When designing a drainage system, the design discharge must be less than or equal to the hydraulic capacity of the outlet pipe. Hydraulic capacity is the capacity of the drainage network to convey flow, and it depends on the pipe properties including diameter, material, and grade. Hydraulic capacity of the outlet pipe can be calculated from the Pipe Capacity Calculator .
The rate of water movement through the drainage pipe network. Choose a drainage coefficient that is greater than or equal to drainage intensity, here.