6. A GIS-Based Estimation of Soil Loss in the Densu Basin in Ghana

Abstract

Distributed erosion simulation models are useful in evaluation of different strategies for land-use and soil management improvement in watersheds. The increased soil erosion in Densu basin of Ghana has led to siltation of the river channel that is causing flooding in some parts of Accra, Ghana. The most urbanized basin in Ghana, Densu, supplies water to 600,000 people, with agriculture employing about 40% of the active population. A PCRaster GIS soil loss risk maps have been developed for Densu basin using models of Universal Soil Equation (USLE) and Revised Universal Soil Equation (RUSLE). Soil loss factors such as rainfall erosivity, soil erodibilty, slope and slope length were also mapped for the basin. The model predicted average, minimum and maximum annual soil loss rates of 2.2, 0, and 63 t ha^–1y^–1 , respectively, indicating that some areas in the basin are above tolerance level of 5.0 t ha^–1yr^–1. The total soil loss was 756,507 tonnes per hectare per year. Among the soil types Lixisols experienced the highest soil loss of 402,080 t ha^–1 yr^–1 with Plinthosols experiencing the lowest soil loss of 64 t ha–1 yr–1. Among the administrative districts in the basin Suhum, Kraboa and Coaltar  experienced the highest absolute soil loss of 216,957 t ha^–1 yr^–1 while Fanteakwa experienced the highest average soil loss of 4.5 t ha^–1 yr^–1. The results can serve as data and information to water resources managers and soil conservationists.