Posted by: coastlinesproject | February 28, 2016

Plum Island; Using drone to map erosion

Chapter 2

Droning On

October 7, 2015

 

In early October Plum Island basked in the sunny, warm El Nino induced weather. North Point State Reservation lay on the north end of the nine-mile long island, and Sandy Point State Park lay on the south end. Squeezed in between were the densely packed beach houses of Newbury and Newburyport.

 

There was an ancient connection between the two communities; in the 1600’s they had both been part of the same town. But now Newburyport was a small city and Newbury was a rural cash strapped town.

 

But there was also another disconnect. Both polities were trying to slow erosion on the island, one by doing everything it could to fight nature and the other by doing everything it could to work with nature. It was like a controlled experiment specifically designed to see which method would turn out to be more effective.

 

Ethan Cohen and I had spent most of the last winter, the snowiest on record, using his drone to document the two story lines. We had watched as people in Newbury built seawalls and convinced the Army Corps of Engineers to repair the South Jetty of the Merrimack River in a vain attempt to stop erosion in Newbury.

 

But we saw that it was at the expense of people in Newburyport. The repaired jetty was now acting like a dam holding back a huge prism of sand that wanted to continue flowing through the jetty to renourish North Point.

 

Without that sand, the point was in the process of rapidly disappearing. We watched, as month by month the ocean gnawed at the dunes. It was easy to see that the dunes had eroded; they were steep and sharply scarped. But because there were so few features on the beach, it was difficult to know if they had eroded two feet, five feet or even more.

 

But when the Corps of Engineers had repaired the jetty in 2014, they had cut two sandy pathways through the dunes so that their eighteen wheelers could deliver hundreds of boulders some of them weighing close to 12 tons. However, they had left the two sandy tracks running along the edge of the dunes and put up snow fencing to prevent people from trampling down the fragile dunegrass.

 

We watched as first one road, then the other, then the snow fencing toppled into the ocean. Gradually we realized that this was the perfect way to gauge the rate of erosion. Each pathway was about 10 feet wide so the dunes were eroding back between 10 and 20 feet a month!

 

Nobody seemed to be aware or concerned about how fast the erosion was happening so we told the head of the Newburyport Conservation Commission, Joe Teixeira, that he might be able to use our footage to map erosion on the island. Joe realized the potential of this new technology right away and gave us a small contract to continue the work.

 

We were especially eager to get back into the field in the fall because the University of New Hampshire had placed several large white research posts in the dunes. We figured we could use the posts as reference points as we flew over the beach.

 

The system worked perfectly until one night after filming it hit me. At the rate of erosion we were recording, our reference posts were going to wash away in about two months. So I started to simply pace off the distance between duneline and the posts. The commission seemed skeptical of our findings. I think they thought I couldn’t count very well, not an altogether erroneous assumption. Finally I bought a tape measure so we wouldn’t be presenting what scientists call broken data.

 

With this high tech piece of equipment we were able to show that during winter months without storms the beach was eroding back 10 feet and that during winter months with storms the beach was eroding back as much as 30 feet. That meant that over 200 homes would be danger in just two short years. But nobody seemed convinced. It would take a good storm to do that.

 

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William Sargent’s latest book, Plum Island; 4,000 Years on a Barrier Beach is available in local bookstores and through Amazon.com.

 

 

 

 

 

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Responses

  1. Excellent piece –

    Sent from my iPhone

    >


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