Water is an integral part of urban life and a precious resource which needs to be conserved and managed. Australia’s cities generate enormous amounts of stormwater, causing significant environmental damage. As our urban development expands, increased utilisation of stormwater is necessary to create sustainable and harmonious spaces.
WHAT IS IT?
Stormwater harvesting involves the collection, treatment, storage and reuse of stormwater run-off from urban areas. Stormwater is rainwater which runs off impervious or saturated surfaces such as roofs, roads, pavements and green spaces. Prior to urban development, natural vegetation and pervious areas would soak up rainwater, allowing for transpiration and evaporation, but urban development replaces these areas with impervious surfaces, resulting in an increased stormwater runoff. It is a relatively new form of water reuse, compared to rainwater tanks, but is increasingly being recognised as an option for meeting the water demands of many projects and is commonly used to irrigate public parks and golf courses.
Most stormwater harvesting and reuse systems will include four elements. First the stormwater is collected from a drain, creek or pond. It is then temporarily stored in dams or tanks to balance supply and demand. Storage is commonly either constructed on the creek or drain or some distance from the creek or drain. The water is then treated to reduce pathogen and pollution levels before being distributed to the area of use.
WHY HARVEST STORMWATER?
As the landscape is transformed from urban development, the way water flows through a catchment changes, which can cause range of adverse environmental impacts.
Almost 90 per cent of Australia’s population lives in urban areas and produce an estimated 3,000 gigalitres of average annual runoff. Due to the large areas of impervious surfaces, it’s estimated at least two thirds of the run off is more than what would have naturally occurred prior to settlement. Australian cities are producing more run off than the combined volume of water which they draw from catchments and groundwater sources (estimated to be 2,100 gigalitres annually). With the exception of Perth, less than three per cent of this rainwater and stormwater is used.
Increased urban stormwater runoff can result in poor water quality, due to the pollutants in the water. When this is disposed in rivers and creeks, it degrades the health of aquatic ecosystems. It’s estimated urbanised environments lead to a 90 per cent increase in the volume of water entering streams. This dramatic change in a pattern of flow in rivers and streams can impact the likelihood and severity of flooding. As more potable water is consumed than recovered, water availability can be reduced, impacting on a community’s quality of life. Stormwater harvesting help urban communities overcome these issues.
BENEFITS OF STORMWATER HARVESTING
A Senate Environment and Communications Committee Inquiry into Stormwater management in Australia last year found stormwater is an underutilised resource. Stormwater differs to other environmental problems as although it is a significant problem, increasing its use can provide environmental, economic and social benefits.
The inquiry found greater utilisation of stormwater can result in the following benefits:
If stormwater is greater utilised, run off volumes for most storms can be lowered to pre-development levels, helping to reduce baseflows, return natural soil moisture levels and maintain water quality. Capturing and storing stormwater for passive irrigation reduces runoff volumes and can improve the flow of rivers and creeks. Stormwater treatment can reduce pollutant loads to waterways, helping to protect ecosystems.
Flooding-related costs, the need to build stormwater infrastructure due to increasing urban populations and the costs of replace existing infrastructure could be reduced by better stormwater management. It may alleviate the need to expand existing infrastructure or to identify other water management solutions. Professor Ana Deletic, Associate Dean, Research and Director of Monash University Infrastructure told the inquiry that to maintain the same level of flood protection in Melbourne, it’s estimated $8 billion will be needed to be invested in the next few decades to keep up with development and to address ageing infrastructure.
Increased use of stormwater can improve the sustainability, resilience and liveability of cities by supporting their greening. Greening of cities can help improve thermal comfort by mitigating heat and reducing the temperature. It can create productive vegetation and increased carbon sequestration, better air quality and improved landscape amenity. Improved water quality can limit blue-green algae growth and the odour it brings, creating more pleasant spaces and encouraging their use. Green infrastructure and proximity to natural systems has also been found to have a positive effect on property prices.
USES FOR STORMWATER
Stormwater harvesting and water recycling has several uses, which can be tailored for each project.
Harvesting of non-potable stormwater can be used to generate long term water storage for drought and emergency supplies or for agricultural uses. It can help control fires, for testing and maintenance of fire-control systems and for fire-training exercises. There are municipal uses such as roadmaking, dust control and street cleaning.
In residential and commercial properties, stormwater may be used for toilets, gardens, car washing, water features and utility washing, while industrial and commercial buildings may use it for cooling water, process water and wash-down water.
Currently most stormwater harvesting projects are for non-potable use, however there is potential for it to be used for potable supply.
On October 10, the Senate received a response from the Government on the five recommendations which rose from last year’s stormwater inquiry.
The government committed to working with the states and territories to discuss reviewing the Australian Guidelines for Urban Stormwater Management and to see if the guidelines could form the basis of a national policy framework. The government said it will seek to incorporate audits, as part of the approach to urban water management and agreed in principal with the recommendation that new funding models and financial incentives would facilitate improved stormwater management outcomes. The response agreed in part that funding be restored for stormwater research and that consideration be given to how co-investment can be attracted.
Rather than waiting for the national stormwater initiative to be developed, several architects are already reaping the benefits of stormwater harvesting in their projects.
THREE RECENT PROJECTS HARVESTING THE POWER OF STORMWATER
Sydney Park Water Re-Use Project by Turf Design Studio and Environmental Partnership
Photography by Ethan Rohlof
The Sydney Park Water Re-Use Project is the City of Sydney’s largest water harvesting project to date. Built in partnership with the Australian Government through the National Urban Water and Desalination Plan, the project has the capacity to capture and clean the equivalent of 240 Olympic-sized swimming pools of water per annum. It is a central element of Sustainable Sydney 2030, targeting 10 per cent of water demand be met through local water capture and re-use in the park.
Mike Horne, Director of Turf Design Studio says the project’s success lies in its unique fusion of design, art, science and ecology.
“Not only have we created an interwoven network of community infrastructures and ‘made’ systems, the City has taken another significant step in transforming this former brick pit and landfill site into a vibrant new urban parkland,” Horne says.
The Sydney Park Water Re-Use Project has improved water quality, visual amenity and detention storage effectiveness by enhancing circulation of water through the ponds and wetlands. The ponds previously suffered poor water quality and from outbreaks of blue-green algae, Azolla and Duckweek, due to the stagnation of water during the warmer months and low rainfall.
Prior to the project, all stormwater flowing through the Munni Channel continued to Alexandra Canal and beyond to Botany Bay untreated. The project now pumps up to 1000L/s of stormwater from Munni Channel into the Sydney Park water re-use scheme. This diverts an average of 840 ML/yr of stormwater for treatment and reuse. The treatment train includes a gross pollutant trap, 5,000sqm of bioretention system, wetlands and the existing ponds. Water re-used for irrigation is further treated by filtration and UV disinfection. Each year, 30 million litres of harvested water is now recycled for improved circulation of the ponds, irrigation of the Alan Davidson oval and the Village Green, and non-potable water supply for the nursery and truck washing at the City of Sydney Depot.
Adam Hunter, Director of Environmental Partnership said the project strived to create “opportunities to immerse and engage with the landscape and to experience the landscape from different perspectives”.
“In conveying the water story through its visible processes; the project is educating the community about the importance of urban water management, and the interdependent nature of our urban and natural environments,” he says.
“The function and processes of water harvesting and cleansing is made legible through its visible ebbs and flows in the landscape.”
Lizard Log Park by McGregor Coxall
Photography by Simon Wood
McGregor Coxall was brought on by the Western Sydney Parklands Trust to revitalise and extend the park facilities. This included an upgrade and extension to the existing toilet blocks, BBQ and picnic facilities, redevelopment of the children’s play area, the development of an events space and access bridge along with a new car park.
Driven by an emphasis on sustainability, the design incorporates power generated by solar panels, dam water for toilet flushing, all grey water is reused for irrigation and recycled materials are used where possible.
The area around Pimelea features waterways, ponds and water storage lakes. At Pimelea, a chain of ponds has been partially constructed near the main entrance road and a naturalised channel leads into the pond. The Sydney Water channel also forms a key feature on the edge of each site, linking the sites to Sydney’s water supply network and offering further opportunities for water efficient fittings, rainwater tanks and grey water recycling at the site.
The site car parks are based on a “no pipe” ecological filtering system. Ground water flow bypasses the traditional pit and pipe system and is navigated to an open wetland swale that captures and cleans the water before discharging into the site dam for reuse.
The play area uses recycled water through a children’s play pump and water course system. Since completion of stages one and two, visitation numbers increased by over 40 per cent per annum from 198,000 (July 2011-June 2012) to 277,000 (July 2012-June 2013) per annum.
Aranda Adventure Garden by Paul Barnett Design Group
Once an unusable dustbowl, Paul Barnett Design Group (PBDG) converted the heart of Aranda Primary School into an adventure garden.
“The water harvested adventure play space has transformed the centre of the school to become an oasis where before no children played as it was too hot,” Paul Barnett, Director of PBDG says.
“They now fill the area with activities ranging from sitting, jumping over rocks and inhabiting the array of social and play space.”
When Barnett first visited by the site, he was taken by the children playing “steam trains” by shuffling their feet in the dust. The playground consisted of hard, compacted clay which had no chance of sustaining any plants.
The team started by looking at the contours, the sun and wind microclimate and the potential for catchment for adjacent roofs and ground surfaces. They created spatial design that included pathways, sandpits, mud spaces, rock terracing and climbing places, tree logs, and meeting spaces.
A water harvesting system was then developed by Paul Totterdell to create an underground trench system that mirrors the surface designs.
The trench and catchment system holds water and allows the water to permeate through the soil, creating plumes of moisture about on metre either side of the water harvesting trenches and enabling roots for trees and plant over time to enter the trenches. The dry creek beds were then created with rocks, sleepers and soil and sand and gravel and geotextiles. Top soil was reused, improved, mulched and placed ready for planting. The five-stage Masterplan covered the playground, sloped areas and ovals. Each area utilises roof water catchment, and existing ground levels were re-sloped to create water holding instead of run-off.
Funding limited the amount of planting so PBDG are now revising the area under a next stage to finish the planting and consolidate the system to ensure that ground covers are connecting and providing a shading of the soil. In about five years’ time, the new adventure play area will create a forest of shade. As plants establish themselves and their roots seek out and enter the water harvesting trenches, there will be no maintenance other than weeding and fine tuning plant cover over the first few years. As the trees mature, the space will require lower amounts of water and will provide a shady summer play space and summer sheltered winter space.