Hydrological modeling of the Kihansi river catchment in South Central Tanzania using SWAT model

Birhanu Zemadim Birhanu

Water Resources and Environmental Engineering Department, Bahir Dar University, P. O. Box 26, Bahir Dar, Ethiopia. E-mail: birhanuzem@yahoo.com . Tel: +251910457450. Fax: +251582202027

Accepted 20 August 2009

   Abstract

This study presents distributed and lumped hydrological modeling approaches for the Kihansi river catchment in south central Tanzania using the Soil and Water Assessment Tool (SWAT). The catchment is source of water for the Lower Kihansi Hydropower Plant (LKHP) that supplies 25% power to the national grid and the bio-diverse gorge eco-system in lower Kihansi Basin. In the distributed modeling sub-watersheds were defined at the existing gauging stations. There are four upper sub-watersheds and ten sub-watersheds located downstream. Three sub-watersheds of the river system were separately modelled in a lumped approach. Subsequent parameterization of physically-based soil parameters, landuse, and management files were defined. Four quantitative and two qualitative evaluation criteria were used to evaluate the prediction performance of SWAT model. Model prediction results using unoptimized parameter sets resulted poor modeling performance. Hence parameter specification and optimization was necessary to ensure correct hydrological processes. Modelling results using optimized parameter sets resulted better prediction of hydrological variables. Finally correction factors were introduced for optimised parameters to facilitate future land cover change studies.

Key words: Hydrology, modeling, SWAT, Kihansi river, calibration, validation.