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Coastal wetlands act as natural buffers against wave energy and storm surges. In the course of energy dissipation, vegetation stems are exposed to wave action, which may lead to stem breakage. An integral component of wave attenuation modeling involves quantifying the extent of damaged vegetation, which relies on determining the maximum drag force (FDmax) and maximum moment of drag (MDmax) experienced by vegetation stems. Existing closed-form theoretical equations for MDmax and FDmax are only valid for linear and weakly nonlinear deep water waves. To address this limitation, this study first establishes an extensive synthetic dataset encompassing 256,450 wave and vegetation scenarios. Their corresponding wave crests, wave troughs, MDmax , and FDmax , which compose the dataset, are numerically computed through an efficient algorithm capable of fast computing fully nonlinear surface gravity waves in arbitrary depth. Seven dominant wave and vegetation related dimensionless parameters that impact MDmax and FDmax are discerned and incorporated as input feature parameters into an innovative sparse regression algorithm to reveal the underlying nonlinear relationships between MDmax , FDmax and the input features. Sparse regression is a subfield of machine learning that primarily focuses on identifying a subset of relevant feature functions from a feature function library. Leveraging this synthetic dataset and the power of sparse regression, concise yet accurate closed-form equations for MDmax and FDmax are developed. The discovered equations exhibit good accuracy compared with the ground truth in the synthetic dataset, with a maximum relative error below 6.6% and a mean relative error below 1.4%. Practical applications of these equations involve assessment of the extent of damaged vegetation under wave impact and estimation of MDmax and FDmax on cylindrical structures. [ABSTRACT FROM AUTHOR]

An analysis of flow was carried out in this study to find the effects of trees on the flow structure in a straight compound open channel. To resemble the vegetation stem, two rows of vertical rods were installed on the floodplain of an asymmetrical compound channel. Two-dimensional flow velocity was measured using Particle Image Velocimetry. The results showed a decreasing trend in turbulent kinetic energy and turbulent intensity along the floodplain. At low flow depth, a significant decrease was observed in mean velocity and kinetic energy. Similar reduction was observed at the intersection of floodplain and main channel and around the stems. Under this condition, the direction of velocity vectors changed from floodplain to the main channel. However, this trend was reversed at higher flow depths. This reversal was due to the changes in momentum transfer and shear stress at the intersection of floodplain and main channel. Additionally, a numerical analysis showed that vortices are formed at the junction of the floodplain and main channel. [ABSTRACT FROM AUTHOR]

Vegetation plays an important role in soil erosion control, but few studies have been performed to quantify the effects of vegetation stems on hydraulics of overland flow. Laboratory flume experiments were conducted to investigate the potential effects of vegetation stems on Reynolds number, Froude number, flow velocity and hydraulic resistance of silt-laden overland flow. Cylinders with diameter D of 2·0, 3·2 and 4·0 × 10−2 m were glued onto the flume bed to simulate the vegetation stems, and a bare slope was used as control. The flow discharge varied from 0·5 to 1·5 × 10−3 m3 s−1 and slope gradient was 9°. Results showed that Reynolds number on vegetated slope was significantly higher than that on bare slope because of the effect of vegetation stems on effective flow width. All the flows were supercritical flow, but Froude number decreased as D increased, implying a decrease in runoff ability to carry sediment. The mean flow velocity also decreased with D, while the velocity profile became steeper, and no significant differences were found in surface flow velocities among longitudinal sections on all slopes. Darcy-Weisbach friction coefficient increased with D, implying that the energy consumption of overland flow on hydraulic resistance increased. Reynolds number was not a unique predictor of hydraulic roughness on vegetated slopes. The total resistance on vegetated slopes was partitioned into grain resistance and vegetation resistance, and vegetation resistance accounted for almost 80% of the total resistance and was the dominant roughness element. Further studies are needed to extend and apply the insights obtained under controlled conditions to actual overland flow conditions. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The flow structure around limited-size vegetation patches is crucial for understanding sediment transport and vegetation succession trends. While the influence of vegetation density has been extensively explored, the impact of the relative diameter of vegetation stems remains relatively unclear. After validating the reliability of the numerical model with experimental data, this study conducted 2D-URANS simulations (SST k-ω) to investigate the impact of varying relative diameters d/D under different vegetation densities λ on the hydrodynamic characteristics and drag force of vegetation patches. The results show that increasing d/D and decreasing λ are equivalent, both contributing to increased spacing between cylinder elements, allowing for the formation of element-scale Kármán vortices. Compared to vegetation density λ, the non-dimensional frontal area aD is a better predictor for the presence of array-scale Kármán vortex streets. Within the parameter range covered in this study, array-scale Kármán vortex streets appear when aD ≥ 1.4, which will significantly alter sediment transport patterns. For the same vegetation density, increasing the relative diameter d/D leads to a decrease in the array drag coefficient C ¯ D and an increase in the average element drag coefficient C ¯ d . When parameterizing vegetation resistance using aD, all data points collapse onto a single curve, following the relationships C ¯ D = 0.34 ln a D + 0.78 and C ¯ d = − 0.42 ln a D + 0.82 . [ABSTRACT FROM AUTHOR]

Green sea dykes, also known as ecosystem-based sea dykes, represent a novel type of coastal defense consisting of both traditional structural engineering and coastal ecosystems, designed to cope with the future trends of sea level rise and intensified storms. Here we focus on the mid-latitude mud coasts (eastern China in particular), which face the most prominent risks of storm surge, storm-induced giant waves, and shoreline erosion, and summarizes the scientific basis of green sea dykes and the current status of engineering practices. We show that the basic mechanisms of nearshore wave energy dissipation include bottom friction, sediment transport, and form drag. These explain the wave damping capacity of oyster reefs and salt marshes on mud coasts. In tidal flat environments, oyster growth increases frictional resistance and even causes wave breaking; the resuspension and transport of fine-grained sediments on salt marsh beds and the movement or resistance to hydrodynamic forcing of salt marsh vegetation stems effectively dissipate wave kinetic energy, and their efficiency increases with the elevation of the bed surface. Based on the wave damping capacity of oyster reefs and salt marshes on mud coasts, ecosystem-based sea dykes are being built in combination with traditional structured sea dykes. By utilizing natural tidal flats outside the dykes or implementing artificial modification projects, a certain scale of salt marshes and/or oyster reefs can be maintained, which serve to protect the sea dykes and enhance their wave resistance functions. From the perspective of system optimization, it is necessary to further improve the efficiency and sustainability of green sea dykes under constraints such as regional environment characteristics, ecosystem health, investment capacity, and ecological resilience. Related scientific issues include the theorization of the wave damping process of salt marshes, the niche and scale control of oyster reef and salt marsh ecosystems, the establishment of engineering standards and the design of the optimal form of sea dykes. [ABSTRACT FROM AUTHOR]

Systematical downslope‐turbidity‐current experiments were performed to clarify the relationship between sediment‐transport modes and current propagation patterns caused by rigid vegetation, as well as adjustments in turbulence characteristics of current. The equations for predicting the front velocities of downslope turbidity currents with emergent vegetation were proposed and validated via experimental data. Experimental results reveal that sediment deposition causes the lower turbulent kinetic energy (TKE) peaks of turbidity currents to decrease or even disappear without affecting their upper TKE peaks, while the rigid vegetation has the opposite effect. Vegetation stems destroy the longitudinal low‐high speed streaks associated with the quasi‐streamwise eddies in the near‐bed region and increase the proportions of the outward and inward interactions. In addition, sediment deposition severely suppresses the turbulent bursting events within turbidity currents but does not influence the relative proportions of the four bursting types. Rigid vegetation and sediment deposition both degrade the absolute values of the third‐order moments of velocity fluctuations without changing their signs to reduce the generation frequency of sweep events. Emergent rigid vegetation accelerates the formation of the reflected bore to provide energy for the deposited sediment to move downstream continuously. On the other hand, the dense submerged vegetation makes turbidity currents easily form the two‐head propagating mode, which allows part of the sediments carried by the upper current head to be transported downstream rather than deposited within or upstream of the vegetation region. Furthermore, the sloping boundary provides favorable conditions to initiate these specific modes for sediment transport adjusted by rigid vegetation. Key Points: Equations are developed and validated to predict the front velocities of turbidity currents flowing slopes with emergent rigid vegetationRigid vegetation and sediment gradation are key factors in controlling the turbulence characteristics of downslope turbidity currentsRigid vegetation distinctly changes the sediment‐transport modes of downslope turbidity currents by adjusting their propagation patterns [ABSTRACT FROM AUTHOR]

Inthis study, we introduce Point2Tree, a modular and versatile framework that employs a three-tiered methodology, inclusive of semantic segmentation, instance segmentation, and hyperparameter optimization analysis, designed to process laser point clouds in forestry. The semantic segmentation stage is built upon the Pointnet++ architecture and is primarily tasked with categorizing each point in the point cloud into meaningful groups or 'segments', specifically in this context, differentiating between diverse tree parts, i.e., vegetation, stems, and coarse woody debris. The category for the ground is also provided. Semantic segmentation achieved an F1-score of 0.92, showing a high level of accuracy in classifying forest elements. In the instance segmentation stage, we further refine this process by identifying each tree as a unique entity. This process, which uses a graph-based approach, yielded an F1-score of approximately 0.6, signifying reasonable performance in delineating individual trees. The third stage involves a hyperparameter optimization analysis, conducted through a Bayesian strategy, which led to performance improvement of the overall framework by around four percentage points. Point2Tree was tested on two datasets, one from a managed boreal coniferous forest in Våler, Norway, with 16 plots chosen to cover a range of forest conditions. The modular design of the framework allows it to handle diverse pointcloud densities and types of terrestrial laser scanning data. [ABSTRACT FROM AUTHOR]

In an open-channel flow, vegetation study is crucial to be investigated with any type of plants including trees, shrubs, and grasses, which are growing within or near the channel banks and beds in natural or artificial waterways, such as rivers, streams, and canals. These plants are different in height, size, shape, and arrangements, which have a big impact on the turbulence and flow resistance structures. In this paper, a regression analysis has been used based on collected experimental data to improve a specific equation for the drag coefficient for rigid vegetation stems and expanded to flexible stem types under emergent and submerged flow conditions. The equation suggests a length scale metric that, by analogy with the log wake law, normalizes velocity profiles of the depth-limited open channel flow with submerged, rigid vegetation. It has been formulated by drawing regression analysis for each parameter including (Re) Reynolds number, (h*) submergence ratio, and (λ) vegetation density by considering the (Fr) Froude number ranges for the water flows and vegetated channel flows. Using the Reynolds number, which is determined by the height and diameter of the vegetation, the results demonstrate an increase and decrease in the drag coefficient. For assessing the impact of vegetation on flow resistance at the surface layer, the notion of the drag coefficient is introduced. It shows better performance than other length scales in collapsing resistance data gathered under a variety of vegetation circumstances. The proposed scaling is more accurate than those based on the logarithmic, velocity-defect, and power laws in collapsing regression analysis for the studied parameters. [ABSTRACT FROM AUTHOR]

Accurate estimation of the drag forces generated by vegetation stems is crucial for the comprehensive assessment of the impact of aquatic vegetation on hydrodynamic processes in aquatic environments. The coupling relationship between vegetation layer flow velocity and vegetation drag makes precise prediction of submerged vegetation drag forces particularly challenging. The present study utilized published data on submerged vegetation drag force measurements and employed a genetic programming (GP) algorithm, a machine learning technique, to establish the connection between submerged vegetation drag forces and flow and vegetation parameters. When using the bulk velocity, U, as the reference velocity scale to define the drag coefficient, Cd, and stem Reynolds number, the GP runs revealed that the drag coefficient of submerged vegetation is related to submergence ratio (H*), aspect ratio (d*), blockage ratio (ψ*), and vegetation density (λ). The relation between vegetation stem drag forces and flow velocity is implicitly embedded in the definition of Cd. Comparisons with experimental drag force measurements indicate that using the bulk velocity as the reference velocity, as opposed to using the vegetation layer average velocity, Uv, eliminates the need for complex iterative processes to estimate Uv and avoids introducing additional errors associated with Uv estimation. This approach significantly enhances the model's predictive capabilities and results in a simpler and more user-friendly formula expression. [ABSTRACT FROM AUTHOR]

This study presents an experimental study on bed‐load transport in the presence of emergent vegetation, which is simulated using uniformly sized circular cylinders arranged in a homogeneous distribution. The spatial variability of bed‐load fluxes in vegetated flows is first examined. Then a model is proposed for evaluating the bed‐load transport rate based on the scour holes that form around the vegetation stems. The influences of spatial variability and intensified turbulence on sediment transport are finally considered by relating the dimensionless transport rate and flow intensity to the stem size and vegetation density. The derived formula for predicting the bed‐load transport rate in vegetated flows is applicable for weak to moderate transport conditions. Key Points: Weak and moderate bed‐load transport in vegetated flows is considered as live‐bed pier scour in multiple stems aligned in tandemThe patch‐averaged bed‐load transport rate is estimated from the bed‐load fluxes in the scour holes around vegetation stemsThe flow intensity and transport rate are parametrized using the vegetation density and stem size to characterize the spatial variability [ABSTRACT FROM AUTHOR]

The condition of emergent or submerged vegetation plays a vital role in affecting the flow behaviour in open channels. To understand the flow processes in free surface flows under emergent rigid vegetation condition, an extensive experimental investigation is performed in a laboratory channel with staggered combination of emergent rigid vegetation. Three‐dimensional velocities data are collected by ADV at various section and position of vegetated channel. The three‐dimensional flow properties such as velocity distribution, turbulence intensity, turbulent kinetic energy, Reynolds shear stress in vegetation, and non‐disturbed region are analysed and compared with the longitudinal and transverse length of vegetated zone. In the vegetation region, the longitudinal velocity in free stream region decreases as compared with non‐disturbed region. However, the vertical velocity also decreases in free stream region except at the centre line of channel cross‐section. Variations in velocity in the vegetation section were observed because of the local effect induced by the vegetation stems. Three‐dimensional Reynolds shear stress and turbulent intensity were weaker in magnitude at vegetation region. The presence of vegetation reduces the longitudinal profile of flow velocity, Reynolds shear stress and turbulence intensities, which means that vegetation can be used as an effective tool to reduce the flow resistance. The turbulent kinetic energy, skewness and kurtosis are also evaluated and compared between the vegetated and non‐vegetated zone. The outcomes of the results provide an important view to understand flow behaviour at immediately front and immediately behind of vegetation stem. [ABSTRACT FROM AUTHOR]

A set of laboratory experiments were conducted to study the impact of vegetation on bed form resistance and bed load transport in a mobile bed channel. Vegetation stems were simulated by using arrays of emergent polyvinyl chloride (PVC) rods in several staggered configurations. The total flow resistance was divided into bed, sidewall, and vegetation resistances. Bed resistance was further separated into grain and bed form (i.e., ripples and dunes) resistances. By analyzing experimental data using the downhill simplex method (DSM), we derived new empirical relations for predicting bed form resistance and the bed load transport rate in a vegetated channel. Bed form resistance increases with vegetation concentration, and the bed load transport rate reduces with vegetation concentration. However, these conclusions are obtained by using experimental data from this study as well as others available in the literature for a vegetated channel at low concentration. [ABSTRACT FROM AUTHOR]

We quantified and compared movement and microhabitat use of Eastern Copperheads (Agkistrodon contortrix) in fragmented and unfragmented habitats to determine the effects of fragmentation on movement and habitat use. We used thread bobbins to track movement and calculate straight-line distance (SLD) moved, total distance (TDM) moved, and occupied area for individual snakes. Microhabitat use was characterized by quantifying number of trees, woody vegetation stems, herbaceous vegetation stems, percent grass coverage, and percent canopy coverage at each location a snake was observed, and at an equal number of randomly selected locations. Neither SLD nor TDM differed between fragmented and unfragmented habitats. Overall average SLD moved was 24.1 m and TDM was 39.6 m over 48 h. Although SLD and TDM did not differ between sites, mean occupied area ± standard error was significantly greater at the unfragmented (2,310.9 ± 272.7 m) compared with the fragmented site (1,025.9 ± 314.9 m). Microhabitat features were similar between the fragmented and unfragmented sites, and herbaceous vegetation and high canopy cover were associated with locations where snakes were observed at both sites. It is likely that Eastern Copperheads can persist in a variety of habitats in the southeastern United States because their preferred microhabitat features are widely distributed and common in both fragmented and unfragmented environments, demonstrating that they retain characteristics of a habitat specialist within heterogeneous environments suitable for generalists. [ABSTRACT FROM AUTHOR]

Numerous studies focus on flow and mixing within cylinder arrays because of their similarity to vegetated flows. Randomly distributed cylinders are considered to be a closer representation of the natural distribution of vegetation stems compared with regularly distributed arrays. This study builds on previous work based on a single, fixed, cylinder diameter to consider non‐uniform cylinder diameter distributions. The flow fields associated with arrays of randomly distributed cylinders are modeled in two dimensions using the ANSYS Fluent Computational Fluid Dynamics software with Reynolds Stress Model turbulence closure. A transient scalar transport model is used to characterize longitudinal and transverse mixing (Dx and Dy) within each geometry. The modeling approach is validated against independent laboratory data, and the dispersion coefficients are shown to be comparable with previous experimental studies. Eight different cylinder diameter configurations (six uniform and two non‐uniform) are considered, each at 20 different solid volume fractions and with seven different transverse positions for the injection location. The new dispersion data cover a broad range of solid volume fractions, for which simultaneous estimates of Dx and Dy have not been available previously. There are no systematic differences in non‐dimensional Dx and Dy between uniform and non‐uniform cylinder diameter distributions. When non‐dimensionalized by cylinder diameter, both dispersion coefficients are independent of solid volume fraction. When non‐dimensionalized by cylinder spacing, both longitudinal and transverse dispersion can be described as linear functions of the ratio of cylinder diameter to cylinder spacing. Key Points: New dispersion data for non‐uniform and uniform cylinder diameter distributions have been generated using a two‐dimensional numerical modelNon‐dimensional dispersion coefficients are unaffected by cylinder diameter distributionBoth longitudinal and transverse dispersion coefficients can be modeled as linear functions of cylinder diameter and cylinder spacing [ABSTRACT FROM AUTHOR]

A numerical model based on the double-averaged (spatial and ensemble averaged) method has been developed to simulate vegetated free surface flows. The classical k - ε model is modified by including additional turbulence generation and dissipation terms. These new terms consider the large-scale turbulence generated by shear flows near the flow-vegetation interface and the small-scale wake turbulence generated by the flow separation behind vegetation stems. A new damping function is introduced in the turbulence closure model to suppress the wake turbulence inside the vegetation domain if the shear-generated turbulence is dominant. A series of dense emergent and submerged vegetated flows experiments have been conducted and the velocities have been measured by ADV (Acoustic Doppler Velocimetry) and PIV (Particle Image Velocimetry) at different locations. The experimental results show that the turbulence characteristics near each stem in a group of cylinders are similar to that of a single cylinder, even when the vegetation is dense. The measured data are then used to calibrate the new turbulence closure model. The numerical model is further validated against other published laboratory data of both dense and sparse emergent, submerged and floating vegetated flows. The comparisons show that the new model provides consistently better predictions for mean velocity and turbulence kinetic energy than those by using the existing models. Article Highlights: A new damping function is adopted into vegetation related terms in k-ε model to suppress the wake turbulence generation where the shear-generated turbulence dominates. The new model performs better than other two existed vegetated k-ε model when predicts velocity and turbulence for flows passing through emergent, submerged and floating vegetation domain, and those empirical coefficients in the new model are fixed in all the simulations. PIV methods are used in the experiments, and it is found that the stem-near-field turbulence inside dense vegetation domain is still similar to that around a single cylinder. [ABSTRACT FROM AUTHOR]

Sediment transport capacity (Tc) is an essential parameter in the establishment of the slope soil erosion model. Slope type is an important crucial factor affecting sediment transport capacity of overland flow, and vegetation can effectively inhibit soil loss. Two new formulae of sediment transport capacity (Tc) are proposed of brown soil slope and vegetation slope in this study and evaluate the influence of slope gradient (S) and flow discharge (Q) on sediment transport capacity of different slope types. Laboratory experiments conducted using four flow discharges (0.35, 0.45, 0.55, and 0.65 L s-1), four slope gradients (3, 6, 9, and 12°), and two kinds of underlying surface (Brown soil slope, Vegetation slope). The soil particle size range is 0.05–0.5mm. The vegetation stems were 2mm in diameter and randomly arranged. The results show that the sediment transport capacity was positively correlated with the flow discharge and slope gradient. The vegetation slope's average sediment transport capacity is 11.80% higher than the brown soil slope that same discharge and slope gradient conditions. The sensitivity of sediment transport capacity to flow discharge on brown soil slope is higher than that of slope gradient. The sensitivity of sediment transport capacity of vegetation slope to slope gradient is more heightened than flow discharge. The sediment transport capacity was well predicted by discharge and slope gradient on brown soil slope (R2 = 0.982) and vegetation slope (R2 = 0.993). This method is helpful to promote the study of the sediment transport process on overland flow. [ABSTRACT FROM AUTHOR]

Aquatic plants play a crucial role in the hydrodynamic and material transport processes within the aquatic environments due to the additional flow resistance induced by vegetation stems. In this study, high-resolution numerical experiments were performed to investigate the drag characteristics of circular vegetation patches fully immersed in a turbulent open channel flow. The submerged vegetation patch was modeled as a rigid cylinder array with a diameter D composed of N cylinder elements with a diameter d. The effects of vegetation density Φ (0.023 ≤ Φ ≤ 1) and relative diameter d/D (d/D = 0.051 and 0.072) were tested. The simulation results show that Φ and d/D affect the flow resistance exerted by the vegetation patch by modifying the bleeding flow intensity. With the increase in Φ, the drag forces acting on the individual cylinder elements decrease, whereas the total drag forces of the patch increase. The oscillation strength of the drag force of individual cylinders depends on Φ and the fixed positions within the patch. The presence of the free end of submerged cylinder array leads to enhanced wake entrainment with the increase in Φ. The drag coefficient of the submerged patch is smaller than that of the emergent patch when the dimensionless frontal area aD > 3. However, the two patches exhibit comparable drag coefficients for smaller aD values. [ABSTRACT FROM AUTHOR]

Vegetation stems and litter cover have different effects on sediment transport capacity under the same experimental conditions, which in essence, may be due to differences in their hydraulic properties, but the availability of comparative studies is limited. This study aimed to compare the hydraulic properties affected by litter and stem cover, compare differences in the drag forces exerted by litter and stems on overland flow, and develop new Manning's n and flow velocity equations for litter cover. Two series of flume experiments were conducted with the same slope gradients (8.8%, 17.6%, 26.8%) and flow discharge rates (0.5, 1.0 × 10−3 m3 s−1). Artificial Gramineae stems with a 0%–30% cover level and Pinus tabulaeformis litter with a 0%–70% cover level were used in series 1 and series 2, respectively. The flow velocity and depth were measured. The results showed that the Froude number and flow velocity affected by stem cover were much lower than those affected by litter cover, while the opposite trend was observed in the relative magnitude of the Reynolds number, flow depth and shear stress. The form resistance caused by stems was 22–57 times greater than that caused by litter for the same cover level, which suggests that stem cover contributes more than litter cover to increasing the flow resistance and reducing the flow's ability for sediment detachment and transport. Two new equations for calculating Manning's n and flow velocity under the influence of litter cover were developed, with R2 and NSE values of 0.96. The results of this study contribute to revealing the mechanisms of the differences of the effects of stem and litter cover on soil erosion. [ABSTRACT FROM AUTHOR]

The sediment transport capacity plays a pivotal role in erosion research, and is usually predicted using hydraulic variables. The transport capacity and hydraulic variables are affected by vegetation cover. Our understanding of the effect of vegetation cover, including the size, density, and arrangement of vegetation stems, on the relationship between the sediment transport capacity and hydraulic variables were rather limited. The objectives of this study were to investigate the effect vegetation stem cover on the relationship between hydraulic variables and the sediment transport capacity and to derive an equation for predicting the sediment transport capacity in the presence of vegetation cover. Five data sets from 288 flume experiments with a wide range of discharge (0.25–2 × 10−3 m3 s−1), slope (8.8–42.3%), median sediment diameter (0.11–1.16 × 10−3 m), stem cover (0–30%), stem diameter (2–36 mm), and stem arrangement (bead, tessellation, zigzag, random, and banding) were compiled for this study. Extensive regression analysis has shown that the sediment transport capacity could be expressed as a power function of flow velocity, shear stress, stream power, or unit stream power. Predictors of the sediment transport capacity were ranked from the unit stream power as the strongest, followed by the stream power, flow velocity, and the shear stress. Vegetation stem cover had no apparent and direct effect on the relationship between hydraulic variables and the sediment transport capacity so long as the unit stream power or stream power was used as its predictor. Vegetation cover became a significant factor only when the shear stress was used to predict the sediment transport capacity. Finally, a new equation involving the slope gradient, flow velocity, and median sediment diameter in a nondimensional form was shown to be a superior predictor of the sediment transport capacity with the Nash–Sutcliffe coefficient of efficiency of 0.92. The product of slope and flow velocity, that is, the unit stream power, captures the effect of vegetation stem cover and surface roughness and was shown to be an effective predictor of the transport capacity in the presence of vegetation cover. [ABSTRACT FROM AUTHOR]

Shallow mixing layers developed in partially-distributed canopy flows (PCFs) are important for water conveyance, sediment transport and solute dispersion. In this paper, we address the response of shallow mixing layers in PCFs to several influential factors associated with bed friction, water shallowness and canopy denseness using depth-averaged Large Eddy Simulation (DA-LES). The results show that under certain canopy denseness, shallow mixing layers in PCFs display asymptotic behaviour for the variation of bed friction and water shallowness, consistent with classic shallow mixing layers. The canopy drag encourages the asymmetric growth of the inner and outer parts of the mixing layer, and this effect decreases when bed friction and water shallowness become pronounced. Characteristic velocity and length scales show similarity well delineated by exponential decay function regarding a stabilization efficiency parameter. The exception happens for the inner length scale of the mixing layer when only changing canopy density. We conclude that changing the canopy denseness can encourage the overall shift of mixing layer scaling regarding a broad range of bed friction and water shallowness. Furthermore, the bed friction parameter thresholding triggering flow instability of mixing layers in PCFs is found about 0.03, lower than 0.09 for splitter-plate induced mixing layers. [ABSTRACT FROM AUTHOR]

Marsh terraces, constructed as a restoration and protection strategy, consist of a series of earthen berms in open water areas of the coastal wetland landscape and are being implemented across the Louisiana coast. To assess the efficacy of the marsh terraces as a nature-based solution, a small-scale, high-resolution hydrodynamic model was developed based on field sampling of vegetation and physical parameters (water level, waves, sediment, turbidity, and terrace elevation). This study tested common marsh terrace designs (e.g., chevron, linear, box, T-shape, etc.), ultimately selecting a preferred design based on the evaluation of factors such as vegetation, water depth, and sediment type on terrace stability and sediment retention under calm and storm conditions. The model results revealed that the 100 m box and the chevron designs exhibited greatest terrace stability and sediment trapping, particularly when installed perpendicular to prevailing wind and waves. The preferred terrace design was the box design due to its higher modeled resilience to wind and waves from multiple directions. Vegetation presence enhanced terrace resistance to erosion, with variations depending on vegetation type. Higher vegetation biomass, especially during the summer, contributed to the greatest stability of terraces. Greater water depth between terraces led to increased sediment retention, and terraces predominantly composed of organic-rich mud demonstrated greater stability than those with higher proportions of sand. Overall, vegetation had the greatest impact on sediment retention in the terrace field compared to water depth and sediment type. However, the potential habitat for submerged aquatic vegetation (SAV) was more influenced by water depth (i.e., 0.1 m < depth <1 m) than shear stress (<0.5 Pa). Even under storm conditions, shear stress rarely determined potential habitat for SAV, as shear stress remained relatively low within the terrace field. Potential SAV habitat was most abundant in shallow areas and increased where sediment stability was lowest (i.e., no vegetation and sand), primarily due to eroded sediment increasing the shallow area. While this model was developed using field data specific to Louisiana marshes, it can be adapted as a tool for terrace restoration project design and planning in most coastal wetlands. [ABSTRACT FROM AUTHOR]

Spillways can present a way to control the overflowing of water during flood events and prevent damage from levee breaches. With increasing interest in nature-based solutions, the interaction between flow and vegetation parameters has to be understood. Aeration usually occurs during the overflow of sloped spillways, leading to the bulking of flow, alterations of flow characteristics, and energy dissipation. The influence of the vegetation parameter on aerated flow characteristics has not yet been investigated in greater detail; no systematic investigation of the effect of vegetation parameters has been conducted. This paper aims to systematically analyze the influence of different vegetation heights on air entrainment during the overflow of spillways. Therefore, a spillway model with a slope of 18° (1:3) was equipped with artificial turf of varying turf heights, and supercritical flows were investigated. The aeration was measured using double-tip conductivity probes, giving insights into air concentration profiles, bubble count rates, estimations of energy dissipation, and flow velocities. The results highlighted the significant influence of vegetation height on the aeration process. Higher air concentrations over the flow depth were observed for higher turf heights tested in this study. Also, the energy dissipation and flow velocity reduction increased with higher vegetation heights. Overall, the present study uncovers the effect of vegetated covers, thereby contributing to the fundamentals of aerated flows. [ABSTRACT FROM AUTHOR]

Estrogens are a growing problem in wastewater discharges because they are continuously entering the environment and are biologically active at extremely low concentrations. Their effects on wildlife were first identified several decades before, but the environmental limits and the remedial measures are still not completely elucidated. Most conventional treatment processes were not designed with sufficiently long retention times to effectively remove estrogens. Nature-based wastewater treatment technologies such as treatment wetlands (TW) and high-rate algal ponds (HRAP) are economically feasible alternatives for decentralized wastewater treatment and have promise for removing steroid hormones including estrogens. For small communities with populations below 50,000, the overall cost of TWs and HRAPs is considerably lower than that of advanced decentralized treatment technologies such as activated sludge systems (AS) and sequencing batch reactors (SBR). This results from the simplicity of design, use of less materials in construction, lower energy use, operation and maintenance costs, and operation by non-skilled personnel. The naturebased technologies show high removal (>80%) for both natural and synthetic estrogens. Estrogen removal in TWs can be enhanced using alternative media such as palm mulch, biochar, and construction wastes such as bricks, instead of traditional substrates such as sand and gravel. While TWs are effective in estrogen removal, they have the disadvantage of requiring a relatively large footprint, but this can be reduced by using intensified multilayer wetland filters (IMWF). Using filamentous algae in HRAP (high-rate filamentous algal pond; HRFAP) is an emerging technology for wastewater treatment. The algae supply oxygen via photosynthesis and assimilate nutrients into readily harvestable filamentous algal biomass. Diurnal fluctuations in oxygen supply and pH in these systems provide conditions conducive to the breakdown of estrogens and a wide range of other emerging contaminants. The performance of these nature-based systems varies with seasonal changes in environmental conditions (particularly temperature and solar irradiation), however a greater understanding of operating conditions such as loading rate, hydraulic retention time (HRT), pond/bed depth, dissolved oxygen (DO) concentration and pH, which influence the removal mechanisms (biodegradation, sorption and photodegradation) enable TWs and HRAPs to be successfully used for removing estrogens. [ABSTRACT FROM AUTHOR]

Slope erosion in the Loess Plateau region has long been a concern, and vegetation plays an important role in slowing down erosion and controlling sedimentation. However, a single vegetation model shows some limitations when facing complex natural conditions and variable rainfall events. Therefore, this study investigated the influence mechanism of vegetation configuration on slope sand production at different slopes through theoretical analyses and indoor experiments. The results of the study showed that certain factors, such as vegetation configuration mode, flow rate, runoff power, runoff velocity, and runoff shear, are closely related to slope runoff sand production. The specific findings are as follows: (1) Under the condition of slope gradient of 2°, the sand reduction effect of the rigid–flexible single-row staggered configuration is the most significant, and the sediment production is reduced by 29.89%. (2) With the increase in the slope gradient and flow rate, the sand production on the slope surface rises significantly, and when the slope gradient is increased from 2° to 6°, the average sand production is increased from 1.43 kg to 2.51 kg.(3) The erosion reduction effects of different vegetation configurations were in the order of rigid–flexible single-row staggered combination > flexible vegetation single combination > rigid–flexible double-row staggered combination > rigid vegetation single combination > upstream rigid downstream flexible combination > bare slope. This study provides a theoretical basis for optimizing the vegetation configuration for effective sand reduction and provides an important reference for the sustainable development of the Yellow River Basin. [ABSTRACT FROM AUTHOR]