Diffuse groundwater recharge in the western Murray Basin

Recharge rates under native mallee vegatation are less than 1mm yr^-1, and under crop rotation range between 1 and 50mm yr ^-1. The increase in soil water flux is not immediately transmitted to the water table. Rather, a pressure front which moves downwards through the soil profile is created. The groundwater recharge rate increases (and the water table begins to rise) only when the presssure front reaches the water table. Where the water table is deep (>30m), the time lag between clearing and increased recharge to the groundwater may be in the order of 50 to 500 yr, depending on the recharge rate and soil type. Chloride tracer techniques provide point estimates of groundwater recharge. The small-scale spatial variability of groundwater recharge is mapped with the aid of electromagentic techniques. A map of groundwater recharge is constructed based on existing maps of soil type and surficial geology. -from Authors