Assessing the impact of farm dams on streamflows, Part II: Regional characterisation

This paper reports on a number of advances in the hydrologic characterisation of farm dams that are required in the assessment of farm dam impacts on stream flows. While the characteristics were derived for input to the TEDI simulation model, the generic nature of the information derived is applicable to any quantitative analysis of farm dam impacts, regardless of the method used. The use of topographic maps and aerial photography to identify the number and volume of farm dams is discussed, and this includes development of a functional relationship between farm dam surface area and volume. An essential component required for the estimation of farm dam impacts is the proportion of a dam's volume used to satisfy demands, and this is investigated using a regional survey of landholders. Typical size distributions of farm dams used for irrigation, and for stock and domestic purposes are presented, as is information on the range of farm dam densities encountered across Victoria. Farm dam and catchment characteristics derived for 1600 Victorian catchments were used along with previously derived prediction equations to estimate the impacts of farm dams on a range of stream flow indices. The manner in which this regional information can be used to rapidly estimate the impacts of farm dams on specific catchments is also discussed and presented.