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

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

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

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

We describe and demonstrate algorithms for treating cohesive and mixed sediment that have been added to the Regional Ocean Modeling System (ROMS version 3.6), as implemented in the Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System (COAWST Subversion repository revision 1234). These include the following: floc dynamics (aggregation and disaggregation in the water column); changes in floc characteristics in the seabed; erosion and deposition of cohesive and mixed (combination of cohesive and non-cohesive) sediment; and biodiffusive mixing of bed sediment. These routines supplement existing noncohesive sediment modules, thereby increasing our ability to model fine-grained and mixed-sediment environments. Additionally, we describe changes to the sediment bed layering scheme that improve the fidelity of the modeled stratigraphic record. Finally, we provide examples of these modules implemented in idealized test cases and a realistic application. [ABSTRACT FROM AUTHOR]

The 2011 Great East Japan Tsunami caused severe morphological changes along the affected coastline on the northeast part of Japan. This study investigates the recovery of river mouths and breaching of sandy coast at the place used to be river mouth in Miyagi Prefecture, Japan after severe erosion induced by the tsunami through analyzing aerial photograph and investigating field data. After several years since the tsunami took place, the morphology of some river mouths has mostly recovered while others still have some damage. Results on the analysis of aerial photograph clearly indicate that the total length of sandy coast on both sides of river mouth plays important role in the recovery process. Moreover, the relevant phenomenon occurring during the morphological recovery process is also investigated. The findings demonstrated the intrusion of sand spit into river mouths due to the tsunami having scoured river mouth deeper than the depth of closure. Interestingly, the intrusion distance was found to be positively correlated with the width of river mouth. In addition, there is an important finding on the practical problem which is related to the intrusion upstream of sand spit. That intrusion shifts the boundary of fresh-sea water upstream, therefore external wave forces must be considered when implementing the design of river structures. [ABSTRACT FROM AUTHOR]

Abstract: Seasonal patterns of seabed erosion and deposition in a dynamic estuarine environment, the York River (USA), are examined through acoustic studies and seabed sampling to identify the dominant environmental controls on sediment mobility. Areas near Clay Bank in the York River were surveyed monthly using a dual-frequency sonar for a 12 month period. In addition, six stations within these areas were sampled during the surveys. Strong spatial and temporal variations of a soft mud layer were identified, providing new insight to recurring seasonal and spatial patterns in deposition and erosion in the middle reaches of the York River estuary. Sub-bottom data indicated maximum thickness (5–22 cm ± 4 cm) of the soft mud layer during spring and winter from April 2008 through March 2009. Minimum thicknesses (1–12 cm ± 4 cm) of the soft mud layer were observed during summer and fall. Maximum thickness coincided with the occurrence of the secondary turbidity maximum near Clay Bank in the York River. Spatial variations in the soft-mud layer thickness were also identified between and within the York River secondary channel, the inactive oyster reef area, the south west flank of the main channel, and the main channel. The upriver secondary channel, the south west channel flank, and the main channel areas were physically dominated. The downriver secondary channel area was biologically dominated and the inactive oyster reef area reflected both physical and biological processes. Water content trends showed no correlation with seabed stability in this area. Observed changes in soft mud thicknesses are interpreted to result from both biological and physical factors, which vary markedly between winter/spring and summer/fall seasons, and among the different environments of the estuary''s channel. [Copyright &y& Elsevier]

The article presents a study on scour protection stability at foundations and offers insights into flow processes by which rock layers can settle into the seabed. It discusses how the study was conducted which addresses the live-bed situation where the horseshoe vortex can penetrate the thickness of the scour protection and generate bed shear stresses causing sediment transport. Several charts to help the design process and applied to a case example from the field are also presented.

Abstract: Appropriate descriptions of turbulence are important in predicting sediment transport and seabed evolution. We use here a three-dimensional model to investigate the impacts of sediment-induced stratification, erosion parameterization, and turbulence closures on sediment transport and morphological simulations. The model is implemented in the Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS), which couples a hydrodynamic model to the General Ocean Turbulence Model (GOTM) and to a sediment transport model. This sediment transport model calculates both suspended sediment concentrations and bed evolution. A large number of turbulence closures can be tested and we focus on the methods used to calculate the turbulent length scale and the stability functions. Different modelling scenarios are assessed against experimental data of velocity profiles, suspended sediment concentrations, and trench migration in a laboratory flume. Numerical results show that the processes investigated have little impact on the flow velocity profiles, in spite of some differences on the bed shear stress. The only exception is the one-equation turbulence closure, which cannot reproduce velocity profiles appropriately. Sediment-induced stratification, erosion parameterization, and turbulence closures can all have significant impacts on the suspended sediment concentration and the bed evolution. Model-data comparisons are found to be particularly sensitive to the method used to calculate the turbulent length scale. [Copyright &y& Elsevier]

Abstract: Benthic trawlers, through the scraping of the upper layers of the seabed sediment, are responsible for major alterations to the distribution of suspended matter in coastal areas. A major trawling site in Greece is that of the Gulf of Thermaikos, located in the NW Aegean Sea (Eastern Mediterranean). In an attempt to assess, for the first time, the quantities of the mobilized sedimentary masses and the properties of their motion in the aquatic domain of the Gulf of Thermaikos, a mathematical model has been formulated. The modeling approach includes the determination of the mechanical erosion rate, the production of turbulence due to the flow through the mesh of the net and the physical processes that control the propagation of the generated sedimentary plume in the marine environment. In the absence of information regarding the haul paths in the gulf, their determination was made stochastically, based on the existing legislative restrictions and trawlers'' fishing practices. The trawling-activated masses thereby defined for the duration of the trawling period in the gulf were very high, indeed several times greater than the related contribution from the major rivers of the area, emphasizing the significance of the activity to the sedimentary input of the local marine environment. The total annual erosion by trawls in the gulf was calculated at 3.38×106 t/yr. Τhe mean mechanical erosion rate per trawled surface (parameter free from the bias raised by the stochastic simulation of the trawl trajectories) was estimated at 430g/m2, values directly comparable to ones defined for similar coastal areas. Results from a simulation of the 2001–02 trawling period were well correlated with in-situ measurements for the same period, while the investigation of the matter''s suspension level and times revealed that the matter exhibits low residence times in the water column and at the same time moves in the vicinity of the bed, contributing to the formation and distribution of benthic nepheloid layers in the gulf. [Copyright &y& Elsevier]

Abstract: Biological activity on the bottom of the seabed is known to have significant influence on the dynamics of cohesive sediment on a small spatial and temporal scale. In this study, we aim to understand the large-scale effects of small-scale biological activity. Hereto, effects of biology are quantitatively incorporated into the process-based sediment transport module of Delft3D. This Bio-mud model is used to study cohesive sediment transport and deposition patterns in the Western Wadden Sea for a period of 1 year to capture seasonal changes. The modeling results suggest that the seasonal variation in the sediment concentration is caused by the combined effect of the suspended sediment concentrations at the North Sea, wind and biological activity. Moreover, the stabilizing organisms are mainly responsible for the seasonal variation in suspended sediment concentrations, while the destabilizing organisms are mainly responsible for the spatial variation in fine sediment on the bed. [Copyright &y& Elsevier]

Submarine landslides can generate sediment-laden flows whose scale is impressive. Individual flow deposits have been mapped that extend for 1,500 km offshore from northwest Africa. These are the longest run-out sediment density flow deposits yet documented on Earth. This contribution analyses one of these deposits, which contains ten times the mass of sediment transported annually by all of the world’s rivers. Understanding how this type of submarine flow evolves is a significant problem, because they are extremely difficult to monitor directly. Previous work has shown how progressive disintegration of landslide blocks can generate debris flow, the deposit of which extends downslope from the original landslide. We provide evidence that submarine flows can produce giant debris flow deposits that start several hundred kilometres from the original landslide, encased within deposits of a more dilute flow type called turbidity current. Very little sediment was deposited across the intervening large expanse of sea floor, where the flow was locally very erosive. Sediment deposition was finally triggered by a remarkably small but abrupt decrease in sea-floor gradient from 0.05° to 0.01°. This debris flow was probably generated by flow transformation from the decelerating turbidity current. The alternative is that non-channelized debris flow left almost no trace of its passage across one hundred kilometres of flat (0.2° to 0.05°) sea floor. Our work shows that initially well-mixed and highly erosive submarine flows can produce extensive debris flow deposits beyond subtle slope breaks located far out in the deep ocean. [ABSTRACT FROM AUTHOR]

Abstract: The nearshore region exhibits many striking morphological patterns with a variety of spatial and temporal scales. The formation of these rhythmic features has been initially ascribed, depending on the pattern in question, to spatial structures in the flow or geological constrains. These forcing templates have been hypothesized to provide the spatial structure that becomes imprinted on the shoreline or seabed morphology. More recently, new explanations for rhythmic patterns have involved interactions between fluid flow and sediment transport that create morphological feedbacks and lead to pattern self-organization. While forcing-template models do not explicitly treat transport of the sediment that makes up the pattern, self-organization models focus on the strong couplings within flow/sediment systems, and on interactions between emergent structures. We illustrate the sweeping shift from template explanations to self-organization by discussing four nearshore patterns: beach cusps, surfzone crescentic sandbars, inner-shelf sorted bedforms, and large-scale cuspate shorelines. Models involving self-organization show that local interactions between flow and sediment transport can collectively give rise to patterns with large-scale coherence and that the driving feedbacks can be associated with either topographical or grain-size composition instabilities. An approach based on self-organization also allows researchers to establish limitations in the predictability of the occurrence of rhythmic patterns and characteristics as well as to study mechanisms leading to the observed variability of pattern or lack of regularity. [Copyright &y& Elsevier]

Abstract: We present a two-dimensional vertical (2DV) flow and morphological numerical model describing the behaviour of offshore sand waves. The model contains the 2DV shallow water equations, with a free water surface and a general bed load formula. The water movement is coupled to the sediment transport equation by a seabed evolution equation. Using this model, we investigate the evolution of sand waves in a marine environment. As a result, we find sand wave saturation for heights of 10–30% of the average water depth on a timescale of decades. The stabilization mechanism, causing sand waves to saturate, is found to be based on the balance between the shear stress at the seabed and the principle that sediment is transported more easily downhill than uphill. The migration rate of the sand waves decreases slightly during their evolution. For a unidirectional steady flow the sand waves become asymmetrical in the horizontal direction and for a unidirectional block current asymmetrical in the vertical. A sensitivity analysis showed the slope effect of the sediment transport plays an important role herein. Furthermore, the magnitude of the resistance at the seabed and the eddy viscosity influence both the timescale and height of sand waves. The order of magnitudes found of the time and spatial scales coincide with observations made in the southern bight of the North Sea, Japan and Spain. [Copyright &y& Elsevier]

Abstract: This paper analyses the morphological response induced by low-crested structures on the adjacent seabed, with particular interest in the erosion patterns that frequently develop at gaps and roundheads. The mechanisms responsible for erosion processes are examined by means of morphodynamic simulations with the numerical suite MIKE 21 CAMS developed by DHI Water & Environment. The main purpose of the paper is to verify how and how far a commercial code can predict bed evolution, in vicinity of defence structures in a real case, in order to get information that may be very useful for structure design and possible maintenance of existing works. The code is applied to a long-term simulation on a study site that is characterized by a composite intervention and suffers from severe erosion, Lido di Dante (Italy). The simulation covers the period (one year and a half) between two available multi-beam surveys, in order to have a detailed real bathymetry as starting point and another one, as accurate as the first, to compare numerical with surveyed results. All the other input data for the model, as waves, tide, wind and sediment characteristics, are derived from measurements in the area; moreover, the code is calibrated using wave and current data acquired during a field campaign. The bed evolution derived from simulations shows a good agreement with the survey both in the locations and in the intensity of erosive and depositional areas. A sensitivity analysis of results to some selected modelling parameters is performed on a shorter simulation period (one month), showing that accounting for bed slope in sediment transport modelling has greater effects in bathymetry evolution than the use of a complex sediment bathymetry or the representation of wave diffraction. [Copyright &y& Elsevier]

The modern Penghu Submarine Canyon is a sea floor expression of the convergent boundary between the frontal Taiwan orogenic wedge and the Chinese cratonic margin. The canyon is about 180km long and trends N–S, parallel to the strike of the Taiwan mountain belt. It is ∼240m deep at the head increasing to ∼3200m deep at its mouth before merging gradually into the Manila Trench. The Penghu Canyon is considered a tectonically controlled canyon rather than a slope canyon dominated by down-slope processes. Tectonic controls prevail over sedimentary processes. Tectonics controls the orientation and location of the Penghu Canyon while sedimentary processes contribute to its excavation and enlargement. The axis of the deep-water, underfilled basin off SW Taiwan dips southward and parallels the strike of the Taiwan orogen with a characteristic longitudinal sediment transport route. Hence, the Penghu Canyon developed under the gravitational mass movement with its main course along the N–S basin axis, not in a SW or SE downslope direction of both margins. The initial Penghu Canyon began at the intersection of the upper slopes of the South China Sea and Kaoping Slopes. Sediment flows cut into the slope sediments following regional dip toward the south, and excavated along the deepest part of the sea floor, forming the present Penghu Canyon. Shifting of axes of Late Pliocene–Pleistocene canyons from onshore SW Taiwan to the present-day position of the Penghu Canyon reflects the evolving foreland basins with a longitudinal canyon transport system progressively migrating southwestward. The linkage of canyon migration and evolution of the foreland basin may have significant implications for the overall sedimentation and tectonics of the SW Taiwan region. [Copyright &y& Elsevier]

Abstract: This study presents the results of a long-term monitoring program of bed level changes measured during 8 yr at an intertidal mudflat in a microtidal, temperate coastal lagoon. Additionally, bed level measurements obtained at a 10-min temporal resolution at the same tidal flat and at the bed of a nearby tidal channel are presented. Short-term changes in bed level are one or two orders of magnitude larger than the annual net-deposition rate, which shows that the environment is highly dynamic with respect to erosion, transport and deposition of fine-grained sediment. Some seasonality in the bed level changes was observed and there is a tendency for mudflat deposition in spring, summer and early autumn and erosion during the rest of the year, but interannual variations are large and different parts of the mudflat show different seasonal signals. A close coupling between sub- and intertidal deposition and erosion was observed. The time-series showed that some of the material eroded from the mudflat was not exported to the open sea, but instead temporarily deposited in a nearby shallow tidal channel and later returned to the mudflat during calmer weather conditions. These findings support previously published hypothesis and results of modelling studies. Based on the observed abundance of fine-grained sediment at the study sites and the high accretion rates generally found on fine-grained tidal flats in the Danish Wadden Sea area, it is argued that these fine-grained tidal flats are not seriously threatened by the expected sea level rise in the 21st century. [Copyright &y& Elsevier]

Abstract: This paper focuses on the analysis of the morphological response induced by low-crested structures on the adjacent seabed, with emphasis on the far-field erosion that is frequently observed close to roundheads and at the gaps between structures. The analysis is based on observations of far-field erosion, both at prototype scale and in laboratory experiments. Mechanisms responsible for the observed erosion are highlighted using coastal area numerical modelling tools to simulate the flow patterns induced by schemes involving low-crested structures. Finally, an example of the use of a coastal area morphological modelling system to investigate the dependence of the far-field erosion processes on the freeboard of the coastal protection structures is presented and discussed. [Copyright &y& Elsevier]

This study was aimed at the investigation of tsunami effects on the seabed profile as these may be important for coastal structures, like sea outfalls or breakwaters. Tsunamis are well known with huge wave heights and destructive effects on the coastal region. A 2D numerical model was set using the software, COSMOS to calculate the cross-shore sediment transport and to evaluate profile changes in the coastal seabed. The study area is Kadikoy region, a densely populated industrial coastal area in South East Istanbul. The model was run for different kinds of tsunami waves. Not only the bed profile changes, but also the wave heights, breaker depths, peak wave bottom orbital velocities, wave set-up and cross-shore sediment transport rates were determined. The results indicated that, at a water depth around 40-50m, some tsunamis were found to have a wave height of order of 15 m, which became about 5m at a depth of 10 m. The wave set up near the coast was about 1.5-2m. The results also implied that tsunami waves, with their destructive nature, could lead to dramatic vertical changes of the seabed. [ABSTRACT FROM AUTHOR]

Abstract: Predictions of nearshore depth evolution using process-based numerical simulation models contain inherent uncertainties owing to model structural deficiencies, measurement errors, and parameter uncertainty. This paper quantifies the parameter-induced predictive uncertainty of the cross-shore depth evolution model Unibest-TC by applying the Bayesian Generalised Likelihood Uncertainty Estimation methodology to modelling depth evolution at Egmond aan Zee (Netherlands). This methodology works with multiple sets of parameter values sampled uniformly in feasible parameter space and assigns a likelihood value to each parameter set. Acceptable simulations (i.e., based on parameter sets with a nonzero likelihood) were found for a wide range of parameter values owing to parameter interdependence and insensitivity. The 95% uncertainty prediction interval of bed levels after the 33 days prediction period was largest (0.5–1m) near the sandbar crests that characterize the Egmond depth profile, reducing to near-zero values in the sandbar troughs and the offshore area. The prediction interval built up during storms (when sediment transport rates are largest) and remained the same or even reduced slightly during less-energetic conditions. The prediction uncertainty ranges bracket the observations near the inner-bar crest, its seaward flank, and at the seaward flank of the outer bar, suggesting that elsewhere model structural errors (and, potentially, measurement errors) dominate over parameter errors. The interdependence and the non-Gaussian marginal posterior distribution functions of the free model parameters cast doubt on the ability of commonly applied multivariate normal distribution functions to estimate parameter uncertainty. [Copyright &y& Elsevier]

To simulate transport of clastic material in the Baltic a sediment transport module is linked to a Baltic Sea Model that is based on the Modular Ocean Model-MOM3. In order to describe the properties of the seabed sediment parameters as mean grain size, critical shear velocity and bed roughness length must be provided as input data to the numerical model system. To obtain maps of these quantities for the Baltic Sea area the proxy-target concept is applied. As proxy-variable the mean grain size of the sediment types is used. For different sediment samples the critical shear velocity was measured and serves as the target variable. Using the relation between the sediment classifications based on the mean grain size (proxy) and the measured critical shear velocity (target) a map of the critical shear velocity in the Baltic is derived. In January 1993 several extreme strong storm events occurred in the Baltic. Using this period for a model calculation maximum values of current and wave induced bottom shear velocities were obtained. Comparing these model results with the critical shear velocity distribution provided by the proxy-target concept we identify potential erosion areas. Further we show the transport path of material initially deposited in the Mecklenburgian Bight. [ABSTRACT FROM AUTHOR]

Abstract: Identified in 1996, during an environmental survey for the Atlantic Frontiers Environment Network, the Afen Slide lies around 95 km northwest of the Shetland Islands. The head of the slide is at a water depth of 830 mbsl, and the debris lobe stretches to over 1120 mbsl along a slope varying from around 0.7° to 2.5°. The overall length (head scarp to toe of lobe) of the slide is in excess of 12 km, and the maximum width attained is around 4.5 km. The relative timing of the various phases can be determined from the morphology, imaged using seabed picks from 3D exploration seismics, and high-resolution deep-tow boomer data. These seem to show at least four major phases of failure and several distinct modes of sediment transport, ranging from hydroplaning to block sliding. The most likely trigger for the failure is a seismic event focused on the nearby Victory Transfer Zone. Sensitising factors include the presence of contouritic sands directly beneath the surface of rupture. These would serve as a plane of weakness and, under seismic loading, may further weaken due to liquefaction. Indeed, previous studies have shown that the slope in this area is stable in the absence of external triggers. The processes of sediment transport subsequent to failure are also investigated using sediment cores, as well as the 2D and 3D seismic, and appear to indicate that flow transformation occurred in at least the first phase of mass movement. [Copyright &y& Elsevier]

High loads of suspended sediment derived from surface water erosion processes are a major source of environmental and economic problems throughout the world. In many places, a reduction in the amount of sediment delivered from arable land to rivers has therefore become a major issue in environmental policy. In Flanders (Belgium), policy makers would like to achieve a reduction in soil erosion and sediment delivery through the use of various control measures adopted under an integrated environmental watershed management program. A distributed modelling approach (SEDEM/WaTEM) showed that although end-of-the-pipe solutions such as buffer strips or sediment retention ponds have a direct impact on sediment delivery, on-site soil conservation measures were more effective in reducing sediment loads in rivers. It remains questionable, however, whether the significant impact that watershed management has on local sediment yields, can be extrapolated to larger river drainage basins. In the case of highly regulated and channelized rivers, the impact may be much higher compared to natural rivers. [ABSTRACT FROM AUTHOR]

Presents a study concerning global estimates of enhanced solute transport in marine sediments. Data and methods; Enhanced oxygen uptake at the seafloor; Patterns in enhanced transport.

Morphological evolution of large river deltas is highly vulnerable to extreme storm events due to insufficient sediment supply. As an abandoned delta lobe, the coasts along the northern Yellow River Delta (YRD) and Gudong Oil Field have recently suffered serious erosion due to extreme storm events and become increasingly vulnerable. In this study, a well validated and tested Delft 3D module by the observing hydrodynamic and sediment data to simulate the hydrodynamics and seabed erosion during a storm event in the littoral area of YRD. Observed wave, current and sediment data under both fair-weather and storm conditions were collected in the study area and used to validate the model. The results indicated that the model can reproduce well the hydrodynamic and sediment transport processes. A series of numerical experiments were carried out to examine the hydrodynamic changes and sediment transports. In the numerical experiment of normal condition, there is hardly any sediment transport off the YRD. The numerical experiment of storm condition showed that storms enhanced tidal residual currents, weakened tidal shear front, and significant wave heights up to 2 m, considerably intensified the sediment resuspension and dispersal. The local sediment resuspension due to the increased wave-induced bottom stress promoted the sediment plume to expand to the central area of Laizhou Bay, which seemed to provide sediment source for offshore and southward transport. During the storm, the active nearshore sediment resuspension provided sediment source for offshore and southward transport. The intensive dynamics and sediment transport under storm conditions caused significant changes in seabed erosion and siltation. The main erosion occurred off the Gudong and northern YRD, while the main siltation appeared in the central area of Laizhou Bay. No significant recovery after a storm and frequent strong winds have an accumulative effect on the erosion, which is very likely to dominate the erosive states of the YRD coast in the future. • Storm-induced energetic hydrodynamic forces intensify sediment resuspension and dispersal significantly. • Wave-induced bottom stress promotes sediment plume and enhances local resuspension. • Storms increase suspended sediment concentration and offshore sediment transport. • Storm-induced accumulative effect on seabed scour tends to cause long-term erosion. [ABSTRACT FROM AUTHOR]

Integrating field observations in the high-erosion rate region of the Chinese coastal zone (northern estuary of the Yellow River) were used to investigate the role of wave–seabed interactions in seabed erosion, combined with laboratory erosion experiments on the variations in sediment erodibility due to cyclic wave loading. The field results highlight a strong erosive event that occurred in the presence of high waves, during which the seawater turbidity increased sharply from 50 FTU to 600–800 FTU and the bed elevation decreased by 7.7 mm/h over 27 h. The laboratory results attribute this type of erosion to the contribution of wave actions on seabed sediments, where the waves probably acted as a plough and reduced the threshold velocity and critical shear stress values, thus enhancing sediment transport that also occurs due to the shear effect of near-bed currents during fair-weather conditions. Wave-induced liquefaction, characterised by the uneven build-up of excess pore pressures at different buried depths, may also enhance sediment erosion by generating vertical pore water seepage within the sediment and inducing internal sediment re-suspension. The field observations allowed us to construct a regional mathematical model of seabed erosion that parameterises the wave–seabed interactions, as well as to explore the implications of this model for extensive erosion of Yellow River estuarine sediments. This research represents a major step towards validating the critical role of wave-induced interactions in extensive sediment erosion events within a shallow estuarine system. • Yellow River estuarine sediments are subjected to extensive erosion. • This study examined the role of wave–seabed interactions in the problematic erosion. • Significant resuspension was detected in the presence of high waves during a storm. • Erosion was related to multiple factors including excess pore pressure. • A regional model was built to estimate erosion fluxes under waves of varying intensity. [ABSTRACT FROM AUTHOR]

Hanes, D.M. and Barnard, P.L., 2007. Morphological Evolution in the San Francisco Bight. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 469 – 473. Gold Coast, Australia, ISSN 0749.0208 San Francisco Bight, located near the coast of San Francisco, USA, is an extremely dynamic tidal inlet environment subject to large waves and strong currents. Wave heights coming from the Pacific Ocean commonly exceed 5 m during winter storms. During peak flow tidal currents approach 3 m/s at the Golden Gate, a 1 km wide entrance that connects San Francisco Bay to the Pacific Ocean. Flow structure in this region varies markedly spatially and temporally due to the complex interaction by wind, waves and tidal currents. A multibeam sonar survey was recently completed that mapped in high resolution, for the first time, the bottom morphology in the region of the ebb tidal delta. This data set includes a giant sand wave field covering an area of approximately 4 square kilometres. The new survey enables the calculation of seabed change that has occurred in the past 50 years, since the last comprehensive survey of the area was completed. This comparison indicates an average erosion of 60 centimetres which equates to a total volume change of approximately 9.2 x 107 m3. Morphologic change also indicates that flood channels have filled and that the entire ebb delta is contracting radially. [ABSTRACT FROM AUTHOR]