Triple-Bottom-Line Assessment of Proposed Urban Stormwater Measures to Improve Waterway Health

Increasingly, urban water managers in Australia are seeking to make significant decisions about the use of stormwater management measures that improve waterway health (e.g. constructed wetlands and bioretention systems) within the context of the so-called 'triple-bottom-line'. That is, such decisions are based on financial, social and ecological considerations. The Cooperative Research Centre (CRC) for Catchment Hydrology has developed and is trialling draft guidelines on how to undertake triple-bottom-line assessments of proposed stormwater projects that aim to improve waterway health (e.g. assessments that involve the design and/or the location of new infrastructure). For the sake of practicality, these guidelines provide different levels of assessment which are commensurate with the scale and complexity of the project. To assist the financial element of the assessment, a life-cycle costing module has been built into version 3 of the CRC's MUSIC model (i.e. the 'Model for Urban Stormwater Improvement Conceptualisation'). This module allows users to estimate the likely value of cost elements and the overall life-cycle cost of common structural stormwater measures that aim to improve waterway health. This module was developed following an analysis of the cost of Australian measures and the development of algorithms that relate the size of measures to their cost. For the financial, social and ecological elements of the assessment, the new CRC guidelines explain how to use a multi criteria analysis procedure as a decision support tool. This procedure incorporates all aspects of the triple-bottom-line and involves a number of steps which are briefly described in this paper. Traditionally in Australian stormwater management, decisions have been made by few people, with little consultation/participation, have been based on limited information (locally or from the literature), and considered only part of the triple-bottom-line (e.g. traditional benefit-cost analyses where 'externalities' were not considered). We have developed guidelines which attempt to improve on this situation, but are practical to use. The new guidelines, supported by the new life-cycle costing module in MUSIC should substantially assist urban stormwater managers to make more systematic, informed, rigorous, participatory, transparent, defendable, socially acceptable, ecologically sustainable and more cost-effective decisions.