Hybrid modelling of dike-break induced flows

In a hybrid approach experimental model data are combined with results from 3D and 2D
numerical modelling. The latter was conducted by two different models solving the depth-averaged shallow
water equations. 3D computations are based on the REYNOLDS-averaged NAVIER-STOKES equations
(RANS) using a volume of fluid approach to capture the free water surface. Measurements were performed
on a scale model which was especially designed to reproduce the specific conditions of dike
breaks. In various simulations it turned out that 2D shallow water models are able to reproduce steadystate
flow patterns of dike-break induced flows and that there is a low sensitivity of the solution concerning
turbulence modelling, bed and wall roughness. Nevertheless, final flow splits and breach discharges
are systematically underestimated. This discrepancy seems to result from inherent modelling assumptions
such as zero-vertical velocity and hydrostatic pressure distribution. Therefore, the complementary use of
3D RANS and 2D depth-averaged modelling frameworks for detailed predictions of dike-break induced
flows is discussed in the present paper, based on BOUSSINESQ and pressure coefficients, which represent
effects of non-uniform velocity profiles and non-hydrostatic pressure distribution over water depth, respectively.
Values of these coefficients are inferred from 3D numerical results for the final steady state.