Prior to the 1990s, engineering approaches to stormwater management were simple: gather as much of it as possible and send it down pipes, into drains and out into the ocean.
Under that model, stormwater was seen as something akin to garbage to be disposed of.
Whilst this approach was straightforward, it has resulted in flooding of downstream urban landscapes, untreated water carrying pollutants downstream to sensitive receiving environments and water merely being carried out to sea as opposed to being used.
Enter a more modern approach known in Australia as water sensitive urban design or WSUD, which first took hold in the 1990s. Under this approach, University of South Australia adjunct professor John Argue AO says, stormwater is now seen less as waste water and more as a resource which can be captured and used. Also known as source control, this concept revolves around six basic words: “hold the rain where it falls.. At its core, Argue says such a concept embraces core themes of quantity control (flood management), pollution control and resource harvesting.
According to Argue, who facilitates the two-day Stormwater Management – Source Control course run by Engineering Education Australia, the genesis of this approach lies at the point where rainfall strikes an urban environment surface, where it can be captured via rooftop gardens and water tanks under a notion of retaining water as opposed to having it wash away. Water which is not captured by these practices can potentially be infiltrated into the soil or be channelled through vegetated bio retention systems or rainwater gardens, he says.
A further technique involves water being cleansed using constructed wetlands to minimise downstream pollution or to prepare the water for entry into aquifers. Constructed wetlands are small artificial wetlands which are created specifically to cleanse stormwater runoff before passing it into aquifers or underground tanks. This water can be retrieved and used for non-drinking purposes such as toilet flushing, irrigation or industrial purposes.
One example of a WSUD system is the redevelopment of portion of the Hamilton Bus Station in central Newcastle. This involved the remediation of a 0.6-hectare portion of the site upon which 27 one, two and three-bedroom low-cost units were constructed. Completed in 1998, the system manages water from 83 per cent of the site for a number of purposes:
- roof runoff is collected and stored temporarily in underground tanks before being used as base (pumped) supply for hot water systems and toilet flushing
- overflow from rainwater tanks passes through gravel filled trenches before percolating down into the unconfined aquifer
- surface runoff is directed to a ‘dry pond’ area where it is cleansed before seeping downward to also recharge the unconfined aquifer
- groundwater is then used to supply the entire water demand of the bus-washing facility in the adjacent bus station and also for open space and garden irrigation in summer.
Across the residential units and bus washing facility combined, Argue says this system has delivered water consumption savings of around 60 per cent.
Internationally, Argue says recognition of source control is growing. In Chicago, for instance, rainwater gardens are now a requirement of approval for construction of all new high-rise buildings.
Argue says engineering challenges occur in several areas, and that each site needs to be assessed individually in terms of soil type, slopes, space and other concerns. Efforts to infiltrate water into soil, for example, necessitate an exploration of the soil type and whether or not this is suitable for infiltration. Whilst such infiltration is easy in a city such as Perth which is located on an extensive sand plain, things become more complicated with the largely clay soil sites encountered in eastern seaboard cities.
Domestic footings pose a particular problem for infiltration systems in clay soils because the soils’ swelling could potentially damage footings and hence the stability of foundations and ultimately, the buildings themselves.
Whilst these problems can be overcome, Argue says these concerns must be addressed when determining appropriate design solutions.
He says the benefits of source control cannot be understated. In terms of flood control alone, the aforementioned solution at the Hamilton Bus Station in Newcastle has the capacity to control a one-in-50-year storm event, he says. Some of the solutions installed in Adelaide can handle a one-in-100-year event. Beyond that, he says management at the source minimises the amount of flood water flowing downstream and reduces costs associated with infrastructure whilst delivering better quality stormwater going into receiving waters and reducing mains water demand.
“Overall, WSUD practices are cost effective and environmentally beneficial,” he said.
Source control represents the modern and efficient way to manage stormwater.