shear induced convective mixing in bottom boundary layers on slopes field data from a stratified lake demonstrate that buoyancy driven convective mixing can be an important mechanism for the formation of well mixed bottom boundary layers bbls on slopes convective turbulence is caused by differential transport of stratified water masses along the slope of a basin because the current velocity usually decreases toward the sediment water at some distance from the bottom is transported faster than is water below during upslope flow this process leads to transport of heavier water on top of lighter water and hence to unstable stratification within the bbls analogously strong bbl stratification occurs during downslope flow high frequency acoustic doppler current profiler adcp and temperature measurements in the bbls of a lake revealed the cyclic occurrence of convective turbulence driven by periodic across slope currents of internal seiching the estimated maximum buoyancy flux within the bbls was in good agreement with the highest observed dissipation rates of turbulent kinetic energy this suggests that in our specific case classical bottom shear production and the mentioned buoyancy driven convective production contributed by similar amounts to the turbulent kinetic energy

asymmetric tidal mixing due to the horizontal density gradient abstract stratification and turbulent mixing exhibit a flood ebb tidal asymmetry in estuaries and continental shelf regions affected by horizontal density gradients the authors use a large eddy simulation les model to investigate the penetration of a tidally driven bottom boundary layer into stratified water in the presence of a horizontal density gradient turbulence in the bottom boundary layer is driven by bottom stress during flood tides with low gradient ri and flux rf richardson numbers but by localized shear during ebb tides with ri and rf 0 2 in the upper half of the boundary layer if the water column is unstratified initially the les model reproduces periodic stratification associated with tidal straining the model results show that the energetics criterion based on the competition between tidal straining and tidal stirring provides a good prediction for the onset of periodic stratification but the tidally averaged horizontal richardson number rix has a threshold value of abou

measurements of shoaling internal waves and turbulence in an estuary 1 the shoaling of horizontally propagating internal waves may represent an important source of mixing and transport in estuaries and coastal seas including such effects in numerical models demands improvements in the understanding of several aspects of the energetics especially those relating to turbulence generation and observations are needed to build this understanding to address some of these issues in the estuarine context we undertook an intensive field program for 10 days in the summer of 2008 in the st lawrence estuary the sampling involved shore based photogrammetry ship based surveys and an array of moorings in the shoaling region that held both conventional and turbulence resolving sensors the measurements shed light on many aspects of the wave shoaling process wave arrivals were generally phase locked with the m2 tide providing hints about far field forcing in the deeper part of the study domain the waves propagated according to the predictions of linear theory in intermediate depth waters the waves traversed the field site perpendicularly to isobaths a pattern that continued as the waves transformed nonlinearly acoustic doppler velocimeters permitted inference of the turbulent energetics and two main features were studied first during a period of shoaling internal waves turbulence dissipation rates exceeded values associated with tidal shear by an order of magnitude second the evolving spectral signatures associated with a particular wave shoaling event suggest that the turbulence is at least partly locally generated overall the results of this study suggest that parameterizations of wave induced mixing could employ relatively simple dynamics in deep water but may have to handle a wide suite of turbulence generation and transport mechanisms in inshore regions

fossil hydrothermal systems tracking eocene climate change in antarctica comment and reply it is an outstanding property of hydrogen and oxygen isotopes in surface fresh waters to be directly climate related since actual traces of ancient waters such as in fluid inclusions are often lost or difficult to read the pressure to use substitute information is intense dallai et al 2001

sediment pumping by tidal asymmetry in a partially mixed estuary 1 observations collected at two laterally adjacent locations are used to examine the processes driving sediment transport in the partially mixed york river estuary estimates of sediment flux are decomposed into advective and pumping components to evaluate the importance of tidal asymmetries in turbulent mixing at the instrumented location in the estuarine channel a strong asymmetry in internal mixing due to tidal straining is documented with higher values of eddy viscosity occurring during the less stratified flood tide as a result of this asymmetry more sediment is resuspended during the flood phase of the tide resulting in up estuary pumping of sediment despite a net down estuary advective flux at the instrumented location on the adjacent shoal where no pronounced tidal asymmetry in internal mixing was found both the pumping flux and advective flux were directed down estuary the down estuary pumping of sediment on the shoal appears to be driven by asymmetries in bed stress the impact of tidal asymmetries in bed stress at the channel location was negated because the amount of sediment available for resuspension was limited as a result the pumping flux was dominated by the overlying asymmetries in internal mixing the asymmetries in stratification appear to exert an important control on the vertical distribution of sediment by both impacting the eddy diffusivity as well as the fall velocity during the more turbulent flood tide the fall velocities are smaller suggesting the kolmogorov microscale is setting the upper bound on floc diameter

residual transport of suspended material by tidal straining near sloping topography abstracttidal straining is known to have an important impact on the generation of residual currents and the transport of suspended material in estuaries and the coastal ocean essential for this process is an externally imposed horizontal density gradient typically resulting from either freshwater runoff or differential heating here it is shown that near sloping topography tidal straining may effectively transport suspended material across isobaths even if freshwater runoff and differential heating do not play a significant role a combined theoretical and idealized modeling approach is used to illustrate the basic mechanisms and implications of this new process the main finding of this study is that for a wide range of conditions suspended material is transported upslope by a pumping mechanism that is in many respects similar to classical tidal pumping downslope transport may also occur however only for the special cases of slowly sinking material in the vicinity of slopes with a slope angle la

particle trapping in estuarine tidal flows particle trapping in estuarine turbidity maxima etm is caused primarily by convergent mean and or tidal fluxes of sediment the result is an approximately bell shaped along channel distribution of vertically integrated tidal cycle mean suspended sediment concentration observations from the columbia river estuary suggest that 1 strong two layer or internal along channel residual and overtide flows are generated by time varying stratification and 2 correlations between the near bed velocity and the suspended sediment fields at these frequencies are important in landward transport of sediment a new spatially and temporally integrated form of the sediment conservation equation has been derived to analyze this trapping process time changes in tidally averaged sediment concentration between two estuarine cross sections can be shown to be related to the divergence of the seaward river flow transport the divergence of velocity shear sediment stratification correlations for the mean flow and each tidal constituent and net erosion or deposition at the bed vertically integrated variables other than seaward river transport are absent from this integrated balance analysis of sediment fluxes using this balance supports the idea that internal residual and overtide circulations are primarily responsible for the landward sediment transport on the seaward side of etm found near the upstream limits of salinity intrusion the balance also shows that attempts to represent fluxes causing trapping of sediment in an etm as a product of a time mean vertically integrated along channel gradient and a diffusivity inevitably lead to the appearance of countergradient transport and thus a negative diffusivity on the seaward side of the etm this result occurs because the trapping process is inherently nonlinear and at least two dimensional and because a one dimensional representation is physically unrealistic

charcoal in the silurian as evidence for the earliest wildfire rare basal pridoli plant fossils which resemble the rhyniophytoid hollandophyton colliculum and have exceptional three dimensional cellular anatomy are preserved as charcoal as such these fossils from ludford lane in the welsh borders are evidence of the earliest recorded wildfire and are the first documented from before the devonian the fossils represent the charred remains of a low growing low diversity in situ rhyniophytoid or cryptospore bearing plant vegetation charred during a low temperature fire

a dynamic equation for the potential energy anomaly for analysing mixing and stratification in estuaries and coastal seas abstract in this paper a time dependent dynamic equation for the potential energy anomaly is rigorously derived from dynamic equations for potential temperature and salinity the continuity equation and the equation of state for sea water the terms locally changing are a the advection b the depth mean straining c the non mean straining d the vertical advection e the vertical mixing f surface and bottom density fluxes g inner sources of density e g due to absorption of solar radiation and the non linearity of the equation of state and h horizontal divergence of horizontal turbulent density fluxes in order to derive the equation in concise form a vertical velocity linearly varying with depth with respect to depth proportional vertical coordinates had to be defined the evaluation of the terms in the equation is then carried out for a one dimensional tidal straining study and a two dimensional estuarine circulation study comparisons to empirical estimates for these terms are made for the one dimensional study it is concluded that the equation provides a general reference for empirical bulk parameterisations of stratification and mixing processes in estuaries and coastal seas and that it is a tool for complete analysis of the relevant terms from numerical models

convectively driven mixing in the bottom boundary layer closely spaced vertical profiles through the bottom boundary layer over a sloping continental shelf during relaxation from coastal upwelling reveal structure that is consistent with convectively driven mixing parcels of fluid were observed adjacent to the bottom that were warm by several millikelvin relative to fluid immediately above on average the vertical gradient of potential temperature in the superadiabatic statically unstable bottom layer was found to be 21 7 3 1024 km 21 or 6 0 3 1025 kg m24 in potential density turbulent dissipation rates increased toward the bottom but were relatively constant over the dimensionless depth range 0 4 1 0z d where d is the mixed layer height the rayleigh number ra associated with buoyancy anomalies in the bottom mixed layer is estimated to be approximately 1011 much larger than the value of approximately 10 3 required to initiate convection in simple laboratory or numerical experiments an evaluation of the data in which the bottom boundary layer was unstably stratified indicates that the greater the buoyancy anomaly is the greater the turbulent dissipation rate in the neutral layer away from the bottom will be the vertical structures of averaged profiles of potential density potential temperature and turbulent dissipation rate versus nondimensional depth are similar to their distinctive structure in the upper ocean during convection nearby moored observations indicate that periods of static instability near the bottom follow events of northward flow and local fluid warming by lateral advection the rate of local fluid warming is consistent with several estimates of offshore buoyancy transport near the bottom it is suggested that the concentration of offshore ekman transport near the bottom of the ekman layer when the flow atop the layer is northward can provide the differential transport of buoyant bottom fluid when the density in the bottom boundary layer decreases up the slope

a modified law of the wall applied to oceanic bottom boundary layers 1 near the bottom the velocity profile in the bottom boundary layer over the continental shelf exhibits a characteristic law of the wall that is consistent with local estimates of friction velocity from near bottom turbulence measurements farther from the bottom the velocity profile exhibits a deviation from the law of the wall here the velocity gradient continues to decrease with height but at a rate greater than that predicted by the law of thewall with the local friction velocity we argue that the shape of the velocity profile is made consistent with the local friction velocity by the introduction of a new length scale that near the boundary asymptotes to a value that varies linearly from the bottom farther from the boundary this length scale is consistent with the suppression of velocity fluctuations either by stratification in the upper part of the boundary layer or by proximity to the free surface the resultant modified law of the wall provides a good representation of velocity profiles observed over the continental shelf when a local estimate of the friction velocity from coincident turbulence observations is used the modified law ofthe wall is then tested on two very different sets of observations from a shallow tidal channel and from the bottom of the mediterranean outflow plume in both cases it is argued that the observed velocity profile is consistent with the modified law of the wall implicit in the modified law of the wall is a new scaling for turbulent kinetic energy dissipation rate this new scaling diverges from the law of the wall prediction above 0 2d where d is the thickness of the bottom boundary layer and agrees with observed profiles to 0 6d

near bottom shear stresses in a small highly stratified estuary 1 this paper examines near bottom shear stresses at two locations in a small highly stratified estuary the navesink river new jersey usa the shear stresses obtained from acoustic doppler current profilers adcps operating in the recently developed mode 11 at a high spatial resolution are examined in detail measurement noise of the adcp is estimated using autocorrelation analyses and is found to be small but correlated with velocity measurement noise in estimates of reynolds stress is found to be somewhat smaller than that obtained in earlier studies for the adcp operating in mode 4 internal waves may have produced observed correlated oscillatory motions the effect of these motions on reynolds stress estimates is quantified and shown to be at least an order of magnitude less than the total measured stress and probably much less the high spatial resolution profiles from the adcp operating in mode 11 allow excellent measurements of near bed vertical velocity gradients log profile estimates of stress are poorly related to reynolds estimates even when stability measures based on near bed density gradients are taken into account we show that upper layer pycnoclines likely inhibit turbulence and bias log profile estimates even at a half meter above the bed where the water column is well mixed

tidal modulation on the changjiang river plume in summer 1 tide effects on the structure of the near field changjiang river plume and on the extension of the far field plume have often been neglected in analysis and numerical simulations which is the focus of this study numerical experiments highlighted the crucial role of the tidal forcing in modulating the changjiang river plume without the tidal forcing the plume results in an unrealistic upstream extension along the jiangsu coast with the tidal forcing the vertical mixing increases resulting in a strong horizontal salinity gradient at the northern side of the changjiang river mouth along the jiangsu coast which acts as a dynamic barrier and restricts the northward migration of the plume furthermore the tidal forcing produces a bidirectional plume structure in the near field and the plume separation is located at the head of the submarine canyon a significant bulge occurs around the head of the submarine canyon and rotates anticyclonically which carries a large portion of the diluted water toward the northeast and merges into the far field plume a portion of the diluted water moves toward the southeast which is mainly caused by tidal rectification this bidirectional plume structure is more evident under certain wind conditions during the neap tide with the reduced tidal energy the near field plume extends farther offshore and the bulge becomes less evident these dynamic behaviors are maintained and are fundamentally important in the region around the river mouth even under the summer monsoon and the shelf currents although in the far field the wind forcing and shelf currents eventually dominate the plume extension

reynolds stress observations in continental shelf seas abstract the three basic observational approaches to estimating turbulence parameters in continental shelf seas are free fall micro structure probes from which dissipation is inferred fast sample 10 20 hz current meters in sea bed frames measuring turbulence intensity directly and fast sample o 1 hz high frequency acoustic doppler current profilers adcps where reynolds stress profiles and hence turbulence production can be estimated from the variance of the along beam data uncertainties are associated with each approach since turbulence is a small scale high frequency phenomenon and since estimates can easily be contaminated by the presence of surface waves this paper concentrates on the latter two approaches particularly the adcp method focussing on the degree of confidence that can be placed on the estimates results are presented from nine experiments from six sites in the north and irish seas and one in the gulf of california involving the deployment of 0 6 and 1 2 mhz standard broadband adcps mounted in sea bed frames the sites ranged from very tidally energetic shallow 20 m deep to low tidal energy deeper 110 m the adcps recorded data with a variety of sample regimes from 2 to 0 5 hz bin sizes ranged from 0 25 to 1 m in two of the experiments the adcp near bed reynolds stress estimates were tested against independent estimates from toroidal electro magnetic current meters measuring the three components of current vertical and both horizontal at 8 hz deployed on a nearby frame in all cases the correlation coefficient squared between the two sets of reynolds stress estimates was 0 7 in a further three recent deployments an acoustic doppler velocimeter adv was deployed on the bottom frame with the adv measuring volume located within the first adcp bin and sampling at 20 or 25 hz the adv measurements also show an explained variance of about 80 and a transfer function of about 1 during periods where waves were not present one objective of these studies was to test and improve representation of dissipation processes in two and three dimensional numerical models including the concept of the constant stress layer at its very simplest bottom stress is estimated from the depth averaged flow via a quadratic drag law calculations from these measurements give values for the drag coefficient between 0 0006 and 0 0019 averaging 0 0011 smaller than the value used in most depth averaged numerical models 0 0025 there is some evidence that the value of the drag coefficient is dependent on the tidal current speed

near bottom turbulence measurements in a partially mixed estuary turbulent energy balance velocity structure and along channel momentum balance abstract a set of moored bottom mounted and shipboard measurements obtained in a straight section of the lower hudson estuary during late summer and early fall of 1995 determine velocity density and along channel pressure gradient throughout the 15 m water column as well as providing direct eddy correlation estimates of reynolds stress and indirect inertial range estimates of dissipation within 3 m of the bottom the analysis focuses on testing 1 a simplified turbulent kinetic energy equation in which production balances dissipation 2 the prandtl karman law of the wall which is a relationship between bottom stress and near bottom velocity gradient and 3 a simplified depth integrated along channel momentum balance involving local acceleration pressure gradient and bottom stress estimates of production and dissipation agree well throughout the entire record the relationship between bottom stress and velocity gradient is consistent with the law of the wall within approximately 1 m of the sea

the cycle of turbulent dissipation in the presence of tidal straining in regions of large horizontal density gradient tidal straining acts to produce a periodic component of stratification that interacts with turbulent mixing to control water column structure and flow a 25 h series of measurements of the rate of dissipation of turbulent kinetic energy e in the liverpool bay region of freshwater influence rofi have revealed the form of this interaction and indicate substantial differences from regions where horizontal gradients are weak in the rofi system there is a pronounced difference between flood and ebb regimes during the ebb the water column stratifies and strong dissipation is confined to the lower half of the water column by contrast during the flood stratification is eroded with complete vertical mixing occurring at high water and high values of dissipation 3 mw m23 extending throughout the water column the cycle of dissipation is therefore predominantly semidiurnal in the upper layers whereas near the bottom boundary the principal variation is at the m4 frequency as observed in regions of horizontal uniformity toward the end of the flood phase of the cycle tidal straining produces instabilities in the water column that release additional energy for convective mixing confirmation of increased vertical motions throughout the water column during the late flood and at high water is provided by measurements of vertical velocity and the error velocity from a bottom mounted acoustic doppler current profiler

an exploratory model study of sediment transport sources and deposits in the bohai sea yellow sea and east china sea a regional ocean circulation model roms is used to simulate the chinese land derived sediment transport in the bohai sea yellow sea and east china sea byecs the model includes the effect of currents tides and waves on the sediment transport and is used to study the pathway and dynamic mechanisms of the fine grain sediment transport from the huanghe river yellow river the old huanghe delta and the changjiang river yangtze river in the byecs the seasonal variability of the sediment transport in the byecs and the sources of the yellow sea trough mud patch the mud patch southwest of cheju island the mud patch offshore from the zhejiang and fujian provinces and the okinawa trough mud patch are discussed the results show that the huanghe river sediment can be transported to the yellow sea trough but little makes it to the outer shelf while the old huanghe delta sediment is mainly transported to the yellow sea trough most of the sediment from the changjiang river mouth is carried to the mud patch off the coast of the zhejiang and fujian provinces but with part of this sediment also transported to the yellow sea trough the model shows that it is difficult to transport land derived sediment to the okinawa trough mud patch under normal conditions the model also has difficulty accounting for the deposition of sediment in the region to the southwest of cheju island and offshore from the zhejiang and fujian provinces an issue requiring further study

structure and dynamics of fluid muds on the amazon continental shelf thick layers of fluid mud occur in strong tidal flows over the inner portion of the amazon continental shelf in regions of strong salinity fronts associated with the plume discharged from the amazon river detailed shipboard profile measurements obtained in this region during a multidisciplinary amazon shelf sediment study amasseds provide an unprecedented opportunity to examine the structure and dynamics of fluid muds under natural conditions the analysis focuses on flows in which the motion is fully turbulent and suspended sediment dominates the stratification under these conditions a comparison of measurements and one dimensional model calculations indicates that vertical transport is controlled by suppression of turbulent mixing at gradient richardson numbers near 1 4 this constraint produces a distinctive vertical structure and leads to an upper bound on the total amount of suspended sediment that may be carried in a turbulent suspension by a tidal flow

observations of tidal straining within two different ocean environments in the east china sea stratification and near bottom turbulence tidal straining describes the straining effect induced by the vertical shear of oscillatory tidal currents that act on horizontal density gradients it tends to create tidal periodic stratification and modulate the turbulence in the bottom boundary layer bbl here we present observations of current hydrology and turbulence obtained at two mooring stations that are characterized by two typical hydrological environments in the east china sea ecs one is located adjacent to the changjiang river s mouth and the other is located over a sloping shelf which is far from the freshwater sources tidal straining induces a semidiurnal switching between stable and unstable stratification at both stations near bottom high frequency velocity measurements further reveal that the dissipation rate of turbulent kinetic energy tke is highly elevated during periods when unstable stratification occurs a comparison between the tke dissipation rate e and the shear production p further reveals that the near bottom mixing is locally shear induced most of the time except during the unstable stratification period within this period the magnitude of dissipation exceeds the expected value based on the law of the wall by an order of magnitude the buoyancy flux that calculated by the balance method is too small to compensate for the existing discrepancy between the dissipation and shear production another plausible candidate is the advection of tke which may play an important role in the tke budget during the unstable stratification period

the effect of sediment stratification on tidal dynamics and sediment transport patterns 1 the western tip of southwest korea is characterized by a tidally dominated turbid coastal environment there are well developed tidal flats along the coast and around islands together with offshore sand ridges several tens of kilometers long in the west the effects of bottom boundary layer bbl sediment stratification on sediment transport and tidal dynamics in this environment were examined using a sediment transport model coupled with a three dimensional tidal hydrodynamic model model experiments using two scenarios with and without the effect of sediment induced stratification showed that bbl sediment stratification influenced the spatial distribution and reduced the magnitude of net sedimentation the presence of a sediment stratified bbl also led to a reduction in suspended sediment fluxes and an increase in the vertical gradient of sediment concentrations in the water column these variations occurred because sediment induced bbl stratification leads to not only a reduction in bottom shear stress but also a decrease in buoyancy production ofturbulent kinetic energy and an associated dampening ofturbulence the significant reductions in turbulence and bottom shear stress result in changes to the vertical current structure of the m 2 tide including alteration of the tidal ellipse configuration and an increase in vertical shears of the tidal current amplitude and phase these reductions also lead to a slight increase in tidal amplitudes due to the decreased tidal energy dissipation the model results indicate that feedback between the sediment transport dynamics and hydrodynamics is an important factor in modeling sediment transport dynamics in tidally dominated turbid coastal environments such environments include the west coast of korea and the yellow sea a suitable approach to simulating the effects of this feedback may be the use of a modified bottom drag coefficient as a stability function together with the inclusion of the effect of sediment stratification on the hydrodynamics

the effects of suspended sediment on turbulence within an estuarine turbidity maximum predictions of cohesive sediment transport are hampered by poor understanding of the effects of sediment suspensions upon the nature of near bed turbulence in this study current velocities associated turbulence and flow characteristics were measured within an estuarine turbidity maximum during two spring ebb tides measurements at two heights both within and above a near bed high concentration layer show the importance of intermittent internal waves the ratio of vertical to horizontal turbulence intensities exceeded 1 0 when waves were present the waves were more significant above the layer than within it comparison between the turbulent kinetic energy and the reynolds stresses showed inactive turbulence occurring at stresses less than about 0 2 n m 2 during these periods negative suspended sediment fluxes occurred indicating that the turbulence could enhance settling of the sediment the effect of the intermittent internal waves on the turbulent bursting structure and their interaction with the concentration profile appears to increase the variability of the reynolds fluxes of suspended sediment and cause downwards reynolds fluxes especially beneath the lutocline

drivers of residual estuarine circulation in tidally energetic estuaries straight and irrotational channels with parabolic cross section the generation of residual circulation in a tidally energetic estuary with constant longitudinal salinity gradient and parabolic cross section is examined by means of a two dimensional cross sectional numerical model neglecting river runoff and stokes drift it is shown how the longitudinal and lateral residual circulation can be decomposed into contributions from various processes such as tidal straining circulation gravitational circulation advectively driven circulation and horizontal mixing circulation the sensitivity of the residual circulation and its components from various processes to changes in forcing is investigated by varying the simpson number nondimensional longitudinal buoyancy gradient and the unsteadiness parameter nondimensional tidal frequency as well as the bed roughness and the width of the estuary for relatively weak salinity gradient forcing the tidal straining circulation dominates the residual exchange circulation in support of classical estuarine circulation up estuary flow near the bed and down estuary flow near the surface the strength of the longitudinal estuarine circulation clearly increases with increased salinity gradient forcing however when the simpson number exceeds 0 15 the relative contributions of both gravitational circulation and advectively driven circulation to estuarine circulation increase substantially lateral residual circulation is relatively weak for small simpson numbers and becomes flood oriented divergent flow near the bed and convergent flow near the surface for larger simpson numbers because of increasing contributions from gravitational and advectively driven circulation increasing the unsteadiness number leads to decreased longitudinal and lateral residual circulation although changes in bed roughness result in relatively small changes in residual circulation results are sensitive to the width of the estuary mainly because of changes in residual exchange circulation driven by tidal straining

role of straining and advection in the intratidal evolution of stratification vertical mixing and longitudinal dispersion of a shallow macrotidal salt wedge estuary 1 a month of flow observations in the snohomish river estuary reveals the complex intratidal and fortnightly stratification mixing and dispersion dynamics in this macrotidal shallow salt wedge estuary system both salt wedge propagation and concomitant straining of the density field dominate temporal and spatial variations in stratification leading to intratidal variability of shear and mixing that differs in important ways from observations in partially mixed estuaries bottom generated turbulent kinetic energy production is enhanced during spring tides and acts in concert with straining to counteract advection and minimize vertical stratification during the spring flood tides this bottom generated mixing contributes to a buoyancy flux near the top of a well mixed layer during strong flood tides during strong ebb tides interfacial shear production and buoyancy flux occur along the sharp straining enhanced interface just before the system becomes well mixed longitudinal dispersion is less sensitive to the spring neap cycle yet exhibits strong intratidal variability reduced longitudinal dispersion is observed during the large floods relative to the rest of the tidal cycle behavior we attribute to a lack of vertical shear overall ebb tide advection and straining enhance stratification and longitudinal dispersion and allow for interfacial mixing intratidal variability which varies on the spring neap scale is a dominant feature of this estuary suggesting the importance of intratidal processes and tidally varying mixing coefficients in similar strongly stratified strongly forced estuaries