DETERMINATION OF GROUNDWATER RECHARGE USING THE CHANGE IN SOIL-TEMPERATURE

The groundwater recharge rate was determined by using the change in so il temperature, beneath two densities of pine plantation on a sandy so il in a region with a Mediterranean climate, in Western Australia. Acc ording to the numerical analysis, with different patterns of water flu x and with the same volume of applied water, it was found that the gro undwater recharge rate could be estimated using the 'relative soil tem perature difference method'. The method may be applied when annual rec harge is low and temperature measurements are available within the top few metres. Using the annual change in soil temperature at 1.5 and 2. 0 m depths, the ratio of estimated recharge rate at the sparse pine si te to that at the dense pine site was about 1.98. Recharge rates so de termined correspond closely to those estimated by tracer methods using natural chloride and artificial bromide. The heat balance method, inv olving change in the heat capacity of the soil after rainfall events, can estimate the water flux only near the surface; it cannot determine water flux at greater depths because the change in soil temperature c aused by rainfall events can be detected only down to a metre or so.