HUME AND DARTMOUTH OPERATIONS REVIEW REFERENCE PANEL

Hume and Dartmouth Dams Operations Review Options Paper N O V E M B E R 1 9 9 8 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL

Hume and Dartmouth Dams Operations Review Options Paper N O V E M B E R 1 9 9 8

Please note! The deadline for comment on this paper is Wednesday 10 February 1999 For details see page 1 (‘About this Options Paper’)

i HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL

Published by: Hume and Dartmouth Dams Operations Review Reference Panel

Postal address: c/- MDBC, GPO Box 409, Canberra ACT 2601 Office location: c/- Murray-Darling Basin Commission, 2nd Floor, 7 Moore Street, Canberra City, Australian Capital Territory Telephone: (02) 6279 0100; international + 61 2 6279 0100 Facsimile: (02) 6248 8053; international + 61 2 6248 8053 E-mail: [email protected] Website: http://www.mdbc.gov.au

Map on cover: © Copyright Commonwealth of 1985

Remainder of publication: © Copyright Murray-Darling Basin Commission 1998

This document may be reproduced in whole or in part, provided that the information in it is not sold for commercial benefit and its source is acknowledged. Dissemination and discussion of the document is encouraged. For further copies and assistance contact the Reference Panel at the above address.

ISBN 1 875 209 92 1

ii HUME AND DARTMOUTH DAMS OPERATIONS REVIEW Contents

1. About this options paper 3

2. Overview 5

3. Introduction 7

3.1 History of River Murray water regulation 7

3.2 Roles of Hume and Dartmouth storages 7

3.3 The Operations Review 8

3.4 Work related to the review 8

3.5 Community consultation 9

4. Water regulation issues 11

4.1 Identification of issues 11

4.2 Issues that do not involve competing claims for water 11

4.3 Issues that involve competing claims for water 12

5. Issues that do not involve competing claims for water 13

5.1 Economic impact of Dartmouth on the Mitta Mitta valley 13

5.1.1 Effect of on pasture productivity 13

5.1.2 Flood duration in the Mitta Mitta valley 14

5.1.3 Adverse effects on agricultural land at peak regulated flow 16

5.1.4 Erosion on the 16

5.2 Economic impact of on the floodplain below 17

5.2.1 Adverse effects on agricultural land at peak regulated flow 17

5.2.2 The need for a comprehensive river management plan between Hume and Yarrawonga 17

5.3 Effect of dams on non-flow environmental values 19

5.3.1 Impact of Dartmouth Dam on water temperature and quality 19

5.3.2 Effects of regulated flows and rain rejections on natural drying cycles in 20

5.4 The need to better manage minimum flows downstream of Mildura 21

5.5 The need for improved communication 21

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6. Issues that involve competing claims for water 23

6.1 Issues and approaches to solving them 23

6.2 Testing single operational changes 24

6.2.1 Natural conditions 26

6.2.2 Benchmark (B42800) 26

6.2.3 Fill and spill (B42810) 26

6.2.4 Provision of airspace (B46770) 27

6.2.5 Relaxed pre-release rules (B42840) 27

6.2.6 Translucent flows (B46750) 28

6.2.7 Use of Dartmouth during floods (B42801) 28

6.2.8 “Sharing the Murray” proposal for the Barmah-Millewa forest (B47850) 29

6.2.9 Increased pre-release from Hume Dam (B46160) 30

6.3 Scenarios outside the scope of the review 32

6.4 Combined scenarios 33

7. Summary of options and preliminary panel views 37

Appendix A: Terms of reference for the Operations Review 41

Appendix B: Reference panel 43

Appendix C: Key issues identified in scoping study 45

Appendix D: Details of “Backgrounder” papers 47

Appendix E: Issue register 49

Appendix F: Supporting documents and references 51

Glossary 53

2 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 1. About this options paper

In December 1996 the Murray-Darling modelling group has carried out the necessary computer simulations. Basin Ministerial Council agreed that This options paper is the result of the review to November 1998. It describes the issues that have been the way in which Hume and identified as needing attention, the way in which the Dartmouth dams are operated should panel has gone about its task, the tensions that arise because of competing objectives for managing the be reviewed. regulated Murray, and possible improvements and changes to the balance between competing objectives. he review has been guided by a reference panel At this stage the panel has reached no fixed Tconsisting of members representing different conclusions. The paper presents options, and in most interest groups and drawn from the general cases also presents a preliminary panel view. community, and supported by relevant government The work to date now needs to be exposed to the agencies. wider community. The Murray-Darling Basin Commission appointed A series of public meetings will be held to present the reference panel, and the panel’s final product will and explain the material in the paper, discuss the be a report and recommendations to the Commission. options, and stimulate comment and feedback. The However the panel is fully independent and its work panel expects to refine its views in the light of public has not been influenced or directed by the comment before making its recommendations to Commission, nor has the Commission considered or the Commission. endorsed this options paper. Comments may be made to any member of the The technical work has been managed by a small panel (see contact numbers in appendix B) or can be project team. The team has utilised private addressed to Clarke Ballard, c/o Murray-Darling Basin consultants, expertise available in government Commission, GPO Box 409, Canberra ACT 2601; agencies and the internal resources of the Murray- telephone 02 6279 0176; fax 02 6230 6005; Darling Basin Commission. The Commission’s email: [email protected]

The deadline for comment is 10 February 1999.

HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 3 2. Overview

The terms of reference of the review (see — for example, the fact that water temperatures are lowered and steady regulated flows diminish appendix A) are essentially to review the riverbank vegetation and can aggravate erosion. operating procedures for the Hume and The panel has been able to arrive at preliminary views on most of these issues, which tend to be reasonably Dartmouth Dams and to recommend self-contained. how they might be amended to better The second group of issues essentially revolves around trade-offs between different management address the competing objectives of water objectives, and judging where the balance between them should lie. Computer models were used supply, environmental enhancement and extensively to analyse different possible operational scenarios. These led the panel to a fairly clear flood mitigation. A broad perspective is understanding of the effects of each strategy and those required, including consideration of a strategies — or packages of strategies — that might be useful in achieving a different balance. However, no wide range of economic, social and option was found that resulted in improvements from the viewpoint of every interest group. environmental factors. The panel has therefore been unable, so far, to reach a definitive view on strategies that should be he reference panel visited many areas of interest recommended. Despite this, it has formed a view that Talong the river, and spent a lot of time collecting the likely direction is towards a package that includes: input from interested groups. The result was a long list • arrangements for effectively watering the Barmah- of issues that were seen as important by one or more Millewa forest using the water already allocated for interest group. It was necessary to be rigorous in that purpose, pursuing only those issues that are related to dam • continued “harmony” operation of Hume and operation. Dartmouth storages, Another difficulty in maintaining focus has been the • some form of varied pre-release strategy to mimic other processes, programs and inquiries (such as the natural variability in flows below the storages, and Snowy Inquiry and work on environmental flows) that • possibly the acquisition of easements over are under way at present. It has been necessary to frequently flooded land between Hume and minimise potential duplication and overlap by forming, Yarrawonga. as clearly as possible, a picture of the boundaries between the various activities and where the review fits Such a package could be implemented with minor into the larger picture. environmental benefits and little adverse effect on The panel has found that issues fall into two distinct consumptive users, beyond that already in train because groups: those that do not involve finding a balance of the water already committed to Barmah-Millewa between competing claims to water, and those that do. watering. However, there would be further environmental The first group of issues includes: benefits, and further adverse effects on consumptive use, • the need for better communication between the if pre-release targets were revised to introduce a higher- Commission’s operational arm and interested than-current risk of storages failing to fill. community groups; Floodplain dwellers would obtain some benefit from • economic impacts of the dams on human uses of these strategies, but those benefits would not the floodplains below them; necessarily increase as the specified risk of storages • management of flow variability in the river failing to fill was increased. downstream; and The panel seeks opinions from the wider • environmental impacts of the dams (excluding the community on where the balance between the various impacts of extraction of water further downstream) competing interests should lie.

HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 5 3. Introduction

3.1 History of River Murray water regulation • erosion was increased by high regulated flows in In its natural state, the Murray was quite different from some reaches of the river system. the present regulated river. During severe droughts it Many of these impacts were unforseen when construction was sometimes reduced to a chain of waterholes, but of major storages commenced. The community has flows generally followed a yearly cycle. This included generally considered that benefits of river regulation late winter and spring flooding in most years, with high greatly outweigh the costs. With increased knowledge of flows continuing into summer and then gradually impacts caused by our actions, however, community receding until, between February and May, the flow values have changed. Therefore, the way in which the was reduced in places to a small saline stream. The Murray is regulated may need to be adjusted to take Murray was too unreliable in that state to allow its account of these changes in community attitudes towards valley to be intensively settled. riverine health. Regulation of the Murray by the construction of large storages has guaranteed a reliable supply of water, 3.2 Roles of Hume and Dartmouth storages which has contributed greatly to the development and Hume storage is the primary regulating storage prosperity of the region. operated by the Murray-Darling Basin Commission (the Without the Hume Dam (completed in 1936), the Commission). Hume is drawn down in the summer natural River Murray would almost certainly have and autumn of every year. In contrast, Dartmouth ceased to flow in 1939, 1945, 1968 and 1983. Instead, a storage (completed in 1979) is primarily used as a flow has been maintained along the river even during reserve storage to supplement Hume in dry years or severe droughts. Without this regulation of water flow sequences of years. Dartmouth has a less regular much of the development and prosperity of the region annual cycle of operation than Hume, and its levels would not have been realised. tend to reflect longer cycles of wet and dry climate. In The largest economic benefit of the storages has been the long term it is expected to be full or close to full in a secure supply of water for irrigation and other about 30 percent of years, but it may remain below full purposes. The value of irrigated agricultural production for periods of many years. from the regulated Murray system is in the order of $700 Although the primary purpose of Hume and million annually. Many towns and cities, the largest of Dartmouth is to store water for consumptive use, they which is Adelaide, also depend on the Murray for their are also operated to mitigate flooding in the valleys water supply. The regulation of Murray flows has also: below them. The two main strategies used to achieve • greatly reduced extremes in salinity levels that this are pre-releases and harmony operation. occurred under natural conditions; Pre-releases may be made in the winter or spring if • mitigated flooding that would have affected human storage levels and inflows are high and the storage is activities on the floodplain; and certain, or almost certain, to fill. The aim is to delay • enhanced recreational opportunities. filling and so provide additional flood mitigation. However, regulation has not been without cost: Harmony operation is the transfer of water from • valuable land was flooded to provide storages; Dartmouth to Hume when the level of Dartmouth is • weirs and storages raised and maintained water high. Harmony operation provides more flood levels, causing salinisation and drowning trees; mitigation below Dartmouth Dam and enhances • wetlands became too wet or too dry; recreational use of Hume without jeopardising • diversity of in-stream biota was reduced by release water supply. Harmony rules are complex, but in of cold water; general tend to equalise the chance of spill of the • more water in summer and less in winter reversed two storages. the natural seasonality of flows; Operational principles and rules are described in • natural flow variability and flooding were suppressed; more detail in background papers which were • red gum forest growth and regeneration were distributed as the review progressed and can be found in adversely affected by reduced spring flooding; and the support papers (see appendix F).

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3.3 The Operations Review make sure that duplication does not occur, but some Against the above background, and because of overlaps are unavoidable. The most important and relevant other work suggestions from landholders below the two dams, the currently under way includes the following: operation of Hume and Dartmouth Dams has been the • Development of River Murray bulk water subject of a detailed review. This document is the result entitlements in , which is well advanced — to date of the review process. including proposals for an enhanced environmental The Murray-Darling Basin Ministerial Council entitlement for the Barmah-Millewa forest. defined the terms of reference for the review in • Catchment-by-catchment development of river flow December 1996, as shown in appendix A. and water quality objectives, which is under way in New To oversee the review and ensure that all views were South Wales but has yet to be applied to the Murray. represented, the Commission appointed a reference • An inquiry into the need for environmental releases panel. Panel members represent various interested from the Snowy Scheme. The results of this inquiry community groups and agencies (see appendix B) and have the potential to decrease water passed to the have been fully involved in all aspects of the project. Murray. Concurrently, relaxation of current fixed The final product of the review will be a report (to be water proportions passed by the Snowy Scheme to prepared after further consultation) that the panel will the Murray and rivers is being examined. present to the Commission. • An Interstate Working Group on River Murray Flows has been established to develop a River 3.4 Work related to the review Murray flow management plan that balances human and environmental needs. Some work To fully address the terms of reference in this review, it conducted by the Operations Review — in is tempting to expand the review to consider: particular, the modelling tools developed for the • operation of the whole river system; review — is likely to augment the work of the • water allocations and in-stream flows throughout Interstate Working Group. the Murray; and To ensure that the scope of this review was • the impacts of the and achievable in an a reasonable time-frame, the review possible changes in its operation, etc. has concentrated on issues that can actually be This would create an immense and unrealistic task and affected by the way in which Hume and Dartmouth overlap with work being undertaken by other groups. It Dams are operated. Figure 1 illustrates the manner in is important to be aware of other work in progress to which the various activities interact.

Figure 1: River Murray Flow Management Stand-alone solutions Hume and Dartmouth Dams from Operations Review Operations Review Inputs including: Scientific Panel report Murray-Darling Basin NSW water reforms and Murray-Darling Basin Interstate Working Group Commission environmental flows on River Murray Flows: Barmah-Millewa forest plan • Community representation Victorian bulk entitlement • Agency representation process • Dedicated resources Murray-Darling Basin Snowy Inquiry Ministerial Council Snowy corporatisation

Future review process River Murray Flow Management Plan

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3.5 Community consultation • A series of background papers was produced (see An essential requirement for conducting the review has summaries in appendix D), describing aspects of the been wide consultation with stakeholders in aspects of review or present operation. A register of interested River Murray management defined in the terms of stakeholders was compiled and all background reference. The broad membership of the reference panel papers and information about the review were has been an important part of the consultative process. distributed to these people. The register is constantly Members of the panel have ensured that their interest being updated. To add a name to the register, please groups are informed of review progress. In addition, the call 1800 630 144. following arrangements were made to ensure that stakeholders’ interests were fully represented. This options paper is the next step in the consultative • The Australian Research Centre for Water in Society process. It is intended to inform people of progress to identified issues that people along the river saw as date and to gather feedback on the options being important, as the first step in conducting the review. considered. The final step in the review will be the Identification of these issues was achieved by preparation of a report to the Commission based on telephone interviews with people from a broad responses to this paper. range of interest groups. A summary of the issues identified is shown in appendix C.

The closing date for comment on this paper is Wednesday 10 February 1999.

HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 9 4. Water regulation issues

4.1 Identification of issues of this sort of issue are as follows: As mentioned earlier, the Australian Research Centre • Provision of space in storages to provide flood for Water in Society identified important issues as the mitigation. This space may decrease reliability of first step in conducting the review. In addition, a supply to irrigators and remove environmentally number of interest groups expressed a desire for the desirable flooding over the broader floodplain. panel to visit their local areas. The panel visited these • Allowing a percentage of winter and spring inflow areas, discussed issues with local people, and conducted through a storage to reinstate some elements of the field inspections in conjunction with scheduled panel natural flow regime. This policy may be beneficial to meetings. the environment but may reduce reliability of Field inspections were conducted in the following areas: irrigation supply and increase downstream flooding • the Mitta Mitta valley; of agricultural land. • the floodplain between Hume and Yarrawonga; • A pure “fill and spill” policy maximising supply to • municipal areas of and Wodonga; irrigators. This policy provides fewer benefits to • (by air) irrigation areas around and the floodplain agriculture and lack of flow variability for Barmah-Millewa forest; and the environment — particularly before spill and • the Sunraysia area. throughout non-spill years. Written submissions were also received from: Issues identified by the review are shown in appendix E • interested parties in the Mitta Mitta valley; in terms of: • Mitta Mitta Community Action Group; • relevance of issue to each river reach; • Upper North-East River Management Authority; • rating of issue according to relevance to the review; • River Murray Action Group; • priority for computer modelling or other assessment • caravan parks; by the review. • irrigators (Deniliquin area); The review addressed most issues that have a • Victorian gravity irrigators; and medium or higher rating. In many cases, issues with • interested parties of the Sunraysia Region of Victoria lower ratings will need to be addressed by other and NSW. processes. An issue register was compiled from these sources The panel has devised options and developed (appendix E), and was progressively updated and preliminary views on many issues that do not involve reviewed to identify all issues important to balancing competing claims for water. They are stakeholders. included in this paper under each section and the The issues were then categorised into two groups: conclusions. The panel expects to be able to make firm • issues that do not involve balancing competing recommendations to the Commission about most of claims, and these issues. • issues that involve balancing competing claims. Firm views have not yet been reached on issues Issues that do not involve balancing competing claims are that do require trade-offs between competing claims for largely equity-based: they can be remedied by water. However, options have been narrowed to what compensation, engineering works, etc., and do not the panel believes are realistic alternatives. The panel require trade-offs between competing claims for water. needs wider input on the process by which these An example is the adverse effect of high regulated flow competing claims should be balanced. between Hume and Yarrawonga on agricultural land. Issues that involve balancing competing claims are concerned 4.2 Issues that do not involve competing with balancing competing management objectives from claims for water different stakeholders. These issues require analysis by Major issues that do not involve balancing competing simulation modelling to compare different operating claims — i.e., issues that do not require balancing of strategies. Some of the costs and benefits of each competing objectives — were identified as: strategy can be quantified in dollar terms but some, • Economic impacts of Dartmouth Dam on the Mitta particularly the environmental ones, cannot. Examples Mitta valley.

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• Impact of peak regulated flow on agricultural land. • providing regular and secure water for irrigation, • Lack of comprehensive river management plans. domestic and industrial consumption; • Impact of water releases from storages (particularly • mitigating floods below storages to maximise Dartmouth) on water temperature and quality. economic benefits to human floodplain users; and • Impact of regulated flows and rainfall rejections on • making releases in a way that better meets the natural drying cycles in wetlands. needs of the riverine environment. • Management of minimum flows downstream of Due to the complexity of issues that involve balancing Mildura. competing claims, computer modelling has been used • The need for improved communication. to assist in decision making. This modelling has allowed These issues are addressed in the following sections objective analysis of changes in flow advocated by (5.1 to 5.5). stakeholder groups in both dollar and non-dollar terms. Considerable effort was devoted to developing a model 4.3 Issues that involve competing claims examining results of operational changes in daily time- for water steps rather than through traditional models that work The major issues identified as requiring simulation in monthly time-steps. This approach enables closer modelling were a complex interaction of competing examination of benefits and costs of these operational objectives broadly classified as follows: changes, particularly for flood events.

12 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 5. Issues that do not involve competing claims for water

5.1 Economic impact of Dartmouth Dam on The panel has examined the economic impact of the Mitta Mitta valley Dartmouth on agricultural profitability under the There is no doubt that Dartmouth Dam has heavily following headings: modified the hydrologic regime of the Mitta Mitta • Effect of Dartmouth Dam on pasture productivity. valley. The change in flow regime since construction of • Flood duration in the Mitta Mitta valley. Dartmouth Dam has probably been the largest change • Adverse effects on small areas of land at peak experienced anywhere along the River Murray. regulated flow. The flow regime differs from the natural regime in the • Erosion on the Mitta Mitta River. following manner: • very low flows (less than 500 ML/day) are less 5.1.1 Effect of Dartmouth Dam on pasture common than under natural conditions; productivity • flows between 500 and 2500 ML/day are slightly Independently of the panel’s review, a study of the more common over all, but less common in effect of Dartmouth Dam on pasture productivity in the summer and autumn; Mitta Mitta valley was commissioned by Goulburn- • flows between 2500 and 6000 ML/day are slightly Murray Water and the Commission. This study was less common over all, but significantly more guided by a steering committee consisting mostly of common in summer and autumn; local landholders and was required to determine: • flows between 6000 ML/day and channel capacity • the effect of changes in river flow regimes and of 10 000 ML/day are significantly more common subsequent water table levels on productivity of — particularly in summer and autumn; and dryland and irrigated pastures; • flows above channel capacity are less common, • the effect of water temperature on irrigated pasture especially at high flood levels, but the duration of productivity; and floods that do occur is extended at some levels. • water usage on irrigated pastures and the effects of This simple description does not fully represent the impact water table variation on this usage. that construction of Dartmouth has had on the flow The study found as follows: regime. There are really two river regimes — either of • Dartmouth Dam has typically reduced winter/spring which may last for many years on end — as follows: flows, flooding and water table levels. • When Dartmouth is filling (after being drawn down • Irrigation releases have been irregular in frequency, to supply water for consumptive use), it fully timing and duration. However, moderate autumn controls inflow and the valley downstream is almost releases have been made on a more regular basis entirely flood-free. since 1990. • After filling, Dartmouth Storage may remain close • Soils are highly permeable in general, and water to full for extended periods — being drawn down table levels are often affected by river height, under harmony rules in the autumn and refilling, rainfall, irrigation, run-off and adjacent lagoons. with pre-releases, in winter and spring. Under this After rainfall or irrigation, water tables generally fall regime, flood duration may be increased but within two weeks to a height related to the river frequency is still less than that which occurs under height. Further from the river, groundwater levels natural conditions. are less clearly related to river height. Landholders are particularly concerned about the • Close to the river (say within 200 m), average negative impacts that the dam appears to have exerted spring water table levels are estimated to be as on agricultural profitability. As a result of fewer floods much as 1.5 m lower than before Dartmouth Dam and lower water tables, pasture growth has been was constructed. Irrigation releases in summer or reduced to the extent that irrigation has become a autumn result in water table levels as much as 2 m necessity. Irrigation can improve production to greater higher during major releases. than pre-Dartmouth levels. However, irrigation • Dryland pasture productivity is reduced by increases operating risks and costs, and requires more Dartmouth Dam where the water table was intensive management and capital investment. previously within 70 cm of the surface —

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particularly during dry spring conditions. Little from Dartmouth during spring/early summer would effect is felt on dryland pasture productivity where reduce the effects of cold water on irrigation water table levels were previously deeper than 70 productivity. These releases would also provide a cm. However, productivity during wet seasons is higher water table in spring/early summer, increased because current water tables are lower emulating natural regimes and enhancing pasture and drainage is better. productivity. • In a well-managed irrigated pasture, there is little Landholders believe actions required to remedy pasture productivity benefit from a higher or problems highlighted by the report include increased lower water table. With less capable management, water allocations and water pricing concessions. a water table less than 70 cm will improve Goulburn-Murray Water, which is responsible for water productivity. licences in the valley, is currently assessing these claims. • Simulations of water releases at 10°C for an entire To address concerns relating to temperature of irrigation season showed that pasture productivity water releases, the issue of a multi-level offtake at would be reduced by up to 15% as a direct result of Dartmouth is considered in section 5.3.1. application of cold water. This situation represents the upper limit of the effect of cold water on pasture Based on the results of this study, the panel (noting that productivity, as irrigation releases associated with the possible increased water allocations and pricing concessions coldest river temperatures would rarely be made for are currently being assessed by Goulburn-Murray Water an entire season. However, colder river temperatures and are now unable to be directly influenced by this occur during releases from Dartmouth. Where colder review) has identified the following options: water releases occur, greater productivity loss than a • Investigate earlier pre-releases in years when 10°C scenario may occur. Dartmouth Dam has spilled, to avoid periods of low • Over 40% of diverted water can be lost through flow between spring spills and autumn harmony infiltration past the root zone of flood irrigated releases. pasture, and through channel seepage, evaporation • Investigate lower and earlier releases in years when and run-off. Modelling shows an average annual resources must be transferred from Dartmouth to irrigation requirement, without losses, of 3.7 ML/ha Hume for supply. to 11.3 ML/ha depending on rainfall. However, actual irrigation applications are less than those The panel’s preliminary views are as follows: suggested by the model. • Goulburn-Murray Water is dealing adequately with • High and low water table simulations show that possible increased water allocations (in the context annual irrigation water requirements could be of the Murray-Darling Basin Commission Cap), reduced from 8.5 ML/ha to about 6 ML/ha if a pricing concessions and any other compensation shallow water table of less than 30 cm were measures for adverse effects on individuals. maintained for the entire irrigation season under • Current harmony rules provide for releases as soon optimal irrigation conditions. If the water table were as practicable following Hume ceasing to spill, and maintained at 50 cm, water requirements would this provision should be retained. only be reduced to 8.3 ML/ha. • When Dartmouth releases are needed for supply Conclusions derived from these results applicable to purposes, there may be some scope for earlier river flow management are as follows: releases at lower rates; however, this could involve • More regular summer flows would provide: increased risk of loss of water for consumption. – improved pump management, – reduced pumping costs, and 5.1.2 Flood duration in the Mitta Mitta valley – reduced irrigation water requirements because It is well understood that Dartmouth markedly reduces of higher water tables and higher pump flow rates. the frequency of flooding in the valley below — • Timing of irrigation releases can have an impact on virtually eliminating flooding for long periods when the dryland and irrigated pasture productivity. Releases storage does not spill. However, there has been much

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Table 1: Modification of flood regime at Tallandoon since construction of Dartmouth Dam

Flow at Average no of floods/year Average flood duration (days) Average days flooded/year Tallandoon Pre Post % Pre Post % Pre Post % ML/day Dam Dam change Dam Dam change Dam Dam change

10 000 (channel 3.59 1.78 -50 7.2 6.3 -12 25.8 11.2 -57 capacity)

13 000 2.75 0.87 -68 5.3 6.3 +19 14.4 5.5 -62

19 000 1.49 0.33 -78 3.5 4.6 +31 5.2 1.5 -71 (minor flooding)

27 000 0.62 0.16 -74 2.8 2.0 -29 1.7 0.3 -82 (moderate flooding)

discussion about the effect of the dam on duration of The panel has reached the conclusion that the dam has floods occurring when the storage is full. a powerful effect in reducing both frequency and peaks Some landholders state that before Dartmouth was of floods in the Mitta Mitta valley. As discussed in constructed “floods never lasted longer than a few days, section 5.1.1, this reduction in frequency and peaks and were beneficial”. However, in a survey conducted provides both advantages and disadvantages to during early stages of dam construction, beef and dairy agricultural productivity. farmers listed fear of catastrophic floods as a major barrier to farm development. While it is true that some floods are extended in To objectively assess the impact of the dam on duration (at the 10 000 ML/day level at Tallandoon), it flooding, the flood frequencies and durations under is equally true that some are decreased in duration. Over pre-Dartmouth and post-Dartmouth conditions were the 63 years modelled, there were 13 such floods that: compared using computer simulation models (see • lasted more than ten days under both the pre- section 6 for a description of the models and the Dartmouth and post-Dartmouth scenarios, and support papers for a detailed report on Mitta Mitta • were individual floods that could be directly compared. flood duration). Comparison of those floods showed that the dam could Modification of the flood regime by Dartmouth extend flood duration by as much as eight days, but Dam at Tallandoon is summarised in table 1. conversely could reduce it by as much as eight days. The This table shows that Dartmouth Dam removes average effect was an increase in duration of 2.4 days. about half the low-level floods and three-quarters of higher level floods. It also reduces average flood days Stakeholders have expressed some concern that the per year by a similar proportion. At some levels, dam sometimes increases the duration of floods at duration is increased for floods that are not removed; at particular levels, despite the powerful overall flood other levels, average duration is decreased. mitigation effect. The review panel believes that it is At the nominal river channel capacity at Tallandoon possible to change storage operation so that duration (10 000 ML/day), average flood duration is somewhat above nominal channel capacity at Tallandoon is not decreased. However, some floods at that level are increased. However, this change would cause increased extended in duration by the storage. This effect is flood peaks. particularly apparent for floods that occur when the storage is already full. This option and the views of the panel are discussed further in section 6.2.7 (‘Use of Dartmouth power station during floods’). In summary, however, the panel

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considers that initially the question of using the power 5.1.4 Erosion on the Mitta Mitta River station to assist in controlling flood duration is a matter The Mitta Mitta stream and floodplain are relatively for the Mitta Mitta community to reach an agreed steep and there are few geomorphic controls — such as position on. bedrock bars — that limit on-going fluvial geomorphic processes. Erosion was prevalent on the river prior to 5.1.3 Adverse effects on agricultural land at construction of Dartmouth Dam. In 1955, almost 25 peak regulated flow years before completion of the dam, the Mitta Mitta The nominal channel capacity of the Mitta Mitta River River Improvement Trust was formed to manage the for regulated releases has been set at 10 000 ML/day. erosion problems. In 1984, several regulators were installed with When Dartmouth Dam was constructed, possible Commission funds on lagoons and anabranches adverse effects on river stability were anticipated. The alongside the lower reaches of the river. These Commission has therefore contributed to erosion regulators were intended to prevent high regulated control work. This work is now conducted by the North flows from backing out on to the floodplain. East Catchment Management Authority (NECMA). Unfortunately, the regulators were generally Most erosion work conducted since formation of the unsuccessful because of construction problems and Mitta Mitta River Improvement Trust has used willows permeable soils allowing lagoon levels to vary with and selective rock beaching as the primary control river levels. Waterlogging, as distinct from inundation, method. This approach has led to two problems: also occurs on a number of properties in this area. • expensive control measures for excessive willow During 1997–98, slightly lower (9500 ML/day) growth, and regulated releases were trialled. The lower releases • lowered environmental values caused by gradual resulted in the affected area being reduced. However, at conversion of the stream to a rock and willow lined least two properties were still affected by waterlogging channel. and/or inundation. In a submission to the review, the Upper North East River Management Authority (the predecessor of The panel considers that there are three options for NECMA) stated that division of responsibilities between resolving this problem: it, Goulburn-Murray Water and the Commission were • investigate nominal channel capacities in the range unclear. Accordingly, the authority identified a need to: 9000 to 10 000 ML/day; • formalise management roles, • investigate construction of regulators where • resolve management requirements, and appropriate; or • clarify funding arrangements. • take flood easements over affected land and pay The submission also suggested that an integrated program appropriate compensation. of waterway and floodplain management should be The panel has further considered these options in light developed for the Mitta Mitta River. It recommended that of the following factors: this program should include plans for: • problems may be minimised by carefully selecting • Floodplain management — including pasture, flood the regulated release figure; and drought management. • regulators may only be required on one or two • Stream health — including stream geomorphology properties; and and stability, riparian vegetation and habitat, in- • easements could be taken over the affected land if stream ecological conditions, and water quality. no structural solution is possible. • Stream operational requirements — such as release rates, drawdown rates, and community awareness It is the view of the panel that further investigations provisions. should be conducted to ascertain the most beneficial option for each affected property.

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Based on the submissions received and analysis Sometimes it takes days or weeks of high regulated flow conducted by the panel, the following options have before waterlogging occurs. Affected areas can be identified been identified: by changes in vegetation — typically weeds replacing • Continue with existing stream erosion control paspalum — even in the absence of visible waterlogging. methods, accepting that the result over time will be As part of the review, Hassall & Associates inspected a willow and rock lined river channel of limited most of these areas in December 1997 to assess the spatial environmental value. extent and cost of mitigating the effects of this waterlogging. • Fund further research into mechanisms and factors They found that about 250 to 300 ha was affected, and contributing to slumping of banks on the Mitta estimated the value of the affected land at about $375 000. Mitta River. • Develop an integrated program of waterway and The panel considers the options for dealing with this floodplain management along the lines suggested by problem are to: the NECMA. • reduce peak regulated flow level to a figure significantly lower than 25 000 ML/day; The panel’s preliminary view is that an integrated • do nothing, on the basis that the negative impacts program of waterway and floodplain management are outweighed by flood mitigation benefits to along the lines suggested by the NECMA should be agricultural land; or developed. • take flood easements over the affected land and pay appropriate compensation. 5.2 Economic impact of Hume Dam on the floodplain below It is the view of the panel that, for equity reasons, taking flood easements over the affected land and paying 5.2.1 Adverse effects on agricultural land at appropriate compensation is the only reasonable option. peak regulated flow

Channel capacity of the Murray between Hume and 5.2.2 The need for a comprehensive river Yarrawonga has been regarded for many years as management plan between Hume and 25 000 ML/day at Albury. Although nominal channel Yarrawonga capacity — and therefore peak regulated release from Hume — have not changed, regulated diversions from River regulation and flow regimes the system have increased steadily over the past three decades leading to longer periods of high regulated flow. Regulation of the River Murray between Hume and This part of the Murray is not a single river, but rather Yarrawonga has progressively increased since a main stream with many anabranches (refer to back construction of the original Hume Dam in the 1920s. cover). In some places the anabranches carry more flow Since then, the Snowy Mountains Scheme has been than the main stream During the late 1970s, regulated built, capacity of Hume has been doubled, and flows of increasing magnitude led to concerns that access Dartmouth Dam has been constructed. Irrigation to islands of freehold land was being cut off by development has matched the increased storage anabranches. In particular, many formerly intermittent available, and the flow regime is now very different anabranches started to run throughout the irrigation from the natural regime, in that: season. Many of these problems have been resolved by • Low flows (1200 – 5000 ML/day) are more common establishing a program in which the Commission — particularly in winter and early spring as storages fill. contributed to the cost of access bridges or acquiring • Flows between 15 000 and 25 000 ML/day are more easements where provision of access was not justified. common — particularly in summer and autumn Another problem, however, is emerging. Areas of when natural flows would be lower. In most years, freehold land on some properties are being inundated there are now extended periods of flow close to at peak regulated flow, or are being waterlogged, 25 000 ML/day during the irrigation season. Pre- because the land is marginally above river level and lies release of water at this rate, to mitigate potential above sand/gravel lenses connected to the river. flooding in winter and spring, is also quite common.

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Table 2: Effect of Snowy and development on floods below Hume

Flow at Average no of floods/year Average flood duration (days) Average days flooded/year Albury Natural Present % Natural Present % Natural Present % ML/day change change change

25 000 (channel 4.37 2.10 -52 13.27 14.88 +12 57.99 31.25 -46 capacity)

31 500 4.25 1.51 -64 9.52 13.60 +43 40.46 20.02 -51

36 000 3.79 1.35 -64 8.33 12.00 +44 31.57 16.20 -49 (minimal flooding)

43 000 0.62 0.16 -74 2.8 2.0 -29 1.7 11.20 -49 (minor flooding)

• Flows significantly above 25 000 ML/day are less downstream of . There has been little common because of the flood-mitigating effect of change in depth between those locations. The depth the storages. However, the duration of low-level throughout the Hume-Yarrawonga reach is now flooding can be extended at times. fairly stable and the bed has become armoured by a • Seasonality of river flows has changed markedly. coarse layer of gravel. Much higher flows are experienced in summer and • The river has historically moved over the floodplain autumn, and lower flows in winter and spring. by a process of lateral migration of bends. This • Total water volume is about 6% more than under migration is occurring at present, but it is not clear natural conditions as a result of water diverted from whether or not the regulated flow regime has the Snowy catchment. affected the rate of migration of bends. Effects of water storages and the Snowy Mountains • In contrast, there is a clear link between river Hydro-electric Scheme on River Murray floods below regulation and general channel widening. River Hume have been quite significant. Table 2 illustrates regulation, in conjunction with other land changes in flooding as a result of these water control management practices, has led to a general structures. widening of the river channel of about 160 mm per The table compares natural and present-day year. It is likely that river regulation has been a frequency, duration and total annual days flooding at major contributor to depleting the incidence and various flow levels. Figures are for events exceeding extent of vegetation on the river bank. The long one day’s duration occurring from June to December periods under regulated flow soften the banks and inclusive. lead to higher rates of bank erosion. • Banks are generally retreating in a parallel fashion — notch erosion at high regulated flow level is not River regulation and erosion the main mechanism. Erosion is occurring across Between Hume and Yarrawonga, erosion is more active the full height of the bank. than in other reaches of the River Murray. Consultants • Anabranches carry large volumes of water under Ian Drummond and Associates (1993 and 1997) regulated conditions. In one location, the main investigated the nature and extent of channel stream carries less than half the peak regulated flow. instabilities in the reach. They concluded as follows: Anabranches need to be examined individually to • The river channel has deepened between Hume assess changes and the possibility of capture of the Dam and Albury, and has become shallower main river channel.

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• Regulation of flows causes a higher proportion of • a decision on the extent to which anabranch flow to pass along the river channel and less along development needs to be contained; the floodplain. It is estimated that re-regulation • setting desired levels of protection for aquatic, within Hume increases the energy within the river riparian and floodplain habitats; and channel (hence potential erosive power) by about • documenting desired aesthetic and recreational values. 6%. Re-introduction of elements of the natural flow Based on the strategic framework, a comprehensive regime, combined with other management tools, river management program should be developed. This may help to control channel erosion. program would: • Erosion rates are high during floods, but the majority • establish an agreed management arrangement of erosion is occurring from flows within the (which needs to work in two states, have proper channel. The flows within the channel are mostly local input, etc); irrigation releases, but also include flood pre-releases. • establish links with associated land management • It is not possible to quantify the relative effects of programs in each state; irrigation releases, flood releases and Snowy • establish agreed funding arrangements — with diversions on channel erosion in the reach. consideration of funding from such sources as the • Factors such as de-snagging (which tends to increase Commission, catchment management authorities both channel capacity and erosion rates), changes in and local government, and input (cash or kind) vegetation (partly but not solely because of increased from landholders; regulation) and boating (probably quite limited) also • set a works program — including both an annual contribute to changed rates of channel erosion. program of necessary patch-up works (done now to The panel accepts that flow regulation has had a major a modest extent with Commission funding) and a coordinated strategy of activities designed to achieve influence on channel stability in the Hume-to- the long-term goals; and Yarrawonga reach of the Murray. However, the panel is • monitor progress and the extent to which the also aware that the river has historically migrated strategic framework might need to be changed. around the floodplain. This fact is obvious from aerial photographs or maps of the area — including the map 5.3 Effect of dams on non-flow on the cover of this paper. environmental values

The panel considers that future options for 5.3.1 Impact of Dartmouth Dam on water management of this reach of the Murray are to: temperature and quality • retain the present management arrangement — under Water from Dartmouth Dam is normally released through which the Commission provides limited funding to the the high-level outlet, except when storage content drops NSW Department of Land and Water Conservation to below about 30% and the low-level outlet must be used. treat actively eroding sites on a priority basis; or The high-level outlet draws water from about 60 m • develop a comprehensive and properly funded below the full supply level of the storage. program for management of the reach. The temperature of water from the high-level outlet is considerably lower than river temperature prior to The panel believes that this issue can only be fully construction of the dam — particularly in summer and addressed by developing a comprehensive and properly autumn. Water quality of releases from the high-level funded program for management of the reach. The outlet is also lower than water near the surface. The management program will initially need a strategic low-level outlet exhibits similar, but amplified, water approach to articulate a vision for the future desirable quality and temperature problems. Releases of low- state of the river. The strategic framework will require: temperature water and/or poor quality water from • developing criteria for acceptable and unacceptable these outlets may be responsible for: erosion rates (& acceptable methods of erosion control); • declining habitat and native fish population in the • setting limits to acceptable rates of channel river (temperature is identified as the critical factor); widening and bed degradation; and

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• landholders being unable to achieve the full • Install shutters on the existing high-level outlet to potential of pasture productivity improvements by provide limited improvement. irrigation partly because of low water temperatures • Raise the top of the existing structure to above full — see section 5.1.1 (‘Effect of Dartmouth Dam on supply level and install a fully functional multi-level pasture productivity’). offtake. During construction of the dam, provision was made in • Agree in principle that a fully functional offtake is the existing high-level-outlet offtake tower for future required, and conduct detailed investigations into extension above full supply level if required. It has been the cost, benefit and optimum way to achieve a provisionally estimated that the extended tower with fully functional offtake. multi-level offtakes would increase temperatures significantly and improve other water quality factors. The panel’s preliminary view is that it agrees in However, it is highly unlikely that the extended tower principle with the last option: that a fully functional would restore temperatures and water quality to offtake is required and that detailed investigations into natural pre-dam levels. A feasibility stage cost estimate the cost, benefit and optimum way to achieve a fully of the extension is $11 million. functional offtake must be undertaken. An alternative to the tower extension would be to add shutters to the existing tower, which would be much 5.3.2 Effects of regulated flows and rain cheaper. These shutters would vary draw-off levels to a rejections on natural drying cycles limited extent, but would provide little improvement in in wetlands water temperature or quality over the current situation. Too much flooding can be as damaging to a naturally In assessing the benefits of extension or ephemeral as insufficient flooding. Many modification of the existing high-level outlet, the panel plants need a wetting and drying cycle for their seeds to considered the following issues to be important: germinate and their roots to be aerated. Drying also • Likely temperature increases will probably not permits oxygenation of sediments — a crucial step in restore pre-Dartmouth conditions to the extent that the process of nutrient cycling — which in turn suitable spawning habitat for all native fish will supports aquatic food webs. return. Conditions may well be favourable for Some wetlands along the Murray are inundated at Murray Cod and Macquarie Perch but not for some peak summer regulated flow. Others are not, but can be other species. This needs to be investigated. affected when summer rain causes rain-rejection of • The dam itself will remain a barrier to fish irrigation water which is returned to, or left in, the river. migration. • Water quality from the low-level outlet will not be The panel considers that this issue will require improved. The low-level outlet was used in 1983 and considerably more work, integrated into river flow briefly during the early 1990s, so its historic frequency management plans, and that solutions are likely to of use is low. However, the storage can remain low for involve the following: years on end: in the long term it is estimated that it will • Improved river operation. Improved river operation be used 15% of the time. Water quality from this outlet may be possible from better weather forecasts, more is potentially poor, with low dissolved oxygen levels accurate ordering from irrigation agencies, and and considerable dissolved iron, manganese and improved estimation of river losses. hydrogen sulphide. • Retention of rain rejections in storage of some kind. Four possibilities have been identified, as follows: Based on submissions received and analysis conducted – storage on-farm, particularly as drainage by the panel, the following options have been recycling dams become more popular; identified: – storage in distribution channels; • No action — accept that temperatures in the Mitta – continued emphasis on drainage diversion Mitta River will remain depressed, and that the river permits to encourage irrigators to pump from ecology will remain altered from its natural state. authority drains, which contain a proportion of

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rain rejection water; and capacity is not often used, because boating interests – provision of storage airspace in some weir pools. tend to object, and the normal operating range is • Physical works on individual wetlands. Works only 0.3 metres below full. There is scope for more would consist of banks, regulating structures and variation in operating levels, subject to local perhaps pumps to control the extent to which water agreement. was introduced into, or kept out of, a particular Potential gains in operational flexibility by allowing wetland at different times of the year. Mildura Weir levels to fluctuate are much smaller than Again the panel considers that it is likely that the at Euston. However, there are likely to be Interstate Working Group on River Murray Flows will environmental benefits in introducing some variation. need to consider this issue in some detail. • Improve measurement. Measurement points are presently at Euston and Wentworth, with no reliable 5.4 The need to better manage minimum measurement at Mildura. Mildura flows can be flows downstream of Mildura calculated from the Wentworth measurement, allowing for Darling inflows and changes in weir level. When demand downstream of the Darling–Murray Considerable improvements in flow control could be junction is supplied from the Darling, flows at Mildura achieved by improved measurement at Mildura. The can be quite low. Current Commission operating most feasible measurement improvement would procedure is to pass a minimum flow at Euston Weir of probably be to reduce or quantify leakage at the weir 2450 ML/day plus expected diversions at Red Cliffs, and measure the flow over it. FMIT, Merbein, Coomealla, Curlwaa and Millewa pump stations. This flow suggests that 2450 ML/day It is the view of the panel that all three options can be covers private diversions between Euston and Mildura adopted. This issue is essentially one of better flow Weir, river losses in that stretch, and the flow past control in this reach of river. Operation of Hume and Mildura Weir. Dartmouth Dams has no direct effect on control of There are operational difficulties in accurately these flows; the problem needs to be solved in the maintaining this small flow at the end of a long river context of flow management of the whole river. system with little re-regulating capacity. On occasions, the flow at Mildura is less than planned, which 5.5 The need for improved communication increases salinity levels and promotes the growth of algae in Mildura Weir Pool. The need for better communication between the Commission (in its role as river operator) and The panel considers that there are three options for communities along the river was identified as a resolving this problem as follows: significant issue during the initial stages of the review. • Obtain more precise orders from diverters. Orders This perception of poor communication was evident for major diversion points (Red Cliffs etc.) are to the panel in various locations. To some extent it received a week in advance, but are not always contrasts with the Commission’s good reputation for adhered to. Private diverters are relatively producing excellent publications and educational uncontrolled. material that target the general public. • Utilise more storage volume in weir pools. Most The panel formed the view that operation of the weir pools are operated at almost constant levels, river system is not well understood, and this may be which is convenient for water diverters and boating part of the problem. Regular communication between interests but provides little or no scope to re- interested groups and the actual river operators is regulate water. The constant pool levels also have required — not a spokesperson or public relations environmental disadvantages. person. It is recognised that, technically, the customers The exception is Euston Weir pool, which has of the Commission (or the newly formed River Murray an official operating range of 1.2 m (20 000 ML) Water) are the states, and that within-state operating below full. In fact it can be drawn down further: as agencies have the primary contact with retail far as 2 metres in an emergency. However, this customers. That is beside the point. The public

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perception is that the Commission operates the river, so knowledge of the likely risk factors. This level of the Commission is blamed if the operation is seen communication should also be planned and continual, (fairly or unfairly) to be inadequate. but need not be as frequent as is needed with those Within-state operating agencies have well interested in actual storage operation. developed communication channels with water users, The communication arrangements must be but not with recreational or tourism interests, or with integrated with other processes such as work of the floodplain users who are not irrigators. This is where Interstate Working Group for River Murray Flows and better communication is needed. the development of comprehensive river management The nature of the communication needed would plans. There is a need for some sort of broad based vary between groups. For example, landholder groups reference group to advise on communication needs. along the Mitta Mitta and between Hume and Yarrawonga have a keen interest in storage operation. The panel has concluded that formal and continuous Therefore, they require regular meetings — perhaps liaison should be set up between the Commission (or with extra communication as storages get close to full. River Murray Water) and interested community Other groups may need less frequent liaison. For groups. This liaison should be: example, there is a need to provide the general • regarded as a permanent commitment — not just community, and developers, with a better something to be fitted in when time is available; and understanding of flow and storage level variation, • of a frequency and form negotiated with particular system operation and actual flood risks, so that interest groups to suit their needs. development decisions are based on a realistic

22 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 6. Issues that involve competing claims for water.

6.1 Issues and approaches to solving them their customers. However, they dislike the adverse As already indicated, some issues amount to tensions publicity that can come with large floods. between competing interests or management objectives. • Boat operators want certainty and, generally, as Examples of different stakeholder groups’ conflicting little variation in river levels as possible. • Recreational fishing interests and ecotourism objectives are as follows: operators want a healthy river. Irrigators desire a consumptive yield as high and Many aspects of these competing interests can be secure as possible. This implies few spills of water and a quantified, or at least clarified, by simulation modelling. high degree of flow control. However, the Ministerial Consequently, the review panel has put considerable Cap on water diversions means that average effort into developing suitable computer models to consumption of water cannot increase above support decision making. benchmark levels. Irrigators seek to maintain the existing water security and water availability on which their business depends. Computer modelling Floodplain landholders want to have as much flood Computer modelling of water supply systems simulates protection as possible to agricultural land on floodplains (as closely as possible) the operation of the water below the storages — except for the Hume-Yarrawonga supply system under any scenario or given set of reach, where they may be interested in allowing conditions, through the historic sequence of climate for frequency of flooding of low-lying land to be increased which information is available. In this case: if better protection can be provided for higher (but still • The system is the River Murray and its storages flood-prone) land. (Dartmouth, Hume, weirs along the Murray, Lake Environmentalists (and all other stakeholders to Victoria, and Menindee ). It is necessary to varying extents) are interested in improving the include the whole system because it is operated in ecological health of the river system. Predictive an integrated way. relationships are not usually available to demonstrate • The conditions that can be specified include: what flow is required to maintain a particular – level of irrigation demand; percentage of habitat, species abundance or diversity of – size of storages; species. In general, any change that tends to return the – detailed operating rules for the storages; and system to its natural (pre-dam) state is seen as moving – any changes in inputs to the system (for in the right direction, and any change in the opposite example, returning water to the Snowy River, direction is seen as detrimental. which would decrease flows into the system). Hydro-electric power station operators want to • Each scenario (or simulated option) operates the maximise the economic value of the electrical energy system under a fully described set of conditions to they generate. This is partly a function of: see what would have happened through the historic • maximising water volume passed through the sequence. The results are available in whatever power station, format and degree of detail is required, allowing • available head, and different scenarios to be compared. • being able to generate when spot prices for energy • The historic sequence for which information is available are highest. is the period for which the necessary data (inflows, Recreation and tourism interests have diverse temperature, evaporation, rainfall) are available. needs, including the following: Two existing Commission models were linked to • Users of Lake Hume want its level kept up — a produce the model used in this review: target of 50% capacity until after Easter is quoted. • The Monthly Simulation Model (MSM) — a well- • Caravan park owners below Hume must evacuate developed and robust model that operates in parks at about 4.3 metres gauge height at Albury, so monthly time-steps. This model is satisfactory for they want floods above this level to be minimised. resource management purposes, but does not • Providers of tourist accommodation want a healthy provide the level of detail needed to look at possible river because the river is the main attraction for changes to flood operation.

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Table 3: Comparison of selected scenarios • BIGMOD — a daily model that provides detail for the part of the water supply system upstream of Run Number Yarrawonga. Essentially, BIGMOD takes MSM Natural output and reprocesses it in daily time-steps to Conditions produce daily output for that part of the system. Run description The daily output is used to estimate costs to floodplain landholders of flooding below the DOLLAR storages. It is also useful for looking at in-stream Absolute variation from the environmental viewpoint. FLOODING (1934-1997) Mitta Mitta at Tallandoon Floods/year 1.21 6.2 Testing single operational changes Average days flooded/year 19 Average flood costs/year ($000) 506 Murray at Albury In total, more than 30 scenarios were modelled to Floods/year 1.38 Average days flooded/year 48 explore the effects of possible changes in operations. Average flood costs/year ($000) 2394 Full details are available in a support paper, ‘Details of Murray at Floods/year 1.02 simulation runs’, which contains a full set of outputs, Average days flooded/year 23 Average flood costs/year ($000) 1358 and a description of output parameters and options modelled. IRRIGATION (1891-1997) New South Wales It is tempting to combine what appear to be Average diversions (GL) 0 Maximum shortfall (GL) 0 promising ideas into packages of proposals early in the Average production value ($000/year) 0 Victoria investigation when modelling a large number of Average diversions (GL) 0 scenarios. This tendency can quickly lead to the volume Maximum shortfall (GL) 0 Average production value ($000/year) 0 of models and results getting out of hand. Consequently, South Australia Maximum shortfall (GL) 0 the panel decided that only single changes to benchmark HYDRO ELECTRIC GENERATION conditions would be modelled as a first step. Only when Dartmouth (1934-1997) all single-change options were complete were a number Average volume spilled (GL/year) - Average power generated (Gwh/year) 0 of carefully selected combinations examined. Value of power generated ($000/year) 0 Hume (1891-1997) Representative examples of single-change options Value of power generated($000/year) 0 modelled by the panel are as follows (numbers in brackets SUMMARY OF DOLLAR IMPACTS ($000/yr) refer to the run modelled under a particular scenario): Irrigation (1891-1997) NSW+Vic 0 Hydro electricity 0 Salinity - Flooding (1934-1997) -4 258 Section Hume recreation (1891-1997) 0 • Natural conditions 6.2.1 Total dollar benefit ($000/year) - • Benchmark run (B42800) 6.2.2 NON DOLLAR • Fill and spill (B42810) 6.2.3 DARTMOUTH TO HUME REACH Absolute Floodplain inundation (1+ day floods Jun-Dec) • Provision of airspace (B46770) 6.2.4 No. years with an event > 13 000 ML/day 43 No. years with an event > 19 000 ML/day 36 • Relaxed pre-release rules (B42840) 6.2.5 Channel stability • Translucent flows (B46750) 6.2.6 Average annual flow within river banks (GL) 1 153 • Use of Dartmouth power station HUME TO YARRAWONGA REACH Floodplain inundation (1+ day floods Jun-Dec) during floods (B42801) 6.2.7 No. years with an event > 25 000 ML/day 57 No. years with an event > 31 500 ML/day 52 • Proposal to water the Channel stability Average annual flow within river banks (GL) 4 016 Barmah-Millewa forest (B47850) 6.2.8 BELOW YARRAWONGA • Increase allowable pre-releases Floodplain inundation (7+ day floods Aug-Jan) No. years with an event > 14 000 ML/day 61 from Hume (B46160) 6.2.9 No. years with an event > 25 000 ML/day 53 Channel stability Average annual flow within river banks (GL) 3 378 Bird & fish breeding indicators (over 106 yrs) The following sections describe the main features of the No of "excellent" years 45 No of "good" years 24 modelling and discuss the results of the scenarios Barmah Forest watering indicators (106 yrs) Years with 1 month or more > 550 GL (Yarra) 98 above. The results are also summarised in table 3. Years with 1 month or more > 912 GL (Yarra) 73 Years with 1 month or more > 1039 GL (Yarra) 68 Hattah Lakes watering indicators (106 yrs) 24 Yrs 1 month or more > 1116 GL (flow to lakes) 93 Yrs 1 month or more > 1487 GL (good floods) 72 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL

B42800 B42810 B46770 B42840 B45770 B46750 B42801 B46160 B46950 Bench- Fill and Allow 200 Pre-release Hume & Hume & Use Increase Sharing mark spill GL airspace based on Dart. 30% Dart. 30% Dartmouth allowable the Murray in Dart. and minimum translucent translucent power Hume pre- Barmah 300 GL irrigation June-Sept. June-Sept. station releases to / Millewa in Hume demands Translucency during 31500 proposal June-Oct. turned off if floods ML/day dams<60% full IMPACTS DOLLAR IMPACTS Absolute Difference (this run minus Benchmark)

0.37 0.18 -0.05 -0.02 0.11 0.08 0.16 0.00 0.02 12 5 -1 -2 2 0 0 -0 -0 244 68 -61 -55 5 -12 56 -0 5

0.70 0.05 -0.16 -0.17 -0.06 -0.03 0.02 0.05 -0.01 260-4-5-4-2-04-0 1133 86 -220 -234 -193 -125 7 3 17

0.54 0.02 -0.02 -0.08 0.03 0.03 0.00 0.03 0.00 13 -0 -0 -2 -0 -0 0 0 0 654 48 -108 -115 -60 -69 10 1 10

1 888 6 -20 -9 -69 -13 0 -0 -18 2 518 -0 -3 -4 -87 -3 0 0 -81 222 478 599 -1 829 -840 -6 431 -1 218 0 -87 -1 570

1 624 0 -4 -0 -15 -0 0 -0 -8 841 0 0 0 39 0 0 0 0 329 327 9 -197 -28 -722 -23 0 -12 -219

396 1 0 -0 57 1 0 0 16

97 44 -27 -21 -10 -10 -85 -2 2 263 -17 5 8 -8 1 32 0 6 4 254 -63 176 120 -51 78 476 7 68

3 989 -163 -42 15 -97 -0 0 -13 -40

551 804 609 -2 026 -868 -7 153 -1 241 0 -98 -1 789 8 243 -227 134 135 -148 78 476 -6 29 -66 633 -101 505 29 285 332 0 -134 427 -2 031 -202 388 404 248 206 -74 -3 -33 2 184 -74 -81 -26 -127 -26 0 -2 -36 493 568 4 -1 080 -326 -6 895 -651 402 -244 -1 403

IMPACTS NON DOLLAR IMPACTS Absolute Difference (this run minus Benchmark)

182-1-131101 92-2-131001

1 244 -23 9 9 -4 -0 -9 0 0

422-40 2-20 2 0 270-4-210000 5 070 -52 92 110 64 47 -3 -16 5

5714120004 360-102000-1 3 475 -9 35 24 31 19 -0 -0 38

9000000029 20 -1 -4 -3 -4 -2 0 -1 -16

5500172002 37 -2 -2 -1 1 -2 0 0 -1 2910241002

4500020000 25 33-10120000 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL

6.2.1 Natural conditions 6.2.3 Fill and spill (B42810)

This is not a real option, but it is included to show how The fill and spill method of storage operation involves the present river regime, and all feasible variations to it, allowing the storage to fill, making no releases for flood have departed from natural conditions. In the natural mitigation, and then passing inflows through the conditions run, Hume and Dartmouth storages are storage by allowing it to spill out of the storage. The removed and irrigation demands are set to zero. storage then remains full until its level is drawn down Outflows from the Snowy Scheme are replaced with by releases for regulated supply. estimated natural flows. The panel modelled this scenario because it was one of the recommendations from the River Murray 6.2.2 Benchmark (B42800) environmental flows scientific panel — particularly This scenario is a best approximation of the way Hume because, at the time of the scientific panel’s findings, no and Dartmouth are operated at present. It is a daily modelling was available to quantify the effects of benchmark, or base case, with which alternative the recommendation. scenarios are compared. Differences between this run and the benchmark Features of the scenario are as follows: are as follows: • Demand is set at 1993–94 levels. • No pre-releases are made from either Hume or • Riparian releases are made in accordance with Dartmouth. present rules. • No discretional or forced releases for hydro- • Hume/Dartmouth harmony releases are made. electricity generation are permitted from Dartmouth Water is transferred from Dartmouth to Hume as until it is full. much as possible, while ensuring that Dartmouth • No Hume/Dartmouth harmony releases are made. fills in the next season if conditions are wet enough • No attempt is made to use the top 100 GL of the for Hume to fill. This tends to equalise the Hume storage to truncate floods. probability of fill of the two storages. Results from the fill and spill scenario show a small • Releases for hydro-electricity generation at Dartmouth increase in average irrigation diversions, and and Hume are modelled using current rules. corresponding increase in value of irrigation • Pre-releases from Hume and Dartmouth are fully production. However, in reality, no increase in average modelled with combined pre-release targets. The diversions is allowed because they are constrained by targets assume minimum inflows and maximum the Cap. Consequently, there are no economic benefits irrigation demands — based on the logic that the to the value of irrigation production. Indeed, there are storage will then always be able to refill if drawn negative economic impacts on hydro-electricity, salinity, down to the pre-release target. Pre-release rates are flood mitigation and tourism. The panel therefore limited to 10 000 ML/day at Tallandoon and 25 000 concludes that overall economic impact from a fill and ML/day at Doctor’s Point. The recent practice of spill operation is negative. sometimes negotiating higher pre-releases from Lake The scenario does provide environmental benefits Hume has not been taken into account in the model. by improving larger flood events — which also • Present rates of rise and fall are used. produces negative economic impacts on human uses of • Existing flood operating rules (no power station releases the floodplain. However, flow variability in small and at Dartmouth, use of the top 100 GL of airspace in medium flow events is non-existent during the pre-fill Hume to attenuate flood peaks) are modelled. period (i.e., during winter months). Consequently, the • Existing practices for Barmah-Millewa forest fill and spill scenario does not produce a beneficial watering are modelled. They provide for up to 40 environmental outcome. GL of water to be used (i.e. extracted from the river, not just released from storage for watering or passed Over all, the panel considers that the simple fill and through the forests). An average volume of 21 GL is spill scenario has little to recommend it. actually used: 13 GL evaporated or otherwise lost in wetlands and 8 GL via small-scale works in NSW.

26 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL

6.2.4 Provision of airspace (B46770) fashion. If the constant flow rates were replaced in This scenario models the idea of providing dedicated practice by more variable flows, the results may tend airspace in storages solely for flood mitigation. For towards a translucent flow scenario. example, if 300 GL of airspace is reserved in a storage for flood mitigation, that space is only intruded upon to Translucent flow store floods. As soon as the flood has passed, the water The concept of translucency relates to the effect of a dam on is released, even if it is not needed for water supply, to flow. If a dam were to pass all inflow, the flow would be restore the flood cushion. “transparent”. If a dam were to stop all flow, it would be Various airspace scenarios were modelled: “opaque”. In between these hypothetical extremes, the flow is • space in Hume only, “translucent” to an extent expressed as a percentage of the • space in Dartmouth only, flow released: the higher the figure, the more translucent. • space in both, Translucent operation of a storage usually occurs in winter • maintaining the airspace for the whole year, and and spring months. A proportion of daily inflow is released so • maintaining it only between June and October. that downstream river flows mimic natural variability — but with All runs made with these various scenarios had the reduced magnitude. same general effect to varying degrees. Run B46770 is For example, 30% translucent operation would indicate that typical of these scenarios. In this run, the changes from 30% of daily inflow was released to mimic natural conditions. the benchmark were: • 200 GL in Dartmouth and 300 GL in Hume are 6.2.5 Relaxed pre-release rules (B42840) reserved in June to October solely as airspace to In the benchmark scenario, pre-release rules are mitigate floods. conservative, as they are based on maximum irrigation • Triggers for pre-release are reduced by the same demands and minimum inflows. In theory, this should amount. result in storages always filling in the spring after pre- • If the storage (despite pre-releases) exceeds the releases are made — so there is never a loss to reduced full supply level, releases are maintained at irrigation supply. The relaxed pre-release rules scenario full channel capacity until the reduced full supply level assumes minimum irrigation requirements in the (incorporating air space) is achieved. However, this following season. An assumption of average level is still below total physical capacity of the storage. requirements was also tested. • At the end of October, storage operations are In this scenario (relaxed pre-release rules), there are returned to benchmark conditions and, if November more pre-releases than under benchmark conditions, and December inflows are sufficient, the storages resulting in a benefit to floodplain landholders are allowed to fill. marginally greater than in the provision of airspace Results of this scenario showed improved economic scenario. However, economic impacts on irrigation are benefits to floodplain landholders and modest hydro- less than half those sustained under the provision of electric and salinity benefits. However, these benefits airspace scenario. The relaxed pre-release rules scenario are far outweighed by penalties to irrigation. Recreation shows a negative net economic effect of $0.33 million on Lake Hume also sustained a small economic penalty. per year. Results indicated an aggregate negative economic effect Environmental impacts under the relaxed pre- of $1.08 million per year. release rules scenario are generally negative in all three The panel notes that similar benefits can be river reaches. There is a minor improvement in provided to floodplain landholders at a far lower cost to frequency of small floods in the Dartmouth to Hume irrigation by changing pre-release rules (see the reach, but frequency and timing of other events is ‘Relaxed pre-release rules’ scenario, in the following generally negative. section 6.2.5). Environmental impacts of this scenario are generally Over all, the concept of relaxed pre-release rules has negative. Flows are often released in the wrong season some merit — but not as a stand-alone scenario. and at constant rates rather than in a translucent

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6.2.6 Translucent flows (B46750) • No translucency releases are made from Hume if Translucent flows allow a proportion of inflow to a the total capacity of Hume and Dartmouth is less storage to be passed downstream during the winter and than 60% of the combined storage capacity. spring so that downstream flow mimics natural • No translucency releases are made from Dartmouth conditions; however, flow amplitudes are reduced, if it is less than 60% full. depending on the percentage of inflow released. There • Pre-release and harmony rules are left in place. would be some adverse effects on regulated supplies, Results of this translucent flows scenario indicate that because releases generally start before there is any economic impacts are positive in all areas except certainty of the storage spilling. irrigation. However, the impact on irrigation is about Translucent release policy can be almost infinitely twice the benefits identified for the other areas. The varied to enhance benefits and minimise costs. translucent flows scenario shows a negative net economic For example: effect of $0.72 million per year. • varying the percentage released — 10% could be In general, translucent releases provide significant considered almost opaque, and 100% fully environmental benefits because they improve flow transparent; variability and seasonality. Translucent flows scenarios • using different percentages for the two storages; generating maximum environmental benefit were • varying percentage according to time of year, found to be those without constraints depending on volume held in store, time since the last reasonable volume in store. However, not surprisingly, those flood, etc.; and scenarios inflict large penalties on consumptive use. • taking only parts of the flow (e.g. allowing the first Suspending translucent flows when storage levels are 500 ML/day to be stored, then passing the next 500 low reduces the impact on consumptive use, but ML/day). environmental benefits disappear during drought and Several variations of translucent flow were examined in when storages are recovering from drought. the translucent flows scenario. Based on A majority of the panel considers that despite the recommendations from the River Murray limitations discussed above, translucent releases appear environmental flows scientific panel, the first scenario to have significant potential to improve environmental tested was a simple 10% translucent flow in June to conditions while reducing flood costs in all three reaches and limiting consumptive-use impacts . September. Results indicated that 10% was not enough As a stand-alone option, there are some concerns to produce significant environmental benefits. about the level of impact on consumptive use. Some A simple 30% translucent flow appeared to produce panel members believe that the same environmental unacceptably large effects on consumptive yield benefits may be obtained for less water, by adopting a compared to benefits achieved. Various ways of more managed approach to flow variation. limiting negative impacts on consumptive yield were also examined. 6.2.7 Use of Dartmouth power station during Translucent flows scenario run B46750 was a typical floods (B42801) example of a simple translucent scenario. This scenario varies from benchmark conditions in the Despite the powerful overall flood mitigation effect of following manner: Dartmouth Dam, under certain conditions the duration • In the months of June to September (subject to of individual floods at some levels is increased (see storage levels below), 30% of natural inflows to section 5.1.2). both Hume and Dartmouth are passed downstream. Current flood operating rules for Dartmouth prohibit • Benchmark minimum flows below the storages are releases through the power station or irrigation valves maintained — apart from the increased benchmark when water is flowing over the spillway if such releases flows below Dartmouth when it is more than 60% would cause the flow at Tallandoon to exceed nominal full. When Dartmouth is more than 60% full, channel capacity (10 000 ML/day). Generally, this mode benchmark releases are replaced by the of operation maximises mitigation of flood-peak levels, translucency releases. but on occasions it extends the duration of floods.

28 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL

It has long been recognised that it is possible to operate Dartmouth Dam so that it never increases the The panel considers that this is initially a matter for the duration of a flood (measured as the duration of flow Mitta Mitta community to reach an agreed position on, as above 10 000 ML/day at Tallandoon) compared with pre- it affects no-one else except the operator of the Dartmouth dam conditions. However, operating that way would, in power station and perhaps the environment to a minor some floods, increase the peak flow at Tallandoon above extent. The power station operator is tied to present the flow that occurs under present operating rules. operation under agreements with the Commission or its Scenario B42801 examines the effect of allowing agents. However, the operator may be open to negotiation Dartmouth power station to operate during floods. on this issue: for example, possibly being prepared to Changes in parameters from the benchmark scenario are: increase contributions to river management funding in • removal of prohibition on releases through the power exchange for revised operating rules. station during spills over the spillway, at times when flow exceeds 10 000 ML/day at Tallandoon; and 6.2.8 “Sharing the Murray” proposal for the • releases during spills up to the capacity of the power Barmah-Millewa forest (B47850) station (assumed to be 9200 ML/day). In recent decades, there has been considerable concern The result is shorter floods — but higher flood peaks — about the effects of River Murray regulation on the in the Mitta Mitta valley. The scenario has little effect Barmah-Millewa forest area. Consequently, much effort outside the Mitta Mitta valley: in fact there are no has been devoted to quantifying those effects and significant effects downstream of Lake Hume. In the looking for ways to improve forest watering. Mitta Mitta valley, flood costs to agriculture are slightly In 1993, the Murray-Darling Basin Ministerial higher ($56 000 per year) but the value of hydro- Council formally resolved to allocate 100 GL of high electric power generation is increased by $476 000 per security water to the forests — half from Victoria’s year. The scenario generates a net economic benefit of resources and half from New South Wales’. However, $420 000 per year. policies and mechanisms to deliver this water have not Marginal environmental benefits are achieved in the been agreed. Under present conditions, an average of Mitta Mitta reach between Dartmouth and Hume as a about 21 GL of regulated flow is supplied annually to consequence of increasing the frequency of medium and the forests. This water is mostly delivered at low flow small flood events. However, no environmental changes rates to stimulate bird and fish breeding. These rules are occur in the other two river reaches. incorporated in the benchmark scenario. This scenario has net economic benefits and In a recent document “Sharing the Murray”, Victoria marginal environmental benefits along the Mitta Mitta has put forward the most recent proposal for a mechanism River. The scenario is worth pursuing if increased flood to supply this water as part of developing bulk water duration in the Mitta Mitta valley is seen as a significant allocations for the Victorian side of the River Murray. The problem. However, the panel identifies the following proposal is quite detailed and has been endorsed by the arguments against implementing this option: Victorian Murray Water Entitlement Committee; although, • Dartmouth, on average, increases flood duration at New South Wales stakeholders have yet to agree with it. some levels and decreases them at other levels. Nevertheless, the panel considers that this proposal is the However, it also markedly reduces flood frequency. best one available for modelling the effects of using this Therefore, the argument for decreasing the flood water for its allocated purpose. duration of some floods appears to be a minor issue. The “Sharing the Murray” proposal was modelled • Aggregate costs to agricultural users of the Mitta Mitta by replacing benchmark forest watering rules with the floodplain appear to be increased a little under this following: option. • An account is established to track the high security • Compared with present operation, this scenario would water (100 GL per year) and lower security water provide marginal benefits to those with low-lying flood- (an extra 50 GL in years of reasonable allocation to prone land, and marginal (but somewhat larger) penalties irrigators). The account includes rules for limited to those with flood-prone but slightly higher land. carryover and overdraw of water.

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• During severe drought, the allocation can be In environmental terms, this scenario improves: borrowed for consumptive use. However, this loan • long-duration breeding event floods, and must be paid back when irrigation restrictions ease. • frequency of shorter floods for forest watering — This condition reflects natural conditions, as the although to a more modest extent. forests would have received little water during These major benefits occur mainly in the reach of river severe drought prior to river regulation. below Yarrawonga. However, benefits from increased • If there have been no floods for the past four years, medium-sized events in upper reaches could also occur the saved water is released with the target of when large volumes of water are being transferred producing 500/500/400 GL per month at down the system to the forests. Yarrawonga in October, November and December respectively — or less if not enough water is The panel considers that while the economic cost is available. These are primarily drought-breaking significant, environmental benefits are also significant. floods, aimed at filling permanent billabongs, The panel is also mindful that a decision, in principle, allowing fish and frogs an opportunity to breed, has already been made by the Ministerial Council to providing for limited plant regeneration and allocate 100 GL to the forest. An effective means to providing a limited opportunity for bird breeding. deliver the allocation must be developed. • In any year, if spring flows at Yarrawonga exceed certain trigger levels, the flood is enhanced to 660 Table 4 Compares natural and benchmark flood regime GL/month if possible. This provides excellent in the Barmah-Millewa forest. Flows at Yarrawonga opportunities for bird and fish breeding, provides for (1934–1996). plant regeneration including Moira grass, waters the red gums, and re-establishes the link between the 6.2.9 Increased pre-release from Hume Dam river and floodplain. (B46160) Several variations to the proposal were also modelled: The River Murray Action Group, which represents for example, using a flow trigger at Wangaratta rather floodplain landholders between Hume and Yarrawonga, has than Yarrawonga, and making variations to trigger indicated that its members may consider selling easements levels. These variations made insignificant differences in over private low-lying flood-prone land. Current nominal economic and environmental results. channel capacity is 25 000 ML/day at Albury. The following Results indicated that diversions for irrigation scenarios were modelled to assess the effects of three decrease by 26 GL on average. Most of this decrease changes to Hume-Yarrawonga pre-releases: occurs in NSW. The scenario increases average forest • Increasing pre-releases to 31 500 ML/day (about consumption of regulated resources from 21 to 47 GL. 3.5 m at Albury) for pre-releases (run B46160). The balance of the allocation is spilled before it can • Increasing pre-releases to 31 500 ML/day for all be used, or is released for forest watering and eventually extracted by water users. To a large extent, releases, including those for irrigation supply. this situation is inevitable because: • Increasing pre-releases to 36 000 ML/day • a proportion of the water released from storage for (about 3.8 m at Albury) for pre-releases. the purpose of forest watering will flow past the Increasing the nominal channel capacity for pre-releases forests, or through them, and return to the river; and was the only change from the benchmark scenario. • storing Barmah-Millewa water from year to year The panel considers that increasing nominal channel rather than using it every year means that water capacity to 31 500 ML/day for pre-releases (run will unavoidably spill from storage in some years. B46160) is the best of the scenarios considered above. Economic impacts of this scenario are small benefits to One possible benefit of an increased rate of pre-release hydro-electricity generation and salinity, and small costs is that watering of the Barmah-Millewa forest should be to floodplain landholders and Lake Hume recreation. improved in years when watering is constrained by However, the largest economic effect is the cost to channel capacity between Hume and Yarrawonga. irrigation. Therefore, net economic effect of the To investigate effects on forest watering of lifting the scenario is calculated to be $1.4 million per year. nominal channel capacity, the panel combined the

30 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL

Table 4: Comparison of natural and benchmark flood regime in the Barmah-Millewa forest Flows at Yarrawonga, 1934-1996.

Natural conditions Current (benchmark) conditions

Jul Aug Sep Oct Nov Dec Year Jul Aug Sep Oct Nov Dec

559 918 837 2036 1501 1043 1934 222 387 202 1329 1582 1005

814 1432 1301 1046 564 282 1935 604 1530 1319 962 441 273

777 2009 1088 686 411 419 1936 318 1659 1191 335 259 337

135 215 751 555 251 153 1937 122 246 336 487 333 476

223 263 383 245 127 21 1938 159 213 198 470 472 469

1164 1997 1646 1487 1174 463 1939 536 1053 1365 1072 842 290

195 257 322 227 150 86 1940 120 243 194 270 485 435

411 303 373 544 255 138 1941 211 190 166 220 294 292

1578 1152 1411 1015 590 330 1942 753 553 583 273 277 297

425 623 815 938 494 205 1943 193 244 289 306 285 334

293 218 178 172 145 77 1944 156 234 204 249 400 476

180 657 679 496 452 174 1945 128 321 236 271 276 287

1603 1511 796 734 559 285 1946 729 802 244 314 333 424

1102 1190 1317 1398 1011 528 1947 473 562 374 469 306 282

338 420 569 703 1117 359 1948 200 217 224 264 383 305

315 435 654 1151 1116 420 1949 147 194 185 470 435 270

381 518 726 977 797 311 1950 152 154 102 145 252 264

1491 1546 1057 1028 597 264 1951 839 1009 750 717 369 269

1852 1196 1905 1292 1467 1062 1952 1903 1199 2035 1210 1492 919

799 1503 1432 1846 1207 468 1953 379 1358 1350 1669 967 296

304 630 621 399 834 711 1954 160 233 211 179 318 577

1091 3185 2139 2306 1287 740 1955 594 3216 2044 2168 1144 326

3305 2435 1958 2092 1290 618 1956 3967 2601 1881 1986 1045 326

556 420 420 610 350 195 1957 225 296 226 295 274 338

927 2758 1218 2257 1023 397 1958 346 1516 776 1876 860 295

163 407 740 719 377 185 1959 115 225 192 270 214 288

1185 1842 1673 1280 715 414 1960 459 988 1371 941 508 304

408 578 607 450 259 177 1961 193 251 177 200 309 372

509 761 629 792 457 234 1962 310 343 213 254 259 284

399 906 870 801 515 246 1963 260 516 326 283 237 318

2188 1437 1570 2358 984 401 1964 923 632 660 1785 667 294

113 522 866 436 308 243 1965 126 339 422 281 289 431

375 876 1248 1291 788 1004 1966 175 386 517 349 265 305

73 142 242 345 144 32 1967 99 212 401 476 472 476

463 1289 937 1548 955 392 1968 308 587 290 363 299 358

1149 889 1203 726 570 394 1969 302 279 803 297 262 269

1020 1930 2224 1380 916 448 1970 407 1259 2100 928 599 282

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(Continued) Table 4: Comparison of natural and benchmark flood regime in the Barmah-Millewa forest Flows at Yarrawonga, 1934-1996.

Natural conditions Current (benchmark) conditions

Jul Aug Sep Oct Nov Dec Year Jul Aug Sep Oct Nov Dec

487 723 1072 1477 1409 590 1971 264 252 607 805 1007 304

357 541 652 344 186 110 1972 162 238 389 349 293 309

1362 1922 2481 1657 923 403 1973 585 1217 2276 1577 880 314

2509 2523 2345 2986 1517 500 1974 1780 2424 2484 2811 1491 402

1061 1642 2309 2854 1537 692 1975 531 1555 2306 2952 1495 692

162 311 421 1106 461 261 1976 99 231 212 273 242 273

540 601 495 442 215 137 1977 225 150 210 259 295 309

1025 1255 1219 1038 726 542 1978 402 617 382 298 347 276

249 452 1271 1663 565 201 1979 143 202 640 848 264 299

465 792 1006 783 496 366 1980 248 332 290 270 471 476

2813 3347 1653 1198 565 302 1981 1667 2060 1326 745 315 351

170 148 217 165 79 13 1982 113 305 268 338 485 476

819 1478 1970 1305 665 492 1983 405 666 821 271 243 287

230 1493 1696 1567 492 188 1984 126 609 878 928 314 262

271 1305 848 555 395 301 1985 160 670 330 275 278 276

1790 1437 1045 1845 1064 548 1986 883 648 360 698 625 305

879 898 661 513 258 208 1987 463 408 198 274 472 476

1110 795 879 564 422 847 1988 500 313 289 178 266 298

825 1321 1235 1002 835 332 1989 445 686 927 548 438 289

2556 2431 1435 1331 669 243 1990 1600 1657 1397 1077 544 298

666 1326 1870 1072 419 212 1991 251 508 1154 545 265 284

353 931 2183 2808 1389 971 1992 253 509 1450 2360 1255 971

1040 1332 1687 2258 1080 715 1993 986 1306 1656 2291 942 568

354 332 289 359 351 221 1994 168 190 285 465 452 453

2063 1207 986 868 752 577 1995 891 473 563 515 518 284

1041 2192 1498 2778 874 360 1996 537 1862 1302 2404 674 277

increased pre-release from Hume scenario and the “Sharing • in other years, the larger channel capacity allows the Murray” proposal for the Barmah-Millewa forest water to be transferred earlier, which may mean scenario. Results of this combined scenario indicated that less can be extracted further downstream and that the economic impact is somewhat greater than for more remains as in-stream flow. the “Sharing the Murray” proposal for the Barmah-Millewa It appears that increased channel capacity does not help forest scenario on its own. In fact, economic impacts are Barmah-Millewa watering significantly. A single additional slightly more than the sum of the two individual watering event in a century is unlikely to provide much impacts, probably because: additional benefit to the forests. However, the larger • the change in channel capacity only allows the capacity would allow increased flexibility for varied or desired volume to be transferred in one extra year, translucent water releases to Barmah. That additional 1917 (however, the extra volume in that year is flexibility may provide environmental benefits to both the quite high); and Hume-Yarrawonga reach and the reach below Yarrawonga.

32 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL

Table 5: Results of three scenarios exploring increased nominal channel capacity

Nominal channel capacity**

increased to increased to increased to 31 500 ML/day for 31 500 36 000 ML/day pre-releases and ML/day for for pre-releases translucency releases all releases and tanslucency (run B46160) releases

Average annual flood costs to land below new channel capacity $187 000 $198 000 $408 000

Increase in costs to land below new channel capacity over benchmark $20 000 $31 000 $38 000

Average annual flood costs to land above new channel capacity $949 000 $949 000 $759 000

Decrease in costs to land above new channel capacity compared to benchmark $16 000 $16 000 $3 000

To adopt the increased nominal channel capacity for • an enhanced ability to vary pre-releases — whether pre-releases would involve the Commission taking by translucency or other more managed means — flood easements over land flooded at flows of about which would also improve within-channel flow 31 500 ML/day (3.5 m on the Albury gauge). The area variability; and of land directly affected is in the order of 1000 ha. • a small enhancement in ability to provide a suitable Some other land would be affected less directly because watering regime for the Barmah-Millewa forest. it would be inaccessible at times. Potential costs and risks of the proposal are: The easement could give the Commission the right • significant capital cost — possibly in the order of to make regulated releases up to 31 500 ML/day: $3 million to $6 million; and • during specified months (say June to November) — • even if most of the affected landholders agree with but not for the other months of the year, or the proposal, the possibility that a minority may feel • for specified purposes (pre-release and forest aggrieved. watering) — but not for other purposes. The panel considers that the increased pre-release from Considerable consultation and detailed work with those Hume scenario has potential to: likely to be affected is needed before the scenario is a • improve environmental conditions — primarily sufficiently robust proposition with reliable cost between Hume and Yarrawonga; estimates. However, an initial estimate is that the cost • provide a small benefit to flood-prone land above of easements — including valuations, negotiation, legal costs and actual compensation payments — might be in the 31 500 ML/day flow level; and the order of $3 million to $6 million. • support river management proposals that involve In summary, the benefits of increasing allowable converting some land from agriculture to riverside pre-releases from Hume to 31 500 ML/day are: redgum plantation. • a modest decrease (modelled at $16 000 per year) in Further, the panel recommends that the proposal should the costs of flooding land above the 31 500GL level; be developed in more detail (subject to acceptance in • substantial environmental benefits to low-level principle by those affected) and that it may well form a wetlands — mainly between Hume and useful part of a scenario package. Yarrawonga, but also below Yarrawonga (this is the main benefit of the scenario);

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6.3 Scenarios outside the 6.4 Combined scenarios scope of the review Five similar combined scenarios, but with significant Panel members have been acutely aware that other related differences, were modelled. All included the following: work — particularly the Snowy Inquiry and discussion of • The “Sharing the Murray” proposal for the Barmah- environmental flows — had the capacity to affect the issues Millewa forest. being considered in the review. A number of scenarios • Harmony operation of Hume and Dartmouth as were therefore modelled, not because they were options specified in the benchmark run. that would be evaluated in the review, but because it was • Channel capacity between Hume and Yarrawonga necessary to understand the possible effects of them. These increased to 31 500 ML/day for the purpose of scenarios are as follows: translucency releases or pre-releases but not for • Snowy releases increased to 150 GL per year (B46180). regulated releases. Effectively that would mean the • Combined Barmah-Millewa and Snowy releases increased capacity would apply in most years (B47910). between June and October or perhaps November. • Irrigation cap reduction of 10% (B46460). The differences were as shown in table 6. These scenarios helped the panel to place its work in The results are set out in table 7, and conclusions context with influences outside its terms of reference. can be drawn as follows: However, the scenarios required so many arbitrary • In terms of economic impact, they can be divided assumptions that the results were not considered useful into two groups. Scenarios A, B and E each enough to show in this options paper. They are constrain the volume of non-consumptive release included in the support paper that provides details of all either via pre-release rules or by cutting off the scenarios investigated. translucent releases when storage levels drop. Each Points of interest were: has a negative net economic impact in the order of • The Snowy releases scenario had about the same $3 million per year. Scenarios C and D include effect on consumptive use as the “Sharing the Murray” translucent releases unconstrained by low storage proposal for Barmah-Millewa forest scenario. However, levels, and each has a negative net economic impact no real conclusion can be drawn from the Snowy in the order of $10 million per year. The economic releases scenario, because of the uncertainty of impacts are dominated by irrigation. measures that might be put in place to offset • In all scenarios, there are economic benefits to increased Snowy diversions. The report of the Snowy floodplain dwellers below Hume, and decreased Inquiry quantifies Snowy proposals in detail. salinity costs. Decreased salinity costs derive from • The combined Barmah-Millewa and Snowy releases higher instream flows, and may also be of some scenario showed the expected negative economic minor environmental advantage. impacts. However, most of the benefits of the forest • The indicators of environmental effects shown in watering scenario remained, even with the the table are a selection of those produced during reduction of total water in the Murray. the review. The panel has found it difficult to come • The irrigation cap reduction of 10 percent showed up with a clear assessment of environmental that, although the volume used for irrigation was advantages and disadvantages, because each reduced by 10 percent in each state, the value of scenario involves some sort of environmental trade- irrigated production was reduced by a smaller off — an improvement in one area, but a decline in amount — about 8 percent in NSW and only 2 another. For example: translucency, in general, percent in Victoria. This is because the irrigation increases flood frequency in spring, but can reduce enterprises affected will be the lower value ones; the number of long-duration breeding event floods. water would flow by trading to the higher value • Nevertheless, in terms of environmental impact, enterprises so their production would be unaffected. scenarios C and D are clearly superior to the other This seems reasonable in qualitative terms, but it three below Yarrawonga and, perhaps less may be stretching the model beyond its capability to demonstrably, between Hume and Yarrawonga. On the place much reliance on the quantitative result. Mitta Mitta River, fewer environmental effects are

34 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL

Table 6: Differences between the five combined scenarios

Package

ABCDE

30% translucency releases yes yes yes yes no made in June to September

Storage capacities below which 60% 60% 0% 0% not applicable translucency is turned off

Pre release rules as in none as in none based on benchmark benchmark minimum run run irrigation demands

apparent, though all of the proposals with translucency In considering what amounts to a possible transfer of are expected to deliver environmental benefits. water from consumptive use to instream use, irrigators • Scenario E is shown as the worst from the make the point that their existing water use is covered environmental point of view, probably because of by some form of property right. The precise nature of the lack of translucent releases as modelled. this right varies between states, between different locations within states, and between different water It is important to understand that the amount of uses. Transfer is likely to be a continuing process as resource committed to instream flows can be decided instream flow requirements are better identified. It is independently of the mechanism used to provide those therefore important to set up an on-going process to instream flows in a suitably varied manner. For explicitly change the property rights held by irrigators. example, it would be possible to decide the degree of risk of storages failing to fill that should be taken when pre-releasing. The effect on consumptive use could be determined by modelling. When that issue was resolved, by whatever process, pre-release rules could be developed to set end-of-month target storages in accordance with the agreed level of risk. It would then be possible to operate from day to day on a translucent (or more planned) varied release basis rather than a fixed release basis.

In summary, there is a very clear trade-off between economic impact and environmental benefit. This can be illustrated, in broad terms, by table 8. It compares scenario A (which is typical of the A, B and E group) with scenario C (which is similar to D). The only difference between A and C is that in scenario A the 30% translucent releases are turned off if storage volumes fall below 60%. In scenario C it remains, irrespective of storage volume.

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Table 7: Results of the five combined scenarios

Run Number B42800 B48190 B48200 B48210 B48220 B48230 Natural Bench- Package Package Package Package Package Run description Conditions mark A B C D E DOLLAR IMPACTS DOLLAR IMPACTS Absolute Absolute Difference (this run minus Benchmark) FLOODING (1934-1997 Mitta Mitta at Tallandoon Floods/year 1.21 0.37 0.05 0.03 0.10 0.11 -0.05 Average days flooded/year 19 12 0 1 0 2 -2 Average flood costs/year ($000) 506 244 -24 2 -14 14 -53 Murray at Albury Floods/year 1.38 0.70 -0.05 -0.01 -0.03 -0.03 -0.14 Average days flooded/year 48 26 -2 -1 -4 -3 -5 Average flood costs/year ($000) 2394 1133 -142 -102 -220 -183 -229 Murray at Tocumwal Floods/year 1.02 0.54 0.00 0.00 -0.02 0.00 -0.08 Average days flooded/year 23 13 -1 -1 -1 -1 -2 Average flood costs/year ($000) 1358 654 -88 -63 -93 -69 -115 IRRIGATION (1891-1997) New South Wales Average diversions (GL) 0 1 888 -36 -35 -101 -100 -29 Maximum shortfall (GL) 0 2 518 -259 -261 -131 -131 -81 Average production value ($000/year) 0 222 478 -3 341 -3 224 -9 415 -9 317 -2 603 Victoria Average diversions (GL) 0 1 624 -10 -10 -25 -24 -10 Maximum shortfall (GL) 0 841 0 0 43 43 0 Average production value ($000/year) 0 329 327 -276 -270 -1 121 -1 112 -305 South Australia Maximum shortfall (GL) 0 396 15 16 40 44 21 HYDRO ELECTRIC GENERATION Dartmouth (1934-1997) Average volume spilled (GL/year) - 97 -15 -1 -15 -3 -20 Average power generated (Gwh/year) 0 263 10 4 -1 -6 13 Value of power generated ($000/year) 0 4 254 166 93 23 -44 181 Hume (1891-1997) Value of power generated($000/year) 0 3 989 -75 -96 -159 -172 -64 SUMMARY OF DOLLAR IMPACTS ($000/yr) Irrigation (1891-1997) NSW+Vic 0 551 804 -3 617 -3 494 -10 537 -10 428 -2 908 Hydro electricity 0 8 243 91 -4 -136 -216 117 Salinity - -66 633 202 336 486 579 187 Flooding (1934-1997) -4 258 -2 031 254 164 328 238 398 Hume recreation (1891-1997) 0 2 184 -90 -89 -193 -192 -77

Total dollar benefit ($000/year) - 493 568 -3 160 -3 087 -10 052 -10 020 -2 282 NON DOLLAR IMPACTS NON DOLLAR IMPACTS Absolute Absolute Difference (this run minus Benchmark) DARTMOUTH TO HUME REACH Floodplain inundation (1+ day floods Jun-Dec) No. years with an event > 13 000 ML/day 43 18 2 1 3 3 0 No. years with an event > 19 000 ML/day 36 9 1 1 3 3 -1 Channel stability Average annual flow within river banks (GL) 1 153 1 244 0 -6 -2 -8 10 HUME TO YARRAWONGA REACH Floodplain inundation (1+ day floods Jun-Dec) No. years with an event > 25 000 ML/day 57 42 1 1 0 1 1 No. years with an event > 31 500 ML/day 52 27 -1 -1 1 1 -1 Channel stability Average annual flow within river banks (GL) 4 016 5 070 54 28 76 52 114 BELOW YARRAWONGA Floodplain inundation (7+ day floods Aug-Jan) No. years with an event > 14 000 ML/day 61 57 3 3 4 4 4 No. years with an event > 25 000 ML/day 53 36 -1 -1 2 2 -1 Channel stability Average annual flow within river banks (GL) 3 378 3 475 70 63 91 84 71 Bird & fish breeding indicators (over 106 yrs) No of "excellent" years 45 9 28 29 24 25 22 No of "good" years 24 20 -16 -16 -14 -14 -12 Barmah Forest watering indicators (106 yrs) Years with 1 month or more > 550 GL (Yarra) 98 55 5 5 9 8 2 Years with 1 month or more > 912 GL (Yarra) 73 37 -3 -3 0 0 -1 Years with 1 month or more > 1039 GL (Yarra) 68 29 3 1 4 3 3 Hattah Lakes watering indicators (106 yrs) Yrs 1 month or more > 1116 GL (flow to lakes) 93 45 1 1 2 2 0 Yrs 1 month or more > 1487 GL (good floods) 72 33 1 1 3 3 1

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Table 8: Trade-off between economic impact and environmental benefit

Combined Combined Scenario A Scenario C (translucency only (translucency if storages more at all storage than 60% full) levels)

SUMMARY OF DOLLAR IMPACTS ($000/year)

Irrigation — New South Wales -3341 (-1.5%) -9415 (-4.2%) — Victoria -276 (-0.1%) -1121 (-0.3%) Hydro-electricity + 91 (+1.1%) -136 (-1.6%) Salinity +202 (+0.3%) +486 (+0.7%) Flooding +254 (+12.5%) +328 (+16.1%) Hume recreation -90 (-4.1%) -193 (-8.8%) Total dollar benefit ($000/year) -3160 (-0.6%) -10052 (- 2.0%)

SUMMARY OF NON-DOLLAR IMPACTS

Dartmouth – Hume reach little change little change Hume – Yarrawonga reach slightly better slightly better Below Yarrawonga Bird breeding (excellent + good years) +12 +10 % shift towards natural +30% +25% Forest watering (sum of low + high level) +8 +13 % shift towards natural +10% +16% Hattah Lakes watering (sum of low + high level) +2 +5 % shift towards natural +2% +6%

The phrase “% shift towards natural” is an indication of • Is it worth $10 million a year, or 2% of the how far the scenario moves that indicator from the productive value of the water supply system, to benchmark value towards the natural conditions value. produce the benefits shown under combined For example, the sum of excellent and good years for scenario C — and if so, who should pay? bird breeding is 69 years under natural conditions and • Is the second set of benefits three times as valuable 29 years under benchmark conditions — a difference of as the first set? 40 years. Combined scenario A produces 12 more of • How do we deal with the reality that irrigators hold these years than the benchmark scenario, which is a property rights to the water they consume? These shift of 30% from benchmark to natural. rights exist in all three states, though they are The table highlights fundamental questions faced by stronger in Victoria and SA than in NSW. the panel to which, as yet, it has no firm answers. The questions are: Despite its inability to answer these questions • Are the benefits under A or B sufficient for definitively, the panel considers that combined sustainability? scenarios of the sort described above hold considerable • Is it worth $3 million a year, or 0.6% of the promise for producing worthwhile environmental productive value of the water supply system, to improvements at tolerable economic cost. It seeks produce the benefits shown under combined opinions from the wider community on where the scenario A — and if so, who should pay? balance between competing interests should lie.

HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 37 7. Summary of options and preliminary panel views

These conclusions simply collect and example, possibly being prepared to increase contributions to river management funding in repeat the options identified and the exchange for revised operating rules. preliminary views of the panel. They Adverse effects on agricultural land at peak regulated flow are re-arranged in river reaches as far The panel considers that there are three options for resolving this problem: as possible. • investigate nominal channel capacities in the range 9000 to 10 000 ML/day, 7.1 Dartmouth – Hume reach of river • investigate construction of regulators where appropriate, or Effect of Dartmouth Dam on pasture productivity • take flood easements over affected land and pay appropriate compensation. The panel notes that possible increased water The panel has further considered these options in light allocations and pricing concessions are currently being of the following factors: assessed by Goulburn-Murray Water: they cannot now • problems may be minimised by carefully selecting be influenced directly by the Operations Review. The following additional options were identified: the regulated release figure, • Investigate earlier pre-releases in years when • regulators would probably only be required on one Dartmouth Dam has spilled, to avoid periods of low or two properties, and flow between spring spills and autumn harmony • easements could be taken over the affected land if releases. no structural solution is possible. • Investigate lower and earlier releases in years when The panel considers that further investigations should resources must be transferred from Dartmouth to be conducted to ascertain the most beneficial option for Hume for supply. each affected property. The panel’s preliminary views are that: Erosion on the Mitta Mitta River • Current harmony rules provide for releases as soon as practicable following Hume ceasing to spill. Based on the submissions received and analysis • When Dartmouth releases are needed for supply conducted by the panel, the following options have purposes, there may be some scope for earlier been identified: releases at lower rates; however, this could involve • Continue with existing stream erosion control increased resource loss risk. methods, accepting that the result over time will be a willow and rock lined river channel of limited Flood duration in the Mitta Mitta valley environmental value. Despite the powerful flood mitigation effect of Dartmouth • Fund further research into mechanisms and factors Dam, under certain conditions the duration of individual contributing to bank slumping on the Mitta Mitta River. floods at some levels is increased. By using the power • Develop an integrated program of waterway and station during floods, it is possible to eliminate this effect. floodplain management along the lines suggested by Peak flood levels would then sometimes be higher, but the NECMA. still less than under natural conditions. The panel’s preliminary view is that an integrated The panel considers that initially this is a matter for program of waterway and floodplain management along the Mitta Mitta community to reach an agreed position the lines suggested by the NECMA should be developed. on, as it affects no-one else except the Dartmouth Impact of Dartmouth Dam on water power station owner and perhaps the environment to a temperature and quality minor extent. The power station owner is tied to present operation under agreements with the Based on the submissions received and analysis Commission or its agents. However, the power station conducted by the panel, the following options have operator may be open to negotiation on this issue: for been identified:

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• No action — accept that temperatures in the Mitta addressed by developing a comprehensive, properly Mitta River will remain depressed, and that the river funded program for management of the reach. The ecology will remain altered from its natural state. management program will initially need a strategic • Install shutters on the existing high-level outlet to approach to articulate a vision for the future provide limited improvement. desirable state of the river. The strategic framework • Raise the top of the existing structure to above full will require: supply level and install a fully functional multi-level • developing criteria for acceptable and unacceptable offtake. erosion rates (and acceptable methods of erosion • Agree in principle that a fully functional offtake is control); required, and conduct detailed investigations into • setting limits to acceptable rates of channel the cost, benefit and optimum way to achieve a widening and bed degradation; fully functional offtake. • a decision on the extent to which anabranch The panel’s preliminary view is that it agrees in development needs to be contained; principle that a fully functional offtake is required and • setting desired levels of protection for aquatic and that detailed investigations into the cost, benefit and riparian habitats; and optimum way to achieve a fully functional offtake must • documenting desired aesthetic and recreational values. be undertaken. Based on the strategic framework, a comprehensive river management program should be developed. This 7.2 Hume to Yarrawonga reach of river program would: • establish an agreed management arrangement Adverse effects on agricultural land (which needs to work in two states, have proper peak regulated flow local input, etc); • establish links with associated land management The panel considers that options for dealing with this programs in each state; problem are to: • establish agreed funding arrangements — with • reduce peak regulated flow level to a figure consideration of funding from such sources as the significantly lower than 25 000 ML/day; Murray-Darling Basin Commission, catchment • do nothing, on the basis that the negative impacts are outweighed by flood mitigation benefits to management authorities, local government and agricultural land; or input (cash or kind) from landholders; • take flood easements over the affected land and pay • set a works program — including both an annual appropriate compensation. program of necessary patch-up works (done now to The panel considers that, for equity reasons, taking a modest extent with MDBC funding) and a flood easements over the affected land and paying coordinated strategy of activities designed to achieve appropriate compensation is the only reasonable option. the long-term goals; and • monitor progress and the extent to which the The need for a comprehensive river management plan strategic framework might need to be changed. between Hume and Yarrawonga Increased pre-release from Hume Dam The panel considers that future options for management of this reach of the Murray are to: In summary, the benefits of increasing allowable pre- • retain the present management arrangement — releases from Hume to 31 500 ML/day are: under which the Commission provides limited • a modest decrease (modelled at $16 000 per year) funding to the NSW Department of Land and Water in the costs of flooding land above the 31 500GL Conservation to treat actively eroding sites on a level; priority basis; or • substantial environmental benefits to low-level • develop a comprehensive, properly funded program wetlands — mainly between Hume and for management of the reach. Yarrawonga, but also below Yarrawonga (this is the The panel believes that this issue can only be fully main benefit of the scenario);

40 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL

• an enhanced ability to vary pre-releases — whether • Physical works on individual wetlands. Works by translucency or other more managed means — would consist of banks, regulating structures and which would also improve within-channel perhaps pumps to control the extent to which water variability; and was introduced into, or kept out of, a particular • a small enhancement in ability to provide a suitable wetland at different times of the year. watering regime for the Barmah and Millewa Again the panel considers that it is likely that the forests. Interstate Working Group on River Murray Flows will Potential costs and risks of the proposal are: need to consider this issue in some detail. • significant capital cost — possibly in the order of $3 The need to better manage minimum flows million to $6 million; and downstream of Mildura • even if most of the affected landholders agree with the proposal, the possibility that a minority may feel The panel considers that there are three options for aggrieved. resolving this problem, as follows: The panel considers that the increased pre-release from • Obtain more precise orders from diverters. Orders Hume scenario has potential to: for major diversion points (Red Cliffs, etc.) are • improve environmental conditions — primarily received a week in advance, but are not always between Hume and Yarrawonga; adhered to. Private diverters are relatively uncontrolled. • provide a small benefit to flood-prone land above • Utilise more storage volume in weir pools. Most weir the 31 500 ML/day flow level; and pools are operated at almost constant levels, which • support river management proposals that involve is convenient for water diverters and boating converting some land from agriculture to riverside interests but provides little or no scope to re- redgum plantation. regulate water. The constant pool levels also have Further, the panel recommends that the proposal environmental disadvantages. should be developed in more detail (subject to • Improve measurement. However, this action is really acceptance in principle by those affected) and that it incidental to improved flow control. may well form a useful part of a scenario package. The panel considers that all the options above can be adopted. This issue is essentially one of better flow control 7.3 Conclusions that are not reach-specific in this reach of river — operation of Hume and Dartmouth Dams has no direct effect on control of these flows. Effects of regulated flow and rain rejections on natural drying cycles in wetlands The need for improved communication

The panel considers that this issue will require The panel has concluded that formal, continuous considerably more work, integrated into river flow liaison should be set up between the Murray-Darling management plans, and that solutions are likely to Basin Commission (or River Murray Water) and involve the following: interested community groups. This liaison should be: • Improved river operation. Improved river operation • regarded as a permanent commitment — not just may be possible from better weather forecasts, more something to be fitted in when time is available; and accurate ordering from irrigation agencies, and • of a frequency and form negotiated with particular improved estimation of river losses. interest groups to suit their needs. • Retention of rain rejections in storage of some kind. Four possibilities have been identified, as follows: 7.4 Broad conclusions from modelling – storage on-farm; • A simple fill and spill arrangement appears to have – storage in distribution channels; few benefits in economic or environmental terms. – continued emphasis on drainage diversion • Airspace scenarios do not present adequate benefits permits; and in return for costs. The same advantages to – provision of storage airspace in some weir pools. floodplain landholders can be obtained at far less

HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 41 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL

cost to irrigators by changing pre-release rules. By could also ensure that flood duration is not changing pre-release rules from the present increased. There would be a small cost to conservative rules (that take almost no risk of failing agriculture in the Mitta Mitta valley, but there to fill) to rules that allow a specified risk, more would be no effects below Hume. airspace is created but often the storages do fill and • The scenario that models the “Sharing the Murray” consumptive use is not affected. In contrast, simple proposal to water the Barmah-Millewa forest airspace rules impose near certainty of failing to fill provides good increases in low-level flooding but and, in effect, reduce the volume of storage useful for has less effect at higher levels. Variations to the water conservation by the airspace volume. proposal produce very little difference in either • Translucent flow scenarios show considerable benefits or penalties. promise. The simple 10% translucency rule is not Modelling of combined scenarios enough to produce worthwhile environmental benefits but 30% translucent flows produce The panel considers that a package of operational worthwhile benefits. However, adverse effects on policies can be developed on the basis of the modelling consumptive yield need to be minimised in some results. This package could include: way. Conceptually, adverse effects could be • a mechanism for watering the Barmah-Millewa minimised by setting storage targets in the same forest, manner as with current pre-release rules (possibly • some form of varied releases (for example, building in a defined risk of failing to spill), and translucent releases), and then operating from day to day on a translucent • possibly an increase in nominal channel capacity rather than fixed release basis. between Hume and Yarrawonga for pre-releases • Allowing pre-releases and Barmah watering releases and forest watering releases. to be made up to an increased nominal channel The key issue is the balancing of environmental benefit capacity (e.g. 31 500 ML/day between Hume and against economic cost. Yarrawonga) has little benefit to forest watering, but The panel has formed the view that combined the increased channel capacity would allow more scenarios of the sort described above hold considerable freedom for translucent-type releases. promise for producing worthwhile environmental • Using Dartmouth power station during floods improvements at tolerable economic cost. It seeks input would have significant net economic benefits and from the wider community on where the balance marginal environmental benefits. This scenario between competing interests should lie.

42 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW Appendix A: Terms of reference for the Operations Review

Purpose • convene as necessary meetings of targeted To review the current operating procedures for Hume stakeholder groups and Dartmouth Dams and recommend how they may • ensure the information generated is provided to the be amended to address the competing objectives of Commission. water supply, environmental enhancement and flood mitigation. The review will take into account: Reference panel • impacts of current and alternate operating arrangements for the Dams on farming and other The reference panel will consist of representatives as groups who occupy the floodplain and on other follows: components of the Murray-Darling systems; • 1 Commission; • the current arrangements for determining target • 1 Community Advisory Committee; storage levels aimed at balancing flood mitigation, • 1 Local Government; • 1 Mitta Mitta valley; water supply and environmental objectives and a • 2 Hume to Yarrawonga Reach (1 from each State); range of alternative strategies and their impacts; • 3 irrigators (1 Vic gravity, 1 NSW gravity and 1 • the current River channel capacity rules pumped districts); downstream of the Dams and whether these can be • 2 environment (1 Vic and 1 NSW); and modified to improve outcomes; and • 3 operating authority reps (1 Vic, 1 NSW, 1 SA). • the provisions of the Murray-Darling Basin Agreement. The Commission representative would chair the In considering these issues, the review should take into Reference Panel. Arrangements for the conduct of the account the Ministerial cap on water diversions, cost Reference Panel will be provided. sharing, economic, social and environmental factors. The review should consider what, if any, other actions (i.e., land-use planning measures) are warranted and Time frame comment on any implications for the operation of other The Study will commence on 1 January 1997 and be major storages. completed by 30 September 1997. The Project Manager will report on a regular basis to the Commission.

Modus operandi Progress reports are to be provided to the March and June Commission meetings with a draft of the final The Study will be conducted by a Project Manager report being available by 1 September 1997. A draft appointed by the Commission. The Project Manager’s report will be released for public comment for a period role is to: of six weeks. The final report is to be in a form suitable • ensure the Terms of Reference are addressed for public release. • manage all the necessary input to the study [Note: Early in the review, it was recognised that the • contract all the necessary technical skills for the Study original timing was unachievable if a thorough review • manage the budget for the Study was to be carried out. Hence, the Commission agreed to • convene and support a reference panel extend it].

HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 43 Appendix B: Reference panel members

Chair

Brian Haisman (02) 6279 1061

Members

Allan Curtis, replaced by Noelene Wallace Community Advisory Committee (02) 6027 5322 Stuart Anderson Local government (03) 5480 9558 Tom Martin Mitta Mitta valley (02) 6072 0384 Arch McLeish Tourism / recreation / Albury-Wodonga (02) 6043 2244 Ian Lobban Hume — Yarrawonga reach (02) 6026 7255 Richard Sargood Hume — Yarrawonga reach (02) 6035 0555 Lance Gardiner NSW gravity irrigators (03) 5882 3583 Alan Major Vic gravity irrigators (03) 5456 8314 Pat Lanigan Sunraysia district (03) 5025 7285 Dietrich Willing Environmental interests (02) 9396 8408 Tim Fisher Environmental interests (03) 9416 1166 David Harriss, replaced by Mel Jackson NSW operating authority (02) 6041 1650 Garry Smith Vic operating authority (03) 5833 5480 Andrew Jessup/ Phil Pfeiffer SA operating authority (08) 8204 1513 Monica Morgan Aboriginal interests (03) 5869 3353

Non-voting members

Kevin Ritchie Dept Nat Resources & Environment Vic (03) 5761 1611 Jody Swirepik Environment Protection Authority NSW (02) 6299 3330 Anne Jensen Dept Environment, Heritage replaced by Paul Harvey and Aboriginal Affairs SA (08) 8204 9137

Project team

Clarke Ballard Project Manager (02) 6279 0176 Michelle Cowan MDBC (02) 6026 4320 Neville Garland MDBC (02) 6279 0136

HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 45 Appendix C: Key issues identified in scoping study

• Need for better information from Commission and better communication with interest groups. • Consumptive yield and security of system. • Use of dams to mitigate floods: – benefits and adverse effects on downstream agricultural land, – adverse environmental effects. • Time of year of releases. • Releases for generation of hydro-electricity. • Impacts on the recreation industry: – flooding of caravan parks, – effects of low levels in Lake Hume, – importance of accurate flood prediction. • Temperature impacts of releases from different storage levels. • Water quality, particularly salinity and algal blooms. • Impacts of river regulation on flora and fauna. • Impacts on river ecology. • Impacts on salinity and other water quality parameters. • Impacts on riparian landholders of peak regulated flows. • Effects of rising and falling river levels, and regulated releases generally, on bank erosion. • The changing shape of the river channel, and its impact on flooding over time. • Interstate water sharing arrangements: – Murray Darling Basin Agreement, – Snowy Mountains Agreement, – effects of privatisation of Snowy Scheme. • Effects of the Ministerial cap on diversions.

HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 47 Appendix D: Details of “Backgrounder” papers

No 1 Review of the operation of Hume and No 5 Dartmouth Power Station — Overview Dartmouth Dams of Water aspects of Operation

• Terms of reference • Introduction • Key questions • Releases for water supply • Demands on the system • Data exchange • Extent of change • Entitlement releases • Conduct of the review • Above-target releases • Reference panel • Flood releases • Rates of rise and fall

No 2 Regulation and Distribution of River Murray Waters No 6 Dealing with the Capacity Constraints of the Barmah Choke (in preparation) • The regulated Murray • Natural flow pattern • Origin of the Barmah-Millewa forest • River Murray Waters Agreement • Peak water demands • Distribution of water • when the Choke causes problems • Major storages • Ways around the Barmah Choke capacity problem • The Snowy Mountains scheme • Impact on water trading • Barrages, weirs and lock • Past work on capacity of the Choke • Other capacity constraints on the Murray • The future No 3 Lake Hume — Overview of Operation

• Summary No 7 River Murray Flow Management • Filling phase • Release phase • The broader context • Pre-release phase • Background to instream flows • Spilling (flood) phase • Outcomes • Power station • Community participation • Rates of rise and fall in River Murray • Progress to date • Special circumstances • Further reading

No 4 Lake Dartmouth — Overview of Operation

• Summary • Filling phase • Release phase • “Harmony” transfer to Hume • Pre-release phase • Spilling (flood) phase • Power station • Rates of rise and fall in the Mitta Mitta River • Special circumstances

HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 49 Appendix E: Issue register

Relevant to reach: Relevance Priority as Priority Dart- Hume to Yarra- Echuca Down- to Hume– issue for as issue for ISSUE mouth to Yarra- wonga to to stream of Dartmouth Review to Review to Hume wonga Echuca Mildura Mildura Review address by address (not modelling bymodelling)

WATER SUPPLY Limitations to water supply by cap ••••• MedLow–med — Potential lowering of security of supply system, including entitlement flows to South Australia ••••• High High — External influences: e.g. possible adverse effects of changes in Snowy Scheme environmental flows or management, changed operation of ••••• Med— Low Inadequate minimum flows downstream of Mildura • • Low — Med Transmission and operational losses in river •••• Med— Med Transmission and operational losses in distribution systems (ie off river) •••• Low— Low River levels — advice and forewarning of changes inadequate ••••• Med— Low Adequacy of licence volumes on Mitta Mitta and below Hume; need for irrigation to maintain production • • Low — — Limitations to water supply imposed by limited river channel capacities • • • High Low — Inadequate minimum river levels — foot valves out of water Low (high on (communication issue?) ••••• Med— Mitta Mitta) Effects of water temperature on agricultural production • • Med — Low–med FLOOD MITIGATION Is management of airspace as good as it should be? • • • High High High Flood mitigation may have adverse environmental effects — what is the best environmental solution? ••••• High High High Are “harmony” rules optimal? • • High High High Effect of Dartmouth in lengthening some floods — operate power station or valves during floods? Different operation of re-regulating pondage? • High High — Effect of Hume/Dartmouth on floodplain productivity, water tables etc • • High Med Med Possible pre-release strategies for regaining airspace — agricultural and environmental effects ••••• High High High Pre-release methods — what other techniques could be used? Variable flows sometimes above channel capacity? • • • High High High Adverse effects on small area of land at peak regulated flow levels • High — High Effect of various operating strategies onland which is flood-prone but above regulated flow levels • • • High High High

HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 51 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL

Relevant to reach: Relevance Priority as Priority Dart- Hume to Yarra- Echuca Down- to Hume– issue for as issue for ISSUE mouth to Yarra- wonga to to stream of Dartmouth Review to Review to Hume wonga Echuca Mildura Mildura Review address by address (not modelling bymodelling)

ENVIRONMENT Minimum flows — are they adequate and seasonally acceptable? ••••• High Med Med Adequacy of flood events for watering of the Barmah–Millewa area • • High High High Adequacy of flood events for wetland and forest watering in general ••••• High High High Environmental releases — release % of inflow, release on top of flood peaks etc? ••••• High High High Management of weir pools — as lakes or variable regimes? •••• MedLowLow Need for river management plans — includes willow encroachment, management of riparian zone • • • Med — High Natural flooding in the lower reaches of the river • • Med Med Med Effect on environment of rapid drops in river level (especially lower river) ••••• Med— Med Environmental effects of temperature ofwater released • • Med — Med Effect of regulated flows and rainfall rejections on ability to restore natural drying cycles in wetlands ••••• High — High

WATER QUALITY Possible improvements to quality of releases — anoxic water, iron, Med (high for manganese, temperature • • Med — Dartmouth) Effects of possible flow regimes on salinity levels • • Med Low–med Low–med Algal management — provision of sufficient flow to dispel blooms • • • • Low — Low Lower Murray water quality — need for Murray flows rather than Darling at least one year in three • Low — Low Management of phosphorus levels ••••• Low— — (manage at source)

CHANNEL STABILITY Effects of possible Hume/Dartmouth operating regimes on channel stability and channel capacity • • • High High High Effect of weir operation and river regulation on rate of fall in river level (especially lower river) • • Med — Low Effects of willow encroachment and riparian zone management on channel stability and channel capacity • • • Low — — Understanding of main channel and anabranch issues between Hume and Yarrawonga • High — High

52 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL

Relevant to reach: Relevance Priority as Priority Dart- Hume to Yarra- Echuca Down- to Hume– issue for as issue for ISSUE mouth to Yarra- wonga to to stream of Dartmouth Review to Review to Hume wonga Echuca Mildura Mildura Review address by address (not modelling bymodelling)

Who pays? (includes possible effects of Snowy increment on channel stability) ••••• High Med High Effects on channel erosion of carp ••••• Low— —

HYDRO POWER GENERATION Effects of possible operating regimes on value of generation • • • High Med — Privatisation of Southern Hydro — effects on operation of Dartmouth • Low — — Generation at particular times: • Low — — • using entitlement water • when Dartmouth is “above target” Implications of Hume power station on pulsed releases • Nil — —

RECREATION Effects on recreation of levels of Lake Hume at different times of the year • Low Low Low Effects on recreation of foreshore erosion — Lake Hume • Low — — Effects on recreation of water quality, especially temperature ••••• Med— Med Effects of dam operation on recreational and commercial fishing ••••• Med - high — Med Levels of weir pools: •••• Low (med for — Low–med • constancy Yarrawonga • timing of changes weir pool)

COMMUNICATIONS (really to do with how the review is carried out, not with what is reviewed) Community participation strategy during the review ••••• High — High Is understanding of interested groups about present operating strategies as good as it could be? ••••• High — Low Interaction with other current ••••• High — Low processes, e.g.: • Interstate Working Group on River Murray Flows • Victorian bulk entitlements • NSW river flow objectives Long-term communications between operators and the interested community ••••• High — Low

OTHER Disaster planning • • Low — — Dam structural safety ••••• Low— — Coordinated operation between Dartmouth/ Hume and the Snowy Scheme ••••• Med— Med Yorta Yorta claim ••••• Low— Low–med Restriction on levels at Lake Victoria ••••• Med— Med Legal issues, especially liability for environmental releases that adversely affect some downstream landholders • • Med — Med

HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 53 Appendix F: Supporting documents and references

Support papers Other sources of information

• All computer runs in tabulated form I.D & A Pty. Ltd, 1997. Murray River — Hume Dam to Lake River Channel Changes Supplementary Study • Detailed description of the parameters of each run — Final Report. Report to the MDBC. • Submissions made by interested parties Chatterton L.A. and Dyson R.K. 1978. Dartmouth Dam • Set of “Backgrounder” documents Environment Study, State Rivers and Water Supply • Investigation of Mitta Mitta flood duration Commission, . Pak Poy and Kneebone, 1988. Hume and Dartmouth Reports produced for review economic study: tourism and recreation studies. Australian Research Centre for Water in Society. Prepared for the MDBC. Operations Review, Hume and Dartmouth Dams — Scoping Goulburn-Murray Water 1998, The effects of Dartmouth Study. Dam on pasture productivity, Mitta Mitta valley — project report. Hassall & Associates. Flood Damage Estimates — A study Murray-Darling Basin Agreement 1992. of the Murray River and the Mitta Mitta River. Murray Scientific Panel on Environmental Flows 1998, Department of Land and Water Conservation, Murray River Murray — Dartmouth to Wellington and the lower Region, Groundwater study — Old Barnawatha. . Dartmouth Power Station — water aspects of the operating agreement. Murray Water Entitlement Committee 1997, Sharing the Murray. Snowy Water Inquiry 1998, Issues paper. Snowy Water Inquiry 1998, Final report.

HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 55 Glossary

anabranch A minor (or in some cases below Hume, quite major) stream that leaves and rejoins the main river. armouring (of river bed) Deepening of a river bed can result in the formation of a veneer of gravel on the bed surface. This “armour” layer is produced by the selective removal of the finer particles from the bed sediment, and is coarser and better sorted than the underlying bed material. It is generally only a single grain thick, but quite static and stable. bed degradation, bed aggradation Bed degradation is the deepening of a river channel by erosion. This often occurs below water storages because the storage traps sediment, increasing the capacity of the river downstream to mobilise fresh sediment. Aggradation is the reverse process, where the capacity of the river to transport sediment is reduced by such factors as lower grade and therefore lower velocity, sediment is deposited and the stream bed level rises over time. biota All living things, including micro-organisms, plants and animals. bulk water entitlement A legal document used in Victoria to formally specify the limits to the water that water authorities may take from a waterway to supply their customers. cap The limit placed on taking water from streams in the Murray-Darling Basin for consumptive use, as determined by the Murray-Darling Basin Ministerial Council. channel, river channel The part of the river where water usually flows; it includes the bed and the lower part of the banks. de-snagging The removal of logs, fallen trees and branches which play an important role in influencing channel capacity, flow patterns in the river, and riverbed formation. Snags also provide habitat for instream biota. DLWC Department of Land and Water Conservation, New South Wales. dissolved oxygen (DO) Water in a healthy stream has oxygen dissolved in it. Low levels of DO indicate a problem, and may kill fish and other instream biota. easement A legal right to do something on someone else’s land. For example it would be possible for a “flood easement” to be taken out over a part of a property authorising a storage operator to deliberately flood the land in some months of the year. A sum of money would normally be payable in exchange for the acquisition of such a right. fill and spill Operating a storage in a simple fashion, making no releases for flood mitigation but simply allowing the storage to fill, and then to generally pass inflows by spilling, until it starts to be drawn down by releases for regulated supply. flood mitigation Generally, any action that reduces or mitigates floods. Can be applied to storage operation when it is varied for the purpose of reducing floods. Storages with free overfall spillways will mitigate floods without specific action by the storage operator. floodplain Land alongside a waterway, which is subject to flooding. flow regime, river flow regime The prevailing system of stability within the river channel.

HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 57 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL

HUME AND DARTMOUTH DAMS OPERATIONS REVIEW 59 HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL