Hydrogeological Investigation of the Fate of Salt Mobilised Under Dryland Cropping on the Cryon Plain, North Western NSW

Client: NSW Department of Primary Industries
Year: 2007
Project Reference: 06054
WRL Technical Reports: Hydrogeological Investigation of the Fate of Salt Mobilised under Dryland Cropping on the Cryon Plain, North Western NSW; Interim Report (2007/38); Final Report (2008/10)

Salinity is a serious issue for land and water management in north-western NSW. Analysis of soil cores taken from cropping paddocks alerted NSW Department of Primary Industries (DPI) to salinity concerns in the Walgett district. Many soils from this region have high salt loads close to the surface (20-200 t salt/ha in the surface 5 m). With cropping paddocks shown to be leaking more than 5 mm water per annum through the surface soils, surface salt is migrating downwards via deep percolation. The fate of this saline drainage and its potential extent over time and space is a major concern for landholders in the area.

In 2007, WRL was commissioned by the DPI to investigate the hydrogeology of the Walgett region, focussing on the mobilisation, flow and discharge of salt. The work included drilling of new bores, geophysical investigations, monitoring of water levels, salinity monitoring, groundwater sampling and analysis, and groundwater modelling. It was found that storage of salts in the unsaturated zone was highly variable between sites, and with depth. Deep drainage below the root zone will recharge shallow aquifers and mobilise salts in some areas on the plains. Already, salt in the soil and vadose zone has been transported down into groundwater at some sites. In the area of study, it was found that while deep drainage may impact on groundwater, it will not affect nearby surface waters. The implication of this study for dryland cropping in the Cryon Plain is that while leaky areas can occur within localised areas of paddocks, cropping of these areas will not impact nearby surface water.