A five-layer finite difference groundwater flow model (MODFLOW) was developed for the Mallee Region to determine the impacts of irrigation on water levels and salinities. The model was calibrated for steady-state conditions over the entire modelled area, with a time-transient calibration undertaken in areas where local pumping data and observation bore hydrographs were available. The model was then validated by running it with inputs of the estimated pumping volumes and water level data that have occurred over the past ten years. Next, various prediction scenarios were run for 25 year periods, including: current use (1997/1998), use of all allocated water, and use of the full present Permissible Annual Volume (PAV). Possible variations to Zone 11 PAVs were also tested. The maximum current usage water level drawdown was about 18 metres, with sufficient recovery at the end of the pumping season to ensure groundwater throughflow. The full allocation/full PAV scenarios had identical results, with drawdowns increasing to 28 metres. This outcome would lead to depressurisation in the centres of the cones of depression. Where this might occur, the Murray Group Limestone aquifer thickness would still be in the range 125 to 140 metres. There would also be permanent cones of depression remaining at the end of the recovery season, with groundwater flow reversals taking place in small areas to the north of Parilla and Peebinga. Groundwater flows out of the model area to the north would still be maintained. Simulated drawdowns within the cones of depression did not appear to level off, even after extending the pumping period to 60 years. They only did so when the pumping was reduced to a bare 10% of the maximum PAV. This outcome indicates that the relatively low aquifer transmissivity does not allow inflows to the pumping areas to keep pace with the outflows, resulting in a gradual decline in storage. It also suggests that inter-aquifer flows by leakage (upward and downward) are relatively low. The likely rate of pumped drawdown initially exceeds 5 cm/year within the cones of depression. However, the rate of drawdown decreases with time, and also with distance from the pumping centres. It appears that there are still significant areas within the developed Zones and Hundreds where the rate of drawdown would stay well below 5 cm/year. The MODFLOW model will be re-calibrated when additional information is obtained on drawdown rates and the water level and salinity changes in the Pliocene Sands aquifer. Salinity impacts due to inter-aquifer leakage and lateral inflows will then be tested.