Are we using nature for urban water management? Not even close

Australia is not only one of the driest countries on Earth, but the country with the most weather extremes. While droughts are destroying crops and emptying water reserves in NSW, severe floods are rampaging through Queensland, destroying people’s lives. And with ongoing climate change and rapid urbanisation things are going to get worse.

For example, Monash has developed rain gardens that retain and treat stormwater run-off that otherwise would pollute our bays and waterways.

This work resulted in practical design guidelines for the adoption of rain garden technologies, published in 2009 and updated in 2015. In inner Melbourne alone, more than 10,000 raingardens have been installed to protect the lower Yarra from stormwater pollution.

More recently, Dr Veljko Prodanovic, currently at UNSW, developed Blue-Green walls – vertical biofiltration gardens in urban areas that, instead of using tap water, use and treat household greywater.

Imagine living in an apartment on a higher floor of a building. Every time you shower or wash your hands, the water you used goes to irrigate a beautiful green wall just outside your building instead of entering the sewerage system. What’s more, that “waste” water gets treated and could be used again for toilet flushing or garden irrigation.

The water we produce while showering is rich with soaps and shampoos which act as fertiliser for plants, so we should harvest these resources. Otherwise, nitrogen and phosphorus from these products can create algae that choke our rivers and bays. The practical recommendations for the blue-green wall design was published in 2018.

Multiple benefits of nature

While using nature for water treatment was the initial driving force for researchers in this field, this is not the only benefit of green systems. Green walls are already valued for their beautifying presence and are highly used architectural features in cities where trees and other greenery can’t fit.

One Central Park building in Sydney, an award-winning structure, shows off its lush green walls across the whole Sydney CBD. Standing close to a green wall, or other vegetated system, it is not hard to understand their unique cooling benefits either. If you are in the street surrounded by green walls, the temperature drop can be as much as 12C.

While this highly important for human comfort, it also reduces temperature stress, which can lead to death. This is especially true across sensitive communities where every heat-wave represents a health risk.

With Sydney’s western suburbs being on average 10C warmer in summer compared to eastern suburbs, application of green technology could be highly beneficial.

Using greenery to reduce temperature has another positive side-effect – it reduces energy consumption in buildings. Researchers have found that using vegetation to shade building walls can reduce cooling costs in Miami, USA, by almost 60 per cent and, incredibly, almost 100 per cent in Brasilia and Hong Kong.

Real estate prices are a hot topic nowadays. The University of Western Australia conducted a research on the effect of rain gardens on property value in Sydney and found that a rain garden within 50 metres of your home can increase its value by 6 per cent.

So here is a tip on how to increase your property value in this falling market – convince your local council to build a rain garden next to your property. However, the amenity value of green systems is usually hard to quantify and not a convincing indicator.

Did you know that nature-based technologies can be used to reduce flood damage? Climate change and urban growth has increased the pressure on drainage infrastructure.

Completely removing flooding from cities is not feasible as total flood control is usually more expensive than the value of infrastructure and buildings in the flooded area.

Major flood events can cause severe and expensive damage but they do not happen frequently. Smaller floods on the other hand cause less damage but they happen more frequently. The cumulative damage of smaller but frequent floods can exceed that of big floods.

Nature-based technologies, such as rain gardens and wetlands, can reduce the risk of smaller floods. The latest work by Dr Behzad Jamali, a flood researcher from UNSW, has estimated that flood damage in a small (270-hectares) catchment in Melbourne can be around $10.3 million per year.

By installing rain tanks in every household for indoor and/or outdoor water use, the expected annual damage bill could be reduced by 30 per cent. Integrated use of rain tanks and rain gardens could cut that even further.

While we recognise the water recycling, cooling and amenity benefits of nature-based systems, it might be time to start considering green infrastructure as a cost-effective and environmentally friendly flood mitigation solution, too.

Unfortunately, current Australian drainage practice does not give any credit to nature-based systems for their flood mitigation benefits.

Not just in Australia …

Backed by research and multiple benefits, green infrastructure is not hard to sell. In Australia, these nature-based systems are known as Water Sensitive Urban Designs (WSUDs) and are starting to be widely implemented across the country, especially in Melbourne.

In Europe, these are “nature-based solutions” and are heavily used for rain water capturing, while in the US they are named Low Impact Developments (LIDs), a popular solution for road run-off treatment and urban cooling.

China has recently launched the “Sponge City” concept, which relies on green technology to hold water during wet periods so that you can “squeeze a sponge” during dry periods and use water where it’s needed.

Adoption of green technologies is happening around the world and this concept is not new. Recent technological advances in the development of green water treatment technology have popularised this sustainable water management practice, but two new issues arose.

For a long time, green technology development was the primary concern of engineers. The pendulum has recently shifted towards delivering widespread adoption, with a focus on planning and regulatory issues.

While these are crucial for the roll-out of green technologies, they shouldn’t be seen in isolation. We need to balance this pendulum and have technology development and system adoption happening hand-in-hand.

The green technology systems are not robust enough for unrestricted implementation, and we need coordinated effort and investment from researchers, state governments, councils, water corporations, developers and households to achieve desired results.

Keep in mind that these are nature-based systems which are specific to different climates, soils and water conditions. They can’t be mass-produced.

This leads me to a second issue which is even more concerning. Some companies have started to “blindly” use green technology guidelines developed in one climatic region in other, incompatible regions.

This can be seen in countries like China, where there are significant investments in this field and business are selling Australian designs for a quick profit.

However, this leads to system underperformance and, in some cases, plant death, which gives rain gardens and other green technologies a negative reputation. For the best results, these systems need to be tailored, tested and validated to local conditions.

What does the future hold?

Now we all must work towards more research-industry partnerships as well as to educate the public about nature-based water treatment systems. Engineers should be working with urban planners, landscape architects and ecologists to build capacity for wide-spread implementation of water and life-saving greenery throughout our cities.

So, are we using all the benefits that nature provides? No, not yet, but let’s keep working towards that goal.