In WA, it is your legal obligation as a homeowner is to retain your stormwater on your property. The installation of soakwells is an effective way to achieve this. Your local council has provided you with recommendations for the volume of soakwell to install in your property, calculated as a multiple of the catchment area. Installing this volume of soakwell will lessen the risk of overflow during heavy downpours. However, you are not legally obliged to install soakwells. As such, the volume of soakwell recommended by your council is a guide only, not a requirement.
The majority of local councils in Perth have used the 1 in 20-year rainfall event to calculate the recommended volume of soakwell. Generally, this equates to the catchment area (m²) multiplied by 12.5, as shown below.
Volume of soakwell (L) = Impervious area (m²) x 12.5
Two exceptions are; The City of Gosnells and The Town of Cambridge, who have both specified volumes calculated for the 1 in 100-year rainfall event.
Please follow the links below if you would like to find out more about your local Western Australian council regulations regarding stormwater drainage and soakwells.