SWAT BASED ASSESSMENT OF LAND USE LAND COVER IMPACT ON STREAMFLOW OF WOYBO RIVER CATCHMENT, SOUTHERN ETHIOPI

Abstract

Land use land cover changes of an ecosystem should be significantly studied, assessed and controlled by any means to cooperate with sequential progress of mankind. This study examined land use land cover changes in Toyboy river catchment located at Mo gibe river basin, Southern Ethiopia with the aim of LULC classification, streamflow modelling in relation with LULC changes of different decades and identifying sub basins of maximum and minimum contribution of surface runoff using ArcGIS 10.3 with its extension ArcSWAT and ERDAS Imagine 2015 with maximum likelihood algorism of supervised classification. Change detection analysis and accuracy assessment was done after Image pre-processing and classification. Significantly; from year 1992 to 2013, both agricultural land and settlements increased from 24.5% to 41% and from 1.02% to 32% respectively while forest and grass lands decreased from 25.4% to 6.7% and from 15.1% to 5.5% respectively. Accuracy assessment of land use classification by confusion matrix and kappa index for 1992, 2000 and 2013 maps indicated an overall accuracy of 87.8%, 80.8% and 90.5% and kappa coefficient of 0.88, 0.8 and 0.9 respectively and image classification accuracy was almost in strong agreement. Model calibration (1999- 2009) and validation (2010-2015) were performed for monthly flow data at Woybo gauging station. The model performance was found very well according to the three objective function results of R2 , NSE and PBIAS with different LULC. Hence it is 0.76, 0.75 and 1.8% for calibration and 0.75, 0.74 and -1.5% for validation. Considerable consequences were obtained in the surface runoff of the watershed which was increased from 1992 to 2000 by 7.4% and from 2000 to 2013 by 10.5% due to change of LULCwhereas soil water content, groundwater flow and interflow were decreased when surface runoff was maximum. Due these results, there is some sort of recommended works for the future studie