Lecture #10 [Fluvial landforms and processes]

Question 1

what are the stream channe; patterns [3]

Answer 1

straight
meandering
braided

Question 2

thalweg

Answer 2

line running in direction of current, connecting deepest points in the channel

Question 3

alluvium

Answer 3

stream deposited debris

Question 4

downcutting is most frquent in which area of a stream

Answer 4

upper reaches
gradient is usually steep
valley is narrow
produces v shape

Question 5

knickpoint migration

Answer 5

waterfalls and rapids

rapid flow cuts backward and smoothens out gradient

Question 6

valley widening

Answer 6

lateral erosion
high speed = erosion
low speed = deposition

Question 7

floodplains

Answer 7

when meandering river moves across wide level valley floor, valley floor covered with alluvium deposits

Question 8

oxbow lake formation

Answer 8

meandering swinging back and forth until its cut off by past widening makes swampy lakes at cross sections

Question 9

Natural Levee Formation

Answer 9

Floodplain slightly higher along stream edges
ØFloodtime: stream overflows
ØPrincipal deposition = on margins of channel
ØNatural levees = deposited sediment on each side of
stream

Question 10

three types of stream flow

Answer 10

emphermeral streams = dry, carry water during and after rainfall

intermittent streams= flow during rainy season

perennial streams=
flow year round

Question 11

Amount of sediment moved by a stream depends on:

Answer 11

• Discharge
• Gradient (slope)
• Velocity
• Bed roughness
• Channel morphology
• Nature of grains

Question 12

relationships between particle sizes and velocities of erosion

Answer 12

small (clay,silt)
cohesive, high eros., remains in suspension in running water

large particles (sand,gravel)
continuously picked up and deposited

intermediate size (coarse silt/fine sand)
most easily eroded

Question 13

Stream Erosion and Deposition

Answer 13

ØStream cuts downward when it could potentially carry more
sediment than is being supplied
lStream bed is lowered (erosion)

ØStream aggrades (builds up) when more sediment is provided than it
can carry
lStream bed rises (deposition)