A Thesis submitted to School of Graduate studies, ArbaMinch University in partial fulfilment requirements for the degree of masters of Science in Hydrology and Water Resources Management.

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 R 2 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. The calibrated parameters were transferred to un-gauged catchments to estimate the ungauged flow contribution based on similarity of the hydrologic response unit (HR Us). The model output indicates that, the annual inflow volume estimated to be 3909 MCM contributed from gauged catchment and about 2431 MCM contributed from ungauged catchment.