Driftwood retention at the river Gürbe

A flood event in 1990 caused great damages in the valley of the river Gürbe due to wood jams at bridges. A flood control concept was developed which involves a trashrack construction for driftwood retention at the end of a widened channel reach (“Ausschütte”). A bypass next to the structure is used to minimize backwater effects, which can be expected due to an obstructed trashrack.

Experiments in a physical model were performed to test the efficiency of the trashrack. These tests demonstrated that the discharge of driftwood during a flood event is so large, that part of the wood is transported through the bypass into the lower reach.

Thus, alternative solutions were tested. A combined solution with a trashrack and a downflow baffle at the inflow to the bypass represented the best variant. With this construction it is possible to retain nearly all wood in the channel widening.