IMPACTS OF LAND USE AND LAND COVER CHANGE ON WATERSHED STREAM FLOW: CASE OF ABELTI WATERSHED, OMO BASIN, ETHIOPIA

Abstract

The study examined land use land cover changes in Abelti watershed located at upper omo river basin, Ethiopia using SWAT and land use maps for the years 2000, 2010 and 2017 derived from satellite images and processed using ERDAS Imagine 2015 and ArcGIS10.1 software with maximum likelihood algorism of supervised classification. Change detection analysis and accuracy assessment was done after Image processing and classification. The agricultural land, settlements (built up area), forest and water body from year 2010 to 2017 increased from 42.617% to 49.327%, 9.439% to 11.528%, 7.800% to 10.892%, and 0.283% to 0.297% respectively while shrub lands and bare lands decreased from 24.459% to 19.305% and 15.402% to 8.652% respectively .There was significant change in the watershed hydrology due to spatial and temporal change of land use land cover. Surface runoff was very high during wet seasons and very low during dry seasons at different parts of the watershed during the study periods. Accuracy assessment of land use classification by confusion matrix and kappa index for 2000, 2010 and 2017 maps indicated an overall accuracy of 86.04%, 90.75% and 89.71% and kappa coefficient of 0.82, 0.88 and 0.86 respectively and image classification accuracy was almost in strong agreement. Model calibration (2001-2010) and validation (2011-2015) were performed for monthly flow data at Abelti gauging station. The model performance was found very well according to the three objective function results of R2, NSE and PBIAS with values of 0.79, 0.78 and 6.3% for calibration and 0.92, 0.85 and 4.1% for validation periods respectively. Land cover types contributeminimum and maximum surface runoff based on the interception capacity of each land cover types in the watershed. Along with land use/land cover changes, considerable consequences were obtained in the surface runoff of the watershed which was increased from 2000 to 2010 by 19.963% but decreased from 2010 to 2017 by 3.898% due to change of LULC in the watershed whereas soil water content, groundwater flow and interflow were decreased when surface runoff was maximum