Demonstrating the need to simultaneously implement all water sensitive design methods for aquatic ecosystem health

The practices commonly known as ‘Water Sensitive Design’, or ‘Low Impact Urban Design and Development’, provide a comprehensive package of practices, (building blocks), that respect and work with the natural water cycle and enhance biodiversity. Much previous research has focussed on determining the sustainability gains achieved by the implementation of a narrow range of closely related techniques, such as the installation of at-source devices for stormwater retention and treatment. Other research has investigated the gains for the health of an ecosystem from the reduction of impervious surfaces, or from riparian revegetation, or from the clustering together of buildings. Relationships between these practices and techniques have been observed, but urban developers continue to implement practices such as these in isolation whereas it is suspected that the aquatic ecosystems need all of the practices and techniques to be implemented simultaneously. Without the synchrony of simultaneous implementation, degradation of the ecosystems may still occur and the real cause of it may be missed. The purpose of this research is to monitor, using a biotic index, the ecosystem responses of streams to the simultaneous implementation of as many as possible of these practices (the building blocks) at two different urban densities in paired sub-catchment studies within the Hauraki Gulf catchment of Auckland, New Zealand. Significant differences in the health of the ecosystems of the streams between some treatment and control sub-catchments are observed at both densities. The failure to apply all the techniques (building block methods), or to apply them appropriately in some of the case study sub-catchments, demonstrates a consequent degradation of the ecosystems of the streams that is expected to have negative consequences, not only for local streams but for the marine receiving environment.