Managing climate, irrigation and ground water interactions using a numerical model: a case study of the Murrumbidgee Irrigation Area

The development of a surface-groundwater interaction model for the Murrumbidgee Irrigation Area (MIA) is described. The model uses MODFLOW coupled with the MT3D solute transport simulator under a PMWIN environment. Several customised programs were written to manipulate datasets on aquifer lithology, piezometric levels, groundwater salinity, aquifer abstractions, channel network and Murrumbidgee River and rice area locations to incorporate them into the MODFLOW MT3D format. Detailed piezometric data and numerical model results show an overall decline in the groundwater levels of the region, which is attributed to improved land and water management practices as well as a relatively dry climate over the last decade. Some areas of the MIA, for example Yenda, Murrumai and some parts of the Kooba and Benerembah areas have very limited groundwater outflow capacities. These areas are likely to result in shallow water table and soil salinity problems if irrigation and winter cropping efficiency are not managed within the regional groundwater flow capacity. The model has been calibrated and used to simulate possible management scenarios.