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Dredging is the removal of earthen materials, including rock or
coral, from under water. It increases the size of the waterway
and provides construction materials for land-based projects. It
also improves logistics. The wider, deeper shipping channel
provides easier passage of vessels with deep draft. The deeper
the draft of a vessel, the more tonnage it can carry. If few
ships are available for logistics, then dredging can make these
ships more efficient.

Material removed during dredging is often a naturally-occurring
construction material. In military operations, natural materials
make up for scarce resources. Typically, sand is available along
the coast and in most rivers. Care must be taken to avoid clay
or fine-grained sediments.

Two primary types of dredging occur: mechanical and hydraulic.

Mechanical equipment dredges easily with a clam shell, shovel,
backhoe, or other device that scoops the material up. A simple
type of mechanical dredge is a land crane, equipped with a
suitable bucket mounted on a barge. This dredge needs barges or
scows to move the material from the dredging site to the
disposal site.

The hydraulic dredge uses water to remove and transport the
material. This system has a pump for moving the water. The pump
creates a vacuum or a pressure head, which moves water rapidly
through the pipe. This system always has at least three
components: dredging device, pump, and discharge system. There
are many common hydraulic dredging systems--hopper dredges,
sidecast dredges, cutterhead dredges, and dustpan dredges.

[Summary provided by the Globe Security Organization]