Annual Recurrence Interval (ARI) for Roof and Surface Drains
Annual Recurrence Interval (ARI) for Roof and Surface Drains
(OP)
Hi,
Can anyone give me a proper explanation why roof drainage systems (downpipes, gutters, etc.) are typically sized different in ARI than the surface drains it outfalls to?
Example, roof downpipes are designed to 20-Yr ARI along with overflow measures e.g. rainheads
However, it discharges to the pit on the ground with outlet pipes designed to 10-Yr ARI as required by councils.
I have always believed that roof downpipes must allow the greater flows to discharge from the roof to reduce chances of ponding/surcharging and causing damage. The flows through the buried pipes are then acting under head during the designed roof ARI.
Thanks very much.
Can anyone give me a proper explanation why roof drainage systems (downpipes, gutters, etc.) are typically sized different in ARI than the surface drains it outfalls to?
Example, roof downpipes are designed to 20-Yr ARI along with overflow measures e.g. rainheads
However, it discharges to the pit on the ground with outlet pipes designed to 10-Yr ARI as required by councils.
I have always believed that roof downpipes must allow the greater flows to discharge from the roof to reduce chances of ponding/surcharging and causing damage. The flows through the buried pipes are then acting under head during the designed roof ARI.
Thanks very much.





RE: Annual Recurrence Interval (ARI) for Roof and Surface Drains
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Annual Recurrence Interval (ARI) for Roof and Surface Drains
RE: Annual Recurrence Interval (ARI) for Roof and Surface Drains
RE: Annual Recurrence Interval (ARI) for Roof and Surface Drains
...is that the requirements were typically brewed up by different government agencies with different engineering backgrounds (if any background at all) so their expectations of what to design for are basically unrelated.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com