DISTRIBUTION OF RECHARGE AND DISCHARGE AREAS IN A 1ST-ORDER CATCHMENT AS INTERPRETED FROM WATER LEVEL PATTERNS

A major problem in managing and reclaiming saline land is identifying areas of recharge and discharge in a catchment. In a first-order catchment in the wheatbelt of Western Australia, four trends of water level changes have been observed: monotonically rising water levels; continuously rising water levels with seasonal fluctuations; continuously falling water levels; seasonally fluctuating water levels. Each pattern is associated with a specific hydrologic mechanism - recharge, recharge-discharge and discharge. The spatial distribution of the aquifer systems in the catchment follows a configuration which is controlled by the basin morphology. Recharge takes place in confined aquifers at the watershed and in the uplands; recharge-discharge occurs in the unconfined to semiconfined aquifer of the midslopes, and discharge becomes dominant along the unconfined aquifers of the drainage lines. The main areas of discharge of higher-salinity groundwater occur just upstream of geological structures along the drainage line. Surface water dams were found to contribute to the establishment of new discharge areas. They cause increased pressure in the deep aquifers, resulting in a rise in water levels and groundwater discharge below the dams.