Measurement and Mitigation Flashcards
Where is depth-averaged velocity typically taken from?
0.3-0.4 times the flow depth
In USGS measurement, where are velocity measurements taken depending on flow depth?
> 1m depth: velocity at 20% and 80%
<1m depth: velocity at 40%
How is a river divided in USGS discharge measurement?
20-30 vertical sections such that no section is >5% of the flow
List 6 devices for velocity measurement in large flows
Propeller meters
Electromagnetic meters
Acoustic meters
Optical strobe meters
Particle trackers
Dynamic pressure head meters
What are the methods for direct measurement of discharge?
Sharp crested weirs
Broad crested weirs
Venturi and Parshall flumes
What must be maintained for flow measurement over a weir to be accurate?
Flow over the weir is critical
Flow downstream of the weir is supercritical
What are the 5 key properties of sediment?
Density
Diameter
Roundness
Settling velocity
Angle of repose
How is total sediment load in a flow calculated?
Suspended load + bed load
What are the 3 types of bed load transportation?
Sliding
Saltation
Rolling
Similar to aerodynamics, what is the equation of flow velocity with shear stress?
u/u* = 2.5ln(11H/ks)
ks is bed roughness
What is the equation for u*?
u* = sqrt(τ0/ρ)
What is critical shear stress?
The bed shear at which sediment transport begins
How and why are τ* and Re* found?
τ* from τ0
Re* from u*
To use the Shield’s diagram for determining motion
