A simplified physically-based model for coastal dike and barrier breaching by overtopping flow and waves

The simplified physically-based breach model, DLBreach, has been developed to simulate the overtopping breaching of coastal dikes and barriers, which can occur either from the sea side or the bay side. The breaching process is divided into two stages: intensive breaching and general inlet evolution, in which the flows are calculated using the weir flow equation and the Keulegan equation, respectively. The Keulegan equation is a simplified energy equation for steady nonuniform flow with local head loss due to channel contraction and expansion, revised herein by adding the wind driving force. Empirical formulas are adopted to calculate phase-averaged wave overtopping discharge, wave setup, and wind setup/setdown. The wave overtopping discharge is combined with the surge overflow discharge, and the wave setup and wind setup/setdown are added to the sea and bay water levels for the hydrodynamic and sediment routing. Alongshore sediment is considered as a source boundary condition for the non-equilibrium sediment transport model at the breach. The model has been tested using the 94' field experiment of sea dike breaching by overflow in the Zwin Channel Estuary, a laboratory experiment of sea dike breaching initiated by wave overtopping, and a field observation of the eight-day breaching and closure event of the Mecox Inlet at eastern Long Island of New York during Sept. 10-18, 1985. The model results agree generally well with the measurements.