The GABHYD model was developed to provide a tool for predicting the effects of groundwater development alternatives for the Great Artesian Basin. Data from flowing artesian wells are averaged and discretised to provide the data base for a finite difference numerical model defined on a regular square grid. A quasi-three-dimensional simplification is employed to represent the different aquifers in the vertical direction. The model was calibrated using a newly developed direct method. The resulting model was found suitable for predicting regional effects of groundwater management for the major artesian aquifers for which adequate data are available. As an example the model shows that controlled pumping of 900 l/ s in one area of South Australia creates drawdowns of 23 m locally, 3 m 100 km away and 1.5 m at a distance of 110 to 170 km. The model also predicts that drawdown for the year 2000 will be little more than these figures.