suspended sediment transport in the surf zone response to cross shore infragravity motion a field experiment to investigate the magnitude and temporal and spatial scales of suspended sediment transport in the inner surf zone was conducted at san marine oregon on october 7 13 1984 instrumentation consisted of five electromagnetic current meters three strain gauge type pressure transducers and 25 optical backscatter sensors to measure the concentrations of suspended sediment the instruments were deployed approximately 70 m x seaward of the mean high water line mean depth h 1 1 1 3 m in a closely spaced cross shaped pattern data were collected for 68 min periods spanning high tide during the 7 day experiment during the experiment waves varied in angle of approach from shore normal to southwesterly offshore significant swell heights were 3 5 m with periods of 12 14 s local sea conditions with wind waves of approximately 8 s also occurred a visual estimation of the width of the surf zone indicated it to be approximately 500 m and the breaker pattern suggested that there were two longshore bars at approximately 200 and 500 m offshore the data resulting from the experiment encompass a broad range of wave and current conditions which included periods of extreme infragravity motion 30 t 300 s and weak longshore currents and periods of low infragravity motion and strong longshore currents periods of incident wave dominance also occurred the field study section of this paper qualitatively describes the sediment response to strong 240 cm s 1 low frequency 0 01 hz cross shore fluid motions which dominated the inner surf zone during two of the data runs the infragravity band accounted for 85 of the cross shore velocity variance the peak 0 01 hz of which was associated with shore normal standing waves concentration gradients of suspended sediment appear to be associated with diffusive processes and develop and decay on time scales of the infragravity motions rather than those of incident waves suspension events during times of infragravity dominance often persisted for periods of 30 45 s and reached peak concentrations of 20 40 g l 1 at elevations in excess of 26 cm mean suspended load was 3 4 times larger than that associated with incident wave motions the modeling section of the paper attempts to quantitatively describe the observed time dependent vertical suspended sediment distribution with a one dimensional turbulent diffusion model formulations of eddy diffusion and erosion rate coefficients associated with peak cross shore flows are found to agree with or fall within the range of values from previous laboratory and field studies and are used in the model the model is evaluated by its ability to reproduce the time dependent vertical distribution of suspended sediment and to estimate the observed mean suspended load and the correct direction and magnitude of the mean longshore and cross shore flux level above the bed z 31 cm of suspended sediment

boundary shear in circular pipes running partially full the distribution of boundary shear stress in circular conduits flowing partially full with and without a smooth flat bed simulating deposited sediments has been examined experimentally ranging from 0 375 f 1 96 f froude number and 65 000 r 342 000 r hydraulic radius using the preston tube technique the invert level of the flat bed and the water depth have been varied to simulate a wide range of possible flow conditions that may occur in culverts sewers and hydropower tunnels the distribution of boundary shear stress around the wetted perimeter is shown to be highly sensitive to changes in cross sectional shape the results have been analyzed in terms of the variation of local global shear stress versus perimetric distance and the percentage of the total shear force acting on the wall or bed of the conduit the sfw results sfw the percentage of the average wall shear force of the overall shear force have been shown to agree well with knight s empirical formula for prismatic channels the influence of secondary flows on the distribution of boundary shear stress and the implications of this for sediment transport have also been examined

observations of currents and water properties in the amazon frontal zone measurements of currents and water properties were obtained at various locations in the frontal zone of the amazon river outflow plume during four cruises in 1989 1991 as part of a multidisciplinary amazon shelf sediment study a salinity front resembling a salt wedge is found approximately 150 km seaward of the river mouth it continues northwestward more than 400 km along the shelf between the 10 and 20 m isobaths tidal currents which are oriented principally in the cross shelf direction reach 200 cm s 1 during spring tides and drop to less than 80 cm s 1 during neaps in the vicinity of the river mouth the nontidal flow is strongly sheared with near surface speeds of up to 100 cm s 1 and weak near bottom velocities the direction of the near surface flow is generally northwestward except near the river mouth where river discharge leads to a significant offshore component of flow the strong velocity shears are stabilized by strong stratification by salinity and by highly concentrated suspended sediment or fluid mud near the seabed variations in stratification and frontal position are due principally to spring neap variations in tidal mixing and seasonal variations in runoff

wave mud interactions over the muddy atchafalaya subaqueous clinoform louisiana united states wave supported sediment transport 1 near bottom fluid mud layers were observed during two experiments conducted on the muddy atchafalaya inner shelf subaqueous clinoform louisiana united states on the face of the subaqueous delta 4 7 m water depth first experiment fluid mud layers are produced by seafloor liquefaction and resuspension forced by swells associated with cold front passages and supported by near bed wave induced turbulence the layers are episodic lifetime of 9 12 h form prior to significant postfrontal settling of sediment in the overlying water column and flow seaward downslope at about 5 cm s farther westward on the delta front finer grain size with negligible sand or coarse silt content second experiment similar wave supported fluid mud layers are observed to last longer 2 days show weaker alongshore westward flow of about 1 3 cm s the results suggest a sequence of near bed sediment transport processes triggered by frontal swell activity bed liquefaction resuspension and advection modulated by the bathymetric characteristics of the clinoform that contribute to the formation of clinoform stratigraphy of muddy subaqueous deltas

winter storm induced hydrodynamics and morphological response of a shallow transgressive shoal complex northern gulf of mexico abstract using extended deployments during seasons of low and high discharge from the atchafalaya river meteorological hydrodynamic and bottom boundary layer parameters were monitored from tiger and trinity shoal complex off louisiana coast usa during winter storms the surface current speed measured at both shoals exceeded 0 5 m s and the entire water column followed the prevailing wind direction the current speed close to the bottom exceeded 0 3 m s during high energy northerly winds the mean water level in the shoal complex increased during southerly winds and decreased during northerly winds such that the difference between wind set up and set down exceeded 0 7 m in tiger shoal and 0 6 m in trinity shoal during high energy frontal passages the swell height was inversely correlated with mean water level and increased during pre frontal phase and decreased during post frontal phase of winter storms the sea short waves height responded quickly to wind direction and speed and within a few hours after the wind shifted and blowing from the north the sea height increased during both deployments bimodal wave frequency spectrum was observed during wind veering from southerly to northerly when both sea and swell intensities were significant the tiger shoal bed sediment texture transformed drastically from mud to shell and shell hash assemblage within a period of two weeks during the december 2008 deployment backscatter signal intensity from a pulse coherent acoustic doppler profiler pcadp and its velocity estimates were used to determine the vertical extend and timing of mud resuspension and their eventual flushing out from the shoal environment when exposed to high energy winter storm passages the computed time frame for a total transformation of bottom sediment texture from muddy bottom to shell and shell hash assemblage was supported by the combined wave and bottom current induced shear stress at shoal bed the bed samples collected from tiger shoal before and after the deployment in spring 2009 consisted of more than 80 shell and shell hash which again confirmed a stable bottom as predicted from the pcadp data however the fine sand and mud dominated bed at trinity shoal was highly dynamic and experienced a few cm of ephemeral sediment deposition during the passage of each cold front as revealed from the analysis of acoustic backscatter data from the pcadp suspended sediment concentration estimated from optical backscatterance sensors obs and pcadp were in good agreement during low river discharge events in december 2008 but significantly diverged during the spring 2009 deployment when a high suspended sediment load was discharged into the shelf from the atchafalaya river and subsequently pushed farther offshore into the deployment sites by wind induced strong currents during the passage of cold fronts

interaction between breaking broken waves and infragravity scale phenomena to control sediment suspension transport in the surf zone time series of near bed sediment water level and velocity were measured in the field and laboratory and analysed to investigate a the role of breaking broken waves b the predominance of infragravity scale transport processes in the surf zone and c the influence of infragravity processes in creating the right conditions for suspension by breaking broken waves instantaneous suspended sediment concentrations were measured using optical backscatter sensors which were found to be sensitive to sediment size cohesive sediment in suspension and bubbles a simple numerical filter was applied to remove the erroneous bubble signal suspension was found to be correlated with wave breaker bores and an associated increase in high frequency velocities the latter deemed to be caused by surface generated turbulence infragravity scale sediment transport flux was found to be more significant than incident scale flux in the transition and inner surf zones sediment suspension was further found to be related to the onset of lower water levels associated with infragravity wave action which corresponded with a predominance of breaking broken waves these breaking broken waves which are induced by the low water level are deemed to be the cause of this suspension

immediate changes in stream channel geomorphology aquatic habitat and fish assemblages following dam removal in a small upland catchment abstract dam removal is becoming an increasingly important component of river restoration with 1100 dams having been removed nationwide over the past three decades despite this recent progression of removals the lack of pre to post removal monitoring and assessment limits our understanding of the magnitude rate and sequence of geomorphic and or ecological recovery to dam removal taking advantage of the november 2012 removal of an old 190 year old 6 m high run of river industrial dam on amethyst brook 26 km2 in central massachusetts we identify the immediate eco geomorphic responses to removal to capture the geomorphic responses to dam removal we collected baseline data at multiple scales both upstream 300 m and downstream 750 m of the dam including monumented cross sections detailed channel bed longitudinal profiles embeddedness surveys and channel bed grain size measurements which were repeated during the summer of 2013 these geomorphic assessments were combined with detailed quantitative electrofishing surveys of stream fish richness and abundance above and below the dam site and throughout the watershed and visual surveys of native anadromous sea lamprey petromyzon marinus nest sites post removal assessments were complicated by two events 1 upstream knickpoint migration exhumed an older ca late eighteenth century intact wooden crib dam 120 m upstream of the former stone dam and 2 the occurrence of a 10 20 year ri flood 6 months after removal that caused further upstream incision and downstream aggradation now that the downstream reach has been reconnected to upstream sediment supply the predominant geomorphic response was bed aggradation and associated fining 30 60 reduction at dam proximal locations aggradation ranged from 0 3 to 1 m where a large woody debris jam enhanced aggradation although less pronounced distal locations still showed aggradation with a mean depth of deposition of 0 20 m over the 750 m downstream reach post removal but pre flood bed surveys indicate 2 m of incision had migrated 25 m upstream of the former reservoir before encountering the exhumed dam which now acts as the new grade control limiting progressive headcutting approximately 1000 m3 of sediment was evacuated in the first year with 67 of the volume occurring by pre flood process driven e g changes in base level controls the combination of changes in channel bed sedimentology the occurrence of a large magnitude flood and the emergence of the new crib dam that is a likely barrier to fish movement was associated with major reductions in abundance and richness in sites downstream and immediately upstream adjacent to the former dam in post removal sampling at the same time we documented the presence of four species of fish including sea lamprey which were not present above the dam prior to removal indicating that upstream passage has been achieved and we also documented lamprey spawning activity at sites immediately below the dam which had previously been unsuitable owing to an excessively coarse and armored riverbed our results point to the importance of interactions between dam removal and flood disturbance effects with important implications for short and long term monitoring and assessment of dam impacts to river systems

on the dynamics of sediment suspension by residual reynolds stresses confirmation of bagnold s theory bagnold s dynamic theory for sediment suspension requires that the immersed weight of suspended grains over unit bed area is supported by an upward directed residual reynolds stress yy arising from asymmetrical shear turbulence the present paper presents an analysis of previously published turbulence data which confirms the existence of this residual stress and indicates its generation in the lowermost part of the buffer layer of turbulent shear flows the magnitude of yy is estimated as about 0 3 yx calculations from experimental data on suspended fine sand transport over upper phase beds reveals that yy is in approximate equilibrium with the weight stress due to the suspended load

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

high resolution comparison of sediment dynamics under different forcing conditions in the bottom boundary layer of a shallow micro tidal estuary 1 data for high resolution profiles of current velocity and suspended sediment concentration ssc were collected in bottom boundary layer bbl of mobile bay alabama the data were used to study the vertical and temporal variability in ssc under various forcing conditions of tide wind and freshwater discharge during the winter stormy season the background ssc was low 0 015 0 03 g l 1 an episodic storm induced erosion resuspension was responsible for the short lasting high ssc in bbl during the spring flooding period the background ssc was relatively high 0 04 0 07 g l 1 likely due to the large amount of suspended sediment from the fluvial input and bed softening and the contribution of wind forcing to sediment resuspension was somewhat enhanced by the destratification in bbl when the freshwater discharge was extremely high 5000 m3 s 1 the entire water column in shallow areas of the bay was influenced by freshwater input therefore the thermohaline anomaly s contribution to the stratification considerably weakened while the ssc s contribution strengthened when the freshwater discharge was relatively low 5000 m3 s 1 a critical wind stress for sediment erosion 0 08 0 1 pa was observed to abruptly increase the ssc despite a micro tidal regime mobile bay exhibited the cyclic erosion and deposition pattern induced by the tidal acceleration and deceleration

biofouling control for optical backscatter suspended sediment sensors abstract the use of optical backscatter instruments for measuring water turbidity for extended periods has been very limited due to the debilitating effect of biological fouling this is particularly the case in tropical coastal waters we describe a simple wiping mechanism attached to a logging nephelometer which can usually control fouling for up to a month even under conditions most favourable for fouling without a wiper deployment periods can be limited to only a few days scratching of the nephelometer by the wiper is not a major contributor to nephelometer error

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

the influence of fish feed pellets on the stability of seabed sediment a laboratory flume investigation superfluous fish food settling below fish farms can have a negative impact on the seabed to aid in the assessment of this impact a series of flume experiments designed to mimic seabed conditions below a fish farm was conducted with the aim of examining the effects of fish pellets on the stability of fine sediments artificial beds with varying quantities of fish pellets incorporated both within the sediment matrix and lying on the sediment surface were allowed to consolidate for different periods of time ranging from 1 to 10 days and then subjected to erosion experiments in flume experiments containing fish pellets a bacterial biofilm developed at the sediment water interface after a few days in the control experiments no fish pellets a diatom biofilm caused extensive stabilisation of the surface sediment the erosion experiments showed that the addition of fish pellets reduced the surface erosion threshold by more than 50 the stability decrease was more pronounced in the experiments with greater amounts of pellets evidence of drag reduction due to high suspended sediment concentration was also observed this phenomenon is discussed and a correction formula is proposed for the effective shear stress experienced by the bed

sediment exchange between amazon mudbanks and shore fringing mangroves in french guiana time series remote sensing data sediment cores and water column profiles of fluid properties and suspended sediment concentration were utilized to examine the mechanisms and volumes of sediment exchange between the mangrove fringe and the coastal zone in french guiana remote sensing estimates of sediment yield from mangrove shoreline erosion by wave attack during the 30 year periods when offshore amazon mudbanks are not adjacent to a 30 40 km long section of the shoreline are 6 23 million tons year 1 7be 137cs and 210pb inventories in sediment cores from inner 5 m water depth mudbank areas suggest the mangrove erosion occurs primarily during the january april period of high wave energy and is responsible for the bulk of sediment deposition on the leading edge of the mudbank remote sensing estimates of shoreline accretion associated with onshore flux of sediment from a mudbank are also large 8 26 million tons year 1 radiotracer generated strata age relationships indicate that the lower intertidal zone of the leading depositional edge of the mudbank is a relict surface suggesting the offshore mudbank is decoupled from the shoreline water column profiles and radiochemical signatures point to fluid mud suspensions 10 400 g l 1 as the primary mechanism for delivering sediment across the relict intertidal zone to create the accretion at the shoreline if the estimates of sediment volume involved in shoreline accretion and erosion in the studied area are extrapolated along the entire 1400 km long guianas coastline possessing offshore mudbanks the annual exchange of sediment to and from the mangrove fringe is at least equivalent to the average input of new sediment from the amazon

observations of internal tides off the coast of shandong peninsula china abstract bottom mounted platforms equipped with current profilers meters temperature salinity and turbidity sensors were deployed for about 10 days in august 2017 over an elongated deposit off the coast of shandong peninsula in order to monitor the hydrodynamics and sediment processes in the bottom boundary layer in total semidiurnal barotropic tides dominate the measured currents accounting for 90 of total variance however in the cross shore direction greater variance is associated with the semidiurnal internal tidal currents than the semidiurnal barotropic currents both the empirical orthogonal functions and normal mode analysis demonstrate that the baroclinic velocity is dominated by the mode 1 internal tides i e the current has a vertical shear with strong opposite flows near the surface and bottom while weak in the middle although the bottom slope is subcritical in most area of the deposit the ratio between the bottom slope and the slope of internal tide characteristics is greater than 0 5 suitable for local internal tide generation the internal tides generated from the deposit are especially significant considering that the shelf of the yellow sea is usually broad and flat the quantitative estimation of the water column mixing indicate that the bottom dissipation induced by the barotropic tides 6 44 10 4 m3 s 3 is greater than the internal tides 0 95 10 4 m3 s 3 and the total dissipation rate due to bottom drag is 5 49 10 4 m3 s 3 which is much greater than the interior one due to internal tides 2 69 10 4 m3 s 3 the internal tidal current alone is not energetic enough to resuspend the local fine grained sediments however in the cross shore direction the sediment flux due to internal tides is twice as much as the barotropic component resulting in a net onshore sediment flux thus highlighting the advection effect of internal tides in the coastal mass transport

new instrumentation for the investigation of sediment suspension processes in the shallow marine environment abstract an instrumentation system has been developed that continuously measures flow velocity water depth and suspended sediment concentration profiles in the nearshore zone the system consists of four components 1 an array of electronic sensors including an electromagnetic current meter a surface piercing resistance wave gauge and a five element array of optical back scatterance sensors 2 a signal processing electronics unit 3 a guyed mast support structure and 4 a data acquisition system the small size of the sensors and their response characteristics make the array suitable for monitoring sediment transport to within a few centimeters of the bed under moderately large breaking waves 2 m results from an experiment on an exposed ocean beach on the coast of washington u s a indicate that sand suspension events of long duration 15 40 sec relative to the period of incident waves contribute a significant quantity of sand to the total littoral drift work is now in progress to modify the system for self contained operation on the continental shelf field investigations with the modified system will focus on the acquisition of a data set to test the validity of the suspended sediment distribution equation

modes of cross shore sediment transport on the shoreface of the middle atlantic bight the mechanisms responsible for onshore and offshore sediment fluxes across the shoreface zone seaward of the surf zone were examined in a 3 year field study the study was conducted in the southern part of the middle atlantic bight in the depth region 7 17 m using instrumented tripods supporting electromagnetic current meters pressure sensors suspended sediment concentration sensors and sonar altimeters the observations embraced fairweather moderate energy swell dominated and storm conditions cross shore mean flows ranged from near zero during fairweather to 20 cm s 1 during the storm oscillatory flows were on the order of 10 cm s 1 during fairweather and 100 cm s 1 during the storm suspended sediment concentrations at about 10 cm above the bed were 5 kg m 3 during the storm three methods were applied to evaluate the relative importance of incident waves long period oscillations mean flows and gravity in effecting shoreward or seaward sediment flux 1 an energetics transport model was applied to instantaneous near bottom velocity data 2 higher moments of near bottom flows were estimated and compared and 3 suspended sediment fluxes were estimated directly from the instantaneous products of cross shore velocity and suspended sediment concentration the results show that measurable contributions were made by all four of the processes most significantly mean flows were seen to dominate and cause offshore fluxes during the storm and to contribute significantly to onshore and offshore flux during fairweather and moderate energy incident waves were in all cases the major source of bed shear stress but also caused shoreward as well as seaward net sediment advection low frequency effects involving wave groups and long period waves made secondary contributions to cross shore sediment flux contrary to expectations low frequency fluxes were just as often shoreward as seaward whereas cross correlations between suspended sediment concentration and the instantaneous near bottom current speed were high and in phase under storm conditions they were weak and out of phase during fairweather conditions this suggests that simple energetics models are probably inadequate for predicting fairweather transport of suspended sediment

winter storms induced high suspended sediment concentration along the north offshore seabed of the changjiang estuary abstract fine grained sediments suspended in coastal waters play an important role in submarine topography evolution and associated environment changes the convergence of suspended sediments concentrated near the seabed results in high sediment concentration and contributes significantly to sediment transport in order to investigate the mechanism triggering high suspended sediment concentration ssc we deployed a tripod to the seabed to obtain in situ bottom boundary layer measurements of sediment dynamics and a buoy to the sea surface to collect meteorological and wave data at the northern changjiang river mouth from december 20 2015 to january 20 2016 the high ssc e g 3 g l events were observed together with fluid mud thicknesses of 4 16 cm near the seabed during neap tides when cold air intrusion generated winter storms and strong waves further we found that the high ssc event was mainly resulted from wind waves and sediment resuspension supported by local benthic fluid mud which was associated with three stages at the setting up stage the winter storm brought long duration of strong waves e g significant wave height 1 5 m more than 15 h resulting in a maximum wave current combined bottom shear stress of 3 2 pa and the increase of ssc to 1 g l at the reinforcement stage the strong waves and bottom shear stress lasted for several hours and further increased the ssc to 3 g l at the final decay stage wind waves and the maximum wave current shear stresses decreased significantly with the disappearance of high ssc thus there was no high ssc event observed even with strong wind waves during spring tides because strong wave duration was too short for the reinforcement process the sediment source for the high ssc events was mainly from bottom fluid mud resuspension as well as the advection transport from the adjacent subaqueous changjiang river delta

sediment delivery from the fly river tidally dominated delta to the nearshore marine environment and the impact of el nino 1 in tidally dominated deltas sediment discharged from the river sources must transit through an estuarine region located within the distributary channels where particle pathways can undergo significant transformations water column profiles and time series data were collected in the distributaries and shallow nearshore region offshore of the fly river papua new guinea during monsoon conditions of 2003 and 2004 within the distributaries of this tidally dominated delta near bed fluid mud concentrations were observed at the estuarine turbidity maximum discharge and morphology of the distributaries determine the location of estuarine processes and control the sediment flux to the marine environment sediment delivery from the delta to the broad shallow nearshore region northeast of the river mouth and to the steep umuda shelf valley is influenced by the shorter pathway of the northernmost distributary the shallowest portion of the nearshore region 10 m water depth is a zone of temporary storage where unconsolidated sediment is easily resuspended umuda shelf valley constrains and enhances tidal currents and provides a steep conduit to seaward transport of fluid muds comparison of 2003 and 2004 data shows evidence of reduction in freshwater supply to the gulf of papua during the moderate 2003 el nino conditions el nino creates a large negative perturbation i e low flow to the relatively constant sediment discharge this reduction of discharge limits transport of sediment from the distributaries to the nearshore zone of temporary storage as the sediment stored near shore feeds the prograding clinoform found seaward the perturbation propagates throughout the dispersal system

laboratory and field evaluations of the lisst 100 instrument for suspended particle size determinations abstract advances in technology have resulted in a new instrument that is designed for in situ determination of particle size spectra such an instrument that can measure undisturbed particle size distributions is much needed for sediment transport studies the lisst 100 laser in situ scattering and transmissometry uses the principle of laser diffraction to obtain the size distribution and volume concentration of suspended material in 32 size classes logarithmically spaced between 1 25 and 250 m this paper describes a laboratory evaluation of the ability of lisst 100 to determine particle sizes using suspensions of single size artificial particles findings show the instrument is able to determine particle size to within about 10 with increasing error as particle size increases the instrument determines volume or mass concentration using a volume conversion factor cv this volume conversion factor is theoretically a constant in the laboratory evaluation cv is found to vary by a factor of about three over the particle size range between 5 and 200 m results from field studies in south san francisco bay show that values of mass concentration of suspended marine sediments estimated by lisst 100 agree favorably with estimates from optical backscatterance sensors if an appropriate value of cv according to mean size is used and the assumed average particle aggregate density is carefully chosen analyses of size distribution of suspended materials in south san francisco bay over multiple tide cycles suggest the likelihood of different sources of sediment because of different size characteristics during flood and ebb cycles

measurements in the bottom boundary layer on the amazon subaqueous delta abstract an instrumented bottom tripod geoprobe recorded flow and suspended sediment data in the bottom boundary layer above the lower foresets of the amazon subaqueous delta in 65 m mean water depth in february 1990 after about two weeks of operation the apparent seafloor at the tripod site rapidly elevated over a 14 hour period by about 44 cm this sudden change which was detected by an acoustic altimeter and which caused the loss of signals from the lowermost geoprobe current and optical sensors is thought to have been caused by the incursion of a dense bottom layer of fluid mud that migrated downslope from shallower sections of the foresets the fluid mud migration across the outer part of the foresets if a repetitive and occasional process in this region could be a major mechanism for episodic seaward growth of the delta current velocity profiles are used to estimate shear velocities u and roughness lengths zo during the first two weeks of measurements the extremely energetic semi diurnal tidal motion required correction of the estimates of u and zo for acceleration average values of u and zo for the two week period were 1 7 cm s and 0 3 cm respectively the effects of strong stratification due to flocculated near bottom suspended sediment on the estimates of u are significant for the lower values of u u

distribution of fluid muds on the amazon continental shelf abstract a comprehensive study of suspended sediment transport on the amazon shelf was conducted as part of the amasseds project a multidisciplinary amazon shelf sediment study to understand the link between physical processes and the fate of amazon river sediment a small instrumented tripod was used to measure the fluid flow and suspended sediment characteristics throughout the water column on varying time scales e g semidiurnal fortnightly seasonal dense nearbed suspensions or fluid muds suspended sediment concentration 10 g l on the order of a few meters in thickness were found on the inner and middle shelf covering an area ranging from 5 700 km2 during falling and low river discharge to 10 000 km2 during rising and high discharge fluid muds generally observed in the region of bottom salinity fronts extend across the topset beds to the foreset beds during rising and high discharge salinity and temperature anomalies frequently observed in fluid muds imply that often the muds do not result from erosion and resuspension from the seabed but from trapping processes at the bottom salinity front and transport across the shelf the vertical structure of fluid mud varies in space and tune variability close to the river mouth is predominantly fortnightly related to the location and structure of the bottom salinity front on the open shelf the variability appears to be related to seasonal differences in river and sediment discharge and the location of the bottom salinity front the total suspended sediment inventory on the shelf during the season of high discharge is approximately equal to the annual sediment discharge from the river 1 2 109 tons yr and 90 of that inventory is within fluid mud suspended sediment transport on the shelf is dominated by fluid mud

laboratory apparatus for calibrating optical suspended solids sensors abstract an apparatus for testing and calibrating miniature to medium sized optical suspended solids sensors is described stable suspensions of sedimentary particles ranging in size from 10 6 to 4 10 3 m can be produced in water with concentrations exceeding 100 g 1 1 flow velocities in the test volume can be varied continuously from 0 1 to 1 5 m s 1 and samples of suspensions can be withdrawn directly with a peristaltic pump for gravimetric and particle size analyses the apparatus has been used to evaluate the effects of particle size flow speed and air bubbles on the performance of optical backscatterance sensors and transmissometers

measurements of high concentration suspended sediments using the optical backscatterance sensor abstract an optical backscatterance sensor obs was used to measure extremely high concentration suspended sediments on the amazon continental shelf as part of the amasseds project a multidisciplinary amazon shelf sediment study using a pumping system for obtaining water samples to calibrate the sensor in situ the obs output was observed to increase approximately linearly for concentrations 36 g l the obs response was nearly continuous from 0 to 320 g l making it possible to obtain continuous suspended sediment concentration profiles through fluid muds

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

tidal and seasonal dynamics of a muddy inner shelf environment gulf of papua 1 subaqueous delta clinoforms are accretionary features created on the continental shelf where there is a large supply of sediment sediment is transported across the shallow topset region and accumulates rapidly in the deeper foreset region in the gulf of papua papua new guinea the absence of cyclonic storms makes tidal currents and seasonal variation of wind direction primary controls on the timing and magnitude of across shelf sediment transport to investigate processes that disperse sediment across the topset of the fly river clinoform anchor stations were occupied during spring and neap tidal cycles of the trade wind season the monsoon season and the transition period during the energetic trade wind season surface waves coupled to strong spring tide currents generated peaks in suspended sediment concentration 100 g l 1 at some locations however seabed erosion and deposition over tidal timescales could not be discerned indicating that sediment was being advected across the outer topset although seaward gravity flows occur with significant spatial heterogeneity they are important for carrying sediment to the foreset region because the near bed circulation generally has a landward net flow seaward transport is restricted to the energetic trade wind season during the quiescent monsoon season 4 11 cm of erosion occurs on parts of the outer topset as fluvial sediment is temporarily deposited closer to shore seasonal patterns in sediment dispersal are likely impacted by el nino southern oscillation and consideration of el nino conditions of 2002 2003 are reflected in the interpretation of observations

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

suspended load and bed load in irrigation furrows abstract the circulation of water in irrigation furrows is a well understood physical process however theoretical understanding of sediment dynamics is less well established this study assesses an approach to determine the sediment load in irrigation furrows involving the use of a suction device for sampling water with suspended sediments at various depths and a trap for sampling water with sediments moving next to the furrow bed in addition an acoustic velocimeter is used to acquire flow velocity profiles which allow sediment loads to be calculated when combined with the sediment concentration measurements use of these devices in irrigation furrows showed that the total sediment load decreases with successive irrigations and increases as it moves downstream while the bed load decreases the bed load represents a small fraction of the total load sediment load can be determined with sufficient accuracy for research purposes using simultaneous measurements of the signal to noise ratio of an acoustic velocimeter and the flow velocity estimation of the load from point measurements at half the flow depth slightly underestimates the integrated load

the effect of air bubbles on optical backscatter sensors the sensitivity of an optical backscatter sensor obs to bubbles is tested using a variety of bubble generating mechanisms that span the range of bubble sizes typically observed in surf zone studies over 1200 one minute runs were performed in a stirred test tank by altering the bubbler type water type air flow rate and sand or mud concentration the laboratory data shows a strong dependence of obs response to bubble size and concentration for sand or mud sediments the optical backscatter sensor voltage is increased by the presence of bubbles and smaller bubbles had a larger effect the effect was more pronounced in salt water than fresh water we conservatively report that obs output voltage is increased due to the presence of bubbles by 25 for the trials undertaken here in the cases performed in vigorously stirred salt and synthetic salt water bubbles were smaller than those measured under quiescent water conditions due to bubble shattering at the bubbler orifices and by the pumps used for stirring it was found in those cases that the bubble effect on obs was larger than the 25 reported here but the extension of this finding to a natural setting such as in the direct vicinity of the breakpoint or a bore is not known

an integrated optic and acoustic ioa approach for measuring suspended sediment concentration in highly turbid environments abstracts accurate measurement of suspended sediment concentration ssc in highly turbid environments has been a problem due to optical or acoustic signal saturation and attenuation the saturation returns a limited measurement range and the attenuation raises an ambiguity problem that a low optical or acoustic output could mean a low or a high ssc in this study an integrated optic and acoustic ioa approach is proposed to i overcome the ambiguity problem ii increase the measurement range to high ssc values and iii obtain high resolution ssc profiles the ioa approach is a combination of argus suspension meter asm optical backscatter sensor obs and acoustic doppler velocimeter adv in this approach the asm derived ssc is preferred because of its lowest relative error followed by obs and adv the asm can produce high resolution 1 cm interval ssc profiles when it is not saturated usually ssc

the effect of particle settling velocity on computed suspended sediment concentration profiles abstract a field study was performed at a site in san pablo bay california to evaluate how well suspended sediment distribution equations reproduce observed concentrations near bed measurements of current velocity suspended sediment concentrations and fluid and particle characteristics were made an in situ settling cylinder was used to determine settling velocity values of aggregated suspended sediments and photographs from a plankton camera provided size estimates in situ weighted average settling velocities were generally an order of magnitude greater than a weighted average for stokes calculations of settling velocity for the grain size distribution of the reference suspended sediment sample and two orders of magnitude greater than a stokes settling velocity for the median grain size of suspended sediment flocs were commonly 100 m in diameter and as large as 450 m with settling velocities as high as 0 2 cm s 1 calculated suspended sediment concentration profiles using in situ estimates of settling velocity yielded closer agreement with observed concentration profiles within 25 than using settling velocities calculated from the grain size distribution of suspended sediment samples within 40 50

two dimensional tide induced residual sand transport applications to the jiangsu coast china abstract the residual sand d 62 5 m transport rst refers to the tidally averaged rate of horizontal sand transport albeit much smaller than the peak rates it determines the morphological evolution the analytical expression for the tide induced rst has been reported in the condition of one dimensional tidal currents by van de kreeke and robaczewska 1993 here we extended the analytical solution to two dimensional the constituents of the residual m2 and m4 tidal current velocities were used to characterize the collinear tidal current in the orthogonal x and y directions i e cross shore and alongshore respectively while the m2 tidal constituent is dominant in both directions based on the solution rst is controlled by a series of triple interactions of the m2 tidal velocity in the x direction m2 tidal velocity in the y direction and the residual or m4 velocity in the x or y direction the solution was applied to the tide dominated continental shelf of the jiangsu coast china where the alongshore current is much stronger than the cross shore component the results show that the triple interactions of the cross shore m2 tidal velocity um2 the alongshore m2 tidal velocity vm2 and the alongshore residual velocity account for the major parts of both the alongshore and cross shore rst in the nearshore area the rst patterns promote sand accumulation in the shallow nearshore area and generate a narrow and active conduit of coastal alongshore sand transport these findings can be applied in similar marine environments to understand the effects of non linear tidal interactions in rst

an instrument system for monitoring and sampling suspended sediment in the benthic boundary layer abstract an instrument system has been constructed that can monitor and sample suspended sediment distributions in the benthic boundary layer it consists of miniature nephelometers and suspended sediment samplers placed within one meter of the seabed the system is capable of continuously monitoring suspended sediment profiles at eight levels between 14 and 100 cm above the seabed and collecting suspended sediment samples at four levels 20 50 70 and 100 cm at three times during a deployment period the suspended sediment system is designed to fit onto the instrumented tripod geoprobe which contains four electromagnetic current meters pressure sensor bottom stereo camera two temperature sensors transmissometer and a savonius rotor current meter sensor operation data recording and sediment sampling events are synchronized thus detailed measurements of the near bottom flow conditions are made concurrently with suspended sediment measurements the combined system has been used in sediment transporting environments within san francisco bay california and puget sound washington

suspended sediment transport and the role of infragravity waves in a barred surf zone abstract collocated optical backscatterance suspended solids sensors and electromagnetic flowmeters were deployed at stanhope lane beach p e i canada to assess the contributions of wind waves infragravity waves and mean currents to the cross shore flux of suspended sediment across a barred surf zone the local net transport of suspended sediment magnitude and direction was highly variable both spatially and temporally with respect to the relative magnitudes of the suspended sediment transport 1 that induced by quasi steady mean currents and oscillatory currents at both incident and infragravity frequencies were almost equal in magnitude when the total surf zone was averaged over the storm event 2 waves in the near infragravity band were quantitatively more important during the waning of the storm especially where when surf persisted well after the initial decay of the offshore wave field 3 incident waves were important where when the waves were not saturated i e during the early stages of the storm at all locations and persistently throughout the storm on the seaward slope of the bar where wave saturation was limited to a very short period with respect to the direction of net sediment transport 1 that attributable to mean currents was directed offshore in the inner surf zone probably reflecting the presence of an undertow while further seaward an onshore transport occurred probably resulting from mass transport induced by surf bores or drift velocities induced by the infragravity wave boundary layer 2 that induced by oscillatory currents at incident wave frequencies was generally onshore at any one location throughout the storm event in contrast oscillatory transport at low frequencies changed direction and also varied in magnitude at any given location in part these changes reflect the existence of significant oscillatory sediment transport at discrete infragravity frequencies the standing infragravity waves consistently transported suspended sediment towards antinodes in the water surface elevation

a new instrument for measuring settling velocities in situ abstract an in situ settling cylinder for determining particle settling velocities has been deployed during a field experiment in san pablo bay california the instrument is a spring loaded cylinder which traps approximately 31 of water and suspended sediment between two end plates mounted between the end plates is a vertical array of five miniature nephelometers positioned 4 20 cm below the top end plate which continuously monitor 5 hz sampling rate suspended sediment concentration at each level as particles settle the resulting settling curve can be divided into components with characteristic settling velocities and a settling velocity distribution obtained for the suspension the results are conservative estimates of settling velocities for the suspension in situ estimates of particle settling velocity are higher than stokes settling velocities calculated for the disaggregated grain size distribution of a suspended sediment sample indicating that the sediment in suspension is in the form of aggregates the aggregates have settling velocities as high as those of sand size quartz spheres