(a) A culvert under a road must be 35m long, have a slope of 0.0035 and carry 4m^3/s. The crown of the roadway is 4.2m above the culvert invert. Assume the outlet will discharge freely. What size of corrugated -metal pipe (CMP: 68mm x13mm corrugation, n=0.025) culvert would you select? Square -edged inlet (Ke=0.5) will be used and coefficient of discharge of cd=0.65. A freeboard of 0.6m will be used
in the design.
Head loss due to pipe friction using Manning's n is
Hf=[(19.63*n^2*L)/R^1.33]V^2/(2g)
L-length of pipe in m
R=hydraulic radius (m)
N=manning's n
V =velocity (m/s)
(HINT: Assume HW controlling since TW flow freely, the entrance is submerged,and look at 2 cases-
(1) Full pipe flow
(2) Not Full pipe flow
(b) A hydrologist made a unit conversion error in his flow estimation. The reported flow rate is now 8m^3/s instead of 4m^3/s. What is your new design? Consider a rounded inlet and outlet design and using smoother concrete pipes or box culverts. For similar cross sectional area, the cost of concrete conduit per unit length is 1.5 times that of the CMP.