ASSESSING IMPACTS OF BASIN MANAGEMENT AND ENVIRONMENTAL-CHANGE IN THEEASTERN MURRAY BASIN

The Lower Murrumbidgee groundwater model was developed to improve the understanding of the regional flow system, and to evaluate the impact of large scale land management options and climate change on the water and salt balance for the major regional aquifers within the Eastern M urray Basin (Punthakey et al., 1994). The model covers approximately 3 9,000 km(2) equivalent to 13% of the Murray Geological Basin, and comp rises three layers. Each layer represents a major regional aquifer sys tem, the Shepparton, Calivil and Renmark. The model was calibrated usi ng observed potentiometric data from 1980 to 1985. Comparison of conto urs of observed heads and modelled heads for the Shepparton, Calivil a nd Renmark showed that the modelled heads matched the observed head co ntours closely. The Lower Murmmbidgee groundwater model has shown that large areas of the current irrigation areas and districts will be aff ected by rising groundwater by 2020 under the 'Do nothing' scenario. T he 'Deep groundwater pumping' scenario appeared to offer the best long -term option for controlling high water tables while at the same time offering the possibility for trading existing surface water entitlemen ts. The use of groundwater models to investigate the impacts of enviro nmental change within the Basin such as planting trees along riverine corridors and their impact on shallow water tables in the Shepparton a quifer was investigated. The 'Shallow groundwater pumping' scenario ap peared to control the rate of rise in water table in the Shepparton, a lthough the disposal of large quantities of saline groundwater pumped from the Shepparton presents a major disposal problem. An increase in irrigation recharge in the irrigation Areas and Districts, and on Priv ate Irrigation Properties would result in unacceptably high water tabl es in the CIA, Wah Wah, and in the northeastern part of the model doma in. Any proposal for increased irrigation would therefore have to be e valuated closely for impacts. The model can be used to provide a windo w into the future of likely impacts to the area under a range of scena rios. The implementation of a specific option will however depend on i ts economic merit to the community and the area. Copyright (C) 1996 El sevier Science Ltd.