HYDROLOGICAL MODELING OF GILGEL ABAY RIVER BASIN, ETHIOPIA USING SWAT

Abstract

problem of soil erosion and land degradeation is crucial in Ethiopian Highlands. This is mainly caused due to poor management practices, lack of adoption of soil conservation measures and poor land-use practices. In recent time a large amount of forest area has been converted to the urban area or agricultural land. For this study SWAT2012 was applied. SWAT model remains a public domain model and a physically based hydrological model it is used for free. In a country like Ethiopia one of the major problems is the scarcity of long term measured data series, the main advantage of the SWAT model is required minimum data. In this study the soil and water assensment tool (SWAT) was integrated within a ArcGIS which is called ArcSWAT 2012 to simulate surface runoff generation and soil erosion of Gilgel Abay river in Ethiopia. The total catchment area of Gilgel Abay river basin is 4016 km2. The main objective of this study was To calibrate and validate the SWAT model, in the Gilgel Abay river basin. to test the performance and feasibility of the SWAT model for prediction of streamflow and sediment outflow in the Gilgel Abay river.and To identify the most sensitive model parameters affecting water and sediment yield by performing sensitivity analysis for the basin. The SWAT model was calibrate for 8 years from (1995 – 2002) on daily and monthly basis. And validate for 5 years from (2003 – 2007) on daily and monthly basis using SUFI-2 algorithm. RCHRG_DP.gw, GW_DELAY.gw, CN2.mgt, and ESCO.hru.are the furthermost sensitive parameters. The most sensitive parameters. The evaluation of the model was checked by graphical and statistical methods. In graphical methods, the visual match of observed and simulation of flow and sediment was fitting good. The statistical evaluation in monthly basis of (R2 = 0.91, NSE = 0.91, PBIAS = 0.7, and RSR = 0.3 in calibration period and R2 = 0.84, NSE = 0.84, PBIAS = -3.6, and RSR = 0.4 for validation period). And the result of daily basis of (R2 = 0.71, NSE = 0.69, PBIAS = 20.8, and RSR = 0.56 in calibration period and R2 = 0.61, NSE = 0.58, PBIAS = 9.9, and RSR = 0.65 for validation period). from computed suspended sediment of the study area at Chinba Station calculated general mean annual sediment out from the whole basin was 382312.0822 tons in the period of 2014 – 2016 based on daily values.