Abstract:
Transfer of hydrologic model parameters from gauged to ungauged catchments is perhaps the most
common procedure in hydrology. In developing countries like Ethiopia most of the Rivers are
ungauged. Therefore, applying regionalization techniques for ungauged or poorly gauged river
basin is crucial. This paper deals with predicting discharge at ungauged catchments using
conceptual rainfall-runoff model HEC-HMS in middle Omo-Gibe sub-basin. Four regionalization
methods (linear regression, spatial proximity, area ratio and sub-basin mean) were applied to
transfer model parameter values from the gauged to the ungauged catchments. In regional model,
gauged catchments model parameters and physical catchment characteristics of ungauged
catchments were used to develop the equations in order to predict discharge from ungauged
catchments. To have better understanding of model parameter performance, the sensitivity analysis
of ten model parameters were performed manually by trial and error. The evaluation shows that
crop coefficient (CC), storage coefficient(R), constant rate (CR), and time of concentration (TC)
are more sensitive than others. The model performance was evaluated using Nash Sutcliff
efficiency greater than 0.75, percent difference lies between +10% and -10%.and coefficient of
determination greater than 0.8 during calibration and validation period The model parameters in
ungauged catchments were determined by using regional model, sub-basin mean, area ratio and
spatial proximity methods and simulated the discharge by using HEC-HMS model. . In predicting
model parameters from ungauged catchments in regional model method p-value ≤ 0.1 and
determination coefficient (R2
) = 0.91 for crop coefficient(CC) and 0.99 for maximum deficit(MD),
constant rate (CR), maximum storage(MS),initial storage(IS),storage coefficient(R), and time of
concentration (TC) were obtained by linear regression. Because of this river flow from ungauged
catchments simulated by regional model method was the best. Therefore, regional model method
is recommended in predicting discharge for ungauged catchments for this research and obtained
30m3
/s and 15m3
/s averaged maximum monthly averaged simulated flow for Denchiya and Mansa
ungauged sub catchments respectively.
