NZ Standard rain garden economically sustainable?

One of the key devices in stormwater mitigation is the rain garden, it captures and treats run-off like nature planned it. Additionally rain gardens are aesthetic landscape features in residential and commercial areas. They present lower impacts to the environment and their importance is recognized by national regulations. Other countries have had success in lowering stormwater management costs by using rain gardens.

The document looks in detail at the hydraulic and hydrological parameters of the Auckland Regional Council (ARC) rain garden design (Technical Publication 10). It discusses the critical rain garden design parameters focusing on the coefficient of permeability (k-value) for filter soils and the driving head, therefore the depth above the filter bed. Stormwater run-off has to be captured, treated and assessed for Water Quality Volume (WQV), Extended Detention Volume (EDV) and for Peak flow attenuation volumes. The effectiveness of the rain garden will be discussed comparing WQV plus EDV with the post development 2-year storm peak detention volume.

The paper will explore the potentially significant economical impacts on stormwater projects. Improving the constructability of rain gardens and thereafter treating and capturing stormwater runoff “at source”, which may in turn decrease cost in storage devices further downstream, will be discussed.