Nature-based Infrastructure
for Coastal Flood and Erosion Risk Management
What is Nature-based Infrastructure (NbI) for Coastal Flood and Erosion Risk Management (CFERM)?
NbI for CFERM is a form of nature-based solution consisting of natural or built assets that rely on or mimic natural system processes to provide coastal flood and erosion mitigation while delivering environmental and other societal co-benefits.
“Nature-based” implies that the infrastructure used for coastal flood and erosion risk management can either be wholly natural or based on nature.
Nature-based coastal infrastructure generally may be grouped according to three main categories:
- Sediment-based Solutions: solutions that are predominantly sediment-based (e.g., beaches, islands, and headlands).
- Vegetation-based Solutions: predominantly vegetation-based (e.g., marsh vegetation, submerged aquatic vegetation, trees, and upland vegetation).
- Hybrid Solutions: incorporate combinations of natural and “grey” or “built” structural elements (e.g., living breakwaters, foreshore marsh-dyke systems, anchored woody debris installations).
Nature-based infrastructure most often incorporates multiple features combining “green” or wholly nature elements, with “grey” or “built” structures that incorporate features that provide some habitat or ecological value.
Key Benefits
Opting for Nature-Based Solutions for CFERM
Coastal flooding and erosion are natural processes essential to natural ecosystem health and function but also a costly natural hazard. Risk occurs when flood and erosion hazards intersect with vulnerable communities and infrastructure, or other valued assets (e.g., cultural heritage) with the potential to cause damage or harm.
Past and present uses and development of coastal lands have exposed communities, like the Tla’amin Nation village of ťišosǝm (including its infrastructure and valued assets) to flood and erosion hazard risk. As sea level on the BC and Sunshine Coast continues to rise in the coming decades, risks associated with coastal flooding and erosion will increase and important coastal habitat will be lost.
In some cases, legacy land uses and development have locked in long-term “protect” or “hold the line” flood and erosion risk management strategies. Nature-based solutions offer a more flexible and scalable solution allowing a dynamic and adaptive management approach that keeps options open as climate conditions and sea levels change. Shorelines are most resilient when coastal and ecosystem processes are able to function intact in their natural state.
Nature-based solutions provide coastal flood and erosion risk management benefits in several ways, including:
- Providing a buffer zone between coastal hazards and communities, infrastructure, or valued assets.
- Attenuating and dissipating storm surges and waves.
- Stabilizing sediments, reducing erosion and encouraging deposition.
- Encouraging establishment of stabilizing flora and fauna.
Nature-based solutions are also often less expensive to implement and maintain than “grey” infrastructure.and provide many co-benefits including:
- Ecological benefits and ecosystem services (habitat connectivity, diversity, preservation of species).
- Social – direct benefits to health and well-being.
- Environmental – improvements in water quality; offset GHG emissions.
Seawalls or Nature-based Flood and Erosion Protection?
Coastal protection solutions have conventionally consisted of “hard” or “grey” infrastructure including sea dikes (also known as “dykes” or “levees”), seawalls, revetments, and rock armouring, often deployed without adequate consideration to natural processes or system responses. Potential drawbacks associated with widespread hardening of the coast include disruption of natural sedimentation processes (erosion and deposition) with implications for adjacent shorelines, communities and infrastructure, loss or degradation of productive habitat (e.g., coastal squeeze), false perceptions of risk in areas protected by hard structures, and escalating maintenance costs and vulnerabilities in the face of rising sea levels.
An alternative approach is to develop an in-depth understanding of natural coastal systems and features and their benefits, and to leverage these strengths to achieve the same goals of reducing risk to communities, infrastructure, and valued assets. Nature-based infrastructure spans a continuum of human intervention, from “green” or wholly natural systems (i.e., which may be conserved or restored to preserve natural system functions and benefits) to hybrid or “green-grey” systems that combine hard (structural) and natural infrastructure elements (e.g., marsh-dike systems, or beach nourishment with control structures). The natural elements may be engineered and constructed or may be created and sustained through natural coastal processes. A key requirement for being nature-based is that the infrastructure (hard or soft, green or grey) must work in harmony with natural system processes. Nature-based infrastructure is under utilized for coastal flood and erosion risk management in Canada, despite being well accepted internationally.
Grey infrastructure has several potential drawbacks of hardening the coast and fixing it in position – as sea level rises the position becomes increasingly difficult to maintain. Runup and overtopping become increasingly severe resulting in flooding, ponding of water, runoff and potential scour of the backshore and direct damage to other infrastructure. The structure itself cuts off essential upland sediment supply to the beach resulting in long term loss of the beach; also the high wave runup/rundown on the structure causes scour at the toe leading to accelerated erosion and loss of beach.
Nature-based (green) and hybrid infrastructure has many potential advantages over “grey” coastal hardening the coast – the shoreline is dynamic so that as storms occur and as sea level rises the shoreline can respond and adapt to changing conditions provided there is space to accommodate the change. Runup and overtopping are reduced, sediment supply is maintained and a healthier beach system is preserved.
An example of shoreline with nature-based assets in the Klahanie Reach at ťišosǝm. This beach is also sloped gently with a vegetated backshore and has a good supply of coarse sediment all of which help to dissipate wave energy effectively and reduce flooding and erosion.
Implementing Nature-Based Solutions at ťišosǝm
Successful implementation of a nature-based approach to coastal flood and erosion risk management at ťišosǝm requires a complete understanding of the dynamics of the coastal processes (e.g., waves, tides, water levels, currents, and sediment transport) which operate on the shoreline in the area as well as the constraints imposed by existing development.
Developing a whole-system understanding is crucial to successful implementation of nature-based infrastructure because it provides a broad perspective on the interplay of ecology, geomorphology, hydrology, and hydrodynamics, as well as interfaces with the social system. A systems approach recognizes that the cumulative effects of multiple, small interventions can have significant impacts on the system as a whole. There are already many excellent examples of how this has been implemented at ťišosǝm.
The shoreline at ťišosǝm is complex and has variable exposure to coastal hazards, varying composition and varying degrees of constraints on possible risk management solutions. There is no “one-size fits all” approach that can be applied universally across the community. However, a number of possibilities for nature-based solutions exist within the different sub reaches of ťišosǝm. These may include:
- Recontouring the beach profile to create a beach slope with gentle gradient that will more naturally dissipate wave energy and create habitat for vegetation that will further enhance energy dissipation. In many parts of the ťišosǝm shoreline beach profiles have been scraped by bulldozers and restoration could involve re-distributing the boulder ridges. In places where seawalls have been constructed near the ordinary high water mark, a resident may consider the opportunity to remove the “grey” infrastructure and replace it with a “green” solution.
- Beach nourishment to replace sediment supply that has been lost due to shoreline hardening (e.g., seawalls, bulkheads, revetments) and long-term erosion. Without natural supply and replenishment, beaches that were once sandy or gravelly, may be stripped to boulders, cobble stones or bedrock. Having the right types of sediments on beaches is critical for creating a suitable slope for wave energy dissipation but also vital for creating habitat for forage fish, which spawn along the high tide line.
- Stabilizing the shoreline and inter-tidal areas with vegetation to help stabilize sediment, encourage deposition and reduce the potential for erosion of the shoreline by dissipating wave energy. Intact shoreline vegetation helps increase bio-diversity support marine food web linkages, and create incredible wildlife viewing opportunities. A salt marsh archipelago is a type of hybrid solution that could help restore habitat and protect backshore areas from flooding and erosion in low-lying areas with extensive inter-tidal space such as Scuttle Bay.
Recontouring the Beach Profile
Shorelines along the Sunshine Coast were scraped to provide easier beach access, but damaged the foreshore habitat. By redistributing the boulders, the beach can be restored. This will increase wave energy dissipation, habitat diversity and shoreline connectivity (e.g. alongshore sediment and salmonid movement) and reduce flood risk. Beach nourishment can also be considered to replace sediment supply lost due to shoreline hardening.
A Salt Marsh Archipelago
Salt marshes provide essential ecosystem services and particularly for supporting juvenile salmonids, food energy, sheltering, carbon sequestration, maintenance of water quality, buffering storm waves, reducing erosion and wave effects flooding.
Inter-tidal Habitat in Scuttle Bay has been degraded and is further threatened by rising sea levels, human interventions, and historical contamination.
An archipelago concept may provide the opportunity for salt marsh restoration with a co-benefit of reducing erosion and flooding to adjacent properties. This includes building up a series of small islands to increase elevation into a range that provides habitat for salt tolerant species as well as energy dissipation for waves.
Buried Revetment or Bio-engineered Revetment?
Coastal protection was needed at the Tla’amin townsite and waterfront park to protect community and residential infrastructure from flooding and erosion during severe events (e.g., storms with large waves and high surges; tsunamis) but not detract from the natural character of the beach and foreshore.
Since 2014, the Town Beach has been backed by a low, sloping stone revetment with a crest approximately 1.5 m above existing foreshore.
Although the revetment limits the exchange of sediment between backshore and foreshore, a mix of salt tolerant vegetation has colonized the foreshore at the toe of the revetment and is beginning to grow in the void space between the armour stones indicating that the toe of the structure is periodically in the zone of wave run up.
Could this solution be enhanced and adapted to future sea levels by raising the crest of the revetment and more selective planting of desirable salt tolerant native species? Fortunately, there is adequate accommodation space landward of the revetment for adaptation of the crest elevation as sea level rises and flooding becomes a problem again in future.
Seeking Help with Shoreline Restoration and Coastal Flood and Erosion Risk Management
Enlisting qualified professionals (coastal geomorphologists/engineers, landscape architects, environmental consultants and biologists) is a critical step and will help you confidently design and plan a solution that considers natural coastal processes, shoreline erosion risk, and the dynamics of the ecosystem as a whole. The Stewardship Centre for BC has compiled a list of Green Shores Approved Professionals that have the skills and experience for such projects.
Contact Us Today
Get in touch with us today to learn how we can help you with nature-based solutions for your next coastal project.