Posted by: coastlinesproject | September 22, 2012

Chatham, MA North Beach Island. Erosion in a double inlet barrier beach system.

SEPTEMBER 6, 2012 • THE CAPE COD CHRONICLE 7

Inlet Changes Cause Erosion To North Beach Island

by Tim Wood
CHATHAM — Recent aerial photos of North Beach
Island show the loss of sand along the outer shore near
the northern tip, an area that had built up extensively prior
to the Cape Cod National Seashore’s March removal of
camps in that area and elsewhere on the island.

But the camps probably have very little, if anything to
do with the erosion.

Rather, the change appears to have more to do with a
change in the location of the channel through the 2007
inlet, directly to the north, which runs along the outside of
the barrier island, according to Coastal Resources Director
Ted Keon.

The build-up of sand occurred last year after the channel
moved to the north, jumping the outer bar. That bar then
moved onshore, creating a wide, sandy beach in front of
the Crowell camp and along a large length of the outer
shore on the north end of the island. That build-up was
“frankly impressive and surprising,” Keon said, since
prior to that erosion of that shore had been the general
trend, and one of the main reasons cited by the Seashore
in its decision to demolish five of the camps it owned on
the island.

The aerial photos taken in late July show most of the
accretion is gone. The change, said Keon, relates to the
inlet channel switching to a “very severe” north-to-south
orientation from the more east-west orientation that allowed
the bar to come ashore and build up the beach.

Such a change could happen again, Keon suggested.
During certain tides, boaters are able to travel directly
east of the inlet; it appears the channel is trying to break
through the existing bar at the inlet throat. He was on the
beach early Friday and at dead low tide there was “still a
lot of water flowing” directly east over the bar.

“I can’t predict whether it will or won’t” break through
and repeat the previous accretion, Keon said. “But it wouldn’t surprise me if it did.”

The aerial photos otherwise show that the beach is
behaving pretty much the way scientists had predicted.
The 1987 inlet opposite Lighthouse Beach continues to
accumulate sand, presumably because the 2007 inlet is
receiving a greater flow of water. Eventually, as scientists
have predicted, the 1987 inlet could close up completely.
When that will happen is impossible to predict, Keon said,
but it won’t be soon. “It isn’t next week,” he said.

Even though there’s a lot of sand swirling around in
the harbor and just offshore, the inner harbor channel
has benefited from the current situation, Keon said. A
diminished current between the old inlet and Aunt Lydia’s
Cove means less sand being pushed into the navigation
channels, which has reduced the need for dredging. For
a number of years, the Army Corps of Engineers dredge
Curituck made an annual visit to the harbor to clear sand
from the channels. The dredge did not pay its yearly early summer visit to Chatham Harbor this year.

“We have fairly good navigation channels that don’t need much mitigation now,” Keon said.

The long-term issue that concerns Keon is what will happen when the 1987 inlet shoals up so much that navigation becomes difficult or impossible. That inlet is still
heavily used by fishing boats and recreational boaters, and
may not be easily dredged. And if dredging is necessary
to keep a channel open to the 2007 inlet, where will that
dredged sand be placed?

The closest location would be North Beach Island. However, the island – even the private and town-owned portions – are within the Cape Cod National Seashore, which has in the past said it will not allow dredged sand to be placed within its jurisdiction.

“You’re getting farther and farther away from the open,
sandy beaches on the mainland side,” Keon noted.

E-mail Tim Wood at twood@capecodchronicle.com

Read more in Tim Woods’ Breakthrough and Beach Wars; 10,000 Years on A Barrier Beach. See Strawberry Hill tab at the top of this page.

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