Author(s)

P. M. Biron, D. M. Carré & S. J. Gaskin

Abstract

Despite the widespread use of in-stream structures in stream restoration projects to enhance the quality of physical habitat, it is only recently that the hydraulics of these structures have been studied in detail, typically using simplistic geometries in laboratory experiments. The objective of this study is to examine hydraulics around complex flow deflectors using a combination of laboratory, field and three-dimensional (3D) Computational Fluid Dynamics (CFD) approaches. In the laboratory, Acoustic Doppler Velocimeter (ADV) measurements revealed that flow overtopping the structure modifies the scour zone and bed shear stress pattern compared to a greater structure height. In the field, a 3D CFD model, which was calibrated at low flow using ADV and Particle Image Velocimetry measurements, was used to investigate both low and high flow (overtopping) conditions. A complex 3D pattern in the recirculation zones downstream of the deflectors is observed in the overtopping simulations, highlighting the limits of habitat structure studies based on depth-averaged (2D) models. The comparison with laboratory data is complicated by the fact that a dug pool was used in the field, which does not correspond to the position of the pools that developed near deflectors over a mobile bed in the laboratory. As natural rivers exhibit a wide range of discharges with various overtopping ratios, it is essential to pursue work using 3D CFD to test how different deflector height, length and angle designs affect the position and dimension of scour zones and the long-term viability of fish-habitat restoration projects. Keywords: three-dimensional velocity, pool, bed shear stress, deflector design, overtopping, computational fluid dynamics, recirculation zone.

Keywords

three-dimensional velocity, pool, bed shear stress, deflector design, overtopping, computational fluid dynamics, recirculation zone