UNDERSTANDING AND DETERMINING THE COST OF LONG TERM MAINTENANCE AND RESILIENCE OF WSD

Unless carefully managed, continual growth pressures on New Zealand’s cities and urban- rural fringes will lead to increasing effects from stormwater discharges on our coastal and freshwater receiving environments. Water sensitive design (or green infrastructure) provides developers and councils with an opportunity to better protect the receiving environment from these effects through the concept of ‘designing with nature’. This is achieved through the acknowledgement, preservation and use of the inherent natural landform and hydrology, and the integration of stormwater design with landscape and architectural elements.

The stormwater industry in New Zealand is coming to the realisation that piped systems provide an on-going asset management liability with regard to operation, maintenance and renewal. These systems are also difficult to monitor, relatively hard to access, prone to blockage and structural failure, and there is an on-going risk of underground systems receiving wastewater cross connections. On the other hand research and recent experience in New Zealand and overseas has shown that green infrastructure solutions are likely to be more robust and resilient than traditional solutions, both in terms of coping with long term changes in climatic conditions and short term chronic events such as earthquakes, in addition to reduced blockage risks. Research and experience has also shown that green infrastructure systems are also more economical to construct, but maintenance costs of diffuse green infrastructure (such as rain gardens and swales) can be more expensive than traditional approaches.

This paper provides a stock take of our current understanding of costs of WSD, and explores the issues of resilience and long term cost effectiveness of green infrastructure stormwater management solutions.