River/stream rewilding

A section of the wetlands in Haikou, China. Photo by Kongjian Yu, Turenscape.

Rivers and floodplain margins play crucial roles in retaining water and nutrients. However, the pressures of urbanisation in these areas have diminished these benefits, necessitating a restorative approach to enhance their water storage capacity. 

River or stream rewilding aims to restore the ecology of riparian and river environments, drawing inspiration from the principles of rewilding, which seek to restore large-scale ecological processes and promote self-sustaining ecosystems (Xie & Bulkeley 2020).

This can be achieved through the revegetation of riparian areas, creating more resilient ecosystems for fish, invertebrates, and microbes. Healthy riparian areas play crucial roles in nutrient cycling, erosion control, and providing habitat for aquatic and terrestrial species (Palmer et al., 2014). Reintroducing native keystone or cultural keystone species may also be part of rewilding strategies.

Rewilding efforts may also involve removing dams or barriers to water flow or fish migration, thereby improving habitat connectivity and biodiversity. Implementing techniques to restore natural channel morphology, such as meander restoration, gravel augmentation, and reconnecting side channels, is also crucial. River daylighting may also fall under the umbrella of reive rewilding. These actions improve habitat complexity, sediment transport, and overall river health. Additionally, allowing rivers to access and interact with their floodplains during high-flow events can help reduce flood risk downstream, recharge groundwater, and create habitat diversity.

In Te Moananui Oceania, rivers and streams are significantly impacted in urban areas where polluted runoff enters them. Therefore, riparian restoration and floodplain restoration are important for mitigating these impacts. River rewilding projects aim to enhance ecosystem resilience, improve water quality, support biodiversity, and provide numerous benefits to both humans and wildlife. By restoring natural processes and functions, river rewilding contributes to the overall health and sustainability of freshwater ecosystems.

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Name of NbS

River/stream rewilding

Type of NbS

Ecosystem restoration

Location

  • Urban
  • Periurban
  • Rural
Cavendish Road Stream, Styx Mill reserve, boxed drain after restoration, 2017. Photo by Christchurch City Council.

Relationship to Indigenous knowledge

Streams and rivers have been heavily impacted by urbanisation development surrounding the environments. This has created runoff of pollutants and heavy sediment loads. Over time this has reduced the health of rivers and in turn, endangered wildlife, decreased freshwater availability and reduced the adaptation and/or mitigation techniques of the systems. These systems have multiple different connections to people, specifically in small island nations where water security is an issue.

For many Indigenous communities in Te Moananui Oceania, rivers hold significant cultural and spiritual importance (Hikuroa et al., 2011; Parson et al., 2021). These water bodies are often seen as living entities and are integral to cultural identity and heritage. Allowing, or restoring rivers to be wild, or in a natural state therefore, has profound implications for the cultural health of people who care for them.

Climate change benefits
  • Biomass cover loss
  • Changes in rainfall
  • Flooding
  • Reduced water quality
  • Sea level rise
  • Soil erosion 
  • Reduced soil quality
  • Reduced freshwater

Restoring rivers and streams using nature-based methods, as opposed to structural systems, aids in both climate change mitigation and adaptation (Blau et al., 2018). This approach can reduce the risk of floods and heat waves while simultaneously improving water health and quantity (Blau et al., 2018). 

River rewilding contributes to carbon sequestration through the restoration of riparian vegetation and natural habitats. By enhancing carbon sequestration, river rewilding helps mitigate climate change by removing carbon dioxide from the atmosphere. 

The restoration of natural floodplains and hydrological processes supports ecosystem resilience during periods of drought or increased rainfall variability. River rewilding serves as a crucial strategy for addressing the impacts of climate change on freshwater ecosystems while promoting their health and sustainability.

Adapting to the escalating impacts of climate change requires larger-scale restoration projects for streams and rivers however (Blau et al., 2018). This necessitates the implementation of innovative solutions alongside river rewilding such as ecosystem-based management, customary resource management, and incorporating or restoring wetlands and other suitable nature-based solutions within existing riverine environments to enhance ecosystem resilience. In urban settings, river rewilding projects should be designed to be a part of larger interconnected green-blue infrastructure.

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

Human settlement has significantly altered hydrological pathways, resulting in the degradation of urban river ecosystems. Restoring streams is crucial not only for flood mitigation but also because these water bodies often serve as essential resources for communities, providing water, food, and energy (Sarvilinna et al., 2017).

The restoration of streams and rivers yields numerous socio-cultural benefits. It enhances environmental health and fosters educational opportunities, and supports community engagement and values (Kenney et al., 2012). They provide spaces for people to connect with nature and can serve as cultural and recreational hubs, enhancing the quality of life for nearby residents and visitors. Through these socio-cultural benefits, river rewilding not only restores ecological health but also potentially enriches the fabric of human society.

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

Rewilding initiatives restore rivers and enhance their ecological functions by returning the flow of water to a more natural state (Blau, M.L et al., 2018). This restoration improves habitat quality, reduces flooding, and mitigates the urban heat island effect (Blau et al., 2018).

Restored rivers and streams play essential roles in transporting water and nutrients downstream (Sarvilinna et al., 2017). The presence of vegetation along riverbanks acts as a buffer, preventing pollutants and heavy materials from affecting the stream and causing flooding in the future (Sarvilinna et al. 2017). Through these mechanisms, river rewilding promotes biodiversity conservation and fosters the ecological resilience of freshwater ecosystems. 

Cleaner, healthier water flowing from rivers into oceans also has profound impacts on the ecosystem health of estuarine and reef environments in the highly ecologically connected context of small islands.

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Conceptual figure of stream restoration to improve floodplain reconnection. Image Mayer et al (2022).  

Technical requirements

River rewilding entails a combination of technological and ecological approaches to restore and enhance riverine ecosystems. In order to get it right, a deep understanding of the specific river’s original hydrology and biology and how conditions will change due to climate change is needed. Local knowledge holders should be part of the design process. River rewilding should be integrated with wider watershed restoration planning.

Technological requirements include the implementation of engineering solutions to facilitate the restoration process. This may involve the removal of artificial barriers such as dams or weirs to restore natural flow regimes and improve habitat connectivity for aquatic species. Channels may need to be removed. 

The use of innovative monitoring technologies may be essential for assessing the effectiveness of rewilding interventions and tracking changes in ecosystem health over time. Remote sensing techniques, such as satellite imagery and aerial drones, can provide valuable data on habitat conditions, vegetation cover, and water quality parameters.

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Issues and Barriers

River rewilding faces several challenges and barriers that can hinder its implementation and effectiveness. One issue is the limited availability of public green space within urban areas, which is crucial for supporting rewilded rivers and streams (Blau et al., 2018). Without sufficient green space, there may be excessive pressure on restored river systems, leading to degradation and loss of ecological benefits.

Regulatory barriers and competing land use interests can pose significant challenges to river rewilding initiatives. Urban rivers may be channelised or piped and buildings built right up to edges or over rivers. This makes rewilding very difficult without removing buildings and infrastructure. Balancing the needs of various stakeholders, navigating complex permitting processes, and securing adequate funding are essential for overcoming these barriers.

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Opportunities

River rewilding initiatives offer the chance to restore degraded riverine habitats, promoting biodiversity conservation and supporting the recovery of native species populations. Through collaboration between stakeholders, policymakers, and conservationists, river rewilding has the potential to foster long-term environmental and socio-economic benefits for present and future generations.

A key opportunity of river rewilding is utilising the linear nature of rivers and streams to connect fragmented habitats and act as a catalyst for urban and river revitalisation, thereby enhancing resilience. Recreation and human-powered transport corridors can be integrated with restored river corridors.

Furthermore, river rewilding presents an opportunity to initiate managed retreat from ecologically sensitive areas prone to climate change-induced flooding, such as riparian zones and (historic) floodplains. This proactive approach can help mitigate the impacts of climate change on vulnerable communities and ecosystems while enhancing natural floodplain functions and ecosystem services.

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Financial case

Investing in river rewilding may yield long-term economic benefits by enhancing ecosystem services, reducing flood risk, and promoting sustainable economic development. Utilising a more natural approach to restoring the riverine environment, as opposed to implementing hard structures, proves to be more cost-effective in many instances (Skidmore,  & Wheaton, 2022). Allowing rivers and streams space to migrate across and inundate floodplains aids in mitigating flood risk and reduces the likelihood of settlements flooding (Skidmore & Wheaton 2022), consequently decreasing the frequency of insurance claims and rebuilding costs.

Rewilding rivers presents economic opportunities through job creation, ecosystem restoration contracts, and the development of nature-based tourism initiatives. These initiatives not only contribute to local economies but also foster community engagement and appreciation for restored river environments.  

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River rewilding, Meers, Netherlands, 2000. Image by Herman Gielen, Vincent Fissette, Avism. https://earthlymission.com/river-meuse-maas-rewilding-restoration-project-belgium-netherlands/
References
  • Xie, L., & Bulkeley, H. (2020). Nature-based solutions for urban biodiversity governance. Environmental Science & Policy110, 77-87.
  • Blau, M.L., Luz, F., & Panagopoulos, T. (2018). Urban river recovery inspired by nature-based solutions and biophilic design in Albufeira, Portugal. Land7(4), 141.
  • Hikuroa, D., Slade, A., & Gravley, D. (2011). Implementing Māori indigenous knowledge (mātauranga) in a scientific paradigm: Restoring the mauri to Te Kete Poutama. MAI review, 3(1), 9.
  • Kenney, M.A., Wilcock, P.R., Hobbs, B.F., Flores, N.E., & Martínez, D.C. (2012). Is urban stream restoration worth It? 1. JAWRA Journal of the American Water Resources Association48(3), 603-615.
  • Mayer, P.M., Pennino, M. ., Newcomer-Johnson, T.A., & Kaushal, S.S. (2022). Long-term assessment of floodplain reconnection as a stream restoration approach for managing nitrogen in ground and surface waters. Urban Ecosystems, 25(3), 879-907.
  • Palmer, M.A., Filoso, S., & Fanelli, R.M. (2014). From ecosystems to ecosystem services: Stream restoration as ecological engineering. Ecological Engineering65, 62-70.
  • Parsons, M., Fisher, K., Crease, R.P., Parsons, M., Fisher, K., & Crease, R.P. (2021). Decolonising river restoration: Restoration as acts of healing and expression of Rangatiratanga. Decolonising Blue Spaces in the Anthropocene: Freshwater management in Aotearoa New Zealand, 359-417.
  • Sarvilinna, A., Lehtoranta, V., & Hjerppe, T. (2017). Are urban stream restoration plans worth implementing? Environmental Management59, 10-20.

Further resources