Identifying the Separate Impact of Farm Dams and Land Use Changes on Catchment Yield

SummaryThis paper presents a method for determining the impact of farm dams on streamflows independent of changes in climate and other land-use. The method is comprised of two components: first, the assessment of the statistical significance of trends in streamflows independent of climatic variation, and secondly, the use of a simulation model to determine the proportion of the assessed trend which is attributable to the impact of farm dams. The method has been successfully applied to a number of catchments throughout Australia. Two case studies have been selected to illustrate its practical application, namely the Marne River catchment in South Australia and the Yass River catchment in New South Wales. The results obtained for these catchments indicate that the nature and magnitude of trends estimated by the two largely independent methods is entirely consistent with the documented changes in farm dam development and other land use changes. There would appear to be a direct correlation between the volume of farm dam development and the decrease in streamflow yield, such that for every 1 ML of farm dam development there is a corresponding decrease in streamflows of between 1 ML to 1.3 ML.