50 terms

Fluvial Processes


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Fluvial Processes
Water is the most influential of all erosional agents, wears down and creates landforms, serves as a deposition agent, and creates V Shaped valleys
Overland flow
The unchanneled downslope movement of surface of water
The channeled movement of water along a valley bottom
A valley is a portion of the terrain with a clearly established drainage system
The higher ground above the valley walls that separates adjacent valleys
Drainage Basin
An Area that contributes overland flow and groundwater to a specific stream. AKA Watershed
Drainage divide
The line of separation between runoff that descends in the direction of one drainage basin and runoff that goes toward an adjacent basin.
Stream Orders
1st order stream: The smallest stream, with no tributaries
2nd order stream: When two 1st order streams meet
Fluvial Geomorphology
Studies how running water affects the shape of the Earth
Beginning of the river
End of the river
Source and mouth of the Platte River
The Platte River has its source at North Platte, Nebraska and its mouth at Plattesmoth, Nebraska
Source and mouth of the Missouri River
The Missouri river has a source at Three Forks, Montana at and its mouth at St. Louis, Missouri
Sheet Erosion
Sheet erosion is the uniform removal of soil in thin layers by the forces of raindrops and overland flow. It can be a very effective erosive process because it can cover large areas of sloping land and go unnoticed for quite some time.
Erosion By Streamflow
As water enters the floor of a valley, it typically is dumped into a river or stream. Rivers and streams are moving bodies of draining water, that have a tremendous amount of force. Because of their strength, streams and rivers can cause a great amount of erosion.
Dissolved Load
Some minerals, mostly salts, are dissolved in the water and carried in solution as the dissolved load
Suspended Load
Very fine particles of clay and silt are carried in suspension
Sand, gravel, and larger rock fragments that rest along the stream bed.
Stream compentence
A measure of the particle size that the stream can carry
Stream capacity
A measure of the amount of solid material a stream has the potential to transport
Sediment in water that is carried by solution suspension and mechanical transport. Alluvium is typically smooth and round, often display a visible strata, and deposits often carry rocks of the same size
perennial stream
A perennial stream or perennial river is a stream or river (channel) that has continuous flow in parts of its stream bed all year round during years of normal rainfall. "Perennial" streams are contrasted with "intermittent" streams which normally cease flowing for weeks or months each year, and with "ephemeral" channels that flow only for hours or days following rainfall.
Recurrence Interval
A return period, also known as a recurrence interval (sometimes repeat interval) is an estimate of the likelihood of an event, such as an earthquake, flood or a river discharge flow to occur.
Stream Discharge
The discharge of a stream is the product of its velocity (V - length of travel per unit of time such as feet/second) times depth of the water (D - unit of length) times width (W of the water - units of length). (Make sure all all three lengths are expressed in the same unit.)
Sinuous channel
Sinuous channels are much more common than straight ones. They are winding and occur in almost every type of topographic setting. The curvature is usually gentle and irregular. Streams on flat land tend to have greater sinuousity, but it can also develop on severe gradients
Meandering Stream
A stream with many meandering curves. Typically develops when the land is flat with a low gradient
Braided Channels
Multiple interwoven and interconnected channels separated by low bars or islands of sand
Antecedent stream
An antecedent stream is a stream that maintains its original course and pattern despite the changes in underlying rock topography.
Dendritic stream
In a dendritic system, there are many contributing streams (analogous to the twigs of a tree), which are then joined together into the tributaries of the main river (the branches and the trunk of the tree, respectively). The underlying rock structure does not affect the structure
Trellis Stream
A trellis drainage pattern occurs when tributaries join a river and erode a valley at right angles in a pattern that resembles a garden trellis. Drainage patterns occur most often where rock or other soil formations can erode easily along weak areas in the rock.
Downcutting, also called erosional downcutting, downward erosion or vertical erosion is a geological process by hydraulic action that deepens the channel of a stream or valley by removing material from the stream's bed or the valley's floor. ... The steeper the gradient, the faster the stream flows.
River base
The base level of a river or stream is the lowest point to which it can flow, often referred to as the 'mouth of the river'. For large rivers, sea level is usually the base level, but a large river or lake is likewise the base level for tributary streams.
Graded stream
"A graded river is one in which, over a period of years, slope and channel characteristics are. delicately adjusted to provide, with available discharge, just the velocity required for the. transportation of the load supplied from the drainage basin. The graded stream is a stream in.
In geomorphology, a knickpoint or nickpoint is part of a river or channel where there is a sharp change in channel slope, such as a waterfall or lake. Knickpoints reflect different conditions and processes on the river, often caused by previous erosion due to glaciation or variance in lithology.
Knickpoint migration
As is observed for many major waterfalls, knickpoints migrate upstream due to bedrock erosion[7] leaving in their wake deep channels and abandoned floodplains, which then become terraces. Knickpoint retreat is easily demonstrated in some locations affected by postglacial isostatic response and relative sea-level drop such as in Scotland. In other areas, dating of exposed bedrock terraces is more consistent with spatially uniform incision and persistence of the knickzone at about the same location.
A river, having gained or lost potential energy with its changed slope, will then proceed to work the knickpoints out of its system by either erosion (in the case of waterfalls; gained potential energy) or deposition (in the case of lakes; lost potential energy) in order for the river to reattain its smooth concave graded profile.
The rates of knickpoint migration, in the case of waterfalls, generally range between 1mm and 10 cm per year, with some exceptional values.[3]
Lateral erosion
Lateral erosion is one of the three different ways that rivers and streams erode their banks and beds. As the term implies, lateral erosion is the erosion that occurs on the sides, or floodplains, of a river or stream, and it is also referred to as bank erosion.
Headward erosion
Head-ward erosion is the process by which a river erodes its source region, seemingly lengthening its channel in a direction opposite to that of flow. When water falls on a planer surface, it has a tendency to flow along slope in form of an oscillating stream.
Stream capture
Stream capture, river capture, or stream piracy is a geomorphological phenomenon occurring when a stream or river drainage system or watershed is diverted from its own bed, and flows instead down the bed of a neighbouring stream.
How is a delta formed
When a river reaches a lake or the sea the water slows down and loses the power to carry sediment . The sediment is dropped at the mouth of the river. Some rivers drop so much sediment that waves and tides can't carry it all away. It builds up in layers forming a delta.
Aggradation (or alluviation) is the term used in geology for the increase in land elevation, typically in a river system, due to the deposition of sediment. Aggradation occurs in areas in which the supply of sediment is greater than the amount of material that the system is able to transport. The mass balance between sediment being transported and sediment in the bed is described by the Exner equation.
Typical aggradational environments include lowland alluvial rivers, river deltas, and alluvial fans. Aggradational environments are often undergoing slow subsidence which balances the increase in land surface elevation due to aggradation. After millions of years, an aggradational environment will become a sedimentary basin, which contains the deposited sediment, including paleochannels and ancient floodplains.
Aggradation can be caused by changes in climate, land use, and geologic activity, such as volcanic eruption, earthquakes, and faulting. For example, volcanic eruptions may lead to rivers carrying more sediment than the flow can transport: this leads to the burial of the old channel and its floodplain. In another example, the quantity of sediment entering a river channel may increase when climate becomes drier. The increase in sediment is caused by a decrease in soil binding that results from plant growth being suppressed. The drier conditions cause river flow to decrease at the same time as sediment is being supplied in greater quantities, resulting in the river becoming choked with sediment.
A floodplain or flood plain is an area of land adjacent to a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge.[1] It includes the floodway, which consists of the stream channel and adjacent areas that actively carry flood flows downstream, and the flood fringe, which are areas inundated by the flood, but which do not experience a strong current. In other words, a floodplain is an area near a river or a stream which floods when the water level reaches flood stage.
Cutoff meander
A meander cutoff occurs when a meander bend in a river is breached by a chute channel that connects the two closest parts of the bend. This causes the flow to abandon the meander and to continue straight downslope.
Oxbow lake
An oxbow lake is a U-shaped body of water that forms when a wide meander from the main stem of a river is cut off, creating a free-standing body of water. This landform is so named for its distinctive curved shape, resembling the bow pin of an oxbow.
Meander scar
A meander scar, occasionally meander scarp, is a geological feature formed by the remnants of a meandering water channel. They are characterized by "a crescentic cut in a bluff or valley wall, produced by...a meandering stream." They are often formed during the creation of oxbow lakes.
Natural Levee
Natural levees commonly form around lowland rivers and creeks without human intervention. They are elongate ridges of mud and/or silt that form on the river floodplains immediately adjacent to the cut banks. Like artificial levees, they act to reduce the likelihood of floodplain inundation.
Deposition of levees is a natural consequence of the flooding of meandering rivers which carry high proportions of suspended sediment in the form of fine sands, silts, and muds. Because the carrying capacity of a river depends in part on its depth, the sediment in the water which is over the flooded banks of the channel is no longer capable of keeping the same amount of fine sediments in suspension as the main thalweg. The extra fine sediments thus settle out quickly on the parts of the floodplain nearest to the channel. Over a significant number of floods, this will eventually result in the building up of ridges in these positions, and reducing the likelihood of further floods and episodes of levee building.
If aggradation continues to occur in the main channel, this will make levee overtopping more likely again, and the levees can continue to build up. In some cases this can result in the channel bed eventually rising above the surrounding floodplains, penned in only by the levees around it; an example is the Yellow River in China near the sea, where oceangoing ships appear to sail high above the plain on the elevated river.
Levees are common in any river with a high suspended sediment fraction, and thus are intimately associated with meandering channels, which also are more likely to occur where a river carries large fractions of suspended sediment. For similar reasons, they are also common in tidal creeks, where tides bring in large amounts of coastal silts and muds. High spring tides will cause flooding, and result in the building up of levees.
Yazoo Stream
A Yazoo stream is a geologic and hydrologic term for any tributary stream that runs parallel to, and within the floodplain of a larger river for considerable distance, before eventually joining it.
Stream Rejuvenation
In geomorphology a river is said to be rejuvenated when it is eroding the landscape in response to a lowering of its base level. Rejuvenated terrains usually have complex landscapes because remnants of older landforms are locally preserved. Parts of floodplains may be preserved as terraces along the downcutting stream channels. Meandering streams often become entrenched, so a product of older river systems is found with steep, very pronounced "V" shaped valleys - often seen with younger systems. Rejuvenation may result from causes which are dynamic, eustatic or isostatic in nature. All of these cause the river to erode its bed vertically (downcutting) faster as it gains gravitational potential energy. That causes effects such as incised meanders, steps where the river suddenly starts flowing faster, and fluvial terraces derived from old floodplains.
Stream Terrace
Fluvial terraces are elongated terraces that flank the sides of floodplains and fluvial valleys all over the world. They consist of a relatively level strip of land, called a "tread," separated from either an adjacent floodplain, other fluvial terraces, or uplands by distinctly steeper strips of land called "risers." These terraces lie parallel to and above the river channel and its floodplain. Because of the manner in which they form, fluvial terraces are underlain by fluvial sediments of highly variable thickness.[1][2]
Fluvial terraces are the remnants of earlier floodplains that existed at a time when either a stream or river was flowing at a higher elevation before its channel downcut to create a new floodplain at a lower elevation. Changes in elevation can be due to changes in the base level (elevation of the lowest point in the fluvial system, usually the drainage basin) of the fluvial system, which leads to headward erosion along the length of either a stream or river, gradually lowering its elevation. For example, downcutting by a river can lead to increased velocity of a tributary, causing that tributary to erode toward its headwaters. Terraces can also be left behind when the volume of the fluvial flow declines due to changes in climate, typical of areas which were covered by ice during periods of glaciation, and their adjacent drainage basins.
Entrenched meander
An entrenched river refers to a river that is confined to a canyon or gorge, and in most cases, it is relatively narrow with very little or no flood plain. It often has meanders already developed into landscapes. ... The feature developed when such processes occur refers to un-incised meander.