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{{short description|Excavation of sediment, usually under water}}
{{hatnote group|
{{Redirect|Dredge}}
{{Redirect-distinguish|Dredgers
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{{Use dmy dates|date=January 2020}}
{{EngvarB|date=July 2018}}
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'''Dredging''' is the [[Digging|excavation]] of material from a water environment. Possible reasons for dredging include improving existing [[Water feature|water features]]; reshaping land and water features to alter [[drainage]], [[navigability]], and commercial use; constructing [[dam]]s, [[Levee|dike]]s, 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 [[heavy machinery|plant]], known as a dredger.
Usually the main objectives of dredging is to recover material of value
Dredging
==Description==
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Ancient authors refer to harbour dredging. The seven arms of the [[Nile]] were channelled and wharfs built at the time of the pyramids (4000 BC), there was extensive harbour building in the eastern Mediterranean from 1000 BC and the disturbed sediment layers gives evidence of dredging. At [[Marseille]], dredging phases are recorded from the third century BC onwards, the most extensive during the first century AD. The remains of three dredging boats have been unearthed; they were abandoned at the bottom of the harbour during the first and second centuries AD.<ref name="MMC">{{cite web |last1=Morhange |first1=Christophe |last2=Marriner |first2=Nick |last3=Carayon |first3=Nicolas |title=The eco-history of ancient Mediterranean harbours |url=https://www.ancientportsantiques.com/wp-content/uploads/Documents/AUTHORS/Morhange-PublGenerales/Morhange2016-HistoryPorts.pdf|access-date=1 July 2018}}</ref>
The [[Banū Mūsā brothers|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. The grab they described was used to extract objects from underwater, and recover objects from the beds of streams.<ref name=Hill-21>{{citation|title=The book of ingenious devices (Kitāb al-ḥiyal)|author=[[Banu Musa]]
During the renaissance [[Leonardo da Vinci]] drew a design for a drag dredger.
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===Suction dredgers===
[[Image:Pogłębiarka „Sawa”, głowica, Wisła, Saska Kępa, Warszawa 3.jpg|thumb|The [[dredge drag head]] of a suction dredge [[barge]] on the [[Vistula River]] in [[Warsaw, Poland]]]]
[[File:Sudging dredger Tuk87-47-10.jpg|thumb|sudging dredger in the [[Beaufort Sea]] used to build artificial islands for oil prospection]]
[[File:2022-10-06 01 Dredger PROVINCIA DE EL ORO NO I, III & IV.jpg|thumb|Cutter-suction dredger, ''Provincia de el Oro No 1'', in Puerto Bolivar, Ecuador]]
[[Image:Geopotes 14.jpg|thumb|The ''Geopotes 14'' lifting its boom on a canal in The Netherlands. (''gēopotēs'' is Greek for "that which drinks earth")]]
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When the hoppers are full, the TSHD sails to a disposal area and either dumps the material through doors in the hull or pumps the material out of the hoppers. Some dredges also self-offload using drag buckets and conveyors.{{citation needed|date=July 2018}}
{{asof|2008}} the largest trailing suction hopper dredgers in the world were [[Jan De Nul]]'s ''Cristobal Colon'' (launched 4 July 2008<ref>{{cite web|url=http://www.sandandgravel.com/news/article.asp?v1=11114 |title=Jan de Nul's mega trailer Cristóbal Colón launched - Dredging News Online |publisher=Sandandgravel.com |date=7 July 2008 |access-date=14 June 2013}}</ref>) and her sister ship ''Leiv Eriksson'' (launched 4 September 2009<ref>{{cite web|url=http://www.sandandgravel.com/news/article.asp?v1=11221 |title=Keel-laying ceremony for Jan de Nul's Leiv Eiriksson held - Dredging News Online |publisher=Sandandgravel.com |date=1 September 2008 |access-date=14 June 2013}}</ref>). Main design
====Cutter-suction====
A cutter-suction dredger's (CSD) suction tube has a cutting mechanism at the suction inlet. The cutting mechanism loosens the bed material and transports it to the suction mouth. The dredged material is usually sucked up by a wear-resistant centrifugal pump and discharged either through a pipe line or to a barge. Cutter-suction dredgers are most often used in geological areas consisting of hard surface materials (for example gravel deposits or surface bedrock) where a standard suction dredger would be ineffective. They can, if sufficiently powerful, be used instead of underwater blasting.<ref>{{cite web | url=https://www.marinelog.com/index.php?option=com_k2&view=item&id=25244:deme-orders-worlds-most-powerful-cutter-suction-dredge&Itemid=257 | title=DEME orders world's most powerful cutter suction dredge | publisher=Marine Log | date=1 March 2017 | access-date=13 November 2018}}</ref>
As of
====Auger suction====
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====Air-lift====
An [[Airlift (dredging device)|airlift]] is a type of small suction dredge. It is sometimes used like other dredges. At other times, an airlift is handheld underwater by a [[underwater diving|diver]].<ref name=RRR4672>{{cite book |author=Robbins, R |chapter=USAP Surface-Supplied Diving |editor=Lang, MA |editor2=Smith, NE |title=Proceedings of Advanced Scientific Diving Workshop |publisher=
===Mechanical dredgers ===
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====Krabbelaar====
This is an early type of dredger which was formerly used in shallow water in the Netherlands. It was a flat-bottomed boat with spikes sticking out of its bottom. As tide current pulled the boat, the spikes scraped seabed material loose, and the tide current washed the material away, hopefully to deeper water. ''Krabbelaar'' is the Dutch word for "scratcher".<ref>https://www.researchgate.net/publication/360967741_Sediment_deficit_and_morphological_change_of_the_Rhine-Meuse_river_mouth_attributed_to_multi-millennial_anthropogenic_impacts#pf7</ref>
====Water injection====
<!--How to classify?-->
A water injection dredger uses a small jet to inject water under low pressure (to prevent the sediment from exploding into the surrounding waters) into the seabed to bring the sediment in suspension, which then becomes a [[turbidity current]], which flows away down slope, is moved by a second burst of water from the WID or is carried away in natural currents. Water injection results in a lot of sediment in the water which makes measurement with most hydrographic equipment (for instance: singlebeam echosounders) difficult.
{{Further|Dredge valve}}
====Pneumatic====
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{{main|Fishing dredge}}[[File:Dedge haul including live clams and empty shells.jpg|thumb|Dredge haul including live clams and empty shells]]
Fishing dredges are used to collect various species of [[clam]]s, [[scallop]]s, [[oyster]]s or [[mussel]]s from the seabed. Some dredges are also designed to catch crabs, sea urchins, sea cucumbers, and conch. These dredges have the form of a scoop made of chain mesh, and are towed by a [[fishing boat]]. Clam-specific dredges can utilize hydraulic injection to target deeper into the sand.<ref>{{Cite web|url=http://safinacenter.org/2015/05/fishing-gear-101-dredges-the-bottom-scrapers/|title=Fishing Gear 101: Dredges – The Bottom Scrapers
===Notable individual dredgers===
{{main|:Category:Dredgers}}
[[File:Dredger near the Dumbarton Bridge in California.JPG|thumb|[[Mallard II]] near the [[Dumbarton Bridge (California)|Dumbarton Bridge]] in 2021]]
As of June 2018, the largest dredger in Asia is
===Dredge monitoring software===
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==Environmental impacts==
{{Globalize section|date=January 2023}}
Dredging can
Dredging can have numerous significant impacts on the environment, including the following:
* Release of toxic chemicals (including [[heavy metal (chemistry)|heavy metals]] and [[Polychlorinated biphenyls|PCB]]) from bottom [[sediment]]s into the [[water column]].<ref name="Bridges, T S. 2010">Bridges, T S., Gustavson, K. E., Schroeder, P., Ells, S. J., & Hayes, D. (2010). Dredging processes and remedy effectiveness: Relationship to the 4 Rs of environmental dredging. Integrated Environmental Assessment and Management, 6 (4), 619-630.</ref>
* Short term increases in [[turbidity]], which can affect aquatic [[species]] [[metabolism]] and interfere with [[spawn (biology)|spawning]].<ref name="Brodie"/> Suction dredging activity is allowed only during non-spawning time frames set by fish and game (in-water work periods).<ref>{{Cite web|url=http://www.ukmarinesac.org.uk/activities/ports/ph5_3_2.htm|title=Timing of dredging and disposal as a means of minimising maintenance dredging impacts|website=www.ukmarinesac.org.uk|access-date=2019-09-22}}{{Dead link|date=August 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>▼
▲* Short term increases in [[turbidity]], which can affect aquatic [[species]] [[metabolism]] and interfere with [[spawn (biology)|spawning]].<ref name="Brodie"/> Suction dredging activity is allowed only during non-spawning time frames set by fish and game (in-water work periods).<ref>{{Cite web|url=http://www.ukmarinesac.org.uk/activities/ports/ph5_3_2.htm|title=Timing of dredging and disposal as a means of minimising maintenance dredging impacts|website=www.ukmarinesac.org.uk|access-date=2019-09-22}}</ref>
* Secondary impacts to [[marsh]] productivity from [[sedimentation]]<ref name="fondriest.com">{{Cite web|url=https://www.fondriest.com/environmental-measurements/environmental-monitoring-applications/monitoring-turbidity-at-dredging-sites/|title=Monitoring Turbidity at Dredging Sites|website=Environmental Measurement Systems|language=en-US|access-date=2019-09-22}}</ref> and general [[Chemistry of wetland dredging|changes in wetland chemistry after dredging]].
* Tertiary impacts to [[bird|avifauna]] which may [[prey]] upon contaminated aquatic organisms.<ref name="fondriest.com"/>
* Secondary impacts to aquatic and benthic organisms' [[metabolism]] and mortality<ref>{{Cite news|url=https://www.theguardian.com/environment/2013/dec/11/the-facts-about-dredging|title=The facts about dredging|last=Milman|first=Oliver|date=11 December 2013|work=The Guardian|access-date=2019-09-21|language=en-GB|issn=0261-3077}}</ref>
* Possible contamination of dredge spoils sites<ref name="Bridges, T S. 2010"/><ref>{{Cite web|url=https://www.brisbanetimes.com.au/national/queensland/inquiry-to-probe-gladstone-harbours-leaking-bund-wall-20140107-30fnp.html|title=Inquiry to probe Gladstone Harbour's leaking bund wall|last=Moore|first=Tony|date=7 January 2014|website=Brisbane Times|language=en|access-date=2019-09-22}}</ref>
* Changes to the topography by
* Releases toxic compound [[Tributyltin]], a
The nature of dredging operations and possible environmental impacts
==Major dredging companies==
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Notable dredging companies in South Asia
* [[Dredging Corporation of India]]
* [[Adani Ports & SEZ]]<ref>{{cite web|url=https://www.adaniports.com/Dredging|title=Adani Dredging}}</ref> (India)
* [[Maldives Transport and Contracting Company]] (Maldives)
==Images==
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Image:Barge on Neva river.jpg|Dredge ship with barges on [[Neva River|Neva bay]] in [[Saint Petersburg]], Russia
Image:Dredge ship top view - 01.JPG|Top view of a suction dredger on the [[Nandu River]], [[Hainan]], China
Image:Cutterhead of dredge Bill Holman Louisville Kentucky USA Ohio River mile 607 July 2002 file a2g092.jpg|Cutterhead of dredge ''Bill Holman'', [[Louisville, Kentucky]], [[United States
File:Xcentric Ripper XR120 in a dredging work.png|Xcentric Ripper XR120 is a large jackup leg backhoe dredger
</gallery>
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{{Industries}}
{{ModernMerchantShipTypes}}
{{Authority control}}
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