Hydraulics Revision - Channel Geometry

Front 1

Define:

1) Hydraulic Radius, R
2) Hydraulic Mean Depth, Dm

Back 1

1) R = A/P (P is the wetted perimeter)

2) Dm = A/B (B is the surface width)

Front 2

Define in terms of b (breadth) and y (depth) the following properties of a rectangular channel:

1) Area, A
2) Wetted Perimeter, P
3) Surface Width, B
4) Hydraulic Radius, R
5) Hydraulic Mean Depth, Dm

Back 2

1) A = by

2) P = 2y + b

3) B = b

4) R = (by)/(b + 2y)

5) Dm = y

Front 3

Define in terms of b (breadth), and y (depth) the following properties of a trapezoidal channel:

1) Area, A
2) Wetted Perimeter, P
3) Surface Width, B
4) Hydraulic Radius, R
5) Hydraulic Mean Depth, Dm

Back 3

Front 4

Define in terms of b (breadth), D (diameter), Φ (depth angle) and y (depth) the following properties of a circular channel:

1) Area, A
2) Wetted Perimeter, P
3) Surface Width, B
4) Hydraulic Radius, R
5) Hydraulic Mean Depth, Dm

Back 4

Front 5

Define steady uniform flow.

Back 5

Water Depth, Width, Flow Area, Velocity remain constant with DISTANCE and TIME.

Front 6

What is the Reynolds Number for open channels?

Back 6

Front 7

What is the Manning equation for velocity (V) and the associated equation for flow rate (Q)

Back 7

Front 8

Define this type of channel. How can values for V and Q be calculated?

Back 8

This is a compound channel and values for V and Q can be calculated separately and summed to give overall values.

Front 9

What does it mean to have the best hydraulic section?

Back 9

The channel should have the least wetted perimeter for a given area.

Use differentiation to optimise the area (given in terms of b and y) to find the best ratios.

Front 10

What are the three main Channel Types?

Back 10

Lines, Unlined or Grassed.

Front 11

Define:

1)Maximum Permissible Velocities
2)Minimum permissible velocity (giving values usually used)

Back 11

1) Maximum permissible velocity is the maximum velocity that will not cause erosion.

2) Minimum permissible velocity is the lowest velocity that will prevent both sedimentation and
vegetative growth. In general, 0.6 to 0.9 m/s is used

Front 12

What is Freeboard?

Back 12

The vertical distance from the top of the channel to the water's surface as a design condition.

Front 13

What types of flow are there?

Back 13

Front 14

Define the Froude Number and what it means to have Fr < 1, Fr = 1 and Fr > 1

Back 14

Front 15

Useful computational info

Back 15

...

Front 16

A sudden change of the channel geometry can lead to which type of flow?

Back 16

Rapidly Varied Flow.

Front 17

Define the energy equation.

Back 17

Always take α = 1

Front 18

For supercritical flows, what happens to the flow depth when

1) Velocity increases
2) Velocity decreases

Back 18

Front 19

What is the value of specific energy at critical depth?

Back 19

Es = 0

Front 20

When does a hydraulic jump occur?

Back 20

When a supercritical flow meets a subcritical flow.

Front 21

Define the momentum and force equations used to evaluate hydraulic jumps.

Back 21

Front 22

Sequent and Initial depths in a rectangular channel are determined by which equation?

Back 22

The first equations are NOT GIVEN IN THE FORMULA SHEET.

The equations involving the Froude number are given.