DAM BREACH ANALYSIS AND FLOOD INUNDATION MAPPING FOR GIDABO DAM

Abstract

This study presented the dam breach analysis and flood inundation mapping for Gidabo rock-fill embankment dam found in Southern part of Ethiopia. The geometrical data used for this study was extracted from the recently released ALOS PLASAR digital elevation model by Alaska Satellite Facility, which is having the spatial resolution of 12.5 by 12.5 meters. One dimensional unsteady flow simulation within HEC-RAS model was used to simulate dam breaching for both overtopping and piping failure scenarios. Dam breach parameters estimation was done for different empirical equations. Froehlich (2008) and Von Thun & Gillete methods was preferred since the results obtained for these methods are more approaches to the envelope curve developed for the historical dam failures for overtopping and piping failures, respectively. RAS mapper and ArcGIS tools was used to present the maps of spatial distribution of flood extent, flood depth and flood velocity, flood inundation, flood hazard maps of the study area. The breach parameters estimated for both overtopping and piping failure scenarios was provided the reasonable values. The maximum breach discharge simulated for overtopping and piping failure was obtained as 15,945.18 m3 /s and 14,904.18 m3 /s, respectively. Since the failure were tested for hydrologic failure and for normal water level condition, the magnitude of flood and the spatial distributions are obviously different. Developed inundation maps from this study could be possibly help as guidance for dam owners to develop the emergency action plan and for future expansion of irrigation project infrastructures, and other developmental activities around the downstream of the dam