Local Hydrodynamic Conditions Research Articles

Using Multibeam Echo-Sounder Data to Identify Shipwreck Sites: archaeological assessment of the Joint Irish Bathymetric Survey data

This paper describes Phase 1 of the project ‘Archaeological Applications of the Joint Irish Bathymetric Survey (JIBS) Data’, analysing bathymetric and backscatter data derived from multibeam surveys off the north coast of Ireland. In particular, the usability of the data for shipwreck detection, identification and site characterization is explored. In Phase 1, the data was screened for anomalous sea-bed features, which were subsequently described, catalogued and categorized according to their archaeological potential and cross-referenced against existing records. A planned second phase of this project will examine each anomaly in greater detail together with the local and regional hydrodynamic conditions.

Investigations of axial and radial variations of heat transfer coefficient in bubbling fluidized bed with fast response probe

A fast response probe used in this study allowed measurements of local heat transfer variations with time in a gas fluidized bed. These variations have been related to local hydrodynamic conditions in the fluidized bed. Measurements have been carried out in a Plexiglas column of inside diameter 0.15m in the fluidized bed section and height of about 2m. The bed consisted of 150μm sand particles of static bed height 0.45m. The gas velocity was varied up to 0.4m/s. The bed hydrodynamics could be mapped by the radial and axial variations in heat transfer coefficients captured by the probe. The limitations and applicability of literature correlations and models for predictions of heat transfer coefficient in gas fluidized bed are pointed out. A correlation to predict heat transfer coefficients at a given radial location is proposed.

Effect of near‐bed turbulence on chronic detachment of epilithic biofilm: Experimental and modeling approaches

The biomass dynamics of epilithic biofilm, a collective term for a complex microorganism community that grows on gravel bed rivers, was investigated by coupling experimental and numerical approaches focusing on epilithic biofilm‐flow interactions. The experiment was conducted during 65 days in an artificial rough open‐channel flow, where filtered river water circulated at a constant discharge. To characterize the effect of near‐bed turbulence on the chronic detachment process in the dynamics of epilithic biofilm, local hydrodynamic conditions were measured by laser Doppler anemometry and turbulent boundary layer parameters inferred from double‐averaged quantities. Numerical simulations of the EB biomass dynamics were performed using three different models of chronic detachment based upon three different descriptors for the flow conditions: Discharge Q, friction velocity u*, and roughness Reynolds number k+. Comparisons of numerical simulation results with experimental data revealed chronic detachment to be better simulated by taking the roughness Reynolds number as the external physical variable forcing chronic detachment. Indeed, the loss of epilithic matter through the chronic detachment process is related not only to hydrodynamic conditions, but also to change in bottom roughness. This suggests that changes in the behavior and dimensions of river bed roughness must be considered when checking the dynamics of epilithic biofilm in running waters.

Sedimentological and palaeoecological integrated analysis of a Miocene channelized carbonate margin, Matese Mountains, Southern Apennines, Italy

Lower–Middle Miocene temperate marine carbonates occur in the Matese Mountains, Southern Apennines (Italy). These carbonates formed in an open-shelf depositional system with an uneven margin, 10 km long and up to 6 km wide. Shelf margin morphology shows multiple submarine channelized carbonate deposits which are dominated by coralline red algae and subordinate bryozoans. Two main channel networks (Pietraroia and Regia Piana channels) with their sedimentary bodies were analysed. The studied submarine channels grew by sediment accumulation as prograding bodies on a tectonic modelled substrate. Shallow-water rhodalgal skeletal debris, from moderately re-mobilized up to significantly re-worked, built up the complex channel-system fills in which sedimentary lenses overlapped and partially amalgamated one another when they were still unlithified. The early channelized succession is characterized by parautochthonous bryozoan floatstone and rhodolith/bryozoan floatstone representing soft muddy substrates in a low water turbulence and high turbidity setting. The rhodoliths, dominated by melobesioid coralline algae, are sub-discoidal and sub-spheroidal in shape with a characteristic loosely-packed inner arrangement. These sediments, whose latter portion underwent submarine diagenetic processes (incipient to evoluted hard-grounds), were eroded and successively covered by shallower water gravitative deposits constituted by rhodolith floatstone/rudstone. Their rhodoliths, constituted by melobesioids, mastophoroids and subordinate lithophylloids and sporolithaceans, are mainly spheroidal/sub-spheroidal in shape with subordinate sub-discoidal specimens, with massive and laminar inner arrangements. The lack in early lithification can be drawn back to the physiography of the channelized shelf margin, to the active tectonic as well as to the temperate-type carbonate dominant biogenic components. The depositional surface profile and local hydrodynamic conditions were the major factors controlling sedimentary facies, which differ in their relative proportions of dominant components, their internal structures and sedimentary-body geometries.

Components, facies and ramps: Redefining Upper Oligocene shallow water carbonates using coralline red algae and larger foraminifera (Venetian area, northeast Italy)

Chattian mixed carbonate-siliciclastic deposits from two palaeogeographic units of Southern Alps, the Lessini Shelf and Venetian foreland basin of northeast Italy, are studied with respect to facies distributions and controlling ecological factors on dominant biogenic components. These ramp depositional systems are located in the western Southern Alps on the Lessini Shelf, and in the eastern Southern Alps in the Venetian foreland basin. The successions show an extensive geographic distribution of at least 150 km × 40 km at the southern margin of the Southern Alps. Palaeoenvironments are inferred following microfacies characteristics and floral and faunal indicators, especially those of coralline red algae and larger foraminifera. An inner- to middle homoclinal ramp morphology is reconstructed based on facies distributions and taxonomic and coralline algal growth-form proxy data. The distribution along depositional strike shows variation from thinner, carbonate dominated sequence in the west (Monti Berici and Monti Lessini) to a more variable, mixed carbonate-siliciclastic dominated environment to the east (Vittorio Veneto, Alpago). Facies character and occurrence are controlled by local hydrodynamic conditions and varying water turbidity of the studied ramp depositional system. The general facies succession shows a transgressive sequence from the proximal inner- to proximal middle ramp. A shoal belt of trough cross-bedded sandstones occurs in a proximal inner ramp position in all of the studied areas. In a gentle-dipping homoclinal ramp, most benthic organisms inhabited the relatively quite environments off these shoals in a distal inner ramp setting. Basinward environments (proximal middle ramp) constitute areas of maximal carbonate production and consist primarily of larger foraminiferal facies and rhodolith pavements. Larger foraminifera, represented by two larger foraminiferal assemblages, are most diversified in the shallower settings (near the fair-weather wave base, distal inner/proximal middle ramp), whereas coralline algae predominate in deeper areas (proximal middle ramp) constructing extensive rhodolith pavements. Rhodolith pavements are distinguished with respect to rhodolith shape, size, growth-forms and coralline algal taxonomic composition. Larger foraminifera are interpreted with respect to shell structures, shell architectures and comparable Recent counterparts. The analysed benthic communities thrived in a mesotrophic regime within trophic gradients constrained by fluvial influence. Coralline algal dominance and a moderately diverse larger foraminiferal assemblage suggest a tropical/warm temperate transition. The considerable stability imposed on sediments by the rhodolith pavement must also have significantly contributed to the maintenance of a middle ramp profile bulge. This study will contribute to a better understanding of Oligocene carbonates which have received less attention than their Eocene or Miocene counterparts.

Impacts of bottom and suspended cultures of mussels Mytilus spp. on the surrounding sedimentary environment and macrobenthic biodiversity

The aim of this study was to quantify the effect of bottom and suspended mussel cultures, cultured in different physical environments, on the sedimentary environmental conditions and thereby the biodiversity structure of the associated macrofaunal community. We compared two bottom cultures (Limfjorden: microtidal, wind-driven; Oosterschelde: macrotidal) and one suspended culture (Ria de Vigo in an upwelling coastal region). The sedimentary environmental conditions (mud fraction, POC, PON, phosphorus content, chl a breakdown products) were significantly elevated underneath and surrounding bottom and suspended cultures compared to culture-free sediments that were nearby and hydrodynamically similar. The relative change in environmental conditions was more pronounced in the Oosterschelde compared to Limfjorden, most likely due to differences in hydrodynamic forcing and characteristics of the mussel bed. The effect of the suspended cultures in Ria de Vigo on the surrounding sediments was influenced by local topographic and hydrodynamic conditions. The impact of mussels on the benthic community due to biodeposition was clearly seen in the community structure. The species composition changed from species which are typically present in sandy environments to more small opportunistic species, which are typically present in organically enriched sediments. The impact of bottom cultures on the benthic community due to changes in the habitat under the presence of mussels was positive, especially in the Oosterschelde where an increase in the number of epibenthic species was seen. The influence of bottom cultures on the sedimentary environment and on the macrobenthic community seems to be very local. Within the mussel site in Limfjorden, differences were detected between sites where none or almost no mussels were present with sites where mussels were very abundant.

A modeling approach of the influence of local hydrodynamic conditions on larval dispersal at hydrothermal vents

Deep-sea hydrothermal vent animal communities along oceanic ridges are both patchy and transient. Larval dispersal is a key factor in understanding how these communities function and are maintained over generations. To date, numerical approaches simulating larval dispersal considered the effect of oceanic currents on larval transportation over hundreds of kilometers but very seldom looked at the effect of local conditions within meters around chimneys. However, small scale significant variations in the hydrodynamics may influence larval fate in its early stages after release, and hence have a knock-on effect on both dispersal and colonization processes. Here we present a new numerical approach to the study of larval dispersal, considering small scales within the range of the biological communities, called “bio-hydrodynamical” scale, and ranging from a few centimeters to a few meters around hydrothermal sources. We use a physical model for the vent based on jet theory and compute the turbulent velocity field around the smoker. Larvae are considered as passive particles whose trajectories are affected by hydrodynamics, topography of the vent chimney and larval biological properties. Our model predicts that bottom currents often dominate all other factors either by entraining all larvae away from the vent or enforcing strong colonization rates. When bottom currents are very slow ( < 1 mm s - 1 ), general larvae motion is upwards due to entrainment by the main smoker jet. In this context, smokers with vertical slopes favor retention of larvae because larval initial trajectory is nearly parallel to the smoker wall, which increases the chances to settle. This retention phenomenon is intensified with increasing velocity of the main smoker jet because entrainment in the high velocity plume is preceded by a phase when larvae are attracted towards the smoker wall, which occurs earlier with higher velocity of the main jet. Finally, the buoyancy rate of the larvae, measured to be in the range of 0.01 mm s - 1 , is generally irrelevant unless hydrodynamic conditions are balanced, i.e. if the buoyancy rate is comparable to both the bottom current speed and the local water velocity due to entrainment by close smokers. Overall, our model evidences the strong effect of the release point of larvae on their future entrainment within local fluxes. Larvae released from smoker walls might have an entirely different fate than those released further away in the water column. The latter are not, or less, affected by near-chimney hydrodynamics.

Precisely proportioned: intertidal barnacles alter penis form to suit coastal wave action

For their size, barnacles possess the longest penis of any animal (up to eight times their body length). However, as one of few sessile animals to copulate, they face a trade-off between reaching more mates and controlling ever-longer penises in turbulent flow. We observed that penises of an intertidal barnacle (Balanus glandula) from wave-exposed shores were shorter than, stouter than, and more than twice as massive for their length as, those from nearby protected bays. In addition, penis shape variation was tightly correlated with maximum velocity of breaking waves, and, on all shores, larger barnacles had disproportionately stouter penises. Finally, field experiments confirmed that most of this variation was due to phenotypic plasticity: barnacles transplanted to a wave-exposed outer coast produced dramatically shorter and wider penises than counterparts moved to a protected harbour. Owing to the probable trade-off between penis length and ability to function in flow, and owing to the ever-changing wave conditions on rocky shores, intertidal barnacles appear to have acquired the capacity to change the size and shape of their penises to suit local hydrodynamic conditions. This dramatic plasticity in genital form is a valuable reminder that factors other than the usual drivers of genital diversification--female choice, sexual conflict and male-male competition--can influence genital form.

BENTHIC FORAMINIFERA ASSOCIATED WITH THE SOUTH BAHIA CORAL REEFS, BRAZIL

The objective of this study was to assess foraminiferal faunas and their relationship to sediment texture and composition in the reef areas from the coastline to the 30-m isobath between the cities of Corumbau and Nova Vicosa in the extreme south of the State of Bahia. Cluster analysis of the species, identified from 38 samples of surface sediments, revealed a strong correlation with grain size. The principal relationships established between these species and the sediments were the following: (i) Amphistegina lessonii and Peneroplis carinatus were abundant in sandy carbonate sediments and (ii) Ammonia beccarii , Elphidium poeyanum , Pyrgo subsphaerica , Quinqueloculina disparilis curta and Q. lamarckiana were abundant in mixed sand and mud, whether carbonate or mixed carbonate and siliciclastic. The fluctuation in the richness index among samples indicated microenvironmental areas that were unfavorable for some foraminiferal species. Local hydrodynamic conditions result in environments with greater energy where finer sediments, together with many foraminiferal species, have been removed. In more protected areas, weaker hydrodynamic conditions permit the accumulation of fine sediments and organic matter, making the environment suitable for diverse forms of foraminifera. In general, faunal composition is typical of tropical carbonate platforms, where the reef structures provide a variety of microenvironments that account for the variations observed in the foraminiferal fauna.

Bar Morphodynamic Behaviour on the Ebb Delta of a Macrotidal Inlet (Normandy, France)

The purpose of this paper is to describe the morphodynamics of bars located on an ebb delta of a macrotidal inlet system. Although there have been numerous studies on the morphology and physical processes affecting such bars, these concern only microtidal and mesotidal settings. The west Cotentin coast (Normandy, France) is a fine example of a macrotidal coast with one of the largest tidal ranges in the world. The mean spring tidal range is up to 11 m. Fieldwork was undertaken during one month and involved the deployment of an electromagnetic current meter, a pressure sensor, and differential global positioning system surveys to measure topographic changes. Along the western coast of Cotentin, in spite of the very large tidal inlets, bars are generally small (2 m high and 250 m long) compared with other tidal environments. During the campaign, the bar migrated exclusively landward over a distance of 4 m. Its volume did not change significantly. This slow migration rate is attributed to the large tidal range. In a macrotidal setting, the tidal water level fluctuations control wave height during storms, the duration of emergence and flooding periods, and the intensity and direction of longshore tidal currents. Field observations showed that bar migration rate is correlated with wave activity, whereas volume variations are controlled both by mean tidal currents and wave conditions. These results indicate a morphodynamic behaviour strongly related to specific local macrotidal hydrodynamic conditions, the tidal prism influence being less important.

Analysis of local heat transfer and hydrodynamics in a bubble column using fast response probes

A fast response probe is used to measure local heat transfer in a bubble column. It captured the variations in local heat transfer coefficients due to changes in local hydrodynamic conditions in radial and axial directions. These measurements have been used to identify flow regime transitions, variations in flow patterns and local hydrodynamic structure as obtained with different gas distributors and varying gas velocity. Standard deviations of pressure measurements obtained with a fast response probe have been compared with heat transfer coefficient fluctuations for the first time and the similarities and differences have been pointed out. Variations in average heat transfer coefficients and standard deviations in radial and axial directions point to different hydrodynamic conditions and are compared with literature studies. Relationships between local heat transfer measurements and hydrodynamic conditions are shown.

Sorted bed forms as self-organized patterns: 2. Complex forcing scenarios

[1] We employ a numerical model to study the development of sorted bed forms under a variety of hydrodynamic and sedimentary conditions. Results indicate that increased variability in wave height decreases the growth rate of the features and can potentially give rise to complicated, a priori unpredictable, behavior. This happens because the system responds to a change in wave characteristics by attempting to self-organize into a patterned seabed of different geometry and spacing. The new wavelength might not have enough time to emerge before a new change in wave characteristics occurs, leading to less regular seabed configurations. The new seabed configuration is also highly dependent on the preexisting morphology, which further limits the possibility of predicting future behavior. For the same reasons, variability in the mean current magnitude and direction slows down the growth of features and causes patterns to develop that differ from classical sorted bed forms. Spatial variability in grain size distribution and different types of net sediment aggradation/degradation can also result in the development of sorted bed forms characterized by a less regular shape. Numerical simulations qualitatively agree with observed geometry (spacing and height) of sorted bed forms. Also in agreement with observations is that at shallower depths, sorted bed forms are more likely to be affected by changes in the forcing conditions, which might also explain why, in shallow waters, sorted bed forms are described as ephemeral features. Finally, simulations indicate that the different sorted bed form shapes and patterns observed in the field might not necessarily be related to diverse physical mechanisms. Instead, variations in sorted bed form characteristics may result from variations in local hydrodynamic and/or sedimentary conditions.

A model for the benthic-pelagic coupling of silica in estuarine ecosystems: sensitivity analysis and system scale simulation

Abstract. A transient, vertically resolved, analytical model for the early diagenesis of silica has been developed to quantify the importance of benthic-pelagic coupling in estuarine biogeochemical silica cycling. A sensitivity analysis based on Monte-Carlo simulations is carried out to assess the intensity and timing of benthic diffusive fluxes in response to a pelagic diatom bloom. The diffusive flux dynamics are analyzed over a realistic range of dissolution rate constants (max kSi ε [6×10−3–3.6×10−1 d−1]), diffusion coefficients of dissolved silica (DSi ε [35×10−6–35×10−5 m2 d−1]) and duration of dissolved silica depletion in the water column (wPDSI ε [1–3 month]). Results show that the diffusive silica flux responds with a time delay of 20 to 120 days to the biogenic silica deposition pulse. For high max kSi, simulated time lags are shortest and completely determined by the dissolution kinetics. However, decreasing max kSi leads to a slower benthic flux response. In addition, the variability increases due to the increasing importance of transport processes. The sensitivity study also allows us to constrain the uncertainties of a system-scale simulation, where a large number of benthic compartments (&gt;50 000) are coupled to a high-resolution (100×100 m) pelagic model of a macrotidal river and estuary (Western Scheldt, B/NL). The model is applied to a diatom bloom event recorded in 2003, characterized by pelagic silica depletion in August. Benthic processes are mainly modulated by the combined influence of local hydrodynamic conditions and pelagic primary production dynamics, and show therefore a high degree of spatial heterogeneity over short distances. Spatially integrated deposition fluxes and dissolution rates of biogenic silica are high throughout the growth period, with maxima of 1.3×105 mol d−1 (=8.0 mmol m2 d−1) and 7.8×104 mol d−1 (=4.8 mmol m2 d−1) in mid-August. The spatially integrated diffusive flux reaches a maximum of 1.5×104 mol d−1 at the end of a pelagic silica depletion period in September. However, the total amount of dissolved silica released from the estuarine sediments between June and December 2003 is small (2×106 mol) compared to the much higher riverine influx of dissolved silica (5.9×107 mol) and plays a minor role in the pelagic primary production dynamics.

Limits to gene flow in the slipper limpet Crepidula fornicata as revealed by microsatellite data and a larval dispersal model

Crepidula fornicata, one of the most invasive marine sessile invertebrates in Europe, has traits commonly associated with a weak population genetic structure (high population connectivity): wide environmental tolerance, high fecundity, and a long planktonic larval stage (21 d). In order to determine the scale at which effective dispersal occurs in this potentially highly dispersive species, we designed a hierarchical sampling protocol and analyzed genetic variation at 4 microsatellite loci in 17 populations from 6 French bays situated in the English Channel and at the entrance of the Eng- lish Channel (Iroise Sea). A strong regional pattern with populations clustered into 3 main groups (Iroise Sea, western and eastern English Channel) was revealed, as was significant isolation by dis- tance along the Channel coasts. Conversely, a high degree of genetic connectivity was observed within the study bays. These estimates of effective dispersal were in agreement with outputs of a 2D larval-dispersal model based on local hydrodynamic conditions, suggesting that connectivity between populations of C. fornicata is influenced by hydrodynamic feature. This study suggests the existence of barriers to gene flow of C. fornicata over moderate distances (ca. 100 km).

Using Computational Fluid Dynamics to predict Damage of a Biological Pesticide during Passage through a Hydraulic Nozzle

The wide variety of agricultural spray equipment commercially available makes it difficult to test equipment components for compatibility with biological pesticides under varying operating conditions. One approach to this problem is to use computational fluid dynamics (CFD) as a tool to numerically simulate the complex flow conditions within different equipment components. From the numerical simulations, the flow-field parameter energy dissipation rate is used to characterise local hydrodynamic conditions potentially resulting in organism damage. Experimental tests measured damage to a benchmark biological pesticide, entomopathogenic nematodes (EPNs), after being passed through a standard flat fan nozzle (Spraying Systems XR8001VS) and hollow cone nozzle (Spraying Systems TXA8001VK) at varying flow rates. Numerical simulations of the internal flow for each nozzle were performed for the experimental flow conditions. An empirical model relating EPN damage as a function of the computed average energy dissipation rate was developed using data from a previous study. The model was validated using experimental and numerical results from the nozzles. Overall, the model was able to predict EPN damage well, in many cases within 5% of observed rates of damage. The results from this study show that CFD is a feasible method to evaluate spray equipment and operating conditions for delivery of biopesticides.

Effect of NAPL film stability on the dissolution of residual wetting NAPL in porous media: A pore-scale modeling study

Wettability profoundly affects not only the initial distribution of residual NAPL contaminants in natural soils, but also their subsequent dissolution in a flowing aqueous phase. Under conditions of preferential NAPL wettability, the residual NAPL phase is found within the smaller pores and in the form of continuous corner filaments and thick films on pore walls. Such films expose a much greater interfacial area for mass transfer than would be exposed by the same amount of non-wetting NAPL. Importantly, capillary and hydraulic continuity of NAPL filaments and thick films is essential for sustaining NAPL–water counterflow during the course of NAPL dissolution in flowing groundwater—a mechanism which maintains and even increases the interfacial area for mass transfer. Continued dissolution results in gradual thinning of the NAPL films, which may become unstable and rupture causing disconnection of the residual NAPL in the form of clusters. Using a pore network simulator, we demonstrate that NAPL film instability drastically modifies the microscopic configuration of residual NAPL, and hence the local hydrodynamic conditions and interfacial area for mass transfer, with concomitant effects on macroscopically observable quantities, such as the aqueous effluent concentration and the fractional NAPL recovery with time. These results strongly suggest that the disjoining pressure of NAPL films may exert an important, and hitherto unaccounted, control on the dissolution behaviour of a residual NAPL phase in oil wet systems.

Hydrodynamic behaviour of Nummulites: implications for depositional models

Large benthic foraminifers are considered to be good indicators of shallow marine carbonate environments in fossil series. Over the last 50 years, the palaeoenvironment of Tertiary Nummulites accumulations has been a matter of debate, particularly because of difficulties in interpreting these deposits, and in this way, the absence of analogues in present-day seas does not help. The aim of this paper is to insight the different ways Nummulites tests and clasts may accumulate according to their hydrodynamic behaviour. Based on experimental measurements and on SEM observations, it appears that the high primary skeletal porosity of Nummulites made them easily transportable. The calculated threshold shear velocities confirm that large-sized Nummulites can be moved by weak wave-driven currents. This peculiar hydrodynamic behaviour of Nummulites could explain the diversity of depositional models. Depending on local hydrodynamic conditions, autochthonous Nummulites deposits can be preserved as in situ winnowed bioaccumulations or be accumulated offshore, onshore or alongshore, away from the original biotope.

Models of temperate carbonate deposition in Neogene basins in SE Spain: a synthesis

Abstract Upper Miocene (Tortonian-Messinian) to Lower Pliocene (Zanclean) temperate bioclastic limestones occur in the Betic intermontane basins mixed with diverse proportions of siliciclastics. Components are mostly originally calcitic skeletons of invertebrates (especially bryozoans and bivalves) and coralline algae. Carbonate mud content is usually low and cementation is generally weak. These temperate carbonates formed in ramps. The depositional surface profile and local hydrodynamic conditions in each example controlled the occurrence of diverse facies at similar positions within the ramp. Shallow-water facies are well represented and formed in beaches and backshore lagoons, spits, rocky shores and submarine cliffs. Shoals developed seawards of shore deposits; the relatively quiet environments basinwards of the shaosl were the areas of maximal carbonate production (factory facies). The lack of early lithification favoured mobilization of skeletal particles. Waves and currents during storms transported carbonate grains landwards from the factory areas to shoals, spits and beaches. Skeletal grains were also transported downslope along the ramp. Re-deposited carbonates occur within basinal marls in submarine lobes and channels fed by channels cross-cutting and excavating the platform sediments. The absence of hermatypic corals and calcareous green algae in shallow-water deposits suggests cool surface water temperatures during carbonate formation. Large benthic foraminifers and oxygen stable isotope values indicate winter surface water temperatures of 16–17°C.

Design of a Side-View Particle Imaging Velocimetry Flow System for Cell-Substrate Adhesion Studies

Experimental models that mimic the flow conditions in microcapillaries have suggested that the local shear stresses and shear rates can mediate tumor cell and leukocyte arrest on the endothelium and subsequent sustained adhesion. However, further investigation has been limited by the lack of experimental models that allow quantitative measurement of the hydrodynamic environment over adherent cells. The purpose of this study was to develop a system capable of acquiring quantitative flow profiles over adherent cells. By combining the techniques of side-view imaging and particle image velocimetry (PIV), an in vitro model was constructed that is capable of obtaining quantitative flow data over cells adhering to the endothelium. The velocity over an adherent leukocyte was measured and the shear rate was calculated under low and high upstream wall shear. The microcapillary channel was modeled using computational fluid dynamics (CFD) and the calculated velocity profiles over cells under the low and high shear rates were compared to experimental results. The drag force applied to each cell by the fluid was then computed. This system provides a means for future study of the forces underlying adhesion by permitting characterization of the local hydrodynamic conditions over adherent cells.

Reply to comment by Z. B. Wang and H. J. De Vriend on “Depth integrated modeling of suspended sediment transport”

[1] Let us first thankWang and De Vriend [2004] for their attention and their careful scrutiny of our paper. Let us also clarify that the motivation of our work was not to show that Galappatti’s [1983] model (hereinafter referred to as G83) was incorrect, but rather to develop a depth-averaged formulation of suspended sediment transport suitable for long-term morphological predictions, able to take into account weak non equilibrium effects of the kind often encountered in tidal as well as fluvial environments. Unfortunately, the mathematical framework appropriate to perform such investigation is precisely that proposed in G83, which forced us to revisit critically the latter work. [2] Let us come to the points raised by the Wang and De Vriend, which do concern G83’s approach rather than our formulation, whose validity does not seem to be questioned. The issue underlined in the discussion is whether or not G83’s perturbation scheme is correct and the basis for the Wang and De Vriend’s defense are the works of Wang [1992] and Wang and Ribberink [1986] (hereinafter referred to as W92 and WR86, respectively). We then also need to revisit the latter works.