Study of groundwater flow in sediments and regolith defined by airborne geophysical surveys

Abstract

An airborne electromagnetic survey over the wetlands north of Esperance was interpreted to assist in defining the groundwater conditions within the surrounding floodplain and its influence on Lake Warden. The study shows the Esperance Floodplain is underlain by sediments of Eocene age deposited in shallow marine conditions onto an undulating granitic, gneiss basement. In the western part of the study area, surface water flow is directed towards Lake Warden from areas of shallow basement above the escarpment. Subsurface drainage is interpreted to flow towards Pink Lake. A continuous basement ridge forms the north side of Lake Warden. The Eocene sediments are thicker towards the south of the lakes and the undulating basement surface has a regional dip towards the east. Deep drainage is indicated from the main lakes into Esperance Bay in the region west of Bandy Creek. Deep drainage from Lake Warden probably also occurs in the northeast of the lake along the direction of the gneissic banding. Small islands of granitic basement poke through the sediments in the region around Windabout Lakes and a more continuous north-south barrier appears to partially separate the east part of the floodplain from the west in the area west of Station Lake. In the eastern parts of the catchment under an area of parabolic dunes, the EM data indicates a deep palaeochannel joining the Neridup area with the sea. This may be part of the Cowan Palaeochannel. Drilling into the edge of this structure showed it is under artesian pressure and some upward seepage may be expected. Deep parabolic sand dunes cover most of the palaeochannel on the floodplain but seepage may occur along the edge of the dune field. High salt storage is indicated under the major lakes and in the eastern parts of the catchment.