Fill in the Dams

Small dams in inland Australia are key farm infrastructure and are essential for the economic survival of rural business during sustained drought. However, harsh arid climatic conditions result in annual evaporation losses greater than annual water usage. The purpose of this study is to investigate the feasibility of replacing small farm dams with groundwater dams, constructed by filling the farm dams with gravel or sand. Water is then stored in the soil pore space, where evaporation decreases as a function of water depth below the surface of the soil, until at a depth of 0.9m, evaporation is negligible. Although storage volume is reduced, this method may be an efficient alternative to the current unavoidable evaporation losses from open surface waters. Daily evaporation data, and storage efficiency of representative farm dams has been compared to the computed evaporation and storage efficiency from equivalent dams filled with coarse material. Data has been taken for a number of sites in western New South Wales from 1966 to 2006. Results have shown that when the water level is below the surface, evaporation is significantly reduced and water saved, particularly from larger dams in arid regions more than semiarid regions. The study concludes that the application of groundwater dams would be beneficial in arid areas of Australia for larger, deeper storages, however not much benefit is seen in their application in semi-arid regions. Groundwater dams reduce evaporation losses and appear to be an effective storage solution but more detailed simulations over longer climatic periods as well as field trials should be undertaken before they are implemented in Australia.