glider observations of enhanced deep water upwelling at a shelf break canyon a mechanism for cross slope carbon and nutrient exchange using underwater gliders we have identified canyon driven upwelling across the celtic sea shelf break in the vicinity of whittard canyon the presence of this upwelling appears to be tied to the direction and strength of the local slope current which is in itself highly variable during typical summer time equatorward flow an unbalanced pressure gradient force and the resulting disruption of geostrophic flow can lead to upwelling along the main axis of two small shelf break canyons as the slope current reverts to poleward flow the upwelling stops and the remnants of the upwelled features are mixed into the local shelf water or advected away from the region the upwelled features are identified by the presence of sub pycnocline high salinity water on the shelf and are upwelled from a depth of 300 m on the slope thus providing a mechanism for the transport of nutrients across the shelf break onto the shelf

internal tide coherence and decay over a wide shelf sea 1 a quasi synoptic hydrography and velocity section is used to determine the structure and the decay rate of the internal tide it across the broad continental shelf of the celtic sea in these observations the it is coherent over more than 170 km about five wavelengths with an estimated shoreward energy decay scale of 42 km the inferred it wavelength averaged dissipation rate near the shelf edge is estimated as 2 08 10 7 wkg 1 in close agreement with tidally and vertically averaged measurements from the region these results provide the firstin situ evidence of it coherence over many wavelengths in a shelf sea

internal tides in a dendritic submarine canyon abstract submarine canyons are a common geomorphological feature along continental slopes worldwide and often found to be hotspots of internal tide activity however the majority of well studied submarine canyons are simple linear incisions or have meandering morphology internal tide energetics in branching dendritic canyons has not previously been investigated here we present a high resolution 500 m numerical modelling study of the internal tide within whittard canyon a large dendritic submarine canyon system that incises the celtic sea continental slope a modified version of the princeton ocean model is used to simulate the m 2 semidiurnal internal tide in the whittard canyon region verified against a hydrographic dataset collected by an autonomous ocean glider much of the internal tide energy entering whittard canyon originates to the southeast along the celtic sea shelf break internal tide generation also occurs within the canyon itself but is in part compensated by areas of negative energy conversion depth integrated internal tide energy fluxes exceed 8 kw m 1 in the eastern limb of the canyon the internal tide is topographically steered through the major limbs and along canyon energy flux is bottom intensified suggesting topographic focusing the down canyon extent of bottom intensification closely corresponds to the point that along canyon slope becomes near critical to the semidiurnal internal tide energetically the multiple limbs of whittard canyon behave differently some are net sources of internal tide energy whilst others are net sinks internal tide energy dissipation also varies between the canyon limbs bulk dissipation rates are 2 1 7 7 10 8 w kg 1 in addition the effect of bathymetric resolution on internal tide generation and propagation is investigated by progressively smoothing the model domain decreasing the bathymetric resolution reduces internal tide generation and energy dissipation in both whittard canyon and the model domain as a whole however internal tide energy flux into the canyon is not consistently changed at least 1 5 km resolution bathymetry is required to adequately resolve the semidiurnal internal tide field in this region of complex topography

wave transformation and wave driven flow across a steep coral reef observations of waves setup and wave driven mean flows were made on a steep coral forereef and its associated lagoonal system on the north shore of moorea french polynesia despite the steep and complex geometry of the forereef and wave amplitudes that are nearly equal to the mean water depth linear wave theory showed very good agreement with data measurements across the reef illustrate the importance of including both wave transport owing tostokes drift as well as the eulerianmean transportwhen computing the fluxes over the reef finally the observed setup closely follows the theoretical relationship derived from classic radiation stress theory although the two parameters that appear in the model one reflecting wave breaking the other the effective depth over the reef crest must be chosen to match theory to data

nearshore hydrodynamics beachface cobble transport and morphodynamics on a pacific atoll motu abstract measurements of wave transformation beachface cobble transport and shoreline morphology change were undertaken over a 14 month period at fatato island a cobble and sand motu on the southeast rim of funafuti atoll tuvalu results document significant cobble transport and beach profile change on fatato during a year in the absence of any significant high energy wave events changes in beachface volume were measured on 11 across shore beach profiles and show marked variations of 7 1 and 7 01 m3 between profiles and between survey periods net volumetric beachface change over the 14 month experiment was approximately zero indicating a balance between erosion and deposition and net conservation of sediment volume on the ocean shoreline cobble movement was measured using passive integrated transponder pit tags inserted in 300 randomly selected clasts mean b axis 75 mm on the mid beachface tagged particles were re surveyed after 6 and 14 months achieving 76 recovery and identify large excursions of clasts on the beachface and dominant southwest alongshore transport with an average net movement of 68 m after 14 months a simple agent based probabilistic model was developed to simulate cobble movement and explore the coupling between hydrodynamic and shoreline processes model simulations reveal predominant south westerly cobble transport is driven by mean wave conditions associated with easterly trade winds and long period swell events that approach the reef from the south drive episodic north easterly transport reversals and significant onshore transport that can strand particles on the upper beach results present the first observations of morphodynamic behaviour of an atoll motu and highlight the highly dynamic nature of motu shorelines under mean energy conditions such results challenge conventional perspectives that motu are storm adjusted landforms that require extreme events to stimulate geomorphic change and inform future projections of island change

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

projected atoll shoreline and run up changes in response to sea level rise and varying large wave conditions at wake and midway atolls northwestern hawaiian islands abstract atoll islands are dynamic features that respond to seasonal alterations in wave conditions and sea level it is unclear how shoreline wave run up and erosion patterns along these low elevation islands will respond to projected sea level rise slr and changes in wave climate over the next century hindering communities preparation for the future to elucidate how these processes may respond to climate change extreme boreal winter and summer wave conditions under future sea level rise slr and wave climate scenarios were simulated at two atolls wake and midway using a shallow water hydrodynamic model nearshore wave conditions were used to compute the potential longshore sediment flux along island shorelines via the cerc empirical formula and wave driven erosion was calculated as the divergence of the longshore drift run up and the locations where the run up exceed the berm elevation were also determined slr is projected to predominantly drive future island morphological change and flooding seaward shorelines i e ocean fronted shorelines directly facing incident wave energy were projected to experience greater erosion and flooding with slr and in hypothetical scenarios where changes to deep water wave directions were altered as informed by previous climate change forced pacific wave modeling efforts these changes caused nearshore waves to become more shore normal increasing wave attack along previously protected shorelines with slr leeward shorelines i e an ocean facing shoreline but sheltered from incident wave energy became more accretive on windward islands and marginally more erosive along leeward islands these shorelines became more accretionary and subject to more flooding with nearshore waves becoming more shore normal lagoon shorelines demonstrated the greatest slr driven increase in erosion and run up they exhibited the greatest relative change with increasing wave heights where both erosion and run up magnitudes increased wider reef flat fronted seaward shorelines became more accretive as all oceanographic forcing parameters increased in magnitude and exhibited large run up increases following increasing wave heights island end shorelines became subject to increased flooding erosion at wake and accretion at midway with slr under future conditions windward and leeward islands are projected to become thinner as ocean facing and lagoonal shorelines erode with leeward islands becoming more elongate island shorelines will change dramatically over the next century as slr and altered wave climates drive new erosional regimes it is vital to the sustainability of island communities that the relative magnitudes of these effects are addressed when planning for projected future climates

laboratory study of wave processes over fringing reefs with a reef flat excavation pit abstract dredging and excavation activities on fringing reefs have potential impacts such as the coastal inundation during extreme wave events and no published laboratory experiments have addressed this issue to verify the previous findings from both field observations and numerical simulations and focus on evaluating the alteration of wave processes over fringing reefs by an excavation pit a new set of laboratory experiments are carried out in a wave flume based on an idealized fringing reef model with and without a reef flat pit experimental results are reported for a series of spectral wave conditions and pit widths it is found that the sea and swell ss waves near the shoreline can be increased or decreased depending both on the incident wave condition and the pit width whereas the infragravity ig waves reaching the shoreline are consistently reduced by an average of 10 5 when the pit exists and such reduction is enhanced with increasing pit width an analysis of the involved hydrodynamic processes indicates that the variation of shoreline ss wave energy depends on the relative importance of such processes as increased wave reflection around the pit decreased dissipation with wave breaking decreased energy transfer with nonlinear wave wave interaction and wave resonance excited in the pit however the reduction of shoreline ig wave energy is due to the combined effects of a disruption of resonant standing wave pattern on the reef flat and increased wave reflection around the pit

a numerical study of circulation in a coastal reef lagoon system 1 a coupled wave circulation numerical model was used to simulate the distribution of wave energy as well as the circulation induced by wave breaking wind and tidal forcing within a coral reef system in kaneohe bay oahu hawaii modeled wave current and wave setup fields were compared with field measurements collected on the forereef reef flat and reef channels and in the lagoon over a 4 week period the predicted wave height transformation across the reef lagoon system was in good agreement with field observations using single parameter spatially uniform values to describe both wave breaking and frictional dissipation the spatial distribution of the resulting wave setup field drove a persistent wave driven flow across the reef flat that returned to the ocean through two deeper channels in the reef both the magnitude and direction of these currents were well described using a spatially uniform hydraulic roughness length scale notably the model lends support to field observations that setup within the coastally bounded lagoon was a substantial fraction of the maximum setup on the reef 60 80 which generated relatively weak cross reef wave driven flows 10 20 cm s 1 compared with reefs having mostly unbounded lagoons e g many atolls and barrier reefs numerical experiments conducted using lagrangian particle tracking revealed that residence times within kaneohe bay are extremely heterogeneous typically ranging from 1 month within its sheltered southern lagoon

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

observations of wave transformation over a fringing coral reef and the importance of low frequency waves and offshore water levels to runup overwash and coastal flooding many low lying tropical islands are susceptible to sea level rise and often subjected to overwash and flooding during large wave events to quantify wave dynamics and wave driven water levels on fringing coral reefs a 5 month deployment of wave gauges and a current meter was conducted across two shore normal transects on roi namur island in the republic of the marshall islands these observations captured two large wave events that had waves with maximum heights greater than 6 m with peak periods of 16 s over the fore reef the larger event coincided with a peak spring tide leading to energetic highly skewed infragravity 0 04 0 004 hz and very low frequency 0 004 0 001 hz waves at the shoreline which reached heights of 1 0 and 0 7 m respectively water surface elevations combined with wave runup reached 3 7 m above the reef bed at the innermost reef flat adjacent to the toe of the beach resulting in flooding of inland areas this overwash occurred during a 3 h time window that coincided with high tide and maximum low frequency reef flat wave heights the relatively low relief characteristics of this narrow reef flat may further drive shoreline amplification of low frequency waves due to resonance modes these results 1 demonstrate how the coupling of high offshore water levels with low frequency reef flat wave energetics can lead to large impacts along fringing reef lined shorelines such as island overwash and 2 lend support to the hypothesis that predicted higher sea levels will lead to more frequent occurrences of these extreme events negatively impacting coastal resources and infrastructure

dynamics of advection driven upwelling over a shelf break submarine canyon 1 the response over a submarine canyon to a several day upwelling event can be separated into three phases an initial transient response a later much longer steady advection driven response and a final relaxation phase for the advection driven phase over realistically steep deep and narrow canyons with near uniform flow and stratification at rim depth we have derived scale estimates for four key quantities observations from 5 real world canyon studies and 3 laboratory studies are used to validate the scaling and estimate the scalar constant for each scale based on 4 geometric parameters of the canyon the background stratification the coriolis parameter and the incoming current we can estimate 1 the depth of upwelling in the canyon to within 15 m 2 the deep vorticity to within 15 and 3 the presence absence of a rim depth eddy can be determined based on laboratory data 4 the total upwelling flux can also be estimated the scaling analysis shows the importance of a rossby number based on the radius of curvature of isobaths at the upstream mouth of the canyon this rossby number determines the ability of the flow to cross the canyon isobaths and generate the pressure gradient that drives upwelling in the canyon other important scales are a rossby number based on the length of the canyon which measures the ability of the flow to lift isopycnals and a burger number based on the width of the canyon that determines the likelihood of an eddy at rim depth generally long canyons with sharply turning upstream isobaths strong incoming flow small coriolis parameter and weak stratification have the strongest upwelling response

the importance of explicitly modelling sea swell waves for runup on reef lined coasts abstract the importance of explicitly modelling sea swell waves for runup was examined using a 2d xbeach short wave averaged surfbeat xb sb and a wave resolving non hydrostatic xb nh model of roi namur island on kwajalein atoll in the republic of marshall islands field observations on water levels wave heights and wave runup were used to drive and evaluate both models which were subsequently used to determine the effect of sea level rise and extreme wave conditions on wave runup and its components results show that specifically modelling the sea swell component using xb nh provides a better approximation of the observed runup than xb sb which only models the time variation of the sea swell wave height despite good model performance of both models on reef flat water levels and wave heights xb sb has a bias of 0 108 0 057 m and scatter index of 0 083 0 639 whereas xb nh has bias of 0 132 0 055 m and 0 122 0 490 respectively however both models under predict runup peaks the difference between xb sb and xb nh increases for more extreme wave events and higher sea levels as xb nh resolves individual waves and therefore captures ss wave motions in runup however for even larger forcing conditions with offshore wave heights of 6 m the island is flooded in both xb sb and xb nh computations regardless the sea swell wave energy contribution in such cases xb sb would be adequate to model flooding depths and extents on the island while requiring 4 5 times less computational effort

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

effects of wave rollers and bottom stress on wave setup 1 setup the increase in the mean water level associated with breaking waves observed between the shoreline and about 6 m water depth on an ocean beach is predicted well by a model that includes the effects of wave rollers and the bottom stress owing to the mean flow over the 90 day observational period the measured and modeled setups are correlated squared correlation above 0 59 and agree within about 30 although rollers may affect setup significantly on beaches with large amplitude several meters high sandbars and may be important in predicting the details of the cross shore profile of setup for the data discussed here rollers have only a small effect on the amount of setup conversely bottom stress calculated using eddy viscosity and undertow formulations based on the surface dissipation and assuming that the eddy viscosity is uniform throughout the water column significantly affects setup predictions neglecting bottom stress results in underprediction of the observed setup in all water depths with maximum underprediction near the shoreline where the observed setup is largest

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

two dimensional modelling of wave dynamics and wave forces on fringing coral reefs abstract two dimensional numerical modelling of swell wave dynamics on idealized fringing reefs is performed using swan covering a wide range of bathymetries climate forcing conditions and water depths over the reefs the results illustrate the impact of reef geometry and bathymetry coral species and sea level rise on key hydrodynamic parameters on the reef and on forces on corals the modelling demonstrates that one dimensional models underestimate the wave action on the reef flat wide short reefs and narrow long reefs have similar wave heights at the centre of the reef flat for a given reef length the wave height first decreases with increasing reef width then increases to a local maximum when reef width is approximately equal to the reef length and then decreases for further increases in width this pattern is a result of combined dissipation and refraction processes which combine to lead to different zones of cross reef wave transformation provided that a reef retains its hydrodynamic functions in breaking and refracting the waves sea level rise enhances the wave heights and wave orbital velocities on the reef flat if vertical coral growth does not keep pace with sea level rise loss of the hydrodynamic functions of the reef may occur on deeper reefs and result in a reduction of near bed velocities with sea level rise hydrodynamic forces on corals vary by coral species and slr changes the magnitude of the forces on different species in different ways which may lead to less favourable conditions for certain coral species for long period swell the intermediate size corals are drag dominated and behave similarly to branching corals whereas for short period swell their behavior is similar to that of the inertia dominated massive corals for intermediate corals different responses to slr may therefore be expected for different overall regional wave climates over time this process may contribute to changes in the structural complexity of reefs the influence of sea level rise on the forces on corals on the reef flat is different under swell and cyclonic wind conditions since wind influences wave period in the latter case

intense variable mixing near the head of monterey submarine canyon abstract a microstructure survey near the head of monterey submarine canyon the first in a canyon confirmed earlier inferences that coastal submarine canyons are sites of intense mixing the data collected during two weeks in august 1997 showed turbulent kinetic energy dissipation and diapycnal diffusivity up to 103 times higher than in the open ocean dissipation and diapycnal diffusivity within 10 km of the canyon head were among the highest observed anywhere e 1 1 10 6 w kg 1 k 1 0 10 2 m2 s 1 mixing occurred mainly in an on axis stratified turbulent layer with thickness and intensity increasing from neap to spring tide strain spectra showed a gentler than k 1z rolloff suggesting that critical reflection and scattering may push energy into high wavenumbers dissipation dependence on shear appears to be much weaker in the canyon than in the open ocean with indications that the dependence maybe as low as e s coastal canyons may account for a small but significant fraction of the int

coral reef drag coefficients water depth dependence abstracta major challenge in modeling the circulation over coral reefs is uncertainty in the drag coefficient because existing estimates span two orders of magnitude current and pressure measurements from five coral reefs are used to estimate drag coefficients based on depth average flow assuming a balance between the cross reef pressure gradient and the bottom stress at two sites wind stress is a significant term in the cross reef momentum balance and is included in estimating the drag coefficient for the five coral reef sites and a previous laboratory study estimated drag coefficients increase as the water depth decreases consistent with open channel flow theory for example for a typical coral reef hydrodynamic roughness of 5 cm observational estimates and the theory indicate that the drag coefficient decreases from 0 4 in 20 cm of water to 0 005 in 10 m of water synthesis of results from the new field observations with estimates from previous field and laboratory studies indicate that coral r

tide effects on wave attenuation and wave set up on a caribbean coral reef abstract the effects of tides on wave attenuation and wave set up were investigated at great pond bay a caribbean reef located in st croix u s virgin islands measurements of wave pressure fluctuations were made at three stations across the reef profile total wave set up was measured between the forereef and the reef crest or backreef lagoon wave spectra indicate significant filtering of energy at the peak frequencies as waves traveled across the reef the energy dissipation calculations imply an average energy reduction of 62 between the forereef and reef crest mean energy reduction between the forereef and lagoon was 90 energy dissipation between the forereef and reef crest increased 15 between high and low tide and 6 between forereef and lagoon tidal reduction of water depth at the reef crest intensified wave breaking and this condition increased energy dissipation measurements of wave set up ranged from 0 8 to 1 5 cm calculations of wave set up using tait s 1972 model showed good agreement with observations

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

nearshore circulation in a tropical fringing reef system 1 the role of waves tide and wind on the circulation of a fringing reef system was investigated using data collected during a 6 week field experiment in a section of ningaloo reef off western australia the high correlation observed between current velocities and wave height throughout the system revealed the dominant role wave breaking plays in driving the overall reef lagoon circulation whereas the modulation of the currents at tidal frequencies suggested that the wave driven currents responded to tidal variations in the mean water level over the reef the influence of the various forcing mechanisms on the current field was investigated for both high and low frequency bands wave breaking was found to be the dominant forcing mechanism for the low frequency subtidal currents with the subtidal flow pattern consisting of a cross reef flow over the reef alongshore flow in the lagoon and water exiting back to the ocean through the main channel the tides controlled the high frequency current variability via two mechanisms one associated with the ebb flood cycle of the tides and the second associated with tidal modulations of the wave driven currents wind forcing and buoyancy effects were both found to be negligible in driving the circulation and flushing of the system during the observation period flushing time scale estimates varied from as low as 2 h to more than a day for the wide range of observed incident wave heights the results suggest that the circulation of ningaloo reef will be strongly influenced by even a small mean sea level rise

wave setup a field study a new and efficient method is described for obtaining field measurements of surf zone mean water levels the method applies manometer tubes rather than the traditional pressure transducers and hence makes it unnecessary to survey the vertical positions of the sensors a substantial data base is obtained which apart from quantitative data for the field site and similar beaches gives clear general indications of where previous wave setup models need to be amended it is clear from the data that while traditional setup models work reasonably well seaward of the still water line the most landward part of the mean water surface on fairly steep beaches at least requires radically different models it is still possible however to obtain reasonable estimates of the shoreline setup by tying together the concepts of setup and runup and utilizing presently available empirical formulae for the maximum runup level

field observations of wave driven setdown and setup wave driven setdown and setup observed for 3 months on a cross shore transect between the shoreline and 5 m water depth on a barred beach are compared with a theoretical balance between cross shore gradients of the mean water level and the wave radiation stress the observed setdown the depression of the mean water level seaward of the surf zone is predicted well when radiation stress gradients are estimated from the observations using linear theory at each location along the transect the observed setdown also agrees with analytical predictions based on offshore wave observations and the assumption of linear dissipationless normally incident waves shoaling on alongshore homogeneous bathymetry the observed setup the superelevation of the mean water level owing to wave breaking is predicted accurately in the outer and middle surf zone but is increasingly underpredicted as the shoreline is approached similar to previous field studies setup at a fixed cross shore location increases with increasing offshore wave height and is sensitive to tidal fluctuations in the local water depth and to bathymetric changes numerical simulations and the observations suggest that setup near the shoreline depends on the bathymetry of the entire surf zone and increases with decreasing surf zone beach slope defined as the ratio of the surf zone averaged water depth to the surf zone width a new empirical formula for shoreline setup on nonplanar beaches incorporates this dependence

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

wave setup over a pacific island fringing reef 1 measurements obtained across a shore attached fringing reef on the southeast coast of the island of guam are examined to determine the relationship between incident waves and wave driven setup during storm and nonstorm conditions wave setup on the reef flat correlates well r 0 95 and scales near the shore as approximately 35 of the incident root mean square wave height in 8 m water depth waves generated by tropical storm man yi result in a 1 3 m setup during the peak of the storm predictions based on traditional setup theory steady state inviscid cross shore momentum and depth limited wave breaking and an idealized model of localized wave breaking at the fore reef are in agreement with the observations the reef flat setup is used to estimate a similarity parameter at breaking that is in agreement with observations from a steeply sloping sandy beach a weak 10 increase in setup is observed across the reef flat during wave events the inclusion of bottom stress in the cross shore momentum balance may account for a portion of this signal but this assessment is inconclusive as the reef flat currents in some cases are in the wrong direction to account for the increase an independent check of fringing reef setup dynamics is carried out for measurements at the neighboring island of saipan with good agreement

combined infragravity wave and sea swell runup over fringing reefs by super typhoon haiyan super typhoon haiyan struck the philippines on 8 november 2013 marking one of the strongest typhoons at landfall in recorded history extreme storm waves attacked the pacific coast of eastern samar where the violent typhoon first made landfall our field survey confirmed that storm overwash heights of 6 14 m above mean sea level were distributed along the southeastern coast and extensive inundation occurred in some coastal villages in spite of natural protection by wide fringing reefs a wave model based on boussinesq type equations is constructed to simulate wave transformation over shallow fringing reefs and validated against existing laboratory data wave propagation and runup on the eastern samar coast are then reproduced using offshore boundary conditions based on a wave hindcast the model results suggest that extreme waves on the shore are characterized as a superposition of the infragravity wave and sea swell components the balance of the two components is strongly affected by the reef width and beach slope through wave breaking frictional dissipation reef flat resonances and resonant runup amplification therefore flood characteristics significantly differ from site to site due to a large variation of the two topographic parameters on the hilly coast strong coupling of infragravity waves and sea swells produces extreme runup on steep beaches fronted by narrow reefs whereas the infragravity waves become dominant over wide reefs and they evolve into bores on steep beaches

field observations of wave driven water level gradients across a coral reef flat 1 field measurements of still water surface elevations were obtained across a narrow leeward reef flat on lady elliot island great barrier reef australia in june 2003 stilling wells were deployed from the reef crest landward to the island beach and waves and mean water levels were monitored over both rising and falling tides during low to moderate wave energy conditions wave setup of up to 13 8 cm above still water level occurred in the presence of incident waves of 0 4 m yielding maximum water surface slopes greater than 6 results show that the magnitude of wave setup varies both temporally and spatially across the reef with changing water depth setup is dominant on the reef edge at low tide evolving into a dual setup system at both the reef edge and shoreline at midtide and finally a dominant shoreline setup at high tide on lady elliot island the dual setup system is considered to result from spatial differences in transformation and breaking of swell and wind waves at midtide stages the presence of a dual setup system across a reef flat has not been previously identified in field or modeling studies and has potentially significant implications for reefal current development sediment transport and the stability of reef island shorelines

wave generated flow on coral reefs an analysis for two dimensional horizontal reef tops with steep faces waves breaking on the seaward rim of a coral reef generate a flow of water from the exposed side of the reef to the sheltered side and or to either channels through the reef rim or lower sections of the latter this wave generated flow is driven by the water surface gradient resulting from the wave set up created by the breaking waves this paper reviews previous approaches to modelling wave generated flows across coral reefs and discusses the influence of reef morphology and roughness upon these flows laboratory measurements upon a two dimensional horizontal reef platform with a steep reef face provide the basis for extending a previous theoretical analysis for wave set up on a reef in the absence of a flow gourlay m r 1996b wave set up on coral reefs 2 set up on reefs with various profiles coastal engineering 28 1755 to include the interaction between a unidirectional flow and the wave set up the laboratory model results are then used to demonstrate that there are two basic reef top flow regimes reef top control and reef rim control using open channel flow theory analytical relationships are derived for the reef top current velocity in terms of the offreef wave conditions the reef top water depth and the physical characteristics of the reef top topography the wave set up and wave generated flow relationships are found to predict experimental values with reasonable accuracy in most cases the analytical relationships are used to investigate wave generated flows into a boat harbour channel on heron reef in the southern great barrier reef c 2005 elsevier b v all rights reserved

wave driven flow over shallow reefs long term 1 month observations of waves and currents over a natural reef are presented which show a strong correlation between offshore rms incident wave height and cross reef currents at subtidal frequencies the energy spectrum of the cross reef currents shows a significant peak at twice the semidiurnal tidal frequency while the spectrum of sea surface elevation over the reef flat shows no corresponding peak furthermore experimental results reported by gourlay 1993 show setup over the reef occurs in the absence of a beach and the cross reef transport decreases with an increase in the sea surface slope across the reef flat due to an increase in setup at the top of the reef face analytic solutions for flow forced by wave breaking over an idealized reef explain the above features of cross reef flows in the absence of a beach through the surf zone on the reef face the cross reef gradient in the radiation stress due to wave breaking is partitioned between balancing an offshore pressure gradient associated with setup over the reef and forcing a mean flow across the reef over the reef flat where the depth is constant there is no forcing due to wave breaking and the flow is driven by a pressure gradient which results from the setup through the surf zone the magnitude of the setup through the surf zone is such that the transport across the reef flat matches the transport through the surf zone which is forced by the gradient in the radiation stress solutions are presented for general reef geometry defined by the reef width and slope of the seaward reef face and incident wave forcing defined by the depth at the breakpoint and the depth of water over the reef as the depth over the reef goes to zero the solutions converge to the plane beach solutions described by longuet higgins and stewart 1964 wave setup is maximized and the cross reef transport is zero in other cases the relative magnitudes of the setup and the cross reef transport depend on the geometry of the reef and the incident wave forcing

physical modelling of reef island topographic response to rising sea levels abstract low lying coral reef islands are considered extremely vulnerable to the impacts of climate change particularly sea level rise and increasing storm magnitude inundation and erosion are expected to destabilise reef islands and render them uninhabitable within decades however such assertions are founded upon the assumption that reef islands are geomorphologically inert landforms whereas recent planform and cross sectional analysis of reef island morphodynamics demonstrates that many islands are highly dynamic landforms changing in size shape and position on the reef platform this paper describes the first physical modelling experiments to model the whole of island morphodynamic response of reef islands to changes in sea level and wave regime a wave basin is utilised to construct a 1 50 scale three dimensional model of fatato island tuvalu and document the whole of island response across a broad range of wave and water level conditions whole of island results corroborate flume studies and provide new insights into the modes and styles of island change spit rotation as well as lagoonward island recession and vertical oceanward crest accretion are identified as the core island responses to increasing water level and wave conditions however results show that the rate and magnitude of physical adjustment is strongly dependent on the rate and magnitude of sea level rise and wave conditions results challenge existing models of future island susceptibility to wave driven flooding demonstrating that washover processes can provide a mechanism to build and potentially maintain island freeboard above sea level these insights highlight an urgent need to incorporate island morphodynamics into flood risk models in order to produce accurate assessments of future wave driven flood risks and better resolve island vulnerability

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

wave transformation across the inner surf zone sea and swell wave heights observed on transects crossing the mid and inner surf zone on three beaches a steep concave up beach a gently sloped approximately planar beach and a beach with an approximately flat terrace adjacent to a steep foreshore were depth limited i e approximately independent of the offshore wave height consistent with previous observations the wave evolution is well predicted by a numerical model based on the one dimensional nonlinear shallow water equations with bore dissipation the model is initialized with the time series of sea surface elevation and cross shore current observed at the most offshore sensors located about 50 to 120 m from the mean shoreline in mean water depths 0 80 to 2 10 m the model accurately predicts the cross shore variation of energy at both infragravity nominally 0 004 f 0 05 hz and sea swell here 0 05 f 0 18 hz frequencies in models of surf zone hydrodynamics wave energy dissipation is frequently parameterized in terms of s the ratio of the sea swell significant wave height to the local mean water depth the observed and predicted values of s increase with increasing beach slope and decreasing normalized by a characteristic wavenumber k water depth kh and are well correlated with kh a measure of the fractional change in water depth over a wavelength errors in the predicted individual values of s are typically less than 20 it has been suggested that infragravity motions affect waves in the sea swell band and hence s but this speculation is difficult to test with field observations numerical simulations suggest that for the range of conditions considered here s is insensitive to infragravity energy levels

wave set up on a natural beach wave set up the superelevation of mean water level owing to the presence of breaking incident waves was measured at the shoreline of a natural beach offshore pressure sensors monitored incident wave conditions the set up of the shoreline was found to be about 0 17hs where hs is the significant wave height in deep water

along isopycnal variability of spice in the north pacific two hydrographic surveys in the gulf of alaska and the north pacific subtropical gyre are presented both surveys are roughly perpendicular to lateral temperature gradients and were collected in the summer when there was a shallow mixed layer and a seasonal thermocline isopycnal displacements and horizontal velocities are dominated by internal waves spice anomalies along isopycnals are examined to diagnose lateral stirring mechanisms the spectra of spice anomaly gradients along near surface isopycnals roughly follow power laws of kx0 6 0 2 variance spectra power laws of kx 1 4 0 2 and in most cases the spectra become redder at depth the near surface spectra are possibly consistent with the predictions of quasi geostrophic turbulence theory when surface buoyancy effects are accounted for but the spectra at depth are inconsistent with any quasi geostrophic theory probability distributions of spice gradients exhibit a large peak at low gradients and long tails for large gradients symptomatic of fronts vertical coherence of the spice signal falls off with a decorrelation depth scale that has a maximum of about 80 m at 100 km wavelengths and depends on horizontal wavelength with a power law of approximately kx 1 2 lateral decorrelation length scales are 20 40 km close to the baroclinic rossby radius lateral stirring occurs over large scales with average lateral displacements of about 200 km in the upper 75 m decreasing to 100 km at greater depths the depth variation of the statistics indicates that time history of tracer stirring on each isopycnal is important or that there are unconsidered depth dependent stirring mechanisms

vivaldi 1991 a study of the formation circulation and ventilation of eastern north atlantic central water abstract a synoptic hydrographic data set comprising 32 full depth ctd casts and 2500 ctd seasoar profiles to 500 m is used to describe the s properties and circulation of central water east of the mid atlantic ridge and between 39 n and 54 n eastward transport of 20 10 6 m 3 s 1 in the north atlantic current turns entirely northwards to the west of 54 n 20 w this transport consists in the upper layers of western north atlantic water freshened at temperatures below 10 c by mixing with subarctic intermediate water northern and southern branches of the north atlantic current are well defined and both turn northwards west of 20 w a further 10 10 6 m 3 s 1 of eastern north atlantic water forms and recirculates anticyclonically to the west of spain south of the north atlantic current and north of 40 n eastern north atlantic water is most weakly stratified east of 20 w and there is clear correlation between weakly stratified pycnostads and positive salinity anomalies relative to western north atlantic water thus eastern north atlantic water is a winter mode water in which strong winter cooling has increased the density and hence also the salinity anomaly at a given temperature near the southern entrance to the rockall trough there is evidence that salinities are also increased by mediterranean water influence circulation south of the north atlantic current is complex there is no evidence for direct ventilation southwards across 40 n where water properties s potential vorticity and cfc 113 and historical data all indicate westward ventilation east of 24 w with weak southward ventilation occurring further west in the vicinity of the azores the circulation pattern suggested is remarkably similar to that proposed by helland hansen and nansen in 1926 the eastern north atlantic geophysiske publicajoner 4 1 76 with anticyclonic circulation of colder eastern north atlantic water north of 40 n meeting warmer water from south of 40 n circulating cyclonically north of the azores current the distribution of pycnostads and s properties between 20 w and 35 w north of the azores indicates alternate bands of western and eastern north atlantic water moving eastward and westward respectively including evidence for westward motion immediately south of the southern branch of the north atlantic current possibly by westward propagation of anticyclonic eddies containing deep pycnostads

discerning the timing and cause of historical mortality events in modern porites from the great barrier reef the life history strategies of massive porites corals make them a valuable resource not only as key providers of reef structure but also as recorders of past environmental change yet recent documented evidence of an unprecedented increase in the frequency of mortality in porites warrants investigation into the history of mortality and associated drivers to achieve this both an accurate chronology and an understanding of the life history strategies of porites are necessary sixty two individual uranium thorium u th dates from 50 dead massive porites colonies from the central inshore region of the great barrier reef gbr revealed the timing of mortality to have occurred predominantly over two main periods from 1989 2 4 1 to 2001 4 4 1 and from 2006 4 1 8 to 2008 4 2 2 a d with a small number of colonies dating earlier overall the peak ages of mortality are significantly correlated with maximum sea surface temperature anomalies despite potential sampling bias the frequency of mortality increased dramatically post 1980 these observations are similar to the results reported for the southern south china sea high resolution measurements of sr ca and mg ca obtained from a well preserved sample that died in 1994 6 2 3 revealed that the time of death occurred at the peak of sea surface temperatures sst during the austral summer in contrast sr ca and mg ca analysis in two colonies dated to 2006 9 3 0 and 2008 3 2 0 suggest that both died after the austral winter an increase in sr ca ratios and the presence of low mg calcite cements as determined by sem and elemental ratio analysis in one of the colonies was attributed to stressful conditions that may have persisted for some time prior to mortality for both colonies however the timing of mortality coincides with the 4th and 6th largest flood events reported for the burdekin river in the past 60 years implying that factors associated with terrestrial runoff may have been responsible for mortality our results show that a combination of u th and elemental ratio geochemistry can potentially be used to precisely and accurately determine the timing and season of mortality in modern massive porites corals for reefs where long term monitoring data are absent the ability to reconstruct historical events in coral communities may prove useful to reef managers by providing some baseline knowledge on disturbance history and associated drivers 2014 elsevier ltd all rights reserved

the spatial distribution and annual cycle of upper ocean thermohaline structure 1 observations of the spatial distribution and persistence of thermohaline structure are presented and show how advection and diffusion affect a passive tracer more than two years of underwater glider observations in the central subtropical north pacific showed thermohaline variability over horizontal scales from 5 to 1300 km thermohaline fluctuations along isopycnals spice fluctuations were elevated in layers throughout the water column with the largest fluctuations near the surface and subtropical frontal regions fluctuations were uncorrelated between the layers but stirred by the same velocity field spice variance had local extrema in the vertical because of differences in source water properties and the influence of neighboring water masses spice variance spanned about three orders of magnitude along deeper isopycnals with larger variance where different water masses met and where velocity and vorticity variance were elevated horizontal wave number spectra of spice had slopes of 2 everywhere in the upper 1000 m submesoscale spice fluctuations had slopes in physical space near the ratio of the coriolis parameter to the buoyancy frequency f n consistent with predictions of quasi geostrophic theory in the mixed layer thermohaline structure had a significant annual cycle with smaller interannual differences thermohaline fluctuations left behind during restratification and isolated from the mixed layer decayed with time because of diffusion along isopycnals horizontal diffusivity estimates in the remnant mixed layer were 0 4 m2 s 1 at 15 28 km wavelengths and 0 9 m2 s 1 at 35 45 km wavelengths

episodic circulation and exchange in a wave driven coral reef and lagoon system we examined the role of wave driven circulation relative to wind and buoyancy forcing in a coral reef lagoon system circulation measurements in paopao bay moorea french polynesia during austral summer show the importance of waves in driving flows over the reef crest through the lagoon and out the reef pass tides were comparatively weak due to proximity to amphidromic points and exhibited an unusual spring neap cycle where the major lunar tide modulated the major solar tide and the overall tidal phase stayed approximately constant wind had only a secondary effect compared to surface waves a simple fluid mass balance indicated rapid flushing of the shallow back reef and export through the reef pass and a reef capture zone width of 2 3 km the reef pass circulation dynamics exhibited two layer baroclinic exchange flow when waves were small which was suppressed during large wave events the unusually weak tidal forcing provided an opportunity to more closely investigate wave driven circulation dynamics as expected theoretically there was a wave driven setup of the free surface across the shallow lagoon which drove a highly frictional flow evident by a large drag coefficient cp 0 1 diverging from extant theory the observed setup varied strongly with significant wave height and period overall the circulation and exchange between this coral reef system and the adjacent open ocean were largely determined by episodic remote forcing events and differed significantly from periodic tidal exchange mechanisms

wave set up on coral reefs 1 set up and wave generated flow on an idealised two dimensional horizontal reef wave set up may be significant in determining water levels on coral reefs particularly in microtidal environments and hence is an important factor for the design of reef top structures and for the stability of reef top islands laboratory experiments have been made on a two dimensional model of an idealised horizontal reef under two different conditions corresponding to a fringing reef or closed lagoon situation and a platform reef or open lagoon situation both wave set up on the reef top and the wave generated flow across the reef were measured and related to wave and tide level conditions all other factors being the same wave set up is greatest at low tide levels whereas wave generated flow is greater at higher tide levels the magnitude of the set up on a platform reef with a wave generated flow is less than on a fringing reef without any net flow by an amount equal to the velocity head of the flow across the reef dimensionless parameters ghrt o and q gho3 are found to be functions of relative submergence parameters hrho or r hr ho for values of ghr hr ho 1 waves break on the reef top and radiation stress theory can be used to calculate set up for ghr hr ho 0 7 waves break on the reef face and set up is determined by broadcrested weir control at the reef edge the symbols are defined as follows g is gravitational acceleration hr is still water depth over horizontal reef top ho is offreef wave height equivalent deep water value q is discharge per unit length of reef edge t is wave period and ghr is maximum wave set up on reef top

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

exploring carbonate reef flat hydrodynamics and potential formation and growth mechanisms for motu abstract atolls which develop as reef building coral platforms extend to near sea level typically consist of a shallow reef flat encircling a central lagoon often sub aerial islets known as motu or reef islands consisting of sand gravel and coral detritus can be found perched atop the reef flat here we use hydrodynamic numerical modeling xbeach to better understand the role of waves and wave driven currents on the reef flat and the processes driving motu formation and evolution by differing representative reef flat geometry e g width and water depth we investigate the effects of varying wave climate on hydrodynamics and resultant bed shear stresses across the reef flat model results suggest that as a reef flat shallows bed shear increases then after passing a critical value decreases again using these results we hypothesize that reef flats should attain a critical water depth just at the threshold for sediment mobilization resulting in a constant depth reef flat in both abrasional and depositional settings as reef flats widen prograding into the back reef lagoon shear stress decreases across the flat with a minimum in shear stress arising approximately midway on the reef flat motu formation would be expected to initiate at this mid flat nucleation site either from a storm when coarse sediment is mobilized and deposited or gradually as the reef flat widens a mid flat deposit need not be subaerial to form a motu sediment piled shallower than the critical depth would continue to accumulate once a motu is present reef flat shear stress directions reverse and the motu shoreline should prograde seawards until reaching a relatively narrow critical reef flat width 200 m together these results suggest that reef flats and motu spatially self organize through a series of morphodynamic feedbacks

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

wave transformation and shoreline water level on funafuti atoll tuvalu the influence of sea swell ss waves infragravity ig waves and wave setup on maximum runup rmax is investigated across different tidal stages on fatato island funafuti atoll tuvalu field results illustrate that ss waves are tidally modulated at the shoreline with comparatively greater wave attenuation and setup occurring at low tide versus high tide a shoreward increase in ig wave height is observed across the 100 m wide reef flat at all tidal elevations with no tidal modulation of ig wave height at the reef flat or island shoreline a 1 d shock capturing green naghdi solver is used to replicate the field deployment and analyze rmax model outputs for ss wave height ig wave height and setup at the shoreline match field results with model skill 0 96 model outputs for rmax are used to identify the temporal window when geomorphic activity can occur on the beach face during periods of moderate swell energy waves can impact the beach face at spring low tide due to a combination of wave setup and strong ig wave activity under mean wave conditions the combined influence of setup ig waves and ss waves results in interaction with island sediment at midtide at high tide ss and ig waves directly impact the beach face overall wave activity is present on the beach face for 71 of the study period a significantly longer duration than is calculated using mean water level and topographic data

on subinertial flow in submarine canyons effect of geometry shelf break canyons on the west coast of canada and the united states have been observed to be regions of enhanced upwelling during southward currents compared to the surrounding shelf break most shelf break canyons from oregon north cross only part of the continental shelf cutting from the shelf break toward the coast but end on the continental shelf well below the mixed layer juan de fuca canyon on the other hand cuts the continental shelf from the slope to and actually continues into the strait of juan de fuca this difference in geometry has a very strong effect on the subinertial flow around the canyon model canyon shapes which include convergent bathymetric contours are constructed and motivated for juan de fuca canyon and a typical shelf break canyon geostrophic analytic solutions show that the in canyon flow in juan de fuca canyon is generated by first order geostrophic dynamics whereas in the majority of canyons of which astoria is an example in canyon flow is generated by higher order effects this difference is postulated to lead to the observed very deep upwelling over juan de fuca canyon compared to more moderate episodic upwelling over astoria canyon

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

flow and mixing in juan de fuca canyon washington we report breaking internal lee waves strong mixing and hydraulic control associated with wind driven up canyon flow in juan de fuca canyon washington unlike the flow above the canyon rim which shows a tidal modulation typical on continental shelves the flow within the canyon is persistently up canyon during our observations with isopycnals tilted consistent with a geostrophic cross canyon momentum balance as the flow encounters a sill near the canyon entrance at the shelf break it accelerates significantly and undergoes elevated mixing on the upstream and downstream sides of the sill on the downstream side a strong lee wave response is seen with displacements of o 100 m and overturns tens of meters high the resulting diffusivity is o 10 2 m2 s 1 sufficient to substantially modify coastal water masses as they transit the canyon and enter the salish sea estuarine system

internal tides in monterey submarine canyon abstract the m2 internal tide in monterey submarine canyon is simulated using a modified version of the princeton ocean model most of the internal tide energy entering the canyon is generated to the south on sur slope and at the head of carmel canyon the internal tide is topographically steered around the large canyon meanders depth integrated baroclinic energy fluxes are up canyon and largest near the canyon axis up to 1 5 kw m 1 at the mouth of the upper canyon and increasing to over 4 kw m 1 around monterey and san gregorio meanders the up canyon energy flux is bottom intensified suggesting that topographic focusing occurs net along canyon energy flux decreases almost monotonically from 9 mw at the canyon mouth to 1 mw at gooseneck meander implying that high levels of internal tide dissipation occur the depth integrated energy flux across the 200 m isobath is order 10 w m 1 along the majority of the canyon rim but increases by over an order of magnitude near the canyon head where internal ti

wave dynamics of a pacific atoll with high frictional effects we report field measurements of waves and currents made from september 2011 to july 2014 on palmyra atoll in the central pacific that were used in conjunction with the swan wave model to characterize the wave dynamics operant on the atoll our results indicate that wave energy is primarily from the north during the northern hemisphere winter and from the south in the northern hemisphere summer refraction of waves along the reef terraces due to variations in bathymetry leads to focusing of waves in specific locations bottom friction modeled with a modified bottom roughness formulation is the significant source of wave energy dissipation on the atoll a result that is consistent with available observations of wave damping on palmyra indeed modeled wave dissipation rates from bottom friction are on average larger than dissipation rates due to breaking and are an order of magnitude larger than what has been observed on other less geometrically complex reefs a result which should be corroborated with future in situ measurements the swan wave model with a modified bottom friction formulation better predicts bulk wave energy properties than the existing formulation at our measurement stations the near bed squared velocity a proxy for bottom stress shows strong spatial variability across the atoll and exerts control over geomorphic structure and benthic community composition

calculating sediment trapping efficiencies for reservoirs in tropical settings a case study from the burdekin falls dam ne australia 1 the brune and churchill curves have long been used to predict sediment trapping efficiencies for reservoirs in the usa which typically experience winter and spring dominant runoff their suitability for reservoirs receiving highly variable summer dominant inflows has not previously been evaluated this study compares sediment trapping efficiency te data with the predictions of the two established curves for the burdekin falls dam a large reservoir in northern tropical australia which receives highly variable summer dominant runoff the measured te of the reservoir ranged between 50 and 85 and was considerably less than estimates using the brune and churchill curves over the 5 year study period we modified the original equations so that daily trapping can be calculated and weighted based on daily flow volumes this modification better accounts for shorter residence times experienced by such systems characterized by relatively high intraannual flow variability the modification to the churchill equation reasonably predicted sediment tes for the burdekin dam for four of the five monitored years and over the whole monitoring period we identified four key sediment particle classes 1 30 m which is almost totally 95 trapped in the dam reservoir we show that the modification to the churchill equation has broader application to predict reservoir te provided that daily flow data are available

setup and swash on a natural beach wave setup and swash statistics were calculated from 154 runup time series measured on a moderately steep beach under incident waves varying from 0 4 to 4 0 m significant wave height when scaled by the incident wave height setup swash height and total runup the sum of setup and half the swash height were found to vary linearly with the surf zone similarity parameter 0 h0 l0 1 2 the foreshore slope appeared the appropriate value for the calculation of 0 although the setup data showed some influence of an offshore bar at low tide for low irribaren numbers the swash height in the incident frequency band becomes saturated while for high irribaren numbers no such signs of saturations were seen thus the infragravity band appears to become dominant in the swash below some value of 0 for these data that value is approximately 1 75 although there is considerable scatter associated with that estimate

momentum balance across a barrier reef this paper reports on a combined experimental and numerical study dedicated to barrier reefs hydrodynamics a network of pressure sensors and velocity profilers has been deployed for more than 2 months over the ouano reef barrier new caledonia the primary aim of the study is to assess the relevance of the classical depth averaged momentum balance in such a complex and poorly documented environment the combined analysis of experimental and numerical measurements reveals a specific hydrodynamic behavior contrasting with sandy beaches and fringing reefs the cross reef current induced by wave breaking over the barrier reef plays an important role in the momentum budget in particular through friction processes the hydrodynamic behavior over the barrier reef is thus characterized by the progressive transition from a nearly classical beach type behavior on the forereef where the gradient of radiation stress is balanced by a barotropic pressure gradient associated to the wave setup to an open channel type regime dominated by frictional head loss the reef top wave setup shows a clear depth dependency mainly attributed to the forereef curvature during extreme wave events the measurements tend to indicate a transition toward a critical hydraulic regime above the reef top the numerical simulations involving a non hydrostatic wave resolving model coupled to a urn x wiley jgrc media jgrc23848 jgrc23848 math 0001 turbulence model highlight the vertical structure of the flow over the reef flat a classical log layer profile is observed in agreement with measurements while above the forereef an anticlockwise circulation develops under the breaking zone

the fleuve manche the submarine sedimentary features from the outer shelf to the deep sea fans bathymetric seismic and coring surveys have been carried out since the beginning of the 1990s on the outer shelf the slope and the continental rise of the western approaches margin most of the sedimentary features studied belong to a sedimentary system built up since the oligocene and fed by a palaeoriver the fleuve manche that flowed in the english channel during eustatic lowstands a geomorphological map details the spatial distributions of the palaeovalleys on the outer shelf the drainage basin like organised canyons on the slope and the channel levee and lobe complexes on the rise the obvious channel canyon connections and the assessed palaeovalley canyon links demonstrate that the fleuve manche was the single source for terrigeneous fluxes of the armorican deep sea fan when it was one of two sources of the celtic deep sea fan amongst parameters controlling the sedimentation two factors play a major role i subsidence controlled the possibly messinian riverine incision the turbidite activities during lowstands as well as marine infilling of the seawards part of the fleuve manche ii quaternary sedimentary supplies were influenced by the melting ice sheets and the connections with the onshore catchment basins copyright 2003 john wiley sons ltd

tidally discontinuous ocean forcing in bar built estuaries the interaction of tides infragravity motions and frictional control shallow bar built estuaries on wave dominated coasts in mediterranean climates experience an intermittent connection to the ocean in the presence of low streamflow their inlets may completely close as a result of nearshore sand transport but even in the open condition these inlets remain constricted extensive field measurements in the highly salt stratified pescadero estuary in northern california show that the shallow mouth causes these estuaries to experience discontinuous tidal forcing while the ocean and estuary are fully connected with near equal water levels tidal velocities are slow but infragravity motions in the nearshore induce large velocity oscillations within the estuary as the ocean tide falls infragravity forcing is cut off because the estuarine mouth is perched above the low tide ocean water level and ebbing velocities are set by bed friction observations reveal this oscillation between ocean forced and frictionally controlled conditions characterizes and sets estuarine hydrodynamics additional wave setup of the lagoon emphasizes the dependence of these estuaries on nearshore ocean conditions but the diurnal or semidiurnal retreat of the ocean below the mouth cuts off this nearshore influence so it too is tidally varying here we present detailed observations and a framework for understanding hydrodynamics in small shallow bar built estuaries

boussinesq type model for energetic breaking waves in fringing reef environments abstract the steep offshore slope and abrupt transition to a shallow lagoon are conducive to formation of energetic breaking waves in fringing reef environments this paper describes an extension of a one dimensional shock capturing boussinesq type model to account for these processes in two dimensions and the numerical formulation to facilitate adaptive time integration and code parallelization the governing equations contain the conservative form of the nonlinear shallow water equations to capture shock related hydraulic processes the finite volume method with a godunov type scheme provides a compatible conservative numerical procedure a two dimensional tvd total variation diminishing reconstruction procedure evaluates the flow variables on either side of the cell interface while a riemann solver supplies the flux and bathymetry source terms at the interface a well balanced scheme eliminates depth interpolation errors in the domain and preserves continuity across moving boundaries over irregular topography time integration of the governing equations evaluates the conserved variables which in turn provide the horizontal velocity components through systems of linear equations corresponding to series of one dimensional problems the application of the model to fringing reef environments is validated with laboratory experiments performed at oregon state university as well as field data collected in hawaii the model describes the flux dominated wave breaking processes through the riemann solver without predefined empirical energy dissipation and reproduces transitions between sub and supercritical flows as well as development of dispersive and infra gravity waves in the processes

flow modification and shelf slope exchange induced by a submarine canyon off the northeast spanish coast we present results from a study of the modifications induced by the short timescale response of a shelf break baroclinic jet to the presence of a downstream canyon the field site was the canyon of palamos located in the northeastern edge of spain to determine the short time scale variability of the area three intensive surveys were carried out at approximately 10 day intervals data indicate that the jet s location usually over the slope is subjected to significant onshore offshore displacements analysis of the data has shown the importance of a small scale temporal variability induced by river runoff and the climatology of the area this variability generates on off shore displacements of the jet which interacts with the head mouth of the canyon the different interactions with the canyon induced by these displacements produce different regimes of shelf slope exchange in the canyon domain that strongly modify the biomass patterns in the area