As I See It,
Bill Sargent, March 10, 2018

“On March 2, winter storm Riley battered the East Coast with rain, hurricane-force gusts, and 20-foot high waves. Most damaging of all it lasted through four tidal cycles when the full moon was 30,000 miles closer to the Earth than usual, when the Earth was closest to the sun and when all these celestial objects were in line.”

“These factors all translated into enough force to erode the entire front face of Plum Island by 10 to 20 feet. But the storm also provided residents and officials with a map to show how to slow erosion in the future.”

“First, let’s look at the southern end of the island. Bar Head is one of the five major glacial drumlins that underlie the island. It is basically a big pile of gravel, rocks, and sand deposited by the glaciers at the end of the last Ice Age. The storm eroded Bar Head back about 20 feet, Vegetation cascaded down the face of the bank and ended up on the boulder field below, then the sand flowed south causing Sandy Point to grow about 50 feet. But nobody ever heard about this because there were no houses on Sandy Point. It was simply a natural phenomenon, nature’s way of healing a barrier beach after a storm.”

“The north end of the island would also like to grow about 100 feet each year. But it is prevented from doing so by the south jetty that the Army Corps of Engineers repaired in 2014. The jetty now holds back about a million cubic yards of sand that nature would like to use to rebuild the beach. Instead, the beach has been eroding back 150 feet a year, putting 250 homes at risk in the Northern Reservation Terrace area.”

“The damage at this end of the island was unnecessary. If the city or state had rebuilt or even just maintained the sacrificial dune, the damage could have been greatly reduced or even prevented.”

“But the most significant feature of this storm was that the center of the island was breached and breached again during four high tides. Water cascaded down Plum Island Turnpike running into water flowing in from the marsh side of the island. This left the shops, markets and restaurants standing in over a foot of water and the Newbury Police Department had to close the island for cars driving on or off for four hours every day during the high tides.”

“This is now the new normal. Whenever the combined height of the waves and high tide is over 20 feet, the island will breach again.”

“The reason that the breaches occurred was that this spot is immediately north of the center groin. The same thing happened with the 4 other groins in the groin field. Waves washed over the seawalls tearing away stairs, garage doors and washing large rocks and seawater into the streets and houses below.”

“The seawalls had slumped as the waves washed over and through them. The reason the new homes had no structural damage is that they were up on pilings, so the waves only washed away garages and stairs rather than slamming into the houses’ first floors. But several houses filled with seawater as the ocean overcame Newbury’s drainage systems.”

“Damage will continue to be inevitable in the center of the island as long as the groins remain. They should have been removed after the 2013 March storm, but at the time, people were convinced that this hotspot of erosion was caused by the offshore sandbar growing south. A few people still believe this despite the study done by the Woods Hole Group in 2016.”

“This sets up an interesting experiment. The state could remove the boulders from center groin and observe what happens. The breaching would stop and the beach would grow to be 60 feet wider at high tide and 100 feet wider at low tides as it is on either side of the groin field. Once people saw the changes they could move on to remove the other groins until the center returned to having a broad swimmable beach better able to dissipate energy and slow erosion. Now we would have to wait and see if it would happen.”