physical processes affecting circulation and hydrography in the sable gully of nova scotia abstract the sable gully is the largest submarine canyon along the shelf break off the east coast of north america the circulation and hydrography in the gully have significant temporal and spatial variability this paper presents a numerical study of the three dimensional circulation and hydrography in the gully using a multi nested ocean circulation model the model is forced by tides wind stress and surface heat freshwater fluxes model results are in fair agreement with the current and hydrographic observations made in the gully in 2006 and 2007 a process study is conducted to examine the main physical processes affecting the circulation and hydrography including tide topography interaction wind forcing and the shelf scale circulation over the eastern canadian shelf the model results demonstrate that the circulation and hydrography above the canyon rim are influenced significantly by wind particularly during storm events while the subsurface flow over the shelf slope is affected by the shelf scale circulation there is also significant tide topography interaction inside the gully

regional differences in the morphologic behaviour of four german wadden sea barriers abstract the sandy barriers japsand norderoogsand suderoogsand and st peter ording sand are located on the seaward border of the german wadden sea previous investigations have documented that the barriers japsand norderoogsand and suderoogsand moved in an eastward direction over a distance ranging from 250 m in the south to 1600 m in the north between 1947 and 1991 it was suggested that this movement by landward rollover occurred in response to a mean 4 9 mm yr rise of mean high water in contrast st peter ording sand which is separated from the other barriers by the hever tidal inlet seems to persist in the same position in this study it is demonstrated that this difference in morphologic behaviour is a result of variations in the littoral sediment supply to the four barriers the morphological development of st peter ording sand between 1949 and 1994 occurred in four phases during phases i 1949 1964 and iii 1981 1988 landward rollover dominated as at the other three barriers however during phases ii 1964 1981 and iv 1988 1994 the development was dominated by a strong sediment supply to the barrier as a result the coastline prograded seaward during these phases the sediment probably originated from sandbanks that migrated into the area from the hever tidal inlet

vertical distribution of suspended sediment in uniform open channel flow the vertical distribution of suspended sediment in an open channel is studied theoretically by means of a new mixing length concept the diffusion coefficient is represented as a function of the distance from the bed and dependent on the magnitude of sediment concentration an equation to predict the sediment concentration is derived analytically using the vertical mass balance equation over the water depth the theoretical concentration distributions are compared with previous experimental data it is found that the present theory is applicable to sediment laden flow with low and high concentrations the ratio of the diffusion coefficient and the eddy viscosity n is larger than unity and increases monotonically with the increase of the sediment load in flows with low sediment concentrations and smaller than unity and decreases with the increase of the sediment load in flows with high sediment concentrations

mean circulation and high frequency flow amplification in the sable gully abstract the sable gully a broad shelf break submarine canyon approximately 40 km east of sable island on the eastern scotian shelf separates banquereau and sable island banks unique among canyons on the eastern canadian continental shelf because of its depth steep slopes and extension far onto the shelf its ecological significance and increasing human pressures led to its designation in 2004 under canada s oceans act as the first marine protected area mpa in the atlantic region to improve the state of knowledge of the gully mpa a multi disciplinary field program was carried out in 2006 07 the physical oceanographic component consisted of the deployment april 2006 and recovery august 2007 of four current meter moorings and ctd surveys analysis of this 16 month mooring deployment demonstrates that the mean circulation above the canyon rim 200 m is characterized by a southwestward flow that appears unaffected by the canyon topography there is also some indication of the existence of an eddy at rim depth below 500 m the circulation is dominated by an upcanyon flow of order 0 02 m s 1 at the mooring array halfway between the canyon head and mouth the mean 200 m bottom transport towards the head of the gully was estimated as 35 500 m3 s 1 implying an upwelling velocity of 1 7 10 4 m s 1 14 m d 1 over the area results also show bottom intensified tidal flows and non linear constituents due to the interaction of k1 o1 m2 and s2 components along the thalweg of the canyon the strong overtides and compound tides observed in the gully make it unique among canyons further analyses provide evidence of enhanced mixing in the gully kv 180 10 4 m2 s 1 which is approximately 20 times that observed on the adjoining scotian shelf total variance of the currents in the gully is about 2 5 times greater than that observed on the nearby continental slope with an equivalent water depth

low frequency circulation at the edge of the scotian shelf abstract records of current temperature and salinity from a two year mooring program at the shelf break off nova scotia are examined to determine the low frequency oceanic responses to the driving surface wind field and fluctuating offshore currents associated with the gulf stream the seasonal mean and subtidal variance at periods of 2 10 days of the cross shelf currents reflect the strong annual cycle in the wind field measured at sable island the mean vertical shear suggests a simple ekman response to winter increases in the longshore wind component but this model fails quantitatively because 1 the inferred surface layer 20 m transport is much too large and 2 the deep 150 m return flow shows no annual signal the excessive offshore near surface transport in winter must be reconciled with the relatively stationary position of the shelf slope water boundary ssb by invoking intense cross frontal mixing and or a seasonal mean alongshore pressure gradient the seasonal mean longshore currents

the flip side of the north atlantic oscillation and modal shifts in slope water circulation patterns a large single year reversal in the phase of the north atlantic oscillation nao during 1996 led to a dramatic shift in the slope water circulation patterns of the northwest nw atlantic analyses of time series data collected from the region over the past half century show that both physical and biological responses are commonly elicited by such phase reversals in the nao here we use a model developed from time series data to predict responses of the nw atlantic slope water circulation patterns to phase reversals in the nao

the influence of ship wave on turbulent structures and sediment exchange in large shallow lake taihu china abstract turbulent burst plays a key role in momentum transfer and sediment movement in large shallow lakes this study addresses the quantitative influence of ship wave on turbulent structures momentum and sediment fluxes in lake taihu a large shallow eutrophic lake that experiences heavy shipping traffic acoustic doppler velocimeter adv and optical backscatter sensor obs were used to obtain high frequency flow velocities and suspended sediment concentration ssc data before and when a cargo ship passed by we found that ship waves mainly propagate along the horizontal direction the near bed turbulent bursting events with ship disturbance increased by 8 42 consequently the vertical momentum and sediment fluxes were increased by 3 4 times and 8 times respectively in terms of bursting processes ejection and sweep possess much stronger capacity in carrying sediment and are largely controlled by the disturbance in the vertical direction while inward and outward interactions are mainly affected by horizontal disturbance these findings represent an important step towards understanding the mechanism and effect of turbulent bursting under ship disturbance and pave the way to future research in order to manipulate turbulent dynamics

downstream fining in contrasting reaches of the sand bedded yellow river compared to downstream fining of a gravel bedded river little field evidence exists to support the process of downstream fining in large fine sand bedded rivers in fact the typically unimodal bed sediments of these rivers are thought to produce equal mobility of coarse and fine grains that may discourage downstream fining to investigate this topic we drilled 200 sediment cores in the channel beds of two fine grained sand bedded reaches of the yellow river a desert reach and a lower reach and identified a fine surface layer fsl developed over a coarse subsurface layer csl in the 3 m thick bed deposits in both reaches downstream the thickness of the fsl increased while that of the csl decreased comparison of the depth averaged median grain sizes of the csl and the fsl separately in both reaches shows a distinct downstream fining dependence to the median grain size which indicates that at a large scale of 600 800 km the csl shows a significant downstream fining but the fsl shows no significant trends in downstream variations in grain size this result shows that fine sediment supply 0 08 mm median grain size from wind borne sediments and cross desert tributaries can interrupt the fsl and coarsen the channel bed surface locally copyright 2011 john wiley sons ltd

is the von karman constant affected by sediment suspension 1 is the von karman constant affected by sediment suspension the presence of suspended sediment in channels and fluvial streams has been known for decades to affect turbulence transfer mechanism in sediment laden flows and therefore the transport and fate of sediments that determine the bathymetry of natural water courses this study explores the density stratification effects on the turbulent velocity profile and its impact on the transport of sediment there is as yet no consensus in the scientific community on the effect of sediment suspension on the von karman parameter two different theories based on the empirical log wake velocity profile are currently under debate one supports a universal value of 0 41 and a strength of the wake that is affected by suspended sediment the other suggests that both and could vary with suspended sediment these different theories result in a conceptual problem regarding the effect of suspended sediment on which has divided the research area in this study a new mixing length theory is proposed to describe theoretically the turbulent velocity profile the analytical approach provides added insight defining as a turbulent parameter which varies with the distance to the bed in sediment laden flows the theory is compared with previous experimental data and simulations using ak eturbulence closure to the reynolds averaged navier stokes equations model the mixing length model indicates that the two contradictory theories incorporate the stratified flow effect into a different component of the log wake law the results of this work show that the log wake fit with a reduced is the physically coherent approximation

vertical dispersion of fine and coarse sediments in turbulent open channel flows through using a kinetic model for particles in turbulent solid liquid flows underlying mechanisms of sediment vertical dispersion as well as sediment diffusion coefficient are investigated four hydrodynamic mechanisms namely gravitational settling turbulent diffusion effect of lift force and that of sediment stress gradient coexist in two dimensional 2d uniform and steady open channel flows the sediment diffusion coefficient consists of two independent components one accounts for the advective transport of sediment probability density distribution function due to sediment velocity fluctuations and the other results from sediment eddy interactions predictions of the kinetic model are in good agreement with experimental data of 2d open channel flows in such flows it is shown that 1 the parameter i e the inverse of the turbulent schmidt number may be greater than unity and increases toward the bed being close to unity for fine sediments and considerably large for coarse ones 2 eff

the summer assemblage of large pelagic crustacea in the gully submarine canyon major patterns abstract we describe the trawl vulnerable crustacean micronekton and macrozooplankton of the gully a large shelf incising submarine canyon off nova scotia canada and a marine protected area over 68 species of pelagic crustacea were collected with an international young gadoid pelagic trawl during three annual summer surveys at one fixed station in the canyon depths sampled ranged from the surface to the upper bathypelagic zone concentrated in the upper 1250 m with a maximum depth of 1500 m the crustacean fauna was dominated by cold temperate species typical of mid to higher latitudes in the north atlantic meganyctiphanes norvegica and eusergestes arcticus were particularly dominant in terms of both observed biomass and abundance above 750 m depth at least 17 species were new records for canadian waters the species assemblage of the station varied primarily with depth and diel cycle the only dominant members of the assemblage showing pronounced inter annual variations in catch being m norvegica and themisto gaudichaudii both relatively shallow living species

drift velocity concept for sediment laden flows the vertical distribution of suspended sediment concentration in open channel flows is usually described by the advection diffusion equation hence only the mechanisms of advection and diffusion affect the movement of sediment particles however recent publications show that the equation could not describe fully the sediment concentration distribution in open channels a new model for particle migration in sediment laden turbulent flow is presented the model assumes there is an additional mechanism influencing the particle movement in sediment laden flows a new mechanism which is called the drift acts independently of advection and turbulent diffusion based on all three mechanisms a new equation for the concentration distribution is derived the equation describes the vertical distribution of sediment concentration more accurately than the advection diffusion equation

fractional dispersion equation for sediment suspension this study proposes a stochastic approach to simulate sediment vertical dispersion in turbulent solid liquid flows by developing a fractional advection diffusion equation fade to characterize the dynamics of sediment suspension the fade is a generalization of the traditional advection diffusion equation ade where the first order spatial derivative is replaced with a fractional derivative of order alpha 0 alpha 1 many previous investigations of sediment suspension in steady sediment laden flows apply the classic or improved rouse equation which was derived from the traditional ade by assuming fick s first law for the sediment dispersive flux recent observations in field and laboratory studies however have indicated that large errors may arise from the traditional ade when applied to flows with coarse sediments instead the vertical dispersion of suspended sediment is most likely a space nonlocal transport process in flows with turbulent bursting because particle vertical jumps with ejection events are no longer constrained to a small distance defined by the representative elementary volume in other words the vertical random displacements of suspended particles follow levy motion instead of brownian motion after validating against field measurements in the las vegas wash as well as a set of published experimental data we find that the proposed fractional model can describe the real world vertical distribution of suspended sediment concentration in steady turbulent flows c 2013 elsevier b v all rights reserved

influence of coherent flow structures on the dynamics of suspended sediment transport in open channel flow the influence of suspended sediments on coherent flow structures has been studied by simultaneously measuring the longitudinal and vertical components of the instantaneous velocity vector and the instantaneous suspended particle concentration with an acoustic particle flux profiler the measurements were carried out in clear water and in particle laden open channel flows in both cases they clearly show the predominance of ejection and sweep phases that are part of a burst cycle the analysis further demonstrates the importance of the ejection and sweep phases in sediment resuspension and transport ejections pick up the sediment at the bed and carry it up through the water column close to the surface it is shown that ejections and sweeps are in near equality in the near bottom layer whereas ejections clearly dominate in the remaining water column the implications of these results for sediment transport dynamics are discussed

turbulent bursting based sediment entrainment function one of the basic impediments to a clear understanding of a variety of fundamental problems in the context of sediment transport has been the lack of a well grounded formulation of bed sediment entrainment this is dealt with herein physically based on the mechanism that bed sediment particles are actually entrained by the bursting process inherent in wall turbulent flows a simple theoretical model for sediment entrainment from flat loose bed is established using the averaged bursting period scaled on inner variables and the spatial scales of turbulent bursts sediment entrainment is shown to depend strongly on bed shear velocity the theoretical entrainment flux is compared to available laboratory data sets covering both hydraulically smooth and transitional bed situations generally good agreement is obtained representing the best performance of the present model in relation to existing entrainment functions it appears to characterize a rather encouraging aspect for a new approach to sediment transport given the enhanced understanding of turbulent bursting

suspension of large concentrations of sands existing methods based on the diffusion theory have been extended to determine the sediment concentration distribution for large concentrations of sand the modifications for volumetric concentrations ranging from 4 to 20 include decreased fall velocity and increased viscosity and specific weight of the suspension the sediment concentration profiles are sensitive to the velocity profiles and the fall velocity of sediment particles in turbulent flows either a power law or a two layered logarithmic law can be used to describe the velocity profiles and the sediment difiusivity the proposed method accurately depicts the deviation from the rouse equation at large concentrations of sands and the agreement with sediment concentration profiles measured by einstein and chien is excellent the proposed numerical solution gradually reduces to the relationships of karim and kennedy and rouse as the volumetric concentration decreases below four percent

predicting paleohydraulics from storm surge and tsunami deposits using experiments to improve inverse model accuracy how accurately can flow depths and velocities of storm surges and tsunamis be predicted from sedimentary deposits inverse models have been proposed to quantify hydrodynamics from suspended sediment deposits but assumptions about how deposit grain size distributions gsds are influenced by flow characteristics remain largely untested using laboratory experiments we evaluate an existing advection settling model in which suspended sediment transport is assumed to reflect horizontal advection constraining flow velocity and vertical settling from the water surface constraining depth while the original model assumed that depth and velocity would be best predicted by the deposit d95 the diameter for which 95 of the cumulative gsd is finer we find that the median deposit size d50 tends to better predict mean flow hydraulics two key factors influencing how flow characteristics control deposit gsds are a dispersion caused by turbulence and b the transport distance required for suspension and settling to effectively sort grains deposits proximal to sediment sources primarily reflect the source gsd while deposits farther from the source preferentially represent transport dependent sorting in our experimental data transport distances longer than 1 2 advection length scales are required for the deposit gsd to reasonably predict flow depths and velocities these results suggest ways that event deposits can be used to more accurately assess coastal risks from tsunamis and storm waves

variation in ebb delta morphologies along the west and east frisian islands the netherlands and germany abstract ebb delta morphologies in the west and east frisian islands differ mainly in terms of the direction and the degree of asymmetry of the ebb deltas in the east frisian islands the ebb tidal deltas and their main ebb channels are asymmetrically directed downdrift to the east in the west frisian islands they are asymmetrically directed updrift to the west except for a few of the small ebb tidal deltas which are asymmetrically directed downdrift earlier theories for the east frisian islands considered wind driven waves coming dominantly from the west to be the main cause of the downdrift asymmetry of the ebb tidal deltas theories for the west frisian islands related the updrift directed ebb tidal deltas to tidal currents none of these theories can explain the morphological variation in the ebb tidal deltas for both the west and east frisian islands observation of the ebb delta morphologies of the west and east frisian islands in relation to tidal and wave regimes shows that the above mentioned difference in the ebb delta morphologies is due to the varying importance of the tidal prism and the wave induced longshore drift for the different inlets the difference is especially pronounced between the large and the small ebb tidal deltas because their tidal prisms are different the inlets with a large tidal prism have large ebb tidal deltas and they are dominated by tidal currents interaction of marine shore parallel tidal currents with onshore offshore inlet tidal currents which is enhanced by the ebb delta shoals causes the large ebb tidal deltas and their main ebb channels to be asymmetrically directed updrift to the west the inlets with a small tidal prism have small ebb tidal deltas and they are dominated by waves eastward moving deep water wave and wave induced longshore drift drive the small ebb tidal deltas asymmetrically downdrift to the east the general model proposed not only explains the varying morphologies of the ebb tidal deltas of the west and east frisian islands but is also applicable to other ebb tidal deltas

the contribution of aeolian processes to fluvial sediment yield from a desert watershed in the ordos plateau china in arid zones many active aeolian dunes terminate at ephemeral and perennial desert rivers the desert rivers show very high rates of sediment transport that cause deleterious downstream effects on the river system and ecology high sediment loading has been attributed to severe water erosion of sparsely covered watersheds during infrequent but heavy rainfall although aeolian erosion is known to lead to high rates of wind blown sand transport direct confirmation of whether the aeolian processes accelerate or inhibit fluvial sediment loss is lacking here we show that an aeolian fluvial cycling process is responsible for the high rate of suspended sediment transport in a sudalaer ephemeral desert channel in the ordos plateau of china frequent aeolian processes but low frequency once every 3 years on average flooding occur in this region wind blown saltating grains appeared to be unable to cross the desert channel because of interruption of channel induced recirculating air flow and therefore tended to settle in the channel during the windy seasons leading to channel narrowing during flooding this narrowed channel was found to yield a threefold increase in suspended sediment loading and a 3 4 fold increase in the weight percentage of the 0 08 0 2 mm sediment fraction on 18 july 2012 loss of stored aeolian sand due to channel erosion accounted for about half of the total sediment yield in this watershed these findings show that aeolian processes play an essential role in accelerating the sediment yield from a watershed characterized by aeolian fluvial interplay and also suggest that the drier the region and the greater the aeolian process the more the aeolian process contributes to fluvial sediment yield copyright 2013 john wiley sons ltd

laboratory analysis of mudflow properties a rotational viscometer has been designed for laboratory measurements of the rheological properties of natural mudflow deposits in colorado the mudflow matrices comprised of silt and clay particles are sheared under temperature controlled conditions at volumetric sediment concentrations ranging from 0 10 0 45 this study stresses the importance of conducting rheological measurements at low rates of shear because 1 those are the conditions found in natural channels and 2 they avoid the slippage problems observed at large sediment concentrations at low rates of shear the bingham model is fitted to the measured rheograms and both the viscosity and yield stress increase exponentially with the sediment concentration of the fluid matrix both the yield stress and the viscosity increase by three orders of magnitude as the volumetric concentration of sediments in the fluid matrix changes from 10 to 40 the addition of sand particles does not significantly alter the rheological properties of the matrix unless the volumetric concentration of sands exceeds 0 20

effects of suspended sediment on the open channel velocity distribution experiments were performed in which suspended sediment concentration in open channel bounded shear flow was varied systematically while flow depth slope and discharge were held essentially constant the effect of variation in suspended sediment concentration on velocity profile characteristics was investigated the experiments showed that the karman coefficient was independent of changes in suspended sediment concentration while the coles wake strength coefficient was very sensitive to such changes the thickness of the logarithmic part of the velocity profile decreased as sediment concentration increased the logarithmic parts of velocity profiles in sediment suspending flow were shifted downward relative to control profiles in comparable clear water flows

grain size distribution in suspension from bed materials experimental results show that the grain size distribution of suspended material is related to flow parameters and grain size distribution in the bed a theoretical model has been developed to compute the suspension grain size distribution on the basis of diffusion equations taking into account the effect of hindered settling due to the increased concentration in suspension fluid velocity closest to the bed is estimated by using the concept of migration velocities of particles in the bed layer comparisons of data computed by the proposed method and data from actual observations show generally good agreement

anti clockwise hysteresis in suspended sediment concentration during individual storms holbeck catchment yorkshire england abstract analysis of the flow sediment hysteresis shape may assist in determining the sediment source area in a small basin a clockwise hysteresis occurs when sediment is derived from the bed and banks of the channel or areas adjacent to the channel whereas an anti clockwise hysteresis occurs when the upper part of the slopes is the sediment source area

aeolian and fluvial evidence of changing climate and wind patterns during the past 100 ka in the western simpson desert australia abstract sediments near finke in central australia provide evidence of late quaternary evolution and the interaction of aeolian and fluvial systems in response to changing climate in the western simpson desert thermoluminescence tl dating is used to develop a chronology of aeolian and alluvial activity and to identify differences in sand provenance quaternary alluviation in the finke valley at this location occurred at or prior to c 90 ka and with no surviving evidence of subsequent activity until the holocene in contrast to rivers in the eastern part of the lake eyre basin substantial alluviation took place here in the early to mid holocene probably due to reactivation of the northern monsoon and its partial penetration into central australia the regional dunefield near finke consists of linear dunes largely reworked and aligned during the last glacial 30 12 ka as part of the great anticlockwise whorl of dunes in central australia the oldest dated source bordering dunes from the finke river are bright red in colour were deposited at c 100 ka and are now buried beneath paler source bordering dunes the latter consist of two exposed units a lower one of unknown orientation that dates at 17 9 ka and an upper unit aligned to the northwest and parallel to the prevailing winds that dates at 5 0 ka the tl signature and sediment texture of the oldest source bordering dunes show them to have probably been derived from weathered alluvial red beds of similar or greater age nearby and to have contributed abundant sand to the regional dunefield immediately north of the river in contrast sand from the younger paler source bordering dunes appears to be from a different source and to have only recently extended into the regional field the finke region would seem to be in a pivotal position for the study of palaeowind patterns that have created and modified australia s whorl of continental dunes the 30 18 ka regional linear dunes near finke are oriented almost due north their cross sectional asymmetry steeper eastern slopes suggests a response to southwesterly or westerly sand transporting winds between 18 and 10 ka these winds appear to have shifted to their present southeast orientation during the past 5 ka from dune ages alignments and asymmetry it is proposed here that there was a northward shift in the wind pattern at finke by about 100 150 km 1 1 5 of latitude during the last glacial but that through this period the regional dune pattern has remained remarkably stable

frequency spectra and intermittency of the turbulent suspension process in a sand bed river previous research suggests that the turbulence driven suspension process in sand bed channels is dominated by intermittent energetic eddies with length scales of the order of channel depth because of the scarcity of data on the turbulent suspension process in alluvial channels the possible variability in suspension intermittency and turbulent frequency content due to contrasts in flow depth velocity or bedforms remains unclear however the present study analyses eddy correlation suspension signals from seven deployments in varied flow conditions around a sandy meander bend deployment depths at near bankfull flow stages varied from 2 to 5 5 m velocities at 0 75 1 m height from 0 6 to 0 9 m s 1 and local mean suspended sand concentrations ranged from 30 to 150 mg l 1 in the intermittence and spectral content of sand suspension between the various deployments are analysed and results are compared with previously published findings study data suggest that the dominant eddy sizes involved in sediment mixing across the sensor level are consistently of the order of 1 5 times flow depth and lie within the energy bearing turbulent range when sand suspension is analysed in the time domain in the various deployments energetic burst like suspension events occupying only 1 5 of the record duration account for 20 90 of the suspension work the degree of intermittence in the suspension process was observed to increase in deeper flows where mixing events contributing extreme vertical sediment fluxes appear to be relatively more frequent

a similarity approach to turbulent sediment laden flows in open channels a basis is developed for a similarity treatment of the coupled mean fields in turbulent open channel flows over a flat sand bed in equilibrium with a suspension of sand hypotheses involving multiple scales asymptotic similarity and matching over an overlapping region are made instead of the traditional dependence on eddy diffusion and reynolds analogies velocity measurements using the laser doppler technique in experiments with well sorted natural sands showed that contrary to the implications of previous models the effect of suspended sediment on the mean velocity profile may over a variety of laboratory conditions be confined to a layer adjacent to the bed this is interpreted within the similarity framework in terms of the existence of an inner lengthscale differing from either the viscous or the grain scale associated with the presence of sediment the suggested lengthscales and concentration scales are examined in light of the experimental results

modeling the growth and migration of sandy shoals on ebb tidal deltas coherent sandy shoals that migrate toward the downdrift coast are observed on many ebb tidal deltas in this study processes that cause the growth and migration of shoals on ebb tidal deltas are identified moreover the effect of the incident wave energy and the tidal prism of an inlet on the migration speed of these shoals is investigated for this a numerical morphodynamic model with an idealized geometric setup is employed the model computes the bed level evolution due to local erosion and deposition of sand driven by tides and waves analysis of model results shows that shoals grow when there is a local imbalance between the bathymetry and the wave conditions which in this study was imposed by manually breaching the ebb tidal delta or by adding storms to the wave forcing there are thresholds for shoal formation that depend on the distribution of the sand and the incident wave energy wave refraction over the shoals leads to focusing of wave energy and increased wave energy dissipation around the location of the local minimum water depth this generates residual currents over the shoal and increased skin friction toward the local minimum water depth which together create a sand transport pattern that induces the growth and migration of the shoal sand transport due to asymmetric waves contributes to keeping the shoal a coherent structure the shoal migration speed increases with increasing incident wave energy and decreasing tidal prism this is because tidal residual currents oppose the wave driven residual currents that cause shoal migration

process response analysis for hornum tidal inlet in the german sector of the wadden sea abstract the hornum tidal inlet is located in the german sector of the wadden sea between the barrier islands sylt and amrum on the basis of seven bathymetric surveys of the tidal inlet covering a 55 yr period from 1939 to 1994 and long term records from two tide gauges a process response analysis for the inlet was carried out following the method described by dean and walton 1975 the volume of sediment stored in the ebb tidal delta vebd was calculated for each survey furthermore the cross sectional area of the tidal inlet throat ac and the area height distribution hypsographic curve of the study area were established between 1939 and 1994 ac increased by about 32 whereas vebd diminished by about 18 earlier investigations by e g o brien 1931 walton and adams 1976 dean 1988 and eysink and biegel 1992 documented a strong positive correlation between these two morphological parameters and tidal currents in the inlet in conformity with the literature regression of the values of ac with the corresponding fall velocities of the water level in the inlet a direct indication of ebb tidal currents produced a correlation coefficient r of 0 87 however vebd shows a weak negative correlation r 0 74 with fall velocities of the water level apparently other factors than changes in ebb tidal currents must have been responsible for the decrease in vebd it is suggested that one factor might be the observed considerable increase in storminess i e wave action in the region since approximately 1960 consequently storm wave action on the ebb tidal delta intensified and erosion was here initiated as a result the swash bars of the ebb tidal delta in particular suffered from severe erosion between 1959 and 1994 as the ebb tidal currents increased simultaneously sand supply to the terminal lobe of the ebb tidal delta increased as well thereby balancing the loss of sediment from the terminal lobe caused by the increasing storminess the results of this case study indicate that the ratio of ebb tidal currents to storm wave action determines in large part the value of vebd

vertical structure biomass and topographic association of deep pelagic fishes in relation to a mid ocean ridge system abstract the assemblage structure and vertical distribution of deep pelagic fishes relative to a mid ocean ridge system are described from an acoustic and discrete depth trawling survey conducted as part of the international census of marine life field project mar eco http www mar eco no the 36 station zig zag survey along the northern mid atlantic ridge mar iceland to the azores covered the full depth range 0 to 3000 m from the surface to near the bottom using a combination of gear types to gain a more comprehensive understanding of the pelagic fauna abundance per volume of deep pelagic fishes was highest in the epipelagic zone and within the benthic boundary layer bbl 0 200 m above the seafloor minimum fish abundance occurred at depths below 2300 m but above the bbl biomass per volume of deep pelagic fishes over the mar reached a maximum within the bbl revealing a previously unknown topographic association of a bathypelagic fish assemblage with a mid ocean ridge system with the exception of the bbl biomass per volume reached a water column maximum in the bathypelagic zone between 1500 and 2300 m this stands in stark contrast to the general open ocean paradigm that biomass decreases exponentially from the surface downwards as much of the summit of the mar extends into this depth layer a likely explanation for this mid water maximum is ridge association multivariate statistical analyses suggest that the dominant component of deep pelagic fish biomass over the northern mar was a wide ranging bathypelagic assemblage that was remarkably consistent along the length of the ridge from iceland to the azores integrating these results with those of previous studies in oceanic ecosystems there appears to be adequate evidence to conclude that special hydrodynamic and biotic features of mid ocean ridge systems cause changes in the ecological structure of deep pelagic fish assemblages relative to those at the same depths over abyssal plains lacking terrigenous input of allochthonous organic carbon increased demersal fish diversity and biomass over the mar relative to the abyssal plains may be maintained by increased bathypelagic food resources the aggregation of bathypelagic fishes with mar topographic features was primarily a large adult phenomenon considering the immense areal extent of mid ocean ridge systems globally this strategy may have significant trophic transfer and reproductive benefits for deep pelagic fish populations

modeling mixed sediment suspended load profiles potential errors in calculated vertical suspended sediment concentration profiles in river flows carrying mixed sediments are investigated these profiles are usually obtained through application of a standard diffusion dispersion model however such models are normally formulated on the basis of a unique grain size for the sediment accordingly in the case of sediment mixtures the grain size distribution is usually divided into several size ranges fractions which are then characterized by their respective geometric means numerical errors induced through this procedure are quantified in a parametric study while depthaveraged concentrations can be over esimated by a factor of 1 2 when the concentration gradient is weak they can be under estimated by a factor of 15 when the gradient is large estimates are found to be particularly sensitive when the chosen reference level is small and the fraction width is large fall velocity coefficients are introduced to correct the discrepancy between the a

toward modeling turbulent suspension of sand in the nearshore 1 we present two depth and phase resolving models based on single and two phase approaches for suspended sediment transport under water waves both models are the extension of a wave hydrodynamic model cornell breaking wave and structure cobras in the two phase approach dilute two phase mass and momentum equations are calculated along with a fluid turbulence closure based on balance equations for the fluid turbulence kinetic energy k f and its dissipation rate f in the single phase approach the fluid flow is described by the reynolds averaged navier stokes equations while the sediment concentration is calculated by an advection diffusion equation for the conservation of sediment mass the fluid turbulence is calculated by k f f equations that incorporate the essential influence of sediment which can also be consistently deduced from the two phase theory by adopting a commonly used sediment flux boundary condition near the bed the proposed models are tested against laboratory measurements of suspended sediment under nonbreaking skewed water waves and shoaling broken waves although the models predict wave averaged sediment concentrations reasonably well the corresponding time histories of instantaneous sediment concentration are less accurate we demonstrate that this is due to the uncertainties in the near bed sediment boundary conditions in addition we show that under breaking waves the near bed sediment pickup cannot be solely parameterized by the bottom friction suggesting that other effects may also influence the near bed sediment boundary conditions

limited depth zonation among bathyal epibenthic megafauna of the gully submarine canyon northwest atlantic abstract the gully is a large submarine canyon incised into the scotian shelf in the northwest atlantic a submersible mounted camera was used to collect 17 km of high resolution video imagery of the soft sediment flanks and floor of the canyon between 1000 and 2500 m depth a depth stratified random survey design with two transects per stratum was followed depth strata were drawn at 1000 1500 m 1500 2000 m and 2000 2500 m reflecting global and regional faunal boundaries the 47 614 individuals or colonies observed on the transects were identified into 49 unique taxa drawn from 7 phyla while 21 additional taxa were observed between the transect lines cnidaria was the most diverse phylum 22 taxa on the transects followed by the echinodermata 15 taxa most fauna were sessile or sedentary suspension feeders a species of xenophyophorida likely syringammina sp was the most abundant taxon cluster analysis of transects based on a bray curtis bc matrix of species abundance identified one cluster of five transects and one independent transect the deepest transect 2406 m average depth a similarity profile test indicated that this structure is not random there was a significant change in the megafaunal assemblage with depth over scales of 10s of kilometers accounting for 65 of the variation in the bc matrix both total organic carbon and labile carbon were higher in cores from the 1000 1500 m stratum than at greater depth consistent with transport of food and sediments into the canyon from shallower waters the first principal component calculated from species abundances separated the two transects from the 1000 1500 m depth stratum from the others indicating that sediment food supply influences community structure and composition over small spatial scales 10 m eight groups of species associations were identified however the associations between the species within each group were not strong with the highest correlation between the xenophyophorida and the pennatulacea 0 66 at this spatial scale substrate type was an important factor with hard and soft bottom species associations being identified

temperature and salinity variability on the scotian shelf and in the gulf of maine 1945 1990 examination of temperature and salinity data from the scotian shelf gulf of maine gulf of st lawrence and the adjacent continental slope has shown that the dominant low frequency event over the last 45 years was a cooling and subsurface freshening of the water masses from 1952 to 1967 followed by a rapid reversal of these trends the largest temperature and salinity changes 1952 1967 were 4 6 c and 0 7 respectively and occurred at about 100 m over the slope exchanges with shelf waters and vertical mixing gave rise to the surface manifestation of this variability the westward transport of the labrador current was found to have similar variability increasing from about 1 106 m3 s 1 in the early 1950s to about 4 106 m3 s 1 in the mid 1960s a simple model that accounts for this variation of transport and has a constant entrainment of north atlantic water indicates that changes of the westward flow of the labrador current could contribute significantly to the t s fluctuations

morphodynamic behaviour of a mixed sand gravel ebb tidal delta deben estuary suffolk uk the morphodynamics of inlets and ebb tidal deltas reflect the interaction between wave and tidal current driven sediment transport and significantly influence the behaviour of adjacent shorelines studies of inlet morphodynamics have tended to focus on sand dominated coastlines and reference to gravel dominated or gravel rich inlets is rare this work characterises and conceptualises the morphodynamics of a meso tidal sand gravel inlet at the month of the deben estuary southeast england behaviour of the inlet and ebb tidal delta over the last 200 yr is analysed with respect to planform configuration and bathymetry the estuary inlet is historically dynamic with ebb tidal shoals exhibiting broadly cyclic behaviour oil a 10 to 30 yr timescale quantification of inlet parameters for the most recent cycle 1981 2003 indicate an average ebb delta volume of 1 x 10 6 m 3 and inlet cross sectional area of 775 m 2 bypassing volumes provide a direct indicator of annual longshore sediment transport rate over this most recent cycle of 30 40 x 10 3 m 3 yr 1 short term increases in total ebb tidal delta volume are linked to annual variability in the north to northeasterly wind climate the sediment bypassing mechanism operating in the deben inlet is comparable to the ebb delta breaching model of fitzgerald fitzgerald d m 1988 shoreline erosional depositional processes associated with tidal inlets in aubrey d g weishar l ed hydrodynamics and sediment dynamics of tidal inlets springer verlag inc new york pp 186 225 although the scales and rates of change exhibited are notably different to sand dominated systems a systematic review of empirical models of sand dominated inlet and ebb tidal delta morphodynamics e g those of o brien m p 1931 estuary tidal prisms related to entrance areas civil engineering 1 738 739 walton t l and adams w d 1976 capacity of inlet outer bars to store sand proceedings of 15th coastal engineering conference 1919 1937 gaudiano d j kana t w 2001 shoal bypassing in mixed energy inlets geomorphic variables and empirical predictions for nine south carolina inlets j coast res 17 2 280 291 shows the deben system to be significantly smaller yet characterised by a longer bypassing cycle than would be expected for its tidal prism this is attributed to its coarse grained sedimentology and the lower efficiency of sediment transporting processes c 2005 elsevier b v all rights reserved

acoustical detection of high density krill demersal layers in the submarine canyons off georges bank high density demersal layers of krill have been detected in the submarine canyons off georges bank by means of a high frequency dual beam bioacoustical technique krill densities in these demersal layers were observed to be two to three orders of magnitude greater than the highest densities observed in water column scattering layers such abundances may help explain the unusually high squid and demersal fish production estimates attributed to the georges bank ecosystem

submarine canyons as important habitat for cetaceans with special reference to the gully a review there has been much research interest in the use of submarine canyons by cetaceans particularly beaked whales family ziphiidae which appear to be especially attracted to canyon habitats in some areas however not all submarine canyons are associated with large numbers of cetaceans and the mechanisms through which submarine canyons may attract cetaceans are not clearly understood this paper reviews some of the cetacean associations with submarine canyons that have been anecdotally described or presented in scientific literature and discusses the physical oceanographic and biological mechanisms that may lead to enhanced cetacean abundance around these canyons particular attention is paid to the gully a large submarine canyon and marine protected area off eastern canada for which there exists some of the strongest evidence available for submarine canyons as important cetacean habitat studies demonstrating increased cetacean abundance in the gully and the processes that are likely to attract cetaceans to this relatively well studied canyon are discussed this review provides some limited evidence that cetaceans are more likely to associate with larger canyons however further studies are needed to fully understand the relationship between the physical characteristics of canyons and enhanced cetacean abundance in general toothed whales especially beaked whales and sperm whales appear to exhibit the strongest associations with submarine canyons occurring in these features throughout the year and likely attracted by concentrating and aggregating processes by contrast baleen whales tend to occur in canyons seasonally and are most likely attracted to canyons by enrichment and concentrating processes existing evidence thus suggests that at least some submarine canyons are important foraging areas for cetaceans and should be given special consideration for cetacean conservation and protection

data analysis of bed concentration of suspended sediment an empirical relation for the bed concentration of suspended sediment cb defined at a few grain diameters above the bed is developed its derivation is based on the experimental data sets of guy et al in 1966 the values of the near bed concentration were obtained by first isolating the suspended load transport from the observed rates of total load transport by use of a bed load formula the suspended load was then equated to einstein s formulation which allowed the determination of cb the influence of large concentrations of suspended sediment and of the reference level for cb on the calculated values of bed concentration has been analyzed the proposed relation compares satisfactorily to values of near bed concentration obtained from independent data sets the procedure used to derive cb provides a simple method for the calculation of the total transport rate of noncohesive sediment