THE $GREEN BENEFITS OF WATER SENSITIVE DESIGN

L. Norman (ACH Consulting Ltd)

ABSTRACT

An economic assessment of the ancillary benefits of Water Sensitive Urban Design (WSUD) leads to a more robust economic analysis when designing infrastructure. Among the benefits are:

• improved air quality;
• greater biodiversity;
• healthy watercourses;
• reduced flood risk;
• lower carbon emissions;
• reduced urban heat island effect;
• increase energy efficiency of buildings;
• increased property values;
• improved health and wellbeing;
• reduced crime and violence;
• increased economic performance, and
• inclusion of Te Mana o te Wai.

Each stakeholder within the development chain will value the above benefits differently. Understanding the needs of the stakeholder and monetising the ancillary benefits of WSUD, that directly affect stakeholders, can foster a willingness to pay the increased capital cost for the construction of WSUD within a project. Applying overseas methodology, and adapting the methodology into a New Zealand context, can yield reliable monetary values of the secondary advantages of WSUD.

This paper provides a basic accounting tool, based on international research and best practice, to assign a monetary value to the unrealized cost benefits of different types of WSUD. Worked examples demonstrate the overall monetary value of amenity, environmental outcomes, biodiversity, carbon reduction, flood prevention and overall livability.

The paper also outlines a matrix for identifying which ancillary economic values of WSUD will benefit specific stakeholders and beneficiaries. By relating the WSUD benefits to the stakeholders, the designer, at the start of the project, can develop WSUD appropriate to the stakeholders. Presenting tangible economic benefits of WSUD will allow for more informed decision making on both greenfield and brownfield projects, getting the most bang for the buck.

For example, a 5 ha greenfield private development requires flood storage and stormwater treatment. With roading there is space for 166 townhouses that would sell for $750,000 each. By constructing a 2 ha central park to act as a flood storage basin with a wetland for treatment, the infrastructure requirements for the development can be met, but the number of townhouses will be reduced. Global research shows that homes within 450 m of that park will sell for about 10% more than those with no park. Using 2 ha of the property for a WSUD flood storage park and building 100 homes, profits remain the same, as the roading infrastructure costs are reduced and the sale price of the townhouses increases to $825,000 each. The flood basin park will not only reduce carbon emissions related to infrastructure construction, but will also sequester carbon. Carbon credits, which have monetary value, are awarded for projects that store, avoid, or reduce greenhouse gas (GHG) emissions in the atmosphere.

If the 5 ha development were for Kāinga Ora, the largest landlord in New Zealand, the WSUD economic analysis would include:

• flood protection;
• energy efficiency;
• reduction in crime;
• improved health, and wellbeing

The tools presented herein, allows a practitioner to develop WSUD that meets the infrastructure requirements for development and demonstrates the economic benefits to stakeholders.