Understanding your site's rainfall and its corresponding design storm event

Have you ever wondered what storm event your site or location received? Did it equate to a 2 year ARI (50% AEP), 10 year ARI (10% AEP) or some other event altogether? Did this event exceed any prescribed design standards for designed drainage or sediment control measures?

If you have observed rainfall data (mm of rain over a specified duration) which has been recorded onsite you can estimate the probability using a function on the Bureau of Meteorology (BoM) IFD website (design rainfall data system 2016).

To do this:

  1. Visit the BoM IFD website;

  2. Select Single Point search on the left tab and enter your location coordinates, then Submit;

  3. Click the + next to Observed Rainfalls on the left tab;

  4. Enter the rainfall depth for the relevant duration/s and select Update.

The observed rainfall will be shown along with the probability (i.e. the observed 15mm over 5 minutes recorded onsite is between a 10 and 20 year ARI event (or between 10% and 5% AEP).

Note that restricted 24 hour totals (say 6am to 6am as recorded within site rain gauge) may underestimate the 24 hour rainfall total for an event, which will result in an underestimate the probability of the event.

Source: BoM

Kyle Robson