Downstream migration system

The downstream migration system has two goals: on the one hand, to enable fish to move downstream of the obstacle and, on the other, to minimise mortality rates during this process.

Downstream migration mainly concerns three diadromous species for which migration is vital for their life cycle: silver eels (adults), Atlantic salmon and sea trout (young fish (smolt)).

Water intake points and turbines can pose a risk to fish as they migrate downstream. Consequently, it is important to adapt the power plants’ facilities to address this risk; there are several downstream migration solutions available.

Fish-compatible turbines

Hydrostadium has designed and built several fish-compatible turbines, such as VLH turbines and hydrodynamic screws. These turbines allow fish to migrate downstream without killing them. However, their installation is subject to a number of technical constraints. It is therefore often necessary to implement other downstream migration systems.

Fish-compatible water intakes

A water intake is considered to be compatible with fish if it :

• blocks fish and stops them from entering the turbines,
• guides fish towards a transfer system,
• channels fish downstream without damaging them.

Hydrostadium designs and builds fish-compatible water intakes and renovates existing screens to ensure that they are compliant with the downstream migration of fish.

Some technical recommendations :

• Ensure the space between mounting rails is compatible with the size of the fish,
• A slope with an angle of 26° from the horizontal is required,
• Ensure a speed of less than 0,5 m/sec over the screen to avoid the risk of plating.

Hydrostadium will be able to help you put your project together, carry out dimensioning calculations and conduct biological research to ensure successful downstream migration.