Assessment of impact of land use change on sedimentation in river Manafwa.

Abstract

Sedimentation is one of the biggest threats to river ecosystems around the world. Sediment deposition reduces their storage capacity as well as river flows. Several rivers in Uganda, including River Manafwa experience sediment related challenges. These challenges include reduction in water quantity and quality, flooding and damage to bridges and culverts. This study sought to investigate the effect of land use change on sedimentation in River Manafwa. The study used the Universal Soil Loss Equation (USLE) model, Geographical Information Systems (GIS) and remote sensing to estimate sediment load in the river. Land use maps were developed in the ArcGIS software and categorized into natural vegetation, bareland/farmland and built up area. The land use change from 2008 to 2018 was established & the correlation between sedimentation and land use change in the River Manafwa catchment was then determined. The study established that the River Manafwa catchment loses 7% of its natural vegetation every year. The bareland/farmland was found to have increased by 30% over the study period and the built up area increased by 800%. The estimated sediment yield in River Manafwa increased from 648,447 tons in 2008 to 2,988,378 tons in 2018. This study established that for every 7% decrease in natural vegetation within the catchment, the sediment yield increases by 36%. The sediment yield is expected to continue rising in the river over the next 10 years with the current rate of land use change. This study recommends that catchment restoration measures, safe farming practices and riverbank protection should be implemented in order to reduce sediment yield in the river.