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Submarine canyons are primary conduits for turbidity currents transporting terrestrial sediments, nutrients, pollutants and organic carbon to the deep sea. The concavity in the longitudinal profile of these canyons (i.e. the downstream flattening rate along the profiles) influences the transport processes and results in variations in turbidite thickness, impacting the transfer and burial of particles. To better understand the controlling mechanisms of canyon concavity on the distribution of turbidite deposits, here we investigate the variation in sediment accumulation as a function of canyon concavity of 20 different modern submarine canyons, distributed on global continental margins. In order to effectively assess the isolated impact of the concavity of 20 different canyons, a series of two-dimensional, depth-resolved numerical simulations are conducted. Simulation results show that the highly concave profile (e.g. Surveyor and Horizon) tends to concentrate the turbidite deposits mainly at the slope break, while nearly straight profiles (e.g. Amazon and Congo) result in deposition focused at the canyon head. Moderately concave profiles with a smoother canyon floor (e.g. Norfolk-Washington and Mukluk) effectively facilitate the downstream transport of suspended sediments in turbidity currents. Furthermore, smooth and steep upper reaches of canyons commonly contribute to sediment bypass (i.e. Mukluk and Chirikof), while low slope angles lead to deposition at upper reaches (i.e. Bounty and Valencia). At lower reaches, the distribution of turbidite deposits is consistent with the occurrence of hydraulic jumps. Under the influence of different canyon concavities, three types of deposition patterns are inferred in this study, and verified by comparison with observed turbidite deposits on the modern or paleo-canyon floor. This study demonstrates a potential difference in sediment transport efficiency of submarine canyons with different concavities, which has potential consequences for sediment and organic carbon transport through submarine canyons. • The impact of submarine canyon concavity on turbidite deposition was assessed. • Distribution of turbidite deposits varies with changes in canyon concavity. • Three distinct deposition patterns were identified. • The recognized deposition patterns align well with the observed turbidite deposits. [ABSTRACT FROM AUTHOR]

Abstract The shape of vortex ripples generated by wave boundary layers determines the local hydrodynamics and sediment motions, and therefore is critical for understanding coastal sediment transport in the rippled-bed regime. In this study, coarse-sand vortex ripples were generated by periodic oscillatory flows mimicking full-scale field conditions in an oscillatory water tunnel. A laser-based bottom profiler was applied for measuring the movable bed's profile. The observed ripple development from a flat bed is in agreement with many previous studies. Small ripple marks appeared within a couple of flow periods, and gradually became 3-dimensional (3-D) transient ripples, which eventually evolved to equilibrium 2-dimensional (2-D) ripples after O (100–1000) flow periods. The shape of equilibrium 2-D ripple was studied based on a representative ripple profile obtained by ensemble averaging a periodic ripple train. The shape of ripples formed under sinusoidal flows become increasingly sinusoidal as the flow becomes stronger (larger Shields parameter) or wave period becomes longer, which is possibly because the influence of coherent vortex becomes more significant. Wave nonlinearities have different effects on the ripple shape. Generally speaking, wave skewness makes ripples onshore-leaning while wave asymmetry makes ripples' crests sharper and troughs flatter. Our measurements also revealed some detailed geometric characteristics, i.e., the roundness of ripple crests and the maximum local slope along ripple flanks. Highlights • A full-scale experimental study on the geometry of coarse-sand vortex ripple is conducted in an oscillatory water tunnel. • Ripple development from a flat bed is reported, and the observation is in agreement with previous studies. • Full-scale coarse-sand vortex ripples can be well described by a sinusoidal profile. • Skewed flows make ripples become asymmetric while asymmetric flows make ripples become skewed. [ABSTRACT FROM AUTHOR]

Abstract The complex interactions between flow hydrodynamics, sediment transport, geometry, and changes in base level control the morphodynamic evolution of tidal channels, inlets, and estuaries. Research on these complex settings have involved decades of field, laboratory, and modeling work. Studies on the one-dimensional morphodynamic of well-mixed, tide-dominated channels demonstrate that the evolution of a horizontal channel subject to tidal fluctuations at the ocean boundary is characterized by erosion in the ocean part of the channel and the formation of a landward migrating shoal that, depending on the channel length, may reach the landward boundary. When the shoal reaches the landward end of the domain, it is reflected and a beach forms as the flow and sediment transport reach conditions of equilibrium. At equilibrium, the elevation of the channel bed profile remains constant over a tidal cycle. Building on previous work, this study focuses on the poorly explored effects of nonuniformity of the sediment size distribution and of the interaction between tidal channel and longshore sediment transport on the equilibrium of tidal channels. The model is verified at laboratory scale, and it is then applied to predict equilibrium conditions with nonuniform sediment and without an imposed input of sediment from the ocean. Model results show that nonuniformity of the grain size distribution of the sediment increases the profile concavity. The equilibrium deposits tend to coarsen from the land to the ocean, and the sediment of the landward deposits presents an upward fining pattern. When the imposed input of sediment from the ocean is relatively small, the equilibrium profile presents a stable shoal at the oceanward part of the channel. In the case of a large input of sediment from the ocean, the channel gradually fills with sediment. The grain size distribution of these channel fill deposits coarsen in the oceanward and upward directions. The comparison between model results and field observations shows that the model can qualitatively capture some of the main features of tidal channels and can thus be of aid in coastal management and restoration with proper site-specific modifications. Highlights • The non-uniformity of the sediment and its caliber play a prime control on estuarine morphodynamics; • Estuarine morphodynamics strongly depends on the interaction between the tidal channel and the longshore sediment transport. • A 1D model of a tidal channel can capture some characteristics of tide dominated estuaries. • The combination of sinusoidal tidal forcing and constant input of sand from the ocean results in cyclic deposition. [ABSTRACT FROM AUTHOR]

Abstract Storm-induced sediment transport across a barrier island can lead to vertical accretion and onshore migration of the barrier island. Many barrier islands either have high dunes that prevent inundation, or are so low-lying that they are inundated several times a year. The Wadden Islands in the Netherlands, Germany and Denmark typically have alongshore-varying topography, where high dunes alternate with low-lying washover openings. The effects of the geometry of the washover openings on hydrodynamics and sediment transport are still unknown and are the main focus of this research. First, we present data on width and for some cases also vertical elevation of bed level for all washover openings along the Wadden Islands. The mean width is 200 m but the actual width ranges from 35 to 1100 m, and the elevation is between 1.5 and 2.1 m above MSL. Further, we present results of an XBeach model study to investigate how the washover opening geometry affects sediment transport during storm-induced inundation. We identify two important effects of washover width: firstly, for narrow openings flow contraction is important, causing relatively larger sediment exchange rates per unit width; secondly, in a wider opening sediment is transported over a larger width, resulting in larger sediment mass exchange rates. Furthermore, the elevation of the washover opening is of high importance: washover openings that are 30 cm higher than the reference case significantly decrease currents and sediment transport across the island. Divergence of sediment transport occurs in the washover opening, which leads to erosional patterns. Landward from the opening, sediment transport converges which leads to depositional patterns. The pressure gradient between North Sea and Wadden Sea across the Wadden Islands is an important forcing parameter: higher water levels in the back-barrier reduce onshore-directed currents and sediment transport. Highlights • Sediment transport during storms depends highly on washover opening width and height. • Beach width and slope are less important for potential washover deposits. • During inundation, currents are the drivers for sediment transport across the islands. • The water level dynamics during storms in the North Sea and Wadden Sea are crucial. [ABSTRACT FROM AUTHOR]

Rising sea levels are expected to cause widespread coastal recession over the course of the next century. In this work, new insight into the response of sandy beaches to sea level rise is obtained through a series of comprehensive experiments using monochromatic and random waves in medium scale laboratory wave flumes. Beach profile development from initially planar profiles, and a 2/3 power law profile, exposed to wave conditions that formed barred or bermed profiles and subsequent profile evolution following rises in water level and the same wave conditions are presented. Experiments assess profile response to a step-change in water level as well as the influence of sediment deposition above the still water level (e.g. overwash). A continuity based profile translation model (PTM) is applied to both idealised and measured shoreface profiles, and is used to predict overwash and deposition volumes above the shoreline. Quantitative agreement with the Bruun Rule (and variants of it) is found for measured shoreline recession for both barred and bermed beach profiles. There is some variability between the profiles at equilibrium at the two different water levels. Under these idealised conditions, deviations between the original Bruun Rule, the modification by Rosati et al. (2013) and the PTM model predictions are of the order of 15% and all these model predictions are within ±30% of the observed shoreline recession. Measurements of the recession of individual contour responses, such as the shoreline, may be subject to local profile variability; therefore, a measure of the mean recession of the profile is also obtained by averaging the recession of discrete contours throughout the active profile. The mean recession only requires conservation of volume, not conservation of profile shape, to be consistent with the Bruun Rule concept, and is found to be in better agreement with all three model predictions than the recession measured at the shoreline. [ABSTRACT FROM AUTHOR]

Erosion and deposition of sediments in the presence of shearing flows are two phenomena commonly encountered in natural, biological and industrial processes. In determining the critical conditions for the initiation of motion (onset of erosion), a force-magnitude approach has been historically used by employing either the time-averaged or the instantaneous peak fluctuating forces exerted on the sediment particles. Such approach however, has been proven to be incapable of uniquely determining the onset of sediment motion under rapidly fluctuating forces and thus alternative formulations, including impulse- and energy-based methods, have been proposed for turbulent flow conditions. Nevertheless, the force-magnitude approach, can still be applied in the case of very slow viscous flows (Stokes regime) when non-cohesive particles are considered. In the present study, we consider the problem of initiation of motion of a single mobile particle resting on a surface populated by similar types of grains and being exposed to a linear shear flow. The hydrodynamic forces and torques are computed numerically by considering Stokes flow conditions and solving the governing equations using the boundary element method (BEM). To further simplify our model, the bed substrate is parametrised by a flat wall while the pocket shielding effects are taken into account by shifting the linear shear flow towards the fluid. Subsequently, the critical conditions are uniquely determined by applying a force magnitude-based approach and considering rolling and sliding to be the possible modes of entrainment. The computed critical Shields numbers are compared to existing experimental data from the literature showing a very good overall agreement. Finally, the differences and similarities between the two extreme regimes, Stokes flow and fully rough turbulent flow threshold conditions, are briefly discussed. [ABSTRACT FROM AUTHOR]

Results are presented from a combined experimental and numerical study aimed at comparing the flocculation behaviour of purely-cohesive (clay) and mixed (sand-clay) sediment suspensions under equivalent controlled hydrodynamic conditions. The experiments were conducted in a grid-stirred settling column and focussed on measuring the parametric influences of grid-generated shear rate and local suspended sediment concentrations on the time-evolution of the micro- and macrofloc size distributions generated in the column, as well as representative maximal and root-mean-square floc sizes. The results indicate that for kaolin clay suspensions under low-medium shear rates, initial aggregation rates and the peak or quasi-equilibrium floc sizes attained increase with the clay input concentration; this latter effect due to the larger proportion of macroflocs generated within these runs. By contrast, under high shear rates, representative floc sizes for kaolin clay suspensions remain largely unchanged over the experimental duration, with little influence from clay input or in-situ concentrations, and no macroflocs present in the resulting floc size distributions. The addition of the fine sand fraction to the kaolin clay suspensions is shown to reduce both initial aggregation rates and the representative floc sizes attained in the column for runs under low-medium shear rates, whilst having negligible effect on the flocculation behaviour for the sand-clay mixtures under high shear rates. These results suggest that the sand fraction inhibits flocculation at lower shear rates due to an additional floc break-up mechanism resulting from direct sand-clay interactions (e.g. particle-floc collisions). The importance of these inter-fractional (sand-clay) interactions diminishes, in comparison to shear-induced floc break-up, under higher shear conditions. A one dimensional vertical (1DV) model incorporating a population balance equation (PBE) that includes new representation of these multi-fractional (sand-clay) collisions is applied to simulate the kaolin clay and sand-clay settling column tests. In general, the 1DV PBE model predictions provide good agreement with the measured in-situ concentrations and quasi-equilibrium floc sizes attained, but under-predict floc sizes during the initial aggregation phase due to uncertainty with the upper boundary condition in the 1DV model domain. Furthermore, the reliance of the 1DV PBE model predictions on empirical floc break-up rates associated with shear-induced floc fragmentation and multi-fractional (sand-clay) collisions warrants further attention to better define the microscale dynamics of these processes for their improved representation in the PBE model. It is anticipated that this multi-fractional approach represents an improved basis for modelling flocculation processes within natural sedimentary environments, such as estuaries and tidal inlets, where bed sediments often consist of interacting cohesive (i.e. muds) and non-cohesive (i.e. silts, sands) fractions. [ABSTRACT FROM AUTHOR]

The salt marshes of Jamaica Bay serve as a recreational outlet for New York City residents, mitigate wave impacts during coastal storms, and provide habitat for critical wildlife species. Hurricanes have been recognized as one of the critical drivers of coastal wetland morphology due to their effects on hydrodynamics and sediment transport, deposition, and erosion processes. In this study, the Delft3D modeling suite was utilized to examine the effects of Hurricane Sandy (2012) on salt marsh morphology in Jamaica Bay. Observed marsh elevation change and accretion from rod Surface Elevation Tables and feldspar Marker Horizons (SET-MH) and hydrodynamic measurements during Hurricane Sandy were used to calibrate and validate the wind-waves-surge-sediment transport-morphology coupled model. The model results agreed well with in situ field measurements. The validated model was then used to detect salt marsh morphological change due to Sandy across Jamaica Bay. Model results indicate that the island-wide morphological changes in the bay's salt marshes due to Sandy were in the range of −30 mm (erosion) to +15 mm (deposition), and spatially complex and heterogeneous. The storm generated paired deposition and erosion patches at local scales. Salt marshes inside the west section of the bay showed erosion overall while marshes inside the east section showed deposition from Sandy. The net sediment amount that Sandy brought into the bay is only about 1% of the total amount of reworked sediment within the bay during the storm. Numerical experiments show that waves and vegetation played a critical role in sediment transport and associated wetland morphological change in Jamaica Bay. Furthermore, without the protection of vegetation, the marsh islands of Jamaica Bay would experience both more erosion and less accretion in coastal storms. [ABSTRACT FROM AUTHOR]

Large perturbations in the coastline, such as the 'Sand Motor' nourishment ( ∼ 21 million m 3 ) at the Holland coast, can initiate considerable spatial and temporal changes in the median grain size ( D 50 ) of the sea bed on the lower shoreface. The relevance of hydrodynamic conditions for the development of the heterogeneity in D 50 at large-scale nourishments was assessed with a numerical model (Delft3D), which required a validation against 2.5 years of D 50 measurements. A good representation of the observed spatial pattern of D 50 was obtained independent of a 2DH or 3D approach and initial condition for the D 50 of the bed. Five sediment size fractions and a multi-layer administration of the bed composition were used. The extent and magnitude of the coarsening of the bed is related to the velocity of the horizontal tide, while a far less pronounced coarsening takes place during energetic conditions (i.e. H m 0 ≥ 3 m). Differential suspension behaviour between the size fractions, which are all mobilized at the bed, causes a preferential transport of fine sediment (in alongshore direction) away from the Sand Motor at the lower shoreface (i.e. seaward of MSL -6 m). Storm conditions may induce a partial removal of the coarse top-layer due to mobilization of all of the size fractions and mixing with the relatively fine substrate material. Simulations also show that transport of the fine sand fraction extents to much deeper water than for the medium and coarse sand fractions. Models with multiple sediment fractions are therefore required for the assessment of environmental impacts of large-scale coastal structures or land reclamation's and sediment transport on the lower shoreface. [ABSTRACT FROM AUTHOR]

The interplay between wave nonlinearity and mud-induced dissipation is studied here using wave and sediment transport measurements collected in winter 2008, on the Atchafalaya Shelf, Louisiana, between the 8-m and the 4-m isobaths. This study focuses on the relatively energetic storm that occurred on March 4th (2-m wave height in 8-m water depth), which caused significant bed reworking and left in its wake a 20-cm layer of hindered-settling fluid mud. While the net wave dissipation rate was maximal during the hindered-settling phase after the storm, consistent with previous observations, significant dissipation was observed throughout the storm duration, with a secondary maximum associated with the peak of the storm and the maximum bed-reworking effects. The effects of mud-induced dissipation on the nonlinear shoaling process are investigated here using TRIADS, a newly-developed spectral model for nonlinear shoaling of waves. With mud-parameter values estimated using a crude inverse modeling approach, the model was used to separate the effects of mud-induced dissipation from nonlinear transfers, during both the erosion and deposition phases of bed reworking. Numerical simulations show that nonlinear transfers are always active, even under strong dissipation regimes. Remarkably, they also suggest that heavy mud-induced dissipation causes the nonlinear energy cascade to revert direction, with bulk transfers occurring from high-frequency to low-frequency spectral bands. This supports the hypothesis that the interplay between mud-induced dissipation, which is much more significant than the bottom dissipation over sandy beds, and wave nonlinearity can drain energy from the entire spectrum, and not just from the frequency bands that interact directly with the seafloor. The decay of high-frequency variance induced by the reversal of spectral flux in effect reduces the nonlinearity of the wave field. [ABSTRACT FROM AUTHOR]

Study of solid transport caused by the flow of an extreme flood such as the propagation of dam failure wave aims to simulate the hydrodynamics behaviour of the solid particles contained in the valley during the flood passage. With this intention, we have developed a numerical model which is based on the resolution of the one-dimensional Saint Venant–Exner equations by the implicit finite difference scheme. Numerical stability of liquid phase calculation is checked by the Courant number and De Vries condition for the solid phase. The model has been applied to the Hamiz dam (Algeria) which is built in the semi arid zone and presents a major risk of failure. The simulation of several scenarios of dam failure has allowed us to trace the cartography of sediment transport in the valley which is induced by the flood of dam failure. [ABSTRACT FROM AUTHOR]

This paper numerically investigates the transport of dissolved and particulate pollutants in turbulent channel flows. We present a predictive hydrodynamic model in order to explore the dispersion phenomenon of a pollutant injected at a free surface around an obstacle. The air/water interface was modeled using the volume of fluid method (VOF). Numerical results agree well with experimental data and the penetration of pollutant released at different inlet positions of the channel is studied. The Lagrangian tracking of individual particles was performed, and the transport and deposition of various particle size, density and velocity in the channel were analyzed. The standard k–ε turbulence model was chosen for this simulation.We found that large particles with a density of 1600 kg/m 3 , a velocity of 2 m/s and a diameter higher than 70 mm are deposited around the obstacle and near the end sill of the channel, while particles of very small size (lower than 5 mm) remain suspended in the flow and arrive at the outlet of the channel without any deposition rate. This factor must be taken into account during the discharge of effluents and pollutants in coastal water. [ABSTRACT FROM AUTHOR]

A detailed understanding of the behaviour of waves in the nearshore is essential for coastal engineers as these waves cause beach erosion, coastal flooding and damage to coastal structures. Significantly, the influence of reflected waves is often neglected in surf zone studies, although they are known to influence wave properties and circulation in the nearshore. In this paper, a phase-resolving model is rigorously applied to model conditions from the prototype-scale BARDEXII experiment in order to examine and assess the influence of swash-based reflection on surf zone hydrodynamics at both the individual wave and time-averaged timescales. Surface elevation is separated into incoming and outgoing signals using the Radon Transform and a crest tracking algorithm is used to extract incident and reflected wave properties. It is found that on steep beaches (tanβ>1:9) the swash-based reflection - the reflection generated in the swash during the backwash - contributes significantly to the intrawave variability of individual wave properties such as the wave height to water depth ratio γ, through the generation of quasi-nodes/antinodes system. For γ expressed with individual wave heights, variations up to 25% and 40% are obtained for the modelled regular and irregular wave tests, whereas it reaches 15% when it is based on the significant wave height. The outgoing wave field-induced hydrodynamics is also found to affect time-averaged parameters: undertow and horizontal velocity skewness. The undertow is mainly strengthened, particularly in the shoaling region where the outgoing component dominates over the contribution from the incoming wave field. Offshore of the bar, an onshore-directed flow streaming close to the bed is also generated under the outgoing wave field, and is suspected to help in stabilising the bar position. This, along with the influence of the outgoing wave field on the horizontal velocity skewness and the presence of quasi-standing waves, suggests a complex contribution of the hydrodynamics induced by swash-based reflection into sediment transport rates and nearshore bar generation/migration. [ABSTRACT FROM AUTHOR]

Mean (wave-averaged) cross-shore flow in the surfzone has a strong vertical variation. Good understanding and prediction of this mean velocity profile is of crucial importance, as it determines the advective transport of constituents, such as sediment, and consequently the coastal morphological evolution. Most modeling systems for coastal hydrodynamics and morphodynamics do no resolve the wave motion, and wave-current coupling is a challenging topic. This paper investigates stresses and forces that control mean surfzone hydrodynamics based on detailed wave flume velocity measurements above a fixed sloping bed including two breaker bars. The data show that the vertical distribution of normal stress below the wave trough level is fairly uniform. At the same time, the data suggest that a significant part is concentrated between the wave trough and crest level. Furthermore, it is concluded that the horizontal radiation stress gradients and the vertical shear stress gradients can be of the same order of magnitude in the vicinity of the breaker bar. Although usually ignored in 3D mean flow modeling systems, the wave Reynolds stress makes an important contribution to the mean shear stress. The normal stress below the wave trough level could be reasonably well predicted using the classical [16] expression, accounting for the contribution between wave crest and trough. The model of [39] reproduces the main trends in the wave Reynolds stresses above the bottom boundary layer. [ABSTRACT FROM AUTHOR]

Long-term decadal-scale shoreline change is an important parameter for quantifying the stability of coastal systems. The decadal-scale coastal change is controlled by processes that occur on short time scales (such as storms) and long-term processes (such as prevailing waves). The ability to predict decadal-scale shoreline change is not well established and the fundamental physical processes controlling this change are not well understood. Here we investigate the processes that create large-scale long-term shoreline change along the Outer Banks of North Carolina, an uninterrupted 60 km stretch of coastline, using both observations and a numerical modeling approach. Shoreline positions for a 24-yr period were derived from aerial photographs of the Outer Banks. Analysis of the shoreline position data showed that, although variable, the shoreline eroded an average of 1.5 m/yr throughout this period. The modeling approach uses a three-dimensional hydrodynamics-based numerical model coupled to a spectral wave model and simulates the full 24-yr time period on a spatial grid running on a short (second scale) time-step to compute the sediment transport patterns. The observations and the model results show similar magnitudes (O(10 5 m 3 /yr)) and patterns of alongshore sediment fluxes. Both the observed and the modeled alongshore sediment transport rates have more rapid changes at the north of our section due to continuously curving coastline, and possible effects of alongshore variations in shelf bathymetry. The southern section with a relatively uniform orientation, on the other hand, has less rapid transport rate changes. Alongshore gradients of the modeled sediment fluxes are translated into shoreline change rates that have agreement in some locations but vary in others. Differences between observations and model results are potentially influenced by geologic framework processes not included in the model. Both the observations and the model results show higher rates of erosion (∼−1 m/yr) averaged over the northern half of the section as compared to the southern half where the observed and modeled averaged net shoreline changes are smaller (<0.1 m/yr). The model indicates accretion in some shallow embayments, whereas observations indicate erosion in these locations. Further analysis identifies that the magnitude of net alongshore sediment transport is strongly dominated by events associated with high wave energy. However, both big- and small- wave events cause shoreline change of the same order of magnitude because it is the gradients in transport, not the magnitude, that are controlling shoreline change. Results also indicate that alongshore momentum is not a simple balance between wave breaking and bottom stress, but also includes processes of horizontal vortex force, horizontal advection and pressure gradient that contribute to long-term alongshore sediment transport. As a comparison to a more simple approach, an empirical formulation for alongshore sediment transport is used. The empirical estimates capture the effect of the breaking term in the hydrodynamics-based model, however, other processes that are accounted for in the hydrodynamics-based model improve the agreement with the observed alongshore sediment transport. [ABSTRACT FROM AUTHOR]

Follet's Island (FI) is a sediment-starved barrier island located on the Upper Texas Coast; a stretch of coastline along the Gulf of Mexico that experiences on average four hurricanes and four tropical storms per decade. During Hurricane Ike, water levels and wave heights at FI exceeded the 100-year and 40-year return values, respectively, leading to significant overtopping and morphology changes of this low-lying barrier island. The physical processes governing the real-time morphodynamic response of the beach and dune system during 96 h of hurricane impact were modeled using XBeach (2D) and CSHORE (1D). Hydrodynamic boundary conditions were obtained from ADCIRC/SWAN model runs validated with measured buoy and wave gauge data while LiDAR surveys provided pre- and post-storm measured topography. XBeach displayed a decent model skill of 0.34 and provided numerical outputs of the entire 2D domain such as topography, suspended sediment load and bed load which was very useful in visualizing erosion and deposition patterns. CSHORE also displayed a decent model skill of 0.33 and was able to accurately predict the post-storm beach slope and shoreline, but was less effective at simulating the foredune morphology. Modeling results show that the complete morphodynamic response of FI to Hurricane Ike was governed by a sequence of impact regimes, including swash, collision, overwash, inundation, and storm surge ebb. [ABSTRACT FROM AUTHOR]

In rivers, coastal seas and transitional waters, sediment transport processes involve a variety of interacting factors that dynamically vary over time and space. The flow dynamics within these highly heterogeneous natural systems influences the spatial patterns of erosion and deposition of the bed sediments, which in turn shapes and conditions the bottom morphology. By taking advantage of the established modelling framework in both two- and three dimensions for unstructured meshes proposed within the Telemac-Mascaret system, the new module Gaia provides a code structure for solving sediment transport and morphological evolution problems. By a clear treatment of sedimentary processes that happen in the water column, in the bed structure, and at the water–bed interface, Gaia efficiently manages the spatial and temporal variability of sediment size classes, properties and transport modes for two- and three dimensions. In addition, this module can easily be expanded and customised to particular requirements by modifying user-friendly, easy-to-read, and well-documented FORTRAN-90 subroutines. • A new sediment transport and morphological evolution module GAIA, is proposed for the TELEMAC-MASCARET system. It aims at replacing the existing module SISYPHE. • Its generalised framework enables any combination of multiple size classes for both non-cohesive and cohesive sediment to be modelled simultaneously. • The full compatibility between 2D and 3D sediment transport processes is ensured. [ABSTRACT FROM AUTHOR]

The morphology and hydrodynamics of the natural tidal inlet Knudedyb in the Danish Wadden Sea were investigated by the analysis of high resolution bathymetric data and hydrodynamic numerical modeling. In contrast to the expected anticlockwise pattern similar to the other inlets in the Wadden Sea, a clockwise tidal residual current was found, which drives the sediment transport and results from the presence of a confluent meander bend. The channel is draped by bedforms of several hierarchical scales (on average, approximately 155 m long and 2.3 m high), with average sizes decreasing from south to north and seaward (i.e., westward). Primary bedforms in the area are mostly asymmetric ebb-directed and migrate in the ebb direction in the order of 3 m yr − 1 . Bedform sections at the northern channel flank show more symmetrical profiles; crests migrate flood-ward, leading to crestal flexing in the central channel. Lateral recirculation cells develop during ebb tide on both sides of the channel seaward of a bend, before the tidal reversal occurs in the rest of the model domain. As a result of the longer flood phase, a main clockwise residual eddy exists in the middle reach of the channel. Bedform migration patterns and hydrodynamic simulations reveal that the pronounced tidal asymmetry in the channel is enhanced by the effects of the channel morphology on the confined flow (at low tide). [ABSTRACT FROM AUTHOR]

Specific environments such as the French Mediterranean coastline are characterized by steep catchments associated to a climate affected by high intensity rainfall events (over 1000 mm/hour). In such costal catchments, development of human activities and urban developments is very challenging and requests to address properly the issue of vulnerability for both water resources and infrastructures. In addition, the coastal area is frequently characterized by complex relationships between underground resources, rivers and sea. Due to the geological and the morphological conditions, the sediment management is a main issue for local communities. Under specific conditions and with a clear understanding of performance limits, 2D hydraulic modelling is a meaningful approach that can provide an accurate view on the physical processes within the river such as morphological dynamic. This paper develops a suitable methodology to build a 2D surface water flow model, including sediment transport in the lower Var valley, France, with MIKE 21 FM (DHI) modelling system. A sediment transport model – MIKE 21 Sand Transport (ST) - is used to find out the movement of sediments along the river. MIKE 21 ST is interfaced with the hydrodynamic module, MIKE 21 Flow Model (FM), which simulates the water level variations and flow in response to a bunch of forcing functions. The results allow to understand the sediment transport along the Var river and to analyse the impacts on the river-aquifer exchange areas. This approach can lead to carry out a model able to simulate properly the behaviour of physical processes within the river bed. [ABSTRACT FROM AUTHOR]

In this study, we modified and applied an open source CFD software package, the TELEMAC, to simulate sediment transport and bed morphology on a meandering stretch of Nakdong River, between Gangjeong and Dalsung Weirs, whose length is about 20 km. The numerical simulations have been carried out on a High Performance Computing Cluster (HPC) with the real river bathymetry and with different operation scenarios of the weirs. The hydrodynamic parameters and bed evolutions obtained from the numerical results have been validated against field observation data. In addition, this study is to figure out a magnitude of bed evolution and the location where the erosion or deposition taking place under the weir operating conditions. [ABSTRACT FROM AUTHOR]

Extensive research efforts in the last decade have improved knowledge of swash-zone processes. This paper reviews and synthesizes from 2004 onward the research advances of small-scale hydrodynamics and sediment transport processes considering field, laboratory and numerical modeling efforts. Swash-zone hydrodynamics are examined by means of shoreline motions, fluid velocities, pressure gradients, flow structure, bed shear stress, friction coefficients and turbulence. Subsequently, advances related to sediment transport mechanisms and morphological changes are described. Detailed descriptions of measuring techniques, novel findings, and the strengths and weaknesses of the different approaches are discussed. The review also acknowledges the major advances in the development of instrumentation to collect highly resolved flow and sediment concentration measurements in direct proximity of the bed and the experimental framework for analyzing local dynamics on a wave-by-wave time scale (e.g., dam break). [ABSTRACT FROM AUTHOR]

Flow, suspended sediment transport and associated morphological changes in the Vietnamese Mekong Delta (VMD) are studied using field survey data and a two-dimensional (2D) depth-averaged hydromorphodynamic numerical model. The results show that approximately 61–81 % of the suspended sediment load in the Hau River during the flood seasons is diverted from the Tien River by a water and suspended sediment diversion channel. Tidal effects on flow and suspended sediment load are more pronounced in the Hau River than in the Tien River. The results show the formation of nine scour holes in the Tien River and seven scour holes in the Hau River from 2014 to 2017. Additional six scour holes are likely to form by the end of 2026 if the suspended sediment supply is reduced by 85 % due to damming. Notably, the scour holes are likely to form at locations of severe riverbank erosion. In the entire study area, the simulated total net incision volume in 2014–2017 is approximately 196 Mm3 (equivalent to 65.3 Mm3/yr). The predicted total net incision volumes from 2017 to 2026 are approximately 2472 and 3316 Mm3 under the 18 % and 85 % suspended sediment reduction scenarios, respectively, thereby likely threatening the delta sustainability. The methodology developed in this study is helpful in providing researchers and decision-makers with one way to predict numerically the scour hole formation and its association with riverbank stability in river deltas. Of equal importance, this research serves as a useful reference on the role of water and suspended sediment diversion channels in balancing landforms in river-delta systems, particularly where artificial diversion channels are planned. [Display omitted] • The diversion channel is important in balancing water and sediment. • Scour holes are mostly formed at locations of severe riverbank erosion. • Serious riverbed incision shall continue if the sediment continues to decline. [ABSTRACT FROM AUTHOR]

In the swash zone, an assessment of swash flow properties requires an understanding of swash depth and swash velocity, which can affect sediment movement, as well as the design of coastal structures. The method of characteristics provides a useful tool to model unsteady shallow water flows, such as dam-break flow, swash flow and tsunami run-up. In this paper, bottom resistance was incorporated into the nonlinear shallow water equations to extend the application of the method of characteristics to account for frictional effects in the swash zone. The new characteristic equations are solved by the specified time interval scheme. The bottom resistance has little influence on the seaward swash hydrodynamics (initial swash stage), e.g., water depth and flow velocity, while its influence becomes significant in the small water depth region near the swash front, which reduces the maximum run-up height. At a specified time and location, and comparing with a frictionless swash solution, the uprush flow velocity reduces due to the bottom resistance, while the flow velocity increases during the initial phase of the backwash owing to the earlier reversal time with the bottom resistance. However, the differences with the inviscid solution are small within the swash lens. Conversely, the maximum backwash velocity is reduced significantly as a result of the shorter duration of the backwash. Consistent with previous field observations, friction does not significantly alter the gradient of the water surface elevation and a seaward-dipping water surface elevation is observed during the majority of the swash process. The dominant effect of bottom resistance is to reduce the range of inundation, particularly with larger resistance coefficients. The incorporation of the bottom resistance extends the application of method of characteristics in the swash zone to more practical problems, particularly where run-up elevation is critically important, e.g. overtopping flows. [ABSTRACT FROM AUTHOR]

Overwash is an important process that controls short-term barrier dynamics, as well as long-term barrier migration, but this process is difficult to study in the field due to its rare occurrence and the challenging conditions under which it occurs. This paper uses data collected during the BARDEX II experiment in the Delta Flume, the Netherlands, where a proto-type barrier was subjected to a range of wave and water level conditions. The objectives of this research are to: (1) compare the morphologic response to overwash on a gravel barrier (BARDEX 2008 experiment) with that on a sandy barrier (BARDEX II); (2) understand the influence of wave period on overwash characteristics and sediment transport; and (3) improve current knowledge of overwash hydrodynamics. The comparative analysis shows that barrier overwash can be affected by negative feedback that stabilises the barrier through barrier crest accretion on gravel barriers, and by submerged bar development on sandy barriers. An increase in the wave period induced a reduction in overwash frequency over the crest, but no significant relation was found between wave peak period and overwash discharge. Nevertheless, overall water discharge during an overwash episode significantly correlates with overall overwash sediment transport rate. Overwash flow depths during the experiment were relatively shallow and velocities were similar compared to those measured during previous studies and reported in the literature. Despite the controlled laboratory conditions, collection of reliable and accurate measurements of overwash velocities remains challenging. [ABSTRACT FROM AUTHOR]

The paper reports on dambreak-type swash experiments in which intra-swash hydrodynamics and sediment flux are measured for swash on a coarse sand beach and a gravel beach. Flow velocity and depth are measured using PIV and LIF respectively; the intra-swash sediment flux is measured using sediment traps. Comparison of measured hydrodynamics with the immobile, permeable bed experiments of Kikkert et al. (2013) indicates that bed mobility impacts on the swash hydrodynamics, reducing the maximum run-up by approximately 8% for both beaches, compared to the maximum run-up on the corresponding immobile beach. The measured intra swash sediment flux at a given location is characterised by high flux at the moment of bore arrival, followed by rapid decay during uprush, becoming zero at some time before flow reversal. For the gravel beach, the backwash sediment flux is negligibly small, while for the sand beach the backwash flux increases slowly as the flow accelerates down the beach, and peaks at about the time of maximum backwash velocity. Intra-swash sediment flux calculated using the Meyer-Peter and Müller bed load transport formula, with measured hydrodynamics as input and bed shear stress estimated using both the Swart and Colebrook formulae, is within a factor 2 of the measured intra-swash flux. The agreement between the calculated and measured flux is better for the sand beach than for the gravel beach, and better for uprush than for backwash. For the sand beach there is good agreement between calculated and measured total uprush and total backwash sediment volumes. The agreement is less good for the gravel beach, for which calculated and measured uprush volumes show a similar trend but the calculated backwash volumes over-estimate the (negligible) volumes observed in the experiments. [ABSTRACT FROM AUTHOR]

Experimental measurements are obtained to investigate the detailed hydrodynamics of wave–wave interactions in the swash-zone. Two bores are generated using a double dam-break mechanism and interact on a 1:10 impermeable rough slope. Measurements of the hydrodynamics are obtained via acoustic displacement sensors and a combined particle image velocimetry and laser induced fluorescent system. Two types of interactions are investigated: wave capture, with the second bore reaching the first one during the uprush, and weak wave–backwash interactions when interaction happens during the backwash of the first wave. The relative strength of the bores at the initial shoreline and time between their arrivals determines the initial type of interaction, however the type as well as the intensity of the interaction may vary throughout the swash-zone for the same swash event. During wave capture and weak wave–backwash interactions, the fluid of the first bore is advected upwards, then mixed with the fluid of the second bore by intense shearing and highly turbulent vortices generated at the front of the second bore because of the relative velocity differences between the two bores. The details of the hydrodynamics during interaction confirm the potential of swash–swash interactions to suspend sediment and transport it shoreward or interrupt seaward sediment transport. [ABSTRACT FROM AUTHOR]

The Bay of Fundy in eastern Canada has the world's largest tidal range of over 16 m with tidal currents up to 5 ms − 1 making it an ideal place for tidal power extraction using tidal in-stream energy conversion devices in the Minas Passage. Field observations collected from ship-based and bottom-moored sensors over an 8-day period in 2013 are used to validate a 3D hydrodynamic and sediment transport model of the Minas Basin with measurements of water levels, current profiles, waves, suspended sediment fluxes and suspended sediment concentration (SSC) profiles. The sediment conditions are initialized using a bi-modal sediment distribution map and the model simulates both cohesive and non-cohesive sediments in the Minas Basin. Model results for fine-grained suspended sediment concentrations are compared horizontally, vertically, and temporally to observations and indicate strong data-model agreement for SSC from 5 to 287 mg L − 1 . The implications of constructing a large-scale turbine farm within the Minas Passage and the impacts on suspended sediment within the Minas Basin are investigated using the model. The farm is simulated by adding semi-permeable structures that use an energy loss term in the fluid momentum equations to parameterize turbine regions in the hydrodynamic model. The results emphasize the sensitivity of the system to changes in flow and suggest that a large-scale tidal energy farm that extracts maximum power could reduce SSC by 37% on average across the basin which would influence physical and biological processes particularly on the fine-grained intertidal areas around the macrotidal basin. [ABSTRACT FROM AUTHOR]

Detailed measurements of bed level motions and sheet flow processes in the lower swash are presented. The measurements are obtained during a large-scale wave flume experiment focusing on swash zone sediment transport induced by bichromatic waves. A new instrument (CCM + ) provides detailed phase-averaged measurements of sheet flow concentrations, particle velocities, and bed level evolution during a complete swash cycle. The bed at the lower swash location shows a clear pattern of rapid erosion during the early uprush and progressive accretion during the middle backwash phase. Sheet flow occurs during the early uprush and mid and late backwash phases. Sheet flow sediment fluxes during these instances are highest in the pick-up layer. Sediment entrainment from the pick-up layer occurs not only during instances of high horizontal shear velocities but also in occurrence of wave–backwash interactions. As opposed to oscillatory sheet flow, the pivot point elevation of the sheet flow layer is time-varying during a swash event. Moreover, the upper sheet flow layer concentrations do not mirror the concentrations in the pick-up layer. Both differences suggest that in the lower swash zone the dynamics of the upper sheet flow layer are not only controlled by vertical sediment exchange (such as in oscillatory sheet flows) but are strongly affected by horizontal advection processes induced by the non-uniformity of the flow. [ABSTRACT FROM AUTHOR]

Vila Praia de Âncoraharbor is subject to a heavy siltation, being necessary an annual dredging of the whole harbour, in order to maintain the sailing conditions for the fishing boats. An hydrodynamic model of the coast area allowed to identify the causes for that heavy siltation and is presented. Additionally, in order to reduce the rate and dredging volume, some alternative remedial works are proposed, and the most interesting solution is detailed. As a consequence of the presented analysis, it can be stated that the problems occurring in this harbour, regarding the high siltation rate, are due to a not enough detailed hydrodynamic study during the project phase, and so the referred harbour's layout is inadequate to the particular hydrodynamic situation of the area. [ABSTRACT FROM AUTHOR]

This study aimed to investigate hydrodynamics and morphology around river mouth. The propagation of long period waves along the river side of sand spit around the Tenryu River mouth was analyzed by means of image analysis. A series of field surveys were conducted using video cameras to observe shoreline morphology on the river side of the sand spit. Characteristics of the swash motion were extracted and used to describe the fluid motion on the river side. On the basis of image analysis, it was concluded that the shoreline undulation was developed by sediment transport affected by edge wave. This was suggested by shoreline undulation properties found in the images and was confirmed by the edge wave wavelength calculated based on frequency of the corresponding swash motion. In addition, longshore transport instability due to oblique wave with large angle appeared to change the shape of the shoreline undulation. [ABSTRACT FROM AUTHOR]

In the swash zone, the vertical flow of water into and out of the bed is one of the factors that may affect the surface sediment transport. To understand swash zone hydrodynamics, detailed measurements of swash front velocity were obtained in the swash zone by image analysis. During wave up-rush, surface water, in general, infiltrates generally perpendicularly into the beach and deflects direction when reaching groundwater table. Swash velocity plays a significant role in the up-rush infiltration process, which can be divided into three stages and positively related to the surface infiltration. As for the subsurface infiltration rate, it decreases rapidly and reaches a steady rate at the end. It is confirmed that swash front velocity can modify the infiltration process and its influence decreases towards the up-rush end. Calculated infiltration rates after incorporating the influence of swash front velocity into Darcy's law fit closely with the measurements. [ABSTRACT FROM AUTHOR]

Tidal flat morphology is continuously shaped by hydrodynamic forces, resulting in a highly dynamic bed surface. The knowledge of short-term bed-level changes is important both for assessing sediment transport processes as well as for understanding critical ecological processes, such as vegetation recruitment on tidal flats. High frequency bed-level measurements with a high vertical resolution are generally needed for hypothesis testing and numerical model validation. However, conventional manual bed-elevation measurements tend to have a coarse temporal resolution (weeks to months) due to the labor involved. Existing automated methods for continuous monitoring of bed-level changes either lack a high vertical resolution or are very expensive and therefore limited in spatial application. In light of this, we developed a novel instrument called SED (Surface Elevation Dynamics) sensor for continuous monitoring with a high vertical resolution (2 mm). This sensor makes use of light sensitive cells (i.e. phototransistors) and operates stand-alone. The unit cost and the labor in deployments are reduced, facilitating spatial application with a number of units. In this study, a group of SED-sensors is tested on a tidal flat in the Westerschelde Estuary, The Netherlands. The obtained bed-level changes are compared with the data obtained with precise manual measurements using traditional Sedimentation Erosion Bars (SEBs). An excellent agreement between the two methods was obtained, confirming the accuracy and precision of the SED-sensors. Furthermore, to demonstrate how the SED-sensors can be used for measuring short-term bed-level dynamics, two SED-sensors were deployed at two sites with contrasting wave exposure. Daily bed-level changes were obtained including a severe storm event. The difference in observed bed-level dynamics at both sites was statistically explained by their different hydrodynamic conditions. Thus, the stand-alone SED-sensor can be applied to monitor sediment surface dynamics with high vertical and temporal resolution, which provides opportunities to pinpoint morphological responses to various forces in intertidal environment. We expect that this sensor can also be applied in other morphological environments, such as rivers, salt-marsh, beaches and dunes, but the actual applicability remains to be tested. Furthermore, the SED-sensors may also offer opportunities for ground-truthing remote sensing techniques aimed at describing morphological changes. Finally, further improvements in future SED-sensors are discussed, including an inclination and compass sensor, wireless data retrieving function and additional IR-light bar for measurements with poor light availabilities. [ABSTRACT FROM AUTHOR]

Field measurements of hydrodynamics, suspended sediment transport rates and bedform sediment transport rates were made in the intertidal section of a dissipative sandy beach (D50 = 0.26 mm, slope = 1/80) at Perranporth (UK). Pressure transducers, acoustic Doppler velocimeters, optical backscatter sensors and an acoustic sand ripple profiler were deployed for 12 tides, measuring in a range of wave heights from 0.5 to 2.2 m, water depths from 1 to 6 m, and in current strengths up to 0.4 m/s. Data were analysed in terms of the distance to shore (x) normalised by the surf zone width (xs), and spanned the region 0.4 < x/xs < 3. Bedform heights up to 30 cm and wavelengths 0.5 to 2.7 m were recorded. Maximum wavelengths were observed just shoreward of the breakpoint. Bedforms were classified as sub-orbital, vortex ripples. Bedform migration was mostly onshore directed, and correlated with positive (onshore) wave skewness. Migration rates increased through the shoaling zone to a maximum of 1.5 cm/min just shoreward of the breakpoint (x/xs = 0.8). The bedform component of sediment transport was generally onshore directed, and maximum just shoreward of the breakpoint (0.021 kg/m/s). Point measurements showed that the cross-shore suspended sediment transport 25 cm above the bed was dominated by the mean component, with an offshore directed maximum at x/xs = 0.5. Contributions to onshore transport were only made by the incident wave (gravity band) component. The total depth integrated suspended sediment transport was offshore directed and maximum in the mid surf zone (− 0.16 kg/m/s). The depth integrated suspended sediment transport dominated over the bedform sediment transport in the inner to mid surf zone (x/xs < 0.5) and in the outer shoaling zone (x/xs > 1.5). The fractional contribution of the shoreward directed bedform transport to the total absolute transport was up to 100%, and occurred broadly in the region of the breakpoint (0.5 < x/xs < 1.5). However, spatial averaging in the cross-shore indicated that a more realistic bedform contribution was up to 15% of the transport, with a maximum at x/xs = 0.9. Results from this dissipative beach experiment generally agree with previous findings on intermediate beaches, steep beaches, and offshore sandbars. [ABSTRACT FROM AUTHOR]

In modeling the morphological impact of an offshore dredging pit using a process-based model, the hydrodynamic conditions, often derived from regional scale models and sometimes incomplete measurements, may not be in equilibrium with the initial bathymetry profile before dredging. This lack of equilibrium causes a fast profile adjustment toward an equilibrium, which may bias the model results representing the direct effect of the pit. In this study, a method is described which uses the parallel computing technique and evaluates only the morphological changes due to a single factor, i.e., the dredging of a pit. The hydrodynamics and morphodynamics are assumed to be in equilibrium before initial dredging of the pit. The morphological evolution is computed based on the change of sediment flux due to the presence of the pit. The model can avoid the computational demanding spin-up period necessary to reach equilibrium conditions. In particular the concurrent correction method is efficient for scenario testing with a large amount of morphological settings and hydrodynamic conditions. [ABSTRACT FROM AUTHOR]

Existing numerical models of the swash zone are relatively inflexible in dealing with sediment transport due to a high dependence of the deployed numerical schemes on empirical sediment transport relations. Moreover, these models are usually not well-balanced, meaning they are unable to correctly simulate quiescent flow. Here a well-balanced and flexible morphological model for the swash zone is presented. The nonlinear shallow water equations and the Exner equation are discretized by the shock-capturing finite volume method, in which the numerical flux and the bed slope source term are estimated by a well-balanced version of the SLIC (slope limited centered) scheme that does not depend on empirical sediment transport relations. The satisfaction of the well-balanced property is demonstrated through simulating quiescent coastal flow. The quantitative accuracy of the model in reproducing key parameters (i.e., the notional shoreline position, the swash depth, the flow velocity, the overtopping flow volume, the beach change depth and the sediment transport rate) is shown to be satisfactory through comparisons against analytical solutions, experimental data as well as previous numerical solutions. This work facilitates an improved modeling framework for the swash hydrodynamics and sediment transport. [ABSTRACT FROM AUTHOR]

Turbulence and sediment transport models are incorporated into a three-dimensional hydrodynamics model to investigate the mechanisms of morphologic evolution of scour holes within the Indian River Inlet, Delaware, USA. The inlet bed had eroded slightly since stabilizing the channel walls in late 1930s through 1976. The mean rate of bed erosion roughly doubled as a response to anthropogenic activities within the inlet such as the removal of ~ 80 piles remaining from an old bridge. Severe erosion near the in-water bridge supports and cofferdams for the replacement bridge necessitated channel bed stabilization that along with the remained debris from the removal of old bridge piles enhanced the growth of two deep scour holes on the bayside and oceanside of the bridge cofferdams. Scour hole and channel bed evolution has decreased drastically since 1994. The present investigation suggests that, initially, flow concentration through the cofferdams of the replacement bridge was the main reason for scour hole development. Bed shear stress over the forward-facing slope of the scour hole entrains sediment from the bed and extends the scour hole along the inlet and in the vertical direction. Flow separation within the developed scour holes after channel bed stabilization enhances turbulence and appears to be the dominant mechanism for further scour hole development. [ABSTRACT FROM AUTHOR]

Nearshore submerged structures made of sand-filled geosystems are an interesting use for this type of coastal protection technology. These systems have an advantage over more traditional materials such as concrete units or rock, which is the limited and non-permanent impact on natural coastal processes. On top of that are also some important research achievements and improvements at the level of the materials. However, at more exposed hydraulic conditions under high wave energy its application is still hampered by the lack of knowledge about their performance. This paper describes research results based on a series of laboratory measurements of the hydrodynamic and morphodynamic change produced in the vicinity of submerged nearshore structures. An analysis of the different model outputs produced, with respect to sediment transport, wave reflection and wave-induced pressures, has been made and is discussed throughout the paper. Such a comparative analysis provides insights into the efficiency of each defence scheme in maintaining a beach and in protecting the shoreline. The sand-filled geosystems as nearshore submerged structures proved to be efficient in retarding the offshore movement of sediments and in maintaining the shoreline, even if instabilities due to elements' displacement and local scour have been observed. [ABSTRACT FROM AUTHOR]

A morphodynamic model for weakly dispersive wave and shallow flows in horizontal two-dimensional (H2D) space is proposed. The horizontal density variation and the bottom evolution are incorporated into a fully nonlinear Boussinesq equation including vorticity effects. By coupling the flow equation with the depth-integrated sediment transport equation, morphodynamic simulation is made possible. A fourth-order finite volume method with an approximate Riemann solver is used to solve the governing equations. For the hydrodynamic test under strong wave–current interaction environment, the accuracy of the computed velocity and water surface was verified. For the three typical morphological benchmark tests, such as tsunami, regular wave and dam break flow, good agreement was obtained when proper parameters were provided. Therefore, the proposed morphodynamic model can be a useful tool for a wide range of shallow and wavy flows under dispersive and nonhydrostatic environments associated with wave, current, and sediment interaction. [ABSTRACT FROM AUTHOR]

A coupled wave–current–sediment transport beach profile model is used to simulate cross-shore sandbar evolution on the time scale from days to months comprising both rapid offshore and slow onshore migrations. The discrimination of four modes of sediment transport driven by velocity and acceleration skewness, mean currents and slope effects allows addressing the dominant hydrodynamic processes governing cross-shore sandbar behavior. Acceleration–skewness-induced transport systematically results in a slow onshore sandbar migration together with a slow bar growth. Velocity–skewness-induced transport can drive onshore and offshore bar migrations with substantially larger rates. Mean–current-induced sediment transport systematically drives an offshore bar migration with either bar growth or decay. Slope effects essentially act as a damping term. The water level above the sandbar crest mainly influences the sandbar migration direction, while wave obliquity regulates the magnitude of the migration rates and is crucial to accurately simulate offshore sandbar migration during energetic obliquely incident waves. The inclusion of acceleration skewness is a necessary requirement to accurately reproduce the onshore migration of shallow sandbars. Detailed inter-site comparison of best-fit model parameters shows large differences meaning that free parameters attempt to compensate some mispecifications of the physics in the model. Although this also applies to other existing beach profile models, this suggests that this model needs further improvements including, for instance, the contribution of the injection of breaking wave turbulence onto the bed to sand stirring. [ABSTRACT FROM AUTHOR]

A fully-coupled hydrodynamic/morphodynamic numerical model is presented and utilized for the simulation of wave-induced scour and backfilling processes beneath submarine pipelines. The model is based on solutions to Reynolds-averaged Navier–Stokes equations, coupled with k − ω turbulence closure, with additional bed and suspended load descriptions forming the basis for sea bed morphology. The morphological evolution is updated continuously, rather than being based e . g . on period- or other time-averaging techniques. Simulations involving wave-induced scour over the range of Keulegan–Carpenter number 5.6 ≤ KC ≤ 30 demonstrate reasonable match with previous experiments, both in terms of the equilibrium scour depth as well as the scour time scale. Wave-induced backfilling processes are additionally studied by subjecting initial conditions taken from scour simulations with larger KC to new wave climates characterized by lower KC values. The simulations considered demonstrate the ability of the model to predict backfilling toward expected equilibrium scour depths based on the new wave climate, in line with experimental expectations. The simulated backfilling process is characterized by two stages: (1) An initial re-distribution phase involving re-organization of sediments in the immediate vicinity of the pipeline, potentially followed by (2) a more lengthy backfilling evolution toward equilibrium scour depth. The simulated backfilling time scales are of the same order of magnitude as in experiments, though the multi-stage process complicates a more systematic characterization. The simulated sequences of scour and backfilling achieved within the present work are estimated to represent temporal durations of up to approximately 12 h at full practical scales. [ABSTRACT FROM AUTHOR]

Modeling hydrodynamics and sediment transport inside a multi-inlet wetland system is a challenging task due to constraints on model efficiency, accuracy and representation of physics, the scarcity of field data for model validation, and more importantly, the availability of high-resolution data sets of channel bathymetry. Lack of field data sets, model assumptions, and limitations often lead to wrong interpretation of the system's nature. To correctly predict the changes in governing hydrodynamics and morphology of shallow wetland environments, it is essential to resolve the channel properties with the best possible accuracy. In this study, we consider the importance of two factors, numerical model grid resolution around channel shorelines, and bathymetry surveys, in improving the interior channel and mudflat hydrodynamics. Channel shoreline element size is observed to be an essential factor in time-varying channel volume estimation. Lower model resolution in channels inside a marsh can provide good agreement with in-situ surface elevation data, even though the channel surface-velocity phase lag, and velocity magnitude and asymmetry are inaccurate. A higher grid resolution at the channel berms and the high-density channel survey help define the time-varying lateral shoaling bathymetry, cross-section area, and bottom friction, and improve the corresponding model skill and tidal wave properties significantly. We have selected Bombay Hook National Wildlife Refuge, a rapidly eroding salt-marsh system in Delaware Bay, to compare model skills for different hypsometric conditions. Model performance is evaluated during two storm conditions; Hurricane Sandy (2012) and Hurricane Joaquin (2015), using tide gauges located on the marsh interior channels. • Poor grid resolution around marsh-channel berm creates artificial channel convergence and inaccurate tidal wave characteristics. • Topo-bathymetry field survey and bias correction improves channel hypsometry and numerical model reliability significantly. • Inaccurate channel bathymetry and inadequate resolution might lead to acceptable surface elevation but poor tidal velocity field. • The conventional grid generation methods based on sparse cross channel surveys is not sufficient for wetland models. [ABSTRACT FROM AUTHOR]

Abstract: Observations of storm-induced fluid mud dynamics have been conducted at the North Passage deepwater navigational channel (DNC) of the Yangtze Estuary in October to December 2010, during the occurrence of a cold-air front. The measurement data reveal that just after the critical wind wave event, a large amount of fine sediment was trapped in a state of fluid mud along the channel. The observed thickness of the fluid mud was up to about 1–5m, which caused some significant economic and safety problems for shipping traffic in the Yangtze Delta area. The mechanisms and transport processes of the storm-induced fluid mud are analyzed and presented from the angles of both process-oriented and engineering-oriented methods. With the help of hydrodynamics and wave modeling, it could be inferred that the behavior of the storm-induced fluid mud event mainly depends on the overall hydrodynamic regimes and the exchanges of sediment, which is released by storm-wave agitation from adjacent tidal flats. These sediments are accumulated as fluid mud, and subsequently oscillate and persist at those locations with weaker longitudinal residuals in the river- and tide-dominated estuary. In addition, the downslope transport of fluid mud is also thought to have stimulated and worsened the fluid mud event observed in this study. Our modeling results and observations demonstrate that: (1) the transport of fluid mud is an advective phenomenon determining the central position of fluid mud layer along the channel, and it's also a tidal energy influenced phenomenon controlling the erosion and accumulation of fluid mud; and (2) both suspended particulate matter availability and local residual flow regime are of critical importance in determining the trapping probability of sediment and the occurrence of fluid mud. [Copyright &y& Elsevier]

Abstract: The present work analyzes the hydro-morphodynamics characterizing the swash region during the uprush stage. A comparison is illustrated between the sediment transport measured in a series of dam-break experiments and that predicted by the numerical hydro-morphodynamic model of Postacchini et al. (2012). The primary aim is to investigate the differences arising between the weakly coupled or uncoupled model and the measurements, in terms of hydrodynamics, tip celerity and sediment transport. The hydrodynamics are well described by the model and results have been used to calibrate both friction factor and subgrid turbulent viscosity. Comparison of numerically-computed tip celerity with experimental data reveals a fairly good agreement, i.e. a mean error of about 10%, while modeled sediment transport differs by about 40% from the available data. No evident differences are found between results obtained from the coupled and uncoupled model runs (2% for the celerity and 11% for the sediment transport rate at the tip), suggesting that for the specific flow under investigation, at the leading edge of the swash front, hydro-morphological coupling is not an issue of fundamental importance. However, for the special case here of a swash forced by a dam-break, scour occurs at the dam location, and in this case the erosion of the bed is significantly larger in the uncoupled model. [Copyright &y& Elsevier]

Abstract: In Part 2 of this work, the hydrodynamic model described in Part 1 is applied for the simulation of sediment transport and the associated morphological development of breaker bars. The sediment description is split into bed load and suspended load, and like the hydrodynamics the sediment transport is phase-resolved in order to get on- and offshore directed contributions to the sediment transport from phase lags between the suspended sediment and the hydrodynamics. First, the sediment transport over a morphologically fixed bed of a constant slope is considered, and the transport rates are discussed in terms of three dimensionless parameters: the surf similarity parameters (ζ 0) and two variants of Dean's parameter (Ω D and Ω HK ). These cover the ranges ζ 0 ∈[0.08, 1.19], Ω D ∈[1.1, 27.7] and Ω HK ∈[0.01, 0.52]. Secondly, the morphological development of the cross-shore profile is considered, where the initial condition is a profile of constant slope. One reference simulation is discussed in detail and the morphological development due to changes in the hydrodynamic forcing (wave period, wave height, wave irregularity and a net cross-shore current) and in other properties (sediment size and beach slope) is discussed relative to the reference simulation. The coupling between sediment transport rate and morphology is analysed and discussed. [Copyright &y& Elsevier]

Abstract: Distributions of woody vegetation on floodplain surfaces affect flood-flow erosion and deposition processes. A large flood along the lower Rio Puerco, New Mexico, in August 2006 caused extensive erosion in a reach that had been sprayed with herbicide in September 2003 for the purpose of saltcedar (Tamarix spp.) control. Large volumes of sediment, including a substantial fraction of sand, were delivered to the reach downstream, which had not been treated with herbicide. We applied physically based, one-dimensional models of flow and suspended-sediment transport to compute volume concentrations of sand in suspension in floodplain flow at a site within the sprayed reach and at a site downstream from the sprayed reach. We computed the effects of drag on woody stems in reducing the skin friction shear stress, velocity of flow, and suspended-sand transport from open paths into patches of dense stems. Total flow and suspended-sand fluxes were computed for each site using well-constrained flood-flow depths, water-surface slopes, and measured shrub characteristics. Results show that flow in open paths carried high concentrations of sand in suspension with nearly uniform vertical distributions. Drag on woody floodplain stems reduced skin friction shear stresses by two orders of magnitude, yet sufficient velocities were maintained to transport sand more than 50m into fields of dense, free-surface-penetrating stems. An increase in shrub canopy extent from 31% in the sprayed reach site to 49% in the downstream site was found to account for 69% of the computed decrease in discharge between the two sites. The results demonstrate the need to compute the spatial distribution of skin friction shear stress in order to effectively compute suspended-sand transport and to predict the fate of sediment and contaminants carried in suspension during large floods. [Copyright &y& Elsevier]

Abstract: This paper describes a unique new physical testing facility for studying ocean-structure–seabed interactions, and in particular pipeline on-bottom stability on erodible seabed under hydrodynamic loading. The facility, named the O-tube due to its shape, is a fully enclosed flume in which ambient and storm-induced near-seabed flows are generated by a computer-controlled flow pump. Combined steady and oscillatory flow can be generated by alternating pump flow directions in a controlled manner, and computer control also allows irregular flow to be generated. The design of the O-tube combines the capabilities of a conventional open channel flume (which provides steady current) with a U-tube (which provides oscillatory flow). The facility is designed to physically model severe storm conditions, as well as ambient or tidal flows. When studying pipeline stability on erodible seabed under severe hydrodynamic loading conditions, tests can be performed at a relatively large scale (typically 1/5) for large diameter pipelines (e.g. 40in. gas trunklines) and at full scale for small diameter pipelines (<8in.) to minimize potential scaling effects associated with movable bed model tests. The specifications of the O-tube, a model pipe and an actuator system that supports the model pipe are given in detail. Preliminary model testing results show that the facility has met its design expectations. [Copyright &y& Elsevier]

To investigate the interactions among geomorphology, hydrodynamics, and sediment dynamics on the inner shelf offshore Louisiana, multiple acoustic and optical sensors were deployed during a 58-day intermediate-energy period from May 23 to July 22, 2016. Time series results show that an elongated bathymetric "trough" between Ship Shoal and Isles Dernieres partially confines flow in the E -W (shore-parallel) direction. Warm water with lower salinity was observed in the mid to upper water column with cool water with higher salinity in the lower water column. High sediment concentrations of 1–10 g/L were observed in the bottom boundary layer during intermediate-energy conditions in response to sustained winds of up to 11 m/s, significant waves heights of up to 1.5 m, occasional 8 s period swells, and a spring tidal range of 0.6 m. The dominant current and sediment transport directions were westward during the study period. About 77% of the sediment flux occurred during three 2-day-long periods (only 10% of the observation period), revealing the nonlinear and episodic nature of sediment transport in this study area. Although intermediate-energy conditions are less energetic than hurricanes and storms, they occur more often and contribute greatly to the long-term net sediment transport. Based on preliminary estimates, ~51.0 million tons of sediment passes along the Louisiana inner shelf annually, comparable with the annual sediment exiting the Mississippi Delta and sourced from marsh edge erosion in coastal Louisiana combined. The inner shelf sediment flux is an integral part of the coastal sediment budget and may provide important mineral sediment for wetland accretion if transported onshore during storms. [ABSTRACT FROM AUTHOR]

Local scour around structures is an important hydraulic phenomenon that involves multiple coupled physical processes, including turbulent flow, sediment transport, and the evolution of erodible bed. This paper presents a new three-dimensional (3D) scour model, ibScourFoam , which is based on an immersed boundary method. This model is capable of dealing with scour around complex structures and thus it paves the way for practical use of 3D scour models. A special wall function has been developed to overcome the non-smoothness problem of wall shear stress in previous immersed boundary methods. Smooth and accurate wall shear is of critical importance for successful simulation of scour. The model was validated against cases reported in the literature and one flume experiment conducted in this work. The validation case of flow and scour around a vertical pile was reproduced well by our model. The flume experiment is for scour around a partially-buried, horizontal cylinder placed on a foundation. The horizontal cylinder is of finite length and the scour is initiated by flow contraction. The model revealed the distinct stages of scour in the experiment. The complex process of undermining and exposure of initially buried cylinder and foundation was captured well by the model. • An open-source three-dimensional (3D) scour model based on an immersed boundary method has been developed. • The model utilizes a new algorithm to produce smooth and accurate wall shear, which is key for sediment transport. • The model can simulate scour around structures with complex geometries under currents, paving the way for practical use of 3D scour modeling. [ABSTRACT FROM AUTHOR]