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

computer simulation of nearshore bar formation a computer simulation model developed from a conceptual model of sediment transport patterns associated with nearshore bars is presented the model simulates wave shoaling breaking and reformation along a profile normal to the shore from deep water to the beach and determines rates and directions of sediment transport under wave orbital currents and rip cell circulation the model successfully generates a barred profile from an initial planar profile and under most conditions achieves a state of dynamic equilibrium with sediment circulating across the bars input values for wave height wave period offshore slope and tidal range were varied in turn in order to determine their individual effect on the shape of the equilibrium profile formed breaker type spilling or plunging is incorporated in the model and also appears to be a significant factor in determining the shape of the equilibrium profile

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

hierarchies and spatial scale in process geomorphology a review abstract the form and functioning of a geomorphic system is the end product of a set of interacting processes which operate at a large variety of spatial and temporal scales an appreciation of the nested hierarchical structure of geomorphic systems offers insight into the effect of scale in process geomorphology a literature review led to the formulation of a series of propositions concerning the spatial scale problem in process geomorphology these propositions are presented in a theoretical framework indicating their association central to the spatial scale problem in process geomorphology is that a geomorphic system must be viewed in its complex hierarchicl context every geomorphic system consists of an array of ever smaller lower level systems and is at the same time part of a sequence of ever larger higher level system in a geomorphic system there exists a similarity between the scales of process and form furthermore within a geomorphic system there is a similarity between spatial and temporal scales so that the timespan to present system behaviour and morphology increases with system size in a geomorphic system differences occur in the sensitivity of morphology to changing process conditions depending on the time elapsed since a change in process conditions morphology in a geomorphic system may be either polygenetic when only partial adjustment of the morphology i e only at smaller scales has occurred or characteristic of the process domain when all aspects of morphology i e at all scales are adjusted to present process conditions in the latter case dominance of landscape evolution by high frequency low magnitude process results in a smooth landscape having small scale irregularities whereas dominance by low frequency high magnitude processes produces an irregular landscape having large scale irregularities when spatial scale is held constant the model of evolution of a geomorphic system varies with the timescale of interest conversely when temporal scale is held constant the model of evolution varies with the spatial scale of interest in both cases the canon fixed rules and options of a geomorphic system vary with the scale temporal or spatial of interest the linkages between spatial and temporal scale and between the scales of form and process of geomorphic systems lead to four additional points first whether or not an event is catastrophic depends on the hierarchical level of the geomorphic system second because of increased travel time and a larger variety of possible pathways differences between the temporal patterns and material properties of input and output increase with the hiirarchical level and scale of a geomorphic system third frequent small scale processes may cause infrequent large scale events when viewed at the same hierarchical level fourth and last differences between geomorphic systems at the same level are controlled by variables varying over distances equal to or smaller than the distance between the system but equal to or larger than the spatial dimensions of the systems

application of marine radar to monitoring seasonal and event based changes in intertidal morphology this paper demonstrates the application of marine radar and a newly developed waterline mapping technique to the continued surveillance and monitoring of inter and intra annual intertidal morphological change thus capturing new detail on coastal system behaviours marine radar data from 2006 to 2009 are used to create a sequence of waterline elevation surveys that show clear morphological evolution of two different sites in the dee estuary uk an estimate of volumetric change was made at two locations west hoyle sandbank and the nw wirral beach both sites exhibited a similar cyclic pattern of volumetric change with lowest volumes in autumn and winter respectively the average beach elevations above admiralty chart datum clearly reflect the observed change in sediment volume with reduced elevations in winter and increased elevations in summer suggesting a trend of high energy storm waves in autumn and winter that remove sediment and simultaneously moderate the vertical dimension of bedforms in the intertidal area data at this temporal and spatial scale are not easily obtainable by other current remote sensing techniques the use of marine radar as a tool for quantifying coastal change over seasonal and event timescales in complex hydrodynamic settings is illustrated specifically its unique application to monitoring areas with dynamic morphology or that is vulnerable to erosion and or degradation by storm events is exemplified

sand spit accumulations at the mouths of the eastern cantabrian estuaries the example of the oka estuary urdaibai biosphere reserve the majority of the eastern cantabrian estuaries occur on a coast with waves approaching dominantly from a nw direction however at their mouths sand spit accumulations occur on their eastern margin these sedimentary features have extended westwards although the main littoral transport path on this coast is dominantly eastwards the origin morphology and development of these sand accumulations can be considered unusual because they do not show the expected sedimentary response through a multidisciplinary approach surface sediment analysis morphodynamic oceanographic and meteorological monitoring and mathematical modelling developed during the period may 2005 april 2006 in the oka estuary it has been possible to establish a genetic hydrodynamic and morphodynamic sedimentary model for these estuaries the main factors to determine the origin of these sedimentary features are wave intensity and direction wave refraction and diffraction processes spatial orientation and morphology of estuarine mouths tidal range and the intensity and direction of tidal currents on this coast but elsewhere due to the influence of headlands usually situated in the western margin of the estuarine mouths wave diffraction and a variation in energy occur along the approaching waves consequently wave set up is forced in the eastern side of the estuarine mouths because of this induced wave pressure gradient an energy compensation is needed and thus wave induced currents towards southwest originate the action of the tidal currents is also important in this paper a cyclical sedimentary transport pattern for the nearshore zone around the mouths of these estuaries is described this process is taking place under tidal influence that induces wave set up and breaking processes and reinforces also the sedimentary transport towards the estuarine inlet the combination of all these hydrodynamic and sedimentary processes has produced these anomalously oriented sedimentary features

morphological evolution of a submerged artificial nearshore berm along a low wave microtidal coast fort myers beach west central florida usa abstract nourishment in the nearshore is becoming an increasingly utilized method for regional sediment management particularly for dredged material that contains more fine sediment than the native beach a nearshore berm was constructed at fort myers beach florida usa using mixed sized sediment dredged from a nearby channel the nearshore berm which is the shallowest of its kind was placed in water depths between 1 2 and 2 4 m with the berm crest just below the mean lower low water level based on time series profiles surveyed from 2009 to 2013 the nearshore berm migrated onshore while the system was approaching a dynamic equilibrium the distant passage of two tropical storms in the third year generated exceptionally high waves for the study area substantial profile change induced by the energetic conditions contributed to rapid evolution of the berm profiles toward equilibrium near the end of the fourth year the berm profiles had returned to the equilibrium shape characteristic of the study area gaps in the berm allowed water circulation when the berm became emergent and watercraft access to the beach for recreational purposes gaps should be considered as a design parameter for future berm nourishments sediment samples collected and analyzed showed that the fine sediment content in the original placed material was selectively transported and deposited offshore while the coarser component moved onshore the dry beach maintained the same sediment properties throughout the study period and was not influenced by the fine sediment in the initial construction of the berm

the influence of long waves on macrotidal beach morphology the aim of the following paper is to demonstrate that standing long waves can generate intertidal morphological features in a dissipative macrotidal setting in this environment the tidal excursion can exceed the length scales associated with long waves this extends the work of simmonds et al 1995 in which it was shown that monochromatic long waves could generate sediment convergence patterns that bore a good similarity to observed topographic features namely ridges and runnels from a field site on the belgian coast the simulation is modified to include a band of long waves and it is found that a good correspondence with real topography can still be achieved on a tidally averaged basis by allowing for a degree of uncertainty in the breaking criterion it is also argued why the observed scales are more likely to correspond with the shorter end of the long wave spectrum the simulation helps to shed light on the conditions in which such features are known to form

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

morphodynamics of a macrotidal beach abstract an intensive field investigation of hydrodynamic processes processes of sediment entrainment and suspension and morphologic change was carried out on an unprotected macrotidal beach near broome in northwestern australia the spring tide range was 9 5 m waves had heights of 0 5 1 2 m and periods of 9 13 s the beach had an overall concave upward profile with low gradient and dissipative subtidal and low tidal zones and steeper more reflective mid tidal and high tidal zones direct measurement of energy flux dissipation over the intertidal profile showed dissipation rates on the order of 1 2 w m 2 of bed and indicated an approximate balance between shoaling and dissipation of unbroken waves so as to maintain a constant wave height time averaged predictive estimates of wave work over the lunar half cycle for different points on the intertidal profile show similar dissipation rates and reveal a relatively uniform distribution of work over most of the profile but with maxima in the middle of the low tidal zone and over the lower part of the high tidal zone most of the work over the low and mid tidal zones was performed by unbroken shoaling waves rather than by surf zone processes surf zone processes only dominate over the high tidal zone the nature of the surf zone processes varied across the profile as local gradient and degree of reflectivity changed with changing tide level the growth of standing waves and infragravity surf beat oscillations as identified from spectra and cross spectra of surface elevation and currents u and v was inhibited over most of the profile however well developed secondary standing wave energy particularly at infragravity frequencies was observed over the high tidal zone at spring high tide and over the mid tidal zone at neap high tide over the low tidal and subtidal zones strong shore parallel tidal currents were subordinate only to the orbital velocities of unbroken incident waves over the subtidal zone asymmetrical tidal currents skewed toward the north attained maximum speeds of 0 5 m s 1 just after high water field measurements of suspended sediment concentration profiles under broken and unbroken waves showed very good fit to a diffusion model for wave induced sediment suspension and suggested that sediment suspension was probably attributable largely to waves northerly advection of wave suspended sediment by asymmetrical tidal currents over the subtidal and low tidal zones accounted for a net northerly longshore transport the greatest morphologic mobility of the intertidal profile occurred over the lower high tidal and upper mid tidal zones corresponding to the position of the coarsest material and secondary maximum of time averaged wave work and to a beach state intermediate between the reflective and dissipative extremes temporally the greatest mobility of the profile as a whole was observed on the short within tidal cycle time scale net changes over the longest time scale of a lunar half cycle were negligible

shoreline recovery on wave dominated sandy coastlines the role of sandbar morphodynamics and nearshore wave parameters abstract this study quantifies and characterises the temporal variability of shoreline recovery on a high energy sandy coastline using a 10 year dataset of daily shoreline and sandbar positions from a coastal imaging station at narrabeen collaroy beach australia following a total of 82 individual storm events rates of the cross shore return of the shoreline to its pre storm position were analysed observed rates during shoreline recovery were characterised by an overall mean of 0 2 m day temporal variability in rates was most evident at shorter timescales of 1 2 weeks and included rates most frequently between 0 and 0 3 m day less frequent more rapid rates of up to 2 m day and also minor landward movements this temporal variability was significantly correlated with nearshore forcing parameters describing the ratio of wave height to wave period the cross shore proximity and attachment of the sandbar to the shoreline and the rate of cross shore sandbar migration these findings are summarised in a new conceptual model that characterises temporal phases and rates of shoreline recovery corresponding to stages of onshore sandbar migration following a storm from fully detached storm deposited sandbar morphology through to complete sandbar welding with the shoreline more gradual shoreline recovery rates are observed with fully detached and semi attached sandbar conditions in contrast more rapid rates of shoreline recovery occur when sandbars are closer and attached to the shoreline observed to be on average 3 4 times greater than for detached sandbars in conditions with attached and semi attached sandbars shoreline recovery rates are negatively correlated to the forcing of nearshore wave steepness and dimensionless fall velocity and coupled with concurrent rates of onshore sandbar migration the findings provide insight into key parameters influencing shoreline recovery following storms

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

morphological changes beach inundation and overwash caused by an extreme storm on a low lying embayed beach bounded by a dune system nw mediterranean abstract the geomorphological evolution of a low lying micro tidal sandy beach in the western mediterranean pals beach was characterized using airborne light detection and ranging lidar data data were collected in prior to and six months after the impact of an extreme storm with a return period of approx 50 years with the aim of characterizing the beach s response to the storm the use of repeated high resolution topographic data to quantify beach geomorphic changes has allowed assessment of the accuracy of different proxies for estimating beach volume changes results revealed that changes in the shoreline position cannot accurately reproduce beach volume changes on low lying beaches where overwash processes are significant observations also suggested that volume estimations from beach profiles do not accurately represent subaerial volume changes at large profile distances on beaches with significant alongshore geomorphological variability accordingly the segmentation of the beach into regularly spaced bins is proposed to assess alongshore variations in the beach volume with the accuracy of the topographic data the morphological evolution of pals beach during the study period showed a net shoreline retreat 4 m and a significant sediment gain on the subaerial beach 7 5 m 3 m the net gain of sediment is mostly due to the impact of the extreme storm driving significant overwash processes that transport sediment landwards increasing volume on the backshore and dunes the increase of volume on the foreshore and the presence of cuspate morphologies along the shoreline also evidence post storm beach recovery observed morphological changes exhibit a high variability along the beach related to variations in beach morphology changes in the morphology and migration of megacusps result in a high variability in the shoreline position and foreshore volume changes on the other hand larger morphological changes on the backshore and larger inundation distances occur when the beach and the dunes are lower favouring the dominance of overwash the observed storm induced morphological changes differ from predicted beach storm impacts because of spatial and temporal variations in the beach morphology suggesting that detailed morphological parameters and indicators used for predicting beach vulnerability to storms should be regularly updated in order to represent the pre storm beach conditions finally observed morphological changes in pals bay evidenced a different behaviour between natural and urban areas with better post storm beach recovery on natural areas where the beach is not artificially narrowed

rhythmic topography in a mesotidal low wave energy environment abstract the intertidal zone in craig bay extends 1200 m offshore making it the broadest non estuarine tidal flat on the east coast of vancouver island british columbia canada superimposed on the low gradient foreshore 1 360 are up to fourteen low amplitude 0 6 m ridges with an average wavelength of 86 3 m these are permanent fixtures of the intertidal zone exhibiting considerable stability in both form and position they are generally symmetrical in cross section and in no instance is a landward slip face evident the ridges have developed in medium to fine sand atop a coarse deltaic platform the thickness of this surficial sand unit is often equal only to the height of the ridges and the gravel sustrate is frequently exposed in the depressions the morphology sediments and hydraulic environment of this rhythmic foreshore were examined to provide insight into the factors controlling ridge development and maintenance although the maximum tidal range exceeds 5 0 m tidal currents are of limited importance only in the major runnels are velocities sufficient to initiate sediment transport waves within the strait of georgia are locally generated h1 3 3 0 m t1 3 7 0 s and appear to the the prime agent responsible for the formation and maintenance of this variant of ridge and runnel morphology the dominant bedform across the intertidal zone is the wave formed ripple although current ripples may locally predominate small scale cross stratification which is associated with these bedforms is the most common primary physical sedimentary structure in the surficial sand unit however a large proportion of the cores were structureless this is attributed to bioturbation by sand dollars dendraster excentricus and to a lesser extent to air entrapment and water escape

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

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

frequency dependent cross shore suspended sediment transport 1 a non barred shoreface abstract the local time varying and time averaged suspended sediment transports across a marine non barred shoreface were obtained from field measurements of the near bed velocity and sediment concentration vectors using electromagnetic current meters and optical backscatterance suspended solids sensors co spectral analyses of velocity and sediment concentration revealed the contributions of waves of different frequencies to the total transport the transport attributable to quasi steady currents was determined from the product of the time averaged cross shore velocity and sediment concentration estimates of the local time integrated sediment volume flux total and net and the associated erosion or accretion were determined using depth of activity rods suspended sediment transport was associated with 1 local wind forced waves 2 swell 3 low frequency waves group bound long waves and 4 offshore directed mean currents undertow these transport components varied spatially and temporally in response to changes in the wave height to water depth ratio the local net oscillatory transport rate at wind wave and swell wave frequencies was directed onshore predominantly and increased as water depth decreased in association with wave shoaling the local mean sediment transport rate was predominantly offshore and dominated the net transport rate wherever wave induced components were weak relative to the mean currents under breaking waves the suspended sediment transport contribution associated with wind waves and swell waves was reduced as a result of dissipation the net suspended sediment transport rate exhibited a distinct vertical structure reflecting the balance at each elevation between the opposing mean and oscillatory components of transport the local time averaged total and net sediment volume flux and resulting erosion and accretion patterns support the hypothesis of a near balance in sediment flux for the complete storm event

undertow over a barred beach the spatial distribution of the mean cross shore flow undertow over a barred beach is examined with field data obtained on three energetic wave days during the duck94 experiment the vertical structure of the undertow is modeled using a turbulent eddy viscosity closure and includes the important effects of wave breaking described using the roller concept and convective acceleration of the current other than a more realistic description of observed turbulence variations a depth dependent eddy viscosity compared with a constant does not improve the agreement between predicted and observed undertow profiles the effect of using different boundary conditions is investigated by extending the formulations of stive and wind 1986 and svendsen et al 1987 to include random waves by ensemble averaging over the wave height distribution the contribution of breaking wave rollers to the surface mass flux can be of the same order or greater than the contribution associated with the organized wave motion the largest discrepancies between model predictions and observations occur over the sandbar where the mass transport of the breaking waves appears to be underestimated

the sedimentary architecture of a holocene barrier spit sylt german bight swash bar accretion and storm erosion abstract the southern german north sea coast was shaped by the last post glacial sea level rise that caused a significant retreat of the coastline approximately 5 ka bp the rate of sea level rise decreased providing space for the formation of the frisian islands which line the coast this study is focused on the island of sylt located at the german north sea coast close to the danish border here two sandy spit systems developed during the holocene combining ground penetrating radar studies and sedimentological investigations based on shallow cores new aspects on the sedimentary history of this holocene spit system have been revealed the data indicate that strong erosional events alternated with phases of progradation and growth the welding of swash bars is shown to be the predominant process during progradational phases of the spit system during these periods progradation was not restricted to linear growth along the spit axis but also included a seaward directed component major erosion surfaces which delimit progradational sediment packages are interpreted to reflect exceptionally severe storms the fossilization potential of this sedimentary record was controlled by a positive net long term sediment balance and the position of the ground water table which controlled eolian deflation only with a stable or rising sea level and associated ground water table position are sediments protected from deflation the proposed sedimentary model may serve as a template for interpretation of comparable settings in the geological record

feedbacks between flow sediment motion and microbial growth on sand bars initiate and shape elongated stromatolite mounds abstract elongated stromatolites are often used as indicators of current direction and shoreline orientation especially in paleoenvironmental reconstructions however mechanisms that create shore parallel m scale elongated stromatolite mounds in carbonate sand are not well understood we propose that this geometry is initiated by microbial growth on the parts of sand bars that experience low wave induced bed shear stresses we test this idea by growing microbial mats on carbonate sand bars in a laboratory wave tank cyanobacterial mats grow on the bar runnels where sediment motion is negligible but are absent from the bar ridges where the waves generate migrating ripples when microbially promoted lithification reinforces and preserves this initial pattern elongated stromatolites should initiate in the runnels of sand bars with long wavelengths 5 100 m and small width to wavelength ratios 0 3 these dimensions are consistent with modern shore parallel stromatolites in hamelin pool western australia and with patterns of microbial colonization in other sandy sediments this model of elongated stromatolite mounds can inform paleoenvironmental reconstructions by clarifying and quantifying feedbacks among waves sediment transport and microbial growth

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

storm impacts and shoreline recovery mechanisms and controls in the southern north sea abstract storm impacts play a significant role in shoreline dynamics on barrier coastlines furthermore inter storm recovery is a key parameter determining long term coastal resilience to climate change storminess variability and sea level rise over the last decade four extreme storms with strong energetic waves and high still water levels resulting from high spring tides and large skew surge residuals have impacted the shoreline of the southern north sea the 5th december 2013 storm with the highest run up levels recorded in the last 60 years resulted in large sections of the frontline of the north norfolk coast being translated inland by over 10 m storms in march and november 2007 also generated barrier scarping and shoreline retreat although not on the scale of 2013 between 2008 and 2013 a calm period recovery dominated barrier position and elevation but was spatially differentiated alongshore for one study area scolt head island no recovery was seen this section of the coast is being reset episodically landwards during storms by contrast the study area at holkham bay showed considerable recovery between 2008 and 2013 with barrier sections developing seaward through foredune recovery the third study area brancaster bay showed partial recovery in barrier location and elevation results suggest that recovery is promoted by high sediment supply and onshore intertidal bar migration at rates of 40 m a 1 these processes bring sand to elevations where substrate drying enables aeolian processes to entrain and transport sand from upper foreshores to foredunes we identify three potential sediment transport pathways that create a region of positive diffusivity at holkham bay during calm periods a general westward movement of sediment from the drift divide at sheringham sources the intertidal bar and foredune development at holkham bay however during and following storms the drift switches to eastward not only on the beach itself but also below the 7 m isobath sediment from the eroding barrier at brancaster bay and especially scolt head island also sources the sediment sink of holkham bay knowledge of foredune growth and barrier recovery in natural systems are vital aspects of future coastal management planning with accelerated sea level rise and storminess variability

morphodynamics of prograding beaches a synthesis of seasonal to century scale observations of the columbia river littoral cell abstract findings from nearly two decades of research focused on the columbia river littoral cell crlc a set of rapidly prograding coastal barriers and strand plains in the u s pacific northwest are synthesized to investigate the morphodynamics associated with prograding beaches due to a large sediment supply from the columbia river the crlc is the only extensive stretch of shoreline on the u s west coast to have advanced significantly seaward during the late holocene since the last cascadia subduction zone csz earthquake in 1700 with associated co seismic subsidence and tsunami much of the crlc has prograded hundreds of meters however the rates of progradation and the processes most responsible for sediment accumulation vary depending on time scale and the morphological unit in question remarkably the 20th and early 21st century shoreline change rates were more than double the late prehistoric rates that include recovery from the last major csz event most likely due to an increase in sediment supply resulting from inlet jetty construction in some locations detailed beach morphology monitoring reveals that at interannual to decadal scale the upper shoreface aggraded about 2 cm yr subtidal sandbars migrated offshore and decayed while intertidal bars migrated onshore and welded to the shoreline the shoreline prograded about 4 m yr and 1 to 2 new foredune ridges were generated a detailed meso scale sediment budget analysis in one location within the littoral cell shows that approximately 100 m3 m yr accumulated between 12 m seaward limit of data and 9 m crest of landward most foredune gradients in alongshore sediment transport net onshore directed cross shore sediment transport within the surf zone and cross shore feeding from a shoreface out of equilibrium with forcing conditions are each partially responsible for the significant rates of sediment supplied to the beaches and dunes of the crlc during the observational period direct observations of beach progradation at seasonal to decadal scale are put in context of measured or inferred changes over time scales of decades to centuries

the biogeomorphology of shark bay s microbialite coasts abstract the world heritage microbialites coquinas and microbialitic sediments of hamelin pool shark bay western australia form through complex community and environmental interactions resulting in surficial co2 sequestration predicted climate change impacts threaten the stability of this setting and the balance of biogeomorphological processes that generate them in this setting long term surficial co2 sequestration occurs through the combination of biomineralisation organomineralisation and lithification which locks atmospheric co2 into caco3 rocks and sediments biogeomorphological processes that control the distribution and effectiveness of these mechanisms including biostabilisation bioconstruction bioerosion and bioturbation have not been addressed in this setting to date a three dimensional biogemorphological mapping unit framework is defined at three locations in hamelin pool within the shallow subtidal to supratidal zones based on historical and recent multiscale datasets this framework is used to review the complex distribution of geomorphological and biogeomorphological processes the distribution of lithification within a biogeomorphological process context is examined and current geological analogue models of microbialite and coquina development are expanded to include biogeomorphological processes the framework is used to understand the impacts of increased water elevation in response to intensification of the leeuwin current during the 2010 2012 ningaloo nino event potential climate change impacts are identified including reduced intertidal bioconstruction and a shift from microbialitic structure generation to increased grain generation reducing stromatolite development review of the uncertainty of impacts of ocean acidification and temperature shifts on biomineralisation organomineralisation and lithification processes crucial to the maintenance of the outstanding universal values in this world heritage location suggests urgent research is required

sediment supply from shoreface to dunes linking sediment transport measurements and long term morphological evolution a significant problem in current coastal research is the understanding of linkages between morphological phenomena occurring on different temporal and spatial scales morphodynamic processes in the nearshore typically exhibit nonlinear behaviour and consequently phenomena which occur on short temporal event scales as e g observed during field experiments have generally been difficult to upscale to provide an understanding of the long term behaviour of the coast on the time scale of seasons or decades this paper documents a persistent onshore migration of nearshore bar features over a period of 3 decades using a set of cross shore profile surveys from a barrier on the danish north sea coast the observed behaviour is consistent with experimental data obtained during weeklong field campaigns when sediment transport and bar migration were found to be landward directed during high energy dissipative conditions hydrodynamic and sediment transport processes leading to onshore bar migration and eventually welding of the bars are documented to provide an explanation for the observed long term evolutionary trends in addition bar welding and the resulting intertidal bar formation represent an onshore sediment storage which is subsequently available for aeolian transport observations on aeolian sediment transport indicate that transport rates and sediment supply to the foredunes critically depend on the presence of dry sand sources as represented by well drained intertidal bars measurements of long term accretion rates in foredunes indicate that volumes deposited on the crest and lee slope of the dunes are in reasonable correspondence with volumes supplied to the subaerial beach through the process of bar welding hence the data suggest that a persistent onshore directed sediment supply occurs from the shoreface across the surf and intertidal zones and into the dunes of the investigated barrier

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

flow regime and bedforms in a ridge and runnel system s e spain abstract during landward migration ridge and runnel systems are subjected to asymmetric oscillatory and or unidirectional flow regimes depending on the stage of development reached by these systems in the early stages of evolution when the ridge is situated in the upper shoreface the whole system is subjected to asymmetric oscillatory flow the runnel is under lower flow regime conditions and the ridge may be under upper or lower flow regime according to water depth and wave energy later when the ridge has migrated to a position on the foreshore the runnel is largely under a unidirectional lower flow regime while the ridge itself is under oscillatory upper flow regime when the ridge welds to berm it is largely emergent and exposed to high tide swash action under upper flow regime conditions the runnel is eventually filled with sand and transformed into a low lying area all these types grade laterally into each other one or more ridge and runnel systems can occur at the same time wave energy tide level and position of the ridge control the variations in the characteristics of the ridge and also the position of the zones of bedforms found at the upper shoreface

morphology formation and migration of longshore sandwaves long point lake erie canada this paper describes the morphology and dynamics of features termed here longshore sandwaves which are developed on a large barrier spit in the great lakes the sandwaves are local beach protuberances with alongshore lengths of 500 2500 m and maximum widths at the downdrift end of 50 90 m which migrate alongshore in the direction of net drift at 150 300 m yr 1 they have a lifespan of 10 yrs or more and their spatial and temporal scales are an order of magnitude greater than the rhythmic topography associated with the nearshore bars and rip cells which are also characteristic of the littoral zone the sandwaves are initiated by the onshore movement and welding of inner nearshore bars during nonstorm periods in areas of local sediment abundance the alongshore movement of the sandwaves occurs through downdrift extension which is initiated by attachment of a landward migrating nearshore bar to the downdrift end of the sandwave and subsequent infilling of the trough landward of the bar the presence and movement of the sandwaves results in a complex spatial temporal pattern of beach and dune erosion and accretion with accretion occurring opposite the sandwave and erosion focused in the embayments between sandwaves

a morphodynamic model for beach gradients this paper outlines a general framework for analysis of the problem of beach gradients which divides the system into 1 the independent controls 2 the hydrodynamics 3 the sediment dynamics and 4 the morphodynamics a model is derived from the combination of these stages which shows close agreement with field data for wave steepnesses of less than about 0 06 but predicts lower beach gradients than arc observed for steeper waves the use of analytical feedback in the present model rather than the iterative feedback which is used in computer simulations demonstrates that differential sediment transport may be responsible for stabilizing the beach gradient

the behaviour of a multiple bar system in the nearshore zone of terschelling the netherlands 1965 1993 abstract the behaviour of a multiple bar system in the nearshore zone of the island of terschelling the netherlands is investigated on the time scale of years using a data set of soundings the data set covers the period from 1965 to 1993 the behaviour is analysed in terms of bar crest position and in terms of morphometric parameters such as bar crest depth height width and volume two or three breaker bars are permanently present in the study area each individual bar passes through three stages during its existence 1 generation close to the shore 2 seaward migration and 3 degeneration at the outer margin of the nearshore bar zone the key factor controlling the behaviour of the inner bars is the crest depth of the outer bar three different couplings between the behaviour of the individual bars have been observed 1 bar stage changes due to the degeneration of the outer bar 2 prevention of the transition of an inner bar from the first to the second stage caused by the appearance from alongshore of a new outer bar having a small crest depth and 3 difference in mean annual seaward migration rate caused by the possible presence of a more seaward positioned bar it is hypothesized that the crest depth of the outer bar governs the relative importance of processes inducing shoreward and seaward migration in the inner nearshore bar zone and therefore controls the behaviour of the nearshore bar zone on the time scale of years

nearshore sandbar migration predicted by an eddy diffusive boundary layer model 1 we simulated the erosion and accretion of a natural beach using a wave resolving eddy diffusive model of water and suspended sediment motion in the bottom boundary layer nonlinear advection was included in this one dimensional vertical profile model by assuming that waves propagated almost without change of form flows were forced by fluctuating pressure gradients chosen to reproduce the velocity time series measured during the duck94 field experiment the cross shore flux of suspended sediment beneath each field deployed current meter was estimated and beach erosion accretion was calculated from the divergence convergence of this flux horizontal pressure forces on sediment particles were neglected the model successfully predicted two bar migration events one shoreward bar migration and one seaward but failed to predict a third seaward migration event simulated seaward sediment transport was due to seaward mean currents simulated shoreward sediment transport was due to covariance between wave frequency fluctuations in velocity and sediment concentration and was mostly confined to the wave boundary layer predicted seaward shoreward bar migration was driven by a maximum in the current generated wave generated flux over the sandbar a wave generated downward flux of shoreward momentum into the wave boundary layer contributed to shoreward sediment transport and often had a local maximum over the bar crest second order nonlinear advection of sediment mostly representing shoreward advection by the stokes drift also often had a local maximum over the bar crest together wave generated momentum fluxes and the stokes drift substantially increased shoreward transport and were essential to predictions of shoreward bar migration

extracting decadal morphological behaviour from high resolution long term bathymetric surveys along the holland coast using eigenfunction analysis abstract the understanding and prediction of coastal behaviour over a time span of decades and alongshore stretches of tens of kilometres is important in coastal management the controlling variables for coastal behaviour on these scales are yet unknown it is hypothesised that regions exhibiting different large scale coastal behaviour lscb regions are controlled by different hydrodynamic forcings or by different sedimentological or morphological constraints or by some combination of these factors the objective of this study is to elaborate a method that effectively quantifies large scale morphological changes from a large bathymetric data set large temporal and spatial extent combined with a high resolution such to define lscb regions the method of analysis consists of a combination of the empirical eigenfunction technique and a moving window approach the method has been applied on a data set of over 14 000 nearshore profiles the data set consists of yearly soundings of the nearshore profile along a coastal stretch of 115 km length the holland coast the alongshore profile spacing is generally 250 m all profiles surveyed in the period 1963 1990 are included in the analysis application of the method on the dutch data set reveals that lscb regions indeed can be identified the sizes of the lscb regions are 5 km 15 km 20 km 32 km and 42 km differences in behaviour of the secondary morphology i e morphology other than the mean profile shape e g nearshore bars are most pronounced the change in behaviour between lscb regions generally occurs over distances as short as about 2 km the boundaries between the regions are therefore surprisingly sharp in general no clear long term trends in the development of the shape of the sub aqueous profile have been observed along the holland coast along certain stretches trends in cross shore shifting of the sub aqueous profile occurred the average shape of the sub aqueous profile seems to have no relation with the trend in cross shore shifting of the shoreline the 1 m contour the sub decadal shoreline fluctuations however are possibly related to the largescale dynamics of multiple bar systems

hydrothermal replacement of biogenic and abiogenic aragonite by mg carbonates relation between textural control on effective element fluxes and resulting carbonate phase abstract dolomitization i e the secondary replacement of calcite or aragonite caco3 by dolomite camg co3 2 is one of the most volumetrically important carbonate diagenetic processes it occurs under near surface and shallow burial conditions and can significantly modify rock properties through changes in porosity and permeability dolomitization fronts are directly coupled to fluid pathways which may be related to the initial porosity permeability of the precursor limestone an existing fault network or secondary porosity permeability created through the replacement reaction in this study the textural control on the replacement of biogenic and abiogenic aragonite by mg carbonates that are typical precursor phases in the dolomitization process was experimentally studied under hydrothermal conditions aragonite samples with different textural and microstructural properties exhibiting a compact inorganic aragonite single crystal an intermediate bivalve shell of arctica islandica and open porous structure skeleton of coral porites sp were reacted with a solution of 0 9 m mgcl2 and 0 015 m srcl2 at 200 c the replacement of aragonite by a ca bearing magnesite and a mg ca carbonate of non stoichiometric dolomitic composition takes place via a dissolution precipitation process and leads to the formation of a porous reaction front that progressively replaces the aragonite precursor the reaction leads to the development of porosity within the reaction front and distinctive microstructures such as gaps and cavities at the reaction interface the newly formed reaction rim consists of chemically distinct phases separated by sharp boundaries it was found that the number of phases and their chemical variation decreases with increasing initial porosity and reactive surface area this observation is explained by variations in effective element fluxes that result in differential chemical gradients in the fluid within the pore space of the reaction rim observed reaction rates are highest for the replacement of the initially highly porous coral and lowest for the compact structure of a single aragonite crystal therefore the reaction progress equally depends on effective element fluxes between the fluid at the reaction interface and the bulk solution surrounding the test material as well as the reactive surface area this study demonstrates that the textural and microstructural properties of the parent material have a significant influence on the chemical composition of the product phase moreover our data highlight the importance of effective fluid mediated element exchange between the fluid at the reaction interface and the bulk solution controlled by the local microstructure

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

bathymetric control of holocene spit migration in a lacustrine environment wave processes are well known for developing spit systems in large or elongated lakes by inducing longshore sediment transport for spit migration while bathymetric interaction is less studied in

onshore sandbar migration at tairua beach new zealand numerical simulations and field measurements abstract we observed the onshore migration 3 5 m day of a nearshore sandbar at tairua beach new zealand during 4 days of low energy wave conditions the morphological observations together with concurrent measurements of waves and suspended sediment concentrations were used to test a coupled wave averaged cross shore model because of the coarse bed material and the relatively low energy conditions the contribution of the suspended transport to the total transport was predicted and observed to be negligible the model predicted the bar to move onshore because of the feedback between near bed wave skewness bedload and the sandbar under weakly to non breaking conditions at high tide the predicted bathymetric evolution contrasts however with the observations that the bar migrated onshore predominantly at low tide also the model flattened the bar while in the observations the sandbar retained its steep landward facing flank a comparison between available observations and numerical simulations suggests that onshore propagating surf zone bores in very shallow water

persistent sand bars explained by geodynamic effects 1 the persistent nature of intertidal sand bars has been the subject of much speculation concerning the hydrodynamic mechanisms involved but its origin remains enigmatic here we introduce salient geophysics in contrast to the physics of fluids above the sediments the geophysical evidence combined with theoretical modeling and analysis demonstrates that the geodynamic processes ensuing during exposure periods have a profound impact yielding the persistent nature of the intertidal bars under severe hydrodynamic forcing which would otherwise lead to unstable bar behavior the feedback between the effects of the dynamics of suction i e negative pore water pressure relative to atmospheric air pressure and sediment transport and morphology is found to play a crucial role in the intertidal bar morphodynamics our finding may fundamentally alter the current perspective leading to a new level of understanding of sediment transport and bar behavior at waterfronts that are ubiquitous in rivers estuaries and coastal seas

nearshore water motion and mean flows in a multiple parallel bar system abstract measurements of surface waves and nearshore water motion were made with wave staffs and electromagnetic currentmeters across the straight outer bars of a multiple parallel bar system at wasaga beach georgian bay ontario three sets of experiments were carried out between 1983 and 1985 and this paper examines the characteristics of spatial and temporal variations in incident waves and mean flows incident wave spectra during storms are typical of fetch limited conditions with a prominent peak in the wind wave frequency and a sharp cut off towards lower frequencies there is little evidence of significant energy at infragravity frequencies mean flows perpendicular to the shoreline during storms measured at 0 1 m above the bed are offshore with speeds of 0 04 0 10 m s 1 during moderate storms and 0 25 m s 1 during intense fall storms longshore currents are relatively weak and their direction closely follows changes in the incident wind angle about shore perpendicular there is no evidence of rip cell development and offshore return flow occurs as an undertow uniformly alongshore forming a simple two dimensional net circulation pattern the presence of the undertow very close to the bed is an important control on the direction of suspended sediment transport and thus in maintaining the equilibrium of the nearshore bars

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

temporal and spatial behaviour of rip channels in a multiple barred coastal system a 15 month data set of daily time averaged video images argus has been analyzed to describe the spatial and temporal variability of the rip channels on a multiple barred coast at noordwijk aan zee the netherlands the landward boundary of the intertidal bars and a proxy of the subtidal bar crest defined as the intertidal and subtidal bar lines respectively were derived from the argus images local seaward directed deviations of the bar lines represent the cross shore and alongshore locations of the rip channels the average intertidal rip spacing was 243 m but the rips were not spaced regularly 0 47 some intertidal rips were observed to fill up during falling tide but the majority remained open the filled intertidal rip channels had more landward positions and migrated more slowly 2 4 versus 4 6 m day in the alongshore direction than the open intertidal rip channels the number and the alongshore migration rate of open intertidal rip channels increased with the preceding wave heights r 0 26 p 0 01 and alongshore component of the offshore wave power r 0 25 p 0 01 respectively the shape of the intertidal bar lines was similar to the subtidal bar line shape suggesting that the intertidal morphology is coupled to the subtidal alongshore variability the phase of two bar lines could vary from in phase 0 to out of phase 180 the phase changes gradually due to different alongshore migration rates of the intertidal and subtidal bar lines copyright 2009 john wiley sons ltd

bar generating cross shore flow mechanisms on a beach random waves normally incident on a dissipative beach induce a variety of cross shore flows such as asymmetric oscillatory flow wave grouping induced long wave flow breaking induced turbulent flow and momentum decay induced undertow these flows are identified analyzed and hindcasted in a set of laboratory experiments with the aim of revealing the role of each of the flow mechanisms in the two dimensional case of bar generation on a beach

nearshore bar formation by non linear wave processes a comparison of model results and field data abstract analogue wave records and associated wave spectra from field measurements of wave transformation across two nearshore bar systems in georgian bay ontario show considerable growth of energy in the higher harmonics in addition there appears to be a regular spatial pattern of energy transfer between the peak frequency and the first higher harmonics with a length dimension equal to the spacing between the bars the characteristic peak period of moderate and severe storm waves affecting the two beaches 4 0 and 7 0 s and the mean nearshore slopes 0 005 and 0 01 are used as input to a mathematical model which describes the non linear evolution of a shallow water wave and the interaction between the first and second harmonics in the model the mass transport velocities associated with the primary wave and the second harmonic are used to calculate net sediment flux across a two dimensional profile model predictions of bar number and spacing starting with an initially planar slope correlate well with the field measurements for the two sets of wave conditions and mean slopes in addition the model is able to predict profile changes reflecting seasonal changes in wave climate

multiple longshore sand bars in the upper chesapeake bay abstract in the upper chesapeake bay maryland u s a field surveys were conducted at 18 multiple longshore sand bar sites the multiple bar systems were found in water depths less than approximately 2 m mean sea level and exhibited mild bottom slopes of 0 0052 or less the number of bars composing each system ranged from four to 17 and the spacing between the crests typically increased in the offshore direction ranging from 12 to 70 m bar height also typically increased with distance offshore and ranged from 0 03 to 0 61 m a grain size analysis of crest and trough sediment did not reveal any significant differences and the sediment was categorized as fine sand a review of the literature data indicated that the chesapeake bay multiple bars possessed similar characteristics to those found in gelding bay baltic sea similarities in fetch wave height and tidal range between the two bays may account for this finding the surf scaling parameter indicated that the multiple bar systems were extremely dissipative with regard to wave energy and wave height appeared to be an important factor in controlling bar spacing and bar height a multiple wave break point hypothesis was discussed as a possible mechanism for the formation of chesapeake bay multiple longshore bars and limited observational evidence appeared to support such a mechanism

a synthetic review of remote sensing applications to detect nearshore bars abstract nearshore bars are important morphologic features associated with intermediate and dissipative natural beaches bars impact the direction magnitude and patterns of sediment transport in the nearshore they serve as a buffer against extreme and meso scale events in this review article we investigate remotely based observations specifically near earth and satellite imagery which have been used to investigate nearshore bars several recent advances in technology and techniques allow the remote measurement of bar width and height beach slope shoreline orientation and bar count video monitoring imagery is presently the most popular method to derive these data however spatial prediction models using satellite imagery can also provide reliable bar morphodynamic information

formation and evolution of multiple intertidal bars on macrotidal beaches application of a morphodynamic model a numerical model is presented to simulate the formation and evolution of intertidal bar morphology dridges and runnelst cross shore sediment transport is modeled using a sediment transport shape function which is a mathematical formulation that expresses the volumetric sediment transport rate as a function of cross shore location for energetic wave conditions the shape function predicts offshore sediment transport in the surf zone and onshore transport outside the surf zone for calm conditions the shape function predicts onshore transport in the surf zone and zero transport outside the surf zone the model is forced by measured wave tide conditions and the time integrated cross shore sediment transport rate is obtained by advecting the shape function up and down the beach with changing tide levels morphodynamic feedback is included in the model specifically the occurrence of relatively flat beach sections troughs leads to the subdivision of the beach profile into distinct cross shore sediment transport cells each forced by its own wave breaking conditions surf zone sediment transport in the troughs is considered zero and the troughs thus effectively serve as sediment transport barriers according to the model and in agreement with field observations intertidal bars form and migrate onshore under the influence of low wave conditions while offshore bar migration and flattening of the morphology occurs under high wave conditions the model supports the contention that ridge and runnel topography has a surf zone origin but the ridges are not breakpoint bars in sensu stricto d 2004 elsevier b v all rights reserved

short term morphodynamics of an intertidal bar on megatidal ebb delta the morphodynamics of an intertidal bar located on an ebb delta of a megatidal inlet system in normandy france was examined during four short experiments under low to high energy wave conditions and spring or neap tide contexts although there have been numerous studies on ebb tidal bar morphology and on the processes affecting such bars these concern only microtidal or mesotidal settings and are mainly based on observations no detailed work involving hydrodynamic conditions embracing the whole tidal cycle has been carried out so far on the mechanisms of onshore migration of these coastal accumulation features especially along macro and megatidal coasts in this study the morphological response of the bar was coupled with the residence times and intensities of each hydrodynamic process swash surf shoaling waves over a representative bar cross shore profile and sediment transport patterns deduced from fluorescent tracer the results show that the bar migrated exclusively shoreward during moderate to storm conditions hs 0 7 m at the bottom of the bar seaward slope during low energy wave conditions no bar movement was observed swash action was not the dominant process mainly due to its duration which did not exceed 8 min in the course of a semi diurnal tidal cycle the movement of sediments and the bar morphology is induced mainly by surf processes and their associated currents the increase in the significant wave height disturbed the general mean current behaviour which was parallel to the bar crest during low energy conditions under surf conditions mean flows are directed onshore with an absence of bed return flow this allows sediment to be transported towards the bar crest causing a landward bar migration an offshore directed cross shore current not favourable for bar migration is recorded with larger water depths and no breaking waves shoaling conditions this study also highlights the influence of the tidal water level fluctuations in such a large tidal range setting which induce a rapid shift in processes such as bed shear and sediment re working across the shore normal profile these conditions explain the relative low rate of migration of the bar over the delta platform about 33 m year this rate is much less than those reported from micro mesotidal environments calculations of bed shear stress also show that the mean currents alone are not responsible for onshore bar movement notwithstanding the megatidal character of the field site

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

landward migration of inner bars abstract a field investigation was carried out to collect data of inner bar migration profiles were measured once or twice a week for a two year period at naka beach ibaraki prefecture japan it was found that the onshore migration of inner bars could be described by two dimensionless quantities as 5d h b max h b max gt 2 max 20d h b max where h b max is the maximum value of daily average breaker height during one interval between surveys t max is the average wave period of the day giving h b max d is the mean size of the beach sediment and g is the acceleration due to gravity analyses based on surfzone sediment dynamics yields v wd b 2 10 11 h b d 3 where v is the average speed of onshore bar migration b is the bar height h b is the average breaker height and w is the fall velocity of the beach sediment nomographs for the speed of landward migrating bars are also presented

location and height of intertidal bars on macrotidal ridge and runnel beaches previous studies devoted to the morphology and hydrodynamics of ridge and runnel beaches highlight characteristics that deviate from those initially postulated by king and williams geographical journal 1949 vol 113 70 85 and king beaches and coasts 1972 edward arnold disagreements on the morphodynamics of these macrotidal beaches include the position of the ridges relative to the mean neap and spring tide levels the variation in the height of the ridges across the intertidal profile and most importantly whether the ridges are formed by swash or surf zone processes the morphological characteristics of ridge and runnel beaches from three locations with varying wave tidal and geomorphic settings were investigated to address these disagreements beach profiles from each site were analysed together with water level data collected from neighbouring ports it was found that the ridges occur over the entire intertidal zone on one site north lincolnshire east england the ridges are uniformly distributed over the intertidal beach whereas on the two other sites blackpool beach northwest england and leffrinckoucke beach north france there is some indication that the ridges appear to occur at preferential locations most significantly the locations of the ridge crests were found to be unrelated to the positions on the intertidal profile where the water level is stationary for the longest time it was further found that the highest ridges generally occur just above mid tide level where tidal non stationarity is greatest these findings argue against the hypothesis that the ridges are formed by swash processes acting at stationary tide levels it is tentatively suggested that the ridges are the result of a combination of swash and surf zone processes acting across the intertidal zone elucidation of the morphodynamic roles of these two types of processes and other processes such as strong current flows in the runnels requires further comprehensive field measurements complemented by numerical modelling copyright 2001 john wiley sons ltd

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

proxy records of holocene storm events in coastal barrier systems storm wave induced markers abstract extreme storm events in the coastal zone are one of the main forcing agents of short term coastal system behavior as such storms represent a major threat to human activities concentrated along the coasts worldwide in order to better understand the frequency of extreme events like storms climate science must rely on longer time records than the century scale records of instrumental weather data proxy records of storm wave or storm wind induced activity in coastal barrier systems deposits have been widely used worldwide in recent years to document past storm events during the last millennia this review provides a detailed state of the art compilation of the proxies available from coastal barrier systems to reconstruct holocene storm chronologies paleotempestology the present paper aims i to describe the erosional and depositional processes caused by storm wave action in barrier and back barrier systems i e beach ridges storm scarps and washover deposits ii to understand how storm records can be extracted from barrier and back barrier sedimentary bodies using stratigraphical sedimentological micro paleontological and geochemical proxies and iii to show how to obtain chronological control on past storm events recorded in the sedimentary successions the challenges that paleotempestology studies still face in the reconstruction of representative and reliable storm chronologies using these various proxies are discussed and future research prospects are outlined