The large velocities in a culvert hinder the movements of migratory and non-migratory fish, particularly small-bodied fishes and juveniles of larger fish. To date, limited hydrodynamic characteristics, such as the turbulence structures in the culvert barrel, were considered in the current fish passage design guidelines for box culverts. This presents a gap in knowledge on the fundamental understanding of culvert hydrodynamics and its effect on fish kinematics. New research was conducted, focusing on box culverts, with the aim of designing a fish passage without additional hydraulic appurtenances such as baffles. The research focuses on the use of low velocity zone (LVZ) in the culvert barrel, that corresponds to the observed fish swimming zone for upstream fish passage. Herein, new physical modelling involved detailed free surface and velocity measurements, and the results are detailed in this paper which include the joint mapping of Reynolds Stresses, integral timescale, advection length scale and turbulent burst analysis in a near-full-scale rectangular channel. Three-dimensional velocity measurements showed some strong secondary currents of Prandtl’s second kind. The channel boundaries and bottom corners contributed to the occurrence of low-velocity zones (LVZs) and the hydrodynamic characteristics of these LVZs were carefully detailed. For a range of less-than-design flow conditions (1.7 × 105 < Re < 4.3 × 105), the low-velocity zone constitutes high Reynolds stress regions with turbulent burst events of large amplitude and long burst duration. Herein, the median secondary current magnitudes corresponded to 4.7% to 6.0% of Vmax. The integral timescale in the corner regions is shorter compared to the central flow region, that is TEx = 50–95 ms, TEy = 10–100 ms, TEz = 5–15 ms in the corner regions, whereas the timescale component in the central region can be equalled or more than 260 ms. This also corresponds to the advection length scale of Lxx = 30–80 mm, Lxy = 10–100 mm and Lxz = 2–15 mm in the corners, comparable to the actual size of the small-bodied fishes. From the turbulent burst analysis, the burst durations are in the range of 14–40 ms in the corners, with some turbulent burst amplitude larger than 20. The outcome of the physical modelling provided a fascinating insight into the hydrodynamics of the observed fish swimming zone (i.e. LVZ) and the data set constitutes a stepping stone for future development of fish passage design guidelines using LVZ with turbulence considerations.

Turbulence characterisation of low velocity zone in box culvert: application to upstream fish passage

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发表日期：

2026年1月31日

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Hui Ling Wong,
Hubert Chanson

摘要

The large velocities in a culvert hinder the movements of migratory and non-migratory fish, particularly small-bodied fishes and juveniles of larger fish. To date, limited hydrodynamic characteristics, such as the turbulence structures in the culvert barrel, were considered in the current fish passage design guidelines for box culverts. This presents a gap in knowledge on the fundamental understanding of culvert hydrodynamics and its effect on fish kinematics. New research was conducted, focusing on box culverts, with the aim of designing a fish passage without additional hydraulic appurtenances such as baffles. The research focuses on the use of low velocity zone (LVZ) in the culvert barrel, that corresponds to the observed fish swimming zone for upstream fish passage. Herein, new physical modelling involved detailed free surface and velocity measurements, and the results are detailed in this paper which include the joint mapping of Reynolds Stresses, integral timescale, advection length scale and turbulent burst analysis in a near-full-scale rectangular channel. Three-dimensional velocity measurements showed some strong secondary currents of Prandtl’s second kind. The channel boundaries and bottom corners contributed to the occurrence of low-velocity zones (LVZs) and the hydrodynamic characteristics of these LVZs were carefully detailed. For a range of less-than-design flow conditions (1.7 × 10⁵ < Re < 4.3 × 10⁵), the low-velocity zone constitutes high Reynolds stress regions with turbulent burst events of large amplitude and long burst duration. Herein, the median secondary current magnitudes corresponded to 4.7% to 6.0% of V_max. The integral timescale in the corner regions is shorter compared to the central flow region, that is T_Ex = 50–95 ms, T_Ey = 10–100 ms, T_Ez = 5–15 ms in the corner regions, whereas the timescale component in the central region can be equalled or more than 260 ms. This also corresponds to the advection length scale of L_xx = 30–80 mm, L_xy = 10–100 mm and L_xz = 2–15 mm in the corners, comparable to the actual size of the small-bodied fishes. From the turbulent burst analysis, the burst durations are in the range of 14–40 ms in the corners, with some turbulent burst amplitude larger than 20. The outcome of the physical modelling provided a fascinating insight into the hydrodynamics of the observed fish swimming zone (i.e. LVZ) and the data set constitutes a stepping stone for future development of fish passage design guidelines using LVZ with turbulence considerations.