Fluvial Geomorphology 2

Question 1

even though average velocity is relatively lower at headwaters, ___ velocity can be very high. Why?

Answer 1

instantaneous

b/c there is lots of up & down (pools and riffles on the bed)

Question 2

If slope/ gradient were the only factor, velocity would ___ downstream, but because channel roughness, wetted perimeter ratio, and discharge all change downstream too, velocity actually ___ as you go downstream

Answer 2

decrease

actually increases

Question 3

why does discharge increase downstream?

Answer 3

Because tributaries combine= increases the volume of water flowing through the channel = higher discharge

Question 4

as area increases, ___ water is in contact with the bed (ie. ____ and ____)- deeper/shallower, wider/ narrower
This means ___ friction and therefore ___ velocity

Answer 4

less
deeper & narrower
less
higher

Question 5

What is the range of manning’s roughness coefficient (n)?

Answer 5

0.01 to 0.05
(smooth to rough)

Question 6

Reynolds number=

Answer 6

measure of flow turbulence (internal friction in the fluid column due to flow destruction)

Question 7

more turbid= bigger or smaller range of instantaneous velocities?

Answer 7

more turbid= bigger range

Question 8

higher bed loads typically= ___ (wider or narrower) channels

Answer 8

wider
b/c harder to move

Question 9

which is easier to measure, bedload or suspended load?

Answer 9

suspended load

bed load hard to measure because it happens very episodically (high velocities are needed)

Question 10

dissolved load relates to rate of ___ weathering

Answer 10

chemical

Question 11

When might chemical weathering be high?
ie high dissolved load

Answer 11

high temp, high rainfall, high groundwater flow inputs

Question 12

t/f
fine clays can be classified as dissolved load

Answer 12

true!
They’re sometimes small enough that they’re classified as ‘dissolved’

Question 13

sediment yield=

Answer 13

amount of sediment transported by a river relative to its upstream basin area

Question 14

sediment yield ___ with drainage basin size

Answer 14

decreases

b/c dilution?

Question 15

how do you convert sediment yield to erosion/ denudation rate?

Answer 15

turn tonnes into density

depth/time x 1/rock density

Question 16

Globally, there is a negative sediment-yield to drainage area relationship, but in Canada we see the opposite (larger drainage area= higher sediment yield). Why is that?

Answer 16

b/c of the glaciation history here!
-lots of loose sediments b/c of glaciers still sitting around, not just bedrock

Question 17

paraglacial=

Answer 17

non-glacial processes that are a direct result of glaciation

Question 18

paraglaciation=

Answer 18

“unstable” conditions caused by a “relaxation time lag” to move sediments from upland valleys to major valleys following glaciation

Question 19

t/f
both sediment load and bedload increase as discharge increases

Answer 19

true

Question 20

suspended load= -% of total sediment load
bedload= __% of sediment transport in river systems

Answer 20

90-99%

1% for bedload

Question 21

If bedload is only 1% of total sediment load, why is it so important for river morphology?

Answer 21

b/c it contributes a lot to roughness!

higher bed load= wide channels

Question 22

bed load=

Answer 22

material transported along the bed by railing, traction, saltating

Question 23

suspended load=

Answer 23

materials transported within the fluid column itself (air or water)
- fine sand and clays

Question 24

dissolved load=

Answer 24

ions being transported, products of chemical + biological weathering

Question 25

laminar sublayer=

Answer 25

zone of low turbulence + lower velocity caused by friction along the bed

Question 26

What’s the main role of turbulence?

Answer 26

changes in the instantaneous velocity are key for entraining particles

Question 27

Once a particle is in motion, it requires ___ (less or more) force to remain in motion

This is empirically described by the ___ curve

Answer 27

less
Hjulstrom

Question 28

What does the Hjulstrom curve represent?

Answer 28

sediments entrained by water and the role of grain size on critical shear stress