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A series of numerical simulations are performed to study the pollutant and sediment transport in free surface channel flow. The present paper examines the dispersion of passive contaminants injected from a time periodic source in a fully developed turbulent flow. More precisely, the pulsation effects on the distribution behaviors of dissolved and particulate pollutants are analyzed and discussed. Simulations are carried out using a commercial Computational Fluid Dynamic (CFD) code, Fluent 6.3, which is based on the finite volume approach. The standard k-ε turbulence closure model is selected to simulate the turbulence generation and the Volume of Fluid (VOF) method is used to accurately capture the time varying free surface. The Discrete Phase Model (DPM) is used for capturing the movement of particles. Numerical results show that increasing pulsation amplitude and decreasing frequency generates higher dispersive effects in the concentration profiles of a dissolved pollutant. It is also concluded that, unlike dissolved substances, the particle transportation can be enhanced only for certain combinations of the pulsation amplitude and frequency due to the synchronization of the particle's movement with the oscillating potential., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

This study aims to investigate the hydrodynamic-morphological interactions on a microtidal intermediate-dissipative beach under low to moderate wave energy conditions using field measurements during two climatic seasons. The separate contributions of currents, sea-swell waves, and infragravity waves to high- and low-frequency sediment fluxes were analyzed. The infragravity wave energy was more relevant near the swash zone than in other areas. Although the currents are the primary suspended sediment transport mechanism, the results suggest that the waves are an important driver of sediment suspension from the seabed. The results indicate that Sea-Swell (SS) waves and cross-shore currents are the prevailing hydrodynamic factors in nearshore sediment transport, and the cross-shore suspended sediment transport rates are higher than those in alongshore transport. The submerged bar intensified during the wet season (1–4 November 2018) when the wave height intensities were lower, contrary to the dry season (24–25 March 2018). Significant accretion nearshore was identified (in the subaerial beach) during the wet season when the suspended sediments were greater, the SS-wave heights nearshore were lower, and sediment flux was directed onshore. A notorious erosion was distinguished during the dry season. The most representative volume changes occurred during the dry season (with high erosion), which is attributed to the high SS-wave energy. [ABSTRACT FROM AUTHOR]

Bottom trawling in submarine canyons can affect their sedimentary dynamics, but studies addressing this topic are still scarce. In the Gulf of Palermo (NW Sicily, SW Mediterranean Sea), bottom trawling occurs on the continental slope, but principally concentrates within Oreto Canyon. Hydrographic profiles and time series data of temperature, turbidity, and currents obtained by a CTD probe and by moored instruments, respectively, revealed increased turbidity values and the presence of bottom and intermediate nepheloid layers coinciding with periods of bottom trawling activity. The delay between the onset of trawling activities along the Oreto canyon axis and the increase in water turbidity at the mooring location indicate that trawling resuspended particles are progressively advected down-canyon by hydrodynamic processes. Topographic waves and near-inertial currents seem to contribute to the sediment transport of resuspended particles as bottom and intermediate nepheloid layers. Results presented in this paper highlight the complex relationship between hydrodynamic processes and sediment resuspension by trawling in submarine canyons. [ABSTRACT FROM AUTHOR]

Coastal erosion poses significant challenges to shoreline management, exacerbated by rising sea levels and changing climate patterns. This study investigates the influence of gap spacing between semicircular coastal defence structures on shoreline dynamics during storm events. The innovative design of these structures aims to induce a drift reversal of prevalent sediment transport while avoiding interruption of alongshore sediment drift, thus protecting the beach. Three different gap spacings, ranging from 152 m to 304 m, were analysed using the XBeach numerical model, focusing on storm morphodynamic behaviour. Methodologically, hydrodynamic and morphodynamic analyses were conducted to understand variations in significant wave heights adjacent to the structures, in accretion and erosion volumes, and changes in bed level under storm conditions. The study aims to elucidate the complex interaction between engineered coastal protection solutions and natural coastal processes, providing practical insights for coastal management practices. Results indicate that installing semicircular coastal defence structures influences sediment dynamics during storm events, effectively protecting stretches of the coast at risk. Optimal gap spacing between structures is crucial to mitigating coastal erosion and enhancing sediment accumulation, offering a sustainable shoreline protection approach. The findings underscore the importance of balanced location selection to optimize protection benefits while minimizing adverse morphological effects. Overall, this research contributes to advancing knowledge of hydro-morphological phenomena essential for effective coastal engineering and informs the design and implementation of more sustainable coastal protection strategies in the face of increasing coastal erosion and sea level rise challenges. [ABSTRACT FROM AUTHOR]

AlMashan, N.; Al-Attar, I., and Neelamani, S., 2024. Assessment of annual sedimentation into Failaka Marina (Kuwait) and possible solutions for reduction of siltation. Journal of Coastal Research, 40(3), 527–553. Charlotte (North Carolina), ISSN 0749-0208. Sedimentation is critical for ports, harbors, and marinas, requiring accurate assessment. Failaka Marina in Kuwait is experiencing a severe noncohesive sedimentation problem. The samples collected at the seven locations along the beach showed that the beach has a uniform grain-size diameter, meaning it is poorly graded sand. The sampling at the tip of the southern breakwater showed that the shoaling is mainly sand. The suspended-sediment concentration varies from 0.025 kg m–3 to 1.2 kg m–3, whereas the mean concentration at the marina entrance is 0.85 kg m–3. The time series of the suspended solids over a year in the seawater surrounding Failaka Island shows a range of 8 to 48,069 ppm. Such a considerable variation in suspended load is due to the massive amounts of dredging and spoil disposal at Boubyan Island and Basra Port (Iraq) when a high sediment load moves around Failaka Island with a concentration of more than 40,000 mg L–1. Annual sedimentation is about 2.35 m y–1, which is responsible for blocking the main entrance for navigation. Kuwait's Ministry of Communication allocates $4 to $6 million annually for dredging and disposal activities. This study evaluates the six marina entrance modification scenarios to determine the best scenario that achieves a measurable reduction in sedimentation rate in the Marina. Six marina breakwater modifications were studied, and annual sedimentation rates were numerically computed. The study use Coupled MIKE 21/3 to simulate hydrodynamic conditions for cohesive sediment transport in a problem area. Field data from 2015 calibrated and validated the model. The primary sediment-moving force is SE wind and sea-swell waves. Littoral drift along Failaka Island's southern coastline and high suspended-sediment concentration result in littoral drift and settling. The best scenario showed a 28% sedimentation reduction and a 26% reduction in maintenance dredging costs from the six studied scenarios. [ABSTRACT FROM AUTHOR]

Smoothed particle hydrodynamics (SPH) is a meshless, particle-based approach that has been increasingly applied for modelling of various fluid-flow phenomena. Concerning multiphase flow computations, an advantage of the Lagrangian SPH over Eulerian approaches is that the advection step is straightforward. Consequently, the interphasial surface can be explicitly determined from the positions of particles representing different phases; therefore, there is no need for the interface reconstruction step. In this review paper, we briefly recall the basics of the SPH approach, and in particular the physical modelling and numerical implementation issues. We also mention the weaknesses of the approach and some remedies to overcome them. Then, we demonstrate the applicability of SPH to selected interfacial flow cases, including the liquid column break-up, gas–liquid flow regimes in a channel capturing the transitions between them and the wetting phenomena. Concerning the two-fluid modelling, it is illustrated with sediment transport in the presence of surface waves. Various other applications are briefly recalled from the rich and growing literature on the subject, followed by a tentative list of challenges in multiphase SPH. [ABSTRACT FROM AUTHOR]

Sediment deposition at the bottom of artificial reservoirs has become a worldwide problem. This comprises a dual issue that is, in the first place, associated with the reduction in storage capacity and lifetime of large reservoirs. The second aspect comprises the threat that the sediment represents for the dam structure. This research is mainly aimed at identifying and inferring the main sediments' triggering processes through a rigorous analysis of deposition shapes in a large reservoir. For identifying the main deposition shapes, a sequential methodology was designed and developed comprising the following stages. First, an analysis of XYZ cartography from bathymetric development was conducted. Then, a shapes categorization was developed that comprises the identification of six types of shapes based on four parameters: slope continuity, slope break, absolute and relative slope, and arc configuration. The third stage comprised a visualization and spatial calculation of shapes through GIS-based cartography. The fourth stage comprised an interpretation of deposition shapes processes: for that, a dual analysis was developed. First, an analysis based on fluvial sediments transport processes was realized. The second stage implied an analysis of the dam influence on fluvial hydrodynamics and sediments transport. Results comprised a quantitative assessment of each shape as well as physical processes identification and interpretation, generating a robust equivalence between shapes and triggering processes. This research proved successful for the identification and characterization of the main deposition and transport processes that may help to prevent, palliate, and/or correct phenomenon of silting in large reservoirs. This detailed knowledge of deposition forms opens new strategies to release sediments from storage water more effectively. [ABSTRACT FROM AUTHOR]

Shorelines face growing threats due to climate change and diminishing sand supply. Coastal headlands, common rocky features along coastlines, are crucial in shaping hydrodynamics and sediment transport. Yet, the influence of future climate conditions, including sea‐level rise (SLR) and intensified storm energy on complex shorelines with headlands has remained relatively unexplored. In this study, we model changes in hydrodynamics and headland bypassing under different SLR and higher storm wave scenarios. Our findings reveal the formation of circulation cells on both sides of a headland, where wave energy converges around the headland zone. Future climate conditions result in larger storm waves on the beach. However, SLR enhances nearshore currents through a landward shifting of the circulation cells, while higher storm waves intensify offshore flow currents due to the seaward movement of the cells. This effect, in turn, increases the potential for headland sediment bypassing. Plain Language Summary: Coastal headlands, prominent rocky features along open coastlines, play a crucial role in protecting nearby beaches from strong waves and erosion. They also affect how sand is exchanged between different beaches. We use a model to explore how future climate conditions including sea‐level rise (SLR) and larger storm waves influence coastal waves, littoral currents, and the transport of sand around headlands. Our findings reveal that headlands converge wave energy forming circulation flow cells. SLR results in stronger nearshore currents, driven by the landward movement of the rotating flow cells. In contrast, larger storm waves can move the rotating flow cells seaward, thereby increasing offshore current strength and the potential for sand transport around the headland. Understanding how coastal waves, flow and sediment transport change under future climate conditions will help determine coastal resilience. Key Points: The formation of circulation cells and wave energy convergence around headlands during storms reduce bottom shear stress at the beachSea‐level rise increases wave heights, currents, and bed shear stress in the nearshore because of landward shifting of the circulation cellsHigher storm waves expand the surf zone, shift circulation cells seaward, and enhance potential headland sediment bypassing [ABSTRACT FROM AUTHOR]

The new navigation channel for large vessels entering the Hau River through the Kenh Tat and Quan Chanh Bo channels was announced in January 2016. The navigation channel route through Dinh An estuary in Soc Trang province to Can Tho port was not deeply concerned by the agency because of the sedimentation phenomenon, which was very serious and complicated. Only small vessels of 1,000-2,000 DWT can pass through the Dinh An estuary navigation channel, whereas large vessels pass through the Kenh Tat and Quan Chanh Bo channels. However, the new navigation channel entering the Hau River is also seriously sedimented, especially in the Cua Dai An area, where the tributary route starts from the Hau River through the Quan Chanh Bo channel and the estuary area in the Duyen Hai harbor basin. These are two important bottlenecks that drastically reduce the throughput capacity of this new navigation channel. This paper proposed five options for the spatial arrangement of works to stabilize and protect the channel through the Dinh An estuary. A MIKE 21 couple mode was used to simulate hydrodynamic and sediment transport in the study area, and the impact of these options on the characteristics, including water level, flow velocity, and bottom topographic change, was analyzed and evaluated. Based on these results, an optimal solution was suggested. [ABSTRACT FROM AUTHOR]

A seasonal variability in flow and sediment flux at the Socheongcho Ocean Research Station (SORS) on the west coast of Korea in 2018 was investigated to elucidate the formation of a two-layered flow structure and changes in sediment transport during stratification. An analysis of SORS data revealed stable temperatures (5–10 °C) in deeper waters, while surface temperatures rose from 6 °C in April to a peak of 30 °C in late August, gradually declining and leading to full water column mixing by late November. This temperature variation induced stratification, influencing the development of a two-layered flow structure. In winter, a singular flow structure was observed, contrasting with the emergence of a two-layered structure as stratification progressed. In the surface layer, residual currents flowed northward in summer and southward in winter, consistent with previous studies. In deeper layers, a southward residual current persisted, irrespective of the season. Sediment flux consistently moved southward, regardless of the season or water depth, with notably higher cumulative sediment flux in the deeper layer (1300 kg·m−2s−1) compared to the surface layer (300 kg·m−2s−1). These findings diverge notably from previous studies, providing new insights into ocean currents and material transport in the Yellow Sea. [ABSTRACT FROM AUTHOR]

River mouths are dynamic systems that can respond rapidly to both fluxes in fluvial water and sediment discharge and marine energy conditions, notably waves. On semi-arid wave-exposed coasts, the morphosedimentary behaviour of river mouths is particularly sensitive to variations in water discharge, which can be significantly influenced by climate variations, in addition to anthropogenic actions such as the construction of dams for water resource needs. In this climatic setting, an increasingly common consequence of decreasing river water discharge is the more or less prolonged closure of river mouths. Most studies have addressed river-mouth closure using analytical, parametric, numerical, or statistical models. The present study uses output from four numerical models to elucidate the hydrodynamic and sedimentary behaviour of the mouth of the Oum-Errabia River (catchment size: 35,000 km2), which debouches on the Atlantic coast of Morocco. The historical evolution of the river mouth and the impact of human interventions, such as the construction of dams, are discussed. The study also briefly discusses the impact of the recent closure of the river outlet, in response to particularly low water discharge, on the marine ecosystem and water quality. The modelling results covering a one-year simulation in this situation of closure indicate a deposition of 427,400 m3 of sediment in front of the mouth of the Oum-Errabia. Ensuring permanent river-mouth opening and tidal flushing and renewal of this river's estuarine waters will necessitate costly regular dredging. [ABSTRACT FROM AUTHOR]

The ecology of the aquatic environment in Poyang Lake, the largest fresh lake in China, is notably impacted by the backflow from the Yangtze River, which conveys a high flux of sediments. This study employs a widely recognized numerical model to replicate the backflow in 2007 (the strongest backflow after the operation initiation of the Three Gorges Dam) to investigate the contributions of wind and backflow to the sediment transport process. The results show that the influences of wind and backflow on flow patterns and sediment transport processes have significant spatial heterogeneity. In the narrow waterway leading to the central lake area, hydrodynamics is mainly driven by backflow. Conversely, the hydrodynamics of the open expanse of the lake is primarily influenced by wind forces. Dominant wind leads to the formation of gyres, which significantly alter flow paths and push sediment into the upstream areas. As a result, the suspended sediment area expands at an average rate of 20.1-21.3 km² daily, marking a 75-85% surge compared to the no wind condition (11.5 km2). The study facilitates a deeper understanding of sediment transport processes in large lakes. [ABSTRACT FROM AUTHOR]

Offshore anthropogenic activities such as the installation of Offshore Renewable Energy (ORE) developments and sediment extraction for marine aggregates have been shown to disrupt current flow, wave propagation, and sediment transport pathways, leading to potential environmental instability. Due to the complexity of the interconnected sediment transport pathways in the south-western Irish Sea combined with an increase in planned anthropogenic activities, the assessment of this risk is imperative for the development of a robust marine spatial plan. Subsequently, this study uses two-dimensional morphological modelling to build upon previous studies to assess the dependency of Arklow Bank's local sediment transport regime on external sediment sources. Additionally, scenario modelling is used to identify vulnerable areas of this offshore linear sand bank to wind and wave-forcing and to examine the nature of this impact. A sediment budget is estimated for Arklow Bank, whereby seven source and nine sink pathways are identified. New evidence to support the exchange of sediment between offshore sand banks and offshore independent sand wave fields is also provided. The areas of the bank most vulnerable to changes in external sediment sources and the addition of wind- and wave-induced flow are analogous. These high vulnerability zones (HVZs) align with regions of residual cross-flow under pure current conditions. The restriction of sediment sources off the southern extent of Arklow Bank impacts erosion and accretion patterns in the mid- and northern sections of the bank after just one lunar month of simulation. Where tidal current is the primary driver of sand bank morphodynamics, wind- and wave-induced flow is shown to temporarily alter sediment distribution patterns. Wind and wave-induced flow can both accelerate and decelerate the east-west fluctuation of the upper slopes of the bank, yet the nature of this impact is inconsistent due to the misalignment of the directionality of these two forces. The methods and new knowledge derived from this study are directly applicable to tidally-dominated environments outside the Irish Sea. [ABSTRACT FROM AUTHOR]

The Bouregreg valley, located on the Atlantic coast of Morocco, has been subject to several anthropogenic and natural impacts that disturb the proper functioning of the estuary's ecosystem. Important dredging operations influenced by both tides and freshwater inflows have created a significant variation of estuary's morphology characterized by a sand bar developed at the mouth. The main objective of this study is to investigate the Morphodynamic processes of the estuary and in particular the impact of dredging operations using a two-dimensional horizontal numerical (2DH) modeling approach based on the shallow water equations. Several numerical tests have been carried out to calibrate the model and to investigate the hydrodynamic and morphological aspects of the estuary. For this technical solution, the modelling simulations show that in addition to the quantities of sand that will be dredged initially, the maintenance of the channel will facilitate a better water circulation between the Bouregreg valley and the Atlantic Ocean and improve the stability of the civil engineering structures and the neighbouring monuments. In addition, this water circulation will guide the river flow in the ebb phase of the tide. The model results show a reduction of about 30% in the impact of erosion, observed before the digging of the canal. [ABSTRACT FROM AUTHOR]

The three-dimensional liquid–sediment system of a coastline was investigated using experimental and numerical approaches. A scaled-down model of the coastline was numerically studied using smooth particle hydrodynamics (SPH). The flow dynamics and the impacts of the wave frequency and the seaward slope angle on the breaking wave characteristics of the two-phase liquid–sediment interaction were parametrically studied. A particle image velocimetry (PIV) experiment was conducted to validate the SPH predictions. It was found that the flow profiles obtained by the PIV and SPH are in good agreement both qualitatively and quantitatively. The maximum velocity of the fluid flow was recorded as 0.5623 m/s in the SPH simulation, but as 0.5860 m/s in the PIV experimental, with a percentage difference of 4.21%. Subsequently, it was found that the breaking wave characteristic is surging at the wave frequency range of f < 0.15 Hz, plunging at 0.15 < f < 0.55 Hz, and spilling at 0.55 < f ≤ 1.0 Hz. It was also established that at a particular Froude number, it is observed that spilling, plunging, and surging wave breakers are produced at low, mid, and high seaward slope angles, respectively. Meanwhile, increasing the Froude number increases the tendency to produce spilling or plugging breaking waves, irrespective of the slope angle. Ultimately, this study has demonstrated the presented methodology's usefulness in investigating coastlines' liquid–sediment interaction properties. [ABSTRACT FROM AUTHOR]

In the development of water resources projects with large hydraulic infrastructures, alterations to the natural flow regime will increase the erosive processes on the discharge structures due to variability of the turbulent velocities and the particle transport. We analyzed the case of the Mazar dam, a project designed to regulate the solid and liquid flows that come from the Paute river basin. Erosive processes of great magnitude are generated in the stilling basin of Mazar dam, due to the intensity of turbulent velocities produced in extreme events. We applied the Delft3D numerical model to simulate the hydrodynamic and sediment transport conditions to evaluate the stability conditions of the Mazar dam stilling basin. With the results obtained, vulnerable zones have been identified in the stilling basin. We recommended mitigation measures with the installation of a geomembrane to reduce the erosive processes in the vulnerable zones. [ABSTRACT FROM AUTHOR]

The relative impacts of changes in the storage capacity of a reservoir are strongly influenced by its hydrodynamics. This study focused mainly on predicting the flow velocities and assessing the effectiveness of groynes as control mitigation structures in changes in the water depth and velocity distributions in Ringlet Reservoir. Initially, the physical model of the Habu River (the main part of Ringlet Reservoir) was fabricated, and flow velocities were measured. Then, a two-dimensional HEC-RAS was adapted to numerically simulate the hydrodynamics of the annual recurrence intervals of 1, 5, and 100 years in the Ringlet Reservoir. Experimental data acquired at the Hydraulic and Instrumentation Laboratory of the National Water Research Institute of Malaysia (NAHRIM) was used to calibrate and validate the numerical models. The comparison of simulation and experimental results revealed that the water levels in all simulations were consistent. As for the velocity, the results show a comparable trend but with a slight variation of results compared to the experiments due to a few restrictions found in both simulations. These simulation results are deemed significant in predicting future sediment transport control based on hydrodynamics in this reservoir and can be of future reference. [ABSTRACT FROM AUTHOR]

Tidal-inlet systems are dynamic features that respond to short-term (e.g., storms) and longer-term processes (e.g., sea-level rise, changes in tidal prism). The Chincoteague Inlet system, located along the northern Eastern Shore of Virginia (USA), is a dynamic coastal complex that experiences rapid change associated with sediment redistribution and a shifting inlet throat due to the southern elongation of adjacent Assateague Island. In this study, a numerical model based on Delft3D with coupled flow–waves, multiclass sediment transport, and morphologic feedback was developed to quantify the hydrodynamic and geomorphic controls within this rapidly evolving inlet–spit system and to develop a more comprehensive understanding of regional to local controls on sediment-transport pathways. Model results show that most of the sand transport along southern Assateague Island is sequestered nearshore and proximally in deeper sinks within Fishing Point, and, of that, only finer sand sizes are transported around the spit, confirming previous analysis and hypothesis. The model also showed that sand transport toward the south increases along Wallops Island and quantified spatially explicit transport trends for selected sediment classes, revealing that coarser sediment bypassing is a punctuated process that is proportional to storms. [ABSTRACT FROM AUTHOR]

The geomorphological stability and ecological environment of megadeltas worldwide are of vital importance for their sustainable development. Deltaic hydro-morphodynamics is extremely sensitive to high riverine flow due to reduced sediment supply. However, the morphological evolution and response of deltas under high riverine flow have remained inadequately quantified. As one of the typical megadeltas, the Yellow River Delta (YRD), is becoming increasingly sensitive to environmental changes and intensified human interventions. In this study, a numerical model and field data were used to investigate the hydrodynamic changes and morphodynamic evolution induced by extreme river discharge in the YRD. The numerical experiments with different runoff scenarios reveal that high-energy riverine floods can cause significant hydrodynamic changes in bed shear stresses, water levels, and flow velocities, particularly in the abandoned river mouth. Moreover, it enhances the ebb-dominated tidal asymmetry, which considerably intensifies fluvial sediment resuspension and transport processes. The results also show high-energy riverine floods in the flood seasons trigger severe erosion in the Yellow River submerged delta, with a net erosion volume reaching −0.07 × 108 m3/year. The hydrodynamic increment in the abandoned river mouth is more significant, and therefore, severe erosion occurs, with the maximum erosion thickness reaching 7 m. These findings highlight the role of high riverine floods on the hydro-sediment dynamics of large river deltas under a sediment starvation condition. [ABSTRACT FROM AUTHOR]

Estuaries along the Amazonian coast are subjected to both a macrotidal regime and seasonally high fluvial discharge, both of which generate complex circulation. Furthermore, the Amazon River Plume (ARP) influences coastal circulation and suspended sediment concentrations (SSCs). The Gurupi estuary, located south of the mouth of the Amazon River, is relatively unstudied. This study evaluates how the Gurupi estuary dynamics respond to seasonal discharge and the varying influence of the ARP using cross-sectional and longitudinal surveys of morphology, hydrodynamics, and sediment transport. The Gurupi was classified as a tide-dominated estuary based on morphology and mean hydrodynamic conditions. However, the estuary was only partially mixed during both the wet and dry seasons. The tides propagated asymmetrically and hypersynchronously, with flood dominance during the dry season and ebb dominance during the rainy season. Seasonal variations of the ARP did not significantly affect the hydrodynamic structure of the lower Gurupi estuary. Estuarine turbidity maxima (ETM) were observed in both seasons, although the increase in fluvial discharge during the wet season attenuated and shifted the ETM seaward. Little sediment was delivered to the estuary by the river, and the SSCs were higher at the mouth in both seasons. Sediment was strongly imported during the dry season by tidal asymmetry. The morphology, hydrodynamics, and sediment dynamics all highlight the importance of considering both fluvial discharge and coastal influences on estuaries along the Amazon coast. [ABSTRACT FROM AUTHOR]

The proportional cover of rubble on reefs is predicted to increase as disturbances increase in intensity and frequency. Unstable rubble can kill coral recruits and impair binding processes that consolidate rubble into a stable substrate for coral recruitment. A clearer understanding of the mechanisms of inhibited coral recovery on rubble requires characterisation of the hydrodynamic conditions that trigger rubble mobilisation. Here, we investigated rubble mobilisation under regular wave conditions in a wave flume and irregular wave conditions in-situ on a coral reef in the Maldives. We examined how changes in near-bed wave orbital velocity influenced the likelihood of rubble motion (e.g., rocking) and transport (by walking, sliding or flipping). Rubble mobilisation was considered as a function of rubble length, branchiness (branched vs. unbranched), and underlying substrate (rubble vs. sand). Rubble was more likely to be transported if ieces were small (4-8 cm) and had no branches, and rubble travelled slightly greater distances (~2 cm) per day on substrates composed of sand than rubble. The effect of near-bed wave orbital velocity on rubble mobilisation was comparable between flume and reef observations. Rubble had a 50% and 90% chance of transport when near-bed wave orbital velocities reached 0.30 m/s and 0.43 m/s, respectively, in the wave flume, and 0.34 m/s and 0.55 m/s, respectively, on the reef. Importantly, the probability of rubble transport per day declined over 3-day deployments in the field, suggesting rubble had settled into more hydrodynamically-stable positions or snagged on the first day of deployment. We expect that settled or snagged rubble may have been mobilised more commonly in locations with higher energy and more variable wave environments. Our results show that rubble beds comprised of small rubble pieces and/or pieces with fewer branches are likely to be more unstable. Such rubble beds are likely to have shorter windows of recovery (stability) between mobilisation events, and thus be good candidates for rubble stabilisation interventions to enhance coral recruitment and binding. [ABSTRACT FROM AUTHOR]

Offshore sand banks are an important resource for coastal protection, marine aggregates, and benthic habitats and are the site of many offshore wind farms. Consequently, a comprehensive understanding of the baseline processes controlling sand bank morphodynamics is imperative. This knowledge will aid the development of a long-term robust marine spatial plan and help address the environmental instability arising from anthropogenic activities. This study uses a validated, dynamically coupled, two-dimensional hydrodynamic and sediment transport model to investigate the hydrodynamic processes controlling the highly mobile upper layer of Arklow Bank, while maintaining overall long-term bank base stability. The results reveal a flood and ebb tidal current dominance on the west and east side of the bank, respectively, ultimately generating a large anticlockwise residual current eddy encompassing the entire bank. This residual current flow distributes sediment along the full length of the sand bank. The positioning of multiple off-bank anticlockwise residual current eddies on the edge of this cell is shown to influence east–west fluctuations of the upper slopes of the sand bank and act as a control on long-term stability. These off-bank eddies facilitate this type of movement when the outer flows of adjacent eddies, located on both sides of the bank, flow in a general uniform direction. Whereas they inhibit this east–west movement when the outer flows of adjacent eddies, on either side of the bank, flow in converging directions towards the bank itself. These residual eddies also facilitate sediment transport in and out of the local sediment transport system. Within Arklow Bank's morphological cell, eight morphodynamically and hydrodynamically unique bank sections or 'sub-cells' are identified, whereby a complex morphodynamic–hydrodynamic feedback loop is present. The local east–west fluctuation of the upper slopes of the bank is driven by migratory on-bank stationary and transient clockwise residual eddies and the development of 'narrow' residual current cross-flow zones. Together, these processes drive upper slope mobility but maintain long-term bank base stability. This novel understanding of sand bank morphodynamics is applicable to bedforms in tidally dominated continental shelf seas outside the Irish Sea. [ABSTRACT FROM AUTHOR]

This study focuses on the numerical investigation of the 3D hydrodynamic processes of coastal zones such as wave breaking, wave-induced currents, and sediment transport, using the multiphase, interFoam solver of OpenFOAM® (a state-of-the-art, open-source CFD numerical tool). The numerical scheme is suitably framed by initial conditions of wave propagation and absorption using waves2Foam wave library. The turbulence closure problem is handled using a buoyancy modified k–ω SST model. In order to predict the sediment transport rate due to waves and currents (bed load, sheet flow, and suspended load over ripples), a transport-rate formula involving unsteady aspects of the sand transport phenomenon is implemented. For the suspended load in the surf zone, the Bailard formula is adopted after considering that the dissipation mechanism is the wave breaking. Results concerning wave height, longshore current, turbulence kinetic energy, and sediment transport are compared against experimental data and semi-empirical expressions. [ABSTRACT FROM AUTHOR]

The estuary delta is an area where human economic activities are active and natural ecological environment is fragile. With global change and the intensification of human activities, coastal and seabed erosion around the world is becoming more and more serious. In this paper, we used the Delft 3D numerical simulation to compare the hydrodynamic effects of sediment transport paths in the Yellow River delta (river-controlled type), Yangtze River delta (tidal type) and Mekong River delta (tidal wave type) in the East Asian monsoon area, and analyzed the causes of accumulation erosion landform distribution in three different types of subaqueous deltas. This study finds the Yellow River Delta has experienced varying degrees of erosion at the estuary, but its subaqueous delta is still dominated by deposition; the Yangtze River Delta has ensured the stability of its shoreline under the influence of artificial shoreline reinforcement, but the subaqueous delta (water depth: 0–15 m) is in a state of erosion all year round; and in the Mekong River Delta the erosion occurs in both its shoreline and subaqueous delta. Additionally, only by analyzing the erosion and deposition within the transport range of resuspended sediment, the changes in the properties of the entire subaqueous delta could be recognized. The research results can not only be helpful to analyze whether the change of river sediment will lead to the change of delta type under human influence, but also provide more powerful scientific support for the protection of delta ecological environment, geological environment safety and geological disaster prevention. [ABSTRACT FROM AUTHOR]

A quantitative understanding of paleotsunamis is a significant issue in tsunami sedimentology. Onshore tsunami deposits, which are geological records of tsunami inundation, are used to reconstruct paleotsunami events. Numerical models of tsunami hydrodynamics and tsunami-induced sediment transport are utilized in such reconstructions to connect tsunami deposit characteristics, flow conditions, and (paleo-) tsunami sources. Recent progress in tsunami numerical modeling has increased the possibility of developing a methodology to estimate paleotsunami sources from tsunami deposits. Several previous studies have estimated paleotsunami sources using tsunami sediment transport simulations. However, the accuracy of paleotsunami source estimation has not yet been explored. Thus, to bridge this research gap, in this study, we showed the potential and limitations of deposit-based tsunami source estimation based on the 2011 Tohoku-oki tsunami deposit data on the southernmost part of the Sendai Plain, northeastern Japan. The tsunamigenic megathrust along the Japan Trench was divided into ten subfaults having similar lengths and widths. The hypothetical source models with varying slips on each subfault were examined by comparing the depositional volume and sediment source of onshore tsunami deposits. Due to limited information on the depositional area of the tsunami deposits used in the modeling, slips only in some parts of the entire tsunami source region could be estimated. The fault slip was slightly overestimated but could be compared with previous well-constrained source models. Thus, these results indicated that vast high-quality datasets of tsunami deposits can improve the accuracy of paleotsunami source estimation. It is also suggested that the amplitude of the receding wave affects the erosion pattern from the shoreface to the nearshore area. Although sufficient data for paleotsunami source estimation are lacking, an effective combination of tsunami deposit data and sediment transport simulations potentially improves the accuracy of the source estimation. The results will contribute to developing a framework of deposit-based paleotsunami source modeling and assessing its accuracy. [ABSTRACT FROM AUTHOR]

River mouths are dynamic systems that can respond rapidly to both fluxes in fluvial water and sediment discharge and marine energy conditions, notably waves. On semi-arid wave-exposed coasts, the morphosedimentary behaviour of river mouths is particularly sensitive to variations in water discharge, which can be significantly influenced by climate variations, in addition to anthropogenic actions such as the construction of dams for water resource needs. In this climatic setting, an increasingly common consequence of decreasing river water discharge is the more or less prolonged closure of river mouths. Most studies have addressed river-mouth closure using analytical, parametric, numerical, or statistical models. The present study uses output from four numerical models to elucidate the hydrodynamic and sedimentary behaviour of the mouth of the Oum-Errabia River (catchment size: 35,000 km2), which debouches on the Atlantic coast of Morocco. The historical evolution of the river mouth and the impact of human interventions, such as the construction of dams, are discussed. The study also briefly discusses the impact of the recent closure of the river outlet, in response to particularly low water discharge, on the marine ecosystem and water quality. The modelling results covering a one-year simulation in this situation of closure indicate a deposition of 427,400 m3 of sediment in front of the mouth of the Oum-Errabia. Ensuring permanent river-mouth opening and tidal flushing and renewal of this river’s estuarine waters will necessitate costly regular dredging.

An estuary delta is an area with active human economic activities and a fragile natural ecological environment. With the intensification of global changes and human activities, coastal and seabed erosion around the world is becoming more and more serious. This study compared the hydrodynamic effect and sediment diffusion path at the Yellow River subaqueous delta (river control type) and the Yangtze River subaqueous delta (tide-river type) in the East Asian monsoon area using a Delft 3D numerical simulation to analyse the causes of the distribution of accumulation and erosion landform in the different types of subaqueous deltas. This study found that the river deltas were dominated by the river when the accumulation landforms concentrated in the direction of the Coriolis forces, which was due to hydrodynamic erosion driven by wind, and the sediment diffusion range was mainly concentrated in shallow water areas (water depth < 6 m), resulting the Yellow River subaqueous delta presenting the pattern of "northern erosion and south accumulation". The Yangtze River subaqueous delta was controlled by tidal effects, making the southern part of the estuary more susceptible to erosion. The research results can not only further deepen the understanding of the physical process and mechanism of erosion and deposition in the subaqueous delta but also provide stronger scientific support for the deltas' ecological environment protection, geological environment safety, and disaster geology prevention. [ABSTRACT FROM AUTHOR]

The water depth and flow velocity of a river may be temporarily disturbed by the water level fluctuations connected with the operation of artificial dam reservoirs located downstream (so-called backwater fluctuations (BF)). In this research, we use the two-dimensional hydrodynamic model iRIC MFlow_02 to quantify the effects of BF on the lowermost section (ca. 1.5-km length) of a small (channel width ≤ 20 m) mountain stream, the Smolnik Stream, which flows into the Rożnów Dam Reservoir, in Southern Poland. To reproduce the hydrological conditions generally observed in the stream, six scenarios were simulated, considering three steady flow discharges at the inlet, with recurrence intervals of 1 year (1.8 m3 s−1, small flood), 2 years (24.5 m3 s−1; medium flood), and 20 years (89.5 m3 s−1; large flood), and two reservoir levels at the outlet: 265 m a.s.l. (normal reservoir water level) and 270 m a.s.l. (maximum reservoir water level). In these simulations, sediment transport and morphodynamics are not considered. The average modelled water depth was increased by backwater fluctuation in the channel, from 28% (from 1.62 m vs. 2.07 m) during a small flood, up to 59% (from 3.46 m to 5.50 m) during a large flood. Contrastingly, the average modelled flow velocity was decreased in the channel (from −8% 0.52 m s−1 vs. 0.47 m s−1) during a small flood to −78% (0.49 m s−1 vs. 0.11 m s−1) during a large flood. Our results demonstrate that backwater fluctuations substantially disturb the hydrodynamics of the studied stream, which is interpreted as a triggering factor of the previously documented alterations in its sedimentology, morphology, and riparian vegetation pattern. [ABSTRACT FROM AUTHOR]

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]

Unexploded ordnance devices (UXO) pose a potential threat to human life and material during offshore construction activities. Extensive survey activities are conducted to locate, identify, and clear these objects as necessary. For the period thereafter, it is necessary to investigate whether areas that have already been cleared, or even objects that remain in place, may be affected by mobilization under tidal currents or waves, and could thus have an impact on operation and maintenance during the lifetime of the offshore installation. In this study, model simulations based on fluid mechanics are described to derive the loads on the objects caused by currents and waves and combined with knowledge of the known burial condition of the objects. Within the model, the hydrodynamic and hydrostatic loads on the object caused by waves and currents are balanced with inertia and rolling resistance. Thus, the critical current velocity and critical wave conditions for the mobilization of different objects are calculated and compared with the environmental conditions prevailing in the North Sea. As a result, a recurrence interval for the potential mobilization of objects on the seafloor is given, which can now be used to optimize route surveys and thus help accelerate offshore construction work. It is shown that currents are not able to mobilize the objects investigated in the study in almost all regions of the North Sea. Waves can mobilize certain objects in very shallow and extreme conditions. [ABSTRACT FROM AUTHOR]

This study proposes an oscillatory water tunnel (O/U-tube) equipped with two impellers to drive flows. The O/U-tube consists of two modes: U-tube mode and O-tube mode. The former can generate oscillatory flow, while the latter can produce both oscillatory and unidirectional flows with velocities up to 1.6 m/s. The hydrodynamics of the U-tube and O-tube modes were examined analytically. For the U-tube mode, a sine-varying rotational speed for the impeller caused higher harmonic components for the velocity, owing to the local inertia and gravity forces. In the steady state of the O-tube mode, owing to the resistance force, the flow velocity was proportional to the rotational speed. To generate the target flow conditions, two open-loop control schemes were proposed according to the analytic approach for the U-tube mode and a genetic algorithm for the O-tube mode. The analytic approach was based on a hydrodynamic model with a given flow condition. In the genetic algorithm, the rotational speed was represented by a square root of the Fourier series. The optimal coefficients of the Fourier series to generate the target flow were determined by using the genetic algorithm and the hydrodynamic model. Both approaches were experimentally validated. Consequently, the O/U-tube with the open-loop schemes can be used to generate the desired oscillatory and unidirectional flows. [ABSTRACT FROM AUTHOR]

Tidal-inlet systems are dynamic features that respond to short-term (e.g., storms) and longer-term processes (e.g., sea-level rise, changes in tidal prism). The Chincoteague Inlet system, located along the northern Eastern Shore of Virginia (USA), is a dynamic coastal complex that experiences rapid change associated with sediment redistribution and a shifting inlet throat due to the southern elongation of adjacent Assateague Island. In this study, a numerical model based on Delft3D with coupled flow–waves, multiclass sediment transport, and morphologic feedback was developed to quantify the hydrodynamic and geomorphic controls within this rapidly evolving inlet–spit system and to develop a more comprehensive understanding of regional to local controls on sediment-transport pathways. Model results show that most of the sand transport along southern Assateague Island is sequestered nearshore and proximally in deeper sinks within Fishing Point, and, of that, only finer sand sizes are transported around the spit, confirming previous analysis and hypothesis. The model also showed that sand transport toward the south increases along Wallops Island and quantified spatially explicit transport trends for selected sediment classes, revealing that coarser sediment bypassing is a punctuated process that is proportional to storms.

Enid Lake is one of the largest reservoirs located in Yazoo River Basin, the largest basin in the state of Mississippi. The lake was impounded by Enid Dam on the Yocona River in Yalobusha County and covers an area of 30 square kilometers. It provides significant natural and recreational resources. The soils in this region are highly erodible, resulting in a large amount of fine-grained cohesive sediment discharged into the lake. In this study, a 3D numerical model was developed to simulate the free surface hydrodynamics and transportation of cohesive sediment with a median diameter of 0.0025 to 0.003 mm in Enid Lake. Flow fields in the lake are generally induced by wind and upstream river inflow, and the sediment is also introduced from the inflow during storm events. The general processes of sediment flocculation and settling were considered in the model, and the erosion rate and deposition rate of cohesive sediment were calculated. In this model, the sediment simulation was coupled with flow simulation. In this research, remote sensing technology was applied to estimate the sediment concentration at the lake surface and provide validation data for numerical model simulation. The model results and remote sensing data help us to understand the transport, deposition and resuspension processes of cohesive sediment in large reservoirs due to wind-induced currents and upstream river flows. [ABSTRACT FROM AUTHOR]

The interconnections between hydrodynamics, coastal sediments, and ecosystem distribution were analysed for a ~250 km strip on the northern Mexican Caribbean coast. Ecosystems were related to the prevailing and extreme hydrodynamic conditions of two contrasting coastal environments in the study area: Cancun and Puerto Morelos. The results show that the northern Mexican Caribbean coast has fine and medium sands, with grain sizes decreasing generally, from north of Cancun towards the south of the region. Artificial beach nourishments in Cancun have affected the grain size distribution there. On beaches with no reef protection, larger grain sizes (D50 > 0.46 mm) are noted. These beaches are subject to a wide range of wave-induced currents (0.01–0.20 m/s) and have steeper coastal profiles, where sediments, macroalgae and dune-mangrove systems predominate. The coastline with the greatest amount of built infrastructure coincides with beaches unprotected by seagrass beds and coral reefs. Where islands or coral reefs offer protection through less intense hydrodynamic conditions, the beaches have flatter profiles, the dry beach is narrow, current velocities are low (~0.01–0.05 m/s) and sediments are finer (D50 < 0.36 mm). The results offer a science-based description of the interactions between physical processes and the role played by land uses for other tropical coastal ecosystems. [ABSTRACT FROM AUTHOR]

This study focuses on the numerical investigation of the 3D hydrodynamic processes of coastal zones such as wave breaking, wave-induced currents, and sediment transport, using the multiphase, interFoam solver of OpenFOAM® (a state-of-the-art, open-source CFD numerical tool). The numerical scheme is suitably framed by initial conditions of wave propagation and absorption using waves2Foam wave library. The turbulence closure problem is handled using a buoyancy modified k–ω SST model. In order to predict the sediment transport rate due to waves and currents (bed load, sheet flow, and suspended load over ripples), a transport-rate formula involving unsteady aspects of the sand transport phenomenon is implemented. For the suspended load in the surf zone, the Bailard formula is adopted after considering that the dissipation mechanism is the wave breaking. Results concerning wave height, longshore current, turbulence kinetic energy, and sediment transport are compared against experimental data and semi-empirical expressions.

This paper presents the hydrodynamics on the western coast of Libya. The investigated area, which is a part of the Mediterranean Sea, is one of the most critical and active coastal regions in the country. A 2DH process-based model for flow based on the Delft3D modelling system from Deltares is constructed for the study area. Extensive field data concerning the tidal constituents were used. The flow model that is necessary to understand the hydrodynamics of the area was calibrated and validated using field measurements. In this paper, only the water levels and tidal components for the astronomical tide are presented. Calibration and validation of the numerical flow model show that the results of the water level represent the field conditions well. The present study gives insight into the basic hydrodynamic processes of the investigated area. It should help designers and the decision-makers maintain the region for any other economic and social activities. The flow model for the investigated area can be also coupled with any other models like wave, sediment transport, morphodynamic and water quality. [ABSTRACT FROM AUTHOR]

The estuary delta is an area where human economic activities are active and natural ecological environment is fragile. With global change and the intensification of human activities, coastal and seabed erosion around the world is becoming more and more serious. In this paper, we used the Delft 3D numerical simulation to compare the hydrodynamic effects of sediment transport paths in the Yellow River delta (river-controlled type), Yangtze River delta (tidal type) and Mekong River delta (tidal wave type) in the East Asian monsoon area, and analyzed the causes of accumulation erosion landform distribution in three different types of subaqueous deltas. This study finds the Yellow River Delta has experienced varying degrees of erosion at the estuary, but its subaqueous delta is still dominated by deposition; the Yangtze River Delta has ensured the stability of its shoreline under the influence of artificial shoreline reinforcement, but the subaqueous delta (water depth: 0–15 m) is in a state of erosion all year round; and in the Mekong River Delta the erosion occurs in both its shoreline and subaqueous delta. Additionally, only by analyzing the erosion and deposition within the transport range of resuspended sediment, the changes in the properties of the entire subaqueous delta could be recognized. The research results can not only be helpful to analyze whether the change of river sediment will lead to the change of delta type under human influence, but also provide more powerful scientific support for the protection of delta ecological environment, geological environment safety and geological disaster prevention.

Marine Microplastics (MPs) exhibit a wide range of properties due to their variable origins and the weathering processes to which they are exposed. MP’s versatile properties are connected to their dispersal, accumulation, and deposition in the marine environment. MP transport and dispersion are often explained by analogy with sediments. For natural sediments, one of the key features linked to transport and marine morphology is particle size. There is, however, no size classification defined for MP particles and MPs constitute all plastic particles sized smaller than the threshold of 5 mm. In this study, based on existing knowledge in hydrodynamics and natural sediment transport, the impact of MP size on turbulent entrainment, particle settling, and resuspension is described. Moreover, by analyzing several quantitative studies that have provided size distribution, size-selective accumulation of MPs in various regions of the marine environment is reported on. The preferential presence of MPs based on their size in different marine compartments is discussed based on the governing hydrodynamic parameters. Furthermore, the linkage between polymer properties and MP shape and size is explored. Despite the evident connection between hydrodynamic transport and MP size presented, classification of MP size presents challenges. MP size, shape, and density appear simultaneously in the definition of many hydrodynamic parameters described in this study. Unlike mineral sediments that possess a narrow range of density and shape, plastics are manufactured in a wide variety of densities and marine MPs are versatile in shape. Classification for MP size should incorporate particle variability in terms of polymer density and shape.

An estuary delta is an area with active human economic activities and a fragile natural ecological environment. With the intensification of global changes and human activities, coastal and seabed erosion around the world is becoming more and more serious. This study compared the hydrodynamic effect and sediment diffusion path at the Yellow River subaqueous delta (river control type) and the Yangtze River subaqueous delta (tide-river type) in the East Asian monsoon area using a Delft 3D numerical simulation to analyse the causes of the distribution of accumulation and erosion landform in the different types of subaqueous deltas. This study found that the river deltas were dominated by the river when the accumulation landforms concentrated in the direction of the Coriolis forces, which was due to hydrodynamic erosion driven by wind, and the sediment diffusion range was mainly concentrated in shallow water areas (water depth < 6 m), resulting the Yellow River subaqueous delta presenting the pattern of “northern erosion and south accumulation”. The Yangtze River subaqueous delta was controlled by tidal effects, making the southern part of the estuary more susceptible to erosion. The research results can not only further deepen the understanding of the physical process and mechanism of erosion and deposition in the subaqueous delta but also provide stronger scientific support for the deltas’ ecological environment protection, geological environment safety, and disaster geology prevention.

Unexploded ordnance devices (UXO) pose a potential threat to human life and material during offshore construction activities. Extensive survey activities are conducted to locate, identify, and clear these objects as necessary. For the period thereafter, it is necessary to investigate whether areas that have already been cleared, or even objects that remain in place, may be affected by mobilization under tidal currents or waves, and could thus have an impact on operation and maintenance during the lifetime of the offshore installation. In this study, model simulations based on fluid mechanics are described to derive the loads on the objects caused by currents and waves and combined with knowledge of the known burial condition of the objects. Within the model, the hydrodynamic and hydrostatic loads on the object caused by waves and currents are balanced with inertia and rolling resistance. Thus, the critical current velocity and critical wave conditions for the mobilization of different objects are calculated and compared with the environmental conditions prevailing in the North Sea. As a result, a recurrence interval for the potential mobilization of objects on the seafloor is given, which can now be used to optimize route surveys and thus help accelerate offshore construction work. It is shown that currents are not able to mobilize the objects investigated in the study in almost all regions of the North Sea. Waves can mobilize certain objects in very shallow and extreme conditions.

This study uses a combination of regional ocean modelling systems (ROMS), a sediment transport model (sedtrans05) and detailed grainsize data with the aim of determining the hydrodynamics and primary sediment transport pathways on the North Canterbury Shelf (NCS), South Island of New Zealand. Combining the results from the hydrodynamic model, sediment grainsize data and sediment transport model in an unsupervised classification scheme, highlights 5 classes of sediment on the shelf. These classes include a high energy inner shelf with coarse sands and gravels (Class 1), a low to medium energy mid shelf allowing for the deposition of fine sediments in a large depocenter (Class 2 and 3), and an area on the mid to outer shelf of relict coarse sediments (Class 4). With the exception of Class 4, the sediment distribution is in equilibrium with the modern hydrodynamics and validates the ROMS and SedTrans05 models. This understanding of the NCS hydrodynamic and sedimentary system will help with the management of the marine environment, with the caveat that this is a highly dynamic environment which is influenced of earthquakes and large storms influencing erosion, transport and distribution of sediment in this region. [ABSTRACT FROM AUTHOR]

This study proposes an oscillatory water tunnel (O/U-tube) equipped with two impellers to drive flows. The O/U-tube consists of two modes: U-tube mode and O-tube mode. The former can generate oscillatory flow, while the latter can produce both oscillatory and unidirectional flows with velocities up to 1.6 m/s. The hydrodynamics of the U-tube and O-tube modes were examined analytically. For the U-tube mode, a sine-varying rotational speed for the impeller caused higher harmonic components for the velocity, owing to the local inertia and gravity forces. In the steady state of the O-tube mode, owing to the resistance force, the flow velocity was proportional to the rotational speed. To generate the target flow conditions, two open-loop control schemes were proposed according to the analytic approach for the U-tube mode and a genetic algorithm for the O-tube mode. The analytic approach was based on a hydrodynamic model with a given flow condition. In the genetic algorithm, the rotational speed was represented by a square root of the Fourier series. The optimal coefficients of the Fourier series to generate the target flow were determined by using the genetic algorithm and the hydrodynamic model. Both approaches were experimentally validated. Consequently, the O/U-tube with the open-loop schemes can be used to generate the desired oscillatory and unidirectional flows.

Present work studied the lesion mechanism of coastal clam and its vulnerability assessment subject to the hydrodynamic disturbance of extreme storm events. A clam habitat at the northeast coast of China was chosen for the demonstration study. Relocation failure after passive transport due to excessive substrate erosion or suffocation in anoxic burial under overburdening sedimentation was identified the major cause of negative biomass responses during the storm. Based on the biological propensity and physiological sensitivity of the clam, a tunable loss probability function correlating the mortality with the shell length and the seabed change was proposed. A hydrodynamic model was then adopted to compute the sediment transport and net changes in the seafloor in response to the comprehensive process of storm waves and surge. The spatial distribution of the damage states was evaluated based on the numerical results incorporating the loss probability function. The estimated damage was mainly concentrated along the wave shoaling and breaking belts parallel to the shoreline. High surge levels pushed the "damage belt" shoreward, in which case large waves were able to propagate close to the shoreline before breaking. The scientific findings are helpful to better understand the vulnerability of the clam habitat to the storm disturbance. The study result as well provides a practical methodology of the storm risk assessment for benthic communities in broader ecological and geophysical scopes. The methodology are expected to be further validated and improved by more widespread sampling on coastal ecosystem or mariculture that will withstand future storms. [ABSTRACT FROM AUTHOR]

In the past few decades, there have been many numerical studies on the scour around offshore pipelines, most of which concern two-dimensional setups, with the pipeline infinitely long and the flow perpendicular to the pipeline. Based on the Ansys FLUENT flow solver, this study establishes a numerical tool to study the three-dimensional scour around pipelines of finite lengths. The user-defined functions are written to calculate the sediment transport rate, update the bed elevation, and adapt the computational mesh to the new boundary. The correctness of the model has been verified against the measurements of the conventional two-dimensional scour around a long pipe and the three-dimensional scour around a sphere. A series of computations are subsequently carried out to discover how the scour hole is dependent on the pipeline length. It is found that the equilibrium scour depth increases with the pipeline length until the pipeline length exceeds four times the pipe diameter.

The coupled biophysical interactions between submerged aquatic vegetation (SAV), hydrodynamics (currents and waves), sediment dynamics, and nutrient cycling have long been of interest in estuarine environments. Recent observational studies have addressed feedbacks between SAV meadows and their role in modifying current velocity, sedimentation, and nutrient cycling. To represent these dynamic processes in a numerical model, the presence of SAV and its effect on hydrodynamics (currents and waves) and sediment dynamics was incorporated into the open-source Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) model. In this study, we extend the COAWST modeling framework to account for dynamic changes of SAV and associated epiphyte biomass. Modeled SAV biomass is represented as a function of temperature, light, and nutrient availability. The modeled SAV community exchanges nutrients, detritus, dissolved inorganic carbon, and dissolved oxygen with the water-column biogeochemistry model. The dynamic simulation of SAV biomass allows the plants to both respond to and cause changes in the water column and sediment bed properties, hydrodynamics, and sediment transport (i.e., a two-way feedback). We demonstrate the behavior of these modeled processes through application to an idealized domain and then apply the model to a eutrophic harbor where SAV dieback is a result of anthropogenic nitrate loading and eutrophication. These cases demonstrate an advance in the deterministic modeling of coupled biophysical processes and will further our understanding of future ecosystem change. [ABSTRACT FROM AUTHOR]

A large-scale field campaign was carried out on the ebb-tidal delta (ETD) of Ameland Inlet, a basin of the Wadden Sea in the Netherlands, as well as on three transects along the Dutch lower shoreface. The data have been obtained over the years 2017–2018. The most intensive campaign at the ETD of Ameland Inlet was in September 2017. With this campaign, as part of KustGenese2.0 (Coastal Genesis 2.0) and SEAWAD, we aim to gain new knowledge on the processes driving sediment transport and benthic species distribution in such a dynamic environment. These new insights will ultimately help the development of optimal strategies to nourish the Dutch coastal zone in order to prevent coastal erosion and keep up with sea level rise. The dataset obtained from the field campaign consists of (i) single- and multi-beam bathymetry; (ii) pressure, water velocity, wave statistics, turbidity, conductivity, temperature, and bedform morphology on the shoal; (iii) pressure and velocity at six back-barrier locations; (iv) bed composition and macrobenthic species from box cores and vibrocores; (v) discharge measurements through the inlet; (vi) depth and velocity from X-band radar; and (vii) meteorological data. The combination of all these measurements at the same time makes this dataset unique and enables us to investigate the interactions between sediment transport, hydrodynamics, morphology and the benthic ecosystem in more detail. The data provide opportunities to calibrate numerical models to a high level of detail. Furthermore, the open-source datasets can be used for system comparison studies. The data are publicly available at 4TU Centre for Research Data at 10.4121/collection:seawad and 10.4121/collection:kustgenese2. The datasets are published in netCDF format and follow conventions for CF (Climate and Forecast) metadata. The http://data.4tu.nl (last access: 11 November 2020) site provides keyword searching options and maps with the geographical position of the data. [ABSTRACT FROM AUTHOR]