Models for the vertical distribution of suspended sediment under waves and currents are compared with field observations. The models include a diffusion-based model, a convection-based model, and a combined convection-diffusion model. The field observations were carried out at Vilano Beach, Florida, in a water depth of approximately 3 to 4 m, with a median grain diameter of 0.14 mm. The rms wave height ranged from approximately 0.4 to 1.2 m. Under low waves the seabed was covered with very small ripples, and under the higher waves, sheet flow conditions were present. The diffusionbased model was found to best describe the observed data under high wave conditions, but the convection model was more accurate under low wave conditions. Over all conditions the combined model was the most accurate. These results are consistent with the different mechanisms for mixing suspended sediment over flat versus rippled beds. Introduction The suspension of sediment by waves and currents involves a series of processes by which sediment particles in the bed or very near the bed are entrained and transported up to higher levels by hydrodynamic forces [Bagnold, 1956]. A steady vertical distribution of particles in suspension is mainly the result of the balance between a net upward sediment flux resulting from hydrodynamic forces and downward settling of particles due to gravity. The upward sediment flux occurs on a variety of temporal and spatial scales. The dominant scales are determined by the flow conditions, the characteristics of the sediment, and the bottom topography. Many models for sediment transport employ gradient diffusion models to describe sediment flux by turbulent mixing. As a recent example, Wikramanayake [1993] suggested a suspended sediment model using a three-layer, time-invariant eddy viscosity, modified from Grant and Madsen [1979]. As an example of an alternative to gradient diffusion models, Nielsen [1992] suggested a convection model which incorporated coherent, structured motions of sediment. A good example of this type of structure is the dense sediment cloud found in vortices above a rippled bed. Nielsen also suggested a combined convection-diffusion model with a time-invariant, vertically uniform, eddy diffusivity profile to accommodate sediment mixing on both small and large scales. In the present study the mechanisms of sediment suspension under combined wave-current conditions are reviewed. We then review a pure diffusion model and a pure convection model for sand suspension under waves and currents. A combined convection-diffusion model is developed using a timeinvariant, vertically varying eddy diffusivity profile, along with a probability distribution function of sediment entrainment. All of the models are then compared to measured field data. Paper number 95JC03283. 0148-0227/96/95 J C-03283 $05.00 Review of Models The time rate of change of the suspended sediment concentration at a certain elevation is given by the following conservation equation, assuming that the horizontal gradients are neglig...

A series of field suction pile installation tests have been conducted inside the Onsan harbor located in southeastern Korea during the summer of 2001. The suction piles were made of steel, having inside diameters ranging from 0.5 meters to 2.5 meters and the length of five meters. The seafloor soil condition at the site is predominantly silty sand. Instrumentation includes the detailed measurement of the applied pressure vs. pile penetration and retrieval length relationships; the pile alignment during installation through a tiltmeter; and the pore water pressures both inside and outside the pile.