Sustainable management of groundwaters in dryland salinity affected Spring Creek catchment, New South Wales, Australia

Environmental degradation and salinisation processes in the Southern Tableland of NSW are associated with groundwater discharge from fractured bedrock aquifers causing loss of agricultural productivity. The driving mechanism behind rising groundwater is clearing of native vegetation in the beginning of the last century. Discharging groundwaters from the confined fractured aquifers interact with the overlying colluvium causing erosion, gullying and soil degradation. The upward movement of saline groundwater in discharge zones on foot-slopes and valley floors, together with the mobilisation of soluble salts stored in clay colluvium, are shown to be mechanisms for the development of dryland salinity. Water-rock interaction and hydrogeochemical processes such as reverse ion-exchange in fractured aquifers and ion-exchange reactions in colluvium clays are the dominant chemical processes. The stable isotopes of deuterium and oxygen-18 provide no evidence for evaporative concentration in these shallow groundwaters. Sustainable management of these groundwaters is achieved through the understanding of hydrogeochemical processes in the mixing zone where deep discharging groundwaters are reacting with colluvium.