numerical modeling of low frequency wave dynamics over a fringing coral reef abstract low frequency infragravity wave dynamics on a fringing coral reef were investigated using the numerical model xbeach roelvink et al 2009 first the skill of the model was evaluated in one and two dimensions based on its predictions of short waves 0 04 0 2 hz infragravity waves 0 004 0 04 hz and water level measurements tidal and wave setup obtained during a 2009 field study at ningaloo reef in western australia the model calibration was sensitive to friction coefficients for short waves and current infragravity bed friction which were assumed independent in this model study although the one dimensional cross shore model captured the gradients in the dominant hydrodynamic processes at the site a high current ig bed friction coefficient was required this resulted in an overestimation and a phase lag between the observed and predicted wave setup signal in the two dimensional model a lower more realistic current infragravity wave friction coefficient was required to achieve optimum performance due to the presence of significant reef and lagoon mean flows in the model which led to reduced setup across the reef the infragravity waves were found to propagate from the surf zone across the reef in a dominantly cross shore direction towards the shore but with substantial frictional damping the infragravity waves were strongly modulated also over the reef by tidal depth variations primarily due to the variability in frictional dissipation rates when the total water depth over the reef varied two mean wave driven circulation cells were observed in the study area with cross shore flow becoming more alongshore dominated before exiting the system via the two channels in the reef the results reveal that short waves dominated bottom stresses on the forereef and near the reef crest however inside the lagoon infragravity waves become increasingly dominant accounting up to 50 of the combined bottom stresses

forcing of resonant modes on a fringing reef during tropical storm man yi 1 open basin resonant modes have been observed at tidal frequencies on coastal shelves but their excitation on coral reef platforms has only been suggested the topography of and water depth over most fringing reefs correspond to resonant periods that are the order of tens of minutes and fall outside of the energetic part of the wave spectrum during tropical storm man yi low frequency near resonant oscillations dominated the variance of the sea surface elevation at the shoreline of ipan reef guam the excitation of the resonant modes resulted both from a large increase in water level over the reef due to wave setup which increased the resonant frequencies and the occurrence of wave group forcing with time scales commensurate with these increased resonant frequencies

long term landscape evolution early miocene and modern rivers in southern new south wales australia basaltic lavas that flowed into river valleys draining westward from the uplands of southern new south wales have preserved the early miocene landscape to a remarkable degree the reconstruction of this landscape shows that the major topographic features of the highest part of the australian continent had taken on essentially their present form by the mid tertiary and that some of these features were formed during the mesozoic plateau surfaces have been lowered by only about 2 to 5 m ma and most major streams have incised by only about 5 to 18 m ma with a maximum incision of 30 m ma since the early miocene despite the passage of 20 ma stream gradients have not waned nor have major breaks in profiles been eliminated on the contrary the modern stream profiles are strikingly similar to their early miocene counterparts suggesting that the evolution of the profiles has been determined mainly by variations in stream power rather than by the headward retreat of nickpoints through the drainage system

wave transformation over coral reefs ocean wave attenuation on coral reefs is discussed using data obtained from a preliminary field experiment and from the seasat altimeter marked attenuation of the waves is observed the rate being consistent with existing theories of bottom friction and wave breaking decay in addition there is a significant broadening of the spectrum during propagation across reefs three dimensional effects such as refraction and defraction can also lead to substantial wave height reduction for significant distances adjacent to coral reefs as a result a matrix of such reefs provides significantly more wave attenuation than may initially be expected

swash on steep and shallow beaches extensive field observations of swash on natural beaches are used to relate the magnitudes of swash oscillations to incident wave conditions and the beach slope swash fluctuations at wind wave frequencies defined here as f 05 hz appear to be saturated as in laboratory experiments with monochromatic waves wave breaking prevents the magnitudes of swash oscillations at incident wave frequencies from increasing past a certain level which depends on the beach slope all data sets considered support this conclusion in contrast the magnitude of swash oscillations at surf beat frequencies defined as f 05 hz varies between data sets possible reasons for the discrepancy are discussed despite their differences all data sets show that motions at surf beat frequencies dominate the swash spectrum on dissipative beaches as in previous studies the frequencies of spectral hills and valleys in the spectra of surf zone sensors suggests that a significant fraction of the surf beat energy is contained in motions which are standing in the cross shore direction preliminary analysis indicates that shoreward propagating surf beat is coupled to incident wave groups

influence of offshore topography on infragravity period oscillations in two rocks marina western australia abstract infragravity ig period oscillations in harbours and marinas can often lead to interruption in harbour operations due to excessive vessel movements field measurements in two rocks marina in south west australia have shown that ig period oscillations were always present and the amplitude of the oscillations was related to incident swell climate and was enhanced during storm events the marina is fronted by two shallow shore parallel reef systems located 3 2 and 4 7 km from the shoreline the area experiences continuous swell and frequent storm systems particularly during winter months this paper describes the application of a boussinesq wave model validated using field data to examine 1 source of the ig waves incident on the marina and 2 modal characteristics of the ig period oscillations inside the marina the cross shore evolution of the ig wave energy was examined using simulations with different contrasting incident wave conditions which included measured and idealised wave spectra the model results indicated that free ig waves were generated as the wind swell waves propagated over the offshore reef systems independent of the external forcing during stormy sea condition the ig energy over the primary and secondary reefs increased by a factor 10 and 8 respectively compared to the ig energy at offshore the ig wave spectrum near the marina entrance did not contain any major energy peaks and has an almost constant energy distribution across the ig wave frequencies however the frequencies similar to the marina s natural oscillation periods were excited within the marina the predicted energy distribution maps and water level snapshots inside the marina identified different oscillation modes which included mode 1 and mode 2 oscillations corresponding to a partially enclosed water body and zeroth mode corresponding to an open ended water body this study showed that in coastal regions characterised by complex offshore topography ig waves are generated independent of offshore wave conditions and harbours located in such environment are at risk of ig period oscillations depending on their geometry

evidence from crater ages for periodic impacts on the earth recent evidence has indicated that the impact of a comet or asteroid may have been responsible for mass extinction at the ends of both the cretaceous1 and the eocene2 4 quantitative analysis by raup and sepkoski5 showed that mass extinctions occur with a 26 myr period similar to the period seen in qualitative pelagic records by fischer and arthur6 to account for the possibility of periodic comet showers davis et al 7 proposed that such showers could be triggered by an unseen solar companion star as it passes through perihelion on a moderately eccentric orbit to test a prediction implicit in this model we examined records of large impact craters on the earth we report here that most of the craters occur in a 28 4 myr cycle within measurement errors this period and its phase are the same as those found in the fossil mass extinctions the probability that such agreement is accidental is 1 in 103

the dynamics of infragravity wave transformation over a fringing reef a 3 week field study was conducted to investigate the dynamics of low frequency infragravity wave motions over a fringing reef at ningaloo reef western australia short period wave motions 0 04 0 2 hz were observed to dissipate on the reef crest beyond which infragravity wave motions 0 004 0 04 hz gradually dominated toward the lagoon however both the short waves and the infragravity waves were relatively small both 0 3 m on the reef flat owing to the shallow water depth 2 m the results revealed that the surf zone generation of free infragravity wave motions on the steep 1 20 fore reef slope was dominated by breakpoint forcing as opposed to shoaling bound waves which was also supported by detailed numerical simulations of the generation process this is consistent with theory suggesting the efficiency of the breakpoint forcing mechanism should be high in this steep slope regime shoreward propagating infragravity waves traveled across the reef but were damped by bottom friction dissipation however this was at a rate much smaller than experienced by the residual short waves with these rates of frictional dissipation also strongly dependent on the water depth over the reef the infragravity wave heights increased at higher water levels and hence were strongly modulated by the tide due to the strong dissipation of infragravity waves over this wide and shallow reef that is hydraulically rough any seaward propagating infragravity waves that reflected at the shoreline were small leading to the dominance of progressive shoreward propagating infragravity wave motions throughout the reef and lagoon

modeling wave processes over fringing reefs with an excavation pit abstract the excavation of reef flat sand and aggregate for engineering projects is a common practice on atoll islands with attendant coastal management and hazard mitigation issues to assess the impact of reef flat excavation pits on wave transformation a numerical study is carried out based on one dimensional weakly dispersive highly nonlinear boussinesq equations model simulations are compared to field observations made at majuro atoll republic of the marshall islands ford et al 2013a at a 75 m wide fringing reef flat with a 17 m wide 4 m deep excavation pit and at an adjacent unmodified reef flat with a calibrated empirical breaking model and uniform friction coefficient the numerical model is shown to satisfactorily reproduce the observed sea and swell ss and infragravity ig frequency band wave heights for a moderate amplitude wave event by removing the lateral morphological differences of the field experiment the model shows that an excavation pit reduces increases shoreline ig ss wave heights compared to numerical tests without the pit in qualitative agreement with ford et al 2013a an eof analysis demonstrates that the reduction in ig wave heights is associated with modifications of the and wavelength ig standing modes across the reef caused by the pit model tests are used to evaluate the effects of cross reef pit location and width on wave transformation shoreline wave heights are least affected by a pit located near the reef crest and both ss and ig wave heights increase as the pit location moves shoreward shoreline wave heights are an increasing function of pit width as the increase in ss wave height exceeds the decrease in ig wave height produced by the pit the effects of incident wave height and spectral bandwidth are also examined for the reef with and without pit it is found that both shoreline ss and ig wave heights increase with the increasing incident wave height for both profiles the numerical model results also demonstrate that the shoreline response is sensitive to the bandwidth of the incident wave spectrum and larger ig shoreline wave heights are excited for narrower spectral bandwidths until wave reflection limits the forcing

the influence of coral reefs and climate change on wave driven flooding of tropical coastlines a numerical model xbeach calibrated and validated on field data collected at roi namur island on kwajalein atoll in the republic of marshall islands was used to examine the effects of different coral reef characteristics on potential coastal hazards caused by wave driven flooding and how these effects may be altered by projected climate change the results presented herein suggest that coasts fronted by relatively narrow reefs with steep fore reef slopes 1 10 and steeper and deeper smoother reef flats are expected to experience the highest wave runup wave runup increases for higher water levels sea level rise higher waves and lower bed roughness coral degradation which are all expected effects of climate change rising sea levels and climate change will therefore have a significant negative impact on the ability of coral reefs to mitigate the effects of coastal hazards in the future

spectral wave dissipation over a barrier reef 1 a 2 week field experiment was conducted to measure surface wave dissipation on a barrier reef at kaneohe bay oahu hawaii wave heights and velocities were measured at several locations on the fore reef and the reef flat which were used to estimate rates of dissipation by wave breaking and bottom friction dissipation on the reef flat was found to be dominated by friction at rates that are significantly larger than those typically observed at sandy beach sites this is attributed to the rough surface generated by the reef organisms which makes the reef highly efficient at dissipating energy by bottom friction results were compared to a spectral wave friction model which showed that the variation in frictional dissipation among the different frequency components could be described using a single hydraulic roughness length scale surveys of the bottom roughness conducted on the reef flat showed that this hydraulic roughness length was comparable to the physical roughness measured at this site on the fore reef dissipation was due to the combined effect of frictional dissipation and wave breaking however in this region the magnitude of dissipation by bottom friction was comparable to wave breaking despite the existence of a well defined surf zone there under typical wave conditions the bulk of the total wave energy incident on kaneohe bay is dissipated by bottom friction not wave breaking as is often assumed for sandy beach sites and other coral reefs

spatial and temporal variations in wave characteristics across a reef platform warraber island torres strait australia a field experiment was conducted at warraber island torres strait australia to investigate spatial and temporal variations in wave characteristics and energy across a mesotidal coral reef platform measurements of water depth were obtained using five pressure sensors deployed across a 2 7 km section of reef flat from july 3 5 2001 the reef surface was uneven and consisted of an outer reef flat a central reef flat depression an inner reef ramp a palaeo reef surface and the shoreline water levels decreased landward across the platform with tide ranges at the shoreline being almost 50 lower than at the outer reef flat rising and falling tides were characterised by a bimodal energy distribution with both short period 0 3 s and wind 3 8 s waves present higher water levels were dominated by wind waves the highest waves occurred at high tides associated with nocturnal tidal cycles with hs decreasing from 0 5 to 0 2 m from the outer reef flat to the shoreline wave energy at swell 8 20 s and infragravity 20 s frequencies was negligible across the reef platform although there was evidence of wave groups at higher water levels reef geometry and changes in water level determine the magnitude of wave energy on the reef platform up to 85 95 of incident wave energy is attenuated by the central reef flat depression at high and low tide respectively and strong linear relationships exist between hs and h at all locations both wave height and wave type are strongly depth dependent critical reef rim depths required to produce hs of a given size vary spatially across the reef rim due to variations in reef topography a distinct depth related threshold exists at which short period and wind wave dominance reverses over a 14 day spring neap tidal cycle the time of occurrence of wave action diminishes across the reef platform to the shoreline larger waves hs 0 2 m occur for only 9 of time at the outer reef flat and for less than 0 5 over the remaining reef platform this implies that on mesotidal reef platforms sediment entrainment and transport are severely constrained under normal wave energy conditions and significant change is likely restricted to extreme events

nonhydrostatic and surfbeat model predictions of extreme wave run up in fringing reef environments abstract the accurate prediction of extreme wave run up is important for effective coastal engineering design and coastal hazard management while run up processes on open sandy coasts have been reasonably well studied very few studies have focused on understanding and predicting wave run up at coral reef fronted coastlines this paper applies the short wave resolving nonhydrostatic xb nh and short wave averaged surfbeat xb sb modes of the xbeach numerical model to validate run up using data from two 1d alongshore uniform fringing reef profiles without roughness elements with two objectives i to provide insight into the physical processes governing run up in such environments and ii to evaluate the performance of both modes in accurately predicting run up over a wide range of conditions xbeach was calibrated by optimizing the maximum wave steepness parameter maxbrsteep in xb nh and the dissipation coefficient alpha in xb sb using the first dataset and then applied to the second dataset for validation xb nh and xb sb predictions of extreme wave run up rmax and r2 and its components infragravity and sea swell band swash sig and sss and shoreline setup were compared to observations xb nh more accurately simulated wave transformation but under predicted shoreline setup due to its exclusion of parameterized wave roller dynamics xb sb under predicted sea swell band swash but overestimated shoreline setup due to an over prediction of wave heights on the reef flat run up swash spectra were dominated by infragravity motions allowing the short wave but not wave group averaged model xb sb to perform comparably well to its more complete short wave resolving xb nh counterpart despite their respective limitations both modes were able to accurately predict rmax and r2

wave set up on coral reefs 2 set up on reefs with various profiles abstract all available laboratory data for wave set up on two dimensional reef profiles of various shapes have been compared with data from an idealised horizontal reef with a steep reef face gourlay 1996 the data is generally well represented by a relationship between the relative set up parameter gh r t o and the submergence parameter g h r h r h o and the relative set up on reef profiles of natural form is found to be less than that observed on the idealised horizontal reef the important influences of reef rim slope and variable water depths on the reef top have been investigated and some methods for allowing for them are suggested comparison of data for irregular waves with that for regular waves has led to the development of a simple method for estimating the effects of wave groups upon the magnitude of the steady state mean wave set up gh r the results of the analyses are applied to the determination of wave set up and its effects at three specific coral reef sites

numerical modelling of short and long wave transformation on a barred beach abstract this work aims to demonstrate an advancement towards the integrated modelling of surf zone hydrodynamics by means of a vof type numerical model cobras uc based on the reynolds averaged navier stokes equations in this paper the numerical model is adapted and validated for the study of nearshore processes on a mildly sloping beach the model prediction of wave energy transformation and higher order statistics skewness and asymmetry are in good agreement with detailed laboratory observations from a barred beach boers m 1996 simulation of a surf zone with a barred beach report 1 wave heights and wave breaking tech rep 96 5 comm on hydrol and geol eng dept of civil engineering delft university of technology moreover the numerical model allows us to study the low frequency motions inside the surf zone it is found that in order to achieve a satisfactory simulation of both short and long wave transformation the numerical model must achieve i the simultaneous second order wave generation and absorption ii the energy transfer between triad of components iii the short and long wave energy dissipation inside the surf zone and iv the wave reflection at the shoreline comparisons between numerical and experimental results demonstrate the model capability to satisfactorily simulate all the aforementioned processes

causation of large amplitude coastal seiches on the caribbean coast of puerto rico abstract sea level oscillations at supertidal frequency with amplitudes of the order of the mean tidal range have been reported from the caribbean coast of puerto rico analysis of a 10 year time series of digital tide data from magueyes island puerto rico demonstrates that sea level variance at the fundamental normal mode sciche frequency of the shelf has a pronounced fortnightly distribution with a maximum occurring 6 7 days after new and full moon the sieche variance also shows a bimodal seasonal distribution with an inverse relationship to easterly wind stress it is argued that the sciches are excited by internal waves generated by strong tides in the southeastern caribbean support is provided by airborne radar imagery showing sea surface patterns suggesting the presence of internal waves near the southern aves ridge and by the results of two field experiments carried out during times when large amplitude sciches were expected to search for evidence of internal wave forcing near the shelf br

wave breaking hydrodynamics within coral reef systems and the effect of changing relative sea level this paper considers the hydrodynamics of wave driven flow across a coral reef and the resultant flushing of its lagoon current depth coefficients are introduced that describe the fractional change of across reef and lagoonal current with change in the relative local sea level i e the depth of water over the reef flat the coefficients are derived from an analytical hydrodynamic model and compared with data from two reefs the first is ningaloo reef in northwest australia which is a typical barrier reef with a narrow coastal lagoon and the second is kaneohe bay in oahu hawaii where the reef is both unusually deep and wide the current depth coefficients are shown to be sensitive to the form of the frictional law on the reef flat and can be deduced from measurements of the astronomical tidal currents in the lagoon both quadratic and linear friction laws are considered for the reef flat and good agreement obtained with a linear law based on the high frequency motion due to surface gravity waves

field study of wave attenuation on an offshore coral reef a major field experiment was conducted which obtained measurements of the attenuation and transformation of short gravity waves as they cross the windward edge of an offshore coral reef water level data were collected for over 3000 individual time series during a wide range of environmental conditions at the innermost measurement site which is located on the horizontal reef flat after the completion of wave breaking the upper bound of significant and maximum wave heights is limited to less than 40 and 60 of the reef flat water depth respectively as with significant wave height both the shape and energy level of the reef flat spectra are strongly affected by changes in reef flat water depth for higher tide levels the spectra on the reef flat closely mimic the corresponding incident spectra however the attenuation is greater for both lower frequencies and higher energy portions of the spectra this causes the reef flat spectra to be broader than those measured windward of the reef at lower water levels considerable energy losses due to wave breaking and bottom friction occur most of the energy loss comes from the vicinity of the spectral peak and energy shifts to harmonics of the peak of the spectrum can be seen

energy transfer between wind waves and low frequency oscillations on a fringing reef ipan guam field observations from a guam fringing reef are used to examine the cross reef energy exchange between high frequency sea and swell ss and low frequency infragravity ig and far infragravity fig waves energetic ss waves significant wave heights 2 4 m break at the outer reef leading to weak 1 m conditions on the shallow reef flat as ss waves shoal on the reef face before breaking ig and fig energy fluxes both increase through nonlinear energy transfer from the ss waves in contrast through the surf zone the ig energy flux decreases whereas fig flux increases the decrease in ig energy flux through the surf zone is attributed to breaking ss waves working against the incident bound ig wave energy which dominates breakpoint forced ig waves yielding a net flux decrease in contrast fig energy flux increases through the surf zone consistent with breakpoint forcing and the absence of an energetic bound fig component on the reef face ig and fig energy fluxes decay on the shallow reef flat due primarily to frictional dissipation with tidal modulations attributed to nonlinear conversion and friction forcing at fig frequencies may lead to a normal mode response on the reef with comparable incoming and outgoing fig energy fluxes at the outer reef flat depending on water level over the reef flat and the degree of frictional dissipation

standing infragravity waves over an alongshore irregular rocky bathymetry rocky reef coastlines typically feature highly variable and often abrupt cross shore and alongshore changes in bathymetry the effects of this irregular rocky bathymetry on the dynamics of infragravity waves are largely unknown most models of infragravity wave dynamics have been developed and validated on smooth alongshore uniform bathymetries which may break down over these highly variable bathymetries a 2 week field experiment was conducted on a rocky reef fringed beach to investigate how the variable bathymetry affects the spatial and temporal variability of infragravity waves the height of short sea swell waves decreased over the shallow reef due to breaking whereas the height of infragravity waves increased toward the shoreline both during a storm event hm0 2 3 m and under moderate wave conditions hm0 1 0 1 8 m the infragravity waves formed a persistent cross shore standing wave pattern along the entire shoreline despite the irregular bathymetry in addition the alongshore components of infragravity waves refracted by the presence of the nearshore reef were observed to propagate in opposite directions up and down the coast resulting in a local alongshore standing wave pattern thus the presence of highly variable nearshore bathymetry which commonly occurs along rocky reef coastlines may produce both cross shore and alongshore standing wave patterns

water level effects on breaking wave setup for pacific island fringing reefs the effects of water level variations on breaking wave setup over fringing reefs are assessed using field measurements obtained at three study sites in the republic of the marshall islands and the mariana islands in the western tropical pacific ocean at each site reef flat setup varies over the tidal range with weaker setup at high tide and stronger setup at low tide for a given incident wave height the observed water level dependence is interpreted in the context of radiation stress gradients specified by an idealized point break model generalized for nonnormally incident waves the tidally varying setup is due in part to depth limited wave heights on the reef flat as anticipated from previous reef studies but also to tidally dependent breaking on the reef face the tidal dependence of the breaking is interpreted in the context of the point break model in terms of a tidally varying wave height to water depth ratio at breaking implications for predictions of wave driven setup at reef fringed island shorelines are discussed

predicting the hydrodynamic response of a coastal reef lagoon system to a tropical cyclone using phase averaged and surfbeat resolving wave models abstract tropical cyclone tc olwyn travelled along the coast of ningaloo reef in northwestern australia as a category 3 tc during 12 13 march 2015 with sustained wind speeds of over 130 km h 1 and significant wave heights on the forereef reaching 6 m observations from tc olwyn showed that contrary to typical wave transformation patterns across a coastal reef lagoon under the tc conditions there was a substantial shoreward increase of wave height this unusual pattern was primarily due to strong local wind wave generation under the extreme wind conditions despite the lagoon itself being relatively small order 1 km wide and shallow order 1 m depth two common types of coastal numerical wave models that include either wave growth i e the phase averaged model swan or infragravity waves i e the surfbeat resolving model xbeach but not both processes were used to assess the capabilities of numerical models to predict the cyclone induced hydrodynamics model results showed that wave conditions in the lagoon and at the shoreline were dominated by locally generated wind waves with the reef efficiently dissipating the large incident waves offshore the infragravity waves in the lagoon were only of secondary importance during the tc compared to the locally generated sea swell waves although both the phase averaged swan and surfbeat resolving xbeach models were able to predict some of the local hydrodynamic responses for this specific site and storm the use of a phase averaged model yielded the most accurate predictions of the hydrodynamics given that it included wind wave growth however because the influence of infragravity waves cannot be neglected in reef environments in general these results emphasize the need for a more general modeling approach that requires the addition of wind wave growth formulations into surfbeat or fully phase resolving classes of numerical wave models and or the addition of an infragravity wave formulation in spectral wave models

wave run up on a high energy dissipative beach 1 because of highly dissipative conditions and strong alongshore gradients in foreshore beach morphology wave run up data collected along the central oregon coast during february 1996 stand in contrast to run up data currently available in the literature during a single data run lasting approximately 90 min the significant vertical run up elevation varied by a factor of 2 along the 1 6 km study site ranging from 26 to 61 of the offshore significant wave height and was found to be linearly dependent on the local foreshore beach slope that varied by a factor of 5 run up motions on this high energy dissipative beach were dominated by infragravity low frequency energy with peak periods of approximately 230 s incident band energy levels were 2 5 to 3 orders of magnitude lower than the low frequency spectral peaks and typically 96 of the run up variance was in the infragravity band a broad region of the run up spectra exhibited an f 4 roll off typical of saturation extending to frequencies lower than observed in previous studies the run up spectra were dependent on beach slope with spectra for steeper foreshore slopes shifted toward higher frequencies than spectra for shallower foreshore slopes at infragravity frequencies run up motions were coherent over alongshore length scales in excess of 1 km significantly greater than decorrelation length scales on moderate to reflective beaches