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During extreme conditions, the transport of the wave-averaged suspended sediment concentrations in the inner surf zone affects dune erosion. Although large-scale laboratory experiments have provided insight in what drives these sediment concentrations, corresponding field data are lacking. To fill this gap, novel field observations of suspended sediment concentrations are compared to drivers that govern sediment suspension during storm conditions known from literature. A total of 128 time intervals of 20 min are analysed, spread over 10 different high water events with different hydrodynamic conditions. For each time interval, the wave-averaged (i.e. 20 min mean) suspended sediment concentration is computed and compared to three suspension drivers. The studied drivers are (1) bed shear due to near bed velocities that originate from mean currents in combination with wave-induced orbital flow, (2) the horizontal pressure gradients under steep wave fronts that increase the forces on the bed material, and (3) bore-induced turbulence that is generated at the free surface and reaches the bed. The derived bore-induced turbulence generates the greatest correlation with the mean suspended sediment concentrations (r = 0.74, p = 4.47E-23). Samples that deviate from this correlation correspond to time intervals with lower values of derived bore turbulence, less wave energy saturation in the inner surf zone, and stronger mean currents. The correlation with the mean suspended sediment concentrations increases when the shear stress originating from mean currents is used for these time intervals (r = 0.83, p = 1.63E-33). For time intervals during which more energetic conditions persist and the wave energy is saturated in the nearshore, bore turbulence was the dominant mechanism in stirring up sediment. The outcome of this study suggests that, based on the events analysed, dune erosion models may achieve more accurate results if computations of suspended sediment concentrations include a bore-induced turbulence term, or if already included, properly address the relative importance of bore-induced turbulence when compared to bed shearing. • A dune erosion field experiment was conducted to study drivers of wave-averaged suspended sediment concentrations. • The studied drivers are (1) flow-induced bed shearing, (2) horizontal pressure gradients under wave fronts, and (3) bore-induced turbulence. • The variability in bore-induced turbulence generated the greatest correlation with the variability in mean suspended sediment concentrations. • When more energetic conditions persisted and wave energy was saturated in the inner surf zone, bore turbulence appeared the dominant driver. [ABSTRACT FROM AUTHOR]

Submarine canyons serve as important sediment transport conduits from littoral zones to the deep sea, with strong impacts on the sedimentation patterns in marginal areas of the ocean. Moreover, such canyons can be major geohazards for submarine infrastructure, warranting a good understanding of their past and current behavior. Here, we present a study of the geological history and the recent activity of the Nahariya submarine canyon, the longest of a system of ∼15 small blind canyons located in the eastern Mediterranean Sea, offshore Israel. Two piston cores retrieved from the middle and outlet of the canyon, at 650 m and 915 m water depth, respectively, were the focus of a multi-proxy study aiming to characterize sediment transport and deposition along the canyon during the Last Glacial and up to the present. Both cores reveal a sequence of homogenous sediment of late last glacial age, which are capped by an unconformity overlying by fine laminated sediment dated to the last ∼200 years. Thus, the deglacial and most of the Holocene intervals are absent from the record. Evidence for down canyon sediment transport are abundant and include a 70 cm interval of mud clasts with disordered glacial ages that appears immediately below the hiatus, as well as broken calcareous shells of dead benthic foraminiferal species of shallow marine habitats, which are abundant throughout both cores. Similarly, shelf-derived living benthic foraminiferal species were found in the core-tops, indicating that active sediment transport persists along this canyon today. We conclude that the history of Nahariya submarine canyon includes a period of sediment accumulation that lasted until the last deglaciation. Thereafter, the canyon was dominated by an erosive regime that persisted throughout the Holocene. Sediment accumulation resumed ∼200 years ago. We suggest that the recent resumption of sediment-accumulation is a result of anthropogenic amplification of on-land soil erosion accompanied by a wet period that persisted in the region and enhanced land to sea sediment transport. • The geological history of a blind submarine canyon of E. Mediterranean is studied. • In-canyon last glacial sediment accumulation and Holocene erosion are observed. • Resumption of sediment accumulation occurred ca. 200 years ago. • This resumption reflects anthropogenic on-land soil erosion and shift to wet climate. • Shelf origin sediment is transported to deep canyon during glacial period and recent. [ABSTRACT FROM AUTHOR]

Estuarine deltas play a critical role in the interaction between the ocean and land and serve as the primary location for the deposition of terrestrial organic carbon and pollutants. However, many deltas are increasingly at risk of erosion due to natural processes and human activities. In particular, abandoned estuarine deltas are extremely prone to erosion in the absence of sediment replenishment. The erosion of sediment in these deltas is crucial in comprehending the evolution of delta erosion as it directly impacts coastal geomorphology, ecological environments, geochemical cycling, and carbon sequestration dynamics. Therefore, determining accurately the erosion characteristics of estuarine deltaic sediments is essential for assessing and managing these evolving coastal systems. Therefore, this study conducted erosion experiments on undisturbed sediment samples collected from the subaqueous delta of the abandoned Yellow River Estuary (Old Qingshuigou Estuary) utilizing the UMCES-Gust Erosion Microcosm System. The aim was to reveal the spatial distribution characteristics of sediment erodibility and explore the erosion process, characteristics, and influencing factors of the surface sediments in the area. Erosion characteristics exhibited a spatial distribution pattern of increased erodibility in nearshore sediment and reduced erodibility in offshore sediments. The critical erosion shear stress of surface sediments ranged from 0.2 to 0.68 N/m2, while the erosion rate increased linearly with an increase in erosion shear stress and reached a maximum value of 2.119 g/m2 s, suggesting that nearshore sediments exhibited strong erodibility. Furthermore, the erosion characteristics exhibited a strong correlation with the type of sediment. Silt exhibited surface erosion and Type I erosion (depth-limited erosion), whereas silty sand primarily underwent volume erosion and Type II erosion (steady-state erosion). Particle size characteristics played a crucial role in influencing erosion. Additionally, our results revealed that the effective particle size of sediment aggregates and the scale effect of turbulence were also important factors that affected sediment erosion characteristics. These findings not only enhance our understanding of the erosion characteristics of silty sediments but also provide valuable parameters for sediment transport models in large river deltas such as the Yellow River Delta, thus facilitating the release of buried organic carbon and heavy metals from estuaries. • The subaqueous delta of the abandoned Yellow River Estuary sediments were assessed. • UMCES-Gust Erosion Microcosm System was employed for erosion experiments. • Sediment erodibility distribution and erosion process characteristics were analyzed. • Particle size characteristics represented the most important influencing factors. • Erosion characteristics were closely related to the sediment type. [ABSTRACT FROM AUTHOR]

Coastal zones are dynamic environments where sediment transport significantly influences erosion, deposition, and ecosystem stability. Accurate modelling of the complex interactions between hydrodynamics, sediment transport, and morphological changes in high-energy shoreface areas is crucial for sustainable coastal management. This study aims to assess sediment dynamics and understand the dominant physical drivers of sediment transport in the shoreface by coupling high-resolution numerical modelling with a shoreface sand tracer experiment. Results from the field experiment showed high diffusion and a net onshore and downdrift movement of the tracer in agreement with the observed hydrodynamic data. The numerical modelling strategy, validated with in situ hydrodynamic data and tracer results, demonstrated good performance and highlighted the dominant modes of shoreface sediment transport. While during low energetic wave conditions, the dominant transport mechanism involves the slow-rate bed load sediment movement toward the shore, under moderate energetic wave conditions, longshore wave-induced suspended transport becomes the prevailing mode of transport. The study provides valuable insights to increase the understanding of sediment transport in the shoreface and highlights the importance of coupling numerical modelling with sediment tracer experiments. • Field observations and numerical modelling are used to understand sediment transport in the shoreface • Conceptual sediment dynamic model combines Lagrangian and Eulerian approaches • Energetic wave conditions increase wave-induced currents and sediment transport rates, with waves breaking over the bar crest. • Streaming and wave nonlinearities are the main drivers of sediment transport in the shoreface • Alongshore suspended transport dominates in the surf zone, distributing sediments downdrift [ABSTRACT FROM AUTHOR]

In the Geum River, a representative altered estuary, in-situ mooring and erosion experiments were conducted to reveal the effects of human-controlled discharge on benthic sediment disturbances. The strong discharge through the estuarine dam increased the current velocities within the benthic boundary layer (BBL) up to 79% and 153% during spring and neap tides, respectively. During the discharge period, the suspended sediment concentration in BBL was five times higher than that during the non-discharge period. During the flood phase, a critical shear stress for erosion (τ ce) was in the range of 0.1278 to 0.1391 Pa. Immediately after the ebb phase with strong discharge, τ ce increased to 0.1848 Pa, and the erosion rate (E) decreased from 33.73 to 14.81 mg m−2 s−1. The repetition of human-controlled discharge removed the erodible sediments within BBL, exposing the underlying consolidated sediment bed with low E and high τ ce. The results suggest that an altered estuary is vulnerable to benthic sediment erosion under combined natural and anthropogenic forcings. [Display omitted] • Human-controlled discharge disturbed benthic sediment transport and velocity structures. • Altered estuary is vulnerable to sediment erosion under anthropogenic forcings. • Discharge removed sediments, exposing consolidated sediment with low erodibility. • Erosion experiments present direct evidence on benthic sediment resuspension. [ABSTRACT FROM AUTHOR]

Field work combining in-situ mooring and erosion experiments was conducted in the intertidal flat of Asan Bay to reveal the relationship between sediment erodibility and external forcing and the contribution of local erosion to sediment transport. A total of 25 tidal cycles occurred during the mooring period with 6-h submergence and 5.7-h air exposure. The erosion rate (E) for sediment bed during air exposure was 0.007 g m−2 s−1, which was 36% of E (0.019 g m−2 s−1) during submergence. Although the sediment bed was influenced by consolidation during air exposure, the erodibility of the submerged bed was closely associated with the unconsolidated deposits of sediments newly supplied from tidal channel and bed shear stress (τ cw) induced by current-wave interactions. In particular, τ cw could be enhanced by strong winds, which depended on the ratio (H s / h) of significant wave height and water level, directly disturbing the sediment bed. Under weak winds (H s / h < 0.06), the newly deposited sediments with high erodibility increased the bed elevation. A small amount of the sediment bed was eroded (E : 0.006 g m−2 s−1), as a floc erosion, with a slight decrease in suspended sediment concentration (SSC T). This increased the contribution (57.2%) of eroded sediments to SSC T. Under strong winds (H s / h > 0.06) with enhanced τ cw , meanwhile, the erodible sediment in the bed was depleted accompanied by a decrease in bed elevation. A large amount of sediment bed was eroded (E : 0.025 g m−2 s−1), as a surface erosion, resulting in the rapid increase in SSC T and the enhanced seaward sediment flux. The sediments eroded from the bed were supplied to water column accounting for 86.8% of SSC T. This suggests that seaward sediment transport under strong winds could be caused by surface erosion shifting from floc erosion in the intertidal flat. [Display omitted] • In-situ erodibility of submerged bed was unaffected by consolidation in exposure. • Bed erosion type was shifted between floc and surface erosions depending on winds. • Surface erosion by strong wind increased fraction of eroded sediment in suspension. • Seaward exported sediments were mostly originated from bed under strong wind. [ABSTRACT FROM AUTHOR]

Western Port is a large tide-dominated embayment located 75 km east of Melbourne, Victoria that is flanked by a rapidly growing population, significant industrial infrastructure, grazing lands and protected RAMSAR habitats. Remarkably little is known about the sediment dynamics of Western Port despite concerning rates of erosion of the swamp and floodplain deposits including cohesive clay cliffs that fringe the sunkland. As in other tide-dominated systems, sediment dynamics in Western Port are complicated by strong tidal currents, multiple sediment sources and complex circulation. We applied the coastal sediment cell framework to Western Port, in conjunction with high resolution satellite derived rates of coastal change to elucidate sediment sharing among the sub-embayment beaches. Using end member modelling of 20 sediment assemblages based on elemental and mineralogical composition we robustly identified seven end members that correspond to different point and diffuse provenances. Hierarchical clustering of the 20 beaches dispersed across the bay yielded nine coastal cells, delimited by headlands, deep water channels, estuaries or disruptive infrastructure. Analysis of shoreline change within the cells suggests most cells are neutrally or positively balanced but a northward movement of sediments is leading to rotation. The deep channels provide a pathway for Bass Strait sediments to bypass the embayment headlands and tidal currents enable cross shore exchange with the channels beyond wave derived closure depth in some locations. Understanding the sediment cell boundaries and direction of sediment transport can assist with the management of erosion hotspots; the novel approach applied here can resolve complex connected coastal systems such as estuaries and embayments. • Combined datasets used to backtrack sediment transport processes in a tide dominated bay. • We identified multiple self-contained sediment cells within the embayment. • Transport is in the direction of time-integrated wind balance, causing in-cell beach rotation. • Headland bypassing facilitated through deep channel and strong tidal currents. • Despite local subsidence and sea level rise, shorelines are, on average, prograding. [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]

Relation among estuarine processes, mixing mechanisms and turbidity maximum zone (TMZ) formation was evaluated in a microtidal tropical estuary of high fluvial discharge (Magdalena River, northwestern South America). Particularly, assessing the effects of vertical stratification over mixing, estuarine circulation and suspended sediment transport processes. Measurements of salinity, temperature, density, currents and suspended sediment concentration (SSC) were performed at the Magdalena river mouth during high and low streamflows to distinguish among two contrasting seasonal conditions (flow conditions, wind patterns, wave energy). Salinity, temperature, density and location of the freshwater-saltwater interface (FSI) exhibited a sharp seasonal variability. The river mouth and delta front were stratified regardless of the hydrologic season, whereas the riverine section was stratified during the low streamflow season, reflecting the balance between fluvial advection and vertical stratification. Reduction of the vertical mixing led to a more clearly defined and extended stratification. Bottom friction is the main mixing mechanism, but as stratification is strengthened along the river mouth, the vertical mixing weakens, promoting the developing of TMZ (SSC >4500 mg l −1 ). Our results indicate that TMZ developing is caused by the convergence of stratified layers near the nodal point and the weakening of bottom turbulence by stratification. Although the TMZ exhibited a strong seasonal variation in its magnitude and extent, it usually formed in the convergence front demarcated by saltwater intrusion. Streamflow is the major influence on the TMZ formation since it allows the development of stratified conditions, which weaken turbulent mixing, and thus promotes particulate matter settling. The Magdalena River estuary can be classified as turbid (4000 mg l −1  < SSC max  < 10,000 mg l −1 ) and extremely turbid during low streamflow seasons (SSC max  > 10,000 mg l −1 ). These values are of the same order as the SSC reported for the Yangtze and Yellow estuaries, classified as having the largest SSC values of the world. [ABSTRACT FROM AUTHOR]

Fluid mud supported by waves can move downslope on a gentle slope under gravity to transport massive sediment across the continental shelf and cause significant geomorphological changes. In order to explore the formation and transportation of fluid mud under extreme conditions, we undertook in-situ measurements and observed fluid-mud-related processes triggered by a typhoon, Danas, in the subaqueous Changjiang Delta. Under the action of waves, firstly, the seabed was eroded slowly for ∼930 min caused by the wave-enhanced bed shear stress; next, rapid erosion occurred when the bed erodibility M e / ρ B doubled the value during no waves. The great change in bed erodibility implied that bed liquefaction occurred due to waves. The fluid mud occurred concurrently with the strongest waves and went through five stages with an interval of 0.5–3.5 h between each stage in which waves weakened continuously. In addition, the five fluid mud stages all underwent three identical phases, i.e. , formation, stabilization, and decay. In the formation and decay phases, the bottom friction force exceeded the buoyancy gravitational force, and the gradient Richardson number (Ri) was lower than the typical threshold of 0.25, indicating that fluid mud was unstable due to high turbulence energy enhanced by Kelvin-Helmholtz instabilities. During the stabilization phase, the buoyancy gravity force was almost balanced with the drag friction force, and Ri was close to or higher than 0.25, suggesting a laminar fluid mud status. Eventually, the fluid mud disappeared when significant wave height decreased to <1.39 m. Our observation results showed that bed erosion and liquefaction both contributed to the formation of the fluid mud, and the fluid mud played an important role in sediment transportation and bed landforms in subaqueous deltas during extreme events. • Wave-induced sediment-bed liquefaction both contributed to sediment resuspension and reduced bed elevation. • Resuspended sediment settled and aggregated near seabed to form fluid mud moving downward along the slope. • Fluid mud was observed to undergo the formation, stabilization, and decay phases. [ABSTRACT FROM AUTHOR]

Large-scale coastal erosion in the Mekong Delta has been dramatically increasing in severity in recent decades. There are several effective hard engineering solutions that have been implemented in this delta to efficiently prevent coastal erosion and stimulate sedimentation while supporting the local ecosystem conservation. These measures include Pile-Rock Breakwaters (PRBW), Hollow Triangle Breakwaters (HTB) and Semicircular Breakwaters (SBW). However, research on the sediment transport, morphological changes and toe erosion for these offshore breakwaters is very limited and is currently in the initial stages of understanding the specific conditions of sediment characteristics and foundations. The objective of this study was to reproduce the morphological changes and toe erosion of three breakwaters due to wave-structure interactions. This was investigated using 2D physical models with 3000 irregular waves during 8 experimental hours (equal to 15,000*T p). To extract the bed morphological changes and toe erosion both specialized laser measurements (SW50M laser ruler) and analysis of high-speed video recording by images digitalization were applied. The experimental results show that the shape and structural design of offshore breakwaters can have a significant influence on the bed morphology on both the seaside and the leeside. We found that generally the toe of the construction on the seaside was eroded due to the occurrence of reflected waves, and that the flow is narrowed while passing through the construction, increasing the flow velocity and causing toe erosion. Additionally, the accretion of sediment at the leeside of the breakwaters was found to be mainly driven by the transport of sediment through the construction. Comparing the breakwater designs the experimental results showed that the HTB has the maximum accretion rate behind the structure, as well as the fastest accretion rate behind the breakwater. The SBW has high wave energy dissipation efficiency, although the toe erosion rate is faster than the other classes of breakwaters. The PRBW shows the fastest toe erosion rate in front of the structure and causes accretion at the leeside of the construction but at a lower rate than the HTB. The findings from this study will help practical designers to reinforce the foot of construction during real breakwater designing and inform stability calculations. We recommendation is to apply these three classes of breakwaters, especially the HTB and SBW, for stimulating sedimentation for mangrove restoration in the mangrove mud-coast delta. • Morphology and toe erosion of three breakwaters were tested using laboratory physical models. • Pile-rock (PRBW), hollow triangle (HTB), and semi-circular breakwaters (SBW) are compared. • PRBW had the largest front erosion and the slowest accretion rate behind the structure. • HTB demonstrates the fastest accretion rate and the largest sedimentation area behind the breakwater. • SBW had high wave energy dissipation efficiency, but a faster toe erosion rate. [ABSTRACT FROM AUTHOR]

Shorelines bordering ebb deltas are often subject to deformation by the approach and attachment of ebb-tidal shoals. Although this is a common behaviour, little attention has been paid to the link between shoal migration and the multi-annual development of the adjacent beach-dune system. This study aims to understand beach-dune systems' behaviour during the approach phase of an ebb-tidal shoal attachment event. Topographic and bathymetric data of the barrier island of Texel (NL) was used to calculate shoreline position, beach and dune volume, dunefoot position, and shoal displacement rates. Two classical beach-dune interaction models were used to understand the observed behaviour: the surfzone-beach-dune model and the sediment budget model. The analysis revealed how a larger bank on the land-facing side of the ebb delta split into two smaller shoals with different morphological behaviours. One of the shoals (S1) moved consistently landwards, recently attaching the shore, whereas the second shoal (S2) is still evolving and presents a milder landward movement than S1. In parallel to the landward movement of S1, the adjacent coastline was subject to erosion, partially counterbalanced by nourishments. However, despite the erosion, dunes are growing in volume, suggesting a net positive transfer of sand from the beach to the dunes. In the surfzone-beach-dune model, regular nourishments positively affect beach state by maintaining sufficient beach size for aeolian sediment transport and reducing shoreline erosion. In the budget model, dune volume growth may occur despite a slightly negative beach budget. Framing Texel in the budget model implies that the beach budget before the start of the approach phase is crucial in defining the behaviour of the dune system during this phase. If the shoal approach significantly reduces the beach budget, the system may cross the budget threshold that dune building is possible. Thus, the dune system may evolve to an erosional state, including dune ridge dissection and blowout development. Hence, nourishments have been essential in keeping the current morphological state during the attachment of the shoal, as they restrict the system from crossing the negative morphological threshold. Thus, without the nourishments, beach erosion driven by the shoal might have led to morphological changes in the dune system that could lead to years of a weakened level of protection until foredune recovery after attachment. • Shoal-induced changes in beach budget influence dune development. • Dune morphology may change depending on the beach state prior to attachment. • Nourishments can retain beach budget at a sufficient level to maintain dune morphology. [ABSTRACT FROM AUTHOR]

Two barrier systems in southeastern Tasmania afford the opportunity to contrast Holocene barrier evolution and explore large-scale coastal morphodynamics under consistent regional-scale boundary conditions on an embayed wave-dominated coastline. New Optically Stimulated Luminescence (OSL) ages for the previously undated seaward ridges of Seven Mile Beach constrain the deposition of the foredune ridges over the past ~1000 years indicating continued shoreline progradation at ~0.4 m/yr. A further 13 OSL ages collected from the foredune ridges of Nine Mile Beach barrier detail the evolution of this barrier system and indicate progradation commenced approximately ~8500 years ago. Following this, a steady rate of shoreline advance at 0.14 m/yr was evident to near present-day with one phase of rapid accretion ~5000 years ago. This occurred as the barrier system extended eastward to span the full embayment width which resulted in the redirection of the estuarine channel and the subsequent erosion of previously deposited ridges due to channel migration likely over several thousand years. The eroded sediment may have contributed to ongoing positive sand budget in the embayment and continued shoreline progradation. Barrier 'recycling' was also suggested as a potential driver of progradation at Seven Mile Beach based on the truncated margin of the landward ridges. However, at both sites, the dynamics of possible sediment exchange between the back-barrier and open shoreline requires further detailed modelling. The relatively small river systems in this region supply minimal sand to the coast at these sites, however, there is some minor alongshore sediment supply along the western margin of these deep embayment's. In light of this, these two barrier systems demonstrate the importance of internal morphodynamic thresholds and cross-shore sediment exchange from the shoreface as key drivers of barrier evolution and large-scale coastal change in embayed coastal settings. • Holocene barrier deposition in Tasmania was driven by onshore sediment transport. • Shoreline advance at Nine Mile Beach averaged 0.14 m/yr from 8500 years to present. • Erosion of inner margin of the barrier may have augmented sediment budget. • Large-scale coastal behaviour is explained by internal morphodynamic thresholds. [ABSTRACT FROM AUTHOR]

Abstract: Coastal dunes can act as a method of soft coastal protection against inundation and direct impact of waves during storms if they are substantially large enough in volume to withstand erosion without breaching. However, the time evolution of sand dunes under direct wave impact is not well understood and many available models require site specific calibration and have had limited verification at field scales. Here we test three models of varying complexity in their ability to predict both dry beach erosion volumes and dune to a retreat for an East Coast Low storm event that occurred on the Gold Coast, Australia. The process-based model, XBeach, which models the entire profile was able to reproduce both dune toe retreat and dry beach volume, however, was sensitive to calibration parameters. The two parametric models that only modeled erosion above the initial dune toe position were capable of accurately predicting dune toe retreat, however, under-estimated dry beach erosion volumes. With no calibration, the parametric model proposed by Palmsten and Holman (2012) produced the smallest errors of dune toe retreat with mean error in final dune position of 6.6m, or 18% of the total measured dune retreat. With minimal calibration estimated absolute error in average dune toe retreat was less than 13% of observed retreat for all three models. [Copyright &y& Elsevier]

Abstract: We present the most complete and new high-resolution multibeam bathymetry datasets from the shelf to the basin in the Ribbon Reef region, northern Great Barrier Reef (GBR). Analysis of these data, combined with existing side-scan sonar data provides a detailed morphologic framework of the submarine canyon system and other related features, their spatial distribution, controlling factors on their evolution, and evidence of recent sedimentary activity. Two morphologically different submarine canyon types are recognised: 1) shelf-incised canyons whose heads are indented into the shelf-break at shallow-water depths (about 60 to 80m). These canyons can be single-fed or multi-fed depending on the number of tributaries that merge into the main canyon valley. According to the degree of connection with the shelf, these canyons can be reef-blocked, partly reef-blocked or shelf-connected; 2) slope-confined canyons, which are located at deeper waters in the slope and show a different canyon head morphology. Canyon formation and development of the different canyon types is explained according to a four-phase model. In the first phase, localised slope failures and/or sediment gravity flows may lead to the formation of an initial canyon by retrogressive headward or downslope erosion respectively. These processes continue during the second transitional phase, leading to upslope canyon progression. Finally, canyons breach the shelf-break during a mature stage that represents the more active phase in the canyon evolution. The development of an extensive shelf-edge barrier reef (Ribbon Reefs) represents a fourth phase that conditioned the sedimentary dynamics of the canyons. The location and morphology of this reef barrier determine the type and amount of sediment supply by controlling the connection of the canyon head with the shelf drainage system. Recent canyon activity is evidenced by the presence of erosive and depositional features that include submarine landslides, gullies and rills on the canyon walls and slopes, sandwaves migrating along the canyons floors, and sediment gravity flows deposited on the lower canyons and adjacent basin floor. [Copyright &y& Elsevier]

Abstract: Overwash is an important process in barrier island evolution and its effects on the barrier morphology and sedimentology have been widely studied. However, the short-term sediment dynamics of overwash processes are not well known due to the lack of specific field studies. This paper presents field data that clarify the sedimentary dynamics of overwash processes on different washover morphologies, and determine the factors leading to non-storm overwash occurrence. Two fieldwork campaigns were undertaken during overwash events: GO.1 (winter of 2001), and GO.3 (winter of 2003), on western Barreta Island (Algarve, Portugal). The fieldwork included measurements of oceanographic conditions, overwash flows, morphology variations, mixing depth and sediment transport paths using tracers. The sediment dynamics induced by overwash varied according to the washover morphology (washover plain versus washover lobe). The sediment transport inside the washover plain was different for the two fieldwork campaigns (average mixing depth of 13cm for GO.1 and 6cm for GO.3); however it had similar main stages: Stage 1 — crest accretion, Stage 2 — onshore transport, and Stage 3 — dynamic equilibrium. The sediment transport inside the washover lobe can be characterised by one onshore flow stage, with erosion of the mouth and channel, and accretion on the washover fan. The main factors governing the occurrence of non-storm overwash in the study area were the combined occurrence of: (1) typical winter waves, (2) spring high tides, (3) washover crest below the high-tide level +2m, and (4) absence of prominent beach berm. This study proved that when the proper conditions are generated, non-storm overwash has sediment transport comparable to storm overwash and therefore may be significant for barrier evolution. Further field studies of overwash are needed, principally for more detailed overwash flow velocity measurements, high-frequency morphologic surveys, and barrier groundwater measurements. [Copyright &y& Elsevier]

Abstract: This paper details the historical coastal evolution of the Columbia River littoral cell in the Pacific Northwest of the United States. Geological data from A.D. 1700 and records leading up to the late 1800s provide insights to the natural system dynamics prior to significant human intervention, most notably jetty construction between 1885 and 1917. All reliable surveys, charts, and aerial photos are used to quantify decadal-scale changes at the three estuary entrances and four sub-cells of the littoral cell. Shoreline, bathymetric, and topographic change over three historical intervals—1870s–1920s, 1920s–1950s, and 1950s–1990s—are integrated to provide an understanding of sediment-sharing relationships among the littoral cell components. Regional morphological change data are developed for alongshore segments of approximately 5km, enabling comparisons of shoreline change to upper-shoreface and barrier volume change within common compartments. The construction of entrance jetties at the Columbia River (1885–1917) and Grays Harbor (1898–1916) has profoundly affected the evolution of the littoral cell, and has accentuated the morphological coupling between the inlets, ebb-tidal deltas, shorefaces, and barriers. The jetties induced erosion of the inlets and offshore migration of ebb-tidal deltas. The change in boundary conditions at the entrances enabled waves to rework the flanks of ebb-tidal deltas and supply enormous quantities of sand to the adjacent coasts. Over several decades the initial sand pulses have been dispersed alongshore up to tens of kilometers from the estuary entrances. Winter waves and coastal currents produce net northward sediment transport across the shoreface while summer conditions tend to induce onshore sediment transport and accumulation of the upper shoreface and barriers at relatively high rates. Historical shoreline progradation rates since jetty construction are approximately double the late prehistoric rates between 1700 and the 1870s. Erosion rates of the mid- to lower shoreface to the south of the jettied estuary entrances have typically been greater than the accumulation rates of the upper shoreface and barrier, suggesting that the lower shoreface has been an important source of littoral sediments over decadal and longer time scales. Until recent decades, sediment supply from the ebb-tidal delta flanks and lower shoreface has largely masked the decline in Columbia River sediment supply resulting from flow regulation and dredging disposal practices. With the contemporary onset and expansion of coastal erosion adjacent to the jettied estuary entrances, proper management of dredged sediment is imperative to mitigate the effects of a declining sediment budget. [Copyright &y& Elsevier]

The relationship between alongshore rip channel migration and sediment transport is investigated using time-averaged video images to identify the positions of rip channels at three sites along southern Monterey Bay, California, over 1–3year periods. Daily migration rates are calculated for each site. The basic Coastal Engineering Research Center (CERC) formula for bulk alongshore sediment transport is used to estimate alongshore transport rates at each site, based on hourly input of directional wave spectra measured at an offshore buoy and shoaled and refracted to the nearshore. The wave transformation model is validated by comparison with measured nearshore directional wave spectra in 13m water depth. An expanded CERC formulation that accounts for the additional forcing of alongshore wave height gradients is also tested but rejected. Correlation coefficients between daily rates of calculated alongshore transport and rip channel migration are low: 0.01, 0.44, and 0.38 at the Sand City, Stilwell, and Marina sites, respectively. The problem of digitization noise, associated with video-based rip channel identification, is discussed and several filtering methods are used to increase the signal to noise ratio and obtain improved correlations. Results indicate that higher frequency migration events (on time scales shorter than 8days) will likely be obscured below the digitization “noise floor”, but that longer period oscillations (such as tidal and seasonal cycles) show up clearly in both rip migration and sediment transport datasets. Daily rates are cumulatively summed to generate time series of representative overall rip migration distance and net alongshore transport, and the cumulative summing procedure is shown to be similar to applying a low-pass filter. Mean migration is demonstrated to lag behind net transport in the summertime, suggesting that a minimum level of alongshore forcing is required to generate detectable rip migration. Rip channel migration and net alongshore transport have correlation coefficients that range from 0.76 to 0.94 at the three sites. [Copyright &y& Elsevier]

Abstract: Field measurements of fluid velocities and suspended sediment concentrations were used to investigate the relative role of coherent vortices (related to wave breaking) in suspended sediment dynamics. The measurements were obtained from a barred (intermediate-type) beach and the instrument rig was exposed to a range of wave types during the experiment; including shoaling waves and both spilling and plunging breakers. The time scale of the observed breaker vortices was <<5Hz and thus in the frequency range of wave orbital motion. Coherent breaker vortices were separated from wave orbital motions and incoherent higher-frequency turbulence using a threshold magnitude for the vertical velocity component. Plunging breakers displayed the largest root-mean-square (RMS) and maximum vertical velocities; the latter reaching approximately 1m s− 1. These measurements were made at an elevation of 0.15m above the bed. Given the observed scale of the breaker vortices and the phase match between suspended sediment concentrations and fluid velocities, the turbulence injected into the water column by the plunging breakers played a significant role in suspending bed sediment. On the other hand the role of coherent vortex structures in suspending sediment under spilling breakers and shoaling waves is more limited. RMS vertical velocities under the spilling breakers and shoaling waves in this experiment were respectively a factor 2 and 4 smaller than for plunging breakers. Different phase relationships were observed between the horizontal fluid velocity and vortex-induced sediment suspension for each of the wave types, which may contribute to an explanation of net offshore and onshore sediment transport observed during episodes of beach erosion and recovery, respectively. [Copyright &y& Elsevier]

Abstract: We examined seasonal variations in offshore and longshore sediment transport along the Shimizu coast, Suruga Bay, Central Japan, facing the Pacific Ocean, and considered the relationship between these variations and coastal erosion, based on coastal topographic data and detailed bathymetric data acquired by narrow multi-beam echo soundings in 2004–2007 and analyses of material collected in 2004–2005, combined with wave data in the nearshore zone. Sediment transport in the study area is divided into two seasonal modes. In winter–spring, a period dominated by the winter monsoon, littoral drift is recognized but offshore-directed sediment transport is minimal. Sediment is deposited around coastal structures during this period; consequently, tombolos are formed from gravelly deposits and offshore banks which represent the bulges of the seafloor (in water depths of 3–7m) are formed seaward of the structures due to the deposition of sandy sediment. In summer–autumn, when typhoons commonly strike the coast, we observe pronounced longshore and offshore sediment transport. Consequently, the deposits that form tombolos and offshore banks are intensely eroded. The bulk of the eroded sediments are transported into the submarine canyons in the case that a canyon is located close to the coastline and the shelf is narrow. As a result of this transport, sand ridges and depressions are formed from sandy and gravelly deposits, respectively. The amount of erosion (−34,000m3) from the seafloor where most of the active transport occurred in the study area during summer–autumn approximately corresponds to the amount of nourishment (35,000m3) recorded throughout the entire study area, corresponding to about 50% of the amount of the sediment carried by longshore transport (70,000m3/year). Long-period deep-water waves and high incident waves generated by typhoons during summer–autumn are essential in transporting sediment from the coast to offshore areas; the winter monsoon makes only a minor contribution in this regard. The amount of sediment outflow generated by high-energy waves appears to increase with the accumulation of sediment around offshore breakwaters built in regions with a narrow shelf. Research on offshore-directed sediment transport, as in this study, is important for managing and preserving the nearshore environment (e.g., to examine the budget between supply and outflow), as deposits that flow out into the deep ocean never return to the beach. [Copyright &y& Elsevier]

Abstract: Record flooding on the Santa Clara River of California (USA) during January 2005 injected ∼5millionm3 of littoral-grade sediment into the Santa Barbara Littoral Cell, approximately an order of magnitude more than both the average annual river loads and the average annual alongshore littoral transport in this portion of the cell. This event appears to be the largest sediment transport event on record for a Southern California river. Over 170m of local shoreline (mean high water (MHW)) progradation was observed as a result of the flood, followed by 3years of rapid local shoreline recession. During this post-flood stage, linear regression-determined shoreline change rates are up to −45ma−1 on the subaerial beach (MHW) and −114ma−1 on the submarine delta (6m isobath). Starting approximately 1km downdrift of the river mouth, shoreline progradation persisted throughout the 3-year post-flood monitoring period, with rates up to +19ma−1. Post-flood bathymetric surveys show nearshore (0 to 12m depth) erosion on the delta exceeding 400m3/ma−1, more than an order of magnitude higher than mean seasonal cross-shore sediment transport rates in the region. Changes were not constant with depth, however; sediment accumulation and subsequent erosion on the delta were greatest at −5 to −8m, and accretion in downdrift areas was greatest above –2m. Thus, this research shows that the topographic bulge (or “wave”) of sediment exhibited both advective and diffusive changes with time, although there were significant variations in the rates of change with depth. The advection and diffusion of the shoreline position was adequately reproduced with a simple “one line” model, although these modeling techniques miss the important cross-shore variations observed in this area. This study illustrates the importance of understanding low-frequency, high volume coastal discharge events for understanding short- and long-term sediment supply, littoral transport, and beach and nearshore evolution in coastal systems adjacent to river mouths. [Copyright &y& Elsevier]

Abstract: A geophysical and geological survey (CHAMAK) has been carried out on the Makran accretionary wedge off Pakistan in order to understand the structure of the margin and the recent sedimentary processes in this self-maintaining prism disconnected from the modern Indus inputs (Qayyum et al., 1997; Gaedicke et al., 2002a; Schluter et al., 2002). Morphostructural analysis, based on the interpretation of bathymetric data and backscatter imagery, as well as a 3.5kHz echo-character mapping, allow us to distinguish three structural domains, from north to south, where sedimentary processes differ: (1) the accretionary wedge to the north, (2) the trench and (3) the northern Murray Ridge at the seaward edge of the trench. The accretionary wedge is cut by canyons responsible for an important erosion of the prism especially in the eastern part of the wedge. Within the trench, sediments transported by the canyons generate sediment waves and are transported westward, parallel to the E–W axis of the trench. The eastern part of the abyssal plain is eroded by strong turbidity currents whereas important sediment deposition occurs in the western part of the abyssal plain, as a consequence of a decrease in the current energy. Nearly no mass transport deposits are recognized in the study area except near the ridges forming the accretionary wedge. Small-scale slope failure scars are described. The prevalence of turbiditic processes and the existence of a morphological barrier formed by the Murray Ridge allow the confinement of turbidites within the trench. Migrating sediment waves seem to be common sedimentary structures in this setting. These features might be produced by important velocity decrease of turbidity currents when reaching the trench. [Copyright &y& Elsevier]

Abstract: The objectives of this work are (1) to examine the mechanisms that influence tsunami erosion and deposition mechanisms in the littoral zone via physical simulations of breaking solitary waves over a fine sand beach, and (2) to provide experimental data for validation of numerical models to predict tsunami erosion and deposition processes. The experiments were carried out in a 48.8m×2.16m×2.1m wave flume. The flume was instrumented to observe free surface elevations, cross-shore velocities, suspended sediment concentrations, vertical and cross-shore pore-pressure gradients near the shoreline, and morphological changes. In addition, wave–sediment interactions were observed via underwater video cameras. The results are systematically analyzed to investigate the roles of wave breaking, bore runup, wave drawdown, and wave-induced pore-pressure variations on tsunami erosion and deposition processes. The studies showed that the wave plunging on a thin layer of water prior to reaching the shoreline did not cause much sediment suspension, while the waterjet impinging directly on the beach entrained substantial amounts of sand. The suspended sediments were subsequently pushed up the slope by fluid momentum as the broken wave transformed to a turbulent bore. A small net deposition region was observed near the maximum runup point where both the flow velocity and the water depth were near zero. A significant amount of the sediment transport occurred during the wave drawdown in the form of thick sheet flow, which resulted in net erosion of the shore face and the beach. A hydraulic jump formed near the wave breaking region toward the end of the drawdown, which caused most of the suspended sand to deposit in the wave breaking region. Consequently, breaking solitary waves over a sloping fine sand beach led to net erosion of the shore face and the beach, net deposition in a small region immediately seaward of the max excursion point, and net deposition in the wave breaking zone. [Copyright &y& Elsevier]

Abstract: A field experiment was conducted on a high energy sandy beach (Truc Vert, France) to examine swash zone processes and shoreline erosion–accretion in response to changing wave and tide conditions. Beachface morphological changes were measured at the swash-by-swash timescale using an array of ultrasonic bed-level sensors and at the tidal timescale through total station surveys. Hydrodynamic and sediment dynamic data were collected using arrays of pressure transducers, electromagnetic current meters, optical backscatter sensors and total load sediment traps. Data were collected for 16 consecutive days (33 tides) over a spring–neap–spring tidal cycle with offshore significant wave heights of 1–4m and periods of 5–12s. The swash motion was predominantly at infragravity wave frequencies. Over the measurement period, the upper beach experienced phases of accretion, erosion and stability. Trapped sediment loads for the uprush and backwash were predicted reasonably well by cross-shore velocity skewness, but the prediction of net transport over individual swash events by velocity-based models was more problematic, particularly lower in the swash zone where swash interactions were more prevalent. Net sediment fluxes over individual swash events often exceeded 100kg per unit meter beach width and such rates were only one order of magnitude less than the net transport typically experienced across the high tide swash zone over complete tidal cycles. Upper beach erosion–accretion at the tidal timescale was reasonably well predicted by the Dean criterion based on offshore wave steepness and dimensionless fall velocity, but the beach gradient also played a significant role in controlling the occurrence of erosion and accretion. [Copyright &y& Elsevier]

Abstract: Laboratory experiments using steady flows and simulated tidal flows were conducted to evaluate two conflicting paradigms for cohesive sediment transport: mutually exclusive vs. simultaneous erosion and deposition. Due to the secondary flow and skewed distribution of bed shear stress (τ b), the deposition space is mostly confined to the inner wall of an annular flume. The area of deposition (or the length of deposition because of the axially symmetrical flow) provides an indicator to determine when deposition at the sediment–water interface starts. The direct observation of deposition stemming from the inner corner suggests that a critical shear stress for deposition (τ cd =0.03–0.06 Pa) does exist. Changes in deposit length and depth-averaged suspended sediment concentration (SSC) under simulated tidal cycles demonstrate that deposition can happen only in tidal decelerating phases when local τ b is less than τ cd. The exclusive paradigm incorporated with the correct erosion threshold (τ ce) profile and erosion behavior could explain changes in laboratory- and field-observed depth-averaged SSC under all tidal regimes. [Copyright &y& Elsevier]

Abstract: Field measurements reported in the literature demonstrate that suspended sediment transport due to infragravity wave motions can sometimes be very large and dominate the net sediment transport at a given measurement location within the surf zone. At other times, however, this transport component is insignificant. Moreover, infragravity transport directions are inconsistent across the shoreface. This study tests the hypothesis that net sediment transport caused by infragravity waves may be due to advection (at infragravity frequencies) of sediment that has been suspended by breaking wind/swell waves. It is shown that infragravity sediment transports are onshore directed at the landward side of relative (incident) wave height maxima, and offshore directed at the seaward side of such maxima. If a longshore infragravity wave structure exists, such as in the case of standing edge waves, the advection process can create a perturbation of the bar crest and/or generate a crescentic bar. These results provide support for the template model for crescentic bar formation, first proposed by Bowen and Inman [Bowen, A.J. and Inman, D.L., 1971. Edge waves and crescentic bars. J.Geophys.Res., 76, 8662–8670] although the template mechanism is distinctly different from the template originally suggested and morphodynamic feedbacks between the evolving bar perturbations and the forcing mechanisms are important. [Copyright &y& Elsevier]

Abstract: The morpho-sedimentary evolution of a pure gravel beach step over a tidal cycle is examined during fairweather conditions using detailed measurements of nearshore hydrodynamics, morphological and sedimentary change, and nearshore sediment transport. The characteristics of the beach step are analysed with specific reference to the concurrent dynamics of the beachface, a departure from previous studies which have treated the step as a feature isolated from the nearshore region as a whole. The step and berm are both accretionary features strongly linked to tidal stage, yet their temporal evolution is independent, the relaxation time of the berm being linked to the spring–neap tidal cycle, and that of the more transient step linked to the semi-diurnal tide. Over this time-scale the beachface is a closed sedimentary unit, although the beach step may be differentiated from the beachface using sedimentary moments. Indeed, despite the location of the step in the region of wave breaking, it has relatively stable sedimentology, remaining characteristically coarser and more leptokurtic than the swash zone. Co-spectral analysis between nearshore bed motion and cross-shore current velocity reveals that significant nearshore sediment transport occurs at sub-incident frequencies in response to wave groups. Motion of the nearshore bed is not a linear function of velocity magnitude or direction, so it is likely that there is a role for the various mechanical properties of the bed. Therefore a better description of nearshore sediment transport in the region of the beach step would require instantaneous sediment size information, allowing the use of a time-variant friction factor. [Copyright &y& Elsevier]

Abstract: The sedimentary processes acting over an intertidal flat (Hythe, UK) located in Southampton Water, Hampshire, UK are investigated on the basis of hydrodynamic, morphological and sediment transport field measurements. Bed level changes, patterns of suspended sediment transport and shell movement over the tidal flats were examined in order to identify sediment transport pathways and salt marsh–mudflat morphological changes. Overall, sediment transport patterns at Hythe can be described in terms of suspended sediment and bedload-shell transport. The hydrodynamic complexity of the tidal flow over the flats determines the patterns of suspended sediments transport. During the young flood phase, tidal currents present a SW orientation (shoreward). About 1 h into the flood, a change occurs and the currents start flowing in a SE direction (estuary mouthward). This veering of the tidal current controls the hydrodynamic pattern over the mudflat inducing sediment transport towards the estuary mouth. Conversely, shell tracer experiment showed a net landward movement. Shells are transported over the mudflat, deposited at the base of the cliff, and eventually transported over the salt marsh where they form extensive chernier deposits. Shell transport rates can reach up to 0.7 m/tide over the upper mudflat. Shell movement over the salt marsh (on cheniers) occurred only during storms (up to 3 m in a storm event). Shell-induced erosion can become an important parameter on morphological changes of a coastal area. Shell transport and deposition over the salt marsh surface can contribute to vegetation deterioration, as shell deposits migrate over the marsh surface. As a result, the seaward limit of the salt marsh showed deteriorated vegetation, which leads to scouring and consequent surface lowering. In terms of bed level changes, no seasonal pattern was observed. A relationship between mudflat bed erosion and cliff retreat is suggested. During periods of high cliff erosion there was a tendency for the mudflats to be stable and, conversely, mudflat bed erosion was greatest when cliff retreat rates were lowest. Hence, morphological characteristics of Hythe intertidal area appear to be controlled by a combination of prevailing hydrodynamic conditions and shell transport over the salt marsh. [Copyright &y& Elsevier]

Abstract: Keppel Bay is a macrotidal embayment on a tectonically stable, tropical coast, which links the Fitzroy River with the Great Barrier Reef continental shelf. Estuaries and deltas act as conduits between catchments and inner shelf environments. Therefore, understanding sediment transport pathways in these complex systems is essential for the management of ecosystems such as coral-reefs that are potentially vulnerable to enhanced river sediment loads. Furthermore, the morphology and sediment dynamics of subtidal sand ridges and dunes are relatively poorly characterised in macrotidal estuaries, particularly in turbid, episodic systems such as the Fitzroy River and Keppel Bay. Our sedimentological analysis of seabed samples, shear-stress modelling and three-dimensional acoustic imaging reveals that Keppel Bay is a mixed wave- and tide-dominated estuarine system. Areas of sediment starvation and shoreward transport characterise the offshore zone, whereas a complex of both active and relict tidal sand ridges, and associated subaqueous dunes, dominate the relatively protected southern Keppel Bay. Transport within this region is highly dynamic and variable, with ebb-dominated sediment transport through tidal channels into the outer bay where there is a switch to wave-dominated shoreward transport. Ultimately, bedload sediments appear to be reworked back inshore and to the north, and are gradually infilling the bedrock-defined embayment. Our characterisation of the Keppel Bay system provides a detailed example of the physiography of the seaward portion of a tide-dominated system, and shows that sediment transport in these areas is influenced by a variable hydrodynamic regime as well as relict channels and bedrock topography. [Copyright &y& Elsevier]

Abstract: The formation and spatial evolution of Chandeleur Island, Louisiana, has been investigated extensively during the past several decades. No significant evaluation of the longshore sediment system, which is instrumental in the island''s evolution and morphodynamic maintenance, has been completed. This paper provides the first quantitative description of the longshore transport system that operates along this transgressive, overwash-dominated barrier island system. The net longshore sediment transport system was investigated via the wave refraction model, WAVENRG, which provided estimates of the transport volumes and drift directions alongshore. Surficial samples were collected from the foredune, midtide and step environments in an effort to characterize the sediments along the island and determine if textural or compositional trends have developed in response to a predicted longshore sediment transport system. Data obtained during this research indicate that the longshore transport system along Chandeleur Island is characterized by a bi-directional drift system, with drift directed both north and south from a nodal point located in the south-central portion of the barrier island. Analysis of the predicted transport volumes indicates that the degree of wave refraction, and therefore the breaker angle, is more instrumental in controlling the alongshore volume rate of sediment transport than the breaker wave heights. Additionally, a larger magnitude of sediment transport is predicted in the southern portion of the barrier, which is in a greater state of deterioration than the north and central portion of the island. This apparent contradiction indicates that factors such as a variable subsidence rate along the island are contributing to the alongshore geomorphology. No significant textural or compositional trends were identified alongshore. This absence of granulometric trends is attributed to the lack of variability of the sediments that comprise the barrier and the frequency of overwash events which occur on this low-profile island. [Copyright &y& Elsevier]

Abstract: High frequency measurements of water depth, current velocity and suspended sediment concentration were used to investigate sediment transport processes in the swash zones of a dissipative beach and a steeper (intermediate) beach. Infragravity frequency motions dominated velocity spectra of the dissipative beach swash, while incident wave frequencies dominated the velocity spectrum of the intermediate beach swash. Velocity variance, the ratio of local wave height to water depth, mean bed shear stress and the mean friction velocity were greater on the intermediate beach. Mean suspended sediment concentrations were an order of magnitude greater on the intermediate beach. Infragravity frequencies dominated the oscillatory component of sediment transport on the dissipative beach. Incident wave frequency sediment transport dominated the intermediate beach. A maximum in the net shoreward transport occurred in approximately the mid swash zone on both beaches, suggesting accretion in the shoreward half of the swash, and erosion in the seaward part of the swash. Net sediment transport rates were lower on the ebb tide than on the flood tide, despite similar incident wave conditions. [Copyright &y& Elsevier]

Abstract: Submarine channels have long been considered analogous to meandering fluvial channels due to their similar planform geometry, and this has given rise to strong analogies in terms of the fluid dynamics of these channel types. However, there is a paucity of direct measurements detailing the structure of velocity or sediment concentration, and nothing is known about the structure of secondary flow, within submarine channels. Within fluvial channels, secondary circulation has been shown to be an important control of erosion, deposition, lateral sediment transport and overall bend stability. This paper presents a series of experiments in which saline gravity currents flowed through a submerged, fixed-form, sinuous channel model. Ultrasonic Doppler velocity profiling provided high-resolution, three-dimensional visualisation of flow fields, thereby allowing the first quantitative visualisation of velocity profiles and secondary flows of a saline gravity current within a sinuous submarine channel. The same model was also used to measure the structure of flow within a subaerial channel, thereby providing a detailed comparison between a submarine and fluvial channel. The data reveal that secondary flow cells in submarine channels are best developed at bend apexes and that the basal component of the flow cell moves from the inside to the outside of the bend, in a reversed direction to that expected from models of fluvial bend flow. These results are of prime importance when assessing the validity of comparisons between submarine and fluvial channels, and the role of secondary flow cells in the migration and evolution of meander bends. This work demonstrates that the fundamental flow processes controlling the evolution and migration of submarine and fluvial channels may be very different, and suggest that the form and evolution of submarine channels may also show different properties to their fluvial counterparts. [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: An extensive barrier-spit system 20 to 30 km long developed on the delta front platform of the Ba lat Delta within a relatively short period (10–20 years). However, it was not evident whether the formation was related to river floods, typhoons or calm weather conditions, or to cross-shore or alongshore sediment transport mechanisms. Therefore a process-based numerical model that simulates sediment transport and morphologic changes by waves, tides, wind, and river flow, is used to analyze the processes that govern this barrier formation. The mechanism that initiates the barrier formation is concluded to be onshore transport by wave asymmetry of sediment previously transported seaward in the buoyant river plume. The main mechanism that counteracts the barrier formation is probably destruction of the barrier by river flow. During the subsequent transformation from a subaqueous barrier into a sub-aerial barrier-spit system, overwashes and alongshore sediment transport become increasingly important. This spit system therefore appears to be dominated by alongshore processes, even though its initial formation is more strongly regulated by cross-shore processes. The importance of cross-shore processes results in a minor contribution of typhoons to the initial formation of these barriers. Typhoons are not very important to destruction of barriers as well, because wave energy is gradually dissipated over the gentle offshore profile, which in turn results from river plume sedimentation. [Copyright &y& Elsevier]

Abstract: Using the average directions of the principal wavefronts that approach the northeastern Brazilian coast, which are coincident with the directions of the prevailing winds, a wave climate model was defined, for approximately 3000 km of coast by construction wave refraction diagrams. A resulting sediment transport model that was obtained by numerical modeling starting with refraction diagrams, taking into account the wave approach angles and their heights permitted the reproduction, on a regional scale, of the sediment dispersion pattern. Several drift cells were identified, the limits of which were based on alterations in the direction or intensity of potential net longshore drift. Although also dependent on other factors such as the supply of fluvial sediments to the coastal zone and to wind activity, the coastal sections that present progradation, erosion or non-deposition, can be reasonably explained, in a first order approximation, by these variations. As a generalization, geomorphic drift indicator match patterns of regional scale sediment dispersal. [Copyright &y& Elsevier]

Abstract: The latest Holocene sedimentary record of a cohesive channel and subtidal shoal in the lower Hudson River Estuary was examined to elucidate natural (sea-level rise, sediment transport) and anthropogenic (bulkheading, dredging) influences on the recent morphodynamic evolution of the system. To characterize the seafloor and shallow subbottom, ∼100 km of high-resolution seismic reflection profiles (chirp) were collected within a 20-km reach of the estuary and correlated with sediment lithologies provided by eight vibracores recovered along seismic lines. Sediment geochronology with 137Cs and 14C was used to estimate intermediate and long-term sedimentation rates, respectively, and historical bathymetric data were analyzed to identify regional patterns of accretion and erosion, and to quantify changes in channel geometry and sediment volume. The shoal lithosome originated around 4 ka presumably with decelerating eustatic sea level rise during the latest Holocene. Long-term sedimentation rates on the shoal (2.3–2.6 mm/yr) are higher than in the channel (2 mm/yr) owing to hydrodynamic conditions that preferentially sequester suspended sediment on the western side of the estuary. As a result, the shoal accretes oblique to the principal axis of tidal transport, and more rapidly than the channel to produce an asymmetric cross-section. Shoal deposits consist of tidally bedded muds and are stratified by minor erosion surfaces that seismic profiles reveal to extend for 10s of meters to kilometers. The frequency and continuity of these surfaces suggest that the surficial shoal is catastrophically stripped on decadal-centennial time scales by elevated tidal flows; tidal erosion maintains the shoal at a uniform depth below sea level and prevents it from transitioning to an intertidal environment. Consequently, the long-term sedimentation rate approximates the rate of sea-level rise in the lower estuary (1–3 mm/yr). After the mid 1800s, the natural geometry of the lower Hudson River Estuary changed rapidly in response to engineering works that forced the channel to self-deepen. Analysis of historical bathymetric data indicates that the channel lost an estimated 3×106 tons of sediment between ca. 1939 and 2002 (50,000 tons/yr average) by subaqueous erosion, increasing in depth by as much as 4 m in places. Erosion appears to have been concurrent with systematic bulkheading of the shoreline after ca. 1865, which decreased the estuary surface area by ∼19% overall. Evidently, self-deepening of the channel is a morphodynamic adjustment to reestablish equilibrium cross-sectional area, yet the state of this change locally and elsewhere in the estuary is unknown. Subaqueous erosion documented in this study is a significant source of sediment with implications to the sediment budget and environmental quality of the Hudson River Estuary. [Copyright &y& Elsevier]

Abstract: The processes responsible for sediment transport and morphological change in the intertidal zone of natural beaches are not well known. Consequently, factors determining whether the intertidal beach erodes/accretes or remains stable in the face of significant wave impact, and the mechanisms behind the elusive concept of ‘equilibrium beach slope’ are poorly understood. A field experiment was designed to measure suspended sediment transport in the swash and inner surf zone through successive tidal cycles in the intertidal zone at Egmond Beach, The Netherlands, using a stack of fiberoptic backscatter sensors (UFOBS-7). The experimental period comprised three large storm events, including an extreme storm with offshore significant wave heights in excess of 7 m. Surveys spanning a >1 km long section of the beach as well as observations from an ARGUS video camera system showed that gently sloping shoreline salients (megacusps) were highly stable in position and displayed only minor slope adjustments through the storm period, whereas steeply sloping embayments were eroded significantly. The sediment transport measurements at a shoreline salient indicated that the subdued net beach response was because offshore sediment transport occurring under surf zone conditions at high tide was compensated by onshore sediment transport at low tide when swash zone processes dominated. Such temporally varying, tidally modulated sediment transport rates and directions are suggested to be able to maintain a quasi-equilibrium intertidal beach slope and the results indicate that a negative feedback existed between initial beach slope and net sediment transport patterns. [Copyright &y& Elsevier]

Abstract: Simultaneous high frequency field measurements of water depth, flow velocity and suspended sediment concentration were made at three fixed locations across the high tide swash and inner surf zones of a dissipative beach. The dominant period of the swash motion was 30–50 s and the results are representative of infragravity swash motion. Suspended sediment concentrations, loads and transport rates in the swash zone were almost one order of magnitude greater than in the inner surf zone. The vertical velocity gradient near the bed and the resulting bed shear stress at the start of the uprush was significantly larger than that at the end of the backwash, despite similar flow velocities. This suggests that the bed friction during the uprush was approximately twice that during the backwash. The suspended sediment profile in the swash zone can be described reasonably well by an exponential shape with a mixing length scale of 0.02–0.03 m. The suspended sediment transport flux measured in the swash zone was related to the bed shear stress through the Shields parameter. If the bed shear stress is derived from the vertical velocity gradient, the proportionality coefficient between shear stress and sediment transport rate is similar for the uprush and the backwash. If the bed shear stress is estimated using the free-stream flow velocity and a constant friction factor, the proportionality factor for the uprush is approximately twice that of the backwash. It is suggested that the uprush is a more efficient transporter of sediment than the backwash, because the larger friction factor during the uprush causes larger bed shear stresses for a given free-stream velocity. This increased transport competency of the uprush is necessary for maintaining the beach, otherwise the comparable strength and greater duration of the backwash would progressively remove sediment from the beach. [Copyright &y& Elsevier]

Abstract: Inductively coupled plasma-mass spectrometry (ICP-MS) analyses were carried out on surface sediments and resuspended material. A statistical analysis was performed on the multi-elemental concentrations to identify the source area of the resuspended material collected in the sediment traps from the SE slope of the Faeroe-Shetland Channel (FSC). Results indicate that the material intercepted by the traps has a composition similar to that of surface sediments from depths greater than 550 m. This suggests that particles advected on the slope do not originate from the upper slope or the shelf edge but from a deeper area and that local resuspended material is deposited deeper than 550 m. Multi-elemental and grain size analysis of trap samples from distinct intense resuspension events illustrate differences among samples. These differences were interpreted as a result of the varying intensity of the resuspension mechanism although separate source areas or different resuspension mechanisms cannot be excluded. The identification of the source area of resuspended material is tempered by the homogeneity of the surface sediments in the region, due to the uniform glacial debris deposits, the high-energy currents and the lack of clearly identifiable continental input sources. [Copyright &y& Elsevier]

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]

Abstract: Data from field experiments carried out in the swash zone on two Pacific beaches in Japan were analyzed to determine net sediment transport rates and the resulting foreshore response. The experiments involved artificial modification of the foreshore slope with a bulldozer, either making the slope steeper or milder, after which a wide range of measurements were performed as the slope evolved back towards its equilibrium value under the action of the incident waves. A sediment transport formula was developed to predict the net transport rate over many swash cycles and compared with the derived transport rates from the surveys of the foreshore. This formula was then combined with the conservation equation for sediment volume to yield a mathematical model for simulating the foreshore evolution under varying waves and water level. Predictions by the model were compared to measurements yielding satisfactory agreement, although the optimum values on the main calibration coefficient displayed some variation between experiments. Further analysis of a limited number of cases indicated that this coefficient may be dependent upon the ratio between the incident wave period and the swash period, which characterizes the interaction between individual waves in the swash zone. A simple analytical solution was also derived for a schematized foreshore shape to estimate the typical time scale of the morphological response. [Copyright &y& Elsevier]

The distribution of deposits, sediment transport pathways and processes on the lower Monterey Fan channel and channel-mouth lobe (CML) are studied through the integration of GLORIA and TOBI sidescan sonar data with 7-kHz subbottom profiler records and sediment cores for ground-truthing. The lower Monterey channel is characterised by an up to 30-m-deep channel with poorly developed levees and alternating muddy and silty muddy overbank deposits. The channel is discontinuous, disappearing where gradients are less than about 1:350. Ground-truthing of the large CML shows that the entire CML is characterised by widespread deposits of generally fine sand, with coarser sand at the base of turbidites. Sand is particularly concentrated in finger-like areas of low-backscatter intensity and is interpreted as the result of non-turbulent sediment-gravity flows depositing metres thick massive, fine sand. TOBI sidescan sonar data reveal recent erosional features in the form of scours, secondary channels, large flow slides, and trains of blocks at the distal end of the CML. Erosion is probably related to increasing gradient as the CML approaches Murray Fracture zone and to differential loading of sandy submarine fan deposits onto pelagic clays. Reworking of older flow slides by sediment transport processes on the lobe produces trains of blocks that are several metres in diameter and aligned parallel to the flow direction. [Copyright &y& Elsevier]

Analyses have been undertaken of 68 beach-nearshore profiles spanning the years 1971–1995 to interpret sub-littoral cells of the Nile Delta that developed during cross-shore and alongshore sediment transport. Bottom sediments of these profiles taken along the 240-km length of the delta coastline have been analyzed to determine seabed level changes, textural and heavy mineral concentration distributions. The spatial distribution of seabed depth changes linked with the heavy mineral concentration allows identification of three zones of erosion (source areas) associated with accretion (sink areas). Erosion zones occur off the Nile promontories at Rosetta (−20 to −50 cm/yr), Burullus and Damietta (0 to −20 cm/yr). Accretion ranging from 0 to 40 cm/yr occurs between erosion zones at Abu Quir Bay, the Rosetta saddle, Gamasa embayments and along the western side of the jetty at the Suez Canal entrance, Port Said. This pattern was generally induced from the temporal variability in the direction and intensity of the incoming waves, currents, orientation of coastline, seafloor morphology and local protective structures. The correspondence among patterns of seabed depth change, heavy mineral concentration, and to some extent the texture of seabed sediments refine boundaries of littoral sub-cells of the Nile including sediment paths, sources, sinks, nodal points and zones of sediment transport convergence and divergence. This correspondence is not strongly correlated, as might be expected in this deltaic system where sediment has been recycled between recent and relict seabed settings moving in the alongshore and cross-shore directions. Nevertheless, the present investigation shows that the relationship between seabed level changes, heavy mineral concentration and to some extent mean grain size of the littoral zone can be practically applied in other deltaic settings to interpret sediment transport pathways particularly where there are less relict sediments. [Copyright &y& Elsevier]