Suspended Sediment Sources Research Articles

Suspended Sediments in Lake Malawi, Africa: A Reconnaissance Study

In order to investigate the source and distributional pathways of suspended sediment in a tropical rift-valley lake, water-column profiles of light transmission (inversely related to water turbidity) were coupled with filtered water samples to determine total suspended sediment (TSS) concentrations at 28 stations throughout Lake Malawi (Lake Nyasa), East Africa, during January, 1992. TSS concentrations of the water column are typically between 0.1 and 0.5 mg/L, lower than those reported for the lower Laurentian Great Lakes. Elevated levels of turbidity are detected both at stations near the shoreline and offshore at four depths: at or near the surface, at the lake floor, at the chemocline, and in a mid-depth layer that is unique to the stations offshore of the Ruhuhu Delta. The latter had the most turbid water detected on this cruise and is interpreted as an interflow injection of fluvial material related to a 2-day rainstorm. Estimates suggest that this event contributed a significant portion of the annual sediment load to the delta. Other important sources of suspended sediment in Lake Malawi probably include biological productivity at the surface, chemical or biological processes at the chemocline, and resuspension events produced by wind-induced waves and currents and by seiche activity.

Mechanism of Suspended Sediment Supply to Headwater Rivers and Its Seasonal Variation in West Central Hokkaido, Japan.

Source of suspended sediment was identified from grain size distribution in two headwater basins in West Central Hokkaido, Japan. The fine grains in river bed sediment were supplied to the river water as suspended sediment in the early snowmelt season, whereas those in hillslope sediment were washed out into the rivers in the summer rainy season. The fine grains probably accumulated in the bed sediment during winter, and were stirred up into river water as the river discharge increased. Since the fine grains in the river bed sediment were gradually exhausted, further stirring up could occur only when the river discharge exceeded that season's previous maximum. The fine grains in the hillslope sediment were most likely to be stored during the dry period from May to July, only to be washed away during the summer rainy season. Thus the suspended sediment supply from the hillslope is sparse in the snowmelt season. This type of seasonal variation in suspended sediment supply is probably common to headwater basins in the cold and humid climate of West Central Hokkaido, Japan.

Variation in suspended sediment concentration during storm discharges in three small streams in upper osun basin, Central Western Nigeria

The suspended sediment concentration response of three small streams draining quartzites and quartz-schists in southwestern Nigeria to storms of varying magnitude are presented. A total of 1468 water samples from 62 storm responses with peak stream discharge values ranging from 80 to 120 l s−2 were analysed and storm and suspended sediment concentration hydrographs and hysteresis loops were used to depict the response patterns. The six different types of responses identified include the single and multiple discharge peak rises with sediment lead and lag and also the mixed response patterns. Both valley slope and channel erosion constituted important sources of suspended sediment. However, sediment availability, exhaustion, and flushing effects determined the variation in the different response types.

The effect of commercial trawling on sediment resuspension and transport over the Middle Atlantic Bight continental shelf

Numerous field observations have revealed that turbulence created in the wake of trawl doors can generate large and highly turbid clouds of suspended sediment. Time-averaged concentrations of sediment resuspended by trawls from various areas of the Middle Atlantic Bight continental shelf have been estimated using a simple mathematical model and National Marine Fisheries Service records of commercial trawling activity. Mean concentrations of sediment put into suspension by currents have also been computed using a modified form of the Glenn and Grant model. The results indicate that sediment resuspension by trawling can be a primary source of suspended sediment over the outer shelf, where storm-related bottom stresses are generally weak. The concentration estimates further suggest that sediment resuspended by trawls makes a sizeable contribution to the total suspended sediment load over the heavily trawled central shelf area of Nantucket Shoals during all times except winter and early spring. The level of trawling activity declines dramatically going seaward across the outer shelf. This decline coupled with cross-shore water motions in the area appears to result in a net offshore transport of sediment across the shelf edge. However, the estimated magnitude of this transport indicates that trawling does not produce significant short-term erosion of outer shelf sediments.

The potential use of pollen in the identification of suspended sediment sources

AbstractPollen and spores form a significant part of the suspended organic load of a New Forest stream. Flood concentrations reach 230 grains ml−1 while baseflow carries under one grain ml−1. Hydrographs from different seasons show differing hysteretic loops for pollen and spore concentrations against discharge and suspended sediment. These variations reflect not only factors of production, but the type and distance of the contributing sources. This investigation suggests that variations in flood pollen and spore concentrations may be used to trace such suspended sediment sources as: eroding bedrock, channel banks, or hillslopes under specific vegetation covers.

Suspended Sediment Transport and Deposition Modeling in the Bay of Fundy, Nova Scotia — a Region of Potential Tidal Power Development

Two recent independent studies of the Minas Basin have been combined to produce a numerical simulation of suspended sediments. One study devised a numerical, barotropic tidal model of the Bay of Fundy and Gulf of Maine, which produced a good simulation of the tides and currents in the Minas Basin. The second, an extensive program of sediment sampling and monitoring addressed the nature of suspended sediments, bottom sediments, their various sediment sources and the postglacial evolution of the system. The only significant source of suspended sediment was from the open boundary to the Minas Basin and was of relatively uniform concentration through the water column. Consequently, the barotropic tidal model was well suited to modeling this material. Sediment laws describing sediment settling, resuspension, and the critical stress for entrainment were obtained from the literature and evaluated. The settling velocity of the suspended sediment was obtained by experimentation using actual water/sediment samples. Because the various parameters and critical stresses show a considerable variation among experimenters, runs were planned to examine a range of parameters. A close fit to existing conditions was obtained with the model generating mudflats in those regions where indeed they exist. Using the various parameters and critical stresses reflecting maximum sedimentation, the model was run to include the effects of a tidal power barrage off Economy Point. It is concluded that suspended sediment would not inhibit the operation of such a barrage through siltation directly in front of or behind the barrier. Increased siltation can be expected in the intertidal areas behind the barrage. Sediment budget considerations further limit the degree of post barrier siltation, insofar as the resident volume of suspended material (30 × 106 m3) is not enough to significantly reduce the headpond area.Key words: suspended sediment, sediment transport, numerical model, tide

Suspended-sediment exchanges between the St. Lawrence estuary and a coastal embayment

Rapid local changes in the bathymetry of the St. Lawrence estuary define several physiographic units which act as distinct reservoirs of suspended sediments. Tidal exchanges between three reservoirs (the South Channel, Baie de Ste. Anne and Rivière Ouelle) lead to a marginal increase of the turbidity and to the reinforcement of the main plume in the South Channel. Baie de Ste. Anne is a large (175 km 2) subtidal platform less than 8 m below MLLW along the South Channel. A two-step intensification of turbidity occurs inside the bay. Estuarine processes in Rivière Ouelle — a small coastal plain estuary — build up a turbidity maximum which provides a local source of suspended sediments to intertidal flats in the bay. Tidal exchanges between these flats and the bay, in turn contribute to maintaining high turbidity levels over the Ste. Anne platform. A total mass of suspended sediments equivalent to more than half the mean solid discharge per tide of the St. Lawrence River may be exchanged during the ebb and flood. Waters in the South Channel are themselves enriched during each tidal cycle by lateral inputs from the platform. On a long-term basis, this multicomponent system appears to have reached a steady state, with no sediments accumulating over the flats. It provides additional suspended sediments to the downstream advection of turbidity in the estuary. Slight tidal phase differences between the three reservoirs are important in controlling the exchanges.

Suspended sediment sources identified by magnetic measurements

A procedure for identifying the main source of the suspended sediment load of a stream by simple, cheap, rapid and nondestructive magnetic measurements is applicable to samples taken during the routine sampling of flood events permitting general characterisation of the load and more detailed investigation of variations in sediment source both during and between individual flood events.

Identification of suspended sediment sources by means of magnetic measurements: Some preliminary results

Rapid, nondestructive magnetic measurements of initial low‐field susceptibility x, saturation isothermal remanent magnetization (IRMsat), and coercivity of IRM provide a means of identifying the source of suspended sediments in rivers. Preliminary results derived from the application of these measurements both to suspended sediment and to potential sources within the instrumented catchment of the Jackmoor Brook near Exeter, United Kingdom, demonstrate the value of this approach in an area of Permian sandstone bedrock where the contrast in magnetic properties between parent material and topsoil is easily characterized. High flows are shown to be associated with suspended sediment, the magnetic properties of which are indistinguishable from those of the cultivated soils of the catchment.

Nutrient Transport in Surface Runoff from a Subalpine Watershed, Lake Tahoe Basin, California

The watershed of Ward Creek, a tributary to oligotrophic Lake Tahoe in the Sierra Nevada, has been investigated since 1971 with the objective of improving our knowledge of processes of nutrient and sediment release and transport to the lake. Quantitative data on selected stream water parameters were collected for 3 yr (1972—1975) at three stations on Ward Creek, two on the main upper tributaries and one near the stream mouth. Comparative data were collected at a stream mouth station on adjacent Blackwood Creek in the 3rd yr. The parameters were selected on the basis of their significance to eutrophication of Lake Tahoe. Precipitation in a normal year is over 90% snow but annual patterns vary widely and rainfall at any time of year can be highly important in sediment and nutrient transport. Water discharge and the flux of suspended sediments, NO3—N, phosphorus, iron and trace metals were dominated by the spring snowmelt runoff from mid—April to mid—June. However, in 1974 heavy fall and summer rains accounted for a large percentage of the annual flux of sediments and nutrients in a total of only 14 d. The spring runoff was characterized by distinct diel water discharge patterns. Similar but not coincident patterns were found to exist for sediments and nutrients, including NO3—N, but not for soluble phosphorus. The Ward watershed has 87% the area of Blackwood but discharge proportionately much lower quantities of sediment and nutrients in comparable water yields per hectare in water year 1975. This contrast in fluxes was probably accounted for in the history of greater disturbance by man in Blackwood Canyon. The principal source of suspended sediments in Ward Creek was streambank erosion in the lower reaches of the channel. The dominant form of inorganic nitrogen in Ward was NO3—N derived from precipitation, symbiotic nitrogen fixation and nitrification of organic nitrogen in forest soil. Phosphorus and iron were almost entirely in particulate form and thus their periods of flux occurred during high flows and sediment transport. Sediment and nutrient loading of Lake Tahoe from the Ward and Blackwood watersheds reflects a history of soil disturbance and vegetation removal. Logging, fire and stream channel diversion have been the dominant perturbations. Conservative extrapolation of annual loading data from this study to the entire basin indicates that algal nutrient levels in the lake probably have increased sufficiently in the century of man's intensive disturbance of the basin watersheds to account for increased phytoplankton and periphyton production that have been measured and observed since 1958.

Mineralogy and Related Parameters of Fluvial Suspended Sediments in Northwestern Ohio

AbstractStream water samples were collected weekly for 17 months at eight sampling sites in the Maumee River Basin to characterize the clay mineralogy of the suspended sediments and to determine the utility of mineralogy as a marker of the source (rural, urban, geologic) of the sediments. X‐ray diffraction analysis of the clay‐sized (< 2 µm) sediments indicated little seasonal or downstream variability in clay mineral composition. The quantities of mica, quartz, and vermiculite‐chlorite were 36 ± 5%, 29 ± 5%, and 20 ± 5%, respectively. The quantities of expandables, interstratified, and kaolinite minerals were usually < 10%. The cation exchange capacity (CEC), amorphous, fine clay, and organic matter content of the clay‐sized suspended sediments were approximately 44 meq/100 g, 4.4%, 25%, and 5%, respectively. Carbonate minerals were not detected in the clay‐sized fraction.The 2 to 50 µm fraction was dominated by quartz in high flow periods and secondary calcite in low flow periods. The stream water was calculated to be saturated with calcium carbonate, thus calcite precipitation could be expected.When fluvial suspended sediment properties were compared to properties of regional soil materials, mineralogy appeared to be a useful index to differentiate between surficial and geologic (parent material) sources of suspended sediments. The clay‐sized fraction of the suspended sediments contained percentages of mica and carbonates analogous to local surficial materials yet in contrast to local geologic (parent material) materials. A lack of carbonate minerals in the silt‐size (2–50 µm) fraction of the suspended sediments during high discharge events when stream bank erosion, hence geologic erosion, should be maximum further negated the geologic origin of the suspended sediments.The mineralogical characterization of the fluvial suspended sediments in combination with chemical data led to the conclusion that the annual suspended sediment load of the Maumee River and tributaries was predominantly surficial in origin.

Source and Dynamics of Suspended Sediments in Near-shore Region, Southwestern Florida: ABSTRACT

Source and Dynamics of Suspended Sediments in Near-shore Region, Southwestern Florida: ABSTRACT