Rain Garden Maintenance Costs in an Industrial Development

Waterloo Business Park is an industrial development in Islington, Christchurch. The site was previously the Christchurch Meat Company factory, or the “Islington Freezing Works” which started operation in 1869. The redevelopment of the site into an industrial business park encompassed the usual challenges of brown field developments, not least the challenge of stormwater treatment and discharge. The site is underlain by deep free draining gravels leading to a discharge to ground approach for stormwater management.

Rain gardens have been constructed to provide road stormwater treatment for the Waterloo Business Park in Christchurch. They provide treatment for approximately 6 Ha of industrial roading. The majority of the roading in Waterloo Business Park is private roading, however, there are two roads vested with the Christchurch City Council (CCC), namely the extension of Halswell Junction Road and Waterloo Road.

Rain gardens have not usually been accepted by CCC within vested roading apart from retrofit scenarios or within new public open space projects. To allow the approval for vested rain gardens to progress the developer agreed to maintain the rain gardens for a 5 year period while keeping detailed records of the rain garden maintenance activities and costs.

The rain gardens were designed and constructed in accordance with Christchurch City Council’s Rain Garden Design Criteria along with a localised soakage system into the underlying free draining gravels. There are a total of 35 rain gardens constructed for the roading catchments ranging in size from 40 m² to 265 m². 33 of the 35 rain gardens are now in operation.

This paper presents 22 months of maintenance costs for the first 12 rain gardens.

The paper also discusses some of the health and safety in design considerations made during the design and construction of the rain gardens and the soakage systems.