Dredges
I
n general, dredges (also known as dredgers)
come in two basic forms: mechanical and hydraulic. Mechanical dredges work by mechanically digging or gathering sediment from
the bottom surface of a body of water typically through use of a bucket or clamshell.
Hydraulic dredges work by sucking up
a mixture of sediment and water (known as slurry) from the bottom surface and then
transferring the mixture through a pipeline to a desired location.
Dredges are used to move a wide variety of materials.
Some examples are human waste, trash, gravel, and gold.
Dredges help to keep many of our canals, ports, harbors, and marinas clean.
Dredges even help to restore beaches
and land lost due to erosion.
Hydraulic Dredges
Hydraulic Dredge Pump
A dredge pump is the heart of what makes a hydraulic dredge function.
A dredge pump creates the vacuum for sucking material from bodies of water and provides the
flow for transferring the material through a pipeline to its disposal location. For more pump information click here.
Cutter Suction Dredge
A cutter suction dredge typically uses a rotating cutter device to agitate and stir up material
on the bottom surface where it sucks up the mixture of sediment and water (known as slurry)
and transfers the mixture through a pipeline. A cutter suction dredge may use a set of spikes
(typically referred to as spuds) along with cable to maneuver while working. Other cutter suction
dredges may use cable entirely to maneuver or just spuds to maneuver such as a swinging ladder dredge
listed below. Most cutter suction dredges work by pivoting from side to side making an arc shaped
cutting path while working. For more cutter suction dredge information click here.
Swinging Ladder Dredge
A swinging ladder dredge is a type of cutter suction dredge that typically operates without cable.
Some swinging ladder dredges may operate in either conventional or swinging ladder mode depending
on machine setup. Once the dredge is maneuvered into position, the ladder is pivoted from side
to side making an arc shaped cutting path. For more swinging ladder dredge information click here.
Chain Ladder Dredge
A chain ladder dredge uses a rotating chain resembling a trencher chain to dig and agitate material
from the bottom surface where it sucks up the slurry and transfers the mixture through a pipeline.
Auger/Horizontal Dredge
An auger dredge uses an auger plighting to loosen material and push it toward the inlet of a suction
pipe. A horizontal dredge resembles an auger dredge but uses a wide rotating cutting device with teeth
in place of an auger to loosen material. Both types of dredges agitate material from the bottom surface
and transfer the mixture through a pipeline.
Bucket Wheel Dredge
A bucket wheel dredge uses a series of bottomless buckets attached to a wheel. The wheel rotates
allowing the buckets to dig at the bottom material while the material is sucked up and transferred
through a pipeline.
Plain Suction Dredge
A plain suction dredge utilizes an open pipe to suck material from the bottom surface without
the use of an agitating or mixing device. Plain suction dredges are generally used where the material is loose and an agitating device is not necessary to suck material from the bottom surface.
Hopper Dredge
A hopper dredge works by storing all the dredged material in its hopper and transporting the material to the disposal location.
Hopper dredges generally take the form of ships and typically use trailing suction arms to sweep along the bottom surface and suck up material to be transported.
Pumps supply the power to suck up the slurry mixture and dump it into the hopper while traveling slowly across the water surface.
Once the hopper is full the dredge then maneuvers to the disposal location to remove the material from the hopper.
Disposal may occur by a few different methods depending on the dredge. Some hopper dredges are equipped with bottom doors or passages in which the material may be directly dumped below the dredge by opening the passages.
Another method may be to mix the hopper material with water creating a slurry and pumping the mixture at a high pressure through a nozzle located at the end of the dredge.
This allows the dredge to spray the material on to land or the desired disposal location.
The other option is to connect the dredge to a pipeline and pump the slurry from the hopper through the pipeline to the disposal site.
Water Jets
Water jets consist of nozzles to direct high pressure water into jet streams targeted to
loosen material on the bottom surface to be sucked up and transferred through a pipeline.
Water jets may be used independently or in conjunction with other digging apparatuses
to create slurry.
Booster Pump
A booster pump may be necessary when pumping long distances or up high elevations.
One or several boosters may be placed in line with a dredge discharge line to assist
the dredge pump in achieving the distance or elevation needed to reach the disposal location.
Mechanical Dredges
Backhoe Dredge
A backhoe dredge works very similar to land based backhoes also known as excavators or
track-hoes. These machines use a set of mechanical arms with a bucket attached at the
end to dig material from the bottom surface and dump the material into a container or
on to a barge to be transported.
Grab/Clamshell Dredge
A grab/clamshell dredge uses a mechanical set of buckets or arms to dig or extract
material from the bottom surface.
Bucket-Line Dredge
A bucket dredge uses a series of buckets attached to a chain to mechanically scoop
and transfer material from the bottom surface to the top for extraction.
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