reflection and tunneling of ocean waves observed at a submarine canyon 1 ocean surface gravity waves with periods between 20 and 200 s were observed to reflect from a steep walled submarine canyon observations of pressure and velocity on each side of the canyon were decomposed into incident waves arriving from distant sources waves reflected by the canyon and waves transmitted across the canyon the observed reflection is consistent with long wave theory and distinguishes between cases of normal and oblique angles of incidence as much as 60 of the energy of waves approaching the canyon normal to its axis was reflected except for waves twice as long as the canyon width which were transmitted across with no reflection although waves approaching the canyon at oblique angles cannot propagate over the canyon total reflection was observed only at frequencies higher than 20 mhz with lower frequency energy partially transmitted across analogous to the quantum tunneling of a free particle through a classically impenetrable barrier

non hydrostatic numerical modelling of nearshore wave transformation over shore oblique sandbars abstract observations from high resolution bathymetric surveys on the coast of north carolina indicate areas with shore parallel depth contours and other areas with shore oblique sandbars these shore oblique bars are large scale morphological features that extend up to 1000 m from shore and previous studies have shown that they are spatially correlated with higher shoreline change rates and induce erosional hotspots to investigate the influence the oblique sandbar morphology has on nearshore wave transformation and energy distribution a non hydrostatic wave model is used with the bathymetry corresponding to two areas with shore parallel depth contours and two areas with shore oblique sandbars the model is applied with a horizontal resolution of 5 m and a boundary condition representative of the directional spectrum of a typical southeast swell event an idealized approach with relatively short alongshore model domains and cyclic lateral boundary conditions is adopted due to limited availability of high resolution bathymetry however this approach elucidates the influence of shore oblique sandbars on the nearshore hydrodynamics the numerical results show that higher alongshore variability in depth due to the shore oblique bars drive large alongshore changes in cross shore wave energy flux and cause spatial variability in dissipation in the nearshore region the simulations indicate that alongshore variations in wave energy caused by the shore oblique bars results in a 50 75 reduction in wave setup and a 25 40 decrease in alongshore velocity averaged across the surf zone for the conditions investigated the results suggest that wave driven hydrodynamics can influence nearshore sediment dynamics to create erosional zones compared to areas with shore parallel bathymetric contours since the morphology of shore oblique sandbars are an important control on wave energy that impacts the beach

field observations of swash zone infragravity motions and beach cusp evolution 1 fluid flows consistent with low mode edge waves were evident in video observations of swash motions during a field experiment in which beach cusps developed on an initially smooth beach as beach cusps grew energy lying along low mode dispersion curves increased the most energetic edge wave propagation direction changed from upcoast to downcoast as the orientation of the cusp horns rotated these observations suggest a coupling between morphodynamics and hydrodynamics and are evidence that beach cusp evolution might control low mode edge wave dynamics

observations of beach cusp evolution at melbourne beach florida usa abstract morphological observations terrestrial laser scanning and sediment analysis are used to study beach cusp morphodynamics at melbourne beach florida usa a moderately sloped beach characterized by fine sand the study couples rapid high resolution surveying with surficial sediment sampling over multiple tidal cycles surveys were run 500 m alongshore and sediment samples were collected intertidally over a period of 5 days beach cusp location within larger scale beach morphology is shown to directly influence cusp growth as either gross erosional or gross accretional sediment characteristics within the beach cusp morphology are reported coincident with cusp evolution variations in particle size distribution kurtosis are exhibited as the cusps evolve however no significant correlation is seen between grain size and position between horn and embayment during the end of the study a storm resulted in beach cusp destruction and increased sediment sorting

geomorphic effectiveness a linear concept in a non linear world geomorphic effectiveness has been an influential concept in geomorphology since its introduction by reds wolman and john miller in 1960 it provided a much needed framework to assess the significance of an event by comparing event magnitude to the resultant geomorphic effects initially this concept was applied primarily in river channels under the linear assumption that geomorphic responses to similarly sized flood events will be consistent numerous authors have since attempted to quantify a direct proportional relationship between event magnitude and different forms of geomorphic response in a variety of geomorphic settings in doing so these investigations applied an array of metrics that were difficult to compare across different spatiotemporal scales and physiographic and geomorphic environments critically the emergence of other geomorphic concepts such as sensitivity connectivity thresholds and recovery has shown that relationships between causes events and geomorphic effects responses are often complex and non linear this paper disentangles the complex historical development of the geomorphic effectiveness concept and reviews the utility of various metrics for quantifying effectiveness we propose that total energy joules is the most appropriate metric to use for quantifying the magnitude of disturbance events cause and volumetric sediment flux associated with landform modification is the most appropriate metric for quantifying geomorphic effects while both metrics are difficult to quantify they are the only ones which facilitate comparison across a range of spatiotemporal scales comparability in a variety of geomorphic environments flexibility the geomorphic effectiveness concept can continue to be useful provided that geomorphologists use flexible and comparable metrics today geomorphologists are better prepared to consider the influence of non linear processes on determinations of geomorphic effectiveness allowing investigators to not only determine if a disturbance event was effective but also to explain why or why not copyright

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

swash oscillations on a natural beach run up swash oscillations were measured on a gently sloping beach face for a variety of incident wave conditions run up energy spectra at wind wave frequencies show an 3 dependence and energy levels that are independent of incident wave height this suggests saturation in contrast run up energy at surf beat periods increase approximately linearly with increasing incident wave energy thus in the inner surf zone where wave breaking limits the energy at wind wave frequencies the principal manifestation of large incident wind waves is energetic surf beat

ambient noise measurements for preliminary site effects characterization in the urban area of florence italy abstract environmental noise measurements and borehole data were used for a preliminary seismic characterization of the plio quaternary sedimentary basin underlying the city of florence italy an extensive survey of ambient vibrations was conducted by using the seismic noise horizontal to vertical h v spectral ratio technique hvsr to map the fundamental resonance frequency of the sedimentary cover in order to use this information to infer main features of the basin subsurface geometry an estimate of the s wave velocity profile in the sediment layer was obtained from array noise recordings along with information on resonance frequency and direct measurements of the sediment thickness available at 23 borehole sites a first order reconstruction of the seismic bedrock topography in the area was provided which shows a good consistency with available geological log data from these pieces of information a preliminary soil classification of the whole area was attempted in order to identify situations where possible seismic amplification effects are expected during future earthquakes and where more accurate investigations are needed to parameterize the local seismic response

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

the configuration of equilibrium beach profile in south china abstract to understand the evolution and stability of beaches prediction of the equilibrium beach profile ebp is theoretically and practically important in the present paper a new equation h ae bx c is developed to predict the change in beach profile for sections above the water level and the adjacent nearshore portions moreover fractal analysis is applied to predict types of ebp for the first time using the field data collected from liao zuikou and nanwan beaches south china three types of ebp termed upward concave ebp u ebp downward concave ebp d ebp and medium characteristic ebp m ebp are given for the studied region of south china

morphological evolution of beach cusps and associated swash circulation patterns abstract a numerical model capable of simulating the motion of water particles on beach cusp morphology under the influence of an initial velocity and gravity is presented the model indicates that the typical swash pattern on beach cusps is three dimensional with wave uprush diverging at the cusp horns resulting in concentrated backwash streams in the embayment the degree of horn divergence is an increasing function of the parameter e s 2 where e quantifies the prominence of the beach cusps s is the horizontal swash excursion length and is the cusp spacing the numerical experiments are supplemented with detailed field measurements of beach cusp morphological change the field data include three types of morphological response each characterised by a particular pattern of swash circulation that can be delineated using e s 2 when e s 2 beach cusp morphology is large and or subdued in relation to the swash length swash circulation is essentially two dimensional oscillatory flow and results in steepening of the beachface and infilling of the cusp embayments for e s 2 0 015 to 0 15 wave uprush is deflected from the cusp horns and flows into the embayments where it exits in a concentrated backwash stream horn divergent flow the ensuing swash backwash inequality reinforces cusp development and maintains existing cusp morphology when e s 2 0 15 beach cusps are small and or pronounced in relation to the length of the swash overtopping and ponding of the cusp horn takes place and swash circulation is from the embayment to the horn horn convergent flow as a result cusp horns are eroded and accretion occurs in the embayments

new observations of sprites from the space shuttle 1 we present the results of space based observations of sprites obtained during the mediterranean israeli dust experiment meidex sprite campaign conducted on board the space shuttle columbia during its sts 107 mission in january 2003 a total of 6 hours of useful data were saved from 21 different orbits of which 1 5 contained lightning we imaged sprites from an altitude of 280 km using a calibrated multispectral camera above thunderstorms in various geographical locations mainly in central africa northern australia and south america and also over the pacific and indian oceans in this paper we report on sprites observed from ranges 1600 2000 km from the shuttle at altitudes of 40 90 km above the ground their brightness was in the range of 0 3 1 7 mega rayleighs mr in the 665 nm filter and 1 44 1 7 mr in the 860 nm filter on the basis of the frequency of observed events and the number of tropical thunderstorms we estimate the sprite rate in the tropics to be of the order of several per minute

field observations of beach cusps and swash motions abstract we tested the hypothesis of cusp formation by the longshore structure of synchronous or subharmonic mode zero edge waves using detailed field measurements of foreshore topography incident waves and swash motions two distinct intervals of cusp formation were observed alongshore separated swash measurements were analyzed to detect structures at wavelengths and frequencies consistent with the measured cusp spacings for both events no statistical support for cusp generation by the traditional subharmonic or synchronous edge wave mechanisms was found however once cusps became well developed there was evidence of interaction between fluids and topography at a wavelength equal to the cusp spacing but at the period of the incident swash we propose that this interaction could have been responsible for the generation of the second set of cusps with a spacing of half the pre existing cusp wavelength

sorted bed forms as self organized patterns 1 model development 1 here we present a modified version of the exploratory numerical model originally presented by murray and thieler 2004 and use it to further investigate the development of sorted bed forms on the inner continental shelf the new version of the model is based on widely accepted parameterizations for hydrodynamics and sediment transport that are more detailed and empirically tested than the parameterizations used in the original model the shallow water wave equations are replaced by the general equations and changes in water depth related to morphological development are accounted for this model reproduces the main results of the previous one supporting the hypothesis that sorted bed forms are a self organized pattern and develop as a result of a coupling between bed composition and sediment flux the sensitivity of the model predictions evaluated in terms of the geometry of the sorted bed forms and their growth rate with respect to external forcing variables and internal model parameterizations shows increasing decreasing sorted bed form spacing height with increasing wave height and period the opposite occurs for increasing water depths more complicated behavior is observed when the ratio fine to coarse sediment diameter or the percentage of fine and coarse material is varied the shape of the suspended sediment and current profiles and the formulation used to predict the geometry of wave generated ripples can significantly affect or even inhibit growth rates of sorted bed forms results from a sensitivity analysis show that there are deficiencies in the description of small scale processes that limit the ability to quantitatively predict sorted bed form evolution highlighting gaps in our knowledge of sediment transport over mixed grain beds that need to be filled

possible evidence for underlying non linear dynamics in steep faced glaciodeltaic progradational successions steep faced glaciodeltaic progradational successions are often studied in order to reconstruct the behaviour of the glacial feeder system or changes in the sediment sink this paper analyses the magnitude and frequency of depositional events associated with steep faced glacier fed progradational successions recorded in scandinavia and ireland the successions exhibit depositional patterns that may be interpreted as a function of underlying non linear dynamics a number of the sequences display fractal scaling in the frequency and thickness of foreset units other successions demonstrate chaotic patterns and strong relationships between delta front angle and bed thicknesses suggesting that the progradation of such sequences is self organized and to an extent occurs independently of forcing by the feeder system that provides sediment to the delta front these patterns of sedimentation appear to be a function of the steepness of the delta front and or the textural characteristics of the sediment this paper provides further evidence for the simultaneous presence of order and chaos in earth surface processes and calls into question the extent to which palaeoenvironmental reconstructions may be made from steep faced progradational successions copyright 2000 john wiley sons ltd

analysis of the scale of errors in nearshore bathymetric data most studies of nearshore hydrodynamics sediment transport and morphology focus on bathymetric variability within a narrow band of spatial and temporal scales typically these studies rely on bathymetry estimates derived from field observations consisting of discrete samples in space and time with varying degrees of measurement error sampling limitations which result in aliasing and measurement errors can significantly contaminate variability at resolved scales and may lead to large errors in the representation of the scales of interest using a spectral analysis interpolation errors were analyzed for three different nearshore bathymetric data sets each of which targeted a different range of spatial scales bathymetric features that were unresolved or poorly resolved e g beach cusps introduced the potential for contamination in two of the data sets this contamination was significantly reduced using an appropriate scale controlled interpolation method leading to more accurate representations of the actual bathymetry an additional benefit of using scale controlled interpolation is that interpolation errors may be estimated independently of actual observations which allows one to design bathymetric sampling strategies that ensure that dominant scales are either resolved or largely removed finally interpolation errors corresponding to a particular sample design can be used to determine which interpolated values contribute usefully to a band limited analysis of bathymetric variability

formation and erosion of sediment cover in an experimental bedrock alluvial channel sediment grains in a bedrock alluvial river will be deposited within or adjacent to a sediment patch or as isolated grains on the bedrock surface previous analysis of grain geometry has demonstrated that these arrangements produce significant differences in grain entrainment shear stress however this analysis neglected potential interactions between the sediment patches local hydraulics and grain entrainment we present a series of flume experiments that measure the influence of sediment patches on grain entrainment the flume had a planar bed with roughness that was much smaller than the diameters of the mobile grains in each experiment sediment was added either as individual grains or as a single sediment pulse flow was then increased until the sediment was entrained analysis of the experiments demonstrates that 1 for individual grains coarse grains are entrained at a higher discharge than fine grains 2 once sediment patches are present the different in entrainment discharge between coarse and fine grains is greatly reduced 3 the sheltering effect of patches also increases the entrainment discharge of isolated grains 4 entire sediment patches break up and are eroded quickly rather than through progressive grain by grain erosion and 5 as discharge increases there is some tendency for patches to become more elongate and flow aligned and more randomly distributed across the bed one implication of this research is that the critical shear stress in bedrock alluvial channels will be a function of the extent of the sediment cover another is that the influence of sediment patches equalises critical shear stresses between different grain sizes and grain locations meaning that these factors may not need to be accounted for further research is needed to quantify interactions between sediment patches grain entrainment and local hydraulics on rougher bedrock surfaces and under different types of sediment supply

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

longshore drift trapped in an expected universe abstract on the basis of a review of current practice in coastal science and engineering with regard to quantitative determination of longshore drift we conclude that coastal scientists and engineers have been trapped in an expected universe of longshore transport sand volumes without critical assessment of assumptions made in pioneering studies as a result workers in this field have come to accept a range of sand volumes and a range of techniques to measure or predict these volumes stabilized by opinion of the leading experts the shortcomings of previous studies and subsequent practice however indicate that these transport volumes and techniques may well be wrong certainly at present we have no dependable verifiable and consistent field measure of net or gross instantaneous or annual longshore transport volumes against which predictions can be compared both field measurements and mathematical model results especially as used for applied purposes and expressed in annual terms are suspect for a number of reasons these include questionable assumptions that lag far behind our current understanding of shoreface processes fudge factor coefficients for equations the lack of storm transport measurement and a cascade of uncertainties that moderate current practice once determined annual longshore transport sand volumes tend to be long lived and in all cases are unverifiable by field measurement more fundamentally the question is raised whether an earth surface system as complex and variable as longshore transport on beaches can ever be quantitatively modeled or measured successfully qualitative mathematical modeling remains a valid and useful approach to understanding the nature of sedimentary processes

experimental study of bore run up bore propagation near the shoreline the transition from bore to wave run up and the ensuing run up motion on a uniformly sloping beach are investigated experimentally as a bore approaches the shoreline the propagation speed first decelerates by compressing its wave form and then suddenly accelerates at the shoreline although this behaviour is qualitatively in agreement with the inviscid shallow water wave prediction the acceleration is caused by the momentum exchange process

timescales of beach cusp evolution on a steep megatidal mixed sand gravel beach abstract field observations are presented of the morphological evolution of beach cusps on a 1 10 slope megatidal 8 12 m range mixed sand gravel beach at the head of the bay of fundy nova scotia cusps had mean wavelengths of 3 6 m and displayed pronounced horn bay sediment size segregation with sand sized material in the bays and gravel sized material in the horns cusp occurrence was limited to the upper third of the beach face shoreline position during the tidal cycle was estimated at three minute intervals from time averaged video imagery three cusp events are examined in detail two exhibiting pronounced topographic relief and the third demonstrating sensitivity of the rate of cusp evolution to the beach surface grain size distribution forcing conditions were weak with significant offshore wave heights of 10 20 cm and peak periods of 4 7 s relict cusp morphology was inundated with the rising tide and destroyed or reworked during high tide new cusps formed during the falling tide through a combination of accretion at the horns and erosion in the embayments timescales of growth and decay were short ranging from 10 to 30 min the location and dynamics of cusp horns appeared to depend on the high water line and its location relative to any pre existing cusp morphology the apparent sensitivity of cusp formation timescales to the local grain size distribution suggests that size segregation is intrinsic to the process of mixed sand gravel cusp evolution

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

chaos fractals and self organization in coastal geomorphology simulating dune landscapes in vegetated environments complex nonlinear dynamic systems are ubiquitous in the landscapes and phenomena studied by earth sciences in general and by geomorphology in particular concepts of chaos fractals and self organization originating from research in nonlinear dynamics have proven to be powerful approaches to understanding and modeling the evolution and characteristics of a wide variety of landscapes and bedforms this paper presents a brief survey of the fundamental ideas and terminology underlying these types of investigations covering such concepts as strange attractors fractal dimensions and self organized criticality their application in many areas of geomorphological research is subsequently reviewed in river network modeling and in surface analysis amongst others followed by more detailed descriptions of the use of chaos theory fractals and self organization in coastal geomorphology in particular these include self organized behavior of beach morphology the fractal nature of ocean surface gravity waves the self organization of beach cusps and simulation models of ripples and dune patterns this paper further presents a substantial extension of existing dune landscape simulation models by incorporating vegetation in the algorithm enabling more realistic investigations into the self organization of coastal dune systems interactions between vegetation and the sand transport process in the model such as the modification of erosion and deposition rules and the growth response of vegetation to burial and erosion introduce additional nonlinear feedback mechanisms that affect the course of selforganization of the simulated landscape exploratory modeling efforts show tantalizing results of how vegetation dynamics have a decisive impact on the emerging morphology and conversely how the developing landscape affects vegetation patterns extended interpretation of the modeling results in terms of attractors is hampered however by want of suitable state variables for characterizing vegetated landscapes with respect to both morphology and vegetation patterns d 2002 elsevier science b v all rights reserved

test of edge wave forcing during formation of rhythmic beach morphology 1 this paper reports on concurrent measurements of evolving rhythmic beach morphology and the associated water motion on a macrotidal coarse sandy beach beach cusps with a spacing of 19 m developed over a 3 day period of low energy swell after which they were destroyed by energetic wind waves the beach cusps were clearly accretionary features and developed mainly during the rising tide detailed hydrodynamic measurements were conducted at three locations in the swash and inner surf zone in the vicinity of a developing cusp horn and revealed that energetic standing mode zero subharmonic edge waves were not present during the initiation of the beach cusps specifically analysis of the hydrodynamic data indicated that 1 the amount of subharmonic energy was limited 10 of the total energy 2 none of the computed energy spectra exhibited a significant peak at the subharmonic frequency 3 the cross shore velocity amplitude at the subharmonic frequency was 2 3 times larger than the longshore velocity amplitude 4 the longshore current motion at the subharmonic frequency was barely coherent between adjacent locations in the surf zone and 5 the time series of pressure and cross shore current were in phase at either side of the developing cusp horn it is concluded that at least during this event of beach cusp formation energetic standing edge waves are not a prerequisite to initiate the development of rhythmic beach morphology

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

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

on beach cusp formation a system of shallow water equations and a bed evolution equation are used to examine the evolution of perturbations on an erodible initially plane beach subject to normal wave incidence both a permeable under darcy s law and an impermeable beach are considered it is found that alongshore periodic morphological features reminiscent of swash beach cusps form after a number of incident wave periods on both beaches on the permeable impermeable beach these patterns are accretional erosional in both cases flow is horn divergent spacings of the cusps are consistent with observations and are close to those provided by a standing synchronous linear edge wave an analysis of the processes leading to bed change is presented two physical mechanisms are identified concentration gradient and flow divergence which are dominant in the lower and upper swash respectively and their difference over a wave cycle leads to erosion or deposition on an impermeable beach infiltration enters this balance in the upper swash a bed wave of elevation is shown to advance up the beach at the tip of the uprush with a smaller wave of depression on the backwash it is found that cusp horns can grow by a positive feedback mechanism stemming from decreased increased backwash on positive negative bed perturbations

a predictive relationship for the spacing of beach cusps in nature abstract modeling is carried out to obtain a relationship that enables the prediction of the spacing of beach cusps using wave and sediment parameters the modeling is based on the concepts that 1 the path of wave uprush flow diverging at a cusp horn has a close connection with the cusp spacing and 2 the flow path is affected by the grain size of beach sediment the following equation is derived a t g h in which is the cusp spacing h is the nearshore wave height t is the wave period is a dimensionless quantity representing the effect of sediment grain size exp 0 23d0 55 where d is the grain size in mm units g is the gravitational acceleration and a 1 35 the value of a is determined using a large amount of existing field data applicability of the predictive equation is examined by using the data from an embayed beach in new south wales australia the result indicates that this equation is capable of reasonably explaining a general trend of the alongshore variation in cusp spacings

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

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

high frequency in situ field measurements of morphological response on a fine gravel beach during energetic wave conditions this paper presents novel data collected over four weeks at loe bar a fine gravel barrier d50 3 5 mm exposed to energetic wave conditions hs10 2 4 m combined remote and in situ measurements were used to identify 3d morphological response profile change and runup behaviour during successive energetic periods hs 2 5 m small intertidal beach volume losses occurred under high steepness waves h0 l0 0 01 but in general the overall beach volume was remarkably stable in fact the greatest morphological response was evident not in cross shore sediment exchanges but due to the alongshore redistribution related to the three dimensional beach cusp system specifically during energetic wave conditions the cusp morphology underwent horn growth and embayment deepening leading to increased cusp definition an additional explanation for the stability of the cross shore beach profile is related to the development of the beach step during energetic conditions and long period waves significant deposition c 1 m occurred at the top of the beach step above the still water line the enhanced step provided a focal point for wave breaking considerably curtailing the swash motion and reducing the runup limit thereby providing protection to the upper beach this study provides much needed insight into complex morphological response and runup characteristics on gravel beaches fundamental for improved model development and leading towards better predictive tools

investigation of a self organization model for beach cusp formation and development a recent numerical investigation of self organization werner and fink 1993 suggests that the feedback process between currents and sediment response can result in self organized patterns and can be used to predict beach cusp formation and spacing a similar model based on self organization is tested here in order to understand the processes occurring during beach cusp formation and development to evaluate the sensitivity toward the parameters used and to examine how the model might relate to field observations results obtained confirm the validity of the self organization approach and its capacity to predict beach cusp spacing with values in fair agreement with the available field measurements with most of the input parameters primarily affecting the rate of the process rather than the final spacing however changes in the random seed and runs for large numbers of swash cycles reveal a dynamical system with significant unpredictable behavior cusp spacing tends to change with time and cusp regularity shows large long term variations cusps are found to be accretionary in the swash zone and in agreement with most observations mean flows are horn divergent over developed topography simulations over nonplanar slopes characterized by the presence of preexisting nonrhythmic or cuspate features have been performed results indicate that preexisting large amplitude cusps are destroyed if their spacing is substantially different from that expected under self organization and that the final spacing is consistent with that predicted by the model for an equivalent plane beach these findings support the hypothesis that self organization is a robust mechanism for beach cusp formation

self organization of sorted patterned ground striking circular labyrinthine polygonal and striped patterns of stones and soil self organize in many polar and high alpine environments these forms emerge because freeze thaw cycles drive an interplay between two feedback mechanisms first formation of ice lenses in freezing soil sorts stones and soil by displacing soil toward soil rich domains and stones toward stone rich domains second stones are transported along the axis of elongate stone domains which are squeezed and confined as freezing soil domains expand in a numerical model implementing these feedbacks circles labyrinths and islands form when sorting dominates polygonal networks form when stone domain squeezing and confinement dominate and stripes form as hillslope gradient is increased

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

morphometric and sediment analysis of beach cusp in correlation to rip currents a case study from tropical coast west coast of india the presence of rhythmic beach cusps in foreshore regions are of persistent research interest to coastal researchers engineers with respect to their formation in beaches morphometric and sediment analysis were used to study beach cusp morphology at vengurla beach a gentle slope beach characterized by medium sand the cusp dimensions such as spacing elevation amplitude and depth were measured for detailed analysis the distinctive sediment characteristics between the horn and the bays of the cusp are different and cusp measurements show a high level of irregularity horns and bays have medium sand but sorting is varying sorting variations clearly demonstrated the difference in energy condition between horns and bay negative skewness of few horn samples has been correlated with erosional trend based on the grain size analysis result it was observed that vengurla beach cusps follow the regular grain size distribution pattern additionally the low intensity rip currents were also noticed in the study area the rate of occurrence and strength of rip currents are decided by the nearshore bathymetry and play an imperative role in rip current formation the present study is based upon the field measurements along vengurla coast and contributes to morphometric analysis of beach cusps regarding beach cusps there are no documented databases along the indian coast understanding the beach cusp formation and its seasonal changes along the beaches will be useful for effective coastal management

a cellular model of braided rivers a broad sheet of water flowing over non cohesive sediment typically breaks up into a network of interconnected channels called a braided stream fig 1 the dynamics of such networks are complex channels migrate laterally split rejoin and develop bars with the flow shifting unpredictably from one part of the network to another many processes are known to operate in a braided river1 3 but it is unclear which of these are essential to explain the observed dynamics we describe here a simple deterministic numerical model of water flow over a cohesionless bed that captures the main spatial and temporal features of real braided rivers the patterns arise from local scour and deposition caused by a nonlinear dependence of bedload sediment flux on water discharge although the morphology of the resulting network depends in detail on the sediment transport rule used in the model our results suggest that the only factors essential for braiding are bedload sediment transport and laterally unconstrained free surface flow

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

sandbars in motion nearshore surf zones are turbulent places yet despite the apparently chaotic nature of the sea surface in these areas sandbars often show complex patterns with an intricate structure in their perspective stive and reniers discuss recent efforts to understand how these patterns form they highlight the report by hoefel and elgar who consider a new transport mechanism based on flow acceleration within the waves this mechanism should help to improve the predictability of sandbar structures

fractal properties of coastal profile evolution at duck north carolina observed variations in coastal morphology on monthly to decadal timescales are often difficult to explain in terms of physical processes operating on shorter timescales one reason could be that the morphology evolves to high dimensional self organized states circumstantial evidence for this would be indicated by fractal distributions of the dynamical variables fractal analysis techniques are applied to beach level time series collected at duck north carolina united states after processing for this study the data set consists of time series of monthly beach and nearshore levels at up to 86 locations at 10 m spacing along each of four shore normal profile lines over a period of 10 5 years time series of shoreline positions are also analyzed several fractal analysis techniques are used based on the hurst exponent h and various sources of error are considered and quantified results indicate different fractal behavior in different cross shore zones h values of around 0 5 are found in the nearshore bar zones and are thus consistent with a random gaussian process while values around 0 8 are found farther offshore and on upper parts of the beach indicating long range persistency further analyses are done to determine time spans over which fractal behavior occurs generally fractal responses are found at locations and timescales where the temporal variations of wave forcing are relatively weak suggestions are made to interpret these findings in terms of forced and self organized morphodynamic change in different cross shore zones and over different timescales some possible implications for predicting future coastal morphology are discussed