Fluvial Processes and Landforms

Question 1

Fluvial Process

Answer 1

processes that involve running water

Question 2

Valley

Answer 2

area where drainage system clearly established

Question 3

interfluve

Answer 3

higher land above valley walls that separates adjacent valleys

Question 4

watershed

Answer 4

AKA drainage basin, consists of valley bottom, sides, portions of surrounding interfluves

Question 5

Stream order

Answer 5

1st - smallest
gets bigger w. numbers

Question 6

Erosion by overland flow

Answer 6

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

Question 7

How does sediment get into river

Answer 7

1) weathering of rock (breaks into smaller particles)
2) mass wasting (sediment moves down)
3) erosion - 3 steps (stream erosion, transportation, deposition)

Question 8

What determines erosive capacity of stream

Answer 8

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

Question 9

what affects flow speed

Answer 9

1) gradient (steeper gradient, faster flow)
2) shape of channel (more narrow, goes faster)
3) volume (more water, higher flow)

Question 10

1) High competence + capacity leads to
2) low competence + capacity leads to

Answer 10

1) erosion
2) deposition

Question 11

Stream load

Answer 11

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

Question 12

Saltation vs traction (relates to bedload)

Answer 12

1) saltation = think of hops of smaller rock
2) traction = larger rocks which slide/roll down streambed

Question 13

Stream Competence

Answer 13

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

Question 14

stream capacity

Answer 14

1) measure of amount of solid material stream can transport, expressed as volume
2) fluctuates over time
3) influenced by velocity + amount of water

Question 15

Flood recurrence interval

Answer 15

1) probability of given-size flood
ex: 100 year flood = 1 in 100 chance of happening more than once a year

Question 16

Stream channel patterns

Answer 16

1) straight
2) sinuous
3) meandering
4) braided

Question 17

Straight stream channel pattern

Answer 17

1) short + uncommon (generally manmade)
2) strong control by underlying geological structure
3) thalweg - line created by deepest water - meanders even in straight channel

Question 18

Sinuous channels

Answer 18

1) Winding + occur in every type of topographic setting
2) very common
3) common in high latitude

Question 19

Meandering channel

Answer 19

1) follows serpentine course, forming VERY SMOOTH curves
2) occurs in FLAT GROUND with suspended load

Question 20

Braided Channels

Answer 20

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

Question 21

Downcutting (valley DEEPENING)

Answer 21

1) lowering of streambed via hydraulic power
2) occurs when stream is very fast or has high volume
3) produces V-shaped cross section

Question 22

Base level

Answer 22

1) limit to amount of downcutting a stream can do
2) at a gradient –> allows stream to flow

Question 23

Sea Level

Answer 23

Absolute, ultimate base level for streams

Question 24

graded stream

Answer 24

when stream reaches dynamic equilibrium
most streams do not achieve this throughout course all the time

Question 25

Knickpoint migration

Answer 25

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

Question 26

Lateral erosion (widening valley)

Answer 26

1) Happens in meandering rivers
2) Erosion on outside of banks
3) deposition in inside

Question 27

How can stream lengthen its valley

Answer 27

1) headward erosion
2) delta formation

Question 28

Delta formation
(lengthening)

Answer 28

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)

Question 29

What is headward erosion?

Answer 29

1) when stream erodes soil/rock at head of stream –> lengthening it

Question 30

Floodplains

Answer 30

1) low-lying nearly flat valley floor that is periodically inundated with floodwaters
2) outer points of meanders

Question 31

bluff

Answer 31

1) steep bank or cliff that forms along a river valley due to erosion and land movements
2) edge of lateral erosion

Question 32

Cutoff meander/oxbow lake (cutoff meander –> oxbow –> meander scar)

Answer 32

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

Question 33

Natural levees

Answer 33

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

Question 34

Yazoo streams

Answer 34

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

Question 35

Flood controls for rivers

Answer 35

1) dams = flood control + to ensure enough water for ships to go through
2) artificial levees = works BUT if it fails –> often catastrophic

Question 36

Cutbank

Answer 36

High velocity –> results in increased competence/capacity on the outside of the meanders – > increased erosion

Question 37

PointBar

Answer 37

decrease velocity on inside –> reduced competence/capacity on inside of meanders –> increased deposition