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

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

morphodynamics of a macrotidal beach abstract an intensive field investigation of hydrodynamic processes processes of sediment entrainment and suspension and morphologic change was carried out on an unprotected macrotidal beach near broome in northwestern australia the spring tide range was 9 5 m waves had heights of 0 5 1 2 m and periods of 9 13 s the beach had an overall concave upward profile with low gradient and dissipative subtidal and low tidal zones and steeper more reflective mid tidal and high tidal zones direct measurement of energy flux dissipation over the intertidal profile showed dissipation rates on the order of 1 2 w m 2 of bed and indicated an approximate balance between shoaling and dissipation of unbroken waves so as to maintain a constant wave height time averaged predictive estimates of wave work over the lunar half cycle for different points on the intertidal profile show similar dissipation rates and reveal a relatively uniform distribution of work over most of the profile but with maxima in the middle of the low tidal zone and over the lower part of the high tidal zone most of the work over the low and mid tidal zones was performed by unbroken shoaling waves rather than by surf zone processes surf zone processes only dominate over the high tidal zone the nature of the surf zone processes varied across the profile as local gradient and degree of reflectivity changed with changing tide level the growth of standing waves and infragravity surf beat oscillations as identified from spectra and cross spectra of surface elevation and currents u and v was inhibited over most of the profile however well developed secondary standing wave energy particularly at infragravity frequencies was observed over the high tidal zone at spring high tide and over the mid tidal zone at neap high tide over the low tidal and subtidal zones strong shore parallel tidal currents were subordinate only to the orbital velocities of unbroken incident waves over the subtidal zone asymmetrical tidal currents skewed toward the north attained maximum speeds of 0 5 m s 1 just after high water field measurements of suspended sediment concentration profiles under broken and unbroken waves showed very good fit to a diffusion model for wave induced sediment suspension and suggested that sediment suspension was probably attributable largely to waves northerly advection of wave suspended sediment by asymmetrical tidal currents over the subtidal and low tidal zones accounted for a net northerly longshore transport the greatest morphologic mobility of the intertidal profile occurred over the lower high tidal and upper mid tidal zones corresponding to the position of the coarsest material and secondary maximum of time averaged wave work and to a beach state intermediate between the reflective and dissipative extremes temporally the greatest mobility of the profile as a whole was observed on the short within tidal cycle time scale net changes over the longest time scale of a lunar half cycle were negligible

tidal influence on the intertidal bar morphology of two contrasting macrotidal beaches abstract analyses of morphological and hydrodynamic data from two macrotidal beaches mean spring ranges respectively 5 6 and 6 4 m with intertidal bars and troughs were carried out in order to detect and explain the relationship between tides and bar morphological attributes bar crest height and location and morphological change the following four aspects are treated in the paper 1 tidal levels vertical tidal translation rates and bar morphology 2 tidal range and morphological relaxation 3 the neap spring tidal variation and 4 tide generated longshore currents bar distribution and bar heights across the profile are not related in a straightforward manner to tidal levels and expected vertical tidal translation rates at these levels because the wave process domains involved in bar formation and bar morphological change are strongly modulated by wave energy by tide modulated water levels which vary with the neap spring cycle and by the beach morphology the variability of these conditions may explain the large variability of bar trough beach morphology the relatively large tidal ranges and rapidly shifting wave domains across the profile imply long periods of non exposure of the bars to wave processes during each semi diurnal tidal cycle and this tide generated effect reduces the scope for prolonged wave reworking while contributing to enhancing the long relaxation times and morphological feedback which minimise change on these beaches the effects of the neap spring tidal range variation on wave activity on these beaches are subordinate to those due to the random wave energy regime but this neap spring variation appears to influence the morphologically important intertidal drainage channels associated with bar trough topography although longshore tidal currents are relatively strong on these beaches digital elevation models show no significant longshore bar and tidal channel migration over time due to the absence of sustained strong wind conditions which considerably reinforce such longshore tidal currents and which therefore are the dominant control on longshore processes on these beaches it is also tentatively suggested that there is no established relationship between tidal range and the number of intertidal bars on these beaches

recent shoreline mobility and geomorphologic evolution of macrotidal sandy beaches in the north of france abstract this paper examines shoreline mobility and sediment budget conditions on a sandy macrotidal coast with a well developed foredune aerial photographs and bunker archaeology covering the last 50 years were analysed in order to determine the meso scale evolution of le touquet beach in northern france both methods show that shoreline retreat has been negligible or very slow and has been accompanied by an elevation of the foredune dgps cross shore profiles show a balanced sediment budget over the last 7 years only a slight change of the beach face profile 0 2 0 5 m rise or fall was observed while the foredune exhibited a sharper change the french coast of the eastern english channel differs from that of the french atlantic coast which is currently being strongly eroded the balanced sediment budget of the former is attributed to sand inputs from nearshore banks which compensate exports due to longshore drift and to foredune development

a study of rocket measurements of ionospheric currents v modelling rocket profiles of low latitude ionospheric current summary some 25 rocket profiles of the current density of the eastward ionospheric lower current layer close to the magnetic dip equator one profile of the reverse westward lower current layer at about 5 dip latitude and five profiles of the eastward upper current layer within 0 to about 8 dip latitude have been modelled giving the following results the parameters of the eastward lower current layer within 0 to 2 dip latitude around local noon are peak current density normalized to dip equator 10 4 f 6 a km peak current intensity normalized to dip equator 145 f 86 a km and half thickness at half of the peak current density 5 7 f 1 km the differences in these parameters between the equatorial electrojet in india and peru are negligible the parameters of the ionospheric eastward upper current layer around local noon are peak current density normalized to the dip equator 2 37 f 0 5 a km peak current intensity normalized to the dip equator 22 1 f 7 a km and half thickness at half of the peak current density 4 1 f 2 km the parameters of the model fitting the rocket profiles extremely well have been provided the suggestion that the lower eastward and the lower westward current layers constitute the equatorial electrojet while the upper eastward current layer is the global part of the sq currents has been substantiated this leads to results consistent with spherical harmonic analysis of geomagnetic sq variations the first contours of the ionospheric eastward upper current layer density have been presented and they are consistent with the features of the worldwide sq

temporal and spatial scales of beach profile change duck north carolina abstract an 11 year time series of high resolution beach profile surveys made on an atlantic ocean beach was analyzed for spatial and temporal characteristics of beach profile change approximately 300 profile surveys most extending from the dune to 8 m depth were available for the analysis on each of four cross shore lines together with electronically recorded and statistically processed wave time series from a nearshore gage located seaward of the survey site the profile survey data set was analyzed for such quantities as depth change frequency of depth change general seasonal shape of the profile seasonal depth change and change in the profile produced by extreme storms the morphodynamics of an inner and outer longshore bar were also examined including depth to bar crest bar height and length and speed of bar movement onshore and offshore several properties of depth change were related to wave characteristics representative results were average profile elevation change from 4 m to 4 m was symmetric about the mean sea level shoreline the average spring and autumn profile shapes were almost identical and occurred as transitional states between the summer and winter profile shapes the depth of active profile movement within survey accuracy of about 0 025 m was 4 m for the summer and 6 m for the winter and the 10 year frequencies of maximum absolute depth change in depths of 2 4 6 and 8 m were 1 64 1 38 0 22 and 0 12 m respectively a surprising result was that typical large storms transported sand into the nearshore from the seaward end of the profile from a depth of about 6 8 m

morphodynamic characteristics and classification of beaches in england and wales abstract the use of beach classification models has become widespread in literature in recent years beach classification models that recognise distinct modal beach states in response to environmental conditions are most widely used these models were developed largely in high energy micro to meso tidal sandy environments and subsequent attention has focussed on extending their use into other beach environments here the applicability of these traditional beach classification models to the highly diverse coastline of england and wales was assessed through collection of detailed morphodynamic characteristics of 92 beaches yielding a comprehensive multi variate data set containing morphological sedimentological and hydrodynamic information the complex and diverse study region incorporates beach morphology covering the full spectrum from reflective to dissipative and non barred to multi barred cluster analysis supplemented by mds ordination resulted in the identification of 9 distinct beach types traditional morphodynamic indices and rtr were found to be effective in discriminating between beach groups providing some support for the beach state models derived using information from australian beaches it was found that absolute wave energy wave power is important as well in controlling beach type for intermediate beaches a wave energy flux p h 2 t value of 3 kw m 1 was found to differentiate between beaches with p 3 kw m 1 and without p 1 three dimensional bar rip morphology a key component controlling recreational beach hazard levels observations presented here inform a beach classification model to be used as the basis for a national beach risk assessment programme beach classification models based on environmental parameters are by necessity simplifications and should be used as tools for understanding morphodynamic systems rather than beach type prediction

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

sedimentology and morphodynamics of a macrotidal beach pendine sands sw wales abstract the foreshore of pendine sands forms the seaward part of an extensive sandy coastal barrier in a shallow carmarthen bay sw wales the sedimentological features of the macrotidal foreshore reflect a tide induced modification of nearshore wave characteristics as the tide ebbs the breaker height may decrease the surf zone widens and becomes increasingly dissipative and swash backwash velocities diminish a concomitant change from plunging to spilling breakers and increasingly symmetrical swash zone flows are associated with a decreasing beach gradient a zero net transport model demonstrates that the beach profile is self stabilising in the short term and periodic levelling has shown that the beach is in long term equilibrium with prevailing conditions though this does not preclude a significant dynamic response to changing tides and waves the flow regimes of wave generated currents decline as the tide ebbs and normal beach processes do not usually affect the lower foreshore accordingly there is an overall seaward fining of the primary framework component of the sands in more detail this framework component displays a slight seaward coarsening across an upper foreshore dominated by high water swash and surf a rapid seaward fining across the mid foreshore in response to the ebb attenuating swash zone flow velocities and a slight seaward fining across the lower foreshore under the action of nearshore shoaling waves bedforms vary from a swash backwash emplaced flat bed across the upper foreshore to the small ripples of nearshore asymmetric oscillatory flows across the lower foreshore the surface sediment veneer is not representative of the subsurface sediments which form in response partly to fairweather conditions partly to storms the upper foreshore is characterised by swash backwash emplaced plane bedding in fine sands frequently disrupted by bubble cavities the mid foreshore is composed of coarser grained shelly traction clogs arranged as landward and seaward dipping large scale cross bedding and or plane bedding these are probably storm breaker surf deposits the lower foreshore though partially and sometimes totally bioturbated shows landward dipping small scale cross bedding in very fine sands sorted by nearshore shoaling waves tide and storm induced modification of the nearshore flow regimes therefore produces a distinctive shore normal array of sedimentary facies each facies is characterised by diagnostic textural and structural signatures a prograding sequence of such macrotidal deposits would be similar to but more extensive than a comparable microtidal sequence

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

hydroclimatic variation in far north queensland since 1860 inferred from tree rings abstract in tropical australia palaeoclimatic proxies derived from tree rings are sought after sources for reconstructing climate variations however dendroclimatology has not been widely applied in tropical forests and even less so in the australian tropics due to the extreme rarity of species producing anatomically distinct annual growth rings furthermore most australian tree species exhibit rather strong opportunistic growth with non annual growth zones that are less suitable for dendrochronology recent studies on the australian red cedar toona ciliata in the upper kangaroo valley near sydney revealed that tree ring based climate reconstructions are feasible with this species this study moved 2500 km further north and concentrated on the tropical stands of t ciliata because it is one of the few deciduous tree species in tropical australia likely characterised by a dormant period of the cambium and thus annual tree rings although dendroclimatological studies indicate that some australian tree species are suitable for reconstructing climate patterns a well replicated tree ring record from far north queensland has not been developed until now tree cores of t ciliata were developed into a 140 year tree ring widths index chronology the analyses showed that the ring widths indices correlate with march june precipitation as recorded at kairi research station march june precipitation was reconstructed using the tree ring data with 35 of the variance explained the reconstructed series contains both high and low frequency climate signals this suggests that growth of t ciliata is influenced by climate phenomena of different wave lengths which can be associated with el nino southern oscillation enso and interdecadal pacific oscillation ipo

storm driven variability of the beach nearshore profile at duck north carolina usa 1981 1991 the us army corps of engineers field research facility frf at duck north carolina has collected approximately biweekly beach nearshore profile data to 8 m depth and associated wave data since 1981 sediment budget analysis was used to examine the medium scale years to a decade variability of the beach nearshore profile from 1981 to 1991 significant changes occurred during four groups of energetic storm events during february march of 1983 1987 1989 and december 1989 each group was comprised of at least two storms within a period of less than 39 days both with hmo 4 m during each storm group offshore sediment movement caused a distinct outer bar to migrate offshore and grow in size resulting in an abrupt increase in the volume of sediment on the upper shoreface the net profile changes were much larger than the changes due to single storms and the cumulative effect of the storms can be considered as one event during these events the first storm appears to have a destabilizing effect on the profile which has insufficient time to recover before the second and subsequent storm s as a result several storms in quick succession are able to have a large impact on the morphology the intervening periods between the groups of storm events termed fairweather conditions lasted up to 4 years they are characterized by slow but steady sediment redistribution averaging 33 m3 m 1 year 1 from the upper shoreface 5 m depth toward the shore while the total sediment volume was effectively constant the onshore feed of sediment was not significantly affected by individual storms during the fairweather conditions these two processes of 1 morphologic change during groups of storm events and 2 the steady onshore feed of sediments from the shoreface during fairweather conditions appear to play an important role on medium and long term profile evolution at least at duck

a new method for dating tree rings in trees with faint indeterminate ring boundaries using the itrax core scanner abstract eastern australia is known to experience multi decadal periods of flood and drought subtropical southeast queensland is one region where these devastating extreme events occur regularly yet a full understanding of their frequency and magnitude cannot be determined from the short duration 100 years proxy rainfall information but locating suitable forest stands is difficult due to extensive land clearing by european settlers another factor deterring the use of trees as proxy data sources is that longer lived species frequently contain anomalous rings particularly faint rings hindering their use for paleoclimate study here we present a method which overcomes the problems of identifying faint ring boundaries in trees by using x radiographs and density patterns developed on the itrax core scanner we analysed 39 tree cores from 20 trees at a site in d aguilar national park located just north of brisbane city in queensland australia each core had a 2 mm lath cut perpendicular to its rings which was then passed through an itrax core scanner the tree ring boundaries were identified on the image by both the visual features in the radiograph and the change in density observed between rings from this information we developed a tree ring chronology the chronology was checked using bomb pulse radiocarbon dating on five trees to confirm the annual nature of the rings and to correct dating errors in the chronology due to false rings which are common in this species climate response function analysis showed austral annual rainfall june may was the dominant environmental variable driving tree growth finally a 69 year statistically significant reconstruction of brisbane precipitation was produced showing that this non destructive itrax ring identification technique together with age validation by bomb pulse radiocarbon dating is useful for dendroclimatological studies of trees with faint ring boundaries

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

floodplain stripping another form of adjustment to secular hydrologic regime change in southeast australia abstract in southeast australia it has been found that river regimes over the last 200 years the period of european settlement have alternated between flood and drought domination flood dominated regimes fdrs are periods of up to 50years of frequent high magnitude floods whereas drought dominated regimes ddrs are characterised by floods of much lower frequency and lower magnitude responses to these secular changes in regime have so far been mainly studied as channel changes however it is now apparent that in high energy reaches where resistant channel perimeters are slow to adjust to such changes overbank adjustment in the form of alluvial stripping can occur especially following the removal of dense floodplain forests by europeans three types of stripping are described across meander chutes parallel chutes and convex bank erosion examples of these are presented for three coastal valleys evidence reveals that they are recent forms and originate after the late 1940s shift to an fdr growth has continued in this regime in the clarence river there is a suggestion that both high and low level stripping at some sites may have been in the late nineteenth century fir at charity creek on the manning river there is also evidence of a large parallel chute active with two ponds in 1890 this healed in the 1901 1948 ddr and has been re stripped in the present regime such findings conflict with interpretations by nanson 1986 geol soc am bull 97 1467 1475 of such forms as evidence of cyclic floodplain evolution in laterally constrained valley floor troughs

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

the effects of storms and storm generated currents on sand beaches in southern maine usa storms are one of the most important controls on the cycle of erosion and accretion on beaches current meters placed in shoreface locations of saco bay and wells embayment me recorded bottom currents during the winter months of 2000 and 2001 while teams of volunteers profiled the topography of nearby beaches coupling offshore meteorological and beach profile data made it possible to determine the response of nine beaches in southern maine to various oceanographic and meteorological conditions the beaches selected for profiling ranged from pristine to completely developed and permitted further examination of the role of seawalls on the response of beaches to storms current meters documented three unique types of storms frontal passages southwest storms and northeast storms in general the current meter results indicate that frontal passages and southwest storms were responsible for bringing sediment towards the shore while northeast storms resulted in a net movement of sediment away from the beach during the 1999 2000 winter there were a greater percentage of frontal passages and southwest storms while during the 2000 2001 winter there were more northeast storms the sediment that was transported landward during the 1999 2000 winter was reworked into the berm along moderately and highly developed beaches during the next summer a northeast storm on march 5 6 2001 resulted in currents in excess of 1 m s 1 and wave heights that reached six meters the storm persisted over 10 high tides and caused coastal flooding and property damage topographic profiles made before and after the storm demonstrate that developed beaches experienced a loss of sediment volume during the storm while sediment was redistributed along the profile on moderately developed and undeveloped beaches two months after the storm the profiles along the developed beaches had not reached their pre storm elevation in comparison the moderately developed and undeveloped beaches reached and exceeded their pre storm elevation and began to show berm buildup characteristic of the summer months

short term morphological change and sediment dynamics in the intertidal zone of a macrotidal beach abstract this paper describes the morphological and sedimentological evolution of amacrotidal beach over a 20 day period under varying hydrodynamicconditions signi cant breaker heights of 0ae3 2 m and tidal ranges of 2 5 m during the eld campaign an intertidal bar developed around the mid tidelevel migrated onshore welded to the upper beach and was then attenedunder energetic wave conditions the bar had a wave breakpoint origin and itsformation was triggered by a reduction in tidal range causing more stationarywater level conditions rather than an increase in wave height most of theonshore bar migration took place while the bar was positioned in the inner tomid surf zone position such that the bar moved away from the breakpoint andexhibited divergent behaviour the depth of disturbance over individual tidalcycles was 10 20 of the breaker height such values are more typical of steepre ective beaches than gently sloping dissipative beaches and are consideredto re ect the maximum height of wave generated ripples the grain sizedistribution of sur cial sediments did not vary consistently across the beachpro le and temporal changes in the sedimentology were mostly unrelated tothe morphological response the lack of clear links between beach morphologyand sedimentology may be in part due to shortcomings in the samplingmethodology which ignored the vertical variability in the sediment sizecharacteristics across the active layer keywords beach sediment depth of disturbance intertidal bar macrotidalbeach morphology introductionbeaches respond rapidly to changing wave andtide conditions through the redistribution of theirsediments by oscillatory and quasi steady cur rents resulting in spatial patterns of erosion sediment divergence and accretion sedimentconvergence given suf cient time these bed level changes modify the beach shape by theformation modi cation destruction and ormigration of secondary morphological features such as berms beach cusps swash bars ripchannels and nearshore bars the dynamics ofthese secondary morphological features and theirrole in affecting beach stability has been a majorfocus of beach research over the last few decades e g komar 1998 short 1999 most short term days to weeks eld investi gations addressing the morphological response ofsandy beaches to wave and tide forcing have beenconducted in microtidal or mesotidal settings beaches in macrotidal settings have on the otherhand only received limited attention despitetheir common occurrence short 1991 a mainreason for this imbalance is that macrotidalbeaches are often planar and lack pronouncedsecondary morphological features indeed theonly type of macrotidal beach that does featureprominently in the coastal literature is the ridgeand runnel beach which is characterized bysedimentology 2007 54 39 53

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