Waterways were once the beating hearts of our cities.
They bore the boats laden with the goods, tradesmen and settlers that transformed inlets and backwaters into hubs of humanity.
However, all that changed 200 years ago with the advent of the industrial revolution: as cities became crowded, rivers were polluted with human and industrial waste, becoming sources of disease; at the same time the development of the railways meant waterways were no longer the essential mode of transport they once were.
The result was that all across the world cities covered over their rivers, forcing them into culverts or tunnels below the metropolis.
Today, waterways across the world are fighting back.
In a trend known as “daylighting”, towns in Europe, Asia, North America and Australasia are breaking open culverts to reveal the hidden rivers that have always been at their heart.
The two most active cities by far have been London and Zurich.
The British capital was the world’s largest city during the industrial revolution.
As a result, despite being famous for the River Thames, dozens of London’s rivers were covered over or converted into sewers during the Victorian era.
Some of these hidden rivers have world-famous streets that run above them: the Fleet, the Strand.
While these iconic roads are unlikely to be torn up anytime soon, many other rivers in the city have seen daylight.
The UK’s most famous river restoration project is the clean-up of the River Lea for the London 2012 Olympics.
At the same time, more than 17km of other waterways have been opened up across the capital since 2009.
It is a trend being repeated across the UK, with the most recent example of daylighting coming in the centre of the Yorkshire city of Sheffield.
While the UK’s industrial heritage means it has plenty of rivers to de-culvert, it is Zurich, Switzerland’s largest city that has carried out more daylighting than any other to date.
Since the 1980s Zurich’s officials have supported the Bachkonzept (Stream Concept), which seeks to “daylight” as many covered watercourses as possible.
Why is it so popular?
There have been two main drivers behind Zurich’s daylighting of its hidden rivers.
First, there’s a public desire to recapture lost spaces and improve quality of life in the city.
Second, there’s an economic incentive: by having clean water flowing through rivers instead of sewers, it means less water flows to sewage works, reducing wastewater treatment costs.
The combined social, environmental and economic benefits help explain why daylighting is becoming so popular around the world.
The Cheonggyecheon stream in Seoul is an almost 11km-long artificial water corridor that diverts water from an underground river.
Located in the city centre at the site of what used to be an elevated expressway, the stream is both a tourist attraction that draws more than 60,000 visitors each day, and a major flood-relief channel.
At a time when the planet is experiencing record levels of flooding, opening up hidden rivers to use as flood channels can help relieve some of the flooding in towns and cities.
As well as climate benefits, daylighting also brings benefits for wildlife: the opening up and cleaning of the Saw Mill River in Yonkers, New York, has created a natural habitat for migratory fish and native vegetation to attract insects and encourage food chains.
In addition, the Saw Mill River project is expected to create 950 permanent jobs in the area surrounding the river.
Little wonder daylighting is so popular among urban planners today.