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calculations. First, settling speeds in the vicinity of the turbidity maximum varied by an order of magnitude, in these plots between approximately 0.25 to 2.5 mm sec-1, and the upper Bay appeared to be a very efficient trap for particles that settle in this range. Second, settling velocity was most clearly correlated with distributions of D50, though not perfectly because of its dependence on bulk density. Third, the highest settling speeds tended to occur at mid-depth or near-bottom and as the tide was decelerating toward slack.

Figure 10.9 summarizes the relationships between settling velocity and floc diameter derived from the VISTA, using data collected at the times and depths indicated by the + symbols in Figure 10.7 and Figure 10.8b. The regression equations noted in each panel are of the form of Equation (10.3), and are indicated by the heavy solid lines on each plot. Table 10.2 summarizes the VISTA data presented in this figure, and presents the fractal parameters derived from the regressions. Both mean settling velocity and floc size tended to increase with depth, significantly so for settling velocity (from 0.66 to 2.26 mm sec-1) and marginally so for floc size (from 170 to 294 ixm). Average bulk density derived from each pair of settling velocities and sizes remained nearly constant with depth at 1.05 to 1.06, similar to the LISST estimates in Figure 10.6. The fractal dimensions of the surface, middle, and bottom distributions were not significantly different, averaging 2.02. However, the reference particle size of the bottom regression (16 ^m) was much greater than those of the middle (3.2 ^m) and top (3.9 ^m) regressions. Clearly, though there is significant scatter, a fractal description of the relationship between particle size and settling d (m)

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