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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/2270

Title: Predicting Discharge at Ungauged Catchments Using Rainfall-Runoff Model (Case study: Omo-Gibe River Basin)
Authors: Bogale, Tesfaye
Advisors: Dr. Bayou Chane
Copyright: Jul-2011
Date Added: 3-May-2012
Abstract: Abstract This paper deals with predicting discharge at ungauged catchments, the case of Omo-Gibe river basin, using the WATBAL conceptual lumped 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 Omo-Gibe river basin, most of the catchments are ungauged. Hydro-meteorological data from twenty four metrological and twenty two hydrological gauging stations of the basin are used to calibrate and validate the model parameters. Sizes of gauged catchments whose data are used vary from about 40 to 3242 km2. Key model parameters considered consist of sub-surface runoff coefficient (α), surface runoff coefficient (ε), and maximum water holding capacity of catchments (Smax). These parameters are calibrated using an automatic optimizing routine of the WATBAL model and through routine iteration; Smax is found to vary from 3403mm to 466mm, α from 64mm/day to 0.26mm/day and ε from 9.6 to 2.6. Some more model parameters, namely, direct runoff coefficient (β), subsurface runoff coefficient (γ), and base flow (Rb) are calibrated manually. The hydrograph characteristics of observed and simulated events are compared using various evaluation criteria consisting of Nash-Sutcliffe coefficient (NS) greater than 0.6, relative volume error (RVE) between -10 and 10%, and coefficient of determination (r2) greater than 0.7. Among the catchments of the basin that are used in the modeling work, 73% fulfilled the criteria. 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. In addition to the PCCs, input data including precipitation, observed flow, temperature, relative humidity and sunshine are used in the WATBAL rainfall-runoff model. Four parameter regionalization methods (multiple regression, spatial proximity, area ratio and sub-basin mean) were applied to transfer model parameter values from the gauged to the ungauged catchments.
URI: http://hdl.handle.net/123456789/2270
Appears in:Thesis - Civil Engineering

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