Prediction of fisheries physical habitat values based on hydraulic geometry and frequency distributions of depth and velocity

Abstract

We propose a technique that allows the estimation of available physical fish habitat in small sized stream reaches (mean annual flow less than 3.5 m³/s) without the need to acquire and analyze extensive site‐specific data commonly used in many instream flow studies. The technique utilizes a modified form of previously published equations that estimate velocity and depth frequency distributions based on reach average velocity and depth which in turn can be calculated using widely known at‐a‐station hydraulic geometry equations. Velocity and depth frequency distributions are then combined with fish preferences for velocity and depth to produce habitat versus discharge relationships for a desired range of flows. When the resulting physical habitat versus discharge relationships for target fish species and life stages are compared to weighted usable area relationships (habitat versus discharge relationships derived using hydraulic and habitat models) developed from site‐specific studies, the prediction error was shown to be less than 15%.

Keywords:

• Fish habitat
• hydraulic geometry
• velocity and depth frequency distributions
• instream flows