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FIGURE 10.11 Large flocs remained intact during erosion of this core collected in the Upper Chesapeake Bay in May 2001. This photo was taken during an intermediate shear stress step of an erosion experiment, at an applied stress of approximately 0.15 Pa. The core tube is 10 cm in diameter.

and TSS.62 However, there is no apparent relationship between settling velocity and particle concentration in Figure 10.10a; very high settling speeds occurred at relatively low concentrations, and relatively low speeds occurred at high concentrations. There is, however, a reasonable correlation between settling concentration (defined as all material collected before the last bottom withdrawal sample) and nonsettling concentration. In particular, the maximum settling concentration seems to be approximately five times the nonsettling concentration. This is consistent with either flocculation of the nonsettling population to form the settling population, or resuspension of large flocs and their consequent disaggregation into the nonsettling population, or both.

Figure 10.11 is a photograph taken during an erosion experiment on a core collected in upper Chesapeake Bay in May 2001, at an intermediate applied shear stress. This photograph confirms that direct resuspension of large flocs occurs from the surface of the sediment bed. The diameter of the core tube is 10 cm, such that the visible flocs collecting near the center of the core and resuspending upward are at least several hundred micrometers in size. Visual observations of this and many similar erosion experiments have indicated that these flocs move initially as bedload, followed by resuspension at slightly higher stresses.

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