Terminology of the
subenvironments of a river
Fluvial Environments
Meandering rivers.- based on the recognition of point bars from their distinctive vertical profile
Sediments in meandering rivers may be gravel-, sand- or silt-dominated.
The lateral accretion of the point bar is the most distinctive feature of meandering-river deposits, but some bars in braided rivers also exhibit lateral accretion.
Braided river is characterized by a wide active valley with several or many component channels of varying sinuosity
The main sediment load may be sand or gravel
Individual channels undergo rapid migration, switches in position and
abandonment
The deposits of braided rives are typically composed of an assemblage of crossbedded fragments of bar deposits, exhibiting accretion directions oriented in almost any direction, the most common
being downstream and oblique to channel orientation.
Anastomosed rivers occur in areas of active vertical aggradation, such as coastal systems during a time of rapidly rising sea level, and in the case of inland systems where a river valley is
backfilling behind a constriction
Many channels of variable sinuosity occur
They are relatively stable in position, showing little or no evidence of the
lateral migration common to the meandering and braided styles
Broad floodplains occur between the channels
These may be wetlands, peat swamps or desiccated flats, depending on the climate
Straight rivers occur in areas of very low slope, such as near base level. As such, they are most common as the distributaries of certain deltas.
Although the river itself may be nearly straight,
there is typically a slightly sinuous deep channel, and long, narrow bars, called
alternate bars, accumulate along the banks inside the meanders defined by this
channel.