Abstract:
Fogera flood plain, located at the foot of Ribb catchment, has been repeatedly devastated
by powerful flash floods. As the flood pass through center of the flood plain, it causes
tremendous losses in terms of life and property. Even though various mitigation measures
were undertaken so far, they are not adequate to withstand the flood threats. Hence, this
study carried out flood damage reduction analysis in order to evaluate and identify the
competent flood mitigation plans. The required components for this analysis, flow
frequency functions for each alternative flood control plans were generated by modifying
watershed characteristics and geometry using HEC-HMS model. The output from HMS
was then used to run the HEC-RAS model and generate water surface elevations. These
functions were then used with HEC-FDA to compute expected annual damage and
evaluate performance of the alternative flood damage reduction plans. Based on the result
of flow-frequency analysis, implementations of detention pond and diversion control
create significant impact on probability-discharge functions for the study area. The
potential vulnerable areas for the 100 year return period flood event are Ambua Kokit
kebele. Under the stated assumptions, the project that is most desirable from an economic
viewpoint is diversion control flowed by detention pond. However, before making a final
decision the social and political aspects also should be considered. EAD is reduced from
9.676 million$ to 3.626 million$ due to application of the proposed diversion control.
Whereas, the Ribb dam restricts the downstream flow not to go beyond the target
flow,76.5 m3/s for this study. So in this study the dam reduces the expected annual
damage by 5.285 million$ (54.6%).
