Evaluating The Impacts Of Land Use Land Cover Change On Streamflow And Sediment Yield: A Case Study Of Modjo Watershed, Awash River Basin, Ethiopia

Abstract

Water resources study under watershed level requires hydrological models in order to design, plan and manage the water resources. The main objective of this study is to evaluate the impacts of land use land cover change on stream flow and sediment yield.Modjo watershed is experiencing significant land use land cover dynamics due to urbanization effects and population growth. SWAT model is a semi distributed physically based hydrological model, and GIS and remote sensing application tool is used under this study. The model was calibrated and validated at Modjo gauging station. Highly increasing amount of stream flow and sediment yield has been directly drains to Koka dam which is a major problem the watershed facing. Input parameters are hydrological data (stream flow and sediment yield), meteorological data (temperature, precipitation, relative humidity, and wind speed and sunshine hour), DEM, soil map, and land use land cover map were generated using GIS. Land use land cover classification was done by ERDAS IMAGINE 2014 application for four (1989, 1999, 2009 and 2018) periods. Land use land cover classes of the watershed are agricultural land, shrub land, forest, bare land, built-up and water body. Supervised classification technique using maximum likelihood classifier was applied during classification. The overall accuracy results of the classified images were 87.22%, 90.56%, 91.67% and 89.44%, and kappa coefficient values were 0.82, 0.87, 0.89 and 0.84, respectively for the years 1989, 1999, 2009 and 2018. The performance of the model was evaluated using statistical indices. The statistical analysis of calibration results for Modjo watershed showed satisfactory agreement between observed and simulated monthly values. The model calibration and validation indicates R2=0.76, NSE=0.57, PBIAS= -21.3, for streamflow calibration; R2=0.78, NSE=0.69, PBIAS=16.6, for streamflow validation. Similarly, R2=0.71, NSE=0.71, PBIAS=8.0, for sediment yield calibration. R2=0.86, NSE=0.78, PBIAS= -20.2, for sediment yield validation. Among the 29 sub-catchments, five (sub-catchments 8,7, 9, 25, and 10) produced the highest sediment yield and are more exposed to erosion. The average annual streamflow of Modjo watershed is 416.13mm for 1989 and 487.87mm for 2018, respectively. The mean annual sediment yield of the watershed was 13.93 t/ha/yr and 39.93 t/ha/yr in 1989 and 2018, respectively. In general, the model was capable of simulating streamflow and sediment yield from Modjo watershed.