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The suspended sediments in water flushing on and off an estuarine tidal flat have been examined for relative changes in concentration as a function of wind speed, local wave conditions, salinity, temperature, and tidal currents. The shallow water was sampled by "plumbing" the upper 20 cm of the sediment surface with buried plastic pipes and pumping water samples from an orthogonally spaced matrix of intake valves positioned across the tidal flat to permit observation of "natural" sedimentary processes. The sediment interface has been modified over parts of the matrix by introducing roughness elements in the form of small closely spaced stakes and stabilizers, such as eel grass.
The data show a decrease in sediment concentration as the water floods over the tidal flat primarily as a function of dilution by more marine waters. As high slack tide is reached, sediment deposition occurs when wave heights are at a minimum. This deposition appears to continue even on the ebbing tide until water depths are extremely shallow, at which time a minor resuspension usually is noted. In contrast, if a slight "surface chop" develops, the falling water maintains the sediment in suspension and flushes it out on the ebbing tide.
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