THE IMPACT OF LAND USE LAND COVER CHANGE ON STREAMFLOW (A CASE STUDY OF UPPER GUDER WATERSHED

Abstract

Land use land cover change is altering the hydrologic system of many watersheds. It is also a scientific challenge to predict their effects on streamflow. The main objective of this study was to assess the impact of land use land cover changes on the stream flow of the upper Guder watershed by integrating the Soil and Water Assessment Tool (SWAT) and Geographic Information System (GIS). Within watershed land use is undergoing major changes due to the pressures of human activities. Changes in land use have potentially large impacts on streamflow by causing more surface runoff, decreased water retention capacity, loss of forest, and drying of the river. To address this concern, the selected model must be able to represent the impact of land cover/use on various runoff components. The land cover/use change was evaluated properly using techniques of Remote Sensing to Landsat images; thematic mapper (TM) with the support of historical trends and recent ground-based data. Land-use land cover maps of 1990,2001 and 2017 were developed using satellite images through the maximum likelihood algorithm of supervised classification using Earth Resources Data Analysis System (ERDAS Imagine 2014). The change detection analysis showed that the upper Guder watershed experienced an increase in agricultural land and settlement (by 26.22%, and 0.82%) over the past two decades. However, shrubland, grassland, forest, and water body were decreased (by 14.85%,9.38%,2.64%, and 0.15% respectively) in the same period. SWAT was calibrated and validated for the sensitivity of streamflow parameters. The model closely relates runoff with catchment physical properties in a distributed manner and allows operating at different spatial-temporal scales. The calibrated and validation reasonably reproduced the volume (Model Volumetric efficiency of 0.8 and 0.78) and pattern (Nash-Sutcliffe model efficiency of 0.8 and 0.75) of the observed hydrograph. The watershed had experienced a slight change in stream flow in the study period. The direct runoff had gradually increased and interflow and ground water flow were reduced. Changes in surface runoff were high for the main rainy season. However, the interflow and ground water flow were slightly reduced in the dry season. These changes could be attributed to spatial increases in agricultural land and settlement at the expense of shrub and grass land over the study period.