Fine Sediment Transport Research Articles

Storm-induced fine-sediment transport, west coast of south Korea

Archived data, together with field observations collected between 1980 and 1982 off the west coast of Korea, suggest that the onset of winter monsoon winds in late fall initiates a residual southward flow that potentially carries large volumes of resuspended bottom sediments into the Korea Strait. During the calm conditions of summer, muds are replenished by high river discharges and reform the band of soft material, which characteristically occurs as a series of mudflats near the coast. Thus, these mudflats serve as a temporary storage facility during summer accumulation and as a source during winter erosion.

A stochastic modeling approach to the fine sediment budget of the New York Bight

A stochastic model of fine sediment transport on the continental shelf is modified to incorporate the effects of storm flows. The model, based on surface gravity wave resuspension, now includes transport by both tides and episodic storm flows. Effects of gravity wave/storm flow correlation as deduced from near bottom current meter measurements are also included. Sediment dispersion is significantly faster when the effects of storm flows are included. The effects of the gravity wave/storm flow correlation and the regional net flow pattern are small. The model is solved numerically for equilibrium dispersal patterns for sediment entering at estuary inlets bordering the New York Bight region. Additional dispersal patterns are found for upcoast and downcoast sources as well as the dredge spoil dump site. Combinations of these dispersal patterns are least squares fit to the observed fine sediment distribution in the New York Bight to evaluate the magnitudes of the sources of sediment; negative source magnitudes are interpreted as sediment sinks. The results are consistent with other estimates of sediment sources and sinks in the New York Bight.

A FORTRAN program for suspended sediment dynamics and tidal flux monitoring

Research into estuarine and coastal fine sediment transport and sediment deposition is aided by a proposed routine for collection and analysis of hydrodynamic, particulate, and salinity data. Field measurements taken over a number of depth intervals and over one or more tidal cycles are used to calculate the point, depth-integrated, and net horizontal movements of water, suspended solids, and salt at a fixed sampling site.

A numerical model of fine sediment transport on the continental shelf

A numerical model of fine-grained sediment dispersion in the New York Bight of the North American continental shelf is presented. Large amounts of waste material have been dumped in this region and the dispersal patterns of this material are of great interest to environmental managers. The model assumes that fine sediment resuspension is determined by surface wave activity and that transport is determined by tidal currents. Considering surface wave activity to be a random process reduces sediment motion to a random walk which is governed by a diffusion equation. The diffusion equation is solved numerically by an implicit time difference, finite element algorithm for a number of initial conditions.

Geochemical Indices of Fine Sediment Transport, Northwest Gulf of Mexico

ABSTRACT The 210Pb distribution, the clay mineralogy distribution, and the distribution of three trace metals, barium, lead, and manganese, in the sediments of the south Texas shelf are related to the dynamics of the sedimentary transport process. 210Pb, whose concentration is time dependent, defines three loci of recent sediment accumulations. In addition, the variation of 210Pb activity at the sediment-water interface delineates areas of terrestrial sedimentation from hemipelagic sedimentation. The clay mineralogy composition of the bottom and suspended sediments assists in defining the origin of the persistent nepheloid layer and bottom sediment. Barium, a major element used in drilling mud, tags sediment movement from areas of hydrocarbon exploration. Lead concentrations, anthropogenically introduced from urban areas, tag the sediment derived from the metropolitan complexes of coastal Texas. Manganese, because of diagenic mobilization, is concentrated in areas of very slow sediment accumulation. The distribution of these geochemical properties of the sediment are in direct response to the sediment regime of the shelf. Based on this data, a model of sediment transport and deposition which relates currents, wind, tides, sediment flux, and precipitation has been formulated. This model differs from the advective transport or convergent current schemes previously proposed for this shelf.

Reactor-released radionuclides and fine-grained sediment transport and accumulation patterns in Barnegat Bay, New Jersey and adjacent shelf waters

Anthropogenic radionuclides have been introduced into the Barnegat Bay environment via global fallout from nuclear weapons testing and by low-level discharges from the Oyster Creek Nuclear Generating Station. A significant portion of these radionuclides have been adsorbed to fine-grained particles and consequently provide excellent tracers for fine-sediment transport and accumulation patterns in the Bay and adjacent shelf environment. Fine-grained particles tagged with reactor nuclides are presently accumulating along the landward shore of Barnegat Bay at rates between I and 7 cm year−1. There is some indication that reactor-tagged sediments are also being transported into the mouths of small tributaries which discharge into the Bay. Reactor-tagged particles that escape from the Bay, through Barnegat Inlet, onto the shelf, are accumulating during the summer with fine-grained material from other sources, in depressions along the shelf bottom. These near-shore mud deposits are apparently resuspended and dispersed by major storms probably on a seasonal basis. By comparing radionuclide ratios in the reactor releases with the ratios observed in the fine-grained sediments in the vicinity of the reactor, it appears that (I) 35% to 50% of the total 137Cs activity in the top 30 cm of the sediments in Oyster Creek is attributable to reactor releases, (2) if transuranic releases have occurred from the Oyster Creek Reactor, the increments of 239,240Pu and 238Pu are not distinguishable from the fallout plutonium burden in the sediments and (3) radiocobalt is removed from the liquid effluent and stored in the sediments at least 20× more effectively than radiocesium. A budget of 60Co, based on inputs from the reactor, storage in the Bay sediments, and outputs through Barnegat Inlet on particles and in the dissolved phase, indicates that 40% of the 60Co released by the Oyster Creek reactor resides in the sediments of Barnegat Bay. The accumulation and dispersal patterns of reactive activation products such as 60Co released during routine nuclear reactor operations provide important clues to the probable transport pathways of a wide variety of pollutants including transuranic nuclides if significant releases of such materials were to occur.

DYNAMICS OF SILT IN ESTUARY, RESIDUAL CURRENT OR FLOCCULATION WHICH PREVAILS?

The transport of fine suspended sediment in a partly-mixed estuary has been simulated on a physical model of a schematic estuary reproducing the main geometrical and hydrodynamical characteristics of the Gironde Estuary (France). The natural sediment consisting of silt and clay is simulated using a light and fine material, gilsonite, and the flocculation-'processes in salt water and under turbulence induced by tidal currents have been reproduced by adding in salt water a flocculating salt solution (sodium pyrophosphate). Then the formation of the turbidity maximum surveyed in the field and its upstream-downstream migration in response to varying river discharge have been successfully simulated and the results of different series of tests lead to the following conclusions : - flocculation processes - which are responsible of the variation of the settling velocity with salinity and turbulence-have to be reproduced to explain the formation of the turbidity maximum ; - after high river discharges the convergence of bottom residual currents (null point) due to the salinity intrusion creates a trap for suspended sediments supplied by the river flood which accumulate in the form of the turbidity maximum. Without salinity intrusion, a large amount of sediment would escape out of the estuary to the sea ; - during low river flows, a part of the suspended sediment migrates upstream but the amplitude of this migration is small compared with the displacement of the upstream limit of the salinity intrusion ; - the upstream migration of the turbidity maximum-is increased when a transverse bottom morphology (existence of a deeper navigation channel) is represented.

Sedimentation of organic detritus in Lochs Etive and Creran, Argyll, Scotland

The rates of sedimentation of organic detritus were measured at 3 stations in two Scottish sea lochs, Loch Etive and Loch Creran, using sedimentation jars exposed at various depths. Details are given of the seasonal and depth distribution of sedimenting material, and its composition for a 1-year period. Differences in the pattern of sedimenting material collected at different depths and in the seasonal patterns of sedimentation at the different stations suggested that, in each case there were differences in the relative importance of detritus from various sources. At all stations, phytoplankton production made a relatively small contribution to the total detritus collected, either directly as dead cells, or indirectly as the faeces of zooplankton organisms. Near the head of Loch Etive there were contributions by filamentous algae and Enteromorpha sp., but a major source of detritus was terrestrial debris, mainly carried into the loch in the waters of the River Etive. In the lower basin of Loch Etive, terrestrial detritus also contributed to the total sedimenting near the surface, but at greater depths much of the material collected in the sedimentation jars probably resulted from short-term resuspension and re-deposition of bottom material, reflecting a net transport of fine sediment from the shallower to the deeper areas of the loch. Secondarily resuspended material was also a major source of material collected in the jars exposed in Loch Creran.

Flocculation of Suspended Sediment in the Sea

INORGANIC sediment suspended in the sea is unstable as single mineral particles and occurs as flocculated aggregates with settling speeds many times greater than that of the constituent grains. This has been demonstrated both through observations of natural samples1–5 and through laboratory experiments6,7. In near-shore waters with high concentrations of terrestrially derived mineral matter the transport and deposition of fine sediment are greatly affected by flocculation. The exact mechanism of floc formation in the sea is not well understood. The concentration, mineralogy and grain size of the suspended particles and the salinity, turbulence and temperature of the water are commonly regarded as controlling factors8,9. Flocculated aggregates composed largely of organic matter have been observed in the sea10,11 and organic matter may be an important ingredient in the flocculation of inorganic sediment.

Transport Paths Of Suspended Matter AlongThe Dutch Coast

A three-dimensional numerical baroclinic model for hydrodynamics and coupled fine sediment transport is used for the computation of dispersion of suspended fine sediment along the Dutch coast. Computational results are in agreement with observations that horizontal salinity gradients, due to the presence of river water, induce an estuarine-like cross shore circulation along the entire coast. Sediment transport paths are determined for various sub-areas. Computed residual eddies and shoreward near bottom currents have a major influence on transport paths. Long term transports of suspended fine sediment are computed with a fast PC-model for tidally integrated transport computations. Results show that suspended matter with fall velocities around 10 m/s tends to concentrate in a narrow strip along the coast.

Significance of Constituent Composition, Texture, and Skeletal Breakdown in Some Recent Carbonate Sediments

ABSTRACT A study of sediments along a 35-mile length of the Florida reef tract indicates the presence of two sub-environments between the reefs and the Keys. Variational trends of mean phi, standard deviation, percent fines (less than 62 microns), roundness, and constituent composition indicate a distinct change in the sediment at a point about half-way between the reefs and the Keys. Trends show a general increase or decrease in the outer (reefward) one-half, but general uniformity within the inner one-half. Bottom observations indicate a correlation between the area in which the change in sediment takes place, and the area in which density of growth of marine grass increases. Analysis of the sediments and the processes affecting them indicates that marine grasses not only modify the effect of current and cause the entrapment of fine sediment, but they also exert an indirect control on processes of skeletal breakdown and textural evolution of the sediment. For instance, in the outer (reefward) area, skeletal breakdown is dominantly a mechanical process and the sediment textures at least partially reflect current phenomena. In the inner (Keyward) area, however, skeletal breakdown is dominantly a biological process and the ultimate texture of the sediment reflects a complex of processes inc uding those associated with growth and the life cycle of the organisms, the reaction of the shell carbonate to breakdown, and transport of fine sediment from the outer area. Of particular importance are the relative rates at which these processes take place; the variability of these rates strongly influences texture and constituent composition of the sediment. Though little quantitative data concerning these processes is yet available, and their relative importance is poorly known, knowledge of their possible effects suggests caution in some aspects of interpretation of carbonate rocks.