the prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models the accuracy of the predictions of distributed hydrological models must depend in part on the proper specification of flow pathways this paper examines some of the problems of deriving flow pathways from raster digital terrain data in the context of hydrological predictions using topmodel distributed moisture status is predicted in topmodel on the basis of spatial indices that depend on flow path definition the sensitivity of this index to flow path algorithm and grid size is examined for the case where the surface topography is a good indicator of local hydraulic gradients a strategy for the case where downslope subsurface flow pathways may deviate from those indicated by the surface topography is described with an example application

wave turbulence interactions in the upper ocean part ii statistical characteristics of wave and turbulent components of the random velocity field in the marine surface layer abstract we present the results of an analysis of field data collected by donelan who used a miniature drag sphere to measure velocities beneath wind waves on lake ontario linear statistical techniques are used to separate the velocity into wave and turbulent parts while we mostly aim at demonstrating the effects of surface wind waves on the statistical characteristics of the turbulent field in the upper mixed layer we also interpret several features of the data on the hags of recent theoretical results one of the most intriguing features of the turbulent velocity spectra so obtained is a large peak near the dominant wave frequency we review various possible explanation for this behavior although we prefer a model in which the turbulence is assumed frozen on the timescale of the waves this model requires no new dynamics and gives explicit formulae relating the dissipation rate to the magnitude of the spectral densities for high and low frequencies on this basis we have determined a dissipation leng

stone mobility and longshore transport at reshaping breakwaters abstract physical model tests have been performed in two different wave flumes to analyse the threshold of stone movement and quantify the frequency and length of displacements due to head on wave attacks at a reshaping breakwater data on stone movements were obtained from the observation of cumulative displacements at the end of each wave attack and from video records during the attack threshold conditions frequency of movement and displacement length are expressed as function of a suitably modified stability number a simple model is defined relating longshore transport due to oblique wave attack to stone mobility the transport model is based on the assumption that movement statistics is affected by obliquity only through the appropriate mobility index and that stones move during up and down rush in the direction of incident and reflected waves without any calibration results compare favourably with experimental data available in literature in the range of low mobility conditions where movement statistics was observed a calibration is provided in order to obtain an accurate transport formula valid in a wide mobility range i e for reshaping breakwaters and up to gravel beaches

a comparison of shear and buoyancy driven planetary boundary layer flows abstract planetary boundary layer pbl flows are known to exhibit fundamental differences depending on the relative combination of wind shear and buoyancy forces these differences are not unexpected in that shear instabilities occur locally while buoyancy force sets up vigorous thermals which result in nonlocal transport of heat and momentum at the same time these two forces can act together to modify the flow field in this study four large eddy simulations less spanning the shear and buoyancy flow regimes were generated two correspond to the extreme cases of shear and buoyancy driven pbls while the other two represent intermediate pbls where both forces are important the extreme cases are used to highlight and quantify the basic differences between shear and convective pbls in 1 flow structures 2 overall statistics and 3 turbulent kinetic energy tke budget distributions results from the two intermediate les cases are used to develop and verify a velocity scaling and a tke budget mode

sea surface roughness and drag coefficient as functions of neutral wind speed abstract near the surface it is commonly believed that the behavior of the turbulent atmospheric flow can be well described by a constant stress layer in the case of a neutrally stratified surface layer this leads to the well known logarithmic wind profile that determines the relation between near surface wind speed and magnitude of stress the profile is set by a surface roughness length which over the ocean surface is not constant rather it depends on the underlying ocean wave sea state for instance at the european centre for medium range weather forecasts this relation is parameterized in terms of surface stress itself where the scale is set by kinematic viscosity for light wind and a charnock parameter for strong wind for given wind speed at a given height the determination of the relation between surface wind and stress expressed by a drag coefficient leads to an implicit equation that is to be solved in an iterative way in this paper a fit is presented that directly expresses the

singular points at berm breakwaters scale effects rear round head and longshore transport abstract design aspects other than the profile development of the seaward side have been investigated in this paper aspects such as scale effects rear stability round head design and longshore transport have been treated here based on extensive test series on two different berm breakwater designs a first conclusion is that scale effects were not present in a 1 35 scale model compared with a 1 7 large scale model with wave heights up to 1 7 m a first design rule was assessed on the relationship between damage at the rear of a berm breakwater and the crest height wave height wave steepness and rock size tests on a berm breakwater head showed that enlarging the berm height at the crest and therefore the amount of rock in the berm was effective with regard to stability finally the onset of longshore transport due to oblique wave attack was studied and compared with literature formulae were derived for this onset of transport and also for the range of more serious transport up to longshore transport of coarse gravel

tangential stress beneath wind driven air water interfaces the detailed structure of the aqueous surface sublayer flow immediately adjacent to the wind driven air water interface is investigated in a laboratory wind wave flume using particle image velocimetry piv techniques the goal is to investigate quantitatively the character of the flow in this crucial very thin region which is often disrupted by microscale breaking events in this study we also examine critically the conclusions of okuda kawai toba 1977 who argued that for very short strongly forced wind wave conditions shear stress is the dominant mechanism for transmitting the atmospheric wind stress into the water motion waves and surface drift currents in strong contrast other authors have more recently observed very substantial normal stress contributions on the air side the availability of piv and associated image technology now permits a timely re examination of the results of okuda et al which have been influential in shaping present perceptions of the physics of this dynamically important region the piv technique used in the present study overcomes many of the inherent shortcomings of the hydrogen bubble measurements and allows reliable determination of the fluid velocity and shear within 200 m of the instantaneous wind driven air water interface the results obtained in this study are not in accord with the conclusions of okuda et al that the tangential stress component dominates the wind stress it is found that prior to the formation of wind waves the tangential stress contributes the entire wind stress as expected with increasing distance downwind the mean tangential stress level decreases marginally but as the wave field develops the total wind stress increases significantly thus the wave form drag represented by the difference between the total wind stress and the mean tangential stress also increases systematically with wave development and provides the major proportion of the wind stress once the waves have developed beyond their early growth stage this scenario reconciles the question of relative importance of normal and tangential stresses at an air water interface finally consideration is given to the extrapolation of these detailed laboratory results to the field where the present findings suggest that the sea surface is unlikely to become fully aerodynamically rough at least for moderate to strong winds

beach and dune erosion during storm surges this paper presents the set up and results of an extensive research programme concerning the erosion of coastal dunes during storm surges a large number of two dimensional and three dimensional mobile bed model tests has been carried out to investigate the process of dune erosion the state of art after a series of small scale tests is summarized attention is focussed on large scale tests carried out in the delta flume with random waves up to 2 m significant height sediment concentration and orbital velocity measurements are discussed the large scale tests have confirmed the validity of a modelling technique based on the dimensionless fall velocity parameter h tw the model results are being applied to check the safety of existing coastal dunes as a water retaining structure that has to protect the major part of the netherlands from inundation during storm surges

a review and assessment of longshore sediment transport equations for coarse grained beaches previous assessments of analytical longshore sediment transport formulae have been heavily biased towards sand sized sediment all have noted the shortage of high quality field data from coarse grained beaches against which to test predictions of longshore transport rates in this paper 12 existing formulae were identified as being potentially applicable for coarse grained sediments and predictions from these formulae are compared using a measured annual transport rate from a shingle beach and a concurrent hindcast wave climate two new empirical equations are also derived one from a numerical model calibrated against the same data set the other derived from field experiments on coarse grained beaches energetics based equations are found to give reasonable predictions of the shingle transport despite being derived for sand beaches in contrast those dimensional analysis type equations which had been validated using laboratory data grossly over predicted the measured transport rates the most accurate predictions were from formulae previously validated at sites similar to that used for this comparison and therefore require further testing against field data from dissimilar sites

airborne measurements of surface wind and slope statistics over the ocean abstractas reported in 1954 more than a half century ago c cox and w munk developed an empirical model of the slope distribution of ocean surface waves that has been widely used ever since to m

stability of the seaward slope of berm breakwaters abstract an extensive research on stability of statically and dynamically stable rock slopes and gravel beaches was reanalysed and focussed on berm breakwaters berm breakwaters are initially dynamically stable under severe wave attack but become more or less statically stable after reshaping the effects on the seaward profile of wave height period storm duration spectral shape initial slope rock size rock shape and grading water depth and angle of wave attack are described in a qualitative way relationships between these variables and the profile parameters are described leading to a computer program this program was verified with independent data of berm breakwaters from various international institutes the program showed to give a good prediction of the behaviour of the seaward slope of berm breakwaters and can therefore be used as a conceptual design tool

aeration due to breaking waves part i bubble populations abstract the population of bubbles produced by breaking waves in 10 m winds of up to 12 m s 1 is analyzed using calibrated images from a vertical pencil beam sonar system placed on the seabed near the dutch coast the structure in the images is parameterized and the volumetric bubble backscatter is inverted to yield bubble concentrations data were obtained at three acoustic frequencies with inversion effected by prescribing a bubble spectrum with two free variables leaving a redundant measurement to test the robustness of the model median concentrations may in this way be obtained up to the sea surface measurements are multiply regressed on wind and dominant wave variables bubbles penetrate to a depth of about a factor of 6 1 times the significant wave height hs where is the wave age or ratio of dominant wave phase speed to wind speed the measured mean bubble radius decreases weakly with depth unless waves are gently sloping at about 5 m 1 at 0 4 m the mean radius ranges from 30 to 80

a new formula for front slope recession of berm breakwaters the front slope stability of breakwaters with a homogeneous berm was studied in a large number of two dimensional model tests at aalborg university denmark the results are presented together with a new formula for prediction of the berm recession which is the most important parameter for describing the reshaping the formula has also been calibrated and validated against model test data from other researchers the significance of the new design formula is that it predicts berm recession much better than the existing methods especially in case of more stable structures

convective boundary layer structure in the presence of wind following swell the marine boundary layer is known to be influenced by fast long ocean swell waves travelling away from their generation area where they were initiated by momentum transferred to the ocean wave field during storms the atmospheric boundary layer during wind following swell and various stability states has been investigated using large eddy simulation les data the dominant energy containing motions in the near neutral atmospheric boundary layer over flat terrain are known to be dominated by near ground shear induced regions of high and low speed flow wind fields and momentum fluxes from les for swell dominated situations have been used to interpret field measurements suggesting that these motions are disrupted by effects related to the underlying wave field in the presence of swell waves statistical analysis and visualization are used to further describe the effects of stratification during swell for convective boundary layer winds and fluxes a mechanism for transport of momentum to the upper levels of the boundary layer is suggested from interpretation of les data coherent detached eddies from the directly wave induced motions near the surface are found to maintain an upward momentum transfer this mechanism is found to strengthen during stronger swell conditions and also during slightly convective conditions in this way it is argued that processes related to both the wave field and surface convection can have a significant influence on the global structure of neutral and convective boundary layers during swell this has implication for the turbulence length scales during wind following swell copyright 2012 royal meteorological society

bursting layer modeling based on the assumption of the averaged sea surface for strong wind driven currents abstract in the sea which is affected by strong winds that cover the water surface with wind wave breakers the sea surface layer called the bursting layer by authors is generated immediately below the mean water level for treatment of strong wind driven currents it is necessary to model the bursting layer correctly based on observed data however an essential difficulty occurs in that because of large water surface displacement caused by developed wind waves water particle velocities above the wave trough level cannot be measured continuously in the eulerian coordinates when measuring the velocity of strong wind driven currents consequently it is impossible to apply the reynolds average rule to the velocity field above the wave trough level in this study an experiment that uses a wind wave tank with a double bottom is performed to measure the horizontal velocity of currents driven only by the wind stress the vertical distribution up to the mean water level is determined to make its verticall

influence of toe berm geometry on stability of reshaping berm breakwaters reshaping berm breakwaters have been mainly designed and built for water depth less than 20 m in such conditions a toe structure may be needed to reduce bottom settlements and increase geotechnical stability in the loose subsoil condition also a toe berm can be deployed to reduce the berm recession and increase the stability of the reshaping berm breakwater especially in deep water although many studies have been conducted to study the effects of toe berms on stability of conventional breakwaters investigations on the influence of a toe berm on stability of reshaping berm breakwaters are rare this paper presents results of an experimental work that has been carried out to investigate the influence of a toe berm on the hydraulic stability of reshaping berm breakwaters in a 2d physical test setup in a wave flume a total of 207 tests were conducted to systematically examine the effects of toe berm configuration on the reshaping of berm breakwaters with three types of armor stones the experimental program covers the influence of different geometrical parameters of the toe berm on the berm recession under various sea state conditions comparing results of berm recession of the cases having a toe structure with the cases without a toe berm shows that the amount of berm recession with toe berm is considerably less than the analogous amount for without toe structure it is observed that an increasing toe berm width and thickness both have considerable influence on recession reduction however the toe depth has a relatively larger influence on recession than the toe width and the influence is larger for higher stability numbers it is concluded that a toe berm in front of reshaping berm breakwater not only does have influence on recession due to the depth influence and the changing wave conditions but also the toe depth has a direct influence on the reshaped profile by preventing the displaced rocks to fall down to deeper parts using the test results a new formula is developed for estimation of berm recession by taking into account the influence of the toe berm configuration given an acceptable stability number ho as a design criterion for reshaping berm breakwaters the present method predicts that the recession can be reduced up to 35 by the application of a toe berm thus the main berm width can be shortened resulting in reduction of the required armor stones volume so by using a smaller stone size for the toe berm the stability of the structure is secured and also the total cost of the breakwater can be reduced

wave driven wind jets in the marine atmospheric boundary layer abstract the interaction between ocean surface waves and the overlying wind leads to a transfer of momentum across the air sea interface atmospheric and oceanic models typically allow for momentum transfer to be directed only downward from the atmosphere to the ocean recent observations have suggested that momentum can also be transferred upward when long wavelength waves characteristic of remotely generated swell propagate faster than the wind speed the effect of upward momentum transfer on the marine atmospheric boundary layer is investigated here using idealized models that solve the momentum budget above the ocean surface a variant of the classical ekman model that accounts for the wave induced stress demonstrates that although the momentum flux due to the waves penetrates only a small fraction of the depth of the boundary layer the wind profile is profoundly changed through its whole depth when the upward momentum transfer from surface waves sufficiently exceeds the downward turbulent momen

introducing surface waves in a coupled wave atmosphere regional climate model impact on atmospheric mixing length 1 the marine atmospheric boundary layer is strongly influenced by the moving surface in the presence of surface waves the impact depends on the wave conditions and the interaction with the atmosphere previous studies using measurements as well as numerical simulations with large eddy simulations have shown that surface waves propagating faster than the wind swell alter the surface exchange as well as turbulence properties in the atmosphere this impact is here introduced in a coupled wave atmosphere regional climate model with a so called e l turbulence scheme where e is the turbulent kinetic energy and l is a mixing length a wave age dependent coefficient here called wmix is added to the mixing length in the turbulence parameterization this acts similarly to inducing additional convection with larger mixing length and increased eddy diffusivity when we have near neutral stratification and strong swell for shallow boundary layers the regional coupled climate model shows a larger response to the introduced wave coupling with increased near surface wind speed and smaller wind gradient between the surface and middle part of the boundary layer the impact for the studied areas is relatively minor for parameters averaged over 1 year but for limited periods and specific situations the impact is larger one could expect a larger impact in areas with stronger swell dominance we thus conclude that the impact of swell waves on the mixing in the boundary layer is not insignificant and should be taken into account when developing wave atmosphere coupled regional climate models or global climate models

hydraulic stability of reshaping berm breakwaters using the wave momentum flux parameter abstract an empirical new berm recession formula is derived based on the assumption that the maximum wave force causing armor movement and berm recession is proportional to the maximum wave momentum flux near the structure toe this concept introduces a more physics based first principles approach to estimate the berm recession recession seems well predicted by the new formula for reshaping berm breakwaters the results from this formula show a better estimation than earlier formulae used for estimating the berm recession

channel initiation and the problem of landscape scale since the 1940s it has been proposed that landscape dissection into distinct valleys is limited by a threshold of channelization that sets a finite scale to the landscape this threshold is equal to the hillslope length that is just shorter than that necessary to support a channel head a field study supports this hypothesis by showing that an empirically defined topographic threshold associated with channel head locations also defines the border between essentially smooth undissected hillslopes and the valley bottoms to which they drain this finding contradicts assertions that landscapes are scale independent and suggests that landscape response to changes in climate or land use depends on the corresponding changes in the threshold of channelization

correlations between interannual sst oscillations and modeled swell impacts on turbulent mixing abstractthe possibility of teleconnections between southern ocean swells and sea surface temperature sst anomalies on interannual time scales in the eastern pacific nino 3 region and southeastern indian ocean is investigated using numerical wave models two alternative parameterizations for swell dissipation are used it is found that swell dissipation in the models is not directly correlated with large interannual variations such as el nino southern oscillation enso or the indian ocean dipole iod however using one of the two swell dissipation parameterizations a correlation is found between observed sst anomalies and the modification of turbulent kinetic energy flux tkef by southern ocean swells due to the damping of short wind waves modeled reduction of tkef is opposite in phase to the sst anomalies in the nino 3 region indicating a potential positive feedback the modeled bimonthly averaged tkef reduction in the southeastern indian ocean is also well correlated with the iod mode

armor stability of hardly or partly reshaping berm breakwaters abstract this paper deals with stability of hardly or partly reshaping berm breakwaters a simple physical argument is used to derive a new stability formula based on the assumption that the maximum wave force causing damage of armor layer is proportional to the maximum wave momentum flux near the structure toe the main goal of the present paper is to provide an estimation technique based on this physical principle to predict the deformation of the front slope in terms of the eroded area the proposed method is verified by comparison with model test data it is found that by using the maximum wave momentum flux approach the damage to the front slope eroded area can be very well predicted moreover a simple method to estimate the eroded area based on measured or calculated berm recession rec and depth of intersection of reshaped and initial profile h f is presented the performance of the simple method based on measured data of rec and h f is better than the presented stability equation based on wave momentum flux parameter when using the best prediction formulae for recession and depth of intersection the simple method and the momentum flux stability equation provide similar uncertainty

impact of swell on the marine atmospheric boundary layer a model that describes the impact of swell on the marine atmospheric boundary layer is proposed the model is based on the two layer approximation of the boundary layer the near surface inner region and the outer region above the swell induced momentum and energy fluxes are confined within the inner region swell loses energy to the atmosphere and enhances the turbulent kinetic energy in the inner region the transfer of momentum results in acceleration or deceleration of the airflow near the surface following wind swell accelerates the flow which for a very low wind results in a swell driven wind opposite wind swell decelerates the airflow which for a steep swell could cause the reverse airflow the sea drag in the case of opposite wind swell is considerably enhanced as compared with the following wind swell case cross wind swell causes the rotation of the wind velocity vector with height which leads to the deviation of the turbulent stress vector from the wind velocity vector the impact of swell becomes more pronounced when the wind speed decreases or when the swell phase velocity increases in fact it is the wave age of the swell that characterizes the swell impact because the dimensionless wave induced fluxes of energy and momentum are proportional to the wave age parameter both fluxes are also proportional to the swell slope so that the swell impact is stronger for a steeper swell the model reproduces qualitatively and quantitatively the main experimental findings for the ocean swell the impact of swell on the sea drag is very pronounced for opposite wind swell is less pronounced for cross wind swell and is only at low wind speeds

evidence of energy and momentum flux from swell to wind abstractmeasurements of pressure near the surface in conditions of wind sea and swell are reported swell or waves that overrun the wind produces an upward flux of energy and momentum from waves to the wind and corresponding attenuation of the swell waves the estimates of growth of wind sea are consistent with existing parameterizations the attenuation of swell in the field is considerably smaller than existing measurements in the laboratory

a probabilistic approach for channel initiation 1 the channel head represents an important transition point from hillslope to fluvial processes there is a nonlinear threshold transition across the channel head with sediment transport much larger in channels than on hillslopes deterministic specific catchment area a thresholds for channel initiation sometimes dependent on slope s in the form of as c have been suggested in this paper the channel initiation problem is viewed probabilistically with a spatially variable probability of channel initiation that depends on slope specific catchment area and the probability distributions of median grain size surface roughness and excess rainfall rate the channel initiation threshold c is cast as a random variable to characterize the variability of as at channel heads using field measurements from the idaho batholith we show that median grain size measurements at each channel head explain a significant part of the observed variability of as we then characterize the variability of model inputs median grain size roughness and excess rainfall using probability distributions and show that the probability distribution of area slope threshold derived from these inputs matches the probability distribution of area slope thresholds measured at field channel head locations a gamma probability distribution provides a reasonable match to the distributions of area slope threshold measured and modeled at channel heads in our study area and in other published channel head data

the influence of swell on the atmospheric boundary layer under nonneutral conditions the anomalous phenomena induced by the prevailing swell at low wind speeds prevent a complete understanding of air sea interaction processes many studies have considered this complex problem but most have focused on near neutral conditions in this study the influence of the swell on the atmospheric boundary under nonneutral conditions was addressed by extending the turbulent closure models of makin and kudryavtsev and the monin obukhov similarity theory most monin and yaglom to the existence of swell and nonneutral conditions it was shown that wind profiles derived from these models were consistent with each other and both departed from the traditional most at low wind speeds a supergeostrophic jet appeared on the upper edge of the wave boundary layer which was also reported in earlier studies under nonneutral conditions the influence of buoyancy was significant the slope of the wind profile increased under stable conditions and became smoother under unstable conditions considering the effects of buoyancy and swell the wind stress derived from the model agreed quantitatively with the observations

vertical profiles of the wave induced airflow above ocean surface waves abstractan analysis of coherent measurements of winds and waves from data collected during the onr southern california 2013 socal2013 program from r p flip off the coast of southern california in

a case study of air sea interaction during swell conditions air sea interaction data from a situation with pronounced unidirectional swell have been analyzed measurements of turbulence at three levels 10 18 and 26 m above mean sea level together with directional wave buoy data from the site ostergarnsholm in the baltic sea were used the situation which lasted for 48 hours appeared in the aftermath of a gale the wind direction during the swell situation turned slowly within a 90 sector both during the gale phase and the swell phase the over water fetch was 150 km the wind speed during the swell phase was typically 4 m s 1 during the swell phase a wind maximum near or below the lowest wind speed measuring level 10 m was observed the net momentum flux was very small resulting in cd values 0 7 10 3 throughout the lowest 26 m covered by the tower measurements turbulence intensities in all three components remained high despite the low value of the kinematic momentum flux u w resulting in a reduction of the correlation coefficient for the longitudinal and vertical velocity from its typical value around 0 35 to between 0 2 and 0 and with some positive values at the higher measuring levels appearing abruptly at wave age c0 u10 equal to 1 2 turbulence spectra of the horizontal components were shown not to scale with height above the water surface in contrast to vertical velocity spectra for which such a variation was observed in the low frequency range in addition spectral peaks in the horizontal wind spectra were found at a frequency as low as 10 3 hz from a comparison with results from a previous study it was concluded that this turbulence is of the inactive kind being brought down from the upper parts of the boundary layer by pressure transport

trends in stability of dynamically stable breakwaters the reshaping of dynamically stable breakwaters was studied subject to variations in armour stone gradation and shape wave characteristics and duration of wave attack from head on waves in a two dimensional wave flume tests were undertaken at the coastal engineering research laboratory of queen s university kingston canada using irregular waves profiles of the structure during the various stages of reshaping were measured using a semi automatic profiler developed for this study the volume of stones and the initial berm width required for development of a stable profile along with the extent to which the toe of the structure progressed seaward were chosen as the characteristic parameters of the reshaped breakwater the results indicated that the toe width formed as a result of reshaping and the area of stones required for reshaping were dependent on the wave height gradation of the armour stone and duration of the storm the initial berm width required for reshaping was also found to be dependent on the wave height armour stone gradation percentage of rounded stones in the armour and the duration of the storm

on front slope stability of berm breakwaters abstract the short communication presents application of the conventional van der meer stability formula for low crested breakwaters for the prediction of front slope erosion of statically stable berm breakwaters with relatively high berms the method is verified burcharth 2008 by comparison with the reshaping of a large norwegian breakwater exposed to the north sea waves as a motivation for applying the van der meer formula a discussion of design parameters related to berm breakwater stability formulae is given comparisons of front erosion predicted by the use of the van der meer formula with model test results including tests presented in sigurdarson and van der meer 2011 are discussed a proposal is presented for performance of new model tests with the purpose of developing more accurate formulae for the prediction of front slope erosion as a function of front slope relative berm height relative berm width method of armour stone placement and hydraulic parameters the formulae should cover the structure range from statically stable berm breakwaters to conventional double layer armoured breakwaters

characterization of turbulent airflow over evolving water waves in a wind wave tank 1 results of an experimental investigation of the turbulent boundary layer in airflow over evolving young wind waves are presented the experiments were conducted in a laboratory wind wave flume consisting of a closed loop wind tunnel capable of generating wind speed that may exceed 15 m s atop of a 5 m long wave tank simultaneous measurements of mean wind velocity and of instantaneous fluctuations of the horizontal and vertical air velocity components were carried out along the test section at different airflow rates and at numerous heights above the highest wave instantaneous surface elevation at the air sensors location was simultaneously recorded the friction velocities at all locations and for all airflow rates were determined by two independent methods by fitting the logarithmic velocity profiles and by extrapolating the measured reynolds shear stresses to mean water surface level the variation with height and along the test section of the fluctuations of two velocity components in the mean flow and in the vertical directions was also studied and the results compared with flow behavior over rough and smooth plates wave induced airflow parameters were then investigated by application of cross spectral analysis results on the vertical extent of wave induced boundary layer on the phase relation between the wave induced velocity fluctuations and the surface elevation as well as on the wave induced reynolds shear stress are reported

the southern ocean waves experiment part i overview and mean results the southern ocean waves experiment sowex was an international collaborative air sea interaction experiment in which a specially instrumented meteorological research aircraft simultaneously gathered atmospheric turbulence data in the marine boundary layer and sea surface topography data over the southern ocean for a wide range of wind speeds the aim was to increase present knowledge of severe sea state air sea interaction this first paper presents an overview of the experiment and a detailed discussion of the methodology and mean results a companion paper describes the findings on variability of the wind speed and wind stress and their relationship to variations in the underlying sea surface roughness

observations of mean and wave orbital flows in the ocean s upper centimetres sophisticated measurements of fluid velocity near to an undulating air water boundary have traditionally been confined to the laboratory setting developments in camera technology and the opening of novel modes of analysis have allowed for sensitive measurements of the current profile in the ocean s uppermost layer taking advantage of the research platform r p flip as a laboratory at sea here we present first of their kind thermal and polarimetric camera based observations of wave orbital velocities and mean shear flows in the upper centimetres of the ocean surface layer measurements reveal a well defined logarithmic layer as seen in laboratory measurements and described by classical surface layer theory however substantial spread of observations is found at low levels of wind forcing where the stokes drift of swell may have a substantial impact on the near surface current profile a novel application of short time window fourier transforms allows for the estimation of near surface wave orbital velocity magnitudes these are found to be in general agreement with the prescriptions of linear wave theory although observations diverge from theory at high levels of wind forcing where the interface is subject to surface wave breaking finally the surface gravity wave phase coherent short wave growth is presented and discussed in the context of hydrodynamic wave and airflow modulation

observational study of marine atmospheric boundary layer characteristics during swell abstract by combining simultaneous data from an instrumented air sea interaction spar asis buoy and a 30 m tower profiles of wind and turbulence characteristics have been obtained at several heights from about 1 to 30 m above the water surface during swell conditions five cases formed as averages over time periods ranging from 2 5 to 9 5 h representing quasi steady conditions have been selected they represent a range of typical wave age and include wind following swell cases and cross swell cases for relatively large wave age the wind profile exhibits a well defined maximum in the height range 5 10 m for more modest wave age this maximum turns into a sharp knee in the wind profile below the maximum or knee the wind increases rapidly with height above that point the wind is very nearly constant up to the highest measuring level on the tower 30 m analysis of balloon data from one day with swell indicates that the layer with constant wind in fact extends to the top of the boundary layer

wave induced wind in the marine boundary layer recent field observations and large eddy simulations have shown that the impact of fast swell on the marine atmospheric boundary layer mabl might be stronger than previously assumed for low to moderate winds blowing in the same direction as the waves swell propagates faster than the mean wind the momentum flux above the sea surface will then have two major components the turbulent shear stress directed downward and the swell induced stress directed upward for sufficiently high wave age values the wave induced component becomes increasingly dominant and the total momentum flux will be directed into the atmosphere recent field measurements have shown that this upward momentum transfer from the ocean into the atmosphere has a considerable impact on the surface layer flow dynamics and on the turbulence structure of the overall mabl the vertical wind profile will no longer exhibit a logarithmic shape because an acceleration of the airflow near the surface will take place generating a low level wave driven wind maximum a wind jet as waves propagate away from their generation area as swell some of the wave momentum will be returned to the atmosphere in the form of wave driven winds a model that qualitatively reproduces the wave following atmospheric flow and the wave generated wind maximum as seen from measurements is proposed the model assumes a stationary momentum and turbulent kinetic energy balance and uses the dampening of the waves at the surface to describe the momentum flux from the waves to the atmosphere in this study simultaneous observations of wind profiles turbulent fluxes and wave spectra during swell events are presented and compared with the model in the absence of an established model for the linear damping ratio during swell conditions the model is combined with observations to estimate the wave damping for the cases in which the observations showed a pronounced swell signal and almost no wind waves the agreement between observed and modeled wind profiles is remarkably good the resulting attenuation length is found to be relatively short which suggests that the estimated damping ratios are too large the authors attribute this at least partly to processes not accounted for by the model such as the existence of an atmospheric background wind in the model this extra momentum must be supplied by the waves in terms of a larger damping ratio

a physically based model for calculating contributing area on hillslopes and along valley bottoms 1 most existing methods of calculating contributing area are unable to accurately model the pattern of contributing area on hillslopes and along valley bottoms this paper describes a new flow algorithm the adjustable dispersion routing algorithm adra rather than calculating contributing area using predetermined flow characteristics that are insensitive to location in the landscape adra predicts channel location and adjusts flow characteristics accordingly adra increases the degree of flow divergence downslope from divides until a channel head is detected channel head locations are estimated on the basis of a user defined threshold of an area slope function therefore the algorithm overcomes the problems of aggregated flow on hillslopes and divergent flow along valley bottoms the pattern of catchment area produced by adra was compared with similar patterns calculated using a similar flow algorithm for a variety of natural landscapes adra produced patterns of contributing area that were more consistent with the theory of channel initiation

flow separation and resuspension beneath shoaling nonlinear internal waves 1 laboratory observations are presented showing the structure and dynamics of the turbulent bottom boundary layer beneath nonlinear internal waves nliws of depression shoaling upon sloping topography the adverse pressure gradient beneath the shoaling waves causes the rear face to steepen flow separation to occur and wave induced near bottom vortices to suspend bed material the resuspension is directly attributed to the near bed viscous stress and to near bed patches of elevated positive reynolds stress generated by the vortical structures these results are consistent with published field observations of resuspension events beneath shoaling nliws elevated near bed viscous stresses are found throughout the domain at locations that are not correlated to the resuspension events near bed viscous stress is thus required for incipient sediment motion but is not necessarily a precursor for resuspension resuspension is dependent on the vertical velocity field associated with positive reynolds stress and is also found to occur where the mean wave averaged vertical velocity is directed away from the bed the results are interpreted by analogy to the eddy stress and turbulent bursting resuspension models developed for turbulent channel flows

on rubble mound breakwaters of composite slope abstract the geometrical properties of the armor layer of rubble mound breakwaters were investigated by observations made on two cases the first case is a laboratory scaled model of natural rock designed with a composite slope the second is a breakwater in the sea constructed with a uniform slope of tetrapods in both cases the cross section underwent changes resulting in an apparently stable profile of composite slope this implied that for stability the optimal armour layer should be of composite slope the general nature of this profile was implied by the geometrical similarity between the two cases which were basically so different

wave follower field measurements of the wind input spectral function part ii parameterization of the wind input abstract nearly all of the momentum transferred from wind to waves comes about through wave induced pressure acting on the slopes of waves known as form drag direct field measurements of the wave induced pressure in airflow over water waves are difficult and consequently rare those that have been reported are for deep water conditions and conditions in which the level of forcing measured by the ratio of wind speed to the speed of the dominant spectral peak waves is quite weak u10 cp 3 the data reported here were obtained over a large shallow lake during the australian shallow water experiment auswex the propagation speeds of the dominant waves were limited by depth and the waves were correspondingly steep this wider range of forcing and concomitant wave steepness revealed some new aspects of the rate of wave amplification by wind the so called wind input source function in the energy balance equation for wind driven water waves it was found that the exponential growth rate parameter fra

a global perspective on langmuir turbulence in the ocean surface boundary layer the turbulent mixing in thin ocean surface boundary layers osbl which occupy the upper 100 m or so of the ocean control the exchange of heat and trace gases between the atmosphere and ocean here we show that current parameterizations of this turbulent mixing lead to systematic and substantial errors in the depth of the osbl in global climate models which then leads to biases in sea surface temperature one reason we argue is that current parameterizations are missing key surface wave processes that force langmuir turbulence that deepens the osbl more rapidly than steady wind forcing scaling arguments are presented to identify two dimensionless parameters that measure the importance of wave forcing against wind forcing and against buoyancy forcing a global perspective on the occurrence of wave forced turbulence is developed using re analysis data to compute these parameters globally the diagnostic study developed here suggests that turbulent energy available for mixing the osbl is under estimated without forcing by surface waves wave forcing and hence langmuir turbulence could be important over wide areas of the ocean and in all seasons in the southern ocean we conclude that surface wave forced langmuir turbulence is an important process in the osbl that requires parameterization citation belcher s e et al 2012 a global perspective on langmuir turbulence in the ocean surface boundary layer geophys res lett 39 l18605 doi 10 1029 2012gl052932

stable profiles of reshaping breakwaters with a berm below the water level an experimental study of breakwaters with an initially horizontal berm below the swl was conducted in a wave flume the study aimed at defining the shape and geometrical features of the adjusted stable profiles and at confirming the existence of a zone of non significant profile adjustment below the initially flat and horizontal slope

a new formula for the sea state and structural parameters influencing the stability of homogeneous reshaping berm breakwaters the berm recession of a reshaping berm breakwater has a very important role for the stability of this kind of structure based on a 2d experimental modeling method in a wave flume the recession of the berm due to sea state and structural parameters has been studied irregular waves with a jonswap spectrum were used a total of 215 tests have been performed to cover the impact of sea state conditions such as wave height wave period storm duration and water depth at the toe of the structure and structural parameters such as berm elevation from still water level berm width and stone diameter on berm recession in this paper first a new dimensionless parameter is introduced to evaluate the combined effect of wave height and wave period on berm recession using results of the experimental work then a formula that includes some sea state and structural parameters is derived using the new dimensionless parameter for estimating the berm recession a comparison is made between the estimated berm recessions by this new formula and formulae given by other researchers to show the preference of using the new dimensionless parameter the comparison shows that the recession estimated by the new formula has not only a better correlation with the present experimental data but also has an improved correlation with other experimental results within the range of parameters tested outside the range of parameters tested the lykke andersen 2006 formula performed best

stone movement on a reshaped profile physical model tests were carried out aiming to provide information on armor stone movements in a berm breakwaters the following items were examined displacement threshold frequency and length of stone displacements data were obtained from the observation of cumulative displacements at the end of each wave attack and from video records during the attacks basic statistical analysis was performed threshold conditions moving frequency and cumulative displacements are expressed as function of a modified mobility number as stone mobility increases with both wave height and wave period information on mobility and displacement is eventually used to estimate longshore transport and abrasion the longshore model is based on the assumption that stones move during up and down rush in the direction of incident and reflected waves the model compares favourably with experimental existing results the abrasion model is based on a proportionality assumption between abrasion volume and abrasion work the proportionality coefficient characterizing the stone material resistance to abrasion is derived from latham and poole mill abrasion tests

the transition from downward to upward air sea momentum flux in swell dominated light wind conditions fifteen hours of consecutive swell data from the experiment flux etat de la mer et teledetection en condition de fetch variable fetch in the mediterranean show a distinct upward momentum flux

boundary layer development and gravity waves in conventionally neutral wind farms while neutral atmospheric boundary layers are rare over land they occur frequently over sea in these cases they are almost always of the conventionally neutral type in which the neutral boundary layer is capped by a strong inversion layer and a stably stratified atmosphere aloft in the current study we use large eddy simulations les to investigate the interaction between a large wind farm that has a fetch of 15 km and a conventionally neutral boundary layer cnbl in typical offshore conditions at the domain inlet we consider three different equilibrium cnbls with heights of approximately 300 m 500 m and 1000 m that are generated in a separate precursor les we find that the height of the inflow boundary layer has a significant impact on the wind farm flow development first of all above the farm an internal boundary layer develops that interacts downwind with the capping inversion for the two lowest cnbl cases secondly the upward displacement of the boundary layer by flow deceleration in the wind farm excites gravity waves in the inversion layer and the free atmosphere above for the lower cnbl cases these waves induce significant pressure gradients in the farm both favourable and unfavourable depending on location and case a detailed energy budget analysis in the turbine region shows that energy extracted by the wind turbines comes both from flow deceleration and from vertical turbulent entrainment though turbulent transport dominates near the end of the farm flow deceleration remains significant i e up to 35 of the turbulent flux for the lowest cnbl case in fact while the turbulent fluxes are fully developed after eight turbine rows the mean flow does not reach a stationary regime a further energy budget analysis over the rest of the cnbl reveals that all energy available at turbine level comes from upwind kinetic energy in the boundary layer in the lower cnbl cases the pressure field induced by gravity waves plays an important role in redistributing this energy throughout the farm overall in all cases entrainment at the capping inversion is negligible and also the work done by the mean background pressure gradient arising from the geostrophic balance in the free atmosphere is small

rock stability of rubble mound breakwaters with a berm the stability of rock slopes with a horizontal berm has been studied by means of physical model tests this paper is focussed on the rock slope stability of the slopes above and below the berm by applying a berm the rock size can be reduced compared to the required rock size for a straight slope without a berm this reduction can be significant for the slope above the berm the influence of the slope angle 1 2 and 1 4 the width of the berm the level of the berm and the wave steepness have been investigated based on the test results prediction formulae have been derived to quantify the required rock size for rubble mound breakwaters with a berm

boundary layer turbulence over surface waves in a strongly forced condition les and observation abstractthe impact of sea state on air sea momentum flux or wind stress is a poorly understood component of wind wave interactions particularly in high wind conditions the wind stress and mean

a laboratory study of spilling breakers in the presence of light wind and surfactants spilling breaking waves in the presence of light wind and surfactants are studied experimentally in a wind wave tank the breaking waves are mechanically generated with a single wave maker motion that produces a weak spilling breaker in clean water without wind separate experiments are performed with the same wave maker motion at different low wind speeds in clean water and in water with various concentrations of triton x 100 soluble surfactant the crest profiles of the waves along the center plane of the tank are measured with a laser induced fluorescence lif technique that utilizes a high speed camera in clean water with wind speeds lower than 2 3 m s the minimum wind speed of wind generated waves for clean water in our tank the breaking of the waves is initiated with a similar bulge capillary waves pattern on the forward face of the wave crest as reported in duncan et al 1999 when the wind speed is above 3 m s wind waves are generated the wind waves strongly affect the breaking process of the mechanically generated waves it is found that the bulge capillary waves pattern is independent of the wind but is dramatically affected by surfactants the slope of the back face of the wave crest decreases with increasing wind speed at the moment of incipient breaking the distances between the leading edge of the bulge called the toe and the highest point of the wave crest in all cases are linearly proportional to the surface wind drift after the fluid in the bulge slides down the front face of the wave the maximum horizontal distance of the toe away from the crest increases as the wind speed increases this article is protected by copyright all rights reserved

comparison of single and multiple flow direction algorithms for computing topographic parameters in topmodel single flow direction sfd and multiple flow direction mfd algorithms were used to compute the spatial and statistical distributions of the topographic index used in the watershed model topmodel an sfd algorithm assumes that subsurface flow occurs only in the steepest downslope direction from any given point an mfd algorithm assumes that subsurface flow occurs in all downslope directions from any given point the topographic index in topmodel is in a tan 3 where in is the napierian logarithm a is the upslope area per unit contour length and tan 3 is the slope gradient the in a tan 3 distributions were computed from digital elevation model dem data for locations with diverse topography in arizona colorado louisiana nebraska north carolina oregon pennsylvania tennessee vermont and virginia the means of the in a tan 3 distributions were higher when the mfd algorithm was used for computation compared to when the sfd algorithm was used the variances and skews of the distributions were lower for the mfd algorithm compared to the sfd algorithm the differences between the mfd and sfd algorithms in the mean variance and skew of the in a tan 3 distribution were almost identical for the various dems and were not affected by dem resolution or watershed size topmodel model efficiency and simulated flow paths were affected only slightly when the in a tan 3 distribution was computed with the sfd algorithm instead of the mfd algorithm any difference in the model efficiency and simulated flow paths between the sfd and mfd algorithms essentially disappeared when the model was calibrated by adjusting subsurface hydraulic parameters

on berm breakwaters stability scour overtopping abstract experimental studies on the stability of multilayer berm breakwaters have been carried out two stone mass densities have been used the results have been compared with the results of homogenous berm breakwaters and with other results of multilayer berm breakwaters an equation for the berm recession for homogenous berms has been derived including the effect of stone gradation and water depth erosion at and erosion protection of berm breakwaters have been investigated as well as wave overtopping discharges

scour around coastal structures a summary of recent research abstract this paper summarizes the results of the european union marine science and technology eu mast iii project scour around coastal structures scarcost the summary is presented under three headings 1 introduction 2 flow and scour processes with the subheadings flow and scour processes around vertical cylinders flow and scour processes at detached breakwaters flow and scour processes at submerged breakwaters and the effect of turbulence on sediment transport and 3 sediment behaviour close to the structure with the subheadings field measurement and analysis of wave induced pore pressures and effective stresses around a bottom seated cylinder non linear soil modelling with respect to wave induced pore pressures and gradients wave induced pressures on the bottom for non linear coastal waves including also wave kinematics development of a numerical model linear soil modelling to calculate wave induced pore pressures the effect of liquefaction on sediment transport penetration of blocks in non consolidated fine soil and cyclic stiffness of loose sand the paper also includes a discussion of the role of scale effects in laboratory testing and the applicability of the results obtained in supporting engineering design

use of conventional stability parameters during swell the situation with swell is of climatological importance over the baltic sea since swell is present during as much as 40 of the time in this study two periods with unstable and two periods with stable stratification and wind following swell are investigated data are taken at a small flat island in the baltic sea during unstable stratification the turbulent structure shows great resemblance to the free convective boundary layer and scales with the boundary layer height since surface heat flux is too small to support the high levels of turbulence present inactive turbulence is probably the dominating source for the stably stratified layer there are smaller differences between data with and without swell the turbulence is mainly transported upward into the atmosphere with the aid of pressure fluctuations induced by the waves for most of the data with swell the gradients are smaller than for growing sea during unstable conditions the wind gradients are negative indicating the presence of a wave driven wind the gradients increase with increasing height above the surface the drag coefficient is smaller than is usually found for both stable and unstable stratification and varies very little with wind and stratification there are only small variations in the heat transfer coefficients with changing stratification but they are significantly different for stable and unstable stratification

investigating a floodplain scaling relation using a hydrogeomorphic delineation method 1 floodplains are critical landscape features that are highly distinguished from neighboring uplands in terms of their hydrologic geomorphologic biogeochemical and ecological processes thus an essential step in floodplain studies is the determination of the lateral floodplain extent and its variability within a basin recent advances in topographic mapping and gis based analysis provide a means for developing automated techniques to determine floodplain extent in this study we propose a hydrogeomorphic floodplain delineation which links a simplified inundation algorithm with the river basin properties we utilize the method to investigate the physical controls on floodplain formation as captured by scaling relations between floodplain width and contributing area our hypothesis is that an efficient delineation grounded in hydrogeomorphic theory can improve our understanding of floodplain geometry across a range of conditions we test the method for two distinct watersheds a humid catchment in italy and an ephemeral basin in new mexico and note the existence of power law scaling of the floodplain width after averaging over stream orders an analysis of the algorithm parameters is conducted to identify possible limitations further systematic tests are needed to establish the generality of the floodplain scaling and its control on floodplain processes

swell impact on wind stress and atmospheric mixing in a regional coupled atmosphere wave model over the ocean the atmospheric turbulence can be significantly affected by swell waves change in the atmospheric turbulence affects the wind stress and atmospheric mixing over swell waves in thi

local scour at roundhead and along the trunk of low crested structures abstract this paper summarizes the results of an experimental study on scour around submerged breakwaters the objective of the study is to make a systematic study of scour around low crested structures submerged breakwaters both the trunk scour and the roundhead scour have been investigated the breakwater models have a side slope of 1 1 5 to substantiate scour measurements velocity measurements also were made the latter data were used to obtain steady streaming in front of the breakwater regarding the trunk scour study the experiments indicated that substantial scour may occur at the toe of the structure this is irrespective of whether the breakwater is impermeable or porous the scour data although very limited indicated that the scour depth is in the same order of magnitude as in the case of emerged breakwaters the trunk experiment further showed that scour deposition bathymetry does not exhibit the pattern experienced in the case of emerged breakwaters where the scour and deposition areas are correlated with the nodal and antinodal points of the standing wave in front of the structure furthermore it was found that scour occurs not only at the offshore side of the breakwater but also at the onshore side as for the roundhead scour study it was found that severe scour can be experienced at the roundhead the scour can occur both at the offshore side of the roundhead and at the back the one at the offshore side is caused by the combined effect of severe waves and the steady streaming and that at the back is caused by wave breaking wave overtopping it was found that the streaming induced scour is governed by the free board to wave height ratio f h and the keulegan carpenter number kc while the plunging breaker induced scour is governed by the free board to water depth ratio f h and the plunger parameter t w g h h tw being the wave period the maximum scour depth at the toe of the structure and the plan view extent of the scour hole are given in terms of the governing parameters the results from the present laboratory tests for the roundhead scour are compared with prototype observations undertaken in the present study recommendations are made for toe protection for both the trunk scour and the roundhead scour

digital elevation model networks demon a model of flow over hillslopes for computation of contributing and dispersal areas current algorithms for computing contributing areas from a rectangular grid digital elevation model dem use the flow routing model of o callaghan and mark 1984 which has two major restrictions 1 flow which originates over a two dimensional pixel is treated as a point source nondimensional and is projected downslope by a line one dimensional moore and grayson 1991 and 2 the flow direction in each pixel is restricted to eight possibilities we show that large errors in the computed contributing areas result for any terrain topography divergent convergent or planar we present a new model called digital elevation model networks demon which avoids the above problems by representing flow in two dimensions and directed by aspect demon allows computation of both contributing and dispersal areas demon offers the main advantage of contour based models e g moore et al 1988 the representation of varying flow width over nonplanar topography while having the convenience of using rectangular grid dems

the influence of armour stone gradation on dynamically stable breakwaters abstract dynamically stable or berm breakwaters are structures in which the armour layer is comprised of a wide range of stone sizes and undergoes reshaping in response to wave action as a result of this wave action a stable profile is achieved the effect of gradation of armour stones and the amount of rounded stones in the armour on dynamically stable breakwaters was assessed in a two dimensional wave flume a total of 52 series of tests were undertaken at the coastal engineering research laboratory of queen s university kingston canada using irregular waves profiles of the structure during the various stages of reshaping were measured using a semi automatic profiler developed for this study four gradations of armour stones were used giving a range in uniformity coefficient d 85 d 15 of 1 35 to 5 4 the core of the breakwaters was relatively permeable the volume of stones and the initial berm width required for development of a stable profile along with the extent to which the toe of the structure progressed seaward were chosen as representative parameters of the reshaped breakwater the results indicated that the toe width formed as a result of reshaping and the volume of stones required for reshaping were dependent on the gradation of the armour stone the initial berm width required for reshaping was also found to be dependent on the gradation and the percentage of rounded stones in the armour

stability of rubble mound slopes under random wave attack the objective of the present research project is to give new practical design formulae for rubble mound slopes under random wave attack the study is based upon a series of model tests more than two hundred tests have been performed in order to vary systematically all the relevant variables the main shortcomings in hudson type formulae have been solved as a result of the present series of investigations stability formulae are given which include the influence of wave period number of waves armour grading spectrum shape groupiness of waves and the permeability of the core

large eddy simulations and observations of atmospheric marine boundary layers above nonequilibrium surface waves abstract winds and waves in marine boundary layers are often in an unsettled state when fast running swell generated by distant storms propagates into local regions and modifies the overlying turbulent fields a large eddy simulation les model with the capability to resolve a moving sinusoidal wave at its lower boundary is developed to investigate this low wind fast wave regime it is used to simulate idealized situations with wind following and opposing fast propagating waves swell and stationary bumps les predicts momentum transfer from the ocean to the atmosphere for wind following swell and this can greatly modify the turbulence production mechanism in the marine surface layer in certain circumstances the generation of a low level jet reduces the mean shear between the surface layer and the pbl top resulting in a near collapse of turbulence in the pbl when light winds oppose the propagating swell turbulence levels increase over the depth of the boundary layer and the surface drag increases

effects of gradation on the long shore transport processes and reshaping of rubble mound breakwaters under construction exposed to head on and oblique waves abstract breakwaters under construction are prone to undesired reshaping because their core is not designed to withstand severe or moderate wave loads while the reshaping of a finished breakwater was subject of comprehensive research few studies dealt specifically with the reshaping mechanisms of a breakwater under construction i e of the breakwater core this paper presents a set of experimental tests focused on the reshaping of rubble mound breakwater trunks and roundheads undergone during the construction phase the study accounts for oblique wave attacks and grading of the construction material better insights on how and how far such reshaping takes place are derived in the perspective of providing coastal designers and constructors with valuable information for optimising the selection of the fractions and volumes of the construction materials and for taking into account potential damages within the construction schedule and therefore additional costs

measurements of the viscous tangential stress in the airflow above wind waves 1 the stress and drag at the surface of the ocean are crucial parameters for both short term forecasting and the modeling of long term global climate trends however the partition between viscous turbulent and wave stresses and in particular the effects of airflow separation are not well understood we present direct measurements of the velocity in the airflow above wind generated waves we observe intermittent separation of the viscous sublayer past the crest of the wind waves leading to dramatic along wave variability in the surface viscous tangential stress these results hold for wind speeds that would normally be considered low to moderate these viscous stress measurements in the airflow above the wavy surface and within the separated region are to the best of the authors knowledge the first of this kind

surface wave dynamics in delaware bay and its adjacent coastal shelf this study presents a broad overview of surface gravity wave dynamics in delaware bay and the adjacent continental shelf by employing the wave model simulating waves nearshore one way coupled to the ocean model regional ocean modeling system for a period from 2006 2012 the distributions of simulated wave statistics agree well with observations obtained from three wave buoys located on the shelf in the bay near the open ocean and about 35 km up the bay a partitioning analysis to separate the two dimensional wave height spectrum into wind forced and swell parts reveals that waves on the shelf are predominantly remotely generated swell bathymetric refraction shelters the bay from energetic open ocean waves which is supported by an idealized ray tracing analysis waves near the bay entrance are also refracted by oblique tidal currents whose refraction characteristics critically depend on the detailed spatial distributions of the currents opposing tidal currents flowing against the wave propagation direction focus wave energy outside the bay entrance and in the deeper bay channels where currents are relatively strong a spectral partitioning analysis for waves in the bay indicates that less energetic wave fields are likely not directly forced by the wind more energetic waves on the other hand are dominantly driven by winds and the wave response in the bay depends on the fetch setting wind direction our results for wind driven waves in the bay are consistent with previous fetch limited observations but we find a systematic bias between wind and wave directions due to bathymetric refraction

the near neutral marine atmospheric boundary layer with no surface shearing stress a case study abstract data from a marine coastal experiment over the baltic sea comprising airborne measurements and mast measurements have been used to highlight the turbulence dynamics of a case with most unusual flow characteristics the boundary layer had a depth of about 1200 m the thermal stratification was near neutral with small positive heat flux below 300 m and equally small negative heat flux above the entire situation lasted about 6 hours turbulence levels were unexpectedly high in view of the fact that momentum flux was negligible in fact positive in the layers near the surface and buoyancy flux was also small the turbulence was found to scale with the height of the boundary layer giving rise to velocity spectra having the shape of those characteristic of convectively mixed boundary layers analysis of the turbulence budget for the entire planetary boundary layer pbl revealed that energy was produced from shear instability in the uppermost parts of the pbl and was distributed to the lower par