Q. Full bore flow in drainage design?

In the design of gravity drainage pipes, full bore flow capacity is usually adopted to check against design runoff. Though one should note that maximum flow rate doesn't take place under full bore conditions. Maximum discharge takes place when the water depth in circular pipes reaches 93.8% of the pipe diameter. Consequently the use of full bore discharge is on the conservative side though pipe's maximum capacity isn't utilized. 

In the same way maximum velocity doesn't take place in full bore conditionsand for circular pipes it takes place when the water depth is 81.3% of the pipe diameter. Henceforth in checking for the maximum velocity of flow in pipes to avoid possible erosion by rapid flow, usage of full-bore velocity may not be on conservative side.