Culvert Barrel Research Articles

Anchor chains—A simple low‐cost device to assist passage of small‐bodied mass fish

AbstractAttention has been placed on a variety of barriers that hinder fish passage in modern times. The most prevalent fish barriers were culverts which have negatively impacted waterway connectivity and fish habitats. For small‐bodied mass fish, high barrel velocities and turbulence have reduced fish swimming performance because of their weak swimming capabilities. In the present study, physical testing was conducted under controlled flow conditions to assess the extent and magnitude of turbulence characteristics, secondary flow and low‐velocity zones in a 0.5‐m‐wide box culvert barrel. Two cases were investigated; a reference case consisting of a smooth rectangular channel and a low‐cost design solution to improve upstream fish migration consisting of a single galvanized anchor chain fitted within a smooth rectangular channel. The single anchor chain was positioned towards one corner of the channel to induce asymmetric flow, reducing overall energy losses and enhancing the existing low‐velocity zone in the adjacent channel corner. The anchor chain induced a strong turbulent flow motion away from the anchor chain, characterized by higher Reynolds stress and turbulent kinetic energy, along with a distinct channel flow asymmetry. Conversely, the low‐velocity zone, between the anchor chain and the bottom channel corner, was significantly expanded with reduced longitudinal mean velocities and turbulent scales. Whilst the anchor chain link contributed to some complex localized wake flow, the anchor chain also influenced the distributions of normal turbulent stresses (v'z2 – v'y2), which in turn influenced the location of secondary flow cells. This secondary flow redirected low momentum fluid into the low‐velocity zones, setting the conditions for the favorable upstream passage of small‐bodied mass fish species.

Interactions between water depth, velocity and body size on fish swimming performance: Implications for culvert hydrodynamics

Understanding how fish traverse man-made barriers (e.g. road-crossings and culverts) ensures that engineering and design guidelines achieve positive outcomes for fish communities. Water velocity, depth and fish body size are interrelated factors that influence fish passage through culverts. Velocity barriers have been a major focus of culvert remediation efforts to improve fish passage, however wide culvert designs that aim to limit high water velocities, often create shallow depths in the culvert barrel that can potentially impede fish passage. Here, we quantified how water velocity, depth and body size interact to affect fish swimming performance and their ability to traverse a 12 m culvert-scale swimming channel. Juveniles and sub-adults of three large-bodied native Australian fish species, silver perch (Bidyanus bidyanus), Murray cod (Maccullochella peelii) and eel-tail catfish (Tandanus tandanus), were chosen to represent a range of body shapes, swimming styles and capabilities. Each species was swum in nine treatments, consisting of three velocities at three water depths, with their time to fatigue and traverse success rates over 8 m of flume length quantified. We found that B. bidyanus had an exceptional probability of traverse success, with larger individuals traversing faster than smaller sized fish, but they were physically hindered by shallow water depths. The interaction between velocity and depth was non-linear and highly affected the swimming performance and traverse success of M. peelii and T. tandanus, particularly for fish >250 mm and < 100 mm. Our results demonstrate the importance of considering size class and species-specific swimming capabilities in culvert design criteria.

Novel hydraulic guidelines can assist upstream fish passage through smooth box culverts

ABSTRACT Culverts are important hydraulic structures for delivering a range of valuable socioeconomic services; however, they are also known to have negative impacts on freshwater and estuarine river systems, including the blockage of upstream fish passage, particularly small-bodied fish species. Herein new guidelines are proposed for fish-friendly multi-cell smooth box culvert designs, with a focus on small-bodied Australian native fish species and juveniles of larger fish. The new set of hydraulic engineering design guidelines, in the process of being implemented in New South Wales (Australia), optimise culvert design for fish passage for water discharges Q < QT = 0.1× Qdes, for which the reduced-velocity zone (RVZ) represents 15% of the flow area where 0 < Vx < Ufish, with Vx the local time-averaged longitudinal velocity component and Ufish the maximum prolonged swimming speed of target fish species. After a presentation of the basic concepts, a design application is developed based upon a real-world case study in north-eastern New South Wales (Australia). The novel approach relies upon a sound understanding of the velocity flow in the box culvert barrel at less-than-design discharges to accurately characterise the RVZ next to the barrel walls and corners, combined with a detailed understanding of the swimming performance and behaviour of native fish species.

How full-height sidewall baffles affect box culvert capacity: balancing fish passage and discharge requirements

ABSTRACT Low-level river crossings and culverts deliver valuable transportation and hydraulic control services to the society, but have negative impacts in terms of upstream fish passage. Recently, full-height sidewall baffles have been imposed in north-eastern Australia to assist upstream passage of small-bodied fish in box culverts, although the impact on the culvert discharge capacity was ignored. Detailed physical modelling was conducted under controlled flow conditions in a near-full-scale culvert barrel channel, equipped with such full-height sidewall baffles. The results provide a quantitative assessment of the impact of full-height sidewall baffles on the discharge capacity of box culverts. Applications were developed for single- and multi-cell box culverts, and practical implications are discussed.

Hybrid modelling of low velocity zones in an asymmetrical channel with sidewall longitudinal rib to assist fish passage

AbstractChannels with longitudinal beams have been studied for decades in chemical engineering, environmental and sanitary engineering, aeronautics, astronautics, biology and geology. In the current study, a combination of physical and numerical Computational Fluid Dynamics (CFD) modelling was undertaken to test whether an asymmetrical channel equipped with a sidewall longitudinal rib could provide flow conditions conducive to upstream fish passage. The study focused on small‐bodied fish and juveniles of larger fish, typically less than 100 mm in total length. A detailed hydrodynamic study was conducted in an asymmetrical rectangular channel equipped with a sidewall square rib in a culvert barrel channel. Both free‐surface velocity and boundary shear stress measurements showed strong secondary currents of Prandtl's second kind. The channel asymmetry contributed to intense secondary motion, associated with turbulent dissipation. The channel design provided a small well‐defined highly turbulent low‐velocity zone beneath the rib. In the context of hydraulic structure designs, uttermost care must be considered because of manufacturing, installation and operational practices. In many instances, alternative engineering designs with small baffles and asymmetrical appurtenance should be preferred to assist with fish passage in hydraulic structures.

Generalize new method to determine the location of the control setion in the box culvert under inlet control

The control section is a location at which a unique relationship between the flow rate and the water depth (critical depth) exists. When the culvert flows under inlet control, the location of the control section exists into the culvert barrel at some distance from the entrance. The exact location of the control section has not been investigated until now. The present study demonstrates the exact location of the control section experimentally based on the measured elevations along the barrel for each run undertaken. Then the correlation between the critical depth and its location is presented as proposed deterministic equations. Thus, the aim is to find the section at which the critical depth is achieved, measured from the beginning of the barrel by using the empirical equations. The application of the proposed equations is specified in terms of the geometric and hydraulic conditions that have been adopted in the present study.

Developing Cost-Effective Design Guidelines for Fish-Friendly Box Culverts, with a Focus on Small Fish.

Low-level river crossings can have negative impacts on freshwater ecosystems, including blocking upstream fish passage. In order to restore upstream fish passage in culverts, we developed physically-based design methods to yield cost-effective culvert structures in order to maintain or restore waterway connectivity for a range of small-bodied fish species. New guidelines are proposed for fish-friendly multi-cell box culvert designs based upon two basic concepts: (1) the culvert design is optimised for fish passage for small to medium water discharges, and for flood capacity for larger discharges, and (2) low-velocity zones in the culvert barrel are defined in terms of a percentage of the wetted flow area where the local longitudinal velocity component is less than a characteristic fish speed linked to swimming performances of targeted fish species. This approach is novel and relies upon an accurate physically-based knowledge of the entire velocity field in the barrel, specifically the longitudinal velocity map, because fish tend to target low-velocity zone (LVZ) boundaries. The influence of the relative discharge threshold Q1/Qdes, characteristic fish swimming speed Ufish, and percentage of flow area on the size of box culvert structures was assessed. The results showed that the increase in culvert size and cost might become significant for a smooth culvert barrel with Ufish < 0.3 m/s and Q1/Qdes > 0.3, when providing 15% flow area with 0 < Vx < Ufish. Similar trends were seen for culvert barrel with recessed cell(s).

Modelling small ventilated corner baffles for box culvert barrel

During the last decades, concerns regarding the ecological impact of standard culverts have led to some design evolution. The installation of baffles along the culvert barrel yields smaller velocities and larger water depths in the barrel, potentially more suitable for upstream fish passage, albeit with a decrease in discharge capacity. Small triangular corner baffles were proposed to facilitate the upstream passage of small-body-mass fish, without compromising the discharge capacity of the culvert at design flow. Although fish benefited from low velocity regions for resting and sheltering, a small fraction of small-body-mass fish were observed to become disoriented by the adverse effect of flow reversal regions in the wake of plain baffles. This study presents the hydrodynamic testing of small ventilated triangular corner baffles for standard box culverts. The baffle ventilation was introduced to reduce the impact of negative wake behind the baffles. Two designs were tested: a baffle with three holes and a brush baffle. Detailed modelling in a near-full-scale culvert barrel showed that the ventilated corner baffles created a smaller negative wake region. A lesser negative velocity magnitude was observed behind the ventilated baffles, in comparison to plain baffles, for the same flow rate, baffle height and spacing. With ventilated corner baffles, the longitudinal distribution of low-velocity zone was more uniform, yielding a better longitudinal connectivity for upstream passage, compared to plain baffles. A comparison between various boundary treatments suggested however that the requirements for continuous, sizeable low positive velocity zone suitable to small-bodied fish might be better fulfilled with an asymmetrically roughened culvert barrel than with triangular baffles, even with ventilation.

Three‐dimensional numerical simulations of smooth, asymmetrically roughened, and baffled culverts for upstream passage of small‐bodied fish

AbstractTraditional box culvert designs lead to development of high velocity zones in the culvert barrel that often impede upstream migration of fish. Herein, three‐dimensional Reynolds‐averaged Navier‐Stokes (RANS)‐ and Large eddy simulation (LES)‐based computational fluid dynamics (CFDs) simulations were performed to compare the effectiveness of smooth, asymmetrically roughened, and corner‐baffled barrels, in creating low‐velocity zones (LVZs) and providing opportunity for upstream passage of small‐bodied fish. The results revealed distinctive benefits provided by the asymmetrically roughened and corner‐baffled barrels relative to the smooth barrel. Cross‐sectional asymmetry, corners, and obstructions are important factors that contribute to the generation of LVZs conducive to fish passage, albeit contiguity of LVZs is required, particularly for weak swimmers. The study demonstrates the adequacy and effectiveness of CFD models to complement traditional laboratory studies in understanding basic mechanisms beneficial to fish passage and to provide insights into future designs.

Using small triangular baffles to facilitate upstream fish passage in standard box culverts

A culvert is a covered channel to pass streams and floodwaters through an embankment. The ecological impact of culverts has been recognised, in particular in terms of stream connectivity, but existing guidelines lead often to un-economical culvert design. Herein, a small triangular corner baffle system was tested physically in a near-full-scale fish-friendly facility of a box culvert barrel. Experiments were repeated with several configurations to characterise the flow properties for a range of less-than-design flows, baffle sizes and spacings. In presence of triangular corner baffles, the flow was asymmetrical, owing to the wake behind each baffle. The presence of triangular corner baffles had a moderate effect on the flow resistance and discharge capacity, albeit the data indicated the combined effect of relative baffle height and spacing on the friction factor. With triangular baffles, the surface area of slow velocity regions increased by a factor of two to three. Such low velocity regions are preferential swimming zones for fish, beneficial to small-bodied fish passage. Testing with small-bodied fish showed that fish preferred to swim upstream in slow-velocity regions, typically next to the sidewalls and in the left corner where the triangular baffles were located. The presence of small triangular baffles facilitated substantially the upstream passage of small fish, including in terms of endurance, compared to a smooth un-baffled box culvert barrel, when the baffle size was comparable to the fish length. The present findings highlighted the importance of physical modelling at near full-scale for the development of fish-friendly culvert designs.

On upstream fish passage in standard box culverts: interactions between fish and turbulence

ABSTRACTThe challenge to understanding the fluid mechanics of fish swimming is knowing exactly what the water is doing where the fish swims. Recent field and laboratory observations in box culvert barrel showed that fish tend to swim preferentially close to the channel sidewalls, in regions of slow velocity and often high turbulence intensity. An analogy with human swimming is developed herein. Fish minimise their energy expenditure by swimming in inter-connected low-velocity zones (LVZs) and minimising acceleration-deceleration amplitudes. In a box culvert barrel, the mechanical energy expenditure is drastically reduced in sidewall and corner flow regions, characterised by low velocities and secondary current motion. These regions were “sweet spots” used by small bodied fish to minimise their rate of work. Both bed and sidewall roughness must be scaled to the fish dimensions. More generally, the methodology brings rigorous scientific insights into why certain culvert designs, possibly equipped with baffles and apertures, are more efficient in promoting fish passage. One may foresee an evolution of the scientific approach towards using advanced physics-based theory supported by high-quality data sets. The results also raise questions on limitations of current fish swim tunnel tests, and matching swimming performance data to hydrodynamic measurements.

Outlet Flow Velocity in Circular Culvert

Abstract The outlet flow velocity in the end section of the culvert barrel depends in most cases on the culvert geometry, including the barrel slope, as well as on upstream and downstream channel parameters. Flowing water can create pressure flow or free surface flow in the culvert barrel. In the case of an unsubmerged barrel outlet, the free-surface flow is more frequent than the full flow. Increased velocities can cause channel bed scour and bank erosion downstream of the culvert outlet. Different culvert flow cases in which the barrel outlet is unsubmerged are presented in this paper. The influence of the flow regime on the outlet velocity is also discussed.

Energy Dissipation in Culverts by Forced Hydraulic Jump within a Barrel

Riprap and concrete stilling basins are often built at culvert outlets to keep high-energy flows from scouring the streambed. Two simple alternatives to large basins are examined: a horizontal apron with an end weir and a drop structure with an end weir. The two designs are intended to reduce the flow energy at the outlet by inducing a hydraulic jump within the culvert barrel without the aid of tailwater. This research examines the jump geometry and the effectiveness of each jump type and proposes a design procedure for practicing engineers. The design procedure is applicable to culverts with approach Froude numbers from 2.6 to 6.0. Both designs are effective in reducing outlet velocity 0.7 to 8.5 ft/s (0.21 to 2.59 m/s), momentum 10% to 48%, and energy 6% to 71%. The design layouts allow easy access for maintenance activities.

Energy Dissipation in Culverts by Forced Hydraulic Jump Within a Barrel

Riprap and concrete stilling basins are often built at culvert outlets to keep high-energy flows from scouring the streambed. Two simple alternatives to large basins are examined: a horizontal apron with an end weir and a drop structure with an end weir. The two designs are intended to reduce the flow energy at the outlet by inducing a hydraulic jump within the culvert barrel without the aid of tailwater. This research examines the jump geometry and the effectiveness of each jump type and proposes a design procedure for practicing engineers. The design procedure is applicable to culverts with approach Froude numbers from 2.6 to 6.0. Both designs are effective in reducing outlet velocity 0.7 to 8.5 ft/s (0.21 to 2.59 m/s), momentum 10% to 48%, and energy 6% to 71%. The design layouts allow easy access for maintenance activities.