coupling mechanisms in double sandbar systems part 1 patterns and physical explanation crescentic sandbars and rip channels along wave dominated sandy beaches are relevant to understand localized beach and dune erosion during storms in recent years a paradigm shift from hydrodynamic template models to self organization mechanisms occurred to explain the formation of these rhythmic features in double sandbar systems both the inner and outer bar rip channels and crescentic planshapes are now believed to be free instabilities of the nearshore system arising through self organization mechanisms alone however the occasional occurrence of one or two inner bar rip channels within one outer bar crescent suggests a forced morphologically coupled origin here we use a nonlinear morphodynamic model to show that alongshore variability in outer bar depth and the relative importance of wave breaking versus wave focussing by refraction across the outer bar is crucial to the inner bar rip channel development the coupling patterns simulated by our model are similar to those observed in the field morphological coupling requires a template in the morphology outer bar geometry which through the positive feedback between flow sediment transport and the evolving morphology that is self organization enforces the development of coupling patterns we therefore introduce a novel mechanism that blurs the distinction between self organization and template mechanisms this mechanism may also be extended to explain the dynamics of other nearshore patterns such as beach cusps the impact of this novel mechanism on the alongshore variability of inner bar rip channels is investigated in the companion paper copyright 2010 john wiley and sons ltd

morphodynamic response to wave group forcing a numerical model is used to compute the time dependent behaviour of the nearshore bathymetry under wave group forcing using the depth averaged shallow water equations in combination with an advection diffusion equation for the sediment concentration after verification with prototype flume measurements a morphodynamic computation for a pocket beach has been carried out for two different conditions the first case consideres wave groups made up by a bichromatic wave resulting in an alongshore rhythmic double barred beach the second case considers wave groups made up by a directionally spread short wave field resulting in a single barred beach intersected by irregularly spaced rip channels

decoupling spatial and temporal patterns in short term beach shoreline response to wave climate this paper describes the use of a combined approach which merges numerical models and remote video techniques to derive the spatial and temporal patterns in short term beach shoreline forcing response to wave climate on a microtidal low energy sandy beach shorelines are obtained after applying an artificial neural network ann to daily raw video images the data comprise directional hydrodynamic conditions propagated from deep water to 10 m depth and video derived daily shorelines over the span of one year and a half the spatial and temporal variability of the beach is split by empirical orthogonal function eof decomposition time series exploration between eof and wave height shows a decoupling in spatial shoreline response to wave climate with a more immediate effect in cross shore sediment transport than in alongshore sediment transport the first eof which accounts for the cross shore variability is significantly correlated with wave height averaged for the previous four days while the second eof which explains the alongshore beach variability correlates with the averaged waves of the previous 7 days

objective beach state classification from optical sensing of cross shore dissipation profiles remote sensing using terrestrial optical charge coupled device cameras is a useful data collection method for geophysical measurement in the nearshore zone where in situ measurement is difficult and time consuming in particular optical video sensing of the variability in human visible surface refraction due to the nearshore incident wave field is becoming an established method for distal measurement of nearshore subtidal morphology we report on the use of a low mounted shore normal camera for gathering data on cross shore dissipative characteristics of a dynamic open beach data are analyzed for the purposes of classifying three of wright and shorts intermediate classes of morphological beach state as determined by expert raters although these beach states are usually thought of as being distinctive in terms of their longshore bar variability theory predicts that differences should also be observed in cross shore dissipative characteristics three methods of generating features from statistical features from the archived optical data are described and compared in terms of their ability to discriminate between the beach states principal component scores of the percentile distributions were found to provide slightly better classification performance i e 85 while approximating the data using relatively fewer features whereas classification using intensity distributions alone resulted in the worst performance classifying 78 of beach states correctly class center moment profiles for each beach state were constructed and results indicate that cross shore wave dissipation becomes more disorganized as linear bars devolve into more complex transverse structures

longshore variability of beach states and bar types in a microtidal storm influenced low energy environment beach classification models are widely used in the literature to describe beach states in response to environmental conditions these models were essentially developed for sandy barred to barless beaches in micro to mesotidal environments subject to moderate to high wave energy conditions and have been based on field studies over limited stretches of coast here we further interrogate the performance of the australian beach classification scheme by analysing beach states and corresponding bar types on a regional scale in a storm influenced low wave energy microtidal environment using a large and unique spatial and temporal dataset of supra and subtidal beach morphology and sedimentology the 200 km long coast of the gulf of lions in themediterranean consists of quasi continuous sandy beaches with a well developed double sandbar system all the reported classical beach stateswere observed on this coast from reflective to dissipative alongwith two more unusual states the rock platform constrained beach state which is associated with bedrock outcrops and the non barred dissipative beach statewhich ismore commonly found in large tidal range settings lidar bathymetry shows that the transitions between beach state zones are marked mainly headlands but transitions also occur progressively along stretches of continuous sandy beach the longshore distribution of beach states and associated bar types on a regional scale can be related to the variability of hydrodynamic conditions wave incidence and energy and sediment characteristics particle size however the influence of these parameters on beach state seems to be largely controlled by the geological context such as the presence of a river mouth headland or rock platform finally we assessed the ability of the parameter commonly used to characterise beach states which combines wave characteristics and sediment fall velocity to predict the observed beach states and bar types using a very large set of hydrodynamic and sedimentary data our results based on high frequency spatial sampling show that the fall velocity of the subtidal sediment coupled with wave statistics one month prior the observed beach state strongly improved the predictive power of the parameter

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

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

geological control of beach morphodynamic state the concept of beach morphodynamic states has achieved widespread acceptance in the coastal geological literature since its inception in the mid 1980s and expansion in the 1990s much of the pioneering work was undertaken in australia under a range of environmental conditions in microtidal environments and a close empirical relationship between beach 3 dimensional morphology and the dean s parameter h b wst was established subsequently the relative tidal range parameter h b tr was extended to beaches of all tidal ranges in this paper observations are presented from 25 beaches around the north coast of ireland these beaches exist on an environmental gradient that encompasses marked tidal and wave energy variability micro to macrotidal and low to high wave energy each beach was visually categorised into one of several established beach states described in the literature on the basis of field observations for each beach the rtr and dean s parameter were calculated for the immediately antecedent period and used to predict the beach state using published relationships observed and predicted beach states were then compared comparison of observed and predicted beach states showed that while beaches with observed dissipative morphology typically matched the expected criteria most other beach states did not lack of agreement between predicted and observed beach states has been reported elsewhere and attributed to failings in the rtr and dean s parameter in addition this study identifies geological factors as important constraints on actual beach state in the majority of beaches studied inherited geological factors appear to be more important determinants of beach morphology than contemporary dynamics c 2005 elsevier b v all rights reserved

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

semi empirical treatment of wave transformation outside and inside the breaker line a semi empirical method is developed which predicts the wave height shoaling up to the break point on laboratory and natural beaches linear shoaling is enhanced with empirical curves for the wave shape obtained from field measurements of wave height through the break point and the surf zone made on an ocean beach in southern australia from 1987 to 1989 wave height shoaling breaking and attenuation are unified in a mixed lagrangian eulerian numerical model of random wave height transformation which with the semi analytical enhancements provides improved predictions of the height transformation of individual waves through the surf zone this is demonstrated for a wide variety of cases from the field and laboratory

field observations on the morphodynamic evolution of a low energy rip current system abstract a field experiment was conducted at palm beach nsw australia to investigate morphodynamic relationships operating within a rip current system during a near complete sequence of beach state evolution under decreasing energy conditions observations and measurements were obtained from nearshore surveys multiple dye releases oblique photographs and the deployment of various combinations of nine ducted impellor flow meters and five pressure sensors over a seven day period in rip and feeder channels the dataset provides a unique opportunity to assess and quantify aspects of the accretionary model of wright and short mar geol 56 1984 93 118 for intermediate beaches the morphology of the main rip channel exhibited distinct sequential adjustments with a narrowing of channel width an increase in channel depth a reduction in the cross sectional area available for rip flow and an increase in morphological relief rip flow velocity increased during the observed evolution and was also modulated by the tide experiencing maximums at low tide and minimums at high tide morphologic and kinematic adjustments of the rip system were most pronounced during the transition to a transverse bar and rip state the existence of a dominant feeder in a twin feeder and rip system contributed to the migration and establishment of a rip head over the seaward slope of the opposite longshore bar net erosion in the rip channel was balanced by net deposition in the feeder channels and bar crests and qualitative observations suggest that this rip head bar both receives transported sediments from the rip channel and contributes sediments to the ongoing accretion of the beach system a direct relationship was found to exist between rip morphology and flow with rip velocity increasing as cross sectional rip channel area decreases and these results are incorporated in a conceptual modification of the model of wright and short the results of this study are restricted to a subset of commonly occurring beaches but show that accretionary beach state evolution on intermediate beaches is indeed characterised by an increase in rip current velocity the nature of which can be linked to morphologic control in addition the rip head bar is identified as a potentially key component of low energy rip system evolution

a morphological stability analysis for a long straight barred coast a morphological stability analysis is carried out for a long straight coast with a longshore bar the situation with oblique wave incidence and a wave driven longshore current is considered the flow and sediment transport are described by a numerical modelling system the models comprise i a wave model with depth refraction shoaling and wave breaking ii a depth integrated model for wave driven currents and iii a sediment transport model for the bed load transport and the suspended load transport in combined waves and current the direction of the sediment transport is taken to be parallel to the depth integrated mean current velocity neglecting the effects of a bed slope and secondary currents an instability is found to develop around the bar crest the instability is periodic in the alongshore direction and tends to form rip channels and to steepen the offshore face of the bar between the rip channels the alongshore wave length of the most unstable perturbation is determined for different combinations of the wave conditions and the geometry of the profile

laboratory measurements of the vertical structure of rip currents 1 this paper describes the three dimensional variation of rip currents through the use of experimental measurements of rip currents in a directional wave basin the rip currents are unstable appearing sporadically at any given location the vertical profile of the rip current is found to vary from depth uniform inside the channel to depth varying further offshore offshore from the channel the rip current has much stronger velocities at the surface than near the bottom the instantaneous profiles twist rapidly over depth farther offshore and are fairly uniform in the channel the depth variations are shown to be sensitive to the total volume flux in the rip

extreme erosion on high energy embayed beaches influence of megarips and storm grouping abstract megarips have long been recognised as an important yet poorly documented mechanism of beach erosion on high energy embayed beaches the persistence and cumulative effect of megarips during storm groups are described from three embayed beaches arrifana mt clerigo and amoreira exposed to high energy wave conditions in the mesotidal bedrock dominated southwestern coast of portugal morphological changes determined by topographic monitoring and supplemented by interpretation of digital imagery over two years revealed the development of storm induced megarips which exerted a major influence on beach erosion differences in megarip influence within and between beaches are related to embayment geometry and orientation which significantly influence the nearshore wave field rip location is topographically controlled being determined by alongshore variations in breaking wave height and obliquity along with interaction of wave driven circulation patterns and embayment nearshore topography moderate beach sand loss during individual storms was linked to the development of megarips with associated rip neck and feeder channels extreme erosion however occurred when megarips and feeder channels persisted during successive storms promoting continued erosion and seaward sediment export observations show that once initiated megarip channels persist for several months and continue to act as conduits for offshore sediment transport under non storm conditions the maintenance of such rip circulation systems driven by morphodynamic feedback reduces beach recovery ability until the rip neck and feeder channels are infilled

shoreline instability under low angle wave incidence 1 the growth of megacusps as shoreline instabilities is investigated by examining the coupling between wave transformation in the shoaling zone longshore transport in the surf zone cross shore transport and morphological evolution this coupling is known to drive a potential positive feedback in case of very oblique wave incidence leading to an unstable shoreline and the consequent formation of shoreline sand waves here using a linear stability model based on the one line concept we demonstrate that such instabilities can also develop in cases of low angle or shore normal incidence under certain conditions small enough wave height and or large enough beach slope the wavelength and growth timescales are much smaller than those of high angle wave instabilities and are nearly in the range of those of surf zone rhythmic bars o 102 103 m and o 1 10 days the feedback mechanism is based on 1 wave refraction by a shoal defined as a cross shore extension of the shoreline perturbation leading to wave convergence shoreward of it 2 longshore sediment flux convergence between the shoal and the shoreline resulting in megacusp formation and 3 cross shore sediment flux from the surf to the shoaling zone feeding the shoal even though the present model is based on a crude representation of nearshore dynamics a comparison of model results with existing depth averaged two dimensional model output and laboratory experiments suggests that the instability mechanism is plausible additional work is required to fully assess whether and under which conditions this mechanism exists in nature

shoreline response to multi functional artificial surfing reefs a numerical and physical modelling study the results of a series of 2dh numerical and 3d scaled physical modelling tests indicate that processes governing shoreline response to submerged structures such as artificial surfing reefs are different from those associated with emergent offshore breakwaters unlike the case of emergent offshore breakwaters where shoreline accretion salient development is expected under all structural environmental conditions the principal mode of shoreline response to submerged structures can vary between erosive and accretive depending on the offshore distance to the structure the predominant wave incidence angle and structure crest level also have important implications on the magnitude of shoreline response but not on the mode of shoreline response i e erosion vs accretion based on the results obtained here a predictive empirical relationship is proposed as a preliminary engineering tool to assess shoreline response to submerged structures

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

applicability of parametric beach morphodynamic state classification on embayed beaches abstract use of parametric classification of beach morphodynamic state has been steadily increasing in coastal research despite identification of several shortcomings of their representativeness as elementary beach descriptors in this paper we analyse the parametric classification of beach morphodynamic state in a set of six embayed beaches in southwestern portugal exposed to diverse settings from high energy dissipative to intermediate to low energy intermediate to reflective conditions applicability of parametric approaches considered within the dimensionless space defined by dimensionless fall velocity and rtr relative tidal range according to averaged wave tide and sediment characteristics of beaches was assessed in association with a probabilistic analysis implemented through a bayesian network model that considered the full range of wave tide and sediment conditions at each site both parametric approaches were compared to field based beach state classification implemented using a novel hierarchical framework for beach state analysis the classification obtained within a probabilistic framework provided an innovative approach for analysis of beach state and mobility extending the insights on beach morphodynamic behaviour obtained from averaged environmental parameters reflective to lower intermediate beach conditions showed better agreement with parametric approaches while poor beach state differentiation was achieved for intermediate beach types limitations in the application of beach classification models result from i an inadequacy of existing beach state types in differentiating beaches particularly within the intermediate domain and for geologically controlled embayed beaches and ii shortcomings involved in the parametric approaches the beach state models disregard the major role of geological control in embayed beach morphodynamic behaviour in modulating beach shape and segmentation influencing sediment size and availability causing alongshore variations in the wave field and creating topographically induced nearshore circulations existing beach state models are unable to adequately represent the widely variable conditions observed in embayed beaches

statistical simulation of wave climate and extreme beach erosion abstract recent developments in extreme values modelling have been used to develop a framework for determining the coastal erosion hazard on sandy coastlines this framework quantitatively reproduced the extreme beach erosion volumes obtained from field measurements at narrabeen beach australia this encouraging finding was achieved using kriebel and dean s kriebel d l and dean r g 1993 convolution method for time dependent beach profile response journal of waterway port coastal and ocean engineering 119 2 204 226 simple beach erosion and accretion model the method includes allowances for joint probability between all basic erosion variates including wave height period and direction event duration tidal anomalies and event spacing a new formulation for the dependency between wave height and period has been developed it includes the physical wave steepness limitation event grouping where significantly more erosion can occur from two closely spaced storms is handled by temporally simulating the synthetic wave climate and the resulting beach erosion and accretion

bars formed by horizontal diffusion of suspended sediment abstract the mechanism responsible for the ubiquitous presence of convex beach profiles and shoreward migration of linear bars is examined using numerical circulation and sediment transport models the models are validated against laboratory measurements and observed natural beach cross sections while not discounting the importance of infragravity and advective horizontal circulation or bed return flow mechanisms a robust diffusive process explains the convex profile shape and bar formation in the presence of concentration gradients across the surf zone a diffusive sediment flux from high to low concentration results in the transfer of sediment outwards from the breakpoint both onshore and offshore and the subsequent formation of a diffusion bar and diffusion profile the profiles are characterised by single and double convex dome like shapes developing during shoreward migration of the bars by the diffusion mechanism the mechanism explains several phenomena observed on natural beaches including i convex beach profiles ii shoreward migration of the bar with concomitant beach accretion under narrow band swell iii reduced propensity for bar formation on low gradient fine sand beaches or under wide band wave spectra even though multiple bars are common on some low gradient beaches and iv offshore migration of the bar during periods of increasing wave height the diffusion mechanism can be dependent on orbital motion alone and as such requires no frequency selection or strong correlation between multiple processes for bar formation

an experimental study of rip channel flow a laboratory study of the flow over a bar with a single rip channel has been performed first the well known pattern of a bar circulation cell with a strong offshore directed current out through the rip channel and a weaker onshore directed return flow over the bar is documented then measurements of the three dimensional structure of the flow in the area where the rip channel the bar and the trough meet and well inside the rip channel are presented these measurements reveal that 3d effects play an important role and that a depth integrated viewpoint may not always be sufficient for predicting the flow in the near bed region particle tracking experiments illustrate the near bed flow pattern over the entire area these demonstrate how the overall trajectory pattern changes as a function of the distance of wave breaking from the bar crest for some conditions the rip current is fed from the trough and for other conditions it is fed directly from the bar both the 3d measurements and the trajectory tests show the existence of a weaker onshore directed near bed drift in the area where the rip current ceases finally in a series of sensitivity tests measurements of the rip current intensity for different wave climate and water level conditions reveal a strong correlation between the rip current intensity and the wave height both normalized

role of wave forcing storms and nao in outer bar dynamics on a high energy macro tidal beach abstract outer sand bar dynamics on a high energy macro tidal beach were investigated using long term multi year field datasets of intertidal morphology and offshore bathymetry utilising a 15 year time series of argus video images five distinct outer bar types were identified mega rip longshore crescentic crescentic attached and welded the most common classification was crescentic attached with the outer bar oscillations being out of phase with the inner bar oscillations as would be expected for the shore normal wave approach at this site the outer bar had a typical amplitude of 0 5 1 m and a longshore wavelength of 600 m changes in outer bar morphology were related to measured and modelled nearshore wave data however the outer bar morphology changed over a much longer timescale monthly to annual than the daily to weekly variations in wave height and period an extended duration of energetic wave action was required to bring about an upstate bar transition to the longshore or mega rip state where the bar then remained arrested for a significant amount of time requiring several months of low wave conditions to induce a down state transition through crescentic to welded this slow morphological response is explained by extended relaxation times attributed to the large tidal range at the study site where the outer bar morphology is only active for part of the tidal cycle several hours around low tide the configuration and position of the outer bar were related the more upstate downstate bar types being associated with a more offshore onshore bar position the detrended outer bar position was significantly related to a forcing term based on wave power and disequilibrium of the dimensionless fall velocity with offshore onshore bar migration occurring when wave conditions were more less energetic that the antecedent conditions the upstate end member longshore or mega rip was attained sometime during the winter months for 14 out of the 16 years of monitoring the outer bar remained attached to the low tide shoreline over the winter 2005 2006 and 2010 2011 these two winters with incomplete upstate cycles were characterised by the lowest winter wave conditions and negative winter north atlantic oscillation nao indices suggesting that the winter nao is correlated with both beach state and nearshore bar configuration

role of morphological variability in the evolution of nearshore sandbars abstract computations using a depth averaged morphological process based model of a double nearshore bar system have been used to test the hypothesis that bathymetries with small variability adapt more easily to new hydrodynamic conditions than bathymetries with distinctly imprinted crescentic patterns the computations are used to investigate the assumption that nearshore bathymetries tend to evolve toward a rip channelled pattern matching concurrent constant hydrodynamic forcing if these conditions prevail for an extended period of time in each computation an initially alongshore uniform double barred bathymetry seeded with a small random bed level perturbation was forced by two sequential constant hydrodynamic conditions for each set of conditions four different computations show the effect of a later transition moment and thus more distinctly evolved patterns on the level of adaptation to the second condition after the transition to the second condition different hydrodynamic circulations occur due to differences in the bathymetry at the transition moments depending on how pronounced the existing features were at the moment of transition these circulations either reinforce the existing bathymetric pattern or allow the bathymetry to evolve to a new rip chanelled pattern with a spacing similar to the one that occurs if the second condition had been applied from the start as hydrodynamic conditions generally change more rapidly than the adaptation time which is at least in the order of days it is highly unlikely that observed rip channel distances match length scales expected for concurrent hydrodynamic conditions consistent with field observations e g holman et al 2006 it is therefore concluded that nearshore patterns are formed by a combination of both the antecedent morphology and thus antecedent hydrodynamics and the current local hydrodynamic conditions next to factors like sediment characteristics

rip current type spacing and persistence narrabeen beach australia abstract long term daily rip observations on narrabeen beach australia were made together with daily measurements of wave height period direction surf zone width and beach state a total of 3513 rips were observed on 270 days over a 19 month period results show that rips accompany moderate to high waves and are associated with intermediate beach types rip spacing follows wave conditions increasing in spacing size and intensity as waves rise and conversely as they fall rips are a function of both the prevailing and antecedent wave conditions and the rate and direction of change in wave conditions rips are classified into three types erosion mega and accretion erosion rips are initiated by rising seas in the transverse bar and rip and higher beach states they accompany general beach erosion they are widely spaced narrabeen ys 300 500 m 100 200 m increasing in size and intensity with the waves until the fully dissipative ripless state is reached they are both temporally and spatially highly variable persisting in one location for only hours to a day or so except where topographically controlled they are a major mechanism for the seaward transport of sediment and under extreme conditions may extend over a kilometer seaward of the breaker zone mega rips are large scale 1 km topographically controlled erosion rips that persist when nearshore and or embayment topography prevents the development of the fully dissipative state by inducing wave refraction and persist longshore gradients in surf zone dynamics that in turn drive the rip circulation accretion rips prevail during stable or falling wave conditions usually following erosion rip formation they are associated with general beach accretion are more closely spaced narrabeen ys 170 250 m 100 m less intense and become increasingly topographically arrested by crescentic bars and rhythmic bar beach morphology of the longshore bar trough rhythmic bar and beach and transverse bar and rip beach states they are relatively stable both spatially and temporally and may persist in one location for days to weeks if wave conditions remain favorable they are fair weather rips which may disappear by infilling in the low tide terrace beach state or be destroyed by rising seas rips generally are absent from the reflective low tide terrace and fully dissipative beach states

physical modeling of three dimensional intermediate beach morphodynamics experiments have been performed in a large wave tank in order to study the morphodynamics of rip current systems both accretive and erosive shore normal wave conditions were applied the beach evolving through all the states within the intermediate beach classification under the so called down state accretive and up state erosive morphological transitions results show that any prescribed change in the wave conditions drastically increases the rate at which the morphology changes the surf zone morphology tends toward a steady state when running a given wave climate for a long duration we quantitatively describe a full down state sequence characterized by the progressive evolution of an alongshore uniform bar successively into a crescentic plan shape a bar and rip channel morphology and a terrace from the analysis of a large data set of dense eulerian measurements and bathymetric surveys we depict several feedback mechanisms associated with wave driven rip current circulation wave nonlinearities and the seabed evolution at first a positive feedback mechanism drives a rapid increase in the rate of morphological change beach three dimensionality and rip intensity by the time the sandbar evolves into a bar and rip morphology a negative feedback mechanism characterized by a decaying beach change rate and an increasing beach alongshore uniformity overwhelms the former mechanism an erosive sequence characterized by both an overall offshore bar migration and an increase in beach three dimensionality is also described

short term changes in the morphodynamic states of beaches and surf zones an empirical predictive model a time series of 6 5 years of daily observations of beach states and wave characteristics from southeastern australia was analyzed with the aim of determining the degree to which time varying beach state can be explained and predicted the six commonly occurring beach states dissipative longshore bar trough rhythmic bar and beach transverse bar and rip low tide terrace and reflective discussed earlier were related by means of discrete discriminant analyses to the parameter hb wst where hb is breaker height ws is the fall velocity of the beach sand and t is peak breaker period using a total of 1545 cases two values were used in the analyses the immediate value occurring on the day the particular state was observed and a weighted mean value expressing recently antecedent conditions the immediate value made a negligible contribution to explaining day to day beach state observations however the antecedent conditions showed a strong relationship and provide a successful means of prediction by examining cases where the time derivatives of both state and were near zero it was possible to define the equilibrium conditions associated with each state directions of change erosional or accretionary are predicted in terms of departures of from the equilibrium value appropriate to the beach state prevailing at the time change begins

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

mechanisms controlling the complete accretionary beach state sequence accretionary down state beach sequence is a key element of observed nearshore morphological variability along sandy coasts we present and analyze the first numerical simulation of such a sequence using a process based morphodynamic model that solves the coupling between waves depth integrated currents and sediment transport the simulation evolves from an alongshore uniform barred beach storm profile to an almost featureless shore welded terrace summer profile through the highly alongshore variable detached crescentic bar and transverse bar rip system states a global analysis of the full sequence allows determining the varying contributions of the different hydro sedimentary processes sediment transport driven by orbital velocity skewness is critical to the overall onshore sandbar migration while gravitational down slope sediment transport acts as a damping term inhibiting further channel growth enforced by rip flow circulation accurate morphological diffusivity and inclusion of orbital velocity skewness opens new perspectives in terms of morphodynamic modeling of real beaches

comment on the article morphodynamic classification of sandy beaches in low energetic marine environment by gomez pujol l orfila a canellas b alvarez ellacuria a mendez f j medina r and tintore j marine geology 242 pp 235 246 2007 abstract in a recent study gomez pujol et al gomez pujol l orfila a canellas b alvarez ellacuria a mendez f j medina r tintore j 2007 morphodynamic classification of sandy beaches in low energetic marine environment mar geol 242 pp 235 246 used the wright and short beach classification scheme fed with hindcasted wave and sediment settling velocity data to classify the morphodynamic states of a group of low energy mediterranean beaches mallorca spain here we use morphodynamic data obtained from an argus video station and a morphodynamic model to assess the validity of this type of model for predicting beach states under typical mediterranean wave conditions the results show that values alone do not provide a realistic prediction of beach states statistics and that the intensity of the forcing represented by the wave energy level and the duration of the events must also be taken into account

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

megacusps on rip channel bathymetry observations and modeling abstract the formation of beach megacusps along the shoreline of southern monterey bay ca is investigated using time averaged video and simulated with xbeach a recently developed coastal sediment transport model investigations focus on the hydrodynamic role played by the bay s ever present rip channels a review of four years of video and wave data from sand city ca indicates that megacusps most often form shoreward of rip channels under larger waves significant wave height hs 1 5 2 0 m however they also occasionally appear shoreward of shoals when waves are smaller hs 1 m and the mean water level is higher on the beach after calibration to the sand city site xbeach is shown to hindcast measured shoreline change moderately well skill 0 41 but to overpredict the erosion of the swash region and beach face simulations with small to moderate waves hs 0 5 1 2 m suggest similar to field data that megacusps will form shoreward of either rip channels or shoals depending on mean daily water level and pre existing beach shape a frequency based analysis of sediment transport forcing is performed decomposing transport processes to the mean infragravity and very low frequency vlf contributions for two highlighted cases results indicate that the mean flow plays the dominant role in both types of megacusp formation but that vlf oscillations in sediment concentration and advective flow are also significant

the morphodynamic effects of incident wave groupiness and tide range on an energetic beach abstract the roles played by daily tide range and incident wave groupiness in affecting the short term morphodynamic responses of an energetic beach are examined demodulation of original tide and wave time series from the moderate energy narrabeen beach australia resulted in new time series of daily tide range and a daily grouping factor which expresses the relative amplitude of the alternation between groups of high and low waves using these new time series together with time series of daily beach state and changing breaker conditions statistical analyses were performed aimed at determining the contributions made by tide and groupiness in explaining time varying beach state additional to those made by time varying wave conditions eigenvector analyses of monthly surveyed beach and surf zone profiles provided a set of time series on modes of profile configuration change which were also analyzed to determine the relative effects of waves and tide range on profile shape both tide range and groupiness are significant determinants of beach state the six beach states are reflective low tide terrace transverse bar and rip rhythmic bar and beach longshore bar trough and dissipative wright and short 1984 provided that wave conditions are within the appropriate range to favor beach states at the reflective end of the sequence spring tides will tend to favor the low tide terrace over the transverse bar and rip state higher tide ranges are also associated with more subdued bar trough topography the more accentuated bar trough profiles are developed when tide range is minimal overall higher relative incident wave groupiness favors the more dissipative states incident wave groupiness is the dominant factor determining whether the low tide terrace state or transverse bar and rip state prevails provided incident wave steepnesses permit one or the other of these states groupiness is also important in discriminating between the transverse bar and rip and rhythmic bar and beach states

efficacy of beach dewatering alassio italy abstract the goal of this study is to estimate the efficiency of dewatering operations in alassio beach north italy by following an integrated approach which included beach volume calculations daily mapping of the shoreline position examination of specific beach widening events and daily comparisons of morphodynamic characteristics of the drained beach versus a control section which included wave run up bar patterns rip migration evolution of the berm and cusp morphology alassio beach was documented by a daily time lapse photography by repeated dgps profile measurements and by an hourly wave and sea level monitoring following one year of draining the shoreline position and the beach volume of the drained beach and the control section showed little differences i e accumulation of 0 28 m 3 m 2 and a shoreline advance of 1 1 m on the drained beach whereas on the control beach the volume change was 0 03 m 3 m 2 and the shoreline retreated 1 2 m short episodes of beach widening 1 7 days long which coincided with onshore bar movement and a relative low sea level occurred simultaneously on the drained and the control sector this data indicated the inefficiency of the draining operation an improved resolution for determining the draining effect was attained by the sequential snap shot photography which showed many systematic morphological differences between the drained beach and the reference segment the drained beach developed a berm crest and a linear often scarped foreshore with a narrow swash zone no such cumulative morphologies were observed on the non drained control beach which commonly displayed cusps that were usually absent on the drained foreshore the wave data showed recurrent medium wave events of hs 1 2 m which repeatedly interrupted the calms thus cutting off the beach evolution the draining in alassio was unable to promote beach accumulation by counteracting the erosive effect of the medium interrupting storms

a simple equilibrium model for predicting shoreline change abstract this contribution describes the development calibration and verification of a 1 d behaviour orientated shoreline prediction model the model primarily encapsulates shoreline displacement forced by wave driven cross shore sediment transport hysteresis effects are shown to be important and are included in the model whereby present shoreline change is influenced by past hydro morpho dynamic conditions the potential magnitude of shoreline change increases with incident wave power and the degree of disequilibrium the latter disequilibrium term eq is expressed in terms of the time evolving equilibrium eq and instantaneous dimensionless fall velocities and dictates the direction of shoreline movement following wright et al 1985 the equilibrium fall velocity is defined as a function of the weighted antecedent conditions and is a proxy for the evolving beach state the decay rate of the weighting function used to compute eq is a model free parameter determined by calibration against measured data which physically reflects the degree of observed memory of the system the decay in amplitude of this weighting function with time is controlled by a memory decay term where the weighting reaches 10 1 and 0 1 at 2 and 3 days prior to the current calculation time the model is applied to two multi year 6 years data sets incorporating hourly wave and weekly shoreline measurements from two contrasting energetic sites in se australia the first is the relatively dissipative straight gold coast qld and the second is a more intermediate embayed beach at narrabeen nsw the model shows significant skill at hindcasting shoreline change at both sites predicting approximately 60 of the total shoreline variability the gold coast shoreline is dominated by a strong seasonal signal conversely at the narrabeen embayment shoreline variability and morphology is more dynamic responding at storm frequency evidence suggests that there is a strong coherence between the shoreline position and morphodynamic state and that both have response times characterised by it is hypothesised that optimised values in the shoreline model physically relate to the efficiency of sediment exchanges between the shoreface and offshore bars and the prevalence of one or two dimensional horizontal circulation the general success of this new shoreline model for hindcasting the observed shoreline behaviour at two distinctly different open coast sites suggests that this approach may be suitable for broader application

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

investigation of medium term barred beach behavior using 28 year beach profile data and rotated empirical orthogonal function analysis abstract a 28 year beach profile dataset for a stretch of the hasaki coast in japan was examined using rotated empirical orthogonal function reof analysis to investigate the cross shore variation in the characteristics of beach profile change the data were obtained weekly on a micro tidal wave dominated intermediate beach along a survey line extending from the backshore to a water depth of approximately 5 m reof analysis using the first eight empirical orthogonal functions led to the study area being divided into five unique zones based on beach profile change patterns namely the backshore the foreshore the inner and outer transition zones and the bar trough zone although these zones were notably distinct from one another the profiles in foreshore and the shoreward part of the inner transition zone changed in the same way over periods of 6 and 12 months

morphodynamic modelling of rip channel growth the morphological evolution of a rip channel system due to normally incident waves has been investigated using two different approaches the first approach is a state of the art commercial 2dh coastal area model whereas the second approach is a linear stability analysis the results of the two different approaches have been compared and both models predict rip channel spacings and initial growth rates of similar magnitudes

the statistics and kinematics of transverse sand bars on an open coast abstract ten years 1987 1996 of time exposure video images of the nearshore region at duck nc were used to study transverse sand bars bathymetric features of intermediate length scales 10 200 m oriented oblique or perpendicular to the shoreline these transverse sand bars extend seaward from both the shoreline trough transverse bars and the shore parallel sand bar offshore transverse bars transverse bars had not previously been observed in an energetic coastal environment such as that at duck and their dynamics and role in nearshore processes is unknown frequency of occurrence statistics and length scales of the transverse bars were calculated using the video images trough and offshore transverse bars appeared a mean of 39 and 73 days per year respectively the offshore bars were found to be much larger features than the trough bars with mean wavelengths alongshore spacing between consecutive crests of 79 and 172 m for trough and offshore bars respectively both the trough and offshore bars were found to persist for periods of days to months the alongshore movement of the bars was measured and compared to estimates of surf zone longshore currents which were calculated from wave height and wave angle data both sets of bars were observed to move at rates up to 40 m day at times both trough and offshore bars were observed shifting in the same direction as the current was flowing and at other times both sets of bars remained stationary even under relatively strong longshore currents trough bars were also observed moving against the current an hypothesis proposed by barcilon and lau 1973 j geophys res 78 15 2656 2664 that the transverse bars were created as a sea bed instability under longshore currents was tested by comparing the magnitude of estimated surf zone longshore currents with times of formation or presence of transverse bars there was no evidence to suggest that the bars were formed by this simple longshore current instability mechanism instead it is plausible that the combined effects of waves and currents may drive the formation of these features

deterministic profile modelling of nearshore processes part 2 sediment transport and beach profile development abstract this is the second of two companion papers concerned with the modelling of sediment transport and beach profile response to wave and tidal action part i was concerned with the wave and current modelling aspects whilst the present paper considers the sediment transport and profile development predictions particular adaptations of well known theoretical developments that distinguish the present modelling work are described both cross shore and alongshore sediment transport processes the latter including the influence of tides are represented the alongshore transport description is included to allow this quasi 2dv model to act as a module to a quasi 3dh morphodynamic model the q3dh model is not described here the beach profile evolution phase of the model is capable of considering a fixed boundary such as a seawall the fixed boundary may also be erodible as in the case of a sandy beach overlying a cohesive till substratum in both parts i and ii the validity of each individual predictive phase of the model has been assessed where the accuracy was found to be insufficient additional processes were considered until the level of accuracy could be considered suitable for input to the next predictive phase of the model whilst free variables exist within the formulation of the model these have been considered to be fixed in almost every application of the model the consideration of additional processes is the approach used to achieve improved model prediction not the arbitrary tuning of free variables some of the validation tests for the sediment transport phases alongshore and cross shore are presented in this paper along with evaluations of the integrated model for profile change the foremost value of the model rests with the ability to identify links between observed beach changes and the underlying coastal processes

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

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

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

understanding coastal morphodynamic patterns from depth averaged sediment concentration this review highlights the important role of the depth averaged sediment concentration dasc to understand the formation of a number of coastal morphodynamic features that have an alongshore rhythmic pattern beach cusps surf zone transverse and crescentic bars and shoreface connected sand ridges we present a formulation and methodology based on the knowledge of the dasc which equals the sediment load divided by the water depth that has been successfully used to understand the characteristics of these features these sand bodies relevant for coastal engineering and other disciplines are located in different parts of the coastal zone and are characterized by different spatial and temporal scales but the same technique can be used to understand them since the sand bodies occur in the presence of depth averaged currents the sediment transport approximately equals a sediment load times the current moreover it is assumed that waves essentially mobilize the sediment and the current increases this mobilization and advects the sediment in such conditions knowing the spatial distribution of the dasc and the depth averaged currents induced by the forcing waves wind and pressure gradients over the patterns allows inferring the convergence divergence of sediment transport deposition erosion occurs where the current flows from areas of high to low low to high values of dasc the formulation and methodology are especially useful to understand the positive feedback mechanisms between flow and morphology leading to the formation of those morphological features but the physical mechanisms for their migration their finite amplitude behavior and their decay can also be explored

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

the extreme 2013 2014 winter storms beach recovery along the southwest coast of england abstract sand and gravel beaches naturally act as a coastal buffer absorbing wave energy and dynamically adapting to the seasonal and long term wave climate significant shifts in nearshore morphology can occur during extreme wave events which can have a significant impact on coastal vulnerability during the winter of 2013 14 the atlantic coast of europe received an unprecedented sequence of very energetic wave conditions 8 week mean offshore h s 4 4 m these events caused extensive physical beach and dune erosion and socio economic flooding damage to infrastructure impacts throughout the west coast of europe many monitored sites in the uk and france were in their most eroded state since morphological records began 5 10 years we consider the geomorphological significance of the storm response at 38 natural beaches in the southwest of england ranging from semi sheltered reflective gravel barriers to ultra dissipative exposed sand beaches with dunes the extent and patterns of post storm recovery are examined in detail at three beaches with characteristic storm response behaviours exposed sandy beaches were dominated by cross shore transport processes leading to significant loss of sediment offshore from the intertidal zone 200 m 3 m exposed gravel beaches were dominated by overwash with significant loss landward and semi sheltered sites exposed to more oblique wave forcing were dominated by a rotational response due to alongshore sediment redistribution due to these contrasting responses mechanisms and timescales for beach recovery displayed strong inter site and intra site variations in offshore and rotational cases the recovery processes were multi annual comprising seasonal to decadal signals and were intrinsically linked to the storm response mechanisms while permanent losses occurred when overwash dominated we show that post storm recovery does not necessarily occur during calm periods and that in many cases high energy wave events appear to be essential for recovery of sediment offshore and counter rotation our results highlight the significance of dominant climatic oscillations multi annual storm sequencing storm tracks and resultant variations in wave angle in controlling the impact that extreme wave events have on contrasting sand gravel beaches in exposed sheltered locations

styles of volcano induced deformation numerical models of substratum flexure spreading and extrusion the gravitational deformation of volcanoes is largely controlled by ductile layers of substrata using numerical finite element modelling we investigate the role of ductile layer thickness and viscosity on such deformation to characterise the deformation we introduce two dimensionless ratios a volcano radius ductile layer thickness and b viscosity of ductile substratum failure strength of volcano we find that the volcanic edifice spreads laterally when underlain by thin ductile layers a 1 while thicker ductile layers lead to inward flexure a 1 the deformation style is related to the switch from predominantly horizontal to vertical flow in the ductile layer with increasing thickness increasing a structures produced by lateral spreading include concentric thrust belts around the volcano base and radial normal faulting in the cone itself in contrast flexure on thick ductile substrata leads to concentric normal faults around the base and compression in the cone in addition we show that lower viscosities in the ductile layer low b lead to faster rates of movement and also affect the deformation style considering a thin ductile layer if viscosity is high compared to the failure strength of the volcano high b then deformation is coupled and spreading is produced however if the viscosity is low low b substratum is effectively decoupled from the volcano and extrudes from underneath it in this latter case evidence is likely to be found for basement compression but corresponding spreading features in the volcano will be absent as the cone is subject to a compressive stress regime similar to that produced by flexure at volcanoes where basement extrusion is operating high volcano stresses and outward substratum movement may combine to produce catastrophic sector collapse an analysis of deformation features at a volcano can provide information about the type of basement below it a useful tool for remote sensing and planetary geology also knowledge of substratum geology can be used to predict styles of deformation operating at volcanoes where features have not yet become well developed or are obscured

experimental study of nearshore dynamics on a barred beach with rip channels 1 wave and current measurements are presented from a set of laboratory experiments performed on a fixed barred beach with periodically spaced rip channels using a range of incident wave conditions the data demonstrate that the presence of gaps in otherwise longshore uniform bars dominates the nearshore circulation system for the incident wave conditions considered for example nonzero cross shore flow and the presence of longshore pressure gradients both resulting from the presence of rip channels are not restricted to the immediate vicinity of the channels but instead are found to span almost the entire length of the longshore bars in addition the combination of breaker type and location is the dominant driving mechanism of the nearshore flow and both are found to be strongly influenced by the variable bathymetry and the presence of a strong rip current the depth averaged currents are calculated from the measured velocities assuming conservation of mass across the measurement grid the terms in both the cross shore and longshore momentum balances are calculated and their relative magnitudes are quantified the cross shore balance is shown to be dominated by the cross shore pressure and radiation stress gradients in general agreement with previous results however the rip current is shown to influence the wave breaking and the wave induced setup in the rip channel analysis of the longshore balance shows that the overall strength of the longshore feeder currents is governed by a balance between longshore pressure gradient forcing and an opposing radiation stress gradient in addition the longshore feeder currents show maxima in the bar trough region providing experimental evidence that longshore pressure gradients can shift longshore current maxima shoreward from the bar crest finally since the longshore radiation stress gradient in the surf zone is governed by the amount of wave dissipation on the rip current there exists a positive feedback mechanism whereby a strong rip current can weaken the radiation stress gradient opposing the feeder currents and lead to even stronger feeder currents and rips

analysis of far field erosion induced by low crested rubble mound structures this paper focuses on the analysis of the morphological response induced by low crested structures on the adjacent seabed with emphasis on the far field erosion that is frequently observed close to roundheads and at the gaps between structures the analysis is based on observations of far field erosion both at prototype scale and in laboratory experiments mechanisms responsible for the observed erosion are highlighted using coastal area numerical modelling tools to simulate the flow patterns induced by schemes involving low crested structures finally an example of the use of a coastal area morphological modelling system to investigate the dependence of the far field erosion processes on the freeboard of the coastal protection structures is presented and discussed

response of wave dominated and mixed energy barriers to storms wave dominated and mixed energy barriers are extremely dynamic landforms responding to processes operating over a spectrum of time scales ranging from daily to monthly fluctuations related to storm and post storm conditions to century to millennium scale evolution driven by relative sea level change two types of storms are of particular relevance warm core tropical and cold core extratropical cyclones both are responsible for generating very large waves highly energetic surf zone dynamics and sediment transport elevated inshore water levels and extensive morphological responses all cyclones are affected by climate change which governs their frequency intensity and tracks barrier storm response is primarily governed by maximum storm runup and barrier morphology as conceptualised in abby sallenger s storm impact scale model sallenger 2000 this model defines four storm impact regimes and includes erosive as well as accretionary responses on the erosion side the swash regime drives bar and berm flattening the collision regime is marked by dune scarping and beach lowe the overwash regime leads to dune scouring and channel incision and the inundation regime may result in barrier destruction on the deposition side storm berms and beach ridges may form and accrete in the swash and collision regimes localised vertical beach and barrier accretion are associated with the collision and overwash regimes and washover deposition takes place in the overwash and inundation regimes site specific factors play a key role in moderating the morphological response and include storm characteristics type duration and track longshore sediment supply upwelling downwelling currents coastal setting and inner shelf topography the response of a barrier to a tropical or extratropical cyclone can however not be considered in isolation and has to be appreciated in a longer temporal context involving morphological preconditioning due to antecedent wave and water level conditions additionally a simple process response approach of the cause and effect type is inappropriate and a more complex conceptual framework involving thresholds feedbacks resilience and vulnerability will need to be adopted a useful way to visualise and conceptualise more complex storm behaviours and the longer term vulnerability of barriers is the resilience trajectory which maps out the changes in barrier geometry elevation and width over various time scales from weeks to years or even longer and under varying forcing conditions including changes in storminess and sea level rise an increased understanding of barrier response to storms and sequences of storms is required to better quantify long term barrier response to climate change high resolution and comprehensive decadal records of barrier response to storms are a prerequisite to achieve this ambition linking site specific coastal settings hydrodynamic drivers and morphological responses and allowing the recognition of recovery and impact dominated phases the enhanced insights in barrier response to extreme events must then be incorporated into improved coastal response models to help predict the impacts of future climate change on wave dominated and mixed energy barriers around the world 2013 elsevier b v

spectral signatures for swash on reflective intermediate and dissipative beaches in this paper we synthesise a large data set gathered from a wide variety of field deployments and integrate it with previously published results to identify the spectral signatures of swash from contrasting beach types the field data set includes the full range of micro tidal beach types reflective intermediate and dissipative with beach gradients ranging from approximately 1 6 to 1 60 exposed to offshore significant wave heights of 0 5 3 0 m the ratio of swash energy in the short wave f 0 05 hz to long wave f 0 05 hz frequency bands is found to be significantly different between the three beach types swash energy at short wave frequencies is dominant on reflective and intermediate beaches and swash at long wave frequencies is dominant on dissipative beaches consistent with previously reported spectral signatures for the surf zone on these beach types the available swash spectra were classified using an automated algorithm clara into five different classes the ordered classes represent an evolution in the spectrum shape described by a frequency downshifting of the energy peak from the short wave into the long wave frequency band and an increase in the long wave swash energy level compared to a relatively minor variation in the short wave swash energy level a universally common feature of spectra from all beach states was an f 4energy roll off in the short wave frequency band in contrast to the broadly uniform appearance of the short wave frequency band the appearance of the long wave frequency band was highly variable across the beach states we incorporate the results presented here and previously published observations into the morphodynamic beach state model and propose an ordered sequence of swash spectra under increasing and decreasing incident wave energy level this extension of the beach state model to include the swash zone leads to the following propositions for morphodynamic controls on the nature of the swash spectrum 1 the short wave part of the swash spectrum is relatively constant in form across all beach states f 4 energy roll off and the energy density per unit frequency is controlled by the beach face gradient alone 2 the spectral bandwidth of the energy roll off varies directly with offshore wave energy level and inversely with beach face gradient or beach state in a manner consistent with the non linear wave breaking criterion 3 the infragravity part of the swash spectrum is highly variable in form across all beach states and the energy level is related to the offshore wave energy level and surf zone morphology

wave breaking patterns control rip current flow regimes and surfzone retention recent research into rip currents has revealed the existence of multiple circulation patterns meaning that no single escape strategy is appropriate in all situations rip circulation is influenced by surfzone morphology which can be inferred from wave breaking patterns in video imagery wave breaking often occurs over the bars adjacent to the rip channel with little breaking over the seaward end of the rip however under varying wave and tide conditions breaking can also occur at the seaward extent of rip channels here we use this difference as a novel wave dissipation parameter to classify a rip channel as either open or closed in terms of rip head wave breaking a 4 day field study provided lagrangian rip current data at a macrotidal dissipative beach monitored by a coastal imaging system using this new parameter rip channels that were identified as closed exhibited a 31 increase in current speeds and 43 increase in horizontal vorticity compared to open channels the transition between open and closed channels occurred over a single tidal cycle which altered surfzone retention rates closed channels promoted surfzone retention with 25 of drifters exiting the surfzone in comparison open channels were more conducive to exchange with exit rates up to 91 analysis of the royal national lifeboat institution lifeguard rip incident database showed that open rips were disproportionately represented in the occurrence of rescue events and calculated here to be twice as dangerous as closed rips the use of this new open closed parameter could be used by surf lifesaving organisations and may have implications for the cross shore exchange of sediment and pollutants

dynamics of single barred embayed beaches abstract the dynamics of single submerged sandbars of two artificial embayed beaches la barceloneta and bogatell barcelona nw mediterranean has been studied with a video recorded data set of 4 3 years the alongshore averaged cross shore migration the orientation with respect the shoreline and the sinuosity of the barlines have been analyzed and related to wave conditions alongshore sediment transport and shoreline variability in general the submerged bars follow the general cyclic morphological behaviour observed in natural beaches switching among the four intermediate morphodynamic states but the studied beaches can be arrested during long periods of low wave conditions the dominant up state transition in barcelona beaches during storms is the transition toward the rhythmic bar and beach state the complete morphodynamic reset longshore bar and trough state only occurring during extreme wave events the cross shore migration of bars is dominated by the weekly and interannual components the interannual component shows an onshore bar migration trend at both beaches in contrast with the net offshore migration observed in multibarred open beaches bar disposition is located progressively seaward in the dominant alongshore transport direction i e oblique with respect to the shoreline at la barceloneta beach shoreline and barline orientations change consistently and a significant correlation between the accumulated alongshore sediment transport and the associated change in bar orientation has been found suggesting that alongshore transport can play a significant role in barline orientation finally bar sinuosity increases during eastern storms in both beaches this indicates that the formation of crescentic bars occurs for approximately shore normal waves some of the differences observed in bar morphology and mobility in the two studied beaches are related to their different level of protection with respect to the incident waves beach indentation

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

storm driven changes in rip channel patterns on an embayed beach this paper introduces a semi automatic computer algorithm designed to detect rip current channels in video imagery as a case study this method is applied to 3 3 years of video data from an embayed beach to demonstrate the link between antecedent surf zone morphology wave energy and up down transitions in beach state an objective measure of rip channel change was developed to define six significant rip reconfiguration events and relate these events to wave energy over the period of study no complete resets of the nearshore morphology occurred the analysis indicates that direct correlation of rip patterns with the instantaneous wave conditions is not a useful way to demonstrate how rips and waves interact the average wave energy over a period of ten days combined with storm duration were good indicators of rip channel change demonstrating that in general beach morphology responds with a time lag to changes in forcing rip channels with a short cross shore length and narrow alongshore spacing responded faster to changes in wave conditions than rips with a long cross shore length and wider alongshore spacing to force changes in the rip morphology longer rip channels required wave events of higher energy and or a longer duration offshore islands protect the beach under certain wave approach angles sometimes resulting in a dual width surf zone which was narrow at the sheltered end and wide at the exposed end of the beach the wider surf zone end was characterised by three dominant and persistent rip channels whereas the narrow surf zone section contained a number of smaller rips which evolved rapidly under wave forcing our observations demonstrate the importance of rip channel size in controlling the response time of nearshore morphology

quasi three dimensional modeling of rip current systems 1 the focus of the paper is the analysis of the flow in rip current systems generated by channels in longshore bars on a beach the horizontal variations of rip current systems are described through the use of the quasi three dimensional nearshore circulation model shorecirc model predictions are compared to laboratory measurements of waves and current velocities throughout the entire rip current system and show reasonable agreement the rips in the two channels are found to behave differently because of the depth variation across the basin it is found that higher bottom stress leads to more stable flow where the rip current meanders less and fewer eddies are generated the wave current interaction creates forcing which reduces the distance rip currents flow offshore and can lead to a slow pulsation of the rip current this pulsation is in addition to the instabilities of a jet which can also be present in rip currents the three dimensionality of the rip current system is found to have a significant effect on the overall circulation patterns index terms 4255 oceanography general numerical modeling 4512 oceanography physical currents 4546 oceanography physical nearshore processes keywords rip currents nearshore circulation numerical modeling waves

swash zone boundary conditions derived from optical remote sensing of swash zone flow patterns 1 optical remote sensing is used to measure flow patterns in the swash zone timestack images are analyzed to measure the asymmetry and the relative duration of the inflow into the swash zone this varies significantly between individual swashes contrary to the classical analytical swash model for runup induced by bores which predicts a similar flow pattern for all events for swash forced by breaking bores the gradient of the x t locus of flow reversal varies over a wide range and flow reversal can occur simultaneously across the whole swash zone this variation of the gradient of the locus of flow reversal in x t space can be parameterized in terms of a single free variable in recent solutions to the nonlinear shallow water equations which fully defines the swash boundary inflow condition consistent with the theory the horizontal runup the swash period and the swash similarity parameter were observed to be independent of the swash inflow conditions but the flow asymmetry is not only a weak correlation was observed between the swash boundary condition and the iribarren number and beach slope conversely the analysis suggests that the degree of swash swash interaction does influence the swash boundary condition and the resulting internal flow kinematics the variation in inflow conditions is expected to influence the magnitudes of the velocity moments within the swash zone and therefore sediment transport rates

morphodynamics of intermediate beaches a video imaging and numerical modelling study four years of time exposure images of palm beach sydney australia are used to a develop a phenomenological scheme based on surf zone properties for the classification of the four intermediate beach states low tide terrace ltt transverse bar rip tbr rhythmic bar beach rbb and longshore bar trough lbt identified by wright l d short a d 1984 morphodynamic variability of surf zones and beaches marine geology 56 93 118 and b determine environmental conditions associated with the different beach states the overall agreement between beach state classifications obtained by visual classifications of images and those predicted by the phenomenological scheme exceeds 90 analysis of time series of intermediate beach states and wave data indicates that the nearshore morphology continuously cycles through the four beach states in response to variations in the incident wave energy the results also indicate that lbt morphology is produced by high energy wave conditions erosive while the progression towards ltt occurs under lower waves accretive a depth averaged morphodynamic model is employed to determine the morphodynamic processes governing the rbb to tbr and tbr to ltt transitions model results indicate that the rbb to tbr transition is governed by the erosion of the original longshore bars in the initial rbb morphology and the formation and subsequent welding of shoals in the lee of the original longshore bars model results also indicate that rbb to tbr transitions can occur under shore normal and oblique wave conditions the tbr to ltt model simulations indicate that under obliquely incident waves progressive erosion of the transverse shoals and deposition of the eroded sediment in rip channels gradually diminishes the longshore variability in morphology resulting in an ltt morphology

bars bumps and holes models for the generation of complex beach topography in shallow water any two waves of the same frequency are shown to produce complex patterns of drift velocity above the sea bed if the longshore components hi h of the wave numbers of the two waves are different these steady flow patterns exhibit a longshore periodicity of wave number hi h irrespective of whether the waves propagate in the same direction say hi he positive or in opposite directions he negative the interaction of two edge wave modes is examined in detail the drift velocities are calculated and a simple sediment transport model is used to predict the beach topography that would be in equilibrium with these flow patterns as expected crescentic sand bars are produced by the special case of standing edge waves hi h intriguingly for all other cases a combination of complex transverse bars plus meandering or straight offshore bars result patterns that are surprisingly reminiscent of many published descriptions of complex rhythmic topography the extension of the model to three or more waves produces topography that appears to be very irregular although the pattern should repeat over sufficiently long distances along the beach even with only three waves these distances may be very large compared to the scale of the bars

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

coupled sandbar patterns and obliquely incident waves 1 in double sandbar systems the alongshore variability in the inner bar often resembles that of the outer bar suggesting that the outer bar acts as a morphological template for the inner bar earlier observations have indicated that this resemblance also termed coupling may take several forms here we apply a nonlinear 2dh morphodynamic model with time invariant forcing to show that the angle of wave incidence is crucial for the alongshore variable morphodynamic evolution of the inner bar for a given crescentic outer bar in contrast to previous modeling efforts of double barred systems which mostly used highly idealized boundary conditions we force our model with realistic hydrodynamics and bathymetrical data derived from video observations at the double barred gold coast australia the results show that for small angles of wave incidence 10 over a crescentic outer bar cell circulation patterns govern the flow at the inner bar giving rise to rip channels that incise the inner bar at the locations of the landward perturbations in the outer bar horns on the other hand for obliquely incident waves 10 20 over a crescentic outer bar the circulatory nature of the flow disappears and gives way to a meandering alongshore current the offshore directed sections of this meandering alongshore current erode the inner bar downdrift of the outer bar horns leading to landward perturbations of the inner bar that are coupled to the outer bar horns an observed coupling type that had not been reproduced as yet oblique wave incidence thus proves to be crucial to the development of this type of sandbar coupling as previously hypothesized from sandbar coupling observations at the gold coast additional simulations including tidal water level variations and bar depth variations demonstrate the robustness of our findings

analysing decadal scale crescentic bar dynamics using satellite imagery a case study at anmok beach south korea abstract understanding long term sandbar dynamics can be crucial for informed coastal zone management but is often hampered by data availability to increase the number of sandbar observations available from bathymetric surveys this study proposes and evaluates a method to manually extract the sandbar location using freely available satellite imagery for the case study of anmok beach in south korea validation of the satellite extracted sandbar locations against 9 in situ measurements shows good agreement with errors well within the pixel resolution of the satellite imagery i e 30 m for landsat missions the applicability of the method is constrained to locations where 1 the cross shore crescentic length scales are larger than the image resolution 2 frequent wave breaking and clouds are absent and 3 the water clarity is sufficient to enable the manual extraction of the sandbar crest line using the additional sandbar observations from the satellite imagery significantly increases the temporal extent and resolution of the dataset for anmok beach this allows the study of sandbar characteristics dynamics and impacts of human interventions to an extent that would not have been possible without the satellite imagery within the study period 1990 2017 it is found that the sandbar maintains a persistent crescentic pattern that is only altered during prolonged and very intense storm conditions the cumulative alongshore migration of the sandbars is investigated and found to be in the order of hundreds of meters over the 27 years study period comparing the sandbar characteristics prior and after the construction of gangneung port shows that both the amplitudes and wavelengths of the sandbar crescents near the port have decreased after its construction

morphodynamic classification of sandy beaches in low energetic marine environment abstract morphodynamic classification of beaches has achieved widespread acceptance in both geological and geomorphological literature in this sense the present work classifies twelve mediterranean low energetic beaches according to the dimensionless fall parameter parameter in the island of mallorca propagation of 44 yr of wave data as well as a detailed sediment study allows to provide probabilities for morphodynamical beach state on an annual and seasonal basis consequently beaches in mallorca fall between three major categories which are a truly reflective b reflective skewed to intermediate and c intermediate beaches the mallorcan beach position in the morphodynamical scheme is close related to the physiographical and geological framework comparison of observed values with those obtained in the analysis leads that for gross beach classification there is agreement between predicted and real state however on a seasonal classification mainly during summer there is no agreement between the predicted state and the real one as the model does not incorporate the role of summer sea breezes beach reflective states are highlighted real beach configurations correspond to more energetic wave dynamic conditions and to intermediate state scenarios

a behavior oriented dynamic model for sandbar migration and 2dh evolution 1 a nonlinear model is developed to study the time dependent relationship between the alongshore variability of a sandbar a t and alongshore averaged sandbar position xc t sediment transport equations are derived from energetics based formulations a link between this continuous physical representation and a parametric form describing the migration of sandbars of constant shape is established through a simple transformation of variables the model is driven by offshore wave conditions the parametric equations are dynamically coupled such that changes in one term i e xc drive changes in the other i e a t the model is tested on 566 days of data from palm beach new south wales australia using weighted nonlinear least squares to estimate best fit model coefficients the model explained 49 and 41 of the variance in measured xc and a t respectively comparisons against a 1 d horizontal 1dh version of the model showed significant improvements when the 2dh terms were included 1dh and 2dh brier skill scores were 0 12 and 0 42 respectively onshore bar migration was not predicted in the 1dh model while the 2dh model correctly predicted onshore migration in the presence of 2dh morphology and allowed the bar to remain closer to shore for a given amount of breaking providing an important hysteresis to the system the model is consistent with observations that active bar migration occurs under breaking waves with onshore migration occurring at timescales of days to weeks and increasing 2dh morphology while offshore migration occurs rapidly under high waves and coincides with a reduction in 2dh morphology citation splinter k d r a holman and n g plant 2011 abehavior orienteddynamicmodelforsandbarmigrationand2dh evolution j geophys res 116 c01020 doi 10 1029 2010jc006382

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

variability of sandbar morphometrics over three seasonal cycles on a single barred beach understanding the morphodynamics of surfzone sandbars is very relevant from a sediment transport perspective three complete annual sandbar migration cycles were studied on a single barred beach the study period included the 2015 2016 el nino anomaly and the incidence of a highly energetic swell storm the sandbar responded directly to the seasonal wave forcing thus it migrated offshore during the energetic winter and onshore during the milder summer conditions its seasonal migration cycle comprised four stages 1 generation in autumn november at lower than 1 m depth 2 offshore migration over the winter until january february while h s 1 3 m 3 onshore migration over the early spring march and april while h s 1 0 m and during may june 4a subaerial beach welding unbarred beach when a dynamic equilibrium reached or 4b terrace bar formation sandbar flattening as a consequence of a lack of a dynamic equilibrium the energetic el nino winter conditions induced the same amount of offshore sandbar displacement as the individual extreme swell storm placing the sandbar at a maximum cross shore distance of 190 m beyond the dynamic equilibrium contrary to the expected a period of mild wave conditions during the 2017 winter favored the landward migration of the sandbar locating it near its generation point the duration of mild wave energy conditions and the offshore sandbar location and volume are considered relevant factors that limit the capabilities of the sandbar to reach shallow waters and weld to the subaerial beach before the summer

mean currents and sediment transport in a rip channel measurements of hydrodynamics and suspended sediment transport were carried out along a cross shore transect in a rip channel a tidally induced threshold for rip flow initiation was found this threshold depended upon the degree of wave energy dissipation and could be identified through a critical value of the ratio of significant wave height to water depth s in the rip neck with normally incident waves rip current velocities were well correlated with velocities predicted from a simple model involving the onshore mass transport in asymmetric breaking waves crossing the bar hydrodynamics and sediment transport were tidally modulated with strong offshore directed rip currents and associated offshore sediment transport due to the mean flow at low tide at high tide when the rip was inactive the tendency was for weak onshore directed mean flows and or oscillatory incident waves transporting smaller amounts of sediment landward the net result was a gradual lowering of the topographic relief along the rip channel with net deposition seaward of the rip outside the surf zone transport was mainly landward due to oscillatory incident waves

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

late pleistocene palaeolakes in the andean and extra andean patagonia at mid latitudes of south america abstract late pleistocene palaeolakes on the eastern side of andes glacial lakes and in the patagonian steppe pluvial lakes along 41 s latitude were studied natural dams glaciers moraines that maintained a high water level in glacial palaeolakes were melted or cut by erosion during late pleistocene climate amelioration with the retreat of the glaciers from the andean valleys during prominent regional deglaciation outflow from the eastern side of andes to the pacific ocean was formed about 13 2 ka bp as a result the water level in glacial palaeolakes fell rapidly in stages these changes were often preceded by volcanic tectonic activity which is suggested to be the touch of butterfly releasing mass balance adjustment in the changing landscape the lacustrine tephra stratigraphic pattern from the andes comprising more than 50 horizons since the last glaciation is presented the correlation of palaeoenvironmental changes between the andes and the patagonian steppe is suggested on the basis of two dacite marker horizons the deglaciation event that led to development of the new hydrological system in the andean palaeolakeland formed several large but short lived palaeolakes in closed basins in the patagonian steppe probably due to melting of local ice and permafrost accumulated during glaciation on the surrounding mountains and elevated plains