ASSESSMENT OF RESERVOIR SEDIMENTATION OF IRRIGATION DAMS IN NORTHERN GHANA

Abstract

Sedimentation in reservoirs of irrigation dams is a serious issue that threatens their functionalities. Since information on this phenomenon in irrigation dams in northern Ghana is almost nonexistent, a study was necessary. The study used bathymetric survey integrated with geographic information systems (GIS) tools to assess reservoir sedimentation of 9 irrigation dams in 3 northern regions of Ghana. The bathymetric survey was conducted during August–October 2017 using a hand-held Hondex digital depth meter. Reservoir depths at full supply level were found to range from 0.10 to 14.70m. The volumetric storage capacity loss in the reservoirs ranged from 0.1 to 7.94Mm3, while the percentage storage capacity loss ranged from 8.54 to 34.12%. The reservoirs were found to be losing volume by 0.26–0.91%/yr. The water surface area of the reservoirs lost due to sedimentation ranged from 5.53 to 24.10%. Estimated mean annual sediment load and sediment inflows into the reservoirs ranged from 3159 to 12,850mg/L and from 1594 to 355,017m3/yr, respectively. Estimated useful life of the reservoirs ranged from 22 to 160yr. All the reservoirs except Bontanga and Tono had a well-formed delta and slightly formed tapering deposits. Major causes of the sedimentation were observed to be mainly human activities within the reservoir catchments. Enactment and enforcement of bylaws to restrict farming, burning, and sand/gravel mining activities in the buffer zones of the reservoirs are necessary to reduce the rate of sedimentation. Improved catchment management practices, construction of check dams, installation of hydrosuction sediment-removal systems, and periodic desilting are also recommended.