DAM BREACH MODELING and INUDATION MAPPING A CASE STUDY OF JEMA DAM, ABAY BASIN, ETHIOPIA

Abstract

Preparing dam safety plans and hazard management strategies are unquestionably vital, since lots of human lives have been lost and tremendous amount of economic crisis have been recorded from dam failure events throughout the world in history. Setting out risk management, emergency action plans or evacuation planning system to protect both lives and materials during sudden dam failure phenomena and resulting flood waves is highly essential. This thesis analyzed the probable failure of a dam under a set of pre defined scenarios, within the framework of a case study, the case subject being the Jema dam located at Amhara Region of Ethiopia. A probable maximum flood of Gilgel Abay river (tributary of Jema River) has been computed using Hershfield’s technique .Breach parameters prediction, peak outflow hydrograph were determined by HEC-RAS model based on available technical and geometric data. Different maps such as flood areal extent map, flood depth map and velocity map have been produced by HEC-GeoRAS. The worst scenario was found to be scenario three (when Jema dam failed by overtopping with PMF of Gilgel Abay River). Probable maximum flood of Gilgel Abay river by Hershfield’s technique was found to be 1726.28 m3 /s. The maximum breach discharge resulted from HEC-RAS model was 79,886.37m3/sec and the maximum area inundated by this flood in downstream was found to be 41.6km2 . The areal maps show that the part of command area at right side and farm in left side, Bikolo Abay Town and settlement villages to be prone to flooding. The depth and velocity of flood also depict that the downstream rural village near the river bank are under extreme hazard category and the maps reveals that Jema dam is categorized under high hazed dam