Design Flow Rate (rainwater drainage)

In the context of rainwater drainage, the computation of design flow rate can be categorised into the following:

1. Effective plan catchment
2. Elevation catchment (for wind driven rain)

Design flow rate $(l/s)=$ Effective Catchment Area $(m^2)$ X Rainfall Intensity $(mm/hr) \div 3600$

The method of calculating Effective catchment areas can be referred to Catchment area (effective) (roof drainage).

References:

1. BS EN 12056-3:2000