Search

The phenomenon of rhythmic patterns of the coastal-zone morphology (beach cusps, longshore sand waves, spits, and nearshore bars) is considered the result of self-organization of the relief when a positive feedback is established between sediment transport and morphology. It is shown that the dynamics of the contour and profile of the coast can be described in terms of the diffusion equation, which allows for both attenuation and growth of relief perturbations. The conditions are determined under which the self-organization mechanism is activated and the resulting perturbations grow over time. Rhythmic structures of the coastal contour are traditionally associated with waves propagating at a large angle relative to the coastal normal. However, it has been shown that the self-organization of beach cusps and megacusps also occurs in normal coast waves due to the development of circulation cells in the surf zone. The conclusion is substantiated that the formation of nearshore bars under certain conditions is also determined by the self-organization mechanism. The results obtained help to interpret the available observational data regarding the evolution of multiple bar systems. [ABSTRACT FROM AUTHOR]

A numerical model is presented for ship-induced sediment transport, focusing on the fundamental role of propeller jet flow. The new module has been implemented in the open-source numerical model FUNWAVE in order to reproduce the effect of the propeller on sediment transport. Numerical simulations have been performed for both stationary and moving vessel cases, as well as for different values of propeller revolution speed. Numerical results are presented for the propeller-induced velocity field and the resulting morphological evolution of the seabed. Qualitative similarities are observed between the numerical results and literature experimental findings, showing the ability of the model to mimic complex morphodynamic processes induced by ship propellers. Compared to stationary vessel cases, smaller scour depths are generated in moving vessel cases. It is concluded that the effect of the propeller provides a major contribution to the mobilization and suspension of seabed sediment, and it should not be neglected in numerical models for ship-induced sediment transport. [ABSTRACT FROM AUTHOR]

In this study, the sediment transport two-phase flow model named SedFOAM is expanded to include soil cohesion, creating a new model named SedCohFOAM within OpenFOAM. The local scouring flume experiment involving a pile on silty seabed and sandy seabed is conducted in a curved flume. Due to the influence of cohesion, the scouring depth at different locations on sandy seabed is 15%–18% greater than that on silty seabed. Observations from this experiment informed the analysis of force balance, wherein the agglomerated silt particles are modeled as large singular entities and the cohesive force is treated as a downward influence that keeps the aggregated particles stationary. Meanwhile, the experimental outcomes are utilized to validate the accuracy of the SedCohFOAM model. The numerical findings demonstrated that SedCohFOAM can simulate the flow field distribution around the pile, variations in seabed shear stress, and alterations in seabed surface morphology. Compared with the SedFOAM model, the SedCohFOAM model has a significantly reduced simulation error in simulating scour on silty seabed. When comparing the cross-sectional profiles of the scour holes derived from the flume experiments with those simulated by SedCohFOAM, it was observed that the ultimate-equilibrium scour depth predicted by the model is consistently lower, but the scour radius in the numerical simulations is larger. The deviation from the experimental results is nearly within 8%, while when the flow velocity is high, the simulation error of the simulated scouring depth behind the pile and the scouring radius in front of pile is amplified. [ABSTRACT FROM AUTHOR]

Sandy beaches high in recreation value make up 16% of the over 4000 km long shoreline of Estonia. The shore processes associated with climate change have remarkably accelerated over recent decades. Many sandy shores have suffered from strong erosion, including an excellent former beach at Valgeranna. The jetties, which were built in the 1860s to protect the navigation channel of Port Pärnu from clogging, have prevented natural sediment transport along the coast from south to north. At the same time, the sandy beach in Pärnu is expanding, and part of the sand accumulates with strong storms also in between the jetties, reducing the width of the shipping channel. The channel needs regular dredging, but, so far, the dredged sediment has been taken far away to the open sea and accumulated on the seabed. The current paper addresses the possibilities of using that sand for beach restoration in destructed and eroded areas. An overview of the applied methods and measurements during field studies is given. The results of modelling the processes of wave activity and sediment transport are discussed. The recycling of shore sediments is an important measure in sustainable coastal zone management. Different options and scenarios are analysed in order to find the most reasonable ways to bring sand back onto beaches and stabilize natural processes. Support from the state by working out respective laws and regulations would be motivating as well. [ABSTRACT FROM AUTHOR]

Internal solitary waves (ISWs) occur in stratified seawater and are characterized by substantial amplitudes and short periods. ISWs engender significant interactions between seawater and seafloor topography. They resuspend seabed sediments in various ways, and the submarine canyon acts as a main channel for transporting the suspended sediments from the shallow sea to the deep sea. Among the seas worldwide where ISWs are prevalent, the South China Sea exhibits the largest amplitude of ISWs, and the ISWs directly interact with the seafloor topography near the Dongsha area in the northern South China Sea. Through the analysis of the water profile and high-resolution multi-beam detection data in the vicinity of the Dongsha area, it was found that the submarine canyon exerts a great impact on the sediment resuspension and the bottom nepheloid layer formation induced by ISWs. The observation results show that the concentration of suspended particulate matter within the submarine canyon is remarkably higher than that outside the canyon. The concentration at the bottom of the canyon can reach twice that of the outside regions, forming a vast bottom nepheloid layer. In addition, with the presence of the submarine canyon, the suspended matter carried by the ISWs accumulates in the water column above the canyon, leading to a higher concentration above the canyon. ISWs not only could influence the submarine canyons, but also interacted with it. This interaction enhanced the resuspension and transport of seafloor sediments along submarine canyons and trenches. This study deepens the understanding of the effect of ISWs on sediment resuspension in submarine canyons. [ABSTRACT FROM AUTHOR]

The problem of shoaling on coastal structures is the result of an event that occurs as part of the natural cycle. In cases where shoaling cannot be detected or prevented, various economic and operational problems may arise and may cause disruptions. In this study, the complex coastal dynamic impact of shoaling on three sequential fishery coastal structures located within the borders of Rize province in the Eastern Black Sea region of Türkiye was examined in terms of bathymetric changes and sediment transport under the influence of the incident wave climate. The effects of these structures on each other were also investigated. With this aim, bathymetric measurements were carried out to examine the impact of waves on seabed erosion and deposition. A serious shoaling problem was identified at one of the harbor launches under investigation, where approximately 13,200 m3 of deposition occurs annually in a relatively small harbor launch area. Such physical problems are thought to be the result of shoaling, the selection of sites that are not viable for fishery-related coastal structures, or the wrong positioning of the breakwater. [ABSTRACT FROM AUTHOR]

Below a certain threshold of wave energy for a given depth, unconsolidated sediment should respond to wave action poroelastically. To this end, a generalized simple poroelastic model was applied to in situ data collected in coastal sediments near Oceanside, California. Pore pressure data were recorded by sensors attached to cylindrical unexploded ordinance surrogates, and water pressure sensors on bottom moorings. Orientation data were collected from inertial motion units attached to the surrogates, which were placed on the seabed and subsequently shallow buried during a high‐energy event on 13 February 2021. The model is characterized by two parameters. A consolidation coefficient controls the depth of diffusive flow, and Skempton's coefficient represents the ratio of the original signal into components transmitted by the sediment matrix and the pore fluid. The model assumes that the pore pressure signal is coherent with the seafloor signal; spectral coherence above 0.75 was used to select the frequency range from 0.05 to 0.2 Hz for the analysis. Spectral analysis methods were then applied to obtain averaged auto spectral densities of the pore pressure and bottom mooring signals over the coherent frequency band. Attenuation between sensor pairs was calculated. The results yielded burial depths over time for the surrogates that agreed with changes in significant wave heights, liquefaction, and recovery depths. Plain Language Summary: Dry porous material behave differently than porous material saturated with water. A poroelastic model is a way to describe how saturated porous material and the water it contains behave when forces act on it. It is often assumed that seafloor sediments can be described using a poroelastic model; however, this assumption is based primarily on laboratory experiments. We examined if real‐world sediments could be described by a poroelastic model. To do this, we looked at how the pressure of the water in the sediment, or "pore pressure," changed compared to the water pressure at the seafloor as ocean waves traveled over the sediment. Pore pressure was measured using sensors on instrumented cylinders, while the seafloor pressure was estimated using a sensor attached to a bottom mooring. The attenuation of the pressure signal between two sensors was estimated using the measurements. The poroelastic model was then applied to the calculated attenuation and used to estimate how deeply the instrumented cylinders buried. By comparing the estimates to observed burial depths, we determined both how well the poroelastic model works and how sediment above the instrumented cylinders changed over time. Our results show that the poroelastic model works, but that improvements are needed. Key Points: In situ pore pressure data was analyzed to determine adequacy of a poroelastic model in describing near‐surface sedimentsThe poroelastic model was found to be adequate, and can be used to estimate bedform heights of sandy sedimentsFuture work will need to take into account enhanced interaction at the seabed from higher energy at specific frequencies [ABSTRACT FROM AUTHOR]

The oceanic bottom mixed layer (BML) is a well mixed, weakly stratified, turbulent boundary layer. Adjacent to the seabed, the BML is of intrinsic importance for studying ocean mixing, energy dissipation, particle cycling and sediment-water interactions. While deep-seabed mining of polymetallic nodules is anticipated to commence in the Clarion-Clipperton Zone (CCZ) of the northeastern tropical Pacific Ocean, knowledge gaps regarding the form of the BML and its potentially key influence on the dispersal of sediment plumes generated by deep-seabed mining activities are yet to be addressed. Here, we report recent field observations from the German mining licence area in the CCZ that characterise the structure and variability of the BML locally. Quasi-uniform profiles of potential temperature extending from the seafloor reveal the presence of a spatially and temporally variable BML with an average local thickness of approximately 250 m. Deep horizontal currents in the region have a mean speed of 3.5 cm s - 1 and a maximum speed of 12 cm s - 1 at 18.63 ms above bottom over an 11 month record. The near-bottom currents initially have a net southeastward flow, followed by westward and southward flows with the development of complex, anticyclonic flow patterns. Theoretical predictions and historical data show broad consistency with mean BML thickness but cannot explain the observed heterogeneity of local BML thickness. We postulate that deep pressure anomalies induced by passing surface mesoscale eddies and abyssal thermal fronts could affect BML thickness, in addition to local topographic effects. A simplified transport model is then used to study the influence of the BML on the interplay between turbulent diffusion and sediment settling in the transport of deep-seabed mining induced sediment plumes. Over a range of realistic parameter values, the effects of BML on plume evolution can vary significantly, highlighting that resolving the BML will be a crucial step for accurate numerical modelling of plume dispersal. Article Highlights: Field observations detail the presence of bottom mixed layer in the abyss of the Clarion-Clipperton Zone in the northeastern tropical Pacific Mean local thickness of the layer is approximately 250 m, with large spatial and temporal heterogeneity that needs further understanding The transport of benthic sediment plumes generated by deep-seabed mining can be greatly influenced by bottom mixed layer variability [ABSTRACT FROM AUTHOR]

A two-dimensional, vertically integrated, non-linear numerical model was applied to investigate the Urias coastal lagoon's (URCOL) tide-driven currents, bed load sediment transport, and seabed morphodynamics. The coastal body of water, located on the eastern side of the Gulf of California, includes the Mazatlán harbour, the most important port on the Pacific Mexican coast due to the relevant activities like the heavy vessel traffic. URCOL also includes an extensive aquaculture infrastructure at the lagoon head. The tidal hydrodynamic modelling revealed the mixed character of tides predominantly semidiurnal in the lagoon. The numerical computation at the harbour entrance showed an ebb-dominant tidal distortion. The distribution patterns of the erosion and accretion rates are consistent with the convergent and divergent character of the vectors of sediment transport rates. The sediment accretion has been predicted mainly in the middle part of the channel, right where the channel starts curving, changing the alignment of the lagoon. The tidal hydrodynamics, sharp topographic gradient, and geometric features of the lagoon seem to determine the location of accretion and erosion areas. Article Highlights: A mixed character of predominantly semidiurnal tides and an ebb-dominant tidal distortion were predicted in the lagoon. The erosion and accretion areas are consistent with the sediment transport vectors predicted by the model. A non-linear numerical model study determined that tidal hydrodynamics and morphodynamics influence sediment transport in the lagoon. The sediment accretion-erosion areas mostly occur in the middle part of the lagoon. Sediment exchange took place occur between the lagoon and the Gulf of California; the predicted net bed load sediment transport was seaward. [ABSTRACT FROM AUTHOR]

Gas transport through sediments to the seabed and seepage occurs via advection through pores, faults, and fractures, and as solubility driven gas diffusion. The pore pressure gradient is a key factor in these processes. Yet, in situ measurements for quantitative studies of fluid dynamics and sediment deformation in deep ocean environments remain scarce. In this study, we integrate piezometer data, geotechnical tests, and sediment core analyses to study the pressure regime that controls gas transport along the Vestnesa Ridge in the eastern Fram Strait. The data show a progressive westward decrease in induced pore pressure (i.e., from c. 180 to c. 50 kPa) upon piezometer penetration and undrained shear strength of the sediments, interpreted as a decrease in sediment stiffness. In addition, the data suggest that the upper c. 6 m of sediments may be mechanically damaged due to variations in gas diffusion rates and exsolution. Background pore pressures are mostly at hydrostatic conditions, but localized excess pore pressures (i.e., up to 10 kPa) exist and point toward external controls. When analyzed in conjunction with observations from geophysical data and sediment core analyses, the pore pressure data suggest a spatial change from an advection dominated to a diffusion dominated fluid flow system, influenced by the behavior of sedimentary faults. Understanding gas transport mechanisms and their effect on fine‐grained sediments of deep ocean settings is critical for constraining gas hydrate inventories, seepage phenomena and sub‐seabed sediment deformations and instabilities. Plain Language Summary: Seafloor methane seepage occurs persistently in response to pressure changes. The scarcity of sub‐seabed pressure data limits our understanding of the mechanisms of methane release. Here we document observations from 4 days monitoring of pressure and temperature within the upper 10 m of sediment at a seepage site in the Fram Strait. The survey extends for 60 km between the continental shelf off west‐Svalbard and the mid‐ocean ridge. The data show that the geothermal gradient increases and that sub‐seabed sediments become softer and more susceptible to deformation as they approach the mid‐ocean ridge. When analyzed in conjunction with cross‐disciplinary data it seems plausible that the changes in sediment properties are associated with an increase in the amount of dissolved methane transported to the seafloor. We suggest that changes in the geological setting have resulted in the locking of fractures that would otherwise allow the release of trapped methane to the ocean. Trapped gas in the sediment pores is pumped by tides and causes damages beneath the seafloor. This study is an important step in understanding the mechanisms involved in the transport of methane into the ocean, with implications for climate research, assessment of geological hazards and alternative energy resources. Key Points: This study documents in situ pore pressure measurements along the gas charged Vestnesa sedimentary ridge in the eastern Fram StraitIntegrated piezometer and calypso core analyses indicate spatial variations in sediment stiffness and localized excess pore pressuresGas transport and sub‐seabed sediment stiffness are interrelated and affected by sea‐level changes and fault behavior [ABSTRACT FROM AUTHOR]

In the construction process, a trailing suction hopper dredger exploits the drag head and pipes to transport seabed sediment to the spoil hopper for storage. When the liquid level of the mixture was elevated in the spoil hopper, the mixture overflowed to the hopper via the overflowing cylinder. The spoil hopper sedimentation significantly affected the control decision and hopper loading efficiency of the dredger. In this study, mathematical modelling, simulation, and computational fluid dynamics (CFD) simulations were performed to build a sedimentation model of the sediment in the spoil hopper. Subsequently, the movement of the sediment after it entered the spoil hopper was stimulated was calculated based on the simulation, as well as the sediment distribution, overflow loss, and dry soil production of the spoil hopper. As indicated by the results, the mathematical model and CFD simulation methods were consistent with the simulation results of the built spoil hopper sedimentation model, thereby demonstrating that the built model was credible and could help guide the hopper loading control strategy research, as well as construction optimization. [ABSTRACT FROM AUTHOR]

Sediment transport on silty and muddy coast had been a research hotspot because of its uniqueness. Based on the cross-section characteristics of channel, and in view of the problem that most of the existing formulas are semi-empirical and semi-theoretical, with assumption and simplification of the motion of sediment-laden flow, this paper deduces the formulas for calculating the flow carrying force and seabed scouring and silting strength from the perspective of hydrodynamic equilibrium of sediment-laden flow. [ABSTRACT FROM AUTHOR]

A coupled nearshore hydrodynamics and sediment transport model with adjoint‐based uncertainty quantification has been applied to sand bar morphodynamics in the Duck94 field experiment (Duck, NC). The model, which is based on previously established physical process formulas, is capable of producing accurate predictions of sand bar migration during the experiment. However, reasonable perturbations to the model inputs—namely initial conditions, boundary conditions, and calibration coefficients—can produce a range of model predictions. This range is taken to represent the potential for uncertainty of the model, for scenarios where one or more model inputs are poorly constrained. Experiments are presented that quantify the relative impact of different input types on uncertainty, and the results are contrasted for accretive versus erosive wave conditions. During accretive conditions (shoreward bar migration), uncertainty is dominated by the growth of errors in initial conditions, owing to positive feedbacks in the model. In contrast, during erosive conditions (seaward bar migration), there is a smaller impact of errors in initial conditions, and uncertainty is instead dominated by errors in sediment transport coefficients. The results thus point to qualitative differences in the nature of nearshore morphodynamic uncertainty under different wave conditions, with a greater role of internal error growth (positive feedbacks) during accretive conditions and errors in model physics being more important during erosive conditions. Plain Language Summary: Sandy wave‐exposed beaches are in a constant state of change due to sediment transport by waves and wave‐driven currents. The relevant physical processes are mostly concentrated within 1–10 cm above the seabed and vary on timescales of order 0.1–10 s—these scales are several orders of magnitude smaller than those of practical interest for nearshore morphodynamics, hence simplified approximations are needed to represent subgrid‐scale physical processes. In addition, the interplay between morphology and sediment transport can trigger feedbacks, such that even small model errors may become amplified over time. Both these factors (process errors and feedbacks) are generally understood to cause considerable uncertainty in model predictions, but their relative importance is not well known. The present work quantifies effects of feedbacks and model parameters, showing their relative importance changes depending on whether the beach is accreting or eroding. By better understanding the nature of uncertainty, these results can inform future efforts into predicting nearshore coastal change at storm‐to‐seasonal timescales. Key Points: Uncertainty quantification in a nearshore morphodynamic model using an adjoint‐based approachMorphodynamic uncertainty is dominated by positive feedback during accretive conditions and by model parameter error during erosive onesNearshore sediment transport formulas are highly sensitive to uncertainties in wave hydrodynamics [ABSTRACT FROM AUTHOR]

Oyster farming may impact the estuarine tidal circulation with a series of effects on environmental conditions and cultures' growth. Hydrodynamic numerical models set up in estuaries integrated the presence of oyster structures by simply increasing the bottom friction coefficient over farming areas. However, for elevated oyster tables in tidal environments, such default calibration ignored the temporal variations of the friction coefficient between the conditions of submerged or unsubmerged structures. Thus, an original formulation of the Chézy coefficient was here proposed to integrate these modulations. Assessed against measured and predicted vertical velocity profiles on a 1/2 scaled model, this formulation was implemented in a simulation of the tidal circulation within the Aber Wrac'h estuary (Brittany, France). Particular attention was dedicated to the changes induced on the current magnitudes and sediment transport. Oyster tables were found to impact current magnitudes in the vicinity of elevated structures, with major differences at times of local peak flood and ebb. These modifications were characterised by (i) a reduction of current magnitudes over oyster farming areas and (ii) a tidal-flow acceleration on both sides of these structures. Increased sediment transport was, therefore, expected in the vicinity of these cultures, with potential implications on seabed morphology and water quality. [ABSTRACT FROM AUTHOR]

This study constructs a digital elevation model of the coastal waters of the Shandong Peninsula using GIS-based interpolation methods to investigate the 15-year characteristics of seabed scouring and siltation. It utilizes depth data of the Shandong Peninsula's offshore area between 2004 and 2006 and 2017 and 2019. The results indicated that the Shandong Peninsula's coastal-water seabed is characterized by integral siltation and local point scouring. In addition, the northwest Shandong Peninsula is dominated by siltation, mainly distributed between 2 and 5 m isobaths, with the largest siltation area located in Laizhou Bay. The net volume of siltation is 2.13 × 108 m3, the siltation rate is 0.152 × 108 m3.a−1, and the scouring is concentrated in the estuary and the west coast of Laizhou Bay. Scouring and siltation balance generally characterize the seabed in the northern coastal waters of the Shandong Peninsula, and the degree of scouring and siltation is weak. The siltation occurs primarily near the land area, while scouring occurs as the sea deepens. In the northeast of the Shandong Peninsula, the degree of scouring and siltation is extreme, and their distribution range is small, whereas in the south, siltation is distributed in large bays and straight coastal offshore waters, and its degree is relatively weak. At the southernmost end of the study area, the scouring and siltation in Jiaozhou Bay are spatially distributed and balanced. In reality, the key factors affecting the distribution of coastal-seabed scouring and siltation are materials transported by river sediment, coastal scouring, and human activities. [ABSTRACT FROM AUTHOR]

Hadal trenches are considered to act as depocenters for organic material, although pathways for the material transport and deposition rates are poorly constrained. Here we assess focusing, deposition and accumulation of material and organic carbon in four hadal trench systems underlying different surface ocean productivities; the eutrophic Atacama and Kuril‐Kamchatka trenches, the mesotrophic Kermadec trench and the oligotrophic Mariana Trench. The study is based on the distributions of naturally occurring 210Pbex, 137Cs and total organic carbon from recovered sediment cores and by applying previously quantified benthic mineralization rates. Periods of steady deposition and discreet mass‐wasting deposits were identified from the profiles and the latter were associated with historic recorded seismic events in the respective regions. During periods without mass wasting, the estimated focusing factors along trench axes were elevated, suggesting more or less continuous downslope focusing of material toward the interior of the trenches. The estimated organic carbon deposition rates during these periods exhibited extensive site‐specific variability, but were generally similar to values encountered at much shallower settings such as continental slopes and margins. Organic carbon deposition rates during periods of steady deposition were not mirrored by surface ocean productivity, but appeared confounded by local bathymetry. The inclusion of deposition mediated by mass‐wasting events enhanced the sediment and organic carbon accumulations for the past ∼150 years by up to a factor of ∼4. Thus, due to intensified downslope material focusing and infrequent mass‐wasting events, hadal trenches are important sites for deposition and sequestration of organic carbon in the deep sea. Plain Language Summary: Hadal trenches (>6,000 m water depth) occupy ∼1% of the world's ocean floor yet are largely underexplored, but recent studies have shown that these environments are depocenters for organic material and microbial activity is intensified when compared to shallower abyssal plains. However, transport and accumulation of sediment material to these hadal trenches is poorly understood. This study investigates sedimentation and accumulation dynamics of organic carbon in trenches using results of radionuclide analysis (in sediment from the Atacama, Kuril‐Kamchatka, Kermadec, and Mariana trenches). The analysis shows that trench sediments consist of discreet layers representing both periods of continuous deposition and sudden mass‐wasting events often triggered by historic earthquakes. Down slope focusing of material, intensified the deposition along the trench axes. However, the deposition rates exhibited extensive site‐specific variations that were partly related to mass‐wasting events which greatly enhanced not only mass accumulation but also organic carbon accumulation at the trench axes. Our results illustrate that mass‐wasting events play an important role on supplying organic carbon to hadal communities and suggest that hadal trenches might be quantitatively important for sediment and organic carbon sequestration in the deep sea. Key Points: Hadal trench systems act as important hot spots for accumulation and retention of organic material in the deep seaThe sediment and organic carbon accumulation in trench systems is partly mediated by ongoing material focusingInfrequent mass‐wasting events triggered by earthquakes play a significant role on mass accumulation and organic carbon deposition [ABSTRACT FROM AUTHOR]

Glaciers erode their beds and the adjacent landscape by abrasion and plucking and entraining sediment on their way downwards driven by gravity. Ice becomes a sediment transport agent. To determine glacial transport of sediment, measurements of both the ice flux and its concentration of sediment are needed. Once glaciers reach the ocean, ice and its entrained sediment is released into the ocean by calving. Further transport takes place by icebergs. Quantification of IRD (ice‐rafted debris) fluxes, which upon ultimate deposition on the ocean floor is an important climate indicator, becomes even more complicated as icebergs topple and differentially melt while being in transport. While the volume of tidewater glacier ice released by recent calving is quite well constrained by satellite measurements, there is a lack of measurements of the concentration of sediment within the moving ice. Here, we describe a method to collect samples of ice from icebergs systematically for the first time in Greenland together with a strategy to obtain representative samples. Our method is tested in Scoresby Sound, East Greenland in order to describe the transport of sediment into the fjord system related to calving from known glacial source areas. Our data clearly demonstrate that biased and sparse sampling potentially produces unrealistic values of sediment concentrations. Seventy‐two samples from 24 icebergs had an average concentration of sediment of 35.5 g/L of ice with a standard deviation of 97%, between the 24 individual icebergs. The origin of the sediment is related to specific source areas. Based on the samples, we present an estimate of the annual transport of sediment out of Scoresby Sound related to calving ~100 (0.3–200) million t year−1. Finally, we discuss the uncertainties of our estimate. [ABSTRACT FROM AUTHOR]

The effect of wave skewness and sediment particle size on near-bed sediment dynamics and transport owing to wave-induced streaming is examined in this study. Here, wave-dominated flow over a flat rough bed is studied, with wave propagation forming a nonzero angle with the current. It was observed that the increase in wave skewness increases the mean sediment transport, which is consistent with prior findings for the particular situation of horizontally uniform Stokes forcing. The mean sediment transport beneath combined second-order Stokes waves and current has been investigated for fine, medium, and coarse sand, respectively. Due to inertia, both the mean bed-load vector and the depth-integrated suspended flux vector are less rotated (relative to the wave propagation direction) for coarse sand than for fine sand. The mean bed-load transport is largest for coarse sand, whereas the mean suspended sediment transport is largest for fine sand. [ABSTRACT FROM AUTHOR]

The potential response of shoreface depositional environments to sea level rise over the present century and beyond remains poorly understood. The shoreface is shaped by wave action across a sedimentary seabed and may aggrade or deflate depending on the balance between time-averaged wave energy and the availability and character of sediment, within the context of the inherited geological control. For embayed and accommodation-dominated coastal settings, where shoreline change is particularly sensitive to cross-shore sediment transport, whether the shoreface is a source or sink for coastal sediment during rising sea level may be a crucial determinant of future shoreline change. While simple equilibrium-based models (e.g. the Bruun Rule) are widely used in coastal risk planning practice to predict shoreline change due to sea level rise, the relevance of fundamental model assumptions to the shoreface depositional setting is often overlooked due to limited knowledge about the geomorphology of the nearshore seabed. We present high-resolution mapping of the shoreface-inner shelf in southeastern Australia from airborne lidar and vessel-based multibeam echosounder surveys, which reveals a more complex seabed than was previously known. The mapping data are used to interpret the extent, depositional character and morphodynamic state of the shoreface, by comparing the observed geomorphology to theoretical predictions from wave-driven sediment transport theory. The benefits of high-resolution seabed mapping for improving shoreline change predictions in practice are explored by comparing idealised shoreline change modelling based on our understanding of shoreface geomorphology and morphodynamics before and after the mapping exercise. [ABSTRACT FROM AUTHOR]

Numerical simulations were conducted to investigate steady current scour around rectangular and square subsea caissons. The caissons, which are representative of subsea structures, have a submerged height ranging from 0.5 to several times their longest base dimension. The flow model used is based on the Reynolds Averaged Navier-Stokes equations, and the scour model simulates bed load and suspended load transport to predict the evolution of the seabed profile. The aim of this study is to investigate the mechanisms of local scour, specifically the contribution of the horseshoe vortex and the local streamline contraction near the caisson corners to local scour. The model is validated through comparisons with experimental measurements, indicating reasonable agreement. Based on the numerical model results, the mechanisms of local scour around square and rectangular caissons are found to be qualitatively similar. If the flow is directed perpendicular to one of the caisson faces, both the horseshoe vortex and the local streamline contraction contribute to scour. The maximum scour depth is located at the two upstream corners of the caisson due to the combined effects of the horseshoe vortex and streamline contraction. When the flow approaches the caisson with a diagonal attack angle of 45°, the two upstream faces act like a streamlined wedge that splits the incoming flow. The study found that the horseshoe vortex almost disappears and the scour is primarily caused by the local velocity amplification at the two side corners. If the flow attack angle is 45°, the scour does not initiate near the upstream corner without the contribution from the horseshoe vortex. These findings are expected to serve as a valuable theoretical foundation for the design of scour protection. • Scour around subsea caissons is studied by fully three-dimensional simulations. • The contributions of the horseshoe vortex and the local streamline contraction near the caisson corners to local scour are identified. [ABSTRACT FROM AUTHOR]

Transport of continental shelf sediments to the deep ocean can be studied from displaced symbiont‐bearing larger benthic foraminifera found in turbidity current deposits. The larger benthic foraminifera habitat depth, physical characteristics and preservation serve as indicators for understanding sediment transport dynamics near the seabed and in the water column. Here, an experiment was designed to explore sediment transport in a closed flume system using simulated high current velocities. Shelf sediments from the Gulf of Eilat/Aqaba, dominated by Amphistegina papillosa and Operculina ammonoides, were subjected to 60 cm s−1 and 80 cm s−1 current velocities while collected in a 10 cm vertical sediment trap. Larger benthic foraminifera abundance, shell physical properties and preservation were analyzed and compared with the original bulk sediments. The experiment results showed that at 80 cm s−1 velocity, larger benthic foraminifera shells of all sizes and preservations are efficiently resuspended and transported in large quantities throughout the water column, as opposed to their transport as bedload by the lower velocity current. Larger benthic foraminifera shape also has a role in the transport distances and accumulation depths. Operculina ammonoides shells were found to be more portable, compared to Amphistegina papillosa, due to their flatter discoid shape. The results suggest that a threshold velocity of ca 80 cm s−1 was needed to generate the thick coarse deposits found in the Gulf of Eilat/Aqaba slope sedimentary record, which were previously suggested to be triggered by large magnitude seismic events. Lower velocities probably winnowed minor amounts of larger benthic foraminifera shells (with little or no coarser sediments) that were deposited as a thin sand layer may point to lower magnitude seismic triggers. In conclusion, larger benthic foraminifera shells are transported and deposited in accordance with their hydrodynamic properties, resulting in assemblage differentiation along the transport pathway. This study shows that the fossil biogenic composition in slope sediments includes valuable information on current velocities, transport dynamics and possible triggers in the geological record. [ABSTRACT FROM AUTHOR]

We develop and investigate an advection-diffusion-settling model of deep-sea mining collector plumes, building on the analysis of midwater plumes in Part 1. In the case of collector plumes, deposition plays a predominant role in controlling the mass of sediment in suspension, and thus on setting the extent of the plume. We first discuss the competition between settling, which leads to deposition, and vertical turbulent diffusion, which stretches the plume vertically and reduces deposition. The time evolution of the concentration at the seabed is found to be a highly nonlinear function of time that depends non-trivially on the ratio of diffusion to settling time scales. This has direct implications for the three extent metrics considered, namely the instantaneous area of the seabed where a deposition rate threshold is exceeded, the furthest distance from the discharge where the plume exceeds a concentration threshold and the volume flux of fluid in the water column that ever exceeds a concentration threshold. Unlike the midwater plume, the particle velocity distribution of the sediment has the greatest influence on the extent metrics. The turbulence levels experienced by the plume also markedly affects its extent. Expected variability of turbulence and particle settling velocity yields orders of magnitude changes in the extent metrics. [ABSTRACT FROM AUTHOR]

A numerical model was developed to predict mobility and burial of seafloor cylindrical objects. The model contains four components: 1) object's physical parameters such as diameter, length, mass, and rolling moment; 2) dynamics of rolling cylinder around its major axis; 3) empirical sediment scour model; and 4) seabed environmental characteristics such as currents, waves (peak period, significant wave height), sediment density, and medium sediment grain size. Under the sponsorship of the Department of Defense Strategic Environmental Research and Development Program, a field experiment was conducted from April 21 to May 23, 2013 off the coast of Panama City, FL, USA to measure both objects' mobility using sector scanning and pencil beam sonars and simultaneous environmental time-series data of the boundary layer hydrodynamics and sediment transport conditions for driving mobility. Comparison between modeled and observed data shows the model capability. Future work needs to consider more realistic object shapes and motions such as pitch and yaw, and wavy seabed. [ABSTRACT FROM AUTHOR]

Sandy beaches generally are influenced by various coastal dynamic processes and undergo constant changes. The present study is an attempt to understand the hydromorphodynamic characteristics of a sandy pocket beach situated along the central west coast of India through field observation and numerical modeling. Multiple oceanographic instruments are deployed to capture the actual nearshore hydrodynamics, and sediment transport is measured using the streamer trap method suggested earlier during the premonsoon season. The observed vertical distribution of sediment fluxes showed a typical upward decrease from the seabed to the water surface. It is also noted that nearly 75% of the trap measurements showed that near-bed transport is higher than the depth-integrated values, confirming that the maximum sand remobilization is in the vicinity of the seabed rather than in suspension. The beach profiles of selected transects were measured during the pre- and postmonsoon seasons to understand the bed evolution. A one-dimensional numerical model, developed using XBeach and validated with field-observed values, demonstratively captured the effect of monsoon hydrodynamics on the beach profiles with fair accuracy. The various significant numerical parameters that govern the morphodynamics in the sandy beach are evaluated through a comprehensive analysis. In the end, the simulated beach profile that captures the effect of monsoon and storm are in good agreement with that obtained from field observations, with Brier Skill Scores (BSSs) of 0.69, 0.76, and 0.74 for Profiles 1, 2, and 3, respectively. [ABSTRACT FROM AUTHOR]

Elevated concentrations of organic matter are found in sediments of hadal trenches relative to those found in the abyssal seabed, but the origin of such biological material remains elusive. Here, we report the composition and distribution of cell membrane intact polar lipids (IPLs) in surface sediments around the deepest points of the Atacama Trench and adjacent bathyal depths to assess and constrain the sources of labile organic matter in the hadal seabed. Multiscale bootstrap resampling of IPLs' structural diversity and abundance indicates distinct lipid signatures in the sediments of the Atacama Trench that are more closely related to those found in bathyal sediments than to those previously reported for the upper ocean water column in the region. While the overall number of unique IPL structures in hadal sediments is limited and they contribute a small fraction of the total IPL pool, they include a high contribution of phospholipids with mono- and di-unsaturated fatty acids that are not associated with photoautotrophic sources. The diversity of labile IPLs in hadal sediments of the Atacama Trench suggests the presence of in situ microbial production and biomass that resembles traits of physiological adaptation to high pressure and low temperature, and/or the transport of labile organic matter from shallower sediment. We argue that the export of the most labile lipid component of the organic matter pool from the euphotic zone and the overlying oxygen minimum zone into the hadal sediments is neglectable. Our results contribute to the understanding of the mechanisms that control the delivery of labile organic matter to this extreme deep-sea ecosystem, whereas they provide insights into some potential physiological adaptation of the in situ microbial community to high pressure and low temperature through lipid remodeling. [ABSTRACT FROM AUTHOR]

The coupled Delft3D-object model has been developed to predict the mobility and burial of objects on sandy seafloors. The Delft3D model is used to predict seabed environmental factors such as currents, waves (peak wave period, significant wave height, wave direction), water level, sediment transport, and seabed change, which are taken as the forcing term to the object model consisting of three components: (a) physical parameters such as diameter, length, mass, and rolling moment; (b) dynamics of the rolling cylinder around its major axis; (c) an empirical sediment scour model with re-exposure parameterization. The model is compared with the observational data collected from a field experiment from 21 April to 13 May 2013 off the coast of Panama City, Florida. The experimental data contain both object mobility using sector scanning sonars and maintenance divers as well as simultaneous environmental time series data of the boundary layer hydrodynamics and sediment transport conditions. Comparison between modeled and observed data clearly shows the model’s capabilities and limitations. [ABSTRACT FROM AUTHOR]

Intermediate nepheloid layers (INLs) form important pathways for the cross‐slope transport and vertical export of particulate matter, including carbon. While intermediate maxima in particle settling fluxes have been reported in the Eurasian Basin of the Arctic Ocean, direct observations of turbid INLs above the continental slope are still lacking. In this study, we provide the first direct evidence of an INL, coinciding with enhanced mid‐water turbulent dissipation rates, over the Laptev Sea continental slope in summer 2018. Current velocity data show a period of enhanced downslope flow with depressed isopcynals, suggesting that the enhanced turbulent dissipation is probably the consequence of the presence of an unsteady lee wave. Similar events occur mostly during ice free periods, suggesting an increasing frequency of episodic cross‐slope particle transport in the future. The discovery of the INL and the episodic generation mechanism provide new insights into particle transport dynamics in this rapidly changing environment. Plain Language Summary: In the Arctic Ocean deep basins, only a tiny fraction of the algae that grows in the surface layer sinks down to the sea floor. Most of the particles reaching the sea floor originate from the shallower regions closer to the coast. These particles have already settled on the sea floor once, and originate from rivers or algae that grew, died and sank down in shallow regions. Later, these particles are lifted off the ground again by strong turbulent motions and transported toward deeper regions in the middle of the water column. These lift‐off and transport events happen only occasionally, and have not been directly observed in the Eurasian part of the Arctic Ocean yet. Also, we present a new mechanism for the creation of turbulence, which is necessary to lift particles off the sea floor. This mechanism happens mostly during the summer season, when less sea ice is present. Based on this seasonality, it is likely that sediment transport events will become more frequent in the future, when the Arctic sea ice is further declining. Key Points: First direct observation of an intermediate nepheloid layer in the Eurasian part of the Arctic OceanCoinciding strong midwater turbulence is likely caused by a down‐slope current displacing isopycnalsSimilar downslope flow events exhibit a strong seasonality toward the ice free season [ABSTRACT FROM AUTHOR]

Shipwrecks are an integral part of our maritime archaeological landscape and are associated with diverse societal and cultural interests, yielding significant management challenges. Coupled hydrodynamic and geomorphological processes significantly impact the effective in situ preservation of these fragile sites. In this study, we assess sediment budget change and hydrodynamic triggers at metal‐hulled shipwrecks lost between 1875 and 1918, all located in the tidally dominated Irish Sea at depths between 26 and 84 m. This is conducted using time‐lapse, multibeam echosounder surveys at multiannual, annual, and weekly time steps, supported by sediment grain‐size analysis, modeled ocean currents, and shallow seismic data. Results indicate significant changes at all time steps for sites located in sand‐dominated environments, whereas the seabed around shipwrecks settled in multimodal sediments shows virtually no change outside of measurement errors (±30 cm). Variability in geomorphic change is attributed to local environmental factors, including bed shear stress, sediment supply, and spatial barriers to scour. We demonstrate that individual wrecks in similar shelf sea regions can be in very different equilibrium states, which has critical implications for the in situ management of underwater cultural heritage. [ABSTRACT FROM AUTHOR]

Internal solitary waves (ISWs) can cause strong seafloor sediment resuspension and induce nepheloid layers in both shallow and deep-water environments. However, the roles of ISWs in the >1000 m deep sea sediment resuspension and seafloor geomorphic changes are still unclear. To answer the above question, in the Dongsha area of the northern South China Sea, we measured suspended particulate matter along with a section covering the entire continental slope between 300 and 2000 m water depths, together with high-resolution multibeam bathymetric data for examining geomorphic changes. The results indicate that, on the upper slope with water depth <700 m, seafloor sediments were heavily disturbed and resuspended. We find that ISWs could suspend seabed sediments and shape a bedform at water depths ≲1000 m. The maximum water depth of sediment resuspension by ISWs measured is found as deep as 1500 m. The distribution pattern of the seafloor surface sediments on the east of the Dongsha continental slope (fine and silty sand in <700 m water depth, clayey silt between 700 and 1500 m, and silty clay > 1500 m) also indicates that they are mainly controlled and impacted by ISWs. The wave refraction theory could be applied to the upper slope, but sediment resuspension is related to the seabed topography on the lower slope. Our study shows that the suspension and transport of sediments induced by episodic ISWs on the Dongsha slope of the northern South China Sea could shape the bedform and affect the sedimentary seabed geomorphology. This research will help explain the impacts of the ISWs on the deep-water sediment resuspension and seafloor geopmorphic changes along with the continental slope in the margin sea. [ABSTRACT FROM AUTHOR]

The sediment transport in the seabed boundary layer due to wave-induced streaming has been investigated for nonzero angle between the current and the waves. The mean sediment transport is a result of interaction between streaming due to wave skewness, the Longuet-Higgins streaming, and the wave-current interaction. For colinear waves, the mean sediment transport is directed along the wave propagation direction, with the largest transport taking place beneath the waves propagating in the direction of the current. Mean sediment transport decreases with increasing angle between the current and the waves. For a particular angle, the mean sediment transport beneath second-order Stokes waves is largest and decreases in the following order: linear propagating waves followed by horizontally uniform Stokes forcing and smallest for horizontally uniform linear forcing. The direction of the mean sediment transport is rotated toward the current away from the direction in which the wave propagates. The magnitude of rotation is smallest for second-order Stokes waves and increases in the following order; linear propagating waves followed by horizontally uniform Stokes forcing, and largest for horizontally uniform linear forcing. [ABSTRACT FROM AUTHOR]

The process of solute transport into marine sediments from overlying water can be accelerated by waves. However, the effect of wave-induced deformation of seabed on solute transport has been ignored in most investiga tions. In response this paper investigates the influence of sandy bed deformation on the mechanism of solute transport using a modified solution- transport numerical model, in which the process of solute transport into deformable marine sediments from overlying water could be simulated under progressive waves. The results have shown that the seabed deformation will increase the velocity of pore water, which in turn increases the vertical hydrodynamic dispersion coef ficient and the mechanical dispersion of solute transport. Therefore, the wave-induced deformation of soil will ad vance the process of solute migration into marine sediments. Case studies have indicated that in deformable soil the maximum vertical hydrodynamic dispersion coefficient could be 8. 5 times that ignoring soil deformation, and about 545 times the molecular diffusion coefficient. The smaller the shear modulus of seabed soil, the more obvious soil de formation occurs, and the greater the influence of soil deformation has on solute transport. Furthermore, the reduc tion of degree of saturation will advance the solute transport into marine sediments. [ABSTRACT FROM AUTHOR]

Copyright of Anuario do Instituto de Geociencias is the property of Universidade Federal do Rio de Janeiro, Instituto de Geociencias and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The action of propellers induced jets on the seabed of ports can be responsible of erosion and deposition of sediment around the port basin, potentially inducing important variations of the bottom topography in the medium to long time scales. Such dynamics constantly repeated for long periods can result in drastic reduction of ships' clearance - in the case of accretion - or might be a threat for the stability and duration of the structures - in the case of erosion. These sediment related processes are sources of problems for the port managing authorities, both for the safety of navigation and for the optimization of the management and maintenance activities of the ports' bottom and infrastructures. In the present work we study the erosion and sediment transport induced by the action of the vessel propellers of naval traffic in the passenger Port of Genoa (Italy) by means of integrated numerical modeling and we propose a novel methodology and state of the art modeling science-based tools useful to optimize and efficiently plan the ports managing activities and the of maintenance of ports seabed. [ABSTRACT FROM AUTHOR]

A bolus is a vortex formed by an internal wave propagating upslope with the shoaling wave. The amount of sediment and biota transported by boluses travelling up the world's continental slopes and onto the continental shelves has not been established but could be vital for maintaining nutrient‐rich coastal ecosystems. Previous laboratory experiments and simulations of shoaling boluses have considered a two‐layer density stratification or a linear density profile. We present experiments on bolus formation and propagation in a stratification with a density profile ρ(z) represented by a tanh‐profile, which describes many ocean pycnoclines. Our laboratory experiments examine pycnoclines with thicknesses varying from nearly zero (a two‐layer system) to large thicknesses where the density varies almost linearly with depth. The bolus volume, displacement upslope, and available potential energy are measured as a function of pycnocline thickness. Maximum upslope displacement is found to be twice that observed for a two‐layer stratification. Plain Language Summary: Interfacial waves can be observed along the surface of the ocean, and as they approach the coastline the waves steepen, break, and ultimately surge up the beach. These waves are analogous to internal waves, which occur within the ocean at the horizontal interface of more and less dense water. These internal waves can be an order of magnitude taller than the waves seen at the beach, and the surge (called a bolus) can move kilometers along the ocean bottom. Previous efforts to model these boluses have approximated the ocean's density as two layers of different density water. However, the ocean has a more gradual transition between the layers, which can be over 100 meters thick. The impact of this transition layer, called a pycnocline, on bolus transport is poorly understood. Here, we perform laboratory experiments to demonstrate that the presence of a thick pycnocline can double the distance the bolus travels upslope and increase the amount of energy for mixing. This demonstrates the need for a better model of bolus propagation to understand how these breaking internal waves move material along the bottom of the ocean. Key Points: Boluses propagate further for pycnoclines of finite thickness than for a discontinuous stratification with two layers of uniform densityThe experiments reveal the existence of a pycnocline thickness that results in a maximum bolus propagation displacement upslopeThin pycnoclines yield large bolus volumes with high available potential energy despite short bolus propagation displacement [ABSTRACT FROM AUTHOR]

In southeastern Brazil, the Serra do Mar coastal mountain range blocks the sediment influx from arriving at a ca. 1,500 km long continental margin comprising Santos and Pelotas basins. Despite this deprivation, the margin accumulated a ca. 1 km thick sedimentary succession since the Mid‐Miocene. Examination of seismic reflection and oceanographic data indicates that shelf‐margin clinoform formation exhibits a regional variability, with major sigmoidal clinoforms developed in the transitional area between both basins. Laterally, poorly developed oblique clinoforms constitute isolated depocenters along the shelf margin. The continuous clinoform development in the transitional area is attributed to the major influence on sediment transport patterns of several ocean bottom currents flowing along the margin, such as the Brazil Coastal Current, the Brazil Current and the Intermediate Water Brazil Current. These currents erode, transport and distribute sediments across the shelf break and upper slope from distant sediment sources located either north or south of the study area. The progressive southward strengthening of the Brazil Current could be responsible for a major southward sediment redistribution from the northern Campos Basin, and/or for sediment entrainment from northward‐induced transport by the Brazil Coastal Current, originally derived from the De la Plata Estuary. In the transition between Santos and Pelotas basins, the Intermediate Water Brazil Current splits forming the Santos Bifurcation, allowing for a continuous depositional process and clinoform generation. We suggest that ocean bottom currents may shape other shelf‐edge 'contouritic clinoforms' in continental margins mainly constructed by along‐strike sediment transport largely driven by long‐term geostrophic currents. [ABSTRACT FROM AUTHOR]

Double sandbar systems often characterize the surf zone of wave-dominated beaches and display a variety of poorly explained spatial configurations. Here, we explore the morphodynamic stability of double-barred beaches using a model based on linear stability analysis. Surf zone hydrodynamics are described by coupling depth and wave-averaged conservation of mass and momentum with the wave energy and phase equations, including roller dynamics. A simplified sediment transport formulation relates flow to seabed changes. Under normal wave incidence, an alongshore uniform coast with a cross-shore profile characterized by the presence of two sandbars can be unstable, thereby resulting in the development of crescentic and/or rip channel patterns. Our study demonstrates that sandbar coupling can be either in phase (highs and lows of both sandbars are at the same alongshore position) or out of phase (highs and lows of one sandbar correspond to lows and highs of the other sandbar). In line with observations, results of simulations show a large variability in the possible emerging bottom patterns. Our analysis indicates that modes of which the amplitude of the inner sandbar perturbation is larger than that of the outer sandbar are dominant for large height–depth differences between the two sandbar crests and small offshore wave heights. Patterns related to the outer sandbar dominate for small values of the difference in sandbar depth. For intermediate differences between the two sandbar depths, patterns on both longshore bars appear to be fully coupled (similar growth rates and strongly correlated pattern shapes). For relatively large waves and large depth over the outer sandbar, patterns can also develop close to the shoreline and/or inner surf zone together with patterns in the inner or outer sandbar. [ABSTRACT FROM AUTHOR]

Do, J.D.; Chang, Y.S.; Kim, C.H.; Kim, W-.H.; Lee, B-.G.; Wie, G. J., and Jin, J.-W., 2020. Measurement of nearshore seabed bathymetry using airborne/mobile LiDAR and multibeam sonar at Hujeong Beach, Korea. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1067-1071. Coconut Creek (Florida), ISSN 0749-0208. Accurate bathymetric measurements are important, especially in nearshore areas, because coastal sediment transport and the resulting beach erosion/accretion processes are significantly affected by seabed topography. At Hujeong Beach in Korea, for example, local shorelines show severe spatiotemporal variations as a result of seabed topography including underwater rocks. The accuracy of bathymetry measurements are not guaranteed, however, because high-accuracy acoustic sensors—such as multi-beam echo sounders—have a limited measurement capability. In this study, we investigated the accuracy of the nearshore bathymetry at Hujeong Beach using airborne LiDAR (a-LiDAR) data from May, 2017. One of the benefits of a-LiDAR is its ability to conduct both onshore and offshore mapping by detecting laser pulses reflected from land, the sea surface, and seabeds. The a-LiDAR measurements were validated onshore in a sloped roadside area using data measured via ship-mounted mobile LiDAR (m-LiDAR). A high agreement was found between the two datasets, with R-squared values of 0.9999 and mean square errors less than 0.05 m2. In measurements of seabed bathymetry, a-LiDAR agreed well with measurements from a multi-beam echo sounder over a sandy seabed and showed an accuracy similar to the m-LiDAR validation results. However, the accuracy of a-LiDAR measurements decreased significantly over rocky seabed; the mean square error compared to the multi-beam data increased to 0.6–0.8 m2. The high a-LiDAR errors over this rocky area may be a consequence of the irregular shape of its surface. Return signals from underwater rocks of varying shapes may be spread over wider angles, causing signal interference and reducing the measurement resolution in the area. [ABSTRACT FROM AUTHOR]

Fang, K.; Wang, H.; Sun, J.; Zhang, J., and Liu, Z., 2020. Including wave diffraction in XBeach: Model extension and validation. Journal of Coastal Research, 36(1), 116–127. Coconut Creek (Florida), ISSN 0749-0208. An extended version of the XBeach model is presented in this paper to improve the accuracy of predicted wave and current fields and sandy beach evolution in scenarios in which wave diffraction takes effect. Following the approach successfully implemented in the Simulating Waves Nearshore (SWAN) spectral wave model, a diffraction parameter is introduced into the wave action balance equation in XBeach to take wave diffraction into account. An alternative wave breaking index and the formulation for the critical velocity are also tested in the extended model to achieve better model–data agreement. The extended model is validated by comparing the simulation results with those of physical tests for fixed and movable sea beds. The computed wave height, wave-induced current field, and beach evolution are found to be in satisfactory agreement with the measurements, and the numerical modeling capacity of the extended model to represent wave diffraction effect is thus demonstrated. [ABSTRACT FROM AUTHOR]

The role of wave forcing on the main hydro‐morphological dynamics evolving in the shallow waters of the nearshore and at river mouths is analyzed. Focus is mainly on the cross‐shore dynamics that evolve over mildly sloping barred, dissipative sandy beaches from the storm up to the yearly timescale, at most. Local and non‐local mechanisms as well as connections across three main inter‐related subsystems of the nearshore – the region of generation and evolution of nearshore bars, river mouths and the swash zone – are analyzed. The beach slope is a major controlling parameter for all nearshore dynamics. A local mechanism that must be properly described for a suitable representation of wave‐forced dynamics of all such three subsystems is the proper correlation between orbital velocity and sediment concentration in the bottom boundary layer; while specific dynamics are the wave–current interaction and bar generation at river mouths and the sediment presuspension at the swash zone. Fundamental non‐local mechanisms are both infragravity (IG) waves and large‐scale horizontal vortices (i.e. with vertical axes), both influencing the hydrodynamics, the sediment transport and the seabed morphology across the whole nearshore. Major connections across the three subsystems are the upriver propagation of IG waves generated by breaking sea waves and swash–swash interactions, the interplay between the swash zone and along‐river‐flank sediment transport and the evolution of nearshore sandbars. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Numerical modeling using Surface-water Modelling System (SMS) is carried out to simulate the hydrodynamic and sediment transport pattern in Monano Bay, Gorontalo Province, Indonesia. The model applies scenarios of the existing bay before and after berthing structures development. Field data acquisition and secondary data collection are carried out to complete the model. The field measurement includes bathymetry, tide elevation, and current velocity measurements. Validation of the model and field measurement shows good agreement. The validated parameters are the tidal elevation and velocity data. The model shows that in flood and ebb condition, the current flows to the south-east and north-west direction, respectively. The velocity is in the range of 0.1 - 0.25 m/s. The sedimentation modeling shows that the seabed changes are not significant for model scenarios before and after the port development. It is found that the potential increment of sedimentation in Monano Bay with berthing structure being there is about 10 - 15 cm in a one-year simulation. [ABSTRACT FROM AUTHOR]

The problem of local scour around a submarine pipeline is vital for oil and gas projects. Conventional scour models around pipeline practically include the flow and sediment transport characteristics, but they ignore the interactions between flow and seabed soil in the scouring process. In this study, a new two-dimensional model for simulating the scouring process is established while considering the impact of the wave-induced soil response and the associated seepage. With the present model, the influence of seepage and soil response on the modified Shields number, repose angle and prediction of the local scour depth and profile are examined. The numerical results indicate that the influence of repose angle when modified by seepage in the whole scour process is small. Meanwhile, the wave-induced dynamic soil response promotes the development of the scour profile and eventually increases the maximum scour depth to some extent, regardless of the change in the soil characteristics. However, at smaller KC numbers, the variations in the maximum scour depth with seabed properties become more significant. [Display omitted] • A novel scour model considering soil response is numerically established in OpenFOAM. • The shape of the scour hole is asymmetrical due to the asymmetrical horizontal flow velocity. • The maximal scour depth with the soil response is larger than that without the soil response. • The difference in S / D with and without soil response would decrease with increasing in the KC number. • The soil response should be considered for a smaller shear modulus, lower soil permeability, and lower saturation. [ABSTRACT FROM AUTHOR]

Sediment transport and resuspension are essential processes in soft-sediment environments that mediate shellfish population dynamics, water column turbidity, and estuary geomorphology at multiple scales. Adult cockles, Austrovenus stutchburyi (in New Zealand), are key organisms on intertidal sand flats that influence sediment properties, and their removal could impact the stability of the seabed and affect crucial feedback processes in this system. We conducted a field experiment to explore our hypothesis that the loss of adult cockles will increase sediment transport and resuspension non-linearly. Changes in sediment transport regimes will then influence the properties of sediment such as grain size, organic content, and chlorophyll a content. We also expected that the direction and magnitude of this effect would depend on the varying environmental characteristics across the sites, such as hydrodynamic activity and sediment grain size. We excluded adult cockles from 3 × 3 m intertidal plots at 15 sites across a natural adult cockle density gradient (300–3500 ind/m2). After seven months, sediment traps were deployed in exclusion and control plots to measure the sediment transported over two tidal cycles associated with the bedload and water column with differing densities of adult cockles. Adult cockle density was a significant predictor in all models to explain sediment transport and accounted for the largest proportion of variability explained. Relationships between cockle density and sediment transport changed between sites and over time. In these situations, simple linear relationships were not always apparent due to the interacting effects of cockle density, hydrodynamic process, and sediment characteristics. The influence of adult cockles on sediment transport was also affected by the standing stock of microphytobenthos and interacted with the mud content in their surrounding environment. Our study demonstrates the existence of an important feedback between adult cockle density, sediment stability and sediment transport that is mediated by hydrodynamic processes and sediment characteristics. • We used traps to measure sediment transport across a cockle density gradient. • Changes in adult cockle densities alters sediment stability non-linearly. • Adult cockles interact with their environment to drive sediment transport processes. • Sediment transport is highly context-dependent, influenced by physical processes. [ABSTRACT FROM AUTHOR]

Sediment transport over Sandy Point dredge pit in the northern Gulf of Mexico during a cold front event in November 2014 was examined using a finely resolved numerical model. The Delft3D model was used to perform numerical experiments that simulate the effect of wind-generated waves, wind-driven currents, river discharge, and tides on sediment dynamics in Sandy Point dredge pit. The hydrodynamics and sediment models were validated and calibrated using field data of current, wave, water level, and suspended sediment concentration. Two potential sources of sediment were examined: fluvial sediment from the Mississippi River and resuspended sediments from the seabed. Results showed that during a cold front, shear stress from wave motions played a significant role in the resuspension of sediments in Sandy Point dredge pit. The maximum cold front-related wave impact on sediment resuspension could increase near-bed sediment concentration in Sandy Point dredge pit by 20–50 times. In addition, the results suggest that the primary source of sediment for Sandy Point dredge pit during a cold front was resuspension from the ambient seabed due to increased bottom shear stress by wind-induced waves and strong southward wind-driven currents. Currents dispersed sediments from the Mississippi River passes and inhibited riverine sediment supply from Sandy Point dredge pit. Results also showed that cold fronts contribute 16%–24% of the annual sedimentation in Sandy Point dredge pit. • A coupled wave-current-sediment model was used to study the sandy dredged pit. • The combined effect of waves and currents on sedimentation was assessed. • The reverse bottom current inside the pit was identified. • Bottom boundary layer was significantly affected by waves. • Sediment accumulation occurs mostly on the north of the pit. [ABSTRACT FROM AUTHOR]

A model is proposed to determine the sediment transport rate generated by the combined action of sea waves and tidal currents, the latter being modelled as a sequence of steady currents because of the large values of the Keulegan-Carpenter number of the tidal flows, which allow to neglect inertial effects in their modelling. The hydrodynamic module solves Reynolds-averaged momentum equations by introducing a two-equation turbulence model, which considers also the flow in the region closest to the sea bottom and enforces the no-slip condition and the vanishing of the turbulent kinetic energy at the bottom without the need to assume the existence of a logarithmic velocity profile and to fix the normal derivative of the turbulent kinetic energy close to the sea bed. Hence, the evaluation of the velocity profile in the near-bed region turns out to be accurate. The sediment transport module determines the sediment concentration and sediment transport for a mixture of non-cohesive and cohesive sediments. To validate the model, its predictions are compared with laboratory measurements and field data collected over rippled beds at two different tidal estuaries. Then, results are obtained for values of the parameters chosen to mimic a site close to Punta Umbría (Huelva, Spain) and considering different hydrodynamic conditions and different sediment mixtures. The influence of the waves on the suspended sediment concentration is lower for the cohesive fraction than for the non-cohesive fraction. For all the sediment mixtures, it turns out that the cohesive fraction is well mixed over the whole water depth, meanwhile the concentration of the non-cohesive fraction has significant values only near the bottom, thus showing that an accurate description of turbulence dynamics in the buffer layer and viscous sublayer (if it exists) is important to quantify the sediment transport rate. • Sediment transport module that reproduces the concentration of cohesive fraction is presented. • Tidal current is modelled as a sequence of steady-currents due to the large values of the Keulegan-Carpenter number. • Menter's turbulence model to predict the turbulence structure both in the wave bottom boundary layer and in the core region. • Turbulence dynamics description in the buffer layer and viscous sublayer is important to quantify the sediment transport. • Applicable to any type of sediment mixture. [ABSTRACT FROM AUTHOR]

In order to reveal the effects of seepage on the sediment initiation in swash zone,the experimental and numerical studies were performed in this paper. Firstly,the experiments of solitary wave run-up over permeable and impermeable slope was carried out in an indoor flume,the wave height and flow velocity were measured. Secondly,corresponding numerical simulations were performed and validated by the flume test results. Finally,the influence of seepage on the hydrodynamics in the swash zone and sediment initiation were assessed. The test results show that the asymmetry of wave becomes obvious under the effect of seepage. Strong infiltration during uprush increases the shear stress on the seabed surface,and wave downrush leads to the reduction of seabed shear stress due to the flow loss. It is also found that the seepage changes the effective weight as well as the shear stress of seabed soil particles,which leads to the variations of Shields parameter and greatly increase instability of sediment particles. The change of shear stress over permeable slope is the main reason for the Shields parameter variation of seabed particles. This study can provide guidance for the assessment and treatment of sediment transport in the swash zone. [ABSTRACT FROM AUTHOR]

Abstract The seabed is sloped in shallow coastal regions, where strong nonlinear shoaling waves can generate sheet-flow sediment transport. Both wave nonlinearity and bottom slope can lead to a wave-averaged (net) sediment transport rate, but the bottom slope effect is often overlooked in existing sediment transport models. A full-scale experimental study of sheet-flow sediment transport under the oscillatory flows with nonlinear features (skewness or asymmetry) was conducted in an inclinable oscillatory water tunnel, so the bottom-slope-induced net transport rate in the context of nonlinear waves was experimentally investigated. The tests cover a variety of nonlinear wave shape, bottom slope (0 to 2. 5 ∘ ) and two sediment diameters (0.24 and 0.51 mm). Since the downslope direction is the "offshore" direction in our tests, it is found that bottom slope reduces the net "onshore" transport rate due to wave nonlinearity. The slope contribution to the net transport rate is evaluated by taking the difference between the measured net transport rate from a sloping-bed experiment and the measured net transport rate from the corresponding horizontal-bed experiment. The results suggest that slope-induced net transport rate is insensitive to wave nonlinearity, and its variation with bottom slope can be considered linear in the context of predicting net transport rate. Comparisons between this study and a preceding sinusoidal-flow study of Yuan et al. (2017b) suggest that nonlinear waves can be approximated as sinusoidal flows for estimating the slope contribution to the net transport rate. Subsequently, an empirical model for predicting net sheet-flow transport rate due to bottom slope is established based on dimensional analysis. This model can be simply added to existing sheet-flow sediment transport models to improve their applicability in coastal regions. Highlights • Presented experiments on the sheet-flow sediment transport under skewed and asymmetric oscillatory flows above a sloping bed. • Test results show that the slope-induced net transport rate is insensitive to nonlinear wave shape. • Proposed an empirical model for slope's contribution in net sheet-flow sediment transport rate. [ABSTRACT FROM AUTHOR]

Most terrestrial sand seas form at 'horse' latitudes, where the wind direction exhibits seasonal variation. Here, we extend the two-dimensional linear stability analysis of a flat sand bed associated with a unidirectional wind to the three-dimensional case in order to account for multidirectional wind regimes. Focusing on the simplest case of bidirectional flow regimes, we show that the transition from transverse to oblique or longitudinal patterns is controlled by the transport ratio and the divergence angle between the two flows. Our predictions agree with previous results for dune orientation, and also provide a wider range of possible alignments depending on flow strength, especially when the two winds are perpendicular, at which the transition occurs. This analysis also predicts the selected pattern wavelength, which either decreases close to the transition angle for strong winds, due to a geometric effect, or increases at low winds, when the bed slope affects the transport. This theoretical analysis is complemented by analogous subaqueous experiments, where bedforms are submitted to alternate water flows. For transverse bedforms, the experimental data validate the model at strong flows, providing evidence for the predicted geometric effect, but also for the increase of the wavelength close to the transport threshold. For longitudinal bedforms, a discrepancy is observed, which we interpret as the sign of enhanced nonlinearities induced by the development of slip faces when the flow alternately blows on both sides of the dune. [ABSTRACT FROM AUTHOR]

The mechanism of a ripple formation process under swash zone, which is shallower than surf zone, has not yet been fully investigated due to the difficulty of a precise measurement or of an implementation of accurate numerical simulation, under complex boundary conditions caused by wave breakings or bores. To simulate the formation process of the ripples resulting from a sediment transport around swash seabed, the enhanced MPS (moving particle semi-implicit) is employed, which enable simulating wave breakings with a high degree of accuracy. On the other hand, the DEM (distinct element method) is adopted for simulating the ripple formation from tracking individual sand particle. This DEM-MPS coupling model based on particle method will have a high potential to accurately simulate violent flow and its induced sediment transport. The interaction between fluid flow and sediment particles in the formation process of ripples on the swash zone has been numerically examined from the spatial profiles of the flow field and interparticle forces. In this study, the effect of pore water on the formation process of rolling grain ripples is discussed, in particular. Numerical results indicate that the pore water plays an important role in fluidization of sediment DEM particles and contributes development of the ripple formation. [ABSTRACT FROM AUTHOR]

Abstract High resolution bathymetry combined with structural modelling is used to estimate changes in the on-bottom stability of an offshore pipeline due to scour and sedimentation over an 11 year period. Detailed observations of post-lay embedment changes have been combined with the pipeline structural characteristics and an elastic-plastic model of soil resistance to estimate the vertical and horizontal stability of the pipeline using a finite difference solution to the beam bending equation. Application of the design approach indicates that post-lay increases to the critical (break-out) velocity of 1–2 m/s occur along the full 19 km of surveyed pipeline due to scour and sedimentation, which act to reduce load and increase soil resistance. The rate at which this increase in stability occurs with time is found to vary along the pipeline, and is dependent on the mechanism of pipeline lowering (i.e. whether the pipe lowered due to sagging into widely spaced scour holes, or by sinking into the shoulders between many closely spaced scour holes). By incorporating sediment transport into the pipeline design, the present results suggest potential for significant improvements in pipeline on-bottom stability and associated reductions in minimum required specific gravity and/or secondary stabilisation. Highlights • Seabed mobility driven changes to pipeline embedment are observed in the field. • The resulting changes to pipeline on-bottom stability are quantified. • Increases in critical velocity of 1–2 m/s are calculated for a steady current. • The amount of increase is dependent on the mechanism of pipeline lowering. • Increased soil resistance and hydrodynamic shielding are both shown to be important. [ABSTRACT FROM AUTHOR]