Abstract:
Dams are designed and built for a variety of purposes, including hydropower, irrigation,
domestic water supply, flood control, navigation, recreation, and drought mitigation. Dams,
on the other hand they are a source of disruption for human life, property and the dam itself
by causing a maximum catastrophic flood event during their failure. Therefore, the purpose of
this study is to evaluate the Hossana Wuha Limat embankment dam breach as well as to map
flood inundation and identify flood-prone areas. The study area's likely maximum flood was
generated using the probable maximum precipitation (PMP) estimate by the Harshfield (1965)
statistical approach and the HEC-HMS model. By combining field data with DEM 12.5 m
resolution, the accuracy of the digital elevation model (DEM) in showing the river terrain
channel was modified. Overtopping and piping dam breaches were simulated using a HEC RAS hydrodynamic model. Combining the effects of flood depth and velocity, flood hazard
categorization due to dam breach was established. The results show that during the probable
maximum flood, the reservoir's peak inflow and outflow were 1393.88 and 1339.48 m
3
s
-1
,
respectively. Peak outflow raised the reservoir's elevation to 2286.85 m a.m.s.l., which is 0.25
m over the dam crest level. This suggests that there was an overtopping breach event. Peak
floods along the dam axis are 4460.60 m3
s
-1 for overtopping and 2459.77 m3
s
-1
for piping
modes of failure, respectively. An overtopping breach event floods 11.4 km2
, whereas a pipe
breach event floods 6.80 km2
of the study area. Flood hazard classification indicated that the
Hossana Wuha Limat embankment dam has a high to extremely high flood hazard due to the
result of flood depth times velocity over a wide floodplain being greater than 0.5 m2
s
-1
. To
maintain public safety and safeguard economic interests in the flood-prone area, this study
recommends the implementation of an emergency action plan for better hazard management
techniques.
