Quantity or Quality - Management Challenges Addressing Changes in the Gascoyne River Alluvial Aquifer System

The economic sustainability of the Carnarvon Horticultural District (CHD) is dependent upon the formulation and implementation of appropriate groundwater management strategies. The CHD, located on the mouth of the Gascoyne River approximately 150 km south of the Tropic of Capricorn on the west coast of Australian, is a highly productive horticultural area that commenced around 1928 and has grown into a major horticultural precinct with 1030 hectares under cultivation and a gross volume of produce exceeding 40 000 tonnes. Rainfall averages about 230 mm/year such that the area is reliant upon water developed from the Gascoyne River alluvial aquifer system. The Gascoyne River is an ephemeral river that is predominately dry with an extensive fresh water alluvial aquifer system recharged during sporadic and infrequent flow events. Bananas, the mainstay cash crop grown in the CHD, require high quality water with production falling as water salinity increases above 500 mg/L of total dissolved solids (TDS). Government intervention and the implementation of controls to limit abstraction occurred in the 1960s as a result of significant degradation of groundwater quality and the failure of numerous plantations. Legacy issues have resulted in the system being over–allocated. The management of the Gascoyne River aquifer system is based upon the measurement of groundwater salinity and standing water level that are used to estimate “fresh” groundwater storage and restrict the production of groundwater with salinity greater than 1000 mg/L TDS. This process utilizes a range of tools that include an Excel spreadsheet calculator, groundwater salinity contouring and a groundwater model (GASFAMS). Groundwater management issues have recently become more complex due to renewed expansion pressure under the State Government's Gascoyne Food Bowl initiative, changes in crops and land tenure, climatic variability, proposed groundwater entitlement trading and the requirement to address groundwater resource over–allocation.