Do Not Let Perfect Be the Enemy Of Good

The existence of TP 124 and TP10, the Auckland regional government guidelines for incorporating Low Impact Design (LID) techniques, indicate to me that this region is switched on to a forward thinking stormwater management philosophy.

The guidelines have been in place for a number of years however there are relatively few successful LID projects constructed in Auckland. There are a number of reasons why the implementation of LID developments has been limited. This paper is focused on the competing interests of the stakeholders in relation to the technical parameters of biofiltration systems.

It is believed that the TP 10 guidelines and their applicable review are overly conservative for bio-filtration systems. This results in the traditional “end of pipe treatment systems” being more cost effective to consent and build. URS recently developed a stormwater management plan for a western Auckland catchment exclusively utilised bio-filtration systems to treat stormwater. In this paper we will review the development of the management plan and explore the standard engineering practices that were used to alter key parameters; coefficient of permeability, live storage area and treatment volumes. Results show a stormwater management system successfully treating a 313 hectare catchment of intensive development with significant cost savings.