Coupling 3D hydraulic simulation and fish telemetry data to characterize the behaviour of migrating smolts approaching a bypass

Abstract

Human-induced river fragmentation is a major threat to migratory fish species. Restoring river connectivity requires the construction of fish passage solutions, such as fishways for upstream and downstream migration. While many studies focussed on the upstream migration of diadromous fishes, and especially of adult Atlantic salmons (Salmo salar), we analyze juvenile behaviour under different hydraulic conditions at reservoir to improve the development of effective bypass systems for downstream passage of salmon smolt. Based on coupling three-dimensional (3D) computational fluid dynamics (CFD) simulations to smolt positions tracked by two-dimensional (2D) telemetry, the present study aimed to explore smolt behaviour in relation to hydraulic cues. More specifically, we explored how hydraulic conditions influence fish behaviour and how fish navigate depending on this behaviour. In 2017, 23 smolts were tracked in the reservoir of Pout es (Allier River, France), associated with different turbine discharge rates. 3D CFD simulations were performed and validated against field measurements in the reservoir upstream of the hydropower plant. The study of fish displacements in relation to flow conditions provided new insights with the use of thrust force, swimming orientation and direction as means to precisely characterize smolt behaviour, which can help in the design of downstream migration passage facilities. At Pout es dam, flow velocity, flow acceleration and turbulent kinetic energy are very low and therefore can lead to fish disorientation. However, results underlined that having a minimum flow velocity of 20 cm/s in reservoirs is sufficient to prevent delay and allow fish navigation.

Evaluation of a fine-spaced angled rack with surface bypass in providing safe and timely downstream passage for salmon smolts and silver eels

“…The effectiveness of an angled fine-spaced rack (20 mm with vertical bars) in protecting salmon smolts and silver eels and guiding them to a surface bypass was assessed in a medium-sized HPP, with a higher intake capacity than in the majority of previous studies (Havn et al, 2018;Nyqvist et al, 2018;Tomanova et al, 2018Tomanova et al, , 2021Tomanova et al, , 2023Økland et al, 2019;Calles et al, 2021;Kjaerås et al, 2023). Globally, impediment passage efficiency (89.6% and 96.9% for salmon smolts and eels, respectively), FDPS specific passage efficiency (89.1% and 93.3%), and passage times (median 3 and 7.5 min) were very satisfying, although, admittedly, high hydrological conditions favored passage (Ben Jebria et al, 2021). This also reflects a great improvement in fish protection, as salmon smolt passage efficiency in the former FDPS (bypass associated to a conventional trash-rack with 45 mm bar spacing) was 64.7% (Lauters and Segura, 1998).…”

“…(2021) (12.5-19 m). Another explanation is the larger size of the intake zone, requiring longer search behavior to find a passage route, as previously reported for salmon smolts in other studies (Ben et al, 2021Ben Jebria et al, 2021Renardy et al, 2023). Several other reasons, linked to bypass location and hydraulic conditions on the rack may, however, also explain this poorer performance.…”

Assessment of the Attractiveness and Passage Efficiency of Different Fish Passage Solutions at a Hydropower Plant by Combining Fine Scale 2D-Telemetry and Hydraulic Numerical Modelling

“…Elevated water velocities and shallow water depths at the entrance of the nature-like fishway may have repulsed the smolts from using this migration route. Typically, smolts are attracted to flow velocities between 0.2 m s −1 and 0.5 m s −1 [22,27,46] and prefer water depths greater than 1.5 m [27], contrary to the conditions present in the nature-like fishway. Therefore, the use of a nature-like fishway will depend on the associated discharge, the river discharge, as well as flow velocities and water depths.…”

“…The correlations between encountered flow velocities or water depths and crossing time were low, but these variables may have still have influenced and delayed smolt downstream migration. Water velocities greater than 0.2 m s −1 usually promote downstream movements of the smolts [22,46], but can become repulsive beyond a certain threshold. In the naturelike fishway, the combination of a shallow average water depth of 0.35 m and water velocities that reached around 2 m s −1 in some areas may have induced hesitation in the smolts to migrate rapidly.…”

Numerical Simulation of Habitat Restoration for Floating Fish Eggs in the Upper Yangtze River Tributaries

“…Noor Ben Jebria et al [25] explored the relationship between juvenile fish behavior and hydraulic cues by integrating three-dimensional computational fluid dynamics (CFD) simulations with two-dimensional telemetry tracking of fish positions. Their findings provide new insights that contribute to the design of downstream migration passage facilities.…”