Interactions between perched and deeper groundwater systems in relation to secondary, dryland salinity in the Western Australian wheatbelt: processes and management options

[Truncated] This thesis examines the physical processes responsible for secondary, dryland salinity resulting from perched and deeper groundwater systems in the wheatbelt of Western Australia. It also details a range of management options available for the reclamation of salt-affected land. The role of an ephemeral, perched aquifer in streamflow generation, and the nature and hydraulic properties of the deeper aquifers, are also investigated. Fourteen catchments ranging in size from 10 to 130,000 ha were instrumented, and management options including tree planting, shallow drainage and aquifer pumping were assessed. It was found that in the western, wetter areas (~500 mm/yr mean rainfall), the ephemeral perched aquifer was not the source of salt responsible for saline seeps, but provided recharge to the deeper system and was the major agent in the initiation of streamflow. In some drier (~350 mm/yr), eastern wheatbelt areas, characterised by deep (< 8 m) sandplains where a perennial, perched aquifer has developed, the perched aquifer was found to be the sole cause of saline areas. These areas are termed sandplain seeps. This perched aquifer was also found to recharge the deeper system. Reclamation of the sandplain seeps was achieved by installing conventional deep drains and by planting eucalypts to intercept groundwater before it was able to discharge downslope. At the sites studied, reclamation of sandplain seeps was achieved within one and three years. The reclamation method is suitable for at least 10% of the wheatbelt's currently salt-affected land.