Pas trouvé d'occurence en français, mais le principe semble être le suivant: au lieu d'une prise d'eau avec une cheminée verticale, on met un couvercle-dalle qui admet l'eau à l'horizontale, et crée une accélération du débit (d'où "velocity") qui a pour effet d'effrayer les poissons et donc de limiter les prises accidentelles.

"Offshore Intake Velocity Cap. This is a behavioral technology associated with a submerged offshore intake structure(s). The velocity cap redirects the area of water withdrawal for an offshore intake located at the bottom of the water body. The cap limits the vertical extent of the offshore intake area of withdrawal and avoids water withdrawals from the typically more productive aquatic habitat closer to the surface of the water body.
This technology operates by redirecting the water withdrawal laterally from the intake (rather than vertically from an intake on the bottom), and as a result, the water entering the intake is accelerated laterally and is more likely to provide horizontal velocity cues to fish and allow fish to respond and move away from the intake. Potentially susceptible juvenile and adult fish that are able to identify these changes in water velocity as a result of their lateral line sensory system, are able to respond and actively avoid the highest velocity areas near the mouth of the intake structure."
http://www.slc.ca.gov/Reports/Carlsbad_Desalinization_Plant_...