Simulation of dam break due to overpass flow and study of its effects on downstream areas (Case study: Shahrchay Dam)

Abstract Shahrchay Dam is one of the dams that, due to its geological and climatic conditions, there exists a considerable possibility of overflow and consequently its break. The Dam is considered an imminent threat to Urmia city due to its proximity to the downstream residential areas. Therefore, this study aims to investigate the dam break modeling and, finally, the resulting flood zonation in the downstream areas of the Dam. To achieve this goal, we developed two hydraulic models, viz. BREACH-GUI, OpenFOAM of dam break based on (physical parameters of the Dam and downstream geographical features) and then using HEC-RAS, Arc-GIS software vulnerable areas against floods marked by a 100-year return period. The results show that the two hydraulic models in question have yielded similar dam break results. More precisely, the BREACH-GUI model has calculated the maximum output velocity at the bottom of the Dam at a distance of 1 km at about 13 meters per second with a height of 12 meters. In contrast, the OpenFOAM model has calculated the maximum velocity at a distance of 900 meters at an altitude of 11 meters at 20 meters. Flood zoning due to dam break shows about 18% of the area of Urmia city, 73% of Band village, 68% of Noshan Sofla village, and 76% of Noshan Olya village due to rising water flow caused by dam break with a population of 136,000 people directly affected.