Latest Experiance with Nature-Like Fishpasses in Germany/Europe

Fish-passes form either a part or the entire river width. The construction of fish passes is confined to the available space, especially at locations of hydro power stations. The traceability of a fish-pass depends on its position in the river and on the volume of the discharge which is directed through the fish-pass.

Fish-passes which form the entire river width are easier to locate for the ascending fish because the main current flows though them. With regards to the restoration of river continuity and removing dams, this option is given preference over any other solutions. Increasingly fish-passes are being designed in a nature-like form.

In Germany many fish-passes of this type were built and a long- term experience has been recorded. New design criteria for such fish-passes were formulated on the basis of this experience. The results were published in the official Manual on the Design of Fish-Passes. Experiences from other European countries were taken into account.

The analysis of existing facilities reveals that the term “nature-like” does not always describe them correctly. Because the morphology of the individual running waters might differ significantly from the rocky structure of the migration corridor within fish-passes. For this reason the term “nature-like” is replaced by the term “roughened channel” in future . This new term refers to the hydraulic mechanism as the energy is dissipated. The emphasis is placed rather on it’s function as a migration route rather than of a romantic impression. 

Traceability and passability of a migration corridor decides about its operational functionality. To achieve optimal efficiency of passage the hydraulic regime has to be appropriate for the swimming performance of the local fish population. Therefore, the design criteria were strictly derived from the sustained swimming speed of the local fish species within the individual river zones.

In addition possible construction types for roughened channels (ramps with flat surface, pool type or perturbation boulder structure) were examined and the criteria for their application and maximum length were formulated.