A Field Study of Fluid Mud Dredged Material. Its Physical Nature and Dispersal.

摘要

Open-water disposal of dense suspensions of fluid mud with concentrations of 10 to 480 g/1 was studied at field sites in Mobile Bay, Alabama, and the James River, Virginia. The study aimed to determine the significance of fluid mud in dispersal of dredged material and in generation of turbidity. The bulk of the dredged material, more than 99 percent at the Mobile Bay site was dispersed in the form of fluid mud near the bottom, whereas less than 1 percent was dispersed through the water column. As suspended solids flocculate and settle, they contribute to the fluid mud. In turn, fluid mud resists resuspension and reduces turbidity. Disposal created a deposit that spread over an area 5 to 13 times the dredged area in the channel. Disposal raised the bed, forming dense layers in mounds 0.8 to 2.2 m high having slopes 1:125 to 1:2000. Broad spreading at the Mobile Bay site was associated with a high discharge rate over a short period, a low discharge angle, and muds with high plastic and liquid limits. Mounding at the James River site was associated with a moderate discharge rate over a long period, a vertically oriented discharge configuration, and muds with a moderate plastic limit and a relatively low liquid limit. After disposal, the fluid mud consolidated, bulk density increased, and slopes decreased. Height and volume of the James River mound decreased about 50 percent in a year. More field investigations of the movement of fluid mud are needed for a detailed understanding of its dynamics. (Author)