Localised recharge in the vicinity of the Woolpunda groundwater mound

It has been estimated that, if the mound was derived solely from localised recharge, the regional recharge rate in this area would have to be in the order of 10 mm yr^-1 greater than in the surrounding areas. Estimates of the rates of localised recharge through depressions in the landscape have been attempted using both unsaturated zone and groundwater data. The unsaturated zone chloride data suggests a minimum mean recharge rate of 7 mm yr^-1 through the base of the depressions, and a maximum in the order of 100 mm yr^-1. The chloride concentration of this recharging water is approximately 100 mg L^-1. Extrapolating this to obtain a regional picture is difficult. However, the apparent infrequency of localised recharge sources in the landscape suggests that their contribution to regional recharge is probably much less than the contribution from diffuse recharge. Vertical profiles of groundwater salinity suggest the possibility of some surface dilution from these point sources, although this would probably not amount to more than about 0.1 mm yr^-1 on a regional scale. This strongly suggests that the mound is not predominantly the result of higher rates of rainfall-derived recharge in the area. -from Authors