Calculations made with less than 1Y, 5Min IFD are unlikely to be compliant…
As engineers we are ultimately responsible for the compliance of our design solutions. Regardless of the SQID technology being considered, the system capacity must be sufficient to manage the load from the entire catchment in local conditions. The Australian Runoff Quality: Guide to Water Sensitive Urban Design (ARQ) section 2.4.2 states that a one-year Average Recurring Interval (ARI) is necessary to export up to 90% of the catchment load. Clearly, using a rainfall event such as a three-month ARI to calculate treated flow and SQID capacity is at best a high-risk approach.
Treated Flow: the flow of water required to wash pollutants from a catchment and transport those pollutants to a point where they can be removed.
Compliant Treated Flow Calculation
For this reason, Enviro Australis calculate treated flow and system capacity based on a one-year, five-minute IFD. This ensures that Environmental Protection System (EPS) capacity specifications protect both the environment and the design engineer.
A technical description of the treated flow calculation method with diagrams and data tables is available from the Enviro Australis Technical Manual. To discuss treated flow or any further information on EPS, please contact technical support on 08 8564 2347.