Offshore sand could help replenish beaches – The Westerly Sun

NARRAGANSETT Frequent storms and sea-level rise will make beach replenishment increasingly necessary in southern Rhode Island, and there is more than enough offshore sand to do the job.

Bryan Oakley, an assistant professor of geology at Eastern Connecticut State University who monitors beach erosion, and URI oceanographer John King, who located the sand deposits, presented their findings at the University of Rhode Islands Narragansett Bay campus on Feb. 28 as part of Sea Grants Coastal State discussion series.

Westerlys most dramatic beach restoration was in 2014, after Superstorm Sandy damaged Misquamicut State Beach. The U.S. Army Corps of Engineers $3 million restoration effort involved trucking in 84,000 cubic yards of sand from an inland quarry.

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Oakley, who lives in Westerly and tracks changes to the profile of Misquamicut Beach, showed photographs of the beach before, during and after the replenishment of the beach, or berm.

They came in and put 65,000 cubic meters thats 84,000 cubic yards of sand, he said. It cost $3.1 million from glacial upland material .... After replenishment, one of my students said it looked a lot like a highway, not a bad description of it, about as soft as macadam if you were trying to sit on it that first spring.

Oakley said he wanted to see how long the new sand would remain on the beach, so he and his students mapped the area using a global positioning system. They created a model that showed that 39 percent of the sand had been washed away less than a year after the project was completed.

Thats actually not bad, Oakley said. Weve also had no major storms, and since January we havent been out. Well be back out in a couple of weeks, and were looking at some other techniques to get detailed pictures of sections of the beach and see if we can get a handle on some of the offshore distribution as well.

At $36 a cubic yard, upland sand is considerably more expensive than sand dredged from the ocean bottom, which costs $15. Oakley said the benefits of supporting a vital sector of the Rhode Island economy outweighed the expense of replenishment if those costs were kept low. Its economically practical when your rates are relatively low and the economic benefits are high, he said.

In comparison with states like New Jersey, the southern Rhode Island coast is relatively undeveloped, so beach replenishment here is less frequent.

If you think about the stretch from Watch Hill to Point Judith, weve got several large sections of undeveloped barrier beach, Oakley said. Quonochontaug, East Beach, Moonstone thats a great resource, and we should be happy we dont have this level of development that warrants running out and spending millions of dollars to dump a lot of sand on the beach.

Offshore deposits

King warned that sea-level rise would eventually render discussions of beach replenishment irrelevant. You kind of have to put this in the context of were in the midst of a slow-moving disaster of a magnitude weve never seen before due to global climate change, he said. And Im a climate scientist. So when these folks start talking about OK, were going to stop the ocean, I just say, Yeah, sure you are. You may slow it down for a while, but youre not going to stop it.

With funding from the federal Bureau of Energy Management, King mapped sections of the ocean floor in federal waters just outside Rhode Islands 3-mile limit. The goal of the project was to find a source of sand that would be large enough to be used for extensive beach replenishment initiatives.

With beach replenishment, you either go big or go home, he said.

Kings team first used sonar to determine the composition of the ocean bottom and the thickness of the sand deposits. They also took samples of the bottom to determine the quality of the sand. The upland sand used in the Misquamicut replenishment was coarser than natural beach sand and did not match the texture of the existing beach.

When youre doing this kind of thing, you not only need to know if its sand, you need to know if its high-quality sand, he said. King said he knew from looking at geological data that the best sand would likely be found off the coast near Charlestown, where it had been deposited when the glaciers retreated 20,000 years ago.

We sort of zeroed in on this area along the south coast, he said. Theres a thing called the Charlestown moraine, its like a long pillow, which is actually a glacial terminal moraine a big pile of material that builds up in front of an ice sheet.

In front of the terminal moraine was a huge lake, which was created by a dam made by the ice sheet and the moraine behind it.

So you had a very, very big glacial lake, and streams coming off of this ice sheet into the lake, forming big deltaic deposits. So these loaves of material are deltas that were actually debris coming from the melting ice sheet, sometimes underneath, a little bit over the top, carrying a lot of sand and gravel, he said.

Kings team decided to take a closer look at the sand and gravel deltas and created profiles of what are known as glaciodeltaic deposits, and they are huge. The newly mapped deposits are estimated to contain approximately 160 million cubic meters, or 209,272,099 cubic yards, of sand.

We have an order of magnitude more sand out there than we need anytime soon, King said.

The next phase of the project will involve a Special Area Management Plan of the areas where promising deposits have been found to determine the effects that mining the sand might have on the marine ecosystem.

The question is, can you go out there and remove 5 to 10 feet of this material without having a really devastating impact to the bottom, and thats a question we dont have an answer to yet, King said. Thats where the SAMP approach comes in. At some point, we have to talk about what are the impacts to habitat.

cdrummond@thewesterlysun.com

@CynthiaDrummon4

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Offshore sand could help replenish beaches - The Westerly Sun