Turbulent flow-based habitat complexity metrics around instream boulders in support of river restoration.

Instream boulder placement has been commonly used to restore degraded streams by enhancing instream complexity and ecological value. Boulder-induced variations in turbulent flow characteristics affect the quality and availability of aquatic habitats in riverine systems. This experimental study, for the first time, systematically assesses the influence of boulder placement in rock-ramp arrangement on turbulent flow-based habitat complexity metrics. Acoustic Doppler velocimeter measurements were performed in an open channel flume to obtain turbulent flow-based habitat complexity metrics important to fish, such as turbulent kinetic energy, turbulent energy dissipation rate, integral length scale, and near-bed Reynolds shear stress for multiple boulder concentrations and flow events. The findings offer insights into the implications of these metrics for fish habitat suitability. This study introduces novel relationships that can facilitate the estimation of the turbulent flow-based habitat complexity metrics in boulder-bed streams. The results of this study may aid stream restoration projects that employ boulder placement techniques by providing a better understanding of the interactions between boulders, turbulent flow, and instream habitat quality and availability.