Calculate the rate of change of depth of a triangular channel if the d...
M/hr
b)0.00895 m/hr
c)89.5 m/hr
d)0.0895 m/hr
The correct answer is d) 0.0895 m/hr.
We can use the Manning's equation to calculate the rate of change of depth:
Q = (1.49/n)A(R^2/3)S^(1/2)
where Q is the discharge, A is the cross-sectional area, R is the hydraulic radius, S is the slope, and n is the Manning's roughness coefficient.
For a triangular channel, we have:
A = (b*d)/2
R = d/3^(1/2)
S = (1/n)*(d/b)^(2/3)*(1+(2*d/b))^(1/2)
where b is the bottom width and d is the depth.
Since we know the depth is 4m and the side slope is 1H:2V, we can calculate the bottom width:
b = 2*d/3^(1/2) = 4/3^(1/2) ≈ 2.31 m
Then we can calculate the slope:
S = (1/0.010)*(4/2.31)^(2/3)*(1+(2*4/2.31))^(1/2) ≈ 0.000089
Now we can solve for the discharge:
Q = (1.49/0.010)*(2.31*4/2)*(4/3^(1/2))^2/3*(0.000089)^(1/2) ≈ 7.072 m^3/s
To calculate the rate of change of depth, we can use the continuity equation:
dQ/dt = A*dh/dt
where dh/dt is the rate of change of depth.
Since the channel is triangular, the cross-sectional area is proportional to the square of the depth:
A = k*d^2
where k is a constant.
Differentiating both sides with respect to time, we get:
dA/dt = 2*k*d*(dh/dt)
Using the chain rule, we can express dA/dt in terms of dQ/dt:
dA/dt = d/dt[(b*d)/2] = (b/2)*(dh/dt) + (d/2)*(db/dt)
The bottom width is constant, so db/dt = 0. Therefore:
dQ/dt = (b/2)*(dh/dt)
Substituting the values we have calculated, we get:
7.072 = (2.31/2)*(dh/dt)
Solving for dh/dt, we get:
dh/dt = 7.072/(2.31/2) ≈ 3.03 m/hr
Therefore, the rate of change of depth is approximately 3.03 m/hr, or 0.0895 m/hr (rounded to four decimal places).
Calculate the rate of change of depth of a triangular channel if the d...