Hydrogeology and hydrochemistry of the Parmelia aquifer, northern Perth Basin, Western Australia

摘要

This study aims to characterise the hydrogeology and hydrochemistry of the Parmelia aquifer and to understand controls on recent water-level changes as these are needed to underpin a quantitative analysis of recharge. The Parmelia aquifer, a layered sequence of sand, silt and discontinuous lenses of clay, receives diffuse rainfall recharge on its outcrop and groundwater recharge occurs across the Dandaragan Plateau at different rates. Water levels have risen steadily over the last three decodes between 10 and 55 cm/y in response to the replacement of native vegetation with pasture and annual crops. The mean aquifer properties from sediment analyses indicate a very wide range of porosity (8.9-49.5%) with an arithmetic mean of 26% and consequently a very broad range of specific yield (0.0004-0.4) with an arithmetic mean of 0.14. Groundwater in the Parmelia aquifer has an underlying meteoric origin with compositional changes due to reactions with silicate minerals and leaching of chloride that has concentrated in the soil by evapotranspiration. The hydrochemistry sampled at different depths and locations in the aquifer indicates that the groundwater is not well mixed, and variations arise due to relatively recent recharge that has undergone evaporation in some areas.