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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]

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 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]

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]

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]

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]

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]

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]

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]

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]

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]

Woo, H.J.; Lee, J,-H.; Choi, J.U., and Kang, J., 2020. Changes in sedimentary processes in macrotidal flats in Garolim Bay, West Coast of Korea. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 722-726. Coconut Creek (Florida), ISSN 0749-0208. Garolim Bay, on the central western coast of Korea, is a semi-enclosed macro-tidal bay with extensive tidal flats that occupy approximately 77% of the bay surface area. The study investigated the sediment characteristics and sedimentation rates to elucidate the spatial and temporal variations in the sedimentary processes in the bay. Surface sediments were sampled to grain-size distributions at 158 stations in July 2002 and July 2014 in the spring tidal cycle. Grain-size distributions were analyzed using standard sieving for the sand fraction and a particle size analyzer for the mud fraction. The geomorphic changes associated with sediment deposition or erosion were investigated along six transect lines on the tidal flats from February 2014 to February 2015 in the ebb tide. The area of sand and muddy sand sediments had extended from the outer to the middle bay in summer 2014, and the percentages of mud were higher in the inner bay compared to the surface sediment distributions in summer 2002. The short-term sedimentation rates from February 2014 to February 2015 showed that erosion was dominant on the tidal flats in the inner bay during spring and on those in the outer bay during winter, with net erosion rates of –1.55 and –55.23 mm/year, respectively. In the middle bay, deposition dominated on the tidal flats, with net deposition rates from 4.85 to 18.94 mm/year. The sediment transport vectors calculated using grain-size parameters for 2002 and 2014 showed that in 2002, sandy sediments were predominantly transported along tidal channels at the bay entrance. However, in winter, sediments from the tidal flats in the outer and middle bay areas are transported to the inner bay by wind-driven waves and tidal currents, resulting in the deposition of sediment on the tidal flats in the inner bay. In summary, the results show that the sediment transport patterns in Garolim Bay changed between 2002 and 2015 due to increased suspended sediment supply and erosion of the tidal flats in the outer bay. Based on these knowledge of sedimentary processes, the major control factors for seasonal variations in sedimentation on the tidal flats in Garolim Bay are tidal currents, wind-driven waves, and sediment inputs. [ABSTRACT FROM AUTHOR]

Muin, M. and Muslim, A.B., 2023. Anak Krakatau Landslide Tsunami and sediment transport simulation using non-orthogonal boundary fitted technique in spherical coordinate model. In: Lee, J.L.; Lee, H.; Min, B.I.; Chang, J.-I.; Cho, G.T.; Yoon, J.-S., and Lee, J. (eds.), Multidisciplinary Approaches to Coastal and Marine Management. Journal of Coastal Research, Special Issue No. 116, pp. 146-150. Charlotte (North Carolina), ISSN 0749-0208. This paper presents a simulation of a tsunami induced by the Anak Krakatau Landslide in Indonesia and the sediment dispersion transported by the tsunami. The hydrodynamic model of this simulation used a non-orthogonal curvilinear technique in Spherical Coordinates and was developed in GIS on Windows System, named MuTsunami. The advantages of MuTsunami are rapid computation, accurately solving complex geometry, and integrating with the sediment transport model. This software is suitable for an early warning system. MuTsunami has also been applied in the 2010 Mentawai and 2004 Aceh Tsunami. The results show good agreement with the observation data. The simulation results indicate that the tsunami reached Serang, Ciwandan, Kota-Angung, and Panjang within 1860, 2760, 2100, and 4140 seconds after the Anak Krakatau Landslide occurred. The waves along the coast occurred up to 9 m and 8 m for Banten and Lampung coasts. The sediment transport result shows bathymetric changes along the Banten coast 30 minutes after the landslide. The required time to simulate the tsunami from the Anak Krakatau Landslide is only 15 seconds which is suitable for an early warning system. [ABSTRACT FROM AUTHOR]

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

River deltas are built by cycles of lobe growth and abrupt channel shifts, or avulsions, that occur within the backwater zone of coastal rivers. Previous numerical models differ on the origin of backwater‐scaled avulsion nodes and their consistency with experimental data. To unify previous work, we developed a numerical model of delta growth that includes backwater hydrodynamics, river mouth progradation, relative sea level rise, variable flow regimes, and cycles of lobe growth, abandonment, and reoccupation. For parameter space applicable to lowland deltas, we found that flow variability is the primary mechanism to cause persistent avulsion nodes by focusing aggradation within the backwater zone. Backwater‐scaled avulsion nodes also occur under less likely scenarios of initially uniform bed slopes or during rapid relative sea level rise and marine transgression. Our findings suggest that flow variability is a fundamental control on long‐term delta morphodynamics. Plain Language Summary: River deltas are important for farming and drinking water, human populations, and diverse wildlife. Rivers on deltas are unstable and abruptly change course every 10–1,000 years. These channel shifts are necessary for sustaining coastal landscapes and also pose significant hazards. Here we present a mathematical model that shows how rivers require occasional floods, similar to what is observed on natural rivers, to give rise to a predictable location where rivers shift their course. Model simulations without floods produce rivers that change course at random locations, unlike natural rivers. Our findings resolve differences in previous studies about the importance of floods and illustrate that occasional floods are necessary for natural delta growth. Key Points: Rivers on lowland deltas have repeated avulsions at a preferential location at the delta apex that scales with the backwater lengthA preferential avulsion node occurs due to flow variability that focuses bed aggradation in the backwater zoneA preferential node under constant discharge simulations in previous work resulted from assumed initial conditions of uniform bed slope [ABSTRACT FROM AUTHOR]

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

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

Li, H.; Beck, T.M.; Moritz, H.R.; Groth, K.; Puckette, T.; Marsh, J., and Sánchez, A., 2019. Sediment tracer tracking and numerical modeling at Coos Bay inlet, Oregon. Journal of Coastal Research, 35(1), 4–25. Coconut Creek (Florida), ISSN 0749-0208. An investigation was conducted on transport of dredged material placed in the nearshore area of an ocean dredged material disposal site (ODMDS) adjacent to the Coos Bay inlet, Oregon. A sediment tracer release/sampling and field data collection program was carried out and a numerical hydrodynamic, wave, and sediment transport model, the Coastal Modeling System, was developed to perform the analysis of sediment transport around the inlet system and the ODMDS. The data were used to calibrate and validate model calculations, and the model was set up to calculate sediment fluxes and to simulate the process of sediment tracer release and movement, and determine the pathways of sediment tracer under combined wave, current, and wind conditions within and around the immediate vicinity of the Coos Bay ODMDS. The calculations and the measurements indicate that sediment tracer movement is primarily controlled by tidal current inside Coos Bay and at the inlet entrance, and responding to wave and storm conditions in the open coastal area. A divergence in net sediment transport directions in the adjacent nearshore beach was apparent in the results of the tracer release and numerical simulations. This methodology may be used to determine sediment bypassing pathways and optimal placement of sediment within a nearshore environment adjacent to tidal inlets. [ABSTRACT FROM AUTHOR]

To quantify the detailed mechanisms that cause sedimentation at the tidal inlets in the Messolonghi-Aetoliko lagoonal system, the MIKE 21 FM (HD & ST) numerical simulation models were applied. The study focuses on the hydrodynamic circulation in the vicinity of the tidal inlets and the associated wind and tide-induced currents, as well as sediment transport, bed level evolution and total sediment load accumulation, with emphasis on the vicinity of two tidal inlets, where the problem is more acute. Based on the numerical predictions, which have been qualitatively corroborated via satellite images from Google Earth, it is shown that under the prevailing winds and tidal action, sandbars are formed in front or behind the tidal inlets depending on the wind direction, resulting in a gradual decrease of the mean water level at the mouths. Under the combined action of the tide and the wind the characteristic horizontal structure of the flow includes cyclonic and anticyclonic eddies that form at the near tip area of the jetties, which are associated with sediment transport mechanisms. [ABSTRACT FROM AUTHOR]

Appeaning Addo, K., 2018. Assessing ocean wave dynamics, potential sediment transport, and coastal erosion along Accra coast in Ghana. In: Almar, R.; Almeida, L.P.; Trung Viet, N., and Sall, M. (eds.), Tropical Coastal and Estuarine Dynamics. Journal of Coastal Research, Special Issue No. 81, pp. 76–85. Coconut Creek (Florida), ISSN 0749-0208. This study assessed wave dynamics and sediment transport along the coast of Accra in Ghana and compared the results with coastal erosion trend. Wave data from NOAA global wave model and measured buoy wave data were analysed as well as the potential sediment transport using the CERC's equation. The estimated mean significant wave height was 1.40 m and the period was between 10 and 15 seconds. The potential sediment transport rate was between 4.1 ×105 m3/yr and 4.1 ×105 m3/yr, while coastal erosion rate was 1.13 m/yr. Potential sediment transport rate increases from west to east. Coastal erosion is relatively high along the eastern and western coasts of Accra, while the central coast is relatively stable. Wave heights increased gradually from 1.00 m in January to a peak of 1.73 m in August, and eventually decreased to 1.10 m in December. The shape of the nearshore profile is significantly different along the eastern coast relative to the western and central coasts. This indicates that sediment transport intensity and nearshore bathymetry interaction in part explain the rate of erosion observed along the Accra coast in Ghana. [ABSTRACT FROM AUTHOR]

Sequence stratigraphy relies on the identification of unconformity-bound sedimentary packages in order to understand variations in sediment supply, subsidence, and eustasy, which are themselves controlled by external (allogenic) drivers such as climate and tectonics. However, intrinsic (autogenic) river dynamics can also create a rich stratigraphic architecture in the absence of allogenic changes. Here, we outline scaling relationships for the expected depth and length scales of autogenic scour resulting from non-uniform flows in coastal rivers, and apply these relationships to the Upper Cretaceous Castlegate Sandstone--a classic fluvial sandstone unit in the Book Cliffs of Utah (USA). Theoretical and experimental work suggests that hydrodynamics within the backwater reach of coastal rivers--the zone of non-uniform flow that extends upstream of the river mouth--causes spatially extensive erosion during floods; this in turn creates erosional surfaces within fluvio-deltaic stratigraphy that may appear similar to sequence boundaries. Results demonstrate that scour patterns within the Castlegate Sandstone are consistent with the predictions of backwater-induced scours, and show how allogenic versus autogenic erosional surfaces can be parsed within fluvio-deltaic stratigraphy. [ABSTRACT FROM AUTHOR]

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

ABSTRACT Fernández-Fernández, S.; Silva, P.A.; Ferreira, C.; Ribeiro, A.S.; Abreu, T.; Romão, S.; Baptista, P.; Fontán-Bouzas, A.; Dias, J.M..; Coelho, C., and Bernardes, C. 2018. Assessment of Dredging/Dumping Scenarios for Figueira da Foz Coastal Region (W Portugal). In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1266–1270. Coconut Creek (Florida), ISSN 0749-0208. Figueira da Foz coastal region (W Portugal), that comprises sandy beaches and the Mondego estuary-inlet, is exposed to the high energetic wave climate of the North Atlantic Ocean, which induces important local morphological changes. These changes entail shoaling problems as the formation of a submerse sandbar at the inlet which can block navigation towards local harbor. Therefore, coastal dredging is a non-structural temporal solution for this problem. Nevertheless, dredging activities have an impact on local hydrodynamic processes that should be known beforehand. The aim of this study is to clarify this issue using modeling tools dedicated to help stakeholders in decision making process. For that purpose, Delft3D-WAVE module propagates the most representative regional wave conditions under four dredging scenarios including the respective dump areas. Additionally, Delft3D-FLOW module simulates tidal flows along spring and neap tides. The hydrodynamic parameters, significant wave height, orbital velocity, wave-induced currents, tidal current velocity and total sediment transport are analyzed in comparison with numerical solutions obtained in reference scenario (no dredging and no dumping). The results highlight changes in these hydrodynamic parameters in dredging and dumping areas as well as in surrounded areas. Different scenarios draw a similar change pattern for different parameters, namely a reduction of flow velocity intensity within dredged areas and their increase in adjacent areas. Furthermore, hydrodynamic alterations intensify in response to the increase in significant wave height and wave direction considered. These findings are the basis for understanding the influence of dredging and dumping operations on the hydrodynamic of this coast. [ABSTRACT FROM AUTHOR]

Fernández-Fernández, S.; Silva, P.A.; Ferreira, C.; Ribeiro, A.S.; Abreu, T.; Romão, S.; Baptista, P.; Fontán-Bouzas, A.; Dias, J.M..; Coelho, C., and Bernardes, C. 2018. Assessment of Dredging/Dumping Scenarios for Figueira da Foz Coastal Region (W Portugal). In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1266–1270. Coconut Creek (Florida), ISSN 0749-0208. Figueira da Foz coastal region (W Portugal), that comprises sandy beaches and the Mondego estuary-inlet, is exposed to the high energetic wave climate of the North Atlantic Ocean, which induces important local morphological changes. These changes entail shoaling problems as the formation of a submerse sandbar at the inlet which can block navigation towards local harbor. Therefore, coastal dredging is a non-structural temporal solution for this problem. Nevertheless, dredging activities have an impact on local hydrodynamic processes that should be known beforehand. The aim of this study is to clarify this issue using modeling tools dedicated to help stakeholders in decision making process. For that purpose, Delft3D-WAVE module propagates the most representative regional wave conditions under four dredging scenarios including the respective dump areas. Additionally, Delft3D-FLOW module simulates tidal flows along spring and neap tides. The hydrodynamic parameters, significant wave height, orbital velocity, wave-induced currents, tidal current velocity and total sediment transport are analyzed in comparison with numerical solutions obtained in reference scenario (no dredging and no dumping). The results highlight changes in these hydrodynamic parameters in dredging and dumping areas as well as in surrounded areas. Different scenarios draw a similar change pattern for different parameters, namely a reduction of flow velocity intensity within dredged areas and their increase in adjacent areas. Furthermore, hydrodynamic alterations intensify in response to the increase in significant wave height and wave direction considered. These findings are the basis for understanding the influence of dredging and dumping operations on the hydrodynamic of this coast. [ABSTRACT FROM AUTHOR]

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

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

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

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

Confluences are a common feature of riverine systems, where are located converging flow streamlines and potential mixing of separate flows. The confluence of the Negro and Solimões Rivers ranks among the largest on Earth and its study may provide some general insights into large confluence dynamics and processes. An investigation was recently conducted about that confluence in both low and high-flow conditions using acoustic Doppler velocity profiling (ADCP), water quality sampling and high-resolution seismic data. First, the study gained insights into the characterization of the basic hydrodynamics parameters about the confluence as well as of those affecting sediments transport. Second, the analysis of the results showed that common hydrodynamic features noted in previous confluence studies were herein observed. Finally, some differences between low-flow and relatively high-flow conditions about the transfer of momentum from the Solimões to the Negro side of the Amazon Channel were identified. [ABSTRACT FROM AUTHOR]

The confluence of the Negro and Solimões Rivers is an interesting study area under several points of view: it represents the second largest river confluence of the Amazon Basin; the rivers are characterized by very distinct hydrologic behaviour; and it is situated in a peculiar tectonic setting. A field investigation was undertaken to study the characteristics of this confluence, aiming to better understand the bed morphology and stratigraphy resulting from the complex interaction of geological setting, hydrodynamics, and sediment load. Two field campaigns were carried out, during low- and high-flow conditions, using high-resolution seismic, echosounding, and acoustic Doppler current profiling. A third campaign was carried out just in a limited area of the confluence, with a multi-beam echosounder. The results of these surveys provided a more detailed view of the geology, morphology and sediment distribution about the confluence. [ABSTRACT FROM AUTHOR]

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

A mechanistic-cum-stochastic theory describing the sediment transport phenomenon from the particle scale of entrainment to the continuum scale of bedload flux under a steady unidirectional flow over a compact sediment bed is developed. The sediment particles, considered as discrete spherical particles, are subjected to hydraulically smooth, transitional, and rough wall-shear flows. At the particle scale, the hydrodynamic forces acting on a sediment particle resting over three closely packed bed particles are analyzed. The criteria for entrainment threshold in rolling, sliding, and lifting modes are determined introducing the velocity fluctuations. Comparison of the computed threshold curves with the experimental data reveals that the entrainment threshold primarily belongs to the transition of the sliding to the lifting modes. Then, at the particle scale, the entrainment probabilities in rolling, sliding, and lifting modes for a given median size of sediment particles are obtained. The rolling and sliding probabilities increase with an increase in Shields parameter, and after attaining their individual peak values, they decrease, while the lifting probability increases. Finally, the bedload flux, in a continuum scale, is obtained using the lifting probability. [ABSTRACT FROM AUTHOR]

The hypoxia of the bottom waters in the Razdolnaya River estuary was observed for the first time in September 2014 during the survey. It is formed as in the seaward part: oxygen is absorbed as a result of destruction of excessive phytoplankton biomass that settles to the bottom and is synthesized on the upper horizon. The high value of primary production in the riverine part of the estuary was caused by the pycnocline formed. Thus, phytoplankton 'blooms' above and undergoes destruction beneath the pycnocline. Oxygen is distributed symmetrically in both parts of the estuary with respect to a bar: similar oxygen concentrations, which are maximum on the surface and minimum at the bottom, 300 and <60 μm/L, respectively, are recorded. The anomalies of hydrochemical parameters that have been formed during this process are sharply different in the two parts of the estuary, which most vividly manifests itself in the N/P value and the partial pressure of carbon dioxide pCO. The causes of this unique situation are discussed. [ABSTRACT FROM AUTHOR]

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

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

In this work a fast computational particles tracer model is developed based on Particle-In-Cell method to estimate the sediment transport in the access zone of a river port area. To apply the particles tracer method, first it is necessary to calculate the hydrodynamic fields of the study zone to determine the velocity fields in the three directions. The particle transport is governed mainly by the velocity fields and the turbulent dispersion. The mechanisms of dispersion and resuspension of particles are based in stochastic models, which describes the movement through a probability function. The developed code was validated using two well known cases with a discrete transformation obtaining a max relative error around 4.8% in both cases. The simulations were carried out with 350,000 particles allowing us to determine under certain circumstances different hydrodynamic scenarios where the zones are susceptible to present erosion and siltation at the entrance of the port. [ABSTRACT FROM AUTHOR]

Explaining the unexpected presence of dune-like patterns at the surface of the comet 67P/Churyumov-Gerasimenko requires conceptual and quantitative advances in the understanding of surface and outgassing processes. We show here that vapor flow emitted by the comet around its perihelion spreads laterally in a surface layer, due to the strong pressure difference between zones illuminated by sunlight and those in shadow. For such thermal winds to be dense enough to transport grains--10 times greater than previous estimates--outgassing must take place through a surface porous granular layer, and that layer must be composed of grains whose roughness lowers cohesion consistently with contact mechanics. The linear stability analysis of the problem, entirely tested against laboratory experiments, quantitatively predicts the emergence of bedforms in the observed wavelength range and their propagation at the scale of a comet revolution. Although generated by a rarefied atmosphere, they are paradoxically analogous to ripples emerging on granular beds submitted to viscous shear flows. This quantitative agreement shows that our understanding of the coupling between hydrodynamics and sediment transport is able to account for bedform emergence in extreme conditions and provides a reliable tool to predict the erosion and accretion processes controlling the evolution of small solar system bodies. [ABSTRACT FROM AUTHOR]

Son, S.; Kim, J.; Yoon, H.-D.; Jung, T.-H.; Do, K., and Shin, S., 2017. An observational and numerical study of storm-induced morphologic changes at Sanpo Beach, Korea. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 334-338. Coconut Creek (Florida), ISSN 0749-0208. This study was conducted to investigate morphological changes at Sanpo Beach due to the storm through field observation and numerical simulation. Sanpo Beach located on the southeast coast of Korea had been significantly affected by typhoon Goni while some changes in beach profile was expected due to the strong storm-induced currents. Series of field observations on the beach topography, bottom bathymetries, shorelines, sand samples, and incident waves were carried out in order to investigate the morphological changes at Sanpo Beach during the typhoon season. In particular, Real Time Kinematic-Global Positioning System (RTK-GPS) and single-beam echo-sounder were deployed to collect beach topography and bottom bathymetry data, respectively. Observational results represented spatial and temporal changes of shoreline and sand bars during a storm event. For more close look at the process of morphologic changes derived by the sediment transport mechanism, field-scale numerical simulations were performed in parallel using Xbeach. Xbeach is one of the widely-used, open-source models which calculate sediment transports and morphologic changes by hydrodynamic processes of short (and/or long) waves, wave-induced setup and unsteady currents. Bathymetric evolutions, as well as shoreline changes predicted by the numerical results, revealed good agreements with observational data. [ABSTRACT FROM AUTHOR]

Kim, H.-J.; Suh, S.-W.; Seok, J.-S., and Park, W.-K., 2017. Sedimentation for a flood-dominant estuarine harbor induced by anthropogenic activities. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 339-343. Coconut Creek (Florida), ISSN 0749-0208. Sedimentation around the Kunjang harbor area in Korea has intensified at a rate of ~2.0 m/yr because of the construction of an estuarine dam in 1988, which resulted in the tidal energy being blocked and the development of a flood-dominant environment. The construction of several harbor facilities cumulatively altered the tidal hydrodynamics and yielded sedimentation. Moreover, the annual maintenance dredging for the main channel accelerated alteration. In order to understand the sedimentation characteristics, archived intensive depth measurements were used to assess the variations in the bottom shear stress. Our results showed that the bottom shear stress and tidal prism have lessened. The resulting sedimentation should be managed through dredging or minimization plans based on an appropriate engineering solution. In this paper, we suggest an optimized weighting factor to represent diverse physical morphological variations that affect the shear stress. It can be used to compensate for unsatisfactory results generated by a morphological model. Our findings can help in devising an efficient engineering approach to mitigate sedimentation for a flood-dominant estuarine harbor. [ABSTRACT FROM AUTHOR]

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

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

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

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

Kong, J.; Pan, M.; Shen, C.; Hua, G., and Zhao, H., 2016. Analysis of the morphological changes and related sediment transport mechanisms of the Baisha Shoal in the Qiongzhou Strait, China. The morphological changes and evolutionary mechanism of the Baisha Shoal in the Qiongzhou Strait were investigated using various methods, including bathymetric chart comparisons, geomodeling, hydrodynamic modeling, and hydrologic statistical analysis. Water depths were extracted from digitized charts to explore the evolution of the Baisha Shoal and to quantitatively estimate the changes in the shoal area within the 5-m isobath. The grain-size trend analysis (GSTA) model was introduced to explain the features of bed sediment distribution and to analyze the sources of the sediment. Tidal flow models and wave models were adopted to simulate the tidal flows and wave fields around the Baisha Shoal and to reveal the sediment transport dynamics. Further comparisons based on a Mann-Kendall trend analysis and remote-sensing image data from different years were used to discuss the reason for the recent evolution of the Baisha Shoal. The results show that the formation of the Baisha Shoal was caused by the combined effects of reciprocating flow in the eastern and western directions and waves from the NE direction. However, in recent years, the Baisha Shoal has demonstrated an unsteady geomorphological state and is transitioning from a deposition-dominated state to an erosion-dominated state. Erosion has become most significant since 2004, as reflected in the shoal area within the 5-m isobath, which is decreasing by 0.732 km2/y. The analysis demonstrated that a reduction in sediment load and increased sand mining are the two most significant factors that are progressively altering the shoal morphology. If these issues cannot be resolved, the strong dynamic surroundings will aggravate the erosion of the Baisha Shoal. This study on the Baisha Shoal highlights the necessity of combining different approaches to better understand coastal evolutionary features, dynamic mechanisms, and evolutionary causes, as well as to guide future coastal protection engineering design. [ABSTRACT FROM AUTHOR]

Our study aims to enhance process understanding of the long-term (decadal and longer) cyclic marsh dynamics by identifying the mechanisms that translate large-scale physical forcing in the system into vegetation change, in particular ( i) the initiation of lateral erosion on an expanding marsh, and ( ii) the control of seedling establishment in front of an eroding marsh-cliff. Short-term sediment dynamics (i.e., seasonal and shorter changes in sediment elevation) at the mudflat causes variation in mudflat elevation over time ( δzTF). The resulting difference in elevation between the tidal flat and adjacent marsh (Δ Z) initiates lateral marsh erosion. Marsh erosion rate was found to depend on sediment type and to increase with increasing Δ Z and hydrodynamic exposure. Laboratory and field experiments revealed that seedling establishment was negatively impacted by an increasing δzTF. As the amplitude of δzTF increases towards the channel, expanding marshes become more prone to lateral erosion the further they extend on a tidal flat, and the chance for seedlings to establish increases with the distance that marsh has eroded back towards the land. This process-based understanding, showing the role of sediment dynamics as explanatory factor for marsh cyclicity, is important for protecting and restoring valuable marsh ecosystems. Overall, our experiments emphasize the need for understanding the connections between neighbouring ecosystems such as mudflat and salt marsh. [ABSTRACT FROM AUTHOR]

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

The transformation during wave propagation is significantly important for the calculations of hydraulic and coastal engineering, as well as the sediment transport. The exact wave height deformation calculation on the coasts is essential to near-shore hydrodynamics research and the structure design of coastal engineering. According to the wave shoaling results gained from the elliptical cosine wave theory, the nonlinear wave dispersion relation is adopted to develop the expression of the corresponding nonlinear wave shoaling coefficient. Based on the extended elliptic mild slope equation, an efficient wave numerical model is presented in this paper for predicting wave deformation across the complex topography and the surf zone, incorporating the nonlinear wave dispersion relation, the nonlinear wave shoaling coefficient and other energy dissipation factors. Especially, the phenomenon of wave recovery and second breaking could be shown by the present model. The classical Berkhoff single elliptic topography wave tests, the sinusoidal varying topography experiment, and complex composite slopes wave flume experiments are applied to verify the accuracy of the calculation of wave heights. Compared with experimental data, good agreements are found upon single elliptical topography and one-dimensional beach profiles, including uniform slope and step-type profiles. The results indicate that the newly-developed nonlinear wave shoaling coefficient improves the calculated accuracy of wave transformation in the surf zone efficiently, and the wave breaking is the key factor affecting the wave characteristics and need to be considered in the nearshore wave simulations. [ABSTRACT FROM AUTHOR]