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Natural and Artificial Mitigation

You and your family finally move to the beautiful Gulf Coast. A remote, but developed, landscape surrounds your town, making for the perfect ocean-front experience. However, the overdevelopment of the coast leaves this entire life at risk of destruction and irreversible damage, as there is nothing between your family and the onslaught of hurricane season.

Is there an answer to the constantly evolving threat of natural disasters?

This question seems to be front-of-mind to policymakers and those on the front line of such hazards and dangers. The answer, simply, is “no, but there are things we can do to help.” Natural disasters are increasing in intensity and randomness due to climate change and anthropogenic activity, and all we can do is mitigate and protect our communities to the best of our ability. One of these mitigation efforts is quite counterintuitive to the thought process behind sea-walls and flood-levees, and it involves leaving coastline vegetation as it is and actually preventing the development of coastal areas. The thought process behind it is simple, more vegetation between society and a hurricane, for example, equates to more protection and buffering of a storm before it reaches inland areas. 

Is coastal vegetation a better solution for mitigating hydrological disasters than man-made protection?

In this blog, I’ll be exploring the differences between anti-storm development and anti-storm vegetation use.

Vegetation Use

First, we will explore how vegetation has been used in the past and present. Rusty Feagin and his colleagues define the idea of natural “bioshields,” or the use of vegetation and coastal ecosystems as a mitigative barrier to tsunami and hurricane activity (2). The call for the use of bioshields arose out of disaster events presumably being exacerbated by the removal of mangrove forests, such as Hurricane Katrina (2005) and Cyclone Nargis (2008). In Myanmar, Cyclone Nargis’ fatality count eclipsed 100,000, and the 4-meter storm surge engulfed much of the low-lying country. Researchers suggest that this effect would have been severely dampened if the mangrove forests were preserved rather than removed. There is already a great body of evidence supporting that vegetation lowers the intensity of small wave-events, but storm surge behaves in a more dangerous way, maintaining a high sea level with long, powerful tides (1). Feagin found, by investigating a case of mangrove use in India, that these forests were able to dampen the force of storm surges, protecting the land behind it from dangerous volumes of moving water. He did, however, note that the forests did not completely prevent flooding, as they still allow water and surge to pass through them, as the bioshields are not a complete barrier. Tanaka discusses this in more detail and recognizes that although bioshield methods are effective, they can be completely pointless if not properly planned or maintained. Tanaka’s research finds that an ideal forest density is difficult to maintain because large trees that are perceived as more effective due to their trunk size actually require more open space between them in order to grow. For this reason, a “perfect” barrier forest would involve trees of every possible size, so that branches and crowns of smaller plants are filling the empty space between the wide-trunked trees and maximizing density (6). 

Controversies There are a few controversies surrounding bioshield plantation use. As they may be effective at dampening storm effects, they often are not native species to the regions they are planted in, putting the local vegetation at risk. Along with this, the method may not have a net-positive effect on the economies of the region. In the eastern states of India, mangrove plantations have replaced the presence of many fuels and lumber trees that were originally relied on by the communities (2). Because of these issues, communities need to go through a web of decisions to make sure bioshields are truly the most appropriate mitigation method for them. The idea that bioshields must be near-perfect to be effective enough to justify their maintenance leads to the question of whether a full-density sea wall would be a better option for some communities.

Sea Walls

Japan has been utilizing sea walls for a long time, however, the cost of building and maintaining an artificial barrier that is damaged and eroded constantly is astronomically high (6). The cost may be justified by the economic damage a physical barrier can prevent during disasters, but all barriers are not a surefire fix for hazards, and incurring the high initial investment is a risky dice roll when natural barriers are cheaper and generally more durable. Other artificial mitigation methods, such as conveyance lines, are proven to be helpful in the aftermath of disasters, but are costly and fail to dampen the effects on the front-line of a disaster (4).

The Better Option Natural mitigation techniques seem to be the more beneficial and less risky option. Bioshield forests have tangible positive effects, and the hidden benefits of vegetation make natural options even more appealing. One of these indirect benefits of constructed natural barriers is the cleaning of water pollution post-disaster. Microbial organisms in wetland ecosystems, along with the high volume of water-demanding plants, allows for efficient cleansing of stormwater and wastewater (5). The pre and post-disaster benefits show a dynamic mitigation system at a much lower investment than artificial mitigation and adaptation methods. Islands tend to be the best example of using wetland and forestry for mitigation, Vanuatu utilizes mainly forest management to counteract rising sea-levels and flood risks (3). Another great example of vegetation interaction on islands can be seen below (Figure 1), as Sri Lanka sees much more success in keeping coastal areas dry by utilizing buffer-zones.

Figure 1: Sri Lanka use of mangrove vegetation

The evidence that natural barriers create a dampening effect at such a low cost of maintenance clearly outweighs the risk of possibly faulty and extremely expensive artificial barrier construction. Along with this, the accessibility that natural methods provide to less developed countries over artificial methods concretes them as a better option to promote on a global basis. Forestry and coastal vegetation management can create a sense of security and well-being that not only supports local communities but also creates ecosystems, rather than destroying them for artificial development. It’s clear to me that these benefits are well communicated, but more developed countries may feel that they have a better practice of “outbuilding” nature. I have learned that this is a naive stance to take, as sometimes, especially in the case of disaster dampening, the cheaper option can be far more beneficial.

Endnotes

Barbier, E. (2006). Natural Barriers to Natural Disasters: Replanting Mangroves after the Tsunami. Frontiers in Ecology and the Environment, 4(3), 124-131. Retrieved from http://www.jstor.org/stable/3868682

Feagin, R. A., et. al. (2010), Shelter from the storm? Use and misuse of coastal vegetation bioshields for managing natural disasters. Conservation Letters, 3: 1-11.

Filho, W L. (2013). Climate change and disaster risk management. [electronic resource]. Springer. Retrieved from https://search.ebscohost.com/login.aspx?direct=true&AuthType=ip,url,uid&db=cat00344a&AN=mucat.b4307865&site=eds-live&scope=site

Fox, K. (2019). FEMA Ready Report: Invest in Mitigation to Protect Infrastructure Before Disasters Strike. Retrieved from https://www.hstoday.us/federal-pages/dhs/fema-dhs-federal-pages/fema-ready-report-invest-in-mitigation-to-protect-infrastructure-before-disasters-strike/

Nagabhatla, N., & Metcalfe, C. D. (2018). Multifunctional wetlands. [electronic resource] : pollution abatement and other ecological services from natural and constructed wetlands. Springer. Retrieved from https://search.ebscohost.com/login.aspx? direct=true&AuthType=ip,url,uid&db=cat00344a&AN=mucat.b4611482&site=eds-live&scope=site

Tanaka, N. (2009). Vegetation bioshields for tsunami mitigation: review of effectiveness, limitations, construction, and sustainable management. Landscape and Ecological Engineering, 5(1), 71-79.