Water Sensitive Design is being implemented via the Housing Accords and Special Housing Areas Act which implements the Proposed Auckland Unitary Plan (PAUP). Special Housing Areas have allowed Auckland Council to test planning provisions to encourage Water Sensitive Design (WSD) in greenfields and brownfields scenarios. Our recent experience with implementing WSD is that it leads to a decentralised approach which provides strong commercial benefits which have been well received by the private development sector.
While WSD is intended to lead to good ecological, urban design and amenity outcomes, it also has less obvious benefits. Good WSD can do away with the need for large scale communal stormwater devices. The retention and protection of streams avoids engineered flood management approaches because stream corridors can be designed to allow flood flows to be conveyed safely. Hydrology mitigation leads to stormwater management at a sub-catchment level with multiple devices higher in the catchment - a more decentralised approach.
This decentralised approach means that the implementation of stormwater infrastructure is not tied to negotiated agreements between private landowners or cumbersome public land acquisition processes. It also leads to a shift in asset types, the use of smaller pipes and smaller devices which are significantly cheaper to build. Valuable land can be used more efficiently as smaller devices can be located within the road corridor, stream corridors and private lots. Consequently there has been a shift in asset funding sources; from straight ratepayer investment to a mix of private, ratepayer and transport corridor investment. Decentralisation and the use of a treatment train approach is also less likely to result in significant device failure, providing a more resilient network.