New design rainfalls for Australia

Design rainfall estimates are essential in the design of infrastructure such as gutters, roofs, culverts, stormwater drains, flood mitigation levees and retarding basins. They are used by engineers to determine the flood capacity and water level to meet required levels of safety. They are also integral to spillway adequacy assessments undertaken to determine the flood magnitude that existing dams can safely withstand. Other uses of design rainfalls include the assigning of a probability to an observed rainfall event and flood warning and emergency management. The previous design rainfall estimates were derived by the Bureau of Meteorology (the Bureau) in the early 1980s using a database comprising primarily of Bureau raingauges and techniques for statistical data analysis that were considered appropriate at the time. They were provided for durations from 5 minutes to 72 hours (3 days) and for probabilities from the 1 year Average Recurrence Interval (ARI) to the 100 year ARI. More recently, estimates of rare design rainfall estimates for probabilities from 100 year ARI to 2000 year ARI have been derived for each state, using the CRCFORGE method. Design rainfalls for probabilities more frequent than 1 year ARI were not provided. The Bureau has recently completed an 8 year project which has produced new design rainfall estimates. The new design rainfall estimates are based on a greatly expanded database which incorporates rainfall data collected by organisations across Australia. These data have been analysed using contemporary statistical methods that are appropriate for Australian rainfall data. The new design rainfalls are provided for durations from 1 minute to 168 hours (7 days) and for probabilities from 12 Exceedances per Year (or 1 month ARI) to 0.05 % Annual Exceedance Probability (or 2000 year ARI) and are available from the Bureau's website for any location in Australia.