Nield, S.P., and Townley, L.R. (1987), Study of Water Levels in the Capel Wetlands, UWA Environmental Dynamics Reference WP-87-034, 25 pp., August 1987; also published as AMC Wetlands Centre Technical Report No.6.

Over the next 3-5 years, AMC plan to develop their Capel lakes site as a recreational area and a habitat for waterbirds. Some tree-planting work has already been done, and additional work is expected to include more tree-planting and landscaping. The development strategy, however, is dependent on research now being done, of which this report is one part.

The depressions forming the lakes have been created by volume loss due to mining of mineral sands. Water is discharged from a processing plant into the northernmost end of the lake system. At the southernmost end, a weir is used to control the flow of water down a channel to mining operations, which are progressing southward, or into the Ludlow River at times of peak flow. One of the main thrusts of this study is to determine the effect on the lakes after processing is terminated and discharge of effluent from the plant ceases.

It is estimated that water table levels in the area have risen by 1 or 2 metres since mining operations began. This rise may be partly due to discharge from the plant. Another factor which may be equally or even more important has been the clearing of large areas around the lakes, which could contribute to a raised water table via reduced transpiration and interception. It is also possible that the altered permeability of the replaced soils in the mined areas has had an effect on the water table shape. The relative importance of these factors needs to be determined to develop a strategy for maintaining present water table and lake levels after re-vegetation and termination of discharge from the plant.

Water levels in Bentley swamp, which lies adjacent to the lake system on the western side, have increased in recent years to the extent that some tea-trees in the swamp were in water all year around.

The objectives of this research were to determine the factors which control water levels in the Capel Wetlands, and in particular to attempt to predict the effects of reduced inflows and/or outflows. The finite element model AQUIFEM-N (Townley, 1987) has been implemented to model flows in the area. Water residence times have been estimated using volume flow relationships.