Fluvial Processes Flashcards
Who is the knowledge of water and sediment behaviour within river channels important to? (3)
Engineers
Civil defence
Geomorphologists
Why is knowledge of water and sediment behaviour within river channels important to engineers?
Managment
Why is knowledge of water and sediment behaviour within river channels important to civil defence?
Risk mitigation
Why is knowledge of water and sediment behaviour within river channels important to geomorphologists?
Landscape evolution
What are 4 fundamental flow characteristics?
Uniform/ non- uniform flow
Steady/ unsteady flow
Laminar/ turbulent
Tranquil/rapid
How can you identify if a flow is uniform or not?
Look at the velocity and see if it is constant within the cross-section
How do you tell if the flow is steady or not?
See if the velocity is constant with time
How do you identify a laminar flow?
Reynold’s number is less than 500
How do you identify a turbulent flow?
Reynold’s number is more than 2500
What is energy the product of?
Force x Distance through which the force acts
What 4 things is energy in streams expended in?
Overcoming viscous shear and turbulence (internal friction)
Boundary friction
Channel erosion
Sediment transport
What is the hydraulic radius?
A/P
What is shear stress?
The rate of change of vertical velocity
What two things can cause resistance to flow?q
Form roughness
Grain roughness
What is stream power measured in?
Wm-2
What is the equation for stream power
Water density x Gravity x Discharge x Slope
(divided by) Channel width
What are two direct methods of bedload measurements?
Sediment traps
Pressure pillows
What is an indirect method of bedload measurement?
Acoustic monitoring
What are two partial methods of bedload measurement?
Tracers (painted pebbles/ radio pebbles)
Sediment budget- channel cross section change
What curve shows bedload measurement?
Hjulström curve
In terms of bedload entrainment, what is velocity used to define?
A critical threshold for entrainment
When does bedload transport occur?
Once the critical threshold for entrainment in exceeded
What does entrainment represent?
The balance of applied vs resisting forces
What creates a vertical pressure gradient?
The velocity difference between the top and bottom of a grain
What is eddying?
The movement of water in a circular way
What are 3 sources of suspended sediment?
Weathering regime
Slope regime (degree of “coupling”)
Fluid transfer regime
What curve looks at suspended sediment?
Suspended sediment rating curves
What are two key thresholds for erosion/entrainment?
Particle size, shape and density
Cohesive/ non- cohesive
Give two examples of cohesive sediments
Clay
Silt
When are cohesionless sediment grains entrained?
When there is a great enough force
What are 3 measurement techniques?
Units/parameters
Manual/point sampling
Automated sampling
What loops can be found on suspended sediment rating curves?
Hysteresis loops
What is shown on suspended sediment rating curves?
Discharge vs suspended sediment concentration
What 3 things control suspended sediment concentration?
Size of particles (settling velocity)
Degree of turbulence
Sediment availability
What 3 things affect the degree of turbulance?
How uniform the distribution of grains is
Mixing (diffusion)
Pulses of turbulence (eddies)
What is diffusion the balance of?
Upward and downward movement
What 4 things does the rate of settling depend upon?
Class diameter
Specific gravity of clast
Grain shape
Stokes Law
What is the equation for the rate of settling?
Drag coefficient x (Diameter/2)^2
What 5 things to do with chemistry determine water quality?
pH Alkalinity (hardness) Ions in solution (anions, cations) Oxygen-reduction potential or dissolved O2 Organic species
What 6 physical factors determine water quality?
Colour Taste Odour Temperature Suspended sediment Bacterial counts
