An MIT study finds that salt marshes can provide economical and effective coastal protection. The research shows these natural barriers can reduce seawall construction costs while delivering substantial storm surge protection.
Climate change is intensifying the frequency and severity of storms, leading to rising sea levels and more severe coastal erosion. In the United States, coastal storms caused approximately $165 billion in damages in 2022 alone. However, new research from MIT suggests a potential solution that harnesses the power of nature.
A recent study, published in the journal Communications Earth & Environment, by MIT graduate student Ernie I.H. Lee and professor of civil and environmental engineering Heidi Nepf demonstrates that salt marshes, when used in tandem with seawalls, can offer significant protection for coastal areas at a cost-effective rate.
“This study shows that restoring coastal marshes is not just something that would be nice to do, but it’s actually economically justifiable,” Nepf said in a news release.
The research highlights the wave-attenuating capabilities of salt marshes, which allow for the construction of lower seawalls without compromising protection from storm surges. This can lead to substantial cost reductions.
“One of the other exciting things that the study really brings to light is that you don’t need a huge marsh to get a good effect,” added Nepf. “It could be a relatively short marsh, just tens of meters wide, that can give you benefit.”
This insight is particularly valuable for urban areas where space is limited and existing gray infrastructure such as seawalls is already in place. As Lee pointed out, previous studies have often focused on expansive marsh landscapes.
“But we want to show that it also applies in urban settings where not as much marsh land is available,” he said in the news release.
The study utilized computer modeling to simulate waves propagating over different shore profiles and took into account the morphology of various salt marsh plants, including their height, stiffness and spatial density. This method allowed the team to assess plant-wave interactions more accurately without extensive field measurements.
To quantify the benefits, the researchers developed a straightforward metric: for a given length of shoreline, they calculated the height reduction of a seawall if supported by a salt marsh.
Real-world data from projects in Salem, Massachusetts, helped validate their models. The results showed that a healthy salt marsh could reduce the necessary seawall height by about 1.7 meters (5.5 feet), meeting safety standards for wave overtopping and protecting pedestrians.
Nepf acknowledges that collecting detailed data to model a marsh can be labor-intensive. To address this, Lee is developing a method using drone imaging and machine learning, which would simplify the process.
This will allow decision-makers to evaluate a given area of marshland and ask “How much is this marsh worth in terms of its ability to reduce flooding?” according to Nepf.
The study’s timing coincides with new guidance from the White House Office of Information and Regulatory Affairs, which urges the inclusion of ecosystem services in federal project planning.
“But in many scenarios, it lacks specific methods for quantifying value, and this study is meeting that need,” Nepf added.
The Federal Emergency Management Agency also has a benefit-cost analysis toolkit, noted Lee.
“This is one of the applications that policymakers can consider on how to quantify the environmental service values of marshes,” added Lee.
The software developed for this study has been made freely available on GitHub, facilitating its use by environmental engineers and planners.
Xioaxia Zhang, a professor at Shenzhen University in China who was not involved with the research, praised the practical applications of the findings.
“This paper presents a practical tool for translating the wave attenuation capabilities of marshes into economic values, which could assist decision-makers in the adaptation of marshes for nature-based coastal defense,” she said in the news release. “The results indicate that salt marshes are not only environmentally beneficial but also cost-effective.”