River/stream daylighting

Cheonggye River, Seoul. Before and after river daylighting. The river had been covered since 1968 and was freed in 2005. Photo by Hayden Clarkin. https://www.thecooldown.com/outdoors/cheonggyecheon-stream-seoul-restoration-recovery-green/.

River or stream daylighting involves uncovering and restoring natural waterways obscured or diverted by urban infrastructure, typically occurring in urban or peri-urban areas where structures like pipes, bridges, or culverts interrupt natural water flow. Across Te Moananui Oceania, concrete infrastructure often supplants natural streams, directing them underground through pipes.

This process entails removing obstructions hindering the hydrological path of streams and rivers, returning them to open-air natural channels. In areas where significant portions of the catchment are paved, additional nature-based solutions are necessary to manage stormwater runoff. 

See also: river rewilding, riparian restoration, and floodplain restoration.

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Name of NbS

River/stream daylighting

Type of NbS

Ecosystem restoration

Location

  • urban
  • peri-urban
La Rosa Reserve Stream Daylighting. Photo by Boffa Miskell

Relationship to Indigenous knowledge

Urban growth has resulted in many streams and rivers being piped undergound, leading to significant ecological and environmental impacts on the health of waterways and the biodiversity within them. This has also caused a social disconnection from water in urban areas, particularly affecting peoples who have a spiritual connection to water, as many Indigenous people in Te Moananui do (Dickie, 2005; Nursey-Bray et al., 2024). Daylighting streams is crucial not only for restoring ecological balance but also for fostering relationships with Indigenous knowledge, preserving cultural ties to waterways.

Climate change benefits
  • Changes in rainfall
  • Flooding
  • Reduced water quality
  • Sea level rise
  • Reduced freshwater
  • Urban heat island effect

Daylighting rivers offers several adaptation to climate change benefits. Restoring natural waterways helps mitigate the urban heat island effect prevalent in densely populated areas. By replacing concrete structures with vegetated and blue surfaces, daylighting increases green and blue-green spaces, which absorb less heat than paved surfaces, thus reducing local temperatures and alleviating heat stress in urban communities.

Daylighting restores natural hydrological processes, reducing the risk of urban flooding and erosion exacerbated by climate change-induced extreme weather events.

The re-establishment of riparian vegetation along daylighted rivers enhances carbon sequestration. Riparian plants absorb and store carbon dioxide from the atmosphere, aiding in the mitigation of greenhouse gas emissions and climate change impacts.

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Societal / socio-cultural benefits
  • Disaster risk reduction 
  • Water security
  • Waste management and sanitation

Improving water quality and reducing flooding are primary objectives of urban river daylighting, particularly crucial amid increasing urbanisation densities where water security is becoming more vital. Daylighted streams not only augment water availability within urban areas but also facilitate water filtration through associated riparian planting. 

Given the escalating occurrence of extreme climatic events, flood adaptation in urban spaces has become a key priority in many places. Daylighting streams offers more effective water storage during such events compared to culverts (Buchholz & Younos, 2007). Restored riparian planting or attached constructed wetlands associated with daylighted rivers further enables water storage and purification, improving water quality during runoff transportation to larger connected systems including reefs.

One of the key advantages of daylighting streams is improved stormwater management (Sinclair 2012; Buchholtz 2016). As urbanisation persists, and in some cases as sea levels rise, the demand on old, piped infrastructure to hold streams increases, potentially straining their capacities. This is particularly true during intense storm events. When pipes are overcome flooding occurs. Stream daylighting is a potential solution, facilitating a natural process of water storage with capacity flexibility over time, unrestricted by confined spaces (Buchholz & Younos 2007). Open streams facilitate more efficient stormwater management, and when naturalised with vegetation, they can filter pollutants and function as bioretention systems, further enhancing the environmental benefits. When floodplains are restored concurrently, flooding may be further mitigated.

Daylighting rivers enhances recreational and aesthetic values, promoting public engagement with nature and fostering community resilience to climate change impacts. This beneficial impact of daylighted rivers is complemented by the associated creation of urban recreational spaces or human-powered transport corridors alongside (Sinclair, 2012). 

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Ecological and biodiversity benefits
  • Disturbance prevention
  • Habitat provision
  • Purification

A key motivator for daylighting streams is the restoration of riparian habitats, which improves conditions for wildlife species threatened by urbanisation. Daylighting streams restores natural stream structures, allowing exposure to sunlight and aerial colonisation, which creates healthier streams that support diverse wildlife (Neale, & Moffett, 2016). Restored waterways foster biodiversity, which is crucial for ecosystem resilience amidst climate variability and environmental changes.

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Conceptual diagram of change in stream ecology arising from daylighting. Image by Neale & Moffett, (2016).

Technical requirements

Before daylighting a stream or river, several key requirements must be considered to ensure the project’s success. Adequate space for buffer zones is essential, along with a comprehensive understanding of the hydrology of the entire watershed, both currently and in the future (Sinclair, 2012). Detailed site assessments, including hydrological, geological, and ecological studies, are crucial to grasp the current conditions and potential impacts of daylighting.

Engineering and design plans are necessary to strategically remove or modify existing grey infrastructure like culverts, pipes, and concrete channels. Natural stream beds and banks will need to be created to replicate or emmulate the original river morphology.

To ensure biodiversity within riparian buffer zones, a variety of plantings is necessary. Careful selection of local plant species that will support biodiversity and stabilise the banks is important (Sinclair, 2012). Ongoing maintenance is required to sustain these plantings, manage weeds, and preserve the ecological integrity of the area.

Water quality management is needed to prevent pollution and manage stormwater runoff. This may include the installation of sediment traps, constructed wetlands, and other bioretention systems to enhance water quality as it flows through the restored stream.Finally, long-term maintenance and monitoring plans must be established to ensure the ongoing health and functionality of the daylighted stream. This includes regular inspections, invasive species management, and adaptive management practices to address any emerging issues or unforeseen climate changes.

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Issues and Barriers

River daylighting faces several issues and barriers that can hinder its success. The complexity of existing infrastructure, including buried pipes and concrete channels, makes the process technically demanding and costly. 

Limited space in densely populated areas can restrict the feasibility of creating adequate buffer zones necessary for effective restoration. Additionally, hydrological changes caused by urbanisation can lead to unpredictable water flows, complicating the river daylighting process.

Financial constraints are a significant barrier, as daylighting projects require substantial investment for planning, implementation, and ongoing maintenance. Ensuring long-term success requires continuous monitoring and adaptive management, which can strain resources and commitment over time.

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Opportunities

River daylighting presents numerous opportunities, especially in areas of Te Moananui Oceania that have streams and rivers. Integrating daylighted streams within urban parks and recreational walkways can enhance both ecological and social value.

In rapidly urbanising areas of Te Moananui Oceania, river daylighting can be a cost-effective alternative to traditional grey infrastructure. Constructing additional pipes, culverts, and concrete channels to manage stormwater is often expensive and resource-intensive. Case studies have found that the costs associated with daylighting a stream can be less than designing new higher capacity pipes and re-burying the stream (National Park Service). This a key opportunity of daylighting rivers in Te Moananui Oceania.

By showcasing successful daylighting initiatives, communities can be inspired to adopt more nature-based solutions, promoting broader environmental and societal benefits across the region.

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Financial case

In urban areas, daylighted streams offers potential cost savings in stormwater management by reducing the need for expensive infrastructure to mitigate flood risks. By restoring natural waterways, communities can enhance their resilience to flooding and storm surges at a lower cost.

The maintenance costs of green or blue infrastructure are often lower over time compared to grey infrastructure, which requires frequent repairs and upgrades. This is often difficult in Te Moananui Oceania where materials are often imported.

Economically, daylighting projects can stimulate local economies by creating attractive urban spaces that boost property values and attract tourism. These projects can also generate employment opportunities in environmental restoration and landscape management.

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References
  • Buchholz, T.A., Madary, D.A., Bork, D., & Younos, T. (2016). Stream restoration in urban environments: concept, design principles, and case studies of stream daylighting. Sustainable Water Management in Urban Environments, 121-165.
  • Buchholz, T., & Younos, T.M. (2007). Urban stream daylighting: case study evaluations. VWRRC Special Report SR35-2007. Virginia Water Resources Research Center: Blacksburg. https://vtechworks.lib.vt.edu/server/api/core/bitstreams/2f9955e5-11ec-445e-ac28-5f432c6b07e7/content 
  • Dickie, R.A. (2005). Indigenous traditions and sacred ecology in the Pacific Islands. UW-L Journal of Undergraduate Research. VIII, 1-9.
  • National Park Service (n.d). Giving New Life to Streams in Rural City Centers. Indian Creek Brochure. Available online: http://npshistory.com/publications/rtca/city-center-streams.pdf. Date accessed 17 May, 2024.
  • Neale, M.W., & Moffett, E.R. (2016). Re-engineering buried urban streams: Daylighting results in rapid changes in stream invertebrate communities. Ecological Engineering87, 175-184.
  • Nursey-Bray, M., Korerura, S.J., Fiu, M., Lui, S., Malsale, P., Mariner, A., … & Ronneberg, E. (2024). Adapting to Change? Traditional Knowledge and Water. In The Water, Energy, and Food Security Nexus in Asia and the Pacific: The Pacific (pp. 229-247). Cham: Springer International Publishing.
  • Sinclair, C. (2012). An exploration of stream daylighting and urban attitudes towards the environment. Trail Six: An Undergraduate Journal of Geography6.

Further resources