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Demonstrating the value of natural and nature based defenses: 5 steps for assessing coastal habitats

As part of a 2-year project, an industry group collated and analyzed evidence for natural coastal defenses, including their effectiveness, costs and benefits.

Extreme weather events have served as a wakeup call for many coastal communities around the world, and today, numerous cities are seeking solutions to strengthen their infrastructure to protect against extreme weather events and climate change. Over the last decade, we have seen an increased level of interest in quantifying the benefits of coastal habitats as flood and erosion defenses. Coastal habitats can augment, or in some settings, even offer an alternative to traditional grey engineering structures, like sea walls and levees that are widely used to manage flood and erosion risk.

Forging a global partnership, United Nation agencies, governments, international institutes, nongovernmental organizations and academics created the World Bank Wealth Accounting and Valuation of Ecosystem Services or WAVES partnership. As part of a 2-year project, the group collated and analyzed evidence for natural coastal defenses, including their effectiveness, costs and benefits. Findings demonstrate hybrid approaches consisting of both grey infrastructure and green solutions that use the natural environment can be beneficial in helping coastal communities avoid future costs, while providing critical climate change resiliency.

Results from the WAVES partnership study suggest that coastal habitats can reduce wave heights between 31 and 72 percent and provide risk reduction services at a lower cost than traditional defenses. Using a generic framework and five simple steps, coastal communities can better assess the true value of coastal habitats in erosion and flood risk reduction. The steps include:

  1. Estimating offshore waves
  2. Estimating nearshore waves
  3. Estimating effects of coastal habitats
  4. Estimating flooding level
  5. Assessing damages and valuing coastal protection benefits

These five steps make it possible to assess the coastal habitat’s value in terms of the damages averted by conserving or restoring the habitats. A variety of tools and models for solving each step, including analytical or semi empirical approximations, databases and numerical models exist. The process can be applied at different scales (local, regional and global) for many ecosystems, including coral reefs, mangroves and more.

This approach was applied on a global scale to determine the economic benefit provided by coral reefs. Coral reefs can reduce wave energy by up to 97 percent in some settings. This can reduce the risk of erosion and flooding during storm events. For 1-in-10-year events; storm costs were shown to more than triple without reefs; reefs also provide significant benefits for higher intensity, 100-year events too, where damages were shown to increase to more than US$200 billion if reefs were not well managed. On an annual basis, coral reefs provide approximately $6 billion of coastal protection services.

These headline numbers show why plans for coastal development, which may include such things as port development or the creation of fish farms, should take into account the risk reduction services provided by existing habitats. The removal of coastal habitats can increase levels of risk leading to increased economic damages and the requirement to install costly new defense structures. The removal of habitats also removes many other valuable ecosystem services. By providing more information and demonstrating the economic benefits provided by coastal habitats, we hope more coastal cities will see the value of nature and natural based defenses in protecting coastlines and properties.

Nigel Pontee, CH2M’s Global Practice Leader for Coastal Planning and Engineering, will join coastal and marine engineering experts from around the world at the Institution of Civil Engineers Breakwaters 2017 conference, being held in Liverpool, UK, September 5-7. He will present the paper, “Assessing the performance of natural and nature based defences,” co-authored by Siddharth Narayan, University of California Santa Cruz; Borja Reguero, University of Santa Cruz; Michael Beck, The Nature Conservancy; and Inigo Losada, IH Cantabria.

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