In the design of gravity drainage pipes, full bore flow capacity is normally adopted to check against the design runoff. However, one should note that the maximum flow rate does not occur under full bore conditions. The maximum discharge occurs when the water depth in circular pipes reaches 93.8% of the pipe diameter. Therefore, the use of full bore discharge is on the conservative side though the pipe’s maximum capacity is not utilized.
Similarly, the maximum velocity does not occur in full bore conditions and for circular pipes it occurs when the water depth is 81.3% of the pipe diameter. Hence, in checking for the maximum velocity of flow in pipes to avoid possible erosion by rapid flow, the use of full-bore velocity may not be on the conservative side.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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