Hybrid modelling of a spillway to prevent dam breaks at the Linth Canal

Since river engineering concepts are designed to work properly not only under design conditions, but as well for the overload scenario, the flood control project 'Linth 2000' is investigated at the VAW using a hybrid modelling approach, where physical and numerical experiments are combined. A regulated overfall weir in a newly built local river widening of 800 m length is planned to limit the downstream discharge in the Linth Canal. The spillway is designed to reduce the peak flow of 500 m3/s to a maximum of 420 m3/s. The mean discharge in the Linth Canal is about 54.6 m³/s.

In the laboratory, the physical model on a 1:30 scale covers 90 m2. It includes parts of the local widening, the spillway construction and the runoff in the stream course downstream of the spillway.

To guarantee correct upstream boundary conditions in the physical model, numerical 2D simulations are performed covering a larger flow domain up- and downstream of the local widening. In the numerical model, the water levels, the bed shear stress and the averaged flow velocities are calculated for several flood scenarios. In the physical model, the functionality of the spillway and the riverbed stability are tested. For the numerical computations, the modular software BASEMENT is used.