Water Supplementing
In an overused system where water use or allocation is greater than 70% of sustainable yield important water users such as the environment can sometimes not receive their water requirements. Water supplementing takes water from one source (groundwater or surface water) and uses it to augment another source. Because of the cost involved, water supplementation can generally only be used for a short period of time depending on the needs of targeted users such as the environment (during spawning season) or irrigators (growing season). It can take a number of forms such as using groundwater to increase flow in rivers, using surface water to maintain a high water table in ecologically important regions or injecting water near groundwater dependant ecosystems.
Groundwater to Increase Surface Water Flows
In areas with a heavy reliance on surface water for consumptive use, it may be necessary to maintain river levels by pumping groundwater and then adding it to the river. It is probably only an option in poorly connected systems or systems with a long lag time in the responses between groundwater and surface water. In a highly connected system, the decline of the water table due to pumping would increase the loss of the river into the groundwater system and be counterproductive. Because of the cost associated with such a scheme, pumping can only be carried for short periods to maintain water levels during extreme low-flow conditions.
Water to Maintain Groundwater Dependent Ecosystems
In regions of high groundwater extraction, it may be viable to maintain high value groundwater dependent ecosystems (GDEs) by injecting water (from any source) near the ecosystem to artificially maintain a high water table. On a map showing the potentiometric surface of the water table, the area in the vicinity of the GDE would be totally enclosed by contours and look like an island. This technique has been trialled in the Great Artesian Basin near the Bopeechee Springs by Western Mining (Mudd, 2000). While there was some increase in the pressure surface around the injection bore, the number of vents and the size of the wetlands surrounding the springs did not increase (Mudd, 2000). Also, Australia has a rich diversity of cave fauna in Tasmania, Western Australia, and the Nullarbor. Due to the isolated nature of the cave environment they are particularly susceptible to disturbance. Lowering the water table in a karst environment can cause the extinction of rare and vulnerable cave fauna and threaten the stability of the cave system itself. In Western Australia, water supplementing has also been used as a temporary measure to maintain water levels around the Yanchep Caves region (WRC, 2003). Heavy use of groundwater in the region has lowered the water table threatening vulnerable cave fauna and speleothems.
Relevant Links
Cave Research Foundation
UK Environment Agency Shropshire Groundwater Scheme. Using groundwater to maintain flow in the River Severn [PDF 2.1MB]
References
Mudd GM, 2000. Mound Springs of the Great Artesian Basin in South Australia: a case study from Olympic Dam. Environmental Geology, March 2000, 29(5), Springer Verlag
WRC, 2003. EPA Progress Report 2003- Section 46 Review of Environmental Conditions on Management of the Gnangara and Jandakot Mounds. Water and Rivers Commission http://www.wrc.wa.gov.au/PDF/EPA_Progress_Report_2003.pdf [PDF 3.9MB]