Design, operation, and evaluation of an inverted, inclined, outmigrant fish screen

A unique screening device for juvenile fish has been built on, and is operating in, a hydroelectric canal on Vancouver Island, British Columbia. The canal diverts up to 42.5 m3/s, and the screen is designed to remove outmigrant smolts of steelhead Oncorhynchus mykiss and coho salmon O. kisutch from the canal inflow and return them to the Salmon River. The 25-m-long by 6.7-m-wide screen is supported on a removable steel truss suspended in a rectangular section of the canal flowing at a depth of 2.9 m. It incorporates 170 m2 of slotted woven-wire-mesh screen, and when in service, it inclines downward in the downstream direction, forcing fish into a collector resting on the canal floor at its lower end. The collector diverts the fish laterally out of the canal and into the bypass works. Although the screen provides less than 100% protection, because of compromises required by budgetary constraints, it is a practical, cost-effective alternative to more conventional designs. With appropriate design modifications, this type of screen could function with higher efficiencies at little additional cost, and in streams with fish of all life stages.