Dredging Process Equipment and Techniques

Framework for Dredged Material Management

May 2004

and others. However, for the purposes of this document, dredging is actually

accomplished basically by only two mechanisms:

Hydraulic dredging--Removal of loosely compacted materials by cutterheads,

dustpans, hoppers, hydraulic pipeline plain suction, and sidecasters, usually

for maintenance dredging projects.

Mechanical dredging--Removal of loose or hard, compacted materials by

clamshell, dipper, or ladder dredges, either for maintenance or new-work

projects.

Hydraulic dredges remove and transport sediment in liquid slurry form. They are

usually barge mounted and carry diesel or electric-powered centrifugal pumps with

discharge pipes ranging from 6 to 48 in. in diameter. The pump produces a vacuum on its

intake side, and atmospheric pressure forces water and sediments through the suction

pipe. The slurry is transported by pipeline to a disposal area. Hopper dredges are included

in the category of hydraulic dredges for this report even though the dredged material is

simply pumped into the self-contained hopper on the dredge rather than through a

pipeline. It is often advantageous to overflow hopper dredges to increase the load;

however, this may not always be acceptable due to water quality concerns near the

dredging site.

Mechanical dredges remove bottom sediment through the direct application of

mechanical force to dislodge and excavate the material at almost in situ densities.

Backhoe, bucket (such as clamshell, orange-peel, and dragline), bucket ladder, bucket

wheel, and dipper dredges are types of mechanical dredges. Sediments excavated with a

mechanical dredge are generally placed into a barge or scow for transportation to the

disposal site.

Selection of dredging equipment and method used to perform the dredging will

depend on the following factors:

Physical characteristics of material to be dredged.

Quantities of material to be dredged.

Dredging depth.

Distance to disposal area.

Physical environment of the dredging and disposal areas.

Contamination level of sediments.

Method of disposal.

Production required.

Type of dredges available.

Cost.

More detailed descriptions of dredging equipment and dredging processes are

available in Engineer Manuals (USACE 1983 and USACE in preparation), Houston

(1970), and Turner (1984).