Project Overview
This project is the result of a successful partnership between the Blue Mountains City Council, the Roads and Maritime Services and multi-disciplinary design house HBO+EMTB. Together the project team has transformed a highway upgrade project into a leading example of Water Sensitive Urban Design (WSUD).
The original objective of the development was to provide a safe and convenient shop front parking on the service road parallel to the highway. The site is located in the south of Lawson in the Blue Mountains and is enclosed by World Heritage National Park. The project team developed an innovative Multipurpose Eco-Garden alongside the service road and carpark which successfully addressed the stormwater and environmental issues associated with the surrounding landscape.
The Multipurpose Eco-Garden provides all the benefits of a typical soak-away, rain garden. “Eco-Pits” convey water to landscape areas just as swales do, without alienating precious public domain open space in a densely developed area. The Eco-Garden exceeds the NSW Government Draft Water Quality Guidelines for Best Practice. It has also provided Council with a repeatable WSUD planning and implementation strategy across the entire LGA for future projects.
Project Commissioner
Project Creator
Project Brief
The project is located in the south of Lawson in the Blue Mountains, surrounded by World Heritage National Park. The original objective of the development was to provide a safe and convenient shop front carpark and service road as part of the nearby highway upgrade.
The local Council and community were concerned that recent infrastructure developments in Lawson would significantly increase the impervious ground surface areas with consequent modification of the hydrology, drainage, stormwater quality, ecosystem health and water cycle.
All stormwater from the city flows directly into the World Heritage National Park, making the receiving environments vulnerable to ongoing stormwater pollution and damaging changes to stream hydrology. These stormwater and environmental issues had the potential to pose a threat to the World Heritage area and specifically the downstream endangered hanging swamps.
As part of the highway upgrade at Lawson, the project team identified an opportunity to reduce the impact on the World Heritage area surrounding the site through the innovative development of the service road, public carpark and eco-garden.
Project Innovation / Need
Designed by HBO+EMTB, the Eco-Garden directs stormwater to adjacent tree planting areas. When the capacity of the “Eco-Pits” to discharge water to the tree is exceeded, the excess simply overflows into the adjacent gully pit. The innovative design also addresses:
1. Water Quality Improvement: This design aims at capturing the first flush and recycling it through the subsoil tree feeding system. The innovative system exceeds the minimum water quality targets of a typical soak-away, rain garden/bio-retention basin, infiltration pit and groundwater recharge system by using specially graded soil horizons and a deeper media.
2. Water Quantity Detention: The runoff captured in the three eco-pits is continuously feeding through a 200m long exfiltration spiral system and soak-away through the gravel. The continuous system reduces the runoff leaving the site and the flooding risk to the receiving catchment.
3. Placemaking: Drainage at the base of the tree pits flow back to gully pits and also introduces aeration at a depth which makes it possible for tree roots to fill the entire soil volume, allowing larger tree species to achieve their full growth potential providing landscape/township features.
4. Environmental issues: Extensive native landscaping along the highway will integrate the manmade landscape with the surrounding park, as well as provide a green corridor for fauna. The captured runoff will provide alternate irrigation waters to the streetscape and reduce potable water consumption. This system will improve the hydrology, water quality and public health of the local environments.
Design Challenge
The Multipurpose Eco-Garden helped the project exceed its original objectives and address the following seven additional objectives with broad sustainable considerations for the project.
1. Flood Mitigation and Drainage: The system reduced peak flow to the receiving catchment, reducing erosion and flood risk.
2. Streetscape: Extensive landscaping and urban design initiatives have enhanced the character of the shops, service road and reduced the visual and noise impact from the Highway.
3. Microclimate Improvement: Extensive native landscaping using large trees along the highway will improve the amenity of the township.
4. Alternate Water Sourcing: The runoff from the footpath, carpark and service road will supply alternate irrigation waters to the streetscape and reduce potable water consumption.
5. Water Quality Improvement: The eco-pits improve stormwater quality, particularly catching first flush from the carpark. This system removes suspended solids, excessive nutrients and other pollutants from reaching the downstream native bushland.
6. Infiltration and Dissipation of Runoff: The unlined system will reduce runoff by allowing the filtered stormwater to infiltrate to the subsoil. The gravel drainage layer at the bottom of the leaky system allows stormwater to dissipate to the subsoil, reducing runoff and flood risk.
7. Protection of endangered species: Endangered native hanging swamps in the Blue Mountains require constant recharge to the groundwater. Infiltration allows rain water to reach and saturate the downstream endangered hanging swamps, improving environmental values of the World Heritage area.
Sustainability
The Multipurpose Eco-Garden has successfully addressed and exceeded all the identified stormwater and environmental issues associated with a World Heritage site as detailed above. As a result it has created a new standard for the Roads and Maritime Services in achieving Water Sensitive Urban Design in their major highway upgrade projects.
Another key environmental factor is the protection of the natural ecosystem in a sensitive World Heritage area. The eco-garden will be able to protect the aquatic and terrestrial ecosystems of the surrounding World Heritage area including the hanging swamps by better managing the stormwater interface between the urban and natural systems.
Above all, this multi-purpose yet simple system can be adopted in all new highway or local road upgrade works in NSW where landscape, stormwater management and other environmental initiatives can be integrated to the benefit of the local environment.
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Landscape Architecture
This award recognises the use of practical, aesthetic, horticultural, and environmental sustainability components, taking into account climate, site and orientation, site drainage and irrigation, human and vehicular access, furnishings and lighting.
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