Bringing Hidden Rivers Back to Life
Beneath the streets of many old cities lie rivers that most residents have never seen. Over the past two centuries, thousands of small streams were covered with concrete or forced into underground pipes. At the time, this seemed a sensible solution. Urban streams were often polluted with household waste, they smelt unpleasant and they were blamed for spreading disease. Burying them also created valuable flat land for roads and buildings. In many cases, the original names of these streams survive only in the names of streets or neighbourhoods. Today, however, a growing number of city planners are asking whether these lost waterways should be brought back to the surface, a process known as 'daylighting'.
The case for daylighting begins with flooding. A stream that runs through a pipe can only carry a fixed amount of water. During heavy storms, which are becoming more frequent in many regions, these pipes quickly fill up, and the water has nowhere to go except into streets and basements. An open channel with natural banks, by contrast, can spread out and slow down, absorbing far more water before it causes damage. An open channel also gives residents more warning, since rising water can be seen long before it reaches their homes. Engineers in one mid-sized city calculated that reopening a single kilometre of stream reduced the risk of serious flooding in the surrounding district by around forty per cent.
Wildlife benefits too. Underground pipes are dark, fast-flowing and almost empty of life, whereas an open stream quickly attracts insects, birds and small fish. In several projects, ecologists recorded the return of species that had not been seen in the area for decades, sometimes within two years of the work being completed. The new stream banks also act as green corridors, allowing animals to move safely between parks that were previously isolated from one another. In my view, this is one of the most underrated advantages of daylighting, since it turns a piece of drainage infrastructure into a living habitat.
Perhaps surprisingly, some of the strongest support has come from local businesses. When a stream was reopened through the centre of one large city, the surrounding area was transformed from a noisy traffic route into a popular public space. Property values rose, new cafés and shops opened, and the number of visitors increased dramatically. Similar, though smaller, effects have been reported elsewhere. Shop owners who had at first opposed the loss of parking spaces often became the project's keenest defenders once they saw the increase in pedestrians. Some planners now present daylighting not as an environmental project at all but as a way of improving the local economy.
Daylighting is not, however, a simple or cheap solution. Removing concrete and rebuilding a natural channel can cost several times more than repairing an old pipe. In crowded city centres, there may simply be no room for an open stream without demolishing buildings. Water quality is another obstacle: if a stream still receives untreated waste from older drains, reopening it may bring back the very smells and health risks that caused it to be buried in the first place. There is also the question of who should pay, since the benefits are often shared by a whole district while the costs fall on a single local authority. It would be unwise, I believe, for any city to begin digging before these problems have been fully investigated.
For these reasons, many cities are choosing a middle path. Instead of fully restoring a stream, they create 'partial' daylighting schemes, in which the water flows through an open but artificial channel lined with stone. Others mark the route of a buried river with lines of trees, small ponds or information panels, so that residents at least become aware of the water beneath their feet. Such approaches may lack the ecological benefits of a fully natural stream, but they are far cheaper, and they keep the possibility of complete restoration open for the future. Ultimately, the success of any scheme depends less on engineering than on whether local people are willing to see their streets in a new way.
