Course:
M.Sc. in Hydropower Development

Author:
Zewdu Tememew Molla (M.Sc. 2005)

Nationality:
Ethiopia

Thesis title:
Dam Safety Evaluation on Koka Dam, Ethiopia

Short summary:
The study was principally carried out so as to evaluate the existing safety of the koka dam. The study area lies 70km South-east of the country capital Addis Ababa on Awash Basin.
Koka was the first large Hydropower plant established in the country. It was commissioned in May/ June 1960. Besides power generation at Koka power plant, Koka dam serves as a regulation dam for power production at Awash II and III. The total installed capacity for all three stations (Koka, Awash II and III) is 107.2MW, which is 17% of the total existing power capacity supplied by the ICS (Inter Connected System). Awash and Modjo are the two main rivers which flow into the reservoir.
According to study conducted Norconsult, 1957, the type of rock found in the Koka area vary from the Tracyte-Cynite to Andesite-Diorite series. The area is dominated by bimodal rainfall type and the mean annual rainfall of the catchment area is estimated to be 1012mm.
Literature study on concrete gravity dam and gated spillway, dam safety guidelines, hazard evaluation, and reservoir sedimentation was carried out during the study.
According to a bathymetric survey conducted in 1998, the capacity of Koka reservoir has been reduced from 1650Mm3 in 1959 to 1186 Mm3. The loss on total storage capacity over the last 39 years is estimated to be 464 Mm3, which is 28.1% of the total storage volume of the reservoir. The average annual loss of capacity is about 0.72%. To date, the loss is estimated to be 532 Mm3.
Preliminary Hazard Analysis (PHA) on Koka dam was carried out after mapping potential upstream and downstream hazardous events on the dam. The aim of the analysis was to examine the existing safety of the dam and to come up with risk reduction measures. The analysis is shown in Appendix B.
Based on the results from the PHA, cost-effective risk reduction measures were proposed for the identified hazardous events and clearly stated in chapter 9.


Name of the library / database / publication where the thesis is available:
University library (BIBSYS)



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