Lecture 4 - Sediment Transport Flashcards
What physical properties affect sediment entrainment?
Size, shape and density of a sediment
What is cohesion, and how important is it?
Cohesion is the bond between particles.
The more cohesive particles are, the stronger the bond between them is.
What are the three threshold states?
a) Critical Velocity
b) Critical shear stress
c) Lift forces
What is the terminology for when smaller particles hide under larger, less moveable sediments?
Protrusion and hiding
What are the 4 modes of sediment load transport?
1) Fine wash load
2) Suspended load
3) Dissolved load
4) Coarse bedload
Define fine wash load
Neutrally buoyant particles
What is suspended load?
sediment transported by turbulent eddies
Define how coarse bedload moves in a channel
By rolling, sliding and saltating (to move in leaps)
What are the 2 main classifications for bedforms?
a) ripples, dune and anti dunes
b) pools, riffles and bars
Where can ripples and dunes be found?
In a lower flow regime (sub-critical flow).
What is a plane bed and where can it be found?
A plane bed is a flat riverbed, it can be found in the transition zone, between sub and super-critical flow.
Where can anti dunes be found?
In an upper flow regime (super-critical flow)
What are bars and how are they formed?
A bar is a sub-aerial feature, grain sizes vary from sand to boulders. They form in the lower flow of a river
What are pools?
pools - topographic lows - bed scour - associated with meander bends
What are riffles?
Riffles - topographic highs - sediment accumulation - inflection point of thalweg (thalweg is a line that shows the natural diretion of a channel)
