River island

A river island is any exposed land surrounded by river water. Properly defined it excludes shoals between seasonally varying flows and may exclude semi-coastal islands such as in deltas.

These islands result from changes in the course of a river such as interactions with a tributary or the opposing fluvial actions of deposition and/or erosion such as forming a natural cut and meander. Nascent vegetation-free shoals and mudflats may dissipate and shift or build up into such islands through deposition and which may be assisted through artificial reinforcement or natural factors such as, reeds, palms, evergreen trees or willows, to large examples covering many square kilometers, examples of which are given below.

Regional nomenclature

The term "towhead" implies a little islet or shoal within a river (most often the Mississippi River) having a grouping or thicket of trees, and is often used in the Midwestern United States. Many rivers, if wide enough, can house considerably large islands. The term "towhead" was popularised by Mark Twain's Adventures of Huckleberry Finn.

In England, a river island in the Thames is referred to as an "ait" (or "eyot").

Largest and smallest

Majuli in India, being non-coastal and being between two channels of one river is recognised by the Guinness Book of World Records as world's largest example.,[1] but Ilha do Bananal meets the same qualifications and is much larger. Umananda is among contenders as the smallest permanently-inhabited river island with fixed dwellings at 0.02 km². Majuli and Umananda lie in the Brahmaputra River. Many as tiny as Umananda or smaller, inhabited, exist in the Amazon basin and Bangladesh. On canalised rivers such as the Thames and the Seine one-home islands of permanent-materials homes exist such as Monkey, Friday, Holm and D'Oyly Carte islands, as canalisation reduces the erosion of the islands and in particular limits the height of flash flooding by maintaining substantial "heads" of water through barrages.

Lists of river islands

  • Note: Includes some river islands that also have an ocean coast.
Name Area (km²) Country River
Marajó40,100BrazilAmazon River / Pará River
Ilha do Bananal19,162BrazilAraguaia River
Tupinambarana11,850BrazilAmazon River
Bahr al Jabal Island7,929South SudanBahr al Jabal Bahr el Zeraf
Holland/Utrecht7,361NetherlandsRhine River IJssel River
Ilha Grande de Gurupá4,864BrazilAmazon River
Margarita Island (Colombia)2,832[2]ColombiaMagdalena River
Uarini Island2,339BrazilUarini River, Amazon River
Boven Digul2,171IndonesiaDigul River, Kawaga River
Richards Island2,165CanadaMackenzie River
Krasnoslobodsk2,002RussiaVolga River, Akhtuba River
Veľký Žitný ostrov1,885.2[3]SlovakiaDanube
Hatiya Island1,508.23BangladeshMeghna River
Letea Island1,480RomaniaDanube River
Camargue1,453FranceGrand Rhone, Petit Rhone
Bhola Island1,441BangladeshMeghna River
Chongming Island1,267[4]ChinaYangtze River
Majuli1,250IndiaBrahmaputra River
Ile à Morfil1,250SenegalSenegal River
Dibru Saikhowa765IndiaBrahmaputra River
Sandwip Island762.42BangladeshMeghna River
Great Brăila Island720.2RomaniaDanube
Sumba Island500[5]Democratic Republic of CongoCongo River
Montreal499CanadaSt. Lawrence River, Ottawa River
Szigetköz375Hungary, SlovakiaDanube
Manpura Island373BangladeshMeghna
Inhacamba340MozambiqueZambezi
Hoeksche Waard323.74NetherlandsOude Maas, Nieuwe Maas
Yangzhong Island320ChinaYangtze
Csepel Island257HungaryDanube
Île Jésus242CanadaRivière des Mille Îles, Rivière des Prairies
Voorne-Putten220NetherlandsOude Maas, Nieuwe Maas
Hisingen199SwedenGöta älv
Mosqueiro191BrazilAmazon River
Mbamou Island180[6]Republic of the CongoCongo River
Roberts Island 133[7] United States San Joaquin River
Union Island 130[7] United States San Joaquin River
Davis Island120United StatesMississippi River
Taiama Island115.55BrazilParaguay River
Lulu Island112.4CanadaFraser River
Sarpinskiy Island110RussiaVolga River
Sauvie Island105United StatesColumbia River
Dordrecht Island79.53NetherlandsOude Maas, Hollands Diep
Srirangam74.4IndiaKaveri[8]
Grand Island73.8United StatesNiagara River
Rangitata Island~65New ZealandRangitata River[notes 1]
Ostrvo60SerbiaDanube
Manhattan Island59United StatesHudson River/East River/Harlem Creek
Hengsha Island55.74ChinaYangtze River
Woodford Island37AustraliaClarence River
Wilhelmsburg35.3GermanyElbe
Isla Teja15ChileCau-Cau River/Cruces River/Valdivia River
Srirangapatna13IndiaKaveri
Shivanasamudram[9]IndiaKaveri
Grosse Ile25United StatesDetroit River
Inch Clutha~24New ZealandClutha River
Khortytsia23.59UkraineDnieper River
Island of Šarengrad9Disputed (Serbia/Croatia)Danube
Yeouido8.4South KoreaHan River
Sedudu/Kasikili5BotswanaCuando River
Hayden Island4.4United StatesWillamette River
Nanjido2.8South Koreaa branch of the Han River
Rŭngrado1.3North KoreaTaedong River
Yanggakdo1.2[10]North KoreaTaedong River
Nakanoshima0.7JapanKyū-Yodo River
Zhenbao Island0.7ChinaUssuri River
Bhavani Island0.53IndiaKrishna River
Bamseom0.24South KoreaHan River
Île de la Cité~0.2FranceSeine
Nakasu~0.2JapanNakagawa River
Island of Vukovar0.032Disputed (Serbia/Croatia)Danube
Umananda Island0.02IndiaBrahmaputra River
Some Sevit
(Gavit,Chavit,Solvit,Yevit)
0.0104
(0.0048,0.0034,0.0012,0.0008)
South KoreaHan River
Pheasant Island0.00682Condominium between France and SpainBidasoa

Most populous river islands

This list ranks river islands with a population of at least 25,000.

Name Population Area [km²] Country City River
Salsette Island15,111,974619IndiaMumbai and ThaneUlhas River
Île de Montréal1,942,044 (2016)[11]499CanadaMontrealSt. Lawrence River
Manhattan Island1,628,701 (2018)[12]59United StatesNew York CityHudson River/East River
Chongming Island660,000 (2010)1,267ChinaShanghaiYangtze River
Île Jésus422,993 (2016)[13]242CanadaLavalSt. Lawrence River
Veľký Žitný ostrov226,446 (2001)1,885SlovakiaseveralDanube
Vasilievsky Island209,188 (2017)10.9RussiaSt. PetersburgBolshaya Neva/Malaya Neva
Lulu Island198,309 (2016)[14]122.4CanadaRichmondFraser
Srirangam181,556 (2001)13IndiaSrirangamKaveri
Majuli167,304 (2011)422IndiaVaishnavite ShrinesBrahmaputra River
Csepel Island166,953 (2012)257HungaryseveralDanube
Hisingen130,000199SwedenGothenburgGöta älv
Wilhelmsburg49,132 (2006)35.3GermanyHamburgElbe
Yeouido30,988 (2006)8.4South KoreaSeoulHan River
Mosqueiro27,000191BrazilBelémAmazon River

See also

  • Ait  Islands found on the River Thames and its tributaries in England
  • Anabranch  A section of a river or stream that diverts from the main channel and rejoins it downstream.
  • Archipelago  A group of islands
  • Distributary
  • Fluvial landforms  Processes associated with rivers and streams
  • Island  Any piece of sub-continental land that is surrounded by water
  • Lake island
  • Point bar  A depositional feature of alluvium that accumulates on the inside bend of streams and rivers below the slip-off slope
  • River bifurcation
  • River delta  Silt deposition landform at the mouth of a river

Notes

  1. Due to redirecting of water from the Rangitata River, the river's southern distributary channel is now dry except after heavy rain or snow melt. As such, Rangitata Island is usually connected to the South Island mainland.

References

  1. Majuli, River Island. "Largest river island". Guinness World Records. Retrieved 6 September 2016.
  2. "Río Grande de la Magdalena - Colección Ecológica del Banco". Retrieved 3 January 2015.
  3. "Žitný ostrov". Retrieved 3 January 2015.
  4. address, author,email. "崇明县". www.shanghai.gov.cn.
  5. "Largest Islands of Countries". Retrieved 3 January 2015.
  6. "Malebo Pool". Encyclopædia Britannica. Accessed June 2017.
  7. "SUMMARY REPORT ROBERTS ISLAND AND UNION ISLAND RIPARIAN WATER RIGHTS INVESTIGATION, SAN JOAQUIN COUNTY, CA, JUNE 2008" (PDF).
  8. W. Francis (1906). Gazetteer of South India. p. 199.
  9. Shivanasamudra
  10. Historical Dictionary of Pyongyang, by Justin Corfield, p.227
  11. "2016 Census Profile - Montréal, Territoire équivalent (Census division)". Statistics Canada. Retrieved 2017-03-23.
  12. "U.S. Census Bureau QuickFacts: New York County (Manhattan Borough), New York; United States". www.census.gov. Retrieved 2019-09-12.
  13. "2016 Census Profile - Laval, Territoire équivalent (Census division)". Statistics Canada. Retrieved 2019-09-11.
  14. "2016 Census Profile - Richmond (Census division)". Statistics Canada. Retrieved 2019-09-11.
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