C E N T R a L R E G Io N S U S T a in a B L E W a T E R S T R a T E G Y
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22 CENTRAL REGION SUSTAINABLE WATER STRATEGY / CHAPTER 1 River and Aquifer Health Rivers naturally have variable flow regimes reflecting the rainfall and Importance of flow for rivers run-off within their catchments. This includes low flows during summer European settlement and the associated landscape changes together with small freshening flows occurring periodically and higher winter with our reliance on rivers for water supply in the Central Region has flows including bank-full flows and floods of adjacent land. Each of taken its toll and some are in poor or very poor condition. Some of these components of the flow regime plays an important role in the these rivers are heavily utilised for consumptive purposes and in some ecology of the river, see Figure 3.1. For example, high flows stimulate cases have only about half of their natural flows, which becomes even fish breeding and maintain estuary openings. Similarly, groundwater less in drought years. Some of the catchments that these rivers flow can provide base flows in summer to maintain fish refuges. Floods in through are greatly modified by a combination of water extraction spring regenerate floodplains and wetlands, and replenish the river urbanisation, clearing of native vegetation, draining of wetlands and channel. Water extraction can change these crucial flow components pollution from adjacent land. with negative effects on the ecology of the system. Several rivers in the Central Region are not so heavily used and still retain 70% to 90% of their natural flows (see table 3.1). However, even in these rivers, this is no guarantee of environmental health. In many cases, these rivers are showing signs of environmental damage due to major changes in the pattern of flows (i.e. flow regime) and/or broader catchment changes. Figure 3.1 Importance of the pattern of flow to the health of a river Freshes Bankfull Overbank Flow Help Maintain or improve water qaulity Helps with sediment movement and channel maintenance Maintains floodplain and wetland connectivity ������������������� ������������� �� �� �� �������� �� �� ��������� 3 CHAPTER ������� �� �� ������ �������� ������� �� � ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� Low Flow Cease to Flow High Flow Connects inter-stream habitats Dries out habitats - important for some ecological processes. Allows for fish migration. Low Flow Cease to Flow High Flow CENTRAL REGION SUSTAINABLE WATER STRATEGY / STRATEGY WATER CENTRALSUSTAINABLE REGION 23 In undertaking these scientific studies, some of the constraints under Assessing the flow needs of our rivers which these river systems operate are built into the final environmental In 2002, the Victorian Government commissioned a review of flow recommendations. For example, overbank flooding is not environmental flow assessment methodologies across the world to included in the Lower Yarra, Werribee, Barwon and Maribyrnong rivers develop a ‘best practice’ that could be applied to Victorian rivers. The because of urban development on these floodplains. resultant approach – the FLOWS method - is now the standard in Victoria Table 3.2 provides estimates of the additional volume of water required for assessing the flow needs of rivers in water allocation decisions. to meet the full environmental flow recommendations for each of the The FLOWS method is applied to rivers where further water extraction key rivers in the Central Region. These have been calculated under is being considered to determine whether and how much additional full use of consumptive entitlements and current operating and water water can be taken without further environmental damage. It is also harvesting rules. applied to rivers identified as flow-stressed in regional river health This confirms that many rivers in the Central Region are flow stressed, strategies to identify how much additional water is required to sustain which is impacting on their environmental condition. Decisions on the environmental values of the river. These regional river health whether to return water to these rivers and how much, will take into strategies have been prepared by catchment management authorities account environmental benefits, the impacts on consumptive users in consultation with their broader communities. and any other costs. Scientific studies using the FLOWS method have now been Appendix 3 provides a detailed reach-by-reach breakdown for each completed for all the key rivers in the Central Region (see Table 3.1), river, of the compliance with the flow regime under full consumptive except for the Tarago River, which will be completed later this year. use with the scientific recommendations (SKM 2005). In the FLOWS method, teams of independent scientists determine the flow components required to maintain and where necessary, enhance environmental values with a high probability of success. As part of the process, community advisory groups are established for each river to provide local knowledge and advice, particularly on environmental objectives and values. The Government acknowledges the extensive time, effort and valuable input these groups have put into each study. Table 3.1 Independent scientific studies on environmental water requirements completed for rivers in the Central Region River Scientific Environmental Flow Studies Gellibrand Assessment of Environmental Flow Requirements for the Gellibrand River, Draft Recommendations Revision B, Earthtech, January 2006. Barwon/Leigh Environmental Flow Determination for the Barwon River: Final Report – Flow Recommendations, Lloyd Environmental Pty Ltd, Ecological Associates Pty Ltd, and Fluvial Systems Pty Ltd, October 2005 Moorabool An Assessment of Water Use and Environmental Flow Requirements for the Moorabool River - Moorabool River Water Resource Assessment. Sinclair Knight Merz, 2004 Werribee The Environmental Water Needs of the Werribee River: Final Report – Flow Recommendations, Ecological Associates Report BN001-3D, September CHAPTER 3 CHAPTER 2005 Maribyrnong Assessment of Environmental Flow Requirements for the Maribyrnong River, Final Recommendations – Draft for comment, Revision B, Earthtech, January 2006 Yarra Determination of the Minimum Environmental Water Requirements for the Yarra River, Final, Sinclair Knight Merz, December 2005 Latrobe Assessment of Environmental Flow Requirements for the Latrobe River, Final Recommendations Revision C1, Earthtech, January 2006 Thomson/Macalister Environmental Flow Options for the Thomson and Macalister Rivers, Final Report - Conclusions and Recommendations. The Thomson Macalister Environmental Flows Task Force February 2004 Gippsland Lakes Gippsland Lakes Environmental Study: Assessing options for improving water quality and ecological function, CSIRO, South Australia, 2001 CENTRAL REGION SUSTAINABLE WATER STRATEGY / STRATEGY WATER CENTRALSUSTAINABLE REGION 24 Table 3.2 Estimated addition required to the environmental flow regime10 to meet all the recommendations determined in the independent scientific studies River Estimated addition (ML/year) 1 Yarra 20,000 Werribee 14,500 Maribyrnong 6,900 Bunyip/Tarago To be determined Latrobe To be confirmed 2 Thomson/Macalister 47,000 Barwon/Leigh 4,700 Moorabool 20,000 Gellibrand n/a as current flows are sufficient Total 113,100 1. These estimates are on the basis of the full use of entitlements and are long-term average flows. This is an approximation only assuming current operating and harvesting rules remain unchanged. It is subject to further refinement over time as our understanding of delivering environmental water reserves improves 2. This is to be confirmed pending the outcomes of a review of the environmental flow study by the Technical Audit Panel Outlined below are the key findings from each environmental flow riparian vegetation is encroaching on the river channel. Reduced study and a summary of how well the full scientific recommendations freshes are affecting water quality and cause sediment to build u determined in the studies compare with the flow regime associated in the pools. Lack of overbank flow means that wetlands (eg Banyule with full use of consumptive entitlements. Complete environmental wetlands) are now watered less often. However, it is recognised that flow study reports are available at www.dse.vic.gov.au/riverhealth/ reinstating overbank flows, including the lower Yarra floodplain, would not be desirable due to impacts on urban centres. It may be possible Yarra River to undertake works to provide water to specific wetlands. The Yarra River is an icon with high conservation, social and economic The Yarra estuary, although highly modified, plays a critical part in the values. A combination of flow and non-flow related issues influence river’s health. A number of native fish species, including the threatened the condition of the Yarra River and its tributaries. While the overall Australian grayling, need to migrate between fresh and estuarine or condition through the upper and mid reaches remains good, some marine waters as part of their life-cycle. Processes occurring in the elements of the flow regime under full use of consumptive entitlements estuary are strongly linked to interactions between freshwater inflows are insufficient to support important environmental values. For the from the Yarra River and tidal movement. most part, this is related to a reduction in the number and duration In general, maintaining the existing flow regime, with some of fresh and high flow events that would provide cues for Australian improvements to the low flows and