Resuspension of Estuarial Fine Sediments by Tethered Wings

Abstract

A theory and companion experiment are given which describe the resuspension of fine sediments by the action of wings moored near the bottom of an estuary. Calculations by matched inner and outer image expansions indicate that the vortex system of a wing can exert two distinct effects on estuarial sedimentation: (1) it can elevate the shear stresses in the neighborhood of the wing by a sufficient amount to induce erosion of partially consolidated layers of the bottom; and, (2) it can promote vertical transport to either enhance or inhibit downstream deposition. Deposition in the wake trail is found to be dependent upon the direction of the lift force generated by the wing. Wings which produce a downward lift force deplete the region adjacent to the bottom of suspended sediment and thereby diminish downstream deposition. Conversely, wings generating an upward lift force increase the density of suspended sediment near the bottom, thus increasing the rate of downstream deposition. Optimal wing configurations are formulated which maximize erosion and minimize deposition. Density measurements behind prototype wings are consistent with these theoretical expectations. Short term changes in bottom contours are in general agreement with predicted erosion in the inner domain, and with diminished accretion in the outer domain.