What to do with lost urban rivers beneath our feet

In my first post, I showed how urban rivers have become hidden and eventually lost. Have you done your homework? A little test to begin with then:

Lost urban rivers might be physically buried in culverts beneath our feet, but they might instead be simply obscured from everyday view, and therefore forgotten about. There is a trend towards rediscovering and uncovering lost urban rivers. The process of removing the culverts is called “de-culverting”, or more commonly “daylighting”.

This post discusses the types, the benefits, and the costs of daylighting our lost urban rivers. Some examples will follow in a future post.

Types

Daylighting is often considered to be the most “radical expression” of river restoration; removing the lid and exposing a watercourse to sunlight once more is a dramatic change to a river. In reality, daylighting rarely just involves removing the lid of the river, it will also usually necessitate some additional work to restore and improve the channel. We can consider perhaps three degrees of physical daylighting, as shown in the diagram below.

Design typologies for deculverting, showing the generalised degrees of culvert removal and associated river restoration when daylighting. Diagram by author, copyright © 2013, Catchment Science Centre, University of Sheffield.

There is also an important distinction to make in terms of the style of daylighting. It is easiest to consider this on a spectrum from “architectural” (typically artificial, designed, hard engineered, components included for human enjoyment) to “naturalistic” (typically a more natural channel shape, geomorphic processes, less managed). This is illustrated below:

Daylighting style guide on a spectrum from “architectural” to “naturalistic”, with example images shown to illustrate this. All photos by author, except bottom centre by Environment Agency NW, and bottom right by ERZ Zurich.

An additional form is non-physical, socio-cultural daylighting. Providing education, awareness, information boards and so on can reconnect people to a river buried beneath them, even if it cannot be physically uncovered. I think this is a really interesting and positive approach, and there are a few examples. Various groups celebrate hidden rivers through art, poetry, education and outreach, public walks, historical studies, and urban exploration. The River Moselle is made visible briefly through a glass floor in the public library – children especially are excited to learn more about this hidden river. Another project traced a lost watercourse, installing speakers along the route playing audio of the water flow – “sonic daylighting“.

We need more examples of where non-physical,  socio-cultural daylighting has been attempted, to evaluate whether it can still deliver useful benefits.

Benefits

Daylighting is claimed to bring various environmental, social and economic benefits. It is currently difficult to assess these as shown in recent research, but CIWEM summarises the range of benefits in its Policy Position Statement:

• Providing valuable wetland/aquatic habitat, aiding fish passage and significantly adding to the visual attraction of an area.
• Offering educational and play opportunities for children, enhancing pedestrian and cycle routes and giving people a touch of the countryside and its seasons in the town.
• Restoring historic canals for amenity or for navigation by powered and unpowered boats.
• Using water in motion to mask city noise and provide an atmosphere of quiet and calm.
• Complementing other urban regeneration initiatives and bringing commercial benefits such as enhanced image for properties and up to 20% increase in land values or rents.
• Reducing maintenance and construction costs by using natural bioengineering techniques rather than concrete constructions.
• Reducing flood risk and creating balancing ponds to help reduce flooding downstream.
• Giving a place a sense of identity, because each combination of landform, waterway, bank side buildings and bridges is unique.

The list above is not exhaustive – it doesn’t for example capture the benefits of deculverting directly on water quality, by enabling better nitrate processing in the water column. Nor does it capture the benefits arising from making pollution and misconnections more visible, promoting better public stewardship of urban rivers, or mitigating the urban heat island effect.

Costs

Physical daylighting can be expensive. We currently don’t have a good way of estimating the costs, as there are so many site-specific interventions, such as contaminated land being revealed along the river banks, structural works to buildings, roads and buried sewers, and the style of deculverting required. Reported costs have varied between £45 – £10,000 per metre. We need further case studies to help to improve these cost estimates.

What is clear, however, is that culvert removal is increasingly considered as a viable alternative to costly repairs of existing, ageing, and structurally poor culverts. This is both important for initial capital construction costs, but also the ongoing culvert maintenance (dangerous and costly) and risk of blockage and flooding. This financial argument is often a key driver for initiating a deculverting project, more important than the potential environmental or social benefits themselves.

The River Darwen was daylighted with multiple drivers in mind: flood risk management, Water Framework Directive, protected species habitat improvement, fish passage, reducing culvert maintenance / repair costs, and providing public access to the watercourse. Photo by the Environment Agency NW.

Conclusion

What can we learn from this? Four things:

1. We can do something about the lost urban rivers beneath our feet.
2. Daylighting is both physical removal of the culvert, as well as the social reconnection to hidden watercourses – and although it is becoming more widely known, many people, practitioners, planners and policy makers should be aware of this.
3. There are plenty of examples of daylighting projects, with numerous drivers and claimed benefits.
4. Most daylighting projects have not attempted to quantify or assess whether the benefits they anticipated are achieved. If this post-work appraisal was conducted, it is rarely publicly available.

To address this challenge, there is a map-based website where practitioners and researchers working on deculverting projects are encouraged to enter case study information, as well as browse past case studies for inspiration or information. With enough examples, it will be possible to assess the many claimed environmental, social and economic benefits of daylighting. More on that next time.

@losturbanrivers — Facebook.com/DaylightingUrbanRivers — www.daylighting.org.uk