Combined use of 1-D and 2-D models for simulating dam break waves

Because of the uncertainties linked with the hypothesis concerning the initial conditions and the breaching, the calculation of the propagation of a dam-break wave is generally performed using 1-D model, even for large dams. A 2-D model provides detailed velocity field and water levels which may be useful locally. The cases of three dams in the Southern France show that the combined use of a 1-D and of a 2-D models is sometimes necessary to assess the risks in a suitable way: neither over estimate nor under estimate, a reduction of uncertainty which may be important in an inhabited area. In both cases of I-D model upstream or downstream from the 2-D model, the discharge hydrograph calculated by the upstream model is used as the upstream boundary condition for the downstream model. Without the introduction of complementary data, global results provided by I-D and 2-D models are generally similar. Thus, the more frequent case of combined use will be a general 1-D model and local detailed 2-D models in areas with high vulnerability.