flow structure and turbulence characteristics of the daytime atmosphere in a steep and narrow alpine valley aircraft measurements radio soundings and sonic data obtained during the map riviera field campaign in autumn 1999 in southern switzerland are used to investigate the flow structure temperature profiles and turbulence characteristics of the atmosphere in a steep and narrow alpine valley under convective conditions on all predominantly sunny days of the intensive observation periods a pronounced valley wind system develops in the southern half of the valley the daily up valley winds have a jet like structure and are shifted towards the eastern slope these up valley winds advect potentially colder air a process which appears to be balanced by vertical warm air advection from above the profiles of potential temperature show that with the onset of up valley winds the mixed layer consistently stops growing or on days with very strong up valley winds even stabilizes almost throughout the entire valley atmosphere this is probably due to a pronounced secondary circulation in the southern part of the valley which induces advection of warm air from above the secondary circulation appears to be a consequence of sharp curvature in the along valley topography turbulence variables are calculated from flight legs in the along valley direction turbulent kinetic energy tke scales surprisingly well i if a tke criterion tke 0 5 m2s 2 is employed as a definition of the boundary layer height and ii if the surface fluxes which exhibit a substantial spatial variability from the slope sites are used rather than those from directly beneath the profile considered significant site to site differences in incoming solar radiation seem to be the reason for this characteristic behaviour profiles of momentum flux scaled with a surface friction velocity reveal more scatter than the tke profiles but still show a consistent behaviour a surprisingly strong shear in the cross valley direction can be observed and is probably a result of the secondary circulation copyright 2004 royal meteorological society

a simple model of pressure build up caused by porosity reduction during burial summary the fluid pressure build up due to porosity reduction in sedimentary basins during burial is studied the model assumes that the void ratio decreases exponentially with depth and that the permeability is proportional to the void ratio to an arbitrary exponent simple analytical solutions are obtained for the darcy velocity and the fluid excess pressure the pressure build up during burial is studied with these solutions and it is found to be inversely proportional to the gravity number the importance of the permeability exponents on the fluid pressure is also studied gravity numbers much less than 1 are shown to yield high excess pressures during burial a reasonable approximation for the maximum darcy velocity is found to be the product of the surface void ratio and the burial rate hydrofracturing is discussed in relation to the pressure build up and cases characterized by gravity numbers much less than 1 are found to yield hydrofracturing over large depth ranges it is suggested that the average permeability of hydrofractured sediments during burial corresponds to a gravity number equal to 1

observations of downslope winds and rotors in the falkland islands a field campaign aimed at observing the near surface flow field across and downwind of a mountain range on the falkland islands south atlantic is described the objective was to understand and eventually predict orographically generated turbulence the instrumentation was based primarily on an array of automatic weather stations awss which recorded 30 s mean surface pressure wind speed and direction at 2 m temperature and relative humidity for approximately one year these measurements were supported by twice daily radiosonde releases the densest part of the aws array was located to the south of the wickham mountain range across mount pleasant airfield mpa in northerly flow the array provides a detailed study of the flow downwind of the mountain range the dataset contains several episodes in which the flow downwind of the mountains is accelerated relative to the upwind flow during some of these episodes short lived typically 1 hour periods of unsteady flow separation are observed and these are associated with the formation of rotors aloft such events present a significant hazard to aviation at mpa examination of radiosonde profiles suggests that the presence of a strong temperature inversion at a height similar to the mountain height is a necessary condition for both downwind acceleration and the formation of rotors the data are used to show that the downwind fractional speed up is proportional to the non dimensional mountain height based on upstream near surface winds and a depth averaged brunt vaisala frequency diagnosed from radiosonde data similarly a relationship is established between a quantity that describes the spatial variability of the flow downwind of the mountains and the upstream wind and depth averaged brunt vaisala frequency the dependence of the flow behaviour on the froude number defined in the usual way for two layer shallow water flow and ratio of mountain height to inversion height is presented in terms of a flow regime diagram

observations of cross ridge flows across steep terrain a field experiment gaudex has been conducted to address the need for quantitative measurements of turbulence in the vicinity of steep terrain a dense network of automatic weather stations and turbulence towers was deployed along cross ridge transects over gaudergrat a steep triangular cross section ridge in eastern switzerland a new feature whereby ridge normal cross ridge flows develop at the crest even when the flow in each valley is oriented parallel to the ridge axis is identified this occurs independently of whether the flow is thermally or synoptically driven pressure measurements across the ridge show that this flow is driven by a cross ridge pressure gradient two mechanisms for generating cross ridge flows have been identified from measurements of pressure wind and temperature in most cases the pressure gradient arises from a difference in flow speeds between the two sides of the ridge caused by different valley geometries less commonly the cross ridge flow is explained by linear speed up of the ridge normal flow copyright 2008 royal meteorological society

along channel flow and sediment dynamics at north inlet south carolina in may of 2005 an observational program was carried out to investigate the along channel hydrodynamics and suspended sediment transport patterns at north inlet south carolina along channel variability which is important in establishing sediment transport pathways has not been characterized for this system measurements of water column currents salinity bed sediment suspended sediment concentration and particle size distribution were obtained over a complete tidal cycle along the thalweg of the inlet entrance along channel currents shear stress and bed sediment distributions vary significantly in space and time along a 3 km section bracketing the inlet throat most of the variability is consistent with geomorphic controls such as bed elevation variability and channel width the highest velocities shear stresses suspended sediment concentration and bed sediment grain size are observed in the narrowest section of the inlet throat magnitudes systematically decrease along the channel toward the marsh as changes in channel geometry and branching reduces flow energy due to tidal asymmetry the ebb phase contains significantly higher currents and associated sediment transport over the complete tidal cycle depth integrated transport is directed towards the marsh landward of the intersection of town and debidue creek in contrast net transport is out of the inlet seaward of this intersection sediment grain size distributions show 35 more material less than 63 m on flood suggesting net landward transport of fines

the use of microstructures for discriminating turbiditic and hemipelagic muds and mudstones the microstructures of turbiditic and hemipelagic muds and mudstones were investigated using a scanning electron microscope to determine whether there are microstructural features that can differentiate turbiditic from hemipelagic sedimentary processes both types of muddy deposits are in general characterized by randomly oriented clay particles however turbiditic muds and mudstones also characteristically contain aggregates of edge to face contacts between clay particles with long axis lengths of up to 30 m based on observations of the clay fabric of the experimentally formed muds settled from previously agitated muddy fluids these types of aggregates hereafter referred to as aggregates of clay particles are interpreted as having been formed by the collision of component flocs in turbulent fluids furthermore some aggregates of clay particles have face to face contacts between clay particles this is similar to face to face aggregates characteristically developed in fluid mud deposits that are commonly recognized only in turbiditic mudstones indicating the possibility of a final stage of deposition under highly dense conditions such as temporary fluid muds in conjunction with earlier proposed lithofacies based and ichnofacies based criteria aggregates of clay particles should be useful for the differentiation of turbiditic and hemipelagic muddy deposits particularly with limited volumes of non oriented samples from deep water successions

estimation of high resolution sediment concentration profiles in bottom boundary layer using pulse coherent acoustic doppler current profilers abstract the capability of two acoustic profilers sontek s 1 5 mhz pulse coherent acoustic doppler profiler pc adp and rdi s 600 khz acoustic doppler current profiler adcp with pulse coherent mode was evaluated for estimating high resolution suspended sediment concentration ssc profiles in bottom boundary layer in the laboratory measurements with a pc adp two types of sediments were tested to study acoustic responses to grain size a natural sediment sample from clay bank a mixture of clay and very fine sand showed a good linear relationship between range corrected volume scattering s v and backscattered strength e until ssc increased up to about 10 g l 1 in contrast a commercially available kaolinite exhibited earlier signal saturation and non unified linear regressions between s v and e most likely because the particle size is much smaller than the transmitted acoustic wavelength using a pulse coherent adcp the field measurement results from mobile bay alabama showed that the acoustically derived ssc profiles were well matched with the optically derived outcomes although slight discrepancies were noted the overestimation of acoustically derived ssc near the bed may be related to the side lobe interference near the bed and the enhanced acoustic sensitivity by coarser particles and denser aggregates eroded from the bed mean absolute error of acoustic estimates was within 4 1 7 3 of the optically derived ssc range which is attributable to the different acoustic and optical scattering responses to given sediment size spectra despite some error sources in acoustic inversion the results from laboratory and field experiments suggest that the pulse coherent acoustic profiler is able to reveal the evolution of in situ near bed ssc profiles with high vertical and temporal resolutions

in situ high frequency long term measurements of suspended sediment concentration in turbid estuarine system seine estuary france optical turbidity sensors response to suspended sediment characteristics abstract the aim of this study is to investigate the complex response of optical turbidity sensors side and back scattering sensors to suspended particle matter spm characteristics and the consequences when investigating spm dynamics from long term high frequency monitoring networks our investigation is based on the analysis of a unique dataset of monthly 12 h cycle measurements of spm characteristics such as turbidity concentration floc size distribution floc density and organic matter content in the macrotidal seine estuary france between february 2015 and june 2016 results reveal that despite calibration to a formazin standard turbidity sensor response to spm concentrations in the range of 7 7000 mg l 1 are strongly variable from the tidal scale to the annual scale and in different compartments of the seine estuary the variability in the calibration relationships is related to changes in the sensor sensitivity according to i the sensor intern technology mainly due to optical geometry and ii the variability in inherent optical properties iop of spm side scattering optical instruments measuring scattering at 90 provide at the annual scale a more stable optical response than backscattering sensor measuring scattering at angles larger than 100 for a wide variety of floc size and density in the estuarine environment while at the tidal scale the backscatter sensors are the most accurate sensor sensitivity is strongly affected by floc characteristics i e their median size d50 dry density and the scattering efficiency qb results highlight that the median particle diameter contribute to modify the scattering efficiency qb as well as the dry density qb increases with increasing floc size and for a given floc size qb increases with floc density in this study the results are next applied to turbidity data from the long term automated monitoring network in order to estimate spm concentrations and estimate the related uncertainties

mechanisms of natural fracturing in a sedimentary basin mechanisms of natural fracture generation in a sedimentary basin may be studied by the use of physical properties of sedimentary rocks and of pore fluid pressure the physical properties of rocks such as poisson s ratio and young s modulus under laboratory conditions are available but only a few of these are reported under subsurface conditions in this paper in situ values of poisson s ratio derived from analysis of artificial hydrofracturing data in the gulf coast are used for estimating horizontal stresses in both hydrostatically and abnormally pressured zones there in a tectonically relaxed basin such as the gulf coast the horizontal stress can be a function of vertical overburden stress fluid pressure and poisson s ratio the horizontal stress increases with depth in the hydrostatic pressure zone but is abnormally low in the abnormally pressured zone fracture pressure and its gradient given as a sum of least horizontal stress and fluid pressure is however not abnormally low in the abnormally pressured zone because the fluid pressure there is abnormally high this paper describes the in situ fracture pressure gradient estimated for the gulf coast area on the basis of models of vertical fluid charging through an aquifer and a fault system during continuous burial the depth at which the charged fluid pressure gradient exceeds the fracture gradient or the point of natural hydrofracturing is estimated after an erosional event the most significant decline of fracture pressure gradient is expected in the uppermost part of the original abnormal pressure zone hydrofracturing there could occur if an effective fluid is charging from deep to shallow through an aquifer or a fault system if the erosion continues to a point at which approximately two thirds of the total sediment thickness is removed the horizontal stress may become almost zero if such a stress condition is developed the sedimentary rocks become greatly relaxed possibly causing fractures

gap flows results from the mesoscale alpine programme an overview of advances in the observation modelling forecasting and understanding of flows through gaps achieved in the mesoscale alpine programme is given gaps are lateral constrictions of topography level gaps often combined with vertical terrain changes passes of the possible flow configurations only an asymmetric one relatively deep and slow upstream accelerating and thinning downstream which connects two different reservoirs on each side of the gap is examined the flow is strongly nonlinear making hydraulics reduced gravity shallow water theory rather than linear theory the simplest conceptual model to describe gap flow results from idealized topographical and flow conditions are presented together with gap flows through a pass in the central alpine wipp valley for a given depth of the upstream reservoir the gap controls the mass flux through it and marks the transition from a subcritical flow state upstream to a supercritical one downstream which eventually adjusts to the downstream reservoir in a hydraulic jump three gap flow prototypes were found a classical layer one with neutral stratification and a capping inversion and two with a continuous stratification for which a special analytical self similar hydraulic solution exists in all three cases a deepening wedge of nearly mixed and stagnant air forms on top of the gap flow plunging down from the pass the descent causes a warming and relative drying of the air making gap flows a special case of fohn topographical variations smaller than the gap scale cause additional hydraulic jumps flow separation vorticity banners gravity waves and interactions with cold pools turbulent friction cannot be neglected the climatological frequency of gap flows depends on the establishment of two different reservoirs and reaches 20 for the wipp valley copyright 2007 royal meteorological society

a simple method for calculating in situ floc settling velocities based on effective density functions abstract we present a simple method to obtain settling velocity estimates of fine grained suspended sediment using the following 1 in situ floc volume fraction measurements 2 calculations of in situ floc mass 3 measurements of in situ floc size 4 laboratory measurements of primary particle size and 5 laboratory measurements of organic matter obtained through loss on ignition this method is based on the mass distribution over the particle size spectra floc properties are incorporated by using information concerning the primary particles and the ratio between the volume concentration and the mass concentration of the in situ measurements in this manner the changes in effective densities caused by flocculation and biological mediation are approximated this method relies solely on measurements conducted with a particle sizing instrument and on an analysis of water samples the method is applied to measurements obtained with a lisst and data from three different estuaries in different climatic zones are used the settling velocity estimates found using this method are compared to settling tube measurements and to mass settling method estimates as well as to calculations using fractal dimension methods from the literature settling velocities calculated using the method presented in this study lie within the ranges of the three other methods demonstrating that this simple method produces results within the ranges of settling tube velocities and those predicted by the more comprehensive multiparameter fractal dimension models the presented method allows for easy intercomparisons between studies by utilising instruments such as the lisst and it is believed that this method would also produce reliable settling velocities using other instruments that yield a volume distribution as well as a proxy for total volume and mass concentration e g some camera systems

the role of algae in fine sediment flocculation in situ and laboratory measurements abstract the precise interactions between organic and inorganic particles in the context of flocculation is an on going topic of research the suspended particulate matter spm found in estuaries is composed of both organic and inorganic particles with specific particle size distributions psd s these psd s are a function of the hydrodynamic conditions suspended sediment concentration ssc organic matter composition salinity and seasonal variations a field campaign was carried out in august 2015 in the turbidity maximum zone of the yangtze estuary where the spm dynamics were recorded the concentration of algae in the water column was indirectly measured through the chlorophyll a concentration cc we show that there is a strong correlation between ssc and cc in the whole water column for the whole tidal cycle additional flocculation experiments in the laboratory confirm that the largest observed flocs are predominantly organic based and that salinity alone could not induce the flocculation of the yangtze mineral particles a key parameter for the maximal floc size is the algae concentration to sediment concentration ratio when this ratio is high the d50 is high and vice versa

measurements and one dimensional model calculations of snow transport over a mountain ridge wind transport of snow can cause an additional snow load on leeward slopes which often has a considerable influence on avalanche danger for a quantitative assessment of this process a model is proposed which calculates the snow transport over a two dimensional mountain ridge based on input measurements of wind speed and precipitation since the topography is idealized the model is focused on the snow mass that is transported over the ridge and no statements are made about the exact snow distribution over the slopes three transport modes are distinguished snow transport in saltation snow transport in suspension and preferential deposition of precipitation suspension is modelled with a one dimensional diffusion equation and for the saltation layer a newly developed model based on the microscale physical processes is implemented the effect of speed up of the wind over the ridge is included by assuming an analytical wind profile with a maximum wind speed at a few meters above the ridge advective effects are taken into account in a parameterization of the turbulent shear stress profile the model is compared with measurements taken at the experimental snowdrift site gaudergrat in the parsenn area switzerland and good agreement is obtained between calculated and measured results

pressure and temperature evolution in sedimentary basins summary this article is about what influence continuous sedimentation has on the excess pressure compaction and temperature in a sedimentary basin we give an answer in terms of two dimensionless numbers 4 and a1 which characterize the pressure and the temperature solution respectively 1 is shown to define a transitional zone between excess pressured basins with low compaction and hydrostatic basins with high compaction the 4 parameter generalizes earlier results of gibson the most important physical parameter in a is the ratio between the permeability and the sedimentation rate by means of we can quantify when high sedimentation rates and low permeability yield high excess pressures this analysis is based on the porosity given by formulae of the form 4 aps where ps is the effective stress and a is some scaling factor in an analogous manner ai 1 defines a transitional zone when moving boundary effects become marked on the temperature the most important parameter in ai is the ratio between a and the sedimentation rate simulation results are obtained by solving dimensionless pressure and temperature equations the numerical pressure solution is compared with the exact solution given by gibson and is shown to be in excellent accordance

contributions of compaction and aquathermal pressuring to geopressure and the influence of environmental conditions reply luo and vasseur 1992 presented a useful methodology of simplifying the complex equations that describe basin compaction and thereby directly assessing the contribution of aquathermal effects in the development of abnormal pressures their methodology leads to the conclusion that aquathermal pressuring plays only a small role in the development of overpressures in sedimentary basins although this conclusion follows from the cases studied it is possible to conclude otherwise using 1 a more general model of sediment compaction and 2 material properties that are more representative of conditions at depth the primary factor behind objection to the conclusion in luo and vasseur 1992 is that is fundamental equations which formed the basis for the simplifying methodology do not account fully for conditions in which a sediment s effective stresses are reduced we emphasize here that we do not claim that thermal effects are the dominant cause of overpressures rather our calculations suggest that they are not negligible in all cases there is a complex interplay of the various mechanisms that cause excess pore water pressures no one mechanism of overpressuring dominates all others for all situations because thermal effects not only cause higher excess pore pressures but also reduce effective stresses thermal effectsmore will be minimized by default in calculations that do not account for effective stress reduction the resulting reduced effective stresses also have important implications for geological questions such as acoustic velocities and fracture potential less

measurements of the near surface flow over a hill the near surface flow over a hill with moderate slope and height comparable with the boundary layer depth is investigated through field measurements of the mean flow at 2 m surface pressure and turbulent momentum flux divergence between 8 and 15 m the measurements were made along an east west transect across the hill tighvein height 458 m approximate width 8 km on the isle of arran south west scotland during two separate periods each of around three weeks duration radiosonde ascents are used to determine the variation of a froude number fl u nl where u is the wind speed at the middle layer height hm n is the mean brunt vaisala frequency below this height and l is a hill length scale measurements show that for moderately stratified flows for which fl 0 25 a minimum in the hill induced surface pressure perturbation occurs across the summit and this is accompanied by a maximum in the near surface wind speed in the more strongly stratified case fl 0 25 the pressure field is more asymmetric and the lee slope flow is generally stronger than on the windward slope such a flow pattern is qualitatively consistent with that predicted by stratified linear boundary layer and gravity wave theories the near surface momentum budget is analysed by evaluating the dominant terms in a bernoulli equation suitable for turbulent flow measurements during periods of westerly flow are used to evaluate the dominant terms and the equation is shown to hold to a reasonable approximation on the upwind slope of the hill and also on the downwind slope away from the summit immediately downwind of the summit however the bernoulli equation does not hold possible reasons for this such as non separated sheltering and flow separation are discussed copyright 2002 royal meteorological society

a model of turbidity maximum maintenance in the irish sea a two dimensional model has been developed in order to improve understanding of the processes which interact to maintain the sediment concentrations at an isolated turbidity maximum in the irish sea throughout the year the model comprises two interchangeable populations of particles with different diameters one of fine cohesive material the other made up of flocs both populations are slow settling and subject to horizontal diffusion resuspension settling aggregation and disaggregation the equations used to describe the processes of aggregation and the break up of flocs in response to sediment concentration and turbulent shear have been developed by the tuning of the model to observations due to high turbulent shear at the turbidity maximum the particles are predominantly fine while the sediment in the surrounding water is made up of larger flocs diffusion of small particles out of the turbidity maximum balanced by the diffusion of aggregated material towards it provides a mechanism for its maintenance the modelled sediment concentrations at the turbidity maximum can be reproduced year on year with no loss due to diffusive processes this is achievable with a limited exhaustible source of material which is not replenished once resuspended through comparison with satellite imagery the correlation of the modelled sediment concentrations with observations is investigated both spatially and temporally the seasonal cycle is reproduced well by the model with winter and summer concentrations matching those observed spatially the model also performs well in both turbid regions and those where the surface sediment load is low

on effects of skewed and asymmetric oscillatory flows on cohesive sediment flux numerical study 1 to investigate the effects of wave shape on cohesive sediment flux in shallow water environments a one dimensional vertical 1dv model for cohesive sediment transport previously validated with field measurement is applied to conditions of skewed and asymmetric oscillatory flows cohesive sediments usually portray behaviors different from those of noncohesive sediments this is mainly due to the flocculation process through which the density and the size of cohesive sediment change continuously therefore a robust flocculation model is incorporated with a 1dv model in this study under the condition of skewed oscillatory flow second order stokes wave type oscillatory flow the flux of cohesive sediment is significantly affected by the change of flow skewness whereas the flux of noncohesive sediment of which size is 100 m does not show a clear relationship with skewness under the condition of forward leaning asymmetric oscillatory flow saw tooth wave type oscillatory flow the direction of cohesive sediment flux is negative whereas the flux of noncohesive sediment shows the positive direction the phase lag effect is considered as the main mechanism of these behaviors the interactional relationship between the settling velocity the variation of concentration profile and hydrodynamics of carrier fluid enhances the phase lag effect and causes different behaviors in cohesive sediment compared to the flux of fine noncohesive sediment

flow during the evening transition over steep alpine slopes a field campaign the slope experiment near la fouly self 2010 was conducted to monitor the evening transition of slope flows on clear sky days from july to september 2010 in a narrow valley of the swiss alps a steep west facing slope with inclinations ranging from 25 to 45 was instrumented from 1900mto 2200mabove sea level detailed measurements were made along a linear transect of the slope with two turbulence towers two weather stations five surface temperature measurement stations and a tethered balloon system the present study focuses on nine exemplary convective days characterized by weak synoptic flow and clear sky conditions during which thermal circulations prevail the analysis of the observational data shows that topographic shading triggers the evening transition the topographic configuration around the experimental site results in a sharply defined shading front propagating up slope causing a sudden decrease in incoming short wave radiation on the order of several hundreds of wm 2 within a few minutes the slope surface rapidly responds to the advancing shading front in some cases reductions in surface temperatures of some 10 c in less than 10 min are observed this is rapidly followed by an early evening calm period with very small turbulent kinetic energy tke 0 05m2 s 2 and extremely light wind speeds 0 5ms 1 when the inertia driven upslope flow is fully stopped by the katabatic acceleration a shallow local drainage flow forms and reaches a quasi equilibrium 1 5 h after the local sunset an analysis of the tke budget close to the surface shows that the buoyancy flux is much greater than the shear production in the last hours before the local sunset possibly due to valley curvature effects copyright c 2012 royal meteorological society

inhomogeneous precipitation distribution and snow transport in steep terrain 1 the inhomogeneous snow distribution found in alpine terrain is the result of wind and precipitation interacting with the snow surface over topography we introduce and explain preferential deposition of precipitation as the deposition process without erosion of previously deposited snow and thus in absence of saltation a numerical model is developed describing the relevant processes of saltation suspension and preferential deposition the model uses high resolution wind fields calculated with a meteorological model arps the model is used to simulate a 120 h snow storm period over a steep alpine ridge for which snow distribution measurements are available the comparison to measurements shows that the model captures the larger scale snow distribution patterns and predicts the total additional lee slope loading well however the spatial resolution of 25 m is still insufficient to capture the smaller scale deposition features observed the model suggests that the snow distribution on the ridge scale is primarily caused by preferential deposition and that this result is not sensitive to model parameters such as turbulent diffusivity drift threshold or concentration in the saltation layer

a laboratory examination of floc characteristics with regard to turbulent shearing abstract turbulent shear generated within the water column is recognised as having a controlling influence over both the flocculation of fine grained cohesive sediments within estuarine waters and their respective aggregate break up this study examines the inter relationships between floc characteristics over increasing turbidity 80 200 mg l 1 and turbulent shear 0 0 6 n m 2 environments by the use of a laboratory flume within which a suspension can be sheared at a controlled rate and with an unintrusive macro lens miniature video camera mounted in a viewing port on the flume channel wall the camera enables the direct simultaneous measurement of both floc size and settling velocity from which accurate estimates of floc effective density and porosity can be made measurements were made 120 s after the induced turbulence has ceased the instrument has an upper viewing turbidity limit of 210 mg l 1 and a lower resolution of 20 m the sediment was collected from the inter tidal mudflats at weir quay on the tamar estuary in devon southwest england the results indicated that increasing turbidity at low shear levels encouraged floc growth but the effect of the increasing turbulent shear 0 35 n m 2 together with increasing concentration in suspension causes disruption rather than enhancing the flocculation process at shears up to 0 35 n m 2 the largest size and settling velocity flocs were produced at high concentrations whereas above 0 35 n m 2 disruption caused smaller flocs at higher concentrations the use of algorithms which were based either on a single floc characteristic i e size or settling velocity or a mean fractal dimension were seen not to accurately approximate the experimental data a multiple regression analysis of the experimental data produced the following formula based on mean values of the 20 largest flocs sampled under each of the imposed environmental conditions referred to as max20size mean values settling velocity 0 301 0 00337 rms of the gradient in turbulent velocity fluctuations 0 000606 spm 0 00335 floc size which proved to be the most accurate representation with an r 2 value of 0 95 a similar formula was determined for the average value of the four fastest settling flocs within each sample group max4w s this highlights the importance of modelling algorithms that are developed from data that take into account effective density variations i e simultaneous size and settling velocity measurement

river plume induced variability of suspended particle characteristics a shipboard experiment using r v ocean researcher iii was conducted on july 6 9 2012 to focus on the temporal variability of the suspended particle characteristics off the zhuoshui river mouth in central taiwan the experiment included hydrographic profiling using a ctd rosette with a lisst 100x and collection of near surface water samples these samples were immediately filtered on board by a nested filtration system catnet to separate the suspended particles into four grain size classes 153 m 63 153 m 10 63 m and 10 m the filtered particles were analyzed for suspended sediment concentration ssc poc and pn a downward looking adcp aquadopp 1200 khz mounted on a tethered floating platform measured the current velocity profile the results show that the river plume fluctuating at the semidiurnal tidal frequency was the most important factor affecting suspended particle characteristics in the ambient seawater regime surface suspended particles consisted of fine grained size classes 10 m 10 63 m with low ssc values 10 mg l in the statically stable river plume regime ssc value reached 40 60 mg l surface particles were composed of biological particles and flocs with fluffy structures in the unstable plume front regime floc breakage occurred resulting in particles of high bulk density values also biological particles were drawn by the convergent flows to the frontal zone eof empirical orthogonal function analysis indicates that the three most important processes affecting the characteristics of the suspended particles at the study site include 1 tidal currents that affect dispersal of the buoyant river plume in the surface water 2 convergence and water column instability in the frontal zone of the plume and 3 resuspension of the seafloor sediment into the water column

mechanical and chemical compaction model for sedimentary basin simulators abstract this article presents a sediment compaction model for sedimentary basin simulators the concepts previously used in sedimentary basin models are generalized and described in our model based on the formalism specific to rock and soil mechanics sediment compaction is described on a geological time scale by an elastoplastic model in which the elastic modulus and the strain hardening modulus increase when deformation increases the plastic limit is the maximum vertical effective stress reached by the sediment the rheology of the sediment is defined by a relationship that couples the porosity or volume of the sediment with the vertical effective stress assuming uniaxial deformation the model also incorporates a viscoplastic term in the compaction equation this component macroscopically considers viscous compaction phenomena such as pressure solution the viscosity coefficient is considered to be a function of the temperature some theoretical considerations allow us to conclude that the thermal dependency of the viscosity is given with an arrhenius law in which the activation energy ranges from 20 kj mole to 50 kj mole using viscosity coefficients extrapolated from previous laboratory experiments a sensitivity study shows significant effects of viscous deformation on the compaction of basins older than 1 ma in another study the viscosity coefficient is determined by matching the results of numerical simulations with laboratory and borehole data obtained from literature for chalk a constant viscosity coefficient of 2 5 gpa ma 8 1022 pa s has been determined assuming viscosity as a function of temperature with an activation energy of 40 kj mole chalk viscosity at 15 c is calibrated around 25 gpa ma simulations with different thermal gradients show that porosity is a function of the temperature furthermore simulations covering different lengths of time show that porosity is also a function of time

stress fields a key to oil migration a coherent oil migration model based on geomechanical considerations includes both the high molecular kerogen structure and the capillary properties of source rocks oil is squeezed from kerogen by compaction following oil generation this squeezing effect should be created by the differential stress maximum compressive stress minus least compressive stress acting on the kerogen which has been chemically broken up by oil formation in sedimentary bodies whose water is at hydrostatic pressure the migration of oil seems to involve two processes 1 lateral transfer by channeling into the more coarsely microporous layers of the source rocks from the oil generation site toward the geologic structure or lower pressured zone and 2 vertical transfer from source rock to eservoir by the opening or reopening of vertical fractures in the few areas such as structural tops where the least compressive stress is slightly greater than or equal to the pore pressure and where the capillary pressure increment 2 ggr r of oil in the microporosity exceeds the tensile strength of the rock in sedimentary bodies whose water is overpressured the pore pressure should be governed by the least compressive stress and thus migration should begin by oil transfers in a system of small open fractures and eventually in larger fractures the theory demonstrates the impossibility of oil being transferred to the reservoir under true tensile conditions negative effective compressive stress and thus explains the large asphaltic veins of southeastern turkey and the well known bitumen veins of the uinta basin

investigation of flocculation dynamics under changing hydrodynamic forcing on an intertidal mudflat abstract in situ floc size and turbulent shear stress were measured together with suspended sediment concentration to investigate the floc properties under changing hydrodynamic forcing over the intertidal mudflat a tripod system was established in the field for a period of approximately one month including 6 days of stormy conditions in the middle of the investigation period mean floc size exhibited strong temporal variations within a tidal cycle and inverse relationship was found between mean floc size and shear stress suspended sediment concentration ssc can modulate the flocculation dynamics when shear stress decreases down to enhancing flocculation asymmetrical behaviors of floc sizes between flood and ebb phases were identified with overall larger floc sizes in flood than in ebb tide under the same shear stresses floc structure showed different properties under calm and stormy conditions and the variable fractal dimension and variable primary particle size were more convincing in simulating the variation of floc effective density with mean floc size during the storm period which was inferred to be related to the resuspension of bed sediment as well as organic matter a total of 110 mm bed erosion was measured during the storm and erosion events occurred only around low water due to the high current wave combined bed shear stress and off shore current after the storm 40 of the erosion recovered within one week and the fast settling of large flocs around high water plays significant role in the deposition process leading to 60 of the recovery

generation of overpressure by cementation of pore space in sedimentary rocks summary overpressure build up is studied when the main cause for porosity reduction is cementation of the pore space sourced locally the average porosity reduction for siliclastic sediments is modelled with nth order kinetics it is shown that the overpressure in one layer at a constant depth will decrease exponentially with time in the case of first order kinetics for the porosity reduction the overpressure is studied in one layer subjected to cementation during constant burial along a thermal gradient a small overpressure build up is shown above the window for cementation with a steep rise in overpressure in the upper part of the window the overpressure build up is then seen to decrease rapidly towards the end of the window for cementation overpressure build up is also studied when cementation is the main cause for porosity reduction in the entire column of sediments during deposition and burial the overpressure regime characterized by gravity numbers larger than one is studied this regime corresponds to low or moderate overpressures in the case of mechanical compaction cementation is shown to imply a steep pressure build up in the window of cementation which will easily exceed the lithostatic pressure the porosity loss due to cementation is seen to have a strong impact on the permeability which leads to the formation of a pressure seal although most of the potential for fluid expulsion is exhausted below the seal because most of the porosity is cemented up the permeability of the seal is sufficiently low for hydrofracturing to take place this scenario is consistent with overpressure observations in many wells

inssev an instrument to measure the size and settling velocity of flocs in situ abstract an instrument has been developed to observe the settling of individual flocs in turbid water in order to measure size and settling velocity spectra of estuarine cohesive suspended sediments inssev in situ settling velocity instrument is bed mounted and comprises a computer controlled decelerator chamber that collects a sample of water from which some of the suspended matter is allowed to enter the top of a settling column the settling flocs are viewed using a miniature video system subsequent analysis of video tapes can provide direct measurements of size and settling velocity of individual flocs down to 20 m from this information floc density can be estimated the main feature of the instrument is its ability to video flocs in situ irrespective of the concentration in the estuary with as little disturbance to their hydrodynamic environment as possible preliminary field testing in the tamar estuary has given useful results in flow velocities up to 0 4 m s 1 and in concentrations up to 200 mg 1 1 the video recordings show large numbers of low density flocs with multiple structures linked by fine organic fibres

modeling of porosity loss during compaction and cementation of sandstones irreversible inelastic processes are responsible for mechanical and chemical compaction of sedimentary rocks at the time of burying our purpose is to describe the inelastic response of the rock at large time scales in order to do this we build a model that describes how porosity progressively decreases at depth we use a previous geometrical model for the compaction process of a sandstone by grain interpenetration that is restricted to the case of mass conservation in addition we introduce a compaction equilibrium concept solid grains can support stresses up to a critical effective stress c before plastic flow occurs this critical stress depends on temperature and is derived from the pressure solution deformation law pressure solution is the plastic deformation mechanism implemented during compaction our model predicts a porosity destruction at a depth of about 3 km this model has the property to define a range of compaction curves we investigate the sensitivity of the model to the main input parameters liquid film thickness grain size temperature gradient and activation energy

variable fractal dimension a major control for floc structure and flocculation kinematics of suspended cohesive sediment while the fractal dimension of suspended flocs of cohesive sediment is known to vary with the shear rate electrochemical properties of the sediment and environment geometrical restructuring and presence of organic matter experimental data presented in this work suggest changes in fractal dimension also during floc genesis at constant sedimentological and hydraulic conditions a power law function is proposed to describe these changes in floc fractal dimension during floc growth and is used to analyze its impact on floc structural parameters settling velocity and kinematics of aggregation and breakup an analysis of this model for the fractal dimension highlights changes of approximately a factor of 2 or more in floc porosity and aggregation and breakup frequencies and of approximately 1 order of magnitude in floc excess density and settling velocity compared to values estimated with constant fractal dimension the results from this model compare well with prior experimental data collected in situ khelifa and hill 2006 manning and dyer 1999

a unified approach to geopressuring low permeability zone formation and secondary porosity generation in sedimentary basins geopressuring secondary porosity and low permeability zones occur in many of the world s sedimentary basins and are often associated with major petroleum reservoirs we present a mechanical model which simultaneously reproduces these phenomena assuming pressure solution to be the dominant rock deformation mechanism a solid state rock skeleton viscosity is introduced which relates the deformation of the rock skeleton to the effective stress numerical solutions for compaction indicate that a soft sedimentary layer preferentially compacts to form a low permeability zone there is a large liquid pressure gradient through the low permeability zone in the more slowly compacting region beneath the low permeability zone the pressure gradient remains hydrostatic but the absolute pressure can exceed the lithostatic pressure in the absence of hydraulic fracturing this results in the formation of secondary porosity

sediment resuspension flocculation and settling in a macrotidal estuary national natural science foundation of china 40876043 papd fund china scholarship council 2010832427 mel young scientist visiting fellowship melrs0938

settling speeds of floes in fresh water and seawater the settling speeds of floes of fine grained natural sediments approximately 10 200 m in diameter have been measured in both fresh water and seawater these floes were formed at fluid shears of 100 200 and 400 s 1 and at sediment concentrations of 10 100 and 400 mg l values typical of conditions in the near shore areas of lakes and oceans especially during storm conditions it is demonstrated that the settling speed of a floe is a strong function of fluid shear and sediment concentration as well as of the diameter of the floe but it is a weak function of salinity for the same diameter and salinity floes produced at the lower fluid shears and sediment concentrations have lower settling speeds than do floes produced at higher fluid shears and sediment concentrations if the conditions of fluid shear and sediment concentration under which the floes were produced are unknown or ignored it is shown that the settling speed of a floe is a weak function of diameter and salinity

coagulation rates of clay minerals and natural sediments abstract coagulation experiments conducted using illite kaolinite montmorillonite and four natural sediment samples in blade and couette reactors with solutions of various salinities yielded collision efficiency factors significantly higher than those in the previous literature indicating that coagulation begins at lower salinities 1 2 1 the natural sediments do not generally behave as might be predicted for a mixture of the standards of the minerals of which the natural sediment samples were comprised the half times for coagulation of the particles indicate that in nature the coagulation process would probably be completed in the first few parts per thousand salinity

in situ settling behavior of marine snow1 the settling velocities of undisturbed macroscopic aggregates known as marine snow were measured with scuba in surface waters off southern california and analyzed as a function of aggregate size mass and density the mean settling velocity was 74f39 m d l for aggregates ranging from 2 4 to 75 mm in maximum length sinking rates in the field varied exponentially with aggregate size and dry weight and were consistently up to four times slower than rates measured in the laboratory the excess densities of the 80 aggregates examined were calculated from volume and dry weight and ranged over four orders of magnitude with a median of 1 4 x 1o 4 g cm 3 aggregates of marine snow sank more slowly than predicted for either solid or porous spheres of equivalent volume and density although their velocities were within the range expected for equivalent sinking prolate ellipsoids no relationships between settling velocity and either excess density or particle shape were found drag coefficients of marine snow were also higher than predicted by theory for spheres of equivalent volume and density these deviations from theoretical expectations may be partially explained by errors in the estimation of the excess densities of aggregates variability in the densities of the heterogeneous primary particles comprising marine snow fecal pellets claymineral particlcs phytoplankton molts etc and the potential for buoyancy regulation by individual phytoplankton cells inhabiting aggregates make determination of excess density especially

observations of particle density and scattering in the tamar estuary abstract to investigate the relationships between the optical scattering and the physical properties of suspended sediments such as size and density the absorption and scattering coefficients a and b mass concentration and particle size spectra have been measured at 30 stations along a transect of the tamar estuary and plymouth sound the apparent density of the suspended sediment a which dropped significantly in the upper reaches of the estuary was found to vary negatively as a function of both the chlorophyll concentration and median particle size by volume d v a relationship of the form i p d p d i relating the density of individual particle size fractions i of diameter d i has been assumed and used to predict the total apparent density of the size spectrum by comparing this to the measured apparent density the size and density of the primary particles d p and p and value of a measure of the fractal dimension which in combination produce the best fit of predicted to actual have been found they were found to be 3 9 m 1787 kg m 3 and 0 65 respectively these values were closely reproduced by repeating this method for the specific scattering coefficient b which was determined by applying mie theory to the measured particle size spectra for a refractive index consistent with that used by the lisst instrument using the calculated values of d p and p the best fit value for the fractal dimension was determined for each station the fractal dimension is shown to be strongly correlated with the apparent density and varies significantly from 2 05 in turbid chlorophyll rich tamar water to 2 56 in the clearer water out in plymouth sound results suggest that the relationship between fractal dimension and particle density is robust and can be used to predict primary particle size and density from bulk properties until now these values which are important for aggregation models have not been easily determined

marine isotope stage 6 canyon and spillover deposits of the bryant and eastern canyon systems northwest gulf of mexico importance of fine grained turbidites on a delta fed prograding slope abstract a large set of long sediment cores and high resolution seismic reflection data were used to study the sedimentology of the delta fed prograding slope of the northwest gulf of mexico during marine isotope stage mis 6 125 180 ka bryant and eastern canyon systems were the main pathways during this period through which mississippi river sediment was delivered down the continental slope two mis 6 sedimentary environments have been defined on the slope of the northwest gulf of mexico intracanyon and overbank environments the erosional action of turbidity currents in bryant and eastern canyons was focused mainly on the thalweg whereas on the rest of the canyon floors the flows acquired a mainly depositional character resulting in the formation of inner levees and terraces mis 6 deposits in overbank environments consist entirely of thick 50 m widespread 15 20 km and continuous successions of mud turbidites which indicate that spillover processes were dominant along bryant and eastern canyons the total absence of bioturbation structures and hemipelagic sediments in mis 6 overbank deposits indicate high sedimentation rates exceeding 200 600 cm ky the majority of the overbank deposits are normally graded indicating that most of the turbidity currents during mis 6 resulted from sediment failures on the outer shelf and upper continental slope sedimentological observations indicate that a complete mud turbidite sequence t0 8 sequence in the nomenclature of stow and shanmugam 1980 results from a waning low density turbidity current consisting of four successive flow regime stages 1 an initial erosional stage 30 cm s 2 deposition of the coarsest noncohesive fraction silt of the suspended sediment in the flows 30 100 cm s 3 cyclic deposition of cohesive mud and noncohesive silt laminae due to fluctuations in the shear stress in the boundary layer of the flow 12 30 cm s and 4 deposition from a silt depleted and slowly moving 15 cm s sediment cloud

compaction and overpressuring in pleistocene sediments on the louisiana shelf gulf of mexico abstract pleistocene shales on the louisiana shelf have accumulated at relatively high sedimentation rates 1400 m ma resulting in compaction disequilibrium and excess pore pressures mathematical models of gravitational compaction are useful tools for quantifying the rates at which various diagenetic processes affect porosity effective stress and pore pressure one of the major constraints in compaction modelling is characterising the mechanical compressibility of the sediments under one dimensional loading soil mechanics theory provides a useful framework by quantifying sediment effective stress in terms of two mechanical parameters both of which can be determined from uniaxial compression tests using a tri axial apparatus these mechanical parameters have been measured for natural and remoulded sediments and many values are published in the geotechnical literature if mechanical compaction is quantified accurately then it is possible to distinguish and quantify other porosity reducing mechanisms in sedimentary basins this paper re examined published data from two wells in the eugene island area of the louisiana shelf in order to characterize the effective stress behaviour of shale sediments mechanical parameters were estimated and found to agree with values from consolidation tests on core samples recovered from nearby sites during leg 96 of the deep sea drilling program using a continuum mechanics model for gravitational compaction the estimated mechanical parameters were used to forward model the sudden increase in pore pressure at 2 km burial depth the modelling results gave a lower bound on the effective permeability of the shallow nearly normally pressured section and an upper bound for the deeper overpressured section the effective permeability in the overpressured section has to be only about 5 times lower than that of the normally pressured section in order to account for the pressure contrast theoretical models for the effective permeability of sand shale mixtures suggest that the permeability difference between the two sections may be due to variations in the shale fraction

effective energy controls on flocculation under various wave current regimes transport of sediments is a critical process in the coastal zone because of its relation with coastal erosion productivity and pollution of particular interest are the dynamics of suspended cohesive sediments known as flocs which can aggregate and break up during the flocculation process this changes their size density settling velocity and overall transport even though turbulence is widely accepted to be an important control on floc aggregation and break up specific and detailed floc behaviour is still not fully understood the present study seeks to help in the understanding of the intra tidal turbulence induced flocculation under different current wave regimes observations of floc size and currents at high sample rates are used to investigate the changes throughout a fortnightly cycle the occurrence of waves at different stages during the sampling period enabled determination of three regimes of currents dominant combined waves and currents and wave dominant the first two regimes showed quarter diurnal floc size variability with aggregation during low turbulence slack waters and higher floc aggregation magnitude on low water slack break up occurred with high turbulence flood and ebb with higher magnitude after ebb during the currents waves regime waves were tidally modulated and led to enhanced aggregation and break up with larger floc size range than during the current dominant regime wave tidal modulation and quarter diurnal variability of floc size were lost when waves were dominant flocs sizes exhibited a low range related to wave height inverse relationships between turbulent properties and median floc size were found for the three regimes with higher scatter of data for the kolmogorov microscale and shear rate due to different floc behaviour during flood and ebb phases effective kinetic energy obtained from the combined effect of both currents and waves seems to have a better relationship with floc size which suggests its use as a floc size predictor instead of shear stress

a mathematical model for compaction in sedimentary basins summary a mathematical model for the non equilibrium compaction of clay rocks in sedimentary basins is formulated the model generalizes those of earlier authors the simplest assumptions are made concerning the rheology and diagenesis is neglected in this case we show that the model reduces to a generalized consolidation equation which for the classical darcy flow is a non linear diffusion equation for the porosity with a free boundary the model is non dimensionalized and it is shown that solutions depend on one significant dimensionless parameter a which is the ratio of the darcy flow rate and the sedimentation rate the model is solved numerically and asymptotic descriptions of the solutions are given for the cases of large and small a

deterministic coastal morphological and sediment transport modeling a review and discussion 1 modern coastal ocean modeling systems are now capable of numerically simulating a variety of coastal and estuarine problems and can thus provide useful information for managing coastal zones here we review state of the art eulerian implementations of bottom up sediment transport and morphological change in coastal ocean hydrodynamic models in order to investigate the fate of suspended sediment in coastal and estuarine waters as well as the evolution of sea or river beds sediment dynamics need to be represented at a scale relevant to the numerical discretized solution and significant effort is devoted to parameterize sediment processes we discuss boundary layer hydrodynamics and the computation of the bed shear stress we also focus on approaches used to represent near bed processes such as bed load transport and sediment erosion and deposition sediment diffusivities settling velocities and cohesive processes such as flocculation all have an impact on suspended sediment throughout the water column we then describe the implementation of process parameterizations in coastal hydrodynamic models explicitly reviewing five widely used systems the approaches implemented in these coastal models may present distinct strengths and shortcomings with regard to some important issues for coastal zones both numerical and physical while these detailed limitations need to be considered as part of model assessment more general issues also hinder present state of the art models in particular sediment transport is inherently highly empirical which is further compounded by issues arising from turbulence closure schemes we conclude by suggesting some possible directions toward improving sediment dynamics understanding and coastal scale predictive ability

floc properties in the turbidity maximum of a mesotidal estuary during neap and spring tidal conditions in order to improve the understanding of how fine cohesive matter behaves during different tidal conditions within an estuary turbidity maxima high quality in situ data is of a prime requirement as part of the european commission cosinus project a series of measurements were carried out in the upper reaches of the tamar estuary to investigate how flocculated mud properties vary within the turbidity maximum zone floc populations were sampled at regular intervals using the optical inssev instrument the floc data was supplemented by simultaneous time series of near bed profiles of turbulent shear stress and suspended particulate matter the proportion of macroflocs 160 m changed significantly across the turbidity maximum before the passage of the turbidity maximum the total floc mass tended to be equally divided between the macroflocs and microflocs on neaps whilst on springs the macroflocs contributed 60 70 at spring tides a peak near bed spm concentration of 6 g l 1 was measured in the turbidity maximum this was over an order of magnitude higher than observed at neaps the turbulence measurements showed significant drag reduction at spm concentration gradients above 3 6 kg m 4 within the turbidity maximum the macrofloc proportion rose rapidly until they contributed at least 75 of the floc dry mass during neap conditions and at spring tides this reached in excess of 90 96 an abundance of fast settling macroflocs from spring tides accounted for a time series average of 83 of the mass settling flux where as during neap tides the macroflocs contributed 15 less to the settling flux rate this was partly due to a time series averaged macrofloc settling velocity of 3 9 mm s 1 from the spring tidal data 2 1 mm s 1 higher than for neap tide conditions during the turbidity maximum passage at springs macroflocs reached 2 2 mm in diameter these flocs had settling velocities of up to 16 6 mm s 1 but effective densities were less than 50 kg m 3 which means they would be prone to break up when settling to a region of high shear at the opposite and of the scale low turbidity and quiescent slack water conditions severely restricted floc production

variability in cohesive sediment settling fluxes observations under different estuarine tidal conditions the mass settling flux which is defined as the product of the concentration and the settling velocity is of prime importance with respect to both stratified and well mixed estuarine conditions the determination of these fluxes for applied modelling purposes in high energy tidal estuarine environments is very problematic this is because the muddy sediments which dominate in estuaries flocculate producing a variety of sizes and settling velocities and this flocculation process is not understood well enough to be fully described theoretically by drawing on examples of floc spectra acquired in situ using the inssev system this study explains how mass settling fluxes in the near bed region can vary by three or four orders of magnitude in meso and macro tidal estuaries throughout a single tidal cycle a floc population representative of dilute suspension conditions on a neap tide indicated only 35 of the floc mass was macroflocs 160 m however the macrofloc settling velocity 2 4 mm s 1 three times faster than the microflocs which meant the former fraction contributed 57 of the 205 mg m 2s 1 settling flux both highly concentrated 4 6 g l 1 and very turbulent spring tide conditions 1 6 n m 2 produced a bi modal distribution in terms of the floc size and dry mass with the former 54 of the mass was contained within the 240 480 m size fraction with a further 25 of the dry floc mass in the flocs over 480 m in diameter these large flocs had settling velocities between 4 8 mm s 1 which meant 99 5 of the settling flux 33 5 g m 2s 1 was accredited to the macroflocs the high turbulence environment saw the dry floc mass distribution shift 60 40 in favour of the microflocs the microfloc settling velocity was 1 45 mm s 1 0 35 mm s 1 faster than the larger macrofloc fraction in terms of the total mass settling flux 0 9 g m 2 s 1 this translates into the microflocs contributing 70 during high turbulence at slack water the flux only reached 12 mg m 2 s 1 and macrofloc growth was mainly attributed to differential settling continuous floc observations made over a complete tidal cycle revealed that the asymmetrical distribution of the tidal energy generated throughout the spring conditions in the tamar estuary demonstrated a distinct control on the flocculation process the less turbulent ebb produced 86 of the total tidal cycle mass settling flux of which only 8 of the settling flux was outside the turbidity maximum an attempt to simulate these large settling fluxes by using a constant settling rate of 0 5 mm s 1 under estimated the tidal cycle settling flux by 78 with less than 15 of the total flux being estimated during the advection of the turbidity maximum on the ebb in contrast using a faster constant settling velocity parameter of 5 mm s 1 representative of the macrofloc fraction resulted in a mass flux over estimate of 116 for the tidal cycle duration

vertical migration of hydrocarbons modelled with fractional flow theory summary we present a simple 1 d and one lithology model of integrated hydrocarbon generation and vertical migration although the model is very simple it captures some of the most basic features of the vertical migration process like expulsion from source rocks and vertical migration in carrier beds above and below the source rock the dynamics in the model are caused by sedimentation which is done at a constant rate owing to sedimentation the source rock is brought down to the depths where kerogen breakdown starts this two phase model is based on fractional flow theory which makes it possible to avoid a pressure equation the solution of the saturation equation is characterized by a dimensionless number the gravity number and the size of the capillary forces when the gravity number is less than 1 buoyancy is less important while for gravity numbers greater than 1 buoyancy is dominating we discuss capillary effects and estimate a peclet number for the migration process which shows that capillary forces are less important in this one lithology model in the special case of no compaction negligible capillarity and no generation of pore space due to the kerogen breakdown we can approximate a solution to the saturation equation by considering riemann problems we find that above the source region we get at least a shock and possibly a rarefaction too below the source region we have at least a rarefaction wave and possibly a shock we present explicit expressions for the shock position and the characteristics propagating saturations these solutions enable us to decide if and when the shock will reach the top of the basin if we know the total oil production we can read off from the flux function curve an approximation of the saturation propagated upwards although these solutions apply to the case of no compaction negligible capillarity and no generation of pore space they are useful approximations if any of these restrictions is only weakly violated

estuarine flocs their size settling velocity and density the size and settling velocity of flocs of suspended sediments from the chesapeake bay were measured in laboratory experiments and in the field the curves between floc diameter and settling velocity showed a non stoke s relationship that was best described by the following settling velocity cm s 1 73 floc diameter cm 0 78 furthermore the relationship between floc diameter and settling velocity indicated that the floe density decreased as the floes increased in size in addition to changing density a cylinder shape was found to be the best shape factor