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The Changing Shape of the Cape & Islands: Lewis Bay, from Hyannis Port to Kalmus Beach & Great Island

The changing shape of the Cape & Islands Lewis Bay: From Hyannis Port to Kalmus Beach & Great Island, May 2017 Cape Cod LIFE |

Aerial views of Yarmouth’s Great Island, looking northwest, and Point Gammon Light, located on the southern tip of the island. Main photo by Paul Rifkin. Inset photo by Josh Shortsleeve

“Two fundamental things have resulted in a wholesale dynamic change to the entire ecosystem of the bay,” “Two fundamental things have resulted in a wholesale dynamic change to the entire ecosystem of the bay,” Braginton-Smith says. “The first is the population growth around the bay and the resulting reliance of onsite septic systems. The second is the federal navigation channel.” The route ships travel from the Sound to the Inner Harbor was in 1940 designated a federal navigation channel, Braginton-Smith says, so federal funds could be acquired to dig a deeper, wider channel into Hyannis to further expand it as a port. Naturally, the larger channel allowed for more water to flow in and out of the harbor.

Dan Horn, Barnstable’s harbormaster, says this has caused some problems. “The flood tide coming in from the Sound is stronger than the ebb tide going out,” Horn says. “More water is being pushed into the harbor. This stirs up sediment and leads to shoaling. It has been a gradual process and it’s a mixture of natural and manmade causes.”

According to Braginton-Smith, the increase in tidal flow has caused some damage to the local ecosystem. He recalls the bay’s scallop harvest in 1965 yielding 1,500 bushels, while in 2016 that amount had dwindled to just 100. He says the vessel traffic that’s grown steadily since the channel was expanded has increased wave action in the bay to a scenario underwater that’s comparable to “an intermittent (when the boats are going by) mid-level storm.” And Horn adds, the harbor is home to more than 1,000 boats—especially during the summer.

Horn says the boating traffic has contributed to the intense shoaling in the Inner Harbor. The channel, which is maintained by the U.S. Army Corps of Engineers, was last dredged in 2013. Though Horn says it’s in pretty good shape today, he says there are a few spots that may soon need a touch-up.

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