Ratio of occupied water velocity (velocity within the region where the fish swims) to cross sectional average water velocity. The average water velocity is multiplied by the reduction factor to account for areas of reduced velocity utilized by a swimming fish to conserve energy. The use of Velocity Reduction Factors is usually only applicable for small fish.  Different Velocity Reduction Factors can be applied to the inlet, barrel, and outlet zones.

See: Occupied Velocity, Culvert Zones