SILTATION OF DAMS AND RESERVOIRS AND ITS EFFECT ON AGRICULTURAL PRODUCTION IN NORTHERN GHANA: A CASE STUDY OF CHABCHAB IRRIGATION PROJECT, SAVELUGU-NANTON DISTRICT

Abstract

This study was conducted in March 2003 to calculate the rate of siltation of the proposed Chabchab Reservoir in the Northern Region of Ghana. This project concept was developed under Village Infrastructure Project of MoFA in 2001 to serve the needs of some of the communities in the Savelugu-Nanton District. The aim of the work was to suggest the management practices far reduction of high levels of silt carried into reservoirs, which is a common problem with this type of developments in Northern Ghana. The study covered Nyamadu, Dohi, Gunglianyilli and Kpundili communities in the Savelugu-Nanton District, where the Chabchab stream is located. Field data (soil samples, slope measurement, sampling of vegetative cover and rainfall data) were collected from the project site and analysed in the laboratory and further processed using statistical tools. Results of the study revealed that sandy soils predominate in the catchment area and can be easily dispersed. Further, the slope of the land indicates afiat to relatively gentle sloping land, associated with low velocities of water and limited transport of soil material. The vegetative cover of the area is poor and sparsely distributed with large portions of bare ground on cultivated fields during dry season. Direct impact of raindrops received at the start of the rainy season April in these conditions results in soil particle dispersal and its consequent entrainment. Rainfall analysis for the study area showed that high amounts and intensities of individual rainfall events occur in August and September every year. The high intensities result in considerable level of soil particle detachment, which varied with the soil types in the study area. To reduce the level of detachment of soil particles and subsequent transport, improvement, in the vegetative cover of surrounding farmlands around the catchment needs to be taken into consideration.