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Article

Ecohydraulic Characteristics of a Differential Weir-Orifice Structure and Its Application to the Transition Reach of a Fishway

1
School of Water Conservancy, North China University of Water Resources and Electric Power, Zhengzhou 450046, China
2
St. Anthony Falls Laboratory, Department of Civil, Environmental and Geo-Engineering, College of Science and Engineering, University of Minnesota, Minneapolis, MN 55414, USA
*
Authors to whom correspondence should be addressed.
Academic Editor: Dibyendu Sarkar
Water 2022, 14(11), 1711; https://doi.org/10.3390/w14111711
Received: 15 December 2021 / Revised: 19 May 2022 / Accepted: 23 May 2022 / Published: 26 May 2022
A transition reach is usually necessary to connect two channels with different cross-sections to facilitate a gradual variation of the water depth and a mean flow velocity profile. A modified weir–orifice structure named differential weir-orifice (abbreviated DWO) is proposed here and applied to the transition reach of a fishway. Considering the preferred flow velocity and body shape of specific migrating fish, the design guidelines of a DWO plate are firstly discussed in terms of basic hydraulics. Then, by means of hydrodynamic numerical simulation and scale model tests, the design of a non-prismatic transition reach in a proposed large fishway is studied and optimized with a DWO. The simulation results indicate that the velocity profile in conventional weirs varies in the range of 2.5 to 3.2 m/s, and the head drop of each stage is up to 0.4 m, which is not suitable for fish migration. However, the flow could be improved by adopting the DWO: the split ratio of each weir gradually increases from 13% to 40%, with weir height decreasing along the reach, which allows the water drop of each stage to decrease by 35% to 50%. This causes the velocity over the weir to reduce in the range of 1.2 to 2.1 m/s, while the velocity in the orifice flow remains limited to 0.8 to 1.3 m/s. The flow velocity profile in the DWO also presents a bimodal distribution, with different flow layers increasing the suitability for fish migration. Moreover, the DWO also performs well in decreasing the vertical turbulent intensity together with the turbulent kinetic energy, reduced by about 33% at the weir crest. The energy at the bottom orifice is only about 28% of that at the weir crest. This indicates that the turbulent kinetic energy profile could be adjusted by the DWO, part of which is transferred from the weir crest to the bottom orifice. The model test results also show that the water surface experienced only gradual variation along the DWO. The adjusting functionality of the DWO can enable the fishway to be more effective, promoting an ecohydraulic design solution for fishway structures. View Full-Text
Keywords: differential weir–orifice; transition reach; fish migration; hydraulic modeling; turbulent kinetic energy differential weir–orifice; transition reach; fish migration; hydraulic modeling; turbulent kinetic energy
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MDPI and ACS Style

Liu, M.; Xu, M.; Liu, Z.; Sun, D.; Guala, M. Ecohydraulic Characteristics of a Differential Weir-Orifice Structure and Its Application to the Transition Reach of a Fishway. Water 2022, 14, 1711. https://doi.org/10.3390/w14111711

AMA Style

Liu M, Xu M, Liu Z, Sun D, Guala M. Ecohydraulic Characteristics of a Differential Weir-Orifice Structure and Its Application to the Transition Reach of a Fishway. Water. 2022; 14(11):1711. https://doi.org/10.3390/w14111711

Chicago/Turabian Style

Liu, Mingxiao, Mengxin Xu, Zhen Liu, Dongpo Sun, and Michele Guala. 2022. "Ecohydraulic Characteristics of a Differential Weir-Orifice Structure and Its Application to the Transition Reach of a Fishway" Water 14, no. 11: 1711. https://doi.org/10.3390/w14111711

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