Randolph Avenue streetscape upgrade

The Randolph Avenue streetscape upgrade converts an underutilised space into a softer, more environmentally friendly area through the inclusion of raingardens. It improves local amenities, and achieves stormwater quality objectives. This project was delivered as a pilot project to demonstrate street level action that can be taken to improve urban water quality and the quality of Adelaide’s coastal waters.

• Demonstration: Pilot project to demonstrate action that can be taken at a street level to improve urban water quality and the quality of Adelaide's coastal waters.
• Multiple benefit landscapes: Provide multiple benefits within the landscape by including water sensitive urban design (WSUD) elements to meet water quality objectives while also enhancing landscape character, engaging the community with nature, and providing environmental benefits.

• Streescape raingardens: All road runoff and stormwater systems from adjoining multi-dwelling complexes are directed to a series of raingardens that are located and sized to cater for stormwater flows generated from the contributing sub-catchment.
• Collector drain and street tree infiltration wells: Treated stormwater from the raingarden underdrains overflow to a dedicated ‘collector’ drain, which distributes the water to a number of soak wells located adjacent to street trees. The infiltration wells are designed with waterproof membranes at the top and bottom, and with geofabric and 200mm screenings around the perimeter, providing later infiltration to adjacent trees and garden beds.
• Extended saturation zone: A saturated zone of 450mm depth is used in the raingardens to assist plant viability and storage capacity of the systems.

• Innovative design requires more construction supervision: Additional site inspections are needed when contractors have little exposure to the innovative design, to ensure the systems are constructed and established as designed.
• Repeat community engagement: The early design that was based on extensive community consultation was later discarded as other opportunities for the project arose. The project team later reflected that further community consultation should have occurred after discarding the early design, which would have helped with issues that arose regarding community concerns and expectations.

Streetscape raingardens are highly transferable across urban areas, however the design and benefits will vary greatly between sites. Randolph Avenue had the benefit of being able to retrofit the streetscape layout with pathways, garden beds, replacement of existing trees, and creation of additional greenspace. These changes led to strong outcomes for water quality, landscape amenity, and community connection to the outdoors. Opportunities can typically be maximised for greenfield development, where neat integrations between the raingardens and other competing elements of the streetscape (carparking, service locations, pedestrian movement and safety) can be achieved.

Passively irrigated trees are also a highly transferable solution for existing streetscapes (as well as new developments). Where opportunities to modify the streetscape are limited, improved tree growth/canopy cover and reduction of urban runoff is still achievable, which can deliver water quality outcomes, urban cooling benefits and landscape amenity. The choice of design solution will be driven by physical constraints and design costs, and will always need to ensure adequate soil volume, drainage, and pedestrian safety are achieved.