Evaluation of the impact of land use change on catchment hydrology: the case of Wundanyi river catchment in Taita Hills, Kenya

Abstract

The conversion of forest land to agricultural land and urban settlement usually increases soil erosion, and volume of storm runoff in a catchment. In Kenya, the rural communities are encroaching into the humid and marginal areas to open up new lands for agricultural production and settlement. These changes have led to environmental degradation, which has negatively altered the hydrologic regimes of many catchments in Kenya. The Wundanyi River catchment is one of the catchments that have undergone rapid land use changes over the last 30 years. It requires intervention to improve and sustain hydrologic processes to prevent further degradation. However, the catchment lacks continuous records for hydrologic data that can be used. Therefore, there was need to apply remote sensing and modelling approach in getting hydrological data for this catchment for analysis and management. The study applied the Soil and Water Assessment Tool (SWAT) model to evaluate the impact of land use change on the catchment hydrology. The input data used included digital elevation model (DEM), land use maps, soil maps and rainfall. Changes of land use in the catchment were characterised and quantified using remote sensing and GIS. The land use evaluation results showed that the agricultural land and built up area increased by 10% and 156% respectively between 1975 and 2004, while the forest land cover reduced by 57%. Simulation of land use change scenes showed that average annual surface runoff and sediment yield increased from 8.74mm to 99.30mm and 0.43t/ha to 20.10t/ha, respectively. These findings can be used by catchment stakeholders and policy makers to address challenges resulting from catchment degradation. This research will further help in making informed decisions in selecting and developing viable catchment management options that will promote sustainable utilization of land and water resources within Wundanyi River Catchment.