How does the Fish ladder work?
Migratory fish cycles
Throughout their lives, migratory fish move between freshwater rivers and the sea, depending on which phase of their life span they are in.
Salmon, sea trout, shad, lamprey and sturgeon swim upriver to reproduce in their spawning grounds.
Young salmon, for example, remain in frehswater rivers for one to three years. Once they have grown to the size of a sardine, they reach the sea off the coast of Greenland and remain there until they reach sexual maturity. One to three years later, they return to the river where they were born in order to spawn.
The fish ladder principle is simple
It consists in drawing migratory fish towards an artificial waterway, which bypasses the obstructing hydroelectrical structure from a downstream direction.
As migratory fish have the distinction of swimming againts the current, a stream flow of about 153m/s is deflected towards the pass entrance. Salmon, sea trout and other species reach the pass by means of this natural guiding current.
In Gambsheim, they climb to a height of almost 11 meters, by crossing a series of weirs linked to each other by slots. After clearing each little slope, the fish can rest in the upper pond.
Monitoring the passage of migratory fish
From a viewing room, the movement of fish inside the pass is recorded on video. It is possible to recognize different species by their shapes. A hoop net is also used to count, measure and identify the fish.
The migratory species’ biological needs had to be taken into account in the fish pass design: deflection flow, weir size, and compatibility of current velocity with fish swimming speed. Scale-model tests were carried out at EDF’s hydroelectric testing facility, the Laboratoire National Hydraulique.
Now that the water quality of the Rhine has been restored, salmon and other migratory species are back. The Iffezheim fish pass and the one in Gambsheim, open their way to the rivers of Alsace and of the Northern Black Forest.
You can find the current results of the counting either on the homepage of
Landesfischreiverband Baden e.V. (in German) link
or Association Saumon Rhin (in French) http://www.saumon-rhin.com/
