Nature-Based Solutions for Coastal and Riverine Flood and Erosion Risk Management

Citation

  • Vouk, I., Pilechi, V., Provan, M., Murphy, E. (2021). Nature-Based Solutions for Coastal and Riverine Flood and Erosion Risk Management. Canadian Standards Association, Toronto, ON.

Executive Summary

Canadian communities and infrastructure are vulnerable to coastal and riverine flood hazards. The risks associated with coastal and river flooding are escalating as a result of development in river floodplains and coastal zones, and the effects of climate change on flood and erosion hazards. There is growing interest in the potential for Nature-based Solutions (NbS) to play a role in managing these risks, owing in part to Canada’s co-leadership of the Nature-based Solutions Action Track of the Global Commission on Adaptation. Despite this increasing interest in NbS for coastal and riverine flood and erosion risk management, they remain relatively underutilized in Canada. Standards and guidelines can contribute to mainstreaming NbS by clarifying the underlying concepts and principles, raising awareness, and educating practitioners, potential project proponents, and the public. This review and synthesis of published literature and interviews with stakeholders and experts was conducted to:

  • Assess how NbS can be used to manage flood and erosion risks in coastal and riverine environments in Canada; and
  • Determine needs and opportunities for standards to support deployment of NbS to reduce coastal and riverine flooding and erosion risks.

NbS for coastal and riverine flood and erosion risk management are strategies or measures that depend on, or mimic, natural system processes to provide flood and erosion risk management function, while delivering a suite of environmental and other societal co-benefits. NbS embrace the principles of “whole system” analysis, adaptive management, multi-disciplinary teams, innovation, and long-term planning for uncertainty. They can be deployed through sustainable planning and regulatory frameworks that recognize the value of natural assets and infrastructure in supporting risk management objectives (e.g., Integrated Water Resources Management and Integrated Coastal Zone Management), and/or the targeted deployment of nature-based features to provide specific flood and erosion risk management functions. Nature-based features can deliver flood and erosion risk management benefits in a variety of ways, for example:

  • In coastal regions – beaches/dunes, reefs, and wetlands provide buffers against wave action, storm surges, and erosion;
  • In river watersheds – wetlands, reconnected floodplain areas, and restored river channels enhance groundwater infiltration, reduce or delay runoff, and attenuate peak flood flows and water levels; and
  • In estuaries – marsh and wetland systems can be preserved, expanded, or restored to provide additional hydraulic storage and attenuate waves.

NbS span a continuum of human intervention from green (least intervention) to grey (traditional hard infrastructure); from simply conserving or protecting existing natural systems (e.g., floodplain preservation), to enhancing or restoring natural processes (e.g., beach nourishment), to hybrid or grey-green solutions that integrate hard engineering or structural measures with more natural features (e.g., buried revetments), to “greening” traditional infrastructure (e.g., by incorporating features to enhance ecological value or provide habitat).

Although there are Canadian examples of NbS for flood and erosion risk management that date back to the 1970s, they remain relatively underutilized today. Key barriers to broader uptake include challenges in predicting performance of NbS in distinct and varied Canadian regional settings, a paucity of data demonstrating the performance and track record of NbS, a shortage of highly qualified professionals, stakeholder perceptions that NbS are more uncertain or less effective than (hard engineering) alternatives, project funding models that disincentivize NbS, undervaluation of the co-benefits of NbS in conventional economic analyses and financing models, a lack of authoritative technical guidance, and complex governance and regulatory environments.

The growth in research and interest surrounding NbS has led to the proliferation of numerous reports and guidance documents relevant to the implementation of NbS for coastal and riverine flood and erosion risk management. With a few exceptions, the majority of guidance is relatively high-level, and lacks either the technical detail or region-specific contexts needed to support effective design and implementation of NbS for coastal and riverine flood and erosion risk management across Canada. Collectively, however, available and emerging guidance provides a sound foundational basis for working towards implementation of best practices through future Canadian national standards and design guides. The benefits of national standardization and guidance would include mainstreaming of NbS principles, education of stakeholders and potential proponents on factors affecting the performance of NbS, and increased investor confidence in NbS projects. In particular, monitoring and evaluation protocols for NbS, and frameworks supporting evaluation and deployment of NbS represent potential short-term opportunities for standardization to facilitate wider adoption.

Knowledge and research gaps to be addressed to enable the development of Canadian guides and standards for NbS in coastal zones and river watersheds include:

  • Evidence of NbS performance across distinct and varied Canadian coastal and river settings, particularly northern environments, where NbS are relatively untested;
  • Improvement and validation of predictive tools;
  • Potential adverse impacts of NbS; and
  • An improved understanding of the comparative performance of non-structural (i.e., planning-based), conventional, and nature-based (including hybrid) flood and erosion risk management solutions in achieving multiple benefits.