Abstract:
Flooding in Lower Awash sub-basin of the Awash River Basin, alike the other eight
basins in Ethiopia, are attributed to rivers that overflow or burst their banks to
inundate low lying areas. Logiya and Mille rivers are the two rivers in Lower Awash
sub-basin that flow through the flat fields of flood plain areas.
The objective of this study was to develop early flood warning system for the Lower
Awash Sub basin in order to reduce the impacts of flood problem in the sub basin
using the hydrological, meteorological and spatial data. Rainfall runoff models were
processed for both catchments, Logiya and Mille using the hydrologic engineering
center hydrological modeling system and the soil moisture accounting and routing
models. The predicted hydrograph was calibrated against observed one and the model
parameters were optimized automatically for good simulation. HEC-HMS model was
found better in both the coefficient of determination and Nash-Sutcliffe efficiency
criteria and fairly applied in both catchments for supporting flood warning decision
making. The calibration and verification results of the HEC-HMS rainfall-runoff
model for both Mille and Logiya catchmentsrevealed good (ENS>0.65) efficiencies.
The hydrologic engineering center HMS model and the soil moisture accounting and
routing model were tested to estimate the possible lead time, and the former
performed well. From the hydrological routing the lead time was estimated as two
days for Logiya catchment and one day Mille catchment using the hydrologic
engineering center HMS model. Therefore, the decision makers can use this lead time
as input data what kind of measure to take and to evacuate the public and their
properties.
