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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.

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.

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.

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.

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 laboratory study of sand transport by currents and waves provides useful information on current velocities, physical bed roughness, suspended sediment concentrations and sediment transport rates in the accompaniment of irregular waves. Some issues, however, are raised regarding equations and generalizations on bed roughness, apparent roughness and current profile. Specifically, the validity of equation 5 for wave-dominated flows is questioned. Likewise with the perceivable impact of wave-current angle theta on k(sub a)/k(sub s) and the method of approximating k(sub s).