SILTATION OF THE RESERVOIR OF VEA IRRIGATION DAM IN THE BONGO DISTRICT OF THE UPPER EAST REGION, GHANA

Abstract

The Vea Irrigation Dam was constructed in 1980 to promote the production of food crops in the dry harmattan season. Thirty three years after construction, this study was conducted to assess the level of siltation in the reservoir and farming practices that impacts siltation within the catchment. Ten soil profiles, five on either banks of the reservoir and each of surface dimensions 1.2 m x 1.2 m were dug in the reservoir 30 m away from the water to ascertain the depth of soil sediments. Average depth of sediments was multiplied by the area of reservoir to obtain the volume of deposited sediments, from which annual depositions were estimated. Eighty (80) farmers in the four fringe communities within the catchment (Vea, Gowrie, Kunkua, and Kuyelingo) were purposively sampled and interviewed. At an average depth of 1.1 m, total deposit of about 140000 m3 of sediments into the reservoir should be a cause for concern. Conventional tillage and continuous grazing, practiced by majority of farmers along the steep slope of the dam’s upstream have direct influence on erosion and hence siltation of the reservoir. High intensity rainfall with high kinetic energies, recorded in the months of June, July, August and September results in considerable level of detachment of the already erodible soil aggregates, which contributes to erosion and subsequent siltation of the reservoir. Whilst vegetative cover reduces direct impact of rain drops, these are scanty and scattered: exposing the bare soil to erosion. In order to save the dam and its reservoir from short lifespan as a result of massive siltation, soil conservation measures, and Best Agricultural Management Practices on watersheds are recommended to local farmers within the catchment area.