Dorfbach Sachseln (OW): Trash rack for a sediment basin

In august 1997 a thunderstorm caused severe damage in the village Sachseln in central Switzerland. After an intensive 2-hour rainfall of more than 100 mm the stream across the village overflew which led to a vaste flooding of water, bed load and wood in large parts of the village. Overflow was mainly due to insufficient channel capacity and blocking of sensitive channel sections (bridge-channel crossings) with floating wood.

As an immediate measure it was proposed to install a trash rack in an existing sediment basin upstream the village. The trash rack was designed to hold back a large part of the floating wood and to hold back particularly the arriving trunks.

Due to the present current complexity in the sediment basin, the laboratory of hydraulics, hydrology and glaciology (VAW) was assigned to test and optimise the trash rack in the physical model.

The experiments in the physical model showed that the concept of the trash rack is good and feasible in practice. With the help of the experiments the originally proposed construction could be simplified and the quota of retained wood and trunks improved. The trash rack version realised in summer 1998 guaranteed to hold back the arriving trunks longer than 2.5 m almost completely.