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Dredging is the excavation of material from a water
environment. Possible reasons for dredging include improving
existing water features; reshaping land and water features to
alter drainage, navigability, and commercial use;
constructing dams, dikes, and other controls for streams and
shorelines; and recovering valuable mineral deposits or
marine life having commercial value. In all but a few
situations the excavation is undertaken by a specialist
floating plant, known as a <a
href="http://www.kedadredger.com/dredger/"
target="_self">dredger</a>. Dredging is carried out in many
different locations and for many different purposes, but the
main objectives are usually to recover material of value or
use, or to create a greater depth of water. Dredges have been
classified as suction or mechanical. Dredging has significant
environmental impacts: it can disturb marine sediments,
leading to both short- and long-term water pollution, destroy
important seabed ecosystems, and can release human-sourced
toxins captured in the sediment.
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In a "hopper dredger", the dredged materials
end up in a large onboard hold called a "hopper." A
suction hopper dredger is usually used for maintenance
dredging. A hopper dredge usually has doors in its bottom to
empty the dredged materials, but some dredges empty their
hoppers by splitting the two-halves of their hulls on large
hydraulic hinges. Either way, as the vessel dredges, excess
water in the dredged materials is spilled off as the heavier
solids settle to the bottom of the hopper. This excess water
is returned to the sea to reduce weight and increase the
amount of solid material (or slurry) that can be carried in
one load. When the hopper is filled with slurry, the dredger
stops dredging and goes to a dump site and empties its
hopper. Some hopper dredges are designed so they can also be
emptied from above using pumps if dump sites are unavailable
or if the dredge material is contaminated. Sometimes the
slurry of dredgings and water is pumped straight into pipes
which deposit it on nearby land. These pipes are also
commonly known as dredge hoses, too. There are a few
different types of dredge hoses that differ in terms of
working pressure, float-ability, armored or not etc. Suction
hoses, discharge armored hoses and self-floating hoses are
some of the popular types engineered for transporting and
discharging dredge materials. Some even had the pipes or
hoses customised to exact dredging needs etc. Other times, it
is pumped into barges (also called scows), which deposit it
elsewhere while the dredge continues its work, and it is also
a good <a href="http://www.kedadredger.com/gold-mining-
equipment/" target="_self">gold mining equipment</a>.<br/>A
number of vessels, notably in the UK and NW Europe de-water
the hopper to dry the cargo to enable it to be discharged
onto a quayside 'dry'. This is achieved principally
using self discharge bucket wheel, drag scraper or excavator
via conveyor systems. When contaminated (toxic) sediments are
to be removed, or large volume inland disposal sites are
unavailable, dredge slurries are reduced to dry solids via a
process known as dewatering. Current dewatering techniques
employ either centrifuges, geotube containers, large textile
based filters or polymer flocculant/congealant based
apparatus. In many projects, slurry dewatering is performed
in large inland settling pits, although this is becoming less
and less common as mechanical dewatering techniques continue
to improve. Similarly, many groups (most notable in east
Asia) are performing research towards utilizing dewatered
sediments for the production of concretes and construction
block, although the high organic content (in many cases) of
this material is a hindrance toward such ends.
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