modelling shoreface profile evolution current knowledge of hydro sediment and morpho dynamics in the shoreface environment is insufficient to undertake shoreface profile evolution modelling on the basis of first physical principles we propose a simple panel type model to map observed behaviour the internal dynamics are determined by slope dependent wave induced cross shoreface transports while the external driving factors are lateral sediment supply and sea level rise this model concept is tested with reasonable success against the observed behaviour of the central holland coast considering two hindcast periods one covering the evolution over the last century the other the subboreal subatlantic evolution a limitation of this model is that the cross shoreface dynamics are solely steered by the variations of shoaling short waves since a variety of other wave and current dynamics may be expected to be present in the coastal boundary layer it may well be that the effects of the mechanisms and conditions which are not represented are hidden in the coefficients of the sediment transport formula this limits the accuracy of the coefficients as used and our findings should be considered as an order of magnitude estimate only indeed behaviour oriented modelling implies that generalization of results to arbitrary situations and conditions is not straightforward yet we expect that some of the conclusions are more generally applicable this concerns the substantiation of the assumption that the upper shoreface responds on a much smaller time scale than the lower shoreface and the idea that the shoreface profile is not always and everywhere in equilibrium with its forcing a worthwhile observation from the holland coast application is that the bottom slope effect on the transport is only important at geological time scales the profile evolution at the engineering time scales say 10 to 100 years is effectively quasi static in that there is no feedback between the long term averaged transport and the state of the profile this implies that at these smaller scales the profile changes can be predicted on the basis of a static sediment balance this does not mean that the gravitational downslope transport is unimportant as a physical phenomenon in coastal profile evolution it is only unimportant if a highly aggregated model like this is applied at relatively short time scales

predicting the crest height of a gravel beach the beach crest is a common morphological feature formed by the deposition of sediment carried up slope by wave swash the elevation to which waves can pile gravel is a function of the size and density of the material relative to the hydraulic components of swash velocity wave frequency and runup height two equations 17 and 21 that predict the height of the beach crest to the wave forces and the beach material are derived the first derivation compares the wave force acting to move a stone up the beach face with a weight force acting to hold the stone in place the second derivation relates the potential energy per unit area of the beach crest to the total wave energy that lifted and deposited the material above a given sea level datum as a test of the derived equations the actual crest height of one natural gravel beach was accurately estimated by both equations derived further research and testing on other natural beaches are needed to fully verify eqs 17 and 21 a comparison of other equations eqs 2 3 and 4 that predict crest height is also made the poor fit of the other equations are a result of using values for the coefficients that were established in wave tank experiments another shortcoming of eqs 3 and 4 is that they do not include variables related to the beach material hence they predict that all particle sizes from sand to boulders would be piled to the same elevation by the same wave forcing eq 2 includes a particle size variable but predicts increasingly higher beach crests for larger particles more realistic results for all three equations eqs 2 3 and 4 would be expected with field tested values for the coefficients but a range in values for each different beach would be necessary the advantage of eqs 17 and 21 is that equations are not dependent on coefficients whose values come from correlation with other data sets

the role of bore collapse and local shear stresses on the spatial distribution of sediment load in the uprush of an intermediate state beach abstract spatial variations in sediment load in the swash uprush and textural properties of sediment in transport were evaluated to investigate the mechanisms responsible for sediment transport during wave uprush four streamer traps were deployed at 2 0 m intervals across the swash zone of a sheltered microtidal sandy beach at port beach western australia over a 4 day period during these trapping experiments offshore significant wave heights were 0 3 0 5 m and wave periods were about 10 s the average width of the uprush zone was 6 9 m and the average uprush duration was 5 9 s cross shore distributions of sediment load for 70 uprush events reveal a maximum in sediment load landward of the base of the swash at about 20 of swash width during single events and a maximum closer to mid swash at about 40 of swash width during multiple events characterized by swash interactions settling velocity distributions of trap samples during individual uprush events are similar to distributions found on the beach surface with the lowest settling velocities finest sediments near the base of the swash zone and maximum settling velocities coarsest sediments around the mid swash position it was found that sediment transport during wave uprush occurs through two distinct mechanisms 1 sediment entrainment during bore collapse seaward of the base of the swash zone and subsequent advection of this bore entrained sediment up the beach by wave uprush and 2 in situ sediment entrainment and transport induced by local shear stresses during wave uprush both mechanisms are considered important but the first mechanism is considered most significant during the early stages of wave uprush when sediment is transported mainly in suspension while the second mechanism is likely to dominate the mid to later stages of wave uprush when sediment is transported mainly by sheet flow the relative importance of the two mechanisms will vary between different beaches with the morphodynamic state of the beach reflective versus dissipative expected to play a major role

a field based classification scheme for gravel beaches a tripartite classification of gravel beaches based upon morphodynamic properties is proposed and demonstrated for 42 new zealand beaches the main advantage of this scheme is that it is based on simple visual classification that can be applied globally in the field and is underpinned by morphodynamic differences between the beach types the three types identified from the results are 1 pure gravel beach 2 mixed sand and gravel beach 3 composite gravel beach pure gravel beaches have steep slopes tan 0 08 0 24 and gravels extending from the storm berm to below mean low water spring tide level mixed sand and gravel beaches have moderate slopes tan 0 04 0 13 with sand and gravel entirely mixed both cross shore and at depth composite gravel beaches have a steep gravel berm fronted by a low angle intertidal terrace with overall beach slopes of tan 0 05 0 14 on composite beaches there is distinct hydrodynamic cross shore sorting of the sand and gravel component these broad types are tested using discriminant analysis and the three classes are shown to be highly significant f 16 24 df 8 p 0 00005 the key discriminating variables are iribarren number beach width average grain size and storm berm height

beach cusp morphodynamics detailed measurements of three dimensional beach cusp morphology were made on a steep gradient low energy microtidal beach in perth western australia during the field campaign a variety of wave conditions and tidal ranges were experienced and these differing hydrodynamic conditions were reflected in a consistent pattern of morphological changes to the beach cusp system a useful parameter to delineate between trends of cusp destruction and re formation appeared to be the surf similarity parameter tan i0 l0 where h0 is offshore wave height l0 is deep water wave length and tan is beach gradient for 1 2 a small storm was experienced at the start of the field campaign period and resulted in considerable erosion of the beach face the cusp morphology across the lower beachface was destroyed but a subtle remnant of the pre storm cusp morphology was preserved on the upper beachface when cusps reformed after the storm under the influence of declining wave conditions they appeared at the same location and with the same dimensions as the pre storm cusp morphology hence it is considered that the cusp re formation was controlled more by the antecedent morphology than the hydrodynamic conditions this indicates that positive feedback between swash hydrodynamics and beachface morphology necessary to form beach cusps does not require a large variation in relief 1997 john wiley sons ltd

the origin of swash cusps on beaches abstract genetically there are two types of beach cusps those formed in the surfzone by the nearshore circulation system and those formed on the beachface by the swash and backwash the latter are here called swash cusps and a simple model relating the physical dimensions of swash cusps to the properties of the incident wave field and the mean beach slope is developed as in some previous models the cusp wavelength is controlled by the longshore wavelength of edge waves but the edge waves are now required only to provide small periodic perturbations on an originally uniform beach further cusp growth occurs because of the interactions between the incident waves and the perturbed topography the maximum cusp height apex to valley is hypothesized to be proportional to the significant vertical excursion of swash motions it follows from the above assumptions that the maximum possible cusp steepness cusp height cusp longshore wavelength is proportional to the mean on offshore beach slope this result agrees with field data and the value of the ratio of maximum cusp height to beach slope differs from that obtained theoretically by guza and bowen 1981 using a complicated non linear model with rather different physics the present model implies that edge waves although necessary for initiating the initial bedform perturbation need not persist for the development of mature cusp topography

development of cusp related gravel size and shape facies at malin head ireland samples of beach gravels were obtained from foreshore cusp deposits at portmore beach near malin head republic of ireland axial dimensions a b and c were measured and the maximum projection sphericity was derived for each of 4360 clasts each sample was also categorized according to depositional subenvironment principal components analysis and cluster analysis were used to identify potential facies zonation results indicate that reworking of the foreshore by incident and edge waves resulted in clast size and shape segregation both parallel and perpendicular to the beach patterns of zonation were distinctly different from those described in earlier facies descriptions showing a complex set of foreshore facies the distribution of these facies was controlled primarily by location within beach cusp systems primary and secondary facies demonstrate alongshore variability of a magnitude comparable to across shore differences the results have important implications for palaeoenvironmental reconstruction morphosedimentary description and research sampling design and provide the basis for a conceptual model of gravel beach cusp facies

simulation and prediction of swash oscillations on a steep beach this paper presents numerical simulations and analytical predictions of key aspects of swash oscillations on a steep beach simulations of the shoreline displacement based on bore run up theory are found to give excellent agreement with recent experimental data for regular waves wave groups and random waves the theory is used to derive parameters that predict the onset of swash saturation and the spectral characteristics of the saturated shoreline motion these parameters are again in good agreement with the measured laboratory data and are also consistent with previous experimental data simulation of irregular wave run up using a series of overlapping monochromatic swash events is found to reproduce typical features of swash oscillations and can accurately describe both the low and high frequency spectral characteristics of the swash zone in particular the low frequency components of the run up can be modelled directly using a sequence of incident short wave bores with no direct long wave input to the numerical simulations this suggests that wave groupiness must be accounted for when modelling shoreline oscillations

estimating swash zone friction coefficients on a sandy beach abstract video based swash motions from three studies on two separate beaches were analyzed with respect to theoretical swash trajectories assuming plane beach ballistic motions under quadratic friction friction coefficient values for both the uprush and backwash were estimated by comparing measured swash space time trajectories to these theoretical expectations given an initial velocity and beach slope observations were made spanning high tides and in one case during a light rain analysis of over 4500 individual swash events showed that the uprush friction coefficient was nearly constant during all three studies with a mean value of roughly 0 007 and showed no trends over a tidal cycle in contrast backwash friction coefficient values varied over the tidal cycles ranging between 0 01 and 0 07 with minimum values corresponding to the highest tides although these values are close to the theoretical estimates based on a law of the wall formulation and values commonly referenced in the literature these observations show a consistent tendency for backwash friction estimates to greatly exceed uprush friction estimates the disparity between uprush and backwash friction coefficients can be partially attributed to the exclusion of a pressure gradient term in the ballistic model however results indicate that backwash friction coefficients adjusted to account for this effect may be three times larger than the uprush friction values during lower tides this tidal dependence for backwash friction coefficients is attributed to a complex interaction between swash infiltration and entrained sediment loads these findings imply that friction estimates necessary for sediment transport calculations and hydrodynamic predictions based solely on grain roughness may not be correct for backwash flows

pebble shape and size abstract the mathematical technique of r mode factor analysis was applied to the long intermediate and short axes of one synthetic random data set and three sets of natural pebbles to extract the three fundamental factors related to these parameters one factor corresponds to size which is best described by the mean of the axes two further factors correspond to shape sphericity and disc rodness these factors are revealed whether synthetic data or natural pebble samples are analyzed extending the factor analysis to include shape indices revealed which indices are equivalent which are most useful and which should be discarded sphericity is best described with the corey shape index s il and disc rodness is best described with the disc rod index l i l s accordingly the most effective shape diagram is a triangular plot of these two shape indices the three end members of shape are spheres discs and rods shape is best investigated using this shape diagram a 2 d technique such as contouring point density on this diagram should be used to determine the mean and standard deviation of shape while others ask themselves what is there to do i ask myself what is there that i can avoid doing masanobu fukuoka one straw revolution

long term marine bedload segregation and sandy versus gravelly holocene shorelines in the eastern english channel abstract retreating cliffs comprising fringing gravel or sandy beaches line much of the english and french coasts in the eastern english channel locally gravel has formed significant barrier accumulations overlying thick finer grained deposits although sandy deposits are abundant on the bed of the eastern channel significant aeolian dunes are restricted to embayments on the west facing french coast between the somme estuary and cape gris nez these embayments show holocene continuity of deposition of relatively homogenous sand with the dunes overlying beach washover and estuarine sediments it is argued that the occurrence of gravelly shorelines or of sandy shorelines exhibiting significant aeolian dunes largely reflects a combination of three factors 1 the inherited coastal lithology and morphology characterised by soft rock cliffs with or without embayments that were potential holocene sediment sinks 2 coastal orientation relative to large scale tide and wind driven marine bedload segregation processes that operated during the holocene and have led to preferential sand concentrations in the eastern corner of the channel and possibly concomitant relative enrichment in nearshore gravel elsewhere 3 coastal orientation relative to the synoptic westerly wind field responsible for significant aeolian dune building where such sand concentrations occurred the only coast where these three conditions were met favourably for significant aeolian dune building is the west facing french coast north of the somme estuary which benefitted during the holocene from large scale eastward advection of sand from the bed of the channel this sand was concentrated along a well defined coast parallel transport pathway driven by tidal currents enhanced by coriolis forcing and especially by the coast orthogonal synoptic westerly winds as sea level rise slowed or stabilised following the middle holocene the sand was piled onshore in embayments to form aeolian dunes by these coast orthogonal winds leaving no scope for the formation of gravel shorelines this coastal sand transport pathway is still operational elsewhere the inherited coastal morphology and orientation in terms of both the coriolis effect and westerly wind forcing have not favoured similar large scale sand trapping in coastal sinks as a result the shorelines are characterised by retreating cliffs and fringing beaches with a few major gravel barriers formed in local downdrift sinks and comprising clasts reworked by storms from offshore gravel deposits on the bed of the channel and from cliff retreat the sharp change in facies from fine grained sediments to overlying gravel within these barriers may have been enhanced by sand depletion caused by the large scale holocene bedload segregation processes that operated in the eastern channel it is suggested that if the permanence of the present day 3 d morphology of the eastern english channel and the same hydrodynamic forcing notably the same wind field as during the holocene are accepted then the suggested model of coastal sedimentation involving preferential large scale drift of channel bed sand towards the north south oriented french coast north of the somme estuary would also predict permanent dominantly gravelly high sea level beach sedimentation on the opposite english coast

hydrodynamics and sediment transport in the swash zone a review and perspectives the dominant hydrodynamic forcing and resulting sediment transport mechanisms in the swash zone are reviewed combined with a discussion of future measurement and modelling requirements the importance of swash zone processes in the overall behaviour of the nearshore littoral zone are identified with the paper subsequently focusing on aspects that directly relate to sediment transport on beaches the review considers analytical and numerical modelling work and both field and laboratory data the hydrodynamics of the swash zone are first discussed with reference to the surf zone boundary swash characteristics forcing mechanisms and shoreline oscillations subsequent sections consider more micro scale processes such as the internal flow kinematics turbulence the bed boundary layer and infiltration exfiltration through permeable beds the second part of the paper outlines the fundamental mechanics of sediment transport in the swash zone followed by a more detailed discussion of sediment transport modes induced by the dominant hydrodynamic conditions modelling concepts are reviewed and the strengths and weaknesses of different approaches identified a final summary and future modelling perspectives conclude the paper

hydrodynamics and morphological adjustment of a mixed sand and gravel beach torere bay of plenty new zealand detailed measurements of cross shore wave energy transformation swash sediment transport and beach profile change under low energy conditions are reported from a mixed sand and gravel beach at torere bay bay of plenty new zealand measurements were undertaken during a 10 day period following a storm event and document post storm recovery of the beach nearshore wave spectra identify periods in which incident wave energy is dominated by swell and wind wave energy results show that wind wave energy observed in the nearshore is effectively removed from beachface spectra at the break point step under lower tidal stages swash is driven by longer period swell energy although dissipation of short period wave energy is critical in entraining sediments on the lower beach at higher tidal stages wind wave energy is able to propagate across the break point step shoal and break on the lower beachface tidal modulation of wave processes across the lower beachface under low incident wave conditions is found to stimulate active sediment reworking migration of the break point step and shoreward sediment flux to promote beach accretion

beach steps an evolutionary perspective abstract field observation of contrasting beach step behavior at canaveral national seashore on two subsequent days when incident wave conditions in the inner surf zone were similar prompted this re examination of our conceptual and quantitative understanding of beach steps these lower foreshore features are more complex than previously assumed evolving through erosional as well as accretional phases and displaying equifinality in geometric form but not necessarily internal sedimentary structure past and recent evidence is reviewed that links beach steps to incident waves at the surging plunging transition and to the action of a backwash vortex tides and low frequency waves likely play no direct role in beach step initiation although their presence can have pronounced influences on modulating nearshore hydrodynamics and thus on beach step maintenance and evolution a generalized conceptual model capturing these aspects of beach step dynamics is presented beach step initiation proceeds via step carving excavation or building depending on the erosional accretional character of the beach foreshore system subsequent evolution of the step form may take one of several alternative morphodynamic pathways including stepface retreat step drag down or step infilling elimination depending on tidal stage range or wave set up setdown additional data on equilibrium beach step forms and associated morphodynamic and hydrodynamic conditions in the field are necessary before quantitative models of beach step existence and evolution can be formulated with realistic results

markov chain simulation of soil textural profiles abstract the spatial change of textural layers is an important feature of alluvial soils it influences soil water transport and solute movement in the field data from one or several soil profiles cannot explain processes of field water and solute movement in a large region because of spatial variability within textural layers two stochastic models the mc markov chain model and the mc ln markov chain lognormal distribution model were developed in this study using markov chain theory to simulate textural profiles of regional alluvial soils soil textural layers were divided into six types namely sand sandy loam light loam medium loam clay loam and clay the two models reflect vertical changes of textural layers of soil profiles in the research region excluding the data related to clay loam layers which are quite rare element values of tpm transition probability matrix of textural layers simulated by the mc model deviate less than 15 from measured and those by the mc ln model less than 27 the mc model shows a larger deviation in the probability distribution of textural layer thickness because the simulated textural layer thickness is inclined to be exponentially distributed but the mc ln model is consistent to the measured data which are similar to a lognormal distribution for each textural type simulated mean thicknesses of textural layers from the mc ln model deviate less than 21 1 from measured and those from the mc model less than 7 1 these two models will be useful for further constructing a regional model of field water transport with a consideration of the spatial variability of soil textural layers

sediment growth and aging as markov chains preservation of sediments as a function of their geologic age can be described by stochastic models for the following cases 1 fixed sediment mass with constant probabilities of erosion and preservation 2 fixed sediment mass with erosion and preservation probabilities that vary with geologic age and 3 growing sediment mass with constant probabilities of erosion preservation and removal from the sedimentary cycle for geologically long periods of time the stochastic models can be transformed into such models of sediment preservation as the exponential or compound decay of a fixed sediment mass and a continuous growth of the sediment mass several of the statistical distributions arising out of the stochastic models the geometric exponential compound decay and inverse hypergeometric produce mass age distribution curves for the phanerozoic and late proterozoic sediments that agree reasonably well with the actual masses reported in the literature a general characteristic of the stochastic mode

identifying storm impacts on an embayed high energy coastline examples from western ireland abstract large sections of the western irish coast are characterised by a highly compartmentalised series of headland embayment cells in which sand and gravel beaches are backed by large vegetated dune systems exposure to modally high energy swell renders most of these beaches dissipative in character a mesotidal range c 3 5 4 5 m exists along much of the coast analysis of instrumental wind records from three locations permitted the identification of a variety of storm types and the construction of storm catalogues few individual storms were recorded at all three stations indicating a lack of regional consistency in storm record of the total storms recorded only a small percentage are potentially damaging onshore directed and even fewer span a high tide and thus potentially induce a measurable morphological response at the coast through a combination of historical records meteorological records field observations and wave modelling we attempt to assess the impact of storms quantifiable records of coastal morphology maps air photos and beach profiles are few in number and do not generally record responses that may be definitely attributed to specific storms numerical wave simulations and observations at a variety of sites on the west irish coast however provide insights into instantaneous and medium term decadal storm responses in such systems we argue that beaches and dunes that are attuned to modally high energy regimes require extreme storms to cause significant morphological impact the varying orientation of beaches a spatially nonuniform storm catalogue and the need for a storm to occur at high water to produce measurable change impart site specific storm susceptibility to these embayments furthermore we argue that long period wave energy attenuation across dissipative shorefaces and beaches reduces coastal response to distant storms whereas short period locally generated wind waves are more likely to cause major dune and beach erosion as they arrive at the shoreline unrefracted this apparently variable response of beach and dune systems to storm forcing at a decadal scale over a coastline length of 200 km urges caution in generalising regarding regional scale coastal responses to climatic change

morphologic properties derived from a simple cross shore sediment transport model this paper builds on the now classical discussions by bowen 1980 and bailard 1981 on the applicability and implications of bagnold s 1963 sediment transport model to nearshore profile modeling we focus on the morphologic implications of both the strengths and weaknesses of bagnold s model isolating the transport terms that are well predicted i e mean flow terms from those that are not well predicted i e transport due to correlations between flow and sediment load we factor bagnold s model into a dimensional transport magnitude and a nondimensional term the nondimensional term describes the relative importance of transport due to undertow gravity and correlations between flow and sediment load the transport magnitude largely determines the response time of nearshore profiles for typical nearshore environments this response time was estimated to vary as a function of incident rms wave height hrms from 500 years hrms 0 5 m to 2 years hrms 3 m the relative importance of competing transport mechanisms is shown to depend strongly on the relative wave height defined as the ratio of the rms wave height to the local depth simplified nearshore transport parameterizations that are a function of this variable were derived and were interrogated for the existence and form of equilibrium profiles several differences from previously computed equilibrium profiles were noted first because the relative wave height saturates in natural surf zones equilibrium profiles converge to a relatively flat profile near the shoreline second under some situations a seaward sloping equilibrium profile may not exist third the long response times combined with unknown stability of an equilibrium profile make it difficult to assess the physical connection between theoretical equilibrium profiles and profiles observed in nature

the role of swash infiltration in determining the beachface gradient a numerical study on sand and gravel beaches the increase of the gradient of the beachface with increasing sediment size has been attributed to swash infiltration the present study uses a process based numerical model to examine in detail the role of swash infiltration in determining the beachface gradient it is found that swash infiltration increases the onshore asymmetry in the swash flow thereby enhancing onshore sediment transport and resulting in relatively steep beachface gradients however the accretionary effects of swash infiltration are only evident when the rate of infiltration is sufficiently large i e when the total infiltration volume over a wave cycle exceeds c 2 of the uprush volume this threshold is attained when the hydraulic conductivity exceeds 1 cm s which is approximately equivalent to a grain size coarser than 1 5 mm this finding suggests that the correlation between beachface gradient and sediment size observed on sandy beaches is not due to enhanced swash asymmetry caused by swash infiltration for gravel beaches however swash infiltration is likely to be the dominant factor in controlling the beachface gradient with increased hydraulic conductivity i e sediment size resulting in steeper beachface gradients c 2001 elsevier science b v all rights reserved

quantitative predictions of beach face slopes application of dimensional analysis to the major factors responsible for beach slope changes yields the dimensionless parameter h b g 0 5 d 0 5 t where h b is the breaking wave height t is the wave period d is the sediment grain size and g is the acceleration due to gravity relationships between this parameter and beach face slope tan are determined by using the existing laboratory and field data to yield tan 0 013 h b g 0 5 d 0 5 t 2 0 15 for the laboratory and tan 0 12 h b g 0 5 d 0 5 t 0 5 for the field these equations make possible the prediction of the beach slope

cannibalisation of holocene gravel beach ridge plains northern tierra del fuego argentina abstract gravel beach ridge plains form where there is sufficient availability of gravels and wave energy competent to transport the gravel even though beach ridge plains are formed on coasts where sea level has risen during the holocene they occur extensively on stable or emergent coasts unfortunately the holocene evolution of these plains is hard to decipher because of the lack of datable material and their reworked character minimum age the rollover of barriers is expected on submerging coasts on falling sea level coasts the beach ridge plains are in a punctuated process of progradation cannibalisation is common in both settings that is sediment is eroded to maintain longshore growth we present morphological and sedimentological data from three gravel beach ridge plains san sebastian rio chico and cabo penas of the northern coast of tierra del fuego these beach complexes occupy embayments that were infilled during the last 5000 yr under different environmental conditions depth flooded area local oceanographic processes and sediment availability in the evolution of bahia san sebastian a strong control was imposed by high waves originating within the bay due to the strong westerlies the rio chico beach ridge plain evolved during different stages of beach progradation cannibalisation spit growth and saltmarsh development the cabo penas beach ridge plain evolved in opposite directions due to wave refraction caused by rocky reefs and cannibalisation also took place

a mechanism for the generation of wave driven rhythmic patterns in the surf zone the coupling between topographic irregularities and wave driven mean water motion in the surf zone is examined this coupling occurs because the topographic perturbations produce excess gradients in the wave radiation stress that cause a steady circulation this circulation in turn creates a sediment transport pattern that can reinforce the bottom disturbance and may thereby lead to the growth of large scale bed forms to investigate this coupling mechanism the linearized stability problem with an originally plane sloping beach and normal wave incidence is solved in two different cases first the breaking line is considered to be fixed and second the perturbations in water depth that produce a displacement of the breaker line are accounted for the first case shows that the basic topography can be unstable with respect to two different modes a giant cusp pattern with shore attached transverse bars that extend across the whole surf zone and a crescentic pattern with alternate shoals and pools at both sides of the breaking line showing a mirroring effect in the second case the varying breaker line may have a strong influence on the circulation this is clear for the giant cusp topography whose growth is totally inhibited in contrast the morphology and the growth of the crescentic pattern remains almost unchanged

an intercomparison between visual and acoustic detection of seabed gravel movement abstract an intercomparison between acoustic and visual estimates of sediment transport rates is presented specifically two hydrophones were mounted at 24 cm above a seabed composed of gravel these were used to passively monitor the movement of bedload material by measuring the acoustic intensity generated due to the collision of moving gravel particles with one another and the bed simultaneous underwater tv observations were conducted by directing a low light camera fixed at 50 cm above the bed on to the area of seabed directly below the hydrophones the tv data has been used as a coarse reference scale to which the performance of the acoustic system could be compared high temporal resolution estimates of mass transport rates were derived from the visual and acoustic data the similarity of these two measurement sets has been examined the results show that the measurement of gravel movement by acoustic monitoring is feasible

low frequency swash motion induced by wave grouping abstract this paper concerns the low frequency motion of swash directly induced by wave grouping on a steep beach a new experimental investigation is presented which considers the hydrodynamics of the inner surf zone and swash zone using vertical wave gauges and a run up wire results for regular waves wave groups and random waves are discussed with particular reference to low frequency motions the inner surf zone and swash zone are found to be unsaturated at incident short wave frequencies and as a result significant wave grouping is apparent at the shoreline the low frequency motion in the surf zone is found to be in phase with the incident wave grouping and may therefore be regarded as a time varying set up watson and peregrine 1992 the low frequency motion of the swash is shown to be an order of magnitude greater than that in the inner surf zone inconsistent with cross shore standing long waves for which no evidence is found we demonstrate that the low frequency motion of the shoreline provides an excellent approximation to the run up of individual bores and therefore describes the run up envelope spectral analysis shows that the low frequency motion of the swash is directly linked to the modulations in offshore wave height i e the low frequency energy in the incident wave envelope in addition the random wave run up spectra show an f 4 high frequency roll off as found by huntley et al 1977 the accumulated data show that unless the surf zone is totally saturated a significant proportion of the low frequency swash motion may be directly due to incident wave grouping and not standing long waves

comparison of sediment transport formulae for the coastal environment most existing sediment transport formulae to estimate transport rate in the coastal environment have a restricted range of applicability and are often used beyond this range the aim of this paper is to investigate the limits of five of these formulae the bijker bailard van rijn dibajnia and watanabe and ribberink formulae the sensitivity of these formulae to wave orbital velocity wave period wave asymmetry sediment grain size and steady current has been studied and tested against data for large velocities where significant errors can appear the formulae behave in very different ways if one of the main parameters is slightly modified particularly when fine sediments are present and phase lag effect appears but important discrepancies between formulae can also be observed for medium sand at last the wave related sediment transport due to wave asymmetry has great importance for the morphodynamic and is only accounted for in the bailard dibajnia and watanabe and ribberink formulae

analysis of bed load motion at high shear stress recent pipeline experiments performed in saskatchewan show the existence of a shear layer in which the solids concentration decreases linearly with height this finding has already been used to calculate the velocity distribution within a constant stress shear layer the analysis has now been extended to obtain the solids discharge per unit breadth of bed the result agrees with the modified meyer peter and muller equation and with the writer s sand data for larger nylon particles the solids discharge per unit breadth fell below that expected on the basis of the sand data and the new analysis shows the reason for this apparent anomaly it also shows that a shear layer several grain diameters thick will not be uncommon in open channel flow contrary to the conventional wisdom the new analysis predicts that the threshold of motion curve on the shields diagram must approach a constant value at sufficiently small abscissae a finding which appears to be in accord with recent experimental evidence

chronology of the last glacial cycle in the european alps chronological data for glacier advances in the european alps between the last interglacial eemian and the holocene are summarised 115 to 11 ka during this time glaciers were most extensive extending tens of kilometres out onto the forelands between 30 and 18 ka that is synchronous with the global ice volume maximum of marine isotope stage mis 2 evidence for ice expanding to just past the mountain front for an earlier major glacier advance comes from swiss sites where advances have been luminescence dated to mis 5d 100 ka and mis 4 70 ka up to now no such evidence has been found in the eastern alps by 18 ka more than 80 of the late wurmian ice volume had gone subsequently glaciers readvanced reaching into the upper reaches of the main valleys during the lateglacial gschnitz stadial which likely occurred around 17 ka with final moraine stabilisation no later than 15 4 ka the link of the egesen stadial with the younger dryas climate deterioration is supported by exposure ages from four sites as well as minimum limiting radiocarbon dates from bogs within former glacier tongue areas key questions on the spatial and temporal variability of ice extents throughout the last glacial cycle have yet to be answered copyright 2008 john wiley sons ltd

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

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

particle size and shape in pebble beach sedimentation an in depth investigation was made of beach gravel fabrics at two beach sites located on the glamorgan heritage coast wales u k granulometric data from 31 080 pebbles were obtained and analysis confirmed the existence of a basic shape differentiation structure when the b axis was used at gileston beach a low energy location and nash beach a high energy location the use of the b axis in size and shape analysis seems to have led some workers to incorrect rejection of size as a factor in determining the transportational and depositional potential of a particle an inferred energy model can be constructed where the influence of particle size on sorting is predominant when energy conditions are high and particle shape factors predominate when energy conditions are low the c axis standard deviation value was the most effective discriminator of variation in shore parallel sedimentation structures at both beaches for shore normal structural discrimination the c axis mean and standard deviation values were the most effective

a simple autocorrelation algorithm for determining grain size from digital images of sediment abstract autocorrelation between pixels in digital images of sediment can be used to measure average grain size of sediment on the bed grain size distribution of bed sediment and vertical profiles in grain size in a cross sectional image through a bed the technique is less sensitive than traditional laboratory analyses to tails of a grain size distribution but it offers substantial other advantages it is 100 times as fast it is ideal for sampling surficial sediment the part that interacts with a flow it can determine vertical profiles in grain size on a scale finer than can be sampled physically and it can be used in the field to provide almost real time grain size analysis the technique can be applied to digital images obtained using any source with sufficient resolution including digital cameras digital video or underwater digital microscopes for real time grain size mapping of the bed

concepts in gravel beach dynamics abstract the dominant processes in gravel beach dynamics are reviewed highlighting some common themes which unify the various components of the gravel beach system the repercussions of which impart on how gravel beach dynamics might be understood conceptually in particular gravel beach dynamics are thought to be highly dependent on the temporal and spatial variation in grain size and the continual adjustments made by an active beach step both of which act not only as the expression of changing morphodynamic conditions but also as a controlling influence morphodynamics the notion that the exchanges on beaches between the hydrodynamics sediment transport and morphological change takes the form of reciprocal relationships which are mediated through feedback mechanisms in such a way that they cannot be thought of or studied independently is not a new one yet it appears that for the gravel beach morphodynamics must be re defined to describe conditions where variations in sediment size are thought to deserve parity rather than as merely a sequent entity or boundary condition morpho sedimentary dynamics is a phrase coined to intuit such cause and effect detailing the co evolution of morphology hydro hydraulics and sediment properties whilst acknowledging causative pluralism feedbacks and multiplier effects this is the recommended conceptual framework within which to crystallise thought and organise further research for the gravel beach essentially it increases the minimum number of parameters needed to describe the state of the gravel beach as a physical system therefore it is advised that simplicity will be most expedient in our future modelling efforts if complexity is to be adequately encapsulated

beach groundwater dynamics abstract an understanding of the interaction between surface and groundwater flows in the swash zone is necessary to understand beach profile evolution coastal researchers have recognized the importance of beach watertable and swash interaction to accretion and erosion above the still water level swl but the exact nature of the relationship between swash flows beach watertable flow and cross shore sediment transport is not fully understood this paper reviews research on beach groundwater dynamics and identifies research questions which will need to be answered before swash zone sediment transport can be successfully modelled after defining the principal terms relating to beach groundwater the behavior measurement and modelling of beach groundwater dynamics is described research questions related to the mechanisms of surface subsurface flow interaction are reviewed particularly infiltration exfiltration and fluidisation the implications of these mechanisms for sediment transport are discussed

settling velocity of sediments at high concentrations new data on the settling velocity of artificial sediments and natural sands at high concentrations are presented the data are compared with a widely used semiempirical richardson and zaki equation trans inst chem eng 32 1954 35 which gives an accurate measure of the reduction in velocity as a function of concentration and an experimentally determined empirical power n here a simple method of determining n is presented using standard equations for the clear water settling velocity and the seepage flow within fixed sediment beds the resulting values for n are compared against values derived from new and existing laboratory data for beach and filter sands for sands the appropriate values of n are found to differ significantly from those suggested by richardson and zaki for spheres and are typically larger corresponding to a greater reduction in settling velocity at high concentrations for fine and medium sands at concentrations of order 0 4 the hindered settling velocity reduces to about 70 of that expected using values of n derived for spheres at concentrations of order 0 15 the hindered settling velocity reduces to less than half of the settling velocity in clear water these reduced settling velocities have important implications for sediment transport modelling close to and within sheet flow layers and in the swash zone

artificial neural network correction of remotely sensed sandbar location abstract this contribution details an accurate method for the remote sensing of submerged sandbar location through the application of an artificial neural network to video data lippmann and holman lippmann t c holman r a 1989 quantification of sandbar morphology a video technique based on wave dissipation j geophys res 94 c1 995 1011 have shown that the intensity maxima seen in time averaged video images of the nearshore zone provide a reasonable proxy for sandbar location however recent studies have indicated that there may be a large deviation up to 30 40 m between the measured bar position and predictions based on the intensity maximum in the cross shore direction these deviations occur largely due to modulations of the breakpoint by the tide and variations in the incident wave energy this paper utilises an artificial neural network to model the cross shore movement in the intensity maximum due to tides and waves the resulting signal is then removed from the video estimates to provide an accurate estimation of the sand bar location unique field data sets collected as part of the coast3d experiment are used to train and test the neural network model these data consist of simultaneous measurements of the nearshore bathymetry and video imagery of the double bar system at egmond aan zee the netherlands the resulting model yields accurate estimates of sandbar location with residual errors of less than 5 m for the outer bar and less than 10 m for the inner bar the artificial neural network model is utilised to extend the bathymetric data set for egmond aan zee for times when wave conditions were too large to allow physical measurement

regularity and randomness in the formation of beach cusps abstract controversy still exists on whether rhythmic features such as beach cusps are the result of the presence of standing edge wave motions in the hydrodynamics or if they are the result of self organising processes the compatibility between the two mechanisms is here investigated through the use of a numerical model simulating the formation and development of beach cusps simulations characterised by different forcing conditions have been performed a series of random simulations each individual run simply differing from the others in the seed used in the random number generator showed the typical self organisation behaviour with the features appearing at different locations and even with slightly different spacing regular series of simulations have been run by changing the wavelength of the template superimposed by the hydrodynamic forcing and the number of cycles when the template was present results surprisingly indicate that even a minimum number of cycles with a regular forcing can deterministically induce the final shoreline configuration furthermore if the forcing template has the same wavelength as the one resulting from purely random simulations growth rates are much faster than those obtained with random conditions implications for the kind of field measurements necessary to discern which of the two mechanisms is responsible for beach cusp formation have also been considered

high resolution grain size characterisation of gravel bars using imagery analysis and geo statistics abstract the scarcity of grain size data from gravel bed rivers has traditionally hindered hydraulic sediment transport and river habitat studies a new remote sensing methodology to estimate grain size distribution is presented it combines textural digital images of the riverbed at 1 1000 and 1 40 scales with grain size sampling it was applied to a 12 km reach of the isabena river central pyrenees ne spain first textural patterns for each grain size range were obtained selecting the most closely related texture variables including the use of semivariograms second multiple linear regression equations were derived from the textural variables to estimate each value of the grain size distribution the highest correlation values r 2 were obtained from the central part of the distribution d 50 with a rms error of 12 7 finally new multiple linear regression equations to estimate the d 50 and d 84 were obtained from 1 1000 images and four textural variables these were used to derive d 50 and d 84 maps of the riverbed re sampled at a resolution of 1 5 m pixels with rms estimation errors of 26 and 32 respectively downstream change in grain size is also well reproduced by the method the mean d 50 of 72 and 32 mm were estimated in the upper and the lower reaches of the river respectively the methodology shows great potential for application the relation between the spatial resolution of the images and the mean grain size of the riverbed sediment being the main issue for future development

beach cusps as self organized patterns computer simulations of flow and sediment transport in the swash zone on a beach demonstrate that a model that couples local flow acceleration and alongshore surface gradient is sufficient to produce uniformly spaced beach cusps the characteristics of the simulated cusps and the conditions under which they form are in reasonable agreement with observations of natural cusps the self organization mechanism in the model is incompatible with an accepted model in which standing alongshore waves drive the regular pattern of erosion and deposition that gives rise to beach cusps because the models make similar predictions it is concluded that currently available observational data are insufficient for discrimination between them

net sediment transport patterns inferred from grain size trends based upon definition of transport vectors reply abstract a new approach to the analysis of the grain size trends associated with net sediment transport directions in shallow marine environments is developed here two specific trends modified from mclaren and bowles 1985 on the basis of a literature review are used to define a grid of trend vectors such vectors are filtered and transformed into transport vectors it is suggested that an ordered pattern of the transport vectors represents net transport paths the orderliness of the derived pattern is examined on the basis of a significance test using the average length of the transport vectors as a criterion both the filtering operation and the significance test procedure are based upon the assumption that the trend vectors which are not associated with net transport have the same probability of being in any direction the technique is applied to data from yangpu harbour southern china the technique can be applied to inner continental shelf and coastal environments for such an analysis the area under investigation should be sampled at an interval large enough to reflect the real grain size trends resulting from net sediment transport but small compared with the dimensions of the sedimentary environment the time scale of the results depends upon the sampling depth applicability of the technique is likely to be somewhat limited where the environment is highly variable over short distances furthermore due to its statistical character the analysis may fail to identify net transport patterns

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

depth of activation of sediment by plunging breakers on a steep sand beach abstract field data were collected over a lunar tidal cycle on a meso tidal medium sand estuarine beach in delaware bay usa to document the relationship between wave height and depth of sediment activation in a low wave energy environment dominant energy was at the frequencies of locally generated waves and ocean swell significant wave heights ranged from 0 06 m to 0 52 m periods of locally generated waves averaged 4 0 s during strong onshore winds and 2 6 s during low speed winds waves on the foreshore were always plunging the foreshore maintained a slope of approximately 6 0 throughout the study period mean grain size at mid foreshore was 0 46 mm the greatest net surface elevation change in response to storm erosion and post storm recovery was 0 26 m results confirm previous observations that depths of sediment activation are greater for steeper beaches the spatial variability in depths of activation across the foreshore is comparable to results of tidal cycle studies where the ratio of depth of activation to wave height is great because a large percentage of the foreshore comes under the influence of the breakers the ratio of depth of activation to wave height on the portion of the foreshore that is not transgressed by the breakers is lower and comparable to results of short term investigations provided that the influence of beach slope is considered in the calculation of breaking wave height

organisational controls typologies and time scales of paraglacial gravel dominated coastal systems abstract the fundamental controls on the initiation and development of gravel dominated deposits beaches and barriers on paraglacial coasts are particle size and shape sediment supply storm wave activity primarily runup relative sea level rsl change and terrestrial basement structure primarily as it affects accommodation space this paper examines the stochastic basis for barrier organisation as shown by variation in gravel barrier architecture we recognise punctuated self organisation of barrier development that is disrupted by short phases of barrier instability the latter results from positive feedback causing barrier breakdown when sediment supply is exhausted we examine published typologies for gravel barriers and advocate a consolidated perspective using rate of rsl change and sediment supply we also consider the temporal variation in controls on barrier development these are examined in terms of a simple behavioural model barch for prograding gravel barrier architecture and its sensitivity to such controls the nature of macroscale 10 2 10 3 years gravel barrier development including inherited characteristics that influence barrier genesis as well as forcing from changing rsl sediment supply headland control and barrier inertia is examined in the context of long surviving barriers along the southern england coastline

beach cusp morphology on sand and mixed sand and gravel beaches south island new zealand abstract the morphology of beach cusps on a number of beaches around the south island new zealand is described cusp dimensions such as spacing elevation amplitude depth and spacing variance are interrelated cusp dimensions co vary in regular fashion under different process conditions such that the cusp form displays a high degree of regularity beach cusp amplitude is an exception to this regularity that appears to be controlled by factors such as grain size and beach slope analysis of cusp spacing and elevation dimensions on mixed sand and gravel beaches reveal that cusps having particular spacings form at distinct elevations on the beachface with the largest spacings occurring at the highest levels on the beachface the relationship between cusp elevation and spacing provides a technique through which beach cusp spacing can be used to infer mean sea level

eolian dunes computer simulations and attractor interpretation a simple computer simulation algorithm for the transport of sand by wind produces forms resembling barchan crescentic ridge linear and star natural dune classes sand is moved as slabs composed of many grains that are picked up at random transported in a specified direction and deposited 1 with a probability that depends on the local presence or absence of sand or 2 in shadow zones in the lee of dunes the simulated dune fields are interpreted as complex systems with sand dune classes being dynamical attractors of these systems the evolution of dunes once formed becomes decoupled from the details of eolian sand transport

shear stress and sediment transport calculations for swash zone modelling it is shown that the observed difference in sediment transporting efficiency by the swash uprush compared with the downrush could be mainly due to greater bed shear stress for a given velocity in the more abruptly accelerated uprush the bed shear stress generated by an arbitrary free stream velocity time series is modelled in terms of usual wave boundary layer models plus a phase lead phi tau of the bed shear stress compared with the free stream velocity at the peak frequency with this approach the total transport amounts in uprush and downrush can be modelled satisfactorily with the same sediment transport formula without the need for different uprush and downrush coefficients while the adaptation of sediment transport formulae from steady flow can thus lead to the right total amounts of sediment moved by this method the timing of the instantaneous sediment transport rates are probably not accurately modelled due to the highly unsteady nature of the swash and the presence of pre suspended sediment in the uprush nevertheless the proposed method is a useful intermediate step before we have a complete understanding of sediment transport under very rapid accelerations and of the relative contribution of pre suspended sediment to the onshore sediment transport in swash zones c 2002 published by elsevier science b v

prediction of swash motion and run up including the effects of swash interaction modifications to a model describing swash motion based on solutions to the non linear shallow water equations were made to account for interaction between up rush and back wash at the still water shoreline and within the swash zone inputs to the model are wave heights and arrival times at the still water shoreline the model was tested against wave groups representing idealized vessel generated wave trains run in a small wave tank experiment accounting for swash interaction markedly improved results with respect to the maximum ran up length for cases with rather gentle foreshore slopes tan beta 0 07 for the case with a steep foreshore slope tan beta 0 20 there was very little improvement compared to model results if swash interaction was not accounted for in addition an equation was developed to predict the onset and degree of swash interaction including the effects of bed friction less