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Sediment yields from the world's rivers are generally highest from steep drainage basins with weak lithology, active tectonics, or severe land-use impacts. Here, we evaluate sediment yields from the Western Transverse Ranges of California in an attempt to explain why they are two- to tenfold greater than the surrounding areas of California. We found that suspended-sediment yields across the gauged basins of the Western Transverse Range during 1969-1999 varied by approximately an order of magnitude (740-5300 t/ [km.sup.2]/yr). Similarly, fine-sediment concentrations for normalized discharge rates varied by almost two orders of magnitude (e.g., 1.3-110 g/L for the mean annual flood) for 11 previously unmonitored drainages of the Santa Ynez Mountains. Areas with high sediment yields consistently have weakly consolidated bedrock (Quaternary-Pliocene marine formations) and are associated with the highest rates of tectonic uplift of the region (>5 mm/ yr). These regions are important to the sediment discharge budgets, because ~50% of the total suspended-sediment discharge from the Western Transverse Range is estimated to be generated within these regions, even though they represent only ~10% of the total watershed area. Previous estimates of suspended-sediment discharge from the Ventura River have likely been underestimated by ~50% because the gauging station is located immediately upstream of a high sediment yield region. We also found a significant and positive correlation between sediment yield and the percentage of a watershed with grassland and agricultural land use. These results suggest that there is adequate variation within the lithology, tectonics, and land use of the broader Western Transverse Range geologic province to induce large variations in sediment yield at the local scale.

The problem of suspended sediment transport in river and coastal flows is addressed. High-quality field data of river and coastal flows have been selected and clustered into four particle size classes (60-100, 100-200, 200-400, and 400-600 [micro]m). The suspended sand transport is found to be strongly dependent on particle size and on current velocity. The suspended sand transport in the coastal zone is found to be strongly dependent on the relative wave height ([H.sub.s]/h), particularly for current velocities in the range 0.2-0.5 m/s. The time-averaged (over the wave period) advection--diffusion equation is applied to compute the time-averaged sand concentration profile for combined current and wave conditions. Flocculation, hindered settling, and stratification effects are included by fairly simple expressions. The bed-shear stress is based on a new bed roughness predictor. The reference concentration function has been recalibrated using laboratory and field data for combined steady and oscillatory flow. The computed transport rates show reasonably good agreement (within a factor of 2) with measured values for velocities in the range of 0.6-1.8 m/s and sediments in the range of 60-600 [micro]m. The proposed method underpredicts in the low-velocity range ( DOI: 10.1061/(ASCE)0733-9429(2007)133:6(668) CE Database subject headings: Sediment transport; Suspended sediments: Currents; Waves; Rivers; Coastal environment.

There is increasing demand for simulation tools of flow and suspended sediment transport over complex boundaries in hydraulic engineering. The diagonal Cartesian method, which approximates complex boundaries using both Cartesian grid lines and diagonal lines segments, is presented in the paper to simulate the complex boundaries of two-dimensional shallow-water turbulence equations and nonequilibrium suspended sediment transport equation. The method, which utilizes cell-centered nodes on a nonstaggered grid, uses boundary velocity information at the wall boundary to avoid the specifcation of water level. An enlarged finite-difference method is introduced for momentum and suspended sediment equations on the complex boundary. This paper describes an application of the diagonal Cartesian method to calculate the tidal current and suspended sediment concentration of Quanzhou Bay in the Fujian province of China. The results show that the method predicts the flow and suspended sediment concentration well, and the calculations agree well with the measurement. CE Database subject headings: Numerical models; Simulation: Suspended sediments: Sediment transport; Boundaries.

Standard depth-integrated models of sediment dynamics predict that concentrations of suspended fine sediment should decay at a characteristic rate that is controlled by the particle settling velocity and the depth of the water. In contrast, a model which resolves the processes of settling and dispersion in the water column has suggested that this decay rate should be independent of the settling velocity, and is controlled by dispersive processes in the water column. By revisiting the problem of sediment dispersion and settling following a point release of material, we resolve this discrepancy and confirm that depth-integrated models capture the correct physical behavior. DOI: 10.1061/(ASCE)0733-9429(2006)132:5(533) CE Database subject headings: Sediment deposits; Suspended sediments; Predictions; Numerical model; Velocity.

We examined trace metal ingestion and assimilation (Cd, Se, Zn) by the green mussel Perna viridis in a mixture of diatoms and sediment at concentrations below and above the pseudofeces production levels. Dual gamma radiotracers ([sup.109]Cd, [sup.65]Zn) were used to investigate particle selection on marine diatoms and sediments. The diatom (Thalassiosira weissflogii) was radiolabeled with [sup.109]Cd, and the natural sediment was radiolabeled with [sup.65]Zn. By comparing the ratios of [sup.109]Cd:[sup.65]Zn in the particle mixture, mussel tissues and pseudofeces within a short-term exposure period (35 min), the results demonstrated that the green mussels were able to selectively ingest the diatom particles at a high particle load. Efficiency of selection for nutritious particles (e.g. diatoms) increased with increasing ratio of sediments in the particle mixture. Pseudofeces contained a higher ratio of sediments relative to that in the feeding suspension. No major particle selection was observed at concentrations below the level for pseudofeces production. The assimilation of Cd, Se and Zn by the green mussels was quantified using a pulse-chase feeding technique. The assimilation of Se and Zn by the green mussels from ingested diatoms was reduced with the presence of sediment within the mussel gut, presumably due to the resorption of metals onto the sediment, leading to a quicker passage of metals through the digestive tract and a lower proportion of metals subjected to intensive digestion. In contrast, the presence of diatoms did not significantly affect metal assimilation from ingested sediment. A significant correlation between metal assimilation efficiency and metal gut passage time was also observed. Metal assimilation by the green mussels appeared to be little dependent on the particle concentration in seawater. Our study suggests that particle selection may potentially alter metal influx from ingested food sources, particularly at high particle concentrations. Selective feeding of nutritious particles, coupled with a high assimilation efficiency from these ingested particles, may increase metal influx into mussels from the dietary phase.

A complex problem of turbulent-sediment interactions in an open-channel flow is approached experimentally, using specially designed field experiments in an irrigation canal. The experimental design included synchronous measurements of instantaneous three-dimensional (3D) velocities and suspended sediment concentration using acoustic Doppler velocimeters (ADV) and a water sampling system. Various statistical measures of sediment concentration fluctuations, turbulent sediment fluxes, and diffusion coefficients for fluid momentum and sediment are considered. Statistics, fractal behavior, and contributions of bursting events to vertical fluxes of fluid momentum and sediment are evaluated using quadrant analysis. It has been found that both turbulence and sediment events are organized in fractal clusters which introduce additional characteristic time and spatial scales into the problem and should be further explored. It is also shown that Barenblatt's theory of sediment-laden flows appears to be a good approximation of experimental data. DOI: 10.1061/(ASCE)0733-9429(2002) 128:2(214) CE Database keywords: Suspended sediments; Sediment concentration; Open channel flow; Sediment transport; Turbulence; Bed load.

An evaluation is presented on the accuracy of trapping for generating models of ocean sediment composition, using deep-sea bottom-tethered traps in the Antarctic Ocean. Results support the use of conical, baffled sediment traps at depths greater than 1200m; erratic results achieved at shallower depths may be attributable to hydrodynamic changes of particles undergoing multiple aggregation and disaggregation cycles within the water column.

Northern river breakups are a spectacular process capable of modifying hydrological, geomorphological, and biological regimes. To begin an assessment of the physical and chemical characteristics associated with river-ice breakup, some exploratory field studies were initiated on the Liard River, a large northern river. The primary objective was to conduct time series measurements of basic water chemistry parameters, suspended sediment concentrations and size, and associated trace elements during the active breakup period. Results show that, although water quality characteristics such as pH and specific conductivity remained relatively constant, dissolved oxygen increased rapidly as breakup progressed and reached a level of supersaturation. Just before breakup, a plume of fine-grained sediment developed leading to very high peak suspended sediment concentrations that far exceeded those produced under equivalent open-water discharge. Concentrations of select trace metal paralleled the rise in suspended sediment.

This study examines metal sulfides stability to oxidation in seawater. The acid volatile sulfide/simultaneously extracted metals (AVS/SEM) theory is used to evaluate sediment quality to predict the absence of toxicity of Ca, Cu, Ni, Pb, and Zn.

Particle sinking speed and horizontal advection in the North Atlantic Ocean were measured and analyzed using moored sediment traps and Lagrangian analysis. Findings indicate that particle flux interpretation is dependent on data regarding velocity field spatial and temporal variability above sediment traps in deep-ocean water.

Resuspension of sediments in karstic lakes by multiple bottom-springs is mimicked using a laboratory experiment, wherein an array of axisymmetric vertical jets are forced through a planar bed of noncohesive sediments. Three different types of flow evolution are identified, namely, full deposition, where all the suspended particles settle after initial transients, continuous reentrainment, where the particles remain in individual jet cores without deposition, and particle interface, where the sediments disperse in the entire bottom layer, forming a lutocline between the turbid lower layer and clear upper layer, regimes. Because of its practical relevance, special attention is given to the particle interface regime. A semiempirical criterion for the appearance of this regime and an expression for the height of the resulting lutocline are delineated. Velocity measurements indicate that the intensity of turbulence above the lutocline is determined by the nature of particle-flow interactions in the sediment layer, characterized by the particle Reynolds number.

To determine the suspended load component of sediment transport in open-channel flow, the vertical distribution of the concentration of suspended particles is of importance. It is usual to determine this distribution by solving the diffusion-convection equation under appropriate boundary conditions. The exponent in the resulting equation is the Rouse number, defined as [Mathematical Expression Omitted]. The [Mathematical Expression Omitted]-value has been the subject of much research. In natural alluvial channels the sediment-laden flow is usually in capacity (saturation) condition, implying that the flow will charge (saturate) itself with particles available in the bed load and/or on the bed itself. However, simulation of sediment-laden flow in a laboratory flume is achieved typically by externally adding particles to the flow. Consequently, it is not certain that the flow was in capacity condition. The resulting [Mathematical Expression Omitted]-values are often values for noncapacity conditions. They should not be used for natural alluvial channels, because they are misleading. Reported herein are experiments performed in the laboratory under noncapacity, as well as under capacity, conditions. This study focuses on the experimental determination of the [Mathematical Expression Omitted]-value, which incorporates the ratio of the sediment flux [c[prime].sub.s]v[prime] and the momentum flux u[prime]v[prime], as well as the velocity and concentration profiles, [Mathematical Expression Omitted] and [Mathematical Expression Omitted], respectively. For experiments with small particles, [d.sub.50] = 0.135 mm, the [Mathematical Expression Omitted]-values at capacity condition are smaller than unity; at noncapacity condition, the [Mathematical Expression Omitted]-values are usually larger than the ones at capacity condition, but all are still smaller than unity.

Measurements of dissolvable iron, nitrate and chlorophyll in the California Current System indicate that there were high concentrations of iron during strong upwelling conditions in Mar 1997. There was a low concentration of dissolvable iron in surface waters during the 1998 El Nino. The iron source in the upwelled water does not seem to originate from diffusion of dissolved iron from shelf sediments. Iron may be deficient at ocean margins where upwelling does not take place, even if there is a substantial riverine input.

Using two testing methods, researchers analyzed mercury levels in the sediment of Lavaca Bay. Between 1966 and 1979, Lavaca Bay was contaminated with mercury from an Alcoa plant. The site was put on the EPA superfund list in March of 1994. Both interstitial pore water gradients and benthic flux chamber deployments showed that mercury deposition increased during dark periods at a rate higher than daylight periods. The exact reason for this is uncertain, but may be due to microbes that migrate relative to the amount of light, or an unidentified chemical process.

This paper presents an analysis of a series of laboratory measurements of horizontal velocity and suspended sediment concentration (arrayed vertically) at a number of locations across a simulated shallow water bar built in fine sands ([D.sub.50] = 95 [[micro]meter]) and subjected to irregular waves of varying significant wave height but with a constant spectral shape (JONSWAP spectrum). Near the bar crest the net suspended transport rates, integrated between the lowest measurement point and the water surface (measured zone), are dominated by the time-averaged (current-induced) transport resulting from undertow. Away from the bar crest the net suspended sediment transport in the measured zone resulting from high-frequency oscillatory currents is important (and dominant) and directed offshore everywhere. Comparison of the measured suspended transport rates and those derived from bed elevation changes over time reveals significant fluxes in the unmeasured zone near the bed. These are inferred as being driven by high-frequency oscillatory transport very close to the bed and are critical for understanding bar morphological changes. Finally, the laboratory results are compared with results from field experiments.

The article explores the usage of the in situ aggregate analysis camera system to research fine-grained suspended particles in some estuarine and shallow-water environments. The details of the still-photography system and examples of the results from aquatic environments are given.

Continuous water quality measurements of storm runoff into a single road inlet have been carried out at two experimental catchments, in Belgrade, Yugoslavia, and Lund, Sweden. Both sites were equipped with similar instrumentation for measurements of overland flow, turbidity, pH, conductivity, and temperature. The data were recorded at 10-s time intervals during rainfall events. To measure suspended solids concentration, turbidity meters were calibrated in conditions very similar to the real world. A detailed description of the field-measuring facilities used in the Belgrade catchment and the results of the measurements from both sites are presented. After detailed examination of possible errors in measurement, only the reliable data were used for statistical analysis. Event mean, extreme, and aggregated values were analyzed. The results indicate that the antecedent dry weather period length has only a minor effect upon road sediments wash-off, but it has an influence upon conductivity. The 'first-flush effect' of suspended solids appears only in a limited number of events. Cross-correlation coefficients of rainfall, overland flow, and water quality were calculated for each event, taking into account the time lag between observed characteristics. These coefficients showed that suspended solids loading rate is influenced by rainfall intensity and overland flow rate. The results presented in this paper have been used in development of the physically based wash-off model published by Deletic and coworkers.

Streamer sediment traps were used to measure the distribution of longshore sediment flux in the surf zone at 29 locations along the southeast coast of the United States and the Gulf coast of Florida. Measurements were conducted on both barred and nonbarred coasts under low-wave energy conditions. Results indicate that longshore sediment flux decreases logarithmically upward in the water column throughout the surf zone, and the rate of upward decrease is largest in the trough and smallest in the swash due to stronger mixing energy in the swash. Six types of cross-shore distribution patterns of longshore sediment transport (LST) were found. These six distribution patterns are controlled by nearshore morphology, breaker type, and energy dissipation pattern. For low-wave energy coasts, the swash (nonbarred coast) and inner surf (barred coast) zones contain significant contributions to the longshore sediment transport rate. The cross-shore distribution pattern of the longshore sediment transport rate along nonbarred coasts was well reproduced using energy-dissipation and shear-stress approaches developed mainly from laboratory studies.

The results of new experiments on bed load transport on steep longitudinal slopes are presented. The experiments were carried out in a large tilting duct with a fine sand ([d.sub.50] = 208 [[micro]meter]) covering the range of slope angles [Beta] of [+ or -] angle of repose for the sand [Phi], (32 [degrees]). Measurements included bed shear-stress, flow discharge, and the sediment pickup rate on slopes. The results suggest that existing theories for bed load transport on slopes are not adequate for all bed slopes and the new data are used to formulate a semiempirical relation that satisfactorily predicts the transport rate on horizontal as well as mild and steep slopes. The following are two important findings: (1) Correcting the threshold term (for slope) in the Meyer-Peter and Muller formula adequately describes the transport rate on positive slopes (elevation increasing in direction of flow) and on small negative slopes. On steeper negative slopes an extra correction term is required, although the value of [Beta]/[Phi], at which this term becomes necessary is a function of shear stress; and (2) the influence of slope vanishes at high shear stresses.

The colloid phase of suspended material in the Mississippi River appears to be capable of carrying a greater load of organic nitrogen and organic carbon than the suspended particulate phase. Samples from the river, which were taken a 16 different sites, were centrifuged and filtrated to enable the isolation of the two phases.

The utilization of resuspended material as a food source for sea scallops, Placopecten magellanicus, was investigated. Results of feeding experiments with sediments from Georges Bank showed that scallops utilized resuspended sediment organic matter of up to 40% efficiency. Settling rates indicated long residence time of potential food for scallops. Resuspension appeared to occur with frequency based on calculations with erosion threshold and current meter records.

Pyrite formation in the water column of the Pettaquamscutt River estuary is studied. It is shown that pyrite with framboidal morphology and ferrous monosulfides are found in the water column at depths ranging from just under the oxic-anoxic interface to the sediment-water interface. Pyrite framboids also form in columns with concentrations of dissolved sulfide and ferrous iron wherein bulk samples are undersaturated with respect to iron monosulfides and supersaturated with respect to pyrite.

Analytical theory is used to describe the tidal constituents generated in suspended sediment concentrations of clay, silt, and sand eroded by [M.sub.2] and [S.sub.2] tidal currents. The associated model involves only the fall velocity [W.sub.s], the vertical dispersion coefficient E (assumed constant), and water depth D. For [W.sub.s] > 10 E/D particles remain close to the bed, whereas for [W.sub.s] < 0.1 E/D particles are well mixed vertically. For [W.sub.s] > E/D, deposition occurs by advective settling at a rate approximating (1/2)[W.sub.s][C.sub.z=0] where [C.sub.z=0] is the concentration at the bed. Conversely for E [much greater than] D[W.sub.s] settlement is more dependent on the dispersion coefficient E. A deposition rate [Mathematical Expression Omitted]([Mathematical Expression Omitted] depth-averaged concentration) is derived by assuming an exponential decay rate [e.sup.[Alpha]t], with typical half-lives of 1 min to 2 h for sand and from 1 to 100 d for clay. In shelf seas, the suspended sediment concentration is likely to be determined by the silt-clay fraction with enhanced mean and MSf constituents compared to the associated diurnal and semidiurnal constituents. Opposition of the [M.sub.4] and M[S.sub.4] constituents at neap tide may significantly reduce the anticipated quarter-diurnal component of sediment concentrations.

Vegetated filter strips help reduce non-point source pollution from agricultural areas. Even though they are an accepted and highly promoted practice, little quantitative data exist on their effectiveness under Beld conditions. The objective of this research was to determine the amount of nutrients and sediment removed by natural and planted filters. This was achieved by collecting and analyzing runoff at field edges and at various locations in vegetated buffers. Total weight of sediment and nutrients in runoff from North Carolina agricultural fields showed that the grass and riparian filter strips studied reduced runoff load by 50 to 80%. Total sediment decrease through the filters was about 80% for both grass and riparian vegetation. The reduction in the chemical load depended on the nutrient and its form. Filters' reduced total P load by 50%, but 80% of the soluble P[O.sub..sub.4]-arriving at the field edge frequently passed through the filters. The filters retained 20 to 50% of the NH4 and approximately 50% of the total Kjeldahl N and N[O.sub..sub.3]. High-volume flows commonly overwhelmed both grass and riparian filters next to cultivated fields. Forested ephemeral channels had little vegetation and were effective sediment sinks during the dry season but were ineffective during large storm events because there was little resistance to flow. When possible, drainage ways should be designed to hold sediment and to disperse the discharge into a riparian area.

A numerical model that simulates the sediment transport due to plunging breaking waves has been developed. A plunging breaker is simulated by superimposing a jet on a nonbreaking wave. The hydrodynamics are described by applying a discrete vortex model based on the mixed Eulerian-Lagrangian description of the cloud-in-cell method. Rotation is introduced in the flow where the jet impinges on the surface and in the boundary layer along the bottom. A combined diffusion-convection procedure provides a Lagrangian description of the suspended sediment. The pickup and initial suspension event in the boundary layer is simulated by a diffusion process, while the transport in the outer flow domain is simulated by convection, using the flow field provided by the hydrodynamic module. The bed-load transport is calculated by a conventional formula that relates the transport rate to the Shields parameter. A simulation over a complex bottom topography is compared to the full-scale laboratory experiments performed by Dette and Uliczka in 1986. The calculated and measured time-averaged concentration profiles show good agreement both with respect to the overall concentration levels and the cross-shore distribution.

An empirical relation for the bed concentration of suspended sediment [c.sub.b] defined at a few grain diameters above the bed is developed. Its derivation is based on the experimental data sets of Guy et al. in 1966. The values of the near-bed concentration were obtained by first isolating the suspended load transport from the observed rates of total load transport by use of a bed-load formula. The suspended load was then equated to Einstein's formulation, which allowed the determination of [c.sub.b]. The influence of large concentrations of suspended sediment and of the reference level for [c.sub.b] on the calculated values of bed concentration has been analyzed. The proposed relation compares satisfactorily to values of near-bed concentration obtained from independent data sets. The procedure used to derive [c.sub.b] provides a simple method for the calculation of the total transport rate of noncohesive sediment.

In 1982 the U.S. Department of Agriculture estimated 1,926 million tons of soil was lost annually to water-borne cropland erosion (1). The impacts of this nonpoint source of water pollution [...]

Multiple-parameter magnetic measurements of sediment cores such as magnetic minerals deposited in lakes and oceans were used to obtain accurate global change data, used to construct base-line records. These records were used to interpret climactic changes and provided information for magnetic proxy recordings.

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.

The transport process of fine sands in combined current and wave conditions in a flume was studied. Two types of sediment material were used, a very fine sand with a median diameter of about 100 micrometer and a medium-fine sand with a diameter of 200 micrometer. The current velocities were varied in the range of 0.1-0.5 m/s (following and opposing the waves). Irregular waves with a single-topped spectrum and peak period of 2.5 s were generated. The significant wave height varied in the range of 0.075 m to 0.18 m. The water depth was about 0.5 m in all tests. Time-averaged fluid velocities were measured by an electromagnetic current meter. Time-averaged sediment concentrations were measured by a pump sampler. The transport rate was obtained by integration of the product of velocity and concentration over the dept. The generation of waves in following or opposing currents causes a decrease of the time-averaged velocities in the near-bed region. A larger wave height results in larger concentrations and in a more uniform distribution over the depth. The influence of the current direction on the concentration profile and the transport rate is negligible.

A quantitative theoretical analysis of the effect of porous aggregates on the transport of small suspended particles in ocean waters is presented. The theoretical basis for the analysis was derived from a previous study of particle deposition in biofilms and at the sediment-water interface. The results showed that flow through a sinking porous aggregate increases scavenging efficiency because it can increase the rate at which small particles collide with and stick to it. The results have implications for the vertical transport of trace elements and nutrients in the ocean.

Primary grain-size distribution is not severely affected when suspended sediment samples are filtered and then resuspended. Filtration is an especially useful separation method when sample concentrations are low and grain-size distributions must be maintained. Such filters as Nuclepore polycarbonate plastic membranes and Millipore cellulose membranes have pore clogging and disintegration problems but are effective in limiting grain-size distribution alterations.

The turbulence characteristics of sediment-laden flows in open channels are investigated using two-component laser-Doppler velocimetry. Suspensions of well-sorted sands with diameters ranging from 0.15 mm to 0.24 mm, flowing over nominally flat beds, both fixed and erodible, are studied in a tiltable, recirculating flume. Various conceptual models that have been proposed to explain the mean-field profiles are examined for consistency with respect to their implications for higher-order characteristics. No evidence is found to support either the traditional model, associated with a decrease in the von Karman constant, or the more recently proposed models based on simple analogies to slightly stably stratified wall-bounded flows. A model based on small-scale fluid-particle interaction is suggested as more promising.