A Global Database of Natural Coastal Defenses: Where, When, How and How Well do They Work?

The months of October and November 2014 witnessed four major storms that collectively cost more than 40 lives and an estimated US $10 billion in damages (Odile, Hudhud, Nilofar, Vongfong). As with similar events in the past, these storms have raised significant questions regarding the choices we make when developing, managing and defending our coastlines.

There is mounting evidence that coastal habitats such as reefs, wetlands and mangroves can form an effective first line of defense even against extreme events. Unfortunately, information about the effectiveness of natural habitats for coastal defense is widely dispersed. This has contributed to the prevalent belief that we do not know enough about the coastal defense services offered by natural habitats to include them within coastal risk management plans. As a result, recognition of this important service by coastal engineers, city planners, government agencies and other decision makers remains the exception rather than the rule.

In fact, we do know a lot about whether and how natural habitats defend our coasts and a considerable amount of this knowledge is now is available in one place: the freely accessible SNAP Natural Defenses Database. (Follow the link and click on the Natural Defenses App button in the top left corner.)

SNAP CD database imageRecently launched by the SNAP Coastal Defenses Working Group, the Natural Defenses database maps 67 examples of natural coastal defenses around the globe to help demonstrate that: a) coastal habitats can and do provide considerable coastal protection; and, more importantly, b) we actually do know quite a bit about where, when, how and how well specific habitats work as coastal defenses. In addition to mapping, the database also summarizes information on the coastal defense characteristics of each example. You can view the global distribution of these examples in the database.

The studies cover a range of habitats such as coral reefs, mangroves, salt marshes, seagrass and wetland habitats, and are a synthesis of reports, peer-reviewed journal articles, grey literature such as governmental reports and other types of documentation.

You can sort the projects by habitat type (e.g., mangrove, coral reef), exposure and several other factors. Additional information is also provided for each case study indicating its effectiveness and cost-benefit analysis. Users can therefore easily pull up information on projects that fit specific habitat and site criteria such as mangrove projects in high exposure regions, or salt-marsh projects along estuarine coastal systems, and more.

The 67 examples shown here are the results of a search for demonstration and restoration studies with enough data for further (on-going) synthetic and meta-analyses. While we know there are more projects than this we looked specifically for studies where the methods and effectiveness are well documented. While the examples in the database are extensive, they are not exhaustive. For instance, we have not yet incorporated projects on beaches and dunes; this is a phase 2 SNAP Coastal Defenses Working Group project. More information on site conditions such as exposure to storms and risk characteristics, such as sea-level rise values, will also be added.

As the breadth and depth of the information in the database increases the SNAP Coastal Defenses Working Group will develop a simple, rapid quantitative tool that provides guidance on when habitat restoration may be effective for coastal defense in different geographies. The ultimate aim of this database is to supply examples that provide lessons and guidance for the effective management and use of habitats for coastal defense.

The (on-going) process of populating this online database has been both challenging and rewarding. For instance, the disparity across studies presents challenges of its own: there is substantial variation in terms of where data and information are reported, how they are presented, and the extent of detail in the descriptions.

The combined ecological, engineering, economic and policy expertise of the entire SNAP group has been employed in addressing these challenges and developing this database. The process of database development has highlighted the need to gather and synthesize what we already know to be able to better understand and manage our first lines of defense to our benefit and theirs.

To paraphrase a well-known TV series, “the evidence is out there.”

Siddharth Narayan

Siddharth Narayan is a research scholar at the National Center for Ecological Analysis and Synthesis (NCEAS), UCSB. Sid works on the interactions between coastal engineering… Read More