Water flows at a steady and uniform depth of 2m in an open channel of ...
Area A = 4 ×2 = 8, Perimeter P = 4 + 4 = 8
R = (A/P) = 1 m
Discharge per unit width q = 8/4 = 2
We know that the minimum specific energy corresponds to the point of critical depth and is given by 1.5 times the critical depth
Critical depth = (q2/g)(1/3) = 0.74 m
Minimum specific energy is 1.5 × 0.74 = 1.11 m
Specific energy should be same at all points (neglecting hydraulic losses)
So, E = Eminimum + h (this energy is at position of hump)
E = y + v2/(2*g) = 2.05
h = 2.05 – 1.11 = 0.94 m
View all questions of this test
Water flows at a steady and uniform depth of 2m in an open channel of ...
's roughness coefficient (n) as 0.03 and acceleration due to gravity (g) as 9.81 m/s^2.
To obtain critical flow in the channel, the Froude number (Fr) needs to be equal to 1.
The Froude number is given by the equation:
Fr = V / sqrt(g * d)
where V is the velocity of the water, g is the acceleration due to gravity, and d is the depth of the water.
Since the water depth is given as 2m, we can rearrange the equation to solve for V:
V = Fr * sqrt(g * d)
To determine the Froude number for critical flow, we can use the equation:
Fr = sqrt(g * d) / sqrt(R)
where R is the hydraulic radius of the channel.
The hydraulic radius (R) is given by the equation:
R = (A / P)
where A is the cross-sectional area of the channel and P is the wetted perimeter.
The cross-sectional area (A) is given by the equation:
A = b * d
where b is the base width of the channel.
The wetted perimeter (P) is given by the equation:
P = b + 2d
Substituting these values into the equations, we have:
A = 4m * 2m = 8m^2
P = 4m + 2(2m) = 8m
R = 8m^2 / 8m = 1m
Now, we can solve for the Froude number (Fr) using the hydraulic radius (R) and the depth (d):
Fr = sqrt(9.81 m/s^2 * 2m) / sqrt(1m) = sqrt(19.62) / 1 = 4.43
Since the desired Froude number for critical flow is 1, we need to reduce the velocity by a factor of 4.43.
Using the Manning's equation:
V = (1 / n) * (R^(2/3)) * (S^(1/2))
where V is the velocity, n is Manning's roughness coefficient, R is the hydraulic radius, and S is the slope of the channel.
Substituting the values:
4.43V = (1 / 0.03) * (1m^(2/3)) * (1/10000)^(1/2)
Simplifying:
4.43V = 33.33 * 0.1 * 0.01^(1/2)
4.43V = 0.03333
V = 0.03333 / 4.43
V ≈ 0.0075 m/s
Therefore, to obtain critical flow in the channel, a hump in the bed should be provided to reduce the velocity to approximately 0.0075 m/s.