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Dredging Research Program Understanding and Interpreting Seabed Drifter (SBD) Data

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Final rept.

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Seabed drifters SBDs are inexpensive, current-following drogues widely used in oceanographic studies. This report gives new methods for interpreting SBD results, especially for coastal applications. The general forces responsible for SBD movement are described and contrasted with those responsible for moving sediment on the sea floor. Specific recommendations include that a prerelease desk study be done to rank the transport at the site of any contemplated SBD application. This ranking will help indicate how useful SBDs may be and provide the basis for selecting an experimental design appropriate for the site. A typical SBD design might include repeated releases of batches of SBDs from a number of stations during varying conditions. Recovery patterns will indicate the relative importance of spatial and temporal variations in the currents. Proper SBD interpretations include assessment of potential human and natural influences on the recovery patterns. Natural dispersion can be divided into a mean or deterministic component and a diffusive or random component. A methodology is given for quantifying these components. It is shown that the mean displacement of materials suspended in bottom water can exceed 100 km in a few days during a frontal passage or storm. It is important to understand large variations in the mean and random components of displacement to improve predictions of the likely fate of bottom materials. Better predictions can help maximize beneficial uses for dredged materials and minimize adverse effects from accidental ocean discharges that may be unrelated to dredging. Continued Bottom currents, Drogues, Onshore transport, Coastal Alabama, Fate of dredged materials, SBDSeabed Drifter, Dispersion Longshore currents, Tracer

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  • Physical and Dynamic Oceanography

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