IMPACT ASSESSMENT OF LAND USE I LAND COVER CHANGES ON SHAYA RIVER FLOW USING SWAT (Case Study of Shaya Watershed, ln Bale)

Abstract

In developing countries like Ethiopia where there is ever-increasing population pressure, there is a continuous LULC changes. The continuous land cover changes can have impacts on the environment and the water resources. Therefore, to safeguard and minimize environment from degradation, identifying the impact of LULC on the environment and water resources are very crucial. Likewise, LULC changes and their impacts that occurred for the years 197'.i to 2001 in Shaya watershed of an area 703 . 80 CD km2, and its surroundings were monitored using remote sensing and geographical information system (GIS) with field verification. " The. a_im. of this study is therefore, to utilize a hydrnfogic.al model that can be used to deter�ine the hydrologic�LrespJ;>fises of Shaya watershed to the LULC changes. Landsat images ofMSS 1973, TM 198� and ETM 2001 were classified using ERDAS IMAGINE 8.7 software and finally used for the extraction of LULC changes. The hydrological model that was used for determining the impacts of LULC changes on the river Shaya was SWAT. To use SWAT, different inputs were used in the model and different simulations were conducted .In the first automatic simulation, the s�itivity analysis was conducted using the governing paramete�, automatic and manual calibration was done in so many tries to confirm the simulated and the observed flow fit each other. During the processes, simulation and validation were conducting under different periods and L-- irrespective of same data .In these two methods of model testing, the good fitness of -��imulated with observed flow data was tested by statistical model efficiency indicators. �· From the image classification, the LULC change result indicates that it did not show .. �,...co�tinuous trend, which shows both decreasing and incr easing trends. For impactv assessment, 1 4 parameters were identified during the s�tivity analysis. Accordi ngly, the model efficiency indicators, coefficient of determination (r2) greater than 0 . 60, Nash- ... Sutcliffe (ENS) greater than 0 . 5 0 and Percent of difference (D) less than +25% results were obtained in both calibration and validation tests. M.Sc Thesis November,2009 VI Impact Assessment of Land Use I Land Cover Changes 011 Shaya River Flow In the watershed of study area, the impacts of L ULC were tested in terms of fl � changes \.,- and it was observed that there was a flow change due jo.Jand cover changes. Based on this more than 15% flow variation was obtained in some sub-watersheds where high land cover changes occurred and less than 15% flow variation was obtained in some sub­ watersheds where less land cover changes occurred using land uses of different periods. From the flow variations, it was identified that where the sub-watersheds show more than 15% flow changes, the sub-watersheds are considered to be vulnerable to impacts of L ULC changes. Generally, the SW AT was found to be very useful in determining the impacts of LULC changes on stream flow in Shaya watershed and thus it can be promising to apply in the other nearby watersheds (tropical)