Millewa Forest

COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

ANALYSIS AND MANAGEMENT OF UNSEASONAL SURPLUS FLOWS IN THE BARMAH-MILLEWA FOREST

TECHNICAL REPORT Report 03/2 December 2003

Jo Chong Chong, Jo, 1979- .

Analysis and management of unseasonal surplus flows in the Barmah-Millewa Forest.

ISBN 1 876006 98 6

1. Forest influences - Victoria - Barmah State Forest. 2. Forest influences - New South Wales - Millewa State Forest. 3. Forest conservation - Victoria - Barmah State Forest. 4. Forest conservation - New South Wales - Millewa State Forest. 5. Murray River (N.S.W.-S. Aust.) - Regulation. I. Cooperative Research Centre for Catchment Hydrology. II. Title. (Series : Report (Cooperative Research Centre for Catchment Hydrology); 03/2).

333.75160994

Keywords

Wetlands Forests Floods and Flooding River Regulation Stream Flow Frequency Analysis Seasons Economics Reviews Hydrology

Analysis and Preface

Management The main goal of the Cooperative Research Centre (CRC) for Catchment Hydrology’s River Restoration of Unseasonal program is to provide the tools and understanding that will allow the environmental values of Australia’s Surplus Flows streams to be restored. A national priority for restoration is the Murray River with the ‘Living in the Barmah- Murray’ process providing a focus for governments and the community. A clear goal is to improve the Millewa Forest condition of icon sites along the Murray including the Barmah-Millewa Forest which is also recognised as a wetland of international significance under the Ramsar convention.

This report addresses one major threat to the forest; Jo Chong unseasonal flooding in the summer and autumn when the forest would normally be dry. Based on Technical Report 03/2 analysis of pre-regulation conditions (1908-1929) December 2003 and current conditions (1980 - 2000), forest flooding has increased from 15.5% of days to 36.5% of days between December and April. In particular, small, localized floods, which inundate less than 10% of the forest, occur at least eight times more frequently now, than before regulation. Work by others has related these hydrologic changes to tree death and changes in floristic structure in wetlands. There are also economic costs because much of the water that spills into the forest is lost to downstream irrigation.

There are a range of approaches to reduce unseasonal flooding. The two solutions investigated in this report are intended to decrease the risk of flooding when there is summer rainfall which suddenly decreases the demand for irrigation water. Water from upstream that has already been released to meet irrigation orders, is not required if it rains, so remains in the river and can cause forest flooding. Creating capacity in the river to store or carry this extra flow can decrease unseasonal floods.

I am impressed with the comprehensive analysis of unseasonal flooding that has been carried out byJo Chong and commend this report to anyone interested in improving the condition of Australia’s regulated rivers.

Mike Stewardson Program Leader, River Restoration Program CRC for Catchment Hydrology

i COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

ii iii COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Executive Summary capacity (10,600 ML/day) between Lake Hume and South Australia (approximately 1800km downstream of the forest) (Thoms et. al. 2000). The rain rejection The Barmah-Millewa Forest comprises approximately flows are usually accompanied by river freshes, which 70,000 ha of wetland habitats located on the floodplain are small excess flows, generated by local rainfall, in of the River Murray between Echuca, Deniliquin and the unregulated tributaries of the Murray upstream Tocumwal. The Barmah-Millewa ecosystem contains of the forest. Together, rain rejection flows and river predominantly forests of river red gum (Eucalyptus freshes are referred to as unseasonal surplus flows. camaldulensis Dehn), but also contains swamps and marshes, moira grasslands, giant rushlands, open This project aims to analyse the extent to which waters, billabongs and streams. Together, the Barmah an increase in system flexibility would reduce the Forest (Victoria) and the Millewa group of forests likelihood of unseasonal surplus flows. The goals are (NSW) form the largest river red gum forest in the to identify the patterns between system flexibility (eg. world, and are valued for wood products, grazing, River Murray flows or storage air space) and unseasonal conservation and recreation. The Barmah wetland is surplus flows, to quantify these relationships, and to listed under the Ramsar Convention as a wetland of determine the net economic impact of reducing the international significance. likelihood of unseasonal surplus flows.

The river red gum forests along the Murray and its The emphasis of the initial research phase (Sections tributaries have evolved in an environment characterised 1 to 3) was to document, investigate and understand by natural flooding in the winter and spring months of the physical, regulatory, institutional and economic most years, alternated with dry conditions during the environment of the problem. The information gained summer and autumn months. (Bren 1988a, Maunsell in this phase was used to identify and evaluate possible 1992a). These natural inundations are required to avenues of research, and to determine data requirements sustain the ecosystem and its values. and availability.

However, the natural flow regime of the Barmah- The Literature Review (Section 2) provides a critical Millewa Forest has been changed by regulation of the review of the information relevant to the problem River Murray, since the first filling of the Hume Dam of unseasonal surplus flows in the Barmah-Millewa in 1934. The forest has experienced a reduction in the Forest. The literature included information on the frequency of flows associated with partial flooding and hydrology of the forest, changes to flooding regimes an increase in the occurrence of small summer flows over time, the effect of these changes on flora and (Bren 1988a). The changing flow pattern has, in turn, fauna, and the analysis and management of rain changed patterns of vegetation (Chesterfield 1986). rejection events. The review considered information Leslie and Harris (1996) cite that permanent summer from both refereed journal articles and government inundation of low lying forests has been far more agency publications, in acknowledgement of the damaging than the impacts of drought. scientific, regulatory and economic research conducted by various government agencies in the development of This project focuses on the increases in summer/autumn plans and strategies. The majority of independent work forest inundation. This results when flows are released dealing with the hydrology of the Barmah Forest was from storage but not diverted into irrigation channels conducted by Bren et. al. over the period 1984 - 1988. for distribution to farms. They occur when local rains The literature review revealed that the most significant reduce the irrigation requirement, and irrigators cancel shift in management principles has been the move away their order for water. The released water, intended for from the idea of using rain rejection flows to water the diversion, instead passes down the river. Rain rejections forest (Maunsell 1992a, 1992b). occur because the River Murray is maintained at a high flow level to enable flow to pass through the “Barmah The Background Information (Section 3) documents Choke”, which refers to the reach of the River Murray information including location, natural resources, between the junction of the Edward River and the forest uses and resources, hydrology of the regulated system, and forest hydrology. ii Barmah township. This reach has the lowest channel iii COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Section 4 (Research Methodology) outlines the The main findings of the analysis (sections 5 - 8) are research methodology which enabled an evaluation of described below. how the frequency of unseasonal surplus flows, which affect the Barmah-Millewa Forest, is related to flow Historical Analysis and flexibility in the River Murray system. There has been significant changes in the patterns of River Murray flow at Tocumwal during summer and Section 5 (Historical Analysis) investigates changes autumn. During December to April (particularly in in the patterns of summer-autumn River Murray flows February and March), flows are far more likely to (at Tocumwal) and frequency and areal extent of forest be above 10,600 ML/day now (36.5% of the time) flooding. The historical analysis identified December than before 1908 (15.5% of the time). This means to April as the months during which forest flooding is that regulation has increased the number of days in more frequent now (1981 - 2001) than before regulation summer-autumn during which flooding occurs in the (1908 - 1929). Barmah-Millewa Forest.

Section 6 (Unseasonal Surplus Flow Events) compares However, an application of the relationship derived the characteristics of unseasonal surplus flow events by Bren et. al. (1987) linking flow at Tocumwal identified using three different methods. The flow to proportion of forest flooded revealed that more at Tocumwal is evaluated as the most appropriate extensive floods (in which over 30% of the forest is indicator of unseasonal surplus flooding. flooded) are now less frequent. This is because the construction of dams, locks and weirs has enabled Section 7 (System Flexibility) quantifies (through mitigation of larger River Murray flows. graphical representation) the (individual) effect of increasing airspace at Yarrawonga and reduced Consequently, there are some parts of the forest (~30% unseasonal flows and limiting maximum River Murray of the area) which are flooded more than twice as flow at Tocumwal on flooding frequency (proportion frequently in summer-autumn now than before 1929, of days in season during which flooding occurs in the which leads to tree stress and death. However, the forest); number of events per season; event duration; remainder of the forest (~70% of the area) is flooded and total surplus flow volume per season. less frequently now than before 1929. Both these changes have resulted in changes to the “natural” Section 8 (Economic Analysis) considers the costs and vegetation associations and patterns in the forest. benefits of increasing system flexibility to decrease the frequency of unseasonal flooding in the Barmah- Unseasonal Surplus Flow Events Millewa Forest (proportion of days in season during Of three main methods evaluated the method which which flooding occurs) from 38.3% (current) to 15.5% involves analysing daily data for flows that exceed (pre-regulation). 10,600 ML/day at Tocumwal is the preferred method The economic analysis of the alternative strategies is in terms of a computable data set and applicability to not straightforward. The approach taken here is identify current conditions. both market- and non-market costs and benefits, but The use of this method revealed that during the period to selectively quantify only the following costs and 1980 - 2000, there were 82 surplus flow events (4.1 per benefits (collectively defined as “net conservative year), which caused flooding in the forest in 38.3% of cost/benefit”): days in December-April. The average event duration • benefit of irrigation water “saved” due to reduced was 14.1 days (median 10 days); average peak excess forest flooding (both options); flow was 2211 ML/day (median 1133 ML/day); and • cost of irrigation water foregone due to reduced average total flow per event was 17,833 ML (median diversions (both options); 7960 ML). • cost of the reduction of hydroelectric generation (increasing airspace only).

iv v COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Relation to System Flexibility include the value accrued from reducing flooding If system flexibility had been greater over the period frequency. 1980 - 2000, then there would have been significantly Therefore, significant net benefits accrue from less frequent flooding of the Barmah-Millewa Forest. increasing airspace at Yarrawonga to reduce the If 1980 - 2000 is assumed to represent current water frequency of summer-autumn forest flooding. demand conditions, then flooding frequency can be reduced from 38.3% to 15.5% by: Finally, the research conducted in this project is not • increasing airspace at Yarrawonga by 9100 ML all-encompassing. Rather, this project has opened up (maintaining height at 124.9m, 0.195m below the avenues for further research, including alternative maximum); OR analysis/modelling methods, an extended economic analysis, or investigation of other management • limiting the maximum flow at Tocumwal to 9600 options. ML/day.

Smaller increases in system flexibility can also have a significant impact on reducing flooding frequency, e.g. a frequency of 20% will be achieved by increasing airspace by just 5000 ML or limiting the maximum flow at Tocumwal to 9900 ML/day.

Economic Analysis Approximately $4.4m of water (73000 ML/year) per year is currently “lost” to forest flooding during December-April. Reducing flooding frequency from 38.3% to 15.5% would reduce the total surplus volume per year to 49,000 ML (an equivalent saving of $1.4m).

Limiting the maximum flow at Tocumwal to 9600 ML/ day to reduce flooding frequency to 15.5% results in a net cost of $2.5m (less water available to downstream users, but water saved from flooding for environmental flows). However, this figure is not a true indicator of net economic cost. Net economic cost will be far lower, due market (forestry and tourism) and non-market (environmental) benefits from reduced forest flooding and the potential for greater upstream use.

Increasing the airspace at Yarrawonga by 9100 ML does not limit the outflow into the irrigation areas through Yarrawonga Main Channel and Mulwala Canal. Very minor losses in hydroelectric power generation will be incurred, but they will be more than offset by the value of the water saved from flooding ($1.4m). This figure assumes a marginal value of water equivalent to the agricultural gross margin ($60/ML), which is likely to be an understatement of the value of water if it were used for environmental watering purposes. Furthermore, the $1.4m benefit does not iv v COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

vi vii COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Preface i Executive Summary iii List of Tables x List of Figures xi List of Abbreviations xii Glossary xiii 1 Introduction 1 1.1 Objectives 1 1.2 Stakeholders and Agencies 1 1.2.1 The Barmah-Millewa Forum 2 1.2.2 Commonwealth Agencies 2 1.2.3 Victorian Agencies 3 1.2.4 New South Wales Agencies 3 2 Literature Review 5 2.1 Overview 5 2.1.1 Literature 5 2.2 Hydrology 5 2.3 Flora and Fauna 9 2.4 Rain Rejection Analysis and Management 9 2.5 Summary 11 3 Background Information 13 3.1 Overview 13 3.2 Location 13 3.3 Natural Resources 15 3.3.1 Origin of the Barmah-Millewa Forests 15 3.3.2 History and Heritage 15 3.3.3 Vegetation Associations 15 3.3.4 Fauna 16 3.3.5 Hydrogeology 16 3.3.6 Sedimentology 16 3.3.7 Climate 16 3.4 Forest Uses and Resources 17 3.4.1 Utilisation 17 3.4.2 Recreation and Tourism 18 3.5 Hydrology of the Regulated System 18 3.5.1 The Regulation of the River Murray 18 3.5.2 Unseasonal Surplus Flows 19 3.5.3 Yarrawonga Weir Diversions 19 3.5.4 Murray Irrigation Area (New South Wales) 19 3.5.5 Murray Valley Irrigation Area (Victoria) 20

vi vii COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

3.6 Forest Hydrology 21 3.6.1 Water Management Areas 21 3.6.2 Flow Characteristics of the Barmah-Millewa Forest 22 3.6.3 Drainage Systems for Unseasonal Flows 24 3.6.4 Unseasonal Flooding 25 4 Research Methodology 27 4.1 Overview 27 4.2 Initial Research Phase (Chapters 1 to 3) 27 4.3 Historical Analysis (Chapter 5) 27 4.4 Identification of Unseasonal Surplus Flow Events (Chapter 6) 28 4.5 Analysis of Increased System Flexibility (Chapter 7) 28 4.6 Economic Analysis (Chapter 8) 28 5 Historical Analysis 29 5.1 Overview 29 5.2 Data 29 5.3 River Murray Flow at Tocumwal 32 5.3.1 Methodology 32 5.3.2 November 32 5.3.3 December 34 5.3.4 January 36 5.3.5 February 38 5.3.6 March 40 5.3.7 April 42 5.3.8 May 44 5.3.9 Summary 46 5.4 Forest Flooding 47 5.4.1 Frequency 47 5.4.2 Areal Extent 51 5.5 Summary: December - April 52 5.5.1 River Murray Flow at Tocumwal 52 5.5.2 Forest Flooding 55 6 Identification of Unseasonal Surplus Flow Events 57 6.1 Overview 57 6.2 Data 57 6.3 Methodology 57 6.3.1 General 57 6.3.2 Tocumwal Analysis 58 6.3.3 Yarrawonga Analysis 58 6.3.4 Picnic Point Analysis 58 6.4 Results 58 6.5 Comparative Analysis 61 6.5.1 Degree of Coincidence 61 6.5.2 Advantages and Disadvantages 62 6.6 Summary: Tocumwal Method 63

viii ix COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

7 Analysis of Increased System Flexibility 65 7.1 Overview 65 7.2 Increasing Airspace at Yarrawonga Weir 65 7.2.1 Methodology 65 7.2.2 Results 66 7.2.3 Analysis 67 7.3 Limiting Flow of the River Murray at Tocumwal 67 7.3.1 Methodology 67 7.3.2 Results 68 7.3.3 Analysis 69 7.4 Summary 69 8 Economic Analysis 71 8.1 Overview 71 8.2 Identification of Economic Costs and Benefits 71 8.2.1 Market Costs and Benefits 71 8.2.2 Non-market Costs and Benefits 72 8.3 Option 1: Costs and Benefits of Increasing Airspace at Yarrawonga 72 8.3.1 Cost: Reduced Irrigation Supply Flexibility 72 8.3.2 Cost: Reduced Hydroelectric Power Generation 76 8.3.3 Benefit: Value of Water Saved from Reduced Flooding Frequency 79 8.3.4 Net Conservative Benefit 82 8.4 Option 2: Costs and Benefits of Limiting Maximum Flow at Tocumwal 82 8.4.1 Cost: Reduced Water Supply Downstream of the Barmah- Millewa Forest 82 8.4.2 Benefit: Value of Water Saved from Reduced Flooding Frequency 84 8.4.3 Net Conservative Cost 84 8.5 Summary: Comparison Between Options 86 9 Conclusion and Recommendations 87 9.1 Recommendations for Further Research 88 9.1.1 Alternative Modelling and Analytical Techniques 88 9.1.2 Extended Economic Analysis 88 9.1.3 Investigation of Other Management Options 88 10 References 91 Appendix A: Development of Research Methodology 93 Appendix B: Historical Analysis 103 Appendix C: Unseasonal Surplus Flow Events 107 Appendix D: Analysis of System Flexibility 111 Appendix E: Economic Analysis 113

viii ix COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

List of Tables

Table 2.1 Refereed Journal Articles 5 Table 2.2 Other Publications 6 Table 5.1 Summary of Flow Changes for Months November to May 1908 - 1929 and 1981 - 2000 46 Table 5.2 Areal Extent of Flooding 51 Table 5.3 Summary of Flow Changes at Tocumwal for Period December to April 1908 - 1929 and 1981 - 2000 55 Table 5.4 Summary of Changes in the Extent of Forest Flooding between 1908 - 1929 and 1981 - 2000 56 Table 6.1 Summary of Advantages and Disadvantages of the Three Methods for Identifying Unseasonal Surplus Flow Events 62 Table 6.2 Unseasonal Surplus Flow Events (Tocumwal method) 63 Table 7.1 Surplus Flow Each Day for an Event that Exceeds the Flooding Threshold of 10,600ML/d 65 Table 7.2 Reduction in Surplus Flow when Airspace at Yarrawonga Weir is Increased to 1000ML 65 Table 7.3 Surplus Flow Each Day for an Event that Exceeds the Flooding Threshold of 10,600 ML/d 67 Table 7.4 Reduction in Surplus Flow when Tocumwal Flow is Limited to 10,100 ML/d 67 Table 8.1 Sample Flow Sequence at Tocumwal 82 Table 8.2 Effect of Limiting Flows at Tocumwal on Volumes Available to Downstream Users 83

x xi COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

List of Figures

Figure 5.21 Historical Flow Analysis: Figure 2.1 Relationship Between Extent of Flooding May: Frequency Column Graph 45 in the Barmah Forest and Flow in the Murray-Edward River System 7 Figure 5.22 Historical Flow Analysis: May: Stacked Column Graph 45 Figure 2.2 Pre-Hume and Post-Hume Flooding of the Barmah Forest 8 Figure 5.23 Frequency of Flooding 47 Figure 3.1 Location of the Barmah-Millewa Forest 13 Figure 5.24 Factor Increases in Frequency of Flooding 50 Figure 3.2 Locality Map of the Barmah-Millewa Figure 5.25 Historical Flow Analysis: Forest 14 December-April: Flow duration curve 53 Figure 3.3 Rainfall Statistics 17 Figure 5.26 Historical Flow Analysis: December- April: Frequency Column Graph 53 Figure 3.4 Murray Irrigation Area from Lake Mulwala to the Wakool Escape 20 Figure 5.27 Historical Flow Analysis: December-April: Stacked Column Graph 54 Figure 3.5 Murray Valley Irrigation Area 20 Figure 5.28 Areal Extent of Forest Flooding: Figure 3.6 Water Management Areas 21 December-April 55 Figure 3.7 Flooding of the Barmah-Millewa Forest 23 Figure 6.1 Event Statistics: Comparison Figure 3.8 Eastern Barmah-Millewa Forest Between Methods 59 Drainage Network 24 Figure 6.2 Comparing Degree of Overlap Figure 5.1 Descriptive Statistics 29 Between Methods 61 Figure 5.2 Historical Flow Analysis: Figure 7.1 Increasing Airspace at Yarrawonga November: Flow Duration Curve 32 Weir: Impact on Flooding Frequency 66 Figure 5.3 Historical Flow Analysis: Figure 7.2 Increasing Airspace at Yarrawonga November: Frequency Column Graph 33 Weir: Impact on Surplus Flow Volume 66 Figure 5.4 Historical Flow Analysis: Figure 7.3 Limiting Maximum Flow at Tocumwal: November: Stacked Column Graph 33 Impact on Flooding Frequency 68 Figure 5.5 Historical Flow Analysis: Figure 7.4 Limiting Maximum Flow at Tocumwal: December: Flow Duration Curve 34 Impact on Surplus Flow Volume 68 Figure 5.6 Historical Flow Analysis: Figure 8.1 Lake Mulwala Stage - Volume December: Frequency Column Graph 35 Relationship 73 Figure 5.7 Historical Flow Analysis: Figure 8.2 Lake Mulwala Scatter Plots Showing December: Stacked Column Graph 35 Outflows to Yarrawonga Main Channel 74 Figure 5.8 Historical Flow Analysis: Figure 8.3 Lake Mulwala Scatter Plots Showing January: Flow Duration Curve 36 Outflows to Mulwala Canal 75 Figure 5.9 Historical Flow Analysis: Figure 8.4 Cost of Hydroelecticity Generation January: Frequency Column Graph 37 Foregone 77 Figure 5.10 Historical Flow Analysis: Figure 8.5 Valuing the Water Saved from Reduced January: Stacked Column Graph 37 Forest Flooding 79 Figure 5.11 Historical Flow Analysis: Figure 8.6 Benefit of Saved Water 80 February: Flow Duration Curve 38 Figure 8.7 Benefit of Saved Water 82 Figure 5.12 Historical Flow Analysis: Figure 8.8 Costs of Reduced Downstream Water February: Frequency Column Graph 39 Supply 83 Figure 5.13 Historical Flow Analysis: Figure 8.9 Net Cost of Limiting Maximum Flow at February: Stacked Column Graph 39 Tocumwal 85 Figure 5.14 Historical Flow Analysis: March: Flow Duration Curve 40 Figure 5.15 Historical Flow Analysis: March: Frequency Column Graph 41 Figure 5.16 Historical Flow Analysis: March: Stacked Column Graph 41 Figure 5.17 Historical Flow Analysis: April: Flow Duration Curve 42 Figure 5.18 Historical Flow Analysis: April: Frequency Column Graph 43 Figure 5.19 Historical Flow Analysis: April: Stacked Column Graph 43 Figure 5.20 Historical Flow Analysis: May: Flow Duration Curve 44 x xi COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

List of Abbreviations

BMF Barmah-Millewa Forum DCE Department of Conservation and the Environment (Victoria; now DNRE) DLWC Department of Land and Water Conservation (New South Wales) DNRE Department of Natural Resources and the Environment (Victoria) GMW Goulburn-Murray Water MDBC Murray-Darling Basin Commission MIL Murray Irrigation Limited RMW River Murray Water SFNSW State Forests of New South Wales WMA Water Management Area

xii xiii COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Glossary

Barmah-Millewa forest is the collective name given to approximately 70000 ha of wetland habitats located on the floodplain of the River Murray between Echuca, Deniliquin and Tocumwal.

The Choke refers to the reach of the River Murray, between the junction of the Edward River and the Barmah township, with the lowest channel capacity (10600 ML/ day) between Lake Hume and South Australia.

Flooding frequency the percentage of days (during December-April) during which flooding occurred in the Barmah-Millewa Forest (also “unseasonal flooding frequency”).

River freshes are small excess flows (which are generated by local rainfall) in the unregulated tributaries of the Murray upstream of the forest.

Rain rejection flows are released from the Hume Dam during the irrigation season but not diverted into the irrigation areas from Mulwala Lake.

System flexibility the degree to which the regulated system can accommodate unseasonal surplus flows, either through airspace at Yarrawonga or flow of the River Murray below bankfull capacity.

Unseasonal surplus flows are generated from river freshes and rain rejection flows. Also referred to as “excess flows”.

xii xiii COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

xiv 1 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

1. Introduction Barmah township. This reach has the lowest channel capacity (10,600 ML/day) between Lake Hume and South Australia (approximately 1800km downstream The Barmah-Millewa Forest comprises approximately of the forest) (Thoms et. al. 2000). The rain rejection 70,000 ha of wetland habitats located on the floodplain flows are usually accompanied by river freshes, which of the River Murray between Echuca, Deniliquin and are small excess flows, generated by local rainfall, in Tocumwal. The Barmah-Millewa ecosystem contains the unregulated tributaries of the Murray upstream predominantly forests of river red gum (Eucalyptus of the forest. Together, rain rejection flows and river camaldulensis Dehn), but also contains swamps and freshes are referred to as unseasonal surplus flows. marshes, moira grasslands, giant rushlands, open waters, billabongs and streams. Together, the Barmah This project aims to analyse the extent to which Forest (Victoria) and the Millewa group of forests an increase in system flexibility would reduce the (NSW) form the largest river red gum forest in the frequency of unseasonal surplus flows. The goals are world, and are valued for wood products, grazing, to identify the patterns between system flexibility (eg. conservation and recreation. The Barmah wetland is River Murray flows or storage air space) and unseasonal listed under the Ramsar Convention as a wetland of surplus flows, and to quantify these relationships. international significance.

The river red gum forests along the Murray and 1.1 Objectives its tributaries have evolved in an environment The objectives of this project are to: characterised by natural flooding in the winter and • conduct background research to define the spring months of most years, alternated with dry unseasonal surplus flow problem, including its conditions during the summer and autumn months. occurrence, consequences, and management; (Bren 1988a, Maunsell 1992a). These natural • analyse how summer-autumn River Murray flows inundations are required to sustain the ecosystem and have changed with increased regulation over its values. time; However, the natural flow regime of the Barmah- • analyse how patterns (frequency and duration) of Millewa Forest has been changed by regulation of the unseasonal flooding have changed with increased River Murray, since the first filling of the Hume Dam regulation over time; in 1934. The forest has experienced a reduction in the • identify individual unseasonal surplus flow frequency of flows associated with partial flooding events; and an increase in the occurrence of small summer • analyse selective costs and benefits involved flows (Bren 1988a). The changing flow pattern has, with increasing system flexibility to reduce the in turn, changed patterns of vegetation in the Forest frequency of unseasonal surplus flows. (Chesterfield 1986). Leslie and Harris (1996) cite that permanent summer inundation of low lying forests has This final report includes a literature review, been far more damaging than the impacts of drought. documentation of background information, research methodology, documentation of analysis, conclusions This project focuses on the increases in summer/autumn and recommendations for future research. forest inundation. This results when flows are released from storage but not diverted into irrigation channels for distribution to farms. They occur when local rains 1.2 Stakeholders and Agencies reduce the irrigation requirement, and irrigators cancel Many government departments, rural water distribution their order for water. The released water, intended for companies, and other government and non-government diversion, instead passes down the river. Rain rejections organisations and associations are involved in the occur because the River Murray is maintained at a high planning and implementation of water management and flow level to enable flow to pass through the “Barmah supply operations which affect the Barmah-Millewa Choke”, which refers to the reach of the River Murray Forest. Other stakeholders include community groups xiv between the junction of the Edward River and the 1 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

and individuals who have an interest in the value of environment groups and tourism operators. Membership the River Murray and the Barmah-Millewa Forest, also includes the government agencies of State Forest including environmental groups like the Victorian of NSW, Department of Land and Water Conservation National Parks Association (VNPA). (NSW), Department of Natural Resources and the Environment (Victoria), Goulburn-Murray Water and The MDBC (2000) acknowledges the following Environment Australia. stakeholders in its Water Management Strategy: The Forum helps to implement the business plan and • The Murray-Darling Basin Ministerial Council; water management strategy for the Forest. It provides • Commonwealth and State Government agencies; advice on the operating plans to ensure coordination • local government agencies; between the two States, and also advises the • joint community-government resource manage- Murray-Darling Basin Commission on general water ment entities in the region; management of the Barmah-Millewa Forest (MDBC • community groups with interests in natural 2001a). resource management and the regional and local economy; 1.2.2 Commonwealth Agencies • communities in the region (including Aboriginal The Murray-Darling Basin Commission communities) with strong cultural ties to the The Murray Darling Basin Commission (MDBC) Forest environment; works in partnership with the five state governments • industries and users supported by commercial, to “promote and coordinate planning and management tourist and recreational activities pursued within for the effective, efficient and sustainable use of water, the Forest; and land and other environmental resources of the Murray- • downstream users of River Murray water. Darling Basin.” The MDBC coordinates activities that enhance and integrate water management for the This section focuses on the roles of management Barmah-Millewa Forest, due to its responsibilities for agencies and water distribution companies. It operating the River Murray and because of the impacts summarises the responsibilities of these groups, and of that operation on the Forest (MDBC 2000). provides a brief outline of the evolving set of studies, strategies, plans and frameworks which concern water The MDBC has been directed by the Murray- management of the Barmah-Millewa Forest. An Darling Basin Ministerial Council to “develop water understanding of the network of relationships between management strategies for the Barmah-Millewa Forest major stakeholders also assists greatly in identifying which enhance forest, fish and wildlife values, while the factors which influence the likelihood of rain not creating undue adverse affect in other areas”. The rejection events. Final Report of the Barmah-Millewa Forests Water Management Plan was completed in January 1992. Whilst it is intended that this research project will The six stages of the plan’s development were: involve a significant level of statistical analysis, a • identification of water management areas thorough approach to problem definition is considered (WMA); an important component of the overall research procedure. Thus, stakeholder identification is crucial • determination of water deficits in the forests; to understanding the institutional, regulatory and • evaluation of a range of projects to reduce the economic environment of the problem. It is also useful water deficits identified in stage 2; in identifying sources of data and information required • selection of the best strategies to meet water for further research. deficits for each WMA; • assigning priorities based on costs and water stress 1.2.1 The Barmah-Millewa Forum levels; and The Barmah-Millewa Forum consists of advisors • developing guidelines to implement the water from private water scheme irrigators, non-wood management plan (Maunsell 1992a).

2 based and wood-based forest users, local government, 3 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Subsequent to the completion of the Barmah-Millewa completed the Barmah State Park and Barmah State Forests Management Plan, the Ministerial Council Forest Management Plan which contained a summary directed that 100GL per year be allocated to meet the of resources, a review of present and future use, and environmental needs of the Forest, and that it should plans for the management of natural resources, cultural be managed as a single unit using a single allocation. resources, access, (economic) utilisation, recreation, The Barmah-Millewa Forest allocation was first used tourism and visitor education, forest protection, to augment the September 1998 flood from the Ovens boundaries, and resource requirements. River (a one in 25 year event) and extended the high In August 1994 the DCNR prepared an Interim Water flow period from 14 to 35 days (Maunsell McIntyre Management Strategy for Barmah Forest, Victoria. 1999). DNRE is currently reviewing this strategy, and expects River Murray Water an updated version to be complete by the end of 2002 (Ward, K.A., 2001, pers. comm., 15 March). The River Murray Water (RMW) was established by Interim Strategy established principles and rules for the Murray-Darling Basin Ministerial Council as regulator operation (flood initiation and duration), in internal business division of the MDBC for the proposals for water management areas (including specific purposes of operating and managing the River regulators, diversion and impoundment works), and Murray system (service delivery). RMW commenced general proposals such as de-snagging of the Barmah operations on 1 January 1998 (MDBC 2001b). Choke. The primary services provided by River Murray Water The Goulburn-Murray Rural Water Authority (GMW; are: trading as Goulburn-Murray Water) was constituted by • water storage and delivery; Ministerial Order under the provisions of the Water Act • salinity mitigation; 1989 effective from 1 July 1994. GMW is responsible • navigation; for the headworks within its region, the provision of bulk water supply, and the delivery of irrigation water, • recreation and tourism; and domestic and stock supplies and drainage services • hydro-power. (GMW 2000).

1.2.3 Victorian Agencies GMW is responsible for servicing 1728 irrigated holdings in the Murray Valley Irrigation Area. The The Department of Natural Resources and Environment Yarrawonga Main Channel, which is the major supply (DNRE) and Goulburn-Murray Water (GMW) are the channel for the Area, is gravity fed from Lake Mulwala primary agencies responsible for managing the land (Yarrawonga Weir), 2 flow-days upstream from the and water resources of the Barmah State Forest and Barmah-Millewa Forest. Rejected irrigation orders State Park. from within this region have the potential to cause Specific responsibilities related to various pieces of rain rejection flows in the Barmah-Millewa forest. The legislation, including: Murray Valley Irrigation Area covers 128,372 hectares (88 969 hectares irrigated), and has an annual water • Forests Act 1958 (management of Forest and right of 257,522 ML (GMW 2001). Forest produce); • National Parks Act 1975 (management of the State 1.2.4 New South Wales Agencies Park portion); The New South Wales Department of Land and Water • Water Act 1989 (provision of rural services and Conservation (DLWC) and State Forests of New South bulk water supplies); and Wales (SFNSW) are the primary agencies responsible • Flora and Fauna Guarantee Act 1988 (protection for managing the land and water resources in the of native flora and fauna). Millewa Forest. NSW Fisheries and NSW National Parks and Wildlife Service also have specific statutory In September 1992 the Department of Conservation responsibilities for native fish, wildlife, flora and and Natural Resources (DCNR; now DNRE) 2 cultural heritage (MDBC 2000). 3 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

In July 1996, DLWC and SFNSW completed a Water Management Plan for the Millewa Forest, which incorporated many of the technical findings of earlier forest watering reports and the ongoing community consultation process developed by the MDBC. The plan also provided a statutory framework for the planning and co-ordination of water management tasks between the various agencies with responsibilities for land, water and wildlife in New South Wales (Leslie and Harris 1996).

Murray Irrigation Limited (MIL), a private irrigation company based in Deniliquin, provides irrigation to over 2400 farms covering 716,000 hectares in southern NSW. The Mulwala Canal, which is gravity fed water from Lake Mulwala (Yarrawonga Weir), is MIL’s major supply channel. MIL was established on 3 March 1995 when the NSW Government Murray Irrigation Area and Districts were privatised. The company has an entitlement of 1.445 million megalitres, which is 67% of the NSW share of Murray River irrigation entitlements (MIL 2001).

4 5 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

2. Literature Review (see Section 1.1) in the development of plans and strategies for the management of the Barmah-Millewa Forest.

2.1 Overview 2.1.1 Literature This section provides a critical review of the Table 2.1 and Table 2.2 list the literature reviewed in information relevant to the problem of unseasonal this section. The articles and publications also appear surplus flows (particularly rain rejection flows) in in the References section of this Report (Section 6). the Barmah-Millewa Forest. The literature includes information on the hydrology of the forest, changes to flooding regimes over time, the effect of these changes 2.2 Hydrology on flora and fauna, and the analysis and management of The most extensive, independent and refereed rain rejection events. collection of research on the hydrology of the Barmah Forest was authored or co-authored by Leon Bren The section emphasises the information available (Forestry Section, Faculty of Agriculture and Forestry, from refereed journal articles. However, comparisons The University of Melbourne) between 1984 and 1988. are also made with material available in government Other refereed research during the 1980’s focussed agency publications. This acknowledges the extensive on physiological aspects of flora and fauna (see scientific, engineering, regulatory and economic Section 2.3), or took a broad approach to hydrological research conducted by various government agencies investigation of Murray River forests in general.

Table 2.1 Refereed Journal Articles

• Bren, L. 1988a, “Flooding characteristics of a riparian red gum forest”, Australian Forestry, vol. 51, pp. 57-62.

• Bren, L. 1988b, “Effects of river regulation on flooding of a riparian red gum forest on the River Murray, Australia”, Regulated Rivers: research and management, vol. 2, pp. 65-77.

• Bren, L. 1992, “Tree Invasion of an intermittent wetland in relation to changes in the Flooding Frequency of the River Murray, Australia”, Australian Journal of Ecology, vol. 17, pp. 395-408.

• Bren, L. and N. Gibbs 1986, “Relationships between flood frequency, vegetation and topography in a river red gum forest”, Australian Forest Research, vol. 16, pp. 357-70.

• Bren, L., O’Neill, I. and N. Gibbs 1987, “Flooding of the Barmah Forest and its relation to flow in the Murray-Edward River system,” Australian Forest Research, vol. 17, pp. 127-44.

• Bren, L., O’Neill, I. and N. Gibbs 1988, “Use of map analysis to elucidate flooding in an Australian riparian river red gum forest”, Water Resources Research, vol. 24, no. 7, pp. 1152-1162.

• Chesterfield, E.A,, 1986, “Changes in the vegetation of the river red gum forest at Barmah, Victoria”, Australian Forestry, vol. 49, no. 1, pp. 4-15.

• Leslie, D.J. 2001, “Effect of river management on colonially-nesting waterbirds in the Barmah-Millewa forest, south-eastern Australia”, Regulated Rivers: Research and Management, vol. 17, iss. 1, pp. 21-36.

4 5 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Table 2.2 Other Publications

• Barmah-Millewa Forum (BMF) 2000, Annual Plan 2000-2001 for water operations and works in the Barmah-Millewa Forest, July.

• Department of Land and Water Conservation (DLWC) 1996, Unseasonal Surplus Flow Management - Barmah-Millewa Forest, June.

• Department of Conservation and Environment (DCE) 1992, Barmah Management Plan for Barmah State Park and Barmah State Forest, East Melbourne, September.

• Ife, D. 1998, The Hydrogeology of the Barmah Forest, Investigations Report No. 1988/32, Rural Water Commission of Victoria, November.

• Leslie, D. and K. Harris 1996, Water Management Plan for the Millewa Forests, State Forests of New South Wales, Deniliquin, July.

• Maunsell (Maunsell Pty Ltd) 1992a, Barmah-Millewa Forests Water Management Plan, Final Report, MDBC, January.

• Maunsell 1992b, Watering the Barmah-Millewa Red Gum Forest, Issues Paper, MDBC, January.

• McKinnon, L.J. 1997, Monitoring the Fish Aspects of the Flooding of Barmah Forest, Final Report to the Murray-Darling Basin Commission for Natural Resources Management Strategy Project V014, Marine and Freshwater Resources Institute, Queenscliff, October.

• MDBC 2000, The Barmah-Millewa Forest Water Management Strategy, on behalf of the Barmah- Millewa Forum, June.

• Murray Water Entitlement Committee (MWEC) 1997, Sharing the Murray - Proposal for defining people’s entitlements to Victoria’s water from the Murray, October.

• River Murray Commission (RMC) 1980, River Murray-Tocumwal to Echuca, River Regulation and Associated Forest Management Problems, Review Report, June.

• Thoms, M., P. Suter, J. Roberts. J. Koehn, G. Jones, T. Hillman and A. Close 2000, Report of the River Murray Scientific Panel on Environmental Flows, River Murray - Dartmouth to Wellington andthe Lower Darling River, Murray-Darling Basin Commission, June.

• Ward, K.A., C. Leitch, L.N. Lloyd and B.P. Atkins 1994, Interim Water Management Strategy for Barmah Forest, Victoria, Natural Resources Management Strategy of the Murray-Darling Basin Ministerial Council, Canberra and the Department of Conservation and Natural Resources, Victoria, August.

6 7 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Bren analysed the flooding frequency and duration considering changes in the duration of flooding of floods in the Barmah Forest, and examined the attributable to regulation (Bren, O’Neill and Gibbs relationship between flooding of the Barmah red gum 1987); forests and flow in the Murray-Edward River system. • Analysis of the geographic location of points of Details of Bren’s research included: higher flooding frequency. • Use of historic flow records and grid-cell analysis Subsequent to Bren’s period of research, various of flood maps drawn between 1963 and 1984 to management agencies with responsibilities for the determine the relationship between the extent Barmah-Millewa Forest and River Murray have of flooding in the Barmah Forest and the flow used Bren’s findings to aid development of water in the Murray-Edward River system. The study management plans and strategies. Both Maunsell determined that the peak flow of the Murray River (1992a, 1992b) and Leslie and Harris (1996) cite at Tocumwal is the best predictor of the extent of Bren’s relationship between the percentage of forest flooding (Bren 1988b; Bren, O’Neill and Gibbs flooded and the peak monthly flow of the Murray 1987); River at Tocumwal (see Figure 2.1) in their respective • Estimation of the mean and maximum duration management plans. of flooding in such a riparian red gum forest,

100

(%) 80

orest flooded 40

20 action of f Fr

0 0 50 100 150 200 250 Peak flow at Tocumwal ('000 ML day -1 )

Figure 2.1 Relationship Between Extent of Flooding in the Barmah Forest and Flow in the Murray-Edward River System

The derived relation between the maximum percentage of the forest inundated (P) and maximum daily flow at Tocumwal (Q) during the flood period for all major inundations between 1963 and 1984 is:

P = -435.40 + 47.6 ln (Q) Q<68 500 ML/day

P = 93.5 Q > 68 500 ML/day

6 Source: Bren, O’Neill and Gibbs (1987). 7 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Bren et. al. (1987) used this relationship to analyse The management agencies SFNSW and DNRE provide monthly changes in the extent of flooding (see Figure descriptions of forest hydrology and flow patterns in 2.2) pre- and post-Hume, to illustrate the impacts of their plans and strategies (Leslie and Harris 1996; DCE regulation. However, this analysis assumed that the 1992; Ward et. al. 1994). As these state government relationship between flow and flooding derived for the agencies are responsible for managing rain rejection period 1963-1984 was relevant for the period 1895- flows, they provided descriptions that were more 1963. It is likely that changes to the capacity of the detailed and included greater reference to regulators Choke (due to activities such as de-snagging) and the than in Bren’s research. introduction of raised levees and regulators in the forest have changed the threshold flow level at Tocumwal at For example, Bren (1988a) describes the river flow which forest flooding commences. It is possible that the through the Barmah-Millewa Forest by describing the frequency of “pre-Hume” floods illustrated in Figure geographical layout of the Edward River, “The Choke”, 2.2 is understated. Lake Hume, and the Ovens and Kiewa catchments, and

Figure 2.2 Pre-Hume and Post-Hume Flooding of the Barmah Forest

Pre-Hume Post-Hume

Jan. + Jan. + * Feb. + Feb. + ** Mar. + Mar. + *

April + April +

May + May +

June + June + ** * July + July +

Aug. + Aug. +

Sept. + Sept. +

Oct. ** + Oct. + Nov. + Nov. +

Dec. + ** ** Dec. +

0 20 30 40 50 60 0 20 30 40 50 60 P (%)

Upper and lower quartiles Range + Median * Outliers Extreme outliers

Box-and-whisker plots showing the monthly statistical distributions of the percentage P of forest flooded for the pre-Hume (1895 - 1929) and post-Hume (1935 - 1984) periods.

Source: Bren, O’Neill and Gibbs (1987). 8 9 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

provides details of channel and river capacities. In absence of moisture competition from the Moira grass. contrast, Leslie and Harris (1996) provide hydrological Bren’s findings are reiterated by Leslie and Harris descriptions of individual water management areas (1996), who emphasise that: (WMAs) in the Millewa Forests, referring to the flows of and drainage patterns into specific creeks, swamps Drying, rather than watering, is... a critical element and lagoons. in wetland management in the Millewa forests, as important ecological processes which sustain Excluding the Barmah-Millewa Forests Water the health and productivity of wetlands require a Management Plan (Maunsell 1992a), state government regular periodic drying phase in late summer and agencies’ water management plans do not include autumn. numerical hydrological analysis. However, one older publication by the Rural Water Commission of Victoria Other papers and studies examine the watering (Ife 1988) did present the results of a hydrogeological requirements of Forest vegetation, whether of a investigation of the Barmah Forest, including specific vegetation type such as the Moira grass plains hydrograph analysis of water table fluctuations. (Ward et. al. 1994), or a more general summary of flora water needs (Maunsell 1992b).

2.3 Flora and Fauna Research into fauna water requirements has not been less extensive than research into vegetation water This section reviews a sample of literature which requirement. Two more recent publications which presents research into the flora and fauna of the evaluate the effects of seasonal flooding on native fauna Barmah-Millewa Forest. As it is not an objective of this are Leslie (2001) and McKinnon (1997), who examined research project to conduct a rigorous investigation of native waterbirds and native fish respectively. the ecological impact of unseasonal flows, this section is brief and considers only a few of the many available refereed journal articles on flora and fauna of the 2.4 Rain Rejection Analysis and Management Forest. The majority of research which involves analysis of Agency publications frequently refer to Chesterfield rain rejection events and opportunities for managing (1986) when summarising the changes in the vegetation these flows is conducted by government agencies, of the Barmah State Forest due to the effect of river due to their responsibilities in managing River Murray regulation. This article also examines changes due to Flows and the Barmah-Millewa Forest. The MDBC reduction in frequency of burning, increased grazing does not currently have a publicly available working or by rabbits and increased domestic stock. It mentions technical paper on rain rejections. A detailed brief for that high summer river levels have contributed to tree a future study is expected to be finalised in April 2001, death, and emphasises that, in other areas, seepage into and the study is scheduled to commence during this low areas has caused some grassland to change into year (Brian Lawrence 2001, pers. comm., 8 March). rushland and trees to regenerate where previously there This section provides a chronological review of was none. management plans and strategies that have, at various The encroachment of moira grass plains by rushes levels of detail, addressed the problem of rain rejection and river red gum is also outlined in DCE (1992) and flows in the Barmah-Millewa Forest. Leslie and Harris (1996). Bren (1992) used grid cell Maunsell (1992a and 1992b) proposed that watering analysis to develop a model which extrapolated an using rain rejection flows and river freshes would be almost complete extinction of extensive grass plains a significant way to increase spreading of water in in the future. In certain areas, regulation causes plains the forest, Analysis of individual rain rejection events to suffer less flooding in the winter-spring period, with was presented in the Barmah-Millewa Forests Water a slightly earlier recession, which favoured survival Management Plan (Maunsell 1992b). The results of of river red gum germinants because of the reduced modelling runs indicated that rain rejection flows could depth and duration of flooding. The increased summer be used to water the forest. 8 flooding allows young seedling to develop in the 9 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

However, the rules for regulator operation presented Despite the lack of recent analysis into rain rejection in the Interim Water Management Strategy for Barmah management, Objective 2 of the Barmah-Millewa Forest (Ward et. al. 1994) do not reflect the use of rain Forest Water Management Strategy (2000) is rejection flows for environmental purposes. Rather, “to optimise use of river flows to enhance water the report made the following recommendations for management of the environment”. The strategies regulator operation during the irrigation season (1 relating to this objective are: January - 12 May): • Ameliorate, as far as is practicable, the impacts • regulators should be closed where possible; of river regulation exerted through high summer • full use should be made of the Mulwala Canal for flows and rain rejection flows; the diversion of rain rejection flows; • Where possible, and taking into account the needs • if the MDBC directs that rain rejection flows must of Forest users, reinstate a more natural wetting pass through the Barmah Forest, then flows should and drying cycle by managing water flows within be diverted through numerous small channels that the river and within the Forest to benefit ecosystem radiate from the Murray and feed infrequently requirements; flooded red gums, effluents which have channels • When possible, manage unseasonal Forest rather than open wetlands, and into Giant Rush flooding to minimise damage to environmental, dominated wetlands. commercial and recreational values, in that order; • When possible, manage summer and autumn These recommendations implicitly reflect the goal of Forest flooding to protect sensitive environmental minimising summer and autumn flooding of the forest, areas; particularly of Moira grass plains. This goal is also • When possible, manage summer and autumn emphasised in the Water Management Plan for the Forest flooding to protect, as far as is practicable, Millewa Forests (Leslie and Harris 1996), in which access by fire control, commercial and recreational the authors explicitly state that, unlike in Maunsell vehicles; (1992a and 1992b), there is a need for flood mitigation in summer and autumn: • Refine procedures for ordering irrigation water from Hume Dam and Yarrawonga Weir. ... rain rejection flows and other minor river surpluses, due to occasional availability of Furthermore, Thoms et. al. (2000) recommend that the short duration, low flow and possibly seasonally management of unseasonal summer-autumn flooding unfavourable river surpluses, should not form the should receive a “very high priority status.” The basis of a forest watering strategy. Opportunistic following management recommendations were made: river surpluses cannot be seen as a substitute for • During the period, December 1 to end of the natural floods which have sustained the floodplain irrigation season, Barmah Choke should be run forests and wetlands for many thousands of years. below channel capacity (i.e. < 10,600 ML/day at Tocumwal) in order to prevent summer flooding; In 1996 the DLWC conducted an investigation to assess and the options for managing unseasonal flows affecting • The [River Murray Scientific] Panel [on the Barmah-Millewa Forest. The analysis was of a Environmental Flows] insists on caution in using preliminary nature, and since 1996 little work has been regulators and recommends that a set of ecological, done in this area (Bryan Harper 2001, pers. comm., 19 engineering and hydrological guidelines for the March). The current Annual Plan 2000-2001 for water use of regulators to exclude high summer flows operations and works in the Barmah-Millewa Forest should be developed; the ecological criteria for (BMF 2000), describes the time-sharing arrangement developing these should be based on the impact between SFNSW and DNRE, in which 2001 is Barmah of altered linkages (two-way) between floodplain Forest’s turn to receive rain rejection flows. However, and river; and on local and regional benefits or the BMF has not allocated funds during 2000-2001 for disbenefits. research into rain rejection management.

10 11 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

These recent strategies and recommendations suggest that studies into rain rejection management might form the basis of research by management agencies in the near future. However, the issue of rain rejection management was first raised many years ago, at least as early as 1980 (RMC 1980). There is little evidence to suggest that implementation of the provisions of the current water management strategy is any more likely than the investigation of the recommendations made in previous studies.

2.5 Summary In the mid-1980s, Bren conducted significant and extensive research into the hydrology of the Barmah Forest. His use of grid-cell analysis resulted in important findings such as a quantification of the relationship between percentage of forest flooded and the flow in the Edward-Murray river system. Bren’s research is complemented by other studies which examine the consequences of changed flooding regime on flora and fauna.

From the mid-1980s to the present, government agencies have built on the findings of researchers such as Bren to develop water management strategies and plans for the Forest. Although Bren researched the hydrology of the Barmah Forest, similar hydrological relationships have been assumed for the Millewa Forest.

The most significant shift in management principles has been the move away from the idea of using rain rejection flows to water the forest (Maunsell 1992a, 1992b). Current management publications reveal a trend towards investigation of the use of environmental allocations for forest watering, and an emphasis of the need for (unnatural) summer and autumn flows to be managed to minimise impacts on the forest ecosystems.

10 11 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

12 13 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

3. Background Information proclaimed 7900 ha of the forest as Barmah State Park and two Reference Areas covering 280 ha. The remaining area is classified as State Forest.

3.1 Overview The Millewa Forest covers an area of 40,149 ha and is defined as the Millewa Group of Forests, which This section presents background information relevant consists of the Bama State Forest (3092 ha), Deniliquin to the analysis of unseasonal surplus flow events which State Forest (365 ha), Gulpa Island State Forest (5143 affect the Barmah-Millewa Forest. ha), Horseshoe Lagoon State Forest (15 ha), Mathoura State Forest (1ha), Millewa National Forest (20,457 3.2 Location ha), Moira National Forest (9996 ha), Tuppal National Forest (1040 ha), and Moama State Forest (40 ha). The Barmah-Millewa Forest is the collective name given to the Barmah Forest and the Millewa Forests The easternmost boundary of the Barmah-Millewa which comprise approximately 70,000 ha of wetland Forest lies approximately 2 days downstream of habitats on the floodplains of the Murray between Yarrawonga Weir, which is 4 days downstream of the Echuca, Deniliquin and Tocumwal. The Barmah- Hume Dam. Millewa Forest extends approximately 40 km north- south and 40 km east-west. See Figure 3.1 and Figure 3.2 for maps of the location of the Barmah-Millewa Forest. The Barmah Forest covers 29,500 ha of River Murray floodplain. In 1987 the Victorian Government

��

� � � � � ��

� � � ��

� � � �

�

� � � � � � � � �

� �

� ��

� � ��

Figure 3.1 Location of the Barmah-Millewa Forest

Source: DLWC (1996) 12 13 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

��

�

� ��

�

� � � � �

�

� � � �

��

� ��

��

� ��

� � � � ��

Figure 3.2 Locality Map of the Barmah-Millewa Forest

Source: Maunsell (1992a)

14 15 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

3.3 Natural Resources Prior to European invasion, the Yorta Yorta people occupied a stretch of territory located in what is now 3.3.1 Origin of the Barmah-Millewa Forests known as the Murray-Goulburn region. The majority Approximately 25,000 years ago, an uplift of land in of food was provided from the network of rivers, the southern Murray-Darling Basin created what is lagoons, creeks and lakes which include those in the now known as the Cadell Tilt Block (Cadell Fault). Barmah-Millewa Forest (Atkinson 2001). The edge of the 12 m high block runs north/south near Between 1860 and 1993 the Yorta Yorta made Deniliquin and Echuca. It influenced the course, pattern seventeen separate claims for compensation from and character of about 500 km of the River Murray. government agencies (Atkinson 2001). In 1994, Following the uplift, a large shallow lake was created they lodged a claim under the Native Title Act for by the dammed Murray and Goulburn rivers. The recognition of their native title rights to, and interests Murray took a new course around the northern side of in, public lands and waters in the region (Seidel 2001). the Fault (now referred to as Wakool channel), the river However, in December 1998, the Federal Court ruled bed of which is today occupied by the Edward River. that any native title held by the Yorta Yorta (based on For thousands of years the Goulburn River continued a continuing traditional connection the land) had been to feed the lake but it eventually also broke out to the “washed away” during the 19th century. On 8 February west. 2001, the full Federal Court rejected the Yorta Yorta’s appeal (Farrant 2001a). In March 2001, lawyers (acting Around 8000 years ago, the Murray turned south, on behalf of about 4000 claimants) filed an application breaking through the section between Picnic Point and seeking special leave to appeal to the High Court, Barmah (taking over the Goulburn channel downstream which was subsequently granted (Farrant 2001b). of Echuca). This section is today known as the Barmah Choke. 3.3.3 Vegetation Associations

During major floods, large volumes of water bank up The Barmah and Millewa Forests is the largest river red behind Barmah Choke, flooding the former lake area. gum (Eucalyptus camaldulensis) forest in the world. This flooding created a wetland (Barmah-Millewa The area is called a forest because of the predominance Forests), which contain flora and fauna that are typical of red gums but it could also be termed a wetland of a region which receives three times more rainfall because of its frequency of flooding and the mosaic than it does (MDBC 2001c). of open water bodies, swamps, meadows, and marshes that occur within the red gum forest. 3.3.2 History and Heritage The red gum and affiliated box forests and woodlands The forest’s cultural landscape reflects both Aboriginal are often associated in the vicinity of watercourses, and European activities. Evidence from the Willandra in sites which receive regular flooding (or overlie Lakes area in NSW suggests that Aboriginals first accessible groundwater contained in sandy aquifers). lived in the region over 40,000 years ago, and that the These forests usually have a grass or sedge dominated mid-Murray area would have supported about 4800 understorey with the presence of shrubs being relatively people before European occupation. The diversity of rare. River red gum forests tend to have a low species Aboriginal site types in the area, including occupation diversity, due to the requirement of understorey species sites, burial grounds, canoe trees, shell middens, and to survive seasonal flooding followed by moisture mound sites, gives the forests importance due to the stress over summer, and the possible effect of toxic unusual richness of these features. inhibition by red gum litter (Chesterfield 1986). In contrast, box woodlands have a comparatively rich Relics of early European settlement are scattered herbaceous understorey, though the number of native around the Barmah-Millewa Forest. However, the species present and regeneration of shrubs may have historical value lies in the impact of events on the been reduced. forest, rather than the remains of settlement itself.

14 15 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

The flora of the Barmah Forest consists of more than 3.3.5 Hydrogeology 550 species, of which approximately 30 per cent are The forest geology comprises a sequence of exotics. The majority of species are herbaceous, with unconsolidated clay, silt and sand deposits derived only about 40 species having tree or shrub habit. At from ancient fluvio-lacustrine environments (Maunsell least one third of the flora is associated with the box 1992a). The geological characteristics include: woodlands which occupy only 3.6 per cent of the forest area (Maunsell 1992a). • a shallow system dominated by silty and clayey sediments having low hydraulic conductivities; Vegetation Classification • channelised sand bodies interspersed within this There are two widely referenced classification schemes low hydraulic conductivity system; for the forests along the River Murray. Chesterfield - which have higher hydraulic conductivities et al (1984) identified thirteen vegetation types in the - may supply water to covering forest Barmah Forest based on the composition and structure of the dominant species, and a number of understorey - are partially or fully saturated associations. Smith (1983) classified the red gum - may be confined or unconfined forests according to “site quality”, which was based on - have some potential for upward leakage of mature red gum height (SQ I > 30m, SQ II 21-30 m; groundwater (Shepparton Formation) to the SQ III < 21 m). In contrast, relatively little systematic shallower aquifers information on understorey associations is available for the Millewa Forest (Maunsell 1992a). The more The hydrogeology of the Riverine Plain has been detailed information for the Barmah Forest cannot particularly influenced by the modifications brought be directly applied to the Millewa Forest, because about by broadacre irrigation. Consequently, in order of significant wetland types in the two areas, and the to maintain or improve the health of the trees it may be absence of moira grass in the Millewa Forest. desirable to reduce the depth to the shallow water table in certain areas. 3.3.4 Fauna Forests and wetlands in the Barmah-Millewa Forests 3.3.6 Sedimentology are an important habitat for wildlife, and are particularly Sedimentation in the wetland areas of the Barmah significant as a breeding area for waterbirds. The Forest appears to have increased during the last 50 - Barmah Forest, for example, is inhabited by 31 species 100 years. Studies have inferred average sedimentation of mammals, 219 birds, 16 reptiles, 8 amphibians, and rates of between 1.6 - 3.8 mm/year (Maunsell 1992a). at least 21 species of fish (DCE 1992).

The significance of the Barmah-Millewa forest habitats 3.3.7 Climate are recognised in international treaties. The Barmah DCE (1992) classified the climate of the Barmah- forest has been declared a wetland of international Millewa Forest as “temperate hot summer”. significance under the Ramsar convention. Two international treaties, the Japan-Australia Migratory Rainfall Birds Agreement (JAMBA) and the China-Australia Rainfall across the central Murray Valley decreases Migratory Birds Agreement (CAMBA) recognise that from south-east to north-west as the influence of certain birds migrate between Australia and Japan, and the eastern highlands diminishes. Winter rainfall is Australia and China. Eight species of migratory birds typically of low intensity, whilst summer falls are which inhabit the Barmah-Millewa Forests in summer usually the result of heavy thunderstorms. Mean annual are protected under these Agreements (Maunsell rainfall is about 400 - 450 mm. 1992a).

16 17 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Average rainfall statistics for Echuca, Barmah and 3.4 Forest Uses and Resources Tocumwal are presented in Figure 3.3. 3.4.1 Utilisation Evaporation Utilisation of the Barmah Forest for timber, grazing, Annual evaporation for the region is approximately apiary and other purposes is permitted under the 1400 mm, almost half of which occurs between National Parks Act 1975 and the Forest Act 1958 December and February, and two thirds between (DEC 1992). These activities also occur in the Millewa November and March (DCE 1992). Forest.

Temperature Timber and Wood Products The hot season commences in November and extends Extensive logging has been carried out in the Barmah- until March, with mean maxima and minima ranging Millewa Forests since the 1860s. It has been estimated from 31 to 15ºC in the hottest month of January. that over 2.5 million cubic metres of river red gum Maximum and minimum temperatures in the coldest logs have been harvested since that time in the Barmah month of July range from 13 to 4ºC (BOM 2001). Forest alone (DCE 1992). During 1999/2000, the Barmah Forest red gum timber and wood products The average frost-free period lasts about 7 months yield comprised 4099 m3 of sawlogs, 1012 m3 of from late October to mid May. Severe frosts are limited residual, 7866 sleepers, 355 m3 of hewn, 350 bushsawn to a period of eight weeks in June, July and August pieces and 5720 m3 of firewood (Lacey 2001). A small (DCE 1992). volume of grey box (Eucalyptus microcarpa) is also cut. Yellow box (Eucalyptus melliodora) and black box (Eucalyptus largiflorens) are not harvested (Maunsell BACK GROU N D IN FORMAT I ON 1992a).

��

� ��

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

��

Figure 3.3 Rainfall Statistics �� Source: BOM (2001). ��

16 17 ��

��

�� ∞� �� ∞��

��

�� COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Grazing Other regulation has since included (Bren 1988b; RMC The Barmah Forest has been grazed by stock since 1980): 1840. Since 1885, sheep have been excluded from the • construction of Yarrawonga Weir (1939); forest and grazing has been restricted to cattle (DCE • progressive raising of levees and installation and 1992). There are seven grazing licences in the forest modification of regulators (1939-present); and 50 agistment permit holders (Lacey 2001). Grazing • channel modifications through the forest; currently occurs in the forest in summer and autumn, • de-snagging of the Choke (1950’s); with fences used in an attempt to restrict access to sensitive environmental areas (Maunsell 1992b). In • Kiewa hydroelectric Scheme (1945-1960); 1999/2000 the Barmah Forest was grazed by 1505 • Snowy Mountains Hydroelectric Scheme (1955- head of cattle in summer and 923 head in winter (Lacey 65); 2001). • limited bypassing of the forest by the Mulwala Canal (1941); Apiculture • construction of Buffalo Reservoir (1965); Apiary sites are held under permit allowing bee keepers • construction of Dartmouth Reservoir (1973- to follow the flowering of red gum and box species. 1979).

3.4.2 Recreation and Tourism A major aim of regulation has been the maintenance The forest provides a high value recreation resource of a minimum summer irrigation flow (Bren 1998b). attracting hundred of thousands of people each year Except for the Kiewa and Ovens Rivers, all of the for camping, swimming, fishing, boating, bushwalking Murray’s tributaries below Hume Dam are regulated. and other activities. Inflows from tributaries such as the Murrumbidgee and Goulburn Rivers have been greatly diminished through regulation and use of their waters. 3.5 Hydrology of the Regulated System Flow Characteristics and Patterns This section describes the hydrology of the regulated The channel capacity in the Murray through the forests system as relevant to the cause and management of can cope with a maximum regulated release of about unseasonal flows which affect the Barmah-Millewa 11,400 ML/day from Yarrawonga weir without the Forest. occurrence of significant losses to the forests, when regulators are closed (DLWC 1996). Current MDBC 3.5.1 The Regulation of the River Murray operational procedures allow closed forest regulators History until the flow at Picnic Point exceeds the gauge height The River Murray Waters Agreement (1915) provided of 2.53 m, which corresponds to about 10,600 ML/day for the construction of 26 weirs with locks to ensure at Tocumwal. permanent navigation upstream to Echuca. By the time Bren (1998a) derived flow duration curves for construction of locks commenced in 1922, the main Tocumwal for the pre- and post-Hume periods which purpose of weirs had changed to maintaining a supply show the consequences of regulation: of water for irrigation. • increased frequency of flows in the range 6000 - The other major provision of the Agreement was 10,000 ML/day the construction of an upper Murray storage, so that • decreased frequency of flows in the range 10,000 river flow could be maintained during drought, and - 60,000 ML/day irrigation development greatly expanded. Hume Dam • little effect on the frequency of flows above 60,000 was constructed between 1919 and 1936, and enlarged ML/day in 1961 to its present capacity of 3038 GL. Between Yarrawonga and the Barmah-Millewa Forests the course of the River Murray travels west through the 18 19 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Riverine Plain. Flows may inundated large low-lying 3.5.3 Yarrawonga Weir Diversions areas in the forests, before breaking out on the north From Yarrawonga Weir, irrigation water is diverted side into many anabranches, the principal of which is into Mulwala Canal and the Yarrawonga Main the Edward River. The courses and anabranches of the Channel. The Mulwala Canal supplies part of the Riverine Plain system help to spread a large flood over Murray Irrigation Area (NSW), and is privately owned a very wide area (Maunsell 1992a). and management by Murray Irrigation Limited (MIL). The Yarrawonga Main Channel, which supplies the 3.5.2 Unseasonal Surplus Flows Murray Valley Irrigation Area (Victoria), and is owned DLWC (1996) broadly identified unseasonal surplus and managed by Goulburn-Murray Water (GMW). The flows as those occurring in the period November to maximum operational diversions are 10,000 ML/day May which exceeded the regulated flow limit (11,400 into Mulwala Canal and 3000 ML/day into Yarrawonga ML/day) downstream of the Yarrawonga Weir. This Main Channel. limit is currently under question since overbank GMW and MIL relay irrigators’ water orders to the flooding has been observed at this flow. Weir Keeper at Yarrawonga and the MDBC who Unseasonal surplus flows are generated from rain determine releases from Hume Weir. These agencies rejection flows and river freshes, which often occur in are charged for cancelled water orders which are not combination. Rain rejection flows are defined as flows diverted from Lake Mulwala only if the water cannot released from the Hume Dam during the irrigation be used along the Murray downstream, a situation season but not diverted into the irrigation areas from which rarely occurs (DLWC 1996). Mulwala Lake (the Yarrawonga Weir pool). These Lake Mulwala is maintained near its full supply level flows results when rainfall over the irrigation areas of 117,330 ML to achieve the maximum diversion causes landholders to cancel water orders which are rate necessary to each State. This limits its capacity to already in transit. River freshes are small excess flows mitigate rain rejection flows. in the unregulated tributaries of the Murray upstream of the forest (the Ovens and Kiewa Rivers), and are generated by local rainfall. 3.5.4 Murray Irrigation Area (New South Wales) Description At the onset of an unseasonal surplus flow, the MDBC The Murray Irrigation Area (MIA) comprises five notifies the forest management agencies who then irrigation districts extending from Yarrawonga Weir to negotiate an outcome on how these flows will be the lower Edward River system near Swan Hill. Along distributed (Maunsell 1992a). A time-sharing flooding its course the channel capacity of the Mulwala Canal arrangement exists between SFNSW and DNRE, diminishes as flows are diverted into a network of in which Barmah Forest and Millewa Forest accept smaller canals and supply channels (see Figure 3.4). unseasonal summer flows in alternate years (BMF 2000). Operating Procedure for Water Order Cancellations

There is generally limited scope to control unseasonal MIL reduces inflow diversions from Lake Mulwala flows within bank and outflows into the Barmah- and bars-up the regulators along the canal. Irrigators Millewa forest result. When these flows occur, releases are required to take the first 12 hours of their rejected from Hume Dam are reduced to conserve water and to water order. Excess water in Mulwala Canal is released limit downstream impacts. The MDBC limits this rate via escape structures into the Edward and Wakool of reduction to a decrease in river level at Doctors Point Rivers. Operational rules for the Edward escape mean of 150 mm per day (about 1500 ML/day) to minimise that, after 15 December, there is a 300 ML/day capacity the risk of bank slumping (Maunsell 1992a). for passing rain rejections. Further downstream, the two escapes into the Wakool River have a combined operational escape capacity of 80 ML/day.

18 19 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

3.5.5 Murray Valley Irrigation Area (Victoria) Operating Procedure for Water Order Cancellations Description Diversions from Lake Mulwala into Yarrawonga Main Channel are reduced according to the volume of water The Murray Valley Irrigation Area extends from orders cancelled, up to a maximum daily reduction of Lake Mulwala to the area bordered by Broken Creek 2500 ML. Excess water supply already in the channel to the south of the Barmah forest. See Figure 3.5 for system is released into outfall channels which drain the location of the irrigation area and its generalised into the River Murray or Broken Creek (DLWC 1996). layout. Runoff from landholders is carried from the irrigation

��

� ��

��

� ��

��

� �� Figure 3.4 Murray Irrigation Area from Lake Mulwala to the Wakool Escape Source: DLWC (1996)

�

� ��

��

� � � � � ��

��

�� Figure 3.5 Murray Valley Irrigation Area Source: DLWC (1996). 20 21 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

area by a series of channels which drain into creeks in 3.6 Forest Hydrology the Barmah forest, the Murray River and into Broken Creek, and may exacerbate unseasonal flooding 3.6.1 Water Management Areas problems. The Barmah-Millewa Forests Water Management Plan (Maunsell 1992a) defined seventeen water management Overall, there is little scope to escape excess water areas (WMAs) for the Barmah-Millewa Forest (see from the irrigation area without impacting on forest Figure 3.6). These subdivisions were established flooding. mainly on the basis of natural water distribution

��

�

� ��

�

� � � � �

�

� � � �

� �

� ��

� �

� � � � � ��

��

� � � ��

� � � � ��

Figure 3.6 Water Management Areas

20 Sources: Maunsell (1992a). 21 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

networks, these natural patterns of watering dictated • natural (and raised) levees on both sides of the by the topography of the region. The purpose of River Murray; distinguishing separate water management areas was • block banks; to enable the prioritisation of management activities • closing of regulators. within the Forest. Control is loss and progressive overtopping of banks 3.6.2 Flow Characteristics of the Barmah-Millewa occurs for flows beyond 18,000 ML/day with the Forest regulators open (Maunsell 1992a). Geomorphology Most of the flood flow entering the Millewa forests The flow characteristics in the forests are dictated leaves the River Murray and flows past Deniliquin in by the topography of the region, which has in turn the Edward River. It then enters the Edward-Wakool been determined by the morphologic development system, finally returning to the River Murray some of the river system. The flow patterns in the forest 200 km to the west at Wakool junction (Maunsell are constantly changing, as log or earth barriers alter 1992b). Most of the flow entering the Barmah Forest in height or position, and silt is deposited on flooded returns to the River Murray through Lake Barmah areas. The flat terrain means that a variation ofa (Maunsell 1992b). few centimetres in a barrier across a waterway can markedly affect the location and depth of flooding Flow Patterns (Maunsell 1992a). Flows occurring in the Barmah-Millewa Forest have been divided into two main types of flow pattern Within both forests, ground levels fall generally from (Maunsell 1992a). Channel flow is identified as east to west, from 104 m AHD at the eastern limit of the dominated by flow in channels, depressions or leads), Forests to 93 m AHD to the west (35 km). The gradient whereas broad area flooding spreads and ponds over is uniform over the majority of the length, but flattens broader areas. See Figure 3.7 for a map of broad area significantly in the lake and swamp areas to the west. flooding. The small scale topography of the forests is varied, with topographic features including ridges, depression, Barmah Forest is watered by broad area flooding. As gullies and creeks. indicated by field observations and the relationship derived by Bren, O’Neill and Gibbs (1987), significant Flow Characteristics flooding occurs at a relatively low flow at Tocumwal Under moderate conditions, River Murray flows in (approximately 9000 ML/day). At flows greater than excess of 60,000 ML/day at Tocumwal bypass the forest 68,500 ML/day, 93.5 per cent of the forest is flooded area to the north via the overflow system of Bulltale (see Figure 2.1). and Tuppal Creeks. Remaining River Murray flows in excess of 25,000 ML/day leave the river channel and The main example of channel flow in the Barmah flood into the forests before the Black Engine Creek Forest occurs in the downstream section of the Tullah offtake. Flows greater than 10,000 ML/day which still Creek. Compared to broad area flooding, significantly remain in the channel leave the river channel and flood higher river flows are required to inundate the adjacent into the forests between Black Engine Creek offtake area. and Poverty Point. The documentation and mapping of floods in the There are many effluent creeks in the forests which have NSW forests has not been as thorough as for Victoria. offtakes which cut through the levees and allow water However, indications are that the dominant flow pattern into the forests at quite low river flows. In general, flow to the north of the River Murray is channel flow. enters the Forests through these breaks in the natural “The Choke” levee, rather than by overtopping the levee. Regulators have been constructed at the offtake to many of these “The Choke” refers to the reach of the River Murray effluent creeks. Consequently, high regulated flows are between the township of Barmah and the junction of the Edward River. This reach has the lowest channel 22 prevented from flowing into the forests by: 23 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

capacity (10,600 ML/day) between Lake Hume • once substantial flooding occurs the water leaves and South Australia (Thoms et. al. 1998). Another the Murray channel and passes into the Edward 2500 ML/day can be passed through the Edward River River system to the north; and and associated creeks bypassing the Choke. • because of the need to increase summer flows through this section to meet downstream irrigation The presence of the Choke has several effects (Bren commitments, channel modifications have been 1998b): introduced (including raised river levees and the • if river flow exceeds channel capacity then forest construction of effluent regulators). flooding occurs;

��

�

� ��

�

� � � � � ��

�

� ��

� � � � ��

�

� � �

��

� ��

��

� � � ��

� � � � ��

Figure 3.7 Flooding of the Barmah-Millewa Forest Source: Maunsell (1992a). 22 23 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

3.6.3 Drainage Systems for Unseasonal Flows wetlands along the Gulf Creek system have high Barmah Forest ecological value. However, as the gulf regulator represents more than 50 per cent of available regulator The two major creek systems which carry surplus flows capacity (5000 ML/day), its use is necessary when into the Barmah Forest are Tullah Creek, and Gulf passing larger unseasonal flows into the Barmah forest Creek. These are generally carried in defined creek (DLWC 1996). channels, spreading over wetland areas along their course, and draining towards the Murray River at the Millewa Forest downstream end of the forest via Barmah Lake. The three drainage systems which operate in the Tullah Creek passes through the length of the forest. Millewa forest during unseasonal flood events are the Tullah Creek receives inflows from the Murray at its eastern section of the forest upstream of the Lower offtake (Kynmer Creek), from the unregulated Black Toupna Creek, the section of the forest between Lower Engine Creek / Tongalong Creek system and from the Toupna Creek and the Edward River, and downstream regulated Sandspit Creek. of the Edward River (see Figure 3.8 for drainage network). Gulf Creek carries flows released through the Gulf regulator, and smaller downstream regulators. The The channel capacity of the Murray River in eastern Millewa, upstream of Lower Toupna Creek (Aratula

��

� � � � � ��

��

�

� �

� � � ��

� � � � � � � � ��

� � ��

Figure 3.8 Eastern Barmah-Millewa Forest Drainage Network

Source: DLWC (1996).

24 25 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

WMA), is relatively large and in the range of 25,000 It is degrading wetlands by interfering with the - 35,000 ML/day (Leslie and Harris 1996). Cancelled natural drying-out phase and by disrupting nutrient irrigation flows are maintained within the bank of the cycling processes. Subsequently, the productivity of river and in NSW below the sill level of effluents. the wetlands has been reduced and habitat values, Consequently, only the Lower Toupna Creek in the particularly for waterfowl breeding, have been Aratula WMA is regulated. Flows leave the forest via seriously diminished. Frequent unseasonal flooding is Seven Mile Creek and Deep Creek. contributing to extensive tree deaths by overwatering, as roughly 300 hectares of red gum fringing Moira The channel capacity of the Murray between Lower Lakes are dying from prolonged inundation, and Toupna Creek and the Edward River is restricted and similar effects have been identified along the Edward offtake streams are regulated to prevent outflows from and Gulpa systems (Maunsell 1992a). irrigation flows. The Mary Ada regulator (2800 ML/ day) is the largest of the Millewa forest regulators and In addition to killing areas of forest, prolonged summer is most frequently used to divert surplus flows from the inundation is modifying the floristic structure in major Murray. the remaining regulators have relatively low wetland systems such as increasing the abundance capacity (15-630 ML/day) (DLWC 1996). of water milfoil and clove strip and changing some grasslands into perpetual swamps (Chesterfield 1986). The channel capacity is also restricted downstream The encroachment of Moira grass plains by rushland of the Edward River. Moira Lake, a large wetland at and red gum, due to the increased frequency of the downstream end of the forest, is inundated during summer flows, is well documented (Maunsell 1992a, surplus flow events. Chesterfield 1986, Ward et. al., 1994, Bren 1992). Chesterfield (1986) estimated that since 1930, 1200 ha In the event that unseasonal surplus flows are to be (30 per cent) of the Moira Grass plain has been lost to directed into the Millewa Forest, the operational plans Red Gum regeneration and a further 1200 ha to Giant for flows 15,000 to 18,000 ML/day are to open the Rush (Juncus ingens) encroachment. Walthours, Nestrons, Nine Panel Pinchgut and House regulators, then the top gates of the Mary Ada. The Impacts on Forest Access bottom gates of the Mary Ada are opened once flows Unseasonal flooding of the Barmah-Millewa forest exceed 18,000 ML/day (BMF 2000). during summer and autumn adversely affects commercial operations and recreational use of the 3.6.4 Unseasonal Flooding forest. Restricted access for logging and stockpiling has Changes to Flooding Regime significant economic impacts on the timber industry. The natural flood regime of the Barmah-Millewa Access problems also affect local tourism activities Forest generally consisted of a cycle of flooding during during the Christmas and Easter peak visitation winter and spring and a dry period during summer and periods, and bee-keeping and grazing activities. Fire autumn (Maunsell 1992a). Under natural conditions, suppression management in summer is impeded when 70 per cent of the forest flooded for an average of 2.9 floods block off access tracks. months in 78 per cent of years. Since the completion of the Hume Dam, this level of flooding is only experienced for an average of 1.3 months in 37 per cent of years (Bren 1988a; DCE 1992). Furthermore, in pre-Hume period, summer flooding in January-March was effectively unknown. However, with regulation to maintain irrigation supplies, small inadvertent floods have become common (Bren 1988a).

Ecological Impacts As introduced in section 2.3, unseasonal flooding has a significant effect on the ecology of the forest. 24 25 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

26 27 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

4. Research Methodology 4.2 Initial Research Phase (Chapters 1 to 3) The emphasis of the initial research phase was to document, investigate and understand the physical, regulatory, institutional and economic environment of 4.1 Overview the problem. This section presents an outline of the research methodology which enabled : The information gained in the initial research phase was used to identify and evaluate possible avenues • an evaluation of how the frequency of unseasonal of research, and to determine data requirements and surplus flows is related to system flexibility; and availability. • an analysis of the costs and benefits involved with increasing system flexibility to reduce this The research steps conducted in this phase included: frequency. • identification of problem; The development of this research methodology and • identification of stakeholders and management associated data requirements, which included analysis agencies responsible for the use of the Barmah- and evaluation of different research avenues, was Millewa Forest and the River Murray; documented in the Preliminary Report. It is reproduced • literature review of information available in in full in Appendix A. refereed journals and other publications, including an overview of the evolution of management A detailed description of analytical methodology is principles and practices for the region; presented in each of Chapters 5 to 8. • documentation of background information relevant Components of Research Methodology to the project. 1. Identification and definition of problem (Chapters These steps enabled an understanding of the complex 1 to 3). physical system and the identification of agencies and 2. Analysis of historical data to investigate changes institutions from which further information would be in River Murray flows (caused by regulation), and available. to investigate changes in patterns of flooding in the Barmah-Millewa Forest (Chapter 5). 3. Definition of different methods for identifying 4.3 Historical Analysis (Chapter 5) individual unseasonal surplus flow events (for This analysis involved the use of historical data the period in which the current level of river (daily flows at Tocumwal) to compare pre-regulation regulation and irrigation demands is thought to (1908 - 1929) conditions with present (1981 - 2001) apply). Application of these methods to calculate conditions. such characteristics as total excess volume and peak excess flow rate. Comparison between This analysis determined: results of different methods, and selection of • whether regulation has caused changes in the most “appropriate” method to be used in further pattern of summer-autumn River Murray flows; research (Chapter 6). • whether regulation has caused changes in the 4. Analysing the effects of increased system pattern of summer-autumn Barmah Forest floods; flexibility (increasing airspace at Yarrawonga, • which months in the summer-autumn period and limiting maximum River Murray flow at have experienced a significant increase in forest Tocumwal) of unseasonal surplus flow volumes, flooding. frequencies and event characteristics (Chapter 7). 5. Identify and evaluate selective economic benefits This comparative analysis was facilitated by the and costs of increasing system flexibility to construction of bar and line graphs. reduce the frequency of unseasonal surplus flows (Chapter 8). 26 27 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

The analysis of changes in the frequency of forest • a “lower limit” indication of economic benefits flooding involved consideration of different threshold associated with: Tocumwal flows at which forest flooding commences. • increasing air space at Lake Mulwala; and The analysis of the changes in the areal extent of forest • reducing the flowrate of the Murray between flooding involved the use of the relationship derived by Yarrawonga and the Choke. Bren et. al., (1987).

4.4 Identification of Unseasonal Surface Flow Events (Chapter 6) Different methods for identifying unseasonal surplus flow events were identified in the literature. Three of these methods were used to identify various characteristics related to unseasonal surplus flow events and frequency of forest flooding.

The results of these three methods were compared, and their degree of overlap evaluated.

The advantages and disadvantages of each method were outlined, and one method selected for use in further analysis.

4.5 Analysis of Increased System Flexibilty (Chaper 7) This analysis quantified (through graphical representation) the (individual) effects of: • increasing airspace at Yarrawonga; and • limiting maximum River Murray flow at Tocumwal during December-April;

on: • flooding frequency (proportion of days in season during which flooding occurs in the forest); • number of events per season; • event duration; and • total surplus flow volume per season.

4.6 Economic Analysis (Chapter 8) This analysis identified both market- and non-market costs and benefits. Given resource and data constraints, only selected costs and benefits were quantified. These were selected to provide: • an “upper limit” indication of economic costs, or

28 29 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

5. Historical Analysis River Murray flow at Tocumwal was selected because it was identified by Bren et. al. (1987) as the most significant factor relating to the percentage flooded of the Barmah Forest. Various management plans and 5.1 Overview strategies also cite the flow at Tocumwal as indicative This section presents the data requirements, of the restrictive capacity of the Choke. A record of methodology, results and analysis of historical changes significant length (1908 - present) for mean daily flows in the patterns of summer-autumn River Murray flows is readily available for Tocumwal from RMW. (at Tocumwal) and forest flooding. The purpose of the The months November - May were selected because historical analysis is to define which months comprise this represents the widest range of months suggested the “summer-autumn period” during which regulation in publications as the season in which rain rejections has increased flooding of the Barmah (and Millewa) occur (DLWC 1996). Forest. Key periods were identified to represent the intervals The historical analysis comprises two main parts. between successive, major changes to regulation of First, River Murray flow at Tocumwal is analysed on a the Murray upstream of the forest. The following time month-by-month basis to compare present flows (1981 periods were used in the analysis: - 2001) to flows which occurred before regulation (1908 - 1929). Second, frequency and areal extent of • 1908 - 1929 Before the construction of the forest flooding is analysed on a month-by-month basis Hume Dam; to compare present patterns of forest flooding (1981 - • 1936 - 1960 After the construction of the 2001) to the pattern of forest flooding before regulation Hume Dam, and before its (1908 - 1929). enlargement; • 1961 - 2001 After the enlargement of the Refer to Appendix B for supporting documentation of Hume Dam; the data analysis. • 1981 - 2001 “Present” level of regulation (representing current irrigation 5.2 Data demand conditions).

The mean daily flows of the River Murray at Tocumwal The descriptive statistics for these periods for the HISTORICAL ANALYSIS from 2 January 1908 to 15 March 2001 were divided months November - May are illustrated in Figure into flows occurring in the months of November, 5.1. Characteristic to all months is the reduction in December, January, February, March, April and May standard deviation from 1908 - 1929 to 1981 - 2001, Figure 5.1 Descriptive statistics respectively. i.e. regulation has reduced the variability of flows.

November Statistics

40000 160000 140000 30000 120000 100000 20000 80000

60000 ML/day Standard Deviation 10000 40000 20000 0 0 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Period

Standard Deviation Mean Median Minimum Maximum

Figure 5.1 Descriptive Statistics 28 December Statistics 29

25000 100000 20000 80000 15000 60000 10000 40000 ML/day Standard Deviation 5000 20000 0 0 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Period

Standard Deviation Mean Median Minimum Maximum

January Statistics

15000 60000 50000 10000 40000 30000 ML/day

Standard 5000 20000 Deviation 10000 0 0 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Period

Standard Deviation Mean Median Minimum Maximum

PAGE: 35 DATE: 1/05/03 FILE: BMReport HISTORICAL ANALYSIS HISTORICAL ANALYSIS

Figure 5.1 Descriptive statistics Figure 5.1 Descriptive statistics

November Statistics November Statistics 40000 160000 40000 140000160000 30000 120000140000 30000 100000120000 20000 80000100000 20000 80000 60000 ML/day Standard Deviation 10000 4000060000 ML/day Standard COOPERATIVE RESEARCHDeviation CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY 10000 2000040000 0 020000 0 0 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Period Period Standard Deviation Mean Median Minimum Maximum Standard Deviation Mean Median Minimum Maximum

December Statistics December Statistics 25000 100000 25000 100000 20000 80000 20000 80000 15000 60000 15000 60000 10000 40000 ML/day Standard Deviation 10000 40000 ML/day Standard Deviation 5000 20000 5000 20000 0 0 0 0 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Period Period Standard Deviation Mean Median Minimum Maximum Standard Deviation Mean Median Minimum Maximum

January Statistics January Statistics 15000 60000 15000 60000 50000 50000 10000 40000 10000 40000 30000 30000 ML/day

Standard 5000 20000 Deviation ML/day

Standard 5000 20000 Deviation 10000 10000 0 0 0 0 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Period Period Standard Deviation Mean Median Minimum Maximum Figure 5.1 DescriptiveStandard statistics Deviation (continued)Mean Median Minimum Maximum

February Statistics

PAGE: 35 PAGE: 35 6000 DATE: 24000 1/05/03 ATE 5000 DFILE: 20000 BMReport1/05/03 FILE: BMReport 4000 16000 3000 12000 ML/day

Standard 2000 8000 Deviation 1000 4000 0 0 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Period

Standard Deviation Mean Median Minimum Maximum

Figure 5.1 DescriptiveMarch Statistics Statistics (continued)

6000 24000 5000 20000 30 31 4000 16000 3000 12000 ML/day

Standard 2000 8000 Deviation 1000 4000 0 0 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Period

Standard Deviation Mean Median Minimum Maximum

April Statistics

25000 100000 20000 80000 15000 60000 10000 40000 ML/day Standard Deviation 5000 20000 0 0 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Period

Standard Deviation Mean Median Minimum Maximum Figure 5.1 Descriptive statistics (continued) Figure 5.1 Descriptive statistics (continued)

February Statistics February Statistics

6000 24000 6000 24000 5000 20000 5000 20000 4000 16000 4000 16000 3000 12000 3000 12000 ML/day

Standard 2000 8000 ML/day Deviation

Standard 2000 8000 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY Deviation COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY 1000 4000 1000 4000 0 0 0 0 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Period Period

Standard Deviation Mean Median Minimum Maximum Standard Deviation Mean Median Minimum Maximum

March Statistics March Statistics

6000 24000 6000 24000 5000 20000 5000 20000 4000 16000 4000 16000 3000 12000 3000 12000 ML/day Standard

2000 8000 ML/day Deviation

Standard 2000 8000 Deviation 1000 4000 1000 4000 0 0 0 0 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Period Period

Standard Deviation Mean Median Minimum Maximum Standard Deviation Mean Median Minimum Maximum

April Statistics April Statistics

25000 100000 25000 100000 20000 80000 20000 80000 15000 60000 15000 60000 10000 40000 ML/day

Standard 10000 40000 ML/day Deviation Standard Deviation 5000 20000 5000 20000 0 0 0 0 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 HISTORICAL ANALYSIS1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Period Period

Standard Deviation Mean Median Minimum Maximum Standard Deviation Mean Median Minimum Maximum Figure 5.1 Descriptive statistics (continued)

May Statistics

50000 200000 40000 150000 30000 100000 20000 ML/day Standard Deviation 10000 50000 0 0 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Period

Standard Deviation Mean Median Minimum Maximum

Figure 5.1 Descriptive Statistics (continued)

30 5.3 RIVER MURRAY FLOW AT TOCUMWAL 31

5.3.1 Methodology

For each month between November May, three graphs were constructed to present how the pattern of flows has changed with regulation. Each of these graphs divided the data into the time periods outlined in section 5.2.

1. Flow duration curve

The flow duration curves present plots of daily flow (ML/day) against percentage of time exceeded. They illustrate the cumulative distribution of flows, and provide indication of how the pattern of flows has changed with regulation.

2. Frequency column graph

The frequency column graphs provide alternative representations of how the pattern of flows has changed with regulation. For each of the flows 0 5000, 5000 10 000, 10 000 15 000 (etc) ML/day, a frequency column graph illustrates the frequency of daily flows which fall into each category, as a clustered column graph.

3. Stacked column graph

Stacked column graphs compare how the pattern of flows below 20 000 ML/day has changed with regulation. For each of the time periods, a stacked column graph illustrates the proportion of days in which flow was between 2000 4000, 4000 6000, 6000 8000, 8000 10 000, 10 000 12 000, 12 000 14 000, 14 000 16 000, 16 000 18 000 and 18 000 20 000 ML/day.

PAGE: 37 DATE: 1/05/03 FILE: BMReport COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

5.3 River Murray Flow at Tocumwal with regulation. For each of the flows 0 - 5000, 5000 - 10,000, 10,000 - 15,000 (etc.) ML/day, a frequency 5.3.1 Methodology column graph illustrates the frequency of daily flows For each month between November - May, three which fall into each category, as a clustered column graphs were constructed to present how the pattern graph. of flows has changed with regulation. Each of these 3. Stacked Column Graph graphs divided the data into the time periods outlined in Section 5.2. Stacked column graphs compare how the pattern of flows below 20,000 ML/day has changed with 1. Flow Duration Curve regulation. For each of the time periods, a stacked The flow duration curves present plots of daily flow column graph illustrates the proportion of days in (ML/day) against percentage of time exceeded. They which flow was between 2000 - 4000, 4000 - 6000, illustrate the cumulative distribution of flows, and 6000 - 8000, 8000 - 10,000, 10,000 - 12,000, 12,000 provide indication of how the pattern of flows has - 14,000, 14,000 - 16,000, 16,000 - 18,000 and 18,000 changed with regulation. - 20,000 ML/day.

2. Frequency Column Graph 5.3.2 November The frequency column graphs provide alternative Results are summarised in Figures 5.2 to 5.4. 5.3.2representations November of how the pattern of flows has changed

Results

Figure 5.2 Historical flow analysis: November: Flow duration curve

FLOW DURATION CURVE - November flow of River Murray at Tocumwal

80000

70000

60000

50000

40000

30000 Daily Flow (ML/day)

20000

10000

0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage of time exceeded

1908-1929 1936-1960 1961-2000 1981-2000 1908-2000

Figure 5.2 Historical Flow Analysis: November: Flow Duration Curve

Figure 5.3 Historical flow analysis: November: Frequency column graph

32 November Flow of River Murray at Tocumwal 33 50.0% 45.3% 45.0%

40.0%

35.0%

30.0%

25.0% 21.5%20.7%

Frequency 20.0% 16.2% 17.0% 15.0% 9.5% 10.0% 6.5% 6.2% 7.0% 6.7% 4.7% 4.5% 3.9% 5.0% 3.3% 3.7% 2.8% 3.6% 3.0% 3.0% 2.1% 2.3% 1.5% 0.0% 0.3% 0.6%0.5% 0.9%0.8%0.6% 0.8% 0.0% >70000 0 - 5000 5000 - 10 000 35000 - 40000 40000 - 45000 45000 - 50000 50000 - 55000 55000 - 60000 60000 - 65000 65000 - 70000 10 000 - 15 15 000 - 20 20 000 - 25 30 000 - 35 25 000 - 30 Daily Flow (ML/day)

1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 5.3.2 November

Results

Figure 5.2 Historical flow analysis: November: Flow duration curve

FLOW DURATION CURVE - November flow of River Murray at Tocumwal

80000

70000

60000

50000

40000

30000 Daily Flow (ML/day)

20000

10000

0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage of time exceeded

1908-1929 1936-1960 1961-2000 1981-2000 1908-2000

COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Figure 5.3 Historical flow analysis: November: Frequency column graph

November Flow of River Murray at Tocumwal 50.0% 45.3% 45.0%

40.0%

35.0%

30.0%

25.0% 21.5%20.7%

1908-1929 1936-1960 1961-2000 1981-2000 1908-2000

HISTORICAL ANALYSISFigure 5.3 Historical Flow Analysis: November: Frequency Column Graph

Figure 5.4 Historical flow analysis: November: Stacked column graph

November flows of the River Murray at Tocumwal under 20 000 ML/day

80%

70% 3.7% 3.6% 1.7% 3.0% 4.3% 5.3% 60% 7.5% 4.1% 4.8% 5.7% 18000 - 20000 ML/day 5.0% 50% 9.7% 16000 - 18000 ML/day 8.0% 8.0% 5.9% 14000 - 16000 ML/day 3.5% 12000 - 14000 ML/day 40% 8.2% 6.2% 10000 - 12000 ML/day 5.1% 8000 - 10000 ML/day 4.5% 6.3% 22.9% 6000 - 8000 ML/day 30% 10.5% 2.4% 31.0% 2.8% 4000 - 6000 ML/day 2000 - 4000 ML/day

Relative frequency of flows of frequency Relative 4.0% 12.9% 7.0% 20%

8.0% 14.1% 14.3% 11.3% 10% 5.6% 14.0% 7.5% 5.8% 5.6% 4.5% 0% 0.3% 1.7% 1.0% 1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 Period

Figure 5.4 Historical Flow Analysis: November: Stacked Column Graph

Analysis 32 33 November flows are characterised by an overall DECREASE in the proportion of flows OVER 10 000 ML/day. The following describes changes from the periods 1908 1929 to 1981 2000.

The flow duration curves illustrate the following changes due to regulation: �� An increase in the proportion of daily flows that exceed 5000 ML/day (from 93.5% to 100%); �� A decrease in the proportion of daily flows that exceed 10 000 ML/day (from 77.3% to 54.7%); �� A decrease in the proportion of daily flows that exceed 20 000 ML/day (from 38.8% to 27.8%).

The frequency column graph illustrates the following changes due to regulation: �� A decrease in the proportion of flows under 5000 ML/day (from 6.5% to 0.0%); �� An increase in the proportion of flows between 5000 and 15 000 ML/day (from 16.2% to 45.3%); �� A decrease in the proportion of flows over 15000 ML/day (from 77.3% to 54.7%).

The stacked column graphs illustrate the following changes due to regulation: �� A decrease in the proportion of flows under 6000 ML/day (from 9.1% to 0.3%) ; �� An increase in the proportion of flows between 6000 and 12 000 ML/day (from 20.6% to 54.7%); �� A decrease in the proportion of flows over 12 000 ML/day (from 70.3% to 45.0%).

PAGE: 39 DATE: 1/05/03 FILE: BMReport COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Analysis The stacked column graphs illustrate the following November flows are characterised by an overall changes due to regulation: DECREASE in the proportion of flows OVER 10,000 • A decrease in the proportion of flows under 6000 ML/day. The following describes changes from the ML/day (from 9.1% to 0.3%) ; periods 1908 - 1929 to 1981 - 2000. • An increase in the proportion of flows between 6000 and 12,000 ML/day (from 20.6% to 54.7%); The flow duration curves illustrate the following changes due to regulation: • A decrease in the proportion of flows over 12,000 ML/day (from 70.3% to 45.0%). • An increase in the proportion of daily flows that exceed 5000 ML/day (from 93.5% to 100%); In summary, regulation has reduced the variability of • A decrease in the proportion of daily flows that daily flows in November. In particular, it has decreased exceed 10,000 ML/day (from 77.3% to 54.7%); the frequency of flows under 6000 ML/day and over • A decrease in the proportion of daily flows that 12,000 ML/day, with flows more likely to lie between exceed 20,000 ML/day (from 38.8% to 27.8%). 6000 and 12,000 ML/day. Present flows are less likely to be over 8000 or 10,000 ML/day than those before InThe summary, frequency regulation column graph has illustrates reduced the the following variability regulation. of daily flows in November. In particular, it has changes due to regulation: decreased the frequency of flows under 6000 ML/day and over 12 000 ML/day, with flows more likely• A to decrease lie between in the proportion6000 and of12 flows 000 ML/day. under 5000 Present 5.3.3 flows December are less likely to be over 8000 or 10 000 ML/dayML/day than (from those 6.5% before to 0.0%); regulation. Results are summarised in Figures 5.5 to 5.7. • An increase in the proportion of flows between 5000 and 15 000 ML/day (from 16.2% to 45.3%); 5.3.3 December • A decrease in the proportion of flows over 15,000 ML/day (from 77.3% to 54.7%). Results

Figure 5.5 Historical flow analysis: December: Flow duration curve

FLOW DURATION CURVE - December flow of River Murray at Tocumwal

60000

50000

40000

30000

Daily Flow (ML/day) 20000

10000

0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage of time exceeded

1908-1929 1936-1960 1961-2000 1981-2000 1908-2000

Figure 5.5 Historical flow analysis: December: Flow Duration Curve

34 35 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY HISTORICAL ANALYSIS COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY HISTORICAL ANALYSIS

Figure 5.6 Historical flow analysis: December: Frequency column graph Figure 5.6 Historical flow analysis: December: Frequency column graph

December Flow of River Murray at Tocumwal December Flow of River Murray at Tocumwal 60.0% 60.0%

50.0% 48.4% 50.0% 48.4%

40.6% 39.8% 40.0% 40.6% 39.8% 40.0%

30.0% 30.0% Frequency Frequency 20.0% 17.2% 20.0% 17.2% 15.9% 15.9%

10.0% 7.6% 10.0% 7.6%5.3% 5.1% 5.3% 5.1% 3.2% 1.5% 1.6% 2.3% 1.7% 1.6% 3.2% 2.3%1.1% 0.6% 1.3% 1.0% 0.3%1.3% 0.3% 0.0% 1.5% 1.6% 1.1% 1.7% 1.3% 1.6% 1.3% 0.0% 0.0% 0.6% 1.0% 0.3% 0.3% 0.0% >50000 0 - 5000 >50000 0 - 5000 5000 - 10 000 35000 - 40000 40000 - 45000 45000 - 50000 10 000 - 15 15 000 - 20 20 000 - 25 30 000 - 35 5000 - 10 000 25 000 - 30 35000 - 40000 40000 - 45000 45000 - 50000 10 000 - 15 15 000 - 20 20 000 - 25 30 000 - 35 25 000 - 30 Daily Flow (ML/day) Daily Flow (ML/day)

1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 1908-1929 1936-1960 1961-2000 1981-2000 1908-2000

Figure 5.6 Historical Flow Analysis: December: Frequency Column Graph

Figure 5.7 Historical flow analysis: December: Stacked column graph Figure 5.7 Historical flow analysis: December: Stacked column graph

December flows of the River Murray at Tocumwal under 20 000 ML/day December flows of the River Murray at Tocumwal under 20 000 ML/day

100% 100% 1.0% 0.8% 2.3% 2.4%0.8% 90% 1.0% 2.4% 90% 4.8%2.3% 4.8% 4.8% 4.8% 3.0% 6.0% 4.8% 3.5%3.0% 80% 3.9% 6.0% 4.8% 3.5% 80% 2.6% 3.9% 4.8% 3.5%2.6% 4.8% 4.8% 4.8% 3.1%3.5% 5.6% 70% 7.4% 70% 3.1% 22.2% 5.6% 18000 - 20000 ML/day 4.7% 7.4% 22.2% 18000 - 20000 ML/day 4.7% 5.5% 31.1% 16000 - 18000 ML/day 31.1% 14.4% 16000 - 18000 ML/day 60% 9.6% 5.5% 14.4% 14000 - 16000 ML/day 60% 9.6% 7.4% 14000 - 16000 ML/day 7.4% 12000 - 14000 ML/day 12000 - 14000 ML/day 50% 10000 - 12000 ML/day 50% 16.4% 10000 - 12000 ML/day 16.4% 8000 - 10000 ML/day 21.7% 30.4% 22.7% 8000 - 10000 ML/day 40% 30.4% 22.7% 6000 - 8000 ML/day 21.7% 6000 - 8000 ML/day 40% 4000 - 6000 ML/day 4000 - 6000 ML/day 14.9% 2000 - 4000 ML/day Relative frequency of flows of frequency Relative 30% 37.3% 14.9% 2000 - 4000 ML/day Relative frequency of flows of frequency Relative 30% 37.3% 18.0% 20% 20.0% 18.0% 20% 20.0% 18.2% 17.5% 18.2% 17.5% 10% 10% 11.5% 10.8% 7.4% 11.0% 11.5% 5.8% 10.8% 7.4% 11.0% 0% 5.8% 1.5% 2.1% 0% 1.5% 2.1% 1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 Period Period

Figure 5.7 Historical Flow Analysis: December: Stacked Column Graph

34 35

PAGE: 41 PAGE: 41 DATE: 1/05/03 DATE: 1/05/03 FILE: BMReport FILE: BMReport COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Analysis The stacked column graphs illustrate the following December flows are characterised by an overall changes due to regulation: INCREASE in the proportion of flows OVER 10,000 • A decrease in the proportion of flows under 8000 ML/day. The following describes changes from the ML/day (from 41.3% to 11.1%); periods 1908 - 1929 to 1981 - 2000. • An increase in the proportion of flows between 8000 and 16,000 ML/day (33.9% to 79.2%); The flow duration curves illustrate the following changes due to regulation: • A decrease in the proportion of flows over 16,000 ML/day (from 24.8% to 9.7%) • An increase in the proportion of daily flows that exceed 5000 ML/day (from 82.8% to 100%); In summary, regulation has reduced the variability of • An increase in the proportion of flows that exceed daily flows in December. In particular, it has decreased 10,000 ML/day (from 42.2% to 51.5%); the frequency of flows under 8000 ML/day and over • A decrease in the proportion of flows that exceed 16,000 ML/day, with flows more likely to lie between 20,000 ML/day (from 18.7% to 6.5%); 8000 and 16,000 ML/day. Present flows are more likely to be over 10,000 ML/day than those before regulation, The frequency column graph illustrates the following but less likely to be over 12,000 ML/day. changes due to regulation: HISTORICAL ANALYSIS • A decrease in the proportion of flows under 5000 5.3.4 January ML/day (from 17.2% to 0.0%); Results are summarised in Figures 5.8 to 5.10. • An increase in the proportion of flows between 5.3.45000 January and 15,000 ML/day (from 56.5% to 88.2%); • A decrease in the proportion of flows over 15,000 ResultsML/day (from 26.3% to 11.8%);

Figure 5.8 Historical flow analysis: January: Flow duration curve

FLOW DURATION CURVE - January flow of River Murray at Tocumwal

30000

20000

Daily Flow (ML/day) 10000

0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage of time exceeded

1908-1929 1936-1960 1961-2001 1981-2001 1908-2001

Figure 5.8 Historical Flow Analysis: January: Flow Duration Curve

36 Figure 5.9 Historical flow analysis: January: Frequency column graph 37

January Flow of River Murray at Tocumwal 90.0%

80.0%

70.0% 60.8% 60.0% 50.8% 50.0%

40.0%

Frequency 34.3%

30.0% 26.6%

20.0% 13.2% 10.0% 7.5% 3.8% 0.0% 0.7% 0.6% 0.9% 0.3% 0.3% 0.2% 0.0% >30 000 0 - 5000 5000 - 10 000 10 000 - 15 000 15 000 - 20 000 20 000 - 25 000 25 000 - 30 000 Daily Flow (ML/day)

1908-1929 1936-1960 1961-2001 1981-2001 1908-2001

PAGE: 43 DATE: 1/05/03 FILE: BMReport HISTORICAL ANALYSIS

5.3.4 January

Results

Figure 5.8 Historical flow analysis: January: Flow duration curve

FLOW DURATION CURVE - January flow of River Murray at Tocumwal

30000

20000

Daily Flow (ML/day) 10000

0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage of time exceeded

1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Figure 5.9 Historical flow analysis: January: Frequency column graph

January Flow of River Murray at Tocumwal 90.0%

80.0%

70.0% 60.8% 60.0% 50.8% 50.0%

40.0%

Frequency 34.3%

30.0% 26.6%

20.0% 13.2% 10.0% 7.5% 3.8% 0.0% 0.7% 0.6% 0.9% 0.3% 0.3% 0.2% 0.0% >30 000 0 - 5000 5000 - 10 000 10 000 - 15 000 15 000 - 20 000 20 000 - 25 000 25 000 - 30 000 Daily Flow (ML/day)

1908-1929 1936-1960 1961-2001 1981-2001 1908-2001

Figure 5.9 Historical Flow Analysis: January: Frequency Column Graph

PAGE: 43 Figure 5.10 Historical flow analysis: January: Stacked column graph DATE: 1/05/03 FILE: BMReport

January flows of the River Murray at Tocumwal under 20 000 ML/day

100% 0.6% 0.8% 0.3% 2.0% 2.3% 1.0% 1.5% 0.6% 2.2% 2.3% 2.1% 1.8% 3.6% 3.1% 90% 3.2% 6.5% 8.6% 5.4% 5.0% 7.7% 80% 4.8% 5.9% 17.9% 70% 32.0% 6.5% 18000 - 20000 ML/day 30.6% 16000 - 18000 ML/day 60% 11.7% 50.7% 14000 - 16000 ML/day 22.8% 12000 - 14000 ML/day 50% 10000 - 12000 ML/day

18.6% 8000 - 10000 ML/day 40% 29.3% 6000 - 8000 ML/day 4000 - 6000 ML/day 21.8% 2000 - 4000 ML/day Relative frequency of flows 30% 41.9%

20% 26.9% 34.5% 15.7% 12.1% 10% 7.9% 9.2% 7.1% 9.4%

0% 1.0% 1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 Period

Figure 5.10 Historical Flow Analysis: January: Stacked Column Graph Analysis

36 January flows are characterised by an overall INCREASE in the proportion of flows OVER 37 10 000 ML/day. The following describes changes from the periods 1908 1929 to 1981 2000.

The flow duration curves illustrate the following changes due to regulation: �� An increase in the proportion of daily flows that exceed 5000 ML/day (from 49.2% to 100%); �� An increase in the proportion of flows that exceed 10 000 ML/day (from 22.6% to 65.7%); �� A decrease in the proportion of flows that exceed 20 000 ML/day (from 1.9% to 1.1%);

The frequency column graph illustrates the following changes due to regulation: �� A decrease in the proportion of flows under 5000 ML/day (from 50.8% to 0.0%); �� An increase in the proportion of flows between 5000 and 15 000 ML/day (from 39.5% to 95.1%); �� A decrease in the proportion of flows over 15000 ML/day (from 9.7% to 4.9%);

The stacked column graphs illustrate the following changes due to regulation: �� A decrease in the proportion of flows under 8000 ML/day (from 70.9% to 7.4%); �� An increase in the proportion of flows between 8000 and 14 000 ML/day (17.2% to 86.1%); �� A decrease in the proportion of flows over 14 000 ML/day (from 11.9% to 6.5%).

In summary, regulation has reduced the variability of daily flows in January. In particular, it has decreased the frequency of flows under 8000 ML/day and over 14 000 ML/day, with flows more COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Analysis The stacked column graphs illustrate the following January flows are characterised by an overall changes due to regulation: INCREASE in the proportion of flows OVER 10,000 • A decrease in the proportion of flows under 8000 ML/day. The following describes changes from the ML/day (from 70.9% to 7.4%); periods 1908 - 1929 to 1981 - 2000. • An increase in the proportion of flows between 8000 and 14,000 ML/day (17.2% to 86.1%); The flow duration curves illustrate the following changes due to regulation: • A decrease in the proportion of flows over 14,000 ML/day (from 11.9% to 6.5%). • An increase in the proportion of daily flows that exceed 5000 ML/day (from 49.2% to 100%); In summary, regulation has reduced the variability of • An increase in the proportion of flows that exceed daily flows in January. In particular, it has decreased 10,000 ML/day (from 22.6% to 65.7%); the frequency of flows under 8000 ML/day and over • A decrease in the proportion of flows that exceed 14,000 ML/day, with flows more likely to lie between 20,000 ML/day (from 1.9% to 1.1%); 8000 and 14,000 ML/day. Present flows are more likely to be over 10,000 ML/day than those before regulation, HISTORICALThe frequency column ANALYSIS graph illustrates the following but less likely to be over 12,000 ML/day. changes due to regulation: likely to lie between 8000 and 14 000 ML/day. Present flows are more likely to be over 10 000 • A decrease in the proportion of flows under 5000 5.3.5 February ML/day than those before regulation, but less likely to be over 12 000 ML/day. ML/day (from 50.8% to 0.0%); Results are summarised in Figures 5.11 to 5.13. • An increase in the proportion of flows between 5.3.55000 February and 15,000 ML/day (from 39.5% to 95.1%); • A decrease in the proportion of flows over 15,000 ResultsML/day (from 9.7% to 4.9%);

Figure 5.11 Historical flow analysis: February: Flow duration curve

FLOW DURATION CURVE - February flow of River Murray at Tocumwal

20000

10000 Daily Flow (ML/day)

0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage of time exceeded

1908-1929 1936-1960 1961-2001 1981-2001 1908-2001

Figure 5.11 Historical Flow Analysis: February: Flow Duration Curve

38 39

PAGE: 45 DATE: 1/05/03 FILE: BMReport COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

FigureFigure 5.12 5.12 Historical Historical flow flow analysis: analysis: February: February: Frequency Frequency column column graph graph

FebruaryFebruary Flow Flow of River of River Murray Murray at Tocumwal at Tocumwal 100.0% 100.0% 90.0% 90.0% 80.0% 80.0% 74.0% 74.0% 70.0% 70.0% 58.5% 60.0% 58.5% 60.0% 50.0% 50.0% 39.3% Frequency 40.0% 39.3% Frequency 40.0% 30.0% 30.0% 20.0% 20.0% 13.2% 13.2% 9.3% 10.0% 9.3% 10.0% 2.9% 2.0% 0.0% 2.9% 2.0% 0.6% 0.2% 0.0% 0.0% 0.6% 0.2% 0.0% >20 000 0 - 5000 >20 000 0 - 5000 5000 - 10 000 5000 - 10 000 10 000 - 15 15 000 - 20 10 000 - 15 15 000 - 20 Daily Flow (ML/day) Daily Flow (ML/day)

1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001

Figure 5.12 Historical Flow Analysis: February: Frequency Column Graph

FigureFigure 5.13 5.13 Historical Historical flow flow analysis: analysis: February: February: Stacked Stacked column column graph graph

February flows of the River Murray at Tocumwal under 20 000 ML/day February flows of the River Murray at Tocumwal under 20 000 ML/day

0.3% 0.6% 0.7% 100% 0.3% 0.6% 0.8% 0.7% 100% 0.7% 1.9%0.8% 1.3% 0.8% 4.0%0.7% 1.9% 1.3% 0.8% 4.0% 0.1% 4.5% 5.1% 0.5% 0.1% 4.5% 5.1% 0.5% 0.8% 7.2% 1.5%0.8% 90% 7.2% 1.5% 3.8% 90% 3.8%

80% 80% 18.7% 0.5% 18.7% 0.5% 36.1% 1.3% 36.1% 70% 2.9%1.3% 70% 2.9% 3.4% 18000 - 20000 ML/day 3.4% 41.6% 52.6% 18000 - 20000 ML/day 4.2% 41.6% 52.6% 16000 - 18000 ML/day 4.2% 60% 16000 - 18000 ML/day 60% 7.1% 14000 - 16000 ML/day 7.1% 14000 - 16000 ML/day 27.8% 12000 - 14000 ML/day 4.2% 27.8% 12000 - 14000 ML/day 50% 4.2% 10000 - 12000 ML/day 50% 10000 - 12000 ML/day 8.5% 8000 - 10000 ML/day 8.5% 8000 - 10000 ML/day 40% 32.5% 6000 - 8000 ML/day 40% 32.5% 6000 - 8000 ML/day 4000 - 6000 ML/day 4000 - 6000 ML/day 18.4% 2000 - 4000 ML/day Relative frequency of flows of frequency Relative 30% 18.4% 2000 - 4000 ML/day Relative frequency of flows of frequency Relative 30% 37.3% 37.3% 32.4% 42.0% 32.4% 20% 42.0% 20% 14.3% 8.2% 14.3% 8.2% 10% 10% 6.7% 13.6% 6.7% 8.1% 6.1% 13.6% 8.1% 2.5% 6.1% 0% 2.5% 0% 1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 Period Period

Figure 5.13 Historical Flow Analysis: February: Stacked Column Graph

38 39 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Analysis The stacked column graphs illustrate the following February flows are characterised by an overall changes due to regulation: INCREASE in the proportion of flows OVER 10,000 • A decrease in the proportion of flows under 6000 ML/day. The following describes changes from the ML/day (from 75.9% to 0.8%); periods 1908 - 1929 to 1981 - 2000. • An increase in the proportion of flows between 8000 and 12,000 ML/day (15.4% to 91.1%); The flow duration curves illustrate the following changes due to regulation: • A decrease in the proportion of flows over 12,000 ML/day (from 8.7% to 8.1%). • An increase in the proportion of daily flows that exceed 5000 ML/day (from 26.0% to 100%); In summary, regulation has reduced the variability of • An increase in the proportion of flows that exceed daily flows in February. In particular, it has decreased 10,000 ML/day (from 12.9% to 60.7%); the frequency of flows under 6000 ML/day and over • A decrease in the proportion of flows that exceed 12,000 ML/day, with flows more likely to lie between 20,000 ML/day (from 0.6% to 0.2%); 6000 and 12,000 ML/day. Present flows are more likely to be over 8000 or 10,000 ML/day than those before The frequency column graph illustrates the following regulation. changes due to regulation: • A decrease in the proportion of flows under 5000 5.3.6 March ML/day (from 74.0% to 0.0%); Results are summarised in Figures 5.14 to 5.16. • An increase in the proportion of flows between 5.3.65000 March and 15,000 ML/day (from 22.5% to 97.8%); • A decrease in the proportion of flows over 15,000 ResultsML/day (from 3.5% to 2.2%);

Figure 5.14 Historical flow analysis: March: Flow duration curve

FLOW DURATION CURVE - March flow of River Murray at Tocumwal

20000

10000 Daily Flow (ML/day)

0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage of time exceeded

1908-1929 1936-1960 1961-2001 1981-2001 1908-2001

Figure 5.14 Historical Flow Analysis: March: Flow Duration Curve

Figure 5.15 Historical flow analysis: March: Frequency column graph 40 41

March Flow of River Murray at Tocumwal 90.0%

80.0% 77.3%

69.1% 70.0%

60.0%

50.0%

40.0% Frequency

30.0% 23.2% 20.3% 20.0%

10.0% 6.2% 2.4% 0.0% 1.6% 0.0% 0.0% 0.0% >20 000 0 - 5000 5000 - 10 000 10 000 - 15 000 15 000 - 20 000 Daily Flow (ML/day)

1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 5.3.6 March

Results

Figure 5.14 Historical flow analysis: March: Flow duration curve

FLOW DURATION CURVE - March flow of River Murray at Tocumwal

20000

10000 Daily Flow (ML/day)

0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage of time exceeded

COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY 1908-1929 1936-1960 COOPERATIVE1961-2001 RESEARCH1981-2001 CENTRE1908-2001 FOR CATCHMENT HYDROLOGY

Figure 5.15 Historical flow analysis: March: Frequency column graph

March Flow of River Murray at Tocumwal 90.0%

80.0% 77.3%

69.1% 70.0%

60.0%

50.0%

40.0% Frequency

30.0% 23.2% 20.3% 20.0%

10.0% 6.2% 2.4% 0.0% 1.6% 0.0% 0.0% 0.0% >20 000 0 - 5000 5000 - 10 000 10 000 - 15 000 15 000 - 20 000 Daily Flow (ML/day)

1908-1929 1936-1960 1961-2001 1981-2001 1908-2001

HISTORICAL ANALYSIS Figure 5.15 Historical Flow Analysis: March: Frequency Column Graph

Figure 5.16 Historical flow analysis: March: Stacked column graph

March flows of the River Murray at Tocumwal under 20 000 ML/day

0.4% 0.4% 0.6% 100% 1.3% 0.9% 1.8% 1.0% 2.0% 2.7% 0.4% 3.9% 5.8% 6.3% 1.6% 1.0% 90% 6.6% 4.2%

80%

0.4% 22.0% 70% 0.9% 29.3% 2.1% 0.9% 44.0% 18000 - 20000 ML/day 3.5% 16000 - 18000 ML/day 60% 6.5% 14000 - 16000 ML/day 69.1% 12000 - 14000 ML/day 50% 12.0% 25.1% 10000 - 12000 ML/day 8000 - 10000 ML/day

40% 10.7% 6000 - 8000 ML/day 4000 - 6000 ML/day 47.9% 31.1% 2000 - 4000 ML/day Relative frequency of flows 30% 20.4%

20% 34.0% 7.7% 17.3% 10% 10.6% 7.5% 9.8% 3.4% 0% 1.4% 1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 Period

Figure 5.16 Historical Flow Analysis: March: Stacked Column Graph

40 41

Analysis

March flows are characterised by an overall INCREASE in the proportion of flows OVER 10 000 ML/day. The following describes changes from the periods 1908 1929 to 1981 2000.

The flow duration curves illustrate the following changes due to regulation: �� An increase in the proportion of daily flows that exceed 7000 ML/day (from 20.8% to 100%); �� An increase in the proportion of flows that exceed 10 000 ML/day (from 7.8% to 79.7%); �� No change in the proportion of flows that exceed 20 000 ML/day (from 0.0% to 0.0%);

The frequency column graph illustrates the following changes due to regulation: �� A decrease in the proportion of flows under 10 000 ML/day (from 92.3% to 20.3%); �� An increase in the proportion of flows over 10 000 ML/day (from 7.7% to 79.7%).

The stacked column graphs illustrate the following changes due to regulation: �� A decrease in the proportion of flows under 8000 ML/day (from 85.8% to 3.8%); �� An increase in the proportion of flows over 8000 ML/day, especially from 10 000 - 12 000 ML/day (3.5% to 69.1%).

In summary, regulation has reduced the variability of daily flows in March. In particular, it has decreased the frequency of flows under 8000 ML/day and increased those over 8000 ML/day,

PAGE: 49 DATE: 1/05/03 FILE: BMReport COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Analysis The stacked column graphs illustrate the following March flows are characterised by an overall INCREASE changes due to regulation: in the proportion of flows OVER 10,000 ML/day. The • A decrease in the proportion of flows under 8000 following describes changes from the periods 1908 - ML/day (from 85.8% to 3.8%); 1929 to 1981 - 2000. • An increase in the proportion of flows over 8000 ML/day, especially from 10,000 - 12,000 ML/day The flow duration curves illustrate the following (3.5% to 69.1%). changes due to regulation: • An increase in the proportion of daily flows that In summary, regulation has reduced the variability of exceed 7000 ML/day (from 20.8% to 100%); daily flows in March. In particular, it has decreased the • An increase in the proportion of flows that exceed frequency of flows under 8000 ML/day and increased 10,000 ML/day (from 7.8% to 79.7%); those over 8000 ML/day, with a large increase in the likelihood of flows falling between 10,000 and 12,000 • No change in the proportion of flows that exceed ML/day. Present flows are more likely to be over 10,000 20,000 ML/day (from 0.0% to 0.0%); ML/day than those before regulation, but less likely to with a large increase in the likelihood of flows falling between 10 000 and 12 000 ML/day. Present be over 12,000 ML/day. flowsThe arefrequency more columnlikely to graph be over illustrates 10 000 the ML/day following than those before regulation, but less likely to be overchanges 12 000 due ML/day. to regulation: 5.3.7 April • A decrease in the proportion of flows under 10,000 ML/day (from 92.3% to 20.3%); Results are summarised in Figures 5.17 to 5.19. 5.3.7 April • An increase in the proportion of flows over 10,000 ML/day (from 7.7% to 79.7%). Results

Figure 5.17 Historical flow analysis: April: Flow duration curve

FLOW DURATION CURVE - April Flow of River Murray at Tocumwal

40000

30000

20000 Daily Flow (ML/day)

10000

0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage of time exceeded

1908-1929 1936-1960 1961-2000 1981-2000 1908-2000

Figure 5.17 Historical Flow Analysis: April: Flow Duration Curve

42 43 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

HISTORICAL ANALYSIS

HISTORICALHISTORICAL ANALYSISANALYSIS Figure 5.18 Historical flow analysis: April: Frequency column graph

FigureFigure 5.185.18 Historical Historical flowflow analysis:analysis: April:April: FrequencyFrequency columncolumn graphgraph April Flow of River Murray at Tocumwal 100.0%

90.0% April Flow of River Murray at Tocumwal April Flow of River Murray at Tocumwal 100.0% 100.0%80.0% 90.0% 69.7% 69.7% 90.0%70.0% 80.0% 80.0%60.0% 69.7% 69.7% 70.0% 69.7% 69.7% 70.0%50.0% 60.0% Frequency 60.0%40.0% 50.0% 50.0%30.0% 24.8% 25.2%

Frequency 40.0% Frequency 40.0%20.0% 30.0% 10.0% 24.8% 25.2% 30.0% 3.8% 24.8% 3.5% 25.2% 1.5% 1.3% 0.5% 20.0% 0.0% 20.0%0.0% 10.0% 10.0% 3.8% 3.5% 3.8% 3.5% 1.5% 1.3% 0.5% 1.5% 0.0%

1.3% >20 000 0.0% 0 - 5000 0.5% 0.0% 0.0% 5000 - 10 000 10 000 - 15 15 000 - 20 >20 000 0 - 5000 Daily Flow (ML/day) >20 000 0 - 5000 5000 - 10 000 5000 - 10 000 10 000 - 15 15 000 - 20 10 000 - 15 15 000 - 20 1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 Daily Flow (ML/day) Daily Flow (ML/day)

1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 Figure 5.18 Historical Flow Analysis: April: Frequency Column Graph

Figure 5.19 Historical flow analysis: April: Stacked column graph

FigureFigure 5.195.19 Historical Historical flowflow analysis:analysis: April:April: StackedStacked columncolumn graphgraph April flows of the River Murray at Tocumwal under 20 000 ML/day

0.0% 100% 0.1% 0.7% 1.0% April flows 0.7%of the River Murray at Tocumwal2.8% under0.7% 20 000 ML/day April flows of the0.3% River Murray2.6% at 0.6%Tocumwal under 20 000 ML/day 1.1% 0.4% 90% 3.5% 1.1% 0.0% 0.8% 0.1% 1.0% 1.0% 100% 17.4% 0.7% 0.0% 2.0% 100% 0.7% 0.1% 0.7% 22.0%2.8% 1.0%0.7% 0.3% 2.6% 0.6% 2.8% 0.7% 0.7% 2.6% 0.6% 10.0% 80% 0.3%1.1% 0.4% 90% 3.5% 1.1%1.1% 0.4% 0.8% 3.5%27.3% 1.1% 1.0% 90% 0.5% 2.0% 0.8% 0.8% 17.4% 22.0% 2.0% 1.0% 70% 0.5% 0.6% 17.4% 22.0% 2.7% 10.0% 18000 - 20000 ML/day 80% 10.0% 80% 24.2% 16000 - 18000 ML/day 8.3% 27.3% 60% 0.5% 0.8% 27.3% 32.3% 0.5% 14000 - 16000 ML/day 70% 0.5% 0.8%0.6% 32.7% 70% 0.5%2.7% 0.6% 1800012000 -- 2000014000 ML/dayML/day 2.7%10.9% 18000 - 20000 ML/day 50% 8.3% 24.2% 1600010000 -- 1800012000 ML/dayML/day 60% 8.3% 32.3% 24.2% 16000 - 18000 ML/day 32.3% 140008000 - -10000 16000 ML/day ML/day 60% 32.7% 14000 - 16000 ML/day 32.7% 12000 - 14000 ML/day 40% 10.9%13.2% 6000 - 8000 ML/day 46.4% 27.0% 12000 - 14000 ML/day 50% 10.9% 100004000 - -6000 12000 ML/day ML/day 50% 10000 - 12000 ML/day 27.1% 80002000 -- 100004000 ML/day ML/day Relative frequency of flows 30% 8000 - 10000 ML/day 40% 13.2% 6000 - 8000 ML/day 40% 13.2% 46.4% 32.0% 27.0% 6000 - 8000 ML/day 46.4% 27.0% 4000 - 6000 ML/day 20% 4000 - 6000 ML/day 27.1% 2000 - 4000 ML/day Relative frequency of flows 33.9% 13.8% 30% 27.1% 2000 - 4000 ML/day Relative frequency of flows 30% 12.6% 32.0% 10% 32.0% 20% 13.3% 20% 33.9% 8.2% 13.8%10.5% 33.9% 4.7% 13.8% 0% 0.7% 10% 1.2% 12.6% 10% 1908-1929 1936-196013.3% 1961-200012.6% 1981-2000 1908-2000 13.3% 8.2% 10.5% Period4.7% 8.2% 10.5% 0% 4.7% 0.7% 0% 1.2% 0.7% 1908-1929 1936-19601.2% 1961-2000 1981-2000 1908-2000 1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 Period Period

Figure 5.19 Historical Flow Analysis: April: Stacked Column Graph PAGE: 51 DATE: 1/05/03 PAGEFILE:: BMReport51 42 PAGE: 51 43 DATE: 1/05/03 DATE: 1/05/03 FILE: BMReport FILE: BMReport Analysis

COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY April flows are characterised by an overall INCREASE in the proportion of flows OVER 10 000 ML/day. The following describes changes from the periods 1908 1929 to 1981 2000.

TheAnalysis flow duration curves illustrate the following changesThe stackeddue to columnregulation: graphs illustrate the following April�� flowsAn increaseare characterised in the proportionby an overall of INCREASE daily flows thatchanges exceed due to 3000 regulation: ML/day (from 50.0% to 100%); in the�� proportionAn increase of flows in the OVER proportion 10,000 ofML/day. flows thatThe exceed• A decrease 10 000 inML/day the proportion (from 5.5% of flows to 26.5%); under 6000 following describes changes from the periods 1908 - ML/day (from 75.3% to 8.8%); �� No change in the proportion of flows that exceed 20 000 ML/day (from 0.0% to 0.0%); 1929 to 1981 - 2000. • An increase in the proportion of flows over 6000 ML/day. TheThe frequency flow duration column curves graph illustrateillustrates the the followingfollowing changes due to regulation: changes�� Adue decrease to regulation: in the proportion of flows underIn 5000 summary, ML/day regulation (from 69.7% has reduced to 3.8%); the variability of • ��An increaseAn increase in the in proportion the proportion of daily of flows flows overthat 5000daily ML/day.flows in April. In particular, it has decreased the exceed 3000 ML/day (from 50.0% to 100%); frequency of flows under 6000 ML/day. Present flows The• stackedAn increase column in the proportiongraphs illustrate of flows the that following exceed changesare more duelikely to to regulation: be over 10,000 ML/day than those before regulation. ��10,000A decrease ML/day (from in the 5.5% proportion to 26.5%); of flows under 6000 ML/day (from 75.3% to 8.8%); • ��No changeAn increase in the inproportion the proportion of flows of that flows exceed over 6000 ML/day. 20,000 ML/day (from 0.0% to 0.0%); 5.3.8 May In summary, regulation has reduced the variabilityResults of dailyare summarised flows in in April. Figures In 5.20 particular, to 5.22. it has The frequency column graph illustrates the following decreased the frequency of flows under 6000 ML/day. Present flows are more likely to be over changes due to regulation: 10 000 ML/day than those before regulation. • A decrease in the proportion of flows under 5000 ML/day (from 69.7% to 3.8%); 5.3.8• An increase May in the proportion of flows over 5000 ML/day. Results

Figure 5.20 Historical flow analysis: May: Flow duration curve

FLOW DURATION CURVE - May flow of River Murray at Tocumwal

60000

50000

40000

30000

Daily Flow (ML/day) 20000

10000

0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage of time exceeded

1908-1929 1936-1960 1961-2000 1981-2000 1908-2000

Figure 5.20 Historical Flow Analysis: May: Flow Duration Curve

44 45 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

HISTORICAL ANALYSIS HISTORICAL ANALYSIS Figure 5.21 Historical flow analysis: May: Frequency column graph Figure 5.21 Historical flow analysis: May: Frequency column graph HISTORICAL ANALYSIS May Flow of River Murray at Tocumwal 70.0% May Flow of River Murray at Tocumwal 70.0%Figure 5.18 Historical flow analysis: April: Frequency column graph 60.0%

60.0% 50.9% 50.0% 48.2% 50.9% April Flow of River Murray at Tocumwal 48.2% 43.3% 50.0% 100.0% 40.0% 43.3% 90.0% 34.8% 40.0% 34.8% 30.0% 80.0% Frequency 69.7% 69.7% 30.0% 70.0% Frequency 20.0% 60.0% 20.0% 50.0% 10.0% 6.5% 5.0%

Frequency 3.7% 10.0% 40.0% 6.5% 2.2% 1.5% 1.6% 5.0% 0.5% 0.0% 0.1% 0.0% 3.7% 0.0% 2.2% 1.5% 1.6% 30.0% 24.8% 0.5%25.2% 0.0% 0.1% 0.0% 0.0% 20.0% >30 000 10.0% 0 - 5000 3.8% 3.5% >30 000 0 - 5000 1.5% 1.3% 0.5% 0.0% 0.0% 5000 - 10 000 10 000 - 15 15 000 - 20 20 000 - 25 25 000 - 30 5000 - 10 000

10 000 - 15 15 000 - 20 20 000 - 25 Daily Flow (ML/day) 25 000 - 30 >20 000

0 - 5000 Daily Flow (ML/day)

1908-1929 1936-19605000 - 10 000 1961-2000 1981-2000 1908-2000 10 000 - 15 15 000 - 20 1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 Daily Flow (ML/day)

1908-1929 1936-1960 1961-2000 1981-2000 1908-2000

Figure 5.21 Historical Flow Analysis: May: Frequency Column Graph Figure 5.22 Historical flow analysis: May: Stacked column graph Figure 5.22 Historical flow analysis: May: Stacked column graph Figure 5.19 Historical flow analysis: April: Stacked column graph May flows of the River Murray at Tocumwal under 20 000 ML/day May flows of the River Murray at Tocumwal under 20 000 ML/day 0.1% 100% April flows of the River Murray at Tocumwal under0.3% 20 000 ML/day 0.1%1.2% 0.6% 100% 0.5% 3.9% 0.3% 0.8% 1.2%0.0% 0.6% 90% 100% 0.0% 0.5%1.6%0.1% 0.8% 3.9%6.3% 1.0% 1.1% 0.7% 0.9% 0.7% 3.3% 5.7% 0.8% 2.8% 0.7% 1.1% 90% 0.0% 0.3% 1.6%2.6% 0.8%0.6% 6.3% 1.8% 1.1%1.1% 0.5%1.1% 0.9%1.5% 3.3%1.1% 5.7% 0.4% 1.1% 80% 90% 1.9% 3.5% 9.7% 3.7% 0.8%1.8% 0.9% 1.1% 0.5% 17.3% 2.0%1.5% 1.0% 1.5% 17.4% 22.0% 80% 1.9% 2.3% 9.7% 3.7% 0.9% 18.8% 17.3% 10.0%12.2% 70% 80% 1.5%2.1% 2.3% 18000 - 20000 ML/day 7.2% 18.8%27.3% 12.2% 70% 2.1% 0.5% 16.5% 0.8% 1800016000 - -20000 18000 ML/day ML/day 70% 0.6% 7.2% 0.5% 16.5% 18000 - 20000 ML/day 60% 2.7% 1600014000 - -18000 16000 ML/day ML/day 18.5% 60% 15.0% 8.3% 24.2% 16000 - 18000 ML/day 32.3% 30.6% 1400012000 - -16000 14000 ML/day ML/day 60% 18.5% 14000 - 16000 ML/day 50% 15.0% 25.5% 32.7% 1200010000 - -14000 12000 ML/day ML/day 30.6% 12000 - 14000 ML/day 10.9% 25.5% 23.7% 8000 - 10000 ML/day 50% 50% 1000010000 - 12000 - 12000 ML/day ML/day 6000 - 8000 ML/day 40% 23.7% 80008000 - 10000 - 10000 ML/day ML/day 4000 - 6000 ML/day 40% 40% 24.3% 13.2% 23.4% 60006000 - 8000 - 8000 ML/day ML/day 46.4% 27.0% 2000 - 4000 ML/day Relative frequency of flows 30% 24.3% 23.4% 40004000 - 6000 - 6000 ML/day ML/day 22.5% 27.1% 20002000 - 4000 - 4000 ML/day ML/day Relative frequency of flows Relative frequency of flows 30% 30% 22.5% 20% 32.0%38.4% 20% 33.5% 20% 33.9% 38.4% 13.8% 23.2% 33.5% 23.9% 10% 12.6% 10% 23.2% 14.7% 23.9% 10% 13.3% 14.7% 8.2% 10.5% 4.7% 0% 0.7% 0% 1.2% 0% 1908-19291908-1929 1936-1960 1936-1960 1961-2000 1961-2000 1981-2000 1908-2000 1908-2000 1908-1929 1936-1960 1961-2000PeriodPeriod 1981-2000 1908-2000 Period

Figure 5.22 Historical Flow Analysis: May: Stacked Column Graph

44 45

PAGE: 51 DATE: 1/05/03 FPILEAGE: : BMReport 53 PDAGEATE: : 1/05/0353 DATEFILE: : BMReport1/05/03 FILE: BMReport COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Analysis • A decrease in the proportion of flows over 8000 May flows are characterised by an overall DECREASE ML/day. in the proportion of flows OVER 10,000 ML/day. The In summary, regulation has reduced the variability of following describes changes from the periods 1908 - daily flows in May. In particular, it has increase the 1929 to 1981 - 2000. frequency of flows under 8000 ML/day and decreased The flow duration curves illustrate the following the likelihood of flows over 8000 ML/day.. Present changes due to regulation: flows are less likely to be over 10,000 ML/day than those before regulation. • An increase in the proportion of daily flows that exceed 2000 ML/day (from 84% to 100%); 5.3.9 Summary • An decrease in the proportion of flows that exceed 10,000 ML/day (from 14.4% to 7.4%); The main findings of the flow analysis are (see Table 5.1): • A decrease in the proportion of flows that exceed 20,000 ML/day (from 5.7% to 1.3%); • Flows in all months have lower variability now than before regulation; The frequency column graph illustrates the following • November and May flows are characterised by changes due to regulation: a DECREASE in the occurrence of flows over • A decrease in the proportion of flows under 5000 10,000 ML/day, whereas December - April ML/day (from 50.9% to 48.2%); flows are characterised by an INCREASE in the • An increase in the proportion of flows over 5000 occurrence of flows over 10,000 ML/day, due to ML/day. regulation; • November, December, January and February flows The stacked column graphs illustrate the following are characterised by a decrease in the occurrence changes due to regulation: of low flows, an increase in the occurrence of • An increase in the proportion of flows under 8000 medium flows, and a decrease in the occurrence of ML/day (from 78.4% to 86.3%); high flows, due to regulation;

Table 5.1 Summary of Flow Changes for Months November to May 1908 - 1929 and 1981 - 2000

Month Mean Variability Flow range of Proportion of Proportion of Proportion of (std. dev.) increased flows in range flows > 10,000 flows 10,000 - likelihood ML/day 12,000 ML/day (ML/day) <1929 >1980 <1929 >1980 <1929 >1980 >1929 >1980 <1929 >1980 NOV 21522 17537 15802 14327 6000 - 12 000 20.6% 54.7% 77.3% 54.7% 7.0% 9.7%

DEC 11933 12286 11553 6347 8000 - 16 000 33.9% 79.2% 42.2% 51.5% 9.6% 31.1%

JAN 6775 8948 5240 2493 8000 - 14 000 17.2% 86.1% 22.6% 65.7% 5.9% 50.7%

FEB 4719 7765 4189 1775 8000 - 12 000 15.4% 91.1% 12.9% 60.7% 4.2% 52.6%

MAR 4208 7901 3547 1534 > 8000 14.2% 96.2% 7.8% 79.7% 3.5% 69.1%

APR 4221 7358 3457 2137 > 6000 24.7% 91.2% 5.5% 26.5% 2.7% 22.0%

MAY 6963 7529 8185 3300 < 8000 78.4% 86.3% 14.4% 7.4% 2.1% 3.9%

46 47 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

�� • March and April flows are characterised by a regulation. Both of these graphs divided the data into

�� decrease in the occurrence of low flows and an the time periods outlined in Section 5.2. �� increase in the occurrence�� of higher flows; ��

�� • May�� flows are characterised by an increase in 5.4.1 Frequency �� the occurrence of low flows and a�� decrease�� in the Methodology �� occurrence of higher flows. �� The analysis of forest flooding requires investigation of �� Therefore, the months December - April most closely the “threshold Tocumwal flow” at which forest flooding �� match the description of “unseasonal surplus flows” commences. This threshold has changed over time, due �� caused by regulation. In particular, the flow records to activities such as desnagging of the Choke in the �� for these months exhibit a trend towards maintenance 1950’s and increases in regulator capacity. Various �� of high (>10,000 ML/day) River Murray flows (to publications cite values for threshold flows, including: �� maintain irrigation flexibility). * 9386.8 ML/day derived for the period 1963 - 1984 � (Bren et. al., 1987); The months of November�� and May do not closely match the description of unseasonal surplus flows. Rather, * 11,000 ML/day (RMC 1980; Johnson et. al., 1980); �� and analysis of�� the flow records indicate that regulation has �� actually lowered river flows during these months. * 10,600 ML/day (Thoms et. al., 2000).

�� Further analysis of the impact of these flow changes The graphs of frequency of forest flooding compare �� on the frequency and extent of flooding of the Barmah- the percentage of days during which the forest flooded, �� Millewa Forest is presented in Section 5.4. ��using these three thresholds. The purpose is to illustrate �� the sensitivity of calculated flooding frequency to the �� selection of the threshold. 5.4 Forest Flooding �� Results are summarised in Figure 5.23. For each month between November - May, two �� graphs� �� were constructed to present�� how�� the frequency �� and areal extent of forest floods has changed with ��

��

�� Figure 5.23 Frequency of Flooding ��

�� 46 47

��

� ��

��

�� COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY ��

��

�

��

� ��

��

� ��

��

�� Figure 5.23 Frequency of Flooding (continued) 48 �� 49 ��

��

�

��

COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY �� COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY ��

��

�� Figure 5.23 Frequency of Flooding (continued)

48 49 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Analysis The greatest relative increase in flooding frequency has The main characteristics of the forest flooding plots occurred during March, followed by April, February, are: January and December (if a threshold of 10,600 or 11,000 ML/day is used). Except for April, an increase • For all thresholds, November and May exhibited of the threshold flow results in a decrease in the factor DECREASES in the proportion of days during increase. which flooding occurred in the forest. • For all thresholds, January, February, March and The greatest relative decrease in flooding frequency April exhibited INCREASES in the proportion of occurred during May, followed by November. days during which flooding occurred in the forest. Overall, the results suggest that regulation has not • For thresholds of 9387 ML/day and 10,600 increased the flooding frequency during the months ML/day, December exhibited an INCREASE November or May. Regulation has increased the in the proportion of days during which flooding flooding frequency during December - April, with the occurred. However, for threshold equal to 11,000 greatest impact during March, and the smallest impact ML/day, December exhibited a DECREASE in during December. the proportion of days during which flooding occurred. The choice of threshold value affects the calculated • The greatest increase in the occurrence of forest changes in flooding frequency. In general, a higher flooding was for March (6.67% of days in 1908 threshold results in the calculation of a smaller - 1929, compared with 59.83% of days in 1981 impact of regulation on flooding frequency. However, - 2001, using 10,600 ML/day as the threshold). December is the only month in which the sign of the change in flooding frequency (ie. increase or decrease) To illustrate the extent to which regulation has increased is sensitive to the selection of the threshold, within the forest flooding, “factor increases/decreases” were range 9387 - 11,000 ML/day. HISTORICALcalculated, e.g. regulation ANALYSIS has increased the occurrence of flooding in March by a factor of 59.83/6.67 = 8.97, using 10,600 ML/day as the threshold. These factor changesFigure 5.24are illustrated Factor increasesin Figure 5.24. in frequency of flooding

Changes in flooding frequency from 1908 - 1929 to 1981 - 2001

10.0 9.3 9.0 9.0

8.0

7.0 November 6.5 December 6.0 January 5.0 5.1 February

Factor 4.6 4.2 March 4.0 3.8 April 3.4 3.5 3.0 May

2.0 2.0 2.1 1.6 1.3 1.4 1.0 0.9 0.7 0.7 0.6 0.6 0.5 0.5 0.0 9387 ML/day 10600 ML/day 11000 ML/day Threshold (flow at Tocumwal)

Figure 5.24 Factor Increases in Frequency of Flooding

50 51 Overall, the results suggest that regulation has not increased the flooding frequency during the months November or May. Regulation has increased the flooding frequency during December April, with the greatest impact during March, and the smallest impact during December.

The choice of threshold value affects the calculated changes in flooding frequency. In general, a higher threshold results in the calculation of a smaller impact of regulation on flooding frequency. However, December is the only month in which the sign of the change in flooding frequency (ie. increase or decrease) is sensitive to the selection of the threshold, within the range 9387 11 000 ML/day.

5.4.2 Areal extent

Methodology

The analysis of forest flooding requires investigation of how the area extent of forest flooding has changed over time, due to regulation. Repeated inundation has the greatest ecological impact with regards to tree deaths and changes in patterns of vegetation. Therefore, a large increase in the frequency of the flooding of a small forest area is likely to be more damaging than small increases in the frequency of flooding of a greater area.

This flooding extent analysis uses the relationship derived by Bren et. al. (1987), which relates proportion of Barmah Forest flooded (P percent) to the daily flow at Tocumwal for the period 1963 - 1984:

P = -435.40 + 47.6 ln (Q) Q < 68 500 ML/day

P = 93.5 Q > 68 500 ML/day

PAGE: 59 DATE: 1/05/03 FILE: BMReport COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

5.4.2 Areal Extent This relationship was used to construct column graphs Methodology which show the proportion of days in which 0%, 0 - 10%, 10 - 20%, 20 - 30%, 30 - 40%, 40 - 50%, 50 - 60%, The analysis of forest flooding requires investigation of 60 - 70%, 70 - 80%, 80 - 93,5% and 93.5% (maximum) how the area extent of forest flooding has changed over of the forest was flooded (refer to Appendix B). time, due to regulation. Repeated inundation has the greatest ecological impact with regards to tree deaths Two assumptions were used in this analysis: and changes in patterns of vegetation. Therefore, a • The value “Q” in Bren’s relationship is equivalent large increase in the frequency of the flooding of a to the mean daily flow at Tocumwal, rather than small forest area is likely to be more damaging than the peak value; small increases in the frequency of flooding of a greater area. • The relation (although derived from the period 1963 - 1984) is applicable for the period 1908 - This flooding extent analysis uses the relationship 2001. derived by Bren et. al. (1987), which relates proportion of Barmah Forest flooded (P percent) to the daily flow The consequences of these assumptions are: at Tocumwal for the period 1963 - 1984: • Areal extent of flooding excludes Millewa Forest; • The graphs provide general illustrations of the P = -435.40 + 47.6 ln (Q) Q < 68,500 ML/day trends in area of forest flooded, rather than exact P = 93.5 Q > 68,500 ML/day values. Results The results are summarised in Table 5.2.

Table 5.2 Areal Extent of Flooding

Month Percentage of forest flooded 0 0 - 10 10 - 20 20 - 30 30 - 40 > 40

<1929 >1981 <1929 >1981 <1929 >1981 <1929 >1981 <1929 >1981 <1929 >1981 NOV 18.9% 39.3% 9.25 14.3% 12.4% 9.8% 14.1% 5.0% 9.9% 5.7% 35.5% 25.9% DEC 60.1% 37.1% 12.65 39.0% 5.3% 10.2% 2.6% 6.1% 6.0% 2.4% 13.4% 5.2% JAN 76.4% 18.0% 5.7% 60.8% 6.8% 15.0% 6.8% 3.7% 2.6% 1.8% 1.7% 0.7% FEB 85.4% 25.1% 5.3% 60.9% 4.7% 11.0% 3.1% 2.2% 1.1% 0.8% 0.4% 0.0% MAR 90.6% 12.1% 4.7% 73.7% 2.8% 10.2% 1.5% 3.3% 0.4% 0.6% 0.0% 0.0% APR 92.6% 68.5% 4.1% 25.8% 1.4% 4.0% 0.9% 1.7% 1.1% 0.0% 0.0% 0.0% MAY 84.6% 91.8% 2.6% 4.5% 2.9% 1.7% 1.6% 0.6% 3.7% 0.7% 4.6% 0.7%

greater than 75% decrease in the proportion of days greater than 75% increase in the proportion of days 50 -75% decrease in the proportion of days 50 - 75% increase in the proportion of days less than 50% decrease in the proportion of days less than 50% increase in the proportion of days

50 51 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Blue shading represents an increase in the proportion of All months revealed an increase in the proportion days. Darker blue indicates a greater relative increase of days in which flooding of less than 10% of the in the proportion of days. forest occurred. Thus it could be assumed that from November - May, a proportion of the forest is adversely Red shading represents a decrease in the proportion of affected by increases in flooding frequency. However, days. Darker red indicates a greater relative decrease in the following reasons provide justification of why to the proportion of days. exclude November and May from the “unseasonal season”: This indicates that for the months December to April, regulation has caused an increase in the frequency • overall frequency of flooding has decreased in of floods of small areal extent (<20%). However, November and May; regulation has caused a decrease in larger floods (i.e. • frequency of flooding of more than 10% of Barmah those in which over 30% of the forest is flooded). Forest has decreased in November and May; • relative increases in flooding of less than 10% of Analysis Barmah Forest are not as severe for November and The main characteristics of forest flooding patterns May as for the other months. are: • During May and November, regulation increased 5.5 Summary: December - April the proportion of days during which the forest was dry, and the proportion of days during which The analyses of River Murray flows and forest flooding 0 - 10% of the forest was flooded. It decreased the indicate that November and May should not be included proportion of days during which over 10% of the in the definition of the summer-autumn period (during forest was flooded. which unseasonal surplus flows will be identified). • During December - April, regulation decreased Analysis which employed a high threshold for forest the proportion of days during which the forest was flooding (11,000 ML/day) suggested that flooding dry. frequency in December has actually decreased. - During December and April, regulation However, analysis indicates that the proportion of increased the proportion of days during days in December during which 0 - 30% of the forest which between 0 - 30% of the forest was is flooded has increased. Furthermore, flow analysis flooded; reveals an increase in the overall proportion of flows - during March, regulation increased the between 10,000 and 12,000 ML/day, and an increase proportion of days during which 0 - 40% of in the proportion of flows greater than 10,000 ML/day. the forest was flooded; Therefore, December is included in the definition of the summer-autumn period. - during January and February, regulation increased the proportion of days during This section presents the graphical results of combining which 0 - 20% of the forest was flooded. flow data from the months of December - April to • The most severe increases in the proportion of determine changes in patterns of River Murray flow days that between 0 - 10% of the forest was and forest flooding. flooded occurred in March (4.7% of March days in 1908 - 1929 compared to 73.7% of March days in 5.5.1 River Murray flow at Tocumwal 1981 - 2001). Results are summarised in Figures 5.25 to 5.27. The main consequences of unseasonal surplus flooding are tree deaths (red gum) and encroachment of moira grass plains. These are caused by an increase in the frequency of summer-autumn flooding in particular sensitive areas of the forest.

52 53 This section presents the graphical results of combining flow data from the months of December April to determine changes in patterns of River Murray flow and forest flooding.

5.5.1 River Murray flow at Tocumwal

COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY Results

Figure 5.25 Historical flow analysis: December-April: Flow duration curve

FLOW DURATION CURVE - December - April flow of River Murray at Tocumwal

40000

35000

30000

25000

20000

15000 Daily Flow (ML/day)

10000

5000

0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage of time exceeded

1908-1929 1936-1960 1961-2001 1981-2001 1908-2001

HISTORICAL FigureANALYSIS 5.25 Historical Flow Analysis: December-April: Flow Duration Curve

Figure 5.26 Historical flow analysis: December-April: Frequency column graph

December - April Flow of River Murray at Tocumwal 90.0%

80.0%

70.0%

60.0% 56.8% 52.7% 50.0% 42.0% 40.0% Frequency

30.0% 26.3%

20.0%

9.1% 10.0% 3.8% 3.0% 0.7% 1.5% 0.5%0.6% 0.4% 0.4% 0.3% 0.3% 0.1% 0.4% 0.2% 0.3% 0.1%0.5% 0.1% 0.0% 0 - 5000 >50 000 5000 - 10 000 35000 - 40000 40000 - 45000 45000 - 50000 10 000 - 15 15 000 - 20 20 000 - 25 30 000 - 35 25 000 - 30 Daily Flow (ML/day)

1908-1929 1936-1960 1961-2001 1981-2001 1908-2001

Figure 5.26 Historical Flow Analysis: December-April: Frequency Column Graph

Figure 5.27 Historical flow analysis: December-April: Stacked column graph

December - April flows of the River Murray at Tocumwal under 20 000 ML/day 52 53

100% 0.5%1.4% 0.6%1.5% 1.2% 2.4% 1.1% 1.7% 1.1% 2.3% 1.7% 2.2% 1.5% 4.9% 5.8% 2.4% 90% 2.9% 2.4% 4.2% 3.6% 5.0% 6.5% 80% 8.5% 16.6% 30.4% 70% 11.2% 18000 - 20000 ML/day 45.4% 16000 - 18000 ML/day 29.9% 60% 14000 - 16000 ML/day 24.5% 14.9% 12000 - 14000 ML/day 10000 - 12000 ML/day 50% 8000 - 10000 ML/day 31.1% 6000 - 8000 ML/day 40% 4000 - 6000 ML/day 21.1% 29.9% 2000 - 4000 ML/day

Relative frequency of flows 38.7% 30% 29.2% 0 - 2000

20% 17.1% 10.7%

10% 18.6% 9.0% 11.6% 9.5% 7.9% 5.1% 0% 0.6% 0.4%2.1% 1.8% 1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 Period

PAGE: 63 DATE: 1/05/03 FILE: BMReport COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY HISTORICAL ANALYSIS HISTORICAL ANALYSIS

AnalysisFigure 5.26 Historical flow analysis: December-April:• A Frequency decrease in columnthe proportion graph of flows greater than Figure 5.26 Historical flow analysis: December-April: Frequency column graph The following describes changes from the period 1908 15,000 ML/day (from 7.8% to 4.6%) - 1929 to 1981 - 2001. December - April Flow of RiverThe Murray stacked at Tocumwal column graphs illustrate the following December - April Flow of River Murray at Tocumwal 90.0% changes due to regulation: The flow90.0% duration curves illustrate the following 80.0% changes80.0% due to regulation: • A decrease in the proportion of flows under 6000 70.0% ML/day (from 63.4% to 2.0%); • An70.0% decrease in the proportion of daily flows that 60.0% 56.8% 60.0% 56.8% 52.7% • An increase in the proportion of flows between exceed 3000 ML/day (from 64.7%52.7% to 100%); 50.0% 6000 and 16,000 ML/day (from 29.8% to 94.3%); • An50.0% increase in the proportion42.0% of flows that exceed 40.0% 42.0% • A decrease in the proportion of flows over 16,000 10,000Frequency 40.0% ML/day (from 16.9% to 57.2%); Frequency 30.0% 26.3% ML/day (from 6.8% to 3.7% • A decrease30.0% in the26.3% proportion of flows that exceed 20.0% 20,00020.0% ML/day (from 4.0% to 1.6%); In summary, regulation has reduced the variability of 9.1% 10.0% 9.1% 3.8% 10.0% 3.0% 1.5% daily flows in December-April. In particular, it has The frequency column0.7% graph illustrates3.8% the3.0% following0.5% 0.6% 0.4% 0.4% 0.3% 0.3% 0.1% 0.4% 0.2% 0.3% 0.1%0.5% 0.1% 0.0% 0.7% 1.5% 0.5%0.6%decreased 0.4% 0.4% the0.3% frequency0.3% 0.1% of0.4% flows0.2% 0.3%under0.1% 60000.5% 0.1%ML/day changes 0.0%due to regulation: and over 16,000 ML/day, with flows more likely to lie 0 - 5000 • A decrease in the proportion of flows under 5000 >50 000 0 - 5000 between 6000 and 16,000 ML/day. Present flows>50 000 are 5000 - 10 000 ML/day (from 56.8% to 0.7%); 35000 - 40000 40000 - 45000 45000 - 50000 10 000 - 15 15 000 - 20 20 000 - 25 30 000 - 35 5000 - 10 000 more25 000 - 30 likely to be over 10 000 ML/day than those before 35000 - 40000 40000 - 45000 45000 - 50000 10 000 - 15 15 000 - 20 20 000 - 25 30 000 - 35 25 000 - 30 Daily Flow (ML/day) • An increase in the proportion of flows between regulation, but less likely to be overDaily 12,000 Flow (ML/day) ML/day. 5000 and 15,000 ML/day (from 35.4% to 94.7%; (See Table 5.3) 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001

Figure 5.27 Historical flow analysis: December-April: Stacked column graph Figure 5.27 Historical flow analysis: December-April: Stacked column graph

December - April flows of the River Murray at Tocumwal under 20 000 ML/day December - April flows of the River Murray at Tocumwal under 20 000 ML/day

100% 0.5%1.4% 0.6%1.5% 100% 1.2% 2.4% 1.1% 1.7% 2.3%0.5%1.4% 0.6%1.5% 1.7% 1.1% 2.4%1.1% 2.2%1.2%1.7% 1.5% 4.9%2.3% 5.8%2.4% 1.7% 90% 2.9%2.2% 2.4%1.1%1.5% 4.2%2.4% 3.6%2.4% 4.9% 5.8% 90% 5.0%2.9% 4.2% 3.6% 5.0% 6.5% 80% 8.5% 6.5% 16.6% 80% 8.5% 16.6% 30.4% 30.4% 70% 11.2% 18000 - 20000 ML/day 18000 - 20000 ML/day 70% 11.2% 45.4% 16000 - 18000 ML/day 29.9% 45.4% 16000 - 18000 ML/day 60% 29.9% 14000 - 16000 ML/day 60% 24.5% 1200014000 - -14000 16000 ML/day ML/day 14.9% 24.5% 14.9% 1000012000 - -12000 14000 ML/day ML/day 50% 10000 - 12000 ML/day 50% 8000 - 10000 ML/day 31.1% 60008000 - -8000 10000 ML/day ML/day 31.1% 40% 40006000 - -6000 8000 ML/day ML/day 40% 21.1% 4000 - 6000 ML/day 29.9% 21.1% 2000 - 4000 ML/day

Relative frequency of flows 29.9% 38.7% 2000 - 4000 ML/day 30% 29.2% 0 - 2000 Relative frequency of flows 38.7% 30% 29.2% 0 - 2000

20% 17.1% 10.7% 20% 17.1% 10.7%

10% 18.6% 9.0% 11.6% 10% 18.6% 7.9% 9.0% 9.5% 11.6% 9.5% 7.9% 5.1% 2.1% 1.8% 0% 0.6% 0.4% 5.1% 0% 0.6% 0.4%2.1% 1.8% 1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 1908-1929 1936-1960 1961-2000 1981-2000 1908-2000 Period Period

Figure 5.27 Historical Flow Analysis: December-April: Stacked Column Graph 54 55

PAGE: 63 PAGE: 63 DATE: 1/05/03 DATE: 1/05/03 FILE: BMReport FILE: BMReport COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Table 5.3 Summary of Flow Changes at Tocumwal for Period December to April 1908 - 1929 and 1981 - 2000 December - April Flow at Tocumwal 1908 - 1929 1981 - 2000 HISTORICALMean daily flowANALYSIS (ML/day) 6415.4 10444.6 Variability (std. dev.) 7065.9 3508.2 Proportion of flows in range 6000 - 16,000 ML/day 29.8% 94.3% 5.5.2Proportion Forest of flooding flows > 10,000 ML/day 16.9% 57.2% Proportion of flows > 12,000 ML/day 11.9% 11.8% Results 5.5.2 Forest Flooding

FigureThe extent 5.28 of Areal forest extent flooding of forestbetween flooding: December December-April and April for the various periods is shown in Figure 5.28.

December - April flooding of Barmah Forest (all floods) 90%

80.85% 80%

70%

60% 52.34% 50%

HISTORICAL40% ANALYSIS 31.75% Proportion of days 30%

20%

5.5.2 Forest flooding 10.16% 10% 6.52% 4.18% 2.98% 3.42% 2.28% 1.16% 1.02% 0.19% 0.72% 0.42% 0.36% 0.26%0.63% 0.23% 0.45% 0.06% 0.00% 0.00% 0% Results 0 0 - 10 10 - 20 20 - 30 30 - 40 40 - 50 50 - 60 60 - 70 70 - 80 80 - 93.5 93.5 percentage of forest flooded

Figure 5.28 Areal extent of forest flooding: December-April 1908 - 1929 1936 - 1960 1961 - 2000 1981 - 2000 1908 - 2000

December - April flooding of Barmah Forest (all floods) December - April flooding of Barmah Forest (major floods) 90% 4% 80.85% 80% 4% 3.42% 70% 2.98% 3% 60% 52.34% 3% 50% 2.28%

2% 40% 31.75% Proportion of days

Proportion of days 2%30% 1.16% 1.02% 1%20% 0.72% 0.63% 10.16% 10% 0.45% 1% 6.52% 0.42% 0.36% 4.18% 3.42% 0.26% 2.98%0.19% 2.28% 0.23% 1.16% 1.02% 0.72% 0.42% 0.63% 0.45% 0.19% 0.36% 0.26% 0.23%0.06% 0.06% 0.00% 0.00% 0% 0.00% 0.00% 0% 0 0 - 10 10 - 20 20 - 30 30 - 40 40 - 50 50 - 60 60 - 70 70 - 80 80 - 93.5 93.5 20 - 30 30 - 40 40 - 50 50 - 60 60 - 70 70 - 80 80 - 93.5 93.5 percentage of forest flooded percentage of forest flooded

1908 - 1929 1936 - 1960 1961 - 2000 1981 - 2000 1908 - 2000 1908 - 1929 1936 - 1960 1961 - 2000 1981 - 2000 1908 - 2000

54 DecemberFigure 5.28 - April Areal flooding Extent of ofBarmah Forest ForestFlooding: (major December-April floods) 55 4%

4% 3.42%

Analysis 2.98% 3%

3% The main characteristics2.28% of the forest flooding frequency plots are:

Proportion of days 2% PAGE: 65 1.16% 1.02% DATE: 1/05/03 1% 0.72% 0.63% FILE: BMReport 0.45% 1% 0.42% 0.36% 0.26% 0.19% 0.23% 0.06% 0.00% 0.00% 0% 20 - 30 30 - 40 40 - 50 50 - 60 60 - 70 70 - 80 80 - 93.5 93.5 percentage of forest flooded

1908 - 1929 1936 - 1960 1961 - 2000 1981 - 2000 1908 - 2000

Analysis

The main characteristics of the forest flooding frequency plots are:

PAGE: 65 DATE: 1/05/03 FILE: BMReport COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Analysis - If the threshold is set at 11,000 ML/day, the The main characteristics of the forest flooding forest is calculated to flood 0.7 times more frequency plots are: frequently during 1981 - 2001 (23.8% of the time) than in 1908 - 1929 (14.3% of the • The proportion of days during which flooding time). occurred in the forest increased with regulation, whether the threshold was set at 9387 ML/day, The main characteristics of the areal extent of forest 10,600 ML/day, or 11,000 ML/day. flooding during December - April are: • An increase in the threshold value decreases the • Regulation has decreased the proportion of days relative increase of the proportion of flood days, during which the forest is dry from 80.9% in 1908 i.e. - 1929 to 31.8% in 1981 - 2001; - If the threshold is set at 9387 ML/day, the • Regulation has increased the proportion of days forest is calculated to flood 2.3 times more during which 0 - 30% of the forest is flooded (from frequently during 1981 - 2001 (65.7% of 10.7% of the time to 65.91% of the time; the time) than in 1908 - 1929 (19.8% of the - in particular, forest floods which cover time); less than 10% of the Barmah Forest have - If the threshold is set at 10 600 ML/day, the increased in frequency from 6.5% to 52.3%; forest is calculated to flood 1.5 times more • Regulation has decreased the proportion of days frequently during 1981 - 2001 (36.5% of during which over 30% of the forest is flooded the time) than in 1908 - 1929 (15.5% of the (from 8.4% of the time to 2.3% of the time). time);

Table 5.4 Summary of Changes in the Extent of Forest Flooding between 1908 - 1929 and 1981 - 2000

Percentage of Forest Flooded 0 0 - 10 10 - 20 20 - 30 30 - 40 > 40 <1929 >1981 <1929 >1981 <1929 >1981 <1929 >1981 <1929 >1981 <1929 >1981 80.9 31.8 3.5 52.3 4.2 10.2 3.0 3.4 2.3 1.2 6.1 1.4

56 57 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

6. Identification of Unseasonal • Mean daily flow at Tocumwal greater than 11,000 Surplus Flow Events ML/day (RMC 1980; Johnson et. al. 1980); and • Gauge height at Picnic Point greater than 2.53m (MDBC operational rules 2001).

6.1 Overview Methods 1 and 5 are not included in this analysis. This section presents the data requirements, Method 1 was derived for the period 1963 - 1984, methodology, results and analysis of unseasonal and is thus unlikely to be accurate for the period 1981 surplus flow events identified using three different - 2001. Similarly, method 5 was suggested in 1980 and methods. The purpose of this section is to compare is unlikely to be accurate for the period 1981 - 2001. the characteristics of unseasonal surplus flow events Therefore, this section uses the three methods derived identified using different methods, to evaluate the from the most recent literature. appropriateness of these methods, and to determine As detailed in section 5, the months December - April which method should be used in further analysis. were analysed for the occurrence of unseasonal surplus The unseasonal surplus flow events were defined during flows. Surplus flows which began before 1 December the season December - April (as identified in section 5) were included if the event ran for a greater number of for the years 1980 - 2001. This period represents the days after 1 December than before 1 December. This “current” level of regulation and irrigation demands. excluded many large flood events which commenced in July, August or September and still had high flows Refer to Appendix C for supporting documentation of in December, including the flood which occurred the data analysis. during summer 2000 - 2001 (which was not due to rain rejections).

6.2 Data Surplus flows which began before the end of April and ran into May were included if the even ran for a greater The mean daily flows were obtained from RMW for: number of days before 30 April than after 30 April. • River Murray at Tocumwal (available from pre- regulation to 15 March 2001) The following characteristics of each unseasonal • River Murray downstream of Yarrawonga surplus flow event were determined: (available from pre-regulation to 15 March 2001) • start date • River Murray at Picnic Point (available from 16 • end date March 1983 to 15 March 2001). • duration For comparative purposes, data for all series was used • peak date from 16 March 1983 to 15 March 2001. • peak excess flow • total excess volume

6.3 Methodology For each method, the following statistics were derived: 6.3.1 General • total surplus flow days Five methods for identifying unseasonal surplus flow • mean length of event events have been identified in the literature: • median length of event • Peak daily flow at Tocumwal greater than 9387 • variability of event length (standard deviation and ML/day (Bren et. al. 1987); percentile rankings) • Mean daily flow downstream of Yarrawonga • proportion of days in which surplus flow occurred greater than 11,400 ML/day (DLWC 1996); • average number of events per year • Mean daily flow at Tocumwal greater than 10,600 ML/day (Thoms et. al. 2001); 56 57 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

6.3.2 Tocumwal Analysis • Purpose This method for identifying unseasonal surplus To allow drying of the forest during the summer flow events is derived from Recommendation Z3.1 period. This allows for: forestry access, access by MDBC’s River Murray Scientific Panel on for fire control, tourism access, simulation of Environmental Flows (Thoms et. al. 2001, p. 102): drying/wetting cycle which would occur under unregulated conditions. During the period, December 1 to the end of the • Rule Summary irrigation season, Barmah Choke should be run below channel capacity (i.e. 10,600 ML/day at Tocumwal) in During the summer months, do not exceed 2.53m order to prevent summer flooding. on Picnic Point gauge.

Unseasonal surplus flow events were defined as The stage-discharge relation plotted for Picnic Point follows: was not static. The relation took a different position during the period 1 July 1989 to 30 May 1994, but • start date: first day that mean daily flow at shifted back to its original (pre- July 1989) position Tocumwal exceeds 10,600 ML/day after 31 May 1994 (see Appendix C). However, as the • end date: last day that mean daily flow at rule was derived in 1996, the stage-discharge relation Tocumwal exceeds 10,600 ML/day derived for the period 31 May 1994 - present was used • total excess volume: total volume of flow above to determine the flow value corresponding to gauge 10,600 ML/day height of 2.53m.

Furthermore, the data record for Picnic Point was 6.3.3 Yarrawonga Analysis incomplete. Where flow data was missing, infilling This method for identifying unseasonal surplus flow occurred by taking the mean of the flow value before events is derived from analysis conducted by the and the flow value after the missing data point(s). Department of Land & Water Conservation’s Technical Services Directorate in 1996 (DLWC 1996, p. 8): Unseasonal surplus flow events were defined as follows: Unseasonal surplus flows were broadly identified as • start date: first day that mean daily flow at Picnic flows occurring in the period November to May which Point exceeds 8156 ML/day; exceeded the regulated flow limit (11,400 ML/day) downstream of Yarrawonga Weir. • end date: last day that mean daily flow at Picnic Point exceeds 8156 ML/day; Unseasonal surplus flow events were defined as • total excess volume: total volume of flow above follows: 8156 ML/day. • start date: first day that mean daily flow downstream of Yarrawonga exceeds 11,400 ML/ 6.4 Results day Results from the three different methods are compared • end date: last day that mean daily flow downstream in Figure 6.1. of Yarrawonga exceeds 11,400 ML/day • total excess volume: total volume of flow above 11,400 ML/day

6.3.4 Picnic Point Analysis This method for identifying unseasonal surplus flow events was derived from an authorisation of the Water Policy Committee and Water Audit Working Group of MDBC (effective date 23/2/96):

58 59 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY 6.4 RESULTS

Summary statistics are provided in Figure 6.1.

Figure 6.1 Event statistics: comparison between methods

Comparison of event statistics

80% 80 77 76 70% 70

60% 60 58

50% 50

40% 41.3% 40 36.6% 30% 30 Number of events of Number Flooding frequency Flooding 20% 20 18.3% 10% 10

4.28 3.22 4.22 0% 0 Tocumwal Analysis Yarrawonga Picnic Point Method of Analysis

Proportion of days in December - April which are flood daysdays Number of events Number of event per year

Comparison of Event Duration statistics

40 37.50 35

27.40 25

21.60 20 Days 17.00 16.00 15 14.78 12.92 11.60 10 10.00 8.57 8.00 6.00 5 4.00 3.20 2.70 2.00 2.00 8.29 1.00 0 11.60 20.63 Tocumwal Analysis Yarrawonga Picnic Point Method of Analysis

Variability (std. dev.) Median 10th percentile 20th percentile 80th percentile 90th percentile Mean

Figure 6.1 Event Statistics: Comparison Between Methods

58 59 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

UNSEASONAL SURPLUS FLOW EVENTS

Figure 6.1 Event statistics: comparison between methods (continued)

Comparison of Peak excess flow statistics

7000 6647.90 6236.80 6000

5000 4673.40

4000

3000 2948.80 2691.68 2571.66 2534.52 Peak excess flow (ML/day) 2000 2079.97 1589.00

1129.00 1000 887.00 894.00 533.82 244.60 319.20 446.02 418.50 112.40 159.80 104.00 0 44.00 Tocumwal Analysis Yarrawonga Picnic Point Method of Analysis Variability (std. dev.) Median 10th percentile 20th percentile 80th percentile 90th percentile Mean

Comparison of total excess volume statistics

45000

40000 40473 38630

35000

30000

26989 26417 25000 23784

20000 20636 18244 18090 16249 15000 Total excess volume (ML) volume excess Total 14357

10000 8519 7081 6650 5000 5188 2691 956 967 435 138 0 178 57 Tocumwal Analysis Yarrawonga Picnic Point Method of Analysis Variability (std. dev.) Median 10th percentile 20th percentile 80th percentile 90th percentile Mean

Figure 6.1 Event Statistics: Comparison Between Methods (continued)

60 61

PAGE: 71 DATE: 1/05/03 FILE: BMReport COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

6.5 Comparative Analysis 2534 ML/day for mean peak excess flow; 8519 ML compared with 16,249ML and 14,357 ML for mean 6.5.1 Degree of Coincidence total excess volume). Picnic Point events exhibit the Descriptive Statistics lowest variability in terms of peak excess flow and total Examination of Figure 6.1 reveals that the choice of excess volume. Yarrawonga events have the highest identification methodology has a significant influence variability of peak excess flow, and Tocumwal events on the calculated event statistics. have the highest variability of total excess volume.

Analysis of Tocumwal and Picnic Point data yields Degree of Overlap similar results in terms of number of events per year Figure 6.2 presents the degree of overlap between the (4.28 and 4.22), and the corresponding frequency of methods. flooding during the summer - autumn period (36.6% • The overlap between Yarrawonga and Tocumwal and 41.3% of days). However, analysis of Yarrawonga analyses is given a score of “1” for each unseasonal data yields a significantly lower number of events per surplus flow day at Yarrawonga (date = t) which year (3.22) and corresponding frequency of flooding corresponds to an unseasonal surplus flow day at (18.3% of days). Tocumwal the following day (date = t + 1); For all three methods, the calculated mean event • The overlap between Tocumwal and Picnic duration is greater than the median event duration, Point analyses is given a score of “1” for each which indicates that there are more events of length unseasonal surplus flow day at Tocumwal shorter than the mean (i.e. the distribution of event (date = t) which corresponds to an unseasonal length is skewed to the right). The different methods surplus flow day at Picnic Point the following day also yield different event duration statistics. However, (date = t + 1); the mean and median values for event length differ • The overlap between Yarrawonga and Picnic considerably between methods (Tocumwal: 12.92 days Point analyses is given a score of “1” for each and 10.00 days; Yarrawonga: 8.57 days and 6.00 days; unseasonal surplus flow day at Yarrawonga (date = Picnic Point: 14.8 days and 8.00 days). The variability t) which corresponds to an unseasonal surplus flow (standard deviation) of event duration also varies day at Picnic Point, two days later (date = t + 2); (Picnic Point 20.63, Tocumwal 11.60, Yarrawonga and 8.29). • The overlap between all three methods is given Although events identified using Picnic Point data a score of “1” if an unseasonal surplus flow are of longer duration, these events have lower mean day at Yarrawonga (at day t) corresponds to an peak excess flow and total excess volume values unseasonal surplus flow day at Tocumwal (at day than Tocumwal or Yarrawonga-identified events. t+1) and an unseasonal surplus flow day at Picnic (533.8 ML/day compared with 2080 ML/day and Point (at day t + 2).

60 Figure 6.2 Comparing Degree of Overlap Between Methods 61 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

This method accounts for approximate travel time 2. Accurate methodology for current conditions. down the Murray from Yarrawonga to Tocumwal to Picnic Point. Computable Data Set Daily flows downstream of Yarrawonga and at There are numerous unseasonal surplus flow event Tocumwal are available as a complete data set, and days (587 days; 21.2% of total days in season) extend prior to 1980. However, the data set for Picnic identified under the Picnic Point method that are not Point is not considered as robust, due to missing data identified under the Yarrawonga or Tocumwal analyses. (which required infilling) and the shift in the stage- Relatively few of the identified unseasonal surplus flow discharge relation in 1989. days are exclusive to the Yarrawonga or Tocumwal Accurate Method for Current Conditions analyses. There is a greater degree of overlap between The Picnic Point method of analysis uses a currently Tocumwal and Picnic Point analyses than Yarrawonga applicable MDBC operating rule. Similarly, the and Picnic Point analyses. Tocumwal analysis uses a threshold recommended by the MDBC. Use of either of these two methods 6.5.2 Advantages and Disadvantages attempts to represent the objectives of the MDBC The three methods of identifying unseasonal surplus with regards to maintenance of unseasonal surplus flow events produce different results with regards to flooding. However, the Yarrawonga method is not frequency, timing, duration and severity of events. The related to MDBC operating rules or recommendations. following objectives were identified to assist selection The threshold for flooding was “broadly defined” by of the most appropriate method: (See Table 6.1) DLWC, and its source was not referenced. 1. Computable data set - this relates to the availability, quality and length of data required for the method; and

Table 6.1 Summary of Advantages and Disadvantages of the Three Methods for Identifying Unseasonal Surplus Flow Events

Method Advantages Disadvantages

Picnic Point • Relates to current MDBC • Incomplete data set operational rule (1996) • Unstable stage-height relation • Identifies several unseasonal surplus flow days not identified by other methods Yarrawonga • Previous study conducted • Does not relate to MDBC rules recently (1996), facilitating or recommendations comparison • Bren et. al. (1987) identified that flow at Tocumwal is a better indicator of forest flooding than flow at Yarrawonga. Tocumwal • Relates to current MDBC recommendation (2001) • Flow at Tocumwal identified by Bren et. al. (1987) as the best indicator of forest flooding

On the basis of these advantages and disadvantages, the Tocumwal method will be used to identify unseasonal surplus flow events for further analysis.

62 63 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

6.6 Summary: Tocumwal Method The period December 1980 - December 1999 was selected to provide a 20-year data set which excluded This section summarises the unseasonal surplus flow the major floods which occurred over the summer of event characteristics as identified by the Tocumwal 2000 / 2001, as these were due to unusual operating method. (See Table 6.2) circumstances rather than rain rejections or river flushes.

Table 6.2 Unseasonal Surplus Flow Events (Tocumwal method)

Start record 1-Dec-80 Surplus flow days 1160.0 Events per year 4.1

End record 1-Dec-00 Surplus flow events 82 Flooding frequency 38.3%

Years 20

Event Characteristics Duration Peak Date Peak Excess Flow Total Excess (ML/day) Flow (ML)

AVERAGE 14.1 0.57 2211 17833

MEDIAN 10.0 0.57 1133 7960

MAX 84.0 1.00 10807 162545

MIN 1.0 0.00 8 12

SD 14.0 0.25 2572 28868

10th percentile 2.0 0.20 116 195

20th percentile 4.0 0.42 259 982

30th percentile 6.3 0.50 422 2667

40th percentile 8.0 0.50 615 4882

50th percentile 10.0 0.57 1133 7960

60th percentile 11.6 0.66 1914 11352

70th percentile 16.0 0.68 2697 15772

80th percentile 22.0 0.80 4105 22442

90th percentile 29.8 0.89 6345 43140

62 63 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

64 65 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

7. Analysis of Increased System Refer to Appendix D for supporting documentation of Flexibility the data analysis.

7.2 Increasing Airspace at Yarrawonga Weir

7.1 Overview 7.2.1 Methodology This section presents the methodology, results and To determine the impact of increasing the airspace at analysis of the effects of increased system flexibility Yarrawonga Weir (by 500, 1000, 1500... 20,000 ML), on unseasonal surplus flow volumes, frequencies, and each unseasonal surplus flow event was analysed on a event characteristics. The purpose of this analysis day-by-day basis. is to quantify (through graphical representation) the (individual) effect of: To illustrate, an imaginary event is described in Table 7.1. • increasing airspace at Yarrawonga and reduced unseasonal flows; and Table 7.1 Surplus Flow Each Day for an Event that • limiting maximum River Murray flow at Tocumwal Exceeds the Flooding Threshold of 10,600ML/d during December-April. Day Flow at Tocumwal Surplus flow1 on: (ML/day) (ML/day) • flooding frequency (proportion of days in season 0 10,500 - during which flooding occurs in the forest); 1 10,900 300 • number of events per season; 2 11,100 500 • event duration; and 3 11,300 700 • total surplus flow volume per season. 4 11,000 400 The results will be used in Section 8 to analyse the 5 10,700 100 costs of increasing system flexibility to reduce the Total 2000 flooding frequency. 1 Surplus flow = Flow at Tocumwal - 10,600, the threshold Throughout this section, the analysis is assisted by the at which flooding starts assumption that events are independent of one another. If airspace at Yarrawonga was increased by 1000ML, Refer to Section 9 for a discussion of how the analysis there is the potential to contain the first 1000ML of an could be refined by relaxing this assumption. unseasonal surplus flow event whilst maintaining flow The events analysed in this section were identified in at Tocumwal at 10,600 ML/day (see Table 7.2). Section 6.4. They occurred between December 1980 to Without increasing airspace, this event is five days April 2000 inclusive (20 seasons). long, with a total surplus flow of 2000 ML. If 1000ML

Table 7.2 Reduction in Surplus Flow when Airspace at Yarrawonga Weir is Increased to 1000ML

Day Flow at Surplus flow Airspace Adjusted flow Adjusted Tocumwal (ML/day) at Tocumwal surplus flow (ML/day) (ML/day) (ML/day) 0 10,500 - 1000 10,500 - 1 10,900 300 700 10,600 - 2 11,100 500 200 10,600 - 3 11,300 700 0 11,000 500 4 11,000 400 0 10,000 400 5 10,700 100 0 10,700 100 64 65 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

free storage was available at Yarrawonga, this event Graphs were plotted to illustrate how the increased would7.2.2 be Resultsthree days long with a total surplus flow of airspace affected event duration, excess flow per 1000ML. season, excess flow per event, days per season, events Figure 7.1 Increasing airspace at Yarrawonga Weir:per season impact and on flooding flooding frequency. frequency Thus increasing airspace at Yarrawonga by “A” ML would7.2.2 effectively Results capture all events with total surplus 7.2.2 Results Effect of increased storage capacity on frequency of unseasonal surplus flows flow < A, i.e. increasing airspace at Yarrawonga Results are summarised in Figures 7.1 and 7.2. reducesFigure 60%the 7.1 number58 Increasing of surplus airspace flow events. at Yarrawonga Weir: impact on flooding frequency 60

51 50% Effect of increased storage capacity on frequency of unseasonal surplus flows 50 47 44 60% 58 41 60 40% 39 40 37 35 51 33 50% 32 50 30 47 29 28 30% 44 27 30 26 26 41 25 24 24 23 39 22 40% 21 21 40

surplus flows occur 37 20 19 35 19 19 20% 18 18 20 year per events or Days 33 17 17 16 16 16 32 15 15 15 30 14 14 14 29 13 28 30% 27 30 Proportion of days in season during which 26 26 10% 25 10 24 24 23 22 4.1 21 21 surplus flows occur 3.4 3.3 3.1 3.1 3.0 2.8 2.7 20 19 2.6 2.6 2.4 2.4 2.3 2.3 2.2 2.1 2.1 2.1 2.0 2.0 2.0 19 19 20% 1.8 1.7 1.7 1.6 1.6 1.6 181.5 1.4 1.4 1.3 1.3 1.3 1.3 1.3 1.3 1.2 1.2 1.2 20 year per events or Days 18 17 1.1 1.1 17 16 16 16 15 0% 15 15 14 0 14 14 13 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000 16000 17000 18000 19000 20000 Proportion of days in season during which 10% Increased storage capacity (ML) 10

4.1 Days per season Events per season Proportion of season 3.4 3.3 3.1 3.1 3.0 2.8 2.7 2.6 2.6 2.4 2.4 2.3 2.3 2.2 2.1 2.1 2.1 2.0 2.0 2.0 1.8 1.7 1.7 1.6 1.6 1.6 1.5 1.4 1.4 1.3 1.3 1.3 1.3 1.3 1.3 1.2 1.2 1.2 1.1 1.1 0% 0 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000 16000 17000 18000 19000 20000 Increased storage capacity (ML)

Days per season Events per season Proportion of season Figure 7.2 Increasing airspace at Yarrawonga Weir: impact on surplus flow volume Figure 7.1 Increasing Airspace at Yarrawonga Weir: Impact on Flooding Frequency

Effect of increased storage capacity on surplus flow volume

Figure80000 7.2 Increasing airspace at Yarrawonga Weir: impact on surplus flow volume 20

70000 Effect of increased storage capacity on surplus flow volume

60000 15 80000 20

50000 70000

40000 10 60000 15

30000 50000 Surplus flow volume (ML) Average event duration (days) duration event Average 20000 5 40000 10

10000 30000 Surplus flow volume (ML)

0 0 (days) duration event Average 20000 5 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000 16000 17000 18000 19000 20000 Increased storage capacity (ML) 10000 Event duration Average excess flow per season Average excess flow per event Average excess flow per day

66 0 Figure 7.2 Increasing Airspace at Yarrawonga Weir: Impact on Surplus Flow Volume 0 67 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000 16000 17000 18000 19000 20000 Increased storage capacity (ML)

Event duration Average excess flow per season Average excess flow per event Average excess flow per day COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

7.2.3 Analysis 7.3 Limiting Flow of the River Murray at Tocumwal Flooding Frequency Increasing airspace decreases the flooding frequency 7.3.1 Methodology (proportion of days in which forest flooding occurred). To determine the impact of limiting the flow of the The relationship is logarithmic in form, i.e. the River Murray at Tocumwal (to a maximum of 10500, marginal benefit of increasing airspace diminishes as 10,400, 10,300...9000 ML/day), each unseasonal airspace increases. Put simply, considerable benefit surplus flow event was analysed on a day-by-day basis. accrues from increasing airspace by 5000ML [reduces (See Table 7.3). flooding frequency from 38% (58 days per year) to 20% (30 days per year)], but increasing airspace by To illustrate, an imaginary event is described below: a further 5000ML (to 10,000 ML) has lower benefits [only reduces flooding frequency from 20% to 14% (22 Table 7.3 Surplus Flow Each Day for an Event that days per year)]. Exceeds the Flooding threshold of 10,600 ML/d Day Flow at Tocumwal Surplus flow1 Event Frequency and Duration (ML/day) (ML/day) The relationship between increasing airspace and 0 10,500 - decreasing event frequency is also logarithmic, e.g. 5000ML extra airspace reduces event frequency from 1 10,900 300 4.1 to 2.4; another 5000ML extra airspace reduces 2 11,100 500 event frequency from 2.4 to 2.0. There is no distinct 3 11,300 700 trend between increased airspace and average event 4 11,000 400 duration (grey bars in figure 2). 5 10,700 100 Surplus Flow Total 2000 The surplus flow volume per season decreases from 73 000ML to 58,000ML (with 5000ML extra airspace) 1 Surplus flow = Flow at Tocumwal - 10,600, the threshold to 48,000 ML (with 10 000ML extra airspace) to at which flooding starts 34,000ML (with 20 000 extra airspace). If the flow at Tocumwal was limited (in non- The average excess flow volume per event increases surplus flow times) to 10,100ML/day, then on with increase storage capacity. This reflects the day 0 of this illustrative event (the day before the distribution of events by total volume. The mean total surplus flows commenced) the flow would have surplus volume (17,833 ML) is much greater than the been 10400 ML/day (instead of 10,500ML/day). median (7960 ML), which suggests that the majority [If an event is preceded by a flow of, say, 10,000 of events have total surplus volume less than the mean. ML/day, then there will be no change to the event, Therefore whilst increasing storage capacity reduces because the constraint is the imposition of a maximum the total surplus volume of all events, it has a greater flow of 10,400ML/day.] (See Table 7.4) effect in reducing the number of events.

Table 7.4 Reduction in Surplus Flow when Tocumwal Flow is Limited to 10,100 ML/d

Day Flow at Surplus flow Adjusted flow at Tocumwal (ML/ Adjusted Tocumwal (ML/day) day) surplus flow (ML/day) (ML/day) 0 10,500 - 10,100 (limit) - 1 10,900 300 10,500 (= 10,100 + (10,900 - 10,500)) - 2 11,100 500 10,700 (= 10,500 + (11,100 - 10,900)) 100 3 11,300 700 10,900 300 4 11,000 400 10,600 400 5 10,700 100 10,300 100 66 67 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

ANALYSIS OF INCREASED SYSTEM FLEXIBILITY Without limiting the maximum flow at Tocumwal, this event starts. Put simply, limiting the maximum flow at event is five days long, with a total surplus flow of 2000 Tocumwal to “B” ML reduces the number of surplus ML. If the flow at Tocumwal is limited to a maximum flow events. of 10,100ANALYSIS7.3.2 ML/day, Results OF this INCREASED event would be SYSTEM two days FLEXIBILITYlong Graphs were plotted to illustrate how the increased with a total surplus flow of 400ML. airspace affected event duration, excess flow per Thus limitingFigure 7.3 the maximum Limiting maximum flow at Tocumwal flow at Tocumwal: to “B” season, impact excess on flooding flow per frequency event, days per season, events ML 7.3.2(where B<10,600 Results ML) would effectively capture per season and flooding frequency.

all events with peak flowEffect of< decreased (Flowday River 0 Murray - FlowB), on where frequency of unseasonal surplus flows Flowday0 is the flow at Tocumwal the day before an 7.3.2 Results Figure 7.3 Limiting maximum flow at Tocumwal: impact on flooding frequency 60% 58 Results are summarised in Figures 7.3 and 7.4.60 56

Effect51 of decreased River Murray Flow on frequency of unseasonal surplus flows 50% 50 46 60% 58 60 56 41 40% 40 51 36 50% 50 46 32 30 30% 28 30 41 40% 24 40 36 22 21 surplus flows occur 20

20% 18 20 year per events or Days 32 17 30 16 15 30% 28 30

24 Proportion of days in season during which 10% 22 10 21 surplus flows occur 20

20% 4.1 4.0 3.7 3.5 18 20 year per events or Days 3.2 2.8 2.6 17 2.5 2.4 2.3 2.2 2.1 2.1 2.1 2.1 161.9 1.9 15 0% 0

Proportion of days in season during which 10600 10400 10200 10000 9800 9600 9400 9200 9000 10% 10 Maximum flow at Tocumwal (ML/day) 4.1 4.0 3.7 3.5 3.2 2.8 2.6 Days per season 2.5Events per2.4 season2.3 2.2Proportion2.1 of season 2.1 2.1 2.1 1.9 1.9 0% 0 10600 10400 10200 10000 9800 9600 9400 9200 9000 Maximum flow at Tocumwal (ML/day)

Days per season Events per season Proportion of season Figure 7.4 Limiting maximum flow at Tocumwal: impact on surplus flow volume Figure 7.3 Limiting Maximum Flow at Tocumwal: Impact on Flooding Frequency

Effect of decreased River Murray Flow on surplus flow volume

Figure80000 7.4 Limiting maximum flow at Tocumwal: impact on surplus flow volume 20

70000 Effect of decreased River Murray Flow on surplus flow volume

8000060000 2015

7000050000

60000 15 40000 10

5000030000 Surplus flow volume (ML) Average event duration (days) duration event Average 4000020000 105

3000010000 Surplus flow volume (ML) Average event duration (days) duration event Average 200000 50 10600 10400 10200 10000 9800 9600 9400 9200 9000

10000 Maximum flow at Tocumwal (ML/day)

Event duration Average excess flow per season Average excess flow per event Average excess flow per day 0 0 68 10600Figure 7.4 10400 Limiting 10200 Maximum 10000 Flow at Tocumwal:9800 Impact9600 on Surplus9400 Flow Volume9200 9000 69 Maximum flow at Tocumwal (ML/day)

Event duration Average excess flow per season Average excess flow per event Average excess flow per day

PAGE: 81 DATE: 1/05/03 FILE: BMReport

PAGE: 81 DATE: 1/05/03 FILE: BMReport COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

7.3.3 Analysis Pre-regulation Conditions Flooding Frequency Prior to regulation (1908 - 1929), flooding occurred in Limiting flow decreases the flooding frequency the forest 15.5 per cent of the time (see Section 5). To (proportion of days in which forest flooding occurred). achieve this pre-regulation frequency: The marginal benefit of increasing airspace diminishes • airspace must be increased by 9100 ML; or as airspace increases. Put simply, considerable benefit • flow at Tocumwal must be limited to a maximum accrues from limiting flow to 10,000 ML/day [reduces of 9600 ML/day. flooding frequency from 38% (58 days per year) to 21% (32 days per year)], but limiting flow to 9400 ML/ Consequently, the volume of surplus water entering the day has lower benefits [reduces flooding frequency to forest would be significantly reduced, from 73,000 ML 13% (20 days per year)]. per year to 48,000 ML per year.

Event Frequency and Duration The relationship between increasing airspace and decreasing event frequency is also logarithmic, e.g. a 10,000 ML/day limit reduces event frequency from 4.1 to 2.6 times per year, but a 9400 ML/day limit results in event frequency of 2.1 times per year. Event duration decreases from 14.1 days to 12.2 days (10,000 ML/day limit) to 9.4 days (9400 ML/day limit).

Surplus Flow The surplus flow volume per season decreases from 73,000 ML to 56,000 ML (10,000 ML/day limit) to 44,000 ML (9400 ML/day limit).

The average excess flow volume per event does not change considerably with decreasing the maximum flow limit.

7.4 Summary Based on an analysis of historical events, increasing system flexibility by increasing airspace at Yarrawonga or limiting the maximum flow at Tocumwal has the following effects: • reducing flooding frequency (proportion of days during which forest flooding occurs); • decreasing the number of events per season; and • reducing the total surplus flow volume per season.

Minor increases in system flexibility can have a significant impact on reducing flooding frequency: • increasing storage capacity by 5500 ML reduces the flooding frequency by a factor of 2; • limiting maximum flow to 9900 ML/day reduces the flooding frequency by a factor of 2. 68 69 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

70 71 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

8. Economic Analysis As detailed in Section 8.2, the net operation costs involved with decreasing flooding frequency are likely to be negligible. Therefore, quantifying the abovementioned “net conservative cost/benefit” 8.1 Overview provides a lower limit of the actual net benefit of each This section outlines the methodology and analysis of option (or an upper limit of the actual net cost of each the economic costs and benefits of increasing system option). flexibility to decrease the frequency of unseasonal The actual market benefit/cost would include value flooding in the Barmah-Millewa Forest (proportion (benefit) from increased activities such as forestry and of days in season during which flooding occurs) tourism during December-April. The actual economic from 38.3% (current) to 15.5% (pre-regulation). The (market- and non-market) benefit/cost would further economics of two options are analysed: include benefits such as amenity, option and intrinsic • increasing airspace at Yarrawonga; value. • limiting the maximum flow at Tocumwal. Refer to Appendix E for supporting documentation of The economic analysis of the alternative strategies is the data analysis. not straightforward. The approach taken here is identify both market- and non-market costs and benefits, but 8.2 Identification of Economic Costs and to selectively quantify only the following costs and Benefits benefits (collectively defined as “net conservative cost/benefit”): 8.2.1 Market Costs and Benefits • benefit of irrigation water “saved” due to reduced These are costs and benefits which have a direct forest flooding (both options); quantifiable financial value within the market. • cost of irrigation water foregone due to reduced Market Costs diversions (both options); • cost of the reduction of hydroelectric generation • Operation (increasing airspace only). The annual cost of regulation to increase airspace at Yarrawonga OR limit the maximum flow The quantification of other market benefits and non- at Tocumwal. Due to the automation of River market costs and benefits is outside the scope of this Murray regulation, these costs are likely to be low, project. This is because an accurate valuation (eg. of and offset by the reduced cost of forest regulator increased forestry yields) is prohibited without further, operation (see below). detailed investigation of the complex patterns of forest hydrology (in which each vegetation association • Water requires a distinct watering regime). Furthermore, The value of net reductions in diversions from the although methods such as hedonic pricing, travel cost River Murray system. demand, contingent valuation and conjoint analysis are - Increasing airspace at Yarrawonga has used to value non-market costs and benefits, these tools the potential to reduce irrigation supply require significant amounts of information and data to flexibility to the Murray and Murray Valley prevent biased results (Kahn 1998). Irrigation Areas. Lowered head may restrict the outflow into the Yarrawonga and Mulwala The non-market costs of reduced amenity value are irrigation channels. also likely to be negligible, given the small changes to Murray River and Lake Mulwala levels. The non- - Limiting maximum flow at Tocumwal market benefits (environmental values) are likely to reduces the supply of water to areas in exceed the non-market costs. Victoria downstream of the forest (South Australia must still receive its entitlement).

70 71 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

• Hydroelectricity Non-market Benefits Annual expected cost of decreased power • Amenity value generation due to reduced head at Yarrawonga Associated with the increased amenity value (relates to increasing airspace at Yarrawonga (anthropocentric) from reduced tree death and only). maintenance of vegetation associations.

• Water quality • Option and bequest value Annual expected costs (eg. reduced agricultural Associated with the preservation of non-market production) incurred by consumers of River benefits for an individual’s future use, or the use of Murray Water downstream of Yarrawonga the individual’s descendents. diversions, due to reduced water quality (higher Ecw) (relates to reducing maximum flow at • Ecological services Tocumwal only). Associated with the value of services such as Market Benefits nutrient cycling, carbon cycling, clean air, clean water and biodiversity. • Operation The annual reduction in cost of reduced need to • Intrinsic value operate regulators in the Barmah-Millewa Forest Unlike amenity value, intrinsic value refers to the (due to reduced flooding frequency). preservation of ecosystems and habitat for their own sake, in addition to the value of that preserved • Water for human benefit. Intrinsic value is not accrued The volume of water which is “saved” through anthropocentrically, except through the indirect reduced forest flooding may be used for irrigation value that (some) individuals may gain because (or other) purposes. they are sympathetic to the preservation and well- - Although under the accounting rules of the being of other species, independent of the use to Murray-Darling Cap, Victoria would not humans. be able to sell this water, it could be stored for environmental flows (eg. flooding the Barmah-Millewa Forest in winter and spring) 8.3 Option 1: Costs and Benefits of at an assumed equivalent marginal value. Increasing Airspace at Yarrawonga

• Timber production 8.3.1 Cost: Reduced Irrigation Supply Flexibility Annual expected value of increased yield due to Methodology and Data Requirements reduced tree death in highly stressed areas. This section quantifies the costs of increasing airspace at Yarrawonga associated with reduced irrigation supply • Recreation flexibility. From Figure 7.1, airspace at Yarrawonga Annual expected value of increased recreational would need to be increased by approximately 9100ML opportunities due to increased access. to lower unseasonal flooding frequency to 15.5% (pre- regulation frequency). 8.2.2 Non-market Costs and Benefits Non-market Costs It has been suggested (Ladson 2001, pers. comm. 9 May) that authorities maintain Lake Mulwala at a high • Amenity value level in December-April because they believe that it is Associated with the loss of amenity value necessary to ensure that maximum flows can be released (anthropocentric) from lower levels at Lake down Yarrawonga Main Channel and Mulwala Canal Mulwala or the River Murray between Yarrawonga for irrigation. Reportedly, this is a more significant and Tocumwal. problem at the end of the irrigation season, when weed growth obstructs Yarrawonga Main Channel.

72 73 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

The FSL (full supply level) of Lake Mulwala is 124.9 Scatter plots were constructed (using data from 1 mAHD (GMW 2001b), however the absolute limit is December 1980) of: approximately 125.1m, when water begins to flood • lake height (mAHD) vs. outflow at Yarrawonga property in nearby low-lying areas. Main Channel (ML/day) Data provided by RMW reports daily height upstream of Yarrawonga Weir from 1 December 1967 Data provided by RMW reports daily height upstream • lake height (mAHD) vs. outflow at Mulwala Canal and daily volumes of Lake Mulwala from 1 March 1993. A stage-volume curve was constructed to of Yarrawonga Weir from 1 December 1967 and daily (ML/day) determine the relation between height (mAHD) and volume (ML) using available data from 1 volumes of Lake Mulwala from 1 March 1993. A stage- March 1993 ñ 15 March 2001. Scatter plots were constructed using data from volume curve was constructed to determine the relation December-April, and compared to scatter plots between height (mAHD) and volume (ML) using constructed using data from the end of the irrigation availableScatte datar plo fromts we 1r eMarchcons 1993truct e- d15( uMarchsing d 2001.ata from 1 December 1980) of: season (March-April). (See Figures 8.2 and 8.3) lake height (mAHD) vs. outflow at Yarrawonga Main Channel (ML/day) lake height (mAHD) vs. outflow at Mulwala Canal (ML/day)

Scatter plots were constructed using data from December-April, and compared to scatter plots constructed using data from the end of the irrigation season (March-April).

Results

Figure 8.1 Lake Mulwala stage ñ volume relationship

Lake Mulwala stage - volume relationship

125.3

125.2 y = 2.1475E-05x + 1.2237E+02 125.1 )

D 125 H A m

( 124.9 e g a t 124.8 S

124.7

124.6

124.5 100000 105000 110000 115000 120000 125000 130000 135000 Volume (ML)

Figure 8.1 Lake Mulwala Stage - Volume Relationship

72 73 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

ECON OMI C AN ALYSIS

Figure 8.2 Lake Mulwala scatter plots showing outflows to Yarrawonga Main Channel

Yarrawonga Main Channel flow (ML/day)

125.2

125.1

) 125 D H A

m 124.9 ( a l a

w 124.8 l u M

e 124.7 k a L

124.6

124.5

124.4 0 500 1000 1500 2000 2500 3000 3500 ML/day

Yarrawonga Main Channel Flow ML/day Nominal maximum capacity 3300 ML/day Lake height at which flooding frequency to 15.5%

Yarrawonga Main Channel Flow (ML/day) (MARCH APRIL)

125.2

125.1

125 ) D H 124.9 A m ( a l 124.8 a w l u

M 124.7 e k a L 124.6

124.5

124.4 0 500 1000 1500 2000 2500 3000 3500 ML/day

Yarrawonga Channel Flow ML/day Nominal maximum capacity (ML/day) Lake height at which flood frequency reduced to 15.5%

Figure 8.2 Lake Mulwala Scatter Plots Showing Outflows to Yarrawonga Main Channel

74 75

PAGE: 87 DATE: 1/05/03 FILE: B MReport COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Figure 8.3 Lake Mulwala scatter plots showing outflows to Mulwala Canal

Mulwala Canal flow (ML/day)

125.2

125.1

) 125 D H A

m 124.9 ( a l a

w 124.8 l u M

e 124.7 k a L

124.6

124.5

124.4 0 2000 4000 6000 8000 10000 12000 ML/day

Mulwala Canal Flow ML/day Nominal maximum capacity 10000 ML/day Lake height at which flooding frequency reduced to 15.5%

Mulwala Canal Flow (ML/day) (MARCH APRIL)

125.2

125.1

125 ) D H A 124.9 m ( a l a 124.8 w l u M

e 124.7 k a L

124.6

124.5

124.4 0 2000 4000 6000 8000 10000 12000 ML/day

Mulwala Canal Flow ML/day Nominal maximum capacity 10000 ML/day Lake height at which flooding frequency reduced to 15.5%

Figure 8.3 Lake Mulwala Scatter Plots Showing Outflows to Mulwala Canal

74 75 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Analysis regulation) does NOT result in any costs incurred due Yarrawonga Main Channel to reduced irrigation supply flexibility.

Both the scatter plots for Yarrawonga Main Channel 8.3.2 Cost: Reduced Hydroelectric Power indicate that the nominal maximum flow (3300 ML/ Generation day) occurred when Lake Mulwala was between Methodology about 124.8m (11,3162 ML) and 125.1m (12,7131 Increasing airspace at Lake Mulwala results in a ML). The maximum recorded flows (>3300 ML/day) cost due to the value of lost hydroelectric power corresponded to lake heights between 124.8 and 124.9 generation. mAHD. The hydro-electric generation facility at Yarrawonga In order to reduce flooding frequency to 15.5% (pre- Weir was a venture undertaken between the Rural regulation frequency), approximately 9000 ML extra Water Corporation of Victoria and Power Facilities storage space is required at Lake Mulwala. This Pty Ltd. Electricity generated by the station is sold corresponds to a volume of 12,7131 - 9000 = 11,8132 under contract to Power Australia Ltd. Construction ML, or 124.9 mAHD. commenced in December 1992 and power was first The scatter plots reveal that at least 3300 ML/day generated in June 1994 (GMW 2001b). can flow in Yarrawonga Main Channel when the lake The station’s maximum capacity is 9.4 MW, which height is 124.9m, i.e. increasing the airspace at Lake corresponds to a maximum head differential of 9m. Mulwala to reduce flooding frequency to 15.5% does The average wholesale price of electricity in Victoria NOT have any negative impact on irrigation supply over the period 1 December 1999 to 30 April 2001 was flexibility (Yarrawonga Main Channel flows). $46.36/MWh (NEMMCO 2001). Mulwala Canal A linear relationship exists between maximum capacity Similarly, both the scatter plots for Mulwala Canal and maximum head differential (eg. increasing airspace indicate that the nominal maximum flow (10000 by 0.1m reduces maximum capacity by 0.1/9.0 *9.2 = ML/day) occurred when Lake Mulwala was between 0.1044 MW). about 124.8m (11,3162 ML) and 125.1m (12,7131 Thus a graph can be constructed illustrating cost (value ML). The maximum recorded flows (>3300 ML/day) of foregone electricity generation) vs. unseasonal corresponded to lake heights between 124.8 and 125.05 flooding frequency. (See Figure 8.4). mAHD. The following assumptions underlie the analysis: In order to reduce flooding frequency to 15.5% (pre- regulation frequency), approximately 9000 ML extra • If the maximum allowable level at Lake Mulwala storage space is required at Lake Mulwala. This is “X” mAHD, electricity generation is only corresponds to a volume of 12,7131 - 9000 = 11,8132 affected on days where the historical records ML, or 124.9 mAHD. indicate a level “Y” mAHD where Y>X; • On days where lake level is Y>X, it is assumed The scatter plots reveal that at least 10000 ML/day that the power facility was running at full capacity can flow in Mulwala Canal when the lake height is (maximum head of 9m), i.e. 9.4MW*24 hours = 124.9m, i.e. increasing the airspace at Lake Mulwala 225.6 MWh; to reduce flooding frequency to 15.5% does NOT have • Thus if the lake level was held at “X” rather than any negative impact on irrigation supply flexibility “Y” m, it would reduce the head by (Y - X)m to (9 (Mulwala Canal). - (Y - X))m , which corresponds to a power level Conclusion of ((9 - (Y - X))m * 9.4MW / 9m) MW, and an energy level of ((9 - (Y - X))m * 9.4MW / 9m) * Increasing airspace at Lake Mulwala to reduce 24 MWh unseasonal flooding frequency to 15.5% (pre- 76 77 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

This results in a significant overestimate of the costs due to foregone electricity because in practice, the system rarely (if ever) runs at full capacity (GMW 2001b).

ECON OMI C AN ALYSIS

Results

Figure 8.4 Cost of hydroelectricity generation foregone

Cost per season of hydroelectricity generation foregone

Level at Yarrawonga (mAHD) 0 9 8 7 6 5 4 2 1 0 9 8 7 6 5 4 3 2 1 0 9 1 0 0 0 0 0 0 0 0 0 9 9 9 9 9 9 9 9 9 9 8 ...... 5 5 5 5 5 5 5 5 5 5 4 4 4 4 4 4 4 4 4 4 4 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 $10,000

202.2 $9,000

$8,000 ) h W M $7,000 152.2 ( n ) o h s a W $6,000 e M s / r 6 e 4 p $ $5,000 t e

a 102.2 n ( o t g s $4,000 e o r C o f

$3,000 y g r e

52.2 n

$2,000 E

$1,000

$0 2.2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 1 Increased airspace at Yarrawonga (ML)

Figure 8.4 Cost of Hydroelectricity Generation Foregone Cost per season of hydroelectricity generation foregone

Flooding frequency % % % % % % % % % % % % % % % % % % % % % 3 7 8 2 3 6 5 3 1 2 1 4 6 0 5 1 5 1 7 1 7 ...... 8 3 0 9 7 5 4 3 2 1 0 9 8 8 7 7 6 6 5 5 4 3 3 3 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 $10,000 202.2 $9,000

$8,000 ) h W M $7,000 152.2 ( n ) o h s a

W $6,000 e M s / r 6 e 4 p $ $5,000 t e

a 102.2 n ( o t g s $4,000 e o r C o f

$3,000 y g r e

52.2 n

$2,000 E

$1,000 76 77 $0 2.2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 1 Increased airspace at Yarrawonga (ML)

PAGE: 91 DATE: 1/05/03 FILE: B MReport ECON OMI C AN ALYSIS

Results

Figure 8.4 Cost of hydroelectricity generation foregone

Cost per season of hydroelectricity generation foregone

202.2 $9,000

$8,000 ) h W M $7,000 152.2 ( n ) o h s a W $6,000 e M s / r 6 e 4 p $ $5,000 t e

a 102.2 n ( o t g s $4,000 e o r C o f

$3,000 y g r e

52.2 n

$2,000 E COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY $1,000

Cost per season of hydroelectricity generation foregone

$8,000 ) h W M $7,000 152.2 ( n ) o h s a

W $6,000 e M s / r 6 e 4 p $ $5,000 t e

a 102.2 n ( o t g s $4,000 e o r C o f

$3,000 y g r e

52.2 n

$2,000 E

$1,000

$0 2.2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 1 Increased airspace at Yarrawonga (ML) Figure 8.4 Cost of hydroelectricity generation foregone (continued)

Cost of hydroelectricity power foregone due to increased airspace at Yarrawonga

$10,000

$9,000

$8,000 PAGE: 91 DATE: 1/05/03 $7,000 FILE: B MReport

$6,000 t s

o $5,000 C

$4,000

$3,000

$2,000

$1,000

$0 14% 16% 18% 20% 22% 24% 26% 28% 30% 32% 34% 36% 38% 40% Flooding frequency

Figure 8.4 Cost of Hydroelectricity Generation Foregone (continued)

Analysis

78 To reduce flooding frequency to 15.5%, approximately 9100 ML extra airspace is required i.e. a 79 reduction in maximum lake height from 125.1m to 124.9m. Reducing the maximum head differential by 0.2m reduces energy generation, at a cost of about $8000 per season.

8.3.3 Benefit: Value of water saved from reduced flooding frequency

Methodology and data requirements

The relationship between surplus flow volume per season, increased airspace and reduction in flooding frequency was illustrated graphically in section 7 (i.e. increasing airspace by 5000 ML reduced surplus flow by 73000 ñ 58000 = 15000 ML per season, which corresponds to a flooding frequency of 20%).

Under the current accounting rules of the Murray-Darling Cap, water that floods the forest is not included in the calculation of net diversions for Victoria. Therefore any water ìsave dî by reducing flooding cannot be sold for irrigation purposes. However, this saved water could be used for environmental flows and watering the forest during winter and spring. Ladson (2001, pers comm., 20 May) suggests that the marginal value of water saved for environmental benefits is at least as great as if the water saved had been used for agriculture. Thus the gross margins for irrigated agriculture have been adopted as the marginal value of water saved from reduced flooding frequency. COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Analysis Under the current accounting rules of the Murray- To reduce flooding frequency to 15.5%, approximately Darling Cap, water that floods the forest is not included 9100 ML extra airspace is required i.e. a reduction in the calculation of net diversions for Victoria. in maximum lake height from 125.1m to 124.9m. Therefore any water “saved” by reducing flooding Reducing the maximum head differential by 0.2m cannot be sold for irrigation purposes. However, this reduces energy generation, at a cost of about $8,000 saved water could be used for environmental flows and per season. watering the forest during winter and spring. Ladson (2001, pers comm., 20 May) suggests that the marginal value of water saved for environmental benefits is 8.3.3 Benefit: Value of Water Saved from Reduced at least as great as if the water saved had been used Flooding Frequency for agriculture. Thus the gross margins for irrigated Methodology and Data Requirements agriculture have been adopted as the marginal value of The relationship between value of water saved and water saved from reduced flooding frequency. flooding frequency was derived and is illustrated in Figure 8.5. Gross margins (activity income less associated variable costs) associated with irrigated agriculture vary The relationship between surplus flow volume per considerably between region and for different landuses. season, increased airspace and reduction in flooding Gordon et. al. (2000) estimated that the average farm frequency was illustrated graphically in Section 7 (i.e. gross margin foregone by irrigated agriculture is $60/ increasing airspace by 5000 ML reduced surplus flow ML. This is the figure adopted for the value of water by 73,000 - 58,000 = 15,000 ML per season, which saved from reducing the flooding frequency (Figure corresponds to a flooding frequency of 20%). 8.6).

Figure 8.5 Valuing the Water Saved from Reduced Forest Flooding 78 79 ECON OMI C AN ALYSIS

Gross margins (activity income less associated variable costs) associated with irrigated agriculture vary considerably between region and for different landuses. Gordon et. al. (2000) estimated that the average farm gross margin foregone by irrigated agriculture is $60/ML. This is the figure adopted for the value of water saved from reducing the flooding frequency.

The relationship between value of water saved and flooding frequency was derived and is illustrated in Figure 8.5.

Figure 8.5 Valuing the water saved from reduced forest flooding

reduction in section 7 section 7 reduction in surplus flow increased flooding volume per airspace frequency season

$value of reduced surplus flow volume per season

COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Results Results Figure 8.6 Benefit of saved water

Benefit per season of saved water

Level at Yarrawonga (mAHD) 0 9 8 7 6 5 4 2 1 0 9 8 7 6 5 4 3 2 1 0 9 1 0 0 0 0 0 0 0 0 0 9 9 9 9 9 9 9 9 9 9 8 ...... 5 5 5 5 5 5 5 5 5 5 4 4 4 4 4 4 4 4 4 4 4 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 $1,600,000 25000.0 $1,400,000

$1,200,000 20000.0 ) L M ( n o

$1,000,000 s a e s t 15000.0 i r f e e p n $800,000 e d B e v a

$600,000 10000.0 s e m u l o

$400,000 V 5000.0 $200,000

$0 0.0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 1 Increased airspace at Yarrawonga (ML)

Figure 8.6 Benefit of saved water (continued)

Benefit per season of saved water PAGE: 93 DATE: 1/05/03 Flooding frequency FILE: B MReport % % % % % % % % % % % % % % % % % % % % % 3 7 8 2 3 6 5 3 1 2 1 4 6 0 5 1 5 1 7 1 7 ...... 8 3 0 9 7 5 4 3 2 1 0 9 8 8 7 7 6 6 5 5 4 3 3 3 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 $1,600,000 25000.0 $1,400,000

$1,200,000 20000.0 ) L M ( n o

$1,000,000 s a e s t 15000.0 i r f e e p n $800,000 e d B e v a

$600,000 10000.0 s e m u l o

$400,000 V 5000.0 $200,000

Figure 8.6 Benefit of Saved Water Benefit per season of saved water due to increased airspace at Yarrawonga

$1,600,000

80 $1,400,000 81

$1,200,000

$1,000,000 t i f

e $800,000 n e B

$600,000

$400,000

$200,000

$0 14% 16% 18% 20% 22% 24% 26% 28% 30% 32% 34% 36% 38% 40% Flooding frequency Figure 8.6 Benefit of saved water (continued)

Benefit per season of saved water

Flooding frequency % % % % % % % % % % % % % % % % % % % % % 3 7 8 2 3 6 5 3 1 2 1 4 6 0 5 1 5 1 7 1 7 ...... 8 3 0 9 7 5 4 3 2 1 0 9 8 8 7 7 6 6 5 5 4 3 3 3 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 $1,600,000 25000.0 $1,400,000

$1,200,000 20000.0 ) L M ( n o

$1,000,000 s a e s t 15000.0 i r f e e p n $800,000 e d B e v a

$600,000 10000.0 s e m u l o

$400,000 V 5000.0 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY $200,000

Benefit per season of saved water due to increased airspace at Yarrawonga

$1,600,000

$1,400,000

$1,200,000

$1,000,000 t i f

e $800,000 n e B

$600,000

$400,000

$200,000

$0 14% 16% 18% 20% 22% 24% 26% 28% 30% 32% 34% 36% 38% 40% Flooding frequency

Figure 8.6 Benefit of Saved Water (continued)

Analysis During 1980 - 2000, an average of 73,000 ML of unseasonal surplus water entered the forest each year (refer to section 7), corresponding to a flooding frequency of 38.3%. The equivalent cost of this (at a marginal value of $60/ML) is $4.4m.

At a marginal value of $60/ML, significant benefit accrues from reducing flooding frequency. If the flooding frequency was reduced to 15.5% (pre- regulation frequency), then the volume of surplus water entering the forest each year would be reduced by 24,000 ML to 49,000 ML, representing a saving of $1.44m.

80 81 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

8.3.4 Net Conservative Benefit To calculate the volume of reduced water, daily The costs of decreased hydroelectricity generation flow data at Tocumwal was analysed for each day in are insignificant compared to the benefits of saved December-April from 1980 - 2000. water. (See Figure 8.7). Thus, net benefits accrue from To illustrate, consider the following imaginary daily increasing airspace to reduce flooding frequency, in flow sequence (see Table 8.1): the order of $1.44m (benefits of reducing flooding frequency to 15.5%). Table 8.1 Sample Flow Sequence at Tocumwal

Day Flow at Flow 8.4E C OptionON OM 2:I C CostsAN AandLY SBenefitsIS of Limiting Tocumwal downstream of Flow at Tocumwal (ML/day) forest (ML/day) Analysis 1 10,200 10,200 8.4.1 Cost: Reduced Water Supply Downstream of 2 10,250 10,250 the Barmah-Millewa Forest During 1980 ñ 2000, an average of 73000 ML of unseas3onal surplus 10,350water entered th10,350e forest each Methodologyyear (refer to section 7), corresponding to a flooding 4frequency of10,50038.3%. The equi10,500valent cost of this (at a marginal value of $60/ML) is $4.4m. Limiting the maximum flow at Tocumwal reduces the 5 10,700 10,700 volume of water available for downstream users. Note 6 10,800 10,800 At a marginal value of $60/ML, significant benefit accrues from reducing flooding frequency. If the that Victoria’s total diversions may remain constant, 7 10,300 10,300 flooding frequency was reduced to 15.5% (pre-regulation frequency), then the volume of surplus i.e. part of the loss to downstream Victorian users will Total (ML) 72,800 water entering the forest each year would be reduced by 24000 ML to 49000 ML, representing a be offset by a gain in irrigation supply by upstream Note that on days 5 and 6, the flow available to downstream users.sav Asing thisof $section1.44m only. costs the loss to downstream users is at a maximum 10,600 ML/day. users, it represents an overestimate of the net costs of If the flow was maintained at 10,300 ML/day, the flow reduced8.3.4 waterNe supplyt con downstreamservative ofb theen forest.efit available to downstream users would be reduced (see Table 8.2).

Figure 8.7 Benefit of saved water

Net benefit from increasing airspace at Yarrawonga

$10,000,000

$1,000,000

$100,000

) $10,000 $ ( e u l a

V $1,000

$100

$10

$1 14% 16% 18% 20% 22% 24% 26% 28% 30% 32% 34% 36% 38% 40% Flooding frequency

Net benefit Benefit: water saved from reduced flooding Cost: less hydroelectricity generation

Figure 8.7 Benefit of Saved Water

82 The costs of decreased hydroelectricity generation are insignificant compared to the benefits of 83 saved water. Thus, net benefits accrue from increasing airspace to reduce flooding frequency, in the order of $1.44m (benefits of reducing flooding frequency to 15.5%).

PAGE: 95 DATE: 1/05/03 FILE: B MReport COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Results The cost to downstream irrigators of limiting flows at Tocumwal is shown in Figure 8.8.

Table 8.2 Effect of Limiting Flows at Tocumwal on Volumes Available to Downstream Users

Day Flow at Tocumwal Flow available to If flow limited to a maximum of (ML/day) downstream users 10,300 ML/day (ML/day) Flow (ML/day) Flow downstream (ML/day)

1 10,200 10,200 10,200 10,200

2 10,250 10,250 10,250 10,250

3 10,350 10,350 10,300 10,300

4 10,500 10,500 10,300 10,300

5 10,700 10,600 10,500 10,500 ECON OMI C AN ALYSIS 6 10,800 10,600 10,600 10,600 Note that on days 5 and 6, surplus flows occurred, with flow adjusted accordingly as in section 7. 7 10,300 10,300 10,300 10,300

TotalResu (ML)lts 72,800 72,550

Note that on days 5 and 6, surplus flows occurred, with flow adjusted accordingly as in Section 7. Figure 8.8 Costs of reduced downstream water supply

Cost of reduced irrigation supply dowsntream

Flooding frequency % % % % % % % % % % % % % % % % 3 8 5 2 8 7 9 7 4 2 6 8 1 0 1 5 % ...... 7 8 6 3 0 6 3 0 9 8 6 4 3 3 2 1 0 . 3 3 3 3 2 2 2 1 1 1 1 1 1 1 1 1 9 $8,000,000

120000 $7,000,000

$6,000,000 100000 ) L M (

$5,000,000 e 80000 m u l o t v s r o

$4,000,000 e t C 60000 a w d

$3,000,000 e c u d

40000 e $2,000,000 R

20000 $1,000,000

$0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 4 2 0 8 6 4 2 0 0 0 0 0 9 9 9 9 9 1 1 1 1 Maximum flow at Tocumwal

Figure 8.8 Costs of Reduced Downstream Water Supply

82 Cost of reduced irrigation supply downstream 83

$8,000,000

$7,000,000

$6,000,000

$5,000,000 t s

o $4,000,000 C

$3,000,000

$2,000,000

$1,000,000

$0 10% 12% 14% 16% 18% 20% 22% 24% 26% 28% 30% 32% 34% 36% 38% 40% Flooding frequency

PAGE: 97 DATE: 1/05/03 FILE: B MReport ECON OMI C AN ALYSIS

Note that on days 5 and 6, surplus flows occurred, with flow adjusted accordingly as in section 7.

Results

Figure 8.8 Costs of reduced downstream water supply

Cost of reduced irrigation supply dowsntream

Flooding frequency % % % % % % % % % % % % % % % % 3 8 5 2 8 7 9 7 4 2 6 8 1 0 1 5 % ...... 7 8 6 3 0 6 3 0 9 8 6 4 3 3 2 1 0 . 3 3 3 3 2 2 2 1 1 1 1 1 1 1 1 1 9 $8,000,000

120000 $7,000,000

$6,000,000 100000 ) L M (

$5,000,000 e 80000 m u l o t v s r o

$4,000,000 e t C 60000 a w d

$3,000,000 e c u

COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY d COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

40000 e $2,000,000 R

20000 $1,000,000

$0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 4 2 0 8 6 4 2 0 0 0 0 0 9 9 9 9 9 1 1 1 1 Maximum flow at Tocumwal

Cost of reduced irrigation supply downstream

$8,000,000

$7,000,000

$6,000,000

$5,000,000 t s

o $4,000,000 C

$3,000,000

$2,000,000

$1,000,000

$0 10% 12% 14% 16% 18% 20% 22% 24% 26% 28% 30% 32% 34% 36% 38% 40% Flooding frequency

Figure 8.8 Costs of Reduced Downstream Water Supply (continued)

PAGE: 97 DATE: 1/05/03 FILE: B MReport

Analysis 8.4.3 Net Conservative Cost The cost of reducing flooding frequency to 15.5% Analysis by limiting the maximum flow at Tocumwal to The reduction of flooding frequency achieved by 9600 ML/day is in the order of $3.7m. limiting maximum flow at Tocumwal incurs a net cost, because the volume of water saved is less than Significant decreases in flooding frequency (38.3% to the reduced volume of water available to downstream 27.5%) can be achieved at a cost of $1m. Victorian irrigators. This cost is an “upper limit” estimate, which does not include analysis of the 8.4.2 Benefit: Value of Water Saved from Reduced potential for increased upstream use. Flooding Frequency Refer to Section 8.3.3 for the methodology, data The flooding frequency could be reduced to 15.5% at requirements and analysis of the benefit of water saved a net cost of $2.5m. However, the flooding frequency from reduced flooding frequency. could be significantly reduced (from 38.3% to 21%) at a net cost of $1m. (See Figure 8.9).

84 85 Analysis

The cost of reducing flooding frequency to 15.5% by limiting the maximum flow at Tocumwal to 9600 ML/day is in the order of $3.7m.

Significant decreases in flooding frequency (38.3% to 27.5%) can be achieved at a cost of $1m.

8.4.2 Benefit: Value of water saved from reduced flooding frequency

Refer to section 8.3.3 for the methodology, data requirements and analysis of the benefit of water saved from reduced flooding frequency.

COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY 8.4.3 Net conservative cost

Figure 8.9 Net cost of limiting maximum flow at Tocumwal

Cost of reduced irrigation supply dowsntream

Flooding frequency 38.3% 36.8% 33.5% 30.2% 26.8% 23.7% 20.9% 19.7% 18.4% 16.2% 14.6% 13.8% 13.1% 12.0% 11.1% 10.5% 9.7% $4,000,000 66667

46667 $2,000,000 26667

6667 )

$0 L M r ( e

-13333 r t e a t a w f w

o -$2,000,000 -33333 f o e u e l a -53333 m V u l o

-$4,000,000 V -73333

-93333 -$6,000,000 -113333

-$8,000,000 -133333 10600 10400 10200 10000 9800 9600 9400 9200 9000 Maximum flow at Tocumwal

Benefit: water saved from reduced flooding Cost: less downstream water Net cost ECON OMI C AN ALYSIS

Figure 8.9 Net cost of limiting maximum flow at Tocumwal (continued)

Net cost of limiting maximum flow at Tocumwal

$3,000,000

$2,000,000

$1,000,000

-$1,000,000

-$2,000,000 e u l a

V -$3,000,000

-$4,000,000

-$5,000,000

-$6,000,000

-$7,000,000

-$8,000,000 10% 12% 14% 16% 18% 20% 22% 24% 26% 28% 30% 32% 34% 36% 38% 40% Flooding frequency

Benefit: water saved from reduced flooding Cost: less downstream water Net cost

Figure 8.9 Net Cost of Limiting Maximum Flow at Tocumwal Analysis

84 85 The reduction of flooding frequency achieved by limiting maximum flow at Tocumwal incurs a net cost, because the volume of water saved is less than the reduced volume of water available to downstream Victorian irrigators. This cost is an ìuppe r limitî estimate, which does not include analysis of the potential for increased upstream use.

The flooding frequency could be reduced to 15.5% at a net cost of $2.5m. However, the flooding frequency could be significantly reduced (from 38.3% to 21%) at a net cost of $1m.

8.5 SUMMARY: COMPARISON BETWEEN OPTIONS

The reduction of flooding frequency to 15.5% can be achieved by: increasing airspace at Yarrawonga by 9100 ML, at a net benefit of $1.44m; or limiting maximum flow at Tocumwal to 9750 ML/day, at a net cost of $2.5m.

Clearly, it is preferable to increase airspace at Yarrawonga.

The benefit of $1.44m is understated, because it does not include: increased timber production due to reduced tree death; increased tourism and recreation increased ecological, environmental and heritage values.

PAGE: 99 DATE: 1/05/03 FILE: B MReport COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

8.5 Summary: Comparison Between Options The reduction of flooding frequency to 15.5% can be achieved by: • increasing airspace at Yarrawonga by 9100 ML, at a net benefit of $1.44m; or • limiting maximum flow at Tocumwal to 9750 ML/ day, at a net cost of $2.5m.

Clearly, it is preferable to increase airspace at Yarrawonga.

The benefit of $1.44m is understated, because it does not include: • increased timber production due to reduced tree death; • increased tourism and recreation; • increased ecological, environmental and heritage values.

86 87 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

9. Conclusion and Recommendations Consequently, there are some parts of the forest (~30% of the area) which are flooded more than twice as frequently in summer-autumn now than before 1929, The detrimental impacts of summer-autumn flooding which leads to tree stress and death. However, the of the Barmah-Millewa Forest have been well remainder of the forest (~70% of the area) is flooded documented since the early 1980’s. Both the results of less frequently now than before 1929. Both these analytical research and anecdotal observations point to changes have resulted in changes to the “natural” increased red gum tree death in low-lying areas and the vegetation associations and patterns in the forest. increasing loss of moira grass plains. Unseasonal Surplus Flow Events The management agencies at State and Federal There are three main methods identified from the government level pay heed to this problem by literature for identifying unseasonal surplus flow highlighting its importance in their published events, which yield significantly different results. management strategies and plans for the forest. The method which involves analysing daily data for However, recent priorities have concentrated on flows that exceed 10,600 ML/day at Tocumwal is the environmental flows for winter-spring flooding, rather preferred method in terms of a computable data set and than the management of unseasonal surplus flows. applicability to current conditions. Little analytical work has been conducted to quantify the extent and severity of flooding, or to investigate the The use of this method revealed that during the period feasibility of management options. 1980 - 2000, there were 82 surplus flow events (4.1 per year), which caused flooding in the forest in 38.3% of This report investigated the potential for two days in December-April. The average event duration management options related to increasing system was 14.1 days (median 10 days); average peak excess flexibility, namely increasing airspace at Yarrawonga flow was 2211 ML/day (median 1133 ML/day); and and limiting the maximum flow at Tocumwal. The average total flow per event was 17,833 ML (median main findings of this project are summarised below. 7960 ML).

Historical Analysis Relation to System Flexibility A comparison of historical flow data from 1908 - 1929 If system flexibility had been greater over the period (before the construction of the Hume) and 1981 - 2001 1980 - 2000, then there would have been significantly (present regulation conditions) revealed that there less frequent flooding of the Barmah-Millewa Forest. have been significant changes in the patterns of River If 1980 - 2000 is assumed to represent current water Murray flow at Tocumwal during summer and autumn. demand conditions, then flooding frequency can be During December to April (particularly in February reduced from 38.3% to 15.5% by: and March), flows are far more likely to be above • increasing airspace at Yarrawonga by 9100 ML 10,600 ML/day now (36.5% of the time) than before (maintaining height at 124.9m, 0.195m below the 1908 (15.5% of the time). This means that regulation maximum); OR has increased the number of days in summer-autumn during which flooding occurs in the Barmah-Millewa • limiting the maximum flow at Tocumwal to 9600 Forest. ML/day. Smaller increases in system flexibility can also have However, an application of the relationship derived a significant impact on reducing flooding frequency, by Bren et. al. (1987) linking flow at Tocumwal e.g. a frequency of 20% will be achieved by increasing to proportion of forest flooded revealed that more airspace by just 5000 ML or limiting the maximum extensive floods (in which over 30% of the forest is flow at Tocumwal to 9900 ML/day. flooded) are now less frequent. This is because the construction of dams, locks and weirs has enabled Economic Analysis mitigation of larger River Murray flows. Approximately $4.4m of water (73,000 ML/year) per year is currently “lost” to forest flooding during 86 87 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

December-April. Reducing flooding frequency from surplus flow events are independent, and enable the 38.3% to 15.5% would reduce the total surplus incorporation of forecasted changes in irrigation volume per year to 49000 ML (an equivalent saving demand). The MDBC currently runs a model, which of $1.4m). simulates these conditions on a monthly timestep, and is in the process of refining the model to generate daily Reducing Limiting the maximum flow at Tocumwal to data. 9600 ML/day to reduce flooding frequency to 15.5% results in a net cost of $2.5m (less water available to The results from this project could be used in a detailed downstream users, but water saved from flooding for analysis of the changes in forest ecology which will environmental flows). However, this figure is not a true be experienced under “do-nothing” or “increase- indicator of net economic cost. Net economic cost will flexibility” situations. be far lower, due market (forestry and tourism) and non-market (environmental) benefits from reduced 9.1.2 Extended Economic Analysis forest flooding and the potential for greater upstream A detailed investigation of forest ecology would use. facilitate the economic analysis of the changes to Increasing the airspace at Yarrawonga by 9100 ML does timber production. There may also be implications for not limit the outflow into the irrigation areas through salinity levels in the Murray River from the proposed Yarrawonga Main Channel and Mulwala Canal. Very operational changes and these could be investigated by minor losses in hydroelectric power generation will the MDBC using their models. be incurred, but they will be more than offset by the Attempts could also be made to use and evaluate value of the water saved from flooding ($1.4m). This valuation techniques to determine the non-market figure assumes a marginal value of water equivalent gains from reduced forest flooding. to the agricultural gross margin ($60/ML), which is likely to be an understatement of the value of water Alternative values for the agricultural gross margin if it were used for environmental watering purposes. could be adopted under different scenarios of water Furthermore, the $1.4m benefit does not include the allocation, e.g. for the situation of limiting maximum value accrued from reducing flooding frequency. flow at Tocumwal, the value of the water depends on which downstream regions/land uses will have The analysis conducted in this project indicates that restricted availability. significant net benefits will accrue from increasing airspace at Yarrawonga to reduce the frequency of summer-autumn forest flooding. 9.1.3 Investigation of Other Management Options This project considered only two management options for reducing the frequency of unseasonal surplus flows. 9.1 Recommendations for Further Research Other management options (some of which may require There are three main areas in which further research capital works) could be evaluated for their effectiveness could be undertaken in reducing the frequency of unseasonal surplus flows, • Alternative modelling/analytical techniques; and corresponding net discounted cost/benefit.

• Extended economic analysis; and Possible management options are discussed below. • Investigation of other management options. Hume to Yarrawonga Weir Operations

9.1.1 Alternative Modelling and Analytical The current operational rules governing rates of Techniques drawdown in the Murray reach between Hume Dam A more extensive system approach could be taken and Yarrawonga (150mm/day maximum at Doctors to modelling the River Murray flow, storage at Lake Point) are designed to protect against the risk of bank Mulwala and forest flooding (this would involve slumping. The drawdown rates are based on empirical relaxing the assumption that individual unseasonal estimates and past observations of bank slumping. 88 However, it has been suggested that the regulated 89 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

drawdown rate may be conservative in comparison to rates of natural recession (DLWC 1996). The development of riparian vegetation may also allow the drawdown rate to be increased without compromising bank stability.

With a higher drawdown rate, releases from Hume can be reduced more quickly if rain rejections occur. Therefore Hume to Yarrawonga would be reduced, mitigating unseasonal flooding in the Barmah-Millewa forest.

On-Route Storages The operation of on-route storages adjacent to the irrigation systems would allow rejected water orders to be captured for later use. On-route storages would increase flexibility of the operation of the water delivery system and may help to overcome current problems of inaccurate water ordering (DLWC 1996).

Forest Diversions This involves the establishment of regulators in the eastern part of the forest to enable a diversion of unseasonal surplus flows to Bullatale Creek, increasing escape capacities and constructing a bypass system.

During summer and autumn, the escape capacity for excess water within the irrigation system is restricted because of operational requirements. This is so because Mulwala Canal is run at near-full capacity to supply irrigators, with limited capacity for excess water.

A combination of increased escape capacity and a system of channels to bypass the forest would reduce the volume of surplus irrigation water continuing to the forest.

Streamlining Water Ordering Procedure Currently, there is no incentive in place for irrigators or irrigation authorities to cancel water orders early when localised rainfall occurs. Irrigators can reduce their water orders at short notice without decreasing their water entitlement or being charged for the water they ordered but did not use.

A water ordering system that encouraged irrigators to order accurately and cancel early could reduce the volume of unseasonal surplus flows.

88 89 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

90 91 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

10. References Department of Land and Water Conservation (DLWC) 1996, Unseasonal Surplus Flow Management - Barmah-Millewa Forest, June. Atkinson, W. 2001, “Yorta Yorta struggle for justice continues”, http://users.mcmedia.com.au/~yorta/ Dwyer Leslie Pty. Ltd. 1991, “Barmah-Millewa Forests wayne.htm (accessed 4 April). Water Management Plan Working Paper 11: Economic Analysis”, October. Barmah-Millewa Forum (BMF) 2000, Annual Plan 2000-2001 for water operations and works in the Farrant, D. 2001a, “Can our courts deliver the kind of Barmah-Millewa Forest, July. justice that Aborigines seek?”, The Age, 10 February.

Bren, L. 1988, “Flooding characteristics of a riparian Farrant, D. 2001b, “Yorta Yorta claim off to High red gum forest”, Australian Forestry, vol. 51, pp. 57- Court”, The Age, 10 March. 62. Gordon, S., A. Kemp and C. Mues 2000, Irrigation Bren, L. 1992, “Tree Invasion of an intermittent wetland in the Murray Darling Basin and the Impact of Water in relation to changes in the Flooding Frequency of Policy Reforms, ABARE Report prepared for the the River Murray, Australia”, Australian Journal of Natural Heritage Trust MD 2001 - Fish Rehab program, Ecology vol. 17, pp. 395-408. Canberra, August.

Bren, L. and Gibbs, N. 1986, “Relationships between Goulburn-Murray Water (GMW) 2000, Annual Report flood frequency, vegetation and topography in a river 1999/2000. red gum forest”, Australian Forest Research, vol. 16, GMW 2001a, “Murray Valley”, http://www.g- pp. 357-70. mwater.com.au/browse.asp?ContainerID=murray_ Bren, L., 1988, “Effects of river regulation on valley (accessed 6 February 2004). flooding of a riparian red gum forest on the River GMW 2001b, “Yarrawonga Weir”, http://www.g-mwater Murray, Australia”, Regulated Rivers: research and .com.au/article.asp?ContentID=yarrawonga_ management, vol. 2, pp. 65-77. weir&ContainerID=murray_storages (accessed 6 Bren, L., O’Neill, I. and Gibbs, N. 1987, “Flooding February 2004). of the Barmah Forest and its relation to flow in the Ife, D. 1998, The Hydrogeology of the Barmah Forest, Murray-Edward River system,” Australian Forest Investigations Report No. 1988/32, Rural Water Research, vol. 17, pp. 127-44. Commission of Victoria, November. Bren, L., O’Neill, I. and Gibbs, N. 1988, “Use of map Johnson, K.E., I.R. Meacham and W.H. Martin 1980, analysis to elucidate flooding in an Australian riparian “The River Murray Between Tocumwal and Echuca” river red gum forest”, Water Resources Research, vol. Problems of River Operation Through the Barmah 24, no. 7, pp. 1152-1162. and Millewa Forests”, conference paper, Hydrology Bureau of Meteorology (BOM) 2001, “Climate and Water Resources Symposium, Adelaide, 4 - 6 Averages”, http://www.bom.gov.au/climate/averages/ November. tables/cw_074106.shtml /cw_074128.shtml /cw_ Kahn, J.R. 1998, The Economic Approach to 080015.shtml (accessed 31 March). Environmental and Natural Resources 2nd edn., The Chesterfield, E.A,, 1986, “Changes in the vegetation Dryden Press, Orlando. of the river red gum forest at Barmah, Victoria”, Lacey, G. 2001, Logging and Grazing in the Barmah Australian Forestry, vol. 49, no. 1, pp. 4-15. Forest, Preliminary Draft for a Briefing Note, Department of Conservation and Environment (DCE) unpublished. 1992, Barmah Management Plan for Barmah State Park and Barmah State Forest, East Melbourne, September. 90 91 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Leslie, D. and K. Harris 1996, Water Management Plan Murray Water Entitlement Committee (MWEC) 1997, for the Millewa Forests, State Forests of New South Sharing the Murray - Proposal for defining people’s Wales, Deniliquin, July. entitlements to Victoria’s water from the Murray, October. Leslie, D. and K. Harris 1996, Water Management Plan for the Millewa Forests, State Forests of New South National Electricity Market Management Company Wales, Deniliquin, July. Ltd. (NEMMCO) 2001, “Average monthly prices”, http://www.nemmco.com.au/data/tables.htm (accessed Maunsell (Maunsell Pty Ltd) 1992a, Barmah-Millewa 22 May). Forests Water Management Plan, Final Report, MDBC, January. River Murray Commission (RMC) 1980, River Murray-Tocumwal to Echuca, River Regulation and Maunsell 1992b, Watering the Barmah-Millewa Red Associated Forest Management Problems, Review Gum Forest, Issues Paper, MDBC, January. Report, June.

Maunsell McIntyre (Maunsell McIntyre Pty Ltd) 1999, Seidel, P. 2001, “The Yorta Yorta native title Report on Barmah-Millewa Flood of October 1998 and determination application” /Working with the Native The First Use of Barmah-Millewa Forest Allocation, Title Act: alternatives to the adversarial method: The Barmah-Millewa Forum, August. proceedings from a workshop held 4-5 June 1997/, NTRU, AIATSIS, Canberra, 1998. McKinnon, L.J. 1997, Monitoring the Fish Aspects of the Flooding of Barmah Forest, Final Report to Smith, R.B. 1983, Analysis of growth in red gum forest the Murray-Darling Basin Commission for Natural - Barmah 1983, Barmah Forest Inventory Report No. Resources Management Strategy Project V014, Marine 46, Forests Commission Victoria, Melbourne. and Freshwater Resources Institute, Queenscliff, October. Thoms, M., P. Suter, J. Roberts. J. Koehn, G. Jones, T. Hillman and A. Close 2000, Report of the River Murray Murray Darling Basin Commission (MDBC) 2000, The Scientific Panel on Environmental Flows, River Murray Barmah-Millewa Forest Water Management Strategy, - Dartmouth to Wellington and the Lower Darling on behalf of the Barmah-Millewa Forum, June. River, Murray-Darling Basin Commission, October.

MDBC 2001a, “The Barmah-Millewa Forum”, http:// Ward, K.A., C. Leitch, L.N. Lloyd and B.P. Atkins www.mdbc.gov.au/naturalresources/barmah_millewa/ 1994, Interim Water Management Strategy for Barmah index.html (accessed 6 February 2004). Forest, Victoria, Natural Resources Management Strategy of the Murray-Darling Basin Ministerial MDBC 2001b, “River Murray Water”, http:// Council, Canberra and the Department of Conservation www.mdbc.gov.au/river_murray/river_murray_water/ and Natural Resources, Victoria, August. rmw.htm (accessed 14 March). Ward, K.A., C. Leitch, L.N. Lloyd and B.P. Atkins MDBC 2001c, “Fact Sheet 6: The Barmah Choke”, 1994, Interim Water Management Strategy for Barmah http://www.mdbc.gov.au/river_5Fmurray/river_ Forest, Victoria, Natural Resources Management Fmurray_Fsystem/barmah/barmah.htm (accessed 4 Strategy of the Murray-Darling Basin Ministerial April). Council, Canberra and the Department of Conservation Murray Irrigation Limited (MIL) 2001, “About Murray and Natural Resources, Victoria, August. Irrigation Limited”, http://www.murrayirrigation.com. au/Theco/aboutmil.htm (accessed 24 March).

92 93 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Appendix A: Development of These steps enabled an understanding of the complex Research Methodology physical system and the identification of agencies and institutions from which further information would be available. A record of personal correspondence is included in Appendix A. 1. Research Methodolgy and Data Requirements 1.3 Research Avenues 1.1 Overview 1.3.1 Components of Research Methodology This section presents the development of a research To enable the aims and objectives of this project to be methodology which enabled an evaluation of how met, the following research methodology components the risk of unseasonal surplus flows, which affect the were identified: Barmah-Millewa forest, is related to flow in the River 1. Analyse historical data to investigate changes in Murray system. River Murray flows (caused by regulation), and to investigate changes in patterns of flooding in the This section includes a brief review of the research Barmah-Millewa Forest; methodology to date. The emphasis of the initial research phase was to document, investigate and 2. Define and establish a method for identifying understand the physical, regulatory, institutional and individual unseasonal surplus flow events (for the economic environment of the problem. period in which the current level of river regulation and irrigation demands is thought to apply), The information gained in the initial research phase including calculation of event characteristics was used to identify and evaluate possible avenues including total excess volume and peak excess of research, and to determine data requirements and flow rate; availability. This section should be read as a proposed 3. Define what is meant by the “risk” of a unseasonal research plan, as it is likely that the methodology will surplus flow event occurring, and establish a evolve as data and results become available. methodology for calculating this risk; 4. Use knowledge of physical environment to identify Furthermore, it is recognised that this research project factors (including those relevant to the regulation is constrained by limited time and resources. It is of the Murray) which influence this “risk”; expected that the majority of “possible avenues of research” will become “recommendations for further 5. Establish a method establishing a relationship research”. between the factors identified in Part 3 and the “risk” of unseasonal surplus flows; and 1.2 Initial Research Phase Methodology 6. Evaluate the economic benefits and costs of increasing system flexibility to reduce the risk of The research steps conducted so far include: unseasonal surplus flows. • identification of problem; 1.3.2 Analyse Historical Data • identification of stakeholders and management agencies responsible for the use of the Barmah- Possible Research Avenues Millewa Forest and the River Murray; Most of the material in Background Information • literature review of information available in (Section 3) about the changes caused by regulation is refereed journals and other publications, including qualitative. Numerical analysis of historical data (for an overview of the evolution of management example through flow duration curves) will provide principles and practices for the region; some quantification of the patterns of change. • documentation of background information relevant to the project. These patterns of change could include: • proportion of the Barmah Forest flooded during summer; 92 93 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

• flow characteristics at Tocumwal and Yarrawonga 1.3.3 Defining and Identifying Unseasonal Surplus before and after the construction of the Hume Flow Events (1934) and the increase of its capacity (1961); Possible Research Avenues • flow characteristics of the main irrigation diversion channels from Yarrawonga Weir (Mulwala Canal Sections 2 and 3 outline the situation in which and Yarrawonga Main Channel). unseasonal surplus flow events (rain rejections and river freshes) occur, and the impacts of these events. Evaluation Unseasonal surplus flows could thus be identified according to cause (cancellation of irrigation orders) The purpose of historical analysis is to support or effect (on flow levels in the River Murray system, or background information, to provide evidence that flow flooding patterns in the Barmah-Millewa Forest). and flooding patterns have changed over time, and thus to validate the aim of this research project. Analysis of Unseasonal surplus flow events should be defined in the changes in seasonality of flooding would support terms of duration (start date and end date), severity the choice of unseasonal surplus flow season (eg. (peak excess flow volume and total excess flow November - May, or December - May). volume), and season.

Proposal 1: Historical Analysis This step analyses the patterns of change (to flows and floods) caused by regulation.

(a) ANALYSIS OF RIVER MURRAY FLOWS IN SUMMER-AUTUMN Establish flow duration curves for daily flows during the summer-autumn period at Tocumwal. Analyse individual months as well as combinations of months. i) Divide record sets according to periods of regulation, including one or both of the following: • construction of the Hume Dam • extension of the Hume Dam ii) Divide record sets according to periods of time, eg. into periods of 10 or 20 years.

(b) ANALYSIS OF BARMAH FOREST FLOODING IN SUMMER-AUTUMN Using the relationship derived by Bren, O’Neill and Gibbs (1986), analyse available daily flows at Tocumwal to determine changes in the proportion of Barmah Forest flooded during the summer-autumn period of November - May. Analyse individual months as well as combinations of months. Divide record sets as in (a).

The presentation of this analysis could include: i) Time series graph of proportion of forest flooded, averaged over a month, for each month from November to May. ii) Flow duration curves representing: vertical axis - frequency (% of days) during summer-autumn period that the forest is flooded; horizontal axis - proportion of forest flooded greater than (0 - 100)% of total area.

94 95 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Possible ways to define the season in which unseasonal Evaluation surplus flow events can be identified are: Option (a) for defining the season of unseasonal (a) The irrigation season, which is that part of the surplus flow events would require analysis of flows year during which diversions are made from in the Mulwala Canal and Yarrawonga Main Channel Yarrawonga Weir for irrigation purposes; to identify the start and end of irrigation season each (b) The summer-autumn season during which flows year. This would be a simpler and more direct method in the Barmah-Millewa Forest are greater, more than (b), but may extend beyond the summer-autumn frequent and/or of greater duration than in pre- period during which flows in the Forest are considered regulation (before 1934) times; undesirable. Method (b) is a component of Proposal 1. It (c) A definition (such as November - May or December would involve analysis of flow data for Tocumwal and - April) based on references or definitions in other rely on the assumptions of Bren’s model in calculating research papers. the proportion flooded of Barmah Forest. Possible ways to identify the duration and severity Definition (c) proposes a standard season which could unseasonal surplus flow events are: be used for all years of data to define unseasonal surplus (d) An unseasonal surplus flow event occurs flow events, but it is possible that using Definition (c) when irrigator(s) cancel water orders, and the might exclude unseasonal surplus flow events which configuration of flowrates and volumes in the occurred outside the season, and include events which regulated system is such that the MDBC orders are largely natural floods and not rain rejection flows that flow must be diverted into the Barmah or the (depending on the method of identifying an event). Millewa Forest (NSW and Victoria take unseasonal surplus flows in alternate years). The regulator Method (a) of identifying the duration and severity of capacity of the forest is insufficient to prevent all unseasonal surplus flow events requires operational flows from overflowing the forest levees. information from the MDBC about flows in the Barmah-Millewa Forest. It is unlikely that this The duration could refer to the time during which information is readily available. Data is obtainable to the MDBC has ordered that offtake regulators stay identify the duration and severity of unseasonal surplus open, and the severity could refer to the peak flow flow events using Methods (b) or (c). The advantage of and total volume of water released into the forest. using Method (b) is that it relates unseasonal surplus (e) An unseasonal surplus flow event occurs when flows directly to the impact on the Forest. However, flooding occurs in the Barmah Forest. The severity the relationship derived by Bren relates only to the could refer to the proportion of area flooded, Barmah Forest, there are several assumptions implicit which could be determined from the relationship in this relationship, and the capacity of regulators with peak flow at Tocumwal or monthly flow at to prevent flooding in the forest has increased since Yarrawonga established by Bren, O’Neill and his study period (1963 - 1986). Method (c) relates Gibbs (1986). The duration could refer the time unseasonal surplus flows to their impact on the forest in which the proportion of area flooded is greater only indirectly, but total volume of flow for the event than a specified level. Note that river freshes could is a useful indicator of severity. Method (d) relates to exacerbate the flooding caused by rain rejections. current operational rules established by the MDBC. (f) An unseasonal surplus flow event occurs for the duration of flows exceeding the regulated flow limit (11,400 ML/day) downstream of Yarrawonga Weir. Indicators of severity could be the peak daily flow or total volume of flow for the event. This methodology was used by DLWC (1996). A similar method would set the threshold at 10,600 ML/day at Tocumwal (the capacity of the Choke). (g) An unseasonal surplus flow event occurs when the flow at Picnic Point exceeds a gauge height of 2.53 m. 94 95 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Proposal 2: Identifying Unseasonal Surplus Flow Events

(a) Use the results from “Historical Analysis” to identify the months of the year in which regulation has caused significant increases in forest flooding. Use these months as the established season for identifying unseasonal surplus flow events. (b) Identify the start, end, duration, peak volume and excess volume of unseasonal surplus flow events for the period 1980 - 2000. The following methods can be used and their sensitivity to assumptions evaluated: i) Flow exceeds 11,400 ML/day downstream of Yarrawonga Weir (DLWC 1996); ii) Flow exceeds a gauge height of 2.53 m at Picnic Point (MDBC operating rule); iii) Flow exceeds 10,600 ML/day at Tocumwal (current capacity of the Choke);

If the methods identify significantly different unseasonal surplus flow events, then further evaluation could be conducted to determine which method is preferred.

96 97 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

1.3.4 Defining “Risk of Occurrence” this project. This is essentially an “instantaneous risk”, i.e. it asks: given the current state of the system, what is Possible Research Avenues the risk that a unseasonal surplus flow event will occur Having defined and identified individual unseasonal now? surplus flow events, a meaningful and working definition must be applied for the risk (or probability) Consideration should be given as to whether absolute of occurrence. In this context, the two aspects of risk (eg. the risk of an event occurring at a specific river probability are timing and severity. Possible definitions flow) or relative risk (eg. the increase in risk dueto of risk are: higher river flows) is more relevant. (a) the probability of a unseasonal surplus flow event Further evaluation is required to determine whether commencing within the next 24 hours, the next sufficient data exists to create an index which provides two days, or within the next week (for example); a meaningful description of unseasonal surplus flow (b) the probability of a unseasonal surplus flow event probability, severity and duration. of X severity and/or Y duration commencing Measuring the severity of an event according to within the next 24 hours, the next two days, or total excess volume will enable the analysis of how within the next week; increasing air space at Lake Mulwala will reduce the (c) an index value which encompasses the probability number of unseasonal surplus flows. of a unseasonal surplus flow event of X severity and/or Y duration commencing within the next 24 Measuring the severity of an event according to peak hours, the next two days, or within the next week. or daily excess flow rates will enable the analysis of The greater the probability, severity and duration, how restricting the flow of the River Murray upstream the higher the index value. of the forest will reduce the likelihood of unseasonal surplus flow events and unseasonal surplus flow days Evaluation respectively.

The selection of “within the next 24 hours” as the timing for risk would adequately satisfy the aims of

Proposal 3: Defining“ Risk of Occurrence” (a) The risk of occurrence has been defined as the instantaneous probability that a unseasonal surplus flow event will commence. This risk may be absolute or relative. (b) Two measures of severity of a unseasonal surplus flow event are: i) total excess volume (which will onflow into the Forests). ii) peak and daily excess flowrates

96 97 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

1.3.5 Identifying Factors which Influence Risk (c) Climate Possible Research Avenues • rainfall (current daily, previous daily, current forecast, average over past day(s)/week(s)/ The following factors influence the risk of unseasonal month(s)) surplus flow occurrence: • temperature and evaporation (a) Flow rates / levels in the Murray River System (d) Irrigation variable • The flow variables could be measured at: • ordering and rejecting procedures - Tocumwal • volumes of current and future orders - Yarrawonga - Hume (e) Rate of drawdown allowed for Hume reservoir • The flow variables could include Evaluation - daily flows Many of these variables are likely to be highly - previous daily flows correlated with each other. Some, such as ordering and - average flow over last X days/week(s)/ rejecting procedures for irrigation water (d), may be month(s) difficult to quantify. The maximum rate of drawdown allowed for Hume reservoir has been constant since (b) Level of storages and channels (air space) 1961. • Lake Mulwala • Hume Dam This project aims to evaluate system regulation and flexibility with regards to unseasonal surplus flow • Irrigation and bypass canals events. A useful, and reasonable, simplification would • Forest offtake channels be to assume rainfall patterns and irrigation variables have remained constant for the period of analysis.

Proposal 4: Identify Factors which Relate to Risk

(a) Possible flow rates (size of unseasonal surplus flows) i) daily flow of the River Murray at Tocumwal; ii) daily flow of the River Murray at Doctor’s Point; iii) daily flow of the River Murray at Picnic Point; and iv) daily flow of the River Murray at Yarrawonga.

Average previous weekly and monthly flow rates could also be analysed.

(b) Level of storages (ability to regulate) i) U/S Yarrawonga Weir (the day before a unseasonal surplus flow event commences);

Average previous weekly and monthly flow rates could also be analysed.

98 99 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

1.3.6 Determine Methodology for Testing Significance Evaluation of Variables DLWC (1996) conducted some analysis of unseasonal Possible Research Avenues surplus flow events for the period 1975-1996. Graeme Correlation analysis could provide an indication Hannan of Goulburn-Murray Water (pers. comm. of which variables listed in (3) are significant in 2001, 21 March) suggested that unless changes to determining the risk of unseasonal surplus flow irrigation demands and operational procedures could occurrence. be accounted for, flows should not be analysed before 1970. However, sensitivity tests and comparison of risk An important aspect of testing the significance of indices calculated for different time periods (eg. 1975- variables is establishing a relevant time period from 1985 compared with 1985-1995). which to draw data. This is likely to vary for different variables. The longest time period should be chosen which is relevant to all factors.

Proposal 5: Establish Relationships Between the Risk of Unseasonal Surplus Flows and Influencing Factors

(a) Calculate correlation coefficients to determine correlation between: i) total excess volume and risk of unseasonal surplus flow event; ii) peak excess flow rate and risk of unseasonal surplus flow event; and iii) daily excess flow rate and risk of unseasonal surplus flow event.

(b) Establish cumulative probability plots to illustrate: i) distribution of total excess volumes amongst unseasonal surplus flow events; ii) distribution of peak excess flowrates amongst unseasonal surplus flow events; and iii) distribution of daily excess flowrates amongst unseasonal surplus flow days.

98 99 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

1.3.7 Economic Analysis Evaluation Possible Research Avenues It is expected that this project will not involve quantification of the benefits of “intangibles” associated A cost-benefit analysis could be conducted to with reduced summer-autumn flooding, such as determine the economic impacts of increasing system improved access to tourists, although methods such as flexibility to reduce the likelihood of rain rejections. travel cost and hedonic pricing are well documented. System flexibility includes increasing air space at Lake Mulwala and reducing the flowrate of the Murray An economic analysis requires establishment of the between Yarrawonga and the Choke. time period over which costs and benefits are to be identified, and the applicable discount rate. Costs include the reduction of supply flexibility to irrigators downstream of Lake Mulwala. Benefits include improved forestry yield, improved access, and the value of water that would otherwise cause summer- autumn flooding.

Proposal 6: Economic Analysis

(a) Identify and quantify costs and benefits associated with increasing system flexibility and reducing rain rejections.

(b) Establish plots of: net discounted cost/benefit vs. reduction in unseasonal surplus flow events/days.

100 101 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

1.4 Proposed Research Methodolgy The results of this analysis can be presented in plots of This proposed research methodology was developed net discounted cost/benefits vs. reduction in unseasonal based on the evaluation of possible research avenues. surplus flow events/days.

1.4.1 Part 1: Historical Analysis 1.5 Data Requirements As outlined in “Proposal 1”, this analysis will Table 1.1 summarises the data requirements identified determine: in the proposed methodology. • whether regulation has caused changes in the pattern of summer-autumn River Murray flows; • whether regulation has caused changes in the pattern of summer-autumn Barmah Forest floods; • which months in the summer-autumn period have experienced a significant increase in forest flooding;

1.4.2 Part 2: Identify Individual Unseasonal Surplus Flow Events As outlined in “Proposal 2”, this analysis will involve comparison of various methods of identifying individual rain rejection events. These methods will be used to identify: • start and end dates of individual unseasonal surplus flow events; • peak excess flow rate; • total excess volume.

1.4.3 Part 3: Relation to System Regulation As outlined in “Proposals 3 to 5”, this analysis will use the unseasonal surplus flow events characterised in Part 2 to relate the instantaneous risk of occurrence to factors involving the regulation of the River Murray.

A preliminary methodology for characterising risk would involve the calculation of correlation coefficients and establishment of cumulative probability plots as outlined in “Proposal 5”.

1.4.4 Part 4: Economic Analysis As outlined in “Proposal 6”, this analysis will use the risks characterised in Part 3 to determine the economic impacts of increasing system flexibility to reduce the likelihood of rain rejections. The two aspects of system flexibility are identified as: • increasing air space at Lake Mulwala; and • reducing the flowrate of the Murray between Yarrawonga and the Choke.

100 101 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Table 1.1 Data Requirements

Data Unit Dates required Possible source(s) PART 1 River Murray flow at ML/day historical - present RMW; DLWC; GMW Historical Tocumwal Analysis Diversions to ML/day historical - present RMW; DLWC; GMW Mulwala Canal and Yarrawonga Main Channel Choke capacity ML/day historical - present Bren et. al. (1997); (flooding threshold) Hansard; Thoms et. al. (2000); RMC (1980) Flooding area relation historical - present Bren et. al. (1997). PART 2 River Murray flow at ML/day 1975 - present RMW Identify Yarrawonga Events River Murray flow at ML/day 1975 - present RMW Tocumwal River Murray gauge mAHD; ML/day 1975 - present RMW height and flow at Picnic Point PART 3 River Murray flow at ML/day 1975 - present RMW Relation Tocumwal to System River Murray flow at ML/day 1975 - present RMW Regulation Doctor’s Point River Murray flow at ML/day 1975 - present RMW Picnic Point River Murray flow at ML/day 1975 - present RMW Yarrawonga Full storage level of mAHD, ML 1975 - present RMW Lake Mulwala Storage in Lake mAHD, ML 1975 - present RMW Mulwala PART 4 Costs of lost timber $ current Maunsell (1992a); Leslie Economic production per ML and Harris (1996). or area of unseasonal Analysis flooding Value of water to $/ML current GMW; RMW irrigators

102 103 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Appendix B: Historical Analysis

November 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Mean 21552.02273 26561.116 18510.05583 17536.58 21969.67455 Standard Error 615.1121758 672.3189329 504.1766227 584.8924591 335.1771687 Median 16529 22031.5 10785.5 10701 15726 Mode 19137 7342 9028 10462 16784 Standard 15802.51792 18412.21227 17465.19053 14326.88079 17704.20908 Deviation Sample Variance 249719572.6 339009560.7 305032880.2 205259513.2 313439019 Kurtosis 1.215727519 -0.349074188 7.752152583 5.022917616 2.831435296 Skewness 1.287216593 0.703433629 2.443697111 2.098501994 1.551423458 Range 81948 83636 146243 86265 146907 Minimum 1232 3707 1896 5926 1232 Maximum 83180 87343 148139 92191 148139 Sum 14224335 19920837 22212067 10521948 61295392 Count 660 750 1200 600 2790

December 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Mean 11933.18475 13423.49032 10918.41613 11672.50161 12286.1273 Standard Error 442.3933177 311.2924613 182.2384245 254.8991715 168.7871193 Median 7908 9640 9479.5 10069 9468 Mode 4446 5857 9468 10818 5857 Standard 11553.15888 8666.015361 6417.277131 6346.938185 9062.783856 Deviation Sample Variance 133475480 75099822.24 41181445.77 40283624.32 82134051.21 Kurtosis 4.770382866 2.296757647 10.76115203 15.16581969 6.411129636 Skewness 2.209381151 1.607071081 2.935817625 3.644172915 2.365330324 Range 60152 42652 51817 47638 60152 Minimum 985 4812 1783 5962 985 Maximum 61137 47464 53600 53600 61137 Sum 8138432 10403205 13538836 7236951 35420905 Count 682 775 1240 620 2883

January 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Mean 6774.957416 8954.003871 10016.44847 10746.78034 8948.352214 Standard Error 200.8269423 141.6276785 128.4331565 97.71829785 89.60137048 Median 4886 7978 9748 10409 8367 Mode 8196 9640 8616 11922 8196 Standard Dev. 5240.775207 3942.747706 4578.781629 2493.253215 4835.984438 Sample Variance 27465724.77 15545259.47 20965241.21 6216311.593 23386745.49 Kurtosis 2.804626383 8.313359337 37.78416366 17.8506913 16.04957001 Skewness 1.593846129 2.68018389 5.026673166 3.052009599 2.709611767 Range 32145 27294 50181 26519 53134 Minimum 729 1771 3682 5846 729 Maximum 32874 29065 53863 32365 53863 Sum 4613746 6939353 12730906 6996154 26066550 Count 681 775 1271 651 2913 102 103

C-1 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

February 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Mean 4719.488746 8365.468175 9434.564767 10284.85835 7765.26619 Standard Error 167.9634848 82.59761418 72.18143177 72.88996517 68.13392228 Median 3114 8073 9672.5 10342 8318.5 Mode 3195 8659 5162 10810 8659 Standard Dev. 4188.997189 2196.226916 2456.290746 1774.986644 3511.376725 Sample Variance 17547697.45 4823412.669 6033364.229 3150577.585 12329766.51 Kurtosis 2.608905999 11.80995994 2.049787152 6.125869411 0.6388524 Skewness 1.732218602 2.590821965 0.174008113 1.275819738 0.178838561 Range 22283 19169 17841 14517 23179 Minimum 430 4440 2373 5697 430 Maximum 22713 23609 20214 20214 23609 Sum 2935522 5914386 10925226 6098921 20624547 Count 622 707 1158 593 2656

March 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Mean 4208.202346 8243.68129 9950.541036 10796.90394 7901.008627 Standard Error 135.8570162 96.70215973 62.50578515 60.89477448 66.8245392 Median 2836 7511 10229 10754 8467 Mode 330 8659 11033 11033 8659 Standard 3547.9236 2692.074194 2214.328643 1534.499987 3597.370453 Deviation Sample Variance 12587761.87 7247263.465 4903251.338 2354690.21 12941074.18 Kurtosis 1.910904996 7.650386603 2.608968289 5.986439577 0.299827257 Skewness 1.43756925 2.375444266 -0.064704551 1.488768016 -0.045846942 Range 18552 19983 16414 11764 22692 Minimum 330 3039 2459 7109 330 Maximum 18882 23022 18873 18873 23022 Sum 2869994 6388853 12487929 6856034 22897123 Count 682 775 1255 635 2898

April 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Mean 4221.574242 8836.254667 8043.1725 8632.806667 7358.602509 Standard Error 134.5667579 288.6725284 74.37989939 87.25883406 99.52356904 Median 3012 7503 8171 8498 7300 Mode 2373 6459 8073 9301 6459 Standard Dev. 3457.082606 7905.622777 2576.595296 2137.39619 5256.879761 Sample Variance 11951420.14 62498871.49 6638843.321 4568462.473 27634784.82 Kurtosis 4.034830161 53.83247172 0.812309774 1.367078476 82.57693711 Skewness 1.738929644 6.727809698 -0.021565235 0.5933104 6.677837027 Range 20976 88903 17851 13939 89459 Minimum 330 886 1664 3225 330 Maximum 21306 89789 19515 17164 89789 Sum 2786239 6627191 9651807 5179684 20530501 Count 660 750 1200 600 2790

C-2 104 105 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

May 1908-1929 1936-1960 1961-2001 1981-2001 1908-2001 Mean 6963.55132 8304.093333 7218.16 5649.658333 7529.122222 Standard Error 313.4331115 382.8542453 294.8142157 134.7165276 183.356735 Median 4910 6300 5389 5164 5628.5 Mode 5856 9039 6669 2569 9039 Standard Dev. 8185.346364 10484.89532 10212.66401 3299.867525 9684.98536 Sample Variance 66999895.09 109933029.9 104298506.1 10889125.68 93798941.42 Kurtosis 17.83418796 24.06694032 113.8053627 7.648840382 71.3247196 Skewness 3.784645543 4.639593109 8.933686556 2.307596052 6.673640633 Range 56655 84101 181789 20423 182823 Minimum 539 795 1573 2069 539 Maximum 57194 84896 183362 22492 183362 Sum 4749142 6228070 8661792 3389795 21006251 Count 682 750 1200 600 2790

104 105

C-3 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

106 107 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Appendix C: Unseasonal Surplus Flow Events

Picnic Point stage-discharge relation

2.8

2.6

2.4

2.2 ]

m 2 [ t h g

i 1.8 e h 1.6 e g a t 1.4 S

1.2

0.8

0.6

0.4 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 Discharge [ML/d]

1994 - 2001 1989 - 1994 1982 - 1989

TOCUMWAL ANALYSIS Duration Peak excess flow Total excess flow Average excess flow (ML/day) (ML) (ML/day) SUM 1160 181277 1462310 91711 AVERAGE 14.15 2210.70 17833.50 1118.42 MEDIAN 10.00 1132.50 7959.50 638.21 MAX 84 10807 162545 5424 MIN 1 8 12 6 SD 14.02 2571.63 28867.52 12841.33 10th percentile 2.00 115.50 194.50 81.70 20th percentile 4.00 259.20 981.80 164.08 30th percentile 6.30 421.80 2666.80 255.11 40th percentile 8.00 614.80 4882.40 348.21 50th percentile 10.00 1132.50 7959.50 638.21 60th percentile 11.60 1913.60 11351.80 925.52 70th percentile 16.00 2697.20 15771.80 1286.55 80th percentile 22.00 4104.80 22442.20 1811.30 90th percentile 29.80 6345.30 43139.80 2693.94 EVENTS 82 Start record 1-Dec-80 End record 1-Dec-00 Years of record 20.0 EVENTS PER YEAR 4.1 Total days 3025 PROPORTION OF FLOOD DAYS 38.3% 106 107

D-1 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

YARRAWONGA ANALYSIS Duration Peak excess flow Total excess flow Average excess flow (ML/day) (ML) (ML/day) SUM 497 147002 832720 80277 AVERAGE 8.57 2534.52 14357.24 1384.09 MEDIAN 6.00 1589.00 5188.00 820.60 MAX 53 10131 132654 4886 MIN 1 1 1 1 SD 8.29 2691.68 23784.05 1404.99 10th percentile 2.70 159.80 434.70 122.73 20th percentile 4.00 319.20 967.20 188.50 30th percentile 4.10 482.90 2770.20 295.40 40th percentile 5.00 807.40 3805.20 562.15 50th percentile 6.00 1589.00 5188.00 820.60 60th percentile 7.00 2214.80 8360.00 1383.91 70th percentile 8.90 3356.50 11105.10 1854.00 80th percentile 11.60 4673.40 18243.80 2363.65 90th percentile 16.00 6647.90 40472.60 3533.34 EVENTS 58 Start record 16-Mar-83 End record 15-Mar-01 Years of record 18.0 EVENTS PER YEAR 3.222467295 Total days 2722 PROPORTION OF FLOOD DAYS 18.3%

PICNIC POINT ANALYSIS Duration Peak excess flow Total excess flow Average excess flow (ML/day) (ML) (ML/day) SUM 1123 40570 647453 24948 AVERAGE 14.78 533.82 8519.12 328.26 MEDIAN 8.00 418.50 2690.50 251.95 MAX 100 1664 106750 1068 MIN 1 4 4 4 SD 20.63 446.02 18090.27 271.99 10th percentile 1.00 44.00 56.50 26.67 20th percentile 2.00 104.00 138.00 81.00 30th percentile 4.00 221.50 556.00 143.46 40th percentile 5.00 334.00 1036.00 209.00 50th percentile 8.00 418.50 2690.50 251.95 60th percentile 10.00 504.00 3514.00 330.82 70th percentile 13.50 751.00 4787.00 421.40 80th percentile 17.00 894.00 6650.00 602.33 90th percentile 37.50 1129.00 26417.00 695.19 EVENTS 76 Start record 16-Mar-83 End record 15-Mar-01 Years of record 18.0 EVENTS PER YEAR 4.22 Total days 2722 PROPORTION OF FLOOD DAYS 41.3%

108 109 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Sub getevents()

Dim peakdate, startdate, enddate Dim peakflow, totalflow

peakflow = totalflow = 0

Do While ActiveCell.Value = 0 ActiveCell.Offset(1, 0).Range("a1").Select Loop

If ActiveCell.Value = 9999999 Then Exit Do End If peakflow = 0 totalflow = 0 startdate = ActiveCell.Offset(0, -2).Value Do While ActiveCell.Value <> 0 totalflow = totalflow + ActiveCell.Value

If ActiveCell.Value > peakflow Then peakflow = ActiveCell.Value peakdate = ActiveCell.Offset(0, -2).Value End If ActiveCell.Offset(1, 0).Range("a1").Select If ActiveCell.Offset(0, -2).Value - ActiveCell.Offset(-1, -2).Value > 1 Then Exit Do End If Loop enddate = ActiveCell.Offset(-1, -2).Value Sheets("Events").Select ActiveCell.Value = startdate ActiveCell.Offset(0, 1).Value = enddate ActiveCell.Offset(0, 3).Value = peakdate ActiveCell.Offset(0, 4).Value = peakflow ActiveCell.Offset(0, 5).Value = totalflow ActiveCell.Offset(1, 0).Range("a1").Select Sheets("Data").Select peakflow = 0 totalflow = 0 Loop

End Sub

108 D-5 109 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

110 111 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Appendix D: Analysis of System Flexibility E-1 40 2.0 474 23.7 11.9 15.7% 2099.1 994955 49747.8 24873.9 42 2.1 486 24.3 11.6 16.1% 2088.4 50749.0 1014979 1014979 24166.2 42 2.1 500 25.0 11.9 16.5% 2071.0 51774.0 24654.3 1035479 0.6 0.6 38995.8 37619.0 42 2.1 516 25.8 12.3 17.1% 2046.5 52799.0 25142.4 1055979 1055979 44 2.2 528 26.4 12.0 17.5% 2039.7 53847.6 24476.2 1076951 1076951 45 2.3 545 27.3 12.1 18.0% 2016.2 54941.2 24418.3 1098823 46 2.3 562 28.1 12.2 18.6% 1994.8 56053.0 24370.9 1121060 1121060 47 2.4 586 29.3 12.5 19.4% 1952.0 57194.5 24338.1 1143889 1143889 980998 941793 906236 872770 840512 809612 779916 752380 47 2.4 609 30.5 13.0 20.1% 1916.9 58369.5 24838.1 1167389 1167389 51 1025732 1025732 2.6 642 32.1 12.6 21.2% 1857.1 59611.8 23377.2 1192236 1192236 5987 52 2.6 668 33.4 12.8 22.1% 1823.3 60898.0 23422.3 1217959 1217959 54 2.7 705 35.3 13.1 23.3% 1764.9 62214.2 23042.3 1244284 1244284 55 2.8 740 37.0 13.5 1184568 1128112 107 24.5% 1718.3 1271556 1271556 63577.8 23119.2 59 3.0 774 38.7 13.1 25.6% 1679.3 1247880 1247880 1299794 1299794 64989.7 22030.4 61 3.1 827 41.4 13.6 27.3% 1608.3 1315189 1315189 66502.7 21804.2 1330054 1330054 61 3.1 882 44.1 14.5 29.2% 1542.6 1378381 1378381 68027.7 22304.2 1360554 1360554 65 3.3 931 46.6 14.3 30.8% 1495.2 1427445 1427445 69602.3 21416.1 1392046 1392046 82 79 74 70 63 56 52 49 48 45 43 42 42 42 41 38 38 68 3.4 51.0 15.0 1019 10600 10500 10400 10300 10200 10100 10000 9900 9800 9700 9600 9500 9400 9300 9200 9100 9000 1260.6 1282.5 1359.4 1437.4 1538.7 1654.4 1782.2 1805.3 1844.8 2006.1 2130.8 2168.0 2209.5 2309.1 2402.4 2460.3 2576.6 33.7% 1399.4 17833.0 18068.9 18626.8 18788.4 19807.6 21153.0 21694.5 21958.9 21369.4 21800.0 21902.2 21577.0 20780.2 20012.2 19746 .6 20524.1 19799.5 1462310 1462310 71297.4 20969.8 1425948 1425948 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 82 4.1 58.0 14.1 1160 38.3% 1260.6 73115.5 17833.0 1462310 E-2 Maximumat flow (ML/day)Tocumwal TOTALEXCESS FLOW NUMBEROF DAYS 1160 1113 1014 915 811 716 633 596 556 489 442 418 395 364 337 317 292 NUMBEROF EVENTS Frequencyand Duration Days perDays season 58.0 55.7 50.7 45.8 40.6 35.8 31.7 29.8 27.8 24.5 22.1 20.9 19.8 18.2 16.9 15.9 14.6 Proportionseasonof 38.3% 36.8% 33.5% 30.2% 26.8% 23.7% 20.9% 19.7% 18.4% 16.2% 14.6% 13.8% 13.1% 12.0% 11.1% 10.5% 9.7% Events perEvents season 4.1 4.0 3.7 3.5 3.2 2.8 2.6 2.5 2.4 2.3 2.2 2.1 2.1 2.1 2.1 1.9 1.9 Eventduration 14.1 14.1 13.7 13.1 12.9 12.8 12.2 12.2 11.6 10.9 10.3 10.0 9.4 8.7 8.2 8.3 7.7 Surplusvolume Average excess flowAverage excess perseason 73115.5 71372.3 68919.1 65759.5 62394.0 59228.4 56405.6 53799.4 51286.6 49049.9 47089.7 45311.8 43638.5 42025.6 4048 Average excess flowAverage excess perevent Average excess flowAverage excess perday Extra storage capacity (ML) TOTAL EXCESS FLOW NUMBER OFDAYS NUMBER OF EVENTS Frequencyand Duration Days per Days season Proportion of seasonof Events perEvents season Event duration Surplusvolume Average excess excess flowper season Average excess excess flowper event Average excess excess flowper day

110 111 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY 23 1.2 281 14.1 12.2 9.3% 706156 2513.0 35307.8 30702.4 E-3 23 1.2 289 14.5 12.6 9.6% 2481.5 717156 35857.8 31180.7 24 1.2 295 14.8 12.3 9.8% 2469.5 728496 36424.8 30354.0 25 1.3 301 15.1 12.0 10.0% 2459.1 740192 37009.6 29607.7 25 1.3 305 15.3 12.2 10.1% 2466.2 752192 37609.6 30087.7 25 1.3 312 15.6 12.5 10.3% 2449.3 764192 38209.6 30567.7 26 1.3 322 16.1 12.4 10.6% 2410.9 776310 38815.5 29858.1 26 1.3 329 16.5 12.7 10.9% 2397.6 788810 39440.5 30338.8 26 1.3 335 16.8 12.9 11.1% 2392.0 801310 40065.5 30819.6 27 1.4 341 17.1 12.6 11.3% 2387.9 814274 40713.7 30158.3 28 1.4 350 17.5 12.5 11.6% 2365.1 827774 41388.7 29563.4 30 1.5 361 18.1 12.0 11.9% 2332.3 841976 42098.8 28065.9 32 1.6 372 18.6 11.6 12.3% 2303.2 856790 42839.5 26774.7 32 1.6 381 19.1 11.9 12.6% 2289.5 872290 43614.5 27259.1 32 1.6 389 19.5 12.2 12.9% 2282.2 887790 44389.5 27743.4 34 1.7 400 20.0 11.8 13.2% 2259.3 903718 45185.9 26579.9 34 1.7 413 20.7 12.1 13.7% 2228.1 920218 46010.9 46010.9 27065.2 27065.2 36 1.8 427 21.4 11.9 14.1% 2195.2 937355 46867.8 46867.8 26037.6 26037.6 40 2.0 445 22.3 11.1 14.7% 2148.2 955955 47797.8 23898.9 40 2.0 457 22.9 11.4 9500 10000 10500 11000 11500 12000 12500 13000 13500 14000 14500 15000 15500 16000 16500 17000 17500 18000 18500 19000 15.1% 2134.5 975455 48772.8 24386.4 Extra storage capacity (ML) TOTAL EXCESS FLOW NUMBER OFDAYS NUMBER OF EVENTS Frequencyand Duration Days per Days season Proportion of seasonof Events perEvents season Event duration Surplusvolume Average excess excess flowper season Average excess excess flowper event Average excess excess flowper day

112 113 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Appendix E: Economic Analysis

Marginal value of water Marginal value of electricity $60 per ML $46.36 per MWh Increased Level Flooding Cost: less hydroelectricity Benefit: water saved from Net benefit airspace frequency generation reduced flooding ML mAHD MWh/ Value ML/season Value Cost Value season 0 125.1 38.35% 2.2196533 $0 0 $0 $0 $0 500 125.089263 33.69% 3.661138 $67 1818.1 $109,086 -$67 $109,019 1000 125.078525 30.78% 5.5133865 $153 3513.2 $210,792 -$153 $210,639 1500 125.067788 29.16% 8.033826 $270 5087.8 $305,268 -$270 $304,998 2000 125.057051 27.34% 11.090198 $411 6612.8 $396,768 -$411 $396,357 2500 125.046313 25.59% 14.860919 $586 8125.8 $487,548 -$586 $486,962 3000 125.035576 24.46% 19.260686 $790 9537.7 $572,262 -$790 $571,472 3500 125.024838 23.31% 24.542368 $1,035 10901.3 $654,078 -$1,035 $653,043 4000 125.014101 22.08% 30.879217 $1,329 12217.55 $733,053 -$1,329 $731,724 4500 125.003364 21.22% 38.19759 $1,668 13503.7 $810,222 -$1,668 $808,554 5000 124.992626 20.13% 46.749811 $2,064 14746.05 $884,763 -$2,064 882,699 5500 124.981889 19.37% 56.522234 $2,517 15921.05 $955,263 -$2,517 $952,746 6000 124.971152 18.58% 67.649458 $3,033 17062.5 $1,023,750 -$3,033 $1,020,717 6500 124.960414 18.02% 80.351678 $3,622 18174.35 $1,090,461 -$3,622 $1,086,839 7000 124.949677 17.45% 94.919913 $4,297 19267.95 $1,156,077 -$4,297 $1,151,780 7500 124.938939 17.06% 111.13294 $5,049 20316.55 $1,218,993 -$5,049 $1,213,944 8000 124.928202 16.53% 129.02644 $5,879 21341.55 $1,280,493 -$5,879 $1,274,614 8500 124.917465 16.07% 148.75123 $6,793 22366.55 $1,341,993 -$6,793 $1,335,200 9000 124.906727 15.67% 170.01591 $7,779 23367.75 $1,402,065 -$7,779 $1,394,286 9500 124.89599 15.11% 192.84751 $8,837 24342.75 $1,460,565 -$8,837 $1,451,728 10000 124.885253 14.71% 217.1941 $9,966 25317.75 $1,519,065 -$9,966 $1,509,099

112 113 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

Marginal value of water $60 per ML Maximum Flooding Cost: less downstream water Benefit: water saved from Net cost flow at frequency reduced flooding Tocumwal ML/day ML/season Value $ ML/season Value $ ML/season Value $ 10600 0.383 0 - 0 - 0 - 10500 0.368 2493 149,607.00 1743 104,595.00 750 -45,012 10400 0.335 6107 366,423.00 4196 251,787.00 1911 -114,636 10300 0.302 11414 684,867.00 7356 441,363.00 4058 -243,504 10200 0.268 17984 1,079,067.00 10722 643,290.00 7263 -435,777 10100 0.237 25248 1,514,904.00 13887 833,226.00 11361 -681,678 10000 0.209 32937 1,976,244.00 16710 1,002,594.00 16228 -973,650 9900 0.197 40948 2,456,883.00 19316 1,158,969.00 21632 -1,297,914 9800 0.184 49320 2,959,173.00 21829 1,309,734.00 27491 -1,649,439 9700 0.162 58002 3,480,111.00 24066 1,443,936.00 33936 -2,036,175 9600 0.146 66988 4,019,292.00 26026 1,561,551.00 40962 -2,457,741 9500 0.138 76184 4,571,010.00 27804 1,668,222.00 48380 -2,902,788 9400 0.131 85663 5,139,759.00 29477 1,768,620.00 56186 -3,371,139 9300 0.120 95449 5,726,961.00 31090 1,865,394.00 64359 -3,861,567 9200 0.111 105543 6,332,562.00 32635 1,958,094.00 72908 -4,374,468 9100 0.105 115957 6,957,429.00 34120 2,047,182.00 81837 -4,910,247 9000 0.097 126653 7,599,198.00 35497 2,129,790.00 91157 -5,469,408 133333 8,000,000.00 41667 2,500,000.00

114 COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY

CENTRE OFFICE CRC for Catchment Hydrology Department of Civil Engineering Building 60 Monash University Victoria 3800 Australia

Tel +61 3 9905 2704 Fax +61 3 9905 5033 email [email protected] www.catchment.crc.org.au

he Cooperative Research Centre for Catchment Hydrology is a cooperative venture formed under the Australian Government’s CRC Programme between:

• Brisbane City Council ASSOCIATE:

• Bureau of Meteorology • Water Corporation of Western Australia • CSIRO Land and Water • Department of Infrastructure, Planning and RESEARCH AFFILIATES: Natural Resources, NSW • Australian National University • Department of Sustainability and • National Institute of Water and Atmospheric Environment, Vic Research, New Zealand • Goulburn-Murray Water • Sustainable Water Resources Research • Griffith University Center, Republic of Korea Established and supported • Melbourne Water • University of New South Wales under the Australian • Monash University Government’s Cooperative Research Centre Program • Murray-Darling Basin Commission INDUSTRY AFFILIATES: • Natural Resources, Mines and Energy, Qld • Earth Tech

• Southern Rural Water • Ecological Engineering • The University of Melbourne • Sinclair Knight Merz

• Wimmera Mallee Water • WBM