URI researchers: Hurricane Irene caused less coastal erosion then feared

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KINGSTON, R.I. – August 31, 2011 – Beaches in Narragansett, South Kingstown and Charlestown were lowered by about four feet due to the erosion of sand by Hurricane Irene, but a researcher at the University of Rhode Island said that beach erosion was considerably less than had been feared.

“The volume of change did not approach the magnitude of what happened during Hurricane Bob,” said Jon Boothroyd, URI emeritus professor of geosciences, who has monitored erosion on Rhode Island beaches since 1977. “Some of the displaced sand went over the top dunes and was deposited in the beach driveways and parking lots. Some sand went offshore, but some of that will come back.”

He said that municipal workers in the area are already collecting sand from some of the beach parking lots and preparing to return it to the beaches.

Boothroyd, doctoral student Bryan Oakley of Middletown and undergraduate Scott Rasmussen of Cumberland collected pre-storm beach profiles last Friday at Charlestown Beach, Browning’s Beach in Matunuck, South Kingstown Town Beach and Narragansett Town Beach. They returned on Monday to profile the same beaches and document erosion and other changes.

They found that the berm – the area where most beachgoers place their blankets – lost about four feet in vertical thickness of sand, causing the beach to slope downward more steeply.

“The beaches in Rhode Island are definitely eroding, but some years it doesn’t erode at all,” Boothroyd said. “If there are no storms, there is no erosion. If we have a winter without many storms, then some of that sand comes back.”

According to Boothroyd, five factors dictate the amount of erosion that takes place: the size and intensity of the storm, the speed of the storm through the area, the tidal phase, the path of the storm in relation to the beach, and the time between storms.

Irene was relatively fast moving and hit as the tide was dropping, but it also spread out over a large geographic area with a path that put Rhode Island where the strongest winds occur. Wind speeds only reached about 50 miles per hour, and the storm surge was just three feet, which was a foot lower than during Hurricane Bob.

Boothroyd said that the net movement of sand from Rhode Island beaches is from west to east along the shore. That means that much of the sand that is displaced from beaches in South Kingstown, Charlestown and Westerly ends up in Galilee Harbor, where it is dredged out periodically. About 4,000 cubic yards of sand is deposited in Galilee each year on average, with an additional 5,000 cubic yards ending up in the breachways in Charlestown, Weekapaug and Quonochontaug.

Pictured above

The calm before the storm at Charlestown Beach.