Hybrid Modeling Framework for Simulating Compound Floods in a Coastal City

Low lying coastal cities are under high risk of the compound flood with frequent storm surge occurrence and sea-level rise. This study attempted to develop a hybrid modeling framework to simulate various physical process of the compound flood. In this regard, first, the storm surge process is simulated using a wave-flow coupled model i.e., Delft3D-FLOW and simulated wave nearshore (SWAN). The meteorological forcing for the hydrodynamic model has been done by integrating a parametric Holland cyclone model in this framework. The urban flood process in compound flood is also simulated using a rainfall-runoff model, the storm water management model (SWMM). The case study to evaluate the performance of the modeling framework is selected as the northern Bay of Bengal and extends to surge affected areas of Chittagong coast of Bangladesh. The modeling system is employed to simulate compound flood associated with cyclone 1991 in Chittagong City. The storm surge and wave boundary conditions from the hydrodynamic model are used as downstream boundary conditions, while generated runoff from SWMM is used as a dynamic upstream boundary condition. The results showed that the compound flood modeling is sensitive to dynamic changes of storm surge height and rainfall intensity of cyclone induced rainfall. This study introduces a new modeling approach contributes to the existing knowledge of compound flood modeling and complex interactions among urban runoff process, the atmospheric process of the cyclone, and coastal storm surge.