Dam Break Simulation Using DHI-MIKE21 in the Eg Hydropower Plant, Mongolia

This chapter focuses on a dam break assumptions and assesses a flood risk in the downstream area of the Eg hydropower plant, Mongolia. Two-dimensional DHI-MIKE model was set up. The model presents the volume of water in a reservoir, a flood mapping, and flood risk zone in the downstream area of the hydropower station. The model has been supplied by the Eg-Hantai, Selenge-Khutag, and Selenge-Khylganat hydrological stations data from 1994 to 2006, which are a water level, inflow discharge, and precipitation, and it has been collected by the Mongolian Institute of Meteorology Hydrology and Environment. Terrain property of objects in schematic outline was determined on a digital elevation model (DEM), the elevation data were produced by digitizing topographic maps. The dam break has been simulated with Mike21 modeling software. The initial elevation is 887.8 m (water depth 59 m) at the reservoir. Before dam failure, the observed discharge and the simulated Mike21 model’s outflow were analyzed to make a reasonable assumption (the purpose of assumption is that a failure and the resulting flood wave would affect the downstream area of the dam planned site). After analyses and model simulation, an artificial reservoir was built on the model to release water to the downstream area. In the model, it has been assumed that the dam failed completely and instantaneously. It means it will approach the maximum peak of flood. As a result, the total amount of 262.10⁶ m³ water has been collected behind the dam. After water is released, flood area was determined and the maximum affected area is 145.1 km² and the maximum depth is 15.1 m. The Mike21 model simulation result was closest to the observed peak, and the correlation (R) was 93%. Therefore, a floodplain in Mike21 results is an efficient tool to make a flood mapping and to assess flood risk in the downstream area of the hydropower plant.