Wave Flume Experiments Research Articles

Experimental assessment of the performance of a bi-stable point wave energy absorber under harmonic incident waves

Intentional introduction of a bi-stable nonlinear restoring element to the design of point wave energy absorbers (PWAs) has been recently investigated as a means to broaden the steady-state response bandwidth of the PWA and shift it towards lower frequencies. The underlying hypothesis, which is supported by many previous theoretical investigations, is that this will help (i) reduce the sensitivity of the PWA’s response to variations in the frequency and amplitude of the incident waves, and (ii) permit the PWA to effectively harness energy from the low-frequency high-energy content of the incident wave spectrum. In this study, we investigate this hypothesis experimentally by designing, fabricating, and assessing the response behavior of a prototype bi-stable PWA (B-PWA) excited by harmonic incident waves in an experimental wave flume. We create bifurcation maps in the wave frequency and amplitude parameters’ space and use them to define an effective frequency bandwidth outside which the B-PWA generates negligible power levels. We compare the effective bandwidth of three different B-PWAs (different bi-stable restoring elements) to the traditional linear design and demonstrate that bi-stability does not seem to improve the effective bandwidth over the linear design; at least not for the three designs considered. Moreover, the difficulty of defining the effective bandwidth of the B-PWA and its sensitive dependence on the wave amplitude adds more layers of complexity, which make the process of optimizing its performance a cumbersome task. Nonetheless, a key advantage remains in the ability of the bi-stable restoring force to push the effective bandwidth of the B-PWA towards lower frequencies, where most of the wave energy is trapped.

Fluid characteristics of wave-induced liquefied silty seabed and the resulting wave attenuation

Wave-induced liquefaction of silty seabed is a common submarine geological hazard that poses a significant risk to the safety of marine structures. The liquefied seabed exhibits fluid properties and fluctuates with the overlying wave. To investigate the interaction between waves and the liquefied seabed, a wave flume experiment was conducted to simulate the wave-induced liquefaction process. During the experiment, the variation in the fluctuation trajectory and viscosity coefficient of liquefied silt with the wave intensity and liquefaction process were measured. Additionally, the wave energy dissipation due to seabed liquefaction was analyzed. The results indicate that the viscosity coefficient of the liquefied seabed is closely related to the wave intensity and liquefaction process, with the viscosity coefficient of the liquefied seabed being larger in the liquefaction deposition stage than in the liquefaction development stage. Seabed liquefaction can lead to a considerable increase in wave energy dissipation, up to 15 times greater than when the seabed is stable. Furthermore, wave energy dissipation is greater for high waves than for low waves conditions. The primary factors causing wave energy dissipation are the viscosity friction inside the liquefied seabed and the suspended sediment in the upper water column.

Sandy beach dynamics by constrained wave energy minimization

This paper focuses on a new approach to describe coastal morphodynamics, based on optimization theory, and more specifically on the assumption that a sandy beach profile evolves in order to minimize a wave-related function, the choice of which depends on what is considered the driving force behind the coastal morphodynamic processes considered. The numerical model derived from this theory uses a gradient descent method and allows us to account for physical constraints such as sand conservation in wave flume experiments. Hence, the model automatically adapts to either wave flume or open sea settings and only involves two hyper-parameters: a sand mobility and a critical angle of repose. The ability of OptiMorph to model cross-shore beach morphodynamics is illustrated on a flume configuration. Comparison of the beach profile changes computed with OptiMorph with experimental data as well as the results from the coastal morphodynamic software XBeach demonstrates the potential of a model by wave energy minimization.

Experimental study on dynamic response of pile-supported wharf under wave and ship berthing collision

Pile-supported wharf is widely used in deep-water port engineering, which is inevitably subject to joint action of wave and ship berthing collision in marine environment. The evaluation of dynamic response of pile-supported wharf under wave and berthing collision is particularly essential for the design of deep-water port infrastructures. In this study, a wave flume experiment was carried out to investigate the dynamic response of pile-supported wharf embedded in a saturated sand stratum under a given wave and a three-stage pendulum steel ball collision. The pendulum collision was applied at the corner and edge midpoint of the wharf deck, respectively. A variety of representative responses are explored, including time histories of acceleration, displacement, hydrodynamic pressure, pore water pressure, and strain, which characterize the important aspects of dynamic behavior of pile-supported wharf-ground system. Acceleration and displacement of deck as well as acceleration of sand stratum are dominated by the berthing collision; hydrodynamic pressure on piles and pore water pressure of sand stratum are controlled by the wave action; and strain and bending moment on piles are depended on the joint action of wave and collision. It should be noted that dynamic response characteristics of pile-supported wharf will change significantly due to the decreasing of pile effective buried depth near berths induced by the berthing collision energy accumulation. Furthermore, pile group effects including wave scour around piles, collision energy propagation in a sand stratum, and peak bending moment on piles are explored. For comparison, dynamic response of a single pile-ground system and free field are also discussed. Dynamic response of sand stratum around single pile induced by berthing collision on wharf deck is greater than that of free field at the same distance. Experiment techniques and insights from this study may be of significance to the design and maintenance of pile-supported wharves.

Development, calibration and validation of a phase-averaged model for cross-shore sediment transport and morphodynamics on a barred beach

Simulating cross-shore sediment transport and associated sandbar migration is still a challenging task for phase-averaged coastal morphological models. Numerical studies have mostly relied on beach morphology prediction for calibration and validation, without examining in much detail the underlying hydrodynamics, sediment concentrations and transport rates. This paper reports on a new three-dimensional coastal morphodynamic model based on the hydrodynamic model of Zheng et al. (2017), combined with an advection-diffusion type suspended sediment transport model and the extended SANTOSS near-bed sediment transport formula of Van der A et al. (2013), to represent the key cross-shore transport mechanisms. The model is are calibrated based on comprehensive measurements from a large-scale laboratory experiment involving regular plunging breaking waves over an evolving sandbar, covering detailed comparisons on hydrodynamics, sediment suspension, transport rates, and bed level evolution. Separate validation using large scale wave flume experiments were also conducted to confirm the model's performance on different conditions. Good agreements are obtained between measurements and model results, which demonstrates the model's ability to reproduce cross-shore sediment transport processes under breaking waves correctly, given that the appropriate parameterizations for intra-wave processes are included. Model results also reveal the onshore near-bed transport is related to wave-induced near-bed streaming, wave skewness and asymmetry, and bed slope effects at different locations across the beach surface. Wave breaking-induced turbulence enhances the near-bed transport within the bed boundary layer which needs to be taken into account in order to achieve good model prediction skills.

Efficient time-domain approach for hydroelastic-structural analysis including hydrodynamic pressure distribution on a moored SFT

This study investigates the hydroelastic analysis of a moored SFT (submerged floating tunnel) and the corresponding hydrodynamic pressure distribution under wave excitations. Time-domain discrete-module-beam (DMB) method, in which an elastic structure is modeled by multiple sub-bodies with beam elements, is employed to express the deformable tunnel with multiple mooring lines. Moreover, the top-down scheme is also adopted for detailed structure analyses with less computational cost, which applies the calculated hydrodynamic pressure distribution over SFT's surface to the three-dimensional finite element model. The hydrodynamic pressure includes both wave-induced diffraction pressure and motion-induced radiation pressure. For the validation of the developed numerical approach, comparisons are made with computationally intensive hydroelastic-structural direct-coupled method, two-dimensional wave flume experiment, and independently developed inhouse moored-SFT-simulation program. Furthermore, the influences of flexural motions with buoyancy-weight ratio (BWR) (or bending stiffness) and regular/irregular wave conditions on the dynamic pressure distribution and the resulting local stresses are investigated.

Numerical and experimental investigation of a hinged wave energy converter with negative stiffness mechanism

In this study, the performance of a simple and effective negative stiffness mechanism (NSM) from our previous work [1] is investigated by numerical simulation and wave flume experiment. This is one of the few experiments on multiple degrees of freedom (DOF) hinged wave energy converters (WEC) with NSMs. Firstly, the nonlinear governing equations of motions for a multi-modular WEC with NSMs are established based on the Cummins equation. Then, a wave flume experiment for two and three-module WECs is implemented to validate the numerical model and investigate the NSM effect on wave energy capture. Experimental results show that the NSM can enhance the relative pitch response of the raft-type system by up to 60% and thus significantly improve the WEC's capture efficiency. Finally, the wave energy capture performance of the hinged WEC with the NSM in irregular waves is investigated by combining the wave scatter diagram in the South China Sea. The results show that the NSM can enhance the peak of capture width ratio and broaden the capture band at low frequencies.

Solitary wave interaction with upright thin porous barriers

The interaction of fluid flow with porous barriers has numerous practical applications, including as a partial barrier to water waves that damp some of the approaching energy at the same time as allowing environmental flow. However, surprisingly little effort has been expended on understanding the fundamentals of this interaction. Therefore, this study aims to model the interaction between waves and thin, upright porous barriers. This is undertaken by modelling the porous barrier empirically within a Smoothed Particle Hydrodynamics (SPH) framework that is then used to model wave flume experiments. Although detailed modelling of the interaction is possible at the laboratory scale, it is not feasible in practical settings where a barrier will contain many thousands of holes that cannot be individually modelled. The key information needed to model the barrier empirically is obtained from solitary wave-porous barrier interaction experiments. Our results indicate that, for each barrier, irrespective of the properties of the wave interacting with it, there is a coefficient value that is able to account adequately for the energy dissipation by the barrier. The reliability of the approach has been demonstrated by comparing SPH model predictions against companion sinusoidal wave-porous barrier experimental measurements. The SPH model was then used to determine the energy dissipation characteristics of porous barriers kept at different draught to water depth ratio, D/d, without reference to the wave flume experiments. Simulation results indicate that barriers are more effective in dissipating the incident wave energy if its draught is over 75% of the water depth.

An ISPH with modified k–ε closure for simulating breaking periodic waves

The Incompressible Smoothed Particle Hydrodynamics (ISPH) method, solving the 2D RANS (Reynolds Averaged Navier-Stokes) equations with the modified k–ε turbulence closure developed by Wang and Liu (2020) [ Coastal Engineering , 157, 1–28], is further extended to periodic waves. The capability of this numerical model is demonstrated by applying it to three laboratory experiments: (1) Dynamics of surf-zone turbulence generated by a spilling breaker and a plunging breaker over a plane slope in small-scale wave flume experiments, (2) breaking wave generated turbulence over a stationary barred beach in large-scale wave flume experiments, and (3) spatial and temporal distributions of turbulence generated by bi-chromatic breaking waves over a submerged stationary barred slope in medium-scale wave flume experiments. In this new ISPH model, the gradient correction_ dynamically stabilized scheme is adopted to reduce numerical dissipation. The experimental data for the spilling breaker on a plane beach is used to calibrate the model. Once the model is calibrated, all the empirical coefficients in the turbulence closure model, including the stress limiter coefficient λ 3 , which is required in modifying the eddy viscosity, are fixed for the validation processes with other experimental data sets. All model-data comparisons are made in terms of free surface profile, mean velocity field and turbulent kinetic energy. The differences between experimental observations and numerical simulations are quantified by the percentage error. Overall, good agreement is observed for all experiments. This paper presents the first comprehensively validated 2D ISPH model with the modified k–ε turbulence closure, which can be applied to periodic wave breaking problems. • The Incompressible Smoothed Particle Hydrodynamics (ISPH) method is coupled with the modified k–ε turbulence closure equations to solve the 2D RANS (Reynolds Averaged Navier-Stokes) equations. The gradient correction_ dynamically stabilized scheme is adopted to reduce numerical dissipation. • The model has been checked with three laboratory experiments for periodic breaking waves. (1) Spilling and plunging cnoidal waves over a plane slope in small-scale wave flume experiments, (2) plunging periodic breaking wave over a stationary barred beach in large-scale wave flume experiments, and (3) bi-chromatic breaking waves over a submerged stationary barred slope in medium-scale wave flume experiments. • All model-data comparisons are made in terms of free surface profile, mean velocity field and turbulent kinetic energy. • The differences between experimental observations and numerical simulations are quantified by the percentage error. • Overall, good agreement is observed for all experiments. Good agreements are observed in terms of free surface profile, mean velocity field, vorticity field, turbulent kinetic energy and turbulent shear stress.

Experimental study of bed evolution around a non-slender square structure under combined solitary wave and steady current actions

This paper presents the findings from the laboratory wave flume experiments designed to investigate the formation and evolution of scour around a non-slender, square vertical structure, under three flow conditions, solitary wave, combined solitary wave and steady following current, and combined solitary wave and steady opposing current. The structure was placed on a sandy berm, either fastened to the flume wall or positioned at the centerline of the flume. For the wave only case, the scour on the seaside edge turned out to be deeper than the one on the leeside regardless of the structure's position. The analyses showed that the depth, width, volume, and location of the scour were all significantly influenced by the introduction of steady currents. The following current, for example, deepened the seaside scour, while leading to shallower leeside scour holes as a result of the backfilling process. Contrary to the opposing current, which shifted the scour area in the upwave direction, the scour was transported downwave under the effect of the following current. The scour depth was determined to be a function of the structure position and the Keulegan-Carpenter number, whereas the scour width mostly depended on the structure’s position. In this regard, the structure fastened to the wall experienced the widest scour area and the largest volume regardless of the flow condition.

The effects of capillary fringe on solitary wave induced groundwater dynamics

The capillary fringe is an important factor influencing the groundwater hydrodynamics in the coastal aquifer. The mechanism of the water table changes with the effect of capillary fringe under the wave action is still unclear. In this study, laboratory wave flume experiments were conducted to investigate the groundwater hydrodynamic features, paying particular attention to the capillary effects, in different areas of the beach under the solitary wave action. In the present experiments, medium sands were used to form the beach, resulting in a large capillary fringe height. Accordingly, the entire swash process occurred within the capillary truncated area. Based on the experiment measurements, three mechanisms are confirmed with respect to the coastal water table fluctuations, i.e., the flux mechanism, the gradient mechanism and the newly-proposed meniscus mechanism. The meniscus mechanism in the capillary truncated zone and the gradient mechanism in the capillary untruncated zone contribute to the non-hysteresis of the pressure head variation in the beach landward of the swash zone. The capillary truncated zone can be deemed as an extent of the swash zone since the effect of the swash process plays roles beyond the swash zone through a truncated capillary fringe. In addition, detailed observation of the evolution of the meniscus profile among the beach surface particles suggests that both vertical and horizontal seepage flows are important in the capillary truncated zone. In the swash zone, temporal variation of the hydraulic head can be classified into four/five stages in the case that the measuring position is near to/far from the uprush limit, and the effects of shoreline, water surface elevation, seepage face and exit point on the groundwater dynamics are discussed. Findings from the present study provide useful insights into the wave-induced coastal groundwater dynamics. • Capillary fringe effects on solitary wave induced groundwater dynamics are investigated through wave flume experiments. • Observation of the meniscus dynamics among beach surface particles provides new insights into the capillary fringe behaviors. • Flux mechanism, gradient mechanism and the newly-proposed meniscus mechanism for groundwater fluctuations are confirmed. • Meniscus mechanism dominates the hydrodynamic process in the capillary truncated zone. • Hydrodynamic process in swash zone can be divided into four or five stages with different dominant influencing factors.

Empirical estimation of the breaker index using a stereo camera system

To understand the wave-breaking phenomenon that affects coastal structures and sediment transport, various experiments have been conducted using an experimental wave flume equipped with point observation instruments including wave gauges. However, it has been still challenging to precisely measure the wave propagation in the breaking region. In this study, the water surface elevation is observed using stereo cameras, and a modified index for the breaking wave height is proposed. Water surface fields are retrieved spatially and temporally from synchronized stereo images using the wave acquisition stereo system (WASS), and then the breaking wave height, location, and wave front slope angle (WFSA) are analyzed. For the verification of the camera system, a three-dimensional reconstructed map is compared with the wave elevation measured by the wave gauge. The critical WFSA is empirically formulated and used to modify the breaker index. We verify the proposed breaker index formula by applying the index to the spilling breakers with a wide range of relative water depths. The prediction of the breaker index that rapidly decreases under high relative water depth conditions is considerably improved. Using the proposed critical WFSA formula and modified breaker index, the breaking wave heights in coastal areas can be accurately estimated.

Connector configuration effect on the dynamic characteristics of multi-modular floating structure

In this study, a wave flume experiment is implemented in order to investigate the effect of connector topology on the dynamic characteristics of a modular floating structure. Three configurations of flexible connectors were designed for the experiment tests of a three-modular floating platform under various wave conditions. The results illustrate the module responses, relative displacements of connecting points between adjacent modules, and connector loads for floating structures with different types of connectors in the parameters region of non-dimensional module length. The comparison study demonstrates that the connector type III, which can provide appropriate constraint stiffness in all three degrees of freedom, generally delivers better dynamic stability to the floating platform. The longitudinal loads for the three types of connectors remain at the same level. Additionally, the mechanism of different types of connectors on the dynamic features of system is analyzed. This work can provide a few experimental guidelines for the connector design of floating structure in engineering practice.

Experimental study on the effect of flare barriers on wave run-up and wave loads of a rounded-square column

Extreme waves are prone to produce critical wave run-up on the surface of column and have potential damage to offshore platforms. In order to suppress the wave run-up and improve the air gap performance of the column-stabilized platform, three configurations of flare barriers, namely, monolayer, multi-layer-solid and multi-layer-intermittent flares, were proposed in this study. A series of wave flume experiments were carried out under five focused waves to examine the mitigation effect of different flare barriers attached to a rounded-square column. For each configuration, four incline angles (30°, 40°, 50° and 60°) were considered. The flare barriers have different mitigation effect on the wave run-up. The monolayer flare barrier can completely deflect the uprush flow and generate a strong water jet. The multi-layer-solid flare barrier dissipates the wave run-up by dividing the uprush flow into deflected and unblocked components. The mitigation effect of the multi-layer-intermittent flare barrier on extreme waves is limited. In consideration of the spraying trajectory of water jet and the wave loads on the column, the multi-layer-solid flare barrier with an incline angle of 40° can be recommended for mitigating the wave run-ups on the column under extreme waves.

The Unique Ability of Fine Roots to Reduce Vegetated Coastal Dune Erosion During Wave Collision

Vegetated coastal sand dunes can be vital components of flood risk reduction schemes due to their ability to act as an erosive buffer during storm surge and wave attack. However, the effects of plant morphotypes on the wave-induced erosion process are hard to quantify, in part due to the complexity of the coupled hydrodynamic, morphodynamic, and biological processes involved. In this study the effects of four vegetation types on the dune erosion process under wave action was investigated in a wave flume experiment. Sand dune profiles containing real plant arrangements at different growth stages were exposed to irregular waves at water levels producing a collision regime to simulate storm impact. Stepwise multivariate statistical analysis was carried out to determine the relationship of above- and below-ground plant variables to the physical response. Plant variables included, among others, fine root biomass, coarse root biomass, above-ground surface area, stem rotational stiffness, and mycorrhizal colonization. Morphologic variables, among others, included eroded sediment volume, cross-shore area centroid shift, and scarp retreat rate. Results showed that vegetation was able to reduce erosion during a collision regime by up to 37%. Although this reduction was found to be related to both above- and belowground plant structures and their effect on hydrodynamic processes, it was primarily accounted for by the presence of fine root biomass. Fine roots increased the shear strength of the sediment and thus lowered erosional volumes and scarp retreat rates. For each additional 100 mg/L of fine roots (dry) added to the sediment, the erosional volume was reduced by 6.6% and the scarp retreat rate was slowed by 4.6%. Coarse roots and plant-mediated mycorrhizal colonization did not significantly alter these outcomes, nor did the apparent enhancement of wave reflection caused by the fine roots. In summary, fine roots provided a unique ability to bind sediment leading to reduced dune erosion.

Measuring free surface elevation of shoaling waves with pressure transducers

An assessment of formulas to recover wave surface elevation from pressure measurements was carried out in the present study. The investigation focused on the formulas’ performance in the shoaling region, i.e. where the wave nonlinearity gradually increases as the wave travels towards shallower waters. Formulas based on linear wave theory alongside nonlinear reconstructions were considered. Experiments in a large-scale wave flume provided with a concrete beach profile were performed, in which regular waves were generated and surface elevation was measured with acoustic, resistive and pressure gauges. The considered formulas require the application of a cutoff frequency to the wave signal in order to avoid high frequencies amplification that progressively arise as wave shoaling occur. A simple but effective method to obtain a reference cutoff frequency is proposed in the present work; the method is based on a polynomial fitting of the unfiltered wave energy spectrum. A sensitivity analysis of each formula to the variation of this cutoff frequency was carried out. Results showed that all the investigated formulas recover wave elevation fairly well for low-nonlinearity waves, whereas overestimating wave crest height as nonlinearity increases. Wave reconstruction of the linear formulation performance was comparable to nonlinear formulations in terms of wave crest height reconstruction, although tending to amplify frequencies in the wave trough. Moreover, the performance of the formulas to correctly recover the asymmetry and flatness of the surface elevation distribution was assessed by analysing third- and fourth-order moment statistics. In this sense, nonlinear reconstruction formulas performed better in recovering the asymmetric distribution of the wave elevation, with the formula based on linear wave theory underestimating skewness and kurtosis for large nonlinearity waves.

A novel Geno-fuzzy based model for hydrodynamic efficiency prediction of a land-fixed oscillating water column for various front wall openings, power take-off dampings and incident wave steepnesses

Accurate efficiency estimation of a wave energy converter (WEC) is a key concept in the design stage. Oscillating water column (OWC) is a promising type of WEC due to its advantages such as proved concept, operational simplicity, accessibility, reliability etc. In this study, for accurate efficiency estimation of an OWC, a novel Geno-fuzzy based model (GENOFIS) was developed, firstly, by improving Adaptive Neuro-Fuzzy inference system (ANFIS) and secondly, incorporating the Genetic algorithms (GAs). Data for training and testing phases of the models were obtained from an extensive wave flume experiments for various OWC underwater opening heights and applied PTO dampings under different incident waves. Both models performed remarkably with a slightly better performance of GENOFIS. The superiority of the GENOFIS model stemmed from that its high performance was attained with substantially low fuzzy rules (only three) where ANFIS required incomparably large fuzzy rules (twenty-seven) and yet achieved a slightly lower performance. Accordingly, very few numbers of fuzzy rules enable the construction of GENOFIS model structure with low complexity, which, in turn, immensely reduce the computational time required. Developed less complicated GENOFIS model is parsimonious, unlikely to suffer from overfitting and has high interpretability and practicality.

Spatial distribution models of horizontal and vertical wave impact pressure on the elevated box structure

The extreme wave impact is among the most severe loads the elevated box structure can suffer. This paper illustrated the spatial distribution of wave impact pressure on the elevated box structure with a rectangular cross-section. An existing wave flume experiment for an elevated box structure was reproduced numerically. The wave impact pressure on the front and bottom face of the elevated box structure was simulated and used as the dataset to investigate the horizontal and vertical impact pressure distribution. The spatial distribution of horizontal impact pressure on the front face was proposed as a piecewise empirical model of structural height, clearance height, and wave height. The spatial distribution of vertical impact pressure was developed by a joint probability model of the maximum impact pressure and the maxima loading position using Frank Copula to include randomness. The proposed spatial distribution models were verified through a validation case, and the effect of the pile group on the wave pressure distribution was finally discussed. This paper provides useful tools for assessing the wave impacts on the elevated box structure.

A review of breaking wave force on the bridge pier: Experiment, simulation, calculation, and structural response

In the course of the propagation of waves from the offshore to the nearshore zone, the wave may break due to the shoaling effect. Strong impact forces are observed when the breaking wave acts on the pier of the bridge. This impact force might not only change the dynamic load pattern on the pier but also cause strong structural vibration, which may threaten the driving and structural safety of the bridge. Many studies have been carried out to study the issues in the aspect of wave flume experiment, numerical simulation, calculation of breaking wave force, and random vibration response of the structure. Considering the studies of breaking wave load on bridge piers are lack of systematic summaries, this paper presents a comprehensive and up-to-date literature review of breaking wave research and practice related to bridges. Firstly, a brief introduction is given, which includes recent cases of bridge failures caused by breaking waves. Then, both scientific and technical studies are reviewed, categorized into four aspects: experimental study, numerical simulation, analytical calculation of breaking wave force, and the structural response under breaking wave. Finally, Discussion is provided on four emerging ideas to investigate breaking wave forces on the pier from both science and engineering perspectives. • Breaking waves threaten the bridge located in the nearshore water. • A comprehensive and up-to-date literature review of breaking wave research and practice related to bridges is presented. • Prospects on breaking wave force in bridge engineering are put forward from both science and engineering perspectives.

Mechanisms of sediment transport around finite patches of submerged aquatic vegetation

Feedback between flow transformation by submerged aquatic vegetation (SAV) and bed morphodynamics influences the long-term survivability of SAV habitats and the engineering services that SAV provides. We conducted a full-scale wave flume experiment to investigate the mechanisms through which finite patches of mimic SAV produce shoreward depositional features. Hydrodynamic observations indicate that a depositional mound is built in two phases, depending on the strength of nearshore seaward mean currents (undertow). During milder wave conditions when undertow is weak, the patches enhance TKE, wave velocity skewness, and within-canopy shoreward currents that together suspend and transport sediment shoreward to form near-symmetrical depositional mounds. Although patch-induced transport mechanisms are greater with higher within-patch stem density, the size and volume of the depositional mound are shown to depend more on patch diameter (i.e., form drag) rather than stem density for the range of patch geometries tested; the small dense patch produced a smaller depositional mound than the larger sparser patch. When waves are more energetic and undertow strengthens, the convergence of undertow with canopy-induced shoreward currents and wave velocity skewness enhances deposition and skews the depositional mound’s shape. As such, the convergence of canopy-induced shoreward currents and undertow-induced seaward currents causes the volume of the depositional mound to nearly triple shoreward of the largest tested patch of SAV.