Fluvial processes

In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluvioglacial is used.[1][2]

Matanuska River 8727
Deep, eroding glaciofluvial deposits alongside the Matanuska River, Alaska

Fluvial processes

Fluvial processes include the motion of sediment and erosion or deposition on the river bed.[3][4]

Erosion by moving water can happen in two ways. Firstly, the movement of water across the stream bed exerts a shear stress directly onto the bed. If the cohesive strength of the substrate is lower than the shear exerted, or the bed is composed of loose sediment which can be mobilized by such stresses, then the bed will be lowered purely by clearwater flow. However, if the river carries significant quantities of sediment, this material can act as tools to enhance wear of the bed (abrasion). At the same time the fragments themselves are ground down, becoming smaller and more rounded (attrition).

Sediment in rivers is transported as either bedload (the coarser fragments which move close to the bed) or suspended load (finer fragments carried in the water). There is also a component carried as dissolved material.

For each grain size there is a specific velocity at which the grains start to move, called entrainment velocity. However the grains will continue to be transported even if the velocity falls below the entrainment velocity due to the reduced (or removed) friction between the grains and the river bed. Eventually the velocity will fall low enough for the grains to be deposited. This is shown by the Hjulström curve.

A river is continually picking up and dropping solid particles of rock and soil from its bed throughout its length. Where the river flow is fast, more particles are picked up than dropped. Where the river flow is slow, more particles are dropped than picked up. Areas where more particles are dropped are called alluvial or flood plains, and the dropped particles are called alluvium.

Even small streams make alluvial deposits, but it is in the flood plains and deltas of large rivers that large, geologically-significant alluvial deposits are found.

The amount of matter carried by a large river is enormous. The names of many rivers derive from the color that the transported matter gives the water. For example, the Huang He in China is literally translated "Yellow River", and the Mississippi River in the United States is also called "the Big Muddy". It has been estimated that the Mississippi River annually carries 406 million tons of sediment to the sea,[5] the Yellow River 796 million tons, and the Po River in Italy 67 million tons.[6]

See also

Fluvial processes

  • Bradshaw model – A geographical model, which describes how a river's characteristics vary between the upper course and lower course
  • Erosion – Processes which remove soil and rock from one place on the Earth's crust, then transport it to another location where it is deposited
    • Downcutting – Process of deepening a stream channel by erosion of the bottom material
  • Saltation (geology) – Particle transport by fluids
  • Corrosion – Gradual destruction of materials by chemical reaction with its environment (solution)
  • Suspension (chemistry) – Heterogeneous mixture of solid particles dispersed in a medium

Fluvial channel patterns

  • Channel pattern – Characteristic geometry of a channel system
  • Braided river – A network of river channels separated by small, and often temporary, islands
  • Meandering river – A sinuous bend in a series in the channel of a river
  • Anastomosis – A connection or opening between two things that are normally diverging or branching

Fluvial landforms

  • Channel (geography) – A type of landform in which part of a body of water is confined to a relatively narrow but long region
  • Confluence – Meeting of two or more bodies of flowing water
  • Cut bank – Outside bank of a water channel, which is continually undergoing erosion
  • Crevasse splay – Sediment deposited on a floodplain by a stream which breaks its levees
  • Drainage basin – Area of land where precipitation collects and drains off into a common outlet (watershed)
  • Esker – Long, winding ridge of stratified sand and gravel associated with former glaciers
  • Floodplain – Land adjacent to a stream or river which is flooded during periods of high discharge
  • Fluvial terrace – Elongated terraces that flank the sides of floodplains and river valleys
  • Canyon – Deep ravine between cliffs (Gorge)
  • Gully – Landform created by running water eroding sharply into soil
  • Island – Any piece of sub-continental land that is surrounded by water
  • Levee § Natural levees
  • Meander – A sinuous bend in a series in the channel of a river
  • Oxbow lake – U-shaped lake formed by a cut-off meander of a river
  • Pendant bar
  • Plunge pool – Depression at the base of a waterfall created by the erosional force of falling water and rocks where it lands
  • Point bar – A depositional feature of alluvium that accumulates on the inside bend of streams and rivers below the slip-off slope
  • Riffle – Shallow landform in a flowing channel
  • River – Natural flowing watercourse
  • River delta – Silt deposition landform at the mouth of a river
  • River island – Exposed land within a river.
  • Shoal, also known as bar – A natural landform that rises from the bed of a body of water to near the surface and is covered by unconsolidated material
  • Spring (hydrology) – A point at which water emerges from an aquifer to the surface
  • Stream – A body of surface water flowing down a channel
  • Stream pool – A stretch of a river or stream in which the water is relatively deep and slow moving
  • Valley, also known as vale – Low area between hills, often with a river running through it.
  • Waterfall – Place where water flows over a vertical drop in the course of a river
  • Yazoo stream – Tributary stream that runs parallel to, and within the floodplain of a larger river for considerable distance

Related terms

References

  1. ^ K.K.E. Neuendorf, J.P. Mehl, Jr., and J.A. Jackson, eds., 2005, Glossary of Geology. American Geological Institute, Alexandria, Virginia. 800 pp.
  2. ^ Wilson, W.E. & Moore, J.E. 2003. Glossary of Hydrology, American Geological Institute, Springer, 248pp.
  3. ^ Charlton, Ro (2008). Fundamentals of fluvial geomorphology. London: Rutledge. p. 234. ISBN 978-0-415-33454-9.
  4. ^ Wohl, Ellen (2014). Rivers in the Landscape: Science and Management. Wiley-Blackwell. p. 330. ISBN 1118414896.
  5. ^ Mathur, Anuradha; Dilip da Cunha (2001). Mississippi Floods: Designing a Shifting Landscape. New Haven, CT: Yale University Press. ISBN 0-300-08430-7
  6. ^ Dill, William A. (1990). Inland fisheries of Europe. Rome, Italy: UN Food and Agriculture Organization. ISBN 92-5-102999-7. http://www.fao.org/docrep/009/t0377e/t0377e00.htm
Bank (geography)

In geography, the word bank generally refers to the land alongside a body of water. Different structures are referred to as banks in different fields of geography, as follows.

In limnology (the study of inland waters), a stream bank or river bank is the terrain alongside the bed of a river, creek, or stream. The bank consists of the sides of the channel, between which the flow is confined. Stream banks are of particular interest in fluvial geography, which studies the processes associated with rivers and streams and the deposits and landforms created by them. Bankfull discharge is a discharge great enough to fill the channel and overtop the banks.The descriptive terms left bank and right bank refer to the perspective of an observer looking downstream, a well-known example of this being the sections of Paris as defined by the river Seine. The shoreline of ponds, swamps, estuaries, reservoirs, or lakes are also of interest in limnology and are sometimes referred to as banks. The grade of all these banks or shorelines can vary from vertical to a shallow slope.

In freshwater ecology, banks are of interest as the location of riparian habitats. Riparian zones occur along upland and lowland river and stream beds. The ecology around and depending on a marsh, swamp, slough, or estuary, sometimes called a bank, is likewise studied in freshwater ecology.

Banks are also of interest in navigation, where the term can refer either to a barrier island or a submerged plateau, such as an ocean bank. A barrier island is a long narrow island composed of sand and forming a barrier between an island lagoon or sound and the ocean. A submerged plateau is a relatively flat topped elevation of the sea floor at shallow depth (generally less than 200 m), typically on the continental shelf or near an island.

Channel pattern

Channel patterns are found in rivers, streams, and other bodies of water that transport water from one place to another. Systems of branching river channels dissect most of the sub-aerial landscape, each in a valley proportioned to its size. Whether formed by chance or necessity, by headward erosion or downslope convergence, whether inherited or newly formed. Depending on different geological factors such as weathering, erosion, depositional environment, and sediment type, different types of channel patterns can form.

Cirque de Navacelles

The Cirque de Navacelles is large erosional landform, an incised meander, located towards the southern edge of the Massif Central mountain range in France. It is located near Saint-Maurice-Navacelles and Blandas between the Hérault department and the Gard department.The cirque is isolated, with only a few small villages in the surrounding area. However, with the completion of the Millau Viaduct in 2004 and the A75 motorway between Clermont-Ferrand and Pézenas, tourism in the region has increased.

Dune

In physical geography, a dune is a hill of loose sand built by aeolian processes (wind) or the flow of water. Dunes occur in different shapes and sizes, formed by interaction with the flow of air or water. Most kinds of dunes are longer on the stoss (upflow) side, where the sand is pushed up the dune, and have a shorter "slip face" in the lee side. The valley or trough between dunes is called a slack.

An erg or sand sea is a large broad, flat area covered with wind-swept sand and/or dunes with little or no vegetation. Smaller areas are called dune fields.Dunes occur in some deserts, inland and along some coasts. Some coastal areas have one or more sets of dunes running parallel to the shoreline directly inland from the beach. In most cases, the dunes are important in protecting the land against potential ravages by storm waves from the sea. Although the most widely distributed dunes are those associated with coastal regions, the largest complexes of dunes are found inland in dry regions and associated with ancient lake or sea beds. Dunes can form under the action of water flow (fluvial processes), and on sand or gravel beds of rivers, estuaries and the sea-bed.

The modern word "dune" came into English from French around 1790, which in turn came from Middle Dutch dūne.

Fountain Formation

The Fountain Formation is a Pennsylvanian bedrock unit consisting primarily of conglomerate, sandstone, or arkose, in the states of Colorado and Wyoming in the United States, along the east side of the Front Range of the Rocky Mountains, and along the west edge of the Denver Basin.

G. K. Warren Prize

The G. K. Warren Prize is awarded by the U.S. National Academy of Sciences "for noteworthy and distinguished accomplishment in fluviatile geology and closely related aspects of the geological sciences." Named in honor of Gouverneur Kemble Warren, it was first awarded in 1969 and has been awarded every four years since 1982.

Geomorphology

Geomorphology (from Ancient Greek: γῆ, gê, "earth"; μορφή, morphḗ, "form"; and λόγος, lógos, "study") is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or near the Earth's surface. Geomorphologists seek to understand why landscapes look the way they do, to understand landform history and dynamics and to predict changes through a combination of field observations, physical experiments and numerical modeling. Geomorphologists work within disciplines such as physical geography, geology, geodesy, engineering geology, archaeology, climatology and geotechnical engineering. This broad base of interests contributes to many research styles and interests within the field.

Lag deposit

A lag deposit is the deposition of material winnowed by physical action. Aeolian processes, fluvial processes, and tidal processes can remove the finer portion of a sedimentary deposit leaving the coarser material behind.

Lag deposits are found in processes such as central island formation in streams and rivers. One theory of desert pavement formation is that they are an aeolian lag deposit. Armored beaches and inlets can be composed in part by lag deposits of shells or cobbles created when tidal forces strip away the finer sand and silt.

Lagoon

A lagoon is a shallow body of water separated from a larger body of water by barrier islands or reefs. Lagoons are commonly divided into coastal lagoons and atoll lagoons. They have also been identified as occurring on mixed-sand and gravel coastlines. There is an overlap between bodies of water classified as coastal lagoons and bodies of water classified as estuaries. Lagoons are common coastal features around many parts of the world.

Lake Kankakee

Lake Kankakee formed 14,000 years before present (YBP) in the valley of the Kankakee River. It developed from the outwash of the Michigan Lobe, Saginaw Lobe, and the Huron-Erie Lobe of the Wisconsin glaciation. These three ice sheets formed a basin across Northwestern Indiana. It was a time when the glaciers were receding, but had stopped for a thousand years in these locations. The lake drained about 13,000 YBP, until reaching the level of the Momence Ledge. The outcropping of limestone created an artificial base level, holding water throughout the upper basin, creating the Grand Kankakee Marsh.

Lake Kankakee was a prehistoric lake during the Wisconsin glacial epoch of the Pleistocene Era. The lake formed during the period, when the Michigan and Saginaw lobes of the Laurentian glacier had receded back to the Valparaiso and Kalamazoo moraines. While the glacial advance became stagnant, the summer runoff formed a large lake covered parts of 13 counties in two states.

Around 1840, Mr. F. H. Bradley applied the name Lake Kankakee to the lake which he thought formerly occupied the Kankakee basin. The sand deposits outside the marsh were the first clue that the lake existed. These sands were the result of Aeolian or wind processes, not lacustrine, or fluvial processes. He predicted that the lake would have been at an elevation of 685 feet (209 m) above sea level.

Luna Leopold

Luna Bergere Leopold (October 8, 1915 – February 23, 2006) was a leading U.S. geomorphologist and hydrologist, and son of Aldo Leopold. He received a B.S. in civil engineering from the University of Wisconsin in 1936; an M.S. in physics-meteorology from the University of California, Los Angeles in 1944; and a Ph.D. in geology from Harvard University in 1950.Leopold is widely known in his primary field for his work in fluvial geomorphology and for the classic book, Fluvial Processes in Geomorphology, that he wrote with Gordon Wolman and John Miller.Leopold suggested that a new philosophy of water management is needed, one based on geologic, geographic, and climatic factors as well as traditional economic, social, and political factors. He argued that the management of water resources cannot be successful as long as it is naïvely perceived from an economic and political standpoint, as it is in the status quo.

M. Gordon Wolman

Markley Gordon Wolman (August 16, 1924 – February 24, 2010) was an American geographer, son of Abel Wolman. He was born in Baltimore, Maryland. He attended Haverford College before being drafted into the U.S. Navy during World War II. After the war, he returned to Baltimore and graduated from the Johns Hopkins University in 1949 with a degree in Geography. He earned a doctorate in Geology from Harvard University in 1953.At the age of 12, he was sent to work on a Connecticut dairy farm for the summer. “My mother said she wanted me to know that milk didn’t come from a bottle.” Returning to the farm for several years after that, he first became exposed to the problem of soil erosion and the effect it has on water supplies. After serving in the US Navy during World War II, he returned to Baltimore and earned his BA in geology in 1949.As a scientist at the U.S. Geological Survey in the 1950s, he and colleague Luna Leopold published pioneering studies on how and why rivers change. With their emphasis on measuring rivers' characteristics, including depths and velocities and the size of river-bottom pebbles, they transformed geomorphology—the study of landforms' evolution—from a descriptive to a quantitative discipline, making it possible to predict how natural and human-caused perturbations might affect river channels. Their 1964 textbook, "Fluvial Processes in Geomorphology," co-written with John Miller, is considered a seminal work. His method for sampling particle size distribution of riverbeds became known as the “Wolman Pebble Count” and is still a standard technique for geomorphologists.Dr. Wolman applied his expertise to local problems beginning in the 1960s, when his report on how runoff from construction projects was choking Maryland's streams with sediment helped lead to new state regulations. He later headed the Oyster Roundtable, a coalition of environmentalists, watermen and scientists that designed a plan to reverse the Chesapeake Bay's catastrophic oyster decline during the 1990s. Wolman was also one of the leading forces behind Maryland’s sediment and erosion control law, passed in 1970, based on the US federal Clean Water Act.In 1958, Dr. Wolman accepted a faculty position at the Johns Hopkins University. An early proponent of interdisciplinary education, he helped combine the departments of geography and sanitary and water resources to create the department of geography and environmental engineering, which he chaired for 20 years until 1990. In 1988, Wolman was elected to the National Academy of Sciences, and in 1992 he was elected to the National Academy of Engineering.

Sadler effect

The Sadler effect describes variation in apparent sediment accumulation rates and bed thicknesses back through time inherent to the geological sedimentary record. Peter Sadler analysed what structure you would expect in a stratigraphic section under the hypothesis that bigger geological events – episodes of deposition, erosion, and the gaps between those events – are rarer. He showed that under these conditions it is inevitable that, on average, thinner stratigraphic sections, which cover shorter amounts of time, record faster accumulation rates than thicker sections, which record longer amounts of time.The effect equivalently states that more ancient packages of sediment in the stratigraphic record will record slower sedimentation rates stretched over longer periods of time. For instance, it explains the fact that in general, the more ancient geological periods of the Phanerozoic are longer than the more recent ones; i.e., the periods of the Palaeozoic are much longer than those in the Cenozoic. Conversely, it also explains that the maximum sediment accumulation rates seen in the Cambrian at the start of the Phanerozoic are almost two orders of magnitude lower than those observed in the Quaternary, at its end.The Sadler effect provides a powerful framework for understanding how information extracted from any given stratigraphic section differs from what should be expected under constant conditions – that is, it provides a null hypothesis for analysing stratigraphy. It also provides techniques to estimate the completeness of a given stratigraphic section on a given timescale. Sections are less complete at shorter timescales, which means that at sufficiently short timescales and for some purposes, some sedimentary successions may contain essentially no useful information.For example, the Sadler effect has since been used to investigate whether apparent increases in global sedimentation rates across the last 5 Ma are real; how we might read the record of sediments deposited on continental margins; to interpret fluvial processes such as river avulsion; and to understand what information, and which processes at what timescales, can be preserved in sediments.

Schmon River

The Schmon River (French: Rivière Schmon) is a river in the Côte-Nord region of the province of Quebec, Canada. It flows south into Lake Walker.

Sediment

Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation. If buried, they may eventually become sandstone and siltstone (sedimentary rocks) through lithification.

Sediments are most often transported by water (fluvial processes), but also wind (aeolian processes) and glaciers. Beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice-transported sediments.

Slip-off slope

A slip-off slope is a depositional landform that occurs on the inside convex bank of a meandering river. The term can refer to two different features: one in a freely meandering river with a floodplain and the other in an entrenched river.

Subaerial unconformity

In geology, a subaerial unconformity is a surface that displays signs of erosion by processes that commonly occur on the surface. These processes generating the subaerial unconformity can include wind degradation, pedogenesis, dissolution processes such as karstification as well as fluvial processes such as fluvial erosion, bypass and river rejuvenation.

Tidal strait

A tidal strait is not technically a river, but a strait, connecting two oceans, or seas. Tidal straits are narrow seaways through which flow tidal currents. Tidal current are usually uni-directional, but sometimes can be bi-directional. Frequently they are of tectonic origin. Currents in them develop due to elevation differences between the water basins at either ends.Due to tides, sediments can collect in tidal straits.

Two-stage drainage ditch

A drainage ditch is a depression in the land created to channel water. Drainage ditches are typically formed around low-lying areas, roadsides or fields proximate to a water body or created to channel water from a more distant water source for the purpose of plant irrigation. The two stage drainage ditch is classified as a 'surface' sustainable drainage system, contrary to a sub-surface system. The two stage drainage ditch is a modification of the land whereby grass benches which serve as floodplains are formed within the land of the watershed of the water system, shown in the diagram to the right. By implementing benches either side of the water body, the energy of surface runoff dissipates, sustaining fluvial processes of the channel, thereby improving the water stability and water quality of existing channel.

Large-scale features
Alluvial rivers
Bedrock river
Bedforms
Regional processes
Mechanics
Water
Glacial
Hillslope
Aeolian

Languages

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.