3.3.3 Uncovering Europe’s hidden rivers

3.3.3 Uncovering Europe’s hidden rivers

Urban rivers are frequently culverted and diverted to enable urban development. The extent of historically covered (or culverted) rivers in some European cities is considerable. For example, there is an entire network of rivers culverted under central London (Barton 1992), many of which were once noted for their rich fisheries (Walton 1653). Other examples of covered rivers in major European cities include the River Bièvre in Paris, River Fleet in London, Ladegårdsåen in Copenhagen, and the Zenne in Brussels.

The result of covering rivers is that in many urban areas, local communities may be completely unaware of the existence of a river or a stream running beneath streets, buildings or open spaces (Wild et al 2011).  

Culverted rivers are widely considered to exhibit very low ecological integrity, due to dark or reduced light levels, habitat modifications, geomorphological changes and increased diffuse and point source pollution, especially due to misconnections into surface water sewers. The darkness and other modifications to the channel often prevent passage of fish just like weirs do (Wild et al 2011).

Awareness of the problems associated with culverted rivers has increased significantly over the last decade. For example, the London’s Lost Rivers project has documented dozens of tributaries of the Thames which flow largely underground as a subterranean tangle of unseen streams.

De-culverting (uncovering or daylighting) rivers involves opening up buried water courses and restoring them to more natural conditions. Projects can vary from the simplest form – removing the ‘roof’ of a culvert and retaining existing bank walls and natural bed material – to the major reconstruction of both bed and banks using soft-bioengineering measures and river restoration techniques (Wild et al. (2011).

De-culverted rivers and streams 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 de-culverted streams support, with knock-on positive effects for health and well-being, education and recreation.  Open rivers and streams can also help to reduce the urban heat island effect and can (and are) being used to drive regeneration in downtown areas.[1]

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In western and central Europe, there are already several cases of reopening covered rivers. In Berlin, large parts of the urban stream Panke has been covered or moved to underground pipes in the last 200 years. Nowadays, the restoration of this urban stream is being planned in order for the stream to obtain its natural structure.[2]

In the outskirts of Paris, a section of the river Bièvre has recently been reopened in Fresnes park and this was an important step for the local residents to rediscover this riverside area.[3] Indeed, projects of reopening urban rivers are often connected to city initiatives to enhance the aesthetics of the city and actions to improve surface water quality.

In the city of Aarhus, the city authorities decided in 1989 to uncover the urban river which was initially covered to its full stretch across the city due to water pollution from sewage and general waste, new traffic requirements and ambitions to develop the town into a modern city (see section 3.2.2).

In the city of Leuven, covered branches of the River Dyle are opened up, as part of a bundle of activities of the city and the Flanders Environment Agency to enhance the role of rivers in the urban fabric and live in close vicinity with the water. Opening up the river and the creation of green river banks within the city, improves the structural quality of the river and makes it more interesting for nature (even within the city). The realisation that open water courses in the city create significant added value is gaining in importance, not only among public administrations, but also among private project developers.

In Brussels, about 400 metres of the Woluwe stream, which had been enclosed since the mid 19th century, and its banks have been restored in recent years. This has created an open natural stream and a green corridor that is also part of the region’s Green Network. The project also involved the separation of stormwater and sewage flows and therefore reduces the undesirable dilution of the influent into the Brussels wastewater treatment plant (OECD, 2007). The opportunity to proceed with the re-opening of the Woluwe stream was given after the Brussels Central Region program Blue Network was set up (partly to link up with the existing Green Network).

In the UK, specific policy has been developed to prevent culverting, promote the removal of these structures and restore urban rivers back to a more natural condition. A few rivers have already been reopened, such as the formerly “lost” River Quaggy, whose course was recently brought back to the surface as part of the broader strategy London Rivers Action Plan. Its restoration entailed breaking the river out of a narrow concrete channel and recreating a functional floodplain as part of an attractive parkland landscape. The project had the effect of decreasing local flooding and achieving an additional integrated set of biodiversity, leisure, amenity and educational benefits, contributing to the regeneration of the area (Everard & Moggridge 2011). Since then the Quaggy has become a major feature of Sutcliffe Park in south London.

In Zürich, a clean-water concept for separating uncontaminated water from sewage channels has been extended into a stream restoration concept (Zürich stream daylighting program). The goal was to re-open (daylight) as many streams as possible, re-aligning them on the surface so as to increase ecological and recreational values within the urban area of the city of Zurich (Conradin & Buchli, 2004).

As mentioned in previous sections, a strategy dedicated to de-culverting streams has been developed in the city of Oslo. The Oslo de-culverting strategy has succeeded in recuperating the value of natural streams, in retaining and cleaning urban stormwater, thus leading to an improved water quality in the larger streams of the city.

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The de-culverted Quaggy (London, UK): A   multi-functional blue-green city space

The   Quaggy river is 5.6 km in length and crosses London’s Sutcliffe Park, a large   area of open parkland. For years, the Quaggy was culverted at Sutcliffe Park,   and local residents only became aware that a river was there when their homes   flooded more frequently as development in the floodplain increased.  From 2003-2007, a project to de-culvert the   Quaggy was implemented in a multi-disciplinary scheme combining flood risk   management with river restoration to benefit the local community.

The   project was part of the London Rivers Action Plan (2009) and entailed the   establishment of a new 'low-flow' meandering channel through the park,   following the Quaggy’s original alignment. The previous culvert was retained,   enabling it to take excess water in times of extreme flood events. Flow is   now regulated between the two water courses by a sluice. To provide further   flood water storage, the park itself was lowered and re-shaped to create a   floodplain capable of storing a maximum of 85,000 cubic metres of flood   water. A network of boardwalks, pathways and viewing points were designed to   encourage access to the river and ponds, all of which were an integral part   of the scheme. Furthermore, the project employed a community liaison officer,   interacting with schools, colleges and local charities, who also became   actively involved in the delivery of the project.

The   project has been successful in achieving a flood risk reduction for the   surrounding area, and in reconnecting people to nature (since opening the   park visits have increased by 73%). The implementation of the project as part   of a wider catchment scheme has enabled other habitat mitigation measures in   more constrained environments downstream to be implemented.                                                                          

River Quaggy before and after restoration. Photo: @xxx

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De-culverting the streams of Oslo

Most of   the streams passing through Oslo on their journey towards the Oslo Fjord were   culverted as they entered urbanized areas since the 19th century,   in order to reduce water pollution and allow for infrastructure development.

The city   of Oslo has developed a dedicated strategy for de-culverting its streams. The   implementation of the strategy, which focuses on the major streams (River   Akerselva, River Alna), but also covers smaller tributaries, started in   November 2013. In some cases where de-culverting took place in public   parks and green spaces, substantial additional financing could be raised   making it possible to develop blue-green solutions with high aesthetical and   multi-functional values. As an example, the Bjerkedalen Valley section of the   Hovinbekken stream was awarded in 2015 the City of Oslo Architectural Prize   for its high aesthetical and functional values. In the stream segment of   Hovinbekken stream where the Bjerkedalen Valley is located, there is now   trout swimming.  

Bjerkedalen   Valley. Photo: @Tharan Fergus, Oslo Agency for Water and Sewerage Works

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