While primarily applied in urban and suburban environments, daylighting of rivers and streams can also be relevant in rural areas where waterways have been modified and diverted for agricultural or infrastructural purposes. The effects of river daylighting extend beyond the immediate surroundings, potentially improving riparian ecosystems downstream. In cities, resurfacing of water bodies can also help reducing urban heat island effects. 

Why

River and stream daylighting can address several societal challenges. It can improve water management and contribute to climate adaptation by reducing flood risk by restoring natural floodplains and increasing the capacity for handling large water quantities during heavy rains that overload the sewage system. Water quality can also improve through natural filtration systems. Open rivers, streams, and water surfaces also help regulate temperature and humidity. Focusing on restoring the natural ecosystems also creates new and better habitats for birds, insects, small animals, fish and other aquatic species, contributing positively to biodiversity enhancement.  Reopened streams with green surroundings are popular recreational spaces contributing to human health and wellbeing.  

How

The implementation of river daylighting projects involves several stages, from preliminary research and planning to construction and post-restoration monitoring. The approach is inherently interdisciplinary, requiring collaboration among e.g. hydrologists, ecologists, urban planners, engineers, and local stakeholders. Engaging with local communities is crucial for success, as river daylighting requires space and can significantly change the landscape.  

The practical implementation can vary from removing hard pavement surfaces and redirecting water flow into newly created or restored riverbeds, to more complex processes of relocating underground waterways. The techniques used depend on the urban layout and existing infrastructure, and the original state of the buried waterway.  

The process of reopening of urban streams sometimes happens incrementally, by planning the process in several phases and starting with opening a section of the stream first. This can have benefits by reducing disruptions in the construction phase, providing better opportunities for budget management and involving local stakeholders. However, this also means that many such projects have a time span over many years. Furthermore, it is still important to have a holistic and watershed-based approach.  

Potential positive outcomes of resurfacing historic streams and rivers include enhanced climate resilience and adaptation and improved water quality. It also contributes to urban biodiversity by creating new habitats for fish, plants, birds, and urban wildlife. Urban rivers and streams also provide public recreational opportunities and can increase awareness and connection to local water bodies.

There may be challenges, such as managing increased water flow in densely built areas, potential displacement of existing infrastructure, and ensuring long-term maintenance and ecological health. 

ATTENTION

Key considerations involve:

• Understanding the historical flow and ecological function of the waterway
• The impact on existing urban infrastructure
• Impact on legal and property rights issues
• Flood risk during extreme weather events
• Water quality aspects: Reopened urban streams quite often have low water quality when first resurfaced.
• Societal acceptance, funding, and ongoing management are also critical factors.
• Policies related to urban development, water management, and environmental conservation, which will directly influence project feasibility and design.  

When resurfacing an urban river, the riparian zone and how this is done is crucial for stabilizing the riverbanks and biodiversity. It is important to be considerate about native vegetation, ecological connectivity, and accessibility for both people and wildlife.

In most cases in urban areas, river and stream openings cannot be fully ecologically restored due to space limitations. There is often not enough space for natural processes such as meanders and broader floodplains with natural riparian vegetation.

Resurfaced urban rivers are furthermore often so-called “hanging rivers” lined with membranes without natural water exchange with groundwater due underground infrastructure and historical changes in the landscape that makes this connection difficult. This limits the possibilities for meanders and broad floodplains and often results in more canal-like water courses.

Care should still be taken concerning the riparian zone and vegetation and in early phases the possibilities for making space for this should be considered.  

The concept of river daylighting is supported by a growing number of case studies demonstrating projects in diverse urban settings, as well as some in rural settings. Research typically focuses on hydrology, ecology, urban planning, and social sciences, providing multidisciplinary perspective on implementation practices and benefits.  

• Scientific studies focusing on the hydrological impacts shed light on changes in water flow, sediment transport, and flood dynamics post-daylighting.
• Ecological research evaluates biodiversity gains, habitat restoration success, and improvements in water quality. 
• The interdisciplinary nature of river daylighting necessitates the integration of knowledge across several domains to address the interactions between spatial development, natural water cycles, and ecological restoration.

As the field evolves, ongoing research and the accumulation of new case studies will be crucial for refining methodologies and maximizing the benefits of projects on reopening streams and rivers.  

Costs

The costs associated with river daylighting can be significant, including excavation, property acquisition, infrastructure modification, and habitat restoration. Operational costs encompass maintenance of the waterway, flood management systems, and public amenities.