The effectiveness of management options for dryland salinity control at Wanilla, South Australia

Abstract

A calibrated groundwater flow model was used to assess several options for management of dryland salinity at Wanilla on Lower Eyre Peninsula of South Australia. The management options were chosen as potentially able to rectify the hydrological imbalance produced by the clearing of native vegetation which will reverse the salinisation process. The model predicted that current agricultural practices will result in groundwater levels continuing to rise in saline areas over the next 20 years (although tending towards equilibrium) increasing soil salinisation. As groundwater levels rise seepage of groundwater to the local drainage (natural) line will also increase, flowing down-gradient towards the catchment outlet and a seasonally flooded lower lying basin. A 50–90% reduction in catchment recharge, achieved with improved management of existing crops and establishment of perennial pastures, is predicted to reduce groundwater levels across the catchment over a 10–20 year period. This will lead to recovery of saline areas and lower baseflow. However, the model predicts that management of recharge needs to be implemented at least at the catchment scale to be effective. Treatments at the sub-catchment scale (e.g. property) have limited impact. Short term benefits (less than 1 year) can be gained from pumping groundwater from a high transmissivity zone close to discharge area. Groundwater levels are lowered over a small area leading to less evaporative discharge and reduced salt accumulation in the root zone. This option needs to work in conjunction with longer term management such as recharge control.