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Research on water flow resistance characteristics in a vegetation environment is a hotspot in environmental fluid research, which is primarily concentrated on the calculation of the vegetation drag coefficient C d. At present, relatively few studies exist on the resistance characteristics of vegetation under non-uniform flow conditions, resulting in few general expressions for the research of C d for this type of condition. In response to these scientific problems, this study selects shrub vegetation as the research object and generalised it as cylinders for the simulation study. This study adopts quadratic and Gaussian functions to change the coordinate expression of cylindrical vegetation C d and then proposes the drag formulas of cylindrical vegetation in non-uniform flow for non-rainfall and heavy rainfall conditions based on regression analysis. Finally, this study substitutes the proposed C d formula into the Saint-Venant equation to calculate the depth of channel flow. The newly proposed equations are verified by comparing the measured flow depth data with the calculation results. This study provides technical support for refined hydrodynamic simulations of vegetated flow regions. [ABSTRACT FROM AUTHOR]

Water flow under vegetated environments is a noteworthy research topic in environmental hydraulics and restoration ecology, and this research is particularly important for maintaining water transport and streambed stability in water ecosystems. The calculation of the resistance coefficient in vegetated water flow is the core of this research. But there are still problems such as complex expressions and low simulation accuracy in this research field. To solve this scientific problem, this research, based on the theoretical study of environmental hydraulics and genetic algorithm, selected three basic parameters of vegetation submergence, resistance length and curvature degree, and successfully constructed the formula for calculating the resistance coefficient for flexible vegetated flow by using a wide range of data sets. New quantitative relationship between the drag coefficient and the relative roughness of flexible vegetation was established in this study. The formula of drag coefficients for flexible vegetation conditions has a more concise form and can be successfully applied to both flexible and rigid vegetation. As flexible vegetation is deformed under the action of water flow, and the quantitative expressions of Vogel number and relative roughness are given quantitatively through the analysis of its physical properties. Overall, this study improves the basic theoretical study of vegetated flow in environmental fluid dynamics and provides scientific theoretical support for vegetation restoration. [ABSTRACT FROM AUTHOR]

• New analytical velocity model is proposed for vegetation with spherical canopy. • New power series, exponential and trigonometric methods are used in flow model. • New formula of penetration length scale is proposed. Vegetation exists widely in natural rivers, resulting in unique characteristics of flow movement, affecting river flood processes and water quality. The flow movement of vegetated channels is defined as vegetated flow, and is currently receiving close attention. Influenced by vegetation, the classical logarithmic velocity profile turn into a more complex function according to the vegetation morphology and flow pattern. Several research teams have studied analytical models for simple cylinder-type vegetation; however, few studies have been conducted on analytical velocity models for vegetation with spherical canopy, and previous models cannot make accurate prediction of velocity profile in this case. To address this issue, new analytical models are proposed adopting the power series, exponential and trigonometric models. A comparison between the measured velocity profile and the analytical solution confirms that the newly proposed models are suitable for vegetation with spherical canopy. This analytical model can capture the vertical non-monotonic characteristics of velocity profile, which is what the previous models lack. Moreover, in contrast to numerical models, which require a lot of computational cost, this analytical model allows a quick and intuitive description of the flow profile, which provides hydrodynamic support for the restoration of vegetated channels. [ABSTRACT FROM AUTHOR]

• New hyperbolic tangent formula for vegetated mixing layer is proposed. • A formula to predict flow velocity at vegetation top is built. • These new formulae are proved to be effective for various types of vegetation. Flow velocity profile in the vegetal mixing layer was investigated using data collected in the present experiments and those reported in the literature, which indicates that the inflection point of the velocity profile does not coincide with the middle position of the vegetal mixing layer. Aiming to solve this problem, the hyperbolic tangent formula that is applicable to the plane mixing layer is modified by revising the inflection point and applying different characteristic scales in the free flow and penetration regions. For the problem of predicting flow velocity on top of vegetation, we constructed a new calculation method for flow velocity on top of vegetation based on correlation analysis. The proposed formula yields significant improvements in representing measured velocity profiles in the vegetated open channel flows. In comparison with previous ones, the modified formula performs better in exhibiting the similarity of measured velocity profiles over a wide range of flow and vegetation conditions. The research results provide technical support for the high precision calculation of the vegetated mixing layer. [ABSTRACT FROM AUTHOR]

• An innovative expression for calculating vegetation roughness is presented. • New vegetative roughness has the highest precision with fewer parameters. • New formula of Darcy–Weisbach coefficient of vegetated flow is derived. • Numerical model is used to build analytical resistance formula of vegetated flow. Assessing the flow resistance caused by vegetation in rivers is a hot topic in the field of hydraulics and eco-hydrology. Based on mathematical experiments by first-order closure models, new roughness height of vegetation is proposed linked with the three factors that vegetation arrangement concentration, submergence ratio, and the ratio of width to height of vegetation. Besides, new Darcy–Weisbach friction factor is built for vegetated flow. Moreover, both collected and present experimental data are adopted for verification of the roughness height and friction factor. Compared with models from other research groups, results show that the new formulas proposed in this study have high accuracy for predicting vegetation resistance in ecological restoration and water resources management in rivers. [ABSTRACT FROM AUTHOR]

• An innovative and eco-friendly artificial vegetation system is proposed. • Momentum thickness, velocity and Reynolds stress distribution, are reported. • Spectral and quadrant analyses reveal coherent vortical motion. • Linking a closure model to spectral and quadrant analyses is studied. An innovative approach was recently proposed to increase water depth and improve navigation in rivers by increasing overall roughness through an adaptive placement of artificial vegetation. In this approach, a section of the river width is covered with artificial vegetation constructed from an array of dampers that can be added or removed while maintaining sufficient width for navigational purposes. The goal of the work here is to explore the mean flow and turbulent momentum transport properties of such flow in a controlled flume setting, where the flow rate is steady, the vegetation placement is uniform, and the Froude number is maintained at sub-critical conditions. The focus is on vegetation-induced roughness alterations to the bulk flow statistics as well as the structure of turbulence impacted by the presence of such artificially engineered vegetation. The canopy flow experimentally explored here differs from the well-studied planar uniform emergent canopy flow because the interface between the vegetation and non-vegetation areas occurs along a lateral direction instead of the vertical direction. The flume experiments were conducted by partially covering the channel width with emergent artificial vegetation that is flexible and can interact with the flow. The quantities studied are the equilibration distance of the flow statistics from the leading vegetation edge as such distance is essential to any engineering design. Moreover, the mean flow and turbulence regimes at several longitudinal sections were analyzed using spectral analysis and conditional sampling to identify the main vortical structures and their contribution to momentum transport. Spectral analysis demonstrated that the sizes of the dominant vortices can be classified into stem-scale (small-scale) and shear-scale (larger scale) vortices as conventional in canonical canopy flows. The shear layer formed in the planar direction and its associated coherent vortices are spawned near the edge of the vegetated area in a manner analogous to a plane mixing layer. Quadrant analysis showed two contributions to the overall shear stress and lateral momentum exchange between the vegetated and non-vegetated zone, namely, ejections and sweeps. The measured ejection-sweep contributions are short-lived but significant to the overall turbulent momentum transport consistent with other canopy flow studies. Approximately 80% of the turbulent stress contributions at the interface occur within 30% of the time. Because the flume experiments were conducted at sufficiently high Reynolds number and sufficiently low Froude number, the scalability of the experimental findings here to much larger settings encountered in engineering practice are briefly discussed. [ABSTRACT FROM AUTHOR]

• The validity of RDM method to simulate suspended sediment concentration is verified. • Integrated sediment diffusion coefficient K z ′ = β K m is proposed to study the dispersion and diffusion. • Results show that β in flow with submerged canopy is larger than that in emergent canopy flow. Based on the Lagrangian approach, this study proposes a random displacement model (RDM) to predict the concentration of suspended sediment in vegetated steady open channel flow. Validation of the method was conducted by comparing the simulated results by using the RDM with available experimental measurements for uniform open-channel flows. The method is further validated with the classical Rouse formula. To simulate the important vertical dispersion caused by vegetation in the sediment-laden open channel flow, a new integrated sediment diffusion coefficient is introduced in this study, which is equal to a coefficient β multiplying the turbulent diffusion coefficient. As such, the RDM approach for sandy flow with vegetation was established for predicting the suspended sediment concentration in low-sediment-concentration flow with both the emergent and submerged vegetation. The study shows that the value of β for submerged vegetation flow is larger than that for emergent vegetation flow. The simulated result using the RDM is in good agreement with the available experimental data, indicating that the proposed sediment diffusion coefficient model can be accurately used to investigate the sediment concentration in vegetated steady open channel flow. [ABSTRACT FROM AUTHOR]

Morphological evolution in tidally influenced estuarine channel networks has strong influence on the redistribution of fluvial discharge and tidal motion. Based on channel bathymetry and hydrological data observed in 2002 and 2016, this study investigated the influence of morphological evolution on subtidal flow division in the Yangtze River Delta. Experiments using a 2D hydrodynamic model revealed the subtidal discharge was allocated more equally to the downstream channels at the main bifurcation in 2016. The bathymetric variation results in reduction of the discharge asymmetry index by reducing the effect of tidal motion. The decreased channel volume and cross-sectional area of the North Branch has been responsible for the reduction of the tidal flow intrusion into this channel. Allocation of the subtidal discharge to the North Branch has increased because of the reduction of tidal motion in this channel, induced by accretion in this channel during 2002–2016. • Morphological variation in the Yangtze River Delta from 2002 to 2016 was compared. • Morphological change hampered (enhanced) tidal propagation in North (South) Branch. • Morphology change reduced inequality of subtidal flow division at main bifurcation. [ABSTRACT FROM AUTHOR]