Abstract:
Many streams in Ethiopia are ungauged and do not have flow records. Even when streamflow
gauges are available, records are too short. In Awash River Basin, which is one of the largest
Ethiopian rift valley Basins, many catchments are ungauged. Consequently, in estimating
streamflow, applying regionalization techniques for ungauged or poorly gauged catchments is
crucial. This paper deals with estimating streamflow at ungauged catchments using HBV-light
model in Awash River Basin. Hydrological and meteorological data for the selected gauged
catchments were collected and the respective catchment characteristics were derived for both
gauged and ungauged catchments. To optimize the model parameters for gauged catchments,
model calibration were performed using automatic and manually techniques for a period of
2000 – 2010. The model was then validated for a period of 2011-2015. A sensitivity analysis
was performed for model parameters. Two regionalization methods which are multiple
regression (regional model) and similarity based were applied to transfer model parameter
values from gauged to ungauged catchments. The calibration and validation result shows that
all the seven selected gauged catchments have a good agreement since the Nash-Sutcliffe
Efficiency (NSE) value greater than 0.60 and Relative Volume Error (RVE) lies between
±10%. Sensitivity analysis of HBV light model parameters evaluation shows that with respect
to NSE parameters like; MAXBAS, K0, BETA, K1 and FC are the most sensitive. Besides this,
with respect to RVE parameters like; BETA, LP and FC are the most sensitive for all
catchments. Both the regional model and similarity based methods have shown good
performance in estimating streamflow at ungauged catchments, but the performance
comparison of the regionalization methods indicates that estimation of streamflow at
ungauged catchments using similarity based method yields better performance. Finally, on the
bases of parameter transfer; similarity based method gives the total average annual flow at
ungauged catchments as 3.07BMC and this estimated flow can be used as data for different
water resource applications.
