Dryland salinity in Western Australia: managing a changing water cycle.

Clearing of agricultural land has resulted in significant changes to the surface and groundwater hydrology. Currently about 10% of agricultural land in Western Australia is affected by dryland salinity and between a quarter and a third of the area is predicted to be lost to salinity before a new hydrological equilibrium is reached. This paper develops a general statement describing the changes to the surface and groundwater hydrology of the wheatbelt of Western Australia between preclearing, the year 2000 and into the future. For typical catchments in the wheatbelt it is estimated that average groundwater recharge and surface runoff have increased about tenfold when comparing the current hydrology to that preclearing. Saline groundwater discharge and flood volumes have also increased significantly. Saline groundwater discharge and associated salt load will probably double in the future in line with the predicted increase in the area of dryland salinity. In addition, future increases in the area of dryland salinity/permanent waterlogging will probably double the volumes in flood events and further increase surface runoff in average years. The outcomes of surface and groundwater management trials have been briefly described to estimate how the hydrology would be modified if the trials were implemented at a catchment scale. These results have been used to formulate possible integrated revegetation and drainage management strategies. The future hydrology and impacts with and without integrated management strategies have been compared.