SIMULATION OF HYDROLOGICAL PROCESSES USING SWAT+: A CASE STUDY OF GUDER WATERSHED, ABAY BASIN, ETHIOPIA.

Abstract

Global environmental change, such as climate change, land use and land cover change is noticeably influencing hydrological processes. The Guder watershed which is found in the south eastern side of the Blue Nile Basin embraces most of the steep and long slopes of the basin. The SWAT+ is a new restructured version of SWAT that offers greater flexibility in connecting spatial units and capable to more realistically represent hydrologic connectivity within a watershed. In this study, SWAT+ Tool box was used to calibrate and validate a hydrological component on Guder river gauging station. Meteorological and hydrological data used for this model collected from National meteorological agency (NMA) and Ministry of water and energy (MoWE) respectively. Model calibration for the period (1992-2003) and for validation period (2004-2009) within 2 warm up period were simulated and get the final result, while doing this you can checked the model performance by the value of statistical parameters changed in both stream flow and sediment yield. The coefficient of determination (R2 ), Nash-Sutcliffe efficiency (NSE) and Percent of bias PBIAS) was used to evaluate model performance. The modeled performed in the acceptable range (R 2=0.82 and 0.85, NSE=0.73 and 0.83 and Pbias=2.23% and 5.6%) during calibration and validation respectively in the stream flow. Also, for sediment yield R2=0.83 and 0.86, NSE=0.76 and 0.79 and Pbias=2.45% and 3.6% during calibration and validation respectively. The results revealed that, the model showed a fairly good and satisfactory agreement between monthly observed and simulated streamflow and sediment yield respectively. A maximum annual average sediment yield was attributed due to topographic slope and land use of this sub basin. Guder watershed contain 33 sub basins, from those sub basin 11 was the highly affected (hot spot area) produce 46.783 ton/ha/yr. Generally, Guder watershed was generating average annual sediment distribution ranges from 0.798 ton/ha/yr to 46.783 ton/ha/yr. This can be reduced by using sediment yield intervention strategies such as land slope stabilization, construction bench terraces (stone bund), changing the land use of steep area and afforestation. Due to the lack of observed data the calibration and validation of the evapotranspiration was not done. But from the simulated data the distribution of evapotranspiration in each sub-basin was analyzed. To minimize the environmental change related to the drought, analysis of evapotranspiration in each sub basin was done.