Appendix 1 Wimmera-Mallee Water Quality Management Plan
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Department of Environment, Land, Water and Planning Appendix 1 Wimmera-Mallee Water Quality Management Plan Table of Contents Part 1 - Wimmera-Mallee Water Quality Management Plan overview • Wimmera- Mallee WRP area • Water resources of Wimmera- Mallee WRP area • Surface water resources • Groundwater resources • Basin Plan and Water Quality Application Zone • Water quality in the WRP area Part 2 - Water quality management strategies • 2.1 State Environment Protection Policy (SEPP) • 2.2 Basin Salinity Management Strategy 2030 • 2.3 Groundwater (Border Agreement) Act 1985 • 2.4 Murray-Darling Basin Plan objectives Part 3 - Recommended target values for the Wimmera- Mallee WRP area • Freshwater-dependent ecosystem • Raw water treatment for human consumption • Irrigation water • Salinity • Water used for recreation purpose Part 4 - Causes or likely causes of water quality degradation 4.1 Preliminary risk assessment for WRPs 4.2 Risks to groundwater quality 4.3 Causes or likely causes of water quality degradation in Wimmera-Mallee WRP area Part 5 - Water quality measures Part 6 - Monitoring, data management and reporting Wimmera Mallee Water Resource Plan Wimmera Mallee Water Resource Plan Appendix 1 | 259 Department of Environment, Land, Water and Planning Part 1 – Wimmera-Mallee Water Quality Management Plan overview 1.1 Wimmera-Mallee WRP area Victoria is a signatory to the Murray-Darling Basin Plan (the Basin Plan). Under the Basin Plan the Department of Environment, Land, Water and Planning (DELWP) is responsible for the development of water resource plans (WRPs) for five WRP areas under Chapter 10 of the Basin Plan. This responsibility includes the development of a Water Quality Management Plans (WQMP) for each WRP area. The Wimmera-Mallee WRP is the first plan being developed by combining the surface water WRP area (SW4) and the groundwater WRP area (GW3) as a single instrument. The Wimmera- Mallee WQMP addresses the surface water and groundwater resources within three catchment management authorities (CMAs). The Wimmera-Mallee WRP area is located in north-west Victoria and extends from the Grampians and the Pyrenees Ranges in the south to Ouyen and Kerang in the north. The western extent of the WRP area is bounded by Victoria’s border with South Australia and the Northern Victoria WRP area to the east (Figure 27). 1.2 Water resources of Wimmera-Mallee WRP 1.2.1 Surface water resources Surface water resources in the WRP area are dominated by the Grampian Ranges to the south, and the broad floodplains of the Wimmera and Avon-Richardson and Avoca River systems (Figure 27). The region is relatively flat and sits on the geologically stable western plains of Victoria. The Wimmera River is the largest closed drainage basin that retains its water flow through a range of wetland systems and does not outflow to river, ocean or other external bodies. In exceptionally wet years, it fills in Lake Hindmarsh and Lake Albacutya. The Avoca River flows into a series of lakes and wetlands such as Avoca Marshes and Lake Boga. The Avoca River regularly ceases to flow for many months of the year. During flooding, it occasionally discharges into the Murray River or via stream channels to a further series of lakes. Similarly, the Avon-Richardson catchment is internally drained, with most surface water flowing into Lake Buloke. The Avoca Marshes, part of the Kerang Wetlands Ramsar site, are a series of lakes and swamps that differ in permanence, depth and salinity. Other wetlands in the south include Lake Lalbert, Sandhill and Sandhill West lakes, Lake Marmal, Griffiths swamp and Terappee swamps including Bradshaw Swamp. The waterways in the WRP area have been modified to varying extent from their natural state. The modifications have impacted on the hydrologic regime, physical form, riparian vegetation, and water quality and in-stream ecology. Rising saline groundwater, turbidity and algal blooms are among the most common causes of water quality degradation. Land clearing practices, including removal and destruction of native vegetation through overgrazing, cropping and wood removal threaten the riparian values of these waterways. The Wimmera-Mallee headworks system is a complex network of storages, channels and pipes that regulates flow in many of the waterways of the Wimmera-Mallee WRP area. This headworks system enables water to be shifted between storages and interconnects the three major basins of the Wimmera, Avoca and Glenelg. There are four regulated systems in the Wimmera-Mallee WRPA. A notable feature of these systems is the dynamic change that has been occurring in recent years, following the completion of the Wimmera Mallee Pipeline in 2010 and the cessation of the Wimmera Irrigation Area. These two factors have greatly reduced the consumptive water demand requirements from the Wimmera-Mallee headworks system and resulted in a wide-scale reconfiguration of the regulated water systems. The largest unregulated systems in the WRP area include the Avon-Richardson, Avoca and Upper Wimmera rivers. Surface water resources of the Wimmera-Mallee WRP area have historically been managed under a series of local management rules in each catchment, except the Upper Wimmera River where no local management rules are in place. 260 | Appendix 1 Wimmera Mallee Water Resource Plan Wimmera Mallee Water Resource Plan Department of Environment, Land, Water and Planning Figure 27 - Wimmera-Mallee WRP area showing AWRC drainage boundaries and SDL resource unit Surface WaterElevation SDL (mAHD)Resource Value Unit AWRC Drainage Divisions1000 mAHD and River Basins MILDURA 0 mAHD M U R R A B Y O R IV U E R N R E D V A I R R Y Y E A X R Hattah C R L U U M DES THE MALLEE Ouyen LAKE SWAN HILL TYRRELL (Direl) AVOCA RIVER LAKE T ALBACUTYA Y R (Nalbagatja) R E L LAKE LAKE L C R LASCELLES COORONG EE K Y A R R I A M B I Birchip A LAKE C K HINDMARSH Brim C W R Wycheproof IM E M E LAKE E K R BULOKE A Charlton R Warracknabeal I V Nhill E (Wurunibial) R Donald A WIMMERA-AVON V Dimboola O C RIVERS A RI VE AV R R O (Y I ER a C N RIV n H St Arnaud g HORSHAM TAYLORS a A n R g LAKE D M S ) Natimuk A PINE O C NORT N RIVER K O LAKE E N N C Z Glenorchy TOOLONDO R IE Navarre E R RESERVOIR E I K V LAKE LONSDALE ER F Y Stawell Avoca A WHITE N S LAKE LAKE C R LAKE WARTOOK E E FYANS K ROCKLANDS LAKE RESERVOIR BELLFIELD ARARAT Wimmera Mallee Water Resource Plan Appendix 1 | 261 Department of Environment, Land, Water and Planning 1.2.2 Groundwater resources The geology of the Wimmera-Mallee includes alluvium and dune deposits in the vast floodplains, signifying wind-blown Aeolian landscapes over the Woorinen Formation to the north of the WRP area and Cambrian rock of the Grampians and St Arnaud groups in the south-east. Most of the Wimmera River system overlies the regional groundwater flow system within the Parilla Sands, which is very saline, ranging from 5,000 mg/L in the south to more than 35,000 mg/L in the north of the Wimmera (Wimmera CMA, 2005). Typically the groundwater table is well below all waterway channels except the Wimmera River. Analysis of depths to the water table and base flow filtering for the Wimmera River Environmental Flows Study (Alluvium, 2013) confirmed that there are no significant groundwater contributions to surface water flow beyond the intrusion of hyper-saline groundwater into the river channel when it intersects with the water table in the lower Wimmera River. In the lower Wimmera River, groundwater enters pools typically at depths greater than 2m. During low flow conditions, the water quality can become extremely poor and unable to support fish and macroinvertebrates with salinity levels more than 50,000 μS/cm. The density difference between the deeper hypersaline water and overlying surface water leads to stratification, which reduces the amount of oxygen reaching the hypersaline layer from the surface. Bacterial oxidation of organic matter further reduces oxygen in the hypersaline layer, leading to a bacterial reduction of sulfate, which then creates toxic hydrogen sulfide as a by-product. These processes all contribute to the low water quality during these conditions. Mallee groundwater systems are predominately saline and unsuitable for agriculture or human use. The exception to this is the Murray Group Limestone Aquifer, a confined aquifer that lies deep under the western portion of the Mallee, on the Victoria-South Australia border (Figure 28). The Murray Group Limestone Aquifer is shared by Victoria and South Australia and is under management arrangements. In Victoria, the aquifer is managed as the Murrayville Groundwater Management Unit (GMU) and extraction is under licence from GWMWater. The Murrayville GMU covers 1,578 square kilometres and is centred on the town of Murrayville, between Murray-Sunset National Park (to the north) and the Big Desert State Forest. As per the Victoria-South Australia Groundwater (Border Agreement), the aquifer is managed as a non-renewable resource and any extraction is referred to as mining. The current total permissible consumptive volume of the Murrayville GMU is 10,883ML per annum. The most significant water quality threats to the groundwater resource include inappropriate water use practices such as excessive pumping that can lead to considerable localised drawdown of the aquifer, and contamination with saline groundwater from leakage between aquifers (e.g. due to failed bore infrastructure). Excess water accumulation underlying clay in the landscape due to excessive drainage can lead to perched water table causing waterlogging, salt accumulation, crop or vegetation loss and in some cases damage to infrastructure such as roads.