Delaware Public Media

iSeeChange: Exploring the connection between increasing storms and the pace of coastal erosion

Apr 10, 2015

The Northeastern U.S. is no stranger to coastal storms. Especially in recent winters, it's hard to go a couple of weeks without hearing that folks should steer clear of yet another Nor'easter. When storms like these happen and especially in succession, that’s questions start to arise about what might be driving these weather patterns and if it’s going to get worse.

Elsa Partan lives in Falmouth, Massachusetts, a small town near Cape Cod. According to a recent U.S. Geological Survey report, sea levels along the Cape are rising 2 to 3.7 millimeters per year, about three to four times faster than globally. She’s lived in the area since 2009 and she says that folks in Cape Cod are very concerned with erosion along the coast.

 

“Beach erosion on the coast of Massachusetts and especially certain parts of Cape Cod are experiencing very heavy erosion -- and at least in Nantucket, there are some houses that are threatening to fall into the ocean," said Partan.

The town of Sandwich, she says, has it especially rough.

 

“In Sandwich, they have a way of saying, 'what will Sandwich will be without the sand?' as their little tagline," laughed Partan. "It seems that Sandwich is   losing most of its beaches. That seems sad for a Cape Cod community.”

When a storm, like the recent winter storm Juno, hits the Northeast, she says it exacerbates the erosion.

 

“Every time these storms come along, they pound the coastline even more and wash away yet more coastline from these certain spots that are so vulnerable," said Partan. "It’s something that since 2013, has happened a number of times.”  

Here's what Elsa Partan wants to know.

 

“I guess my question would be: will we see increasing storms that will make erosion of beaches in Massachusetts go faster? Are we going to lose our beaches faster because of climate change?”

Answering that query is Art Trembanis, a coastal science professor at the University of Delaware’s College of Earth Ocean and Environment.

While the campus is about 500 miles south of where Elsa lives, the problem of coastal erosion is still quite relevant in Delaware. Both scientists and political leaders have voiced concern about the impacts of climate and sea level rise on the lowest lying state in the country -- and a sea level rise vulnerability study from DNREC, Delaware's Department of Natural Resources and Environmental Control, noted that 8 to 11 percent of the state could be underwater by the end of this century.

Trembanis says there is a lot factors involved when you’re talking about erosion, natural and man-caused.

 

“When we get a set of storms, whether it’s Hurricane Sandy or Katrina, we tend to focus entirely on those singular events. I try to think of it like music," said Trembanis.

“You can hear the symphony, if you only listen for the cymbal crashes, maybe that’s all you’re going to hear. And storms are like those cymbal crashes at the coastline. They’re punctuated, they’re intense. They resonate out of the rest of the sound of the orchestra. But they’re just part of the symphony of the coastline. The thing to keep in mind though is that in addition to those cymbal crashes, there’s this overall crescendo -- and that’s sea level rise. We don’t tend to talk about it because we focus on those cymbal crashes.”

 

Trembanis is very concerned about sea level rise because he said it could be exaggerating the impacts of storms that would be normally have low impacts, based on historical records.  

 

“In 2003, Hurricane Isabel hit through the Chesapeake Bay," he said. "I had to evacuate my house and in Gloucester Point, VA. I had to be out of my house for a week before we could get back in."

 

Trembanis said that when Hurricane Isabel's impact on the coast  are compared to other storms in the tidal record, it actually had the impact of a larger storm. 

 

"It was a category 1 storm--a low impact storm--when it came through. But it had storm surges that were equal or bigger than a 1933 hurricane, which was the storm of the century. And that was a category 2 storm."

 

Keeping in line with his symphonic metaphor, Trembanis then compared this shift in storm impact intensity to when notes in a symphony increase in pitch. Hurricane Isabel, he said, would have had a lower storm surge if it occurred in 1933. But due to the contributing factor of sea level rise that had accumulated in the 70 years between the two storms, 

 

"[Sea level rise] actually effectively kicked it up from a category one to a category two impact storm. With the natural process of sea level rise, we can expect storms that used to not have much of an impact have more of an impact.”

 

Trembanis is more concerned about Nor’easters than hurricanes.

“Sandy was an anomalous storm," Trembanis said. "The thing that makes nor’easters more of a concern is that we get more of them. They tend to be spatially larger storms. So if you’re taking storms that were marginal and making them have more impact because of sea level rise, then suddenly you’re turning jabs into uppercuts. And we know we get far more jabs coming across in the form of Nor’easters than we do hurricanes.”  

Over stretches of time, beyond the immediate aftermath of a storm, it’s hard to measure how these storms contribute to coastal erosion, especially when sea level rise and human development along the coast play important roles in the process.

 

“Part of our challenge in understanding the coast is teasing out the natural processes and variability that can go through cycles, from those that are anthropogenic, climate change and whatnot," said Trembanis.

In his research, Trembanis tries to meet the challenge by using eroding barrier islands like Cape Cod as living laboratories to understand how storms fit into the bigger picture. He looked at barrier island in particular -- Cedar Island, an abandoned island off the coast of Virginia, which he said is the most rapidly retreating island on the East Coast.

"In the course of the span of one of my students’ PhD term, we watched a row of houses go from being near the surf zone, then out of the surf zone and then gone, wiped out," said Trembanis.

What’s taking place at these eroding barrier islands is a process called shoreline transgression. Basically, sea level rise and storms push sand over the islands, effectively inundating them. When Trembanis and his colleagues looked at the long-term data on erosion at Cedar Island, they noticed something interesting about the pace the shoreline was retreating.

 

“While the island had been retreating since the 1850s, it wasn’t doing so at a steady rate," he said. "The pace had changed. It’s almost like someone changed the tempo of the music. From the 1850s, into the 1960s and 70s, it was at a pretty even tempo, about 7 meters per year. But then starting in the 80s, 90s, into the 2000s, the rate started to pick up the tempo -- the tempo doubled. The tempo doubled went from 8 to 10, to 12, to 14 meters per year.”

It was a curious observation, so he wondered what would be the cause of the change in tempo. 

 

“We drew a big box around Cedar Island and we asked how many times have storms passed close enough by that it could make an impact on the coastline," Trembanis said. "We went back through storm databases--that includes hurricanes and nor’easters--and we found that the storminess -- the number of storms that passed through the area -- over that same interval was almost an identical pattern to that. We saw generally low storminess, then an increase in storminess in the last few decades, which made us think wow, maybe that’s helping explain what was already a fast retreating shoreline was picking up in speed.”

 

Though it’s just an up close look at one island, it’s a strong correlation that can’t be ignored. Right now, no one lives at Cedar Island. But in areas where people do live, there are efforts underway to deal with coastal erosion.

 

On top of a pile of dead grasses on the bank of the Lewes-Rehoboth canal in Delaware, stood Josh Moody, a restoration coordinator at the Partnership for the Delaware Estuary. On an early April day, he and employees of DNREC were building a "living shoreline" along the canal.

 

“This is an area where the salt marsh is eroding a lot faster than what’s happening naturally around it," he said, pointing between a healthy-looking shoreline nearby and their work site. "One of the goals for this project is to stabilize the shoreline, to stop the erosion, to get it back out where it needs to be.”

 

They’re essentially building what’s known as a living shoreline. The definition of these structures are often debated among restoration ecologists, but for the purposes of this one here in Lewes, let’s say it’s a manmade shoreline that’s composed of local plants and animals. Beneath this tall pile of grasses we’re standing on are rows, or logs of mud that contain these living components and allow them to grow even when confronted with wave energy from the waters.   

“What [these logs] do is they give plants and animals, the mussels we’re going to put in, time to establish themselves without having to deal with the energy," said Moody. "So that allows them to become a robust community.”

This living shoreline includes ribbed mussels and spartina alterniflora, which is a tall grass associated with salt marshes. Because this living shoreline is intended to keep up with the pace of sea level rise, Moody says how the grasses are planted is crucial to the process. Moody explained how the salt marsh becomes eroded.

 

"As the water’s rising, the shorelines start sinking a little, and the grasses spend too much time underwater," he said. "And it’s just not healthy for the grass. As the grass starts dying back, its roots can’t hold together the sediment anymore, so the water moves in further, which starts hurting that grass and it’s kind of a positive feedback where the more water comes in. The lower the marsh gets, the more it dies, the more it goes.”

If the grasses are meant to be the shoreline, Moody says it’s crucial that the living components -- the ribbed mussels, the plants, the mud, build up to the right elevation for the grasses to grow.

 

“You really want the materials you’re going to plant the grass in up to the proper elevation, so that the grass once it’s there is in its happy spot, where it’s going to do what grass does effectively," said Moody. "There’s a lot of scientific literature out about where the grass should be within the natural tidal prism, where it stands the best chance to trap sediment as it comes in keep pace with sea level rise.”

 

At the first week of April, this living shoreline looked like a pit of mud. But they expect over the summer, it’ll eventually grow out and blend in with the rest of the shoreline.

 

Living shorelines are important for the city of Lewes, which was recognized as an at-risk community on a sea level rise report by the Union of Concerned Scientists released last fall. The city has seen coastal waters rise over a foot in the past century, and experts project that the waters will keep rising at faster rates in the coming decades.

Structures like bulkheads that are built to protect shorelines actually speed up the pace of erosion and thus can do a lot of damage. The Partnership for the Delaware Estuary has built shorelines that have actually weathered the effects of storms quite well.

“One of our longest living shorelines, which is in Heislerville, NJ," he said. "We installed that six years ago. So it’s gone through Irene, Sandy and tropical storm lee. Our treatments weathered all three of these storms, completely, not a lot of debris in them. The bulkheads got completely destroyed.”

 

The long term impacts of living shorelines, however, are unknown. It’s still a completely new science, so Moody and his colleagues acknowledge there’s always a chance something could go wrong. But for now, it’s a promising strategy for mitigating the effects of rising seas and increasing storms.

 

Meanwhile, Elsa says that Cape Cod communities are desperately trying to hang on to their beaches.

 

“The towns are spending a lot of money and effort to get federal dollars to dump more sand on the beaches, which gets washed away in the next storm," she said. "It’s very costly and it’s hard to see what the solution is, what the end game is.”

 

It’s possible that the future of Cape Cod could look like the present at Cedar Island. But as Trembanis said, it’s challenging for researchers like him to measure how quickly erosion will take place in a specific timeframe, such as the length of one’s mortgage. So it’s difficult to say whether people in these areas should look into moving elsewhere. People like Elsa are attached to their seaside towns and are building their lives there -- she just had a baby this past winter.

 

But if and when things get to a point of no return, we may have no choice but to just appreciate nature taking its course. Like with Cedar Island, we’ll do what humans do best, which is adapt, and let the things we can’t take with us fall away into the sea.  

P.S. One thing that wasn't mentioned was that Elsa Partan gave birth during winter storm Juno this year and she wanted to know whether more babies are born during snowstorms. Got a blizzard birth story you’d like to share? Tell us at iSeeChange.org and we’ll let you know if we find an answer Elsa’s question.

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This piece was produced in collaboration with iSeeChange - a national public radio project about the impacts of climate and environmental changes on our lives.  If you’ve got a question about the environment that you’d like for us to explore, post it online at iSeeChange.org