The Central Plains of the Western Davenport is underlain by a layered sequence of Palaeozoic aged rocks that dip gently to the south west.They are faulted against older Proterozoic rocks on the south west margin of the plains but unconformably overlie them on the north eastern margin. The sub-surface geology is relatively well known in the central part of the plains but it is less well known in areas remote from the Stuart Highway due to sparser drilling data.
There are five geological layers with distinctive hydrogeological properties; the Lake Surprise Sandstone, Dulcie Sandstone, Arrinthrunga Formation, Chabalowe Formation and Cenozoic alluvial deposits. The Hanson River beds and the Tomahawk Formation have been grouped with the first two respectively. Each formation constitutes separate aquifers but because they are considered to be interconnected to varying degrees in many areas, the whole sequence is referred to as the Central Plains aquifer system. Two of the aquifers, the Chabalowe and Lake Surprise, are capable of producing moderately high bore yields of the order of 30 L/s.
Recharge to aquifers is episodic and not spatially uniform. It is mainly related to ephemeral streams that drain the adjoining ranges and flood out onto the Central Plains. Historic groundwater monitoring data shows that over the past 50 years there have been only three notable recharge episodes in response to substantial rainfall events. Distributed recharge may occur in areas where the main aquifers outcrop or are near surface. Northern Neutral Junction, west of Taylor Creek and on northern Murray Downs are two areas flagged as potential sites where this recharge mechanism occurs.
On a regional scale the groundwater flows south to north and the watertable depth generally shallows northwards. There are no known permanent groundwater discharges to the surface via springs or stream bed seepages but groundwater discharges to the surface via evapotranspiration (tree water use) in areas in the north where watertables are shallow enough to be available to tree roots.
A “Groundwater Resource Risk” Map is presented here. It categorizes the Central Plains Aquifer into four risk categories for the development of irrigated agriculture. They are based on properties of the aquifers and of the groundwater including the capability of the aquifer to supply water, the depth of the watertable and groundwater salinity.,
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