Geomorphology

Lake Cowal is located on the fluvial landforms of the Jemalong Plains. The Jemalong Plain is bounded to the east by the Jemalong Range, to west by the Manna anticline and its associated ridge, to the north by the Lachlan River and to the south by the Bland Creek Catchment. The plain has been formed by the fluvial infilling of the Lachlan and Bland Creek paleochannels with sediments of the Lachlan and Cowra formations. The depth of these sediments is over 100 m above the Bland Creek paleochannel and decreases to the east and west and as bedrock ridges are approached. Gravel and sand lenses within the Lachlan and Cowra formation, as well as gravels at the base of the Bland Creek paleochannel are important groundwater stores and conduits and play a major role in the regional groundwater hydrology.

Lake Cowal is underlain by sediments from 1m to more than 50m, which in turn overlie bedrock of the Lake Cowal volcanic complex. In contrast to other sediments of the Jemalong Plain, those beneath Lake Cowal are dominated by dark grey clays suggesting a strong lacustrine influence. These clays extend to the considerable depth of 80 m in the area.