Modelling of flood propagation due to levee breaches induced by overtoppig flows

Numerical hydraulic models for flood propagation induced by levee breaches offer the potential to characterize the flow and to map flood hazard, to design mitigation measures, and to support effective land use and emergency planning. The accuracy of numerical results relies highly on the simulation of the breach expansion (widening and deepening). In this work, we compare different approaches to simulate breach development in non-cohesive, homogeneous fluvial dikes induced by overtopping flows: (1) empirical laws, (2) simplified physically based approach, and (3) detailed physically based approach which considers sediment transport and bank slope failure. All approaches are used within the two-dimensional depth-averaged numerical solver TELEMAC2D which solves the Shallow Water Equations on an unstructured mesh using the finite-element method. The numerical solver has been applied to simulate two large-scale dike breaching tests on the floodway channel of the Tokachi River, Japan. The numerical results are compared against measured breach outflow and water level time series as well as the evolving breach topography.