Assessing impacts of basin management and environmental change in the Eastern Murray Basin

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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 Murray Basin (Punthakey et al., 1994). The model covers approximately 39,000 km 2 equivalent to 13% of the Murray Geological Basin, and comprises three layers. Each layer represents a major regional aquifer system, the Shepparton, Calivil and Renmark. The model was calibrated using observed potentiometric data from 1980 to 1985. Comparison of contours of observed heads and modelled heads for the Shepparton, Calivil and Renmark showed that the modelled heads matched the observed head contours closely. The Lower Murrumbidgee groundwater model has shown that large areas of the current irrigation areas and districts will be affected by rising groundwater by 2020 under the ‘Do nothing’ scenario. The ‘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 entitlements. The use of groundwater models to investigate the impacts of environmental change within the Basin such as planting trees along riverine corridors and their impact on shallow water tables in the Shepparton aquifer was investigated. The ‘Shallow groundwater pumping’ scenario appeared to control the rate of rise in water table in the Shepparton, although 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 Private Irrigation Properties would result in unacceptably high water tables in the CIA, Wah Wah, and in the northeastern part of the model domain. Any proposal for increased irrigation would therefore have to be evaluated closely for impacts. The model can be used to provide a window into the future of likely impacts to the area under a range of scenarios. The implementation of a specific option will however depend on its economic merit to the community and the area.