Climate change, sea level rise and urbanisation are increasing demand worldwide for new infrastructure to protect shorelines.
But coastal defences have to do more than just withstand storm surges and extreme weather events – they also need to be sustainable, safeguard ecosystems and add value to communities.
The solution can be found by working with nature.
In recent years we have seen an increase in the deployment of shoreline or flood protection schemes that are inspired and supported by nature.
These types of interventions – also referred to as green infrastructure, natural infrastructure, living shorelines or soft engineering – include coastal habitat restoration, vegetation replanting and beach nourishment schemes.
Nature-based solutions look beyond protection and resilience, focusing on the relationship between people and their natural environment and the delivery of long-term sustainable outcomes for communities.
“Corals reefs, seagrass meadows, mangrove forests, beaches, sand dunes and sand bars retain water and dissipate wave energy, acting as a buffer against tidal waves, storms and coastal flooding,” explains Beth Riley, Mott MacDonald’s coastal account lead in the UK.
“Restoration activities, such as mangrove regeneration and dune naturalisation, can promote these natural ecosystem functions.
“A key benefit of nature-based interventions over hard interventions is that they often increase the resilience of existing ecosystems and provide a wide range of benefits for other sectors, such as tourism and fisheries, as well as coastal protection.”
Important role of ecosystems
In the past decade, a general understanding of the value of ecosystem services has gained traction with governments and public authorities and become more mainstreamed into coastal management and policy making.
A large amount of research now exists to assess the important role ecosystems can have on disaster risk reduction and to highlight the importance of reducing ecosystem degradation to increase coastal resilience, as well as provide a habitat for plants and animals.
Beth Riley adds: “Good practice in environmental management can increase the resilience of coastal ecosystems and therefore decrease the vulnerability of coastal communities and coastal infrastructure.
“It is generally accepted that environmental management is required as part of any comprehensive disaster management plan, as it helps reduce exposure to hazards, such as extreme weather events and tsunamis, and promotes rapid recovery and reconstruction of natural coastal infrastructure.”
Breathing new life into shorelines and communities
Mott MacDonald has been at the forefront of designing living shoreline solutions to prevent shoreline erosion and stimulate nearshore habitat development for species that rely on coastal, wetland, and riverine environments for nesting, food, and shelter.
“Our solutions moderate the impact of waves and storm surges while providing self-sustaining protection and increasing biodiversity,” says Scott Fenical, coastal practice leader in North America.
“We have restored natural dunes and vegetation, improved water quality, created marshes and enhanced habitats through the use of living shoreline technologies.
“Our engineers designed Louisiana’s first artificial reef project which was also one of the first engineered living shoreline projects of its kind in the Gulf of Mexico.
“Since then, we have designed nearly 24km of living shorelines and evaluated artificial reef performance and constructability using more than 12 different artificial oyster reef products.
“Successful implementation of living shoreline projects that incorporate oyster reef technology requires a thorough understanding of the coastal environment.
“Using advanced 2D and 3D modelling tools validated by on-site field observations, we take an in-depth look into how waves pass through these structures and determine the optimal placement, configuration and orientation that will deliver the desired results.”
Mott MacDonald has a long track record in designing and delivering habitat regeneration and natural flood management solutions. Projects include:
- Greatham South Flood Alleviation Scheme, UK – creating intertidal saltmarsh, mudflat and transition marsh habitats to offset the impact of sea level rise.
- Integrated Coastal Zone Management, Bahamas – using creek and mangrove habitats to increase flood protection.
- Coastal Management and Beach Restoration Guidelines, Jamaica – improving climate resilience through nature-based interventions such as beach nourishment, wetland morass management and mangrove restoration.
- Coastal Texas Protection and Restoration Study, USA – integrating a 145km beach and dune system consisting of floodwalls, gates and new pump stations with ecosystem restoration measures to prevent inland flooding from surge events during hurricanes.
- Cedar Bayou Restoration, USA – restoration of a marsh and estuarine ecosystem, attracting wildlife and boosting the fishing and tourist industries.
- Biloxi Marsh Living Shorelines Project, USA – protecting the Biloxi Marsh complex and generating biodiversity with artificial oyster reef systems, designed using advanced computational fluid dynamics technology to assess performance and minimise cost.
- Portland Place Bluff Restoration, USA – a ‘living wall’ concept was added to a geosynthetic-based revetment to protect a bluff along the Navesink River.
- Middle Harbor Habitat, USA – reutilised dredged material from Port of Oakland navigation channel improvements was used to repurpose a former US Navy harbour into the largest seagrass restoration site in the US (at the time), which included a public access beach, bird roosting islands and marsh ecosystem.
Worldwide there is growing interest from governments and investors in integrated coastal protection schemes that combine nature-based approaches with more traditional hard engineered structures, such as sea walls, groynes, breakwaters and levees.
These hybrid interventions can provide a good compromise between the risks and benefits of soft and hard engineering measures. These solutions include:
- Temporary hard infrastructure – a natural approach can take time to establish and hard infrastructure can be used to temporarily reduce disturbances.
- Protection of hard infrastructure – natural infrastructure can be used to protect built infrastructure (eg managed realignment).
- Inspired by nature – using designs inspired by nature to enhance the benefits provided by built infrastructure (eg adding rock pools to seawalls that mimic intertidal habitats).
Multiple lines of defence – involves using environmental features (eg barrier islands and mangroves) to complement hard infrastructure (eg levees and flood gates) as well as non-structural measures (eg raised homes and evacuation routes).
Greening of grey infrastructure
There is a growing body of evidence that demonstrates how hard coastal infrastructure can be cost-effectively adapted to sustain greater biodiversity.
“The ecological value of estuarine and coastal protection structures can be improved through the selection of ecologically favourable materials and niche habitat designs, while still meeting engineering performance requirements,” says Rowan Byrne, Mott MacDonald’s technical principal for marine ecology.
“Research worldwide shows the operational applications of these techniques to be successful.”
Mott MacDonald supported a project in Hartlepool, UK, where rock armour was ecologically enhanced – through choice of materials and positioning – to accelerate the colonisation of rock revetments by key intertidal species such as limpets, barnacles and fucoid seaweeds.
Preliminary data suggests that passive ecological enhancements can help mitigate ecological impacts of new rock revetments in as little as 12 to 18 months.
Sustainable coastal management
Beth Riley adds: “Designing and engineering a successful coastal protection project requires an acute awareness of coastline processes and an impressive battery of technical skills, from geomorphology to hydraulics.
“More and more, communities are seeking resilience in their infrastructure while at the same time minimising impacts on the environment or, better still, enhancing it for wildlife and for people to enjoy.
“Successful coastal management is dependent on resolving conflicts of interest between environmental, physical and human factors in order to enable use of the coast in a sustainable and mutually beneficial manner.”