Open Channel Flow

Question 1

True or False
Natural rivers and streams have an uppermost boundary that is a free surface, adding an additional degree of freedom, making their flow dynamics more complex than pipe flow.

Answer 1

True

Question 2

Man-made canals and sluiceways typically have more regular geometries and constant dimensions, allowing for _______ flow.

Answer 2

Uniform

Question 3

What does the term ‘gradually varied flow’ imply in the context of river/stream flow?
A) There are abrupt changes in water height along the flow direction.
B) Water height does not change with the flow direction.
C) Water height slowly changes along the flow direction.

Answer 3

C) Water height slowly changes along the flow direction.

Question 4

What is meant by the energy friction slope (dH/dx) in open channel flow?

Answer 4

The energy friction slope represents the rate of energy loss per unit length of the channel due to friction, indicated as dH/dx = -S_f

Question 5

True or False
In open channel flow, the water surface slope, bed slope, and energy slope are all the same for uniform flow.

Answer 5

True

Question 6

The Froude number (Fr) in open channel flow is calculated as Fr^2 = U^2/gh, where U is the flow velocity, g is the gravitational acceleration, and h is the ______.

Answer 6

depth of the flow

Question 7

What is the ‘normal depth’ (h_n ) in the context of open channel flow?
A) The depth at which flow becomes turbulent
B) The depth at which gravitational forces balance drag/shear forces resulting in uniform flow
C) The maximum depth achieved during rapid flow variations

Answer 7

B) The depth at which gravitational forces balance drag/shear forces resulting in uniform flow

Question 8

True or False
The ratio f/8 in the formula for energy slope (S_f) represents the ratio of boundary shear to momentum flux in the channel.

Answer 8

True

Question 9

In open channel flow, the expression P/(A/H) simplifies to h/R_H, where R_H is the hydraulic radius and h is the _______.

Answer 9

normal depth

Question 10

Why is it significant that man-made canals often allow for uniform flow?

Answer 10

Uniform flow in man-made canals is significant because it simplifies the hydraulic design and management of these waterways, ensuring more predictable and stable conditions for various uses such as irrigation, navigation, and flood control.

Question 11

What does f/8 denote?

Answer 11

Ratio of boundary shear to mom. flux

Question 12

What does h/R denote?

Answer 12

Channel shape, wetted-perimeter per channel width

Question 13

What does Fr^2 denote?

Answer 13

Ratio of inertial forces to gravitational forces

Question 14

For uniform flow what is required?

Answer 14

Water surface slope = Bed slope = Energy slope

Question 15

True or False
In gradually varied flow (GVF), the water surface profile is parallel to the bottom profile.

Answer 15

False (In GVF, the water surface profile is not parallel to the bottom profile)

Question 16

In the context of gradually varied flow, the variable
h(x) represents the water surface profile, which is slowly varying with x but under steady flow conditions, the discharge Q is _______.

Answer 16

constant

Question 17

What does the term -S_f = dH/dx represent in gradually varied flow equations?
A) Bed slope
B) Energy slope
C) Hydraulic grade line slope

Answer 17

B) Energy slope

Question 18

What is the significance of the critical depth in open channel flow?

Answer 18

The critical depth is the depth at which the specific energy is minimal and the flow state is critical, characterized by a Froude number of 1. This depth also corresponds to the minimum energy state for the flow.

Question 19

True or False
The critical depth is always greater than the normal depth in open channel flow.

Answer 19

False (The critical depth may be less than, greater than, or equal to the normal depth depending on the flow conditions)

Question 20

The specific energy E(h) in an open channel flow is given by the formula E(h) =2 h 43 m 5.815 s h+ q^2/2gh^2, where q is the flow rate per unit width, g is gravitational acceleration, and h is the ______.

Answer 20

depth of flow

Question 21

Which classification describes a channel slope that is greater than the critical slope?
A) Mild (M)
B) Critical (C)
C) Steep (S)

Answer 21

C) Steep (S)

Question 22

True or False
In a channel with an adverse slope, the flow moves uphill.

Answer 22

True

Question 23

In open channel flow, if the depth is between the normal and critical depths, it is classified as Type _______.

Answer 23

2

Question 24

How does the slope of the bed affect the classification of water surface profiles in open channel flows?

Answer 24

The slope of the bed dictates the primary classification of water surface profiles, where it can be mild, critical, steep, horizontal, or adverse, each affecting how uniform or critical the flow is and influencing the flow dynamics significantly.

Question 25

If the depth is greater than both the normal and the critical depth then what is the type?

Answer 25

1

Question 26

If the depth is less than both the normal and the critical depth what is the type?

Answer 26

3

Question 27

True or False
Normal/uniform flow can occur on adverse or zero slopes.

Answer 27

False

Question 28

In open channel flows, the Normal Depth Line (NDL) and Critical Depth Line (CDL) help visualize the relationship between flow depth and _______ conditions.

Answer 28

Energy

Question 29

What does an M1 profile indicate in the context of mild slopes in open channel flows?
A) It is common where there are no changes in channel features.
B) It often results from control structures or natural features causing a backwater effect.
C) It represents the fastest flow in mild slope conditions.

Answer 29

B) It often results from control structures or natural features causing a backwater effect.

Question 30

What is characteristic of an S1 profile on steep slopes?

Answer 30

An S1 profile typically begins with a hydraulic jump and is often produced by control structures like dams or sluices, enhancing rapid transitions in flow conditions.

Question 31

True or False
The critical slope condition always results in a stable flow profile.

Answer 31

False (The critical depth condition can lead to surface undulations due to its inherent instability)

Question 32

In the classification of water surface profiles, an M3 profile occurs downstream of a change in slope from steep to _______.

Answer 32

mild

Question 33

Which profile is typically found at the entrance to a steep slope?
A) M2
B) S2
C) C1

Answer 33

B) S2

Question 34

In critical slope conditions, profiles like C1 and C3 are found upstream and downstream of sluice gates, respectively, tending towards horizontal flows as they travel downstream.

Answer 34

True

Question 35

On steep slopes, an S3 profile is specifically produced downstream of a _______.

Answer 35

Sluice gate

Question 36

How does the classification according to depth of flow enhance the understanding of water surface profiles?

Answer 36

By categorizing the depth relative to normal and critical depths, this classification helps predict how the flow will behave under varying channel conditions and influences—providing insights into potential flooding, flow stability, and control measures needed.

Question 37

True or False
A horizontal bed represents the lower limit of the mild slope in open channel flow, where the normal depth is considered to be infinite.

Answer 37

True

Question 38

In the context of open channel flow, an adverse slope is unusual because normal (uniform) flow _______.

Answer 38

cannot establish

Question 39

Why are water surface profiles on an adverse slope extremely short?
A) The slope facilitates rapid velocity increases.
B) The gravitational pull enhances the flow resistance disproportionately.
C) The flow quickly reaches a critical state due to opposing gravitational forces.

Answer 39

C) The flow quickly reaches a critical state due to opposing gravitational forces.

Question 40

What is the implication of having a horizontal bed in an open channel flow regarding the energy gradient and flow behavior?

Answer 40

With a horizontal bed, the normal depth is considered infinite, implying that there is no gradient in energy height along the channel, resulting in highly subdued flow dynamics under theoretical conditions.

Question 41

True or False
Adverse slopes in open channel flows are common and often result in long, stable flow profiles.

Answer 41

False (Adverse slopes are very rare and result in extremely short flow profiles due to instability and inability to establish uniform flow.)