Water Journal : Water Journal September 2012-1
sustainable water management water SEPTEMBER 2012 81 Options were explored to locate above-ground storages for both sites, given that using the permanent pool depth was unacceptable. It was fortunate that for both schemes the landholders, CC and WCC, could accommodate the installation of above-ground tanks. Retrofitting stormwater projects into urban landscapes is often very expensive because of the need to install underground storage tanks. After support was achieved for above- ground storage, CWW and the appointed consultants began to develop designs to harvest flow from the overflow of the wetlands. For Scheme A, this included harvesting water from the wetlands outfall culvert. For Scheme B, diversion design ideas were not finalised. During the modelling phase it was revealed that the Scheme B wetlands included numerous 'open groundwater' ponds. Groundwater in the Western Melbourne region is known to be high in Total Dissolved Solids (TDS), which above a certain concentration makes the reuse of water for long-term irrigation unsustainable. Field tests were undertaken to determine the presence of groundwater in each of the ponds. The tests confirmed the presence of groundwater in most of Scheme B ponds, with TDS values ranging from 700 to 3700mg/L. Some ponds were found to have lower TDS in the range of 150 to 500mg/L. These ponds were in the north- west corner of the wetlands, where the wetlands were designed to exclude the infiltration of groundwater. The concentration in the north-west ponds was considered satisfactory to harvest for irrigation end use. Scheme A field tests returned a maximum TDS concentration of 100mg/L. No evidence of groundwater infiltration was witnessed in the field or in the designs. As a result of the water quality findings, the diversion location for Scheme B was relocated from the last pond (farthest east) to the freshwater ponds (farthest west). Functional designs and cost estimates were completed for both schemes. As a result of the water quality issues with Scheme B and the need to move the diversion location, the capital cost estimates more than doubled, making this project financially unviable. Alternative arrangements were explored for Scheme B and the demands are now being met by CWW's recycled water system. Environmental assessments, including of flora and fauna, and a cultural heritage Phase 1 site assessment, were undertaken for Scheme A. The flora and fauna assessment determined that the wetlands are likely habitat for the Growling Grass Frog (GGF), which is an Environmental Protection Biodiversity Conservation Act (EPBC) listed species. No disturbance to the habitat could be undertaken until it was determined whether the GGF was present. Moving the diversion point from the wetlands outfall, surrounded by vegetation, to the barrel drain 15m downstream alleviated disturbance to potential GGF habitat and, hence, further flora and fauna investigations. The cultural heritage investigation indicated that the Scheme A area was a likely place of Aboriginal activity (DSE, 2012; DPI, 2012). Records (DoS, 1979; MMBW) show that the wetlands and WCC oval have been constructed in a depression that would accumulate water, which could provide resources and food for the traditional owners. The land developer and Council provided supporting documentation that was used to determine areas of significant disturbance. This includes areas that were used to lay drainage lines, raise and construct roads, and to raise and contour the WCC oval. The locations that were identified as significantly disturbed are as much as 50% of the project area. Carranballac College, Jamieson Way Campus Jamieson Way Wetlands Point Cook Community Centre X Figure 2. Scheme B.
Water Journal November 2012-1
Water Journal August 2012