” and “Hurtles” paddocks. There is no

black box in this area, which is attributed by a local landholder (HyD) to the relative

steepness of the land here (about 15’ (4.6 m) over 7 km). The large channel is an

enhancement that was completed in 1956 (HyD). This well-watered reach eventually gives

way to infrequently inundated sinks and swamps (Whitehead and McAuliffe 1993). The

Creek below Cuba dam flows into the Tarwong Lakes system, the wetlands of Chilichil

swamp, Tin Tin Lake and Pitapunga Lake. Beyond Lake Tarwong, the Creek is known as

86

Box Creek and runs through numerous depressions, finally reaching the Murrumbidgee

River (Whitehead 1992). The 1988 Lachlan Valley database (Bennet et al. 1988, DWR

1988) lists 17 wetlands from Gonowlia Weir Pool to Lake Tarwong (Whitehead 1992).

Historically, Merrowie Creek started to flow at the same time as Willandra Creek, that is, at

8280 ML/day (HyD, OB). Currently, when Gonowlia weir is open (ie. when flows are not

being deliberately diverted down Merrowie Creek) Merrowie Creek will run when Lachlan

River flows get to about 1500 ML/day at Hillston weir (OB, Table 11). This lower

commence-to-flow is presumably a result of channel enhancement in 1956. For controlled

flows, boards are placed in Gonowlia Weir on the Lachlan River to raise the height of the

River to the height of the Merrowie Creek channel and, consequently, to send flow up the

Lachlan River. The time taken for flows to run from the Lachlan River at Gonowlia weir to

Cuba Dam depends on the flow volumes. It can take 4-5 weeks to get to Cuba dam in an

uncontrolled flow (1500 ML/day at Hillston or more) or 6-7 weeks for a 200 ML/day

controlled flow. Typically, these flows take about 28 days (TK). In 1998 a diversion was

sent down on the 17 April and this flow arrived at Cuba dam on 11 June (TK).

According to a local landholders (AJ) 1999 accounts the section of the Merrowie Creek

floodplain between the Cuba dam and the Tarwong Lake used to receive good spreading

floods over the country until the Wyangala Dam was enlarged in 1971. The lignum and

other plant growth along the channel bank are reported to have helped the spreading of

floodwaters (AJ). The dieback of the plant life and the arrival of carp were considered to

have aided the development of a defined creek channel, which, in turn, reduced the

spreading of creek water. 1998 was a “good year” as it did flood a lot of country, although

flows stayed “pretty much” in the channel from Cuba Dam to Tarwong Lake. In spite of the

1998 floods it was reported in 1999 that had been a loss of bird life and an increase in

insect pests20. “Since the drying of these wetlands and Tarwong Lake the increase in grubs

and caterpillar plagues in the dry saltbush country around here has greatly increased over

the last 20 years” (AJ).

Replenishment stock and domestic flows have been supplied to the Marrowie Creek Trust

District since 1952. The Marrowie Creek Water Trust District extends from Gonowlia Weir

20 The increase in insect pests could be a consequence of the decrease in birds (cf. ecosystem services, Table 1).

87

to Cuba dam (OB, PK, Whitehead and McAuliffe 1993). This has involved the diversion of

about 150 ML/day over a six-week period (about 6000 ML) typically during April/May.

During the early 1990’s, these flows were frequently complemented by a secondary

diversion during Winter/Spring as surplus water has found its way down the system

(Whitehead and McAuliffe 1993). More recently, replenishment flows have been made

only in the autumn. In order to allow continuing delivery of the replenishment stock and

domestic flows, the Merrowie Creek Trust has had an ongoing program of ‘creek cleaning’

similar to that of the Torriganny, Muggabah and Merrimajeel Creeks Trust. The statement

of receipts and payments (Anon 1958) suggests this.

There are several privately owned and licensed regulators and dams at the lower end of

Merrowie Creek. Whitehead (1992) listed about 14 licensed regulators exist along

Merrowie Creek. Box Creek also has a regulator to stop flows going into the Merrimajeel

Creek as opposed to the Merrowie Creek (OB). Cuba dam was one of the original works in

the Lachlan River built by James Tyson, and has been there since the mid-to-late 1800’s. In

a report dated 1885, Tyson also described how he made a seven-mile cutting which ran

from the Lachlan River, through Lake Comayjong (just north of Oxley, see Figure 12) to

Merrowie Creek (‘Royal Commission on Conservation of Water’ cited in Lloyd 1988).

Currently ‘all landholders’ below Cuba Dam ‘have been making applications to have the

trust extended, to gain regular flows in the Merrowie Creek to try and return this country

back to its original state without any success‘ (AJ).

(g) Middle (Middle Billabong) and Moolbong Creeks

Middle Creek used to have a cutting on ‘Hunthawang’ which flowed to Merrowie Creek

15 km upstream of the present off-take at Merrowie Creek (HyD, Whitehead 1992,

Whitehead and McAuliffe 1993). This was facilitated by flows, which were pushed through

to Middle Creek using a cypress pine weir on the Lachlan River at ‘Hunthawang’, from the

1890’s to before WWI. This weir fell into disrepair and was then destroyed by fire by an

unknown person(s) during a dry period. All these works diverted water into Merrowie

Creek (OB, KP, Whitehead and McAuliffe 1993). The mouth of the Middle Creek was

cleared during the 1890’s; probably through some government project. Later (pre-1930)

some bends were cut and there was further channel clearing (HyD).

88

Middle Creek requires about 2600 ML/day at Willandra weir to flow. In big floods such as

1956 and 1990 Middle Creek gets overflow from Willandra Creek (HyD). Middle Creek

runs just upstream of a fast flowing section of the Lachlan River21, and is therefore running

from “higher ground”. It therefore also runs at higher flows than the Merrowie Creek

(HyD).

Around Hunthawang at the mouth of Middle Creek there is now a 2 km stretch of river red

gums which have grown since flows became almost perennial. Historically, and presently,

most of the mouth of Middle Creek is a meandering box lined channel. This box has an

understorey of mainly grasses, and some nitre goosefoot (HyD).

Moolbong Creek is one of several small effluent creeks whose flows are poorly described

(other creeks include Yangellawah, Umbrella and Canoble Creeks; cf. maps CMA 1980,

1985). Moolbong Creek has its offtake on Middle Creek (see the 1: 100,000 ‘Willandra’

map, CMA 1985) and requires Lachlan River flows higher than those required to start

Middle Creek running (OB). In 1998 Moolbong Creek was flowing at least by 21 August

(SA).

(h) Flow modelling of Middle and Merrowie Creeks

The effluent creek-IQQM runs combine the flows of Middle and Merrowie Creeks, and

indicate that these creeks are now receiving about 118% of the annual undeveloped flow.

The current flow variability (measured by the standard deviation) is 123% of undeveloped

on an annual basis (this dips to 71% in March). In the usually dry months of

summer/autumn (Jan-May) the creeks now receive 95% of undeveloped flows. During the

wetter winter/spring rainfall months (June-December), the high flow period, the creeks

currently receive 118% of undeveloped flows (Figure 14).

21 Damien Hynes described this section as between ‘Rennie’s potato-shed’ and the ‘Hunthawang woolshed’; these are

presumably the two sheds evident at either side of the offtake on the Hillston 1: 50,000 topographic map (CMA 1980).

89

(i) Willandra Creek

(1) Willandra Creek - overview

Willandra Creek is recognised as a wetland system of local and regional significance. This

includes two gazetted nature reserves, Willandra National Park and Morrisons Lake Nature

Reserve. Willandra Homestead is found within Willandra National Park (Whitehead 1994).

Many other parts of this creek contain important waterbird breeding and aquatic fauna

habitat (Whitehead 1994). The habitats along the creek support numerous birds including

the endangered plains-wanderer found in grasslands of Willandra National Park

(Whitehead 1994).

The Willandra Creek system consists of a number of distributary creeks that extend west

and then south-west over a flat and almost treeless floodplain (Whitehead 1994). The

present hydrological extent22 of Willandra Creek runs from the weir at “Willanthery”

between Hillston and Lake Cargelligo (known as the Willanthery or Willandra Weir) to the

terminating basin of Gunnaramby swamp 40 km south-west of Ivanhoe and also to Lake

Moornanyah (OB, Whitehead 1994). At the easterly (or Lachlan River) end of Willandra

Creek a number of ephemeral swamps dominated by nitre goosefoot exist can be found on

‘Hunthawang’. Historically, and presently, most of the eastern end of Willandra creek is a

meandering channel lined with black box. That is, the river red gums of the Willandra

Creek-Lachlan River confluence give way to a long narrow band of black box, cooba and

lignum associations along the creek (Whitehead 1994). According to the local landholder,

at ‘Hunthawang’ (HyD) there has been an increase in river red gums since Willandra Creek

flows became more regular (presumably from the 1970’s onwards), and there never has

been a large cover of lignum. The abundance of black box diminishes downstream; ‘the

semi-permanent water of many wetlands … have led to the development of extensive but

isolated stands of black box’ (Whitehead 1994). Cumbungi is not extensive throughout

Willandra Creek; it only chokes the channel near the Willandra Homestead (HyD). Away

from the creek open shrublands of bimble box, Callitris, Casuarina, rosewood and bladder

saltbush dominate (Whitehead 1994).

22 This relates to surface water only. Groundwater movement extends along the full length of the Willandra Creek system

(see Kellet 1997 and Section 5.2(i)(7)).

90

(2) History of works and flows in Willandra Creek

Willandra creek would have been largely or completely dry for much of the year, and

occasionally for successive years, before flow regulation. Whitehead (1994) proposed that

the flows of Willandra creek were probably dominated by winter/spring freshes, and low

flow/dry periods during summer to autumn before flow regulation. Memoirs of James

Gormly describing experiences in 1870’s recount ‘many instances of death and suffering

from lack of water’ in the ‘Lachlan backblocks’. Consequently, they attempted to improve

water delivery to by ‘widening the mouth of the Willandra Creek’ (cited in Lloyd 1988,

p.62). Hydrological modelling supports these accounts, and the comments by Whitehead

(1994), indicating that the creek currently receives about 14 times undeveloped flows in the

usually dry months (Jan-May, Figure 13), and about three times undeveloped flows during

the wetter winter/spring rainfall months (June-December, Section 12).

The history of modification of Willandra Creek for modern agriculture goes back to the late

1800’s. Squatters initiated rudimentary water conservation measures in the 1890’s (Lloyd

1988):

“A weir was placed on the Lachlan 28 miles above Hillston to divert water into the Willandra

Billabong, whose channel was deepened and straightened. In the early days of settlement, the

Willandra Landholders under George Desailly had banded together, spending an estimated £20,000

to build a rough dam of logs at this point and improve the billabong’s channel. Although the dam

had been cut, it still provided some benefit and its value was enhanced by the weir whose

construction was impeded by heavy flooding and the drowning of the contractor.”

The early history of Willandra Weir is dominated by the Willandra Homestead, which was

very influential up until about WWI. Willandra Homestead had considerable control over

flow in these times; in fact, they were even once offered a ram from Willandra station to

release water down the creek (OB). There was also a cutting through 12 mile creek/Gigibak

creek, with cuts through creek bends about 100 years ago (OB).

Landholders have built many structures along Willandra Creek but few of these remain.

Topographic maps (eg DNM 1976) indicate a number of structures along the length of

Willandra Creek: Roto dam near ‘Roto’; Gunnings, Reynolds, Reeths-Castle (or Ratz

Castle) and Junction Dams near ‘Willandra’ and Broken Dam near ‘Kilfera’. Other

structures are eight-mile dam (where Canoble Creek enters, CMA 1985) and Tarrawarra

91

Dam (LaP). ‘Years ago’ there used to be a ‘dam every five miles’. Many dams were put in

Willandra Creek in the late 1800’s (FI). Dick Watkin of ‘Wakefield’ and his father also put

a dam down at Tholloloboy. Most of the dams were scoured out in the big floods of 1950,

1952 and 1956 (1956 was the biggest). Only Tholloloboy and Ratz Castle remain (WD),

and only Ratz castle is on the main channel of Willandra Creek. The weirs, while in

operation, also provided suitable conditions for tree growth; many of these trees have now

died since the weirs ceased to operate (FI).

River flows required for Willandra Creek to flow have changed over time. Before the

cutting and regulator was built at the Willandra Creek Weir in 1891 (Lloyd 1988,

Whitehead 1994), Willandra Creek would have required about 8 280 ML/day to flow from

the Lachlan River off-take (OB). At about the same time the Gigibak Creek ran from the

Lachlan River, and would eventually flow into Willandra Creek (HyD). Before the

regulator on Willandra Creek was refitted with an automated gate in 1999/2000 Willandra

Creek ran when flow in the Lachlan River was about 1 700 ML/day (with the Willandra

Creek regulator fully closed). Now the creek runs at about 2 400 ML/day (OB).

The regulator on Willandra Creek is a fixed crest structure that has gates that can restrict

Lachlan River flows into the creek. This regulator is below the level of the weir on the

Lachlan River, and therefore small river flows can be delivered to the creek when the

regulator is open. Willandra weir and the regulator on Willandra Creek are used to divert

water (typically 50-100 ML/day) over summer as far as Willandra Homestead. Typically

the creek flows for most of the year up to Willandra Homestead. This section has been

running nearly permanently since Wyangala Dam was enlarged in 1971 (HyD, DLWC flow

records).

Landholder accounts of the flows of 1998 help illustrate the slow rate of flows along this

creek. Local observations suggest the creek was flowing at the offtake by 3 July (HyD).

The flows stopped on 12 December when they just got across the Lowlands Rd-Trida Rd

intersection (SA), near the Ratz-castle dam (Figure 12).

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Table 8 Flows through Willandra weir in early July 1998.

Date Flows at Willandra Weir

(ML/day; DLWC records)

1-Jul-98 0

2-Jul-98 0

3-Jul-98 76

4-Jul-98 240

5-Jul-98 334

6-Jul-98 424

7-Jul-98 2124

8-Jul-98 3718

(3) The loss of pools along Willandra Creek, and the possible importance of

Morrison’s Lake and weir pools as a refuge

In the lower reaches of Willandra Creek there once was a series of pools along the creeks

length, which presumably acted as refuges for plants and fish reliant on water prior to

regulation. These pools have subsequently filled up with silt (FI). Now the only potential

refuges of this nature in the Willandra Creek system are Morrison’s Lake and the pools

behind weirs (Whitehead 1994). Morrison’s Lake lies within a natural depression

immediately downstream of the Cobb Highway (Whitehead 1994). Between 1964 and 1987

Morrison’s Lake was used for Ivanhoe town water supply (Whitehead 1994). Currently, on

the supply channel to Morrison’s Lake there is a 20 ML settling storage tank and a supply

tank of 360 ML that are used for Ivanhoe town water supply. The supply tank is filled from

the supply channel when Willandra Creek flows are diverted towards Morrisons Lake (FI,

Whitehead 1994).

(4) Current land and water use along Willandra Creek

Land use along Willandra Creek is predominantly grazing and wool production but also

includes the use of irrigated water for cash crops, pastures and fodder. Irrigation-based

operations that rely on regulated water supply are found between Willandra Weir (the

offtake) and Willandra Homestead Weir at Willandra National Park. Irrigation flows have

been delivered according to an area restricted irrigation policy since the embargo on

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irrigation licences in 1981 (Whitehead 199423). Since 1965 irrigators have put forward a

case for the regulated section to receive entitlements comparable to irrigation entitlements

from the Lachlan River. Currently, some allocations are being negotiated, but most active

licences now receive volumetric allocations of 6 ML/ha with an additional transferred

12 ML/year. Consequently, active water-users on the Willandra Creek now have

entitlements comparable to irrigation entitlements on the Lachlan River.

(5) Willandra Creek flow modelling

The effluent creek-IQQM runs, which simulate the years 1898-2000, indicate that annually

Willandra Creek now receives about 417% (about 4 times as much) of the undeveloped

flow (Figure 13). The current flow variability (measured by the standard deviation) is 105%

of undeveloped. Comparisons between undeveloped and current flow IQQM runs also

indicate that in the usually dry months of summer/autumn (Jan-May) the creek now

receives 1365% (ie. about 14 times as much) of undeveloped flows. During the wetter

winter/spring rainfall months (June-December), the high flow period, the creek currently

receives 330% of undeveloped flows.

(6) Effects of Willandra extraction on downstream effluents

The effluent creek IQQM indicates that the month when Willandra Creek most exceeds

undeveloped flows (March, when flows are about 22 x times undeveloped) is also the

generally driest month naturally (in terms of stream flows, not local rainfall or

evapotranspiration). In contrast, the creeks downstream of Willandra receive less water

during March than they would have naturally under the ‘current’ run, partly because of the

enhanced Willandra Creek flows (Figure 16). The average March flows in the Lachlan

River at Willandra weir in 1998, 1999 and 2000 were 589, 314 and 263 ML/day

respectively (DLWC data). The modelled current mean of inflow for Willandra Creek is

285 ML/day versus the undeveloped mean flow of 13 ML/day. This indicates that the flow

into Willandra Creek can be a large proportion of Lachlan River flows, with significant

downstream effects. This effect is likely to be even more marked during the drier periods

(eg March).

23 This arrangement could have changed by the time this document is published.

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(7) Groundwater flow in Willandra Creek

Groundwater flow is likely to be relevant to the health of the Willandra Creek, as there is a

strong positive correlation between water levels of aquifers and adjacent streams

(Whitehead 1994). The alluvial and unconsolidated sediments of the Willandra Creek

floodplain are considered to have a moderate to high potential for groundwater movement.

Accordingly, it is likely that surface water is required to maintain a groundwater mound

under Whipstick Lake in the Willandra Creek system (OM). A shallow groundwater system

flows from east to west with salinities generally less than 1000 mg/l but increasing

westwards. Large yielding bores exist within a 30 km radius of Hillston, extend to 250m

deep and pump rates in 1994 ranged up to 21.6 ML/day (Whitehead 1994). Moreover,

modelling of groundwater flow across the Lachlan, Murrumbidgee and Murray catchments

by Kellet (1997) has indicated that the lower reaches of the Willandra Creek at a small risk

of being affected by saline groundwater discharge. In particular, activities such as cropping,

clearing of Mallee vegetation and thinning of the river red gum forests in the lower Lachlan

area could cause groundwater discharge in the lower Willandra Creek system (especially

near Prungle Lakes).

95

Section 6. Current and historical flows of the lower Lachlan storages:

Lakes Brewster and Cargelligo

Figure 18 Lake Cargelligo with White-bellied sea-eagle nest in background (Photo: Alastair Mackenzie-

McHarg 26/11/01).

6.1 The lowland storages of the Lachlan River - overview

The lowland storages of the Lachlan River have played a vital role in the economic, social

and ecological health of the Lachlan valley. Lake Cargelligo (Figure 18-Figure 20) and

Lake Brewster (Figure 21) are off-river storages that have stored, regulated and

redistributed upstream flows to the lower end of the Lachlan River. (Currently Lake

Brewster is not being used as an off-river storage, because of concerns about the release of

waters with low water quality into the river). Additionally, Lake Brewster is also used for

lakebed cropping and Lake Cargelligo is used as a town water supply and as a major

summer recreational facility. Although their flows and the adjacent land of these lakes are

substantially modified, both these storages have wetland values. In particular, Lake

Brewster is considered to be of conservation value, as it has been listed in the Directory of

Important wetlands (EA 2001).

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6.2 Lake Cargelligo

(a) Overview

Lake Cargelligo is a large off-river storage (Table 9) in the middle section of the Lachlan

River. Lake Cargelligo is generally kept at around 75 percent capacity, but may be drawn

down to less than 50 percent capacity in times of drought. When full Lake Cargelligo has a

storage capacity of 36,000 ML and a surface area of 1,500 ha. It plays an important role in

the re-regulation of upstream flows to the lower end of the Lachlan. Modified since 1902,

Lake Cargelligo was naturally linked to the Lachlan by Lake Creek. The present inlet is

from a fixed crest weir in the river with a capacity of 800 ML/day, and the outlet via Lake

Creek has a capacity of 1000 ML/day.

Table 9 Physical dimensions of Lakes Brewster and Cargelligo

Surface area when

full (ha)

Maximum storage

depth (m)

Storage capacity

(ML)

Useable water (ML)

Lake Cargelligo 1 500 3.7 36,000 23,000

Lake Brewster 6 100 3.7 153,000 133,000

The Lake Cargelligo storage consists of three lakes - ‘The Sheet of Water’, ‘The Curlew

Water’ and ‘Lake Cargelligo’ connected by a series of artificial channels (Figure 20).

Water is diverted from the Lachlan River at Lake Cargelligo Weir (a block dam across the

Lachlan River) which causes a flow through a regulator, down an excavated cutting and

into ‘The Sheet of Water’. The Sheet of Water, on the inflow channel, is a small shallow

water body fringed with river red gum that often attracts wading birds. Another cutting

connects ‘The Sheet of Water’ to ‘The Curlew Water’, which in turn is connected by a

cutting to Lake Cargelligo. Curlew water is deep and the lake itself is a more extensive

deep body of water. Water exits Lake Cargelligo through a regulator into Lake Creek.

River inflow capacity is 800 ML/day and outlet is 1,000 ML/day. During floods the area

between the lake and the river becomes inundated, which forms a nesting site for birds.

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(b) Regulation

Prior to regulation the Lake Cargelligo system functioned very differently than it does

today. The lake was a low floodplain that carried water only during times of high river

flows. It consisted of a chain of three 'Lakes' (Lakes Cargelligo, Maine's and Maria's)

connected by a natural channel fed from Lake Creek (Figure 19). Flow between the Lakes

followed from Lake Cargelligo to Maines to Maria's and was drawn back in the same

pattern. How far floodwaters travelled towards Maria's Lake was dependent upon the

volume of water entering the system. Lake Cargelligo was the largest and deepest of the

lakes (PK; Maria's and Maine's Lakes are not what is now Curlew Water and Sheet of

Water).

Regulation of the system began early in the 1880's with the construction of a small lock

designed to prevent floodwaters receding back into the Lachlan River. In 1885 a proposal

was put forward suggesting the suitability of the lakes as a major regulated storage. In 1902

the NSW government built a weir and a regulator to channel water from the Lachlan River

into Lake Cargelligo for storage. A number of clay core levee banks were constructed to

prevent the spread of water. These are located on the eastern side of Curlew Water, on the

eastern side of Lake Cargelligo and two on the southern side of Lake Cargelligo

(Lachlander 1902) cutting off Maine's and Maria's Lakes from the system.

(c) Flooding sequence

Prior to regulation Lake Cargelligo was filled by back-flows up Lake Creek (cf. Figure 19).

Back flow into the lake occurred when a river height of 12 feet (3.65 M) was reached

(Maclean 1885), at this level river flow was within its bank. Under current conditions river

water will begin to bank up against the regulator when the water level is at 0.75 m

(3,000 ML) at Lake Cargelligo Weir (OB).

Water flowed from Lake Cargelligo along a natural channel into Maine's Lake and if

sufficient volume into Maria's Lake. Most of the water that fed into the Lake subsided back

into the river with lowering river heights leaving only some water in the lake system

(average depth 1 m). Lake Creek acted as both an influent and effluent channel to the lake

system.

98

A number of floodrunners that break out of the Lachlan between Lake Cargelligo Weir and

Lake Creek also influence flow patterns around Lake Cargelligo. The first break-out is

about 100 m (in a straight line) below Lake Cargelligo Weir and flows into Sheet of Water.

This flood runner begins to flow at a river height of 1.08 m (6 500 ML) at Lake Cargelligo

weir. The second feeds directly into the weir, and also begins to flow at 1.08 m (OB).

Under pre-regulated conditions Lake Creek would begin to fill Lake Cargelligo well before

the flood runners began to flow and only during major floods would Sheet of Water be

linked to Lake Cargelligo.

Sheet of Water held water during times of high flow, when river water broke out at flood

runner No. 1. During major floods Sheet of Water would have been connected to Lake

Cargelligo itself. Curlew Water, however did not form a part of the Lake system, instead

Curlew Water was one of several coogees (natural low depressions) that rarely contained

water (Lachlander 1902). Curlew Water currently collects the flows of a small local

catchment (OB).

99

Figure 19 The Lake Cargelligo system prior to river regulation

100

Figure 20 The current Lake Cargelligo system

101

6.3 Lake Brewster

(a) Overview

Lake Brewster (previously Lake Ballyrogan,) is a large, modified and shallow, off-river

storage located in the middle sections of the Lachlan river (Figure 21, Table 9). Located

approximately midway between Hillston and Lake Cargelligo the storage is used for re-

regulate upstream flows to the lower end of the Lachlan River, storing flood flows and

capturing upstream rainwater rejections.

Lake Brewster is subject to low-level agricultural activities. The lake bed is grazed and

leasees occasionally lakebed-crop a small area in Lakes Brewster (this also occurs in Lake

Cowal, but not Cargelligo). Lakebed cropping is considered to be a relatively low impact

form of agriculture, particularly if cropping only occurs once after each rainfall event or

natural fill event, and the ground is not ploughed following harvest (Briggs 1994, Briggs

and Jenkins 1997).

Vegetation communities of Lake Brewster have been substantially degraded. The lake is

predominantly open water with patches of Typha spp. and an extensive stand of dead trees.

Lake Brewster and the Lake Brewster weir pool provide important refuge habitat as they

often retains water longer than surrounding natural lakes. The islands fringed by Typha spp.

in Lake Brewster, and the emergent dead trees in the Lake and weir pool make these areas

valuable as fish and waterbird habitat. Since the early 1980’s Lake Brewster has been

suffering the effects of weed infestation when the lake bed is exposed. Golden dodder

(Cuscuta campestris) and Noogoora burr became serious weed threats around the

foreshores of the lake in the 1980s. By 1988 the total infestation was approximately

2000 ha. Aerial spraying of pesticide to control these weeds was undertaken a number of

times by DLWC (formerly DWR) during the late 1980’s. The infestation of Lake Brewster

by these weeds remains an ongoing problem.

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Figure 21 Lake Brewster (formerly Lake Ballyrogan) under current conditions

103

(b) Current and historical flows

The flows of Lake Brewster have been fundamentally modified. Under pre-regulated

conditions, flow into Lake Brewster from the Lachlan River was uncommon and local

information indicates that uncontrolled flows entered the lake only in the large floods of

1931 and 1956 over the past 100 years. Under these conditions river water would have

broken out of the Lachlan River and flowed into Mountain Creek, which in turn back-filled

Lake Ballyrogan. The works that converted Lake Ballyrogan to Lake Brewster were

completed in 1954. Subsequent to these works, flows through the Lake Brewster system

follow a complex route (Figure 21). Water is diverted from the Lachlan River by a fixed

crest weir (Lake Brewster Weir) along Lake Brewster inlet channel and into Lake Brewster.

Water is released from Lake Brewster through an outlet regulator that joins mountain creek

and then re-joins the Lachlan River just above Willandra Weir. The inlet channel capacity

is 5000 ML/day and the outlet channel capacity is 2000 ML/day. Water can also flow

directly along the Lachlan River either by flowing over Lake Brewster weir or via a conduit

into the Lachlan river channel below Lake Brewster Weir.

(c) Water quality

The regulation of Lake Brewster’s flows can have a large impact on flow and water quality

of the lower Lachlan River, and therefore within-lake water quality and the supply of

reasonable water quality flows to downstream users have been ongoing management

concerns. Lake Brewster is a highly turbid system because of re-suspension of lake bed

sediments by wind induced wave action and the feeding activity of carp. Hence, the release

of highly turbid water from Lake Brewster often increases the turbidity of the Lachlan

River (Thurtell et al in prep). Furthermore, the seeding of the Lachlan River with blue-

green algae is a management concern (Thurtell et al in prep.).

These concerns about the release of poor-quality water from Lake Brewster are usually

most relevant from late winter to the end of summer. Typically, Lake Brewster is filled

rapidly with late winter and early spring flows that are released from Wyangala storage.

The lake bed is usually well vegetated (mostly grass) at the time of filling and, as a result,

suffers from depleted dissolved oxygen concentration as organic matter decays (Thurtell et

al in prep.). In spite of these water quality concerns, the Lake has often been rapidly drawn

down in summer to supply downstream water-users. Hence, Lake Brewster is often almost

104

empty during the summer months, with only the deepest areas in the south east of the lake

retaining water.

(d) Bird breeding and bird mortality in Lake Brewster

Lake Brewster is recognised as a nature reserve and provides a habitat for waterbirds,

particularly pelicans, black swans and cormorants. The pelican rookery is sustained in large

numbers because of managed storage of water supplies (Harris 1989). Lake Brewster is

considered to be of national significance (EA 2001). The freckled duck (Stictonetta

naevosa) has been recorded at the lake and the man-made islands of the lake provide

habitat for breeding pelicans which are regularly present in their thousands. Breeding

colonies of black cormorant have also been observed. Lake Brewster is an important habitat

for Australasian Shovelers, Swans, Grey Teal and Pacific Black Duck also recorded.

The number of breeding birds varies considerably among years. For example, the pelican

breeding event in 1998/1999 (ca. 10-15,000 breeding pairs) was considered to be about

fifty percent bigger, in terms of both total numbers and the aerial extent of the colony than

the pelican breeding event in the summer of 1990/91 (LP, OB).

Table 10 Abundance of waterfowl of Lake Brewster, 1977-1985 (BJ)

1977

1978

1979

1980

1981

1982

1982 (Oct)

1983

1984

1985

15,000 10,440 3,280 8,650 Dry 10,300 9,160 Dry NI* 16,700

* Not inspected and assumed to be dry because of previous inspections and climatic conditions

Bird deaths are occasionally reported for Lake Brewster, and will probably continue to be

an occasional matter of concern. It is known that a small proportion of the total of young

birds in the Pelican colonies get caught in the current that runs to the outlet regulator and

are unable to swim out. Consequently and when possible, the outlet current is shut down

temporarily to allow birds to swim out (OB). For example, at Lake Brewster in late

February to early March 1999, observations were made of dead chicks at the Lake Brewster

outlet channel (eg twelve and eight dead young birds were observed at the regulator on the

3 and 26 February respectively, OB, PCJ). During this time there was a large, healthy

colony with very few deaths in proportion to total numbers and no evidence of adult birds

leaving nests. There were also no reports of mortality or sickness in stock or other fauna in

105

the Lake Brewster area (OB, PCJ). Estimates of numbers ranged from about 10,000 to

15,000 adult birds with about two chicks per adult pair (based on aerial counts by DLWC

on 1 December 1998). Various reports suggested there were about three cohorts of young

within the 1998/99 season. During this time there was no evidence of chicks having been

abandoned by adults (OB, PCJ). Blue-green algae poisoning could have caused bird deaths

or abandonment of nests but there was no evidence for this at Brewster in 1998/99 (it

should be noted that DLWC regularly monitors this lake for blue-green algae). From

1 January 1999 to 2 March 1999 the lake storage dropped from 84 to 33 percent. It is

conceivable therefore that these drops in water level could lead to abandonment of nesting

sites by pelicans. The eastern and western sides of the colony became dry and the colony

may have been exposed to predators, such as the fox, because of a land bridge forming.

However, past breeding events suggest this will not greatly affect the colony.

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Section 7. Discussion: the ‘water required to sustain the Lachlan

wetlands’

7.1 Water required to sustain the Lachlan wetlands

As discussed in Section 2, the primary aim of this project was ‘to identify the water

required to sustain the Lachlan wetlands’ (DLWC 1998, 2000). For wetlands to be healthy

the water that flows into the wetlands must be of a quality that does not interfere with

growth, reproduction and survival of wetland biota, and must be delivered to wetlands as

part of a flow regime which, in terms of the rainfall-river flow and rainfall-wetland

inundation relationships, is similar to what occurred before humans of European origin

arrived.

In the sections below these two components of wetland health, water quality and flow

regimes, are addressed. Firstly, however, a summary of the key processes that, previously

and currently, determine wetland health in the Lachlan Valley is provided. Moreover,

because it is not simply enough to identify resource management problems, indicators of

wetland health that can be used to inform river managers in the Lachlan Valley are

discussed.

7.2 There is a complex relationship between land and water management, agricultural

sustainability and wetland health

Delivery of water that sustains the health of wetlands requires an understanding of the

complex interactions among land and water management, agricultural sustainability and

ecosystem health. As discussed in Section 1.1 there is considerable evidence that complete

loss of wetland and other ecosystem functions could have devastating effects on human

economies and quality of life. In the floodplains of the Lachlan River the loss of

productivity because of salinity effects is one example of degraded ecosystem function (cf.

Table 1). A conceptual model, which incorporates the impact of various management

decisions and these various measures of wetland integrity, is shown in Figure 22. This

conceptual model attempts to illustrate the complexity of appropriate wetland management

(interested readers are advised to read more detailed discussions on this subject; eg. see

Reid and Brooks 1998, Young et al. 2001). The model also draws attention to the need for

inter-agency and community collaboration (such models already exists; for example,

Landcare groups and River Management Committees).

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The monitoring box in the conceptual model (Figure 22) indicates the need for continual

information to support land and water management, and, accordingly, this project provides

indications of the components of the ecosystem monitoring should focus on. Various

monitoring approaches are currently being developed for the Lachlan and similar rivers, (cf.

Chessman et al., in prep.). These monitoring approaches all require benchmarks for

ecological integrity. This document describes such benchmarks, using the ecological

history that can be gained from landholder knowledge (our interviews and those in Roberts

and Sainty 1996), field monitoring, DLWC knowledge and historical and scientific

literature. In particular, we have attempted to describe pre-European or undeveloped

conditions, which are often labelled as ‘natural’ and used as a benchmark. This is not the

only approach to setting benchmarks, but it is beyond the scope of this study to consider all

possible approaches. Moreover, it is impossible to fully restore the current landscape back

to pre-European conditions because of practical and economic limitations, and, in

particular, the requirements of a first-world economy. Nonetheless, partial restoration of

natural conditions allows for the restoration of the ecosystem functions and the

development of sustainable agricultural systems, as described previously. Hence, in this

study we have attempted to further understand what pre-European conditions were like in

the Lachlan Valley and its wetlands.

7.3 How the floodplain components of the Lachlan River have changed

The ‘natural’ Lachlan River had more complex habitat, supported more species and had a

different hydrology. Before European settlement, the Lachlan River would have had

extensive riparian vegetation, aquatic vegetation and more snags and pools in the river.

These pre-European environments supported more animal and plant species because of

these complex habitats. The dense in-channel vegetation would also have reduced the

general velocity of flow in the river and reduced the frequency of erosion. Turbidity would

have been maintained at lower levels in the rivers and distributaries, except during higher

flows. Moreover, distributary streams flowed only in large flood events compared to the

current situation. Clearly, these pre-European conditions allowed supported a greater

diversity of ecological communities.

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Management activities Responses to management activities

environmental flow rules

biotic response (eg bird numbers, plant species richness, % cover of weeds) in wetlands and in stream habitat

weed control

geomorphic responserestoration of riparian zones and in-stream habitat

reduction of unseasonal flows water quality response

carp control & rehabilitation of native fish communities

modifications of off-river storages that reduce nutrient and algal-rich inputs into the river

increased sustainability of agricultural practices & concurrent reductions in erosion, water use, rising water tables and reliance on unseasonal flows

adaptive management monitoring

(inter-agency) government support & community support

Figure 22 Conceptual model for the interactions between management, land and water use and the

integrity of the Lachlan floodplain wetlands

109

Currently, river flows tend to be less variable on a seasonal basis and smaller overall, and

wetland flows have showed similar changes. There are now numerous structures and land

management practices along the Lachlan River that have changed the seasonal and inter-

annual patterns and volume of flows in the Lachlan River and its creeks and wetlands. In

particular, the total amount of water delivered to the lower Lachlan River and its wetlands

has been reduced by about 50 percent. The diversion of irrigation water in Willandra and

Merrowie Creeks is an important contributor to this process. Additionally, the use of levees

in the middle reaches of Lachlan River diverts a large proportion of non-abstracted flows

towards the lower Lachlan, and away from mid-Lachlan wetlands.

Although the changes of bank shape along the river are highly variable, the river and its

wetlands have generally become more clogged with fine sediments. The Lachlan River and

its creeks have become wider, shallower, have steep banks and fewer pools, are turbid and

are full of poorly packed fine-sediments. There has also been substantial loss of riparian

vegetation, particularly native understorey vegetation. The rivers and its wetlands are also

continually degraded by carp and, particularly in the middle reaches, grazing. Much of this

erosion has occurred in the mid-Lachlan (at least over the last 50 years). In contrast, the

impacts of carp are evident throughout the floodplain sections of the Lachlan River (eg in

the Cumbung swamp, McB). Without substantial efforts in river rehabilitation these

ongoing effects are likely to continue to deliver a high biomass of fine sediment into

wetlands, terminal creeks (the effluents) and the lower Lachlan.

7.4 How water quality has changed

The Lachlan wetlands have been degraded by a degradation of water quality. Water quality

consists of numerous components (ANZECC 2000), and this study only considers salinity

and turbidity. Moreover, the relationships between the growth, reproduction and survival of

various wetland biota and water quality have not been accurately quantified. In this study

health of wetland biota is primarily focussed on the survival or presence of certain taxa (eg

the presence of Lippia). Nevertheless, even when these narrow definitions of water quality

and health are used, the Lachlan River and its wetlands appear to have been fundamentally

degraded.

It is likely that the water quality has been substantially turbid since the arrival of

Europeans, but European agriculture and associated activities, particularly flow regulation

110

and the dispersal of exotic species, have made the river even more turbid. The Lachlan is a

naturally turbid river. John Oxley noticed that the Lachlan was a very turbid river in the

early 1800’s (Oxley 1920). However, it is clear that, subsequent to Oxley’s expedition, the

Lachlan River and its associated wetlands, anabranches and ephemeral creeks have been

fundamentally altered by bank and catchment erosion, the loss of natural vegetation ‘filter

strips’ within the river and on the river banks, and carp. Such modifications very likely

have substantially increased the sediment load within the river. There is not consensus

within the community with regard to which of these processes is the most detrimental effect

on water clarity and bank stability. Most landholders consider carp to be the most

detrimental effect. As a general rule, the scientific community is more circumspect about

the effects of carp, and places more emphasis on the role of vegetation clearance and flow

modification when discussing water clarity and bank stability (eg Fletcher et al. 1985,

Frankenberg 1997, Abernathy and Rutherford 1999). Irrespective of which emphases are

correct, it is likely that this combination of processes have substantially reduced the health

of the Lachlan River. In particular, in turbid and eutrophic waters, algae, including toxic

blue green algae, tend to replace aquatic plants (Timms and Moss 1984, Scheffer 1990,

Blindow et al. 1993). This explains, in part, the dramatic reduction of soft-bodied aquatic

plant species such as Vallisneria and Potamogeton species along the length of the Lachlan

River. Such soft-bodied plants can, however, also be reduced directly by riverbank erosion,

unnaturally rapid attenuation of flow peaks (cf. Fletcher et al. 1985, DLWC 1997a), or the

direct feeding effects of carp (Roberts et al. 1995).

The Lachlan wetlands are also at risk from the salinity effects of rising watertables, but this

risk is most relevant to restricted areas within the floodplain sections of the Lachlan Valley.

Sections of the upper catchment of the Lachlan Valley are severely affected by salt effects

(Gammie 1999), but this is outside the scope of this study. In this study, the Bogandillon

Creek, Lake Cowal and Lake Forbes are identified as wetland areas that are showing the

effects of salt from rising watertables. The salt that is brought to the surface because of

naturally sodic soil affects other places (eg the Cumbung swamp). Rising watertables are a

particularly concerning issue in the Bogandillon Creek area. Salinity in this area has

already caused many tree deaths, and the dominance of salt tolerant groundcover species

indicates a fundamental alteration of plant communities. Salt tolerant groundcover species

are also evident around Lake Forbes. Given these observations, and the slowly rising

111

salinity of the Lachlan River (Walker et al. 1998), salt effects on the Lachlan wetlands

should be seen as a matter of concern.

7.5 How ‘healthy flow regimes’ for wetlands have changed

The flows of a river can be described in numerous ways, and the relationships between the

various components of flow regimes and plant health are complex. For example,

seasonality, volumes, peak flows and attenuation of peak flows are all components of the

natural ‘flow’ of a river (cf. Walker et al. 1995). In particular, a given wetland plant or

animal species is adapted to specific flow regimes, which includes inundation for given

lengths of time at certain times of the year. The appropriate flow regime depends on the

species and wetland and therefore the management of appropriate flow regimes for an

entire valley is extremely complex. (Presently, the Integrated Monitoring of Environmental

Flow monitoring program is developing some description of the response of wetlands to

environmental flows (Chessman et al., in prep.)). Hence, in order to maximise the health of

Lachlan wetlands flow management has focused on trying to partially restore ‘natural’ flow

regimes (LRMC 1999), and natural flow regimes have been defined using the undeveloped

IQQM.

Even if entirely natural river flows were to be returned to the Lachlan River (which is

highly unlikely) the hydrology of the Lachlan wetlands would still be fundamentally altered

because of floodplain structures, particularly levees. Such structures are obvious in the

lower and middle sections of the Lachlan, although similarly functioning structures can be

much shorter in the lower Lachlan because of the flat terrain.

7.6 The interface between land and water management – weeds and excessive plant

growth

Weed invasion has fundamentally degraded the Lachlan wetlands. Species such as Lippia,

Bathurst Burr, Noogoora Burr and African boxthorn often cover a large percentage of the

groundcover in some areas. Unfortunately, the dispersal of such weeds is an inevitable

consequence of floodplain flows if land management practices are unable to resolve the

weed problem.

Furthermore, flows delivered at the wrong time of the year have had detrimental

environmental effects. Many weeds grow more prolifically in summer, and some species

112

will grow to an extent that they will affect flows. The excessive growth of Lignum in

Merrimajeel and Muggabah Creeks in an example of this, although this thick growth has

probably also been exacerbated by root disturbance (Section 5.2(b)).

7.7 Indicators of ‘health’ for Lachlan wetlands

In order to conserve wetlands of the Lachlan catchment wetland monitoring should focus

on key degrading processes and the responses to the degrading processes; regulated flows,

enhanced erosion because of current land management practices and carp (Figure 22).

Monitoring also needs to be quick, simple and relatively inexpensive. Hence, the link

between river flows, salinity and erosion are best indicated by simple measures such as

water depth, turbidity, conductivity, pug marks (a measure of grazing) and observations of

the presence of carp (Reid and Brooks 1998). Furthermore, the rate of riverbank erosion

should be, and can be simply measured. The biological responses to the key degrading

processes are best measured using the responses of macrophytes and macroinvertebrates

(Reid and Brooks 1998). Current wetland monitoring activities in the Lachlan Valley, the

IMEF (Integrated Monitoring of Environmental Flows) program and the Lachlan

Community Monitoring Program, are consistent with these recommendations, and therefore

they provide some indications of the extent of key degrading processes and the biological

responses to these processes.

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7.8 Conclusion

This project has used a diverse mix of information to determine ‘the water required to

sustain the Lachlan wetlands’ and how the aquatic ecosystems of the Lachlan Valley have

changed. A large amount of information, from the standard use of scientific literature to

conversations with landholders, has been used to gain a more detailed understanding of

how the wetlands of the Lachlan Valley have changed. This information has also been used

to decide which processes have most influenced these changes in the Lachlan wetlands.

That is, catchment and riverbank erosion, degradation of native vegetation communities

and carp have caused the degradation of the water quality within wetlands. Moreover, flow

regulation and a diversity of works on the floodplain have severely modified spatial and

temporal patterns of wetland inundation. A detailed understanding of ecosystem

interactions is required for effective management and rehabilitation of species diversity and

ecosystem function. Accordingly, it is hoped that this synthesis will help to fine-tune future

decisions on the flow regime and water quality requirements of the Lachlan wetlands24.

Many of the processes described in this document are seen and described more thoroughly

elsewhere in the Murray-Darling Basin (cf. Young et al. 2001). The Lachlan River,

however, has many unique features that require special consideration.

24 The Lachlan River Management Committee has already used draft versions of some sections of this document for the

development of the Lachlan River Water Sharing Plan.

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Section 8. Acknowledgments and references

8.1 Acknowledgments

The contributions of the residents and water-users of the Lachlan Valley were/are gratefully acknowledgedfor the development of the original and current Lachlan wetland database, including the participantsof the Lachlan Community Monitoring Program. Members of the scientific community and naturalistgroups also provided invaluable data.

Thanks to all the landholders, other community members and DLWC staff who took the time to share theirknowledge. In particular, Damien Hynes and Len Reade provided detailed feedback on drafts of partof, or this entire document.

The knowledge gained from landholder interviews was an extension of a proper oral history study by Robertsand Sainty (1996, 1997). Much of the information we gained was similar to that obtained in this oralhistory study.

Rebecca Rousel entered much of the original wetland database back into digital form.

Hugh Jones (Senior Biometrician, DLWC, Parramatta), performed the regression analyses described in Figure3 and Table 2.

Thanks to the members of the Lachlan River Management Committee and Clare Moore for their valuablecomments on the drafts.

Mustak Shaikh (DLWC, Parramatta) and Paul Frazier (Charles Sturt University, Wagga Wagga) providedadvice on the use of remote sensing imagery for determining wetland area-river flow relationships

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Warner, R.F. and Bird, J. F. (1988). Human impacts on river channels in New South Wales and Victoria. In:Fluvial Geomorphology of Australia (Ed., Warner, R. F.), pp. 343-363. Academic Press, London.

White, N.E. (1939). Final Return showing quantity and value of work executed or fixed, and materialdelivered on the 2nd day of January 1939. Water Conservation and Irrigation Commission document.

Whitehead, R. (1992). Merrowie Creek Water Management Strategy. Issues and Discussion Paper.

Whitehead, R. and McAuliffe, T. (1993). Merrowie Creek Wetland Management Plan. Department of WaterResources.

Whitehead, R. (1994). Willandra Creek Wetlands. Proposed Management Plan. Department of WaterResources.

Williams, B. G. (1994). Environmental Impact Assessment Bogandillon Swamp. Water Resources, February1994.

WRC (1986). Wetlands Water Management Strategy for the Lachlan River Valley – Progress Report. WaterResources Commission NSW. April 1986.

Young, W. J. (2001). Landscapes, climates and flow regimes. In: Rivers as Ecological Systems: The Murray-Darling Basin (ed. W. J. Young) Pp. 135-172. Murray-Darling Basin Commission, Canberra, ACT.

Young, W. J., Schiller, C. B., Roberts, J. and Hillman, T. J. (2001). The rivers of the basin and how theywork. In: Rivers as Ecological Systems: The Murray-Darling Basin (ed. W. J. Young) Pp. 1-44.Murray-Darling Basin Commission, Canberra, ACT.

122

8.3 References – personal communications

AJ. Armstrong, John. Grazier. ‘Redbank’ and ‘Minarto’. Letter written 2 July 1999.

BH. Hilton Booth. Landholder at the end of Merrimajeel Creek.

BJ. John Brickhill, NSW National Parks and Wildlife, Griffith.

CS. Circuit, Sandy (1999). Grazier. ‘Waljeers’.

CT. Cotton, Terry (2002). Landholder ‘Moolahway’

DBA. Dent, Bruce and Angela. (1999) Landholder ‘Gumbelah’

DP. Patrick Driver (one of the authors), DLWC Forbes. Personal (first-hand) observations.

FD. Field, Daryl (2001). Landholder ‘Kimaroi’

FI. Ian Farrer. Landholder ‘Tooralie’

GB. Green, Bill (2001). Landholder ‘Meadow Flat’

GM. Green, Mark (2001). Landholder ‘Glendale Farm’

GT. Gransden, Tommy (2002). Landholder ‘Smithfield’

HC. Higgins, Chris (2002). Natural Resource Officer (Water Quality), DLWC Forbes. Personal (first-hand)observations

HD. Herbert, Don (2002). Landholder ‘Gundamain’

HH. Hall, Hugh (2001). Landholder ‘Overland’

HN. Higgins, Neil (2002). Landholder ‘Merrigal’

HoD. Hope, Doug (2001). Landholder, ‘Birrack’

HR. Hall, Richard (2001). Landholder ‘Ellerslie’

HyD. Hynes, Damien (1999). Grazier. ‘Hunthawang’.

LA. L’ Estrange, Allan (2001). Landholder ‘Larchwood’

LaP. Laird, Peter. Landholder on the Willandra Creek on the property "Mount View".

LD. Love, Debbie (1999). Natural Resource Project Officer (Water Quality). DLWC, Dubbo.

LlP. Lloyd-Jones, Peter (2002). Natural Resource Officer, DLWC Forbes. Personal (first-hand) observations

LM. Longhurst, Michael (1999). Former Rivercare Officer, DLWC, Forbes.

LP. Little, Pat (1999). Former Assistant Superintendent, Lake Cargelligo. DLWC. Lake Cargelligo.

MaB. Marsh, Bill (2002). Landholder ‘Walangle’

McB. MacFarland, Bob (1999). Grazier. ‘Oxley Station’.

McK. McFadden, Keith. Hydrographer, DLWC Forbes.

MJ. Milton, John (2002). Landholder ‘Lucerndale’

NA. Naughton, Anthony (2001). Landholder ‘North Whoey Station’

OB. Orr, Barry (1999). Superintendent, Lake Cargelligo. DLWC, Lake Cargelligo

OM. O’Rourke, Martin (1999). Hydrogeologist. DLWC, Forbes.

PCJ. Potter, Chris and Julie (1999). landholders near Lake Brewster.

PK. Pola, Kevin (1999). Former employee Superintendent at Lake Cargelligo DLWC, and long-standingmember of the Torriganny, Muggabah and Merrimajeel Creeks Water trust.

PL. Parker, Lance (1999). Farmer and pisciculturalist at ‘Cascade Hatchery’, near Lake Brewster.

123

RB. Robinson, Bruce (1999). Fencing contractor. Booligal.

RB. Royal, Bill (2001). Landholder ‘Burrawang’

RF. Reilly, Frank (2001). Landholder ‘Boronga’

RG. Rousell, Greg (2002). DLWC, Forbes

SA. Andrew Stalley. Landholder. ‘Murrurah’.

SB. Sheaffe, Bill (1999). Grazier. ‘Euragabah’

SN. Neville Schrader. Landholder, naturalist and member of the National Parks Association.

TD. Tildsley, Don (2002). Landholder ‘Rosebank’

TK. Turner, Keith (1999). Grazier ‘Woorandera’

WD. Watkin, Dick. Landholder on Willandra Creek on the property "Wakefield"

Wda, Walker, David, Lachlan (River) Community Monitoring Program

WJ. Woods, John (2001). Landholder ‘Manna Park’

WK. Williams, Ken (2001). Landholder ‘Yarong’

WP. Wettin, Paul. DLWC, Manager-Resource Knowledge, Central West Region, Orange.

WR. Williams, Ross (2001). Landholder ‘West Ooma’

124

Section 9. Appendix 1. Commence-to-flow values for Lachlan Valley

wetlands

9.1 Methods for determining wetland CTF used in this study

CTF’s in this study were determined for wetlands that are monitored as part of Lachlan

IMEF wetland monitoring program (Chessman et al., in prep). CTF’s were also determined

as part of this LFW study. IMEF wetlands were selected randomly within the floodplain

from Forbes to Condobolin (4 billabong wetlands), from Lake Cargelligo to McFarland’s

State Forest (near the Cumbung swamp, 4 billabong wetlands) and non-randomly from

Lake Cargelligo to Cumbung swamp (4 nationally significant open, back-swamp wetlands

were chosen, Chessman et al., in prep.). The wetlands of the lower Lachlan identified as

part of this LFW study are riparian and effluent creek wetlands that are of national

significance and of local interest.

CTF’s, the river heights at which wetlands just start to fill, were calculated from the dates

at which wetlands filled (using observations, wetland height staff gauges or landholders),

flows at the nearest river gauge (ML/day at the nearest telemetered river gauge) and known

travelling times of flows between wetlands and the nearest gauge. For many wetlands

capture of the exact point in time during filling has not been possible so the CTF is

expressed as a range (Table 11). At the request of the Lachlan River Management

Committee, Figure 2 was produced to give an impression of the full range of Lachlan

wetland CTF’s. Flows required to fill most of the IMEF riparian wetlands in any given area

are indicated with the ‘riparian wetland Commence to Flow’ line. The downward tendency

of each flow peak over river distance is largely a consequence of attenuation (‘flattening’)

of the peak. Some holes exist in this data and therefore one point has been extrapolated

where indicated. It should also be recognised that the CTF’s provided are constantly in

revision. Each new flow event behaves differently and can result in (usually minor) altered

calculations of CTF’s.

The CTF of a wetland is not clear-cut as indicated in by the lines in Figure 2; these lines are

simply a guide. For example, the CTF can be affected by preceding flows, vegetation

obstructing flows and diversions. This can be particularly problematic for those wetlands at

a greater distance from the river gauge, and when large river pumps (or properties with

125

large extractive licenses) lie between the wetland and the nearest river gauge. Wetlands

even in the same area can have quite different CTF’s. For example, within the Condobolin

area, riparian wetlands fill from about 3250 ML/day to above the minor flood level of about

15,000 ML/day (Figure 2). In particular, for wetlands further into the floodplain, a

sustained flow above CTF is required. For example, in 1998, 504,822 Ml passed by

Jemalong weir at greater than 15,000 ML/day from the 9th August to the 4th September.

This was enough to half-fill Lake Cowal (DAB). Wetland CTF can also be increased by

works such as levees and irrigation channels that prevent flows from spreading onto the

floodplain. Effects of such works have been reported in other systems (eg Ardill and Cross

1993), and are likely to be pervasive throughout the middle reaches of the Lachlan Valley.

CTF’s of some wetlands are difficult to discern and open to interpretation. Some wetlands

have clearly defined in-flow channels (see cover photo). In these cases the boundary that

relates to biological responses (eg bird breeding) is a clearly definable river. Others

wetlands such as Booligal swamp and the Reed Bed of the Great Cumbung Swamp (Figure

23) are not like this25. With these wetlands even very small flows will enter these wetlands

(eg 250-300 ML/day at Booligal weir for the Booligal swamp); such flows tend to cause

negligible change in water height and little ecological response and are therefore difficult to

monitor.

At Booligal swamp the lower threshold for bird breeding, about 2500 ML/day at Booligal

weir, is used. In the year 2000 this equated to Merrimajeel Creek breaking its banks and

flooding to 0.91 m at the gauge within Booligal swamp; the height that allows full

inundation. The value of 3000 ML/day suggested in Appendix A of the flow rules (LRMC

1999) provides some buffer above this level as this relationship between Booligal weir and

the swamp shows some variability.

25 With the Cumbung swamp it should be noted that the heights of the Cumbung swamp match those of the Booligal flows

except that peaks have attenuated (flattened) and collapsed together and overtopped over time (the latter flows in the

swamp have arrived more quickly and are also larger owing to preceding flows that ‘prime’ the system).

126

The biological response of a wetland is dependent on a complex array of flow

characteristics (eg, the volume, timing, duration and flow history). Booligal swamp

illustrates this well as there is a long-term record that allows a relationship to be determined

between the duration of flows above a threshold (2500 ML/day at Booligal weir) and the

number of breeding ibis (Figure 3; one of many ecological responses). There was positive

relationship between the time flows remained above 2500 ML/day and the number of

breeding ibis (Figure 3). The number of ibis nests can be predicted using the following

equation:

log (number of nests + 1) = 1.32 + 1.92 * log (number of days > 2500 ML/day)26.…………….…Equation 1

Observations indicate that birds not nesting below a specific water depth (usually above

40 cm, Magrath 1992) largely influence this relationship. Additionally, fledglings require a

certain amount of time to reach maturity. This relationship does not, however, allow a

highly accurate prediction of the number of ibis nests (Table 2). There are numerous

influences on the number of breeding waterfowl. In addition to flood duration, such

influences include the ephemerality of the wetland, water-level variability during the

breeding event and the interval between breeding events (Scott 1997, Leslie 2001). Such

complexities in biological responses are being explored further as part of the IMEF

wetlands program.

26 This equation only applies to years when the ‘number of ibis nests’ > 0 (df =1,6; r2 = 0.72; F= 15.5 and P<0.01). A low

count for ibis nests 1991 had a large influence on the slope of the relationship and was removed. This was determined by

comparing ‘robust regression’ which down-weights outliers and regression without the outlier (cf. Figure 2).

127

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Figure 23 Response of the Great Cumbung Swamp (water height (m) in Australian Height Datum to river flows measured at Booligal weir (using data from Brady et al.

1995).

128

9.2 Other approaches for determining wetland CTF

On-ground surveying was not used as a technique for estimating CTF’s, owing to resource

constraints, but also because estimates of CTF from other studies (Ardill and Cross 1993,

Maguire 1998) indicated that the errors in estimated CTF were so high (about 50 cm, James

Maguire, pers. comm.) that this would have provided poor estimates of CTF.

Height-discharge relationships for the Lachlan indicated that such an error in height would

lead to enormous differences in estimated CTF values. Moreover, although some wetlands

have very distinct CTF channels, some wetlands have several entry points and, particularly,

when the terrain is flat determining the lowest point can be difficult. Hence, CTF values

obtained from observations were considered to be more accurate because they can be

narrowed down to one day, or a shorter period in some instances, and are not affected by

surveying errors.

Remote sensing techniques for determining CTF’s were also considered to be inaccurate as

the available images had a temporal resolution of 12 days. Hence, CTF values obtained

from observations were considered to be probably more accurate as they could be narrowed

down to one day, or a shorter period in some instances, and they are not affected by

surveying errors. Remote sensing has been used, however, to determine wetland areal

inundation versus river flows, and this approach does provide a coarse estimate of wetland

CTF for a large wetland area (13.4).

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Table 11 Working values for commence-to-flow of Lachlan wetlands and effluent creeks.

Wetland CTF estimate (height at gauge (m))

Equivalent Flow(ML/day)

Gauge Property

Bocabidgle (IMEF) 2.67 (wet river) 3.3-3.9 (av 3.6 used, dry)

11642 14296

Cottons weir Cottons weir

Bocabidgle

Wilga (IMEF)

3.14 (wet river) 3.82 to 4.805 (dry river)

12983 17211

Cottons weir Cottons weir

Strangelands

Lake Cowal / minor floodheight

7.2 5.5

14469 12284

Jemalong weir Condobolin Bridge

N/A (numerous)

Robsar (IMEF) 4.2 8191 Condobolin Bridge Borambil Park Morgan’s (IMEF) 2.916 5062 Condobolin Bridge Noogooroo Park Willandra Ck 3.10 (pre-weir)

1.12 (with old weir closed; up toJuly 1999) 1.17(with current weir closed)

8280 1700 2400

Willandra weir

N/A (numerous)

CM Bottom Lagoon 3 1.44

7607 5500

Hillston Willandra weir

Willanthery

Merrowie Ck. 3.10 1.07

8280 (pre-weir) 1500 (with Gonowliaweir open)

Willandra weir Hillston weir

N/A (numerous)

Middle Ck. 1.19 2600 Willandra weir N/A (numerous) Moolbong Ck. >1.19 >2600 Willandra weir N/A (numerous) Hazelwood (IMEF) 1.33 2691 Hillston weir Hazelwood Whealbah (IMEF) 5.75-6.15 3062-3584 Whealbah Bridge Gunbar Cabbage Garden Creek 2.13 5000 Hillston weir N/A (numerous) Moon-moon swamp 0.85

4.88 1000 2000

Booligal weir Whealbah weir

Eurugabah

Thomson’s (IMEF) 1.53-1.59 1826-1880 Booligal weir Merrimajeel Erin’s (IMEF)

2.5 3316 Booligal weir Erin

Booligal Swamp(IMEF) /Merrimajeel Ck.

2.1 for bird breeding (0.47 required to get water in)

2500 (236 – water in)

Booligal weir Riverview

MuggabahCk. 0.47 (see Merrimajeel Ck.) 236 Booligal weir N/A (numerous) Lake Waljeers andassociated wetlands

0.76 850 Booligal weir N/A (numerous)

Reed beds/Cumbungswamp (IMEF)

0.5 - 0.67 1.1 for a significant response

275 - 661 713

Booligal weir Boyong

Marrool (IMEF) see Reed beds Juanbung Lignum (IMEF) 1.1 713 Booligal weir Juanbung

131

Section 10. Appendix 2. Current status of the Lachlan valley wetland

database

An inventory of the wetlands of the Lachlan Valley, compiled from 1984 to 1988, lead to

the development of the Lachlan Valley wetlands database (LVWD, Bennet et al. 1988,

DWR 1992a). The LVWD was confined to the floodplain of the Lachlan River and its

effluent's downstream of Wyangala Dam. This included the mapping of ca. 400,000 ha of

wetland and the incorporation of this data into a GIS-based database. This document

provides an explanation of the database (based on Bennet et al. 1988).

This document and the LVWD should not been seen as a final product. Considerable more

work remains to link the information into a format that ensures preservation of the

information, reasonable efficiency in data storage and retrieval, and the linking of this

information to other DLWC and governmental databases.

Additionally, the original hard-copies of a Lachlan wetland vegetation mapping program

(DWR 1992a) have been scanned and stored digitally with the Resource Information Unit

(DLWC, Orange). These maps were all based on 1: 50,000 topographic map series

produced by the then Department of Lands (SSU 1989). These wetland vegetation maps

were derived using 1: 50,000 black-and-white aerial photos, mapping of inundation using

remote sensing imagery (Landsat MSS, November 1984) and some field based ground-

truthing (SSU 1989, WP).

The original ‘explanatory notes’ for the LVWD (Bennet et al. 1988) state:

“Studies to date have revealed that the water supply system does not have the capacity or

operational capability to provide water for all wetlands in the valley. Therefore it is necessary to

compare their attributes and management capability to determine which, if any, wetlands should

receive favourable treatment. To assist in the comparison of wetlands throughout the valley, data

on their attributes have been compiled and stored in a computerised database.”

The rationale and aims for the wetland database have not changed much. The current

environmental flow rules (LRMC 1999), which are part of the water management plan

(LRMC 2002), specifically aim to replenish riparian wetlands. With the current flow rules

it is necessary to know which wetlands are being affected, either detrimentally or

favourably, by current flow practices. This wetland database is therefore a integral part of

132

programs such as the Lachlan wetland component of the Integrated Monitoring of

Environmental Flows program (DLWC 2001 a, b), and the environmental flows

operations and performance reporting (Beumer et al. 1999, Driver et al. 2000a, Moore et

al. 2002).

10.1 Explanatory notes for the wetland database

The LVWD was created to inform the management of flows into wetlands and ,

accordingly, the database structure reflects this bias. Information is presented in three

tiers:

• TIER 1: A summary of wetlands with their identification numbers and

characteristics based on river (‘wetland management’) divisions.

• TIER 2: Data on individual wetlands.

• TIER 3: Detailed information on specific wetland attributes.

Observations primarily come from field observations during a wetland inventory

conducted by the Department of Water Resources in 1985 (cf. WRC 1986), from the

literature search, various community members and subsequent field visits by DLWC staff.

This data has been partially updated with wetland data since this, including the

information gathered as part of the wetland components of the Integrated Monitoring of

Environmental Flows program (DLWC 2001 a, b) and the Lachlan Community

Monitoring Program (Walker 2001). The updating of the database is ongoing.

This division of information into three tiers is necessary for several reasons. Much of the

wetland resource of the Lachlan Valley occurs as floodplain forests and swamp-lands

rather than as discrete lagoons and basins. In some database formats, such as that used by

Pressey (1986) for the Murray River wetlands, these non-discrete wetland areas would

either be omitted or arbitrarily sub-divided. To overcome this problem the valley has been

divided into wetland divisions (see Section 2.2) and data for each division have been

summarised in TIER 1. Specific sites have also been selected for their wetland values and

management capability. The criteria for selection are discussed in Section 2.4. These

wetlands are listed in TIER 1 and their characteristics are itemised in TIER 2 in a more

commonly used database format. For some attributes, detailed and time dependant data

133

have been compiled. For the sake of simplicity, these data are not included in TIER 2, but

are presented as a series of tables in TIER 3.

Presented below is a description of each tier detailing the data presented and its source.

The Tiers are described in order of decreasing complexity, beginning with TIER 3 which

subsequently summarised in TIER 2 and so on.

10.2 TIER 1: Summary of wetland data by wetland management divisions

TIER 1 represents a summary of data from TIER 2 and 3 aggregated into wetland

management divisions. These divisions were first proposed and described in DWR (1986)

and have been further sub-divided on water management criteria (cf. maps, i. e., Figures 1

to 4, in DWR 1988). For each division, information is presented on the value and

management capability of the wetland resource present (currently in ‘wdbase TIER1

values & mngmt.xls’). This data has not been updated at least since 1989, and therefore the

summaries do not incorporate information added after 1989. Moreover, some of the

information regarding management and land-use may also be no longer accurate. The

identification number of each discrete wetland, which has been selected because of its

values or management capability, is also listed. The total wetland area in each

management division is also presented.

134

Table 12 Management divisions used in the wetland database (part 1)

Code Division Sub-division Prefix in LVWD

numbering system

1 UPPER LACHLAN Belubula River - Jemalong Weir 41201

2A MIDDLE LACHLAN Jemalong Weir - Bumbuggan Ck 41202

2B MIDDLE LACHLAN Bumbuggan Ck - Island Ck 41203

2C MIDDLE LACHLAN Goobang-Condobolin 41204

2D MIDDLE LACHLAN Island Ck-Condobolin 41205

2E MIDDLE LACHLAN Condobolin-Booberoi Weir 41206

2F MIDDLE LACHLAN Kiargathur Ck 41207

2G MIDDLE LACHLAN Borapine Ck 41208

2H MIDDLE LACHLAN Big Brotherony Swamp 41209

2I MIDDLE LACHLAN Booberoi Wr - Cargelligo Weir 41210

2J MIDDLE LACHLAN Lake Cargelligo 41211

2K MIDDLE LACHLAN Cargelligo Weir - Brewster Weir 41212

2L MIDDLE LACHLAN Lake Brewster 41213

2M MIDDLE LACHLAN Brewster weir - Willandra Weir 41214

2N MIDDLE LACHLAN Willandra Weir - Gonowlia Weir 41215

2O MIDDLE LACHLAN Gonowlia Weir - Torriganny Weir 41216

2P MIDDLE LACHLAN Torriganny Weir-Waljeers 41217

3A BUNDABURRAH Bundaburrah Ck 41218

3B BUNDABURRAH Bundaburrah Cowal 41219

4A WILBERTROY-COWAL Wilbertroy 41220

4B WILBERTROY-COWAL Lake Cowal 41221

4C WILBERTROY-COWAL Bogandillon Swamp 41222

5A GOOBANG CK Gunning Lagoon 41223

5B GOOBANG CK Gunning Gap - Bumbuggan Ck 41224

6A WALLAMUNDRY Ulguthrie Ck 41225

6B WALLAMUNDRY Island Ck 41226

6C WALLAMUNDRY Wallaroi and Nerathong Cks 41227

6D WALLAMUNDRY Banar Lake 41228

7 BOOBEROI Booberoi Ck 41229

135

Table 13 Management divisions used in the wetland database (part 2)

Code Division Sub-division Prefix in LVWD

numbering system

8A WILLANDRA Willandra Weir - Mossgiel 41230

8B WILLANDRA Yangellawah Ck 41231

8C WILLANDRA Mossgiel - Morrisons Lake 41232

8D WILLANDRA Downstream Morrisons Lake 41233

9A MIDDLE Upstream of Merrowie Ck 41234

9B MIDDLE Downstream of Merrowie Ck 41235

10A MERROWIE Gonowlia weir - Box Ck 41236

10B MERROWIE Box Ck 41237

10C MERROWIE Box Ck - Cuba Dam 41238

10D MERROWIE Downstream of Cuba dam 41239

11A CABBAGE GARDEN Hillston - south of 11B 41240

11B CABBAGE GARDEN Cabbage Garden Ck 41241

12 YANDUMBLIN Moon-Moon Lake & Yandumblin Ck 41242

13A MERRIMAJEEL Torriganny Weir - Lake Merrimajeel 41243

13B MERRIMAJEEL Muggabah Ck 41244

13C MERRIMAJEEL Downstream of Lake Merrimajeel 41245

14A LOWER LACHLAN Lake Waljeers - Lake Bungarry 41246

14B LOWER LACHLAN Waljeers - Oxley 41247

14C LOWER LACHLAN Ita Lake 41248

15 PIMPARA Pimpara Ck 41249

16A CUMBUNG Northern Great Cumbung Swamp 41250

16B CUMBUNG Southern Great Cumbung Swamp 41251

16C CUMBUNG Central Great Cumbung Swamp 41252

16D CUMBUNG Western Great Cumbung Swamp 41253

136

(a) Wetland value

(i) Vegetation

The area of wetland in each division was derived from the Department’s mapping of the

dominant wetland vegetation species (currently in spreadsheet ‘wetland values’ in file

‘wdbase TIER1.xls’). Dominance was determined by subjective assessment. Where one

species could not be regarded as being dominant, co-dominant species were identified.

Black and white aerial photography of various scales and dates was used to map

vegetation together with field inspections of many sites.

The vegetation key used is as follows:

BB Black Box

CG Canegrass

CR Common Reed

CU Cumbungi

GG Golden Goosefoot

LG Lignum

OW Open Water

RR river red gum

YB Yellow Box

Note that the coding used for vegetation types on the 1:50,000 map sheets is, regrettably,

different, and is as follows:

A Open water

B Cumbungi

C Common Reed

D Lignum

E Nitre Goosefoot

F Canegrass

G river red gum

H Black box

I Grey Box

J Yellow Box

X Non-wetland vegetation

137

(ii) Fauna

The number of recorded species of waterbirds, fish, other aquatic fauna and endangered

fauna were aggregated for each wetland management division (currently in spreadsheet

‘wetland values’ in file ‘wdbase TIER1.xls’). Those wetlands selected for their faunal

values in TIER 1 had either:

• a high diversity of species;

• a high abundance of any species;

• presence of endangered species;

• or are breeding sites for large numbers of any species;

(iii) Social

Current (ie. circa 1989) use of any wetland within each division for recreational,

education/research and commercial purposes was recorded (currently in spreadsheet

‘wetland values’ in file ‘wdbase TIER1.xls’). All wetlands used for recreational and

education/research purposes and those with high visual quality were listed for their social

value. Those with commercial values other than grazing or water storage were also listed.

(b) Wetland Management Capability

(i) Water Management Capability

Areas retaining water for some months following the 1984 and 1986 flood events were

assessed for each wetland division. Wetlands were selected because of their water

management capability were those within the range of regulated flow, or with regulatory

structures on their inlets or outlets (currently in spreadsheet ‘Wetland Management

Capability’ in file ‘wdbase TIER1.xls’).

(ii) Land Management Capability

The wetland area, within each division, of each land tenure and land use type is given.

Wetlands listed as significant for their land management capability were generally those

138

on Crown land (currently in spreadsheet ‘Wetland Management Capability’ in file

‘wdbase TIER1.xls’).

10.3 TIER 2 General information for individual wetlands

TIER 2 presents data on the location, values and management capabilities of individual

wetlands (discrete basins, weir pools, sections of floodplains etc.) Because of the very

large number of individual wetlands in the Lachlan Valley, it is impractical to present data

on each one. Wetlands were selected for inclusion in TIER 2 on the basis of their values or

management capability. For example, dominant vegetation type is known for most

wetlands in the valley, but only those with large stands of uncommon species have been

included in TIER 2 on the basis of their vegetation value. As more information becomes

available other wetlands will be added to this TIER.

One field ‘wetland type’ (spreadsheet ‘General Wetland Details’ in file ‘Lachldb_new

TIER 2.xls’) has been retained, and appears to have been entered between 1989 and 1998.

The codes in this field were not explained and therefore the relevance of this data is not

clear. The data is retained in the hope that at some time an explanation for this data can be

determined. All these entries were in management zones 2A and 4A (see Table 12 and

Table 13), and therefore may have been connected with some DLWC activities in the

proximity of the Jemalong Irrigation Area (eg, King 1998).

(a) New fields added in this edition of the LVWD

The year of data entry (‘date of entry’) and the people who entered the data (‘entered by’)

were included to provide information of the origin of the data (in spreadsheet ‘General

Wetland Details’ in file ‘Lachldb_new TIER 2.xls’). All data from the original database is

attributed to Bennett et al. (1988). The more recent data includes:

a. The inexplicable entries in management zones 2A and 4A, as discussed above;

b. Wetlands monitored as part of the Integrated Monitoring of Environmental Flows

(IMEF) program (DLWC 2000b, Chessman et al., in prep.);

c. Wetlands monitored as part of the Lachlan Community Monitoring Program

(Walker 2001);

139

d. ‘Wetlands’ (weir pools and storages) monitored as part of current water quality

monitoring programs: key sites (Preece 1992); the Regional Algal Coordinating

Committee (DLWC 1997b, Thurtell 2001), and the algal component of IMEF

(DLWC 2000b).

e. New fields associated with the additions described above (eg, altitude and property

name).

For those wetlands that are regularly monitored as part of some program, the monitoring

program is indicated in the column ‘Monitoring program’. The key for monitoring

programs is as follows:

LCMP Lachlan Community Monitoring Program

IMEF W Integrating Monitoring of Environmental Flows - wetlands component

IMEF A Integrating Monitoring of Environmental Flows - algal component

KEY Key sites

RACC Regional Algal Coordinating Committee

Additionally, in the hydrology spreadsheet (see Section 2.3.4 a (i)) the CTF’s of wetlands

have been added. Currently, the CTF values listed are primarily from the IMEF and

LCMP programs. The derivation of CTF values is explained in this document and Walker

(2001).

(b) Location

Wetlands are located by their Australian Map Grid (AMG) reference number and grid

zone, identifying their approximate centre (in spreadsheet ‘General Wetland Details’ in

file ‘Lachldb_new TIER 2.xls’). Wetland names are given where known, with names not

approved by the Geographical Names Board being indicated by an asterisk*. The

topographic map sheet on which the grid reference is found is also included.

A numbering system has been applied to the wetlands of the Lachlan Valley consisting of

an integral component which identifies the division in which each wetland occurs

followed by a specific wetland number as the decimal component. This system was

adopted to allow the input of additional wetlands, as more information becomes available.

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(c) Wetland Values

The Wetland values described in TIER 2 can be grouped under the following headings:

(i) Description

This comprises a statement detailing the morphology and dominant vegetation of the

wetland as well as the vegetation fringing or surrounding it. If the vegetation of a

particular wetland has any distinguishing features such as being particularly tall or dense,

or containing any rare species, this was also recorded (currently located in spreadsheet

‘Fauna & Flora Details’ in file ‘Lachldb_new TIER 2.xls’).

The meaning of lagoon in the morphology column is not clear (applied to Kennedy’s and

Berewombenia lagoons only). The terms ‘lagoon’ and ‘billabong’ are probably

interchangeable (cf. Green 1997). Nonetheless, lagoon may refer to a morphology

intermediate between billabongs and lakes. The key for morphology is as follows:

CRE Creek

DEP Depression

FLO Floodplain

IMP Impoundment

LAG Lagoon

LAK Lake

OXB Ox-bow lake

(ii) Fauna

Data compiled in TIER 3 were summarised here. The number of species of waterbirds,

fish and other aquatic vertebrate fauna and endangered species observed in each wetland

were recorded. Endangered species were those listed under Schedule 12 of the National

Parks and Wildlife Act, 1974 (currently located in spreadsheet ‘Fauna & Flora Details’

in file ‘Lachldb_new TIER 2.xls’; fish and other aquatic vertebrate fauna data is currently

on hardcopy only). It should be noted that for many of these wetlands there are very few

species observed compared to the number of species that are likely to utilise these areas.

The number of species observed is, in part, related to the amount of time observing the

wetland.

141

Also listed were species which had been observed in large numbers (currently on

hardcopy only). This was subjectively assessed and species dependant. For example, an

observation of more than several hundreds of an uncommon species in a particular

wetland may have warranted some mention, but for more common species or for

composite groups only counts greater than one thousand individuals constituted a large

(and therefore recordable) number.

The breeding of large numbers of a particular species (‘rookery’ column) or endangered

species (‘endangered species breeding’ column) was also recorded for each wetland.

(iii) Social Values

Present recreational, educational/research and commercial usage was described and its

importance was subjectively assessed for each wetland (currently in spreadsheet ‘Landuse

and tenure’ in the file ‘Lachldb_new TIER 2.xls’). Information on social values of the

Lachlan wetlands was derived from observations during the then Department of Water

Resources studies, and from local informants. Visual quality was assessed according to the

system developed by Geering (SPCC 1981) and modified by the DWR (1987). Codes for

national importance and recreation usage are included in the same column (‘Recreational

Usage’).

The key for recreational usage is:

BW bird watching

BG boating

FI fishing

GC golf course

HU hunting

SA sailing

WS water skiing

UNK unknown

The key for importance rating is:

NAT national importance

REG regional importance

LOC local importance

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(d) Wetland Management Capability

(i) Water Management

(i) Hydrologic Category

The hydrologic categories developed by Pressey (1986) were used to categorise wetlands,

with some modifications to suit the Lachlan system (currently in spreadsheet ‘Hydrology’

in the file ‘Lachldb_new TIER 2.xls’). These categories are:

1. Wetland connected to the river at minimum regulated flow or at pool level, or

potentially connected at these levels but separated by a regulator or by a block

bank on the inlet channel;

2. Wetland actually or potentially connected to the river above minimum regulated

flow but at, or below, maximum regulated flow (includes wetlands to which

regulated flows can be delivered via irrigation supply channels or by pumping);

3. Wetlands above maximum regulated flow, filled by both surplus flows and floods;

4. Wetlands above maximum regulated flow and which receive water from adjacent

irrigated areas via drainage, run-off or seepage or, in a few cases, effluent water

from various sources. Those which receive excess irrigation water or effluent and

which are filled or potentially filled by regulated flows were placed in categories 1

or 2, which were considered to override category 4 in importance for hydrology.

Nearly all category 4 wetlands in the Lachlan Valley receive surplus flows in

addition to irrigation and effluent water.

5. Wetlands which are filled only by floods.

6. Unknown

A distinction is made between surplus flows and floods on the basis of their

manageability. A surplus flow such as that experienced in the Lachlan River during Spring

1986, may be significantly modified by diversion into off-river storage’s (Lake Cargelligo

or Brewster) or effluent creeks, whereas a flood such as occurred during spring 1984,

flows largely uncontrolled by human manipulation.

143

In order to put these flows in perspective, the following information (as stated in the

Bennet et al. 1988 report) is presented:

• The river peaked at Booligal at a flow rate of 3,700 ML/day in the flood of spring 1984.

Preliminary hydrologic analysis indicates that this represents a flow level, which could

be expected to be exceeded on 5% of occasions, based on the past 80 years of records.

However this analysis accounts for flow rates only and is therefore not particularly

meaningful to this study because it does not account for flood duration.

• During the 1984 flood, flows as Booligal in excess of 1000 ML/day persisted for 17 weeks

in contrast the 1986 event was characterised by two peaks which together exceeded

1,000 ML/day at Booligal for over four weeks.

It was assumed that the Department of Land and Water Conservation (then DWR) has the

greatest control over water management in wetlands of category 1, then 2, 3 and category

5 wetlands respectively. Category 4 wetlands will have varying levels of management

capability.

Because the database format used in TIER 2 is unsuitable for linear features, regulated

rivers and creeks were not been included here, except where they had more localised

significant values. For example, Willandra Creek within Willandra National Park has a

high diversity of waterbird species, is used for educational purposes, and has a high land

management capability. This reach of the creek is therefore included in TIER 2.

1) Size

Wetland size was given as an indication of the volume of the wetland. Sizes have been

measured by digitisation of the Departments wetland mapping which is described in

section 2.4.1 (currently in spreadsheet ‘Hydrology’ in the file ‘Lachldb_new TIER 2.xls’;

in column ‘size and description’ ). Water areas were identified from Landsat multispectral

scanner imagery as those retaining water after inundation by the spring 1984 flood.

Because of the coarse resolution of this imagery, water areas are only approximate with

narrow lagoons, and weir pools were omitted. The extent of wetland vegetation may

generally be used as an indicator of the extent of spread of larger floods. In the database,

WGF means within gum fringe.

144

2) Control Structures

Water control structures associated with each wetland were also described in TIER 2

(currently in spreadsheet ‘Hydrology’ in the file ‘Lachldb_new TIER 2.xls’; in control

structures’ ). These included weirs, levees and pumps which may be located some

distance from the wetland.

Some control structures would have required modification before they could be used for

active wetland water management. For instance, some levees would require the

installation or regulators.

The key for control structures is:

ALDF adjacent levees direct floodwaters

ALRE adjacent levees restrict entry of flood water

ACW, ADJUST adjustable crest weir (drop-boards)

BYW bywash

CHAN channel

DAM dam

DRAIN drainage channels

EADAM earthen dam

FCW, FIXED fixed crest weir

IVIAC inflow via channel

LEVEE levee; may control inflows via channel

NIL nil observed

PUMP pump

REGOFF regulator at offtake

REGINF regulator controls inflow

UNK unknown

VLW vertical lift weir

WEIR weir

WRCI weir and regulator controls inflows

3) Hydrologic change

Evidence of hydrologic change includes obvious vegetation changes such as dead trees, or

large scale regeneration of saplings (currently in spreadsheet ‘Hydrology’ in the file

‘Lachldb_new TIER 2.xls’; in column ‘Evidence of Hydrologic Change’ ). Data came from

145

field observations during the inventory of wetlands in 1985, from various informants, and

occasionally from interpretation of historical aerial photographs.

The key for hydrological change is:

CROP central area cropped

DT = PI dead trees indicate permanent inundation

DC = PI dense cumbungi indicate permanent inundation

DC drainage channels

LRFW levees restrict entry of floodwater

NIL nil

NOINS not inspected

REGEN regeneration because of less frequent floods

(ii) Land Management Capability

Land tenure and land use were compiled from field observations, aerial photography,

informants and cadastral maps (currently in spreadsheet ‘Landuse and tenure’ in the file

‘Lachldb_new TIER 2.xls’). Where multiple land tenure types occurred in one wetland,

they were listed according to decreasing area. Because of the format of TIER 2, narrow

linear features such as road reserves were not included. Wetlands on larger travelling stock

reserves were included if the wetland area is greater than 30 hectares.

It was assumed that on Crown Lands sympathetic land management will be easier to

achieve. Land use was recorded as an indicator of a possible constraint on wetland

management. Two columns for land-use exist within the database; ‘inside landuse’ and

‘outside landuse’. It is assumed that inside refers to activities within the wetland, whereas

outside refers to activities immediately around the wetland (note: most entries for ‘outside

land-use’ are listed as ‘do not know’).

146

The key for inside and outside landuse is:

AQ Aquaculture

BW Bird-watching

CR Other cropping

DK Do not know

FI Fishing

FO Forestry

GR Grazing

HU Hunting

IC Irrigated cropping

OR Other

PB Power boats

SA Sailing

YA Yabbying

The key for land tenure is:

CAMP. RES camping reserve

CRLD crown land

FHLD freehold

FTRES forest reserve

NATRES nature reserve

NTFT national forest

NTPK national park

REC. RES recreation reserve

RD. RES road reserve

STFOR state forest

TSR travelling stock route

UNK unknown

WATER. RES water reserve

WLL western land lease

10.4 TIER 3. Specific and detailed information for some wetlands

TIER 3 comprises a series of tables that present data that are time dependent or highly

detailed. Only faunal observations (mainly waterbirds) are recorded in TIER 3, although

similar data on other attributes could be added if available.

147

For each species, the number of individuals observed was recorded according to the date

and location of observations, together with the occurrence of large-scale breeding. Also

recorded in TIER 3 is a listing of all species of aquatic vertebrate fauna observed at each

wetland. These data are aggregated to determine the total number species observed at each

wetland and in each division.

Observations primarily come from field observations during the wetland inventory

conducted by the Department in 1985 and from the literature search and various

informants.

The data contained in TIER 3 have been compiled from various sources and therefore of

limited value for analysis.

These limitations stem from:

a. Variations in survey methods used and the degree of detail of surveys;

b. Some areas, such as Lake Cowal, have been surveyed more thoroughly

than others;

c. Most wetlands studies have concentrated on fauna rather than on other

wetland attributes;

d. Most faunal surveys have concentrated on waterbirds rather than on fish or

other aquatic fauna.

TIER 3 currently exists in digital form as:

a. A record of the size of breeding events for a number of key wetland bird

species in a number of well-recognised wetlands (file ‘wdbase TIER 3 Birdsdb

chron.xls’).

b. The data described above, ie., a matrix of fauna observations, by species, for

individual wetlands (file ‘wdbase TIER 3 Fauna Observations.xls’).

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The key for Endangered Species coding (re. section 12, National Parks and Wildlife Act,

1974) and presence of species is in b. is:

* Fauna of some concern

** Vulnerable and Rare fauna

*** Threatened fauna

Species Score: 1 Species recorded as present

0 Species not recorded as present

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Section 11. Appendix 3. Standard questions used for phone interviews

11.1 General details

Interview 1 Interview 2 Interview 3

Date

Interviewer

Phone number

Phone number Name of property Location of property Nearest wetland(s)/watercourse

11.2 List of questions for phone interviews for ‘Ecology and flows of the lower

Lachlan River and its wetlands and distributaries’

Effluent and wetland flooding over the property during the 1998 flood.

Commence to Flow of the wetlands; there may be several wetlands on theirproperty which take different times - date at which this happened in 1998, any ideaof river heights, gauge heights etc. at this time

Extent of flooding (ha) over property

How long did it take to reach the peak of flooding (record dates)

Factors influencing extent and duration of flow. That is, vegetation, groundinfiltration, rainfall, levees and other engineering works (record names and detailsof any works)

Flooding over their property during previous freshes and floods.

In which years did wetland X fill. Did it only partially fill in some years and howmany times did wetland X flood since 1987.

If on an effluent creek where did the flows each in 1998

Other items of interest from an ecological (natural history) or flow managementperspective

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11.3 List of questions for phone interviews for ‘Ecology and flows of the mid-

Lachlan River and its wetlands and anabranches’

Changes in flows

How often do/did floods occur (defined as river flows which break the bank)currently, and historically?

Discriminate between winter v. summer flows if possible?

Changes in channel shape and location

Has the channel changed in width (width changes on bends or straight sections)?

Has the channel changed in depth (build up of mud/silt/sand or flows cutting intothe stream bed?

Weirs and other structural works on rivers, creeks or billabongs

Do you have any works on watercourses on your property (eg. weirs, drains)?

Past condition of watercourses and billabongs as compared to current (water levelsspecies composition eg. plants, birds.)?

Biological changes

Changes in riparian vegetation

Past versus current Condition

- species composition

- width of riparian veg (eg. 20 m v. 100 m)

Aquatic Vegetation

Past Condition as Compared to Current?

- species composition

- location of species, ie. the inside of bends

Birds

Past Condition as Compared to Current (birds on farm and on the watercourses)?

Occurrence of wetlands your property after floods?

Numbers of resident birds during and after floods, which bird species are they?

Fish

Have you been fishing in the area for a long time?

If so, how have the fish catches changed over time?

Have you observed changes in the abundance of other animals such as water rats,platypuses.

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Section 12. Appendix 4. IQQM’s of current and undeveloped Lachlan

effluent creek flows.

12.1 Introduction

This section outlines the methods and assumptions of the flow modelling of effluent

creeks described in Section 5.2.

The effluent creek-IQQM runs took into account the effects of historical construction of

offtake regulators and channel modification, as well as changes in river flows owing to

regulation. (A more generic explanation of the statewide use of IQQM is available in

DLWC 1999). It is clear that river structures and channel modifications are designed to

reduce the wetland or stream CTF during controlled conditions, and therefore they

increase the reliability of water delivery. Beyond this, very little information existed on

historical/pre-regulation flow relationships CTF’s and channel capacity for many of the

effluent creeks prior to his project. Numerous assumptions were required to generate these

flow relationships and therefore this project aimed to estimate undeveloped and during-

regulation flows. Unaccounted balances between Willandra Weir, Hillston and Booligal

gauges were lumped as a loss in the effluent-creek IQQM. These losses were assumed to

be same in pre-regulation (ie. natural) era.

For the interpretation of effluent-IQQM results a distinction needs to be made between

uncontrolled flows and controlled flows. Controlled flows are actively diverted and are

delivered for operational purposes (irrigation, stock and domestic). Uncontrolled flows can

occur when flow regulating structures are not being used to divert water. Uncontrolled

flows are unregulated flows that exceed the constraints of the river and its regulators and

can flow down effluent creeks. For example, uncontrolled flows can occur in Merrowie

creek when the flow-diverting structure, Gonowlia weir on the Lachlan River, is open.

Controlled and uncontrolled flows have different stream height-discharge relationships.

The wetland CTF is always higher for uncontrolled versus controlled flows.

IQQM runs were used to compare flows on an annual and also on a month-by-month basis

to illustrate seasonal effects. The two effluent creek runs are ‘natural’ (or undeveloped,

152

NO1127) and ‘current’ (or ‘environmental flow rules’, E109). Additionally, an IQQM run

was done for the Lachlan River at Oxley. Oxley station is immediately upstream of the

Great Cumbung Swamp so this IQQM run is a close approximation of effects on the

swamp.

The history of regulation in the effluent creeks is documented in Section 5.2. In summary:

• Merrowie creek - regulation started in the 1890’s with diversions from Middle Creek.

From about 1952 regulation was more marked;

• Willandra creek - regulation started about 1891;

• Merrimajeel and Muggabah creeks - regulation started about 1907 with construction of

Torriganny weir;

• Middle Creek – channel has been flowing more readily since modifications in the

1890’s. Not regulated; and

• Cabbage Garden Creek – has not been regulated and is unmodified or is negligibly

modified.

There have been all sorts of modifications since the 1890’s, so it is more correct to assume

the fully regulated period is post-1972, after Wyangala was upgraded.

Note that for Merrowie Creek, flows are pushed down the creek by having Gonowlia weir

shut and the volume is determined by the use of a drop-board regulator on the creek (the

‘Merrowie Creek Offtake Regulator’). Merrimajeel and Muggabah Creeks flow by having

Torriganny weir (on the anabranch Torriganny Creek) shut. In Willandra Creek the

regulator is on the creek. Middle creek is not regulated but has been modified.

27 All IQQM runs are given numbers by DLWC so that their assumptions can be documented. Note that the model run

E109 is a version of E073 with detailed effluent relationships incorporated for Lower-Lachlan flows (this is explained in

more detail in Appendix 2).

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12.2 Methods

(a) The effluent creek IQQM

There were four main components of the effluent creek IQQM:

1. Climatic data: The climatic input into the IQQM runs included rainfall, evaporation

and inflows from gauged and ungauged catchments. The model was run using climatic

data of 1898 to 2000 (similar to other model runs);

2. River characteristics: Channel characteristics of flow such as losses to floodplain,

seepage and evaporation loss, storage effects on the flood etc. were calibrated based on

unaccounted difference between two gauges and the routing. The calibration period

ranged between 1941 to 1997 depending on the reaches. In absence of any known

measurement the same calibrated parameters were used in the undeveloped run;

3. Regulation and Development: All reservoirs and extractions were ‘turned off’ during

undeveloped run; and

4. Special Model Run: The run number N011 is based on detailed descriptions of

effluent-river flow relationships for the Willandra Weir to Booligal area, as supplied

by P Driver (Appendix 1). The ‘current flow conditions’ or ‘current’ run E109 was

also re-configured to compare it with N011 results. Hence the run E109 is a version of

E073 with detailed effluent relationships incorporated for Lower-Lachlan flows.

Pre- and post-regulation effluent creek CTF’s were derived from analyses of flow data

(Table 14; from DLWC records, OB) and discussions with landholders. These data were

used with 1-4 above to construct the effluent creek IQQM.

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Table 14 Flow responses of effluent creeks for regulated and unregulated flow periods. Sources: HyD,OB and DLWC data.

Effluent Creek Current CTF: uncontrolled flows required at referenceLachlan River gauging station for effluent creek CTFunder current developed conditions.

Willandra Ck 2400 ML/day @ Willandra weirMerrowie Ck 1500 ML/day @Hillston weirMiddle Ck 2600 ML/day @Willandra weirMerrimajeel Ck 250 ML/day @Booligal weirMuggabah Ck 27 ML/day @Merrimajeel Ck at Cobb HighwayMuggabah and Merrimajeel Cks combined 250 ML/day @Booligal weirCabbage Garden Creek 5046 ML/day @Hillston weirEffluent Creek Undeveloped CTF: flows required at reference

Lachlan River gauging station for effluent creek CTFunder undeveloped conditions

Willandra Ck 8437 ML/day @ Willandra weirMerrowie Ck 5000 ML/day @ Lake Brewster junctionMiddle Ck 18000 ML/day @Willandra weirMerrimajeel Ck 250 ML/day @Booligal weirMuggabah Ck 27 ML/day @Merrimajeel Ck at Cobb HighwayMuggabah and Merrimajeel Cks 250 ML/day @Booligal weirCabbage Garden Creek 5046 ML/day @Hillston weir

Flows required at reference Lachlan River gaugingstation for bankfull flows in the effluent creek undercurrent conditions

Willandra Ck 13000 ML/day @ Brewster junctionMerrowie Ck 3937 ML/day @Hillston weirMiddle Ck 26000 ML/day @ Brewster junctionMerrimajeel Ck 6200 ML/day @ Booligal weirMuggabah Ck 6200 ML/day @ Booligal weirCabbage Garden Creek 7600 ML/day @ Hillston weir

Within effluent creek flows at bankfullWillandra Ck 2500 ML/dayMerrowie Ck 985 ML/day (field readings suggest channel may be able

to carry above this – but this is probably above bankfull).Middle Ck 1100 ML/dayMerrimajeel Ck 295 ML/dayMuggabah Ck 144 ML/dayMuggabah and Merrimajeel Cks 439 ML/dayCabbage Garden Creek 70 ML/day

155

(b) Controlled versus uncontrolled flows

(1) Controlled flows

The controlled flows were available in CAIRO, the DLWC operational flow database.

This data is not quality coded and so the values will generally be slightly different to final

quality coded data (much of which is not currently available). For speed and expediency

only this data was used for the modelling. Middle Creek is not regulated so there are no

controlled flow relationships for this creek.

(2) Uncontrolled flows

DLWC flow data and observations were obtained from landholders and DLWC records

(LP, OB) and used to document CTF, and flows at creek bankfull. Most of these creeks

have only sketchy data available so a simple straight-line (linear regression) relationship

was assumed to exist between a nearby river gauge and these two points (commence-to-

flow and bankfull). Within creek flows at bankfull were either known from flow records,

or could be estimated from ratings (river flow-gauge height relationships).

y = 0.5403x - 14.21R2 = 0.9998

0

50

100

150

200

0 100 200 300 400

Merrimajeel Creek (ML/day)

Mug

geba

h C

reek

(M

L/d

ay)

Figure 24 Flow in Muggabah Creek in relation to flow in Merrimajeel Creek during uncontrolled flows.

Based on flow recordings (DLWC data, OB).

156

(c) Willandra Creek

(1) Undeveloped flows

Commence-to-flow undeveloped was obtained from observations (OB) of the historical

offtake/creek mouth filling (Table 14; cf. Section 5.2(i)). The original channel is still

obvious. Although the flow required to achieve channel capacity has increased because of

the widening of the ‘mouth’ (Lloyd 198), this value was assumed not to have changed

significantly because it was not possible to estimate how much the channel has been

enlarged for water delivery.

(2) Regulated flows

Willandra Creek has good continuous flow data and so no modelling (estimations) was

required for this creek for both uncontrolled and controlled flows in the regulated period.

Flow estimates for this creek (and all other effluents) are shown in 12.2.

(d) Middle and Merrowie Creeks


Flow relationships for Middle and Merrowie Creeks under pre-regulation or undeveloped

conditions were derived from values provided by Damien Hynes at ‘Hunthawang’ who

lives near the mouth of these creeks (and has been in the area for many years). Estimates

of CTF’s and bankfull flow values were provided. Currently there is approximately a

linear relationship between the effluent flows and flows in nearby river gauges (in

Merrowie and Willandra Creeks, particularly at higher flows) so linearity was assumed for

the relationship between CTF and bankfull for these undeveloped flows.

(2) Regulated flows

Flow relationships for Merrowie Creek during regulation were based on DLWC staff field

measurements (OB).

Middle Creek was assumed to have the same flow to reach bankfull for regulated,

uncontrolled and pre-regulated flows. The current commence-to-flow is much lower

however (DLWC flow data, Section 9).

157

(e) Merrimajeel and Muggabah Creeks


It was assumed that the pre-regulated flows behaved similarly to how flow currently

operates when Torriganny weir has no boards in it, and boards are not put into Booligal

swamp (on Merrimajeel Creek).

Also note that for both these creeks there remains the high probability that the offtakes

have been modified to allow more flow considering there is a history of ‘creek cleaning’

further downstream (Section 5.2). There is no strong evidence to conclude this however so

modelling was made on the basis that the offtakes are not modified. The difference

between pre- and ‘during regulation’ flows in this modelling exercise is therefore only

because of the effects of the blockbank and Torriganny weir.

Flows in Merrimajeel and Muggabah Creeks were calculated individually but were

clumped together to allow comparison with the CAIRO data which treats these flows as

one.

(2) Regulated flows

Data in CAIRO was assumed to be correct for controlled flows. This flow relationship is

very complex as the size of flow depends on the number of boards in Torriganny weir and

also in the Booligal swamp (‘Ibis Rookery’) blockbank. Uncontrolled flows were

calculated using values in 12.2, and clumped as with undeveloped flows.

(f) Cabbage Garden Creek

This was the only effluent creek on the south side of the Lachlan River for which flow

estimates could be made. It is also a fully unregulated creek. It would, however, be

affected by alterations to natural Lachlan River flows (cf. DLWC 1997a).

Some large assumptions had to be made in order to make some sort of estimates for this

creek. Interpretation of the data should recognise the error margins are likely to be high.

Commence to Flow is about 5135 ML/day at Hillston; this is based on observations in

1988 (OB). Channel capacity was estimated to be about half that of Muggabah Creek;

about 70 ML/day. The flow required to reach capacity is assumed to be less than the flows

158

in 1998 (maximum 6444 ML/day at Hillston weir) that ran the creek to capacity at least up

to the crossing of the Whealbah Bridge road (DP). The flow to reach channel capacity was

therefore estimated to be 6000 ML/day at Hillston.

12.3 Results

(a) Accuracy check for the undeveloped Lachlan River model

Checks of the undeveloped run results with old flow records indicated that the modelled

current/undeveloped volume ratio for the period of 1915 to 1920 (a generally wet period)

is within 1% of the observed value. There was, however, an over estimation for flows

below 3000 ML/d and underestimation for flows higher than 3000 ML/d. It is also

overestimating dry periods pre-1915. The estimated flows at Booligal show up all the

cumulative errors of the entire model upstream. The entire river IQQM would need to be

scrutinised if to get more accurate flow values at Booligal. This suggests that while the

total budget is satisfactory, it may be overestimating the low flows and hence perhaps

underestimating the dry season variability.

The following table shows the average annual effluent flows for the undeveloped and

current condition. The upper limit of the table is kept up to the full capacity level of the

effluent as any flow comparison beyond this level gets very unreliable.

(b) Effects of river development on effluent creek flows

Differences between undeveloped and current (E109) conditions are shown in the tables

below for the various effluent creeks and the Lachlan River at Oxley.

Table 15 Averages of annual effluent flows under undeveloped and current flow conditions.

Average Annual Flow in ML/d Full capacity Undeveloped

(N011)

Current (E109)

Willandra Creek 2500 66 263

Middle and Merrowie Creeks 2160 140 164

Cabbage, Merrimajeel, Muggabah Creeks 439 66 35

159

date:02/07/01 t im e:11:28:45.28

L achlan River I QQM Resul t W i l landra Ef f l uent

01/07/1898 to 30/06/2000

0200400600800

10001200140016001800200022002400

ML

/d

% T im e Exceeded0 10 20 30 40 50 60 70 80 90 100

N atural (N 011) EFR (E109)

Figure 25 Modelled percentage of time for given discharges (ML/day) at the offtake of Willandra Creek

under the current flow rules and without the effects of current flow-regulating structures.

date:02/07/01 t im e:11:31:10.88

L achlan River I QQM Resul ts M iddle and Merrow ie Creeks

01/07/1898 to 30/06/2000

0

200

400

600

800

1000

1200

1400

1600

1800

2000

ML

/d

% T im e Exceeded0 10 20 30 40 50 60 70 80 90 100


Figure 26 Modelled percentage of time for given discharges (ML/day) for the combined flows of the

Merrowie and Middle Creek offtakes under the current flow rules and without the effects of current

flow-regulating structures.

160

date:02/07/01 t im e:11:34 :59.76

L achlan River I QQM Resul ts Cabbage G, M errimajeel & Muggabah Cks

01/07/1898 to 30/06/2000

0

50

100

150

200

250

300

350

400

ML

/d

% T im e Ex ceeded0 10 20 30 40 50 60 70 80 90 100


Figure 27 Modelled percentage of time for given discharges (ML/day) for the combined flows of the

Muggabah, Merrimajeel and Cabbage Garden Creek offtakes under the current flow rules and without

the effects of current flow-regulating structures.

161

Cabbage Garden, Merrimajeel and Muggabah Creeks

Data span 1898-2000

Data for undeveloped conditions

Month Number Volume Mean Std Dev Skew Ymax DateÍÍÍÍØÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍJan ³ 3162 104493 33 57 2.612 295 27/01/48Feb ³ 2881 71281 25 51 3.164 273 23/02/76Mar ³ 3162 76179 24 51 3.044 296 22/03/28Apr ³ 3060 70289 23 56 3.588 429 30/04/50May ³ 3162 97209 31 71 3.113 439 01/05/50Jun ³ 3060 125840 41 77 2.376 380 30/06/52Jul ³ 3162 256232 81 101 1.473 439 06/07/52Aug ³ 3162 398217 126 116 0.736 439 06/08/00Sep ³ 3060 439371 144 116 0.536 439 01/09/56Oct ³ 3162 361492 114 103 0.681 439 02/10/74Nov ³ 3060 276590 90 104 1.188 439 20/11/50Dec ³ 3162 178244 56 78 1.794 426 01/12/50ÍÍÍÍØÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍAll ³ 37255 2455437 66 95 1.643 439 06/08/00

Data for current or regulated conditions

³ Number Volume Mean Std Dev Skew Ymax DateÍÍÍÍØÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍJan ³ 3162 48867 15 32 4.434 244 02/01/17Feb ³ 2881 37369 13 30 4.630 231 24/02/76Mar ³ 3162 25721 8 18 6.424 213 31/03/56Apr ³ 3060 36585 12 35 7.125 349 30/04/50May ³ 3162 49824 16 49 4.860 398 08/05/50Jun ³ 3060 77061 25 59 3.187 358 30/06/52Jul ³ 3162 141470 45 82 2.575 439 07/07/52Aug ³ 3162 242754 77 102 1.499 439 01/08/52Sep ³ 3060 267709 87 105 1.236 439 01/09/56Oct ³ 3162 199680 63 90 1.419 439 04/10/74Nov ³ 3060 133721 44 80 2.467 439 23/11/50Dec ³ 3162 81336 26 55 3.432 419 01/12/50ÍÍÍÍØÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍAll ³ 37255 1342097 36 73 2.761 439 23/11/50

Observed and Simulated Data Comparison (current/undeveloped as a %) --------------------------------------

³ Vol Ratio Coeff Det Coeff Eff DRMS Obj Fn 1 Obj Fn 2ÍÍÍÍØÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍJan ³ 46.7658% 0.6325 0.4837 0.0534 0.0017 0.0076Feb ³ 52.4249% 0.6378 0.5425 0.4471 0.0178 0.0687Mar ³ 33.7639% 0.2952 0.1631 0.0711 0.0035 0.0127Apr ³ 52.0494% 0.5638 0.5109 0.4339 0.0117 0.0547May ³ 51.2545% 0.7015 0.6341 0.0711 0.0045 0.0147Jun ³ 61.2373% 0.8243 0.7599 0.5242 0.0138 0.0650Jul ³ 55.2117% 0.7947 0.6592 0.0534 0.0031 0.0105Aug ³ 60.9602% 0.8302 0.6497 0.3379 0.0073 0.0384Sep ³ 60.9301% 0.8245 0.5888 0.4158 0.0044 0.0326Oct ³ 55.2377% 0.7922 0.5462 1.2449 0.0047 0.0582Nov ³ 48.3463% 0.7060 0.5002 4.6459 0.0159 0.1991Dec ³ 45.6318% 0.6441 0.4816 0.5335 0.0107 0.0577ÍÍÍÍØÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍAll ³ 54.6582% 0.7696 0.6580 0.1502 0.0040 0.0186

162

Merrowie and Middle Creeks Data span 1898-2000







163

Willandra Creek Data span 1898-2000






³ Vol Ratio Coeff Det Coeff Eff DRMS Obj Fn 1 Obj Fn 2ÍÍÍÍØÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍJan ³ 1087.1846% 0.2229 -2.3855 5.4062 0.0335 0.2808Feb ³ 1886.5746% 0.2555 -10.2772 6.3903 0.0473 0.3450Mar ³ 2194.6614% 0.0756 -12.2139 3.3994 0.0322 0.2221Apr ³ 1047.9987% 0.5714 -1.8533 2.9808 0.0252 0.1925May ³ 607.0004% 0.6633 -0.1282 1.8246 0.0255 0.1523Jun ³ 353.3510% 0.6152 0.1377 0.8752 0.0163 0.0893Jul ³ 362.6570% 0.4729 -0.4208 2.0185 0.0223 0.1522Aug ³ 202.9466% 0.3688 0.1225 5.5234 0.0139 0.2046Sep ³ 289.4740% 0.4626 -0.2187 5.4076 0.0268 0.2640Oct ³ 334.6321% 0.4047 -0.4396 3.3608 0.0214 0.1917Nov ³ 285.7416% 0.3801 0.1441 1.4220 0.0090 0.0855Dec ³ 482.0133% 0.4141 -0.3481 2.0153 0.0176 0.1376ÍÍÍÍØÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍAll ³ 417.0975% 0.4227 -0.3434 0.2518 0.0047 0.0257

164

Lachlan R. at Oxley Data span 1898-2000

Oxley 412026 data for undeveloped conditions






165

12.4 Discussion

For the accuracy check for the undeveloped Lachlan River model, it should be noted that

all modelling results were constrained by modelling up to flows at full channel capacity of

the effluent creeks (12.2). Therefore all the undeveloped and current flow comparisons are

also only applicable up to the level of bankfull flows in the effluents. By including flood

overflow the average annuals will be much higher and the pre- and during regulation runs

(E109 and N011) will meet each other as flows get higher.

These results are discussed further in Section 5.2.

166

Section 13. Appendix 5. Flow event analysis of riparian wetland

inundation in the Lachlan River valley

13.1 Introduction

Twelve distinct wetlands and billabongs (shown in Table 16) were identified for this study

between Forbes and Cumbung Swamp. These twelve wetlands have been identified as

monitoring sites for the IMEF program.

The objective of this study was to look into the impact of undeveloped, current flow rules

and proposed river regulation on the frequency of filling the twelve wetlands. It is

envisaged these statistics will provide a measure of the impact of river regulation and land

use changes etc on the filling of wetlands.

A version of this section has already been published as an internal DLWC document

(Chowdhury et al. 2002).

13.2 Methods

(a) Wetland inundation frequency

This study was out for the following flow scenarios:

• undeveloped (N09),

• current flow rules (E73A),

• flow rules as proposed in January 2002 (E151) and

• water sharing plan proposed flow rules (E179).

The total hydrological characteristics of wetlands are too complex to mimic by a simple

model. Each wetland has distinct characteristics governed by its connectivity to the river

and groundwater that governs its wetting and or drying times. Any detailed modelling of

the wetlands would require extensive bathymetry and further collection of wetland

inundation data. However, to get some understanding of some processes within the

wetland system a simplistic approach based on a few key parameters was used.

CTF, duration of inundation (Tw) and the lower threshold for ‘wetland inundation’ (W

(m)) for riparian wetlands were determined for 12 wetlands from numerous field

167

observations from 1998 to 2001. W is the estimated water depth at and above which

aquatic plant growth occurs. W was defined as 10 cm for swamps, and the observed

boundary between aquatic and terrestrial plant growth in billabongs. Tw is the time a

wetland takes to drain below W, or is the time a wetland takes to drain to a level which

can be assumed to be dry from ecological perspective. Tw was estimated for each wetland

using wetland depth data (average N = 7.2, range 5-10)) collected in the field at different

times (Table 16, see Table 11 for CTF’s).

Table 16 Duration of wetland inundation (Tw, days) for riparian wetlands

No Wetland Name Tw

1 Bocabidgle 55

2 Wilga 90

3 Robsar 60

4 Morgan’s 120

5 Hazelwood 5

6 Whealbah 200

7 Thomson’s 50

8 Erin’s 35

9 Booligal Swamp 60

10 Reed beds 65

11 Marrool 70

12 Lignum 300

The following conceptual model was used to estimate the inundation days:

• A fill occurs when a flow event at the designated gauge exceeds the CTF and the

wetland is empty (depth < W) just prior to the fill;

• Once the fill occurs the wetland is ‘inundated’ for the following Tw days;

• The wetland becomes ‘empty’ Tw days after the fill occurred and then remains empty

until another flow event exceeds the CTF level;

• The wetland can be in connection with the river when inundated, but after the

recession of river flows the wetland can remain inundated; and

• For the recession of wetland water depth (over Tw days) the lower threshold for

inundated was defined as the water depth above which aquatic plant growth occurs (W

168

(m)). All depths above this corresponded to wetland inundation. W was determined

from field studies of plant response to flows from 1998-2000.

Accordingly, event analysis was carried out for the twelve wetlands using the CTF and Tw

parameters. The frequency of inundation was then estimated for each model run based on

the daily estimated ‘inundated’ or ‘empty’ conditions in the wetland.

The effect of regulation for individual wetlands (e.g., Booligal swamp) was calculated

using:

(number of wetland inundation days per year in run E73a)/ (number of wetland inundation days per

year in run N09). ………………………………...…………………………………..…Equation 2

The average effect of regulation for wetland areas and types (Lachlan Valley, mid-Lachlan

billabongs etc. ) in Table 3 were determined using:

�(number of wetland inundation days per year in run E73a for each wetland within that category)/

�(number of wetland inundation days per year in run N09 for each wetland within that category).

……………………………………….…….……………………………………………Equation 3

(b) Event duration analyses

Tw should not be confused with event duration analyses. Event duration curves were used

to indicate the relative frequency of different durations (days) of continuous inundation in

wetlands (where water levels did not drop below the CTF). An event is counted once when

the flow hydrograph first climbs above the threshold. That is, as long as the flow remains

higher than the threshold it is counted as a single event. In contrast, the analyses described

above calculated the number of days that wetlands were inundated over the modelling

period, irrespective of whether inundation was continuous. Analyses were carried out to

estimate the duration of events when flows are above 2500 ML/day and 3000 ML/day at

Booligal Weir (lower Lachlan), corresponding to the CTF’s for Booligal and complete

inundation of the Great Cumbung Swamp respectively. Additionally, 13000 ML/day at

Cotton’s Weir at Forbes (mid-Lachlan), the CTF for Bocabidgle Creek (Table 11), was

used in the event duration analyses.

169

Table 17 Average wetland inundation days per year during 1898-2000

Wetland N09 E73a E151 E179

1 Bocabidgle 108 80 81 82

2 Wilga 128 87 87 94

3 Robsar 115 87 86 87

4 Morgan’s 185 188 186 164

5 Hazelwood 65 47 49 47

6 Whealbah 190 153 154 147

7 Thomson’s 110 73 77 75

8 Erin’s 46 24 24 27

9 Booligal Swamp 94 50 53 58

10 Reed beds 139 98 101 92

11 Marrool 229 149 157 130

12 Lignum 173 82 85 91

Table 18 Average wetland inundation days per year during 1898-1920

Wetland N09 E73a E151 E179

1 Bocabidgle 80 45 47 43

2 Wilga 94 45 45 49

3 Robsar 87 55 55 52

4 Morgan’s 142 131 136 125

5 Hazelwood 45 32 32 28

6 Whealbah 154 136 136 118

7 Thomson’s 79 57 52 45

8 Erin’s 35 13 11 13

9 Booligal Swamp 71 22 22 22

10 Reed beds 109 68 74 62

11 Marrool 194 102 102 89

12 Lignum 136 41 41 41

13.3 Results

The following results are described for each IQQM run:

A. Average inundation days: Table 17 lists the annual average number of days per year

the wetland is inundated for the 102 year simulation period;

B. Average inundation days, pre 1920: Table 18 is similar to the table described above,

but the analysis is restricted to the period of 1898 to 1920. This period has been chosen

to represent the relatively dry era in the early 20th century (but acknowledging that

there were high flows 1916-1917);

170

C. Average CTF exceedance days: Table 19. As discussed previously, the model cannot

accurately predict the wetland volume, so it uses a single Tw estimate. To avoid the

uncertainty introduced by those simplification, another way to analyse the conditions

favourable to each wetland is by comparing the number of days flow is higher than the

CTF specified (Table 16). Duration of days above the CTF, as opposed to the number

of days above the CTF over a given period (with or without continuous inundation),

also gives some indication of how successful biological events are (eg, three months of

constant inundation could be required to ensure the completion of a colonial bird

breeding event);

D. Frequency of exceedance of flows above 13000 ML/day at Forbes. Figure 28 shows

the relationship between the number of inundation events and the duration of the

inundation event for wetlands controlled by the flows above 13000 ML/day at Forbes;

E. Frequency of exceedance of flows above 3000 ML/day at Booligal. Figure 29 shows


inundation event for wetlands controlled by the flows above 3000 ML/day at Booligal;

and

F. Frequency of exceedance of flows above 2500 ML/day at Booligal. Figure 30 shows


inundation event for wetlands controlled by the flows above 2500 ML/day at Booligal.

Table 19 Average duration of wetland inundation for 1898-2000

No. Wetland N09 E73a E151 E179 Station CTF (ML/day)

1 Bocabidgle 23 15 15 16 Forbes 13000

2 Wilga 19 12 12 13 “ 15100

3 Robsar 40 26 26 28 Condobolin 8200

4 Morgan’s 58 46 46 45 “ 5100

5 Hazelwood 60 43 44 43 Hillston 3000

6 Whealbah 62 41 42 42 Whealbah 3000

7 Thomson’s 61 39 41 41 Booligal 2150

8 Erin’s 27 16 17 18 “ 3000

9 Booligal Swamp 47 27 28 30 “ 2500

10 Reed beds 74 48 49 49 “ 1550

11 Marrool 126 69 71 66 “ 600

12 Lignum 27 16 17 18 “ 3000

171

date:13/08/02 t ime:16:45:13.51

Event D uration Graph at Forbes 412004 Events Exceeding 13000 ML /d

01/07/1898 to 30/06/2000

0

10

20

30

40

50

60

70

Day

s

N umber of Events50 100 150 200 250 300 350 400 450

N 09 E73a E151 E179

Figure 28 Frequency of duration times for Cotton’s weir (Forbes) flows above 13000 ML/day under modelled regulated (E73a, E151, E179) and undeveloped

(NO9) conditions.

172

date:13/08/02 t im e:17:05:21.44

Event D uration Graph at B ool igal 412005 Events Exceeding 3000 ML /d

01/07/1898 to 30/06/2000

0

20

40

60

80

100

120

140

160

180

200

Day

s

N umber of Events10 20 30 40 50 60 70 80 90 100

N 09 E73a E151 E179

Figure 29 Frequency of duration times for Booligal weir flows above 3000 ML/day under modelled regulated (E73a, E151, E179) and undeveloped (NO9)

conditions.

173

date:13/08/02 t ime:16:58:01.48

Event D uration Graph at B ool igal 412005 Events Exceeding 2500 ML /d

01/07/1898 to 30/06/2000

0

50

100

150

200

250

Day

s

N umber of Events20 40 60 80 100 120 140 160

N 09 E73a E151 E179

Figure 30 Frequency of duration times for Booligal weir flows above 2500 ML/day under modelled regulated (E73a, E151, E179) and undeveloped (NO9)

conditions.

174

Table 20 Modelled monthly frequency of wetlandinundation days for selected wetlands of the LachlanValley under modelled regulated (E73a, E151, E179)and undeveloped (NO9) conditions

a. Bocabidgle Average Inundation Days in a Month

N09 E73a E151 E179

Jan 6 5 4 5

Feb 3 3 3 3

Mar 4 4 4 4

Apr 4 3 3 3

May 4 3 3 3

Jun 6 4 4 4

Jul 13 9 8 9

Aug 17 12 12 12

Sep 16 12 12 12

Oct 14 11 11 12

Nov 11 8 9 8

Dec 10 7 7 7

c. Wilga Average Inundation Days in a Month

N09 E73a E151 E179

Jan 9 6 6 7

Feb 7 5 5 5

Mar 5 4 4 4

Apr 5 4 4 5

May 5 4 4 4

Jun 6 4 4 4

Jul 13 7 7 7

Aug 18 12 12 13

Sep 19 14 14 15

Oct 16 12 12 13

Nov 13 8 8 9

Dec 12 7 7 8

b. Robsar Average Inundation Days in a Month

N09 E73a E151 E179

Jan 6 7 4 5

Feb 5 5 4 3

Mar 4 4 4 4

Apr 4 5 3 3

May 4 4 3 3

Jun 4 4 4 4

Jul 7 7 9 9

Aug 12 13 13 13

Sep 14 15 14 14

Oct 12 13 12 13

Nov 8 9 10 10

Dec 7 8 7 8

d. Morgan Average Inundation Days in a Month

N09 E73a E151 E179

Jan 14 10 11 10

Feb 12 10 11 9

Mar 11 15 14 9

Apr 9 14 13 8

May 9 14 12 7

Jun 11 13 12 8

Jul 17 15 15 14

Aug 22 20 21 20

Sep 23 23 24 23

Oct 22 23 24 24

Nov 18 17 17 18

Dec 16 13 13 13

175

Table 21 Modelled monthly frequency of wetlandinundation days for selected wetlands of the LachlanValley under modelled regulated (E73a, E151, E179)and undeveloped (NO9) conditions (contd.)

a. Hazelwood Average Inundation Days in a Month

N09 E73a E151 E179

Jan 2 1 1 1

Feb 1 1 1 1

Mar 2 0 0 1

Apr 2 1 1 1

May 2 1 1 1

Jun 3 3 3 3

Jul 7 5 5 4

Aug 12 10 10 9

Sep 13 11 11 10

Oct 10 9 8 8

Nov 7 4 6 6

Dec 4 2 2 2

c. Whealbah Average Inundation Days in a Month

N09 E73a E151 E179

Jan 22 18 19 17

Feb 16 14 15 15

Mar 13 11 11 12

Apr 10 5 6 6

May 9 4 5 5

Jun 8 5 5 5

Jul 10 7 7 6

Aug 16 11 11 10

Sep 19 16 15 14

Oct 22 20 20 18

Nov 22 20 20 18

Dec 23 20 20 19

b. Thomson Average Inundation Days in a Month

N09 E73a E151 E179

Jan 9 4 5 5

Feb 5 2 2 3

Mar 4 2 2 2

Apr 4 1 1 1

May 4 2 2 2

Jun 4 3 3 3

Jul 7 5 5 4

Aug 13 10 9 8

Sep 17 14 14 14

Oct 18 15 15 14

Nov 15 10 11 10

Dec 11 7 10 10

d. Erin Average Inundation Days in a Month

N09 E73a E151 E179

Jan 3 1 1 1

Feb 1 0 0 0

Mar 1 0 0 0

Apr 1 0 0 0

May 1 1 1 1

Jun 2 1 1 1

Jul 3 2 2 2

Aug 6 3 3 3

Sep 10 5 5 5

Oct 9 5 5 5

Nov 7 4 5 5

Dec 5 2 2 3

176

Table 22 Modelled monthly frequency of wetlandinundation days for selected wetlands of the LachlanValley under modelled regulated (E73a, E151, E179)and undeveloped (NO9) conditions (contd.)

a. Booligal Average Inundation Days in a Month

N09 E73a E151 E179

Jan 6 3 4 4

Feb 4 2 2 2

Mar 3 1 1 2

Apr 3 1 1 1

May 3 1 1 1

Jun 3 2 3 3

Jul 5 4 4 4

Aug 10 5 5 6

Sep 15 8 8 9

Oct 17 9 9 11

Nov 14 7 8 9

Dec 10 6 7 7

c. Reed Beds Average Inundation Days in a Month

N09 E73a E151 E179

Jan 12 6 7 7

Feb 6 3 3 3

Mar 6 2 2 3

Apr 5 2 1 2

May 5 2 2 2

Jun 5 3 3 3

Jul 10 6 6 5

Aug 17 13 13 11

Sep 21 18 17 16

Oct 22 19 19 17

Nov 17 15 15 13

Dec 14 10 12 10

b. Marrool Average Inundation Days in a Month

N09 E73a E151 E179

Jan 20 10 12 10

Feb 15 9 10 6

Mar 14 9 10 6

Apr 13 7 9 6

May 13 6 7 5

Jun 13 5 5 4

Jul 19 10 10 8

Aug 25 18 18 15

Sep 25 22 22 20

Oct 26 22 22 20

Nov 24 17 18 16

Dec 22 13 15 13

d. Lignum Average Inundation Days in a Month

N09 E73a E151 E179

Jan 17 8 9 9

Feb 16 8 8 9

Mar 18 8 8 9

Apr 17 7 7 8

May 15 7 7 8

Jun 12 6 6 7

Jul 9 4 5 6

Aug 9 5 5 6

Sep 12 6 6 6

Oct 15 7 7 7

Nov 16 8 8 8

Dec 17 8 9 9

177

13.4 Discussion

Development and regulation has reduced the number of days that these wetlands get

filled (Table 19). Obviously, climate influences wetland inundation also. Hence, for a

dry period during an earlier part of the last century (1898-1920) the 12 wetlands

would have be less frequently filled irrespective of regulation, but if they had been

affected by flow regulation the IQQM indicates that they would have received

proportionally less wetland fill (i.e., about 71% versus 61% for 1898-2000 and 1898-

1920 respectively; using E73a/N09).

Unusually for IMEF wetlands, Morgan’s Wetland fills more often (Table 18) because

of regulation (E73a). While regulation and development decreased overall flow

volume at Condobolin, coincidentally the frequency of flows around CTF to Morgan

is increased (discussed further in Section 5.1(a)).

It is important to note that this is a first attempt to assess the affect of flow regulation

on Lachlan riparian wetlands, and therefore the riparian wetland-IQQM should be

viewed as a ‘work in progress’. One of the limitations of this study is the absence of

accurate information on the volumes of each wetland. Estimates of volume and the

surface area of a wetland are necessary to accurately model the filling and drying

cycle. The absence of this information led to the assumption that any flood event

exceeding CTF contains enough water to fill the wetland and it always dries up

exactly Tw days afterward. The true value of Tw would vary significantly with

antecedent conditions because of natural variation in climatic conditions. Hence, these

analyses do not fully reflect the differences between hot and dry years versus cool and

wet years. The model is also not very informative in terms of partial wetland

inundation because it is based on an ‘inundated’ versus ‘empty’ count. Furthermore,

travel time between the reference river gauge and the wetland offtake point is not

incorporated in the model. This could alter the timing of wetland inundation recorded

in the IQQM run output for some terminal wetlands (e.g., travel time for peak flows

above CTF from Booligal gauge to Marrool wetland may take 14 days). The riparian

wetland-IQQM is, however, a useful tool for assessing the relative impacts of flow

management options on wetlands, and its accuracy can be developed and tested over

time.

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Section 14. Appendix 6. Determining wetland area-river flows

relationships in the Lachlan Valley

Authors: Ashley Leatherland and Patrick Driver

14.1 Overview

14.2 Methods

(a) Imagery Selection

Dates for satellite imagery were selected that corresponded with known wetland

flooding events. Ideally, images would have been chosen before, during and after the

flood event but this was not always possible because many images had much of their

area obscured by cloud cover. Landsat TM Band 5 Imagery was then chosen for

classification because of its’ high reflectance values for water bodies.

(b) Classification

The pixel values used for classification of wetland area were chosen based upon a

number of considerations. These variables were subjective in nature and further

ground-truthing would be desirable in the future.

The criteria used to choose pixel values for classification were (cf. Table 23):

1. Visual – is the output presenting a clearly defined boundary or is there extensive bleeding caused

by water reflectance of non wetland bodies (vegetation etc)

2. Field Check –known wetland bodies were used to verify the accuracy of the classification. In some

cases estimates of inundation for given dates were available for specific water-bodies;

3. Comparison – in a comparison of the classified image to the original, does the classification

portray water that can be clearly defined in the original image;

4. Pixel Range – does the original pixel range for the band 5 image begin at zero or does the range

starting at a different value. If the range starts at a different value pixel values were adjusted

accordingly.

5. Wetland boundary check (LFW method only) - the boundaries of wetland areas were pre-

179

determined. The classified features needed to fall within these boundaries.

Table 23 Pixel values used for determination of wetland area

Lachlan Wetlands Project9283 Imagery Pixel Value Used 9383 Imagery Pixel Value Used

26-Mar-88 <36 20-Sep-92 <3620-Oct-88 <36

3-Jun-93 <361-Apr-90 <36 22-Aug-93 <363-May-90 <36 7-Sep-93 <3619-May-90 <36 23-Sep-93 <36

25-Jul-91 <36 11-Jun-96 <3613-Oct-91 <26 30-Aug-96 <36

1-Oct-96 <3610-Jun-98 <3628-Aug-98 <36

EFR Project9283 Imagery Pixel Value Used 9383 Imagery Pixel Value Used

10-Aug-00 <29 15-Jun-00 <1327-Sep-00 <28 20-Oct-00 <43

21-Nov-00 <25

Figure 31 Classified wetland image (based on Landsat TM imagery) with a 40 m boundary along

the Lachlan River

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(c) Defining wetland areas

Two methods were employed to define wetland areas:

- The Environmental Flow Rules (EFR) Project: wetland features located further

than five kilometres from the Lachlan River were removed. The rationale for

wetland choice was to target those wetlands most likely to be affected by

environmental flows.

- The Lachlan Floodplain Wetlands Project (LFW): a shape-file was created that

was based on wetland boundaries estimated by wetland monitoring staff. Features

outside of these wetland boundaries were removed. The rationale for wetland

choice was to select all areas likely to currently contain historical or current

wetlands.

The EFR (Environmental Flow Rules) method was produced in response to a request

from the LRMC to determine wetland area-river flow relationships for recent events.

Because the methods used were both valid but different they are both included in this

report to provide more insight into how methods could be developed in future studies.

There were not sufficient resources for either method to fully ground-truth wetland

area. It is highly likely that a proportion of ‘wetland area’ in both methods contain

areas not currently recognisable as wetlands. These areas are likely to be former

wetland areas that are now degraded to an extent that their ecological condition is

currently very poor. With both (LFW and EFR) approaches the river and riparian

areas within 40 m of the river were removed from the area calculation.

(d) Relating wetland areas to river flows

River flow data from the DLWC hydrological database (HydSys) were related to the

wetland areas (km2) using linear regression (SysStat 1997). The largest discharge over

the last 60 days at a river station upstream of the wetland area (ie. either the mid-

Lachlan or the lower Lachlan) was used. This approach was used Sims (1996) had

demonstrated a reasonably strong correlation between this value and wetland

inundation. Log10 transformations of this flow data (the independent variable) were

181

used when necessary to minimise heterogeneity of variance.

14.3 Results

The LFW wetland area-river flow relationships for the mid-Lachlan (Figure 32 and

Figure 33, Table 25) showed, as expected, more wetland inundation for larger river

flows. Regression analyses on the LFW mid-Lachlan data also showed a positive

relationship between the maximum flow peak and wetland inundation (df = 1,7,

F = 14, P = 0.007, r2 = 0.7, Figure 5):

Wetland area (km2) = 468.7*log10 (flow (ML/day))-1603.7……………….…Equation 4

Although the 1990 data were not reported as outliers in this regression, the 1990 flood

data would have had a large influence on the results. These data were therefore

removed in a separate analysis. Linear regression on this data showed a weaker and

non-significant relationship (df = 1,7, F = 14, P = 0.007, r2 = 0.7) indicating that

reasonably accurate prediction of wetland inundation is unlikely at medium-to-

moderate sized flows with the current methods.

For the EFR approach visual interpretation (Figure 33) indicates the five-kilometre

constraint on wetland selection caused lower estimates of total wetland area in the

mid-Lachlan. There were, however, too few data for formal statistical analyses.

Wetland classification suggested an unexpected relationship between river flows and

wetland area. That is, the LFW analyses indicated (nonsensically) that the wetlands in

the lower Lachlan actually became wetter with larger river flows. This pattern was,

however, largely influenced by two values (Table 26, Figure 34). No regression

analyses were undertaken.

For the EFR approach, visual interpretation (Figure 34) again indicated the five-

kilometre constraint on wetland selection caused lower estimates of total wetland area

in the lower Lachlan. Again, there were too few data for formal statistical analyses.

182

14.4 Discussion

(a) Mid-Lachlan wetland inundation-river flow relationships

Some confidence in the wetland area calculations can be gained from the mid-Lachlan

results. Firstly, there was the (obvious) finding that greater wetland inundation occurs

with larger flows. Moreover, the total wetland area after extremely large floods in

1990 was about 945 km2 (Figure 33). Although exact comparisons are not possible,

this value is close to previous estimates of total wetland area based on vegetation

mapping. The sum of wetland areas in the mid-Lachlan (as defined in this study) in

the Lachlan ‘State of the Rivers’ Report was about 110 square km2 (DLWC 1997a,

Table 24) 28.

Table 24 Comparisons of wetland areas calculated from vegetation mapping (DLWC 1997a) andthis report.

Wetland area name Wetland area (km2)

Gooloogong-Jemalong weir 75

1/2 x Jemalong weir-Booligal 444

Bundaburrah Ck. 39

Wibertroy-Cowal (includes Bogandillon system) 256

Goobang Ck. 52

Wallamundry-Wallaroi 124

Booberoi Ck. 87

Total 1 077

total for mid-Lachlan (LFW) 945

(b) Lower-Lachlan wetland inundation-river flow relationships

Similar comparisons between calculated wetland areas and mapped wetland

vegetation areas were not possible for the Lower-Lachlan. Images during the 1990

flood were not chosen, and therefore a value close maximum inundation was probably

not achieved. Additionally, the wetland area-river flow relationship was the opposite

of what would occur; wetland inundation should be greater with larger river flows.

28 This comparison assumes that the wetland-area for Jemalong Weir-Booligal is about half of the river-floodplain

wetland-area for Jemalong Weir-Lake Cargelligo.

183

Therefore the Lower-Lachlan remote sensing analyses did not provide wetland

inundation-river flow information that can be used with any confidence.

(c) Challenges in further developing wetland inundation-river flow

relationships

The major challenges in the development of this wetland inundation-river flow

method were:

1. Defining wetland boundaries with limited knowledge and inadequate resource

for ground-truthing;

2. Non-discrete wetlands are difficult to map;

3. Choosing the correct pixel value(s) to represent a given level of wetland

inundation;

4. Developing relative measures of the volume of water that should be within the

wetlands at a given point in time using hydrological data.

The dominance of non-discrete wetlands was probably one important contributor to

the negative relationship between wetland inundation and river flows in the lower

Lachlan. Some previous applications of this remote sensing approach have been

applied to discrete wetlands such as billabongs (eg, Green et al. 1998, Frazier 1999).

To the author’s knowledge approaches that have been applied to non-discrete

wetlands were applied within better known (ie., better ground-truthed) and smaller

areas (eg, Sims 1996, Shaikh et al. 1998). Hence, the lower success of the lower

Lachlan inundation mapping is in part explained by additional problems with having

to guess the maximum extent of wetland areas within very large and often poorly

ground-truthed areas.

Problems relating to the uncertainty of wetland boundaries need to be resolved in

future studies. To this end, the wetland areas from DLWC vegetation mapping used in

DLWC (1997) have been re-incorporated into a GIS database as part of the Lachlan

Wetland Database (Section 10). In the future this mapping can be used to more

accurately define wetland boundaries.

184

Incorrect and subjective choice of pixel size for representing the wetland inundation

area was another factor likely to have largely contributed to the questionable lower

Lachlan results. Differences between images, particularly with regard to the cover of

wet vegetation areas and cloud cover, are likely to have largely contributed to this

problem. This would have particularly been the case in the lower Lachlan where

discrete wetland boundaries were unavailable to aid in decision making. Moreover,

unlike some other studies (eg, Green et al. 1998, Mustak Shaikh, pers. comm.), a

single pixel value was inappropriate in this study to represent a given level of

inundation. Pixel range varied among images and, furthermore, point-checks of

known water-bodies indicated the relationship between a given level of inundation

and pixel value varied among images. The two points that caused a negative

relationship between wetland inundation and river discharge were pre-flow images

(LFW images 11 June 1996 and 3 June 1993). This pattern suggested that selection of

incorrect pixel size is more likely during dry times. It appears that a very large area of

dry wetland was classified as wet in these images.

Reducing the subjectively in pixel choice may be reduced in future. Part of the

problem may lie with computer-based techniques. Nonetheless, wetland data from

current monitoring programs could be more effectively utilised for ground-truthing in

future efforts. Two existing wetland monitoring programs, LCMP (Walker 2001) and

IMEF wetlands (Driver et al. 2001) should be able to provide indications of the extent

of inundation of 25 or more wetlands. In this project only some data were available

from the IMEF wetland-monitoring program for 12 wetlands from 1999 onwards.

These data were limited in their use and availability in this study, as these two

programs only became effective during 1999-2000. These programs collect both on-

ground observations of wetland inundation but also data (wetland CTF’s and drying

times) which allow independent prediction of wetland fill.

Other restrictions, often relating to the precision of estimating wetland area, have also

been discussed as possible factors leading to the unexpected results for the lower

Lachlan. These include the large pixel-size (25 m) of Landsat TM imagery, the

limited processing power of available computers and the need for a variety of

software. The coarse use of hydrological data may also have contributed to errors in

the wetland area-river flow relationship. Other studies have, however, derived

185

reasonable estimates of wetland inundation using similar approaches (eg, Shaikh et al.

1998). The critical point is that none of these problems should have substantially

altered the relative differences between estimates of wetland inundation.

Table 25 Wetland inundation areas in the mid-Lachlan for given dates determined fromclassification of Landsat TM imagery

Date of Landsat image Max flow peak at

Cottons weir in last 60 days

LFW area (m2) EFR area (m2)

26-Apr-88 3 567 5 336 785

20-Oct-88 19 313 65 831 766

01-Apr-90 3 418 83 740 936

03-May-90 109 931 945 251 395

19-May-90 109 931 879 420 054

25-Jul-91 6 468 452 718 977

13-Oct-91 24 040 150 258 466

10-Jun-98 2 825 119 329 379

28-Aug-98 32 039 491 339 537

10-Aug-00 7 963 13 110 259

27-Sep-00 16 831 33 080 731

Table 26 Wetland inundation areas in the lower Lachlan for given dates determined fromclassification of Landsat TM imagery.

Date of Landsat image Max flow peak at

Lake Cargelligo

in previous 60 days

LFW area (m2) EFR area (m2)

20-Sep-92 7 720 20 445 597

06-Oct-92 7 720 180 149 122

22-Oct-92 7 720 27 661 857

03-Jun-93 1 100 273 974 087

22-Aug-93 8 757 70 436 773

07-Sep-93 8 757 65 513 100

23-Sep-93 8 757 67 120 589

11-Jun-96 2 078 301 621 669

30-Aug-96 5 735 40 367 615

01-Oct-96 7 883 7 748 865

15-Jun-00 436 20 074 144

01-Oct-00 9 411 42 940 299

21-Nov-00 9 411 21 634 520

186

56684

150119

491

33130

100

200

300

400

500

600

0 10,000 20,000 30,000 40,000

Max peak in the last 60 days (ML/day)

Are

a in

unda

ted

(km2 )

LFW area

EFR area

Figure 32 Wetland area inundated in the mid-Lachlan versus the maximum Lachlan River peak in

the last 60 days at Forbes (Cotton’s weir). 1990 data is removed. LFW and EFR are different

methods (see text).

5 6684

945879

453

150119

491

0

200

400

600

800

1,000

0 30,000 60,000 90,000 120,000

Max peak in the last 60 days (ML/day)

Are

a in

unda

ted

(km2 )

Figure 33 Wetland area inundated in the mid-Lachlan versus the maximum peak in the last 60 days

at Forbes (Cotton’s weir) effects. 1990 data not removed. LFW method shown only.

187

0

50

100

150

200

250

300

350

0 2,000 4,000 6,000 8,000 10,000

Max peak in the last 60 days(ML/day)

Are

a in

unda

ted

(km

2 ) LFW area

EFR area

Figure 34 Wetland area inundated in the lower Lachlan versus the maximum peak in the last

60 days at Lake Cargelligo weir. LFW and EFR are different methods (see text). The relationship

shown for the LFW project is nonsensical if the two figures > 250km2 are included.

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