Tuesday, 19 Apr 2022  |  Reading time:  11 mins  | Read online

Coastal protection

This week we look at how local governments can reduce the risk of coastline erosion to communities – while reducing ecosystem disruption from solutions. 

Coastal protection or management is the defence of coasts and coastal communities from erosion, coastline retreat and flooding.

As sea level rise continues, many coastal communities – who make up 40% of the world’s population – are at increased risk from coastline retreat and flooding. This tool allows you to see the impact of sea level rise anywhere around the world: 2 metres by 2100 is plausible, but even half a metre would pose an existential threat to many cities or island nations (the Maldives famously held a cabinet meeting underwater in protest). 

Coastal protection used to rely on conventional ‘grey’ infrastructure solutions such as seawalls or dikes. While effective, we now have better knowledge of their downsides which can include transferring the problem down the coastline, poor longevity or damage to ecosystems. Today, the use of a wider array of solutions (including nature-based/green infrastructure) can better address local risks, reduce damage to the environment and even improve cost efficiency.

While coastal protection can be physical intervention to slow coastal retreat or flooding, it’s also important to acknowledge that risk from a natural hazard is tied to human vulnerability. In some cases, ‘holding the line’ against erosion may not be possible, but we can still reduce vulnerability though managed retreat, improving forecasting and planning, or making use of innovative architectural designs – the Netherlands’ floating homes being an example.  

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This week's featured content

Tackling sea level rise and the case for managed retreat – lessons from USA experience

Can human settlements survive the effects of climate change at some coastal locations impacted by rising sea levels? Is it always possible or appropriate to implement adaptation measures, or should other options be considered? Is it always the case of armouring the coast or constructing other engineering solutions to hold the tide back? Can the sea be held back in every location? Should it be?

Protection against sea-level rise requires the construction of extensive coastal defences; an option that, at first glance, may find political consensus. However, detailed analysis and design of an appropriate solution is both time-consuming and immensely costly. Proposed defences in Manhattan, as in other Miami, Boston and other US cities, are said to be costing billions of dollars – so, who pays?

To date, most climate adaptation has been small scale and short term, involving minor modifications to standard practices. Given the projected increase in sea levels, the ambition and innovation in adaptation would seem to fall significantly short, not only of future climate risks but also existing risks.

What engineering innovations will be needed to support infrastructure that is permanently inundated, sited on melting ground, or repeatedly exposed to wildfires? The economics of staying in place needs to be contrasted against a managed retreat policy, as mismatched incentives or risk perceptions lead to market failure, though none of the choices are easy or palatable.

Will strategic infrastructure be prioritised over urban settlements or vice versa? Within the at-risk coastal groups, those from the socio-economic categories that have the ability and means will relocate, but what of those without means? Are they forever destined to be trapped in situ? As the stakeholders most immediately affected, how is their voice being incorporated into the solution?

This briefing takes a look at Charleston, South Carolina, where these questions are already being grappled with, to provide insight into how climate risk and public policy making intersect.

So how do these scenarios play out day-to-day, and what can we learn? 

LGIU Global Local Highlights

 

Climate change and coastal communities: envisioning risk

This briefing looks at the increasing coastal hazard risks to property, which will be amplified by climate change, and identifies some key recommendations for local governments to build a stronger understanding of the risks, impacts, and responses to Actions of the Sea outlined in an Insurance Council of Australia report. 
Click here to read this briefing.

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How can nature-based infrastructure provide solutions to flooding? A global look at adoption

The impact of coastal, fluvial and pluvial flooding is set to increase across much of the world, making effective flood risk management crucial. Nature-based flood measures are receiving increasing attention for their ability to not only provide the same protection as grey infrastructure but co-benefits including ecosystem conservation.
Click here to read this briefing.

Innovation & Inspiration

Curated case studies from around the globe

USA: Can a wall of oysters protect New York?

A New project in NYC is using discarded oyster shells to rebuild reefs that once surrounded the city. By building marine mattresses of oysters off of Staten Island, the Living Breakwaters project hopes soften the blow of erosion and break large waves, reducing flooding. After laying the foundation, the stone breakwaters will be seeded with larvae-laden shells, with a view to hit one billion oysters in New York harbor by 2035.
The Guardian / Bloomberg

INDONESIA: Permeable ‘fake mangroves’ seek to help stabilise Java coastal erosion

The island of Java has lost 78% of its mangroves, which help to protect its low-lying shoreline from rising sea levels and subsidence. However, a “building with nature” pilot project in the district of Demak is now helping to protect more than 30km of coastline. Locally-owned permeable structures are constructed that perform a similar function to mangroves – defending land from tidal erosion, while allowing sediment to wash through. These structures also create more fertile soil, supporting new mangrove growth. Local fish farmers have been engaged to grow mangroves in parts of their farming ponds, which has also boosted shrimp yields.
Global Center on Adaptation

AUSTRALIA: Council to install engineered reef to tackle beach erosion

An innovative engineered fringing reef will be installed 100 metres offshore at C.Y.O’Connor Beach, as part of a $565,000 City of Cockburn (WA) project aiming to reduce coastal erosion. 135 precast concrete modules will be craned into place this month, to be colonised by marine flora and fauna. This engineered reef will reduce the wave energy that reaches the beach while being less obtrusive than seawalls and groynes. The project will be Australia’s first engineered modular concrete wave-attenuating fringing reef.
City of Cockburn

USA: Cape Cod coastal resilience enhanced by geodesign and best practice strategies

The Resilient Cape Cod project was launched by the Cape Cod Commission to address the increasingly visible coastal impacts of surging development and climate change holistically. The Commission researched effective global coastal preservation strategies that either protect shorelines, accommodate hazards, or retreat built structures, which were discussed with stakeholders and organised in an accessible database. The interactive Cape Cod Coastal Planner application shows residents’ specific sea level rise risks, locates key infrastructure, and predicts future erosion, hurricane impacts and flood zones. The tool identifies mitigation techniques, plus associated costs and ecosystem impacts, and is used for decision-making and community education.
Esri / Resilient Cape Cod / Cape Cod Coastal Planner

Policy & Resources

Handbook: The Coastal Handbook
This comprehensive guide from the UK provides a single reference point for coastal management information for local authorities and practitioners. Each section provides an easy-to-read summary for quickly brushing up on topics. Read it here.

Guide: International Guidelines on Natural and Nature-Based Features for Flood risk Management 
Available as either a full or shortened version, this 2021 guide provides practitioners with the best available information concerning the conceptualization, planning, design, engineering, construction, and maintenance of NNBF to support resilience and flood risk reduction for coastlines, bays, and estuaries. Find it here.

Case studies: CoastAdapt 
CoastAdapt provides a compendium of case studies from Australia to illustrate what coastal practitioners and decision-makers are doing to adapt to a changing climate. Explore the map of case studies here.

Thanks for reading

Next week, we'll be taking a look at all things roads. Stay tuned!

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