Kings Square raingardens

The Kings Square development in Perth’s Central Business District is part of Perth City Link – an urban renewal project including offices, retail space, community open space and residential development. The project extends the commercial core of Perth and reconnects the City with Northbridge.

As part of the development’s approach to sustainability and total water cycle management, a network of raingardens were incorporated into the streetscape design to provide stormwater treatment, protect sensitive groundwater systems that flow into the nearby Swan River, improve the long term health of street trees, enhance amenity, and integrate with the surrounding built form and elements of the streetscape.

Perth City Link Vision: The project is driven by Perth City Link’s core vision to reconnect Perth’s city centre with Northbridge. As such, it aims to deliver environmentally sensitive design including: integrated streetscape design, stormwater management, on-street street parking, alfresco dining, landscape amenity and shade.

• Raingarden sizing and layout: The raingardens are designed to fit the local streetscape context and dimensions, being sized for hydraulic efficiency and to fit into the cross sectional parking dimension between road crossing points. They are also located to accommodate surrounding alfresco dining and retail opportunities with shade, rest points and amenity provided by the vegetation and trees.
• Raingarden location to capture first flush: Each raingarden is positioned upstream of a traditional 'pit and pipe' stormwater gully drain to catch the first flush events which account for approximately 95% of rainfall. Larger events flow past the raingardens and into the overflow system.
• Dense understorey planting: Dense planting of eight plants per square metre assisted in providing a critical mass of initial vegetation. The vegetation plays a role in removing nutrients and binding pollutants (hydrocarbons, heavy metals, nutrients, dust and leaf litter) into the soil.
• Passive irrigation: Street and pedestrian pavements are graded to sheet stormwater into raingardens around trees and planting beds to promote passive irrigation of the vegetation.
• Use of sedge plantings: Meeboldina scariosa and Lepidosperma calcicola (both locally native) are used in the raingardens to treat the stormwater. Both species were common on the site prior to development.
• Deciduous trees with relatively small leaf size: Two deciduous trees (Ulmus parvifolia and Jacaranda mimosifolia) were selected. Ulmus parvifolia provides summer shade and winter solar access. The relatively small leaf size of these trees also reduces the likelihood of drainage system blockages.

Public safety in the urban streetscape: Public safety features are included in the design of the raingardens. A Safety in Design process was followed. Integrated trafficable ramps along the road edge allow for stormwater ingress (sheetflow into the raingardens), while the selection of stone with a high luminance contrast for the edge material visually deters cars from entering. The sizing of the edge units and their footings acts as a physical deterrent. The integrated stone edge units to the back and sides act as a wheel stop to the parking bays and prevent pedestrians (including vision-impaired) from falling into the raingardens. Bed levels are set to minimise injury if a car or pedestrian does accidentally fall in. Seating integrates and adds amenity.

The neat integration of competing elements (car parking, raingardens, service alignments, pedestrian movement and safety, alfresco dining and retail opportunities) demonstrated at the Kings Square streetscape will not always be achievable on other projects, particularly on retrofit projects. However, for greenfield development, Kings Square is a useful precedent for water sensitive street design that can be adopted in other parts of Perth, Australia and globally.

The raingardens are appropriate in locations where there is adequate room in the street layout, gradients are suitable and the catchment area is appropriate for this approach (e.g. sheetflow across a road into kerb and gutters).