DAM BREACH ANALYSIS AND DOWNSTREAM FLOOD INUNDATION MAPPING: (THE CASE STUDY OF JEMA DAM, WEST GOJJAM ZONE, AMHARA REGION, ETHIOPIA)

Abstract

The failure of a dam can have consequences for people's lives, their property, their infra structure and their industry. Flood mapping to identify potential dam failures is critical to determining risk control strategies. In 2013, Jema earth rock fill dam designed by Lihket Design Supervision Corporation for irrigation purpose and the dam breach analysis and downstream flood inundation map have not been done. The main objectives of this research are to assess the failure of the Jema earth rock fill Dam and to map floods and identify flood risks. The main problem of the study was the lack of high-resolution DEM. Actual topo graphic coordinate survey data were collected on site using a total station and differential GPS to fill an important data gap in the post-construction dam failure analysis contained in the previous study. In this study, dam failures were analyzed before dam construction. Therefore, the draft document may be revised in light of the result of the dam failure. The upstream boundary condition for this study was a probable maximum flood analysis using the SCS composite unit hydrograph, and the initial boundary condition for the HEC RAS model was F.R.L 2131 m.a.s.l. used. During the modeling phase, unsteady flow calculations were carried out to route the breach discharge downstream of Jema Dam from the dam up to the downstream boundary, which is 29.99km from the dam. The modeling simulation was done for two scenarios a piping failure on a sunny day and a rainy day or spillway failure. For the flood mapping and de tailed analysis, however, the overtopping failure scenario was employed. The reservoir's highest discharge during the greatest flood, 1686 m3/s, increased the reservoir's elevation to 2131.44 m.a.sl, 0.44 m over the dam crest level, which indicate an overtopping failure scenario. The HECRAS model offers a peak flow rate of 31,558.82 m3/s. If the Jema rock and earth dam breaks, this maximum flood will inundate 8,136 people, 1,356 houses and 3,296.9 hectares of land. To develop an emergency plan, further studies sh