The estimation of costs associated with urban stormwater treatment measures is currently associated with high levels of uncertainty for most types of measure. The costing algorithms and estimates in music represent the best relationships that could be generated given the information that was available in 2003-04 when real costing data was collected from around Australia. For some measures (e.g. swales, buffer strips, bioretention systems and infiltration systems), these data are very limited.

To ensure transparency and accountability, each of MUSIC’s costing algorithms and estimates is presented in this chapter with a description of its quality (e.g. its explanation of variance [R2], significance [p-value], and/or the number of samples in the data set it has been derived from [n]). Users can therefore assess whether to use a particular ‘cost / size’ relationship derived by the music development team, or alternatively use another estimate. Appendix H: Costing informationsummarises cost / size relationships from the literature. It has been provided to assist music users to review alternatives.

Figure 1 shows the expected, upper and lower estimates for one of the better costing algorithms in music (i.e. for total acquisition costs associated with greenfield constructed wetlands). The area between the upper and lower estimates represents a band within which 68% of individual data points will fall within. It highlights the significant uncertainty associated with these ‘size / cost’ relationships. This uncertainty should be kept in mind when undertaking and reporting the results of life cycle costing analyses using music.

Figure 1: An example of a regression analysis for total acquisition costs involving greenfield constructed wetlands

The uncertainty currently associated with cost estimates also highlights the need for Australian stormwater managers to be diligent with respect to keeping detailed records of costs associated with urban stormwater treatment measures. To assist this process, a simple data recording sheet has been prepared by the music development team (i.e. Taylor, 2003).

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