Airborne geophysical data enhances rapid catchment appraisal in the Upper Kent catchment.

Abstract

The Upper Kent catchment in the south of Western Australia, although under threat of increased land and water salinity, is considered a potential water resource by the State of Western Australia. As a National Dryland Salinity Program (NDSP) focus catchment it is one of the most data-rich catchments in Australia. However, farmers in the catchment have gained little practical information that could be used to guide land management to reduce the potential effects of dryland salinity. To address this problem the available data have been combined in a geographic information system (GIS) and interpreted to investigate the hydrology of the Upper Kent. Electromagnetic data were used to map depth of weathering. Slope analysis of a notional bedrock surface, combined with magnetic data, suggested a palaeochannel system draining to the north and west of the existing surface drainage. The existing Kent River was shown to flow over a basement high which limits downstream movement of groundwater. A saline aquifer in a deep palaeochannel underlies approximately 25% of the Upper Kent. This aquifer is shown to be the main source of salt discharge to the river. Revegetation of the upper catchment is unlikely to prevent this discharge. This new understanding of the hydrology of the Upper Kent catchment indicates that neither simple revegetation nor local surface drainage solutions will reverse salinity in the Kent. A strategic approach that considers the whole catchment, and in particular the presence of a regional palaeochannel aquifer, must be considered in order to target investment in Natural Resource Management in the Upper Kent.