Auckland Unitary Plan SMAF Rules: A Stormwater Engineer’s Experience

Traditionally stormwater management of urban developments within Auckland comprised of water quantity and quality management. Although Low Impact Design (LID) was promoted by Auckland Council for many years, the most common approach was to provide hydrological mitigation using end of pipe stormwater solutions, such as wetlands.

Since the implementation of the Auckland Unitary Plan Operative in Part (AUP OP), the focus of stormwater management in Auckland has shifted to Water Sensitive Design. The stormwater management philosophy promoted by the AUP OP is to mimic the pre-development natural water cycle, in particular by provision of at-source volume management (i.e. by groundwater recharge or reuse). The balance of runoff is then released slowly (detention) to the receiving environment. Stormwater Management Areas - Flow (SMAF) have been created to define where the new approach is to be applied. The focus is on protecting sensitive stream catchments throughout the Auckland region. SMAF has essentially turned the tide on traditional stormwater management.

At the same time, there are increasing pressures to produce residential developments with higher yields and more affordable housing due to the rapid population growth in Auckland. With more compact housing, there are significant challenges in the selection and integration of at source stormwater management devices within residential lots.

This paper will discuss the challenges of implementing at source SMAF devices within high density residential developments. The authors will share their experiences of the constraints encountered and the lessons learned for implementing successful on lot SMAF devices.