Daylighting Urban Rivers
by Freshwater Blog and Adam Broadhead | Freshwater Blog
Many towns and cities around the world have unseen flows of water which snake underneath concrete streets: ‘lost’ rivers which have been rerouted into sewers, drains and culverts as urban areas have grown. See, for example, how the London’s Lost Rivers project has documented dozens of tributaries of the Thames which now flow largely underground as a subterranean tangle of unseen streams.
River restoration – the restoration of water flows and aquatic life to a largely ‘natural’ state – has been a topic of increasing interest over recent years, and organizations like the River Restoration Centre and the European Centre for River Restoration have formed to promote restoration work.
Deculverting or ‘daylighting’ is the process of uncovering buried urban rivers and streams, and restoring them to more natural conditions. Daylighting can create new habitat for plants and animals, potentially reduce flood risks, and create new ‘green corridors’ through urban areas, a good example being the highly successful restoration of the Cheonggyecheon stream in Seoul, South Korea.
Adam Broadhead’s Daylighting website maps deculverting projects around the world as a means of sharing information on their outcomes and effectiveness. We spoke to Adam to find out more about this fascinating and innovative project.
Freshwater Blog: Not only have you been working on a PhD on deculverting urban rivers at Sheffield University, you’ve also put together the Daylighting project. Could you tell us a little about these projects and where you got the inspiration for starting them? Do they overlap and cross-pollinate each other?
Adam Broadhead: They are very much related. Initially, I was looking at the issues surrounding daylighting: what challenges and uncertainties are there in the evidence base that prevent funding and hinder projects? Although there had been some academic reviews on the evidence, most projects had little available evidence on their environmental, social and economic objectives and outcomes.
The Daylighting website gathers this information in one place, along with costs and drivers of projects and contact details. I’ve also been using a lot of Facebook and Twitter to spread the word among other professionals and the wider public about lost rivers and opportunities for opening them up – and by far the most common reaction is one of support.
The PhD work specifically focused on a particular aspect of this topic and arose from some literature from Zurich, Switzerland. Some streams and springs have not only been buried, but completed lost into the sewer system and flow to the sewage works.
My work has been to demonstrate that this happens, and develop methods to identify and predict where. If lost rivers affect water companies too, that means another key stakeholder and funding source to do daylighting to reduce sewer network costs, in addition to the wider flood risk, ecology and public space benefits.
What different benefits can daylighting such ‘lost’ rivers bring?
Buried watercourses receive no sunlight, and so can be ecological deserts to life in the water and around the river banks (fish, birds, insects, plants, mammals). The darkness and other modifications to the channel often prevent passage of fish just like weirs do. Opening them back up can bring back all of this ecology, when done properly.
Daylighted watercourses also have less of a flood risk due to underground blockages or collapse and it is easier to spot and tackle sources of pollution when you can see the water. People can see and enjoy the wildlife that daylighted streams support, with knock-on positive effects for health and well-being, education and recreation. Open watercourses can help to reduce the urban heat island effect and can (and are) being used to drive regeneration in downtown areas.
Where has daylighting been particularly successful?
There are so many good examples. One of the largest and most impressive is the Cheonggyecheon in Seoul, South Korea where miles of river were created through the city center, with fountains and paddling areas in the artificial end, and open wildlife space in the more natural downstream end. One of my favorite examples, though, is the Quaggy River daylighting at Sutcliffe Park, London, which provides a flood storage wetland area, abundant wildlife, amenity space and land value boosts for the area.
You are based at Sheffield University. Does Sheffield have a network of ‘lost’ water?
Yes – Sheffield is a water city. Rivers, brooks and natural springs flow through and beneath the city, sometimes simply culverted (continuing to flow as rivers) such as through the “Megatron” culvert right beneath the station area; others, as my PhD work suggests, completely wiped off the map and now part of our Victorian sewer system.
What happens in the process of daylighting a river? Is it a relatively time and money intensive process? I would imagine that it’s not always easy to ‘reclaim’ waterways through urban areas?
There are capital costs for the engineering to remove the ‘lid’ off the river, plus additional restoration to the channel shape to renaturalise it. Sometimes in old industrial areas there will be a lot of contaminated land and soils, escalating costs and limiting the work that can be done (such as the Darwen at Shorey Bank).
Most of the time, it will be necessary to do some additional flood risk work – often that is the main initial driver and funding source for projects (rather than ecological improvements) – and this will require additional investment. A big cost is the land itself – quite often it will be occupied by buildings or roads, some of which we wouldn’t want to get rid of.
The good news is that the costs and benefits often do stack up to make daylighting a worthwhile investment – we’ve seen daylighting in downtown New York on the basis of that regeneration benefit alone. And there are many much smaller culverted watercourses that could be opened up far more cheaply by local contractors – a fear of the unknown contributes to costs being greater than necessary in my opinion.