|Title:||Effects of hydraulic shearing actions on juvenile salmon|
|Author/Editor:||Alan B. Groves|
|Institution:||Report of the National Marine Fisheries Service, Northwest Fisheries Center|
1. Hydraulic shearing actions that exist along sharply defined margins of velocity differences can kill and injure fish. The injuries are similar to those described for fish that pass through turbines, or more recently, slotted bulkheads.
2. Injury occurs when just the part of the fish that contacts the velocity difference is thereby differentially accelerated. The head region is the most susceptible to tearing injuries resulting from such differential acceleration.
3. Velocity differences are what injure and kill. Thus, higher overall velocities produced more damage, because these in turn caused greater differences to be contacted by the fish.
4. Injuries can occur in 1 millisecond of time, in an area l–inch square. This suggests that fish can be damaged in any high–energy flow situation that may create momentary localized points of sharp velocity difference. Such rapid, transitory events would be difficult to assess or pinpoint in specific field conditions, and impossible for fish to detect or avoid.