Watershed Modelling of Lake Tana Basin Using SWAT

Abstract

The mam purpose of this study was mainly to accurately estimate the inflow components of Lake Tana from both gauged and un-gauged catchments for water balance modeling. Distributed physically based hydrological model known as soil and water assessment tool (SW AT) has been applied. The model was calibrated and validated over the gauged upper reaches of major catchments of Gilgel Abay, Koga, Gumera, Rib and Megech. The model was calibrated for the period from 1996-2001 and validated for the period from 2002-2004. The performance of the model was evaluated on the basis of performance rating criteria, coefficient of determination, Nash & Sutcliff efficiency, and percent deviation. The overall performance of the model appears satisfactory. The R2 for all catchments vary between 0.69 to 0.89 during calibration and 0.81 to 0.86 during validation. The hydrograph fit between the estimated and observed is also adequately represented except the underestimated, which stands out for Gilgel Abay, Gumera and Megech catchments for the year 2003. The year 2003 has been underestimated due to many missed rainfall data of the surrounding stations. The Curve Number (CN) has been found the most sensitive parameters m all the catchments indicating the importance of this parameter during modeling and fine tuning. However, the level of sensitivity of this parameter differs from catchment to catchment.