USE OF SOIL SURVEY INFORMATION TO ASSESS REGIONAL SALINIZATION RISK USING GEOGRAPHICAL INFORMATION-SYSTEMS

Previous experience in southern and western Australia has shown that t ree clearing alters the water balance in a landscape, leading to incre ased deep drainage and consequent rises in phreatic water tables. Asse ssment of the risk of regional salinization involves integration of hy drology, hydrogeology, soil and land management issues. An example of the use of soil survey data, integrated with water resources and digit al elevation data in a GIS, to estimate the risk of salinization after tree clearing is illustrated for the upper Burdekin river basin in th e wet/dry tropics of North Queensland. Soil map unit descriptions incl ude information on soil-landform relations, parent material, soil thic kness, depth to bedrock and dominant and subdominant soil types, Such information can be used to qualitatively estimate permeability and dra inage classes (high, medium, or low) and to determine likely recharge and discharge areas in the landscape. Analysis of the spatial associat ion between surveyed electrical conductivity measurements and estimate d recharge and discharge areas was used to cross-check this qualitativ e classification, The distributions of saline soils and shallow water tables are used to assess the salinity hazard of the region. Where % t otal soluble salts (TSS) are >0.25% and water table <6 m deep, a salin ity hazard is present, This hazard can translate into a salinity probl em if the hydrologic balance is altered so that the salt is remobilize d and redeposited in the landscape, An estimate of the likelihood and amount of increased recharge to groundwater after tree clearing was ob tained using water balance models with soil physical parameters measur ed at key sites, Where physical data were not available, surrogate phy sical properties were estimated from the soil survey data, Results sug gest that tree clearing may increase deep drainage by up to 10 times a nd that in watersheds where shallow unconfined aquifers are present an d where %TSS > 0.25%, recharge areas should not be cleared.