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Determination of the Minimum Environmental Water Requirement for the Yarra River MINIMUM ENVIRONMENTAL WATER REQUIREMENT AND COMPLEMENTARY WORKS RECOMMENDATIONS Final 30 September 2005 Determination of the Minimum Environmental Water Requirement for the Yarra River MINIMUM ENVIRONMENTAL WATER REQUIREMENT AND COMPLEMENTARY WORKS RECOMMENDATIONS Final 30 September 2005 Sinclair Knight Merz ABN 37 001 024 095 590 Orrong Road, Armadale 3143 PO Box 2500 Malvern VIC 3144 Australia Tel: +61 3 9248 3100 Fax: +61 3 9248 3400 Web: www.skmconsulting.com COPYRIGHT: The concepts and information contained in this document are the property of Sinclair Knight Merz Pty Ltd and Melbourne Water. Use or copying of this document in whole or in part without the written permission of Sinclair Knight Merz or Melbourne Water constitutes an infringement of copyright. Minimum Environmental Water Requirement and Complementary Works Recommendations Contents 1. Introduction 1 1.1 Project background 1 1.2 This report 2 1.2.1 Report structure 2 2. Methods 3 2.1 Fieldwork 4 2.2 Hydraulic model 6 2.3 Hydrology 6 2.3.1 Ramp rates 6 2.3.2 HecRas and Getspells output 8 2.4 Development of flow recommendations 10 2.5 Compliance with recommendations 10 2.5.1 Volume compliance 10 2.5.2 Frequency compliance 10 2.5.3 Duration compliance 10 2.5.4 Flow comparisons 11 3. Environmental objectives 13 3.1 Summer/autumn flow period 26 3.2 Winter/spring 28 4. Environmental flow recommendations 30 4.1 Reach 1: Upper Yarra Dam to Armstrong Creek 30 4.1.1 Current condition 30 4.1.2 Flow recommendations 34 4.1.3 Current compliance 43 4.2 Reach 2: Armstrong Creek to Millgrove 44 4.2.1 Current condition 45 4.2.2 Flow recommendations 48 4.2.3 Current compliance 58 4.3 Reach 3: Millgrove to Watts River 59 4.3.1 Current condition 60 4.3.2 Flow recommendations 63 4.3.3 Current compliance 76 4.4 Reach 4: Watts River to Yering Gorge 77 4.4.1 Current condition 78 4.4.2 Flow recommendations 80 4.4.3 Current compliance 92 SINCLAIR KNIGHT MERZ I:\WCMS\Projects\WC03090\Deliverables\final\Yarra EWR flow recommendations report_finaltest.doc PAGE i Minimum Environmental Water Requirement and Complementary Works Recommendations 4.5 Reach 5: Yering Gorge to Mullum Mullum Creek 93 4.5.1 Current condition 94 4.5.2 Flow recommendations 98 4.5.3 Current compliance 109 4.6 Reach 6: Mullum Mullum Creek to Dights Falls 110 4.6.1 Current condition 111 4.6.2 Flow recommendations 115 4.6.3 Current compliance 127 4.7 Reach 7: Yarra Estuary 129 4.7.1 Current condition 129 4.7.2 Flow recommendations 137 4.8 Reach 8: Watts River downstream of Maroondah Reservoir 142 4.8.1 Current condition 143 4.8.2 Flow recommendations 145 4.8.3 Current compliance 155 4.9 Reach 9: Plenty River downstream of Toorourrong Reservoir 156 4.9.1 Current condition 156 4.9.2 Flow recommendations 160 4.9.3 Current compliance 170 5. Priority flow components, risks and monitoring 172 5.1 Cease to flow 173 5.1.1 Rationale 173 5.1.2 Risks and uncertainties 173 5.1.3 Monitoring and investigations 174 5.2 Summer low flows 174 5.2.1 Rationale 174 5.2.2 Risks and uncertainties 174 5.2.3 Monitoring and investigations 175 5.3 Summer freshes 175 5.3.1 Rationale 175 5.3.2 Risks and uncertainties 175 5.3.3 Monitoring and investigations 176 5.4 Summer high flows 176 5.4.1 Rationale 176 5.4.2 Risks and uncertainties 176 5.4.3 Monitoring and investigations 178 5.5 Winter low flows 178 5.5.1 Rationale 178 5.5.2 Risks and uncertainties 178 5.5.3 Monitoring and investigations 179 SINCLAIR KNIGHT MERZ PAGE ii I:\WCMS\Projects\WC03090\Deliverables\final\Yarra EWR flow recommendations report_finaltest.doc Minimum Environmental Water Requirement and Complementary Works Recommendations 5.6 Winter freshes and high flows 179 5.6.1 Rationale 179 5.6.2 Risks and uncertainties 179 5.6.3 Monitoring and investigations 180 5.7 Bankfull and overbank flows 180 5.7.1 Rationale 180 5.7.2 Risks and uncertainties 180 5.7.3 Monitoring and investigations 181 5.8 Flow and reach priorities 181 6. Complementary waterway works and further investigations 184 6.1 Wetland rehabilitation 184 6.2 Riparian revegetation and LWD reinstatement 185 6.3 Water quality management 186 6.4 Further investigations 186 7. References 190 SINCLAIR KNIGHT MERZ I:\WCMS\Projects\WC03090\Deliverables\final\Yarra EWR flow recommendations report_finaltest.doc PAGE iii Minimum Environmental Water Requirement and Complementary Works Recommendations Document history and status Revision Date issued Reviewed by Approved by Date approved Revision type 1 18/08/05 Simon Michael Shirley 18/08/05 Treadwell 2 31/08/05 EFTP members Simon 25/09/05 Technical review Treadwell 2 31/08/05 Gerry Quinn Simon 25/09/05 Technical review Treadwell 3 25/09/05 Michael Shirley Michael Shirley 29/09/05 Technical review Distribution of copies Revision Copy no Quantity Issued to Draft 1 email Jamie Ewert, steering committee & advisory group members 2 & 3 email EFTP and technical reviewers Final 2 hardcopy Jamie Ewert 1 electronic Printed: 18 November 2005 Last saved: 18 November 2005 12:34 PM I:\WCMS\Projects\WC03090\Deliverables\final\Yarra EWR flow recommendations File name: report_finaltest.doc Author: Dr Simon Treadwell Project manager: Dr Simon Treadwell Name of organisation: Melbourne Water Name of project: Determination of the Environmental Water Reserve for the Yarra River Name of document: Minimum Environmental Water Requirement and Complementary Works Recommendations Document version: Final Project number: WC03090 SINCLAIR KNIGHT MERZ I:\WCMS\Projects\WC03090\Deliverables\final\Yarra EWR flow recommendations report_finaltest.doc PAGE v Minimum Environmental Water Requirement and Complementary Works Recommendations 1. Introduction 1.1 Project background There is an increasing awareness in water resource management of the need to incorporate the environmental requirements of ecosystems into the water resource planning process. Determination of environmental water requirements is a key part of the water resource planning process, as alterations to natural flow regimes can have significant impacts on riverine ecosystems. The Department of Sustainability and Environment (DSE) developed the Victorian River Health Strategy (NRE 2002b), in part, to implement measures that provide water to meet environmental needs. The Victorian River Health Strategy sets goals to maintain and, where possible, restore the environmental values of rivers and wetlands, whilst recognising existing entitlements. In 2004 the Victorian Government White Paper, Securing our Water Future Together (DSE 2004), announced a commitment to finalise the Bulk Entitlement (BE) Conversion process for the Yarra River. The aim of the process is to provide authorities with a clearly defined property right to water and protect instream values by allowing specific entitlements for the environment. Currently, Melbourne Water harvests water from the Yarra River and tributaries for urban supply under a draft BE. A BE resulting from the conversion process for the Yarra System will be held by three retail water companies (Yarra Valley Water, City West Water and South East Water) and will include a cap on the extraction of water from the Yarra River. Melbourne Water requires a determination of the environmental water reserve for the main stem of the Yarra River and its tributaries the Watts and Plenty Rivers. This project identifies the minimum environmental water requirements to maintain and enhance the significant ecological values in the Yarra River and tributaries and will ensure that the environmental flow needs of the Yarra River system are protected into the future. The environmental flow recommendations will also provide input to long-term water resource planning to ensure Victoria’s water security over time through the Central Region Sustainable Water Strategy. The project study area includes the freshwater and estuarine reaches of the Yarra River catchment (from the Upper Yarra Reservoir to the West Gate Bridge) and its sub-catchments, the Plenty River (Toorourrong Reservoir to Plenty Gorge) and Watts River (Maroondah Reservoir to the Yarra River). Flow issues of the Yarra Estuary (Dights Falls to West Gate Bridge) have also been considered within the scope of the project, although at this point no specific flow recommendation is made for the estuary. SINCLAIR KNIGHT MERZ I:\WCMS\Projects\WC03090\Deliverables\final\Yarra EWR flow recommendations report_finaltest.doc PAGE 1 Minimum Environmental Water Requirement and Complementary Works Recommendations The objectives of the project are: to identify the water dependent social and environmental values in the Yarra River and tributaries; to gauge the current health of these values; to identify flow regimes that will maintain, sustain or improve these environmental values; to recommended environmental flow objectives that reflect community values for the river; to recommend the minimum environmental flows to meet the objectives, particularly to review the existing minimum environmental flow requirement for 245 ML/d at Yering; and to recommend other waterway works that could also meet the environmental flow objectives. 1.2 This report This report presents the environmental flow and complementary waterway works recommendations for the Yarra River. The current report was preceded by a Site Paper and Issues Paper. The Site Paper described the process used to separate the Yarra River into representative reaches for the purposes of environmental flow assessments (SKM 2005a). The Issues Paper discussed the current environmental status of the study area ―water system operations, ecology, hydrology, geomorphology and water quality― and canvasses those catchment and streamflow issues that affect the environmental condition of the study area and culminated in the determination of environmental objectives required to ensure the Yarra River is an ecologically healthy river (SKM 2005c).