Investigation of Shahrchay Earthfill Dam Break due to Overtopping and Flood Mapping

Dam break due to an earthquake, bombing, piping, overtopping, or some lacks in design and construction process is unavoidable, which could lead to loss of life and property downstream of the dam. In this paper, numerical modelling of Sharchay dambreak, located in Urmiyyah city, is of interesting and the outflow hydrograph of Shahrchay dam site has obtained using Breach model under the scenario that considers the dam break due to overtopping. To numerical modelling of dam break in two dimensional conditions, it has been used CCHE2D software, which utilizes finite element method to solve the shallow-water equations. To verification of the model, the measured data of an experimental model has been used and then the needed number and structure of the cells in computational domain as well as suitable method for discretization of the governing equations has been determined. In addition, using the Graphical Information System (GIS) the information about flood extent obtained and the mapping of flooded zone in downstream prepared. The results revealed that due to dam break and flood spreading that exceeds from the capacity of the river, the flood extends to the surrounding agricultural lands and rural residential areas. Thereafter, with reaching flood to the peak point of hydrograph during 19 hours, the downstream agricultural lands and residential areas is influenced by a great flood. 19 hours after the beginning of dam break, at moment that the flooding reaches to the peak of hydrograph, the critical condition will occur and almost all rural areas will subject in danger of complete submergence.