PREDICTION OF STREAM FLOW AT UNGAUGED CATCHMENTS USING RAINFALL-RUNOFF MODEL: THE CASE OF UPPER TEKEZE BASIN, ETHIOPIA.

Abstract

This paper deals with simulation of stream flow at ungauged catchments, the case of upper Tekeze basin, using HBV-96 rainfall-runoff model. Parameters calibrated with the model are extrapolated from gauged catchments to ungauged catchments of similar physical characteristics with regionalization technique. In the upper Tekeze basin, most of the catchments are ungauged. The basin has 9199km2 and 36381km2 gauged and ungauged catchments respectively. For this study hydro-meteorological stations of the basins were used to calibrate and validate the model parameters for gauged catchments from 1992-2006 years data by using HBV-96 rainfall-runoff model. Key model parameters considered consist of runoff coefficient (Beta), recession coefficient of upper reservoir zone (Khq), limit for evapotranspiration (Lp), field capacity (Fc), percolation (Perc) and general correction factor for evapotranspiration (ecorr). To have a better understanding of model parameter performance, sensitivity analysis of nine model parameters were performed. The result shows that runoff coefficient (Beta), recession coefficient of upper reservoir zone(Khq), limit for evapotranspiration(Lp), field capacity(Fc), percolation (Perc) and general correction factor for evapotranspiration(ecorr) are more sensitive than others model parameters. The gauged catchments satisfies objective function in the calibration and validation period, for Gheba sub catchments NSE, RVE and R2 ,0.81,-4.25,0.77 and 0.71,5.5,0.74 respectively. Four regionalization methods, multiple linear regression, spatial proximity, sub- basin mean and area ratio were applied to transfer model parameters values from gauged to ungauged catchments. Based on availability of required data, six physical catchment characteristics (PCCs) are selected among those commonly used in many regionalization studies. These are catchment area, mean annual precipitation, mean annual evapotranspiration, average catchment slope, longest flow path and mean catchment elevation. Stream flow simulation at ungauged catchments by using spatial proximity and sub basin mean method were contributing high runoff volume compare to other methods Thus Current and future water resources development endeavors may use apply such discharge data for planning and design purposes.