Author(s): Robert T. Milhous

Linked Author(s): Robert T. Milhous

Keywords: Point velocities; Nose velocities; Velocity simulation; Habitat simulation; Aquatic habitat

Abstract: The physical habitat of many species of aquatic animals is partially related to the velocity and depths in a stream. The Physical Habitat Simulation System (PHABSIM) is often used to simulate the physical habitat as a function of the discharge in the stream. In most applications of PHABSIM the mean column velocity is considered to be the appropriate velocity to use in the simulation. But in some situations, the calculations for velocity should be made at the expected location of a fish in the water column. The point velocity at the location of the fish (nose velocity) can be calculated using the power law or the universal logarithmic velocity distribution law. The mean column velocity will result in calculated habitat areas available in mountain streams during spring runoff with a snow-melt hydrograph less than half of the habitat calculated using the nose velocities. When the theoretical velocity distributions are used and when the nose depth is in the order of the roughness elements the nose velocities may need to be adjusted because velocity shelters are not adequately accounted for in the nose velocity and habitat calculations. Adjusting the habitat simulations to consider some of the nose locations are behind roughness elements where the nose velocities are less than the theoretical nose velocities increased the physical habitat calculated for the higher streamflows by 20 percent or more.

DOI:

Year: 1999