River channel migration is the geomorphological process that involves the lateral migration of analluvialriver channel across itsfloodplain. This process is mainly driven by the combination ofbank erosion of andpoint bar deposition over time. When referring to river channel migration, it is typically in reference tomeandering streams. Inbraided streams, channel change is driven bysediment transport.[1]
It has been proposed that lateral migration is a particularly dominant erosive process insavanna landscapes.[2]
As flow enters the bank of analluvial river, the centrifugal force created by the bend instigateshelicoidal flow, a corkscrew like pattern of flow, which drives thehydraulic action acting on the opposing bank.[1] This is where the primary process in river channel migration ofbank erosion 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 criticalshear stress of the stream bed.[3]
The sediment taken from the bank during the process ofbank erosion is deposited on the opposing side of the channel fueling the process called point bar deposition. Thehelicoidal flow also plays a role in this process by acting as a cross channel component that moves the sediment to the other side.[1] 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.[3] In addition, point bars act as topographic obstructions once formed that further drive flow into the opposite bank, creating apositive feedback loop. This leads to the meanders of an alluvial river becoming more well defined over time.
Typical features found in river channel migration arepoint bars,cut banks,meanders,floodplains, andoxbow lakes.[1]
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.[4]
In order to model river channel migrations over time,orthogonal functions 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.[5]
| Large-scale features | |
|---|---|
| Alluvial rivers | |
| Bedrock river | |
| Bedforms | |
| Regional processes | |
| Mechanics | |
