a parametric model for barred equilibrium beach profiles two dimensional implementation abstract a method is proposed for estimating approximate 2dh bathymetry including longshore variable shoreline and sand bar systems the method is based on but extends a previous 1dh model of holman et al 2014 by assuming that this 1dh equilibrium barred bathymetry can be applied for any offshore location if the corresponding mean shoreline orientation is taken to be the local average over a longshore span that is k times the offshore distance thus locations close to the beach are sensitive to shoreline and bar details while more seaward locations are steadily less sensitive the model was tested against 14 ground truth surveys collected over two years and under widely ranging environmental condition spanning a 500 by 1000 m region models inputs for the shoreline and sand bar positions were extracted from measured bathymetries for these tests but would be derived from other sources in real applications while deep water inputs were found from a single deep water survey the model yielded complete 2dh bathymetry maps that were a very good approximation of ground truth the mean bias and rms error over the full region and data set were 0 27 m and 0 49 m respectively and proxy bathymetries were visually very similar to ground truth the largest source of error was occasional cross shore misplacements of otherwise realistic looking sand bars results were only weakly dependent on the value of k when tested over a factor of four and the default value of 1 0 is recommended performance statistics using input locations for the shoreline and bar crest that were manually digitized from breaking patterns in rectified optical time exposure images were no worse than bathymetry based inputs hydrodynamic predictions using these bathymetries would be a substantial improvement over those from monotonic or even barred 1dh equilibrium proxy bathymetries

physical modeling of intermediate cross shore beach morphology transients and equilibrium states laboratory experiments on cross shore beach morphodynamics are presented a lightweight sediment density rho s 1 19 g cm 3 model is used in order to fulfill a shields number and rouse number scaling this choice aims at correctly reproducing bed load transport as well as suspension dynamics terraces and barred beach profiles obtained in the experiments also present close similarities with profiles observed in the field in order to question the concept of equilibrium beach profile wave forcings conforming to a jonswap spectrum were imposed over long periods up to more than a hundred hours an average bottom evolution velocity is defined and used to determine when the profile reaches equilibrium usually beach profiles are characterized according to the wright and short 1984 classification based on the dean number w this well known classification is investigated and refined in the intermediate range that is for 1 omega 5 for w close to 1 a typical reflective profile is obtained terraces are obtained for the omega 2 5 cases for omega approximate to 3 7 the profiles exhibit two parts a mild dissipative offshore slope producing low reflection and a steeper beach face with slightly higher reflection the wave dissipation velocity skewness and acceleration skewness are computed from the free surface elevation time series the dissipation and wave nonlinearities patterns are similar for similar equilibrium beach profiles that is with the same dean number dissipation peaks coincide with bottom slope transitions as higher energy dissipation occurs with milder bottom slope sections besides the uniformity of volumetric wave energy dissipation seems to concern only a limited zone of beaches with a widely developed surf zone

observations of rip spacing persistence and mobility at a long straight coastline three years of daily video observations at a long straight beach were analysed to determine the temporal trends and variability of the location spacing persistence and mobility of rips rips were identified at this site on 684 days of the total 947 days 72 occurrence when suitable images were available a median number of 7 rips were observed within the total 2 km study area on days when rips were present no tendency was identified for rips to reoccur in preferred locations alongshore following storm reset events the average alongshore distance between all rips observed was 209 m but with a high standard deviation of 98 m or approximately 47 of the mean rip spacing there was no evidence at this site that rips tended to be regularly spaced alongshore no clear relationship was identified between the number of rips and the prevailing offshore wave conditions including significant wave height peak wave period and incident wave power the majority of rips persisted for 5 or fewer days with an average of 8 days and standard deviation of 9 days rips were stationary 33 of days with migration rates of less than 5 m day observed on 47 of days when rips were present maximum migrations rates of up to 50 m day were observed and generally though not always occurred in the direction consistent with the prevailing offshore swell direction and resulting alongshore current the occurrence of inshore sea breezes may have accounted for the less frequent observations of rip migration against the opposing regional swell direction the results presented at this site complement a recent four year study at a contrasting short and embayed beach detailed in holman et al holman r a symonds g thornton e b and ransinghe r 2006 rip spacing on an embayed beach journal of geophysical research 111 c01006 doi 10 1029 2005 jc002965 17p the specific mechanism s of rip channel infilling at the long straight and littoral drift dominated coastline may have contributed to the observation of shorter rip persistence relative to the embayed site mean rip spacing was observed at both sites to be highly variable irregular and exhibited no identifiable trend associated with the offshore wave conditions this latter observation supports the notion that rips may become rapidly topographically controlled soon after a storm reset event and their location is then primarily determined by the evolving nearshore morphology rather than hydrodynamic forcing this new dataset of daily multi year observations at an open coast site cannot be reconciled with the majority of existing template and instability models for rip formation that predict a relationship between incident wave conditions and regular spacing of rips alongshore rather these observations tend to support emerging theories of rip genesis that predict the irregular and random spacing of rip channels alongshore

on the use of variance images for runup and shoreline detection abstract the use of variance images for runup and shoreline detection is analyzed in this work a methodology based on the variance images is first motivated with synthetic time stacks and then confirmed with real images a total of 55 time stack images from five different cameras at three video stations in spain and new zealand were digitized and used for the study these images include different tide and wave conditions from the time stack images we 1 obtained the mean shoreline position and maximum runup manually digitizing the water sand interface and 2 computed the variance function the variance function is shown to have a particular cross shore shape with two characteristic positions which allow us to satisfactorily recover the mean shoreline position and maximum runup obtained in the first step variance images were shown to be useful both for detecting mean shoreline and for evaluating runup providing a potential alternative for timex images the method did not work well when runup occurred within the groundwater seepage face

effect of hydrodynamics and bathymetry on video estimates of nearshore sandbar position remote sensing of wave breaker patterns clearly visible as high intensity bands in time exposure video images has become a powerful tool to obtain large scale kilometers and long term years time series of nearshore sandbar position however intensity based bar crest positions xi differ from directly measured positions xb by a time varying distance x which is of o 10 m and depends on the offshore wave height h0 the water level 0 and the bathymetry itself the effect of these parameters on x was investigated from simultaneous video observations and bathymetric surveys obtained in the double barred system at egmond aan zee netherlands and from wave model predictions assuming that the roller energy represents image intensity when the wave field over a bar was predicted to be nonsaturated xi was observed and predicted to move offshore as either 0 decreased or h0 increased under saturated conditions x only responded to changes in 0 additional model investigations showed that an increase in outer bar crest depth similar to that observed during interannual bar behavior significantly reduced the x variability at the outer bar and increased the x variability at the inner bar implications of our observational and model findings for studying sandbar position from video imagery are outlined

observations and modeling of alongshore variability in dune erosion at egmond aan zee the netherlands abstract dunes can erode within a few hours when exposed to high storm surge levels and large waves if the dunes are the primary defense such as in the netherlands this could result in flooding of the hinterland when dunes breach models are often used to analyze how dunes will respond to extreme conditions but they can also be applied to study milder events and with that gain more insight in the processes of dune erosion there is however growing demand for validating existing models under field conditions here we calibrate the xbeach dune erosion model with pre and post storm topography measurements of the dune erosion event in january 2012 at egmond aan zee the netherlands furthermore hydrodynamical data of the intertidal zone along a cross shore transect in the same area collected 3 months prior to the storm event are used to hydrodynamically calibrate and validate xbeach during the january 2012 storm the dune erosion was variable alongshore from the erosion of embryo dunes the forming of a dune scarp to considerable slumping of the entire dune face this caused the erosion volume v to range from 5 to 40 m3 m the calibrated model reproduces the alongshore variability in v with reasonable accuracy additional simulations show that the alongshore variation in v is due to variability on the initial dune topography primarily steepness and that variability in beach and nearshore bathymetry was of secondary importance

alongshore variability in crescentic sandbar patterns at a strongly curved coast sandbars submerged ridges of sand parallel to the shoreline tend to develop crescentic patterns while migrating onshore at straight coasts these patterns form preferably under near normal waves through the generation of circulation cells in the flow field whereas they decay under energetic oblique waves with associated intense alongshore currents recently observations at a man made convex curved coast showed an alongshore variability in patterning that seems related to a spatiotemporal variability of the local wave angle sand engine here we aim to systematically explore how coastline curvature contributes to alongshore variability in crescentic pattern formation by introducing local differences in wave angle and the resulting flow field a nonlinear morphodynamic model was used to simulate the patterns in an initially alongshore uniform sandbar that migrates onshore along the imposed curved coast the model was forced by a time invariant and time varying offshore wave angle simulations show that the presence of patterns and their growth rate relate to the local breaker angle depending on the schematization of the offshore angle and the local coastline orientation growth rates decrease with increasing obliquity as both refraction induced reductions of the wave height as well as alongshore currents increase furthermore simulations of variations in coastline curvature show that patterns may develop faster at strongly curved coasts if this curvature leads to an increase in near normal angles this implies that beaches where the coastline orientation changes substantially for example due to km scale nourishments become potentially more dangerous to swimmers due to strong currents that develop with pronounced bar patterns

rip spacing and persistence on an embayed beach 1 four years of daily time exposure images from an embayed beach were examined to study the spacing persistence and location preferences of rips in a natural rip channel system a total of 5271 rip channels was observed on 782 days occurrence statistics showed no evidence of the preferred location pattern associated with standing edge waves trapped in an embayed beach the histogram of rip spacing the primary diagnostic observable for most models was well modeled by a lognormal distribution mean spacing of 178 m however spacings were highly longshore variable time mean of the standard deviation longshore mean of rip spacing was 39 so they are of questionable merit as a diagnostic variable storm driven resets to the longshore uniform condition required by most models occurred only four times per year on average making rip generation models relevant to only a small fraction of the system behavior rip spacings after the 15 observed reset events were uncorrelated with bar crest distance the lifetime of the 324 individual rip channel trajectories averaged 45 6 days rips were equally mobile in both longshore directions but the coefficient of variation of rip migration rates was large even for high migration rates the mean migration rate was well correlated to a proxy for the longshore current r2 of 0 78 thus there is no significant evidence that the formation spacing and migration of rip channels on this beach can be explained by currently existing simple models moreover the alongshore uniform initial conditions assumed by these models are rare on palm beach making the models generally inapplicable

nearshore bar crest location quantified from time averaged x band radar images abstract the remote sensing of the sea surface is commonly regarded as a logistically simple and cost effective way of obtaining long term years time series of nearshore sandbar location in this paper we demonstrate that similar to video imagery time exposure x band 3 cm wave length radar images contain alongshore breaking related high intensity bands that can be used to compute the location of the underlying sandbar crests analysis of time exposure x band images and bathymetric surveys collected at egmond aan zee netherlands shows that the radar based bar crest location defined as the cross shore location of maximum radar intensity differs from the in situ surveyed crest location by a distance of o 10 m this difference xradar depends linearly on the offshore water level consistent with model predictions in which the radar intensity is assumed to behave as the energy of the surface roller the model additionally suggests a dependence of xradar on the offshore wave height when the wave field across the bar is non saturated in general such wave conditions did not result in radar images with sufficient contrast to determine the bar crest location and accordingly the wave height dependence was not observed clearly in the field because of the dependence of xradar on the offshore water level time series of radar based bar crest location show artificial variability when the images are collected at different water levels various techniques for correcting this variability are discussed

the influence of sea state on formation speed of alongshore variability in surf zone sand bars abstract the formation time of alongshore morphological variability in surf zone sand bars has long been known to differ from one beach to the other and from one post storm period to another here we investigate whether the type of sea state i e distant swell waves or locally generated short period wind sea affects the formation time of the emerging alongshore topographic variability a numerical modeling approach is used to examine the emergence of alongshore variability under different shore normal wave forcing a research version of delft3d operating on the time scale of wave groups is applied to a schematised bathymetry with a single bar the model is then used to investigate several wave scenarios examining the impact of peak period frequency spread and directional spread on the formation time of alongshore variability results show that an increase in wave period has a large effect changing the formation time up to o 250 in case the wave period is changed from a representative value for the dutch coast t p 5 6 s to an australian south east coast value t p 10 12 s in contrast modifications in the directional and frequency spread of the wave field result only in a minor change in the formation time examination of hydrodynamics and potential sediment transport shows that the variations in formation time are primarily related to changes in the magnitude of the time averaged flow conditions variations in the magnitude of very low frequency f f these findings indicate that the development of alongshore topographic variability may be faster at swell dominated open coasts primarily due to the occurrence of longer period swell also at a given site the arrival of a long wave period swell after a storm can accelerate the emergence of variability

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

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

observation and prediction of three dimensional morphology at a high energy macrotidal beach abstract three dimensional beach features such as crescentic sandbars and rip channels influence beach response to and recovery from storm waves as well as significantly affecting the safety and amenity provided by the surf zone for beach water users in this contribution temporal variations in subtidal and intertidal beach three dimensionality are observed at a high energy macrotidal beach and a simple equilibrium model is developed to predict the changes over multi year timescales a dataset of 5 5 years of quasi weekly bar measurements and quasi monthly intertidal surveys from perranporth beach cornwall uk were used to quantify seasonal to inter annual changes in three dimensionality the three dimensionality of the outer bar displayed significant annual periodicity with annual minima and maxima occurring in winter and spring respectively the lower intertidal beach displayed a similar periodicity but developed three dimensionality 1 4 months before the outer bar the model predicts increases or decreases in the scale of three dimensional features by examining the disparity between instantaneous wave conditions and a temporally varying equilibrium wave condition a tidally modulated wave power term determines the rate of morphological change negative feedback was found to be an important process governing the changes in three dimensionality while free morphological behaviour may drive three dimensional growth negative feedback exerts stability in the system making it inherently predictable using a temporally varying equilibrium value the model explained 42 and 61 of the overall variability in outer bar and lower beach three dimensionality respectively it skilfully predicted changes outside the training data range during the most energetic 8 week period of waves measured in the last 65 years off sw england in winter 2013 14 the model outperformed a simple baseline model a linear fit as well as a comparable linearized feedback model from the literature providing the first long term multi year predictions of seasonal to inter annual beach three dimensionality for a macrotidal beach

short term sandbar variability based on video imagery comparison between time average and time variance techniques abstract time exposure intensity averaged images are commonly used to locate the nearshore sandbar position xb based on the cross shore locations of maximum pixel intensity xi of the bright bands in the images it is not known however how the breaking patterns seen in variance images i e those created through standard deviation of pixel intensity over time are related to the sandbar locations we investigated the suitability of both time exposure and variance images for sandbar detection within a multiple bar system on the southern coast of brazil and verified the relation between wave breaking patterns observed as bands of high intensity in these images and cross shore profiles of modeled wave energy dissipation xd not only is time exposure maximum pixel intensity location xi ti well related to xb but also to the maximum pixel intensity location of variance images xi va although the latter was typically located 15 m offshore of the former in addition xi va was observed to be better associated with xd even though xi ti is commonly assumed as maximum wave energy dissipation significant wave height hs and water level were observed to affect the two types of images in a similar way with an increase in both hs and resulting in xi shifting offshore this induced xi variability has an opposite behavior to what is described in the literature and is likely an indirect effect of higher waves breaking farther offshore during periods of storm surges multiple regression models performed on xi hs and allowed the reduction of the residual errors between xb and xi yielding accurate estimates with most residuals less than 10 m additionally it was found that the sandbar position was best estimated using xi ti xi va when xb was located shoreward seaward of its mean position for both the first and the second bar although it is unknown whether this is an indirect hydrodynamic effect or is indeed related to the morphology we found that this behavior can be explored to optimize sandbar estimation using video imagery even in the absence of hydrodynamic data

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

nearshore subtidal bathymetry from time exposure video images time averaged over many wave periods nearshore video observations show the process of wave breaking as one or more white alongshore bands of high intensity across a known depth profile similar bands of dissipation can be predicted with a model describing the time averaged cross shore evolution of organized wave and roller energy this close correspondence between observed and modeled dissipation proxies is used to develop a new remote sensing technique termed subtidal beach mapper sbm to estimate nearshore bathymetry sbm operates on a time series of cross shore intensity profiles to resolve the pattern in depth change on a morphological timescale including overall gain or loss of sediment rather than to focus on the particular change induced by a single intensity profile from each intensity profile the breaking induced component is isolated by removing the contribution of background illumination and persistent foam the depth profile is updated based on a comparison between this video derived dissipation proxy and a cross shore profile of the dissipation of the roller energy this updating is implemented through time dependent mass balance equations for the seabed and a buffer layer above the bed sbm was tested using 1 year of hourly video data collected at egmond aan zee netherlands the dominant morphological changes observed from ground truth data were reproduced reasonably well including the shoreward migration of the outer bar and the net sediment gain in the profile root mean square differences between surveyed and sbm derived depth after 1 year of video based depth updating with an average of about 70 intensity profiles per month were smallest 0 2 m on the inner bar and largest 0 6 m in the outer bar trough with a profile average value of about 0 4 m despite the many processes included in sbm the implementation of a heuristic scaling function in the mass balance equations to spatially adjust morphological growth rates was essential to these results in particular near the shoreline where otherwise the profile is prone to an unrealistic deepening

the mean life of continents is currently not constrained by nd and hf isotopes the paper on crustal recycling by depaolo the mean life of continents geophys res lett 10 705 708 1983 contains errors in the listing and plotting of published hf isotopic data which materially affect the inferred pattern of mantle hf isotopic evolution more generally the impression given in the paper that it is now possible to use nd and hf isotopic data to constrain the degree of crust to mantle recycling is misleading because exactly the same observed effects would be produced by mixing within the mantle itself existing nd and hf isotopic data allow either crustal growth with no recycling of crust to mantle or a model of constant mass continental crust with extensive recycling this implies that all intermediate growth plus recycling combinations are also permitted

shore and bar cross shore migration rotation and breathing processes at an embayed beach a principal component analysis pca is used to decompose data on the coupled morphodynamics of the shoreline and nearshore sandbar of a typical single barred embayed beach tairua beach new zealand dynamic patterns are classified into simultaneous modes where the bar and shoreline move at the same time and non simultaneous modes where the shore moves independently from the bar and vice versa two simultaneous modes accounting for 65 of the variance of the shoreline and barline dominate the system one mode describes inverse shoreline and sandbar cross shore migrations alongshore averaged occurring with simultaneous rotations in the same direction the other mode accounts for migration in the same direction accompanied by variations of the barline curvature similar to breathing modes previously described in embayed beach shoreline modelling studies two non simultaneous modes of lesser importance account separately for independent shoreline and barline rotations 10 to 15 of the variance explained a pca applied to the shore and sandbar behaviours modelled by four standard equilibrium models simulating shore and sandbar cross shore migrations and rotations show that these are interrelated because of a correlation between wave energy and direction shore and bar rotations are coupled partially because the shape of the bay induces a correlation of their respective drivers the wave angle of incidence and the alongshore gradient of wave energy however this correlation depends on the wave energy this in combination with different shore and sandbar response times quantified using the models also explains the independent rotations reflected by the non simultaneous modes

storm impact on the seasonal shoreline dynamics of a meso to macrotidal open sandy beach biscarrosse france abstract a three year dataset 2007 2010 of shoreline and sandbar positions derived from video observations of an open sandy beach biscarrosse france is analyzed to explore the impact of storms on the seasonal shoreline dynamics the results indicate that a clear seasonality is observed in the offshore significant wave height and in the occurrence of winter storm events that are defined as periods with significant wave height greater than 4 m lasting at least 12 h data indicate that the range of variation of the inner sandbar positions 120 m is two and a half times larger than the range of variation of the shoreline position correlation analyses suggest that the offshore conditions do not conclusively explain the position of the inner bar shoreline positions show a clear seasonal pattern displaying a stable position occurring in february and july providing evidence of seasonal recovery although analysis of storm activity indicates that the number and intensity of storms is highly variable over the three years the biscarrosse data show that rapid erosion can be observed also under moderate conditions and that beach recovery after the storm season can be relatively rapid

analysis of observed two and three dimensional nearshore bar behaviour abstract shore parallel sandbar systems often exhibit considerable quasi regular alongshore variations such as crescentic plan shapes therefore morphological change in such systems commonly consists of two and three dimensional variability the former is related to overall on offshore bar migration whereas the latter is induced by the horizontal amplitude growth migration or length scale change of the quasi regular topography in this paper we used a six week data set of bathymetric surveys and video images of breaking induced foam to quantify short term days weeks two and three dimensional variability in the bar crest position of the double barred beach at egmond aan zee netherlands the alongshore uniform response was computed as the mean of each bar crest line whereas the alongshore non uniform behaviour was characterised by the amplitude around each mean a more sophisticated description of the inner bar data set was provided by complex empirical orthogonal function ceof analysis the first complex mode containing about 85 of the variance in the data set corresponded to the amplitude growth and longshore migration of an approximately 600 m long alongshore non uniformity the longshore migration rate varied between 0 and 150 m day and was found to be well related to the longshore component of the offshore wave energy flux the second complex mode explained about 10 of the variance and largely described the alongshore averaged cross shore bar migration the ceof results suggest that short term variability in bar crest position is largely due to changes in the quasi regular topography and not to alongshore uniform on offshore oriented behaviour

dynamics of a nearshore bar system in the northern adriatic a video based morphological classification abstract the aim of this paper is to define a simplified morphodynamic classification suitable for low energy beaches exposed to microtidal conditions the study site is located in the northern adriatic in italy it is an almost 2 km long rectilinear beach bordered at the northern edge by coastal structures and at the southern end by a small river inlet the mechanisms related to the evolution of the submerged part of the beach were derived from video monitoring using argus technology the morphodynamic evolution of the system was studied using an automatic procedure on images for the characterisation of nearshore bars that showed good correspondence with hand based visual interpretation to apply this automatic procedure the bar s plan crest shape was mapped using cross shore pixel luminosity transects traced on time averaged video images a careful sensitivity analysis was undertaken to determine the best spacing between transects for the correct tracing of the shape of the bar crest the error associated to a transect spacing every 25 m resulted in being comparable with the pixel resolution in the area and with the error found comparing the video interpretation with bathymetric surveys from the study of a four and a half year dataset february 2003 may 2007 the submerged beach was found to be characterised by the presence of a single bar in the area next to coastal protection structures however moving southwards of these inner and outer bars were present the morphodynamics of the outer bar and its plan shape modifications were dominated by rhythmic forms occasionally after high energy events the bar became rectilinear but during the following lower energy periods rhythmicity was re established supporting the hypothesis of self organization mechanisms the cross shore position of the bar s crests only showed limited cross shore mobility through time

the effects of tides on swash statistics on an intermediate beach 1 swash hydrodynamics were investigated on an intermediate beach using runup data obtained from video images under mild near constant offshore wave conditions the presence of a sandbar and the tidally controlled water depth over its crest determined whether most of the incoming waves broke before reaching the shoreline this forced a change in the pattern of wave energy dissipation across the surf zone between low and high tide which was reflected by changes to swash on time scales of a few hours significant runup height rs defined as 4 times the standard deviation of the waterline time series was found to vary by a factor of 2 between low tide when most of the waves were breaking over the sandbar rs hs 1 5 where hs is the offshore significant wave height and high tide when the waves were barely breaking rs hs 2 7 the increase in wave energy dissipation during low tide was also associated with changes in swash maxima distribution a decrease in mean swash period and increasing energy at infragravity frequencies bispectral analysis suggested that this infragravity modulation might have been connected with the presence of secondary waves

rip current circulation and surf zone retention on a double barred beach abstract rip currents have an important control on the exchange of water and advected materials such as sediment and pollutants between the surf zone and inner shelf concurrent in situ eulerian and lagrangian gps drifter data of surf zone waves and currents were combined with video data on wave breaking patterns over the inner and outer bars on a high energy double barred beach the data collectively show how the occurrence of wave breaking over the outer bar changes the behavior of a channel rip current and the exchange process on both days there was a prominent clockwise eddy in the surf zone for which the seaward heading portion formed a rip current in a well defined channel rip incised into the inner bar exit rate measured with drifters from the surf zone to inner shelf decreased significantly with increased wave breaking over the outer bar from 71 exits to 6 over the two days exit rate appears to be driven by the balance between wave breaking over the inner and outer bars and pulsing of currents within the surf zone under higher wave conditions there were stronger pulsations in surf zone currents and more surf zone exits however higher wave conditions caused wave breaking over the outer bar this breaking increases vorticity around the outside of the surf zone eddy which increases surf zone retention this is in contrast to previous studies showing that vorticity is highest at the center of surf zone eddies under such conditions drifter exits were rare and occurred due to vortex shedding during lower incident wave conditions eddy vorticity was lower and drifters could relatively freely exit the surf zone this is one of the few studies that investigate surf zone circulation on a high energy double barred beach

observations of shoreline sandbar coupling on an embayed beach we analyse a seven year dataset 1999 2005 of shoreline and sandbar variations derived from video observations at the embayed tairua beach new zealand to explore sandbar shoreline coupling and to determine how this coupling is related to alongshore averaged sandbar shoreline separation and beach rotation our results quantify the coupling between the sandbar and the shoreline which is directly related to the reduced separation between the sandbar and the shoreline using a simple predictive shoreline model we show that this behaviour is related to the energy of the incoming waves our observations are obtained from a headland enclosed beach and show aspects of the morphological state that relate to the existence of headlands that are not considered in the wright and short beach state classification both the sandbar and shoreline at tairua beach rotate relatively quickly 1 month during the winter storm events when the storms are accompanied by strong alongshore components gradually returning during the summer months the sandbar shoreline coupling length scale is controlled by this rotation with large wavelengths occurring when the sandbar is strongly rotated

quantification of sand bar morphology a video technique based on wave dissipation a technique is presented to remotely measure the scales and morphology of natural sand bars based on the preferential dissipation of wind waves and swell over the crests of the bar photographic or video images are recorded and statistical uncertainties associated with incident wave height modulations removed by averaging time exposures ground truth testing of the technique was carried out as part of the superduck experiment in october 1986 the time exposures generally provided a good mapping of underlying morphology allowing detection of the bar and determination of cross shore and longshore length scales however during high waves persistent surface foam obscures the relationship of image intensity to local dissipation modeled theoretically by dissipation of a random wave field and an enhancement technique of image differencing must be done to remove the bias errors in the estimate of bar crest distance from the shoreline are generally less than 35 but this value depends on the geometry of the particular bar logistic simplicity and quantitative capabilities make this technique very attractive

observations and conceptual modelling of morphological coupling in a double sandbar system nearshore sandbars located in 10 m water depth can contain remarkably periodic alongshore undulations in both cross shore position and depth in a double sandbar system the alongshore spacing of these morphological patterns in the inner sandbar may be identical to those in the outer sandbar although this morphological coupling has been observed previously its frequency and predominance remain unclear in this paper we use a 9 3 year dataset of daily low tide time exposure images from the double barred beach at surfers paradise gold coast australia to analyse the temporal and spatial characteristics of morphological coupling within a double sandbar system we distinguish five types of morphological coupling between the inner and outer sandbars of which four coincide with a downstate progression of the outer bar coupling is either in phase with a landward perturbation of the inner bar facing an outer bar horn or out of phase with a seaward perturbation of the inner bar facing an outer bar horn where the coupled inner bar features either consist of rip channels or predominantly perturbations of the low tide terrace cross correlation of the image derived inner and outer bar patterns shows coupling to be a common phenomenon in the double sandbar system studied here with coupling in 40 of the observations in contrast to previous observations of sandbar shoreline coupling at single barred beaches in phase coupling 85 of all coupled bar patterns predominates over out of phase coupling 15 based on our observations and bathymetries assimilated from the images for a restricted set of coupling events we hypothesize that the angle of offshore wave incidence wave height and depth variations along the outer sandbar determine the type of flow pattern cell circulations versus meandering currents above the inner bar and hence steer the type of coupling copyright 2012 john wiley sons ltd

shoreline resilience to individual storms and storm clusters on a meso macrotidal barred beach abstract this study investigates the impact of individual storms and storm clusters on shoreline recovery for the meso to macrotidal barred biscarrosse beach in sw france using 6 years of daily video observations while the study area experienced 60 storms during the 6 year study period only 36 storms were analysed due to gaps in the video data based on the 36 individual storms and 13 storm clusters analysed our results show that clustering impact is cumulatively weak and shoreline retreat is governed by the first storms in clusters while the impact of subsequent events is less pronounced the average post storm beach recovery period at this site is 9 days consistent with observations at other beaches apart from the dominant effect of present storm conditions shoreline dynamics are also significantly affected by previous storm influence while recovery is strongly modulated by tidal range and the bar location our results reveal that not only is the storm energy important but also the frequency of recurrence storms result in greater retreat when time intervals between them are longer which suggests an interaction between short storm events and longer term evolution

erosion accretion patterns and multiple beach cusp systems on a meso tidal steeply sloping beach abstract this study examines daily variations in intertidal topography and beach cusps on a meso tidal steeply sloping beach during a five month period the observations are based on coastal imagery and frequent topographic surveys and are extracted from patterns of contours positioned 1 and 3 m above msl lower higher beach face respectively the intertidal topography was very sensitive to variations in the wave regime triggering rapid transitions from erosive to accretive states and vice versa as well as transformations of the cusp systems often involving severe horn erosion and beach face scarping distinct beach cusp systems were observed at different levels of the beach with their evolution being controlled by i wave forcing ii tidal modulation of the wave power at different levels of the beach and iii interactions between the existing beach cusp systems the lower beach face rhythmical patterns changed constantly and merged with the upper beach face cuspate features typically when the significant wave height exceeded h o 1 5 m the upper beach face pattern was persistent during the monitoring period re emerging with similar spacing and alignment despite being eroded during energetic events this persistence is also maintained by the interactions between swash and irregularities e g embayments in the dune backshore morphology the spacing of the observed beach cusps ranged from c min 8 m to c max 67 m these values were underestimated by the edge wave and self organization theories and were better predicted by the sunamura 2004 formula beach cusp growth was linked to breaker angles of near normal incidence and narrow banded frequency wave conditions bay infilling was found to be the most dominant cusp reduction mechanism for larger features c 30 m while smaller features vanished during erosive conditions the most intense cusp growth episodes were linked to accretive conditions while larger features were shown to emerge during more energetic erosion events these findings highlight the need for more longer term observations of diverse beach morphologies to formulate a global theory regarding beach cusp formation and evolution

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

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

relation between beachface morphology and wave climate at trafalgar beach cadiz spain abstract two years of offshore wave data and daily time exposure images from trafalgar beach a 2 km long sandy beach located on the southwest coast of spain that frequently exhibits rhythmic features were used to 1 explore the variability of the beachface morphology and 2 determine environmental conditions associated with the different morphological states the beachface morphology at three distinct alongshore sectors was analyzed and classified and five different morphological states were found that are related with the presence or absence of beach cusps and a berm 1 large beach cusps 2 small beach cusps 3 low tide terrace 4 plane beach berm and 5 plane beach the predominant beachface morphology is characterized by the presence of large beach cusps and the main wave climate consisted of offshore significant wave heights ranging from 0 5 1 m and wave periods between 4 and 12 s an alongshore variation of the morphology is found which might be related to the nearshore wave variability swan wave model results the morphologies are in some cases well correlated with the daily offshore incident wave climate described by the daily maximum significant wave height and the corresponding period particularly for the moderate to high energy wave conditions small beach cusps appear under short period waves whereas when the wave periods are longer the morphology tends to change to large beach cusps this transition only occurs if the forcing is maintained as constant for a certain duration which depends itself on the wave energy it is concluded that correlations over 90 are only found for the highest wave energy conditions or under long wave periods for the remainder it is not possible to generally correlate the beachface morphology based only on the wave forcing because the previous morphological state cannot be ignored

a laboratory study of longshore currents over barred and non barred beaches abstract a detailed description is given of the results of laboratory experiments on wave driven longshore currents on both barred and non barred beaches the objective is to examine the cross shore distribution of the longshore current velocities for purely wave driven currents with emphasis on the position of maximum current velocity with respect to areas where wave energy is dissipated unidirectional obliquely incident waves both regular and random were used the measurements were performed in a large wave basin with a pump recirculation system to create spatially homogeneous longshore currents the experiments yielded information on wave transformation set up of the mean water level and the cross shore distribution of wave driven longshore current velocity a number of cases are presented and compared with each other the measurements show that in the case of purely wave driven longshore currents the maximum current velocities occur close to areas where wave breaking is most intense the effect of mixing bottom friction and wave rollers on the longshore current velocity profile are examined in more detail with help of numerical modelling existing model equations based on the assumption of alongshore uniformity are used the results for the mean longshore current profile on a barred beach are in close agreement with the measurements

video observations and model predictions of depth induced wave dissipation time averaged video observations of the nearshore zone show the process of wave breaking as one or more white alongshore bands of high intensity corresponding to the preferential location of breaking wave dissipation on one or more sandbars across a known depth profile similar bands of dissipation can be predicted with existing wave transformation models based on the wave energy balance this opens up possibilities for estimating bathymetry from video observations by processing observed intensities into a model predicted proxy of wave dissipation and the inverse modeling of this dissipation proxy into depth the objectives of this paper are 1 to present a technique for processing time averaged cross shore image intensity profiles into profiles that solely contain the contribution due to wave breaking and 2 to empirically determine which modeled wave dissipation proxy relates best to the cross shore shape of the obtained breaking induced intensity the processing technique involves the removal of background illumination and noise and most importantly a correction for white foam that after being generated in the breaking process remains floating at the water surface this foam thus contributes to high image intensities but is not predicted by wave transformation models based on video and bathymetric data collected at the double barred beach at egmond aan zee the netherlands and a standard wave transformation model containing the wave and roller energy balances we find that the modeled cross shore distribution of the dissipation of the energy of the surface roller the white aerated mass of water at the breaking wave front matches the observed cross shore shape of breaking induced intensity well other hypothesized dissipation proxies result in a larger 10 m seaward bias in the locations of maximum breaking induced intensity and model predicted dissipation or do not predict the cross shore change in the area below the breaking induced intensity bands correctly

video monitoring of sandbar shoreline response to an offshore submerged structure at a microtidal beach abstract in early 2013 an 800 m long and 12 m wide submerged breakwater with its crest in 2 m depth was implemented at the wave dominated barred beach of sete se france to fight against erosion and submersion hazards daily video images from april 2011 to april 2016 covering an alongshore distance of 3 5 km are used to analyse the response of both the sandbar s and the shoreline to the structure implementation results show that the breakwater had a profound impact on the nearshore system both shoreward of the structure and well away from it alongshore a progressive rotation and linearisation of the sandbar was observed shoreward of the submerged breakwater this resulted in the splitting of the sandbar adjacent to the structure during a net offshore sandbar migration event driven by a severe storm in december 2013 the typical formation of a salient or tombolo was not observed instead shoreline coupled to the sandbar geometry which resulted in a slight seaward migration of the shoreline in front of the structure overall this study highlights that the role of the sandbar is critical to shoreline response to the implementation of breakwaters on barred beaches

observations of turbulence within a natural surf zone abstract here the reynolds stresses u w and w where u and w are the cross shore alongshore and vertical turbulence velocities respectively and the angle brackets represent time averaging are used to diagnose turbulence dynamics beneath natural breaking surf zone waves the data were collected at truc vert beach france during a 12 day period in 1 3 m water depth with strong cross shore and alongshore currents under high energy wave conditions offshore significant wave heights ranged between 2 and 8 m the u w term is predominantly negative increases with the ratio of wave height hs to water depth h degree of wave breaking and decreases in magnitude toward the bed this supports the view that the cross shore shear stress is due to breaking induced vortices that transport high speed cross shore flow downward and disintegrate close to the bed the occasional positive sign of u w within the lower 15 20 of the water column indicates that sometimes surface generated turbule

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

on cross shore migration and equilibrium states of nearshore sandbars 1 the location of submerged sandbars in the nearshore zone changes over time in response to variability in wave conditions here cross shore sandbar migration is studied with an empirical model consisting of a differential equation relating cross shore sandbar migration to wave forcing model parameters are fitted to data sets containing multiple years of daily observed positions of five sandbars at three field sites from the fitted model parameters we determine the cross shore location of zero migration equilibrium location the stability of this equilibrium and the rate response time at which a sandbar migrates toward or away from the equilibrium location we find that for breaking waves a sandbar moves toward a stable wave height dependent equilibrium location for non to slightly breaking waves however a sandbar moves away from the equilibrium location implying that the beach profile evolves toward a state without submerged sandbars the response times can differ up to a factor three for different sandbars at a particular field site and a factor ten between sandbars at different sites for breaking waves response times are found to decrease with increasing wave height from months to days while for non to slightly breaking waves response times exceed several months in general response times remain larger than the timescale of variability in wave climate several days implying that sandbars spend most of their lifetime out of equilibrium with the wave forcing the model is able to hindcast the relevant features of cross shore sandbar migration on timescales of days to several years and outperforms a baseline prediction of no change for all sandbars when the equilibrium location is reached by both the hindcasted and actual sandbar the hindcast error depends on the accuracy of the predicted equilibrium location only and no longer on the history of accumulated errors as a result sandbars that occasionally reach their equilibrium location can accurately be predicted from the wave forcings over their entire lifespan however it is difficult to predict the exact rate of the yearly to interannual trends that are observed at two field sites because the sandbars at these sites never reach the offshore located equilibrium states associated with high waves

quantification of nearshore morphology based on video imaging abstract the argus network is a series of video cameras with aerial views of beaches around the world intensity contrasts in time exposure images reveal areas of preferential breaking which are closely tied to underlying bed morphology this relationship was further investigated including the effect of tidal elevation and wave height on the presence of wave breaking and its cross shore position over sand bars computerized methods of objectively extracting shoreline and sand bar locations were developed allowing the vast quantity of data generated by argus to be more effectively examined once features were identified in the images daily alongshore mean values were taken to create time series of shoreline and sand bar location which were analyzed for annual cycles and cross correlated with wave data to investigate environmental forcing and response these data extraction techniques were applied to images from four of the argus camera sites a relationship between wave height and shoreline location was found in which increased wave heights resulted in more landward shoreline positions given the short lag times over which this correlation was significant and that the strong annual signal in wave height was not replicated in the shoreline time series it is likely that this relationship is a result of set up during periods of large waves wave height was also found to have an effect on sand bar location whereby an increase in wave height resulted in offshore bar migration this correlation was significant over much longer time lags than the relationship between wave height and shoreline location and a strong annual signal was found in the location of almost all observed bars indicating that the sand bars are migrating with changes in wave height in the case of the site with multiple sand bars the offshore bars responded more significantly to changes in wave height whereas the innermost bar seemed to be shielded from incident wave energy by breaking over the other bars a relationship was also found between a site s mean wave height and inner sand bar location sites with the highest wave heights tended to have sand bars farther from shore than those with relatively low wave heights

coupled and noncoupled behavior of three dimensional morphological patterns in a double sandbar system 1 eight weeks of daily low tide time exposure images of the gold coast australia were used to analyze the development of three dimensional morphological patterns in a double sandbar system under continued low energy wave conditions following a morphological reset storm event the patterns in both the inner and outer bar evolved albeit at different spatial and temporal scales through the accretionary sequence commonly observed at single barred beaches continuous wavelet transforms cwt of the inner bar and outer bar breaker lines show that after a storm the patterns developed at a wide range of alongshore wavelengths and that variations in wavelength over space and time were common with the bivariate extension of cwt continuous cross wavelet transforms it is found that the initial inner bar and outer bar three dimensional patterns were spatially noncoupled however over time the inner bar morphology appeared to couple with that of the outer bar with the inner bar patterns developing in response to the increasingly three dimensional onshore propagating outer bar the wavelet analysis suggests that the outer bar geometry and the distance between the inner and outer bars are critical parameters governing the morphological evolution of the composite double sandbar system

evaluation of video based linear depth inversion performance and applications using altimeters and hydrographic surveys in a wide range of environmental conditions abstract the performance of a linear depth inversion algorithm cbathy applied to coastal video imagery was assessed using observations of water depth from vessel based hydrographic surveys and in situ altimeters for a wide range of wave conditions 0 3

sandbar dynamics in microtidal environments migration patterns in unprotected and bounded beaches abstract novel observations of bar features and migration patterns at three italian sandy beaches in senigallia central adriatic sea and terracina central tyrrhenian sea are presented while two of these beaches are unprotected one is artificially embayed through the presence of a concrete jetty bar locations and motions are analysed with video imagery data sets from coastal monitoring stations wave climate from the copernicus oceanographic model is used to correlate hydrodynamics and beach morphology clear net offshore migration nom patterns are identified at all beaches although exhibiting different response scales at the low slope beach of senigallia mean surf zone slope of 0 009 bars are more sensitive to seasonal changes in wave climate with offshore shifts in winter and inactivity in summer mean annual migration rates of up to 0 26 m day and 0 09 m day are observed for outer and inner bars respectively no significant response to single storms is observed except during a single nne storm no distinct erosive or accretive trend for the shoreline is evidenced at the steep beach of terracina mean surf zone slope of 0 018 conversely bars are strongly responsive to single storm events with displacements of up to 25 50 m across a single storm the mean inter annual migration rate is 0 08 m day for the single outer bar whereas a slight onshore trend 0 02 m day for the newborn inner bar is established the presence of an artificial jetty at the misa river mouth in senigallia finally leaves the bar system typically oscillating around an equilibrium position susceptible to larger seasonal oscillations and strong offshore migration due to two ese storm events numerical simulations of nearshore circulation for two storms from different directions predict the birth of longshore currents higher ratios of significant wave height to water depth and stronger bottom orbital velocities over bars in case of the ese storm suggesting a greater tendency for offshore directed sediment transport

morphodynamic response of a two barred beach to a shoreface nourishment abstract the response to a shoreface nourishment of the two bar system at noordwijk the netherlands is analyzed based on a daily data set of time exposure video images collected during about 6 years complemented with topographic and bathymetric surveys the 1 7 mm 3 nourishment implemented as a 3 km alongshore bump seaward of the outer bar migrated more than 300 m onshore in 4 years before losing its integrity furthermore the nourishment interrupted the autonomous seaward migration of both bars for the entire duration of the study period and allaying earlier fears did not intensify the three dimensional patterns in the bars such as the crescentic plan shape and rip channels the nourishment did result in clear head effects on both flanks with the bar becoming discontinuous and the flank section decaying or becoming attached to an offshore located bar while the section of bar landward of the nourishment became attached to a landward located bar this sequence of morphologies is known as bar switching each switching episode took almost one year to complete and can therefore not be ascribed to individual wave events we suspect that shoreface nourishments enhance the possibility of bar switching by creating alongshore variability in the position and depth of the outer bar and in its cross shore migration rate and direction the noordwijk nourishment did not influence the shoreline position as its trend did not undergo distinctive variations after 1998 differences in the response of the noordwijk sandbars to the shoreface nourishment compared with other dutch nourishments are attributed to the location and size volume per unit length of the nourishment with respect to the sandbars and to the median grain size of the nourished material

alongshore rip channel migration and sediment transport abstract the relationship between alongshore rip channel migration and sediment transport is investigated using time averaged video images to identify the positions of rip channels at three sites along southern monterey bay california over 1 3 year periods daily migration rates are calculated for each site the basic coastal engineering research center cerc formula for bulk alongshore sediment transport is used to estimate alongshore transport rates at each site based on hourly input of directional wave spectra measured at an offshore buoy and shoaled and refracted to the nearshore the wave transformation model is validated by comparison with measured nearshore directional wave spectra in 13 m water depth an expanded cerc formulation that accounts for the additional forcing of alongshore wave height gradients is also tested but rejected correlation coefficients between daily rates of calculated alongshore transport and rip channel migration are low 0 01 0 44 and 0 38 at the sand city stilwell and marina sites respectively the problem of digitization noise associated with video based rip channel identification is discussed and several filtering methods are used to increase the signal to noise ratio and obtain improved correlations results indicate that higher frequency migration events on time scales shorter than 8 days will likely be obscured below the digitization noise floor but that longer period oscillations such as tidal and seasonal cycles show up clearly in both rip migration and sediment transport datasets daily rates are cumulatively summed to generate time series of representative overall rip migration distance and net alongshore transport and the cumulative summing procedure is shown to be similar to applying a low pass filter mean migration is demonstrated to lag behind net transport in the summertime suggesting that a minimum level of alongshore forcing is required to generate detectable rip migration rip channel migration and net alongshore transport have correlation coefficients that range from 0 76 to 0 94 at the three sites

assessing the suitability of video imaging for studying the dynamics of nearshore sandbars in tideless beaches nearshore sandbars an important natural defense mechanism of the beaches can be monitored using shore based video systems before studying bar dynamics with video images we must establish the relationship between the real bar positions and the videoed bar positions detected by the preferential wave breaking on the shallows this analysis becomes essential in the two studied tideless beaches of barcelona due to the critical differences with respect to the sites studied previously bogatell beach is terraced without a trough in more than 50 of the profiles there the videoed barlines are a good proxy of the terrace edge position in la barceloneta beach with dominance of barred profiles the videoed barlines better represent the bar crest position on average the obtained distances between real and videoed bar positions r are 10 15 m with the videoed barlines located shoreward changes in the bathymetric profile shape and the root mean squared wave height h rms induce a variability of r of 16 m in la barceloneta and 13 m in bogatell this apparent variability masks the real changes in bar position and should preferably be reduced before further analysis as a highly significant correlation between r and h rms is detected in the two beaches the proposed reduction method consists of sampling at a specific range of h rms this diminishes the variability by 10 to 14 m in la barceloneta and 11 m in bogatell this paper confirms the suitability of using video systems for monitoring bars and terraces in the barcelona beaches

a parametric model for barred equilibrium beach profiles abstract environment predictions for locations for which bathymetric data is missing poor or outdated requires the use of some sort of representative bathymetric form usually one that is concave up but monotonic we propose and test a parametric form that superimposes realistic sand bars ruessink et al 2003b on a background profile that mixes a concave up nearshore with a planar far field behavior implementation at any new site involves estimation of five parameters three that can be found from approximate information from climatology or old offshore charts one that can be estimated by almost any remote sensing modality and one h sea that is less well understood but mostly affects deeper bathymetry that has little impact on the resulting surf zone hydrodynamics tests against several hundred surveys at three diverse locations show that bathymetry is better estimated by the new barred form than with a previous monotonic profiles in about 80 of cases the remaining cases are usually associated with the parametric prediction of bars that look realistic but are out of phase the presence of parametric bars has an even greater impact on predicted hydrodynamics since wave breaking is concentrated at sand bar locations modeled cross shore transects of alongshore current and wave height over the measured survey profile are well represented by modeled transects over the barred parametric form but not for results over a dean profile the peak alongshore current strength and location are particularly sensitive to the presence of a sand bar

morphodynamic variability of high energy macrotidal beaches cornwall uk abstract spatial data collected over three years are presented to assess the extent of morphological variability under seasonal and storm waves on two high energy macrotidal beaches on the north cornish coast of particular interest was the degree to which the beaches displayed bar rip morphology and a novel approach to quantify the three dimensionality of the beach based on the curvature of the bottom contours is adopted to identify and classify the three dimensional beach response to changes in the dominant forcing conditions morphologically the beaches range from dissipative to intermediate and are characterised by low tide bar rip morphology which plays a key role in the nearshore dynamics and beach safety real time kinematic rtk gps surveys were undertaken using an all terrain vehicle to measure the three dimensional 3d morphology in addition nearshore wave data in situ hydrodynamic measurements local tide gauges and argus video data allowed detailed analysis of process response mechanisms for long term yearly seasonal monthly storm weekly daily and tidal hourly morphological behaviour both sites exhibited net long term accretion derived from the intertidal beach volume throughout the survey period inter site similarity in beach response was observed in response to storm waves yet coupling between the seasonal wave climate and the beach morphology was not evident at either of the sites increased wave conditions exceeding hs 4 m during sustained storm events 50 h led to offshore transport from the beachface to the subtidal bar region post storm recovery was characterised by onshore transport and the development of substantial 3d low tide morphology under normal wave conditions hs 1 6 m the dominant 3d features smoothed out as channels in filled and bar prominence reduced over a period of 2 3 months overall the beaches exhibited a significant storm dominated morphological response cycle unlike the more familiar winter summer seasonal response

observations on sandbar behaviour along a man made curved coast sandbars submerged ridges of sand parallel to the shoreline affect surfzone circulation beach topography and beach width under time varying wave forcing sandbars may migrate onshore and offshore referred to as two dimensional 2d behaviour and vary in planshape from alongshore uniform ridges to alongshore non uniform ridges through the growth and decay of three dimensional 3d patterns referred to as 3d behaviour although 2d and 3d sandbar behaviour is reasonably well understood along straight coasts this is not the case for curved coasts where the curvature can invoke spatial variability in wave forcing here we analyse sandbar behaviour along the 3000 m man made curved coastline of the sand engine netherlands and determine the wave conditions governing this behaviour 2d and 3d behaviour was quantified within a box north and west of the sand engine s tip respectively using a 2 4 year dataset of daily low tide video images and a sparser bathymetric dataset the northern and western sides behaved similarly in terms of 2d behaviour with seasonal onshore and offshore migration resulting in a stable position on inter annual timescales however both sandbar geometry and 3d behaviour differed substantially between both sides the geometric differences bar shape bar crest depth and wavelength of 3d patterns are consistent with computed alongshore differences in breaker height due to refraction the differences in the timing in growth decay and morphological coupling of 3d patterns in the sandbar and shoreline are likely related to differences in the local wave angle imposed by the curved coast similar dependency of bar behaviour on local wave height and angle may be expected elsewhere along curved coasts e g shoreline sandwaves cuspate forelands or embayed beaches copyright 2017 john wiley sons ltd

sandbar straightening under wind sea and swell forcing abstract sandbar straightening on natural beaches is known to occur following storm events however on a typical south west western australia beach sandbar straightening is observed under low amplitude wind sea forcing in summer and remains alongshore variable following high wave events associated with winter storms during summer diurnal variations in wave height and direction are associated with a strong sea breeze cycle at the peak of the sea breeze the local wind sea approaches the beach obliquely driving strong alongshore currents the occurrence of the seasonal obliquely incident wind sea provides the opportunity for testing the role of the wave angle on sandbar straightening the location of the bar crest is observed using time exposure video images and the alongshore variability is quantified using the standard deviation of the sandbar position the role of wave incidence angle on alongshore variability is highlighted as the sandbar straightens in the presence of oblique wave forcing associated with summer sea breezes and remains alongshore variable with normally incident wave forcing the transition from alongshore variable to alongshore uniform also depends on the antecedent bathymetry in particular the distance between the shore and the bar crest when the sandbar is further offshore alongshore variability persists in the presence of strong sea breezes

analytical determination of nearshore wave height variation due to refraction shoaling and friction abstract explicit wave formulae derived from the dispersion relation for linear waves are used to find an analytical solution to the problem of wave height variation on a simple topography i e topographies with incrementally constant slope and straight parallel contours the solution accounts for shoaling refraction and frictional dissipation and will be sufficiently accurate for practical purposes considering the simplifying assumptions that are necessary for treatment of this problem by any method the solution is simple enough to be handled on a personal calculator and has the advantage over numerical solutions that it can be solved for other parameters for example to give friction factors from observed wave height data the last chapter contains updated formulae for wave friction factors over movable beds

intermittent layered convection in a model mantle with an endothermic phase change at 670 km it is not yet known whether convection in the earth s mantle occurs in cells that extend throughout the entire depth of the mantle or if the upper and lower mantle convect in independent layers both possibilities seem to be consistent with geochemical and seismologi cal observations1 4 it is generally accepted however that the seismologically observed boundary between the upper and lower mantle at 670 km depth arises from the endothermic phase change spinel perovskite mgo here we investigate the results of including this phase change in a model of mantle convection for realism and to eliminate scaling problems our calculations use commonly accepted values of geophysical parameters for a clapeyron slope y 2 106 a value close to experimental results and theoretical expectations we observe local intermittent mixing between the upper and lower mantle such behaviour may offer a way to reconcile the existence of geophysical evidence for both whole mantle and layered convection

remote sensing of wave roller lengths in the laboratory 1 the optical intensity signals from surf zone waves in a laboratory flume are analyzed using several different phase averaging techniques and a methodology is developed for estimating wave roller lengths and local wave dissipation the intensity signals i e phase averaged intensity profiles of individual breaking waves are compared with the wave profiles measured by in situ wave gauges and the optical signal of the wave roller is shown to ramp up from the toe of the wave roller on the front face of the wave to a maximum intensity at the wave crest the remote sensing observations capture the growth equilibrium and decay phases of the roller as it propagates over a fixed bed arranged in a bar trough morphology next for the regular wave conditions considered here the local maxima of the phase averaged intensities are shown to better indicate the initial onset of wave breaking and the occurrence of wave breaking in the bar trough as compared to the more commonly used time averaged mean intensity in addition the phase averaged profiles are used to measure the size of the roller and these measurements are compared to previous observations of smaller scale rollers in equilibrium the observed roller lengths are shown to agree with predictions from a wave roller model and to provide a new physical link between the remotely sensed signal and roller dissipation finally as an example application of these new data a simple wave height inversion model is presented that allows an estimation of surf zone wave heights from the remotely sensed roller lengths

observations of nearshore crescentic sandbars 1 the temporal and spatial variability of crescentic sandbars is analyzed with hourly long term months video observations collected at four barred sites and are qualitatively compared to the temporal and spatial variability predicted by hypotheses underpinning existing approaches and models for crescentic bar formation edge wave template model linear stability analysis and nonlinear models the observations coming from the single barred beaches at duck north carolina usa and miyazaki kyushu japan and from the double barred beaches at the northern gold coast queensland australia and noordwijk netherlands show that crescentic sandbar wavelength and amplitude variations over space and time are very common for instance at any moment in time the wavelength of the smallest and longest crescentic bar can differ by a factor of 2 temporal changes in wavelength and amplitude result from merging and splitting of individual crescents causing the final configuration of a crescentic sandbar system to be very different from the initial configuration the gold coast data indicate that these intrinsically nonlinear interactions are an attempt of the crescentic bar system to self organize into a more uniform pattern as splitting is usually confined to the longest crescentic bar observed whereas merging usually combines the smallest crescentic bars into a longer bar the observed spatial and temporal crescentic bar behavior contrasts qualitatively with behavior predicted from the edge wave template model and implies that the predictive skill of linear stability models is limited nonlinear models are potentially better suited for a comparison against these field observations several suggestions to improve these models and hence to facilitate a data model comparison are made