settling velocity and mass settling flux of flocculated estuarine sediments new formulations are presented for the settling velocity and mass settling flux the product of settling velocity and sediment concentration of flocculated estuarine mud physics based formulae for these are developed based on assumptions of a two class floc population microflocs and macroflocs in quasi equilibrium with the flow the settling velocities of microflocs and macroflocs are related to floc size and density via the kolmogorov microscale as a function of turbulent shear stress and sediment concentration including height dependence and floc density dependence coefficients in the formulae are calibrated against an existing large data set of in situ observations of floc size and settling velocity from northern european estuaries various measures of performance show that the resulting formulae achieve an improved level of agreement with data compared with other published prediction methods the new formulae with the original calibration coefficients perform well in tests against independent measurements made in two estuaries

yield stress measurements of mud sediments using different rheological methods and geometries an evidence of two step yielding abstract yield stress materials have a wide range of commercial applications yet the suitable way of determining the yield stress values of a given material has been the subject of many studies and debates yield stresses are dependent on the material shear history and composition which implies that robust protocols should be developed to study the yield stress dependence on a given parameter in this study three natural mud samples from a port having different densities were chosen for analysis four different geometries including concentric cylinders couette cone and plate parallel plates and vane geometries were used our aim was to find the geometry and measurement protocol that best adapted to natural mud samples the measurement should be reasonably fast and the major changes in sample structure two step yielding should be recorded within the same measurement various rheological experiments such as stress sweep oscillatory amplitude sweep creep and stress growth tests were tested two step yielding behavior was observed for the mud samples in stress sweep and amplitude sweep tests the first yield point was linked with the breakage of interconnected network of aggregates flocs while the second one was attributed to the collapse of aggregates into the smaller flocs or individual particles stress sweep tests proved to be practical time efficient and reliable tests for measuring yield stress values our study showed that couette and parallel plate geometries are the most suitable geometries for analyzing the two yield stresses of the samples vane geometry is appropriate to study consolidated solid like systems as for these samples a couette geometry cannot be used because the bob could get stuck during the experiment

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

effect of pre shearing on the steady and dynamic rheological properties of mud sediments abstract mud sediments can exhibit a complex rheological behaviour particularly a thixotropic character or structural recovery after breakup due to the presence of organic matter biopolymer such biopolymers can lead towards the development of flocculated structures having multiple length scales which are sensitive to shearing rate and history in this study the extent and rate of structural recovery of mud sediments was studied by measuring the storage modulus as a function of time using small amplitude oscillatory tests after a destructive steady shearing this linear viscoelastic response of the sediments was further investigated as a function of several parameters including pre shear rate pre shear time measuring geometry mud density and organic matter content the equilibrium storage modulus g and the characteristic time t r for the structural recovery of the sediment matrix were estimated by fitting the experimental data to a stretched exponential function the normalized storage modulus g g 0 i e structural parameter was used to relate it with the yield stresses of mud sediments the results showed that the recovery of structure after shearing was instantaneous t r being of the order of seconds however the extent of recovery was highly dependent on the studied parameters the extent of recovery was higher for the samples with lower density and lower organic matter content the effect of the shearing time on t r and g was almost negligible which implies that the destruction of the structure was achieved within seconds using vane geometry the extent of recovery was higher than using couette geometry which is linked with the distribution of shear stresses within the cell for each geometry yield stresses showed a strong dependency on structural parameter until it reaches very small values at low values of structural parameter the yield stresses were constant as the structural recovery was even faster than the time required to perform the amplitude sweep tests this study provides an extensive knowledge about the structural recovery in mud sediments under different shearing conditions which can be useful for sediment management

modeling the growth of cohesive sediment flocs in three dimensional space abstract this paper presents a model to simulate the growth of cohesive sediment flocs in 3 d space which takes into account brownian motion contribution gravity contribution flow contribution flow shear stress floc breakage and non uniform initial sediment size distribution results of validation tests indicate the model is feasible to simulate the growth of cohesive sediment floc under different contributions floc structure in different water depths and the influence of initial sediment size distribution were tested using the new model taking fractal dimension as an index the simulated results show that the sediment floc at the lower region possesses a larger fractal dimension than that of the upper region it is mainly due to the reproduction of new stronger denser flocs from the breakage and reform under the higher flow shear stress in the lower region additionally on the assumption condition that the initial sediment size distribution follows normal distribution an increase in the standard deviation results in the fractal dimension presents a trend from increasing to decreasing

wisconsin gravity minimum solution of a geologic and geophysical puzzle and implications for cratonic evolution an intense bouguer gravity anomaly minimum extending across much of wisconsin cannot be explained by the surface phanerozoic sedimentary strata the basement precambrian geology or the topography of the region the most intense minus 100 mgal part of the minimum coincides with the 1 47 ga anorogenic granitic wolf river batholith of northeastern wisconsin in southern wisconsin however the densities of the precambrian basement rocks which are older than the batholith provide no clue to the origin of the anomaly the gradients of the minimum indicate that the source of the anomaly is in the upper crust furthermore nearby deep seismic reflection data indicate that lower crustal structures do not significantly contribute to the gravity minimum thus the minimum is appropriately interpreted as originating from the low density wolf river batholith that crops out only in northeastern wisconsin but is buried beneath a veneer of older rocks in the southern and central parts of the state gravity modeling suggests that the batholith is at least 10 km thick and encompasses an area of approximately 50 000 km sup 2 this interpretation provides an important clue to the origin of similar negative gravity anomalies of the phanerozoic strata covered craton also the presence of this massive granitic bodymore appears to have influenced the evolution of the craton e g by controlling the location of the 1 1 ga midcontinent rift system and the paleozoic wisconsin arch the fact that the wolf river batholith is mostly buried suggests that central wisconsin has been tectonically stable for the past 1 47 b y and that the precambrian basement has been minimally eroded less

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

mass settling flux of fine sediments in northern european estuaries measurements and predictions abstract this study describes a new flocculation model which was based entirely on observations of settling floc spectra and turbulent shear stresses acquired primarily from a series of in situ experiments conducted in several european estuaries the synthesis identified that the key components which best quantitatively describe a floc population are the changes in the macrofloc 160 m and microfloc settling velocities ws macroem and ws microem together with how the suspended matter is distributed across each floc sub population spm ratioem the ws macroem algorithm displayed an increase in settling velocity at low shear stresses due to flocculation enhanced by shear and floc disruption at higher stresses for the same concentration the transition being a turbulent shear stress of about 0 36 n m 2 the combination of the three algorithms into a single equation to predict mass settling flux msf em estimated the total flux of the 157 measured floc samples with a cumulative error 1 and 5 mm s 1 were both in error by an average of 86 and 41 respectively a concentration settling parameterisation and the van leussen techniques under predicted the total cumulative flux by 35 and 38 respectively furthermore the analysis indicated that the various existing methods all incurred high predictive errors at times under estimating by over 70 as concentration levels rose in close proximity to the bed the findings of this study demonstrate the new manning floc settling velocity mfsv empirical model has flexibility in adapting to a wide range of both turbulent shear stress and suspended sediment concentration estuarine conditions

dynamics of the sediment plume over the yangtze bank in the yellow and east china seas a distinct sediment plume exists over the yangtze bank in the yellow and east china seas yecs in winter but it disappears in summer based on satellite color images there are two controversial viewpoints about the formation mechanism for the sediment plume one viewpoint is that the sediment plume forms because of cross shelf sediment advection of highly turbid water along the jiangsu coast the other viewpoint is that the formation is caused by local bottom sediment resuspension and diffused to the surface layer through vertical turbulent mixing the dynamic mechanism of the sediment plume formation has been unclear until now this issue was explored by using a numerical sediment model in the present paper observed wave current and sediment data from december 29 2016 to january 16 2017 were collected near the jiangsu coast and used to validate the model the results indicated that the model can reproduce the hydrodynamic and sediment processes numerical experiments showed that the bottom sediment could be suspended by the bottom shear stress and diffuse to the surface layer by vertical mixing in winter however the upward diffusion is restricted by the strong stratification in summer the sediment plume is generated locally due to bottom sediment resuspension primarily via tide induced bottom shear stress rather than by cross shelf sediment advection over the yangtze bank

a note on the krone deposition equation and significance of floc aggregation for modeling the rate of deposition of cohesive flocs in estuaries the krone equation is extensively used it was derived from flume experiments on muddy sediment from the san francisco bay and is applicable to low suspended sediment concentration environments in which shear induced aggregation the growth and break up of flocs has a limited role it is shown that the use of this equation can lead to erroneous estimates of the mass deposition flux at typically higher estuarine concentrations krone s own experimental data permit the development of a more general equation accounting for the effects of concentration and turbulent shear rate on aggregation these effects are dramatically observed in a deposition test in which a wire mesh was inserted in the flow to change the turbulent shearing rate and increase deposition even with the inclusion of aggregation effect in the general equation field based observations from san francisco bay suggest that typical flumes generally may not meet the space and time scaling requirements for field application of laboratory data thus although the krone equation should be eschewed in favor of the general equation interpretations of model predicted deposition rate must not be accepted without robust field based verification

a study of in situ sediment flocculation in the turbidity maxima of the yangtze estuary abstract in order to improve our understandings of temporal and vertical variations of sediment flocculation dynamics within the turbidity maxima tm of the highly turbid yangtze estuary ye we deployed lisst 100c a laser instrument for in situ monitor of the sizes and concentrations of flocculated particles in a wet season field data in terms of vertical profiles of flow velocity suspended sediment concentration ssc salinity flocculated particle size distribution and volume concentration were obtained based on field works conducted at consecutive spring moderate and neap tides data analyses show that the mean floc diameters d m were in the range of 14 95 m and flocculation exhibited strong temporal and vertical variations within a tidal cycle and between spring neap cycles larger d m were observed during high and low slack waters and the averaged floc size at neap tide was found 57 larger than at spring tide effective density of flocs decreased with the increase of floc size and fractal dimension of flocs in the ye was mainly between 1 5 and 2 1 we also estimated the settling velocity of flocs by 0 04 0 6 mm s 1 and the largest settling velocity occurred also at slack waters moreover it is found that turbulence plays a dominant role in the flocculation process floc size decreases significantly when the shear rate parameter g is 2 3 s 1 suggesting the turbulence breaking force combined effects of fine sediment flocculation enhanced settling process and high sediment concentration resulted in a large settling flux around high water which can in part explain the severe siltation in the tm of the ye thus shedding lights on the navigation channel management

modelling flocculation towards an integration in large scale sediment transport models abstract despite recent advancement in the field of sediment transport the integration of cohesive sediment properties in large scale transport models remain a challenging task in order to model adequately the change in particle size that occurs in different environmental conditions flocculation models based on the so called population balance equations pbe are often used these models have to be efficient enough to be implemented in numerical transport models and as full pbe s are time expensive to run and depend on a huge amount of a priori unknown parameters simplifications have to be made these simplifications comes unavoidably at the cost of properly accounting for the complex particle particle and particle fluid interactions in order to stay as close as possible to the physical processes we propose a different approach based on a logistic growth model that mimics the particle size distribution psd measured over time for all size classes the parameters of the model can easily be found from laboratory measurements in contrast to most models the particle classes we propose are not defined by particle size but in terms of mineral sediment composition one class is composed of unflocculated mineral sediment particles another of flocculated sediment particles and a third one of organic particles the mass balance between classes and the way to obtain their corresponding average settling velocity are given mass balance and settling velocities are the required input parameters for all sediment transport models the simplicity of the derived expressions and their link with measurable variables makes them good candidates for future implementation in such models

factors controlling the field settling velocity of cohesive sediment in estuaries abstract it has long been recognized that the suspended sediment concentration ssc is one of the major determinants for the flocculation of cohesive particles into sediment flocs in estuaries it is furthermore well known that the turbulent shear of the water significantly influences the flocculation process and the equilibrium settling velocity of flocculated sediment in a turbulent flow a vast number of authors have reported algorithms relating the median settling velocity w 50 to suspended sediment concentration however only a few studies have dealt with the impact of the turbulent shear in this paper expressed as the root mean square rms velocity gradient g in the water on the w 50 in situ there is a strong need to establish algorithms based on in situ measurements describing the dual impact of both ssc and g on the flocculation process and hence w 50 the present paper addresses this topic field settling velocities of suspended cohesive sediment have been measured in micro meso and macro tidal estuaries regression analyses between the w 50 ssc and g are presented it is shown that by including both g and ssc in the regression analyses a significant increase in the correlation of the description of w 50 and the controlling parameters from each area can be obtained a generic algorithm describing the data from all the investigated areas is suggested it works well within specific tidal areas but fails to give a generic description of the field settling velocity

factors controlling floc settling velocity along a longitudinal estuarine transect a 147 km longitudinal transect of flocculated cohesive sediment properties in san francisco bay sfb was conducted on june 17th 2008 our aim was to determine the factors that control floc settling velocity along the longitudinal axis of the estuary the inssev lf video system was used to measure floc diameters and settling velocities at 30 stations at a distance of 0 7 m above the estuary bed floc sizes d ranged from 22 m to 639 m and settling velocities ws ranged between 0 04 mm s 1 and 15 8 mm s 1 during the longitudinal transect nearbed turbulent shear stresses throughout the transect duration were within the 0 2 0 5 pa range which typically stimulates flocculation growth the individual d ws floc density plots suggest the suspended sediments encountered throughout sfb were composed of both muddy cohesive sediment and mixed sediments flocs mass weighted population mean settling velocity wsmass ranged from 0 5 mm s 1 to 10 mm s 1 the macrofloc and microfloc demarcation at 160 m sub populations demonstrated parameterised settling velocities which spanned nearly double the range of the sample mean settling velocities wsmean the macroflocs tended to dominate the suspended mass up to 77 of the ambient suspended solid concentration ssc from san pablo bay to carquinez strait the vicinity of the turbidity maximum zone microfloc mass was particularly significant typically 60 100 of the ssc in the northern section of south bay and most of central bay the transect took eleven hours to complete and was not fully synoptic during slack tide larger and faster settling flocs deposited accounting for most of the longitudinal variability the best single predictor of settling velocity was water velocity 39 min prior to sampling not suspended sediment concentration or salinity resuspension and settling lags are likely responsible for the lagged response of settling velocity to water velocity the distribution of individual floc diameters and settling velocities indicates that floc density for a given floc diameter varies greatly a small portion a few percent of suspended sediment mass in sfb is sand sized and inclusion of sand in flocs appears likely fractal theory for cohesive sediment assumes that there is a single primary particle size that flocculates which is not the case for these types of mixed sediment flocs the wide variability in the physical biological and chemical processes which contribute to flocculation within sfb means that spatial floc data is required in order to accurately represent the diverse floc dynamics present in the bay system the importance in determining accurate estimates of floc density has been highlighted by the sfb data as these provide the basis for realistic distributions of floc dry mass and the mass settling flux across a floc population however although video floc sampling devices can produce the various floc property trends observed in sfb good survey practice is still paramount one can see that if the sampling coverage i e data collection frequency is poor this could lead to potential mis interpretations of the data and only limited conclusions may be drawn from such a restricted survey for example a limited survey i e only 3 stations compared to the 10 stations in the full survey in south bay produces an under estimate in both the macrofloc sscmacro distribution by a factor of four and the wsmacro by a factor of two to develop sediment transport numerical models for sfb high quality floc size and settling data are needed to understand and simulate the depositional qualities of both suspended cohesive sediment and mixed sediments in san francisco bay this study has shown that the most pragmatic solution is a physically based approach whereby the detailed flocs d vs ws spectra are parameterised in terms of their macrofloc and microfloc properties this aids in model calibration whilst retaining more of the dynamical aspects of the floc populations all forms of flocculation are dynamically active processes therefore it is important to also include both ssc and turbulence functions together with the floc data

morphodynamic evolution of an intertidal mudflat under the influence of amazon sediment supply kourou mud bank french guiana south america the coastal environment between the amazon and the orinoco rivers is characterised by the migration of large mud banks formed by accretion of the muddy discharge from the amazon the migration of mud in the shallow coastal waters is associated with the creation of mudflats that form a surface for the development of coastal mangroves after consolidation this study focuses on the fine scale sedimentary processes involved in the morphodynamic evolution of a consolidated mudflat and its erosion mudflats can be divided into two areas the seafront and the inner part between the seafront and the land this study highlights a link between tidal mud supply biofilm migration and increasing elevation in the latter area the migration of a biofilm through each cycle of tidal supply prevents erosion and permits the continuous accretion of the entire mudflat over several years this increase in topography is also modulated by fortnightly tidal cycles desiccation greatly impacts the mudflat s structure at a yearly scale this process plays an important role in the erosion of the seafront area under wave action by allowing the formation of mud pebbles which are progressively abraded into fluid mud supplied to the inner part of the mudflat by over wash processes this study provides a better understanding of the behaviour of mudflats on the wave exposed coast downdrift of the mouth of the amazon by describing 1 the processes involved in sediment exchanges between mudflats and mud banks 2 the mechanisms associated with the persistence of mudflats along the french guiana coast downdrift of the mouth of the amazon and 3 the processes involved in the erosion and recycling of these mudflats

observations of distribution and flocculation of suspended particulate matter in the minjiang river estuary china abstract in this study we described the distribution pattern of suspended particulate matter spm and its influencing factors in the waters around the minjiang river estuary further we investigated the flocculation process of spm and its underlying mechanism in the study area the objectives were achieved using water temperature salinity turbidity fluorescence and particle size distribution of spm data measured in august 2009 as influenced by dilution from the minjiang river water the water column structure was significantly stratified in the estuary with an obvious thermocline and halocline the turbidity was relatively low in the surface water ssc 15 mg l fluorescence was high up to 10 l l in the surface water which was markedly lower and more uniform in the lower water layer the total volume concentration and particle size of the spm in the upper water layer were significantly higher than those of the lower water layer the in situ particle size frequency distribution of spm markedly changed in the different water layers whereas the dispersed particles were fine with little difference in frequency distribution the mean effective density of spm was generally 3 in the surface and benthic water and the values were slightly higher in the benthic water layer than in the surface water layer with a significant increase in the middle water layer the significant differences between the distribution trends of the total volume concentration and water turbidity were controlled by the size distribution of spm the concentration distribution of spm was mainly influenced by source re suspension and thermocline among other factors flocs widely occurred in the study area and the flocculation mechanism of spm varied in the different water layers in the upper water layer intense biological activity promoted the formation of stable macroflocs in the benthic water layer the biological activity was limited the flocculation of sediment particles was mainly caused by physico chemical attraction of inorganic particles and the hydrodynamic conditions and high settling velocity were also unfavourable to the formation of macroflocs

the effect of periodic stratification on floc size distribution and its tidal and vertical variability geum estuary south korea abstract to understand the spatiotemporal variability in the floc size distribution the factors controlling floc size and the timing of flocculation with sediment flux in the periodically stratified geum estuary korea simultaneous measurements of current salinity suspended sediment concentration ssc and floc size distributions were analyzed and floc size was compared with stratification turbulence ssc and sediment flux salinity measurements indicated that the water column was stratified during ebb and well mixed during flood consistent with the process of strain induced periodic stratification coincident with periodic stratification was an ebb flood asymmetry in floc size where coarser multimodal and variable distributions occurred during the stratified ebb whereas finer unimodal and relatively constant distributions occurred during the well mixed flood vertically flocs coarsened downward during the stratified ebb and were vertically homogenous during the well mixed flood the ebb flood asymmetry in floc size was due to the ebb flood asymmetry in stratification and turbulence furthermore while floc size decreased with turbulence the ssc increased with turbulence as a consequence large flocs occurred with relatively small ebb directed fluxes whereas small flocs occurred with relatively large flood directed fluxes overall these observations indicate that the variability of the floc size distribution in periodically stratified estuaries is different than in well mixed estuaries and that ebb directed fluxes may be more flocculated than flood directed fluxes in these systems

spatial estimation of debris flows triggering rainfall and its dependence on rainfall return period abstract forecasting the occurrence of debris flows is fundamental for issuing hazard warnings and often focuses on rainfall as a triggering agent and on the use of empirical rainfall thresholds based on rain gauge observations a recognized component of the uncertainty associated with the use of rainfall thresholds is related to the sampling of strongly varying rainfall variability with sparse rain gauge networks in this work we examine the spatial distribution of rainfall depth in areas up to 10 km from the debris flow initiation points as a function of return period and we exploit this information to analyze the errors expected in the estimation of debris flow triggering rainfall when rain gauge data are used in particular we investigate the impact of rain gauge density and of the use of different interpolation methods high resolution adjusted radar rainfall estimates representing the best available spatially distributed rainfall estimates at the debris flows initiation point and in the surrounding area are sampled by stochastically generated rain gauge networks characterized by varying densities debris flow triggering rainfall is estimated by means of three rainfall interpolation methods nearest neighbor inverse distance weighting and ordinary kriging on average triggering rainfall shows a local peak corresponding to the debris flow initiation point with a decay of rainfall with distance which increases with the return period of the triggering rainfall interpolation of the stochastically generated rain gauge measurements leads to an underestimation of the triggering rainfall that irrespective of the interpolation methods increases with the return period and decreases with the rain gauge density for small return period events and high rain gauge density the differences among the methods are minor with increasing the return period and decreasing the rain gauge density the nearest neighbor method is less biased because it makes use only of the closest rain gauge to the debris flow initiation point on the contrary inverse distance weighting and ordinary kriging which are using rain gauges located farther from the debris flows in addition to the closest one exhibit negative biases that increase with return period the standard deviation of the interpolated values is larger when the nearest neighbor is used with respect to inverse distance weighting and ordinary kriging for large return period and low rain gauge density the differences among the methods are minor