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The Mass Media

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February 26, 2024
An inside look at Bobby B. Beacon’s insides. Illustrated by Bianca Oppedisano/ Mass Media Staff.
Bobby's Inside Story
February 26, 2024

Biology Seminar Series: Harden Our Coasts With Heart

As part of the Fall 2016 Biology Seminar Series, Dr. Rachel Gittman, a Postdoctoral Research

Associate at Northeastern University, gave the presentation “Living Shorelines: Are We Designing Functional, Sustainable, and Resilient Coasts?” Dr. Gittman shared her research at the Integrated Science Complex on Sept. 9, covering the effects of “shoreline hardening,” or the building of barriers to prevent coastline alteration through loss, recession, or natural disaster damage.

About 10 percent of the New England shoreline is hardened (heavily so in Boston, as housing density is correlated with shoreline hardening), and about 14 percent is hardened nationwide. This hardening takes three common forms.  The first is bulkheads, which are vertical walls to block the sea; the second is riprap revetments; and finally there are breakwaters or sills, which are collections of broken rocks which allow the water to pass through the structure and act as a type of hybrid solution of what is natural and what is engineered.

Land within 100 kilometers of the coast is desirable real estate for human habitation, which spurs coastal development. Yet this development drives habitat loss. The danger of this loss, according to Dr. Gittman, is that, “coastal ecosystems cover only four percent of the earth’s land area, but they serve as highly productive, valuable ecosystems which provide habitat for a high diversity of organisms, including people.”

Therefore Dr. Gittman, an ecologist by training, delved into social, economic, and engineering issues in examining the question, “Do hardened shorelines provide functional habitat?”

For her research, Dr. Gittman compared hardened shorelines to natural shorelines, which are areas free of human intervention. Her study analyzed and compared the biodiversity and abundance of marine organisms found along these two types of shorelines. A large portion of her analysis was conducted on the coastlines of North Carolina, where a combination of erosion, flooding, and human development built on shifting sands and dynamic coasts causes property insecurity and the endangerment of coastline habitat.

Her results showed quite consistently how private actions, such as putting a bulkhead on one’s property, negatively affects the public trust, which results in loss of abundance and biodiversity. This is especially apparent since, as she stated, “not much attention is paid to the seaward side of the walls”.

What matters to homeowners in these areas, she said, is the question, “Are we creating sustainable and resilient shorelines?” In other words, are we keeping the shoreline where it is? Her data shows that the perception of homeowners is that bulkheads are the most effective method of maintaining shorelines, though these homeowners recognized bulkheads as the most expensive method. In reality, bulkheads are the least effective (and most expensive) method.

As an example of this, her research uncovered that after hurricanes, bulkheads and the properties behind them are generally compromised through breaches or failures, while stone sills are not.  The only exception is in the case where pieces of destroyed bulkheads float past the stone sills, damaging them and the properties behind them.

Her research shows a strong likelihood of sills being superior to bulkheads in terms of preserving habitat as well as in preventing natural disaster damage. Sills act as sediment traps that raise elevation even quicker than natural shorelines, and though they are not as effective as am oyster reef, they can act as surrogates for a natural reef. They also contribute to “living shoreline resilience.” Since the coast is not static, like a bulkhead tries to ensure, sills can help foster resilience without human intervention.
Dr. Gittman’s final message to the students at the University of Massachusetts Boston is “incorporating nature or nature-based features into shoreline protection approaches will make our coastlines more sustainable and resilient.”