DAM BREACH ANALYSIS OF UMIAM EARTHEN DAM USING HEC-RAS

Abstract

The Analysis of dam breaches using the Hydraulic Engineering Center's River Analysis System (HEC-RAS) is crucial in assessing the safety of dams and developing effective emergency response strategies. This study explores the utilization of HEC-RAS, a widely employed water flow modelling program, to understand the potential outcomes of a dam breach and its subsequent consequences. Through the simulation of dam breach scenarios and the estimation of flood wave characteristics, HEC-RAS assists in assessing the severity of a dam breach, studying the downstream propagation of floods, and devising effective measures to prevent their occurrence. Providing an overview of the significance of HEC-RAS in enhancing dam safety and safeguarding lives, properties, and ecosystems during dam breach incidents, this abstract emphasizes the importance of preparing an emergency action plan (EAP). Consequently, conducting a dam breach analysis becomes imperative to identify the critical discharge threshold that could potentially lead to the dam's failure in such an event. In this study, the dam breach analysis of the Umiam Earthen Dam in Meghalaya's Ri-Bhoi district utilises a two-dimensional (2D) hydraulic model known as the HEC-RA to improve the accuracy and reliability of hydraulic models when simulating a dam breach scenario and creating flood potential inundation maps., the study incorporates a digital elevation model (DEM) extracted with 30 m resolution from the Shuttle Radar Topography Mission (SRTM) for generating the geometry data and a Geographic Information System (GIS). The probable maximum flood (PMF) uses as reservoir inflow; the reservoir routing using modified Pul’s method was carried out in the Hydraulic Engineering Center's Hydrologic Modeling System (HEC-HMS) model to determine the outflow; the results show the comparison of the inflow and outflow hydrographs. The HEC-RAS model simulates dam breach parameters such as breach width, breach formation failure time, and breach side slope determined from distinct empirical methods. The outflow characteristics, such as maximum water surface elevation, maximum velocity, maximum depth, and minimum travel time, are predicted using the HEC-RAS two-dimensional (2D) model obtained from four distinct empirical methods. A comparison makes between the obtained results. The flood inundation maps prepare using Froehlich’s equation for piping failure for the downstream affected villages using the maximum water levels generated by the dam breach model. As a result of piping failure, the downstream area directly below the dam encounters a peak flow of 3471.36 m3/s, leading to an inundation area of 110 km2 before reaching the Assam border.