modification of a linear bar trough system by a standing edge wave abstract detailed fluid motions and bathymetric changes in the lacustrine nearshore zone at wymbolwood beach georgian bay canada were monitored during storms to test theoretical postulates about the importance of low frequency wave motions to nearshore circulation of water and sediments eighteen continuous resistance wave staffs and two electromagnetic current meters were deployed along one shore normal and two shore parallel instrument arrays over a period of two months during one intense storm a mode 3 standing edge wave at 0 035 hz was the predominant low frequency motion prior to the storm the bathymetry was characterized by linear bar trough systems and during the storm these features migrated onshore and became rhythmic in response to the length scales and relatively fixed locations of nodal and antinodal lines of the standing edge wave however a well defined crescentic bar as predicted by the model under the condition of zero net sediment flux divergence did not evolve because the hydrodynamic forcing ceased before an equilibrium condition could be attained nevertheless the location of scour and accretion features demonstrated the tendency towards such a crescentic form the offshore and alongshore irregularities of the post storm bathymetry are not readily explained by alternative hydrodynamic interactions

storm induced response of a nearshore bar system abstract a nearshore bar system was surveyed periodically through a storm and the following recovery period the data showed a very rapid response of morphology to changing wave conditions and allowed various models on bar formation to be tested under low energy conditions prior to the storm a small bar was surveyed 13 m offshore both the high reflectivity of the beach and the cross shore distance to the bar are consistent with a model of sediment convergence at the node or antinode of a standing wave of incident period such a small scale bar may be a common feature on beaches with steep foreshores and more gentle offshore slopes with the increase in wave height during the storm the bar became better developed and migrated offshore at rates up to 2 2 m h 1 the bar maintained its form in that the ratio of trough depth to crest depth h t h c remained roughly constant the bar was in no way related to processes which would cause the convergence of sediment in the breaker zone through most of the storm the bar crest distance offshore was typically only 10 of the surf zone width analysis of the bar distance offshore in terms of a standing wave motion showed that the causative wave period must have been much longer than that of incident waves probably on the order of a minute surf zone wave data showed significant energy in the infragravity band at these periods although no definite link has been made after the height of the storm the bar had a crescentic morphology the development of this morphology occurred very rapidly with parts of the bar migrating onshore at rates up to 1 2 m h 1 in contrast to the storm during the recovery period h t h c varied by nearly a factor of three analysis of the offshore and longshore length scales showed the bar to be similar to one which would be generated by a standing mode 1 edge wave of period on the order of one minute

mass flux and undertow in a surf zone abstract the mass of water carried shoreward by the breaking waves in a surf zone will in a two dimensional situation be compensated by a seaward return flow the undertow it is shown that the undertow is driven by the local difference between radiation stress and the set up pressure gradient which only balance each other in average over the depth turbulent shear stresses are required to maintain a steady situation comparison with measurements confirms the theoretical results

suspended sediment transport and nearshore bar formation on a shallow intermediate state beach abstract estimates of cross shore suspended sediment flux were obtained during a 3 day storm event on the north sea coast of denmark the suspended sediment flux estimates were correlated with volumetric beach change as registered at 28 permanently deployed survey rods crossing the intertidal beach and inner surf zones during this storm a nearshore bar initially migrated onshore and welded to the beach face at its updrift end subsequently a new bar formed on the seaward slope of the former suspended sediment transport recorded using optical backscatter sensors and electromagnetic current meters corresponded well qualitatively with the morphological evolution indications are that such measurements may account for a significant fraction of the actual cross shore sediment transport the onshore migration of the nearshore bar was the result of onshore directed mean currents associated with a cell circulation renewed bar formation took place when this circulation was locally replaced by an offshore directed mean current undertow suspended sediment transport due to oscillatory waves at incident and infragravity frequencies was generally subordinate to the mean transport

wave energy saturation on a natural beach of variable slope time series of flow were measured across the inner surf zone during a storm these data were used to quantify the dependence of wave height transformed from measured flow and velocity on local slope and depth similar to previous studies as incident waves broke and propagated into the surf zone wave energy became saturated and wave height was strongly dependent on depth however the ratio of rms wave height to local depth rms was found not to be constant but to vary between 0 29 and 0 55 rms increased with local slope and was independent of deepwater wave steepness thus the surf zone similarity parameter the ratio of slope to the square root of steepness did not adequately parameterize rms

infragravity response to variable wave forcing in the nearshore 1 analysis of field observations of sea surface elevation reveals the role of time varying incident forcing and bound wave release mechanisms on the generation of infragravity waves on a barred beach observations of infragravity response were obtained during sea breeze and swell periods with wave height varying from 0 2 to 1 2 m and wave period from 3 to 16 s the observations show a stronger infragravity response to longer period incident swell than to short period wind sea during the peak of the sea breeze short period wind sea is conducive to long wave generation by breakpoint forcing under swell dominated conditions the frequency and wave number of incoming bound waves associated with wave groups may satisfy the linear dispersion relationship leading to resonant forcing of a free wave that appears to be released from the wave group the transition between long wave generation due to bound wave release and time varying breakpoint forcing agrees with the surf beat similarity parameter

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

hydraulics of interrill overland flow on stone covered desert surfaces the hydraulics of interrill overland flow on stone covered desert surfaces depend on the resistance to flow which may be partitioned into grain resistance form resistance wave resistance and rain resistance efforts to model large scale roughness in open channels suggest that resistance to overland flow on such surfaces is a function of grain reynolds number froude number flow depth and the size shape spacing and pattern of the roughness elements the effect of flow depth on flow resistance f is often hidden in the flow reynolds number re in laboratory and field studies alike f re relations have been found to be convex upward and negatively sloping and these shapes have been explained in terms of the progressive inundation of the roughness elements where laboratory or field based models have been developed for predicting f they invariably contain percent stone cover the prominence of this variable reflects the strong influence of stone size and spacing on flow resistance a laboratory study shows that where the froude number f 0 50 wave resistance increases with stone cover and dominates resistance to flow on all surfaces with stone covers greater than 10 a field study indicates that where f 0 50 and wave resistance is inconsequential grain and form resistance typically account for about 5 and 95 of f respectively these findings have important implications for sediment transport modeling because percent grain resistance is equal to percent grain shear stress and it has recently been suggested that in overland flow as in river flow sediment transport capacity is determined by grain shear stress rather than total shear stress a laboratory study however demonstrates that this is not the case sediment transport capacity is in fact greater than predicted by grain shear stress because energy dissipated in the wakes of roughness elements in overland flow is transformed into turbulence sufficiently close to the bed to affect sediment transport

sediment suspension under waves and currents time scales and vertical structure field measurements of the vertical structure of near bed suspended sediment concentrations were obtained from arrays of fast response optical backscatter suspended solids sensors to examine the time dependent response of sediment resuspension to waves and currents and the constraints imposed by bedforms data were recorded from both a nonbarred marine shoreface and a barred lacustrine shoreface under both shoaling and breaking waves significant heights of 0 25 1 50m peak periods of 3 and 8 s and in water depths of 0 5 5 0 m sediment concentrations are positively correlated with increasing elevation above the bed but lagged in time the time lag varies directly with separation distance between measurement locations and inversely with the horizontal component of the near bed oscillatory velocity both the presence of wave groups and the settling velocities of the sediment particules in suspension influence the temporal changes in concentration at a given elevation sediment concentrations appear to respond more slowly to the incident wind wave forcing with distance away from the bed as a result of two factors 1 the sequential increase in concentration induced by a succession of large waves in a group and ii the relative increase in finer sediments with smaller settling velocities bedforms interact with the near bed horizontal currents to impose a distinct constraint upon the timing of suspension events relative to the phase of the fluid motion and therefore the vertical structure of the suspended sediment concentration at a range of time scales the near bed concentrations appear to be strongly dependent upon the vertical convection of sediment associated with the ejection from the wave boundary layer of separation vortices generated in the lee of ripple crests concentration gradients in the presence of vortex ripples are large as are the correlation between concentrations measured at different elevations within the fluid

cross shore mean flow in the surf zone abstract the seaward mean returnflow or undertow in the surf zone which compensates for the shoreward mass flux above the wave trough level is found to be driven by the force imbalance between the wave momentum flux on the one hand and the set up on the other hand in qualitative agreement with the model of dyhr nielsen and sorensen 1970 a model which quantifies this imbalance is shown to yield theoretical results in good accordance with experiments when the proper boundary conditions are accounted for

sediment transport on dissipative intermediate and reflective beaches abstract in this paper we review and synthesize field measurements of suspended sediment transport on the shoreface of dissipative intermediate and reflective beach states the morphodynamic beach state continuum was originally established in the 1970s but at the time only hydrodynamic processes and morphologies in these various states were described since the early 1980s when sensors capable of resolving suspended sediment concentration at intra wave time scale became available many studies have examined suspended sediment transport by waves and currents on the shoreface the synthesis of this work shows that the two end states in the morphodynamic continuum which are the dissipative and reflective states exhibit relatively small rates of cross shore sediment transport and weak gradients in that transport which both ensure that the nearshore morphology is relatively stable the intervening intermediate beach states typically exhibit prominent bar topographies and in these states strong morphodynamic feedbacks between hydrodynamic processes and morphology create locally large transport rates and sharp transport gradients which is the reason for the dynamic nature of these beach states transport processes driving sediment onshore and offshore within beach states are discussed as well as the transport processes responsible for state transitions

resonant wave reflection by transverse bedforms and its relation to beaches and offshore bars abstract on an erodible sand bed there may be a coupling between the reflection of incident wave energy and the development of transverse bedforms the nature of this interaction is examined with particular reference to a laboratory experiment in which a veneer of sand was introduced into a pre existing fixed pattern of bars the observed motion of the mobile sand suggested potential development of this existing bar system in the up wave direction but not in the down wave direction it is argued here that this phenomenon may be significant in terms of the growth of shore parallel bars off beaches and for coastal protection in general

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

morphosedimentary multiyear changes on a barred coast gulf of lions mediterranean sea france abstract an overall estimate of the relationship between the changes in the nearshore morphology the evolution of the sedimentary budget the beach morphodynamics and the variation of grain size characteristics along the beach barrier of thau lagoon languedoc france was attempted by synthesizing the data from different surveys a basic survey of two separate grids of 11 closely spaced 50 m transverse profiles during 1989 1991 a long baseline 11 km survey of 11 beach profiles during 1988 1991 and an earlier long run 1984 1990 survey of 6 widely spaced bathymetric profiles covering discretely the whole stretch of the nearshore zone time intervals between profile monitorings within each type of survey differed but many measurements during the recent 1989 1991 period were coincident the stable two bar system that was generally developed all over this nearshore zone has been gradually changing at the northeastern end south of the town of sete since 1989 under the effect of a series of new defense structures upstream in the dominant ne sw wave induced longshore current with a tendency toward a single bar profile the average nearshore slope was steeper 0 91 in the sete close survey area than in the southwestern area 0 83 during the same period acceleration in beach erosion has been observed at the northeast in contrast with a stable dynamic equilibrium over the southwestern beach and nearshore profiles over a longer period 1984 1990 scouring of the nearshore sand prism down to the 10 m isobath at the northeastern end between the extreme bathymetric profiles could be estimated at about 37 000 m 3 while the overall sedimentary budget was positive bar migration and morphologic changes in the study areas were not related to any seasonal cycle in the wave climate but were more significant when this was more energetic as during 1989 an overall attenuation in nearshore morphodynamics was observed during the following two years although some rapid local changes between consecutive measurements could be detected temporal variation of grain size characteristics were therefore small and or not significant conversely on the subaerial beach alongshore differentiation in mean diameter and in sorting and skewness parameters is consistent with the evolution of the erosion accumulation processes following a long period wave like sand transfer from northeast to southwest

coastal geomorphology through the looking glass abstract coastal geomorphology will gain future prominence as environmentally sound coastal zone management strategies requiring scientific information begin to supplant engineered shoreline stabilization schemes for amelioration of coastal hazards we anticipate substantial change and progress over the next two decades but we do not predict revolutionary advances in theoretical understanding of coastal geomorphic systems paradigm shifts will not occur knowledge will advance incrementally we offer predictions for specific coastal systems delineated according to scale for the surf zone we predict advances in wave shoaling theory but not for wave breaking we also predict greater understanding of turbulent processes and substantive improvements in surf zone circulation and radiation stress models very few of these improvements are expected to be incorporated in geomorphic models of coastal processes we do not envision improvements in the theory of sediment transport although some new and exciting empirical observations are probable at the beach and nearshore scale we predict the development of theoretically based two and three dimensional morphodynamical models that account for non linear time dependent feedback processes using empirically calibrated modules most of the geomorphic research effort however will be concentrated at the scale of littoral cells this scale is appropriate for coastal zone management because processes at this scale are manageable using traditional geomorphic techniques at the largest scale little advance will occur in our understanding of how coastlines evolve any empirical knowledge that is gained will accrue indirectly finally we contend that anthropogenic influences directly and indirectly will be powerful forces in steering the future of coastal geomorphology if you should suddenly feel the need for a lesson in humility try forecasting the future kleppner 1991 p 10

infragravity waves over a natural barred profile measurements of cross shore flow were made across the surf zone during a storm as a nearshore bar became better developed and migrated offshore measured infragravity band spectra were compared to synthetic spectra calculated numerically over the natural barred profile assuming a white run up spectrum of leaky mode or high mode edge waves as in earlier studies the spectra compared closely however for some frequencies the energy of the measured spectrum exceeded the energy of the synthetic spectrum suggesting that the run up spectrum was not white but had dominating frequencies utilizing cross shore flow data and synthetic spectra from a number of cross shore locations an equivalent run up spectrum was calculated for each day on the first day of the storm the equivalent run up spectrum indicated a dominant wave that had a node in velocity reasonably close to the bar crest later during the storm when the bar had migrated farther offshore there was no evidence for a dominant motion having a velocity node at the bar crest the structure of the equivalent run up spectrum compared well with spectra of direct measurements of run up obtained several hundred meters away we have no clear evidence in support of the theory that infragravity waves might form or force the offshore migration of a bar to confirm this finding longer records obtained synoptically over a developing bar are required the dominant wave observed early in the storm was consistent with symond and bowen s 1984 theoretical prediction of resonant amplification of discrete frequencies over a barred profile

standing edge waves on a pocket beach field measurements of edge waves obtained on a narrow pocket beach are described the beach named usgo is located on the north coast of spain immediately to the west of the city of santander and is exposed to the atlantic ocean the edge wave field on this beach is analyzed utilizing data from a longshore array of current meters located in about 3 m of water depth frequency spectra of longshore velocities display several significant peaks suggesting that the edge wave field on this pocket beach consists of several dominant modes this is in contrast to observations on open coastal beaches e g oltman shay and guza 1987 which show the existence of a broad banded edge wave field we isolate four frequency peaks and examine the longshore variation of the motions at these frequencies and find convincing evidence of a nodal structure utilizing the measured bathymetry we compute the cross shore profiles and theoretical wavelengths of edge waves at the dominant frequencies using a numerical solution of the shallow water equations by howd et al 1992 we find that edge waves at these frequencies are theoretically confined between the headlands since their amplitudes decay to insignificant levels within a cross shore distance that is less than the offshore extent of the headlands in addition assuming perfect sidewall reflections the theoretical nodal locations closely correspond to those inferred from the measurements we conclude that discrete standing edge waves resulting from resonances related to the longshore width of the beach are present on usgo beach

effects of rock fragments on soil erosion by water at different spatial scales a review this paper reviews the various effects of rock fragments on soil erosion by water since these effects are scale dependent they are investigated at three different nested spatial scales the microplot 4 10 6 100m2 the mesoplot 10 2 102 m2 and the macroplot 101 104 m2 for each scale the corresponding process mechanisms are discussed particular attention is paid to the effects of rock fragment cover on the intensity of soil erosion processes at the mesoplot scale i e on interrill areas rock fragments at the soil surface can have negative as well as positive effects on sediment yield these ambivalent effects are conditioned by the type of fine earth porosity soil surface slope vertical position and size of rock fragments and by the occurrence of horseshoe vortex erosion at the microplot scale i e the soil surface area which is covered by a single rock fragment and at the macroplot scale i e upland areas where both interrill and rill erosion takes place rock fragments at the soil surface have a negative effect on sediment yield in these two scales rock fragments can thus be considered as natural soil surface stabilizers at the macroplot scale the mean decrease of relative interrill and rill sediment yield with rock fragment cover can be expressed by an exponential decay function the scatter of the data indicates that a given rock fragment cover can have different efficiencies in reducing interrill and rill sediment yield depending on the varying intensities of the hydrological and erosion subprocesses these findings have implications for erosion modelling and soil conservation

dynamics of a high energy dissipative surf zone vright l d guza r t and short a d 1982 dynamics of a high energy dissipative surf zone mar geol 45 41 62 pressure and horizontal current u v time series were measured at different positions across the inner 150 m of a wide 500 m surf zone of a microtidal high wave energy beach incident waves had average heights of 3 4 m with maxima of 5 m and periods of 12 to 15 sec bores of broken waves diminished in height at a nearly constant rate as they progressed across the surf zone the ratio of bore height h to local water depth h was everywhere less than 1 for even the highest bores and was on the order of 0 40 for the significant bores at incident wave frequencies rip circulation was weak or absent but a moderate longshore current was present shore normal flows were vertically segregated with strong net onshore flows prevailing just below the surface accompanied by weaker net seaward flows near the bed spectra of water surface oscillations as determined from pressure u and v reveal that most of the energy in the inner surf zone was at infragravity frequencies periods greater than 30 sec shoreward decay of wave energy at incident wave frequencies was accompanied by shoreward growth of infragravity energy near the beach the infragravity oscillations had heights on the order of 1 m cross spectra show that the infragravity oscillations were standing in the shore normal direction from the relative magnitudes of infragravity versus incident wave currents it is inferred that the surf beat may be an order of magnitude more important than incident waves to the transport of sediment in the inner surf zone

determining friction coefficients for interrill flows the significance of flow filaments and backwater effects friction coefficients in overland flows are customarily estimated from mean flow properties depth velocity slope that subsume spatial variations in flow arising from two majo rc auses microtopography and obstacles this paper uses laboratory experiments in shallow flumes to examine the extent of non uniformity in flow conditions associated with each cause randomly placed emergent obstacles in a flume with a shallow axial channel generally yielded higher hydraulic roughness than the same pattern of obstacles on a planar flume as well as greater variation in roughness as the obstacle locations were altered in both flumes hydraulic roughness fell with increasing reynolds number for 10 obstacle cover showed a flattening trend at 20 cover and exhibited a convex downward trend at 30 obstacle cover these results indicate the progressive onset of flow controls at narrow gaps in the obstacle field in such flows the use of mean flow properties conceals the existence of two main subdivisions of flow flow filaments and backwater flows in the experiments flow filaments involved velocities more than twice the overall mean whereas backwater flows were much slower than the mean the existence of fast moving flow filaments may be significant in understanding soil transport in surface runoff and backwater depths may modify splash detachment similarly friction coefficients that fail to reflect these important non uniform flow components may not be optimal for hydraulic calculations or in erosion models it is concluded that new approaches to observing and processing flow data may be required in order to avoid the loss of important flow detail that is entailed in assuming uniform flow conditions copyright 2003 john wiley sons ltd

trends in research on beaches and dunes on sandy shores 1969 2019 abstract trends in research on morphologic changes on beaches and foredunes on sandy shores are identified from the 1960s to the present research during this period evolved from early descriptive explanation and classification of profile change to instrumented field investigations to modelling of landform change at larger scales research efforts have become increasingly more collaborative with increasing use of field instrumentation data acquisition systems and remote sensing rich datasets are resulting in more comprehensive computational models human altered systems are of increasing interest but knowledge of these systems lags far behind knowledge of natural systems research is becoming more relevant to societal needs as the vulnerability of coastal populations increases the need for investigation of understudied or unexplored environments including human altered ones is ongoing many basic research issues remain but future studies would profit from the development of new models rather than validating or reconfiguring old models collaboration between geomorphologists and engineers may open up research opportunities particularly in modifying beaches and dunes built for shore protection to provide natural values in restricted space application of models to enhance knowledge of effects of sea level rise and coastal storms would be useful to managers developing resiliency plans

skewness in the nearshore zone a comparison of estimates from marsh mcbirney current meters and colocated pressure sensors many of the field studies that have undertaken an investigation of surf zone dynamics e g nearshore sediment transport study canadian coastal sediment study have relied on marsh mcbirney electromagnetic current meters to measure the velocity field data from these instruments have been used to compute higher order moments of the velocity field which are used as an input in many sediment transport models however recent laboratory measurements by aubrey and trowbridge 1985 have raised questions regarding the suitability of marsh mcbirney current meters for surf zone studies and the accuracy of higher order velocity moments fortunately colocated pressure and velocity measurements were made during field programs in effect this provides a calibration check in the field of the performance of these instruments a cross spectral analysis indicates that colocated marsh mcbirney current meter measurements are highly coherent this is true for measurements from inside and outside the surf zone as a result normalized skewness estimates computed with the aid of the bispectrum from these colocated current meter measurements differ by only a few percent a cross spectral analysis between colocated pressure and velocity measurements show a similar distribution of variance for wind wave frequencies observed differences between normalized skewness estimates from colocated pressure and velocity measurements are shown to be consistent with the theoretical expectation that pressure has a nonlinear dependence on velocity these results suggest that the marsh mcbirney current meter is suitable for the estimation of nondimensional velocity moments even in breaking wave conditions

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

waves currents sediment flux and morphological response in a barred nearshore system abstract a shore normal array of seven bi directional electromagnetic flowmeters and nine surface piercing continuous resistance wave staffs were deployed across a multiple barred nearshore at wendake beach georgian bay canada and monitored for a complete storm cycle time integrated estimates of total itvf and net invf sediment volume flux together with bed elevation changes were determined using depth of activity rods the three bars ranging in height from 0 10 to 0 40 m accreted during the storm 0 03 m and the troughs were scoured 0 05 m sediment reactivation depths reached 0 14 m and 12 of the nearshore control volume was mobilized however the invf value for the storm was less than 1 of the control volume revealing a near balance in sediment volume in the bar system landward migration of the inner crescentic and second sinuous bars occurred in association with an alongshore migration of the bar form itself the outermost straight shore parallel bar remained fixed in location the surf zone was highly dissipative throughout the storm 3 8 10 2 192 10 2 and the wave spectrum was dominated by energy at the incident frequency spectral peaks at frequencies of the first harmonic and at one quarter that of the incident wave were associated with secondary wave generation just prior to breaking and a standing edge wave respectively the former spectral peak was within the 95 confidence band for the spectrum while the latter contributed not more than 10 to the total energy in the surface elevation spectrum even near the shoreline during the storm wave height exceeded 2 m h s and periods reached 5 s t p k orbital velocities exceeded 0 5 m s 1 u rm s and were above the threshold of motion for the medium to fine sands throughout the storm shore parallel flows in excess of 0 4 m s 1 were recorded with maxima in the troughs and minima just landward of the bar crest the rate and direction of sediment flux is best explained by the interaction of antecedent bed slopes with spatial gradients in the mean and asymmetry of the shore normal velocity field these hydrodynamic parameters represent steady flows superimposed on the dominantly oscillatory motion and assumed a characteristic spatial pattern from the storm peak through the decay period increases spatially in the magnitudes of both the mean flows and flow asymmetries cause an increasing net transport potential erosion decreases in these values spatially cause a decreasing net transport potential and thus deposition these transport potentials are increased or decreased through the gravity potential induced by the local bed slope shore parallel flow was important in explaining sediment flux and morphological change where orbital velocities mean flows and flow asymmetries were at a minimum

morphodynamics of intertidal bars in wave dominated coastal settings a review abstract intertidal bar systems are ubiquitous features on wave dominated beaches in coastal settings with a significant 1 m tidal range depending primarily on the wave conditions and the tidal range and to a lesser extent on the nearshore gradient they can assume a variety of forms slip face bars represent the most pronounced and dynamic intertidal bar morphology and are generally found on their own around the mean high tide level they usually form low on the intertidal beach after storm induced beach erosion and develop into a berm under prolonged calm wave conditions low amplitude ridges and sand waves represent multiple bar morphologies the bars occur across the entire intertidal profile and they remain present throughout the year multiple intertidal bars tend to be rather subdued and relatively static especially sand waves and their origin remains unclear the morphological response of intertidal bars to changing wave conditions is largely forced bars build up and migrate onshore under calm waves and are flattened and may migrate offshore during storms the morphological response is however significantly affected by relaxation time effects and morphological feedback particularly on beaches with multiple intertidal bars despite their morphological differences the intertidal bar types exhibit pronounced similarities in their morphodynamics sediment transport processes and morphological response are principally controlled by the tidal water levels on the beach because these together with the offshore wave energy level and the beach morphology determine the type intensity and duration of the wave processes operating on the cross shore profile it is the dominant importance of tidal water level variations and wave processes in shallow water depths swash and surf zone bores rather than wave height variability and deeper water wave processes breaking and shoaling waves that constitutes the main difference between intertidal and subtidal bar morphodynamics

an environmental investigation of the mineralogical geotechnical hydrogeologic and botanical properties of subsurface flow constructed wetlands in akumal mexico akumal is one of the few locations where subsurface flow constructed wetland systems can be compared directly without major differences in environmental setting these systems in akumal have highly variable geotechnical properties and performance and most systems are not well functioning a basic water quality survey indicates sfcw effluent in no case meets unep or usepa guidelines for ammonia or phosphate for sensitive waters systems are undersized and many are planted with less than optimal vegetation aggregate is generally too coarse and pores are commonly occluded with organic matter the mineralogy of the locally sourced aggregate used in the systems is dominated by calcite aragonite quartz boehmite and chlorite and is generally beneficial for improving the water quality of the systems however dissolution is observed and is of some concern major systematic retrofit efforts to improve these systems are warranted and should focus on better vegetation choices use of locally sourced smaller and less soluble aggregate exclusive use of the local limestone source containing boehmite more frequent exchange of the aggregate and an increase of overall cell size the systems in akumal are a classic example of a technological solution to an environmental problem caused by human development that has outpaced the designed capacity for wastewater treatment this investigation serves as a baseline for numerous future interdisciplinary investigations and outlines challenges facing coastal communities attempting to use subsurface flow constructed wetlands

investigation of calcareous beach sands in the akumal and tulum areas for use in constructed wetlands eastern yucatan peninsula constructed wetlands can be a low cost ecologically based technology to locally treat domestic wastewater prior to discharge wetland systems implemented in the resort village of akumal in the state of quintana roo in the yucatan peninsula of mexico have been considered moderately successful over approximately 10 years of operation yet the wide scale implementation of constructed wetlands has not occurred in the region nor throughout mexico due largely to the cost of the crushed aggregate used in these systems variation in the geotechnical and mineralogical properties of 29 samples of local calcareous beach sands collected from the tourist areas of akumal and tulum in the yucatan mexico were analyzed and compared to those of crushed aggregate currently used in constructed wetland systems in akumal powder x ray diffraction on beach sand samples from akumal and tulum indicates that the proportion of aragonite varies from 24 to 84 calcite varies from 7 to 38 and mg calcite varied from 8 to 57 compared to crushed aggregate which consists of 0 25 aragonite and 75 100 calcite compared to crushed aggregate beach sands are unimodal and have better uniformity coefficients making them a better geotechnical choice than crushed sands with respect to these properties grain size of the beach sands is much smaller compared to that of the crushed aggregate currently used in the constructed wetland systems in akumal which should enhance the efficiency of the filtration of organic matter and bacteria the average hydraulic conductivity measurements of 0 010 and 0 016 cm s for beach sands from akumal and tulum respectively are comparable or less than the average of 0 016 cm s for crushed aggregate currently used in engineered wetland systems yet a combination of high bulk porosity intragranular pores and the presence of mg calcite observed in beach sands may likely result in higher dissolution rates versus the crushed aggregate preliminary assessment suggests that the use of local sand may be a technical economic and perceptual enhancement to the systems still a careful and thorough analysis of the potential environmental and aesthetic impacts of mining beach sands is necessary

flow characteristics at the rip current neck under low energy conditions abstract this paper presents the flow signature of the rip current neck as determined by fourteen near bottom velocity records with a comparison made to 63 recordings in the surf zone the field experiments including wave monitoring and morphological mapping were conducted under relatively calm dissipative wave conditions tsig 3 6 s hsig 0 3 1 1 m at herzliya beach israel on the mediterranean shore the current data were analysed for shore normal and resultant components the processing of the time series in the form of instantaneous and smoothed velocities provided spectral energy orbital and current velocity specific current discharge and directional distribution data the unique characteristic of the neck environment was found to be its continuous unidirectional seaward flow due to the channeling effect this steady offshore drift constituted the fastest flow in the surf zone with a typically narrow 35 94 directional range through spectral analysis of the unidirectional return flow the morphodynamic process signature at the rip neck was defined by the relative contribution from the incident waves 78 the subharmonic edge waves 14 and the infragravity oscillations 8 the pulsatory jet like rip model with concentration of energy at low frequencies is not corroborated by this study the studied environment of the rip and bar pattern represented an inherited beach morphology at an initial accretional although not yet reflective stage

hydrodynamics and sediment transport within the inner surf zone of a lacustrine multiple barred nearshore abstract it has become increasingly recognized that the typically unexpected behavior of the nearshore profile over a sequence of storm events is a response to strong feedback between the antecedent morphology and the incident wave field this paper systematically examines the suspended sediment transport and morphodynamics within the surf zone of a lacustrine multiple barred upper shoreface a range of significant wave heights h s and local relative wave heights h s h 1 h water depth are considered in order to describe and identify the limits to the feedback mechanisms that can dominate the nearshore response data from collocated concentration and velocity sensors indicate that the direction and magnitude of suspended sediment transport varies with the degree of local wave energy dissipation and the cross shore variation in these relationships depends partly on the local bed slope this dependence indicates the presence of a strong self organization at the scale of the individual bar within the inner surf zone these bar scale relationships are constrained by the shoaling transformations which occur over the outermost bar for ranges of incident wave height defined locally e g intermediate waves h s 0 4 to 0 9 m storm waves 0 9 to 1 4 m the innermost and middle bars remain in a state of self organized equilibrium for intermediate range waves this equilibrium is a consequence of wave height reduction over the outer bar through breaking and the generation of secondary harmonic waves for the storm wave range the equilibrium is maintained through a resonant amplification of discrete edge wave modes with the bars forced to a position coincident with the surface elevation antinodes these upper shoreface scale feedback mechanisms are weakened particularly for intermediate wave heights following threshold storms capable of moving the outermost bar offshore and lower on the profile this allows the middle and inner bars to be forced directly by variations in the offshore incident waves thus the bars respond in a cyclic manner the bar cycle

waves and longshore currents comparison of a numerical model with field data a two dimensional numerical model is used to predict the shoaling and breaking of surface gravity waves and the resulting longshore currents for 5 days of the nearshore sediment transport study santa barbara experiment data with incident waves having narrow banded frequency and directional spectra are selected for comparison in accord with the model assumptions of unidirectional and monochromatic waves the rms wave height is used for expressing wave energy in the calculations the current model includes bottom friction lateral mixing and nonliner convective accelerations the extensive field measurements of waves including quantitative directional information and longshore current distributions are used to test the model results the predicted rms wave heights are consistent with the measurements by tuning the model with field data of longshore currents the comparison between the model and data shows good agreement and the obtained values of free parameters are relatively constant for the five experiment days

the longshore flow component in low energy rip channels the mediterranean israel abstract we examined in the field the near bed longshore v flow component in rip channels at the herzliyya beach israel on the southeastern mediterranean field experiments conducted under relatively calm wave conditions t sig 3 6 s h sig 0 3 1 1 m included current and wave monitoring and morphological mapping time series of instantaneous and smoothed shore parallel current velocities and of the orbital components were analysed including statistical and spectral processing the peak instantaneous velocities of waves and currents combined were in excess of the threshold motion of the local sand taken as 0 3 m s some velocities even exceeded the threshold for sheet flow transport 0 9 m s the feeder and the neck demonstrated the highest longshore flow components whereas the rip head typically showed the lowest longshore velocities the unsteadiness of the net longshore current was very high feeders typically showed a mean unidirectional longshore current however directional fluctuations gradually increased towards the rip head the data suggest a clear spectral structure most energy 46 67 was in the gravity range with 13 35 subharmonic and minor 13 16 in the infragravity band systematic cross shore spatial trends of the energy spectra components were linked to bar morphology and to exposure to incident waves

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

migration of large scale subaqueous bedforms measured with seagrasses cymodocea nodosa as tracers the vertical growth of seagrasses in response to burial by migration of bedforms is combined with dating techniques to provide precise and rapid estimates of the migration speed of subaqueous dunes over seagrass patches two methods to estimate the time interval between the passage of successive dunes and the motion of single dunes through seagrass patches are described the second method is more precise the application of these methods to vegetated cymodocea nodosa subaqueous dunes in the alfacs bay nw mediterranean showed that the dunes traveled at an average speed of 13 0 pm 0 6 m yr 1 and demonstrated that the methods can resolve migration speeds from 0 15 to 980 m yr 1 with this particular seagrass species in areas vegetated with different seagrass species bedform migration can be estimated over different time scales the strong coupling between seagrass and sediment dynamics resembles the coupling of vegetation and land dunes

beach morphodynamics in a strong wind bay a low energy environment abstract the morphodynamic behaviour of a multibarred beach in a fetch limited strong wind bay seaford beach se australia was examined during both high and low energy conditions and considered in the context of a definition of low energy provided in the literature measurements of nearshore waves currents and morphology revealed a bimodal behaviour under initial low energy conditions the beach exhibited a low tide terrace state and waves and currents were of very low magnitude during subsequent high energy conditions the beach demonstrated dynamic behaviour through the formation of a transitional transverse bar and rip rhythmic bar and beach and migration of the middle bar with the morphology remaining in an arrested high energy state during intervening low energy periods although broadly conforming to the morphodynamic model the beach did exhibit some distinct characteristics attributable to its fetch limited location limited progression through the morphodynamic model and the importance of wind direction and magnitude in governing morphodynamic behaviour furthermore rip currents were not significant in driving beach change through intermediate states the presence of infragravity energy in the storm wave spectra a dissipative multibarred surf zone dynamic inner and middle bars and the attainment of a transitional transverse bar and rip rhythmic bar and beach state during rising wave conditions underline seaford beach as bimodal exhibiting process and morphologic features of both higher and lower energy beaches as an example of a beach in a strong wind bay seaford illustrates that not all fetch limited beaches are low energy furthermore the presence of infragravity energy in a highly fetch limited environment indicates that infragravity energy may occur commonly in fetch limited environments that are subject to periodic strong winds a process that has remained largely unrecognised

an energetics bedload model for a plane sloping beach local transport bagnold s energetics based sediment transport model for streams is used as a basis for the development of a model for the time varying transport of bedload over a plane sloping bed the sediment transport vector is found to consist of two components the velocity induced transport directed parallel to the instantaneous velocity vector and the gravity induced transport vector directed downslope the model is applied to the case of sediment transport within the surf zone for the separate cases of weak and strong longshore currents relative to the wave bore oscillatory water velocity the results suggest the bagnold s oscillatory sediment transport model which forms the basis for a number of longshore sediment transport models is only correct for the special case of weak longshore currents and near normal incident waves for an artibrary strength longshore current v and a local incident wave angle a the longshore transport rate is found to be proportional to sina v 1 sin sup 2 a v sup 3 where u is the wave induced oscillatory water velocity the model also predicts the onshore offshore sediment rate for weak longshore currents and near normal incident waves the predicted equilibrium beach slope is equal to tanf strong longshore currents and or significant local wave angle conditions however cause amore change in this equilibrium beach slope less authors bailard j a inman d l publication date 1981 03 20 osti identifier 6767919 resource type journal article resource relation journal name j geophys res united states journal volume 86 c3 research org scripps institution of oceanography university of california la jolla california 92093 country of publication united states language english subject 58 geosciences shores sedimentation coastal waters gravitation sediments silt velocity water currents currents surface waters 580500 oceanography 1980 1989

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

spatial and temporal variations in spectra of storm waves across a barred nearshore abstract wave staffs and electromagnetic current meters were deployed on a profile across a two bar system at wendake beach southern georgian bay this paper examines spatial and temporal changes in the characteristics of wave form and the spectra of surface elevation and on offshore current motion during one storm non linear effects of wave shoaling and breaking across the bars result in the appearance of secondary waves and both the wave and on offshore current spectra have significant harmonic peaks during most of the storm significant low frequency energy occurs only during the peak of the storm while the peak frequency remains constant across the bar system the proportion of energy in the primary peak is greatest in the troughs and lowest over the bar crests and there are similar changes in the proportion of energy in the first harmonic however in both surface elevation spectra and on offshore current spectra the greatest proportion of energy is found in frequencies related to the incident wind waves

morphodynamics of a bar trough surf zone abstract a field study was made of the distinguishing morphodynamic processes operating in a surf zone which perennially exhibits accentuated bar trough topography the longshore bar trough and rhytmic bar and beach states as described by wright and short 1984 characteristic features of the morphology include a shallow bar with a steep shoreward face a deep trough and a steep beach face this morphology which is favored by moderate breaker heights and small tidal ranges strongly controls the coupled suite of hydrodynamic processes in contrast to fully dissipative surf zones the bar trough surf zone is not at all saturated and oscillations at incident wave frequency remain dominant from the break point to the subaerial beach the degree of incident wave groupiness does not change appreciably across the surf zone infragravity standing waves which in dissipative surf zones dominate the inshore energy remain energetically secondary and occur at higher frequencies in the bar trough surf zone analyses of the field data combined with numerical simulations of leaky mode and edge wave nodal antinodal positions over observed surf zone profiles indicate that the frequencies which prevail are favored by the resonant condition of antinodes over the bar and nodes in the trough standing waves which would have nodes over the bar are suppressed sediment resuspension in the surf zone appears to be largely attributable to the incident waves which are the main source of bed shear stress in addition the extra near bottom eddy viscosity provided by the reformed non breaking waves traversing the trough significantly affects the vertical velocity profile of the longshore current whereas the bar is highly mobile in terms of onshore offshore migration rates the beach face and inner regions of the trough are remarkably stable over time

bar formation due to wave groups and associated long waves abstract field observations reveal that waves propagating onto a beach from deeper water have a grouped structure associated with this pattern of alternating high and low waves is a long wave forced by radiation stress variations due to the changing short wave height as the wave groups propagate onshore the relationship between the variation in the short wave height and the long wave motion is complicated by breaking of the short waves reflection of the long wave and the generation of a free long wave by time variation of the breakpoint position nevertheless there may still be a fixed phase relation between the short wave envelope and the long wave motion at any particular location resulting in a net transport of sediment over the timescale of the short wave groups this transport arises from sediment grains mobilised by short waves and moved by the long wave motion model predictions of wave group propagation onto a beach and the associated long wave motions are presented which suggest that sediment transport due to short wave long wave coupling may result in the formation of a bar within the inner surf zone and the possibility of additional bars further offshore outside the surf zone this mechanism for bar formation may provide a new framework for understanding bar morphodynamics

on time delays in the nearshore zone between onshore and longshore currents at incident wave frequencies observations of horizontal velocities just outside the surf zone on two natural beaches show unexpected time lags between the onshore offshore currents and the longshore currents at incident wave frequencies these time lags typically around 20 s appear to have been first noticed by katoh 1981 in data from a beach in japan a number of possible hypotheses to explain these time lags are examined of these propagation of secondary waves formed by reflection or diffraction at a point alongshore from the measurement site seems most able to explain the observations this suggests a significance for reflected diffracted waves some distance from breakwaters or headlands which has not previously been recognized in field studies however a number of questions remain that will only be resolved by further field data particularly from beaches far removed from end effects

waves long waves and nearshore morphology abstract recent field measurements on beaches of different slopes have established that wave motion at periods substantially longer than the incident waves dominates the velocity field close to the shore analysis of a number of extensive data sets shows that much of this long wave motion is in the form of progessive edge waves though forced wave motion standing edge waves and free waves propagating away from the shore may also contribute to the energy theoretically the drift velocities in bottom boundary layers due to edge waves show spatial patterns of convergence and divergence which may move sediment to form either regular crescentic or cuspate features when only one edge wave mode dominates or a bewildering array of bars bumps and holes when several phase locked modes exist together convincing field demonstration of the link between nearshore topography and edge waves only exists for the special case of small scale beach cusps on steep beaches formed by edge waves at the subharmonic twice the period of the incident waves at longer periods the link is proving more difficult to establish due to the longer time scales of topographic changes the interaction between pre existing topography and the water motion and the observation of broad banded edge wave motion which is not readily linked to topography with a well defined scale these ideas are however central to the study of nearshore processes as most of the plausible alternate hypotheses do not seem to lead to quantitative predictions clearly further theoretical and observational work is essential

field observations of surf beat 1 progressive edge waves nineteen biaxial electromagnetic current meters have been used to determine the longshore and on offshore structure of currents at surf beat periods 1 4 min the sensors formed two linear arrays a long shore array within the surf zone and an on offshore array stretching from the shoreline to well beyond the breaker line analysis of the longshore current components yields a clear picture of progressive low mode edge waves with frequency wave number dispersion relations which are in remarkably good agreement with predictions some separation of edge wave modes is found with mode zero energy dominating in the frequency band 0 006 and 0 011 hz and mode one between 0 015 and 0 025 hz on offshore currents present a rather different picture which while not inconsistent with the longshore currents suggests that other sources of energy are also important to the on offshore currents these include standing edge waves probably formed by reflections at nearby scripps canyon and motions which are nonresonantly forced by incoming wave groups

the haida current we present evidence for a narrow poleward flowing surface current over the continental slope of northwestern british columbia and southwestern alaska named for a prominent native indian tribe of the region the haida current occurs predominantly between october and april maximal flow takes place in midwinter from november through february characteristic features of the current include a minimal extent of 200 300 km a width of 20 30 km a depth scale of 500 m and near surface temperature signatures of up to 1 c within the core of the current as well as large amplitude o 10 km mesoscale waves and eddies along its flank the wind stress and alongshore sea surface slope are shown to be the primary driving mechanisms for the current

equilibrium slopes and cross shore velocity asymmetries in a storm dominated barred nearshore system abstract the near bed 0 10 m elevation horizontal velocities were measured across a two barred lacustrine shoreface during a storm and reveal a spatially coherent but temporally variable pattern in the low order moments of the velocity field large cross shore velocity asymmetries indicated 1 1 spatially extensive and temporally persistent offshore mean flows up to 0 18 m s 1 across the landward slope of the linear outer bar reflecting an undertow driven by a wave induced setup 2 2 an onshore directed skewness opposing the mean flow of wind wave origin and persistent under propagating bores in the inner bar system long after this asymmetry had disappeared from the outer bar extensive sediment reactivation with near zero net sediment flux over the whole of the upper shoreface indicated a sediment prism in a steady state volumetrically over the storm cycle uniform depths of sediment reactivation with zero bed elevation change over the storm cycle revealed local slopes in a steady state in the outer linear bar however time integration of the near bed velocity field at this location indicated an offshore net flux of water while sedimentary structures indicated bedform migration and thus at least bedload almost uniformly onshore when ripples and megaripples were present the sediment transport giving rise to the local equilibrium cannot be explained therefore on the basis of the mean properties of the near bed velocity vector but requires knowledge of the time varying instantaneous sediment transport vector onshore migration of the inner bar correlated well with the large and persistent onshore skewness of the velocity distribution in the inner surf zone associated with translatory surf bores throughout the storm decay period low frequency oscillations were only significant close to the shoreline but may have influenced the development of a sinuous three dimensional inner bar form as it migrated onshore

hydrogeology of the south eastern yucatan peninsula new insights from water level measurements geochemistry geophysics and remote sensing summary the yucatan peninsula is one of the world s largest karstic aquifer systems it is the sole freshwater source for human users and ecosystems the region hosts internationally important groundwater dependent ecosystems gdes in the 5280 km2 sian ka an biosphere reserve the gdes are threatened by increasing groundwater abstractions and risks of pollution hydrogeological exploration work is needed as basis for sound groundwater management a multidisciplinary approach was used to study this data scarce region geochemical data and phreatic surface measurements showed distinct hydrogeological units in the groundwater catchment of sian ka an the hilly southwestern areas had a low hydraulic permeability likely caused by a geology containing gypsum whereas the transition zone and flat areas in the east and north had a high permeability in the latter areas the fresh groundwater could be described by a dupuit ghyben herzberg lens geophysical borehole logging and time domain electromagnetic soundings identified a shallow low resistive and high gamma radiation layer present throughout the hilly area and transition zone its thickness was 3 8 m apparent conductivity was 200 800 ms m and natural gamma radiation about 80 counts pr second the layer is proposed to be ejecta from the chicxulub impact cretaceous paleogene boundary spatial estimates of recharge were calculated from modis imagery using the triangle method average recharge constituted 17 of mean annual precipitation in the study area recharge was greatest in the hilly area and towards valladolid near the coast average actual evapotranspiration exceeded annual precipitation the multidisciplinary approach used in this study is applicable to other catchment scale studies

a new locality of palygorskite rich clay from the southeastern yucatan a potential material source for environmental applications a palygorskite unit was discovered in a road cut of undifferentiated tertiary limestone between the villages of el pariso and san roman 18 49 309n 88 37 861w in the southeastern yucatan peninsula mexico this is the southern most locality of a clay rich sedimentary unit reported in the literature for the tertiary carbonates of the yucatan peninsula this occurrence indicates a much wider range of palygorskite rich clay deposition than previously recognized the lithology is 99 clay and 1 sand to silt size diagenetic quartz grains the clay consists of approximately 85 palygorskite 15 montmorillonite and trace amounts of titanium oxides eds analyses on palygorskite are largely consistent with sedimentary palygorskites from other coastal marine settings however palygorskite has a low total fe content average 0 40 wt expressed as fe2o3 compared to many other sedimentary palygorskites montmorillonite chemical compositions are typical and compared to the palygorskite have substantially higher fe2o3 concentrations average 3 90 wt the low percentage of coarse grains in the lithology combined with a high proportion of palygorskite and lack of detrimental trace minerals suggest the deposit is of industrial grade however it has limited reserves 6 000 m3 the unit could be potentially used in a wide array of environmental applications which are needed in the region including liners for landfills and constructed wetlands the unit is in a geographic location which would serve the expanding economy of the region this resource has the potential to have great impact on the quality of the local environment and the economy of a region under great environmental threat

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

coherence of surf zone and shelf current flow on the texas u s a coastal margin implications for interpretation of paleo current measurements in ancient coastal sequences abstract measurements from the texas coastal margin a microtidal fetch limited wind dominated shallow sea reveal a strong correlation in timing and direction of surf zone and shelf flow during both fairweather and storm events coherence of current motion is statistically significant at many frequencies cycle lengths and is highest during storm events the lack of a significant lag between surf zone and shelf flow indicates that both respond rapidly to changes in the magnitude and direction of the wind field the alongshelf component of the wind stress is a major force in generating currents both on the shelf and in the surf zone as exhibited by comparison of numerical predictions and observed velocities during the 140 day study period current flow was mainly directed alongshelf to the northeast and southwest driven by southerly fairweather and northerly storm winds respectively however the threshold for generation and migration of megaripple bedforms in upper shoreface bar troughs was exceeded only during storm events when surf zone flow was oriented to the southwest along the coast this observation coupled with the knowledge that storm generated bedforms have the highest preservation potential imply that multi event traction bedding in upper shoreface bar troughs of analogous ancient environments will be dominated by unimodal alongshore current orientations large scale bedforms which respond to this time averaged flow on the shelf are expected to display a similar unimodal alongshelf orientation with a low angle deviation toward the offshore direction careful study of paleo current measurements in a well documented ancient shelf to shoreline sequence in the cretaceous of new mexico reflects this similarity in transport kinematics

surface tension and friction coefficients in shallow laminar overland flows through organic litter this study investigates the contribution of surface tension forces to friction coefficients in shallow laminar interrill flows friction coefficients in these flows are known to be increased greatly by organic litter and by stems fine litter provides extensive edges along which surface tension menisci can be drawn up and evaluating the significance of this in the frictional retardation of flow was the primary objective of the experiments reported here using both standardized litter particles small wooden blocks of fixed dimensions and natural plant litter meniscus behaviour and the darcy weisbach friction coefficient were evaluated in shallow flows on a laboratory sand board for some tests the surface tension of ordinary water was reduced by 40 per cent by the addition of a surfactant and the friction coefficient redetermined results show that the presence of surface tension menisci flanking litter particles provides areas of deeper flow that are up to 7 mm in width and which can increase flow depths by 100 300 per cent these zones support significantly higher flow speeds increased water depths within menisci are additionally associated with reduced depths beyond the menisci so that an increase in the spatial variability of flow depths is a second consequence of meniscus formation these modifications of flow depth by surface tension menisci are shown to reduce rather than increase the overall friction coefficient applicable to the flow consequently additional frictional retardation does not arise within the menisci flanking litter particles and so cannot account for the greater drag arising from litter than from other surface features different factors possibly the direct obstruction of flow paths must therefore underlie the frictional drag copyright 2002 john wiley sons ltd

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

vertical and horizontal structure in cross shore flows an example of undertow and wave set up on a barred beach greenwood b and osborne p d 1990 vertical and horizontal structure in cross shore flows an example of undertow and wave set up on a barred beach coastal eng 14 543 580 eulerian measurements of the horizontal cross shore velocity field in the lowermost meter of the water column in association with measurements of waves and the mean elevation of the water surface across a nontidal low relief barred surf zone reveal a spatially coherent patterns of the timeaveraged first second and third moments of the velocity field which vary temporally in direct response to the incident waves b large asymmetries in the flow field with offshore directed mean flows upto 0 20 m s a and onshore directed velocity skewness the third moment normalized by the standard deviation upto 0 60 c mean flows decrease and oscillatory flows measured by the standard deviation of the velocity field increase towards the water surface d a fourth order polynomial provides the best fit to the cross shore set up reflecting the influence of variable energy dissipation due to topographic controls on wave breaking e significant linear correlations exist between the cross shore mean velocities and the maximum set up of the still water surface near to the shoreline upto 82 of the observed variability in the former can be accounted for by linear regressions f set up is highly correlated with the incident wave height 86 of the observed variability in the former can be accounted for by a linear regression g gradients in the mean water surface are significantly less than those predicted by a linear function of beach slope as originally proposed by bowen et al even using an appropriate breaking criterion 0 4 0 6 for the spilling breakers recorded cross shore circulation over the low relief barred nearshore slope is predominantly two dimensional over the outer bar in this case study the near bed mean flow is an undertow responding to the balance between the wave generated depth dependent momentum flux directed onshore the stress induced by the onshore mass transport under waves and wind and the hydraulic pressure gradient induced by set up of the mean water level

modification of edge waves by barred beach topography a numerical model to calculate edge wave profiles and wavelengths for arbitrary bottom profiles and given frequency was developed utilizing the model wave equation of berkhoff 1972 following smith and sprinks 1975 surface profiles and longshore wave numbers were found for fixed wave periods using an eigenvalue approach the model was verified by calculating profiles and dispersion for a plane beach of mild slope and comparing results with the analytic solution of eckart 1951 and ursell 1952 the model was then applied to the case of a beach with multiple offshore bars with bar positions determined by the antinodal positions of a standing incident wave of a set frequency calculation of surface profiles for a range of frequencies using a fixed beach indicated that antinodes of the edgewave profiles tend to be trapped by the bars suggesting the possibility that bars affect the long wave climate in such a way as to lead to self maintenance over extended periods no effect of the bars on the dispersion relationship was found and it was concluded that for the particular beach profile used the edge waves respond to the mean beach slope over the offshore length of the profile

refraction and reflection of infragravity waves near submarine canyons 1 the propagation of infragravity waves ocean surface waves with periods from 20 to 200 s over complex inner shelf water depths from about 3 to 50 m bathymetry is investigated with field observations from the southern california coast a wave ray path based model is used to describe radiation from adjacent beaches refraction over slopes smooth changes in bathymetry and partial reflection from submarine canyons sharp changes in bathymetry in both the field observations and the model simulations the importance of the canyons depends on the directional spectrum of the infragravity wave field radiating from the shoreline and on the distance from the canyons averaged over the wide range of conditions observed a refraction only model has reduced skill near the abrupt bathymetry whereas a combined refraction and reflection model accurately describes the distribution of infragravity wave energy on the inner shelf including the localized effects of steep walled submarine canyons

longshore sediment transport and foreshore change in the swash zone of an estuarine beach abstract estuarine beaches often lack well developed surf zones incident waves break and convert directly to swash on the steep foreshore resulting in greater influence of the swash zone in generating longshore flows and sediment transport this study was conducted to evaluate longshore sediment transport in the swash zone of an eroding estuarine beach and relate transport rates to changes in beach position and volume downdrift of a shore perpendicular structure field data were gathered on a sandy beach on the bay side of fire island new york usa in a short fetch 12 15 km microtidal mean range 0 21 m environment wave and swash processes beach changes and sediment tracer and trapping experiments were conducted during strong onshore winds in march and april 2012 daily topographic surveys of the beach revealed pulses of sediment movement alongshore at small temporal daily and spatial 5 m scales the mid foreshore retreated 2 75 m from the beginning to the end of the 24 days of monitoring this retreat was associated with a loss of 2 1 m3 of sediment per meter of shoreline length the greatest amount of foreshore retreat during a single storm event was 1 27 m associated with a volume loss of 0 9 m3 of sediment per meter mean wind speed on that day was 11 3 m s 1 with a maximum of 18 2 m s 1 significant offshore wave height at the time of maximum wind speed was 0 30 m mean significant wave heights ranged from 0 12 to 0 26 m during the five times when trapping occurred resulting in mean longshore swash velocities of 0 08 to 0 23 m s 1 and transport rates ranging from 0 413 to 1 516 m3 h 1 the longshore sediment transport rates are similar to rates gathered under similar longshore current velocities on microtidal low energy beaches transport rates on beaches in sheltered environments can differ from rates calculated using existing formulas that may be more appropriate for high energy beaches where a greater proportion of sediment is transported in the surf zone than in the energetic swash zone under plunging breakers transport rates calculated from three existing formulae bagnold 1963 cerc 1984 kamphuis 2002 revealed that estimates from bagnold compared most favorably with measured rates because of direct measurements of longshore current velocities rates of erosion on beaches in short fetch environments can be high despite low wave energies because the low narrow beaches have little volume magnifying the importance of seemingly low rates of transport in the swash

edge waves on the sydney coast pressure and current oscillations at periods of 40 s to 17 min observed during storm conditions at two locations separated by 560 m in the alongshore direction in the coastal ocean near sydney australia indicate the existence of infragravity waves having amplitudes of 20 cm and velocities of 10 cm s 1 the observed infragravity waves appear to be locally forced by the wind wave envelope through radiation stress yet the observed alongshore phase differences of the infragravity waves are consistent with those predicted from free edge wave theory for low mode edge waves travelling northward and the relationship of pressure to velocity at each location is also consistent with free edge wave theory as a function of time the infragravity wave spectral energy grows and decays in step with the longer period wind waves suggesting a continuous transfer of energy the infragravity waves appear to contain energy in both directly forced and freely propagating edge wave oscillations the edge waves may be generated either by radiation stress as outlined above by a resonant triad mechanism or by a combination of the two

investigations of subsurface flow constructed wetlands and associated geomaterial resources in the akumal and reforma regions quintana roo mexico subsurface flow constructed wetlands in the village of akumal quintana roo mexico were surveyed to determine the general status of the wetland systems and provide baseline information for long term monitoring and further study twenty subsurface flow wetlands were surveyed and common problems observed in the systems were overloading poor plant cover odor and no secondary containment bulk mineral composition of aggregate from two subsurface flow constructed wetlands was determined to consist solely of calcite using bulk powder x ray diffraction some soil structure is developed in the aggregate and aggregate levels in wetlands drop at an estimated rate between 3 and 10 cm year for overloaded wetlands owing to dissolution mineral composition from fresh aggregate samples commonly is a mixture of calcite and aragonite trace amounts of pb zn co and cr were observed in fresh aggregate coefficients of permeability k varied from 0 006 to 0 027 cm s with an average values being 0 016 cm s grain size analysis of fresh aggregate samples indicates there are unimodal and multimodal size distributions in the samples with modes in the coarse and fine sand being common investigations of other geologic media from the reforma region indicate that a dolomite with minor amounts of fe oxide and palygorskite is abundant and may be a better aggregate source that the current materials used a ca montmorillonite bed was identified in the reforma region as well and this unit is suitable to serve as a clay liner to prevent leaks for new and existing wetland systems these newly discovered geologic resources should aid in the improvement of subsurface flow constructed wetlands in the region although problems do exist in these wetlands with respect to design these systems represent a successful implementation of constructed wetlands at a community level in developing regions

longshore bar and trough systems in a microtidal storm wave dominated coast the ebro delta northwestern mediterranean abstract the ebro delta coast is a microtidal sandy shoreline affected by a low energy mean wave climate consecutive topographical and bathymetrical surveys during the years 1990 and 1991 have allowed us to identify nine major longshore bar and trough systems as the main morphological feature of the ebro coast bar systems show high mobility both cross shore and longshore the cross shore migration of these systems may be landward or seaward with mean migration rates of up to 0 25 m day the longshore migration is produced by the longitudinal growth of the bar systems in the downdrift direction with rates of up to 11 m day the major morphological changes in the nearshore zone occurred during storm periods when the nearshore profile is modified as a consequence of shoreline erosion and the cross shore migration and longshore growth of the bar systems produced by these events the modifications in the nearshore profile may continue during some months after the storm before attaining a new equilibrium profile a descriptive model relating the shoreline displacement with the cross shore migration and the longshore growth of the bar and trough systems is proposed

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

the interaction between the undertow and the boundary layer flow on a beach the theoretical result for undertow in a surf zone found by svendsen 1984a is combined with a boundary layer solution at the bottom and it is shown that in this boundary layer the eddy viscosity is small relative to that produced by the breaking the proper eddy viscosity t between the surface and the bottom boundary layer is determined by comparison with measurements which leads to quite accurate reproduction of the velocity profiles the model also predicts the mean flow in the boundary layer and the mean bottom shear stress and the results are analyzed for sensitivity to inaccuracies in the basic assumptions

on the relationship between bedload and suspended sand transport on the inner shelf long island new york data obtained by a near bottom profiling concentration and velocity system pcv deployed in 10 m water depth at a site 1 km from the long island coastline are used to examine links between bedload and suspended sand concentrations calculations of bedload areal concentration c are based on the empirical results of vincent et al 1981 and use the theoretical formulations of grant and madsen 1978 1979 to describe the interaction between wave and current boundary layers suspended sand concentrations were obtained directly from an acoustic concentration meter acm average suspended sand profiles cz were found to fit closely to a log linear profile cz c1 1 a loge z z1 where c1 is the sand concentration at a height z1 1 cm from the bed and a is empirically determined as 0 22 0 005 a linear correlation is observed between the areal bedload concentration c the volume of bedload per unit area of the bed and the suspended sand concentration 1 cm above the bed c1 with a correlation coefficient of 0 82 significant at the 1 level and supports the hypothesis of einstein 1950 that bedload and suspended load are related through bedload concentration it is also shown that the sedment threshold criterion of komar and miller 1973 when expressed as a ratio here called the komar ratio can be used as a useful predictor for c1 under conditions where the wave orbital currents are much greater than the mean flow these relationships offer the opportunity for the calculation of both bedload and suspended sand transport rates from measurements of the steady current velocity and wave parameters combined with information defining the surficial sediments and local bottom topography

suspended sediment transport and the role of infragravity waves in a barred surf zone abstract collocated optical backscatterance suspended solids sensors and electromagnetic flowmeters were deployed at stanhope lane beach p e i canada to assess the contributions of wind waves infragravity waves and mean currents to the cross shore flux of suspended sediment across a barred surf zone the local net transport of suspended sediment magnitude and direction was highly variable both spatially and temporally with respect to the relative magnitudes of the suspended sediment transport 1 that induced by quasi steady mean currents and oscillatory currents at both incident and infragravity frequencies were almost equal in magnitude when the total surf zone was averaged over the storm event 2 waves in the near infragravity band were quantitatively more important during the waning of the storm especially where when surf persisted well after the initial decay of the offshore wave field 3 incident waves were important where when the waves were not saturated i e during the early stages of the storm at all locations and persistently throughout the storm on the seaward slope of the bar where wave saturation was limited to a very short period with respect to the direction of net sediment transport 1 that attributable to mean currents was directed offshore in the inner surf zone probably reflecting the presence of an undertow while further seaward an onshore transport occurred probably resulting from mass transport induced by surf bores or drift velocities induced by the infragravity wave boundary layer 2 that induced by oscillatory currents at incident wave frequencies was generally onshore at any one location throughout the storm event in contrast oscillatory transport at low frequencies changed direction and also varied in magnitude at any given location in part these changes reflect the existence of significant oscillatory sediment transport at discrete infragravity frequencies the standing infragravity waves consistently transported suspended sediment towards antinodes in the water surface elevation