Assessing the impacts of land use changes on stream flows :

Abstract

The hydrology of most tropical catchments is largely influenced by variations in land use. River Malaba sub catchment is experiencing significant changes in land use, this is adversely impacting the river hydrological flow regimes. The catchment is a transboundary with a total drainage area of about 3500 km2 shared between Uganda and Kenya. Hydrological Engineering Center Hydraulic Modelling Service (HEC-HMS) model was used to assess the impact of land use changes on stream flows in the catchment. Changes in land use on the streamflow were evaluated using land change detection analysis. The highest change in the gain of land were mainly experienced from the agricultural land use (23.61%) and Settlement (2.64%); while the highest loss in land use change were experienced from the Grassland (15.79%) and forests (9.02%) land cover types respectively. Data collected included: - DEM, discharge flow data, land use/land cover data, rainfall data and soil data. These datasets were conditioned and processed in the GIS environment using the ArcGIS software. Land use and soil data were used to generate Curve number grid and later geo. hms was used to set up a project which involved basin characteristics and processing and exported into HEC-HMS to generate hydrograph (peak discharges). The Depth Duration Curves (DDC) were generated for a return period of 50 years that gave peak discharge of 235.0m3/s. In addition to modeling the current land use condition, two land use changes were simulated and the outflow result showed that land use changes can affect streamflow. The results also show that a land management program like reforestation could decrease the risk of high flows in the watershed.