River Flow and Landforms Flashcards
Three main types of flow:
- laminar
- turbulent
- helicoidal
Laminar flow is the flow of water in…
sheets, parallel to the channel bed, with no uniform velocity. A smooth and straight and shallow channel is needed. Usually in the lower course of the river.
Turbulent flow occurs where…
there are high velocities and eddies caused by alternating pools and riffles.
Bed roughness also increases…
the turbulence, e.g. mountain streams have more than alluvial channels.
Turbulent flow is associated with…
hydraulic action as turbulences cause variations in pressure within the water.
Helicoidal flow is created by…
horizontal turbulence, creating a corkscrewing motion. It is associated with meandering river channel.
The erosion and deposition by helicoidal flow…
creates meanders. Thalweg travels from the outside bank to the outside of the meander.
Sinuosity is…
the length of a stream channel expressed as a ratio of the valley length.
Low sinuosity has value…
1 which is straight.
Straight channels have sinuosity less than…
1.5
Meandering channels have greater than…
1.5
The braided channel is…
divided by islands or bars. Islands are vegetated and long-lived bars unvegetated and less stable.
Braiding occurs when a stream does not have…
the capacity to transport its load in a single channel, the discharge varies and the banks are easily erodible.
Meanders are formed because the river tries to achieve…
an equilibrium, so energy is equally distributed.
River cliffs are…
created on the outside of the meander.
The meanders may migrate…
downstream or laterally(sideways) and erode the floodplain.
Incised meanders are meanders that are…
well developed on horizontally bedded rocks and forms when a river cuts through alluvium and into the underlying bedrock.
Intrenched meanders are…
symmetrical and occur when down-cutting is fast enough to offset the lateral erosion.
Ingrown meander is a result of…
lateral migration. They are asymmetric in cross-section.
Variation in the cross-
section of the river causes variation in erosion and deposition. Rise to river cliffs on the outside and point bars on the inner bank.
Pools and riffles are formed by…
turbulence.
Eddies(viri) cause deposition of…
coarse sediment forming riffles and fine fine sediment forming pools.
Riffles have…
stepper gradient than pools and are located where the river velocity is reduced midstream, in between pools.
Levees and floodplain forms where…
the river exceeds its banks regularly.
The alluvium is carried further and deposited on…
on the flood plain.
Terraces are formed as…
the old floodplains are eroded.
River bluffs are the edges of…
terrace and it is a line of relatively steep slopes.
Two types of incised meanders:
- entrenched
- ingrown
