With proportional depth (y/D) which appear in Tables for the hydralic design of pipes (Recommended reading 9).
Example 8.13
Design a branch within a storm sewer network which has a lingth of 100 a bed slope of 1 in 150 and roughness size of 0.15 mm and which recei the storm run off from 3.5 hectares of impermeable surface using Rational (Lloyd – Davies) Method. In desingning the upstream pipes maximum ‘time of concentration’ at the head of the pipe has been found be 6-2 minutes. The relationship between rainfall intensity and aver storm duration is tabulated below