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This paper presents a review of cross-shore sediment transport for non-cohesive sediments in the coastal zone. The principles of sediment incipient motion are introduced. Formulations for the estimation of bedload transport are presented, for currents and combined waves and current flows. A method to consider the effect of sediment heterogeneity on transport, using the hiding–exposure coefficient and hindrance factor, is depicted. Total transport resulting from bedload and transport by suspension is also addressed. New research is encouraged to fill the knowledge gap on this topic. [ABSTRACT FROM AUTHOR]

This paper reviews the recent development of numerical modelling of local scour around hydraulic and marine structures. The numerical models for simulating local scour are classified into five categories: sediment transport rate models, two-phase models, CFD-DEM models, equilibrium scour models and depth-averaged models. The sediment transport rate models are the most popularly used models because of their high calculation speed and availability of empirical formulae for predicting sediment transport rates. Two-phase models were developed to simulate sediment transport in the format of sheet flow under strong current velocity or strong turbulence. The CFD-DEM model simulates the motion of every individual sediment particle. Its speed is the slowest, but it provides the opportunity to understand fundamental mechanisms of flow–particle interaction and particle–particle interaction using small-scale simulations. Equilibrium scour models predict the final scour profile at the equilibrium stage but cannot predict scour history. The depth-averaged models that were developed early are not recommended for local scour problems because they are not able to predict three-dimensional features around structures. Although many numerical models have been developed and many studies have been conducted to investigate local scour, some challenging problems remain to be solved, for example, the effects from scaling and sediment gradation. In addition, people's understanding of local scour of cohesive sand is still very shallow, and more experimental and numerical research in this area is needed. [ABSTRACT FROM AUTHOR]

The suspension and transport of sediments in coastal environments influences water column clarity, and also affects the growth of photosynthetic organisms. The presence of benthic vegetation, such as seagrass, can attenuate wave and tidal energy, thereby altering suspended sediment concentrations (SSC) and microphytobenthos (MPB) biomass that secrete biogenic compounds that can increase sediment cohesion. The dual role of seagrass and MPB in altering the seasonal critical bed shear stress, τc, necessary to suspend sediment was studied within a Zostera marina seagrass meadow and an adjacent unvegetated region within a shallow coastal bay in Virginia, USA. Hydrodynamics and MPB biomass were recorded seasonally to determine the critical bed shear stress and subsequent SSC response. Results show that seagrasses reduced mean currents and waves, thus lowering SSC within the meadow. In addition, seagrass created favorable conditions for MPB growth, with annual mean sediment carbohydrate concentrations, a proxy for MPB activity, to be double within the seagrass compared to the unvegetated site. Sediment carbohydrate concentrations within the seagrass bed were higher during winter than summer due to enhanced light penetration, which coincided with an increase in τc to 0.056 Pa compared to 0.024 Pa. τc was found to be 0.021 Pa at the unvegetated site, with bed shear exceeding this threshold > 85% of the time. These findings suggest both MPB and seagrass play an important and interactive role in regulating seasonal sediment resuspension, and constant reworking of the bed sediments in high shear regions prevented the establishment of MPB. [ABSTRACT FROM AUTHOR]

Wave velocity and suspended sediment concentration were measured over a sand bed with and without a model eelgrass meadow. The model meadow was geometrically and dynamically similar to the marine eelgrass Zostera marina. Meadows were constructed with three stem densities: 280, 600, and 820 stems/m2. Ripples formed within the meadow only when the spacing between stem rows was larger than the wave excursion. When ripples formed, the ripple geometry was the same as that observed for bare bed. When ripples were present, the near‐bed turbulent kinetic energy (TKE) was dominated by the ripple‐generated turbulence, and both the near‐bed TKE and averaged suspended sediment concentration were similar across all meadow densities and bare bed at the same wave velocity. When ripples were absent, the near‐bed TKE was dominated by the stem‐generated turbulence, and the averaged suspended sediment concentration was reduced, compared to cases with ripples but at the same wave velocity. For conditions with and without a model meadow, the sediment diffusivity inferred from vertical profiles of suspended sediment concentration increased linearly with distance from the bed. Key Points: Vortex ripples formed in a model eelgrass meadow when the wave excursion was less than the stem row spacingWhen ripples were present in a meadow, the near‐bed turbulence and the suspended sediment concentration were similar to that observed for bare beds with the same wave conditionWhen ripples were absent from a meadow, the suspended sediment concentration was smaller than that observed for bare beds with the same wave condition [ABSTRACT FROM AUTHOR]

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Abstract Despite the prevalence of rippled scour depression (RSD) on the world's continental shelves and their importance as nursery habitats for many commercially-important species, the processes responsible for their formation and geomorphic evolution are still not well understood. Most studies that focused on RSD evolution have been based on data acquired over multiple years to decades, and often during calmer summer months. Here, multiple geophysical seafloor mapping surveys of a field of RSD's off Santa Cruz, California, USA, were conducted over the course of two winters with distinctly different oceanographic forcing; these results were compared to time series oceanographic measurements made within the survey area, and put into the context of long-term trends from survey data collected during previous decades. Although the migration of these features across the seafloor occurs on decadal time scales, significant change was detected within a given year, depending on the wave climate and fluvial sediment input. RSDs shrank up to 16% or grew up to 28% in a span of a few months. Such change was predominantly the result of redistribution of fine-grained sediment input to the system by local rivers. Migration of the seafloor features appears to be the result of accumulation of fine-grained sediment at the boundary between the RSD and the surrounding fine-grained cap. Highlights • Repeat interferometric side-scan surveys reveal significant short-term variability in backscatter of a field of rippled scour depressions • Coupled measurements of oceanographic forcing indicate that riverine input and winter storm waves are responsible for short-term change • Migration of rippled scour depressions is more gradual, and appears to be due to both erosion and transport of fine-grained material by gentler summer swell and accumulation of fine-grained material input to the system by rivers. [ABSTRACT FROM AUTHOR]

The paper considers the major geographic features of the modern Huang He delta, which ranks among the most rapidly varying in the world. The structure of the hydrographic network and the combination of the natural and anthropogenic geosystems of the delta are characterized. The major external riverine and marine, as well as local anthropogenic factors that have affected the development of the Huang He delta in the recent half century are identified. The regularities of the jump-like development of the Huang He delta in the XIX-early XXI centuries are considered. Special attention is paid to the development of the delta after the artificial redistribution of flow in its boundaries in 1996. Satellite images and methods of their interpretation improved by the authors were used. The trends in Huang He delta development are shown to have changed since the last quarter of the XX century under the effect of an abrupt decrease in river sediment load and the growing impact of marine factors. The active progradation of the delta into the sea slowed down significantly, accompanied by erosion and retreat in many segments of its coastline. Huang He delta was used to establish the conditions of changes in the development trends of other deltas under the effect of changes in the climate and economic activity. [ABSTRACT FROM AUTHOR]

Seawater turbidity due to suspended particulate material (SPM) is an important property of a marine ecosystem, determining the underwater light environment and many aspects of biological production and ecology. SPM concentrations are largely determined by patterns of sediment resuspension from the seabed due to shear stress caused by waves and currents. Hence planning for the construction of large scale offshore structures which will alter regional hydrodynamics needs to consider the consequences for SPM concentrations. Here we develop a one-dimensional (vertical) model of SPM dynamics which can be used to scope the effects of changes in wave and tidal current properties at a site. We implement the model for a number of sites off the east coast of Scotland where we have extensive data sets to enable numerical parameter optimisation. The model performs well at simulating fluctuations in turbidity varying from flood-ebb tidal cycles, spring-neap cycles, storm wave events, and an annual cycle of SPM concentration which is attributed to seasonal consolidation of seabed sediments. Sensitivity analysis shows that, for the range of seabed sediment types in the study (water depth 16–50 m; mud content 0.006–0.380 proportion by weight), relatively large (50%) attenuations of tidal current speed are required to produce changes in water column turbidity which would be detectable by observations given the variability in measurements. The model has potential for application to map the large scale sensitivity of turbidity distributions to the installation of wave and tidal energy extraction arrays. [ABSTRACT FROM AUTHOR]

Sedimentation has been a standard methodology for particle size analysis since the early 1900s. In recent years laser diffraction is beginning to replace sedimentation as the prefered technique in some industries, such as marine sediment analysis. However, for the particle size analysis of soils, which have a diverse range of both particle size and shape, laser diffraction still requires evaluation of its reliability. In this study, the sedimentation based sieve plummet balance method and the laser diffraction method were used to measure the particle size distribution of 22 soil samples representing four contrasting Australian Soil Orders. Initially, a precise wet riffling methodology was developed capable of obtaining representative samples within the recommended obscuration range for laser diffraction. It was found that repeatable results were obtained even if measurements were made at the extreme ends of the manufacturer’s recommended obscuration range. Results from statistical analysis suggested that the use of sample pretreatment to remove soil organic carbon (and possible traces of calcium-carbonate content) made minor differences to the laser diffraction particle size distributions compared to no pretreatment. These differences were found to be marginally statistically significant in the Podosol topsoil and Vertosol subsoil. There are well known reasons why sedimentation methods may be considered to ‘overestimate’ plate-like clay particles, while laser diffraction will ‘underestimate’ the proportion of clay particles. In this study we used Lin’s concordance correlation coefficient to determine the equivalence of laser diffraction and sieve plummet balance results. The results suggested that the laser diffraction equivalent thresholds corresponding to the sieve plummet balance cumulative particle sizes of < 2 μm, < 20 μm, and < 200 μm, were < 9 μm, < 26 μm, < 275 μm respectively. The many advantages of laser diffraction for soil particle size analysis, and the empirical results of this study, suggest that deployment of laser diffraction as a standard test procedure can provide reliable results, provided consistent sample preparation is used. [ABSTRACT FROM AUTHOR]

The Misa River on the Italian Adriatic coast is typical of the rivers that drain the Apennine Mountain range. The focus of this study, conducted in the late summer of 2013 and mid-winter of 2014, was to contrast the general wintertime-summertime dynamics in the Misa River estuarine system rather than investigate specific dynamical features (e.g. offshore sediment transport, channel seiche, and flocculation mechanisms). Summertime conditions of the Misa River estuary are characterized by low freshwater discharge and net sediment deposition whereas, in the wintertime, the Misa River and estuary is characterized by high episodic freshwater discharge and net erosion and sediment export. Major observed differences between wintertime-summertime dynamics in the Misa River and estuary are a result of seasonal-scale differences in regional precipitation and forcing conditions driven largely by the duration and intensity of prevailing wind patterns that frequently change direction in summertime while keep almost constant directions for much longer periods in wintertime, thus generating major sea storms. Sediment deposition was observed in the final reach of the Misa River and estuary in the summertime. However, in the wintertime, large flood events led to sediment erosion and export in the final reach of the Misa River and estuary that, in conjunction with storm-wave-induced mud transport, led to sediment deposition at the river entrance and in the adjacent nearshore region. The seasonal cyclic pattern of erosion and deposition was confirmed with bathymetric surveys of the final reach of the estuarine region. A critical component for the balance between summertime deposition and wintertime erosion was the presence of an underlying mat of organic deposits that limited the availability of sediments for erosion in winter, when massive debris transport occurs. Further, suspended cohesive sediments flocs were subjected to smaller hydrodynamic stresses in the summertime favoring deposition within the estuary. Conversely, during wintertime storms, flocs were subjected to larger hydrodynamic stresses favoring breakup into smaller flocs and deposition outside the estuary. [ABSTRACT FROM AUTHOR]

Vegetation in tidal flats can alter flow dynamics by increasing the velocity gradient and attenuating the wave energy. In this study, a flume experiment was performed using the pioneer plant Scirpus mariqueter and suspended sediment. Two cases are analysed: current-only and current-wave conditions with a regular wave. A statistical method is used to analyse the average velocity and the turbulence intensity. Results demonstrate that the plants can cause a velocity decrease in the vegetation region and an increase in the turbulence intensity below the top of the canopy. The combined effect of waves and vegetation on turbulence dramatically increases the flow velocity above the average water depth as well as the turbulence intensity profiles. In this study, the attenuation efficiency of the wave height is 0.0448 m -1 , which is identical to results using artificial plants with the same relative submerged depth. The drag force in current-wave conditions is almost twice of that observed in current-only conditions. The spectral analysis shows that only waves can influence high-frequency motion. In addition, an increase is observed in the bottom shear stress, mean grain size, and suspended concentration of the sediment during current-wave conditions. [ABSTRACT FROM AUTHOR]

Transport of sediments is a critical process in the coastal zone because of its relation with coastal erosion, productivity and pollution. Of particular interest are the dynamics of suspended cohesive sediments, known as flocs, which can aggregate and break-up during the flocculation process. This changes their size, density, settling velocity and overall transport. Even though turbulence is widely accepted to be an important control on floc aggregation and break-up, specific and detailed floc behaviour is still not fully understood. The present study seeks to help in the understanding of the intra-tidal turbulence-induced flocculation under different current-wave regimes. Observations of floc size and currents at high sample rates are used to investigate the changes throughout a fortnightly cycle. The occurrence of waves at different stages during the sampling period enabled determination of three regimes of currents dominant, combined waves and currents, and wave dominant. The first two regimes showed quarter-diurnal floc size variability with aggregation during low turbulence (slack waters) and higher floc aggregation magnitude on low water slack. Break-up occurred with high turbulence (flood and ebb) with higher magnitude after ebb. During the “currents-waves” regime, waves were tidally modulated and led to enhanced aggregation and break-up, with larger floc size range than during the “current dominant” regime. Wave tidal modulation and quarter-diurnal variability of floc size were lost when waves were dominant. Flocs sizes exhibited a low range related to wave height. Inverse relationships between turbulent properties and median floc size were found for the three regimes, with higher scatter of data for the Kolmogorov microscale and shear rate due to different floc behaviour during flood and ebb phases. Effective kinetic energy obtained from the combined effect of both currents and waves seems to have a better relationship with floc size, which suggests its use as a floc size predictor instead of shear stress. [ABSTRACT FROM AUTHOR]

Many Neolithic and Bronze Age cultural layers and pile fields embedded in sediments at the shorelines of pre-alpine lakes in France, Switzerland, Germany, Austria, and Italy (in part UNESCO World Heritage Sites), are threatened by littoral erosion which is partly caused by human agency. Based on measurements of the wave field at four prehistoric sites on Lake Constance (Germany, Switzerland) we discuss the role of passenger ship navigation. We also review the stability and ecological compatibility of archaeological preservation control fills on the littoral platform of Lake Constance, and we make some recommendations for future preservation measures. [ABSTRACT FROM AUTHOR]

While the nature of the suspended load above steep, wave-induced, sand ripples is of practical importance, it also raises intriguing questions about the relative mixing efficiencies of sediment and momentum above the seabed. It has been widely accepted that the mixing efficiency of sediment is substantially greater than that of momentum. But, hitherto, this has not been explained clearly in terms of the underlying, detailed physical mechanisms which revolve around the generation and ejection of sediment-laden vortices at the ripple crest, and their subsequent advection by the flow. A two-dimensional discrete-vortex, particle-tracking research model, with the parameter settings corresponding to a well-documented laboratory experiment, is used here to represent these processes. Both the modelled and also experimental flow and concentration fields are described in detail, together with the horizontally (ripple-) averaged fields, and the cycle-mean, ripple-averaged fields. From these considerations, the ratio ( β ) of the sediment diffusivity to the eddy viscosity, or the inverse of the Schmidt number, is then determined. It is found that β is larger than unity, in fact between 1.3 and 3.1 for two different computational approaches (based on harmonics and exponential fitting) for the model and data. These values for β agree well with previous results reported in the literature. This research elucidates, from fundamental principles related to spatio-temporal correlations between concentration and velocity, the improved efficiency of sediment mixing compared with momentum mixing in the vortex layer above rippled beds and its key role in determining suspension profiles in such flows. [ABSTRACT FROM AUTHOR]

An improved method is presented to determine the threshold boundary velocity required to entrain sediments under waves, using the non-dimensional group settling velocity of sediments ranging from very fine sand to granules (0.1–3.3 mm), together with a dimensionless boundary velocity. In combination with a more accurate method to calculate the actual boundary velocity under linear as well as non-linear waves, this allows sediment entrainment to be predicted from deep water up to the breaker zone. [ABSTRACT FROM AUTHOR]

The mechanisms of the sinking of a scour protection adjacent to a monopile are described in this paper, together with the determination of the equilibrium sinking depth in various wave and combined wave and current conditions based on physical model tests. Sinking of the rocks may ultimately lead to failure of the scour protection. It may cause exposure and free-span of cables, and possibly change the natural frequency of the wind turbine in an unfavourable manner. For these reasons it is important to consider the possible effects of sinking in the scour protection design, and to understand the mechanisms that could lead to unacceptable sinking of the scour protection. The study showed that the sinking is controlled by two mechanisms: removal of sediment adjacent to the pile (destabilizing) and infilling of sediment into the scour protection from the surrounding seabed (stabilizing). The latter mechanism is found to be the strongest, but it might take some time to fill the pores of the scour protection with sediment and during the time delay considerable sinking might take place. This means that the larger the scour protection, the larger the sinking will be (for a given KC-number smaller than approximately 15). The magnitude of the sinking of the scour protection adjacent to a monopile exposed to waves, and combined waves and current, was found to be similar to the current case. [ABSTRACT FROM AUTHOR]

A novel direct measurement strategy of wave near-bed velocity and bottom shear stress based on the use of ferrofluids is presented. The proposed methodology is aimed at overcoming some of the limits of state-of-the-art instruments, for use in presence of both surface waves and sediments. An inductive readout strategy is proposed to sense displacements of the ferrofluid spike over the inductive circuit due to the flow. Experimental tests have been performed in a wave tank both in hydrostatic conditions and in the presence of regular linear waves corresponding to deep and intermediate water depth cases. Obtained results indicate the applicability of the proposed strategy also in the presence of suspended load (either moderate or intense) and of a moderate bed load transport. [ABSTRACT FROM PUBLISHER]

Abstract: Elongated stromatolites are often used as indicators of current direction and shoreline orientation, especially in paleoenvironmental reconstructions. However, mechanisms that create shore-parallel, m-scale elongated stromatolite mounds in carbonate sand are not well understood. We propose that this geometry is initiated by microbial growth on the parts of sand bars that experience low wave-induced bed shear stresses. We test this idea by growing microbial mats on carbonate sand bars in a laboratory wave tank. Cyanobacterial mats grow on the bar runnels, where sediment motion is negligible, but are absent from the bar ridges, where the waves generate migrating ripples. When microbially-promoted lithification reinforces and preserves this initial pattern, elongated stromatolites should initiate in the runnels of sand bars, with long wavelengths (5–100 m) and small width-to-wavelength ratios (∼0.3). These dimensions are consistent with modern shore-parallel stromatolites in Hamelin Pool, Western Australia, and with patterns of microbial colonization in other sandy sediments. This model of elongated stromatolite mounds can inform paleoenvironmental reconstructions by clarifying and quantifying feedbacks among waves, sediment transport and microbial growth. [Copyright &y& Elsevier]

Abstract: Tidal bars and tidal flats in shallow, mesotidal estuaries are subject to the action of tidal currents and waves. This complex forcing gives rise to large variations in bottom sediments and related benthic ecosystems. In this research we study the spatial relationships among tidal currents, waves, sediment characteristics, chlorophyll a, and pheophytin in the shallow bars and flats of Plum Island Sound, Massachusetts, USA. Waves and tides have a mild effect on the sand grain size and percent of silt and mud of these shallow deposits. Average wave conditions are more important than extreme events, like Nor’easters, in sediment sorting. The spatial distribution of pheophytin, an indicator of dead microphytobenthos, mimics that of silt and mud whereas chlorophyll a, a proxy for the live microphytobenthos stock, is greatest in sandy areas characterized by intermediate values of tidal velocity. [Copyright &y& Elsevier]

Two major causes of salt marsh loss are vertical drowning, when sediment accumulation on the platform cannot keep vertical pace with sea level rise, and horizontal retreat, associated with wave-induced marsh boundary erosion. Despite these processes having been extensively documented and modeled, it is unclear which loss modality dominates given a set of environmental parameters. A three-point dynamic model was developed to predict marsh loss as a function of sea level rise, allochthonous sediment supply, wind regime, tidal range, and marsh bank and mudflat erodability. Marsh horizontal and vertical evolutions were found to respond in opposing ways to wave-induced erosion processes. Marsh horizontal retreat was triggered by large mudflats, strong winds, high erodability of marsh bank and mudflat, whereas the opposite conditions acted to reduce the sediment supply to the marsh platform, promoting marsh loss to drowning. With low and moderate rates of sea level rise (∼5 mm/yr), retreat was found to be a more likely marsh loss modality than drowning. However, conditions associated with marsh retreat also increase the system resilience by transferring sediment on the marsh platform and preventing drowning. Our results suggest the use of a modular strategy for short-term marsh management: selectively protect extensive salt marsh regions by maintaining healthy vegetation on the platform, while allowing other areas to retreat, leveraging the natural resilience embedded in the lateral loss of marsh extent. [ABSTRACT FROM AUTHOR]

Flow–structure–seabed interaction in coastal and marine environments is a rapidly growing area of research and applications. In this vision paper, this area is discussed with a view of identifying its state of the art and current research challenges. The discussion draws attention to key issues related to structures such as marine pipelines, offshore windfarms, and multiuse offshore platforms. Tsunamis, which received considerable attention after two recent extreme events (2004 Indonesia tsunami and 2011 Japan tsunami) are also included in the discussion. Marine hydro-geomechanics is highlighted, among other areas, as an emerging branch of Marine Civil Engineering. Predictions of the field development for the forthcoming years are also briefly outlined. [ABSTRACT FROM AUTHOR]

In the coastal sector of "La Guardia -- La Restinga", an accelerated erosion of the beach is produced. In order to mitigate it, a study about wave, current and sediment transport for calm and extreme conditions is done, take into account the data set from Venezuelan environmental authorities. [ABSTRACT FROM AUTHOR]

The effects of regular surface waves on the descent of instantaneously released sediments were investigated experimentally. The detailed wave characteristics, including wave height (), wave period (), and wave phase of release, were controlled systematically through a wave synchronization system. The results showed that the sediment cloud was passively advected by the wave orbital motion, and there was no significant phase lag between the sediments and surrounding water particles. The motion of the center of mass and the growth rate of the sediment cloud averaged over four representative wave phases of release were found to be similar to those in a stagnant ambient condition. However, a shift (in the range of ) in the horizontal equilibrium position of the oscillatory motion was observed and could be related to the wave phase of release. A passive advection model was proposed to predict the motion of a sediment cloud in the wave environment by superimposing the wave orbital velocity onto the descent velocity of the sediment cloud induced by buoyancy excess. The prediction was found to be in reasonable agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Based on field studies, hydro-meteorological data and wave hindcasts, coastal developments and their hydrodynamic forcing conditions are studied on the limestone relict island of Osmussaar. Areal growth of Osmussaar Island, which emerged from the Baltic Sea 2000-3000 years ago and has grown ever since, has practically stopped as the current global sea level rise nearly balances out the local isostatic post-glacial uplift; yet it continues on the southern shores of the island as a result of gradual accumulation of the matter eroded by waves from the north-westerly exposed Osmussaar cliff and the submarine limestone bench in front of it. Based on analysis of old maps, photographical material, and levelling surveys from coastal study sites on Osmussaar, the island as a whole is slowly migrating to the south-east. Compared to the 1960s and 1970s, the rate of coastal changes has increased from 0.2 m² y-1 to 1.2 m² y-1 per shoreline meter. A painted sediment experiment conducted in 2011 revealed the nearshore feeding zones for beach ridges. Storminess and high sea level events have increased on the windward, westerly exposed coast. Wave climate has undergone some cyclical changes with the last high phase in the 1990s and a new cycle probably started again 2010. [ABSTRACT FROM AUTHOR]

Observations of optical and hydrodynamic processes were made on the open beach on Santa Rosa Island, Florida, in March 1995. This study focuses on the passage of two cold fronts. The observations have been supplemented by a bio-optical model; a suite of hydrodynamic models to simulate coastal flows forced by waves, tides, local wind, and coastal sea level; and a geo-optical model that predicts scattering by mineral particles resuspended by wave action. These models have been used to examine the interaction of atmospheric forcing and hydrodynamics with respect to the observed marine hydrosol. The optical and hydrodynamic measurements, and the model results, have been used to conceive a cold-front regime model of the hydrosol for open beaches in the Gulf of Mexico. The optical environment during the cold front was determined by three hydrosol phases: (1) a prefrontal steady-state hydrosol consisting of fine resuspended mineral particles, phytoplankton cells, organic detritus, and colored dissolved organic matter; (2) a frontal phase dominated by resuspended mineral particles; and (3) a postfrontal hydrosol containing large phytoplankton, detritus, and fine mineral particles. This concept is useful for identifying the physical processes responsible for observed optical properties. It should be applicable to other regions and types of events. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents some morphometrical and dynamical features of the South Dobrogea lakes based on the bathymetric data between 2010-2011. The analyze includes the lakes on the Black Sea shore (Siutghiol, Limanu and Tatlageac) and on the right side of the Danube River (Bugeac, Oltina, Mârleanu, Domneasca). The Siutghiol Lake is the deepest one with 7.82 m and has the highest volume (69.69 mil. m3). The Domneasca Lake has the lowest maximum depth (2 m) and the smallest area (0.49 km2). The wind is a main factor which causes the water dynamic, and determines the resuspension of the sediments by the wave action. In order to estimate the bottom dynamic conditions, the form factor (Vd), the erosion and transport areas (ET) of fine sediments and the fine sediments accumulation areas (A0) were determined based on the morphometrical features: lakes area (A, in km2), the mean depth (Dm, in m) and the maximum depth (Dmax, in m). The study shows that the areas of accumulation prevail in the Tatlageac, Siutghiol and Domneasca lakes (62.64-69.36%) and the erosion and transport areas prevail in the Bugeac, Oltina, Mârleanu and Lakes (76.67-99%). The dynamic ratio (the ratio between the area''s square root and the mean depth) ranges between 4.18 (Oltina Lake) and 0.40 (Domneasca Lake). The relation between the lake form and the bottom dynamic conditions is highlighted by the form factor which ranges between 0.78 (Limanu Lake) and 1.83 (Domneasca Lake). Our estimation of the erosion, transport and accumulation areas of the fine sediments could be useful for improving the management of the lakes, especially for the lakes that are used for fish production, imposing some structural and nonstructural measures. [Copyright &y& Elsevier]

Abstract: Field data from a microtidal estuarine intertidal flat (Tamaki estuary, New Zealand) are used to analyse very small waves (height <10 cm; period 1.0–1.8 s) and associated sediment resuspension under light winds. Mean spectral period at the bed varied over the tidal cycle, driven by changes in surface-wave spectrum and depth-attenuation of orbital motions. Wave-orbital currents exceeded 30 cm/s, disturbing the fine-sand (100–200 μm) matrix of the seabed and resulting in the release of fine silt (particle size <20 μm) at concentrations >120 mg/L. Resuspension was initiated when ∼40% of the maximum zero-downcrossing orbital speeds in a burst exceeded the critical speed for initiation of sediment motion. Sediment concentrations were highest around low tide, when waves were smaller compared to high tide because of a reduced fetch but depth-attenuation of orbital motions was less because the water was shallower. Wave period exerted a control on sediment resuspension through the wave friction factor. There was a hysteresis in the wave Reynolds number such that it was greater on the ebbing tide compared to on the flooding tide: since it did not exceed 3 × 105 the bed was hydraulically smooth, and the wave friction factor therefore is inversely proportional to wave period. Hence, the tidal-cycle hysteresis in wave Reynolds number translated into a smaller wave friction factor on the ebbing tide, and accounting for this caused the ebb and flood sediment concentration data to collapse onto one curve when plotted against wave-induced skin friction. A simple model is presented to evaluate the relative contribution to sediment resuspension of waves associated with weak and strong winds. At the base of the flat (waves competent to resuspend sediment for 5% of the inundation time), waves associated with stronger, infrequent winds dominate resuspension. At the top of the flat (waves competent to resuspend sediment for 30% of the inundation time), waves associated with lighter, frequent winds dominate resuspension. Moderate winds – neither the strongest nor most frequently occurring – dominate resuspension integrated across the profile. The mass of sediment resuspended by waves is greatest towards the top of the flat: shoreward of this, resuspension is smaller because of wave dissipation; seaward of this, resuspension is smaller because of greater depth-attenuation of orbital motions. The location of maximum sediment mass resuspended by waves and the location of maximum duration of resuspension are not necessarily the same. [Copyright &y& Elsevier]

Abstract: Data from a three-year long field study of fine sediment dynamics in Cleveland Bay show that wave-induced liquefaction of the fine sediment bed on the seafloor in shallow water was the main process causing bed erosion under small waves during tradewinds, and that shear-induced erosion prevailed during cyclonic conditions. These data were used to verify a model of fine sediment dynamics that calculates sediment resuspension by both excess shear stress and wave-induced liquefaction of the bed. For present land-use conditions, the amount of riverine sediments settling on the bay may exceed by 50–75% the amount of sediment exported from the bay. Sediment is thus accumulating in the bay on an annual basis, which in turn may degrade the fringing coral reefs. For those years when a tropical cyclone impacted the bay there may be a net sediment outflow from the bay. During the dry, tradewind season, fine sediment was progressively winnowed out of the shallow, reefal waters. [ABSTRACT FROM AUTHOR]

The article focuses on a study which investigated the processes causing morphology in muddy coastlines. It determines the factors that govern the regulation of sediment fluxes in Little Constance Bayou and a tidal channel in Rockefeller State Wildlife Refuge, Louisiana, U.S. It discusses the correlation between sediment concentration and wave height and the amount of sediment transferred from one mass of water to another.

Background and Aims: Convective gas flow in helophytes (emergent aquatic plants) is thought to be an important adaptation for the ability to colonize deep water. In this study, the maximum depths achieved by seven helophytes were compared in 17 lakes differing in nutrient enrichment, light attenuation, shoreline exposure and sediment characteristics to establish the importance of convective flow for their ability to form the deepest helophyte vegetation in different environments. [ABSTRACT FROM PUBLISHER]

Velocities and sand concentrations measured along 20 transects at the Field Research Facility (FRF) at Duck, North Carolina during October 16–23, 1997 are analyzed to examine the cross-shore and longshore suspended sand transport in the FRF pier depression. The suspended sand volume Vs per unit bottom area remains large outside the surf zone in the depression. The depth-integrated offshore and longshore suspended sand transport rates are shown to be estimated as a, UVs and VVs, respectively, where the empirical parameter a is in the range of 0.1–0.4 in the depression, U is the cross-shore current and V is the longshore current. The offshore suspended sand transport rate at the end of the pier is estimated to be as large as 3.5 m3/h/m at the peak of a storm with an offshore significant wave height of 3.5 m. The sand transported offshore appears to have been supplied by the longshore sand transport toward the pier depression. [ABSTRACT FROM AUTHOR]

Abstract: Sediment dynamics on a mixed microtidal flat in a sheltered backbarrier position are shown to vary strongly on short term, tidal, and monthly timescales. Bed level changes were ±1 mm per tidal period in the absence of winds. Erosion of 10 to 20 mm within a few hours was possible during high combined current and wave shear stress. Mean grain size in the upper 1 cm bed sediment varied from 34 to 155 μm and was consistently coarser than the mean size of trapped suspended matter (7–10 μm). Threshold for resuspension was low at 0.03 N m−2. No clear correlation was found between resuspension activity and suspended matter concentrations as these concentrations also depend on current induced advection. Due to tidal asymmetry, the net suspended sediment flux was flood directed. On average it was 14 kg m−2 per tidal period in the summer and 3 times higher during November when wave activity generally was stronger. Bed micro topography, was followed on digital photos taken every 1.5 h during the two month study period, showed that (1) ripples started to develop when wave shear stress exceeded 0.15 N m−2, and (2) their wavelength varied with shear stress. [Copyright &y& Elsevier]

This paper presents the results of an experimental investigation of the complete sequence of sediment behaviour beneath progressive waves. The sediment was silty with d50 = 0.060 mm. Two kinds of measurements were carried out: pore-water pressure measurements (across the sediment depth), and water-surface elevation measurements. The process of liquefaction/compaction was videotaped from the side simultaneously with the pressure and water-surface elevation measurements. The video records were then analysed to measure: (i) the time development of the mudline, (ii) the time development of liquefaction and compaction fronts in the sediment and (iii) the characteristics of the orbital motion of the liquefied sediment including the motion of the interface between the water body and the sediment. The ranges of the various quantities in the tests were: wave height, H = 9–17 cm, wave period, T = 1.6 sec, water depth = 42 cm, and the Shields parameter = 0.34–0.59. The experiments reveal that, with the introduction of waves, excess pore pressure builds up, which is followed by liquefaction during which internal waves are experienced at the interface of the water body and the liquefied sediment, the sequence of processes known from a previous investigation. This sequence of processes is followed by dissipation of the accumulated excess pore pressure and compaction of the sediment which is followed by the formation of bed ripples. The present results regarding the dissipation and compaction appear to be in agreement with recent centrifuge wave-tank experiments. As for the final stage of the sequence of processes (formation of ripples), the ripple steepness (normalized with the angle of repose) for sediment with liquefaction history is found to be the same as that in sediment with no liquefaction history. [ABSTRACT FROM AUTHOR]

Ripples take time to evolve to a new equilibrium state in response to a change in wave-generated oscillatory flow. The paper presents results from flow tunnel experiments designed to examine oscillatory flow transient ripple processes under controlled, full-scale laboratory conditions. The experiments include study of the growth of ripples from flat bed and the evolution of existing ripples to new equilibrium ripples in response to a step change in the flow. In general, ripples evolve through a combination of two main processes: (i) from a flat bed or from a bed consisting of ripples that are smaller than the equilibrium ripples through a combination of ‘slide’ and ‘merge’; (ii) from a bed consisting of ripples that are larger than the equilibrium ripples through a combination of ‘split’ and ‘merge’. The experimental results show that equilibrium ripple geometry is independent of initial bed morphology while the time to reach equilibrium is largely independent of the initial bed and the equilibrium ripple size. The time to reach equilibrium depends strongly on the mobility number, and a new empirical equation relating mobility number and the number of flow cycles to equilibrium is proposed. This equation is combined with a simple exponential function for ripple height growth or decay to produce a new empirical model for ripple height evolution, which gives a reasonably good overall agreement with the measurements. The model is based on experiments involving one sediment size only and further work is needed to develop the model for other sand sizes. [ABSTRACT FROM AUTHOR]

Results are presented from the deployment of three bottom-mounted instrumentation systems in water depths of 6–9 m on the sandy inner shelf of Louisiana, USA. The 61-day deployment included nine cold front passages that were associated with large increases in wind speed. Two of the most energetic cold front passages were characterized by distinct meteorological, hydrodynamic, bottom boundary layer, and sedimentary responses and may potentially be treated as end-member types on a continuum of regional cold front passages. Arctic surges (AC storms) have a very weak pre-frontal phase followed by a fairly powerful post-frontal phase, when northeasterly winds dominate. Migrating cyclones (MC storms) are dominated by a strong low-pressure cell and have fairly strong southerly winds prior to the frontal passage, followed by strong northwesterly winds.On the basis of measurements taken during this study, AC storms are expected to have a lower average significant wave height than MC storms and are dominated by short-period southerly waves subsequent to the frontal passage. Currents are weak and northerly during the pre-frontal phase, but become very strong and southwesterly following the passage. Sediment transport rate during AS storms was not as high as during MC storms, and the mean and overall direction tended to be southwesterly to westerly, with low-frequency flows producing easterly transport, and wind-wave flows producing southeasterly transport.MC storms had the most energetic waves of any storm type, with peaks in significant wave height occurring during both the pre- and post-frontal phases. The wave field during MC storms tended to be more complex than during AS storms, with an energetic, northerly swell band gradually giving way to a southerly sea band as the post-frontal phase progressed. Currents during MC storms were moderate and northerly during the pre-frontal phase, but became much stronger and southeasterly during the post-frontal phase. Shear velocity was high during both the pre- and post-frontal phases of the storm, although sediment transport was highest following the frontal passage. Mean and overall sediment transport was directed southeasterly during MC storms, with low-frequency and wind-wave flows producing northerly transport. In summary, the data sets presented here are unique and offer insight into the morphosedimentary dynamics of mid-latitude, micro-tidal coasts during extratropical storms. [Copyright &y& Elsevier]

Egmont Key is a small, elongate island located on the huge ebb-tidal delta at the mouth of Tampa Bay, FL, USA. The multiple sets of intersecting beach/dune ridges that comprise the low-lying island indicate several periods of growth spaced between periods of erosion. The island has experienced considerable expansion and erosion during recorded history. The oldest of these ridges represents accumulation that took place about 1000 years before the present. Over the past century of well-documented change, there has been a general reduction in the area of the island as the result of extended periods of erosion punctuated by short accretion periods. The net change during this period has been a loss of approximately 40% of the area of the island. A 1-year, time-series monitoring of the Egmont shoreline during 1996–1997 showed sediment loss of 26 500 m3, while the annual average over the period of 1877–1996 was only 3360 m3. A single storm is responsible for most of this loss leading to the conclusion that the island is storm-dominated. Inferences from time intervals during which hurricanes took place support this conclusion. This island provides a major contrast in its coastal location, development and stratigraphy as compared to typical barrier islands. There is no underlying sediment deposited in shallow, paralic environments. The development of the island was lateral rather than having a vertical component through time, partly because of its relatively young age but also because of its position on a thick, ebb-tidal delta sand body. [Copyright &y& Elsevier]

King Sound is a 100-km-long embayment located in tropical northwestern Australia with a spring tidal range of 11 m. This is the second largest tide in the world after the Bay of Fundy in Canada. Intertidal areas cover about 800 km2. The upper reaches of the sound are turbid with fine suspended sediment concentration reaching 3 kg m−3. Field studies of the dynamics of water and fine sediment were carried out in the dry seasons of 1997 and 1998. The tide was a propagating wave, shoaling and dissipating by friction as it entered the sound. This mode of propagation generated an asymmetric tidal current with a stronger current at flood than at ebb. An evaporation-driven salinity maximum zone was found in the upper reaches of the sound, and this was also where the turbidity maximum occurred. Tidal pumping by the tidal asymmetry and, possibly, the biological filter formed by muddy marine snow, trapped the fine sediment in the upper regions of King Sound. Wind-driven waves contributed significantly to entrainment of bottom fine sediment, possibly through wave pumping of the sediment and not wave-induced orbital velocities. Field data suggest that erosion of bottom fine sediment was proportional to the sixth power of the tidal current and the third power of the wave height. [Copyright &y& Elsevier]

The calculation of the degree of sediment disturbance through wave action in the surf and swash zone has been examined at various levels in recent years using a number of empirical techniques. Quantifying 'depth of disturbance'(also know as sediment mixing depth) enables a better understanding of nearshore processes, where interaction between sediment and surf zone wave action is complex. Better understanding of how sediment responds to given surf and swash zone parameters is paramount in examining a number of phenomena such as natural beach evolution, sediment movement around engineering structures, the design and planning of beach renourishment schemes, and the monitoring of pollution behaviour. Previous empirical studies have concentrated their efforts in various methodologies such as the use of sediment tracers to mark the sediment, depth of disturbance rods deployed over a tidal cycle and the use of plug-holes filled with marked sediment. All efforts at estimating sediment disturbance in the field to date have resolved their measurements only after a complete tidal cycle and have been unable to measure processes during the actual perturbations caused by wave action within the tidal event, an essential period of activity to understand bed elevation patterns. This paper seeks to address the present shortfall in methodology with the design and construction of a new, high resolution, vertical measurement system. The new instrument, a Sediment Activity Meter (SAM), characterises surface elevation changes in the sediment bed of the surf zone at a given deployment location at approximately 2 minute sampling intervals. This technique will, for the first time, enable realistic comparisons to be made between bed change and the main forcing variables of the system during a tidal cycle. The paper mainly outlines the basic design of the new field instrument and describes, for the first time, surf zone seabed elevation changes (at a single point) measured at approximately 2-minute intervals alongside corresponding wave parameters and water depths within the surf zone. The field trials took place on a high-energy beach system in Northern Ireland. [ABSTRACT FROM AUTHOR]

Erosion of tidal flats is to a large degree determined by the erosion threshold of their cohesive sediments, i.e., the critical bottom shear stress identifying the onset of erosion. Given that the erodibility of tidal flats can vary strongly over both space and time, rapid in situ measuring methods for quantifying the critical bottom shear stress are needed. As the largest changes in tidal flat elevation are generally observed during storms when shear stress is wave dominated, we developed a mobile Oscillatory-Channel Resuspension flume, OsCaR, as a rapid method to measure the critical wave-generated shear stress on sediment cores directly taken from the field. We assessed the performance of the OsCaR-flume by conducting erodibility measurements on a range of artificial sand – mud mixtures, and along a natural longshore estuarine sediment type and benthic assemblage gradient. Measured erodibility of the artificial sediments matched well with sediment transport theory, indicating that the OsCaR-flume is able to reproduce wave-generated shear stress accurately. Moreover, the patterns observed in the influence of total benthic metabolic rate divided over functional groups on sediment erodibility show that the OsCaR-flume is able to capture the main benthic processes, as they corresponded well to previous laboratory based studies. • A new method for measuring natural sediment erodibility under waves is introduced. • Sediment resuspension rates can be used to quantify critical bed shear stress. • Benthic metabolic rate may explain erodibility patterns in a field context. [ABSTRACT FROM AUTHOR]

Sediment resuspension and sediment erodibility were investigated in Hamelin Pool (Western Australia), which is one of the few modern carbonate settings where stromatolites and ooids are actively forming. For this purpose, the first time series of wave height and water turbidity were recorded at a ~2.5 m deep subtidal location in Hamelin Pool from July 2017 to March 2018. Sediment grain size analyses indicate that this environment is nearly free of mud, so the optical turbidity sensor was able to detect the intra-wave modulation of sand resuspension. This allowed us to use the standard deviation of the turbidity within a burst – as opposed to the mean turbidity – as a proxy for sand resuspension. This approach was further validated by wave tank experiments, which also helped to identify the occurrence of biofouling and discard the affected data. Although the wave regime was similar throughout the year, sand resuspension changed with seasons. Sediment erodibility, defined as the sand resuspension normalized by the bed shear stress, was higher during the Austral winter and spring, and lower in summer and autumn. This decrease in erodibility coincided with an increase in temperature and solar irradiance. These two environmental factors likely modulate the growth of benthic microbes, which in turn affects sediment dynamics. This seasonal modulation of sediment dynamics may influence additional processes, including the delivery of sand grains to stromatolites and the precipitation of aragonite around ooids and in stromatolite laminae. • Standard deviation of turbidity can be used as a proxy for sand resuspension. • Sand biostabilization was detected from continuous near-bed turbidity data. • Annual cycle of biostabilization likely occurs in Hamelin Pool, Western Australia. [ABSTRACT FROM AUTHOR]

Abstract: Problems of constructing a sediment budget for an inlet is often a challenge due to constraints on data collection, quality of data, and assumptions one is willing to consider. Existing literature does not provide a systematic foundation for equations considered and often engineers and geologists typically do not properly consider the mathematical constraints placed on the problem of sediment budget construction. The present technical note presents a simple methodology for assessing sediment budget, i.e. what is possible, and what is not possible via a matrix equation system and linear algebra. It is hoped that engineers and geologists will not impose unrealistic expectations on the sediment budget system via using such an approach. Some simple examples are given of both pitfalls and correct approaches to sediment budget development. [Copyright &y& Elsevier]

While estuarine dams can develop freshwater resources and block the salt intrusion, they can result in increased sediment deposition in the estuary. The mechanism of increased sediment deposition in an estuary with an estuary dam is not well understood. To fill this knowledge gap, 7 ADCP measurements of flow and suspended sediment concentration (SSC) were collected along-channel in an estuary with an estuarine dam over a neap-spring cycle. Flow and SSC were used to calculate the sediment flux and sediment flux gradients, which in turn were decomposed into mean-flow fluxes (which occur on timescales longer than a tidal cycle) and correlation fluxes (which occur on the tidal timescale). Then the fluxes were compared with the external forcing to determine the relative importance of tides, dam discharge, and waves in driving the fluxes. The results indicated that the cumulative sediment fluxes at all stations were directed landward. The along-channel sediment flux gradient was negative, which indicated deposition along the channel. The landward mean-flow fluxes were dominant in the deep portion of the channel near the estuary mouth, whereas landward correlation fluxes were dominant in the shallow portion of the channel near the estuarine dam. The tides were the dominant forcing driving the sediment fluxes throughout the estuary. Waves and dam discharge were locally important forcing however. In particular, the dam discharge resulted in seaward mean-flow fluxes for 7 km seaward of the estuarine dam. This distance corresponded approximately to a tidal excursion seaward from the dam. It was the distance a freshwater mass discharged during an ebb tide could propagate before the currents returned landward during the following flood tide. Overall, the along-channel sediment flux gradient in an estuary with an estuarine dam was different from a similar estuary without an estuarine dam because the mean-flow fluxes in the inner estuary are forced by episodic dam discharge which was limited in seaward extent by the tidal excursion. This imposed a limitation for the seaward mean-flow fluxes which counteract the landward mean-flow and correlation fluxes due to the tides. With restricted seaward flushing, the tides could dominate, which could in turn result in increased depositional rates for an estuary with an estuarine dam. [ABSTRACT FROM AUTHOR]

Darwin Harbour is a flood-dominated estuary with a large tidal range. Tides are considered to be the dominant factor influencing sediment resuspension and transport in the harbour during the dry season. However, the sediment dynamics during the wet or monsoon season have been little explored using either field data or numerical hydrodynamic modelling. This study focused on understanding the sediment dynamics during the monsoon and the dominant factors controlling the suspended-sediment concentration (SSC) in Darwin Harbour. Using the Finite Volume Coastal Ocean Model (FVCOM) coupled with the Simulating Waves Nearshore (SWAN) model, we investigated the effect of waves on the SSC during a particular wet season. SSC distributions modelled with tidal currents and wave in the outer harbour were significantly different to those only with tidal currents. Due to the narrow harbour entrance, strong monsoonal waves in the outer harbour barely propagated into the inner harbour; the SSC in the inner harbour was therefore almost hardly affected by waves. Numerical results show that the criterion of neglecting wave forcing in a macro-tidal environment when the tidal range is larger than 3 m is inaccurate, and that the effects of waves on the SSC can still be important in waters with a large tidal range such as Darwin Harbour. • The wave-current coupled sediment dynamics model was, for the first time, developed to investigate the wave effects on sediment transport in Darwin Harbour, during monsoon period. • Sediment flux was landward at the entrance of Darwin Harbour, but there was negligible landward sediment flux in the inner harbour. • Unlike Mehta (1988), the wave effects on sediment dynamics can not be neglected in the macro-tidal environment. [ABSTRACT FROM AUTHOR]

In recent years, with daily progress in technology, application of wind turbines for energy generation has become common all around the world. Installation of these turbines at sea encountered a great deal of challenge. One of the most important challenges is scouring around the piles of these turbines due to sea waves and current interaction. Many studies have been conducted in this respect; however, the results are insufficient, and the phenomenon remains poorly understood in tripod wind turbines. In this work, an attempt is made by combining the waves and currents, and changing the substructure of the turbine and the type of the bed materials, to extend the investigation of this phenomenon. The current research is focused on presenting the trend of changes in the amount of scouring. By changing the conditions (including variation in the wave height, variation of the current velocity, variation of the pile diameter, and variation in the size of bed particles), one can arrive at an appropriate estimate and prediction of the shape and the depth of the scour pit. [ABSTRACT FROM AUTHOR]