10 what causes meandering streams to downcut and become incised meanders? Ideas

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An entrenched river, or entrenched stream is a river or stream that flows in a narrow trench or valley cut into a plain or relatively level upland.
Because of lateral erosion streams flowing over gentle slopes over a time develops meandering (snake like pattern) course.
Meanders form where gradient is very gentle, for example in floodplain and delta. Meandering is the feature of the middle and final course of the river.
But very deep and wide meanders can also be found cutting hard rocks. Such meanders are called incised or entrenched meanders.
The exception is that entrenched meanders are formed during the upliftment of land where river is young.
They widen and deepen over time and can be found as deep gorges or canyons in hard rock.[1][2] In the case of or either an entrenched stream or river, it is often presumed that the watercourse has inherited its course by cutting down into bedrock from a pre-existing plain with little modification of the original course. The down-cutting of the river system could be the result not only of tectonic uplift but also of other factors such as river piracy, decrease of load, increase of runoff, extension of the drainage basin, or change in base level such as a fall in sea level.[1][3][4] General, nongeneric terminology for either a river or stream that flows in a narrow trench or valley, for which evidence of a preexisting plain or relatively level upland can be either absent or present is either valley meander or meander valley with the latter term being preferred in literature.[5]

The meanders that form part of either an entrenched river or meander valley are most commonly known as incised meanders.[5] They are commonly classified as either an ingrown meander or an entrenched meander. For a long time, it was argued that ingrown meander occurs when downcutting process is slow and the river can cause lateral erosion, leading to an asymmetric valley. In addition, it was also argued for a long time that an entrenched meander forms when there is a rapid incision of the river bed such that the river does not have the opportunity to erode the lateral side. This leads to symmetrical valleys with a gorge-like appearance. However, more detailed studies have shown the development of ingrown meanders versus entrenched meanders depends on a complex mixture of factors such as bedrock lithology, tectonic activity, and climate.[3][5]

Causes[edit]

As observed above, an entrenched river can be caused by either tectonic uplift in the area or when the lowering of the sea level occurs. It can also be caused by increased level of downcutting or a collapse of moraine-dammed lake downstream, or capture of the river by another river. Moreover, the process of river rejuvenation can also be the cause of river entrenchment, especially when the process has occurred due to tectonic uplift. River rejuvenation increases the power of the flowing water and, therefore, the process of erosion is accelerated.

Studies show that tectonic movement, particularly movement associated with uplift, can influence spatial patterns of erosion and sedimentation. Although it is very difficult to offer detailed information of past tectonic activity, the basic temporal and spatial scale can show evidence of how this movement leads to the formation of an entrenched river.[6] Various authors have used an entrenched river as evidence of tectonic movement in the past, and in this way they have proven the significant role of tectonic uplifts in the formation of an entrenched river.[7]

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Several studies have cited incised meander a major feature of river entrenchment, as an impact of river rejuvenation. On the other hand, scholars argue that incised meanders and entrenched meanders are features formed before river rejuvenation. Incised meanders occur at the base of the river and they occur when the river base level has reduced, thus giving the river enough power for vertical erosion to take place. Some studies also indicate that anthropogenic factors such as clearing of vegetation, development of dams, and reservoir and urbanization are also causes of river entrenchment. For example, gravel mining along the Russian River developed the Middle Reach pit, which in turn led to the creation of the entrenched river. According to Posamentier, in the 1950s and 1980s, the Russian River had gravel pits and dry creek. However, over time the river has become entrenched due to mining (p. 1777).[8]

Urbanization and clearing of vegetation increase runoff water, which in turn increases water volume, especially during rainy seasons. Therefore, the increased level of vertical erosion of the river increases the power of the water, leading to erosion of the river. A study of San Pedro River and another river in the southwest have indicated that floods were the main cause of river entrenchment in the 18th century. The study shows that increased population and human activities in these places increased floods and, consequently, the volume of runoff water (Hereford 43).[9]

Consequences[edit]

Rosgen indicates that the consequences of incised meander are associated with accelerated stream bank erosion, land loss, aquatic habitat loss, as well as lowering the water table. Additionally, the study also found that incised meanders also cause loss of land productivity and downstream sedimentation (p. 2).[10] The factors are likely to affect not only the economic development on the land where it passes but it is also very costly when restoration is to be initiated.
river entrenchment happens because of the water having the power to cause erosion on the river bed. This increased velocity has shown a negative effect on the riparian habitat, because of increased erosion of the area. For example, a study by Simon revealed that channel incision is a major characteristic of entrenched rivers, and it affects variables in riparian vegetation and growth of fish in the areas (p. 528). Lowering of the channels means that the ground water level has also reduced. Specifically, the development of the entrenched river reduces the amount of ground water due to water loss through infiltration.[11] The movement of the base level changes tributaries and the entrenchment of a tributary channel. Studies of various rivers have revealed that the process of river entrenchment has been associated with adjustment of river positions through bank erosion, as well as widening.[12]

River restoration[edit]

River entrenchment causes negative impacts, such as accelerated stream bank erosion, land loss, loss of aquatic habitat, loss of land productivity, lowering of water table and sedimentation of the river downstream. However, in order to offset these problems, channel restoration measures focusing on restoration of the river in its original or to its previous characteristics are available. Though to achieve good results, a good understanding of the river patterns and profile of stable channels is a critical requirement. The process also needs an elaborate procedure to be followed to ensure all important factors and actions are followed. Numerous projects across the globe involving river restoration have been conducted, and a good example of such projects is Maggie Creek, Nevada. The project was completed in 1990 on upper Maggie Creek in Nevada. It was a partnership between the government and a private ranch, and the project entailed straightening of many miles of unstable gravel bed regarded as the C4/D4 type.

See also[edit]

  • River rejuvenation
  • River Terrace
  • Water Table

References[edit]

  1. ^ a b Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds., 2005. Glossary of Geology (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. ISBN 0-922152-76-4
  2. ^ Licker, M.D., 2003. McGraw-Hill Dictionary of Environmental Science. McGraw-Hill Companies, Inc. 496 pp. ISBN 0-07-143397-X
  3. ^ a b Barbour, J.R., 2008. The origin and significance of sinuosity along incising bedrock rivers. Doctoral dissertation, New York: New York, Columbia University. 172 pp. ISBN 0-922152-76-4
  4. ^ Beckinsale, R.P. and Chorley, R.J., 2003. The History of the Study of Landforms-Volume 3 (Routledge Revivals): Historical and Regional Geomorphology, 1890-1950. Routledge. 524 pp. ISBN 978-0-415568-01-2
  5. ^ a b c Mangelsdorf, J., Scheurmann, K. and Weiß, F.H., 1990. River Morphology. River Morphology. Series: Springer Series in Physics. Environment. Springer Berlin Heidelberg (Berlin, Heidelberg). ISBN 978-3-642-83779-1
  6. ^ Shields Jr, F. Douglas, Andrew Simon, and Lyle J. Steffen. “Reservoir effects on downstream river channel migration.” Environmental Conservation 27.01 (2000): 54-66.
  7. ^ Goldberg, Paul, Vance Holliday T., and Reid Ferring C. Earth Sciences and Archaeology. Boston, MA: Springer US, 2001. Print.
  8. ^ Posamentier, Henry W. “Lowstand alluvial bypass systems: incised vs. unincised.” AAPG bulletin 85.10 (2001): 1771-1793.
  9. ^ Hereford, Richard. Entrenchment and Widening of the Upper San Pedro River, Arizona. Boulder, Colo, 2003. Print.
  10. ^ Rosgen, David L. “A geomorphological approach to restoration of incised rivers.” Proceedings of the conference on management of landscapes disturbed by channel incision. Vol. 16. ISBN 0-937099-05-8, 1997.
  11. ^ Simon, Andrew, and Andrew JC Collison. “Quantifying the mechanical and hydrologic effects of riparian vegetation on streambank stability.” Earth Surface Processes and Landforms 27.5 (2002): 527-546.
  12. ^ Pizzuto, Jim. “Effects of Dam Removal on River Form and Process Although many well-established concepts of fluvial geomorphology are relevant for evaluating the effects of dam removal, geomorphologists remain unable to forecast stream channel changes caused by the removal of specific dams.” BioScience 52.8 (2002): 683-691.
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Entrenched river – Wikipedia

Entrenched river - Wikipedia

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  • Matching Result: Incised meanders occur at the base of the river and they occur when the river base level has reduced, thus giving the river enough power for vertical erosion …

  • Intro: Entrenched river An entrenched river, or entrenched stream is a river or stream that flows in a narrow trench or valley cut into a plain or relatively level upland. Because of lateral erosion streams flowing over gentle slopes over a time develops meandering (snake like pattern) course. Meanders form where…
  • Source: https://en.wikipedia.org/wiki/Entrenched_river

Why Do Streams Meander? – Ausable River Association

Why Do Streams Meander? - Ausable River Association

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  • Sumary: When you see a stream from the air, from a plane or a satellite photo, one thing is quickly apparent: streams meander. They are sinuous, with channels that bend, curve, or loop. In steep topography, channels are straighter, influenced by slope and confined by valleys. On broad, low-slope…

  • Matching Result: Erosion in a stable stream can be minimal from year to year, but as a meander moves outward and becomes more looped, flows intensify on the outer bends.

  • Intro: Why Do Streams Meander? | Ausable River Association When you see a stream from the air, from a plane or a satellite photo, one thing is quickly apparent: streams meander. They are sinuous, with channels that bend, curve, or loop. In steep topography, channels are straighter, influenced by slope and…
  • Source: https://www.ausableriver.org/blog/why-do-streams-meander

Stream Valleys – Geology – Cliffs Notes

Stream Valleys - Geology - Cliffs Notes

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  • Sumary: The erosion and transport of rock and sediment by a stream defines the shape and extent of its valley. V‐shaped valleys and wide valleys with flat floor

  • Matching Result: Incised meanders. Incised meanders are steep‐walled canyons that result from the downcutting of a meandering stream. Usually without floodplains, they are …

  • Intro: Stream Valleys The erosion and transport of rock and sediment by a stream defines the shape and extent of its valley. V‐shaped valleys and wide valleys with flat floors are the most common varieties. Downcutting. A valley is the result of downcutting, whereby a stream’s channel erodes directly downward. As…
  • Source: https://www.cliffsnotes.com/study-guides/geology/running-water/stream-valleys

16 Flashcards – Easy Notecards

16 Flashcards - Easy Notecards

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  • Sumary: Study 16 flashcards. Play games, take quizzes, print and more with Easy Notecards.

  • Matching Result: trunk stream – meander – moderate channel size – moderate volume of water … What causes meandering streams to downcut and become incised meanders?

  • Intro: 16 Flashcards – Easy Notecards Set Details Share created 7 years ago by giacometto 7,265 views show moreless 1Low gradient is associated with deposition. True or false2- mountains – big boulders on the bed – headwaters – steep gradient – small channel size – small volume of water- trunk stream…
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What Causes A Stream To Meander? – Micro B Life

What Causes A Stream To Meander? - Micro B Life

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  • Sumary: Meanders are produced when water in the stream channel erodes the sediments of an outer bend of a streambank and deposits this and other sediment on subsequent inner bends downstream. … Eventually the…

  • Matching Result: Terms in this set (3) What causes meandering streams to downcut and become incised meanders? … Meanders in equilibrium erode primarily in a …

  • Intro: What Causes A Stream To Meander? – Micro B Life Meanders are produced when water in the stream channel erodes the sediments of an outer bend of a streambank and deposits this and other sediment on subsequent inner bends downstream. … Eventually the meander may be cut off from the…
  • Source: https://www.microblife.in/what-causes-a-stream-to-meander/

How Do Meanders Increase In Size – Micro B Life

How Do Meanders Increase In Size - Micro B Life

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  • Sumary: Meanders. As the river makes its way to the middle course it gains more water and therefore more energy. Lateral erosion starts to widen the river. When the river flows over flatter land they develop large bends called meanders .

  • Matching Result: Terms in this set (3) What causes meandering streams to downcut and become incised meanders? … Meanders in equilibrium erode primarily in a side-to-side manner.

  • Intro: How Do Meanders Increase In Size – Micro B Life Meanders. As the river makes its way to the middle course it gains more water and therefore more energy. Lateral erosion starts to widen the river. When the river flows over flatter land they develop large bends called meanders ….
  • Source: https://www.microblife.in/how-do-meanders-increase-in-size/

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Downcutting – an overview | ScienceDirect Topics

Downcutting - an overview | ScienceDirect Topics

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  • Sumary: B.G. Lockaby, … J. Mitchell, in Encyclopedia of Ecology, 2008

  • Matching Result: Graded Rivers and Base Level … An important characteristic of a river is its ability to cut downward into bedrock and form a narrow V-shaped valley, a process …

  • Intro: Downcutting – an overview | ScienceDirect TopicsFloodplainsB.G. Lockaby, … J. Mitchell, in Encyclopedia of Ecology, 2008Geomorphic OriginsStreams in steep topography tend to undergo continual downcutting and, consequently, act as sources of fine and coarse material with little to no opportunity for deposition. Sediment loads are easily carried downstream because the…
  • Source: https://www.sciencedirect.com/topics/earth-and-planetary-sciences/downcutting

Frequently Asked Questions About what causes meandering streams to downcut and become incised meanders?

If you have questions that need to be answered about the topic what causes meandering streams to downcut and become incised meanders?, then this section may help you solve it.

What leads to the development of incised meanders?

Meanders deepen and become entrenched when a mature stream with developed meanders is either uplifted, or the base level descends further.

After reaching equilibrium with its new base level, an incised meander is likely to experience which of the following?

After an incised meander reaches equilibrium with its new base level, which of the following is most likely to happen? The incised meander will only result in minor erosion of the canyon walls.

How does meandering take place?

By strengthening the riffle-pool structure of a stream, meanders are created when water in the stream channel erodes the sediments of an outer bend of a streambank and deposits these and other sediments on succeeding inner bends downstream.

What are carved meanders?

Incised, intrenched, entrenched, inclosed, or ingrown are terms used to describe meandering river valleys that have cut down their bed into the bedrock due to uplift or lowered base level; finer distinctions are recognized by some authorities.

Why do meander cutoffs occur?

A pronounced meander (hook) in a river is breached by a flow that connects the two closest parts of the hook to form a new channel, a full loop. This is known as a meander cutoff.

What causes a meander to diverge from the main channel typically?

Many meanders are cut off because stream energy is insufficient to carry incoming sediment through a bend. When a sediment plug forms on the entrance to a mean- der bend, the stream will cut through the flood plain or point bar. Excess sediment from upstream erosion is a major cause of cutoffs.

Why does downcutting occur?

A geological process by hydraulic action known as downcutting, also known as erosional downcutting, downward erosion, or vertical erosion, deepens the channel of a stream or valley by removing material from the stream bed or the valley floor.

Why do rivers veer off course in their lower reaches?

Because LATERAL erosion, a type of sideways erosion, and deposition within the floodplain replace vertical erosion in the middle and lower course of a river, meanders, which are winding curves or bends, are typical of those areas.

What gives a river its meandering characteristics?

The erosion of bed material and subsequent deposition of the eroded material downstream are prerequisites for the emergence and development of an alluvial channel’s meandering.

What distinguishes meanders from incised meanders?

Ingrown meanders are asymmetrical and form when the river downcuts at a slower rate, giving the river opportunity to erode laterally as well as vertically. Incised meanders are symmetrical because there is little opportunity for lateral erosion to occur, giving them their shape.

How do meanders develop, get stopped, and then disappear?

Describe the formation, growth, cutting off, and abandonment of meanders. Friction causes the fastest-moving current to swing back and forth, eroding the side of the stream. Erosion can eat through the meander neck, causing the cutoff forming an oxbow lake.

What is the name of a cut off meander?

Chutes are formed by lateral erosion of the bank of the upstream arm of a loop, which causes the stream to cut through the neck of the loop and into the downstream arm. Chutes are a shortcut across a meander (q.v.) loop that shortens and straightens the course of the stream.

What transpires when a meander is terminated?

In entrenched valleys, steepened portions of the longitudinal profile may then correspond to cut-off meanders located some miles downstream, standing now high above the valley bottom. The cut-off of a meander produces a fall or rapid which is later removed upstream by headward erosion.

What distinguishes an incised meander from a meander?

Simply put, meanders over flood and delta plains are the result of lateral erosion, whereas incised meanders are the result of vertical erosion.

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