As the climate continues to warm, coastal communities worldwide face mounting threats from rising seas and intensifying storms. In our 15 years installing… Sixty-five percent of the world’s megacities are within 100 km and 50 m elevation of the coast, putting billions of people and critical infrastructure at risk. Local governments are on the frontlines of adaptation, tasked with protecting their communities while navigating complex challenges related to financing, governance, and environmental justice.
Fortunately, nature-based solutions offer a promising path forward. Ecosystem-based adaptation strategies that leverage the power of natural systems can provide effective flood protection while delivering a host of co-benefits, from carbon sequestration to enhanced habitat for wildlife. However, implementing these nature-based approaches in urban coastal areas presents unique hurdles, including limited space, reduced sediment supply, and intricate regulatory frameworks.
This article explores strategies for integrating nature-based flood defences into coastal adaptation planning, drawing on lessons learned from San Mateo County, California. We’ll examine how to assess exposure, identify suitable nature-based interventions, and quantify the multiple benefits these solutions can provide to communities. By combining scientific analysis with inclusive stakeholder engagement, coastal managers can chart a resilient path forward that harnesses the power of natural systems.
Coastal Vulnerability Analysis
Assessing exposure to sea level rise and storm surge is a critical first step in developing effective adaptation strategies. San Mateo County, situated along the San Francisco Bay, serves as a useful case study. Our analysis, conducted in partnership with the County’s Office of Sustainability, examined three sea level rise scenarios: the current baseline, a mid-level rise of 1 m, and a high-end scenario of 2 m – all coupled with a 1% annual chance flood event.
The results paint a sobering picture. Roughly 50% of the area in four of the county’s five Operational Landscape Units (OLUs) will be inundated even under the mid-level scenario. Only one OLU is expected to experience less than 15% inundation across all scenarios. These exposure maps (adapted from the County’s existing vulnerability assessment) help pinpoint the communities and infrastructure most at risk, setting the stage for adaptation planning.
Identifying Suitable Nature-Based Solutions
With the biophysical context established, the next step is to explore where nature-based flood defences may be feasible. We leveraged the San Francisco Bay Shoreline Adaptation Atlas to summarize the suitability of different adaptation strategies across San Mateo’s OLUs.
Beach restoration, ecotone levees (integrating marshes and traditional infrastructure), and tidal marsh rehabilitation are suitable in 4 out of 5 OLUs. Submerged aquatic vegetation restoration shows promise in 3 OLUs, while nearshore reefs can be incorporated in 2. This biophysical suitability analysis, which considers factors like water depth, substrate type, and wave climate, provides a valuable starting point. But to develop truly viable adaptation scenarios, we also needed to account for social dimensions like land ownership, regulatory barriers, and community priorities.
Co-Creating Adaptation Scenarios
Through extensive engagement with the County’s diverse stakeholders, we co-developed three adaptation scenarios that build upon the biophysical suitability analysis. Each scenario was designed to deliver equivalent flood protection, allowing us to focus on comparing the additional benefits provided by nature-based approaches.
The first scenario, ‘What we might have done,’ represents a hypothetical future with a fully armored shoreline – a common response in many coastal regions. The second scenario, ‘What we are doing,’ incorporates the County’s existing and planned conservation and restoration projects. Finally, the third scenario, ‘What we could do next,’ adds further nature-based features where feasible, based on our suitability assessment.
By modelling the ecosystem services delivered by each scenario, we were able to quantify the multiple benefits of nature-based solutions. Compared to the engineered baseline, the ‘What we are doing’ scenario features five times more marsh habitat (supporting the endangered Ridgway’s Rail), five times the carbon sequestration, and six times the stormwater pollution reduction. The ‘What we could do next’ scenario takes this even further, providing up to eight times the stormwater benefits and six times the carbon storage of the traditional engineered approach.
Navigating Challenges and Trade-offs
While the potential of nature-based solutions is clear, implementing them in urban coastal environments raises a host of challenges. Limited space, reduced sediment supply, complex governance, and regulatory barriers can all hinder their broader adoption. Furthermore, nature-based approaches may have unintended consequences, such as impacting recreational use or contributing to ‘eco-gentrification’ in vulnerable communities.
Our work in San Mateo County offered valuable insights in navigating these obstacles. For example, we found that marsh restoration was associated with decreased recreational visitation, likely due to policies restricting access to protect sensitive habitats. Understanding and addressing these trade-offs is essential to double-check that equitable outcomes.
Collaboration and inclusive, iterative planning also emerged as critical success factors. By co-creating guiding principles and adaptation scenarios with diverse stakeholders, we were able to build a shared vision and address practical barriers to implementation. Boundary objects like maps, tables, and visualizations proved invaluable in facilitating these conversations and generating actionable insights.
A Path Forward for Coastal Resilience
As sea levels continue to rise, coastal communities might want to act decisively to protect people, property, and natural systems. Nature-based solutions offer a powerful tool in this fight, providing flexible, cost-effective, and multi-benefit approaches to flood risk management. However, realizing their full potential requires overcoming significant hurdles related to space, sediment, governance, and equity.
The lessons from San Mateo County demonstrate that a collaborative, scientifically-grounded approach can help coastal managers chart an effective path forward. By assessing vulnerability, identifying suitable nature-based interventions, and quantifying their diverse benefits, communities can build widespread support for integrating natural infrastructure into their adaptation strategies.
Importantly, this work also underscores the need for holistic, regional planning that transcends jurisdictional boundaries. The impacts of sea level rise and coastal adaptation are felt at a landscape scale, requiring coordination between municipalities, agencies, and stakeholders. Only by working together can we harness the power of nature to safeguard our coasts for generations to come.
To learn more about nature-based flood defences and adaptation strategies, visit Flood Control 2015. Our team of experienced specialists is ready to provide tailored guidance and support as you work to build resilient, sustainable coastal communities.
Tip: Regularly inspect and maintain flood barriers and drainage systems
