Hydraulics

Question 1

Subcritical Flow

Answer 1

Actual flow&raquo_space; critical depth
Low velocity and high depth
Downstream of hydraulic jump
Culvert outlet flow
Fr < 1 (slow, tranquil, deep)

Question 2

Supercritical Flow

Answer 2

Actual Flow &laquo_space;Critical depth
high velocity and low depth
Upstream of hydraulic jump
Culvert inlet flow
Fr > 1 (fast, rapid, shallow)

Question 3

1 cfs = how many gal/min?

Answer 3

1 cfs = 448 gal/min

Question 4

Weirs

Answer 4

Usually subcritical flow upstream, supercritical flow downstream
Sharp crested weirs = small flows, short in direction of flow
Cipoletti weir = horizontal broad weir with side slope 1 to 4
Q is function of head over weir to width of weir

Question 5

Hydraulic Radius if pipe is flowing full? Half full?

Answer 5

Full and half full: D/4

Question 6

Circular Pipe Sizing

Answer 6

Hydraulic radius is max when d/D = 0.81
Velocity is greatest at 81%
Q of half full channel is 50% of same channel when full
Q is max at 92% depth

Question 7

Culvert Inlet Control

Answer 7

Flow Capacity controlled by: Headwater, flow area at inlet, type of inlet
Always partially full
Critical depth occurs at inlet
Slope usually steep
Supercritical thru culvert

Question 8

Culvert Outlet Control

Answer 8

Flow Capacity controlled by: culvert diamter, area, materia, roughness, slope, tailwater, headwater, flow area at inlet, type of inlet edge
Full or partially full
“Free” = tailwater is equal to or lower than critical depth
Subrticial thru culvert

Question 9

Unit Hydrographs

Answer 9

Hydrograph from unit of EXCESS rainfall
Most reliable method for predicting floods of any frequency
Duration of runoff does not depend on rainfall depth
Rainfall is spatially uniform over watershead area
Runoff is linearly related to rainfall
does NOT consider base flow

Question 10

Hydrostatic Pressure –> 1 psi of pressure = how many ft of head?

Answer 10

1 psi of pressure = 2.31 ft of head

Question 11

Pipes in Parallel

Answer 11

Pipes are split
Q is sum of all flow components
Flow in = flow out, but have to add each pipe split
Head loss across all branches is same regardless of roughness or length
Flow divides itself so head loss is equal in each branch (not necessarily same flow in each branch)

Question 12

Buoyancy

Answer 12

Buoyancy is equal to the weight of the displaced fluid

Question 13

Most Efficient Channel Geometries

Answer 13

Cross section that has the minimum wetted perimeter
Circle is the most efficient shape
Rectangle: depth that is half the width

Question 14

Most likely questions on test:

Answer 14

Partially full circular channel flow
Sizing of circular pipes
Water balance equations
Runoff - Rational Method
Bernoulli Equation