What is Manning’s equation used for in open channel flow?
A
Calculating evaporation rate
B
Calculating sediment transport
C
Determining flow velocity or discharge
Analysis & Theory
Manning’s equation is used to calculate flow velocity or discharge in open channels.
What is the standard form of Manning’s equation for velocity (V)?
C
V = (1/n) × R^(2/3) × S^(1/2)
Analysis & Theory
The standard form is V = (1/n) × R^(2/3) × S^(1/2), where V = velocity, R = hydraulic radius, S = slope, n = Manning’s coefficient.
In Manning’s equation, what does ‘n’ represent?
B
Channel roughness coefficient
Analysis & Theory
‘n’ is the Manning’s roughness coefficient, which depends on the material and surface condition of the channel.
What is the hydraulic radius (R) in Manning’s equation?
B
R = area / wetted perimeter
Analysis & Theory
Hydraulic radius R = A / P, where A is cross-sectional flow area and P is wetted perimeter.
What does the term ‘S’ stand for in Manning’s equation?
B
Slope of the energy grade line (channel slope)
C
Specific weight of water
Analysis & Theory
‘S’ is the slope of the energy grade line or channel bed (usually approximated by bed slope).
What are the units of velocity (V) in Manning’s equation (SI units)?
Analysis & Theory
Manning’s equation gives the flow velocity, typically expressed in meters per second (m/s).
How does increasing the Manning’s ‘n’ value affect the flow velocity?
Analysis & Theory
A higher ‘n’ value indicates more resistance, which reduces the flow velocity.
What is the typical Manning’s ‘n’ value for a smooth concrete channel?
Analysis & Theory
For smooth concrete channels, ‘n’ is typically around 0.012–0.015.
Which of the following channels would have the **lowest** Manning’s ‘n’ value?
A
Natural stream with rocks
Analysis & Theory
Smooth, concrete-lined channels offer minimal resistance, leading to a lower ‘n’ value.
What is the discharge formula (Q) derived from Manning’s equation?
A
Q = A × V = (A × n) / (R × S)
B
Q = A × V = (1/n) × A × R^(2/3) × S^(1/2)
Analysis & Theory
Discharge Q = A × V. Substituting Manning’s V: Q = (1/n) × A × R^(2/3) × S^(1/2).