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Hydrobiologia ◽  
2021 ◽  
J. R. Sánchez-González ◽  
F. Morcillo ◽  
J. Ruiz-Legazpi ◽  
F. J. Sanz-Ronda

AbstractKnowing the relationship between size, morphological traits and swimming performance of fish is essential to understand the swimming capacity to successfully surpass these obstacles and the selective pressure that barriers in rivers and streams could exert on fish. Northern straight-mouth nase, an endemic potamodromous cyprinid fish species from the Northwest of the Iberian Peninsula, was selected to carry out volitionally swimming performance experiments in an open channel against three different flow velocities, using telemetry and video cameras. The use of thin-plate spline, on 10 landmarks, evidenced unknown patterns linked to velocity barriers. At lower flow velocity, size is the main factor explaining the swimming performance; thus, large individuals swim up more efficiently. In contrast, at high flow velocities, shape becomes the essential explanatory variable; thereby, streamlined body shapes with a higher relative position of the tail and a narrower caudal peduncle are more efficient. The obtained results show the existence of a relationship between fish morphology and swimming performance, with potential consequences due to selection pressures associated with velocity barriers and their implications on behavioural and dispersal processes. To sum up, velocity barriers could exert a selection pressure on nase populations, so the fishway design and removal should be (re)considered.

2021 ◽  
Vol 12 ◽  
Shiyu Wang ◽  
Yi Zhou ◽  
Tongshu Li ◽  
Song Li ◽  
Mingwu Zhang ◽  

Ecological management of river channels is a hot topic for current sustainable development and flow measurement of ecological river is an important part. In this article, a flow velocity distribution model of the channel containing flexible vegetation is constructed from the vegetation riverbed theory and the bursting phenomenon to reveal the microscopic mechanism of the flow velocity distribution in the upper layer of vegetation. In the vegetation riverbed law, the effect of flexible vegetation is evaluated by the mixed length formula. The bursting phenomenon law considers the influence of the channel sidewalls on the flow and a two-dimensional velocity model is established by introducing the concept of average turbulence structure. The mechanism of the downward shift of the maximum flow velocity point on the channel sidewall is explained. The verification of the calculated velocity profiles is carried out based on data obtained in laboratory experiments. The results show that the combination of the two models can well describe the velocity distribution of the whole channel. At the end, the phenomenon of flow velocity zoning in open channel is discussed, which provides a solution for flow measurement in ecological channel.

Entropy ◽  
2021 ◽  
Vol 23 (11) ◽  
pp. 1540
Yeon-Moon Choo ◽  
Hae-Seong Jeon ◽  
Jong-Cheol Seo

Korean river design standards set general design standards for rivers and river-related projects in Korea, which systematize the technologies and methods involved in river-related projects. This includes measurement methods for parts necessary for river design, but does not include information on shear stress. Shear stress is one of the factors necessary for river design and operation. Shear stress is one of the most important hydraulic factors used in the fields of water, especially for artificial channel design. Shear stress is calculated from the frictional force caused by viscosity and fluctuating fluid velocity. Current methods are based on past calculations, but factors such as boundary shear stress or energy gradient are difficult to actually measure or estimate. The point velocity throughout the entire cross-section is needed to calculate the velocity gradient. In other words, the current Korean river design standards use tractive force and critical tractive force instead of shear stress because it is more difficult to calculate the shear stress in the current method. However, it is difficult to calculate the exact value due to the limitations of the formula to obtain the river factor called the tractive force. In addition, tractive force has limitations that use an empirically identified base value for use in practice. This paper focuses on the modeling of shear-stress distribution in open channel turbulent flow using entropy theory. In addition, this study suggests a shear stress distribution formula, which can easily be used in practice after calculating the river-specific factor T. The tractive force and critical tractive force in the Korean river design standards should be modified by the shear stress obtained by the proposed shear stress distribution method. The present study therefore focuses on the modeling of shear stress distribution in an open channel turbulent flow using entropy theory. The shear stress distribution model is tested using a wide range of forty-two experimental runs collected from the literature. Then, an error analysis is performed to further evaluate the accuracy of the proposed model. The results reveal a correlation coefficient of approximately 0.95–0.99, indicating that the proposed method can estimate shear-stress distribution accurately. Based on this, the results of the distribution of shear stress after calculating the river-specific factors show a correlation coefficient of about 0.86 to 0.98, which suggests that the equation can be applied in practice.

2021 ◽  
pp. 118117
Guan-Yu He ◽  
Heng-Kwong Tsao ◽  
Yu-Jane Sheng

2021 ◽  
Vol 895 (1) ◽  
pp. 012039
V P Shesterkin ◽  
N M Shesterkina

Abstract The spatial and temporal variability of water salinity and salt composition of the Amur River near Khabarovsk in 2017-2021 was considered. An uneven distribution of water salinity over the river width was established, the greatest differences were observed in the winter low-water period, the lowest in the period of spring floods and floods. The maximum value of salinity was noted in winter, in the period of open channel – after very strong floods.

Lei Xia ◽  
Faze Chen ◽  
Zexin Cai ◽  
Jiaqi Chao ◽  
Yanling Tian ◽  

Somayeh Khani ◽  
Heinz Palkowski ◽  
Klaus Schwerdtfeger

AbstractIn continuous casting of steel, the strand is cooled in the upper part of the secondary cooling zone with water sprayed by nozzles towards the strand surface. The water accumulates in the nip of the lower roll of a roll pair, forming a water pool which then drains off towards the ends of the roll. In the present work, open channel hydraulics was applied for computation of the water pool height in the nip between roll and strand in continuous slab casting. The differential equation describing the change of pool height for the spatially varied flow with increasing discharge was solved with the Runge–Kutta technique using as boundary condition the pool height at the end of the nip. The effects of the Manning friction factor n and the energy coefficient α were determined in sets of computation. It was shown that the hydraulic theory could predict water profiles in the nip of continuous casting rolls to a good approximation.

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