Rapids

Rapids are hydrological features between a run (a smoothly flowing part of a stream) and a cascade. Rapids are characterized by the river becoming shallower with some rocks exposed above the flow surface.{{cite web |title=Rapids |url=https://education.nationalgeographic.org/resource/rapids/ |access-date=February 20, 2024 |website=National Geographic}} As flowing water splashes over and around the rocks, air bubbles become mixed in with it and portions of the surface acquire a white color, forming what is called "whitewater". Rapids occur where the bed material is highly resistant to the erosive power of the stream in comparison with the bed downstream of the rapids. Very young streams flowing across solid rock may be rapids for much of their length. Rapids cause water aeration of the stream or river, resulting in better water quality.{{Cite web |title=Rapids - redzet.lv |url=https://www.redzet.lv/en/info/Rapids |access-date=2024-05-01 |website=www.redzet.lv |language=en}}

For a rapid to form, a necessary condition is the presence of a gradient, which refers to the river or stream's downward slope. When a river has a larger gradient, the water flows downhill faster.{{Cite web |title=Rapids |url=https://education.nationalgeographic.org/resource/rapids |access-date=2024-05-01 |website=education.nationalgeographic.org |language=en}} Gradients are typically measured in feet per mile.{{Cite book |url=https://sitesmedia.s3.amazonaws.com/creekconnections/files/2014/03/StreamGradient.pdf |title=Stream Gradient |publisher=Creek Connections Topographic Map Module}} This impacts the river's flow or discharge, which is measured as a volume of water per unit of time. The faster the water flows, the more likely a rapid will form.

Rapids typically form due to differential erosion in the sloping strata forming the streambed in presence of a gradient, the softer rocks erode away faster whereas the harder rocks persist resulting in an uneven streambed.{{cite book|title=The Ultimate Visual Family Dictionary|chapter=Geology, Geography and Meteorology|page=290|publisher=DK. Pub|year=2012|location=New Delhi|language=en|isbn=978-0-1434-1954-9}}{{cite web|title=Rapids|website=National Geographic|access-date=19 February 2025|url=https://education.nationalgeographic.org/resource/rapids/}}

The safety of a section of river is measured by classes or levels, generally running from I to VI on basis of how navigable the rapids are. A Class 5 rapid may be categorized as Class 5.1-5.9. While Class I rapids are easy to navigate and require little maneuvering, Class VI rapids pose threat to life with little or no chance for rescue, often classified as 'U' for Uraftable.{{Cite web |date=2019-02-18 |title=Whitewater Rapid Classification System - River Difficulty Classification |url=https://kayakbase.com/whitewater-rapid-classification-system/ |access-date=2022-08-21 |website=kayakbase.com |language=en-US}} River rafting sports are carried out where many rapids are present in the course.

Constriction refers to when rivers flow through narrower channels, thus increasing the velocity of the water. This may also lead to the creation of obstructions due to sediment transportation and erosion. Obstacles may occur by human activity, natural landslides and earthquakes, or accumulation of sediment or debris. The more prominent these four factors are present in a river, the more likely that river is to be a rapid river.{{Cite book |last=Nelson |first=Stephen |url=https://www2.tulane.edu/~sanelson/eens1110/streams.htm |title=Streams and Drainage Systems |date=November 3, 2015}}

File:Rapids before the Rhine Falls.jpg|Rapids featuring whitewater, close to the Rhine Falls

File:Violent water below Niagara Falls.jpg|Violent water below Niagara Falls

File:RapidsonMississippiRiverOntario.jpg|Rapids on the Mississippi River (Ontario) in Pakenham, Ontario, Canada.

File:Rapids on Maumee River above Toledo, Ohio - DPLA - 84b5711224c89b44832b7e7d0f6c27c9 (page 1).jpg|Historical image of the river rapids on the Maumee River in Ohio

File:Uusimaa, Finland - panoramio - pan-opticon (22).jpg|The Kuhakoski rapids in Uusimaa, Finland

File:Storforsen-17.JPG|Storforsen, rapids along the Ume River, Norrbotten, Sweden

• Fluid dynamics
• International scale of river difficulty - for classification of rapids
• Rheophile - organisms that live in fast-flowing water
• Riffle - A fast-moving portion of a stream without the vigor of a rapid
• River rapids ride

{{Commons category}}

{{Reflist |refs=

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• {{Cite web| title = River Flow Changes Over Time {{!}} EARTH 111: Water: Science and Society| accessdate = 2023-03-03| url = https://www.e-education.psu.edu/earth111/node/864}}
• {{Cite web| title = Understanding Rivers| accessdate = 2023-03-03| url = https://education.nationalgeographic.org/resource/understanding-rivers}}
• {{Cite web| title = Rivers and Streams, and erosional processes| accessdate = 2023-03-03| url = http://web.crc.losrios.edu/~jacksoh/lectures/rivers.html}}
• {{Cite web| last = Wright| first = Nick| title = How Do Rapids Form in a River?| work = Whitewater Guidebook| accessdate = 2023-03-03| date = 2020-08-14| url = https://www.whitewaterguidebook.com/how-do-rapids-form-in-a-river/}}
• {{Cite web| last = Attal| first = Mikaël| title = Impacts by Moving Gravel Cause River Channels to Widen or Narrow| work = Eos| accessdate = 2023-03-03| date = 2021-09-24| url = http://eos.org/editor-highlights/impacts-by-moving-gravel-cause-river-channels-to-widen-or-narrow}}
• {{cite web | title=Water flow obstructions in watercourses - World Problems & Global Issues | website=The Encyclopedia of World Problems | url=http://encyclopedia.uia.org/en/problem/132933 | access-date=2023-03-03}}
• {{cite book |title=Path of the Paddle |first=Bill |last=Mason |publisher=Northword Press |year=1984 |isbn=9781559710046}}
• {{Cite book| publisher =Geological Society of America| isbn = 978-0-8137-2398-3| volume = 398 | editor-first1 = Sean D. | editor-last1=Willett | editor-first2 = Niels | editor-last2=Hovius | editor-first3 = Mark T. | editor-last3=Brandon | editor-first4 = Donald M. | editor-last4=Fisher | last1 = Brocard| first1 = G.Y.| last2 = van der Beek| first2 = P.A.| title = Tectonics, Climate, and Landscape Evolution| chapter = Influence of incision rate, rock strength, and bedload supply on bedrock river gradients and valley-flat widths: Field-based evidence and calibrations from western Alpine rivers (southeast France)| accessdate = 2023-03-03| date = 2006-01-01| doi = 10.1130/2006.2398(07)| url = https://hal.archives-ouvertes.fr/hal-00083659/file/Brocard_vdBeek_2.pdf| chapter-url = https://doi.org/10.1130/2006.2398(07)}}

• [https://www.nationalgeographic.org/encyclopedia/rapids/ Rapids entry] in National Geographic's encyclopedia

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Category:Fluvial landforms

Category:Limnology

Category:Rivers

Category:Water streams