1.3.3 Airport Method

For catchments where the runoff coefficient, C, is less than 0.40, the Airport formula may provide a better estimate of the time of concentration. This method was developed for airfields and calculates time of concentration as a function of runoff coefficient, length, and slope as follows:

(2)

where:
= time of concentration (min)
C= runoff coefficient
L = catchment length, (m)
= catchment slope (%)