Dredged sediment or sludge dewatering by vacuum bag method preferably includes a foundation, at least one sediment enclosure, a porous media spacer, an air impermeable sheet, and a vacuum source. The foundation may be air permeable or impermeable. The sediment enclosure is filled with sediment or sludge. The porous media spacer is placed against at least one perimeter surface of the sediment enclosure. At least one drain tube may be used to drain water. The air impermeable sheet is placed over the at least one sediment enclosure and the porous media spacer and the perimeter is sealed to an impermeable foundation. A vacuum is applied to the porous media spacer to remove water. A second embodiment uses a second air impermeable sheet. A third embodiment uses a barge. A fourth embodiment discloses a composite vacuum bag. A fifth embodiment discloses the composite vacuum bag with inflatable flotation.