Labyrinth Weirs: Nappe Interference and Local Submergence

Crookston, Brian M.; Tullis, Blake P.

doi:10.1061/(asce)ir.1943-4774.0000466

Cited by 60 publications

(29 citation statements)

References 3 publications

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“…Standard weir equations have been modified to provide stage–discharge relationship for weirs with different geometries and designs, such as triangular‐shaped labyrinth weirs (Tullis, Amanian, & Waldron, ). However, for weirs with non‐linear geometries, this can be particularly complicated because the structures operate as regular weirs with an increased crest length at low heads but have lower discharge coefficients at high heads due to nappe collision and local submergence regions (Crookston & Tullis, ). When weirs incorporate an orifice or gaps between the rocks, there is additional discharge below the weir crest.…”

Section: Introductionmentioning

confidence: 99%

Physical modelling of pool and weir fishways with rock weirs

Kupferschmidt

Zhu

2017

River Research & Apps

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The flow characteristics of pool and weir fishways with rock weirs were studied through physical modelling. Detailed flow measurements were obtained using an acoustic Doppler velocimeter to understand how weir geometry, discharge, and bed slope affect flow patterns, velocity, turbulence kinetic energy, turbulence intensity, and Reynolds shear stresses in the fishway. The weir geometries used in this study are similar to those typically used for river restoration projects.The use of a V-shaped rock weir was found to reduce the mean streamwise velocity in the pools by about 20% but more than double the maximum velocity magnitude. Two stage-discharge relationships were developed using the standard weir equation and a modified discharge coefficient to account for both flow over the weir and orifice flow through the base of the weir. The use of V-shaped rock weirs has the potential to offer significant advantages in assisting multispecies fish migration. The results of this study can be applied to the hydrotechnical design of pool and weir fishways with rock weirs and for river restoration projects. KEYWORDS ADV, fishway, nature-like fishway, pool and weir fishway, rock weir, turbulence

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Section: Introductionmentioning

confidence: 99%

Physical modelling of pool and weir fishways with rock weirs

Kupferschmidt

Zhu

2017

River Research & Apps

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“…The evolution of the flow field is clearly evident as upstream head H and Q increase the volumetric space of the outlet keys restricts jet interaction and energy dissipation caused by the crossing jets. In fact, H/P ≥ 0.2 local submergence is observed to increase and occupies a larger percentage of this region until the majority of B o + B b streamwise distance is locally submerged [39]. Local submergence is a contributor to reduced discharge capacity and is also noteworthy when considering the reduction in energy dissipation for higher H/P ratios, as discussed in the subsequent section.…”

Section: Type a Pk Weir Flow Featuresmentioning

confidence: 82%

Energy Dissipation of Type a Piano Key Weirs

Eslinger

Crookston

2020

Water

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A Piano Key weir (PK weir) is a nonlinear, labyrinth-type weir well suited for rehabilitation projects due to a relatively small footprint and the ability to pass large discharges for lesser upstream-head values when compared with other weir types. A critical component of a hydraulic structure is the energy-dissipative properties. Currently, information and guidance is limited, with previous energy dissipation studies of PK weirs primarily of specific projects. Therefore, to document and quantify energy dissipation, four laboratory-scale Type A PK weir models with different width ratios (Wi/Wo) were studied, with 255 tests comprising this new dataset, along with detailed observations of the flow field. Results were compared to existing published data regarding energy dissipation downstream of trapezoidal and rectangular labyrinth weirs. To support design efforts, two equations, both functions of head-water ratio (H/P) and Wi/Wo, are proposed to predict the relative residual energy downstream of PK weirs. The energy dissipation of PK weirs is largest at low flows and decreases in a logarithmic-like manner as flow increases. PK weirs with increased hydraulic efficiency, caused by an increase in Wi/Wo, resulted in slightly smaller energy dissipation values within the range 0.2 ≤ H/P ≤ 0.8. The energy dissipation of PK weirs was found to be relatively constant, independent of Wi/Wo, and in the ranges 0.07 ≤ H/P ≤ 0.2 and 0.8 ≤ H/P ≤ 0.95.

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“…The discussion also reveals that a labyrinth weir with a smaller side wall angle achieves its maximum flow capacity at a relatively lower water head above the crest than a labyrinth weir with a higher side wall angle. Because the occurrences of nappe interference and local submergence (Crookston and Tullis 2012) in labyrinth weirs with low side wall angles cause a reduction in the discharge capacity, it can be inferred that labyrinth weirs are suitable for the low water head conditions above the crest; hence, they need to be designed for the same condition to achieve economy. However, it is suggested to find a suitable modification in the upstream apex of the labyrinth weirs that can avoid or delay the occurrence of the nappe interference phenomenon to preserve the ability of delivering increased discharge with increasing H t =P value over a relatively wider range of water head above the weir crest.…”

Section: Discussionmentioning

confidence: 99%