* Step 6: Select an underdrain perforated pipe diameter (typically 100 or 200 mm), assign this as an 'embedded' depth equal to the pipe diameter. The perforated pipe depth can be made part of the active storage of the practice when a riser (standpipe and 90 degree coupling) are used to design the underdrain. | * Step 6: Select an underdrain perforated pipe diameter (typically 100 or 200 mm), assign this as an 'embedded' depth equal to the pipe diameter. The perforated pipe depth can be made part of the active storage of the practice when a riser (standpipe and 90 degree coupling) are used to design the underdrain. |