DOGRAMACI Shawan, and RUPRECHT John
Water and Rivers Commission, 3 Plain Street, East Perth WA, 6004 email:shawan.dogramaci@wrc.wa.gov.au
The management of the water resource of the Wellington Reservoir located in the Collie River catchment presents an ideal case study of the conflict between land use and water resources management. The salinity of the inflow to the Reservoir has increased four-fold for a median flow year from < 280 mg/l in 1945 to ~ 1000 mg/l in 1992. The human-induced land use change of replacing deep-rooted native vegetation with annual agricultural plants has altered the natural water balance in the catchment, increasing the recharge rate. The change to the water balance has caused a substantial rise in groundwater levels resulting in land salinisation and seepage of saline groundwater into the Collie River.
A multi-criterion analysis of the potential options to lower salinity to ~ 550 mg/l by 2015 considering the hydrogeological setting, as well as economic, social and environmental impacts, was carried out. The study presented 13 potential options addressing reduction of recharge by re-planting trees and deep-rooted perennials, enhancing discharge by groundwater pumping, and engineering work such as diversion of saline water. The study showed that diverting the highly saline early winter and late summer flows into abandoned mine voids in the catchment is the most viable option as a short-term solution (1-5 years). A combination of groundwater pumping to lower the watertable and the partial diversion of saline early winter flow is considered to be a mid-term solution (5-10 years). In the longer term, however, new farming systems that will be both sustainable and acceptable to the stakeholders will need to be developed.