Posted by: coastlinesproject | January 10, 2017

Chatham points to what could happen if Plum Island breaks through.

Chapter 24

The Chatham Connection

January 3, 2017

 

January 3rd was a warm, blustery day. Ten-foot waves from last night’s storm were breaking over the shoals beyond the Merrimack River. I could just make out a medium-sized boat caught in the maelstrom. She was plunging and bucking into the waves exploding all around her. Each wave would send a twenty foot geyser of freezing water into the air then cascade down on four men clad in survival suits who hung on for dear life. But suddenly the boat broke free and made a dash for the quiet waters inside the jetties.

 

There, I could see she was one of the Coast Guard’s 47- foot shallow draft boats first used in Chatham Harbor. She was soon joined by another life saving boat and after reconnoitering for a bit they sped back into the waves. Were they looking for an overturned fishing boat, or the body of a fisherman swept out to sea?

 

Nah, they were just on a training exercise putting some newbie Coastie through his paces in the mouth of what the Coast Guard calls the most dangerous river on the East Coast. In fact Newburyport is the birthplace of the U.S. Coast Guard, Alexander Hamilton started it here before Lin Manuel Miranda made him into a 21st century hip hop artist, “Our river was so treacherous, we tole the Brits don’t mess wid us.”

 

Having gotten that out of my system, I went to see how North Beach had weathered the storm. All things considered it had done very well. Last night’s waves had only eroded a few feet off the face of the temporary new dune built to protect the houses along Northern Reservation Terrace.

 

But other waves had washed over the dune delivering a new layer of sand that would stimulate the dune grass to grow an internal matrix of roots and rhizomes to hold the dune together. So the sacrificial dune was doing its job, absorbing the waves’ energy while building a barrier to slow future erosion.

 

Things were different on the jetty, however. For the past four months, long period waves had built up a ridge of sand that blocked less powerful waves from crashing through the jetty. But last night’s storm had flattened the ridge protecting the last 204 feet of the jetty. So future waves could now be able to wash sand through the jetty again. Several thousands cubic yards

had washed through just last night.

So now the race was on. Would the temporary sand dune give the jetty enough time to settle so the beach could start growing again?

 

The storm reminded me of a similar storm that struck Chatham Massachusetts on exactly the same day 30 years before. The storm and its ensuing inlet caused seismic changes to the town and they continue to plague the town today. If a storm breaks through Plum Island it could cause similar changes to Newburyport, Newbury, Rowley and Ipswich, so it makes sense to see exactly what happened on Cape Cod.

 

It was not that the storm was particularly strong but that it arrived at exactly the wrong time. The barrier beach that protects Chatham had been growing longer and lower for several years and it had not been helped by boaters who made a habit of walking over the low dunes to get to the ocean beach.

 

That was exactly the area that the 12 foot high storm surge burst through the beach on a full moon syzygy tide. The next morning people awoke to a new reality, but it was not terribly impressive one, just a foot deep channel meandering back and forth through an overwash area the size of a football field.

 

Ten guys with shovels could have filled the break back in on that first low tide, but they didn’t and only a month later the channel was over 18 feet deep and commercial fishermen were using it to cut an hour off the trip to their fishing grounds. But, since nobody had expected an inlet to form, nobody had come up with a plan to fill it back in.

 

 

But the inlet really shouldn’t have taken anyone by surprise. Unlike on Plum Island, a prominent scientist had predicted when the inlet would open in a classic piece of shoe leather coastal geology. Graham Giese, one of the founders of the Provincetown Center for Coastal Geology had detailed a 140 year cycle where the lengthening barrier beach causes hydraulic pressure to build up in Pleasant Bay until a storm breaks the barrier beach and the southern part of the beach welds to the mainland allowing the northern part to grow until it breaks in exactly the same place 140 years later.

 

But because Graham was a correctly conservative scientist he had rounded his cycle off to 150 years. I liked to chide him that if he had stuck to his guns he would have only been two days off because the new inlet had formed on January 2nd. 1987.

 

Despite Graham’s paper everyone had been taken by surprise. It had been a long time since the last inlet formed in 1846. So long that people had forgotten why the called their barrier beach North Beach when it wasn’t really north of anything. But as soon as the new inlet opened they realized they now had a North Beach and South Beach like back in 1846!

 

Prior to the storm, Chathamites like Newburyporters thought they lived behind a permanent barrier. Everyone had always assumed that the fishing camps on the outer beach were vulnerable but nobody realized how much damage the inlet could do to the mainland,

but they were soon disabused of that notion when ocean waves started to sweep houses off the mainland for the first time in over a hundred years.

 

Homeowners had to spend millions of dollars to build several miles of revetments and the Army Corps of Engineers had to spend hundreds of thousands of dollars to dredge the new sand out of Chatham Harbor.

 

Pleasant Bay was now 6 inches higher at high tide and 6 inches lower at low tide and houses like ours, 12 miles from the inlet started experiencing erosion for the first in memory. The bay had experienced the equivalent of 50 years of sea level rise overnight.

 

Ten years later another inlet formed and a dozen camps were lost on the outer beach. Then in 2003 a third inlet formed and it will still take one to three decades for the system to fully stabilize.

 

Similar things could happen if the ocean breaks through Plum Island. If it breaks through on the southern end of the island, streets and homes in Ipswich could be affected, if it breaks through in the middle of the island, streets and homes in Rowley and Newbury could also eventually be affected. But if it breaks through on the north end of Plum Island, Plum Bush, Joppa Flats, The Basin, and even houses on Water Street could be lost.

 

Plum Island still lacked a study equivalent to what Graham Geise produced for the Chatham Conservation Commission. It was still relying on local hearsay and less than rigorous research done in the Seventies with outdated technology. That would start to change when the Merrimack Valley Regional Planning Authority released its Woods Hole study on sediment transport and when the Army Corps released two similar studies. Hopefully they would get it right and they would all agree!

 

 

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