PREDICTING VELOCITY FREQUENCY-DISTRIBUTIONS IN STREAM REACHES

The quantification of management impacts on fish populations requires a reliable estimation of the local hydraulic habitat variability. In t he case of complex natural flows, deterministic hydraulic models are e xpensive and not adapted to the description of local velocities. Stati stical descriptions of the velocity distribution as a function of easi ly obtained input variables are therefore an attractive alternative. E xisting velocity data on several French stream segments with intermedi ate- to large-scale roughness were analyzed statistically to define a shape parameter of the point velocity frequency distributions. Dimensi onal analysis was used to model this shape parameter, and thereby the velocity distributions, as a function of simple average descriptors of stream reaches (discharge, mean roughness, mean depth, and mean width ). Such predictive models of the physical habitat availability for fis h in the probability domain can provide stream managers with cost-effe ctive decision tools.