Dredging: Difference between revisions

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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.

Dredging is carried out in many different locations and for many different purposes, butUsually the main objectives areof usuallydredging is to recover material of value or use, or to create a greater depth of water.<ref name="About">{{cite web |title=EuDA - About dredging - Dredging |url=https://www.european-dredging.eu/Dredging |website=www.european-dredging.eu |access-date=3 July 2018 |language=en}}</ref> DredgesDredging havesystems beencan classifiedeither asbe suctionshore-based, brought to a location based on [[Barge|barges]], or mechanical.<refbuilt name="About"into />purpose-built vessels.

Dredging hascan significanthave environmental impacts: it can disturb [[Marine sediment|marine sediments]], leading to both short- and long-term [[water pollution]], destroydamage importantor destroy [[Marine ecosystem|seabed ecosystems]], and can release [[Legacy pollution|legacy human-sourced toxins]] captured in the sediment. These environmental impacts can reduce marine wildlife populations in some cases, contaminate sources of drinking water and interrupt economic activities such as fishing.

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 Brothersbrothers ]]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‘[[Book of ingeniousIngenious devices’Devices]]’, Aa grab machine that 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]] (authors), |translator=[[Donald Routledge Hill]] (translator)|publisher=[[Springer Science+Business Media|Springer]]|year=1979|isbn=90-277-0833-9|page=21}}</ref>

{{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 specsspecifications for the ''Cristobal Colon'' and the '' Leiv Eriksson'' are: 46,000&nbsp;cubic metre hopper and a design dredging depth of 155&nbsp;m.<ref>{{cite web|url=http://www.jandenul.com |title=Jan De Nul Group |publisher=Jandenul.com |date=7 June 2013 |access-date=14 June 2013}}</ref> Next largest is ''HAM 318'' ([[Van Oord]]) with its 37,293&nbsp;cubic metre hopper and a maximum dredging depth of 101&nbsp;m.

As of 20182024, the most powerful cutter-suction dredger in the world is [[DEME]]'s [[Spartacus (ship)|''Spartacus'']], which is scheduled to enterentered service in 20192021.<ref>{{cite web | url=https://www.bairdmaritimedeme-group.com/work-boat-worldnews/marinedeme-projectstakes-world/1245delivery-constructionspartacus-ofmost-worldpowerful-sand-mostinnovative-powerfulcutter-csdsuction-startsdredger-with-keelworld | title=KeelDEME layingTakes signals startDelivery of world'sSpartacus' most– powerfulThe CSDMost |Powerful publisher=Bairdand MaritimeInnovative |Cutter date=21Suction DecemberDredger 2017in the World | access-date=134 NovemberAugust 20182021}}</ref>

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= Smithsonian Institution |location=Washington, DC |year=2006 |chapter-url=http://archive.rubicon-foundation.org/4672 |access-date=5 April 2013 |archive-date=26 May 2014 |archive-url=https://web.archive.org/web/20140526013827/http://archive.rubicon-foundation.org/xmlui/handle/123456789/4672 |url-status=dead }}</ref> It works by blowing air into the pipe, and that air, being lighter than water, rises inside the pipe, dragging water with it.

The excavator dredge attachment uses the characteristics of cutter-suction dredgers, consisting of cutter heads and a suction pump for transferring material. These hydraulic attachments mount onto the boom arm of an excavator allowing an operator to maneuver the attachment along the shoreline and in shallow water for dredging.<ref>{{Cite web|title=Excavator Dredge Pumps|url=https://www.daepumps.com/products/slurry-pumps/dredge-pumps/excavator-dredge-pumps/|access-date=2020-09-25|website=DAE Pumps|language=en-US}}</ref>

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>

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 |author=Kristjan F. Olgeirsson |date=19 May 2015 |website=The Safina Center|language=en-US|access-date=2019-09-21}}{{Dead link|date=August 2023 |bot=InternetArchiveBot |fix-attempted=yes }}{{clarify|reason=archived copies of this url have a different author|date=October 2020}}</ref> Dredging can be destructive to the seabed and some scallop dredging has been replaced by collecting via [[scuba diving]].<ref name=SPUMS1991>{{cite journal |author=Walker, Margaret |title=What price Tasmanian scallops? A report of morbidity and mortality associated with the scallop diving season in Tasmania 1990. |journal=South Pacific Underwater Medicine Society Journal |year=1991 |volume=21 |issue=1 |url=http://archive.rubicon-foundation.org/9414 |access-date=16 July 2013 |archive-date=20 October 2013 |archive-url=https://web.archive.org/web/20131020041442/http://archive.rubicon-foundation.org/xmlui/handle/123456789/9414 |url-status=usurped }}</ref>

As of June 2018, the largest dredger in Asia is "''[[{{MV |Tian Kun Hao]]''"}}, a {{convert|140 metres|m|adj=on}} long dredger constructed in China, with a capacity of 6,000 cubic meters per {{convert|6000|m3/hour}}.<ref name="xin">{{cite news |title=Asia's largest dredging vessel completes first sea trial |url=http://www.xinhuanet.com/english/2018-06/12/c_137249426_2.htm |archive-url=https://web.archive.org/web/20180613111953/http://www.xinhuanet.com/english/2018-06/12/c_137249426_2.htm |url-status=dead |archive-date=13 June 2018 |access-date=13 June 2018 |publisher=Xinhua |date=12 June 2018}}</ref> An even larger dredger, retired in 1980, was the U.S. Army Corps of Engineers ''[[{{ship|USAV |Essayons (|1949 ship)|Essayons]]''2}}, which was {{Convert|525.17|ft|m}} long.<ref>{{Cite book|url=http://hdl.handle.net/2027/uiug.30112008445915|title=The hopper dredge; its history, development and operation|series=Its Engineer manual, EM 1110-2-1410|publisher=Government Printing Office|year=1954|editor-last=Scheffauer|editor-first=Frederick C.|location=Washington, D.C.|hdl=2027/uiug.30112008445915}}</ref> The [[{{ship||Mallard II]]}}, a clamshell dredger that maintains [[levee]]s in [[San Francisco Bay]], has operated continuously since being built in 1936.<ref name="bcdc">{{cite web|url=https://bcdc.ca.gov/planning/reports/SaltPonds_Jun2005.pdf|title=Staff Report: Salt Ponds|publisher=San Francisco Bay Conservation and Development Commission|date=October 2005|access-date=2021-07-06|archive-date=2021-07-09|archive-url=https://web.archive.org/web/20210709183519/https://bcdc.ca.gov/planning/reports/SaltPonds_Jun2005.pdf|url-status=live}}</ref><ref name="twenty">{{cite web|url=https://www.southbayrestoration.org/sites/default/files/documents/2003.007.03edenlanding2020.12.18_bcdcoriginal_1.pdf|title=BCDC PERMITPermit NO. 2003.007.03|author=San Francisco Bay Conservation and Development Commission|publisher=California Department of Fish and Wildlife|date=2020-12-18}}</ref>{{rp|61}}

Dredging can create disturbance todisturb [[aquatic ecosystem]]s, often with adverse impacts.<ref name="Brodie">{{Cite web|url=http://theconversation.com/dredging-set-to-swamp-decades-of-great-barrier-reef-protection-20442|title=Dredging set to swamp decades of Great Barrier Reef protection|last=Brodie|first=Jon|website=The Conversation|date=2 December 2013 |language=en|access-date=2019-09-21}}</ref><ref>{{cite journal | last1 = Newell | first1 = R.C. | last2 = Seiderer | first2 = L.J. | last3 = Hitchcock | first3 = D.R. | year = 1998 | title = The impact of dredging works in coastal waters: A review of the sensitivity to disturbance and subsequent recovery of biological resources on the sea bed | url =http://www.sussex.ac.uk/geography/researchprojects/coastview/dredging/Impact_of_Dredging_Oc_Bio.Ann_Rev.pdf | journal = Oceanography and Marine Biology: An Annual Review | volume = 36 | pages = 127–178 }}</ref> In addition, dredge spoils may contain [[toxic]] chemicals that may have an adverse effect on the disposal area; furthermore, the process of dredging often dislodges chemicals residing in [[benthic]] substrates and injects them into the [[water column]].{{Citation needed|date=September 2017}}

* Changes to the topography by the creation ofcreating "spoil islands" from the accumulated spoil.<ref>{{Cite web|url=https://spoilislandproject.org/spoil-island-project/|title=About the Spoil Island Project|website=Spoil Island Project|language=en-US|access-date=2019-09-22|archive-date=20 December 2019|archive-url=https://web.archive.org/web/20191220175716/https://spoilislandproject.org/spoil-island-project/|url-status=dead}}</ref>

* Releases toxic compound [[Tributyltin]], a popular [[biocide]] often used in [[anti-fouling paint]] banned in 2008, back into the water.<ref>{{Cite web|url=https://www.epa.gov/enforcement/case-summary-cleanup-settlement-addresses-contaminated-sediment-removal-blair-waterway|title=Case Summary: Cleanup Settlement Addresses Contaminated Sediment Removal in Blair Waterway, Washington State|last=US EPA|first=OECA|date=15 December 2015|website=US EPA|language=en|access-date=2019-09-22}}</ref>

The nature of dredging operations and possible environmental impacts causerequires that the industryactivity tooften be closely regulated and a requirement forrequires comprehensive regional environmental impact assessments withalongside continuous monitoring.<ref name="fondriest.com"/> TheFor example, in the U.S., the [[Clean Water Act]] requires that any discharge of dredged or fill materials into "waters of the United States," including wetlands, is forbidden unless authorized by a permit issued by the [[United States Army Corps of Engineers|Army Corps of Engineers]].<ref>[[Clean Water Act]], {{USC|33|1311}}, {{USC|33|1362}}, {{USC|33|1344}}{{Citation needed|date=September 2017}}</ref> AsDue ato resultpotential of the potentialenvironmental impacts to the environment, dredging is often restricted to licensed areas only, with vessel activity monitored closely using automatic GPS systems.<ref name="fondriest.com"/>

* [[Dredging Corporation of India]]

* [[Adani Ports & SEZ]]<ref>{{cite web|url=https://www.adaniports.com/Dredging|title=Adani Dredging}}</ref> (India)

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|USA]], [[Ohio River]] mile 607, July 2002