Melbourne is currently the fourth fastest growing metropolis in the developed world —and not without consequences: congestion (and its attendant ills) is up and, despite a national drop in real estate prices, affordable housing is still an unrealistic prospect for many Melburnians.

In 2018, Melbourne was toppled from the coveted position of "world's most livable city" after a seven-year reign.

At a time when the city's demography is shifting so quickly and environmental concerns are mounting, improving infrastructure is only part of the solution.

Below we profile four big ideas, drawn from Melbourne Design Week and beyond, that could help Australia's most dynamic city maintain its reputation as one of the world's most livable.

A swimmable Yarra

Imagine floating down a river, bobbing past bending reeds and gaggles of water birds, but in the shadow of a CBD skyline of glass and steel.

It might seem like science fiction, but one Melburnian is working to make it a reality.

Michael O'Neill, an environmental scientist and president of non-profit advocacy group Yarra Swim Co, is working to make the river swimmable.

The Yarra Pools design includes a kayak launching station and a children's play area. ( Supplied: Yarra Pools )

It's currently illegal to swim in the Yarra anywhere South of Dights Falls, ostensibly because of boat traffic — but O'Neill thinks that overcoming the pollution problem is a more pressing hurdle.

Currently, swimming in the Yarra puts revellers at risk of a nasty E. coli infection.

Work to clean up the river is already underway — including the Victorian Government's passing of the historic Yarra River Protection Act in 2017.

"But the major thing now, and particularly for the CBD, is really tackling the storm water pollution and driving that change," says Mr O'Neill.

In the meantime, Yarra Swim Co have partnered with architecture firm WOWOWA to propose a stop-gap solution.

Yarra Pools, a featured project in Melbourne Design Week's Waterfront program, includes designs for a filtered pool and water recreation park to be built on the banks of the river at Enterprize Park.

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Mr O'Neill hopes the pool, if it's commissioned, will help "change the hearts and minds" of Melburnians.

But the endpoint will always be a river that's safe and legal to swim in.

"It would just re-frame how we feel about our whole environment; it would raise our expectations about what we expect our environment and natural places to be.

"That complete mindset change would be quite remarkable."

Smog sucking bicycles

Melbourne is Australia's most bike friendly city — and Dutch designer Daan Roosegaarde has an invention that could turn the city's favourite hobby into an act of environmental repair.

Mr Roosegaarde's Smog Free Bicycles, trialled in Dalian, China, are fitted with a handlebar attachment that 'breathes in' polluted air as the rider pedals, cleans it, and then releases the pollutant-free air into the rider's face.

The design was inspired by manta rays, who filter water for food as they glide through the ocean.

Roosegaarde said he was inspired by China's smog where "sometimes I couldn't see the other side of the street". ( Supplied: Studio Roosegaarde )

While the technology is complex, the process (positive ionisation) has been likened to hair sticking to a static balloon.

The miraculous machines are part of Mr Roosegaarde's Smog Free Project — a series of initiatives that seek to actively reduce air pollution while engaging the public in a dialogue about future-proofing.

Another initiative from the project, a 7-metre-tall Smog Free Tower designed for installation in public spaces, premiered in prototype form in Beijing in 2016.

"If 'the city' has become a machine that is killing us, then maybe we should build machines that can heal us," says Mr Roosegaarde.

The bikes are still in the development stage of design, but there are plans to scale up the project and produce attachments for personal bikes, as well as bicycle-sharing services.

The Smog Free Project also includes a Smog Free Ring, set with a stone made of compressed smog particles. ( Supplied: Studio Roosegaarde )

Mr Roosegaarde, who delivered a keynote as part of Melbourne Design Week's Toxic City symposium earlier this week, is keen to bring the technology to the city.

"[In Dalian] people got really excited because everyone wants clean air there, but at the same time they feel so helpless, so disconnected, waiting for the government [to intervene]."

"So I think these kinds of projects give a sense of hope, and at the same time it's something that they can own or share."

A gender equality map

So much of how we navigate our city these days happens through our smartphones; what if map applications included information about the safety of an area, using crowd-sourced information?

A new web-app called the Gender Equality Map, trialled recently in Darebin and Melton, allows users (of any gender identity) to anonymously log gender-specific experiences of place — positive or negative — by dropping a pin on a map.

Parks and public amenities were hotspots for posting during the Gender Equality Map trial. ( Supplied: CrowdSpot )

"I feel completely unsafe at Ruthven station at night even with PSOs," says one responder. "It is very dark and feels isolated. On some occasions I was the only woman (and about eight men) who got off the train there."

Only a few kilometers away another responder tells a different story: "Reservoir Leisure Center has female only swim nights, also has had trans inclusive swim nights."

The app has been developed by Dr Nicole Kalms, an associate professor at Monash University, and her team at the XYX Lab (a design lab that explores gender sensitive design) in collaboration with crowdmapping developers CrowdSpot.

The trial stage of the Gender Equality Map was launched in partnership with the Victorian State government and, given the positive responses, Dr Kalms is quietly confident that a permanent version will be rolled out across the state.

But Dr Kalms says the project is more than just a log of inequality, and has the potential to activate meaningful change.

"What do you think is the first thing people want to do when they hear there's an app like this operating around their suburb?" she says.

"They want go and look at where they live and to see what stories people are saying about where they are.

"The stories start to corroborate and what we see is a new picture of the city start to emerge … which then starts to form an overlay onto this previously static place.

"We can use this information to agitate for change and shape policy — it starts a dialogue."

Making Melbourne a national park

While this idea might seem far-fetched, there is precedent: in July, the city of London will officially be designated a "national park city", as part of a larger plan to "make the city greener, healthier and wilder".

Dr Bekessy points out that plant-covered walls and roofs can lower a building's internal temperature by ten degrees. ( Supplied: Icon Science )

Sarah Bekessy, a professor of Design and Social Context at RMIT, thinks redesignating Melbourne as a national park city is achievable — and lists three tangible short-term goals towards that objective:

1. Increase the canopy cover of Melbourne by 20 per cent in the next ten years. 2. Create habitat in Melbourne's private and public spaces for 10 native species and literally bring them back to the city. 3. Ensure that every single resident of Melbourne, within 200 meters, has a rich biodiversity experience.

"It's about rewilding the very urban fabric, using streetscapes and roundabouts and green walls and green roofs and courtyards in the city, school yards … [and] having core areas of green, where you can have connected pathways for native plants and animals to exist and to come back into the city."

Dr Bekessy thinks Australia's extreme climate makes a nod to eco-sensitive design particularly urgent. ( Supplied: Icon Science )

The health benefits of being in or near nature are being increasingly documented. "Doctors in London are now writing 'green prescriptions'," Prof Bekessy says.

She cites a recent study: "School children who have biodiversity in their yards have improved cognitive development."

"What more motivation do you need than that?"

Melbourne Design Week runs until March 24.