Measurements of Suspended Sediment Transport: Prototype Shorefaces

by Brian Greenwood, Univ of Toronto, Toronto, Canada,
Philip D. Osborne, Univ of Toronto, Toronto, Canada,
Anthony J. Bowen, Univ of Toronto, Toronto, Canada,

Document Type: Proceeding Paper

Part of: Coastal Sediments


Field measurements of local time-varying suspended sediment flux were obtained using rapid response velocity and sediment concentration sensors at a number of elevations under shoaling and breaking waves from similar water depths on both barred and non-barred shorefaces. Co-spectral analyses of velocity and concentration reveal that the net oscillatory transport across shore is dependant upon the relative contributions from: (i) wind waves (including swell) and (ii) low frequency waves (group-forced bound long waves). Time-averaged mean currents are invariably directed offshore (undertows) and increase in magnitude as waves break; coupled with increases in the average sediment concentration, this can result in sediment flux dominated by the mean transport. The overall transport balance (spatially and temporally) depends upon the relative contribution of each distinct transport component. The wind wave component is directed pedominantly onshore under the skewed shoaling waves; reversals can occur in response to bedform changes and the presence or absence of well defined separation vortices. The net transport can exhibit a distinct vertical structure reflecting changes in the contributions of opposing transport components at each elevation.

Subject Headings: Wave velocity | Suspended sediment | Sediment transport | Long waves | Wave measurement | Wave shoaling | Wind waves | Breaking waves

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