Distribution Of Suspended Sediment Research Articles

Characteristics of the near-bottom suspended sediment field over the continental shelf off northern California based on optical attenuation measurements during STRESS and SMILE

Time-series measurements of current velocity, optical attenuation and surface wave intensity obtained during the Sediment Transport Events on Shelves and Slopes (STRESS) experiments, combined with shipboard measurements of conductivity, temperature and optical attenuation obtained during the Shelf Mixed Layer Experiment (SMILE), provide a description of the sediment concentration field over the central and outer shelf off northern California. The questions addressed are: (1) existence and characteristics of bottom nepheloid layers and their relationship to bottom mixed layers; (2) characteristics of temporal fluctuations in sediment concentration and their relationship to waves and currents; (3) spatial scales over which suspended sediment concentrations vary horizontally; and (4) vertical distribution of suspended sediment.

Assessment of sediment distribution pattern in the Tungabhadra reservoir using satellite imagery

In order to understand the dynamic aspects of suspended sediments in an inland water body, Tungabhadra reservoir on the Tungabhadra river in the Krishna basin was studied. The study has been carried out using Landsat MSS and IRS-1 A LISS-II images. Visual interpretation techniques have been used to obtain information on the location and extent of sediment distribution pattern in the water-spread area of the reservoir. It has been possible to monitor the seasonal fluctuations in the reservoir water-spread; measure corresponding fluctuation in the volume of water in the reservoir, and study seasonal changes in the suspended sediment distribution pattern in the reservoir. An attempt has also been made to prepare area capacity curve for the reservoir. Semi-quantitative assessment of sediment deposits between reservoir levels were made considering water spread area from the satellite images (May 1986, April 1987, Jan. 1988, Jan. 1989 and March 1989) and sedimentation survey report of KERS 1985, (Karnataka Engineering Research Station). The results indicated that the high Concentration of sediments is at the western confluence of the Tungabhadra river. On the basis of tonal variation as observed, the reservoir could be divided into four major zones, viz., very high and high at the river confluence, moderate at the periphery and low at the dam site.

Acoustical discrimination of estuarine turbidity structure

The distribution of suspended sediment in estuaries is often concentrated in turbidity maxima which, because of the association of many contaminants with fine-grained sediment particles, can be important in determining the overall water quality. Acoustic investigations of the turbidity in the Hudson River estuary were done with a 200-kHz transducer and a 600-kHz broadband acoustic Doppler current profiler. (Water temperature and salinity were also measured and samples of suspended sediment were collected.) High turbidity here was found to be associated with tidally modulated and geomorphically controlled salinity intrusions. A salinity front is arrested at the bottom by the ebbing tide. As the tide turns, the front migrates upestuary producing an intense, local turbidity maximum. The re-establishment of a front in the original position on the next ebb can leave high turbidity pockets stranded upestuary. This is a novel mechanism for the generation of estuarine turbidity maxima but probably not unique to the Hudson River estuary; it may prove to be of widespread importance. [Work supported by the Hudson River Foundation, New York, NY.]

Distribution of Suspended Sediment over Wave‐Generated Ripples

Oscillatory flow over wave ripples is described by use of a discrete vortex model using the “cloud in cell” concept. The distribution of suspended sediment over the ripple bed is simulated by a Lagrangian model, following the track of individual sediment particles. A boundary‐layer model is used to determine the strength and the motion of the vortices very close to the ripple surface. The development of the boundary layer is described by the integrated momentum equation, assuming the boundary layer to be turbulent with a logarithmic velocity profile. In the boundary layer, turbulent diffusion is used to describe the distribution of suspended sediment. Outside the boundary layer along the ripple surface, advection with the velocity field resolved by the discrete vortex model determines the suspended‐sediment distribution. The simulated sediment concentrations are compared to measurements from the literature. The agreement between the time‐averaged simulated concentration profiles and the measurements from an oscillating water tunnel is satisfactory.

Drag reduction in open channel flow by aeration and suspended load

In supercritical open channel flows, air is entrained at the free surface. Such air-water flows, called selfaerated flows, exhibit smaller friction losses than non-aerated flows. New data on drag reduction in selfaerated flows are presented. It is shown that the drag reduction process is linked with the presence of an air concentration boundary layer next to the channel bottom. An analogy with dilute polymer solutions and micro bubble modified boundary layers is developed and it is suggested that the presence of air next to the bottom increases the effective viscosity of the mixture and the sublayer thickness. A parallel with sediment laden flows is also developed. Although the distribution of suspended sediments differs from the distribution of air bubbles, it is suggested that the mechanisms of drag reduction observed in suspended sediment flows are similar to those in self-aerated flows.

Suspended sediments of the modern Amazon and Orinoco rivers

The Amazon and Orinoco Rivers are massive transcontinental conveyance systems for suspended sediment. They derive about 90% of their sediment from the Andes that support their western headwaters, transport it for thousands of kilometers across the breadth of the continent and deposit it in the coastal zones of the Atlantic. At their points of maximum suspended-sediment discharge, the Amazon transports an average of 1100–1300 × 10 6 tons per year and the Orinoco transports about 150 × 10 6 tons per year. Relations of sediment discharge to water discharge are complicated by unusual patterns of seasonal storage and remobilization, increased storage and reduced transport of sediment in the middle Orinoco during periods of peak water discharge, and storage of suspended sediment in the lower Amazon during rising discharge and resuspension during falling discharge. Spatial distributions of suspended sediment in cross-sections of both rivers are typically heterogeneous, not only in the vertical sense but also in the lateral. The cross-channel mixing of tributary inputs into the mainstem waters is a slow process that requires several hundred kilometers of downriver transport to complete. Considerable fine-grained sediment is exchanged between rivers and floodplains by the combination of overbank deposition and bank erosion.

Drag reduction in open channel flow by aeration and suspended load

In supercritical open channel flows, air is entrained at the free surface. Such air-water flows, called selfaerated flows, exhibit smaller friction losses than non-aerated flows. New data on drag reduction in selfaerated flows are presented. It is shown that the drag reduction process is linked with the presence of an air concentration boundary layer next to the channel bottom. An analogy with dilute polymer solutions and micro bubble modified boundary layers is developed and it is suggested that the presence of air next to the bottom increases the effective viscosity of the mixture and the sublayer thickness. A parallel with sediment laden flows is also developed. Although the distribution of suspended sediments differs from the distribution of air bubbles, it is suggested that the mechanisms of drag reduction observed in suspended sediment flows are similar to those in self-aerated flows.

Paleoshorelines and coastal processes in Dakshina Kannada, Karnataka, India: a study based on remotely-sensed data

Abstract Coastal features in Dakshina Kannada, southern Karnataka, have been studied using satellite images, aerial photographs and Survey of India toposheets. This study reveals that the shoreline is migratory in nature. The region is characterized by the presence of depositional features, like spits and beach ridges. Most of the estuaries and rivers behave in an unusual manner as they approach the coastline, taking a coast parallel attitude. Assuming that such features in the landward side are indicators of paleoshoreline, several paleoshorelines have been demarcated. Digital processing of satellite data has indicated the nature and distribution of suspended sediments and littoral currents.

The effect of suspended sediment depth distribution on coastal water spectral reflectance: theoretical simulation

Abstract The spectral distribution of water surface reflectance, in the visible region (0.4-0.7 µm), has been numerically estimated, for various concentration profiles of suspended matter in water, including contributions from yellow substances, chlorophyll and mineral sediment. Mie theory for light scattering, has been used to estimate extinction, scattering and absorption coefficients for a system of suspended spherical particles characterized by Junge size-distribution and containing absorbing and non-absorbing components. Significant changes in the shape of the simulated spectral reflectance have been obtained when the suspended sediment distribution in the water column, extending from the surface to the light penetration depth, varies. The preliminary theoretical results presented seem to sustain the possibility of retrieving sediment depth profile from remote sensed spectral data.

Textural characteristics of the Krishna River sediments, India

To evaluate the magnitude of variation in grain size distribution in the Krishna river, bed sediments and suspended sediments collected along the length of the river have been studied. There are both temporal and seasonal variation in the grain size distribution of suspended sediments. The statistical parameters show the change along the river in a non-linear fashion which may be due to human interference and due to different types of sediments contributed by tributaries to the Krishna river. The suspended sediments are mostly fine silt (4 to 16μm), poorly sorted, showing coarse to fine skewed and are platyto leptokurtic. The bed sediments are mostly medium sand (350μm) showing moderate to well sorted, coarse to fine skewed and are platy- to leptokurtic. The CM diagram of Krishna river bed sediments suggests that deposition takes place by (1) rolling (2) rolling and suspension and (3) graded suspension. The suspended sediments represent deposits of uniform suspension.

Distribution of suspended sediment in a partially mixed estuary, Charleston Harbor, South Carolina, U.S.A.

A well-defined turbidity maximum zone (TMZ) exists 15–45 km upstream of the entrance to Charleston Harbor, South Carolina, on the Cooper River, where the salinity varies between 5–15 ppt. The TMZ is characterized by less than 60% light transmission over a 5 cm path-length near the bottom, as compared to 70–90% light transmission elsewhere. The TMZ oscillates along the Cooper River 3–13 km during a tidal cycle. The range of total suspended sediment (TSS) concentration is 40–100 mg l−1 in the TMZ, while 10–30 mg l−1 is the most common TSS concentration elsewhere in the estuarine portion of Charleston Harbor and the Cooper River. Transmissivity is well-correlated with TSS (r2 = 0·77) throughout the estuary. TSS concentration depends largely on tidal stage and varies significantly from spring to neap tide. Spring tide TSS concentrations are 2–3 times greater than concentrations during neap tides. The net downstream transport of suspended sediment is primarily a function of fresh water discharge, but is particularly large when flood events coincide with spring tides as was evident during the sampling of the TMZ following Hurricane Hugo (22 September 1989).

Vertical Distribution of Suspended Sediment in Uniform Open‐Channel Flow

The vertical distribution of suspended sediment in an open channel is studied theoretically by means of a new mixing length concept. The diffusion coefficient is represented as a function of the distance from the bed and dependent on the magnitude of sediment concentration. An equation to predict the sediment concentration is derived analytically, using the vertical mass-balance equation over the water depth. The theoretical concentration distributions are compared with previous experimental data. It is found that the present theory is applicable to sediment-laden flow with low and high concentrations. The ratio of the diffusion coefficient and the eddy viscosity, γ\N, is larger than unity and increases monotonically with the increase of the sediment load in flows with low sediment concentrations, and smaller than unity and decreases with the increase of the sediment load in flows with high sediment concentrations.

Particle size characteristics of suspended sediment in Southern Ontario rivers tributary to the great lakes

AbstractIn spite of the important relationship between sediment particle size and the transport/deposition of adsorbed pollutants in fluvial systems, little information regarding the size characteristics of suspended sediment transported by southern Ontario Great Lakes tributaries is currently available. This paper examines long‐term sediment and hydrometric data collected by the Water Resources Branch of Environment Canada in order to provide information on (1) typical particle size distributions of suspended sediment, (2) relationships between source material and particle size characteristics of suspended sediment, and (3) temporal variation in the particle size characteristics of suspended sediment from six southern Ontario rivers. Results illustrate the complex behaviour and variability of sediment particle size transport in these rivers and demonstrate the need for a better understanding of seasonal effects on sediment availability and conveyance processes in fluvial systems.

Suspended Sediment Character and Distribution in McBeth Fiord, Baffin Island

Sediment concentration, particle-particle morphology and size data are used to identify the processes that control the distribution and dynamics of suspended sediment during the open water season in the McBeth Fiord, Baffin Island. Dominant processes include hemipelagic sedimentation below river plumes and sediment resuspension by wind-driven waves, internal waves and bottom currents, including those related to deep-water renewal. Suspended particles are composed of unflocculated mineral grains, planktonic detritus - such as from diatoms, radiolarian and dinoflagellates - and large particles of marine snow composed of mucoid stringers, fecal pellets, floccules, agglomerates and resuspended clay clasts. Strong offshore winds are capable of temporarily removing the surface seasonal layer in the fiord. That in turn may initiate the autumn cycle of deep-water exchange. Replacement of deep water within McBeth Fiord by water from the Baffin Shelf can also introduce shelf sediment to the fiord and cause the resuspension of sediment covering the outer sill complex. Alternatively, strong onshore winds can push the surface layer to the head of the fiord and significantly increase the surface layer volume of the inner fiord. Internal wave trains associated with such a surface layer surge and travelling in a landward direction can impact on the front of the delta situated at the head of the fiord and initiate resuspension of bottom sediments. Key words: Arctic,fiord, McBeth Fiord, suspended sediment, oceanography, wind events, resuspension

Marine geology of the Gulf of Trieste (northern Adriatic): Sedimentological aspects

The Gulf of Trieste, the northernmost part of the Mediterranean Sea, is a ∼ 20 m deep marine basin influenced by freshwater inflow, bottom sediment resuspension and increasing pollution. The surficial sediments can be subdivided into seven zones on the basis of grain-size and mineral composition. The western part of the gulf consists of up to 70% carbonate shells of various organisms (molluscs, foraminifera and echinoderms). In the inner part of the small bays of Koper, Piran, Muggia and Panzano the surficial sediments consist of clayey silt with approximately 30% carbonate. A part of the carbonate fraction and all the non-carbonate minerals are derived from flysch in the hinterland, while the River Isonzo is the main contributor of these minerals in the northern part of the Gulf of Trieste. The distribution of suspended sediments shows the highest values in the northern part of the gulf, intermediate values in the southeastern part, and lowest values in the southwestern sector in the gulf entrance under the influence of the inflow of western Istrian waters. About one third of the suspended sediment is in the form of organic matter. Sedimentation rates decrease from about 3–5 mm yr −1 within the small bays, to about 1 mm yr −1 in the central part of the gulf, gradually increasing to approximately 2.5 mm yr −1 towards the mouth of the River Isonzo. Depth profiles of Holocene sediments in the inner part of the bays of Koper and Piran reveal a change from fluvial to brackish and marine environments.

An instrument system for profiling suspended sediment, fluid, and flow conditions in shallow marine environments

A new instrument system (sediment profiler) is described which is designed for making suspended sediment transport observations in shallow marine waters. The instrument system is capable of obtaining simultaneous profiles through the water column of suspended sediment concentration ( Cz), fluid properties (conductivity, temperature, depth) and flow conditions ( Uz, Vz), and of collecting water/suspended sediment samples at selected depths. Additionally it can be used in a calibration mode to intercompare multiple optical backscatter sensors (up to eight sensors). The sediment profiler is a relatively small aluminum tripod (91 cm high) that can be lowered through the water column in strong flows (∼2m s −1), measure suspended sediment concentrations between 5 mg l −1 and∼10g l −1, and can be lowered directly to the seabed (sensor elevations∼20cm). It contains internal battery power and on board digital logging capabilities and has no electrical connection with the vessel during operation. Since July 1989 the sediment profiler has been used extensively on a study of the Amazon shelf transport system (AmasSeds). Numerous profiles have been collected from hydrographic surveys off the northeast coast of Brazil to investigate spatial distributions of suspended sediment and to monitor net particle flux over 25 h anchor stations. The instrument system is rugged and reliable and has improved our ability to document the relationships between fluid properties, flow conditions, and suspended sediment characteristics in a complex shelf environment.

Promotion of Sediment Suspension Utilizing Coherent Vortices around Obstacle

The promotion of sediment suspension in a laboratory flume is discussed. Due to strong upward flow behind a spherical obstacle fixed at the bottom, bed materials are transported as suspended load. Horse-shoe vortices in front of the obstacle generate scour hole around it, and arch-shaped vortices behind the obstacle produce ripples in its near downstream area. Sand particles are entrained by the coherent vortices even after the scour hole has developed, which is detected by the distributions of suspended sediment. The obstacle placed in front of a weir can increase the amount of the suspended sediment passing over the weir.

Suspended Sediment Concentration Distribution of Flow over Vegetated Sand Bed

Hydraulics in vegetated streams increasingly becomes important for designing comfortable river environments. In this study, suspended sediment transport is investigated. Firstly, the turbulent structure of open channel flow over a vegetated bed is studied by means of both experiments and numerical analysis based on k-A turbulence model. Secondly, the turbulent flux of suspended sediment is estimated by assuming a similarity between the change of turbulent flux distribution of suspended sediment due to the presence of a vegetated layer and that of turbulent momentum flux (Reynolds-stress distribution). Based on the above, the concentration distribution of suspended sediment of flow in a vegetated-bed channel is predicted against the vegetation density.

Variations in grain-size distribution of suspended sediment in a glacial meltwater stream, Austre Okstindbreen, Norway

AbstractThirty-nine samples of suspended sediment from the meltwater stream of Austre Okstindbreen, Norway, were analysed using both moments and parameters of the hyperbolic distribution. The samples turned out to be non-normally distributed. No direct correlation was found between discharge and grain-size distribution, but it is supposed that the hydraulic influence is hidden behind factors like composition of morainic or stream-bed material. Through comparison of the grain-size parameters from two periods in the field season, it was possible to distinguish between two sediment populations.

Variations in grain-size distribution of suspended sediment in a glacial meltwater stream, Austre Okstindbreen, Norway

AbstractThirty-nine samples of suspended sediment from the meltwater stream of Austre Okstindbreen, Norway, were analysed using both moments and parameters of the hyperbolic distribution. The samples turned out to be non-normally distributed. No direct correlation was found between discharge and grain-size distribution, but it is supposed that the hydraulic influence is hidden behind factors like composition of morainic or stream-bed material. Through comparison of the grain-size parameters from two periods in the field season, it was possible to distinguish between two sediment populations.