Fluvial Processes and Landforms Flashcards
Fluvial Process
processes that involve running water
Valley
area where drainage system clearly established
interfluve
higher land above valley walls that separates adjacent valleys
watershed
AKA drainage basin, consists of valley bottom, sides, portions of surrounding interfluves
Stream order
1st - smallest
gets bigger w. numbers
Erosion by overland flow
1) rain drops fall –> splash erosion, causing particles to move downhill
2) sheet erosion = water flows down surface as thin sheet, transporting particles
3) Moves onto rill, which converge into gullies
How does sediment get into river
1) weathering of rock (breaks into smaller particles)
2) mass wasting (sediment moves down)
3) erosion - 3 steps (stream erosion, transportation, deposition)
What determines erosive capacity of stream
1) direct hydraulic power of moving water
2) rocks, boulders, silt the stream carries contributes to erosion
3) chemical action = hydrolysis + corrosion
4) flow speed
what affects flow speed
1) gradient (steeper gradient, faster flow)
2) shape of channel (more narrow, goes faster)
3) volume (more water, higher flow)
1) High competence + capacity leads to
2) low competence + capacity leads to
1) erosion
2) deposition
Stream load
1) material brought by water
2) 3 components:
1) dissolved load, includes minerals
2) suspended load = fine clay/silt particles that literally are suspended in water
3) bedload = larger rock fragments
Saltation vs traction (relates to bedload)
1) saltation = think of hops of smaller rock
2) traction = larger rocks which slide/roll down streambed
Stream Competence
1) stream competence = measure of particle size stream can transport, mainly depends on flow speed (double speed, 4X particle size)
2) measure of particle diameter
3) influenced by velocity
stream capacity
1) measure of amount of solid material stream can transport, expressed as volume
2) fluctuates over time
3) influenced by velocity + amount of water
Flood recurrence interval
1) probability of given-size flood
ex: 100 year flood = 1 in 100 chance of happening more than once a year
Stream channel patterns
1) straight
2) sinuous
3) meandering
4) braided
Straight stream channel pattern
1) short + uncommon (generally manmade)
2) strong control by underlying geological structure
3) thalweg - line created by deepest water - meanders even in straight channel
Sinuous channels
1) Winding + occur in every type of topographic setting
2) very common
3) common in high latitude
Meandering channel
1) follows serpentine course, forming VERY SMOOTH curves
2) occurs in FLAT GROUND with suspended load
Braided Channels
1) multiple interwoven + interconnected channels
2) takes place in heavy sediment load (Gravel) + in areas with prominent dry seasons
3) active channels of braided stream make cover less than 1/10 width of full channel
Downcutting (valley DEEPENING)
1) lowering of streambed via hydraulic power
2) occurs when stream is very fast or has high volume
3) produces V-shaped cross section
Base level
1) limit to amount of downcutting a stream can do
2) at a gradient –> allows stream to flow
Sea Level
Absolute, ultimate base level for streams
graded stream
when stream reaches dynamic equilibrium
most streams do not achieve this throughout course all the time
Knickpoint migration
1) irregularities in channel + common result of abrupt changes in bedrock resistance
2) rapid when bedrock consists
3) Basically like a retreating cliff that is breaking apart because of water
Lateral erosion (widening valley)
1) Happens in meandering rivers
2) Erosion on outside of banks
3) deposition in inside
How can stream lengthen its valley
1) headward erosion
2) delta formation
Delta formation
(lengthening)
1) lengthening at seaward end
2) process that occurs when a river carrying sediment slows down and empties into a larger body of water, forming new land + lengthening river (forming distributaries)
What is headward erosion?
1) when stream erodes soil/rock at head of stream –> lengthening it
Floodplains
1) low-lying nearly flat valley floor that is periodically inundated with floodwaters
2) outer points of meanders
bluff
1) steep bank or cliff that forms along a river valley due to erosion and land movements
2) edge of lateral erosion
Cutoff meander/oxbow lake (cutoff meander –> oxbow –> meander scar)
1) cutoff meander = when an new channel is created, cutting water off from old loop
2) oxbow lake = when cutoff portion filled with water for temporary period of time (not connect to river anymore) –> eventually dry up becoming meander scars
Natural levees
1) raised areas of sand and mud that form along the banks of rivers and streams
2) because when flooding –> reduced competence + capacity –> therefore drops heavier sediment
Yazoo streams
1) tributary stream that flows parallel to a larger river within its floodplain for a considerable distance before joining it
2) water that cannot go back –> bc of natural levees
Flood controls for rivers
1) dams = flood control + to ensure enough water for ships to go through
2) artificial levees = works BUT if it fails –> often catastrophic
Cutbank
High velocity –> results in increased competence/capacity on the outside of the meanders – > increased erosion
PointBar
decrease velocity on inside –> reduced competence/capacity on inside of meanders –> increased deposition
