Continued from above....
If or when a breach does occur, according to beach manager Culbert, it will probably be during a strong northeasterly gale. This may seem counterintuitive, since such a wind puts Norton Point in the lee. But the mechanism of a breach is not expected to be the pounding of the Atlantic surf on the South Shore; rather, water packed into the bay by the combination of a high tide at Edgartown and a northeast wind will burst through to the open ocean.
It is said that a northeast storm opened up the beach about six months after it first closed in 1792. Over a century and a half later, the actual process was observed at alarmingly close range by J. Gordon "Pete" Ogden 3rd, during an intense storm on Aug. 31, 1954 (a good summary of his account appears in Anne Hale's "Moraine to Marsh: A Field Guide to Martha's Vineyard"): Pounding waves had thinned the beach to only 50#^&75 feet, and a combination of tide and storm surge had jacked the Katama Bay water level well above that of the ocean outside. Under the Katama Bay pressure-head, underlying sand went "quick," flowing outward as slurry. The beach collapsed, and within hours the ensuing gush of water had scoured out a 300-yard opening. Under sunny skies the next day, Ogden reported, the breach looked as if it had always been there. To read of such a cataclysm is to understand that Mr. Culbert had public safety in mind when he announced the possibility of a breach: anyone caught in quicksand, the beach collapse, or the resulting violent erosion would be in deep, deep trouble.
Mr. Culbert emphasizes that there is no certainty a breach will occur, by this mechanism or any other. Basically, he says, a short stretch of beach has been subject to unusually fast erosion: "We've lost 200 to 300 feet there since December 1999," he says. What caused this acceleration is uncertain, but it is likely that a gap in an offshore sand bar has allowed ocean waves to smack the beach here unimpeded. A quarter-mile or so of beach has run out ahead of the more gradual northward march of the beach as a whole, finally cutting into the dunes that form the backbone of Norton Point. Mr. Culbert says that the inside and outside high tide lines are currently just 100#^&120 feet apart at this point, making a replay of the 1954 breach seem just one strong nor'easter away.
From the scientist's perspective, part of the fun is trying to predict what will happen, and Mr. Culbert clearly relishes analyzing the situation. One factor working against a breach, he speculates, may be the historical reduction in the size of Katama Bay. Accumulating sediments, including a load dumped into Mattakesett Bay (near the end of the "Left Fork") during a short-lived breach in the early 1980s, have gradually filled shallow fringes of the bay. Moreover, the northward progress of the beach has whittled away at the bay, which is shaped like a funnel with its wide end to the south. Mr. Culbert wonders whether the bay can hold a volume of water sufficient to generate the forces needed for a breach. If it cannot, then the era of Chappy as the "separated island" might be over for good.
If even the likelihood of a breach is up for discussion, the consequences of a breach are necessarily the subject of even more tenuous speculation. The right wind and current conditions could presumably close the breach almost immediately, leaving little in the way of long-term effects. On the other hand, a wide breach that persisted for decades would substantially alter the flow of water through the bay, with unpredictable but potentially enormous effects on the area's ecology.
Tides on the north and south shores of Edgartown are out of phase: high tide at Eel Pond falls some two hours from low tide at Norton Point. With the barrier beach intact, Katama Bay fills and drains through its single opening at Edgartown harbor, breathing with the rhythm of the Nantucket Sound tide cycle. With a cut in the barrier beach, however, the bay would be filling from the high-tide end as it drained at the low-tide end; the result would be a current through the bay, changing directions four times a day. The tide might be rising or falling at both ends simultaneously for a brief period during each tidal cycle, with results difficult to predict. Stronger currents might move more sediment than the present-day tidal flow, deepening channels and scouring shallow portions of the bay, and tidal flow might carve a hole or trench in the sea floor outside opening.
Whatever the details, increased water flow in Katama Bay could have significant consequences for wildlife. More thorough flushing would probably improve the water quality in the bay, fostering populations of clams and scallops. Nesting and migrating shorebirds, gulls, and terns, and the sea ducks that winter in the region, all stand to gain or lose, depending on how their foraging habitat and prey populations are altered. Finfish would congregate around the beach opening, as they do when the great ponds are opened to the sea, and one can easily imagine pirate fleets of bluefish gnashing their way straight through from the Atlantic to Edgartown and back again.
If Norton Point is breached, the event will receive far more scientific scrutiny than has any previous such occurrence. But it's a sure thing that following every major change in Norton Point Beach, Vineyarders have rapidly developed an unscientific but thoroughly practical grasp of how the bay's ecology has responded. This is a kind of knowledge, though, that tends to be acquired by personal experience, spread by the spoken word, and recorded mainly in the memory of those whom it affects. Perhaps that's why the possibility of a breach is so fascinating: in a community closely linked to the sea, a lot of people just think it would be fun to see what happens.
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Original reply from Fisherwoman at 10am 3/10/01
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Great article JohnR, But I really don't want to see that happen, otherwise our early trips to Wasque will be eliminated, not a good thing when the albies are around and the Chappy ferry doesn't run till 7:00 AM. Not good news for shore, we have seen that beach disipate dramatically in the last 5 years, hope it holds out for another fine year of fishing.
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