Costing Analysis of a Public Stormwater BMP - A Seven Year Review

One of the biggest concerns over the use of a stormwater Best Management Practice (BMP’s) is the ongoing maintenance cost. As land is developed by private developers stormwater BMP’s are often vested in council, and therefore council needs to have a good understanding of what the lifecycle cost of a stormwater BMP is.

A life cycle costing review was performed by Landcare Research and Auckland Council in 2005 on a range of stormwater BMP’s. The results from this study were limited as not a lot of maintenance data was available, suggesting that not a lot of maintenance was being performed.

It is vital that decision makers have good, accurate and real data that considers all externalities. Subjective decision making can often leave government organisations with a legacy of cost that often results in the BMP not being maintained.

Stormwater360 has been working closely with various Auckland legacy council asset managers since December 2005 when the first council device (StormFilter) installed in Crows Road in Waitakere required maintenance.

There are presently 108 StormFilters vested under the new Auckland Council and NZTA with a total of 1,685 cartridges installed in these units. This is possibly the largest body of cost data of a single stormwater BMP in the country.

The Auckland Council and NZTA have run numerous Capital Works projects using the StormFilter technology as a standalone stormwater treatment device. These organisations have also established ongoing maintenance contracts to ensure the devices are maintained appropriately.

The following paper will analysis actual costs for the implementation and ongoing operation of the StormFilter over the last 6 years. The paper will also include some specific case studies discussing the factors that can affect the costs of stormwater BMP’s.

This paper offers benefit to council asset managers and stormwater design engineers in selecting appropriate technologies for new and existing areas.