Managing urban water quality issues has been a focus over recent decades, however, significant water quantity (flooding) issues remain including nuisance and even property damage.
BMT WBM has been investigating urban water quantity and quality issues within the City of Port Phillip and the City of Stonnington, in Melbourne’s eastern bayside suburbs. These investigations looked at incorporating on-lot green infrastructure, such as rainwater tanks and raingardens, into every property within a catchment, and examining the impact of this on flooding, as well as other benefits such as water quality.
A sophisticated 2D modelling framework was developed, capable of assessing high intensity rainfall events as well as the long term performance of the green infrastructure. Beneficial outcomes included changes in flood extents, reductions in property damage and reductions in nuisance impacts, such as loss of access and transport links.
Our results found that for rainwater tanks to provide flooding benefit they needed to have a high demand for water reuse - using rainwater tanks for on-lot irrigation only provided minimal benefit. Further, there were limited benefits from rainwater tanks in larger events such as the 1% AEP (1 in 100 year ARI) event.
On the other hand, we found that raingardens were relatively efficient in reducing flooding, although the land required for raingardens to be effective was significant.
Our results highlight there are potential opportunities for managing water quantity (flooding) and water quality at a lot-scale, but only if rainwater tanks are utilised for maximum reuse and gardens, lawns and other outdoor spaces are designed to be multi-functional, incorporating green infrastructure, such as raingardens and green roofs.