DAM BREACH ANALYSIS OF TUIRIAL DAM USING HEC-RAS

Abstract

A dam is a structure built across a river or stream for storing water or controlling the flow of water for different purpose. Breaching of such dams cause a lot of havoc in the downstream of the dam. This study focuses on the analysis of breaching of such a dam. HEC-RAS software is used for this analysis. HEC-RAS is a simulated software tool developed by United States Army Corps of Engineers for modelling of water surface profiles, flood inundation mapping, study of hydraulics of water flow in rivers and streams, dam breach study etc. It is an open source tool. It is mainly used for floodplain mapping and its management. I have used this software for the dam breach modelling of the ‘Tuirial Dam’ of Mizoram. Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) of 30 m resolution is downloaded from USGS (United States Geological Survey) and used for generating the geometry data. As overtopping failure is more severe than piping failure, so this study is done only for overtopping failure. Probable Maximum Flood (PMF) of 1000 years return period is used over and above the Full Reservoir Level (FRL) and the model is run. Froehlich (2008) regression equation is used for determining the dam breach parameters. As results, outflow hydrographs at different locations are generated and put in a graphical representation. The outflow hydrographs are generated for locations such as at dam site, at 20 Km downstream, at 40 Km downstream and at the confluence of Barak and Sonai River. Flood inundation maps are prepared based on the result obtained from the model. As a result of the overtopping failure, the dam site encounters a peak flow of 19965.26 m3/s. The dam is near to the Assam-Mizoram border. The nearest downstream of the dam falls in the Kolasib district of Mizoram. Fortunately, there are almost no habitants in the nearest downstream to the dam. It falls in the hilly areas. Cachar is a highly populated district of Assam, which is to the downstream of the dam. The inundation area falls mostly in the Cachar district of Assam.