Gascoyne River, Western Australia; Alluvial Aquifer, Groundwater Management and Tools

Abstract

The Carnarvon Horticultural Area adjacent to the Gascoyne River, Western Australia has since around 1928 grown to be the major supplier of fresh fruit and vegetables for the Perth region. Horticulture in this area is sustained by a small niche humid climatic zone within an arid environment with an annual rainfall generally less than 200 mm (8 in.). The Gascoyne River alluvial aquifer system is the sole source of “fresh” water for both the Carnarvon Horticultural Area and Carnarvon Township. This alluvial aquifer system comprises the River Bed Sand and an Older Alluvial Aquifer. Significant “fresh” groundwater is present within these alluvial aquifers, where groundwater storage is recharged only during brief restricted periods of river flow. Management of the Gascoyne River alluvial aquifer system has always been essential to ensure that the required quantity and quality of groundwater for both irrigated horticulture and town water can be sustained through extensive periods of no recharge (no flow). Groundwater management techniques have progressed from an early trial and error process referred to as the “Rules of the River” through to groundwater modelling techniques ranging from spreadsheets in the early 1980s to the current MODFLOW 2000. The Western Australian Department of Water has used the outputs of these processes, together with regular measurement of both groundwater level and salinity obtained from a network of observation bores, to ensure sustainability of the water supply to both the reticulated horticultural precinct and Carnarvon Township.