interpretation of lithofacies of the ashtabula till along the south shore of lake erie northeastern ohio the final advance of the erie lobe into ohio during the port bruce stade of the late wisconsinan deposited the ashtabula till wave erosion and mass wasting along the south shore of lake erie show

midshelf to surfzone coupled roms swan model data comparison of waves currents and temperature diagnosis of subtidal forcings and response abstracta coupled wave and circulation model that includes tide wind buoyancy and wave processes is necessary to investigate tracer exchange in the shelf region here a coupled regional ocean model system roms simulating waves nearshore swan model resolving midshelf to the surfzone region of the san pedro bay california is compared to observations from the 2006 huntington beach experiment waves are well modeled and surfzone cross and alongshore velocities are reasonably well modeled modeled and observed rotary velocity spectra compare well in subtidal and tidal bands and temperature spectra compare well in the subtidal band observed and modeled mid and inner shelf subtidal velocity ellipses and temperature variability determined from the first vertical complex eof ceof mode have similar vertical structure although the modeled subtidal velocity vertical shear and stratification are weaker than observed the ratio of stratification to shear is similar suggesting model vertical mixing i

remote sensing of shelf sea currents using a high frequency ocean surface current radar system in a deployment of an ocean surface current radar system made during may 1985 currents were measured in a region of sea to the northeast of anglesey wales and compared with data obtained from three current meters the uppermost current meter was fixed at 5 m from the surface in a water column of 40 m depth with tidal range of 9 m in the east west direction close to the orientation of the major axis of the tidal ellipse the radar and top current meter show good agreement to within an rms value of 0 16 m s 1 consistent with earlier comparative studies for the weaker north south components of the flow however differences between the radar results and those from the current meters are apparent a larger amplitude north south signal is recorded by the radar in terms of the m2 rotary clockwise and anticlockwise components of the flow the radar data contain amplitude and phase anomalies with respect to a predicted surface behavior deduced from the current meter records and theory in particular anticlockwise phase at the surface is advanced considerably by 20 further analysis shows that the flow field recorded by the radar has two components the predicted tidal response and an additional elliptical term of lower eccentricity than the main east west tidal signal and with major axis directed close to north hourly synoptic maps of tidal circulation patterns derived from the radar show a smooth transition from near westward flows on the ebb to near eastward flows on the flood the variation of north south residual currents with height can be interpreted in terms of a mean state consistent with geostrophic shear and associated with the roughly east west density gradient

residual flows in cook strait a large tidally dominated strait abstractflows at subtidal frequencies are resolved from 20 months of current observations at multiple sites across the narrows of cook strait new zealand the substantial tidal flows spring tides 3 m s 1 are challenging to measure with moored adcps along strait residual flows are on the order of 0 05 0 1 m s 1 but there were differences across the strait and also through the annual cycle the calculated net residual transport is 0 25 sverdrups sv 1 sv 106 m3 s 1 i e negative sign implies to the south from tasman sea to pacific ocean this is smaller by a factor of 2 3 than that estimated from previous sparse current measurements crucially however these new data also suggest that over the austral summer autumn period there is persistent residual flow northward on the western side of the strait so that the summer autumn net 0 15 sv flow can be separated into 0 065 sv westside and 0 22 sv eastside flow this western northward flow had a seasonal bias appearing only in the summer

intratidal variations in stratification and mixing in the hudson estuary this study represents a detailed examination of intratidal variations in boundary layer structure in a relatively narrow straight section of the hudson river estuary during high river discharge the presence of active mixing is inferred from estimates of the richardson number the maximum height above bed to which mixing occurs is comparable during flood and ebb however the regions of mixing differ in density structure during the flood active mixing is confined to a well mixed near bed layer whereas during the ebb active mixing occurs throughout regions of significant stratification tidal straining maintains stratification during the ebb while it promotes the growth of a uniform bottom mixed layer during the flood in general maximum and minimum near bed stratification occur during late ebb and flood respectively reflecting the dominant role played by tidal straining in determining intratidal variation vertical stretching was also found to be an important term in the stratification balance during the ebb

multiple pre wisconsinan glaciations along the northwestern edge of the allegheny plateau in ohio and pennsylvania stratigraphic studies of the glacial geology of the northwestern margin of the allegheny plateau of northeastern ohio and northwestern pennsylvania include evidence for multiple pre wisconsinan gla

physical processes in a coupled bay estuary coastal system whitsand bay and plymouth sound abstract whitsand bay and plymouth sound are located in the southwest of england the bay and sound are separated by the 2 3 km wide rame peninsula and connected by 10 20 m deep english channel waters results are presented from measurements of waves and currents drogue tracking surveys of salinity temperature and turbidity during stratified and unstratified conditions and bed sediment surveys 2d and 3d hydrodynamic models are used to explore the generation of tidally and wind driven residual currents flow separation and the formation of the rame eddy and the coupling between the bay and the sound tidal currents flow around the rame peninsula from the sound to the bay between approximately 3 h before to 2 h after low water and form a transport path between them that conveys lower salinity higher turbidity waters from the sound to the bay these waters are then transported into the bay as part of the bay mouth limb of the rame eddy and subsequently conveyed to the near shore east going limb and re circulated back towards rame head the simpson hunter stratification parameter indicates that much of the sound and bay are likely to stratify thermally during summer months temperature stratification in both is pronounced during summer and is largely determined by coastal deeper water stratification offshore small tidal stresses in the bay are unable to move bed sediment of the observed sizes however the bay and sound are subjected to large waves that are capable of driving a substantial bed load sediment transport measurements show relatively low levels of turbidity but these respond rapidly to and have a strong correlation with wave height

critical hydraulic gradients of internal erosion under complex stress states abstractinternal erosion involves selective loss of fine particles within the matrix of coarse soil particles under seepage flow which affects the hydraulic and mechanical behavior of the soil in this research extensive laboratory internal erosion tests were conducted under complex stress states following three stress paths isotropic drained triaxial compression and triaxial extension stress paths these tests were designed to investigate the initiation and development of internal erosion and the effect of stress state on critical hydraulic gradients the entire erosion process can be divided into four phases stable initiation development and failure accordingly three critical gradients termed as initiation skeleton deformation and failure hydraulic gradients can be defined these critical gradients correspond to the onset of erosion of the fine particles filling the large pores of the skeleton the buckling of the strong force chains formed by the coarse particles and the soil failure re

adcp measurements of momentum balance and dynamic topography in a constricted tidal channel abstract the dynamics of tidal flow through inlets are not fully understood observations are scarce because of the small spatial scales over which the flow varies this paper gives the first detailed measurements of the 2d structure of tidal currents and the dynamical terms of the momentum equation within a tidal inlet leading to an improved understanding of the physics of tidal inlets in the 180 cm s 1 peak flow the near steady state momentum balance is dominated by horizontal advection and the pressure gradient with bottom friction playing a secondary role at slack water there is a balance between local acceleration and the pressure gradient numerical integration of the adcp measured terms in the momentum equation yields 60 m resolution dynamic topography that shows a 7 cm variation at peak flood consistent with bernoulli s equation the surface topography because of friction forms a linear ramp with a peak irreversible head loss of 2 cm over 600 m tidal velocities were extracted from the adcp

intensive surveys of the azores front 2 inferring the geostrophic and vertical velocity fields the geostrophic and vertical velocity fields are inferred using density and horizontal velocity data from three seasoar acoustic doppler current profiler surveys of the azores front the analysis is a two step procedure consisting of 1 objective analyses to reflect the observed length scales and 2 dynamical adjustments so that the density field is statically stable and the velocity field is in geostrophic balance the vertical velocity is inferred using a version of the quasi geostrophic omega equation in which the stratification is allowed to vary in the horizontal the resulting vertical velocity peaks at 2 10 4 m s 1 at 200 300 m there is a tendency for the denser water to the north of the front to be downwelled while the warmer water to the south is upwelled the implied heat flux exceeds 10 w m 2 near 100 m depth so the upper 100 m is warmed while the lower water column is cooled tending to stratify the upper ocean ageostrophic horizontal flow is toward the dense side of the front at the surface the dominant terms in the density balance are time rate of change and horizontal advection the inferred circulation cells may be an important mechanism of subduction in the upper ocean

measurements of tidal flow around a headland with a shipboard acoustic doppler current profiler a shipboard acoustic doppler current profiler adcp and moored current meters were used to obtain detailed measurements of the spatial structure of the tidal flow around a headland in vineyard sound massachusetts where tidal currents typically range from 50 to 70 cm s 1 eight shipboard surveys were conducted each of which followed one of five trapezoidal tracks in the vicinity of the headland completing 11 12 circuits in the course of the tidal cycle 12 4 hours the measurements from the adcp compare favorably with moored velocity measurements at two locations rms deviations of 3 cm s 1 but the comparison showed more scatter at two other sites rms deviations of 7 cm s 1 the adcp measurements from separate cruises were merged to form a composite spatial representation of the tidal and residual currents providing resolution of the spatial structure of the flow around the headland at scales from several hundred meters to 10 km the semidiurnal tidal flow is relatively uniform in space roughly following the bathymetry around the headland while a residual current field consists of counterrotating eddies on either side of the headland with spatial scales of 5 8 km and velocities as high as 25 cm s 1 the instantaneous current field indicates the formation of transient eddies on the downstream side of the headland during flood and ebb with clear evidence of flow separation near the tip of the headland

a comparison of near surface codar and vacm measurements in the strait of juan de fuca august 1978 three days of simultaneous near surface current measurements made by coastal ocean dynamics applications radar codar and surface moored vector averaging current meters vacm in the strait of juan de fuca are compared the study focuses on the mean flow and tidal components that contained approximately 79 of the kinetic energy the mean speed and direction differences were less than 7 cm s and 10 respectively the k1 and m2 tidal constituents agreed to within 14 cm s with a mean difference of 5 2 cm s this study demonstrates that codar yields estimates of the near surface currents that are comparable with conventional vacm arrays to 10 15 cm s

influence of fines on the collapse of loose sands a study has been carried out to investigate the influence of fines and gradation on the skeletal collapse behaviour of loosely prepared sand samples loose sand samples formed by moist tamping and consolidated to the same effective stress level were prepared with varying percentages of both plastic and non plastic fines 74 m samples were isotropically consolidated and subjected to monotonic undrained triaxial compression results indicate that increased percentages of fines 0 5 this change is represented by a decreased strain softening behaviour and a shifting of the steady state line variation of the gradation of the host sand appears to have little effect on the monotonic undrained behaviour a supplemental study involving use of the scanning electron microscope was carried out to evaluate the findings of the test program in terms of sand fabric key words colla

observations of current flow through the mouth of the chesapeake bay abstract seven transects of the narrowly constricted mouth of the chesapeake bay u s a were made using an acoustic doppler current profiler adcp and conductivity temperature depth ctd sensor during the period 16 21 september 1996 data were acquired while participating in the chesapeake bay plume outfall experiment cope i seven ctd stations per transect were conducted across the 17 km wide mouth along with continuous high resolution adcp coverage although discontinuous the transect data covered nearly all phases of a generic tidal current cycle the ratio of water level anomaly to average depth was o 10 3 during the transects with atmospheric pressure and wind accounting for most of the anomaly freshwater discharge from the bay was above normal during this period the resultant flow structure obtained from the adcp is much more complete than was previously possible with point measurements analysis in all tidal phases revealed near isothermal conditions with horizontal and vertical temperature differences across the mouth rarely exceeding 1 0 c in any tidal phase higher surface salinity to the north coupled with higher subsurface salinity in the chesapeake channel and unidirectional flow from surface to depth horizontal and vertical current gradients were found to be quite strong o 10 3 s 1 and o 10 2 s 1 respectively a consistent feature found on nearly every adcp transect was a subsurface flood current core and a surface ebb current core both on the right side of the main channel in the direction of flow

subsurface recirculation and larval retention in the lee of a small headland a variation on the upwelling shadow theme 1 the interaction of alongshore coastal currents with large headlands has been shown to increase the retention of planktonic organisms through the formation of headland eddies or upwelling shadows in their lee this study investigates the circulation within bodega bay in the lee of a small headland in an upwelling region and the potential for retention of plankton during the upwelling season of 2004 time series of temperature and velocity were recorded throughout bodega bay conductivity temperature depth ctd surveys were conducted and surface drifters were released during upwelling downwelling and relaxation conditions postlarval settlement was monitored daily over two periods coinciding with ctd surveys under strong upwelling favorable conditions wind driven surface currents were equatorward both offshore and throughout the bay however there was significant current shear along the eastern shore of the bay where cold bottom waters move poleward counter to the direction of the wind driven surface flow during downwelling and relaxation conditions flow was poleward throughout the water column along the eastern shore of the bay postlarvae settled during all wind conditions but greatest settlement was observed at the onset of upwelling favorable conditions while no typical upwelling shadow is evident in the lee of the bodega headland subsurface recirculation driven by the alongshore flow past bodega head may facilitate the retention of plankton in the bay previous studies have generally focused on large headlands however it is likely that other small embayments in the lee of small headlands may also provide retention opportunities for planktonic organisms in upwelling regions

the role of a man made headland in generating patches in coastal waters of ise bay japan patches of saline water were detected near a tip of a reclaimed land a man made headland in the coastal waters of ise bay japan from ctd casts in addition acoustic doppler current profiler adcp observations indicated that the reclaimed land generated local eddies a hydraulic model and a numerical model provided evidence that the patches were formed by vortices shed at the headland in reversing tidal currents

what is tide induced residual current abstract we carried out a numerical experiment to study the velocity field of a two dimensional tidal current in a simple model basin with a narrow strait it was found that the tide induced transient eddy tite originated from the low pressure area that is generated downstream behind a headland by the nonlinearity or the centrifugal force of the tidal current flowing with a large curvature through a narrow channel the transient eddy is maintained during certain phases of the tide and therefore the eulerian tide induced residual current is the result of the averaging process of transient phenomena the eulerian residual current is only a mathematical representation of the tide induced transient eddy and has no physical reality we should abandon the concept of residual velocity the lifetime of tite depends on the magnitude of vorticity and its dissipation in an inner basin with large bottom friction the eddy diminishes within a short time one or two hours after the generation and the pressure gra

residual and tidal circulation revealed by vhf radar surface current measurements in the southern channel isles region english channel abstract two very high frequency radars vhfrs operating in the southern channel isles region english channel in february march 2003 provided a continuous 27 day long dataset of surface currents at 2 km resolution over an area extending approximately 20 km offshore the tidal range in the region of study is one of the highest in the world and the coastal circulation is completely dominated by tides the radar data resolve two modes which account for 97 of the variability of the surface current velocities with the major contribution of the first mode this mode accounts for oscillating tidal currents whereas the second mode represents motions emerging from the interaction of tidal currents with capes and islands eddy in the vicinity of the point of grouin and jet south of chausey a fortnightly modulation of the modal amplitudes causes the exceptional more than 600 variability of currents which is well captured by the vhfr observations the radar data revealed that tidal circulation in the region is flood dominated with a strong asymmetry of current velocity curve wind events and fortnightly variability affect the course of tidal cycle by modifying the magnitude and duration of ebb and flood in addition to expected features of coastal circulation tidally dominated flow eddies and high wind current coupling the residual currents revealed a strong cross shore structure in the mean and a significant variability which has the same order of magnitude

glacial dispersal rejuvenation on the allegheny plateau north central ohio based on till carbonate patterns abstract carbonate contents of tills deposited by ice of the scioto lobe decrease in the direction of ice flow from the carbonate rocks of the central lowlands across the clastic rocks of the allegheny escarpment and then increase over clastic bedrock on the allegheny plateau thus the distribution of carbonate in till units does not fit glacial dispersal models in recent literature regression analysis of fine carbonate 0 074 mm content with distance down ice along traverses from the carbonate clastic contact to the allegheny plateau are not statistically significant because of the high carbonate contents of till units on the plateau however data from the contact to the escarpment do yield significant regression coefficients one hypothesis to account for the increased carbonate con ent on the plateau is that entrainment of local shale quickly decreased carbonate concentrations because of its low durability relative to carbonate shale was rapidly comminuted and caused a relative increase in fine carbonate on the plateau an alternative hypothesis suggests that as soft shales were eroded the debris content of the basal ice increased causing the basal ice to stagnate along the escarpment more active ice from the englacial zone containing carbonate debris upsheared from the basal zone may have overridden the stagnant basal ice and may have grounded as basal ice on the plateau subsequently dilution of englacially transported carbonate began in the newly formed basal zone as the glacier moved over the plateau and glacial dispersal continued

oscillatory flow across an irregular boundary 1 laboratory experiments examining oscillatory flow along a coastline or isobath with a series of headlands or ridges reveal a mechanism for transfer of momentum and mass from the boundary into the interior flow through the establishment of organized residual flow patterns particle imaging velocimetry is used to visualize the vorticity field and to quantify large scale residual circulations generated near the region of roughness two flow regimes are observed for differing ratios of along coast tidal excursion l to the length of the roughness region d for l d 1 a weak inflow is produced in the vicinity of the roughness region with a corresponding alongshore flow away from the region for l d 1 a strong outflow jet is established near the center of the roughness region the two flow regimes result from different residual vorticity patterns and rely on eddies being long lived relative to the tidal period thus these results are relevant to flows in which dissipation is weak relative to the mean flow kinetic energy such as for tidal flow in deep water flow past a single roughness element is used as an analog to tidal flow past a headland and is represented by the high l d limit

post erosion mechanical response of internally unstable soil of varying size and flow regime one of the leading causes of dam failure is internal erosion the impact of erosion of non plastic fine particles known as suffusion on the soil structure and strength has been studied experiment

tilted baroclinic tidal vortices the structure of baroclinic vortices generated by horizontal flow separation past a sloping headland in deep stably stratified waters is investigated the most distinctive feature of these eddies is that their cores are strongly tilted with respect to the stratification yet their velocity field remains quasi horizontal field observations and numerical simulations are used to explore the consequences of the strong tilt on the eddy baroclinic structure it is found that the background density field is altered in such a way as to maintain a pressure minimum in the tilted vortex cores this adjustment results in a fundamental asymmetry of the density field isopycnals are deflected upward on the shoreward side and downward on the opposite side of the eddy center the resulting pattern closely resembles the asymmetries of azimuthal wavenumber one that develop when tropical cyclones become tilted by an environmental shear the authors provide a simple analytical model that suggests this structure is obtained via a balance between the centrifugal force and the horizontal pressure gradient as the eddies release from the boundary adjust and decay their tilt as well as the associated density perturbation decrease and lose coherence it is suggested that this may lead to a conversion of potential energy into kinetic energy

deposition and flux of sediment from the po river italy an idealized and wintertime numerical modeling study abstract recent studies of sediment dynamics and clinoform development in the northern adriatic sea focused on winter 2002 2003 and provided the data and motivation for development of a detailed sediment transport model for the area near the po river delta we used both idealized test cases and more realistic simulations to improve our understanding of seasonal sediment dynamics there we also investigated the relationship between physical processes and the observed depositional products e g the accumulation of sediment very near the po river distributary mouths sediment transport near the po river was evaluated using a three dimensional ocean model coupled to sediment transport calculations that included wave and current induced resuspension suspended sediment transport multiple grain classes and fluvial input from the po river high resolution estimates from available meteorological and wave models were used to specify wind wave and meteorological forcing model results indicated that more than half of the discharged sediment remained within 15 km of the po river distributary mouths even after two months of intensive reworking by winter storms during floods of the po river transport in the middle to upper water column dominated sediment fluxes otherwise sediment fluxes from the subaqueous portion of the delta were confined to the bottom few meters of the water column and correlated with increases in current speed and wave energy spatial and temporal variation in wind velocities determined depositional patterns and the directions of sediment transport northeasterly bora winds produced relatively more eastward transport while southwesterly sirocco winds generated fluxes towards both the north and the south eastward transport accounted for the majority of the sediment exported from the subaqueous delta most likely due to the frequent occurrence of bora conditions progradation of the po river delta into the adriatic sea may restrict the formation of the western adriatic coastal current increasing sediment retention at the po delta and reducing the supply of sediment to the apennine margin a positive morphodynamic feedback may therefore be present whereby the extension of the delta into the adriatic increases sediment accumulation at the delta and facilitates further progradation

the fine structure of nearshore tidal and residual circulations revealed by h f radar surface current measurements abstract using the ocean surface current radar oscr developed by the rutherford appleton laboratory uk 30 days of synoptic hourly surface current vectors were obtained for 84 locations within a nearshore region some 18 kms square tidal analyses of these data show that the currents associated with the predominant m2 constituent sweep smoothly and regularly through the area unaffected by the finer topographic features moreover contours of the amplitude of the m2 semi major axis are mutually consistent to a precision of better than 0 5 cm s 1 statistical analyses of these data indicate that the standard error of oscr current measurements is less than 4 cm s 1 by contrast the major higher harmonic constituent m4 shows pronounced but ordered spatial variability relating the observed distributions for m4 and m2 is foreseen as an instructive modeling problem that should advance our knowledge of shallow water tidal interaction processes standard relationships between residual surface currents and

assessing the potential of internal erosion and suffusion of granular soils this study presents a new empirical criterion for assessing the potential of internal erosion and suffusion of granular soils this method considers the bimodal structure of a soil having a primary coarse fabric and loose finer particles based on the porosities influenced by the particle size distribution and the degree of compaction by comparing the representative particle size of a loose finer fraction with the controlling constriction size of a primary coarse fabric a distinct boundary between internally stable and unstable soils with respect to internal erosion may be found

shipboard acoustic doppler profiler velocity observations near point conception spring 1983 during april 1983 shipboard doppler acoustic log current profiles were collected in an effort to characterize the flow field near points conception and arguello california subsurface velocity maps derived from these profiles have been used to describe spatial flow structures both on and off the shelf and to investigate flow variability as a function of time and of wind stress persistent westward flow out of the northern half of the santa barbara channel and eastward flow into its southern half were observed regardless of the direction of the local wind stress during one well documented upwelling favorable wind event currents responded in the form of an energetic maximum 21 m speeds of 60 cm s 1 offshore squirt of cold water during weak or downwelling favorable winds currents continuous with the santa barbara channel outflow were observed flowing to the northwest following the local isobaths before turning offshore west of point arguello evidence for wind forcing of current fluctuations nearshore between the points and north of point arguello was found lack of a thermal wind balance between directly measured velocity shear and horizontal density gradient was explained by the presence of large accelerations in the momentum equations lack of a consistent relation between velocity and temperature gradient illustrates the difficulty in estimating velocity from temperature information alone in this area

observations of the phase of tidal currents along a strait abstract the phase of the m2 surface elevation tide changes by 100 along a 40 km length of cook strait new zealand acoustic doppler current profiler measurements are presented that show a change of only 12 in the phase of depth averaged semidiurnal tidal currents along this same length this phase change supports the general result developed by vennell which states that the phase of the cross sectional average velocity is approximately constant along a short strait of variable cross sectional area vennell also developed a relationship between the constant phase of tidal currents along the strait and the amplitude and phase of the surface elevation tide at the ends of a short strait the velocity phase given by this relationship is shown to agree well with the observed tidal velocity phase in cook strait and one other strait

mesoscale current fields observed with a shipboard profiling acoustic current meter abstract measurements of the near surface currents obtained with a shipboard profiling acoustic current meter during the polymode local dynamics experiment are discussed the large scale spatial structure of the directly measured currents is very similar to that obtained from simultaneous hydrographic observations assuming geostrophic dynamics the vertical shear of geostrophic currents is half that observed directly and the two are poorly correlated vertical shear is dominated by currents having spatial scales shorter than about 180 km and having no geostrophic signature although the shear of the ageostrophic component is clearly evident estimation of the ageostrophic current is hampered by large experimental uncertainties

an empirical model of the tidal currents in the gulf of the farallones abstract candela et al 1990 1992 showed that tides in an open ocean region can be resolved using velocity data from a ship mounted adcp we use their method to build a spatially varying model of the tidal currents in the gulf of the farallones an area of complicated bathymetry where the tidal velocities in some parts of the region are weak compared to the mean currents we describe the tidal fields for the m 2 s 2 k 1 and o 1 constituents and show that this method is sensitive to the model parameters and the quantity of input data in areas with complex bathymetry and tidal structures a large amount of spatial data is needed to resolve the tides a method of estimating the associated errors inherent in the model is described

the response of a strongly stratified fjord to energetic tidal forcing abstract the response of upper loch linnhe a strongly stratified scottish fjord to energetic tidal forcing is studied by new analysis of two observational data sets using a ship mounted acoustic doppler current profiler adcp and an undulating conductivity temperature depth ctd we are able to repeatedly sample over a tidal cycle at sufficiently high spatial and temporal resolutions to clearly define the tidal variability in the vertical and horizontal away from the near sill region horizontal velocities are generally orientated along the longitudinal axis of the fjord analysis of the along fjord velocities shows that at the m2 frequency there is a strong 1st mode internal tide with maximum horizontal velocity amplitudes of 23 4 cm s 1 the observed vertical structure of the complex amplitudes of the horizontal velocities are in close agreement with normal mode theory along fjord variations of the fitted amplitude and phase lags from further analysis of the two independent data sets show that the 1st mode internal tide is behaving as a standing wave within the near sill region the circulation is complicated by the formation of a horizontal gyre and a large perturbation in the density field on the flood tide these features are a response to the flood tide currents advecting denser water into the fjord in the form of a strong jet due to the narrow entrance sill being off centre to the axis of the fjord the strong flood tide jet gives rise to eddy formation as the incoming flood tide water is denser than the resident surface water of the fjord the tidal jet sinks and advects the resident water landwards giving rise to the observed density perturbations

shelf slope exchanges associated with a steep submarine canyon off calvi corsica nw mediterranean sea a modeling approach a three dimensional unsteady nonlinear high resolution model is used to investigate the impact of the calvi canyon nw corsica steep topography on the shelf slope exchanges as well as on the circulation in the calvi bay in homogeneous winter and early spring conditions a double coordinate system is considered in order to represent adequately the high depth gradients within the canyon the studied region is under the influence of the west corsica current flowing northeastward along the nw corsican coast right bounded flow model results show that the circulation in the calvi bay is determined by flow modifications in the canyon area the mean horizontal flow is deviated southwestward upstream of the canyon to form an anticyclonic gyre in the western part of the calvi bay within the canyon the circulation is cyclonic leading to an offshore flow downstream of the canyon around the canyon rim the cross shelf currents become important indicating that this region acts as a transition zone of high exchange between nearshore and offshore areas furthermore the canyon topography generates high downwelling upwelling and downsloping upsloping velocities responsible for an intense vertical transport of material in the area numerical runs are performed for typical prevailing wind conditions the wind is responsible for a drastic increase of cross shore transports between the bay and the canyon area 3 4 times larger than in the no wind case sw winds induce a further enhancement of cross shelf exchanges whereas the effect of n ne winds is to reduce exchange at the shelf break apart from the canyon head where an intense offshore flow occurs within the canyon high vertical velocities are shown to be associated with high cyclonic vorticity which is enhanced reduced by the n ne sw wind event a comparison between model results and measured distributions of nitrate and chlorophyll a concentrations in the area shows the role played by this specific hydrodynamics as a strong constraint on the coastal pelagic ecosystem

sedimentary processes bedforms and facies associated with a coastal headland portland bill southern uk this investigation presents new findings on the sedimentary processes and deposits associated with a coastal headland in a mixed tide wave setting using data compilation bathymetric and sediment distribution maps collected field data side scan sonar and seabed sampling and sand transport modelling sand transport pathways are described a on the basis of coupled system seabed morphology sand distribution and b from bed shear stress and medium grained sand transport rate simulations the presence of a sequence of sedimentary deposits associated with a complex suite of bedforms and sedimentary facies within an overall framework of limited sediment supply represents a gradient in shear stress and sand transport towards the headland these sequences are observed on both sides of portland bill tending towards a symmetrical distribution the sedimentary facies distribution is combined with sand transport rates and maximum bed shear stress distribution to suggest a conceptual model for sand dispersal and deposit formation around headlands sand dispersal can be explained in terms of a headland associated eddy bedload convergent zone concept maximum bed shear stress is observed at the tip of the headland and is associated with bedrock exposed on the seabed the sequence of sedimentary deposits away from the headland is sandbanks shambles and portland banks sand gravel flats sand shoals adamant and west shoals and rippled sand sheets the banks lie in an area of very high bed shear stress u 0 08 m s 1 this is greater than that for other tidal sandbanks not associated with headlands bank formation is the result of the strong convergent transport component enhanced by the development of transient headland eddies the sandbanks are to some extent also morphologically controlled i e the portland bank is affected by the deep bathymetry to the west side of portland bill the principal characteristic of headland associated eddy bedload convergent zones is the development of bed shear stress convergent zones on both sides of the headland two conceptually distinct regions of sedimentary processes associated with the coastal headlands are recognised a an inner zone with increasing gradients in sand transport and bed shear stress towards the headland and b an outer zone in which sand transport is away from the headland associated with a decrease in the bed shear stress these zones merge into a bed shear stress sand bedload transport convergent zone which enhances the formation of sandbanks around headlands thus headland associated sedimentary deposits are a complex system compared with the occurrence of isolated sandbanks described elsewhere the identification of a sequence of deposits related to and extending much farther from the headland than previously supposed demonstrates that the tidal stirring concept of headland associated sandbanks may explain the formation of headland associated sandbanks however it ignores the presence of a suite of sedimentary deposits around such headlands the conceptual model proposed here provides a sedimentological perspective on the formation and occurrence of headland associated deposits including sandbanks

dynamical aspects of the flow through the strait of belle isle abstract we present an analysis of 50 days of current meter and sea revel data collected in a long narrow strait connecting the gulf of st lawrence to the atlantic ocean the dynamical balances implied by a scale analysis of the equation of motion are compared with the data for semidiurnal and diurnal tides and for low frequency flows the main result being that the near surface currents along the strait are as expected in geostrophic balance with the sea level slope across the strait the flow appears to be driven by the sea level difference between opposite ends of the strait produced by large scale meteorological forcing and a regression model involving acceleration and friction suggests a spindown time of 1 1 days the near bottom currents are significantly less than those new the surface at both levels the currants are reasonably uniform across the channel apart from the possibility of nearshore intensification at the lower level the vertical and horizontal structure of the low frequency curre

oscillatory flows around a headland by 3d modelling with hydrostatic pressure and implicit bed shear stress comparing with experiment and depth averaged modelling abstract tidal flows around headlands with recirculations have long been of environmental importance and are now considered for tidal stream turbine deployment as flow accelerates around a headland tip interacting with the recirculation zones giving high kinetic energy the 3d telemac model with hydrostatic pressure and k e turbulence modelling where bed shear stress is implicit part of the boundary layer computation and not defined by a friction coefficient is compared with experimental measurements of surface velocity vectors and fluid velocity time series for rough turbulent conditions the magnitudes of tip velocity are predicted with reasonable accuracy while the velocities in the recirculation zones are only predicted approximately the bed friction coefficient around these recirculation zones may be magnified by an order of magnitude over the background level as was previously found for island wakes the boundary layer thickness is generally less than the water depth and a two mixing length model with the horizontal about six times the vertical gives slightly better recirculation zone velocity prediction but requires an estimate of boundary layer thickness the experiment has a distorted exaggerated vertical scale and relaxing this in the model while imposing non dimensional roughness typical of field conditions gave results very similar to those for experimental conditions indicating that the distorted scale physical modelling is justified for these conditions although this should not be assumed to be a general rule results from widely used depth averaged modelling overestimated the tip velocities markedly particularly for the smallest oscillation amplitude presumably associated with the necessarily fixed friction coefficient and absence of secondary flow allowing artificially high velocities in the recirculation zones generating higher velocities near the tip after flow reversal this form of relatively simple 3d modelling thus appears useful for assessing energy capture from tidal stream turbines around headlands

moving vessel acoustic doppler current profiler measurement of tidal stream function using radial basis functions 1 acoustic doppler current profiler adcp measurements from moving vessels have recently been used to obtain detailed observations of the spatial patterns of tidal flows as well as patterns of vorticity and dynamical terms developments in radial basis function rbf interpolation theory are demonstrated to significantly improve the quality of the tidal velocity field extracted from the measurements using thin plate splines these include placing centers at data locations enforcing side conditions on the solution and using higher order splines for tidal flows with a scale less than a few kilometers the differentiability of rbfs can be exploited to fit the stream function directly to the measurements this ensures the observed tidal velocity field satisfies mass continuity enforcing mass continuity is demonstrated to significantly improve the ability of the splines to interpolate across wide gaps between vessel tracks extraordinarily detailed adcp measurements of the tidal stream function within bluff harbour new zealand reveal the stagnation streamline that separates a 200 m wide flood tidal jet from an associated 400 m diameter eddy the stagnation streamline clearly shows that the eddy gains its fluid and vorticity from inshore of the jet s vorticity maximum the eddy forms at 04 45 hours before high tide grows in spiral fashion and becomes isolated from the jet 02 30 hours before high tide after which its vorticity rapidly decays

coastal ocean circulation near barbados west indies spring 1990 and 1991 results are presented of two oceanographic surveys of the coastal waters surrounding barbados west indies during april and may of 1990 and 1991 in both years observations of the hydrographic structure were made with a dense grid of conductivity temperature depth stations over the upper 500 m of the water column acoustic doppler current profiler adcp measurements of currents in the upper 250 m were made on radial transects from the island during three short surveys in each year one fixed mooring was deployed south of the island for the duration of each cruise results from both years showed the circulation to be energetic highly variable over short timescales and sometimes flowing contrary to historical means surface adcp and geostrophic flow patterns during 1990 suggested that the barbados ridge north of the island played an important role in steering the circulation north of the island the sudden reversal of the current south of the island between legs 1 and 2 of 1990 coupled with the presence of low salinity surface water suggested we may have witnessed an encounter between the island and the northern edge of a thin less than 35 m mesoscale pool of brazilian current retroflexion region origin on the other hand in 1991 several eddies both cyclonic and anticyclonic were observed near the island suggesting the possibility of shedding of von karman type eddies from the island

tidally induced clouds of suspended sediment connected to shallow water coral reefs abstract the bay of banten west java indonesia represents a shallow coastal embayment harboring coral reefs subject to extremely turbid conditions the sedimentary regime and flow structure of two contrasting coral reef islands in the embayment were investigated to identify the mechanisms responsible for mean and peak levels of suspended sediment concentration ssc around the reefs arrays of in situ calibrated optical backscatter obs sensors were deployed across the reef slopes far field conditions were simultaneously monitored using an acoustic doppler current profiler adcp and a conductivity temperature and depth ctd probe equipped with an obs sensor in addition hydrographic surveys were conducted using the adcp attached to a small fishing boat navigating transects perpendicular to the reef islands the direct influence of river plumes was found to be insignificant waves act only in the uppermost few meters of the reef slopes where coral growth is most abundant and little sediment is available for resuspension tidal currents are the primary cause of high turbidity which was inferred from peaks in the diurnal and semidiurnal frequency bands of ssc spectra and the large depths where the turbidity variation sometimes initiates the entrained sediment disperses upward across the reef slopes which is likely due to a secondary current associated with bending of the flow along the curved hydraulically rough reef slopes in weakly stratified ambient waters changes in sediment availability variable critical shear stresses for erosion and deposition and the formation and evanescence of island wakes may explain the high variability of ssc at the reef slopes

residual transport model in correlation with sedimentary dynamics over an elongate tidal sandbar in the gironde estuary southwestern france abstract this study qualitatively describes by a multidisciplinary approach hydrodynamic and residual sediment transport over a sandbar in a macrotidal environment the sandbar is elongated and attached to a headland that is located in the gironde estuary southwestern france bathymetric surveys side scan sonar sonograms grain size trends of surficial sediment and 2dh numerical simulations of current patterns were used to define a conceptual model for the dynamics of this sandbar the sandbar is oriented anticlockwise with respect to the main flow the channel oriented bar face is ebb dominated whereas the opposite face is flood dominated resulting in a clockwise residual transport the line of sediment flux convergence corresponds to the crest of the bar the residual flow over the bar appears to originate from the regional estuarine flow the dominant process responsible for the maintenance of the sandbar seems to be the depth averaged main tidal flow rather than secondary circulation due to headlands or the interaction between the tidal flow and the seabed to generalize this regional conceptual model a qualitative comparison is made with the theories of sandbar dynamics due to tidal currents pingree and maddock 1979 zimmerman 1981 huthnance 1982 and others the seabed stability approach developed by huthnance 1982 seems to be the most reliable theory to explain the saint georges bank dynamics even though many natural factors are not taken into account

synoptic flow and density observations near an arctic shelf break analyses of data from three shipborne surveys describe the quasi synoptic density and velocity fields near barrow canyon alaska the canyon parallels the northwestern coast of alaska and contains three different water masses these are 1 warm and fresh alaskan coastal waters that originate from the bering strait 2 cold and moderately salty waters that originate from the chukchi shelf and 3 warm and salty waters that originate from the atlantic layer of the arctic ocean a halocline separates the chukchi shelf and atlantic layer waters the halocline slopes upward into the canyon where it is then twisted to slope across the wide canyon an intensification of the beaufort gyre near the shelf break just seaward of barrow canyon raises the halocline more than 100 m toward the surface locally upwelling favorable winds raise the arctic halocline which thus is ventilated within barrow canyon adjacent to the coast in the absence of winds the halocline slopes acrosscanyon in the thermal wind sense due to a northward flowing coastal current velocity measurements from a towed acoustic doppler current profiler reveal a northward flowing jet that transports about 0 3 sv sv 106 kg m23 of bering sea summer water into the arctic ocean at speeds that exceed 0 7 m s21 total northward transports through the canyon exceed 1 0 sv the warm waters of this coastal current supply more than 100 w m22 of heat to the atmosphere the jet separates both from the bottom and from the coast hence a laterally and vertically sheared jet forms which breaks into three branches at about 71 88n latitude

three dimensional nature of flow near a sill velocity and density sections across knight inlet british columbia demonstrate that lateral recirculations are a first order feature of the flow in the lee of the sill the flow over this sill has been used as a typical example of two dimensional hydraulics with a lower layer that thins and accelerates as it moves downstream below an almost stagnant layer that widens downstream creating a distinctive wedge shape however we find that rather than being stagnant the velocity in this wedge shaped layer is actually quite large consisting of a swiftly recirculating dipole vortex during flood tide and a monopole vortex during ebb tide though we may have missed the matching half of a dipole with our sampling during ebb the recirculations during flood tide carry an amount of water equal to 25 of the tidal flux while the monopole during ebb tide carries 20 of the tidal flux these recirculations bias along channel estimates of volume flux especially in the middle wedge shaped layer and demonstrate that accurate volume fluxes in the lee wave are only possible if three dimensional surveys are made our three dimensional survey shows that there is a net isopycnal convergence of water in the middle layer at a rate adequate to close the volume budget of the flow without recourse to diapycnal fluxes we also calculate the strength of the vorticity in the recirculations observed during flood tide and attribute their formation to boundary layer separation

goodbye hazen hello kozeny carman the century old hazen formula for predicting the permeability of sand is based only on the d10 particle size whereas the half century old kozeny carman formula is based on the entire particle size distribution the particle shape and the void ratio as a consequence the hazen formula is less accurate than the kozeny carman formula it is recommended that the former be retired and the latter be adopted

dynamic sedimentation and geomorphologic evolution of the laizhou shoal bohai sea northern china abstract as a headland associated sandbank off an unconsolidated coast cape in a progression process the laizhou shoal is just located at the coalescent position of the two tidal residual current circumferences its formation and maintenance dynamics sedimentation and geomorphology are different from the models proposed up till the present moment our findings indicate that 1 the tidal residual tidal current circumferences are located along the flanks of the shoal itself instead of the flanks of the headland cape and the sediments under the two circumferences are quite different from those at their coalescent position 2 the sediments made up of the shoal have an ultimate resource of river sediment instead of an erosion recession cape or seafloor nearby and are transported directly from the coastal zone through the wave resulted coastal current rather than through the tidal residual tidal eddies 3 the shoal continually migrates from southwest to northeast extending into the laizhou bay northwest the cape in the past 50 years 4 because more than 100 reservoirs have been built across the rivers in the northwestern shandong peninsula and have greatly reduced the sediments especially gravel and sand grains transported into the coastal zone some locations of the shoal have evolved from deposition to erosion and the shoal itself has become narrower but has not evolved from deposition to erosion as a whole

a comparison of techniques for tide removal from ship mounted acoustic doppler measurements along the southwest coast of vancouver island two approaches are examined for the removal of tidal currents from acoustic doppler current profiler henceforth adcp measurements the first uses predictions from a numerical model foreman and walters 1990 whose domain includes the measurement region although the numerical model is barotropic adjustments are made to correct for baroclinicity in accordance with historical observations from stationary current meters in the region the second approach originally proposed by candela et al 1990 performs a least squares polynomial or biharmonic spline fit to the adcp data in order to determine the spatially varying amplitudes and phases of major tidal constituents and the magnitude of the residual flow both tide removal techniques are applied to adcp data taken during a 3 day cruise off the southwest coast of vancouver island and their relative effectiveness is compared some of the detided currents are seen to compare well with geopotential surfaces and clearly show the juan de fuca eddy freeland and denman 1982 a discussion of the results and limitations of each technique is also presented

effects of hydraulic loading history on suffusion susceptibility of cohesionless soils abstractsuffusion is a selective erosion of fine particles under the effect of seepage flow within the matrix of coarser particles this complex phenomenon appears as a combination of three process

island wakes in shallow coastal waters rattray island northeast australia is 1 5 km long 300 m wide and lies in well mixed water approximately 25 m deep its long axis is inclined at about 60 into the direction of the dominant semidiurnal tidal current the length of the wake in the lee of the island as documented by aerial photographs and satellite imagery appears to equal that of the wake behind a flat plate in a two dimensional flow at a reynolds number of about 10 however current metering drogues measurements and temperature mapping indicate internal wake velocities much greater than would be consistent with such a simple low reynolds number model further estimates of the turbulent eddy coefficient suggest an effective reynolds number more in the vicinity of 103 to reconcile these observational differences and to explain the observed upwelling in the core of the wake an ekman pumping model is proposed it is postulated that the ekman benthic boundary layer driven by rotation in the wake allows the vertical vorticity introduced into the water at the tip of the island at the point of separation to be negated by the vorticity of opposite sign introduced at the bottom further it is shown that a large fraction of the kinetic energy of the upstream flow facing the island is used to drive the wake eddies leading to the conclusions that the trapping of water in the lee of islands greatly increases head losses on continental shelves with numerous islands coral reefs and rock outcrops