Cost benefit analysis of sediment and sedimentation inselected small dams in Lusaka and Southern provinces,Zambia

Abstract

There are many small dams in Zambia constructed for the purpose of collecting and storing runoff from the catchments. The flow of water into dams is accompanied with sediment resulting from soil erosion within reservoir catchments. The deposition of sediment in reservoirs has implications for their sustainability and thus future water supplies. However, accumulated sediment in reservoirs can be dredged to extend the useful lives of dams. This study aimed at evaluating the burden of sediment and sedimentation in selected small dams in Lusaka and Southern provinces of Zambia. A survey research design was employed to gather data from the sampled dams in Lusaka and Southern provinces of Zambia. A cost-benefit analysis was performed to determine the cost and value of burden of sediment and sedimentation on selected six small dams. A Contingent Valuation of Willingness to Pay was conducted to find out the possibility of local peoples’ support of a possible programme of dredging the accumulated sediment in the reservoirs to restore the lost storage capacities. of the dams. The results of the study showed a clear scenario of the burden of sediment to local communities and the potential restoration of lost reservoir storage capacities to sedimentation. The study established that 25 - 52 percent of studied reservoirs initial water holding capacities had been lost to sediment accumulation in 26 – 60 years of dam operations. The rates of sediment accumulation ranged from 283.92 m3 yr-1 to 29,118.63 m3yr-1, indicating that the surveyed reservoirs had less than 60 years of useful lives beyond the year 2015. Sediment and sedimentation was found to lower the annual benefits from reservoirs intended water uses in monetary terms. The Net Present Value (NPV) for removing and selling the accumulated sediment was found to be high and positive for all the dams while the NPVs for operating reservoirs with sediment in them were found to be low and sometimes negative values were recorded. It is concluded that the studied small dams in Lusaka and Southern Provinces were experiencing severe sedimentation which lowers the benefits from intended dam uses. Because of the high potential benefits that could be derived from sediment, local communities and dam owners should be encouraged to exploit this abundant natural resource in their areas.