After-work excursion / Feierabend-Exkursion
Place: Winterthur, Sennhof
Objekt: River bed protection / Töss, Sennschür
Since its expansion, the Töss has been characterised over long stretches by an increased bedload transport capacity, a pronounced bedload deficit and the associated tendency towards deep erosion. Widening to the regime width is not possible in the Sennschür project perimeter in the Leisen valley. In order to ensure the use of drinking water, the river bed must therefore be stabilised in this section. The wooden sleepers in the project perimeter, some of which were hundreds of years old, were now dilapidated and had to be replaced. In addition, the river had major structural deficits and limited longitudinal connectivity, mainly due to the horizontal construction typical of wooden sleepers.
As a replacement for the wooden sleepers, a new system of block stone bars was developed, which, in addition to pure riverbed stabilisation, also brings about targeted structuring. The induced meso-habitats (e.g. various types of scour, structures similar to baffles and sliding banks) represent a great ecological added value. The flow pattern created was accentuated with biological engineering structures. Emphasis was placed on the formation of a compact, dynamic low-water channel. The practical example makes it clear that even in laterally constricted watercourses, bed stabilisation, flow and structural diversity and free fish migration do not have to be contradictory.