wave induced sediment transport and sandbar migration onshore sediment transport and sandbar migration are important to the morphological evolution of beaches but are not well understood here a model that accounts for fluid accelerations in waves predicts the onshore sandbar migration observed on an ocean beach in both the observations and the model the location of the maximum acceleration induced transport moves shoreward with the sandbar resulting in feedback between waves and morphology that drives the bar shoreward until conditions change a model that combines the effects of transport by waves and mean currents simulated both onshore and offshore bar migration observed over a 45 day period

sediment trend models fail to reproduce small scale sediment transport patterns on an intertidal beach a rigorous test is presented of the application of sediment trend models to an intertidal beach environment characterized by bar morphology sediment samples were collected during low tide from a regular grid and their sediment fall velocity distributions obtained using a settling tube were analysed using moment analysis the net sediment transport direction determined from beach surveys hydrodynamic measurements wave ripple observations and sediment transport modelling was compared with predictions by sediment trend models based on the spatial distribution of sediment parameters it was found that the sediment transport pathways and patterns of sedimentation predicted using sediment trend models were at odds with field observations and varied significantly depending on whether surface or sub surface sediment samples were used the sediment trend models are thought to fail because in energetic and morphologically variable beach environments spatial patterns in sediment characteristics are mainly attributed to the presence of different hydrodynamic regions and associated morphology rather than sediment pathways the use of sediment trend models cannot replace the collection of morphological hydrodynamic and sediment transport data in the field to define relationships between flows forms and sedimentation patterns on a dynamic intertidal beach

storm induced response of a nearshore bar system abstract a nearshore bar system was surveyed periodically through a storm and the following recovery period the data showed a very rapid response of morphology to changing wave conditions and allowed various models on bar formation to be tested under low energy conditions prior to the storm a small bar was surveyed 13 m offshore both the high reflectivity of the beach and the cross shore distance to the bar are consistent with a model of sediment convergence at the node or antinode of a standing wave of incident period such a small scale bar may be a common feature on beaches with steep foreshores and more gentle offshore slopes with the increase in wave height during the storm the bar became better developed and migrated offshore at rates up to 2 2 m h 1 the bar maintained its form in that the ratio of trough depth to crest depth h t h c remained roughly constant the bar was in no way related to processes which would cause the convergence of sediment in the breaker zone through most of the storm the bar crest distance offshore was typically only 10 of the surf zone width analysis of the bar distance offshore in terms of a standing wave motion showed that the causative wave period must have been much longer than that of incident waves probably on the order of a minute surf zone wave data showed significant energy in the infragravity band at these periods although no definite link has been made after the height of the storm the bar had a crescentic morphology the development of this morphology occurred very rapidly with parts of the bar migrating onshore at rates up to 1 2 m h 1 in contrast to the storm during the recovery period h t h c varied by nearly a factor of three analysis of the offshore and longshore length scales showed the bar to be similar to one which would be generated by a standing mode 1 edge wave of period on the order of one minute

suspended sediment transport and nearshore bar formation on a shallow intermediate state beach abstract estimates of cross shore suspended sediment flux were obtained during a 3 day storm event on the north sea coast of denmark the suspended sediment flux estimates were correlated with volumetric beach change as registered at 28 permanently deployed survey rods crossing the intertidal beach and inner surf zones during this storm a nearshore bar initially migrated onshore and welded to the beach face at its updrift end subsequently a new bar formed on the seaward slope of the former suspended sediment transport recorded using optical backscatter sensors and electromagnetic current meters corresponded well qualitatively with the morphological evolution indications are that such measurements may account for a significant fraction of the actual cross shore sediment transport the onshore migration of the nearshore bar was the result of onshore directed mean currents associated with a cell circulation renewed bar formation took place when this circulation was locally replaced by an offshore directed mean current undertow suspended sediment transport due to oscillatory waves at incident and infragravity frequencies was generally subordinate to the mean transport

controls on sediment dynamics and medium term morphological change in a barred microtidal beach cala millor mallorca western mediterranean abstract this paper describes the sedimentological and morphological evolution of a microtidal beach over an eight month period under varying hydrodynamic conditions during the monitoring a set of transverse to crescentic bars migrated onshore welded to the upper beach and then they were flattened under energetic wave conditions the grain size distribution of surficial sediments did vary consistently across the beach profile and temporal changes in the sedimentology were mostly related to the seasonal morphological response from our results we can state that changes in the beach morphology resulting from erosion and deposition might induce at least to some degree concomitant changes in the beach when hydrodynamics exceed some intensity and duration levels hs 1 m wave climate rather than wave forcing is the major control on sediment and morphological change co variation

field observations of the fluid granular boundary layer under near breaking waves numerous synchronized time series from video cameras pressure sensors current meters and hot film anemometers on natural beaches show that boundary layer development under the crest of near breaking waves can be idealized as a process composed of three distinct regimes here referred to as streaking roiling and pluming the roiling and pluming regimes fail to develop under the trough as a consequence there is a pronounced asymmetry in instantaneous sand transport and boundary layer phenomena between the wave crest and trough however laboratory waves with field scale periods and wave heights over thin sand beds do not exhibit this crest trough boundary layer asymmetry indicating that a critical element of similitude is absent in laboratory experiments we suggest that wave induced boundary ventilation is responsible

divergent response of an intertidal swash bar this paper examines the processes responsible for the morphodynamics of an intertidal swash bar at skallingen denmark during seven successive storms one with a large surge of 3 02 m dnn during this period a subtidal bar migrated landward onto the foreshore and continued to migrate across the intertidal zone as a swash bar the onshore migration of the inner subtidal bar resulted from the erosion of sediment from the upper foreshore and dune ramp during the large storm surge that was transported seaward causing the landward displacement of the bar through accretion on the landward slope the magnitude and direction of suspended sediment transport within the intertidal zone and more specifically at and close to the crest of the swash bar varied with the ratio of both the significant hs and average havg wave heights to the water depth hcr at the swash bar crest the local depth minimum the transition between onshore and offshore suspended sediment transport was associated with the average wave of the incident distribution breaking on the swash bar crest havgh 0 33 while the onshore directed transport was largest at infragravity frequencies sediment resuspension was best explained by the skewed accelerations under the surf bores offshore transport was dominated by the cross shore mean currents undertow that developed when the significant wave of the distribution broke on the swash bar crest hsh 0 33 and weakened as the average wave of the distribution started to break at the crest havgh 0 33 and the surf zone approached saturation in contrast to subtidal bars the swash bar at skallingen exhibited a divergent behaviour with respect to the cross shore position of the breaker zone migrating onshore when the average wave broke seaward of the crest and migrating offshore when the average wave broke landward of the crest copyright 2006 john wiley sons ltd

sediment transport on dissipative intermediate and reflective beaches abstract in this paper we review and synthesize field measurements of suspended sediment transport on the shoreface of dissipative intermediate and reflective beach states the morphodynamic beach state continuum was originally established in the 1970s but at the time only hydrodynamic processes and morphologies in these various states were described since the early 1980s when sensors capable of resolving suspended sediment concentration at intra wave time scale became available many studies have examined suspended sediment transport by waves and currents on the shoreface the synthesis of this work shows that the two end states in the morphodynamic continuum which are the dissipative and reflective states exhibit relatively small rates of cross shore sediment transport and weak gradients in that transport which both ensure that the nearshore morphology is relatively stable the intervening intermediate beach states typically exhibit prominent bar topographies and in these states strong morphodynamic feedbacks between hydrodynamic processes and morphology create locally large transport rates and sharp transport gradients which is the reason for the dynamic nature of these beach states transport processes driving sediment onshore and offshore within beach states are discussed as well as the transport processes responsible for state transitions

a simple model for interannual sandbar behavior time and length scales of beach variability have been quantified using 16 years of beach surveys sampled at the army corps of engineers field research facility located on the u s atlantic coast between 50 and 90 of the bathymetric variability at this site was explained by alongshore uniform response over the approximately 1 km alongshore span of the surveys although the incident wave height variance was dominated by frequencies at or higher than 1 cycle yr more than 80 of the bathymetric variance at all cross shore locations was explained by frequencies 1 cycle yr interannual cycles consisting of sandbar formation migration and decay contributed to the low frequency variability the observed behavior can be explained by a simple heuristic model the model assumes that bars migrate toward a wave height dependent equilibrium position this position was shown to coincide with the wave breakpoint additionally the rate of bar response is taken to be variable and was empirically determined to be proportional to the wave height cubed the net effect of a variable response rate is to shift the expected long term mean sandbar position offshore toward the equilibrium position associated with the largest waves the model explained up to 80 of the observed bar position time series variance and up to 70 of the variance of bar crest velocity time series which were extracted from three different sandbars characteristic bar response times related to the inverse of the response rate were found to be long relative to the characteristic timescale of the forcing 1 year in our case as a result transient response i e bar position far from equilibrium tended to persist for many cycles of the forcing transient bar behavior appears in the observations when bars formed near the shoreline or when outer bars decayed and inner bars faced a changed wave climate while the present model is able to explain the evolution of these transients it does not contain a mechanism for their introduction

observations of sand bar evolution on a natural beach waves currents and the location of the seafloor were measured on a barred beach for about 2 months at nine locations along a cross shore transect extending 255 m from 1 to 4 m water depth the seafloor location was measured nearly continuously even in the surf zone during storms with sonar altimeters mounted on fixed frames the crest of a sand bar initially located about 60 m from the shoreline moved 130 m offshore primarily when the offshore significant wave height exceeded about 2 m with 1 5 m of erosion near the initial location and 1 m of accretion at the final location an energetics type sediment transport model driven by locally measured near bottom currents predicts the observed offshore bar migration but not the slow onshore migration observed during low energy wave conditions the predicted offshore bar migration is driven primarily by cross shore gradients in predicted suspended sediment transport associated with quasi steady near bottom offshore flows these strong 50 cm s currents intensified near the bar crest by wave breaking are predicted to cause erosion on the shoreward slope of the bar and deposition on the seaward side the feedback amoung morphology waves circulation and sediment transport thus forces offshore bar migration during storms

numerical modeling of flow and scour at pipelines a numerical model for the description of fluid flow and suspended and bed load sediment transport is presented density effects are included in the momentum reynolds equations and in the turbulence kappa and epsilon equations changes in bed levels are calculated from sediment continuity and the finite element grid is adapted to the geometry the reynolds equations and the transport equation for suspended sediment are solved numerically using a taylor galerkin finite element method the flow at a surface mounted cylinder in a steady flow is predicted in good agreement with experiments periodic vortex shedding from a cylinder placed above a rigid bed is predicted in good agreement with laboratory experiments provided that sufficiently detailed grids approximately 5 000 nodes are used scour calculations are performed for a cylinder in a steady flow with its underside placed at the level of the original flat bed predicted scour at a pipeline in steady flow is in good agreement with laboratory measurements reported in the literature

sedimentation induced burial of subsea pipelines observations from field data and laboratory experiments abstract sediment transport induced changes to the embedment of three 26 km long sections of subsea pipeline are analysed and subsequently explained using model scale experiments rather than the scour and scour induced sinking and sagging traditionally thought to dominate post lay pipeline spanning and embedment change the change for these pipelines is shown to be caused by sedimentation the pipelines traverse a range of metocean and soil conditions the variation in embedment correlates well with the variation in metocean conditions with most change occurring in an area where multidirectional high velocity short duration flows associated with internal waves propagate at near perpendicular angles to the pipeline to understand the mechanism driving these changes a series of model scale tests in o tube flumes have been completed under flow conditions mimicking those recorded in the field good agreement is found between the field and laboratory results both in terms of the process timescale and the post sedimentation profile the consistency of the embedment changes between the pipelines their correlation with metocean conditions and the ability to replicate these changes in model scale tests suggests that such changes can be accounted for in more effective pipeline design spans are relatively rare along the pipelines but where they do occur fish rather than scour are shown to be the principal agent of span formation

nearshore bars and the break point hypothesis abstract the set of hypotheses calling for bar formation at the break point was tested with field data during two different experiments waves were measured across the surf zone coincident with the development of a nearshore bar we use a criterion based on the wave height to depth ratio to determine the offshore limit of the inner surf zone during the first experiment the bar became better developed and migrated offshore while remaining well within the inner surf zone during the second experiment the surf zone was narrower and we cannot rule out the possibility of break point processes contributing to bar development we conclude that bars are not necessarily coupled with the break point and can become better developed and migrate offshore while being in the inner surf zone landward from initial wave breaking in the outer surf zone

swash zone sediment fluxes field observations abstract this paper describes newly obtained high frequency observations of beach face morphological change over numerous tidal cycles on a macrotidal sandy beach made using a large array of ultrasonic altimeters these measurements enable the net cross shore sediment fluxes associated with many thousands of individual swash events to be quantified it is revealed that regardless of the direction of net morphological change on a tidal time scale measured net fluxes per event are essentially normally distributed with nearly equal numbers of onshore and offshore directed events the majority of swash events cause net cross shore sediment fluxes smaller than 50 kg m 1 and the mean sediment flux per swash event is only o 1 kg m 1 leading to limited overall morphological change however much larger events which deposit or remove hundreds of kilograms of sand per meter width of beach occur at irregular intervals throughout the course of a tide it was found that swash swash interactions tend to increase the transport potential of a swash event and the majority of the swash events that cause these larger values of sediment flux include one or more interactions the majority of the larger sediment fluxes were therefore measured in the lower swash zone close to the surf swash boundary where swash swash interactions are most common despite the existence of individual swash events that can cause fluxes of sediment that are comparable to those observed on a tidal time scale frequent reversals in transport direction act to limit net transport such that the beach face volume remains in a state of dynamic equilibrium and does not rapidly erode or accrete

nearshore sandbar migration field observations suggest that onshore sandbar migration observed when breaking wave driven mean flows are weak may be related to the skewed fluid accelerations associated with the orbital velocities of nonlinear surface waves large accelerations both increases and decreases in velocity magnitudes previously suggested to increase sediment suspension occur under the steep wave faces that immediately precede the maximum onshore directed orbital velocities weaker accelerations occur under the gently sloping rear wave faces that precede the maximum offshore directed velocities the timing of strong accelerations relative to onshore flow is hypothesized to produce net onshore sediment transport the observed acceleration skewness a measure of the difference in the magnitudes of accelerations under the front and rear wave faces is maximum near the sandbar crest the corresponding cross shore gradients of an acceleration related onshore sediment transport would cause erosion offshore and accretion onshore of the bar crest consistent with the observed onshore migration of the bar crest furthermore the observations and numerical simulations of nonlinear shallow water waves show that the region of strongly skewed accelerations moves shoreward with the bar suggesting that feedback between waves and evolving morphology can result in continuing onshore bar migration

sea level periodic change and its impact on submarine groundwater discharge rate in coastal aquifer abstract this study focused on the interaction between groundwater and seawater and the effect of temporal scale of sea level fluctuation on submarine groundwater discharge sgd rate the numerical code feflow diersch 2005 was used to evaluate the influence of periodic changes in sea level on an increase in sgd at various time scales from diurnal to glacial cycles simulation results showed that not only amplitude but also period of the sea level fluctuation controls total amount of sgd the increase ratio of recirculated submarine groundwater discharge rsgd was found to generally be proportional to the amplitude of sea level and the square root of specific storage of an aquifer while inversely proportional to the square root of hydraulic conductivity of an aquifer and period of sea level fluctuation a nondimensional number p that incorporates combined effect of sea level oscillation and aquifer properties is used to represent the magnitude of periodic forcing from sea boundary into an aquifer as a mechanism for enhancement of rsgd simulation results demonstrate that increase ratios of rsgd are well fitted by an exponential curve as a function of p and variations in rsgd occur only when p exceeds a critical number the dimensionless inland recharge rate where recharge rate is divided by hydraulic conductivity was shown to be important in determining the critical number this implies that sea level fluctuation does not lead to enhancement of rsgd until the specified condition is reached and groundwater recharge rate and aquifer hydraulic conductivity are the key factors controlling the increase of rsgd

generalized time scale for wave induced backfilling beneath submarine pipelines abstract this paper presents 25 new laboratory experiments involving the wave induced backfilling of wave induced scour holes beneath submarine pipelines so called wave to wave backfilling scenarios the experiments complement the previous 8 wave to wave backfilling experiments of fredsoe et al as well as recent current to wave backfilling experiments of bayraktar et al it is found that the wave induced backfilling time scale is generally an order of magnitude larger than for scour and is relatively insensitive to the initial current or wave induced pre backfilling scour profile based on this the data sets involving wave induced backfilling are collectively analyzed resulting in a new generalized expression for estimating the wave induced backfilling time scale beneath pipelines in the live bed regime this expression accounts for primary dependence on the shields parameter as well as secondary dependence based on the difference between the estimated or known initial and expected final equilibrium scour depth due to the backfilling wave condition

bar trough generation on a natural beach mechanisms for bar trough generation are examined using velocities measured in the field applied to the bowen 1980 bailard 1981 energetics based sediment transport model measurements consist of a cross shore array of nine electromagnetic current meters spanning the surf zone and daily bathymetric surveys during a 10 day period during which two storms occurred when the bathymetry evolved from a three dimensional terrace to a well developed linear bar the model predicts bed and suspended load transport separately based on various velocity moments the velocities are partitioned into mean currents low frequency infragravity and shear instabilities 0 05 hz to determine the relative importance of various mechanisms to the total transport velocity moments are computed over 90 min intervals to resolve tidal fluctuations tidal signatures were apparent in all modes of transport predicted transport rates are integrated and compared with daily cross shore bathymetric profiles averaged over a 400 m length of beach the suspended load terms were an order of magnitude greater than bed load terms owing to the low fall velocity of the fine grain sand within the surf zone model results for this experiment indicate the dominant mechanism for bar development was sediments mobilized by the strong longshore current and incident short waves within the surf zone and transported offshore by the mean undertow and shoreward transport onshore due to short wave velocity skewness using standard coefficients the model correctly predicted the first order movement of the bar during storms but underpredicted trough development and did not always perform well during mild wave conditions

relaxation time effects of wave ripples on tidal beaches 1 seabed roughness due to wave ripples is a key factor in controlling sediment transport processes in the nearshore zone roughness is commonly considered a function of the ripple geometry which in turn can be predicted from sediment and hydrodynamic parameters existing ripple predictors consider the bed morphology to be in equilibrium with the hydrodynamics whereas recent laboratory measurements show that the time scale for ripple development is of the order of tens of minutes to hours here we show that wave ripples on tidal beaches are significantly affected by relaxation time effects with ripple height and length progressively increasing during the rising tide and remaining constant during the falling tide moreover we examine the ripples in the context of existing empirical models and suggest how the temporal evolution over a tidal cycle may be predicted

wave induced sediment transport and onshore sandbar migration the 25 m onshore migration of a nearshore sandbar observed over a 5 day period near duck nc is simulated with a simplified computationally efficient wave resolving single phase model the modeled sediment transport is assumed to occur close to the seabed and to be in phase with the bottom stress neglected intergranular stresses and fluid granular interactions likely important in concentrated flow are compensated for with an elevated relative to that appropriate for a clear fluid model roughness height that gives the best fit to the observed bar migration model results suggest that when mean current induced transport is small wave induced transport leads to the observed onshore bar migration based on the results from the simplified phase resolving model a wave averaged energetics type model e g only moments of the near bottom velocity field are required with different friction factors for oscillatory and mean flows is developed that also predicts the observed bar migration although the assumptions underlying the models differ the similarity of model results precludes determination of the dominant mechanisms of sediment transport during onshore bar migration

suspended sediment transport mechanisms in high energy swash abstract measurements of suspended sediment concentration at three heights above the bed and cross shore velocity at a single height were obtained using miniature optical backscatter sensors and a miniature electromagnetic current meter from the swash zone of a high energy macrotidal dissipative beach time series from relatively low h s 0 8 m and high h s 2 2 m energy conditions were chosen for analysis possible onshore and offshore sediment transport mechanisms are identified as a sudden offshore to onshore velocity transition and turbulence in the swash front leading to subsequent onshore advection by the uprush and b low frequency high velocity backwashes exceeding a certain threshold for sediment suspension these mechanisms are related to the velocity field through skewness and asymmetry an increase in negative infragravity skewness in high energy conditions suggests a potential shift towards offshore net transport time averaged vertical profiles of cross shore suspended sediment flux were calculated from the velocity and concentration time series these show a tendency towards offshore transport in high energy conditions particularly at low levels in the water column the actual sediment fluxes are believed to be more offshore than those calculated one reason for this discrepancy is the inability of the instruments to detect swash activity at very low levels in the water column

morphodynamics of intertidal bars in wave dominated coastal settings a review abstract intertidal bar systems are ubiquitous features on wave dominated beaches in coastal settings with a significant 1 m tidal range depending primarily on the wave conditions and the tidal range and to a lesser extent on the nearshore gradient they can assume a variety of forms slip face bars represent the most pronounced and dynamic intertidal bar morphology and are generally found on their own around the mean high tide level they usually form low on the intertidal beach after storm induced beach erosion and develop into a berm under prolonged calm wave conditions low amplitude ridges and sand waves represent multiple bar morphologies the bars occur across the entire intertidal profile and they remain present throughout the year multiple intertidal bars tend to be rather subdued and relatively static especially sand waves and their origin remains unclear the morphological response of intertidal bars to changing wave conditions is largely forced bars build up and migrate onshore under calm waves and are flattened and may migrate offshore during storms the morphological response is however significantly affected by relaxation time effects and morphological feedback particularly on beaches with multiple intertidal bars despite their morphological differences the intertidal bar types exhibit pronounced similarities in their morphodynamics sediment transport processes and morphological response are principally controlled by the tidal water levels on the beach because these together with the offshore wave energy level and the beach morphology determine the type intensity and duration of the wave processes operating on the cross shore profile it is the dominant importance of tidal water level variations and wave processes in shallow water depths swash and surf zone bores rather than wave height variability and deeper water wave processes breaking and shoaling waves that constitutes the main difference between intertidal and subtidal bar morphodynamics

swash zone sediment dynamics a comparison of a dissipative and an intermediate beach 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

fluid acceleration effects on suspended sediment transport in the swash zone 1 suspended sediment concentrations and fluid velocities measured in the swash zone of a high energy steep beach were used to investigate the importance of fluid accelerations to suspended sediment transport swash flow acceleration was nearly constant at about one half downslope gravitational acceleration with two important exceptions we observed strong short lived periods of accelerating uprush at the beginning of the swash cycle and decelerating backwash at the end of the swash cycle magnitudes of both approximately twice that of the expected downslope gravitational acceleration interestingly spikes in suspended load followed the anomalies in acceleration in a way that was not apparent from the nearly symmetric in magnitude ensemble averaged velocity time series suspended load values were largest during accelerating uprush associated with the shoreward propagating turbulent bore or swash front during backwash suspended loads were generally not as large correspondingly suspended sediment transport rates obtained from the sediment concentration and velocity measurements showed best comparisons with a modified sediment transport model that includes a physical mechanism for enhancing transport rates due to flow acceleration the modified sediment transport model reduced the overall root mean square prediction error by up to 35 and shifted the predicted peak in uprush sediment transport rate earlier in the swash cycle resulting in a better fit to the observations these findings suggest that the inclusion of the acceleration term may account for physical mechanisms that include bore turbulence and horizontal pressure gradients typically associated with the accelerating portion of uprush

characteristics and dynamics of multiple intertidal bars north lincolnshire england multiple intertidal bars and troughs often referred to as ridges and runnels are significant features on many macrotidal sandy beaches along the coastline of england and wales they are particularly prevalent in the vicinity of estuaries where the nearshore gradient is gentle and a large surplus of sediment is generally present this paper examines the dynamics of such bar systems along the north lincolnshire coast a digital elevation model of the intertidal morphology obtained using lidar demonstrates that three to five intertidal bars are consistently present with a spacing of approximately 100 m the largest and most pronounced bars height 0 5 0 8 m are found around mean sea level whereas the least developed bars height 0 2 0 5 m occur in the lower intertidal zone annual aerial photographs of the intertidal bar morphology were inspected to try to track individual bars from year to year to derive bar migration rates however there is little resemblance between concurrent photographs and resetting of the intertidal profile occurs on an annual basis three dimensional beach surveys were conducted monthly at three locations along the north lincolnshire coast over a one year period the intertidal bar morphology responds strongly to the seasonal variation in the forcing conditions and bars are least numerous and flattest during the more energetic winter months morphological changes over the monthly time scale are strongly affected by longshore sediment transport processes and the intertidal bar morphology can migrate along the beach at rates of up to 30 m per month the behaviour of intertidal bars is complex and varies over a range of spatial and temporal scales in response to a combination of forcing factors e g incident wave energy different types of wave processes longshore and cross shore sediment transport relaxation time and morphodynamic feedback copyright 2005 john wiley sons ltd

characterizing beach intertidal bar systems using multi annual lidar data intertidal bars are common in mesotidal macrotidal low to moderate energy coastal environments and an understanding of their morphodynamics is important from the perspective of both coastal scientists and managers however previous studies have typically been limited by considering bar systems two dimensionally or with very limited alongshore resolution this article presents the first multi annual study of intertidal alongshore bars and troughs in a macrotidal environment using airborne lidar light detection and ranging data to extract three dimensional 3d bar morphology at high resolution bar and trough positions are mapped along a 17 5 km stretch of coastline in the northwest of england on the eastern irish sea using eight complete and one partial lidar surveys spanning 17 years typically 3 4 bars are present with significant obliquity identified in their orientation this orientation mirrors the alignment of waves from the dominant south westerly direction of wave approach undergoing refraction as they approach the shoreline bars also become narrower and steeper as they migrate onshore in a pattern reminiscent of wave shoaling this suggests that the configuration of the bars is being influenced by overlying wave activity net onshore migration is present for the entire coastline though rates vary alongshore and periods of offshore migration may occur locally with greatest variability between northern and southern regions of the coastline this work highlights the need to consider intertidal bar systems as 3d particularly on coastlines with complex configurations and bathymetry as localized studies of bar migration can overlook 3d behaviour furthermore the wider potential of lidar data in enabling high resolution morphodynamic studies is clear both within the coastal domain and beyond

an energetics total load sediment transport model for a plane sloping beach bagnold s energetics based total load sediment transport model for streams is used as a basis for the development of a total load model of time varying sediment transport over a plane sloping bed in both the bedload and suspended load the transport rate vectors are found to be composed of a velocity induced component directed parallel to the instantaneous velocity vector and a gravity induced component directed down slope the model is applied to idealized surfzone conditions leading to estimates of the local longshore and onshore offshore sediment transport rates as well as the equilibrium beach slope as a function of the local wave and current conditions the model is combined with a nonlinear longshore current model and spatially integrated to obtain predictions of the total longshore transport rate as a function of the incident wave conditions the results support the general form of the wave power equation except that the wave power coefficient is no longer constant but is instead a complex function of the incident wave and beach characteristics

field experiment on secondary wave generation on a barred beach and the consequent evolution of energy dissipation on the beach face a field experiment conducted on a sandy barred beach situated on the southern part of the french atlantic coastline allowed us to investigate the formation of secondary waves when a moderate significant wave height of about 0 8 m in 3 7 m water depth long 11 14 s narrowband swell propagated over an intertidal ridge and runnel system in both breaking and nonbreaking conditions field evidence using higher spectral analysis is given for the sum interactions between pairs of waves at the primary spectral peak and the consequent energy transfer to nearly harmonic wave components although wave breaking appears to weaken the strength of nonlinear couplings the generation of high frequency energy is hardly affected by wave breaking the phenomenon of harmonic decoupling which takes place behind the bar cannot be completely ascribed to the increase in water depth and the so called deshoaling effect indeed the variation in the values of the maximum bicoherence was very moderate when no breaking occurred finally the doubling in the number of wave crests and the consequent decrease in the significant wave period delay the energy dissipation on the beach face d 2002 elsevier science b v all rights reserved

intertidal beach change during storm conditions egmond the netherlands 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

cross shore sediment transport on natural beaches and its relation to sandbar migration patterns 2 application of the field transport parameterization 1 a cross shore sediment transport parameterization shape function based on data from intensive field experiments carried out on five european beaches is incorporated into a simple time dependent model to explore its capability for reproducing sandbar generation and evolution in the medium term o months model results are compared with bar crest migration patterns observed at duck north carolina the model comprises a simple wave transformation routine that accounts for linear shoaling and assumes a saturation law for wave decay inside the surf zone second order statistics derived from the cross shore distribution of wave heights are used to scale the sediment transport parameterizations which estimate the cross shore structure of the third and fourth velocity moments cross shore gradients in sediment fluxes calculated with an energetics approach produce bed elevation changes the updated morphology affects the wave propagation in the next time step forming a fully coupled model for predicting sandbar evolution bar generation close to shore and the details of the sandbar evolution are successfully reproduced r2 0 86 over the 77 day period of the observations using default values for drag coefficients and efficiency factors in accordance with the observations the model shows rapid offshore sandbar migration in response to individual storms and weak onshore bar movement for lower energy conditions owing to its simple nature the model is not capable of reproducing the whole profile morphology especially in the trough no trough generation and it is only valid for replicating bar crest position the results suggest that a convergence of sediment near the breakpoint breakpoint hypothesis combined with morphological feedback can successfully explain the evolution of bar crest over periods of months from the details of forcing incident waves and water levels

double bar beach dynamics on the high energy meso macrotidal french aquitanian coast a review the french aquitanian coast is an approximately 250 km long straight low coast exposed to high energy conditions in a mesomacrotidal setting offshore wave conditions are seasonally modulated predominantly with a wnw incidence with offshore significant wave height likely to reach 10 m during winter truc vert beach representative of most of the aquitanian coast beaches commonly exhibitstwodistinctsandbarsystems theinnerbarcangothroughallthestateswithintheintermediateclassificationandusuallyexhibitsa tansversebarandripmorphology afterafewweeksoflowerenergyconditionsduringsummer theinnerbarcommonlybecomesalow tideterracewithameanwavelengthof400mandameansoutherlymigrationrateofabout2 3m day crescenticbarshavebeenreported in the literature in nontidal to microtidal settings long term persistent crescentic patterns are however exhibited at a narrow range of wavelength mean of 700m by the outer bar at the meso macrotidal truc vert beach most of the time the outer bar is inactive and stagnates as offshore waves ofhsn3 m are required to induce a significant morphological change the crescent shape varies from a symmetric shape to a strongly asymmetric shape likely to be the result of a long period of nw wave conditions a strong and rarely observed elsewhere morphological coupling between the inner and outer bars can sometimes be observed and may be the result of the combined effectsof the initial presence of a well developed outer crescentic bar and a long period of shore normal low energy conditions a synthesis of all the data available on the area combined with observations on other environments leads to a truc vert beach state model ranging from a modal double bar configuration to an occasional triple bar configuration this work also identifies knowledge gaps to be explored by further numerical and field studies in tidal double sandbar environments 2007 elsevier b v all rights reserved

berm formation and dynamics on a gently sloping beach the effect of water level and swash overtopping berm formation and morphological development of the beach face have been observed during a neap neap tidal cycle on the gently sloping and accreting beach at vejers denmark during the field campaign an intertidal bar migrated onshore and stabilized as a berm on the foreshore a new intertidal bar occurred on the lower beach face migrated onshore on the rising tide and finally merged with the pre existing berm as the tide continued to rise the new berm translated further onshore as an intertidal bar to the uppermost part of the foreshore the sediment transport during the berm transition was onshore directed in the upper swash and offshore directed in the lower swash this berm development can be described through both the neap berm ridge and runnel and berm ridge development concepts proposed by hine sedimentology 1979 26 333 351 and all three stages were observed during only three tidal cycles the main factors controlling this fast transformation were the gentle slope of the cross shore profile rapid water level translation rates substantial swash overtopping of the berm and low infiltration rates despite the onshore migration of intertidal bars and berm formation no net foreshore accretion took place during the field campaign this was largely due to the formation of rip channels with strong rip currents cutting through the intertidal bars and the berm which acted as a sediment drain in the profile

an energetics bedload model for a plane sloping beach local transport bagnold s energetics based sediment transport model for streams is used as a basis for the development of a model for the time varying transport of bedload over a plane sloping bed the sediment transport vector is found to consist of two components the velocity induced transport directed parallel to the instantaneous velocity vector and the gravity induced transport vector directed downslope the model is applied to the case of sediment transport within the surf zone for the separate cases of weak and strong longshore currents relative to the wave bore oscillatory water velocity the results suggest the bagnold s oscillatory sediment transport model which forms the basis for a number of longshore sediment transport models is only correct for the special case of weak longshore currents and near normal incident waves for an artibrary strength longshore current v and a local incident wave angle a the longshore transport rate is found to be proportional to sina v 1 sin sup 2 a v sup 3 where u is the wave induced oscillatory water velocity the model also predicts the onshore offshore sediment rate for weak longshore currents and near normal incident waves the predicted equilibrium beach slope is equal to tanf strong longshore currents and or significant local wave angle conditions however cause amore change in this equilibrium beach slope less authors bailard j a inman d l publication date 1981 03 20 osti identifier 6767919 resource type journal article resource relation journal name j geophys res united states journal volume 86 c3 research org scripps institution of oceanography university of california la jolla california 92093 country of publication united states language english subject 58 geosciences shores sedimentation coastal waters gravitation sediments silt velocity water currents currents surface waters 580500 oceanography 1980 1989

rans based simulation of turbulent wave boundary layer and sheet flow sediment transport processes abstract a numerical model coupling the horizontal component of the incompressible reynolds averaged navier stokes rans equations with two equation k turbulence closure is presented and used to simulate a variety of turbulent wave boundary layer processes the hydrodynamic model is additionally coupled with bed and suspended load descriptions the latter based on an unsteady turbulent diffusion equation for simulation of sheet flow sediment transport processes in addition to standard features common within such rans based approaches the present model includes 1 hindered settling velocities at high suspended sediment concentrations 2 turbulence suppression due to density gradients in the water sand mixture 3 boundary layer streaming due to convective terms and 4 converging diverging effects due to a sloping bed the present model therefore provides a framework for simultaneous inclusion of a number of local factors important within cross shore wave boundary layer and sediment transport dynamics the hydrodynamic model is validated for both hydraulically smooth and rough conditions based on wave friction factor diagrams and boundary layer streaming profiles with the results in excellent agreement with experimental and or previous numerical work the sediment transport model is likewise validated against oscillatory tunnel experiments involving both velocity skewed and acceleration skewed flows as well as against measurements beneath real progressive waves model capabilities are exploited to investigate the importance of boundary layer streaming effects on sediment transport in selected velocity skewed conditions for the medium sand grain conditions considered the model results suggest that streaming effects can enhance onshore sediment transport rates by as much as a factor of two moreover for fine sand conditions streaming and related convective effects are demonstrated to potentially reverse the direction of net transport i e from offshore to onshore relative that predicted in oscillatory tunnel conditions the developed model is implemented within the popular matlab environment and hence may be attractive for both research and educational purposes

experimental and numerical study of wave induced backfilling beneath submarine pipelines abstract this paper presents results of complementary experimental and numerical studies involving wave induced backfilling of current generated scour holes beneath submarine pipelines the laboratory experiments are conducted in a wave plus current flume utilizing laser doppler anemometry to measure velocities synchronized flow visualizations using digital image technology along with live bed scour and backfilling measurements each experiment is based on a two stage process 1 initial scour induced by a pure current followed by 2 backfilling induced by pure waves either regular or irregular the time series of scour depths are closely monitored through video recordings systematic analysis of these has resulted in a closed form expression for the backfilling time scale which is demonstrated to be a full order of magnitude greater than the well known time scale of scour with both governed primarily by the shields parameter the developed expression is strictly valid for the current to wave backfilling scenarios considered while likely serving as an upper limit for more general wave induced backfilling circumstances the experiments are complemented by similar backfilling simulations utilizing a fully coupled hydrodynamic and morphodynamic cfd model the numerical simulations demonstrate the ability of the model to predict backfilling towards expected equilibrium scour depths based on the new wave climate with time scales reasonably in line with experimental expectations

the spatial and temporal variability of sand bar morphology the spatial and temporal variability of nearshore sand bar morphology is quantified using a unique data set spanning 2 years the data consist of daily time exposure images of incident wave breaking on an open coast sandy beach which may be used to infer bar morphology lippmann and holman 1989 the morphology in each image is classified into an eight state morphologic scheme in which bars are uniquely defined by four independent criteria the most frequently observed morphologies are the longshore periodic rhythmic bars observed in 68 of the data linear bars occur under highest wave conditions h s 1 78 m and are unstable mean residence time 2 days shore attached rhythmic bars are the most stable mean residence time 11 days and generally form 5 16 days following peak wave events non rhythmic three dimensional bars are very transient mean residence time 3 days eighty seven percent of transitions to lower bar types defined in text occurred one state at a time supporting our selection of the ordering of states and suggesting the suitability of a sequential morphology model transitions to higher states occurred under rising wave energy and were evenly spread among the possible higher states with more substantial changes in morphology resulting from larger wave increases this suggests that up state erosional transitions based on offshore bar migration are better described by an equilibrium model where response is better correlated with incident wave energy than with preceding morphological state time exposure images were also digitized to yield quantitative estimates of bar crest location as a function of longshore distance principal component analysis was used to decompose bar position into two dimensional linear and three dimensional longshore variable components cross shore linear bar position ranges 50 m about the 2 year mean 27 m standard deviation and dominates bar variability 74 6 three dimensional bar structure accounts for 14 of the variance 12 m standard deviation changes in incident wave height precede cross shore bar migration by less than 1 day changes in longshore variability are inversely correlated to changing wave conditions with bar morphology becoming linear rapidly during storms on time scales of less than 1 day evolution to significantly three dimensional structure typically occurs over 5 7 days following peak wave events

headland bay beach planform and tidal range a neural network model abstract an artificial neural network model of headland bay beach planform is presented and developed it differs from conventional models in two fundamental respects first the knowledge of the problem is not input to the model in the form of a given planform equation but is acquired by the model itself from a series of examples of headland bay beaches in the course of a training process in other words the model learns second the new model takes into account tidal range a significant factor influencing sediment transport the artificial neural network is a multilayer perceptron trained with the bayesian regularisation algorithm for the selection of the optimum network architecture a thorough experimental study involving 240 neural networks is carried out the model with the selected network architecture is trained and validated on a data set comprising 29 headland bay beaches and shown to outperform a conventional headland bay beach planform model the model is then applied to investigate the relation between tidal range and headland bay beach planform for this purpose the non dimensional planforms corresponding to two values of the maximum tidal range tr 0 5 m and 4 5 m under different wave obliquities q0 40 50 and 60 are simulated for the smallest wave obliquity 40 the shoreline curves for both tidal ranges practically overlap for greater wave obliquities the larger tidal range is found to produce a greater bay indentation the difference increasing with wave obliquity these results improve our understanding of headland bay beach morphology and in particular of the manner in which it varies between meso macrotidal and microtidal conditions due to the tidal modulation of the sediment transport vectors or its absence respectively

numerical modeling of flow and scour below a pipeline in currents part ii scour simulation abstract a vertical two dimensional 2d numerical model for time dependent local scour below offshore pipelines subject to unidirectional steady flow is developed the governing equations for the flow and sediment transport are solved by using finite difference method in a general curvilinear coordinate system the performance of two turbulence models the standard k model and smagorinsky subgrid scale sgs model on modeling time dependent scour processes is examined both suspended load and bed load are considered in the scour model the suspended load model is verified against two channel sediment transport cases the change of bed level is calculated from the continuity equation of total sediment transport a new time marching scheme and a sand slide scheme are proposed for the scour calculation it is found that the proposed time marching scheme and sand slide model work well for both clear water and live bed scour situations and the standard k turbulence closure is more preferable than the sgs model in the 2d scour model developed in this study

flow velocities sediment transport and morphological change in the swash zone of two contrasting beaches abstract as part of a large uk research project focussing on the role of swash on shoreline change two field experiments were conducted on contrasting sandy beaches a flatter dissipative beach and a steeper intermediate beach this paper describes almost 300 h of nearshore velocity data collected during this project supplemented by suspended sediment transport sediment tracer and beach profile data during both field experiments the upper part of the beach experienced progressive accretion indicating that onshore sediment transport prevailed in the swash and inner surf zones suspended sediment transport and tracer dispersal were also onshore the associated cross shore flow field was however dominated by offshore directed mean flows especially on the steeper beach velocity skewness defined as u 3 u 2 1 5 where u is the cross shore velocity and kurtosis defined as u 3 u u 2 2 were mainly directed offshore implying that energetics based sediment transport models are unable to predict the direction of sediment transport in the swash zone possible explanations for the observed accretion include enhanced bed shear stress on the uprush due to in exfiltration effects flow acceleration and or bore turbulence and advection of bore entrained sediment into the swash zone

cross shore sediment transport partitioning in the nearshore during a storm event 1 vertical profiles of fluid velocity and sediment concentration have been collected across the surf zone during the sandyduck 97 field experiment analysis from data collected during a 3 day storm event shows that in agreement with preceding observations the mean component of cross shore sediment transport throughout the water column and across the surf zone is almost uniformly in the offshore direction similarly the wave coherent component is generally onshore directed but does on rare occasions exhibit offshore transport the infragravity component in these conditions while exhibiting a definite offshore bias is generally a negligible component thus net cross shore transport is predominately a balance between the wave coherent component and the mean component in observations that stress the importance of the near bed region to cross shore sediment transport it is shown that this balance is a function of elevation above the bed the increasing importance of the wave coherent component as the bed is approached can lead to situations where the net transport direction shifts from being directed offshore higher in the water column to onshore directed near the bed

numerical simulation of wave induced scour and backfilling processes beneath submarine pipelines abstract a fully coupled hydrodynamic morphodynamic numerical model is presented and utilized for the simulation of wave induced scour and backfilling processes beneath submarine pipelines the model is based on solutions to reynolds averaged navier stokes equations coupled with k turbulence closure with additional bed and suspended load descriptions forming the basis for sea bed morphology the morphological evolution is updated continuously rather than being based e g on period or other time averaging techniques simulations involving wave induced scour over the range of keulegan carpenter number 5 6 kc 30 demonstrate reasonable match with previous experiments both in terms of the equilibrium scour depth as well as the scour time scale wave induced backfilling processes are additionally studied by subjecting initial conditions taken from scour simulations with larger kc to new wave climates characterized by lower kc values the simulations considered demonstrate the ability of the model to predict backfilling toward expected equilibrium scour depths based on the new wave climate in line with experimental expectations the simulated backfilling process is characterized by two stages 1 an initial re distribution phase involving re organization of sediments in the immediate vicinity of the pipeline potentially followed by 2 a more lengthy backfilling evolution toward equilibrium scour depth the simulated backfilling time scales are of the same order of magnitude as in experiments though the multi stage process complicates a more systematic characterization the simulated sequences of scour and backfilling achieved within the present work are estimated to represent temporal durations of up to approximately 12 h at full practical scales

cross shore sediment transport on natural beaches and its relation to sandbar migration patterns 1 field observations and derivation of a transport parameterization 1 cross shore sediment transport processes are investigated with measurements of horizontal velocity and sediment suspension obtained with electromagnetic current meters and optical backscatter sensors on five different beaches across europe data were gathered under a wide variety of hydrodynamic and morphological conditions spanning the swash surf and shoaling zones results show that the near bed velocity moments normalized by the local energy level ut2 n have consistent shapes shape functions when plotted against normalized cross shore depth h hb according to the energetics approach near bed velocity moments are good descriptors of sediment transport processes consequently the shape functions describe and quantify the cross shore distribution of the most relevant cross shore sediment transport processes the pattern consists of net onshore transport in the swash zone offshore transport in the surf zone and onshore transport in the shoaling zone thereby producing divergence of sediment in the inner surf swash zone and convergence in the breaker zone in consequence the shape function supports the breakpoint hypothesis for sandbar generation this behavior is a product of the balance between multiple opposing mechanisms including undertow coupling between mean flows and short long wave stirring short long wave skewness and long wave coupling with short wave variance the cross shore structure of the measured and normalized cross shore sediment fluxes is consistent with the velocity moment shape functions showing the robustness of the approach apart from the shortcomings bound to the energetics approach the present parameterization is also limited due to the difficulty of defining with confidence a breaker depth hb in bar trough systems

geometry and dynamics of wave ripples in the nearshore zone of a coarse sandy beach 1 extensive measurements of ripple characteristics and dynamics along with associated suspended sediment fluxes and hydrodynamic conditions were made in the shoaling and surf zones of a macrotidal coarse grained beach at sennen cove cornwall england median grain diameter 0 69 mm suborbital vortex ripples were observed during the majority of the study period with height 5 cm and length 35 cm the scale and shape of the ripples did not vary significantly as the bed shear stress increased during wave shoaling and breaking however ripple migration rates onshore directed were strongly dependent on their location relative to the breakpoint increasing from 0 1 cm min 1 under shoaling waves to 2 cm min 1 in the outer surf zone during low energy conditions farther inside the surf zone ripples persisted but migration rates slowed probably owing to the presence of the offshore directed mean flow which impedes landward migration of the ripples under low wave conditions during which measured sediment fluxes peaked around the outer surf zone and decreased through the saturated surf zone bed form transport rates under shoaling waves were of the same magnitude as net suspended sediment fluxes but at least an order of magnitude smaller in the outer surf zone under high energy conditions during which suspended sediment fluxes in the surf zone were offshore directed owing to the presence of the seaward directed mean flow bed form transport rates were several orders of magnitude smaller than suspended fluxes

role of morphologic feedback in surf zone sandbar response several aspects of feedback mechanisms associated with surf zone sandbar response have been characterized using bathymetric surveys sampled approximately monthly over a 16 year period at the army corps of engineers field research facility north carolina the measured bathymetry was alongshore averaged and modeled by the superposition of two gaussian shaped sandbars on an underlying planar slope a third half gaussian shaped bar represented steepening at the shoreline the rms error between the measured bathymetry and the profile model was 0 10 m estimated over 322 different surveys the model explained 99 of the profile variance that remained after first removing the linear cross shore trend from each observed profile bar response which was extracted from the modeled profiles was compared to a local hydrodynamic forcing variable was defined as the ratio of the wave height to water depth evaluated at bar crest locations at low values of i e nonbreaking conditions bars migrated onshore and their amplitude tended to decay at high values of i e breaking conditions bars migrated offshore with relatively little change in amplitude the transition between onshore and offshore migration occurred at a value of that was consistent with the onset of wave breaking bar migration was associated with a stabilizing feedback mechanism which drove bar crests toward an equilibrium position at the wave breakpoint however we observed that the rate of bar response showed no reduction for any nonzero choice of indicating that bars never reached equilibrium systematic bar amplitude decay was observed under nonbreaking conditions bar amplitude decay could drive farther away from breaking conditions allowing further bar amplitude decay this is a destabilizing feedback mechanism potentially leading to bar destruction

short term morphological change and sediment dynamics in the intertidal zone of a macrotidal beach abstract this paper describes the morphological and sedimentological evolution of amacrotidal beach over a 20 day period under varying hydrodynamicconditions signi cant breaker heights of 0ae3 2 m and tidal ranges of 2 5 m during the eld campaign an intertidal bar developed around the mid tidelevel migrated onshore welded to the upper beach and was then attenedunder energetic wave conditions the bar had a wave breakpoint origin and itsformation was triggered by a reduction in tidal range causing more stationarywater level conditions rather than an increase in wave height most of theonshore bar migration took place while the bar was positioned in the inner tomid surf zone position such that the bar moved away from the breakpoint andexhibited divergent behaviour the depth of disturbance over individual tidalcycles was 10 20 of the breaker height such values are more typical of steepre ective beaches than gently sloping dissipative beaches and are consideredto re ect the maximum height of wave generated ripples the grain sizedistribution of sur cial sediments did not vary consistently across the beachpro le and temporal changes in the sedimentology were mostly unrelated tothe morphological response the lack of clear links between beach morphologyand sedimentology may be in part due to shortcomings in the samplingmethodology which ignored the vertical variability in the sediment sizecharacteristics across the active layer keywords beach sediment depth of disturbance intertidal bar macrotidalbeach morphology introductionbeaches respond rapidly to changing wave andtide conditions through the redistribution of theirsediments by oscillatory and quasi steady cur rents resulting in spatial patterns of erosion sediment divergence and accretion sedimentconvergence given suf cient time these bed level changes modify the beach shape by theformation modi cation destruction and ormigration of secondary morphological features such as berms beach cusps swash bars ripchannels and nearshore bars the dynamics ofthese secondary morphological features and theirrole in affecting beach stability has been a majorfocus of beach research over the last few decades e g komar 1998 short 1999 most short term days to weeks eld investi gations addressing the morphological response ofsandy beaches to wave and tide forcing have beenconducted in microtidal or mesotidal settings beaches in macrotidal settings have on the otherhand only received limited attention despitetheir common occurrence short 1991 a mainreason for this imbalance is that macrotidalbeaches are often planar and lack pronouncedsecondary morphological features indeed theonly type of macrotidal beach that does featureprominently in the coastal literature is the ridgeand runnel beach which is characterized bysedimentology 2007 54 39 53

swash zone sediment suspension and transport and the importance of bore generated turbulence a study of swash zone sediment transport was conducted at gleneden beach oregon during february 25 28 1994 the data collected included suspended sediment concentration ssc sea surface elevation and velocity initially 4 and 8 cm above the bed at three cross shore locations within the swash zone spanning high tides ensemble averages of 6 9 and 12 s duration swash events showed that the uprush suspension was high concentrated in the leading edge and nearly vertically uniform above the lower 1 2 cm of the water column shortly after the sensors were inundated by run up the sediment rapidly settled out of the water during flow reversal the ssc was small but increased again in the backwash backwash vertical profiles were markedly different from uprush profiles with much of the suspension being confined to very near the bed where strong vertical gradients in ssc existed these marked differences show that the backwash is not simply the reverse of the uprush implying significant differences in the underlying fluid dynamics and sediment transport mechanisms backwash sediment suspension increased with flow duration however ensemble averaged ssc profiles of varying duration showed that the backwash concentrations were not consistent at the same temporal phases which suggests that water depth in addition to flow duration may be a controlling factor strong cross shore gradients in ssc suggest that bore derived turbulence may affect local sediment transport specifically our data show this bore generated turbulence turbulent kinetic energy directly influences local sediment suspension hence standard bed shear bagnold type sediment transport models may no longer be valid in the vicinity of the bore in the vicinity of the bore a higher correlation between bore generated turbulence and suspended sediment transport was found than between a bagnold type formulation and suspended sediment transport

cross shore sediment transport and morphological response on a macrotidal beach with intertidal bar morphology truc vert france a 3 week field investigation was conducted on a macrotidal beach with intertidal bar morphology with the aim of quantifying cross shore sediment transport rates and beach response cross shore transport rates were estimated in four different ways 1 net transport from bed level changes 2 measured suspended sediment fluxes 3 sediment fluxes associated with migrating wave ripples and 4 total load transport predicted using the bailard bailard j a 1981 an energetics total load sediment transport model for a plane sloping beach journal of geophysical research 86 10938 10954 model excellent qualitative agreement was found between the different measures under all recorded wave conditions with onshore offshore sediment transport and beach accretion erosion observed under low to moderate high wave conditions the agreement is due to the strong correspondence between the direction of mean cross shore flows across the intertidal bar surface and that of the sediment transport significant onshore mean flows u 0 1 0 2 m s 1 were persistently observed under low wave conditions and these were strongest in shallow water depths h 1 m these flows are attributed to the weak three dimensional water circulation in the surf zone associated with the intertidal bar rip morphology and caused onshore bar migration under high wave conditions on the other hand strong mean cross shore flows u 0 2 0 4 m s 1 due to the bed return flow were consistently directed offshore and resulted in bar destruction under low wave conditions vertically integrated suspended fluxes ripple transport rates and predicted total transport fluxes were remarkably similar but when the fluxes are integrated over a complete tidal cycle they are considerably smaller than that derived from bed level changes based on low tide surveys

video based observations of nearshore sand ripples and ripple migration 1 observations of o 1 m length and o 0 1 m height sand ripples at waimea bay a steep slope 0 05 pocket beach on the north shore of oahu hawaii are presented time series of ripple patterns over a 900 m2 section of the nearshore in depths of 1 2 m are obtained using time averaged video images from an argus station overlooking the bay ripples are detected during weak wave conditions in the summer or between winter swell events the ripple field exhibits narrow band wave number structure with ripple crests oriented parallel to the shoreline the ripple wavelengths vary with wave orbital displacements but they are shorter than predicted by orbital vortex ripple scaling relationships a new suspension limited model smith and wiberg 2006 traykovski 2006 in which the suborbital ripple wavelengths vary with wave period appears to describe well the observed ripple wavelength scaling lagged correlations between sequential argus images reveal area average ripple migration rates ranging from 3 3 m day 1 offshore to 4 5 m day 1 the corresponding estimated sediment transport ranges from 0 3 m3 m 1 day 1 to 0 5 m3 m 1 day 1 similar to previous estimates of cross shore transport based on observed volume changes at the subaerial beach this suggests that the recovery of beach sand following major swell driven erosion events may be accomplished in part by the shoreward migration of seabed ripples

morphodynamic response of a meso to macro tidal intermediate beach based on a long term data set article four years of bi monthly topographic surveys have been conducted on a 350 m stretch of the meso to macro tidal truc vert beach france herewe study the dynamics of boththe inner bar and the upper partof the beach where a berm can develop in the presence of fair weather conditions for the inner bar the occurrences of the different states within the intermediate classification following thatof wright and short wright l d short a d 1984 morphodynamic variability of surf zones and beaches a synthesis marine geology 56 93 118 arepresentedandcomparedtoothersitesinbothmicro andmeso tidalenvironments theresultsshowasimilar frequencyofoccurrenceofthetransversebarandrip tbr state whilethemoredissipativestates rhythmicbar and beach rbb and longshore bar and trough lbt are less regularly observed despite the high wave energy levels the lbt and rbb states are also observed in the presence of fair weather conditions and the tbr state can persist during very energetic events similar results are also observed with the upper beach dynamics veryenergeticeventsarenotnecessarilyassociatedwitherosionwhileandlow energyeventsarenotnecessarily

seasonal morphodynamics of the subaerial and subtidal sections of an intermediate and mesotidal beach abstract this study provides a detailed insight into the seasonal morphological evolution of the subaerial and subtidal sections of an intermediate and mesotidal beach in relation to the nearshore wave conditions for this purpose fortnightly to monthly topographic and bathymetric measurements were collected on ensenada beach baja california mexico from november 2012 to february 2016 wave data were concurrently measured at 20 m water depth enabling the correlation of the observed morphological changes to the hydrodynamic forcing the seasonal morphological variability of the beach comprised 200 000 m 3 70 m 3 m 1 and resulted primarily from the cross shore exchange of sediment the volumetric fluctuations alongshore were up to 100 000 m 3 and event driven and played an inportant role in the overall sediment balance in association with the incoming wave conditions the subaerial and subtidal beach sections experienced a strong seasonal variability the subaerial beach reached the maximum volumes in the end of summer september october and minimum in winter january february while the opposite response was obtained for the subtidal beach with the largest and smallest volumes occurring during the same months in winter and summer respectively the morphological fluctuations of the upper and lower beach sections were associated with the preceding monthly averaged wave conditions the subtidal volume variations were highly and positively correlated to the wave height and period while the subaerial section was highly but negatively correlated to the same variables the morphological beach response to energetic waves was more rapid than to low energy conditions the largest subaerial erosion and subtidal accretion happened in three months october january while the subaerial accretion and subtidal erosion occurred smoothly over nine months january october the total beach volume subaerial and subtidal lacked of seasonal variability and an annual loss of 50 000 m 3 17 m 3 m 1 occurred from august 2014 to august 2015 indicating that the beach remained fairly stable over that period of time the largest volumetric variations of 300 000 m 3 105 m 3 m 1 occurred during the beginning of the 2015 2016 el nino winter

formation and development of a breaker bar under regular waves part 1 model description and hydrodynamics abstract in this work a detailed hydrodynamic model is presented which is used for the study of cross shore sediment transport and morphodynamics in two dimensions the model is described in the framework of the generally unstructured finite volume method considerable emphasis is put on those subtleties in the morphological formulation which are required to achieve mass conservation for the amount of sediment in the bed and in suspension in this first part of two the hydrodynamic description over the cross shore profile is presented the model is validated against an experiment with detailed measurements of the free surface and turbulence over a fixed breaker bar profile a test matrix covering a large interval of the surf similarity parameter is simulated and the phase lag between the breakpoint and the initiation of the setup is described the relation of this phase lag to a cross shore delay in dissipation of organised energy into turbulence is described the relation of this phase lag to the distribution of the location of maxima in bed shear stresses and magnitude of the undertow is also described furthermore processes in the hydrodynamics which will have a smoothing effect on the mean cross shore sediment transport and morphodynamic response are considered all simulations are presented for regular waves and for values of the deep water surf similarity parameter 0 in the range from 0 08 to 1 19 i e covering both spilling and plunging breakers