In the course of the flood protection measures of the city of Innsbruck, a redesign of the confluence of the Sill into the Inn is planned. The currently existing, non fish-continuous ramp on the Sill just above its confluence with the Inn is to be replaced by a combination structure consisting of a structured ramp in the outer curve and a white-water sports ramp in the inner curve.
The structured ramp serves the fish ascent and the organism passability, the white-water sports ramp shall enable a standing wave at the downstream end of the ramp for leisure use by paddlers. At the same time, the structure must provide bed support for the Sill (protection against regressive erosion). During floods, both parts of the structure are used to transport bed load towards the Inn river.
With the help of a hydraulic model test with movable river bed, the following questions were answered for the three main functions of morphology, fish passability and recreational use (surfing wave) for the building components: structured ramp and white-water sport ramp:
- Formation of the standing wave in the stilling basin of the white-water sports ramp depending on different discharges of the Sill and water levels downstream in the Inn as well as the different sedimentation scenarios in the bottom area of the standing wave resulting from the bed load transport of the Sill
- Stability of the fish ladder (crossbar ramp) constructed of large stones during floods and level of the river bed at the upstream end of the construction in the Sill (with and without bed load input)
- Division of flow and bed load between the structure parts fish ladder and white-water sports ramp
- Distribution of discharge between the two parts of the structure at low water, so that the permanent supply of the fish ladder and the right bank branch is guaranteed even at low water.
Currently existing ramp in the Sill just above the confluence with the Inn
Estuary of the Sill into the Inn