probabilistic design of dunes an example from the netherlands abstract dunes act as primary sea defences in some regions over the world and they have then the same function as common sea dikes they prevent flooding and protect people against drowning e g in the netherlands in other regions dunes form only the transition zone between sea and land and are sometimes part of important holiday resorts in those cases high investment costs have been made frequently in building houses and hotels close to the edge of the sea under storm surge conditions however dunes can be damaged by the sea knowing the amount of retreat of the dune s toe is in both cases important a design method for dunes primarily directed at the problem of the loss of life safety has been developed in the netherlands in recent years due to the large number of factors determining dune erosion a probabilistic design method was developed

prediction of dune erosion due to storms abstract this paper presents results of experimental and mathematical modelling of beach and dune erosion under storm events re analysis of the experimental results on dune erosion in small scale and large scale flumes shows that the dune erosion for extreme conditions is somewhat smaller than that based on earlier analysis results dune erosion caused by wave impact has been modelled by a cross shore profile model crosmor model which is based on a wave by wave modelling approach solving the wave energy equation for each individual wave the model has been applied to the recent deltaflume experiments on dune erosion the three main processes affecting dune erosion have been taken into account the generation of low frequency effects the production of extra turbulence due to wave breaking and wave collision and the sliding of the dune face due to wave impact the calibrated model can very well simulate the observed dune erosion above the storm surge level during storm events in small scale facilities large scale facilities and in the protoype 1953 storm in the netherlands using the same model settings the mathematical model results have been used to develop a new simplified dune erosion rule

an analytical model to predict dune erosion due to wave impact an analytical model is developed to calculate recession distance and eroded volume for coastal dunes during severe storms the transport relationship used in the model is based on wave impact theory where individual swash waves hitting the dune face induce the erosion combining this relationship with the sediment volume conservation equation describes the response of the dune to high waves and water levels four different data sets on dune erosion originating from the laboratory and the field were employed to validate the model and to determine the value of an empirical transport coefficient appearing in the analytical solutions the time evolution of dune recession observed in the different data sets was well described by the model but the empirical coefficient showed some variation between cases especially for the field data in practical applications of the model it is recommended to use a range of coefficient values to include an uncertainty estimate of calculated quantities such as recession distance and eroded volume

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

atlantic water in the strait of sicily historical and recently acquired hydrographic and current meter data are used to study the behavior and the annual cycle of the surface layer of atlantic water aw within the sicilian channel section of the strait of sicily from january to march the surface layer isotherms and isohalines are much more steeply sloped toward the african coast the transition from winter to summer stratification occurs during the april to may period and by july both temperature and salinity isolines are quite horizontal the seasonal variations in temperature and salinity can be characterized by corresponding values of mean velocity mean kinetic energy and eddy kinetic energy during winter these values increased 2 3 times their summer values hydrographic and satellite data show that the stream of warmer and less saline aw enters the strait of sicily close to the tunisian coast south of cap bon the aw appears to decelerate forming meanders and detached parcels or small rings these structures are seen in satellite images more often during winter than summer when the aw current in the strait of sicily is more energetic

extreme value statistics for wave run up on a natural beach abstract statistics of wave run up maxima have been calculated for 149 35 minutes data runs from a natural beach during the experiment incident wave height varied from 0 4 to 4 0 m incident wave period from 6 to 16 s and beach face slope from 0 07 to 0 20 four extreme statistics were calculated the maximum run up height during each run the 2 exceedence level of shoreline elevation the 2 exceedence height for individual run up peaks and the 2 exceedence level for swash height as determined by the zero upcrossing method these statistics were best parameterized when normalized by the incident significant wave height and plotted against the iribarren number h l 0 1 2 the swash data with set up removed showed less scatter than total run up with set up included for iribarren number greater than 1 5 the run up was dominated by the incident frequencies for lower iribarren number longer period motions dominated the swash a reasonable value of wave steepness for a fully developed storm sea is 0 025 so that a storm iribarren number can be estimated as 6 3 times the beach slope using this and an offshore design wave height the included graphs may provide guidance in determining a design run up height

inter annual variations of surface currents and transports in the sicily channel derived from coastal altimetry twenty year coastal altimetry data set x track is used for the first time to gain insight into the long term inter annual variations of the surface circulation in the sicily channel firstly a spectral along with a time space diagram analysis are applied to the monthly means of the x track geostrophic currents over the period 1993 2013 they reveal a regionally coherent current patterns from track to track with a marked inter annual variability that is unequally shared between the atlantic tunisian current and atlantic ionian stream inflows in the sicily channel and the bifurcation tyrrhenian current outflow northeast of sicily secondly an empirical altimetry based transport like technique is proposed to quantify volume budgets inside the closed boxes formed by the crossing of the altimetry tracks and coastlines over the study area a set of hydrographic measurements is used to validate the method the inferred altimetry transports give a well balanced mean eastward atlantic waters baroclinic flow of 0 4 sv and standard deviations of 0 2 sv on a yearly basis throughout the sicily channel and toward the ionian sea which is fairly coherent with those found in the literature furthermore the analysis allows to quantify the intrusions of atlantic waters over the tunisian shelf 0 12 0 1 sv and highlights two main modes of variability of the main surface waters path over the sicily channel through the bifurcation atlantic tunisian current and atlantic ionian stream systems some physical mechanisms are finally discussed with regards to changes in the observed currents and transports

uncertainty in well test and core permeability analysis a case study in fluvial channel reservoirs northern north sea norway reservoir permeability is one of the important parameters derived from well test analysis small scale permeability measurements in wells are commonly made using core plugs or more recently probe permeameter measurements upscaling of these measurements for comparisons with the permeability derived from drill stem tests dsts can be completed by statistical averaging methods dst permeability is commonly compared with one of the core plug averages arithmetic geometric or harmonic questions that commonly arise are which average does the dst derived permeability represent and over what region is this average valid another important question is how should the data sets be reconciled where there are discrepancies in practice the permeability derived from well tests is commonly assumed to be equivalent to the arithmetic in a layered reservoir or geometric in a randomly distributed permeability field average of the plug measures these averages are known to be members of a more general power average solution this pragmatic approach which may include an assumption on the near well geology is commonly flawed owing to several reasons that are expanded in this article the assessment of in situ reservoir permeability requires an understanding of both core plug and probe and well test measurements in terms of their volume scale of investigation measurement mechanism interpretation and integration this article presents a comparison of core and well test measurements in a north sea case study we undertook evaluation of three dsts and associated core plug and probe data sets from jurassic fluvial channel sandstones in a single field the well test permeabilities were generally found to differ from the core estimates begin page 1930 and no consistent explanation could be found for the group of wells however the probe permeameter data were able to further constrain the core estimates this study highlights the uncertainty in effective in situ reservoir permeability resulting from the interpretation of small core and reservoir well test scale permeability data the techniques used are traditional upscaling combined with the lorenz plot to identify the dominant flowing interval fluvial sandstones are very heterogeneous and this exercise is instructive in understanding the heterogeneity for the guidance of reservoir models in such a system

altimetric signal and three dimensional structure of the sea in the channel of sicily the 1996 altimeter synoptic mesoscale plancton experiment alt symplex was specifically designed to perform in situ measurements simultaneous with the passage of topex poseidon t p and ers 2 over selected tracks in the central and eastern sicily channel this experiment made it possible to have for the first time a validation of altimetry with in situ data over the mediterranean where weak dynamics results in a modest sea elevation rarely exceeding 10 cm historical infrared and altimetric satellite data were first analyzed in order to study the variability of the circulation in the area the comparative and integrative analysis of simultaneous satellite data and in situ measurements permitted investigation of the relation between the altimeter derived surface topography and the three dimensional structure of the sea the pearson correlation coefficients between altimeter data and dynamic heights along track resulted to be 0 72 0 89 t p and 0 88 ers 2 when using conventional repeat track analysis for t p a correlation value of 0 87 was found for time differences computed basing on a collinear analysis technique this analysis also led to the identification of a strong barotropic component of the velocity field located near the sicilian continental shelf where it is responsible for approximately 60 of the signal

modeling dune response to an east coast low coastal dunes can act as a method of soft coastal protection against inundation and direct impact of waves during storms if they are substantially large enough in volume to withstand erosion without breaching however the time evolution of sand dunes under direct wave impact is not well understood and many available models require site specific calibration and have had limited verification at field scales here we test three models of varying complexity in their ability to predict both dry beach erosion volumes and dune to a retreat for an east coast low storm event that occurred on the gold coast australia the process based model xbeach which models the entire profile was able to reproduce both dune toe retreat and dry beach volume however was sensitive to calibration parameters the two parametric models that only modeled erosion above the initial dune toe position were capable of accurately predicting dune toe retreat however under estimated dry beach erosion volumes with no calibration the parametric model proposed by palmsten and holman 2012 produced the smallest errors of dune toe retreat with mean error in final dune position of 6 6 m or 18 of the total measured dune retreat with minimal calibration estimated absolute error in average dune toe retreat was less than 13 of observed retreat for all three models

separation of tidal and subtidal currents in ship mounted acoustic doppler current profiler observations a simple method is developed to analyze current measurements obtained from a moving platform the need for this is motivated by the now common use of the ship mounted acoustic doppler current profiler adcp to acquire absolute velocity data during an oceanographic survey of a given region the full potential of this new measurement technique is severely hindered when the presence of high frequency phenomena e g tidal or inertial motions prevents a clear visualization of the lower frequency current structure of interest our analysis method is based on a spatial interpolation scheme using arbitrary functions that allows for the tidal current time variability which then permits the tide induced motions to be subtracted from the adcp data to yield the subtidal current field the method also allows nearby moored and drifter current measurements if available to be combined with the shipboard adcp observations in a single analysis to obtain the best description of the tidal and subtidal currents to illustrate this method we present results from the analysis of adcp data taken during oceanographic surveys in two different continental shelf regions the east china sea and the amazon shelf a 5 day conductivity temperature depth ctd and adcp survey was made in the east china sea near the mouth of the yellow sea during january 1986 there the currents were essentially barotropic and dominated by the semidiurnal tide the adcp derived cotidal chart for the m2 12 42 hours component agrees well with existing charts derived empirically from sea level observations or from regional numerical models the adcp derived steady flow is also consistent with the observed density field and indicates little flow in or out of the yellow sea and a transport of about 1 sv toward the tsushima strait two ctd adcp surveys lasting 21 and 23 days were conducted over the amazon shelf during march and may 1990 simultaneously moored current observations were also obtained at three locations along a cross shelf array 200 km north of the amazon river mouth for a common period of at least 2 months february 12 to april 13 over the shelf tidal and subtidal currents were comparable in magnitude our analysis indicates that the tidal currents were essentially barotropic semidiurnal and polarized in the cross shelf direction increasing in magnitude toward the inner shelf where current values of more than 2 m s are common the adcp derived steady currents were aligned in the along shelf direction and strongly influenced by the north brazil current nbc during both adcp surveys the northwestward flowing nbc was transporting more than 2 sv over the shelf at depths shallower than 100 m

lithological and zonal porosity permeability distributions in the arab d reservoir uthmaniyah field saudi arabia discussion saner and sahin 1999 considered the porosity and permeability distributions for the arab d reservoir in the uthmaniyah field saudi arabia and presented summaries of the data by 1 reservoir zone and 2 lithofacies type they identified three lithofacies types granular muddy granular and muddy and described the permeability and porosity distributions by layer and by lithofacies this approach breaking down the lithofacies is broadly following that promoted by lucia 1999 because saner and sahin assumed that the pore types are lithofacies controlled this approach is suggested by the representative photomicrographs shown in saner and sahin 1999 although they considered the variability expressed by the coefficient of variation c of both porosity and permeability and showed how this increases with depth in the reservoir figure 1 they did not appear to appreciate the wider implications of their analysis in their interpretation of the permeability data figure 1 plot of coefficient of variation c and tolerance see equation 2 in text

tidal and subtidal currents in the strait of sicily 1 current measurements from shipboard and moored instruments from the strait of sicily are examined to evaluate the importance of tidal and subtidal currents during summer 2000 the results show that the principal tidal components m2 k1 s2 and o1 are particularly important in the western shelf and sill region but are significantly less important over the eastern shelf and almost negligible in the central part of the strait there is a significant internal tide in the narrowest passage through the western sill the residual nontidal currents describe the main pathways and local structures of atlantic water as it crosses the strait the residual currents are compared with the geostrophic velocity calculated from simultaneous hydrographic measurements

lithological and zonal porosity permeability distributions in the arab d reservoir uthmaniyah field saudi arabia permeability vs porosity plots for the arab d carbonate reservoir show a relatively poor correlation so permeability estimation still remains an issue for discussion in this study we integrated basic core measurements with stratigraphic and petrographic analyses to determine porosity and permeability distributions and to identify the association of high permeability in darcy range with lithology and defined reservoir zones carbonate rock types in the arab d reservoir have been grouped into three lithofacies granular muddy granular and muddy the granular lithofacies is the most porous and permeable and all permeability measurements in darcy range are associated with it the muddy facies is represented by low porosity and permeability values porosity and permeability distributions of the muddy granular facies spread over the two regions representative of the muddy and the granular facies porosity and permeability distribution patterns of the arab d zones are controlled by both type and the arrangement of different lithologies zones made up of granular facies demonstrate uniformly high porosity and permeability distributions and reveal the highest permeability intervals zones represented by muddy granular and muddy facies indicate more heterogeneous and mostly bimodal porosity and permeability distributions

large scale laboratory tests of dune erosion an ongoing research program at north carolina state university ncsu has investigated the viability of a mechanics based swash induced dune erosion model early work includes both small scale laboratory and field experiments the overall objective of the experiments was to determine the relationship between the swash characteristics and dune erosion under a variety of conditions a linear relationship between the specific swash force per unit width of the dune as defined by the bore depth and velocity and the specific volume eroded has been documented for an individual swash in the lab overton et al 1988 and for a series of swash events in the field fisher et al 1987 problems of scale dune material and manner of construction in the field led to a series of experiments in the large wave tank at oregon state university osu the objective of the osu tests was to investigate the relationship between the swash force and the volume eroded for two prototype scale dunes of different sand grain size

seasonal variability of flow instabilities in the strait of sicily the eastern and western mediterranean seas are connected by the strait of sicily the mean flow conditions comprise a near surface flow of atlantic water aw into the eastern mediterranean and an outflow of levantine intermediate water liw below we present results of a numerical model investigating the stability of currents in the strait the model is nonlinear and uses a hybrid quasi isopycnic vertical coordinate the model domain is a periodic channel with horizontal dimensions of 400 200 km and different bathymetries as initial conditions we use seasonal climatological density fields varying only in cross channel direction external forcing is not applied combining three different bathymetries with both summer and winter climatological data we show the results of six model integrations in all cases the flow is baroclinically unstable the most unstable waves being 100 and 133 km wavelength in summer and 67 km in winter a cross channel parabolic bottom profile instead of a flat bottom stabilizes the flow in the north on the sicilian side of the strait but causes further destabilization in the south on the african side further modification of the bathymetry in terms of shallow shelf sea areas to the south of sicily leads to a deflection of the summer flow in both the aw and the liw range and to the generation of stationary eddies in agreement with observations the final kinetic and eddy kinetic energies of the model are higher in winter than in summer in all model runs from an inspection of satellite images evidence was found for unstable waves of similar wavelength as predicted by the model records from moored current meters support enhanced flow instability on the african side of the strait the position and circulation sense of the stationary eddies in the aw range are found to be consistent with climatology and previously known patches of low sea surface temperature

numerical simulation of time dependent beach and dune erosion a computational procedure is developed for predicting the time dependent two dimensional beach and dune erosion during severe storms due to elevated water levels and waves the model employs the equation of sediment continuity and a dynamic equation governing the cross shore sediment transport due to a disequilibrium of wave energy dissipation levels these equations are solved numerically by an implicit double sweep procedure to determine the change in position of elevation contours in the profile given sufficient time the profile will evolve to a form where the depth h in the surf zone is related to the distance seaward of the waterline by the relationship h ax23 which is consistent with many natural profiles and in which a depends on sediment characteristics the model is verified qualitatively and quantitatively through application to several idealized cases and through a preliminary simulation of erosion during hurricane eloise in general the time scales for shoreline response were found to be quite long relative to natural storm systems and erosion in the early response stages was found to be sensitive to storm surge height but much less sensitive to wave height the model response characteristics for simulation of erosion due to time varying storm conditions show a lag between the maximum storm surge elevation and maximum erosion with the maximum erosion rate occurring at the time of the peak surge for the simulated erosion due to hurricane eloise reasonable agreement was found between the post hurricane dune profiles and those calculated however the eroded volumes were in better agreement than the profile forms as the steepening of the natural dune profiles was not reproduced in the model

a two dimensional tidal model for the mediterranean sea the tidal propagation in the mediterranean sea is described through a high resolution two dimensional hydrodynamic model forced by the equilibrium tide and the incoming tide at the strait of gibraltar the four most significant constituents m2 s2 k1 and o1 are included in the model good agreement with a set of 63 coastal gauges is achieved the significance of the equilibrium tide and the forcing at the open boundary is investigated the incoming wave from the strait of gibraltar is important in tuning the tides in the whole of the mediterranean for the north aegean sea the solution without the forcing at gibraltar results in a doubling of the amplitudes of the semidiurnal tides the estimated energy dissipation due to bottom friction is 8 8 108 w the major area of dissipation is the gulf of gabes energy fluxes through the major straits are calculated

dense water dynamics along the strait of sicily mediterranean sea abstract hydrographic and current meter data gathered in different periods in the strait of sicily and in the southern tyrrhenian sea allow the outflow characteristics from the eastern toward the western mediterranean basin to be analyzed the evolution through the strait of a deep vein of dense water coming from the eastern mediterranean is described together with the dynamic interaction with overlying layers these data are related to a slightly generalized version of recent density current models such as those of emms and those of baringer and price taking into account the dynamic influence of the overlying currents and in particular their friction and mixing this model explains the path of this deep flow and enables estimates of entrainment and bottom friction to be made with these new data a phenomenon of considerable interest namely the dynamics of density currents crossing and outflowing from a strait is examined and discussed

laboratory investigation of dune erosion as a function of sand grain size and dune density abstract the relationship between swash force sand grain size dune density and dune erosion was investigated in a series of laboratory experiments the sands selected for the experiments were a coarse grain sand from north carolina and a fine grain sand from oregon small scale dunes were built and characterized as either high or low density the swash was modeled as a bore which was generated using a head tank the data consisted of bore height bore velocity specific volume eroded and dune density for ninety seven individual tests these data were analyzed using maximum likelihood estimation mle and likelihood ratio lr test methods the conclusions are 1 swash force and dune erosion are related linearly 2 decreasing the sand grain size of the dune decreases the amount of dune erosion for the same swash force and 3 increasing dune density decreases the amount of dune erosion for the same swash force in addition for these test data the difference in sand grain size influences the amount of dune erosion for a given swash force more than that due to the increase in dune density

the role of internal waves in the late quaternary evolution of the israeli continental slope abstract internal waves are widely present in world s oceans propagating in stratified ocean layers such as the seasonal pycnocline at continental shelves and slopes breaking of internal waves may create turbulence of sufficient energy to erode and transport sediments in this study we investigate the late pleistocene to recent impact of internal waves on the morphology of the israeli mediterranean continental slope based on mooring data we show that the internal wave spectrum on the upper slope contains significant energy at near inertial and semidiurnal tidal frequencies sediment subbottom profiler data show two fields of nearly contour parallel sediment waves located in water depths of 80 m 130 m and 190 m 350 m respectively a zone of flat seafloor morphology and remarkably constant slope inclination of 1 0 1 2 separates both sediment wave fields the entire stretch of seafloor between 80 m and 350 m corresponds to depths of major ocean density stratification supporting the propagation of internal waves in addition this area is critically inclined with respect to semidiurnal internal tides and supercritically inclined with respect to near inertial waves two scenarios previously related to internal wave breaking we propose that breaking internal waves control the inclination of the israeli continental slope and contribute to sediment starvation within the zone of flat seafloor morphology the formation of sediment waves is attributed to high frequency trailing internal waves of similar wavelengths as sediment waves observed within a seismic image of the water column we correlate subbottom profiler data to a radiocarbon dated sediment core no sediment waves formed from 16 cal ka 8 cal ka indicating that the seafloor impact of internal waves ceased during a time of rapid sea level rise and fresh water input in the eastern mediterranean realm the end of this period coincides with the formation of sapropel s1

the dynamics of the sicily strait a comprehensive study from observations and models abstract the dynamics of the sicily strait are investigated in a comprehensive study using recent in situ observations ocean general circulation model ogcm simulations and process model results in particular results of a very high resolution mediterranean model med16 developed in the context of the mercator project are described the circulation in the sicily strait can be described as a two layer exchange of atlantic water aw and eastern mediterranean outflow water eow the algerian current brings aw the upper layer eastwards and splits into two branches at the entrance to the sicily strait one flowing to the tyrrhenian sea the other into the sicily strait the later is composed of two streams referred to as the atlantic ionian stream ais and the atlantic tunisian current atc in winter the atc signature is more pronounced in summer the ais is associated with a number of well known semi permanent features including the intermittent northward extension of the ais called nais at the ionian shelf break which seems to be driven by the surface density contrast between waters of the sicilian and the ionian basins new intermittent patterns are shown by the med16 simulations for example an anticyclonic eddy called mca south of the malta channel and an anticyclonic gyre associated to the nais called naisa upwelling is well developed in august with temperature lower than 24 c along the western and southern coasts of sicily the seasonal transport of the aw through the strait has a maximum value 1 4 sv in winter and a minimum value at the end of summer 0 8 sv in the lower layer at the exit of the sicily strait the eow mainly composed of levantine intermediate water liw outflows into the tyrrhenian sea and veers to the right then as well known the liw flows along the northern coast of sicily before reaching the sardinia channel a new liw path from the sicily strait towards the sardinia channel is shown by the med16 model and is due to intermediate eddy shedding at the exit of the sicily strait the topography of the sill in the sicily strait plays a major role in the circulation a combination of barotropic baroclinic double kelvin waves on both side of the sill provides a mechanism for splitting the algerian current