Comparison of field observations of the vertical distribution of suspended sand and its prediction by models

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 diffusion-based 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.