Fluvial Geomorphology 2 Flashcards
even though average velocity is relatively lower at headwaters, ___ velocity can be very high. Why?
instantaneous
b/c there is lots of up & down (pools and riffles on the bed)
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
decrease
actually increases
why does discharge increase downstream?
Because tributaries combine= increases the volume of water flowing through the channel = higher discharge
as area increases, ___ water is in contact with the bed (ie. ____ and ____)- deeper/shallower, wider/ narrower
This means ___ friction and therefore ___ velocity
less
deeper & narrower
less
higher
What is the range of manning’s roughness coefficient (n)?
0.01 to 0.05
(smooth to rough)
Reynolds number=
measure of flow turbulence (internal friction in the fluid column due to flow destruction)
more turbid= bigger or smaller range of instantaneous velocities?
more turbid= bigger range
higher bed loads typically= ___ (wider or narrower) channels
wider
b/c harder to move
which is easier to measure, bedload or suspended load?
suspended load
bed load hard to measure because it happens very episodically (high velocities are needed)
dissolved load relates to rate of ___ weathering
chemical
When might chemical weathering be high?
ie high dissolved load
high temp, high rainfall, high groundwater flow inputs
t/f
fine clays can be classified as dissolved load
true!
They’re sometimes small enough that they’re classified as ‘dissolved’
sediment yield=
amount of sediment transported by a river relative to its upstream basin area
sediment yield ___ with drainage basin size
decreases
b/c dilution?
how do you convert sediment yield to erosion/ denudation rate?
turn tonnes into density
depth/time x 1/rock density
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?
b/c of the glaciation history here!
-lots of loose sediments b/c of glaciers still sitting around, not just bedrock
paraglacial=
non-glacial processes that are a direct result of glaciation
paraglaciation=
“unstable” conditions caused by a “relaxation time lag” to move sediments from upland valleys to major valleys following glaciation
t/f
both sediment load and bedload increase as discharge increases
true
suspended load= -% of total sediment load
bedload= __% of sediment transport in river systems
90-99%
1% for bedload
If bedload is only 1% of total sediment load, why is it so important for river morphology?
b/c it contributes a lot to roughness!
higher bed load= wide channels
bed load=
material transported along the bed by railing, traction, saltating
suspended load=
materials transported within the fluid column itself (air or water)
- fine sand and clays
dissolved load=
ions being transported, products of chemical + biological weathering
laminar sublayer=
zone of low turbulence + lower velocity caused by friction along the bed
What’s the main role of turbulence?
changes in the instantaneous velocity are key for entraining particles
Once a particle is in motion, it requires ___ (less or more) force to remain in motion
This is empirically described by the ___ curve
less
Hjulstrom
What does the Hjulstrom curve represent?
sediments entrained by water and the role of grain size on critical shear stress
