Sedimentation and its effects on selected small dams east of Lusaka, Zambia

Abstract

In Zambia, the need to conserve water resources has resulted in the construction of small dams. However, small dams are adversely impacted by sedimentation. The aim of this study was to assess the water storage capacity loss for the selected small dams east of Lusaka Zambia. These included Lwiimba, Silverest, Morester and Katondwe dam. Data was collected by bathymetric survey for each small dam using hydrographic boat with echo sounding. The initial storage capacity data were collected from the dam owners and through interviews with key informants on the effects of sedimentation on dam uses and on the existence of sediment control measures. Results of the study revealed that the measured reservoir storage capacities in year 2015 for Lwiimba, Silverest, Morester and Katondwe dams were 101,051.43 m3, 379,480.00 m3, 14,724.88 m3 and 10,714.88 m3, respectively. The estimated rates of sedimentation for Silverest was 14,595.40 m3yr-1; Lwiimba (2,200.99 3yr-1); Katondwe (283.92 m3yr-1), and Morester (251.01 m3yr-1). These rates of sedimentation has led to reservoir capacity storage losses of 99,044.57 m3; 379,480.5 m3; 13,805.68 m3 and 9,937.12 m3 for Lwiimba, Silverest, Morester and Katondwe, respectively, with the general consequences of reservoir drying especially in the dry season. Natural vegetation is the main sediment control measure used in the catchments. It is concluded that the studied small dams East of Lusaka are seriously affected by sedimentation. This calls for periodic dredging of deposited sediment in order to increase reservoir storage capacity for sustainable use of the water resource in small dams’ impoundments. Key words: sedimentation, bathymetric survey, small dam, reservoir capacity, erosion