On a very wet day in May, a group of designers, engineers, landscape architects and horticultural maintenance specialists joined Dale Brown from E2Designlab to learn the art of designing raingardens for maximum water sensitive urban design performance.
Shaun Kennedy, Vegetation Services Specialist at SA Water joined us to share his expertise on the crucial ole plant species selection plays in managing nutrients and ensuring raingardens are a high-quality amenity feature in our urban streets. Estelle O’Donohue, Coordinator Survey & Design at City of Marion explained the plans to rectify an existing raingarden to improve its functionality that was designed many years ago.
The group toured raingardens with Glynn Ricketts, Water Resources Coordinator at City of Marion and Rachel Murchland, City of Mitcham’s Principal Project Manager, who provided valuable insights into the design, installation and maintenance of raingardens that in the streetscapes of Clarence Gardens, Tonsley and Oaklands Park.
Key takeaways:
- Streetscape biofilters (raingardens) improve water quality, support urban greening and mitigate climate impacts such as extreme heat.
- Design considerations should include site conditions, urban design goals, and performance objectives to maximize biofilter efficiency and reduce future maintenance.
- Retaining stormwater within the biofilter zone enables the water to percolate through the soil, supports vegetation and helps sediment deposition for high-performance.
- Strappy, fibrous rooted plants are most effective at nitrogen removal from stormwater and the density of vegetation is important for biofiltration performance, and reduce weed invasion.
- Vegetation should be selected based upon expected water inflow, retention depth and length between rainfall events to ensure resilience without secondary irrigation.
- Effective use of hold-points during the construction phase is essential at key milestones to ensure the biofilters are built as per design, including filter media supply and finished surface levels to ensure extended detention depth is achieved. An example of bioretention hold-point forms can be found here: WSSA Bioretention Construction Hold-point Sign Off Sheets