Distribution Of Suspended Sediment Research Articles

Concentration, clay mineral composition and Coulter counter size distribution of suspended sediment in the turbidity maximum of the Jiaojiang river estuary, Zhejiang, China

Measurements of current velocities, concentrations of suspended matter and Coulter counter size distributions of the suspended matter during the tidal cycle at the surface, at mid-depth and near to the bottom were carried out during spring and neap tide in the Jiaojiang river estuary, Zhejiang, China. The results indicate that a lutocline was present during most of the tidal cycle, except during the highest tides when the suspended-matter concentrations were approximately uniform over the entire water depth. Suspended-matter concentrations showed a relation with maximum flow velocities in the surface water and with increasing flow velocities in the bottom water, with regular deposition and resuspension during the tidal cycle. The clay mineral composition of the suspended matter indicated that most of the suspended matter was supplied by the Chang Jiang river. There was probably also some local supply and local sorting. The suspended-matter particle size, measured with a Coulter counter, became larger (with a larger standard deviation) when the suspended-matter concentration increased, and smaller when the suspended-matter concentration decreased. Size sorting during the tidal cycle indicated deflocculation and reflocculation processes; break-up of about 10 to 20% of the flocs in suspension is sufficient to produce the shift in the Coulter counter size distributions observed. This led to the conclusion that the trend in the smectite concentration in the estuary was the result of local sorting of smectite-containing particles after floc break-up.

Relationship between hydrology and seasonal distribution of suspended sediments on the continental shelf of the Bay of Biscay

Numerous oceanographic cruises (with hydrology, water sampling, drift current measurements) carried out since 1980 on the continental shelf of the Bay of Biscay, together with available NOAA/AVHRR infra-red images, form the basis of a proposed explanation for the processes responsible for the distribution of suspended sediments on the shelf. The seasonal hydrographic structure of continental shelf waters is of paramount importance in sediment distribution. In summer, there is an horizontal stratification of water masses, and suspended sediment distribution is closely related to the thermo-haline structure. A fresher water mass with less suspended material lies on a thicker and more turbid homogeneous layer. During winter, when sediment discharge from the rivers often reaches its annual maximum, an oceanic thermo-haline wedge occurs on the shelf at around −100 m. As a result, winter turbidity values on the outer continental shelf are low (comparable to summer values), and a permanent nepheloı̈d layer is never observed. The wedge, which lasts for several months, may act as a filter, preventing transport to the slope. High turbidities on the external shelf and the continental slope are only measured in spring, when the thermo-haline wedge disappears. It seems possible that during winter time, suspended materials brought by rivers are deposited in the “Grande Vasière” (the “large mud patch”). It is postulated that the position of this mud patch is linked to the long-term stable location of the thermo-haline front that separates oceanic waters from the colder and less salty coastal waters.

Influence of melting icebergs on distribution, characteristics and transport of marine particles in an East Greenland fjord

A detailed study of distribution of suspended sediments in an East Greenland fjord with a high iceberg production rate reveals the existence of intermediate nepheloid layers (INLs). Observed INLs extended from the head to the mouth of the fjord at water depths between 100 and 400 m. Particulate organic carbon and nitrogen, chlorophyll a, and nutrient measurements and observation by microscope and energy dispersive X‐ray analyses were used to characterize marine particles. Particles in the INLs are composed of glacial flour including >50 μm quartz and feldspar grains with angular and sharp edges, considered to be released from melting icebergs. In situ photographs show large aggregates (>1 mm) at high concentration (>300 particles per liter) in and below INLs. These aggregates, in comparison with the dispersed particle size distribution, demonstrate that smaller size particles (e.g., clay) settle effectively along with larger single size grains. In Kangerlugssuaq Fjord, the mass transport of marine particles was governed by the subsurface iceberg melting, producing observed INLs, rather than the surface meltwater plume. This suggests that the subsurface water temperature controls release of iceberg debris and the existence of warm subsurface water, as well as the spread of cold and fresh water in the surface layer, needs to be considered to evaluate the occurrence of ice‐rafted debris layers, including Heinrich layers. This study provides the field evidence of a modern analogue on ocean conditions that could form iceberg‐rafted layers.

Fluxes of suspended matter in the East Anglian plume Southern North Sea

The seasonal variation in the suspended sediment distribution in the Southern North Sea has been defined by direct sampling over a grid of stations. The East Anglian plume, a region of relatively high concentrations, develops eastward from eastern England across the Southern Bight during the winter. During the summer the plume concentrations are lower. Using residual currents obtained from a numerical model, together with the depth averaged suspended matter concentrations, allows estimation of the fluxes within the plume. This suggests that 6.6×10 6 t of suspended matter was transported eastward in one year, with possible errors of ±50%. Comparison with published sediment budgets for the coastal area of eastern England shows that the plume constitutes a major feature transporting sediment across the North Sea.

Sedimentation in the Yellow River delta, part I: flow and suspended sediment structure in the upper distributary and the estuary

A 44-year data record measured by Lijin Hydraulic Station on the Yellow River shows that sediment concentration has been increasing while river discharge has been decreasing into the delta since the 1970s. These changes are important because flood waters of the Yellow River, which are heavily laden with sediment, must be used to supply Dongying City and Shengli Oil Company which are located on the delta. Based on the analyses of data of velocity, sediment concentration, salinity and sediment grain size from four cross-section measurements at Lijin Station and one 8-vessel simultaneous measurement cruise in the estuary, structural characteristics of the river flow and suspended sediments throughout the upper distributary and the estuary have been studied and discussed. Results show that when sediment concentrations of the Yellow River exceed 100 kg/m 3 in the lower layer of the river flow during the flood period, the river flow structure does not coincide with the logarithmic law of wall and becomes vertically layered, and the vertical distributions of suspended sediment do not coincide with the diffusion law. The channel length influenced by the tide wave is less than 15 km and there is no tidal intrusion flow; only weak osmosis of salinity occurs inside the river mouth during the flood period of the Yellow River. Simultaneous 8-vessel measurements and simulation using the method of Preissman show that there is a tidal sensitive zone inside the river mouth bar with a length of 6–7 km, when the discharge is as large as 1100 m 3/s, and an area of very active sedimentation. The tidal sensitive region near the river mouth becomes a low-velocity zone that traps a large amount of river sediment which rapidly forms a `plastic' bed at flood tide, and a high-velocity zone with a strong hydrodynamic action to erode the new bed and transport the sediments into the sea at ebb tide.

Calibration of a Par-Tec 200 laser back-scatter probe FORin situ sizing of fluvial suspended sediment

The in situ or effective particle size distribution of fluvial suspended sediment may differ considerably from that of the chemically dispersed mineral fraction owing to flocculation. Obtaining a meaningful measure of the effective particle size distribution ideally requires that measurements should be made in situ. A rigorous assessment of the associated degree of flocculation also requires that the same measurement technique is used subsequently to establish the absolute particle size composition of the suspended sediment by analysis of the chemically dispersed mineral fraction. While few in situ measurement devices currently exist, a Par-Tec 200 laser back-scatter probe has previously been shown to be capable of making both in situ and laboratory particle size measurements of fluvial sediment. The accuracy and precision of this device is assessed in this paper. While able to distinguish relative size differences with a high degree of precision, the Par-Tec 200 performed poorly in terms of accuracy when compared with measurements made using a laser diffraction device. A calibration algorithm has been devised for the Par-Tec 200 size data, using standard sediment samples sized by means of a laser diffraction device as the reference. Application of the calibration to Par-Tec 200 measurements of heterogeneous sediment samples significantly improved the representativeness of the particle size distribution, both in terms of overall form, and the median particle size.

The distribution of fine suspended sediments in the surface waters of the Irish Sea and its relation to tidal stirring

A time series of 165 Advanced Very High Resolution Radiometer (AVHRR) visible band images covering the years 1982-1988 shows that the reflectance of the Irish Sea pulses on seasonal and spring-neap tidal time scales. The seasonal signal has been analysed by fitting a harmonic curve to a geographical grid of points. Maximum reflectance throughout the whole Irish Sea occurs in January or early February. The annual mean reflectance varies spatially by a factor of three from 0.8% to more than 2.4%. Seasonal amplitudes vary from 0.2% to 0.9%. A smaller, but still significant, cycle of reflectance occurs with the fortnightly springs-neaps cycle, with maximum reflectance occurring at spring tides. Both these cycles are in phase with the known variation of suspended sediments in the Irish Sea. Direct measurements, in situ and in the laboratory, of the inherent optical properties of sediments in the Irish Sea have been used to construct an algorithm relating AVHRR visible band reflectance RA to sediment concentration. The reflectance is most sensitive to changes in mineral suspended solids (mss) with phytoplankton pigments having a secondary effect and yellow substance hardly any at all. The algorithm is a saturating curve: initially RA increases in proportion to mss, but at high mss concentrations RA tends to an asymptotic value of 3.5%. The algorithm has been used to produce mean winter and summer maps of mss in the Irish Sea. Concentrations in winter are greater than those in summer (by a factor of 2.7 for the Irish Sea as a whole), but the spatial pattern is similar. Highest sediment concentrations occur in the shallow eastern Irish Sea and also in the regions of strongest tidal currents. The relationship between suspended sediment concentration and tidal stirring is explored using a simple energy model. Equating the potential energy of the sediment in suspension to the turbulent kinetic energy available from the tide suggests a linear relationship between the concentration of mss and the tidal power density. It is found that there is a significant relationship between these quantities in the water depth range 40 to 80m.

A convection‐diffusion model for suspended sediment in the surf zone

A model is developed to simulate the temporal and spatial distributions of suspended sediment in the surf zone. The model is solved numerically in a time domain and in a two‐dimensional vertical plane. At each time step of computation, the upper moving boundary (water surface) and the velocity field are determined through the solution of a hydrodynamic model which is based on the Reynolds equations of motion. The sediment concentration field is then determined by solving the convection‐diffusion equation of the sediment mass. The comparisons with laboratory data of various experimental conditions show reasonable agreements for the simulated wave field and the concentration field in the surf zone.

Development of a model to reproduce observed suspended sediment distributions in the southern North Sea using Principal Component Analysis and Multiple Linear Regression

As part of the NERC North Sea Project (1987–1992), concentrations of fine suspended particulate matter were determined at over 100 locations on 15 monthly survey cruises. Each of these monthly data sets were interpolated to provide continuous “synoptic” representations over the southern North Sea (south of 56°N). Here, statistical techniques are used in conjunction with numerical model simulations to interpret these data. Principal Component Analysis is performed on these monthly series of observations to locate statistically significant sources and sinks of suspended particulate matter. This analysis reveals the month-to-month variability of a primary source, accounting for around 80% of the total variation in the observations, and located in the vicinity of The Wash estuary and adjacent coast. A numerical dispersion model is then developed to simulate the erosion, settling and transport of fine suspended sediment from this source. The formulations and associated coefficients used to describe re-erosion and settling rates are then fine-tuned by comparison with observations. In the second part of this study, the sediment model developed is used to simulate dispersion from discrete sources. Thence a Multiple Linear Regression technique, as described by McManus and Prandle (1994) (in Marine Pollution Bulletin 28, 451–455), is used to fit these modelled dispersion patterns to the original observations to determine rates of sediment supply from these discrete sources. This technique reveals that (i) riverine sources are not statistically significant and (ii) the East Anglian sources are small in magnitude compared with the Dover Strait and northern North Sea sources. Further analysis explains this apparent contradiction with the first part of the study by illustrating how the longer effective flushing times of the two coastal sources amplifies their net contribution to the suspended particulate matter distribution in the southern North Sea. Estimates of mean annual supply from the statistically significant sources (in 10 6 t) are Dover Strait, 44.4, northern North Sea, 41.7, The Wash, 3.2, and Suffolk Coast, 0.7. Comparable estimates published in the 1993 North Sea Quality Status Report (North Sea Task Force, Olsen and Olsen, Denmark) are generally in reasonable agreement. Likewise, both the location and rates of supply from the sources determined in this study are in broad agreement with the earlier estimates of McCave (1987) (in Journal of the Geological Society 144, 149–152). Thus, the success achieved provides encouragement towards the goal of developing robust suspended sediment models of shelf seas.

Mapping Reservoir Turbidity Patterns Using SPOT‐HRV Data

Abstract Although most orbital remote sensing systems are optimized for viewing terrestrial targets, data from these sensors has frequently been used for detecting and mapping the distribution of suspended sediments in water. In this paper, a linear regression‐based model for mapping turbidity is evaluated in a midwestern U.S. reservoir using October, 1994 SPOT‐HRV data. Results indicate that the red band (SPOT2) is the best predictor of turbidity (r=0.924, R2 = 84.5). Despite relatively low turbidity levels in the water, the radiometric resolution of the SPOT‐HRV sensor was found to be adequate for this application. The high spatial resolution of the sensor permitted observation of very detailed patterns of turbidity.

Remote Sensing of suspended sediments along the Tamil Nadu coastal waters

Indian Remote Sensing satellite (IRS) 1A & 1B digital data in combination with field measurement were used to map distribution and concentration of suspended sediments along the Tamil Nadu coastal waters for monsoon and non-monsoon periods. Qualitative suspended sediment mapping was done for entire Tamil Nadu coast while quantitative studies were taken at two selected sites (eg. Tuticorin and Ennore). For qualitative mapping both monsoon (17-12-90) and non-monsoon (18-4-90) season data were analysed by level slicing technique and a qualitative scale was assigned to different sediment classes based on tonal variations. The suspended sediment concentration (SSC) samples were collected on April 15, 1992 and March 10, 1992 around Ennore and Tuticorin coastal waters respectively, synchronous to IRS-1A satellite overpass. This data was used for quantitative estimation of SSC using digital chromaticity technique. The study shows that the plumes of high suspended sediment concentration are contributed from the nearshore wetlands and river mouths and were finally dispersing towards Jaffna coast. Different classes of high to low SSC values ranging from less than 5 mg/L in offshore areas to 21 mg/L in nearshore of Tuticorin were also delineated. The dispersal pattern of the sediments on different is discussed.

Comparison of field observations of the vertical distribution of suspended sand and its prediction by models

Models for the vertical distribution of suspended sediment under waves and currents are compared with field observations. The models include a diffusion‐based model, a convection‐based model, and a combined convection‐diffusion model. The field observations were carried out at Vilano Beach, Florida, in a water depth of approximately 3 to 4 m, with a median grain diameter of 0.14 mm. The rms wave height ranged from approximately 0.4 to 1.2 m. Under low waves, the seabed was covered with very small ripples, and, under the higher waves, sheet flow conditions were present. The diffusion‐based model was found to best describe the observed data under high wave conditions, but the convection model was more accurate under low wave conditions. Over all conditions, the combined model was the most accurate. These results are consistent with the different mechanisms for mixing suspended sediment over flat versus rippled beds.

Benthic and Intermediate Nepheloid Layers in Lake Biwa

Benthic nepheloid layers and intermediate nepheloid layers in Lake Biwa were observed between 1991 and 1993, and the characteristics of both nepheloid layers are discussed using field data from Pre-BITEX in 1991-1993 and BITEX'93 in 1993.The benthic nepheloid layer in Lake Biwa is formed during a stratified period from May to October. The top edge of the benthic nepheloid layer is very sharp as if it is a step function, and turbidity is higher in the benthic nepheloid layer than outside. The vertical distribution of turbidity in the benthic boundary nepheloid layer does not fit to the Rouse distribution. We showed that internal waves induce the oscillating flows in the benthic boundary layer, and it makes such distributions of suspended sediments as a step function.The intermediate nepheloid layer in Lake Biwa was also discovered during Pre-BITEX and BITEX'93. The intermediate nepheloid layer observed during BITEX moved in one direction with a continuously horizontal velocity of 2.0 to 4.0 cm⋅sec-1, for almost 8 hrs. The intermediate nepheloid layer was about 800 m long and 5 m thick, and it brings suspended sediments rich in Mn.By comparing these physical data with the results of chemical analyses, we can verify that the material in nepheloid layers originated from bottom sediments.

Sediment deposition, accumulation, and seabed dynamics in an energetic fine-grained coastal environment

Sedimentary processes on the continental shelf and shoreline northwest of the Amazon River mouth were investigated as part of A Multidisciplinary Amazon Shelf SEDiment Study (AmasSeds) during four field expeditions between 1989 and 1991. Periodic deposition and resuspension of seabed layers as much as a meter thick dominate sedimentary processes for most of the inner shelf and for the shoreface and foreshore north of Cabo Cassipore. Strata forming as a result of this process consist of decimeter-thick mud beds separated by hiatal (scour) surfaces. The volume of sediment resuspended seasonally from the inner shelf surface layer (SL) is of the same order of magnitude as the annual input from the river, indicating that resuspension is an important control on suspended-sediment distributions in shelf waters. Most resuspension from the SL occurs during February–May (the period of maximum wind stress), which is also the time of rapid deposition on the mudflats, suggesting that sediment resuspended from the SL could contribute to shoreface and foreshore accretion for the northern portion of the study area. In addition, some of the sediment resuspended from the SL is transported seaward periodically in the form of near-bottom fluid-mud flows. This results in non-steady-state input of certain particle-reactive trace metals, which is reflected in the occurrence of quasi-cyclic 210Ph profiles in the foreset region of the subaqueous delta. As determined using 228Ra/ 226Ra geochronology, sediment accumulation rates in this region are 10–60 cm y −1. Farther seaward, in the bottomset region, accumulation rates decrease and there is increased evidence of biological activity preserved in sedimentary structures. However, episodic (but reduced) sediment input from fluid-mud flows also extends to this region, affecting the fauna and fine-scale stratigraphy.

The Amazon shelf setting: tropical, energetic, and influenced by a large river

A Multidisciplinary Amazon Shelf SEDiment Study (AmasSeds) investigated the oceanic processes near the mouth of the Amazon River in order to understand the fate of its enormous discharge of water, solutes and particulates. In addition to receiving a large fluvial discharge, the continental shelf near the Amazon mouth is situated on the equator and experiences an extremely energetic physical regime. As such, it represents an end member in the spectrum of coastal marine settings, with regard to latitude, energy and discharge. The oceanic processes occurring on the Amazon shelf reflect these environmental characteristics. A range of interdisciplinary interactions was observed on the Amazon shelf in response to its low latitude, among them: plume dynamics have little influence from Coriolis acceleration, riverine particles experience intense weathering conditions, high primary productivity occurs during all seasons, and shoreline sedimentation involves mangrove vegetation. The high energy conditions of the Amazon shelf result in: water motions dependent on suspended-sediment distributions, tracemetal adsorption controlled by seabed dynamics, severe restriction of macrobenthos, and deep physical reworking of sedimentary strata (to 1 m or more). The great discharge of fluvial materials (water, solutes, particulates) directly or indirectly causes three-dimensional estuarine-like processes and very high rates of primary productivity, sediment accumulation and carbon burial to occur on the shelf. Although AmasSeds research can link a wide range of interdisciplinary oceanic processes to latitude, energetics or discharge, in many cases the observed process is strongly influenced by a coupling of these characteristics. For example, the dominance of Fe and Mn oxides in controlling redox reactions is a result of tropical weathering that concentrates the Fe and Mn and of intense seabed reworking that regularly reoxidizes these phases. Therefore, the importance of Fe and Mn oxides is a result of both latitude and energy considerations. A fourth characteristic of the Amazon system is its tectonic setting, which determines physiographic features such as drainage-basin size and shelf width. Low latitude and great discharge characterize all areas of the wet tropics; energy expenditure and tectonic setting vary with specific location. All four characteristics must be considered when extrapolating AmasSeds observations to other areas and attempting to predict or interpret oceanic processes.

An assessment of the effects of sample collection, storage and resuspension on the representativeness of measurements of the effective particle size distribution of fluvial suspended sediment

Flocs/aggregates can comprise a significant proportion of the total volume of suspended sediment in the fluvial environment. In situ measurement of the effective size distribution is frequently precluded on grounds of the cost of appropriate equipment or adverse field conditions. An assessment of the potential for using an alternative and simpler strategy involving collection of bottle samples and subsequent analysis of the samples has been undertaken. A field-portable, laser-backscatter particle size analyser has been used to assess the representativeness of measurements made on-site immediately after sample collection, and subsequently in the laboratory after settling and resuspension. On-site measurements of bottle samples were broadly representative of the in situ effective size distribution. Flocculation occurred within settled samples together with a concomitant increase in the volume mean particle size upon resuspension. The magnitude of this increase was, in general, positively related to settling time. Following resuspension, floc break-up during continuous stirring caused mean particle size to decline towards the initial on-site value.

Visual Water Clarity and Suspended Substance under Baseflow Conditions in the Nishibetsu River, Japan.

Visual water clarity of the Nishibetsu River under baseflow conditions was obtained in 1993 by the black disk method which measures the maximum sighting length by horizontally viewing a black disk in river water. The visual clarity was more than 7 m at the upper reach, but it decreased to less than 2 m at the middle and the lower reaches. A very strong negative correlation was found between visual clarity and suspended substance concentration (SSC) of river water. This relation showed that the visual clarity of clear water decreases remarkably with even a slight increase of SSC, whereas that of turbid water is not affected by such an increase. The ignition-loss analysis indicated that the suspended substance was mainly composed of inorganic matter. The grain size distribution of suspended sediment was similar to that of a fine portion of river bed sediment and river bank sediment. Moreover, the suspended substance flux carried out by all tributaries in this basin was considerably less than that of the main stream. Most of the suspended substance was thus judged to be supplied from the banks and/or the beds of the main stream. The increase-rate of suspended substance flux per unit distance was low at both the upper and lower reaches, while that at the middle reach was high.

3D-numerical modelling of cohesive suspended sediment in the Western Scheldt estuary (The Netherlands)

A cohesive sediment transport model considering the effects of flocculation, deposition and erosion is used in an attempt to simulate the suspended sediment distribution in a mesotidal estuary. The numerical model solves the three-dimensional (3D) advection-diffusion equation using a two-time level scheme, and a semi-implicit finite difference approach. The transport model is coupled to a 3D-barotropic hydrodynamic model for the simulation of the major tidal components reproducing the non-linear effects. An application of these models in the Western Scheldt estuary is described. The results of the different tests show that the adopted approach provides a useful basis for a good understanding of the physical processes involved in sediment transport and for the study of practical problems. The sensitivity of the model to key parameters controlling the simulation of bed sediment/water exchanges, shows the importance of a good definition of bottom sediment characteristics and the importance of further development of a consolidation algorithm.

Suspended sediment distribution and residual transport in the coastal ocean off the Ganges-Brahmaputra river mouth

An examination of suspended sediment dispersal in the coastal ocean off the Ganges-Brahmaputra river system using shipboard and satellite data reveal distinct patterns of sediment distribution and sediment motion which help explain the dynamics of the world's largest sediment dispersal system. During the low-discharge period, suspended sediment concentration distribution is mainly a function of tidal energy and the sediments are primarily transported as a suspension population. Satellite and sea-bed data indicate that transport of river sediments is largely restricted to an area landward of about the 20-isobath during the low-discharge period. A simplistic estimate of residual transport and its separation into tidal and non-tidal components indicate that non-tidal transport contributes about 47% of the total transport and has transport directions mostly southwestward during the northeast monsoon. The tidal residual transport, which contributes about 53% of the total transport, however, does not show any particular direction for most of the stations, although some landward stations show shoreward transport. Although few water-column measurements were made during the high-discharge period, data from this and previous studies suggest that the dominant transport direction is to the southwest for most of the year.

In situ measurements of particle settling velocity on the northern California continental shelf

As part of the Sediment TRansport Events on Shelves and Slopes (STRESS) program, a remote optical settling ☐ was deployed on the northern California continental shelf. The device operates by isolating a volume of sediment-laden fluid from the environment and then monitoring its sedimentation behavior with a transmissometer. Results show a bimodal distribution of suspended sediment during low-energy periods on the shelf that reflects the size distribution of bottom sediments. The coarse mode sinks at 0.026 cm s −1 (22 m day −1) and the fine mode settles at 0.0025 cm s −1 (2 m day −1). Between one-quarter and two-thirds of the total mass resides in the coarse mode. Roughly one-quarter is in the fine mode. The remainder sinks too slowly (<0.0015cm s −1 or <1.3m day −1) to be resolved during the 18-h measurement cycles. Greatest uncertainty in assigning mass to the various settling velocity classes comes from sensitivity to ill-constrained particle geometry of the conversion from light attenuation to mass. The device failed during higher energy periods, probably due to penetration of fluid into the ☐. Complete isolation of the fluid from the environment would improve the performance of settling ☐es in energetic settings.