Dredging

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.

Usually the main objectives of dredging is to recover material of value, or to create a greater depth of water.

[1] Dredging systems can either be shore-based, brought to a location based on barges, or built into purpose-built vessels.

Dredging can have environmental impacts: it can disturb marine sediments, creating dredge plumes which can lead to both short- and long-term water pollution, damage or destroy seabed ecosystems, and release legacy human-sourced toxins captured in the sediment.

These environmental impacts can reduce marine wildlife populations, contaminate sources of drinking water, and interrupt economic activities such as fishing.

Dredging can be done to recover materials of commercial value; these may be high value minerals or sediments such as sand and gravel that are used by the construction industry.

[4] The Banu Musa brothers during the Muslim Golden Age in while working at the Bayt-Al-Hikmah (house of wisdom) in Baghdad, designed an original invention in their book named Book of Ingenious Devices, a grab machine that does not appear in any earlier Greek works.

Dredging machines have been used during the construction of the Suez Canal from the late 1800s to present day expansions and maintenance.

[6] The completion of the Panama Canal in 1914, the most expensive U.S. engineering project at the time, relied extensively on dredging.

Main design specifications for the Cristobal Colon and the Leiv Eriksson are: 46,000 cubic metre hopper and a design dredging depth of 155 m.[13] Next largest is HAM 318 (Van Oord) with its 37,293 cubic metre hopper and a maximum dredging depth of 101 m. A cutter-suction dredger's (CSD) suction tube has a cutting mechanism at the suction inlet.

The dredged material is usually sucked up by a wear-resistant centrifugal pump and discharged either through a pipe line or to a barge.

The six largest backhoe dredgers in the world are currently the Vitruvius, the Mimar Sinan, Postnik Yakovlev (Jan De Nul), the Samson (DEME), the Simson and the Goliath (Van Oord).

[citation needed] Some of these are any of the above types of dredger, which can operate normally, or by extending legs, also known as spuds, so it stands on the seabed with its hull out of the water.

Oliver Evans (1755–1819) in 1804 invented the Oruktor Amphibolos, an amphibious dredger which was America's first steam-powered road vehicle.

[27] The Mallard II, a clamshell dredger that maintains levees in San Francisco Bay, has operated continuously since being built in 1936.

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.

[citation needed] 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.

[citation needed] 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.

[citation needed] The proper management of contaminated sediments is a modern-day issue of significant concern.

Because of a variety of maintenance activities, thousands of tonnes of contaminated sediment are dredged worldwide from commercial ports and other aquatic areas at high level of industrialization.

A variety of processes has been proposed and tested at different scales of application (technologies for environmental remediation).

[41] Due to potential environmental impacts, dredging is often restricted to licensed areas, with vessel activity monitored closely using automatic GPS systems.