Evaluation of land-management options for dryland salinity: the next step after airborne geophysical interpretation

Abstract

Dryland areas affected by salinisation are rapidly expanding in the Murray-Darling Basin. Airborne geophysical methods promise information that is highly valuable to the characterisation of a salinised catchment. This paper presents a modelling approach that is well suited to apply this information. The approach models catchment salt and water balance with land management as an input and thus allows comparison of the effects of different land-management options. A model of vertical soil-water movement and solute transport is coupled with a groundwater model. The approach accounts for the effects of depth to water table and soil salinity on vegetation water use. The groundwater model estimates lateral flow from groundwater recharge areas to discharge areas. The modelling approach is demonstrated using a study area at Kialla East near Shepparton, Victoria. The area has shallow water tables, low aquifer hydraulic conductivity, and an average land surface gradient of 1 m/km. The implications of the results for land salinisation processes are discussed. The results indicate that a location where a net groundwater recharge occurs under annual pasture is likely to become a net groundwater discharge area when trees are planted. In addition, to be effective, the establishment of improved land-management options would have to be widespread and would be very expensive in dryland areas where productivity is often low. In future, the use of the modelling approach and airborne geophysical measurements will offer land managers a calibrated evaluation of the effects of different land-management options.