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Greg Hinson

Of course, it is always possible that a single storm can occur during a seven-year stretch of lower high tides and still cause considerable damage. (This happened during “The Perfect Storm” in 1991.) But what we are interested in here is probability: You are about four times more likely to have significant erosion during a proxigean month, when even a run-of-the-mill storm can ride in on tides that are several feet higher than normal.

There is another intriguing possibility: Some researchers think that the reason proxigean tides and La Niñas track so closely together is that the proxigean tides actually cause La Niñas by initiating the upwelling of cold water in the Pacific Ocean.

Some of this might sound esoteric, if not pretty darn complicated. However, if you are a homeowner, the knowledge of proxigean tides can be crucial, and it can help you decide whether your home will be safe for another five, 10, or 15 years. [See sidebar]. Proxigean tide tables can help town officials decide whether to give homeowners permission to build anti-erosion devices like seawalls or gabions to slow down the effects of sea level rise. Marine contractors can use knowledge of proxigean tides to forecast the years when business will be brisk and when it may be lean.

For now, we can expect mercy. We have just entered a stretch of mild erosion that will last for another seven years when we will be in the low part of the proxigean tidal cycle, and when the proxigean tides will coincide with the less stormy summer months. But this will only be a temporary reprieve. The tides will rise again.

William Sargent has been using Chatham as a case study for sea level rise for the past 25 years. He was a consultant for the NOVA film The Sea Behind the Dunes, and the author of Storm Surge: A Coastal Village Battles the Rising Atlantic and Sea Level Rise: The Chatham Story. His newest book, Nauset, Ten Thousand Years on a Barrier Beach, will be released by Strawberry Hill Press in 2012. He can be reached on his daily blog about coastal events at coastlinesproject.wordpress.com

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