Revitalising urban rivers
6 July 2012 by Richard Hollingham
The River Wandle in Carshalton, south-west London, is like many urban rivers. A couple of hundred years ago it flowed through rural fields but today it's flanked by roads, railways and buildings and has been diverted and polluted by urban development. At one stage in the 1960s the Wandle was in such a bad state it was effectively an open sewer.
But all is not lost. Richard Hollingham met Angela Gurnell from Queen Mary University of London, Dave Webb from the Environment Agency and Bella Davies from the Wandle Trust to find out how scientific research is helping revitalise even the most neglected rivers.
Richard: Just to set the scene, we're beside a busy road almost beneath the arches of a railway track, and the river itself - well, there's not a great deal to it, it's more a wide stream. What has this river been subjected to over the last few centuries?
Bella: A couple of hundred years ago this area was much more rural. Even then, though, the Wandle was used by lots of mills - it's actually known as one of the hardest-worked rivers in the world for its size. Then the Industrial Revolution created an awful lot of pollution and there was a general disregard for rivers across the country. By the 1960s, the Wandle was an open sewer and more or less biologically dead. During the 1970s, it was canalised and straightened to help with flood defences. Now we're trying to restore many of its natural processes and habitats.
Richard: Angela, your research has been the basis of this restoration work.
Angela: My job has been to find ways to measure various properties of these rivers and use that to understand which sections are good and which are bad - largely in terms of their aesthetics. If you combine that with information on water quality you can start to understand what the effect might be on organisms, particularly the animals that live in the river.
Originally we wanted to understand how engineering, for flood defences or development, had affected the character of urban rivers. Clearly the highest quality rivers will be those that have space to adjust and where engineers haven't straightened or reinforced them and so on. But when we compared the properties of the engineered and natural stretches of river we were surprised to find that certain types of engineering - particularly bits that are patchy and varied - are compatible with a varied and attractive river. And if the water quality is good they can support diverse ecosystems too.
Richard: So all is not lost, even if a river is surrounded by urban concrete?
Angela: That's right. Clearly it's easier to work on areas where you have the space to do more or less what you like. But you can still do quite a lot to improve sections like this, where we're standing now. Gently pushing away at the engineering and removing the bits that you actually don't need allows the river to recover in a patchy way.
Richard: Let's talk about what you've done here. The river is quite fast flowing and then it disappears under the railway bridge and, apart from the road on one side, you could be in the countryside.
Bella: Yes, it just shows what you can achieve. At this particular site the river used to be too wide and a weir was put in to hold the water back. The weir was an impassable barrier to fish and lots of other organisms, so we knocked part of it out to channel the water through a smaller space, which is why it's flowing faster. We added around 60 tons of gravel in this area and sculpted it to create a range of different habitats. We've also narrowed the river upstream and put in new banks and over a thousand native plants. We're particularly excited that the gravel has provided spawning beds for wild brown trout - in fact they have spawned in this very section.
A lot of this work was done by local volunteers - they've really been at the heart of the project and now this is their patch to look out for. Lots of other local people - anglers or people interested in wildlife and fish - are really supportive too.
Richard: Can this be done in other rivers?
Dave: Absolutely. In some respects, the Wandle is typical of many London rivers. Thirty years ago, poor water quality was the main influence on river ecology - even people were encouraged to keep away. But now that water quality has improved, habitats are more significant in determining what lives in the river. The last few decades have seen habitat destroyed and fragmented, so we need to restore channels in open spaces and remove blockages so animals and plants can move from one good bit of habitat to another.
Removing things like the weir reconnects the river and makes it more resilient to pressures like extreme flooding or even pollution, because animals can move freely along the river and colonise new areas if their previous habitats are damaged. We've been helping many local groups to set up river restoration projects across London.
Richard: And as if to prove everything we've been talking about, you say you saw a kingfisher here?
Dave: I did - it's not that uncommon to see kingfishers on our urban rivers. Thirty years ago, the idea that you'd see trout in Greater London, or kingfishers in Wandsworth and Lewisham, was ridiculous. But now it's quite common.
We now know that we need to manage rivers in an integrated way. So the idea that you only manage a river for flood defence or for moving waste water from A to B has gone. The aim now is to do all those things in a way that maintains the vitality of the life in the river too.
This Q&A is adapted from the Planet Earth Podcast, 31 January 2012.