What is the purpose of a fish pass ?

Hydraulic structures are partly responsible for disrupting ecological continuity, a concept developed by the Water Framework Directive of 2000 (WFD) and defined as the free movement of living organisms throughout their life cycle (feeding, reproduction and rest) and successful sediment transportation.

To ensure the ecological continuity of water courses, living organisms must be allowed to move about freely and access areas that are essential for reproduction, growth, feeding and shelter. Ecological continuity also involves making sure that sediment transportation and biological reservoirs are not disturbed.

Hydrostadium contributes to ecological continuity goals by building fish passes for the upstream and downstream migration of fish.

Strategic location

The habits of fish must be taken into account when considering the location of fish passes.

In the case of upstream migration, the fish pass must be located :

• In the corner of the dam wall and the bank,
• In both corners, in the case of a very wide dam,
• In the sharpest corner, in the event of oblique angles.

In the case of downstream migration, the fish pass must be located :

• In the area closest to the foot of the dam,
• And avoid, as much as possible, areas of turbulence.

With over 15 years of experience in the design and construction of fish passes, Hydrostadium has already designed almost 150 fish passes of all kinds, in cooperation with and under the supervision of the French agency for biodiversity.

Monitoring of fish passes

When a fish pass is situated at a strategic location for the migration of fish, it may be useful to monitor the fish that use it. This enables knowledge of migratory fish populations and their migratory habits to be acquired.

With regards to this matter, Hydrostadium has experience in the use of video-counting equipment that serves to observe and count fish in fish passes.