SWAT BASED ESTIMATION OF SEDIMENT YIELD FROM GUDER WATERSHED, ABBAY BASIN, ETHIOPIA

Abstract

Watershed is considered to be the ideal unit for management of the natural resources. Extraction of watershed parameters using Remote Sensing and Geographical Information System (GIS) and use of mathematical models is the current trend for hydrologic evaluation of watersheds. Soil erosion is a serious threat in the Guder watershed. Deforestation, overgrazing, and poor land management accelerated the rate of erosion. To develop effective erosion control plans and to achieve reductions in sedimentation, it is important to quantify the sediment yield and identify areas that are high contributors of sediment at micro- watershed level and over large areas. In this study SWAT (Soil and Water Assessment Tool) having an interface with ArcView GIS software was used to estimate sediment yield and identify spatial distribution of sediment yield in the watershed. The model was successfully calibrated and validated for measured stream flow and suspended sediment concentration at Guder gauging stations. The calibration and validation result showed that model performance evaluation statistics (coefficient of determination (R 2 ) and Nash- Sutcliffe model efficiency (E NS )) were in the acceptable range (R 2 in the range 0.85 to 0.89 and E NS in the range 0.72 to 0.79). This indicates that the observed values show good agreement with simulated value for both flow and sediment yield. The model prediction result shown that the annual sediment yield leaving the watershed was found to be 5,319,678 ton/yr. It was 5,113,088 ton /yr. by rating curve generation . The model prediction results indicated that about 8.9% of the watershed areas severely eroded with annual sediment load ranging from 18 to 35ton es/ha/yr. and about 21.7% of the watershed area has high erosion with annual sediment load ranging 12 to 17tones/ha/yr. The annual average sediment yield of the watershed was 8.26t/ha/yr. and total of 5.32 m illion tons of sediment yield was leaving the G uder watershed annually. The result of the study could help different stakeholders to plan and implement appropriate soil and water conservation strategies in the watershed.