A rectangular open channel having bed width 2 m is laid at a bed slope...
As per Manning's equation, the discharge in an open channel is given by
Where A = Area of Flow, R = Hydraulic radius, S = Bed Slope of the channel,
When the slope (S) < 0, So the slope is adverse slope
So, uniform discharge or depth cannot be established when the slope is negative
Classification of the channel:
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A rectangular open channel having bed width 2 m is laid at a bed slope...
Problem Analysis:
The problem states that a rectangular open channel with a bed width of 2 m is laid at a bed slope of -0.0009 and carries a flow of 10 cumec. We are asked to determine the normal depth of flow for this channel.
Uniform Flow:
Uniform flow occurs when the flow velocity, depth, and cross-sectional area remain constant along the length of the channel. In this case, we are assuming that the flow in the channel is uniform.
Manning's Equation:
To determine the normal depth of flow, we can use Manning's equation, which relates the flow velocity, channel slope, cross-sectional area, and hydraulic radius.
Manning's equation is given as:
Q = (1/n) * A * R^(2/3) * S^(1/2)
Where:
Q = Flow rate (m^3/s)
A = Cross-sectional area of flow (m^2)
R = Hydraulic radius (m)
S = Channel slope (m/m)
n = Manning's roughness coefficient
Calculation:
In this problem, we are given the flow rate (Q = 10 cumec = 10 m^3/s), bed width (B = 2 m), and channel slope (S = -0.0009). However, we are not given the Manning's roughness coefficient (n).
Since the problem states that the flow is uniform, we can assume that the channel has a trapezoidal or rectangular cross-section.
Trapezoidal Cross-section:
If the channel has a trapezoidal cross-section, we would need additional information such as the side slope, bottom width, and side slope angle to calculate the normal depth.
Rectangular Cross-section:
If the channel has a rectangular cross-section, we can use the following equations to calculate the cross-sectional area (A) and hydraulic radius (R):
A = B * y
R = A / (B + 2y)
Where:
B = Bed width (m)
y = Depth of flow (m)
Since we are not given the side slope or bottom width, we cannot determine the normal depth for a trapezoidal cross-section. Therefore, option 'B' is incorrect.
Conclusion:
Based on the given information, we cannot determine the normal depth of flow for the channel. Therefore, option 'D' is the correct answer.
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