Design of fine-grained dredged material sedimentation basins.
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Sedimentation is an important process in the disposal of dredged material generated from navigable waterways in the United States. The sedimentation basins used in this disposal process are different from those used in water and wastewater treatment in that the dredged material basins must provide for sedimentation to achieve acceptable effluent water quality while providing storage volume for several years of material dredged from the local waterways. This paper presents a methodology for designing fine-grained dredged material sedimentation basins. This methodology can also be used for designing sedimentation basins for other slurries having high suspended solids levels. Settling tests performed in an 8-inch diameter column were found to be satisfactory for defining dredged material settling behavior. Settling behavior in the freshwater environment was best described by a flocculent settling test, while behavior in a saltwater environment was best described by a zone settling test. The same settling columns were used for both tests with only minor procedural changes. Procedures are presented for designing new containment areas for suspended solids retention and for evaluating the suspended solids retention potential of existing containment areas during planned disposal activities. Dye tracer studies indicated that a correction factor of about 2.25 should be applied to design area and detention times to compensate for the deviation from ideal or plug flow conditions.