River channel migration is the geomorphological process that involves the lateral migration of an

alluvial Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. ...

river channel across its

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

. This process is mainly driven by the combination of

bank erosion Bank erosion is the wearing away of the banks of a stream or river. This is distinguished from erosion of the bed of the watercourse, which is referred to as ''scour''. The roots of trees growing by a stream are undercut by such erosion. As the ...

of and

point bar A point bar is a depositional feature made of alluvium that accumulates on the inside bend of streams and rivers below the slip-off slope. Point bars are found in abundance in mature or meandering streams. They are crescent-shaped and located on ...

deposition over time. When referring to river channel migration, it is typically in reference to

meandering streams A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank (cut bank) and deposits sediments on an inner, convex ba ...

. In braided streams, channel change is driven by

sediment transport Sediment transport is the movement of solid particles (sediment), typically due to a combination of gravity acting on the sediment, and/or the movement of the fluid in which the sediment is entrained. Sediment transport occurs in natural system ...

.Bierman, Paul R., and David R. Montgomery. ''Key Concepts in Geomorphology''. New York: W.H. Freeman, 2014. Print. It has been proposed that lateral migration is a particularly dominant erosive process in

savanna A savanna or savannah is a mixed woodland- grassland (i.e. grassy woodland) ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground ...

landscapes.

Physical processes

Bank erosion

As flow enters the bank of an

alluvial river An alluvial river is one in which the bed and banks are made up of mobile sediment and/or soil. Alluvial rivers are self-formed, meaning that their channels are shaped by the magnitude and frequency of the floods that they experience, and the ...

, the centrifugal force created by the bend instigates helicoidal flow, a corkscrew like pattern of flow, which drives the

hydraulic action Hydraulic action, most generally, is the ability of moving water (flowing or waves) to dislodge and transport rock particles. This includes a number of specific erosional processes, including abrasion, at facilitated erosion, such as ''static eros ...

acting on the opposing bank. This is where the primary process in river channel migration of

occurs. Often the bank is undercut, another result of the helicoidal flow, which leads to the creation of cut banks. Factors that limit the rate of bank erosion include the rate of deposition of the point bar, stream power, and the critical

shear stress Shear stress, often denoted by ( Greek: tau), is the component of stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross section. '' Normal stress'', on ...

of the stream bed.Howard, Alan D. "Modeling channel migration and floodplain sedimentation in meandering streams." ''Lowland floodplain rivers: geomorphological perspectives''(1992): 1-41.

Point bar deposition

The sediment taken from the bank during the process of

is deposited on the opposing side of the channel fueling the process called point bar deposition. The helicoidal flow also plays a role in this process by acting as a cross channel component that moves the sediment to the other side. The processes of point bar deposition and bank erosion are intertwined and in most cases the erosion rate of cut banks is equal to the deposition rate of point bars. In addition, point bars act as topographic obstructions once formed that further drive flow into the opposite bank, creating a

positive feedback loop Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the ...

. This leads to the meanders of an alluvial river becoming more well defined over time.

Characteristic features

Typical features found in river channel migration are

cut bank A cut bank, also known as a river cliff or river-cut cliff, is the outside bank of a curve or meander in a water channel (stream), which is continually undergoing erosion.Essentials of Geology, 3rd Ed, Stephen Marshak Cut banks are found in abu ...

meander A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank ( cut bank) and deposits sediments on an inner, convex ban ...

s, and

oxbow lake An oxbow lake is a U-shaped lake or pool that forms when a wide meander of a river is cut off, creating a free-standing body of water. In South Texas, oxbows left by the Rio Grande are called '' resacas''. In Australia, oxbow lakes are call ...

Measurement and modeling

Techniques used for measuring river channel migration vary among different time scales. Over long time scales, sedimentological evidence, botanical evidence, and historical sources are utilized. Over intermediate time scales, planimetric resurveying and repeated cross profiting are utilized. Over short time scales, terrestrial photogrammetry and erosion pins are utilized. In order to model river channel migrations over time,

orthogonal functions In mathematics, orthogonal functions belong to a function space that is a vector space equipped with a bilinear form. When the function space has an interval as the domain, the bilinear form may be the integral of the product of functions over the ...

of erosion path lines can be generated for individual point bar complexes. The orthogonal functions can be used to directly indicate the paths that channels could take in lateral migrations. The modeling of meander patterns can be useful in a variety of physical applications.

Physical processes

Bank erosion

Point bar deposition

Characteristic features

Measurement and modeling

References

Further reading