MODEL RESULTS

The time histories of TSS concentrations at the FPRC site with a bucket release rate of 1.5 percent

at various depths in the water column are shown in Figure 5. Depths are resolved into 2-m- (6-ft-)

thick layers. The dredging started at hour 0 and took approximately one tidal cycle to reach a quasi

steady state. The concentrations vary somewhat from one tidal cycle to the next because of the

added random diffusion in the model. There is a complex structure that varies over the water column.

At the surface (0-2 m (0-6 ft)), the concentration peaks every half tidal cycle in response to the TSS

levels building up during the time of slack water. However, the concentrations are relatively low,

e.g., less than 20 mg/L. Lower in the water column the twice-per-tidal-cycle peaks increase in

magnitude, reaching 34 mg/L at a depth of 6-8 m (20-26 ft). Below this depth, maximum

concentrations rise to 54 mg/L at a depth of 10-12 m (33-39 ft). The peak concentrations occur at

maximum ebb when the material previously released on the flooding tide returns to the source

location and adds significantly to the source-induced concentration. This does not occur during the

flooding portion of the tide cycle because the greater extent of the plume during ebb (see Figure 4)

does not result in material moving back over the source.