Monitoring the hydrological impact of land use change in a small agricultural catchment affected by dryland salinity in central NSW, Australia

Increasing salinity in river systems in the Murray-Darling Basin is a current concern and has the potential to devastate many rural industries. The solution is seen as a move away from traditional agricultural practices which are inefficient water users and lead to high groundwater recharge and toward high water use enterprises that can minimise groundwater recharge. Previous modelling studies have shown that land use change in local groundwater systems has the potential to impact upon groundwater levels and streamflow within a decadal scale time frame, however there are few field based studies to prove the modelling correct.The current study reports on 13 years of groundwater and surface water monitoring on a 129 ha first order catchment in the Boorowa River catchment in NSW, Australia. The land use has changed from annual cropping and pastures to tree belts with perennial pastures. Five years after the land use change, the groundwater levels have fallen dramatically due to almost no recharge, runoff has been significantly reduced and the salt input–output ratio of the catchment has halved. Analysis of the measured components of the water cycle show that the reduction in recharge and runoff are due to the land use change and not merely a reflection of the reduced rainfall since the implementation of the land use change. Numerical groundwater modelling has shown that the reduction in salt affected area in this catchment and the export of salt out of this catchment will reduce for the next few decades.