Rainfall Incidents for Perth (Ref. http://www.BOM.gov.au):

Most councils choose the risk of a 1 in 20 year storm for the 5 minute duration (highest volume flow rate once every 20 years).

### Perth Sand Infiltration Rate = 0.1 m3/m2 per second, = 6L/min per m2

**This means that if the sub base is acceptable as Class A, and for residential traffic or light traffic eg carparks: **

**The sand alone will allow infiltration of 30 L per 5 minute storm, which is well above the required rate. **

**Therefore the Fast Flow pavers can be laid directly onto compacted Bassendean sand and meet the stormwater requirements.**

**Is the Paver Permeability Sufficient?**

From the above table, the Fast Flow Pavers TM must pass a minimum of 12.5 litres per m2 over 5 minutes.

The maximum flow rate through Fast Flow Pavers is >10 L litres per m2 in 1 minute, or over 50L in 5 minutes.

Therefore this 20 year storm event is approximately one quarter of the flow rate through the pavers.

See **Certified Installation Drawings** for this information in easy format.