Influence of land use change on sediment yield: A Case study of Kiboko catchment, Kenya

Abstract

The Kiboko River catchment has undergone tremendous changes in land use in the recent past which is suspected to have impacted negatively on status of the soil of the catchment. The study examines the land use change pattern and quantifies its effects on the sediment yield production in the catchment, using Soil and Water Assessment Tool (SWAT) model. The changes in the land use were quantified through a comprehensive land use change detection carried out between 1980 and 2009 for Kiboko Catchment, using Geographic Information Systems (GIS). This was achieved through analysis of land use maps for 1980, 1986, 2000 and 2009. The results showed that both Irrigated and Rainfed land increased from OHa (0%) in 1980 to 395Ha (0.1%) and 16,955Ha (3%) in 2009 respectively, while shifting cultivation, rangeland, and residential land increased from 10,784Ha (2%), 568,7657Ha (88%) and OHa (0%), in 1980 to 16,955Ha (3%), 574,502Ha (89%), and 773Ha (0%) in 2009 respectively. In the same period, agro-pastoralism decreased from 66,206 Ha (10%) to 22,680Ha (4%). The SWAT model was used to simulate the effects of land use change on sediment yield in Kiboko catchment (20.8 km2) using 24 years of meteorological records. The Digital Elevation model (OEM), Land use map, Soil map and Weather attributes were prepared and classified in ArcSWAT as model input and used to predict sediment yield for the catchment. The model was calibrated for the period 1987 through 1988 and validated from 1996 to 1997 based on observed monthly flows of River Kiboko. The coefficient of determination 2 (R ), Nash-Sutcliffe (ENS)and graphical technique were used for comparing observed and simulated flows to evaluate model performance. The results indicated that the 2 model performance was average for the selected gauging station (R = 0.51 and ENS= 2 0.05) for calibration and (R = 0.50 and. ENS= 0.70) for validation period. The calibrated model was used to predict the effect of changing land use on sediment yield within the basin. The results indicated that change in land use during 1980-2009 period lead to an increase in sediment load-of 0.16 tons/ha per year to River Kiboko. The study shows that the changes in land use significantly resulted to an increase in sediment yields

which will lead to increased sediment load to the river and water reservoirs resulting to reduction of the storage capacity and enhancing environmental degradation. Study of the land use change and their effects on sediment patterns for the catchment level are essential in water resource planning and management.