Deans, Frank Ross (2023) The Hydrologic Feasibility of Building a Weir Within Lake Eildon in the Vicinity of Bonnie Doon. Research Master thesis, Victoria University.

Abstract

Lake Eildon is Victoria’s most popular inland recreational water destination and the only lake which allows registered houseboat access. It is in North-Central Victoria. The township of Bonnie Doon is located within the northern-most catchment area of Lake Eildon. Water is supplied from the lake for the Bonnie Doon township. When surface water is absent, during drought or releases greater than inflows, recreational boating and fishing suffer, along with water availability for the township and firefighting collection. This occurs when water levels of the main dam drop below 46% storage. This impacts on the local and regional economies as visitor numbers decline when water is absent. The aim of this research was to explore the viability, based on consideration of hydrologic data and reference to water quality, geological, structural, and general issues, for the construction of an additional weir, either near the Bonnie Doon pumping point below the road bridge, on the Mooroondah Highway, or within three kilometres downstream of that point. The primary purpose of the weir will be to provide and maintain a secure local body of water whilst the main dam at Lake Eildon continues to meet its Goulburn-Murray Water responsibility for downstream irrigation, townships’ drinking water supply and for a range of environmental purposes. The main methodology was a quantitative approach, with three potential weir sites chosen and at each site, a weir with crest elevations at each of 272 and 275 mAHD was considered. The components factored into the models created included precipitation, surface area of potential weir sites, evaporation, streamflows, and resulting water movement (water levels below crest heights or volumes passing downstream into the main dam, where that dam failed to overtop the weir crest). Models were constructed, firstly to assess their viability using historical data for forty years from 1980 to 2019. These six sets of models showed that the weirs were viable. However, the more important test was to determine their viability with climate change factored in. With predictions for climate change, modelling used projections for the year 2065 (for worst outcomes) as supplied by the (Victorian) Department of Energy, Environment and Climate Action (DEECA). These projections were also modelled with probabilities of 50 and 90 percent. Only the worst forecasts for the year 2065 were used, as it was considered that those for year 2040 had already started to appear to some extent earlier than expected. The outcomes reached using climate change models indicated that all six weir options were still viable. An extra model to determine the outcome if there was no water overtopping by the main dam ever occurring, and the weir still delivered a viable result. Also, as the absence of water in this location seriously impacts on recreational pursuits in the Bonnie Doon arm of the lake, including fishing, powered boating, houseboats and canoeing, this research, with feasibility proven, may influence future government strategic water infrastructure planning for regional Victoria.

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