Floodplain restoration

South Florida water management, 2015. Annotated photograph by MacArthur Ditch restoration project.

A floodplain is the area bordering a river that naturally provides space for the retention of flood and rainwater. Floodplains play a crucial role in maintaining the natural functions of a river system. They mitigate erosion, alleviate flooding, revitalise local habitats, and mitigate water pollution. By serving as natural buffers, floodplains help reduce the impacts of climate change on residents and the environment.

Floodplain restoration involves either fully or partially restoring the floodplain of a river to the original conditions. This can be achieved through improving planting, but mainly by reconnecting rivers to floodplains allowing a natural flow of water. This depends on the context of the area though as urbanisation and infrastructure placement may limit this. Specific strategies of floodplain restoration include revegetation, bank reshaping, removal of sediment, invasive species removal, riparian buffer installation and development, and wetland restoration or construction. The goal is to achieve a more natural hydrologic regime. 


Floodplain restoration initiatives can be implemented in areas adjacent to existing rivers or in projects where rivers have been daylit or rewilded. These restoration efforts typically target flat terrains prone to flooding. Restoring the floodplain is important near residential areas to reduce areas that flood and maintain or manage water levels through extreme weather events.

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Name of NbS

Floodplain restoration

Type of NbS

Ecosystem restoration

Location

  • Urban
  • Periurban
  • Rural
Phase I restoration area abandoned river channel and floodplain. Photo by South Florida Water Management District.

Relationship to Indigenous knowledge

In Te Moananui Oceania, floodplain restoration projects often intersect with Indigenous knowledge and practices. Indigenous communities possess deep-rooted knowledge of local ecosystems, including floodplain dynamics and their ecological significance. Traditional ecological knowledge may offer valuable insights into sustainable floodplain management practices, such as Indigenous agricultural techniques that work with natural flood cycles, including terraces, or traditional methods of floodplain restoration using native plants.

Indigenous communities may have historical practices of living in harmony with floodplains, including traditional settlement patterns and land management practices that can inform modern restoration strategies. These are reflected in certain pūrākau (stories) in Aotearoa New Zealand for example (Holman-Wharehoka, 2023). Collaborative approaches that incorporate Indigenous knowledge alongside scientific expertise can lead to more holistic and effective floodplain restoration initiatives in Te Moananui Oceania.

Involving Indigenous peoples in floodplain restoration projects can ensure that their cultural values and perspectives are respected and integrated into restoration efforts.

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Climate change benefits
  • Biomass cover loss
  • Changes in rainfall
  • Flooding
  • Soil erosion

Floodplain restoration offers numerous climate change benefits. Firstly, restored floodplains act as natural buffers against extreme weather events, such as floods and storms, mitigating their impacts on nearby communities and infrastructure. Additionally, healthy floodplains help regulate water flow, reducing the risk of both droughts and floods. They also enhance carbon sequestration by trapping and storing carbon in vegetation and soil, thereby mitigating greenhouse gas emissions. Furthermore, restored floodplains promote biodiversity by providing habitat for diverse plant and animal species, enhancing ecosystem resilience to climate change.

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

Rapid urbanisation has resulted in floodplain degradation (Gourevitch, 2020), leading many lower-income individuals to reside in flood-prone areas due to the affordability of such land, or in some cases, because it may be the only available option without land tenure. Floodplain restoration mitigates the risk of extreme rainfall events, sea level rise, and eroding river paths for these vulnerable populations. By restoring floodplains, communities gain resilience against natural disasters while also benefiting from ecological enhancements. These include increased biodiversity, enhanced water quality, and greater carbon sequestration potential. Consequently, floodplain restoration not only safeguards infrastructure and residents but also fosters healthier and more sustainable environments.

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

Restoration of floodplains offers a multitude of ecological benefits, including enhanced water quality both of rivers and coastal and reef areas. Revitalising these ecosystems through revegetation improves water purification and stabilises soil (Gourevitch, 2020). These riverine floodplains are rich ecosystems, supporting diverse species and serving as vital habitats for fish reproduction (Paillex et al., 2009; Roni et al., 2019). 

Healthy river systems foster sediment and nutrient accumulation, stabilising floodplains and providing breeding grounds for river species (Acreman, 2003). This sediment buildup aids in water quality improvement by filtering pollutants and recycling nutrients and pollutants. Consequently, floodplains play a crucial role in mitigating freshwater flooding concerns.

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Technical requirements

Floodplain restoration necessitates expertise tailored to the specific landscape context, as different areas may require varying approaches. Ongoing maintenance is generally minimal, primarily focused on preventing inundation by invasive weeds and sediment buildup. Continuous assessment of floodplain biodiversity is crucial to ensure that native fish species are not displaced by non-native species (Paillex et al., 2009). This targeted approach to restoration and vigilant monitoring of ecosystem health help sustain the long-term effectiveness of floodplain restoration initiatives.

Stream characteristics diagram, 2007. Image by placeuvm.

Issues and Barriers

Rapid urbanisation in recent decades has imposed significant stress on riverine systems, with development encroaching on many floodplains and altering natural water courses. However, this situation presents an opportunity to adapt to areas facing increased pressure.

Competing land-use demands, such as urbanisation and agriculture, often prioritise economic interests over ecological restoration. Limited funding and resources for restoration projects further impede progress. 

Insufficient awareness and understanding of the importance of floodplain ecosystems may hinder support for restoration efforts. 

Finally, the impacts of climate change, such as increased frequency and intensity of extreme weather events, exacerbate existing restoration challenges by altering floodplain dynamics and increasing restoration costs.

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Opportunities

In Te Moananui Oceania, several opportunities exist for floodplain restoration that can yield significant ecological, social, and economic benefits. Firstly, growing recognition of the importance of floodplain ecosystems for biodiversity conservation and climate resilience presents an opportunity to garner support and funding for restoration initiatives. Collaborative approaches involving Indigenous communities, local stakeholders, and government agencies can leverage traditional ecological knowledge and foster community engagement, enhancing the success and sustainability of restoration projects.

Advances in technology, such as remote sensing and Geographic Information Systems (GIS), facilitate more precise mapping and monitoring of floodplain ecosystems, aiding in the identification of priority restoration areas and the assessment of restoration outcomes. Integration with existing land management practices, such as agroforestry and sustainable agriculture, can promote multifunctional land use and enhance the resilience of floodplain ecosystems to climate change.

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Financial case

By mitigating the impact of extreme weather events, such as floods, restoration efforts have the potential to reduce property damage costs significantly (Gourevitch, 2020).

The cost-effectiveness of floodplain restoration is evident in its implementation and maintenance. While initial implementation costs are represented as a one-off payment, ongoing maintenance expenses are minimal. This makes floodplain restoration a cost-efficient investment with long-term benefits (Gourevitch, 2020).

Restored floodplains may provide numerous ecosystem services that contribute to economic prosperity. These services include water purification, flood regulation, and carbon sequestration, which have tangible economic value. Improved water quality, for instance, benefits industries reliant on clean water, such as tourism, fisheries, and agriculture, thereby enhancing their productivity and profitability.

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References
  • Acreman, M.C., Riddington, R., & Booker, D. J. (2003). Hydrological impacts of floodplain restoration: a case study of the River Cherwell, UK. Hydrology and Earth System Sciences7(1), 75-85.
  • Gourevitch, J.D., Singh, N. K., Minot, J., Raub, K. B., Rizzo, D.M., Wemple, B.C., & Ricketts, T.H. (2020). Spatial targeting of floodplain restoration to equitably mitigate flood risk. Global Environmental Change61, 102050.
  • Holman-Wharehoka, M. (2023). Investigating the relationship between the built environment and climate change from a Te āo Māori perspective using Pūrākau as a methodology. Master of Architectural Science Thesis. Wellington, New Zealand: Victoria University of Wellington.
  • Paillex, A., Dolédec, S., Castella, E., & Mérigoux, S. (2009). Large river floodplain restoration: predicting species richness and trait responses to the restoration of hydrological connectivity. Journal of Applied Ecology46(1), 250-258.
  • Roni, P., Hall, J.E., Drenner, S.M., & Arterburn, D. (2019). Monitoring the effectiveness of floodplain habitat restoration: A review of methods and recommendations for future monitoring. Wiley Interdisciplinary Reviews: Water6(4), e1355.

Further resources