For the past 50 odd years scientists have concluded that Plum Island behaves like any other barrier beach with a system of beach-building longshore currents and protective offshore sandbars.
That view has been largely countered by those of dog walkers, surfers and homeowners who argue that Plum Island is unique and that a complex pattern of wind, waves and currents build a sandbar that grows south creating a traveling hotspot of erosion.
Now we have a new study that may help clarify the situation. Chris Hein from the Virginia Institute of Marine Sciences has long argued that Plum Island is unique among barrier beaches because its drumlins make it so stable.
Then in mid-May he published research that revitalized the argument that Plum Island is unique and that a complex pattern of wind, tides and waves push the ebb tide delta of the Merrimack River south creating a hotspot of erosion that travels from the Center Island groin to the Annapolis Way and Fordham Way groins over a 25 to 40 year cycle.
One thing scientists try to do is avoid confusing the noise in a system from the signal that is actually driving the system.
The other thing they do is look for the simplest solution that fits their data. So the traditional scientific argument would say that the most parsimonious theory that fits Plum Island’s dynamics is that it is the groins themselves that create the erosion. They do this by redirecting the longshore currents offshore where they break up the parallel sandbars that normally protect the beach.
Evidence for this argument is that the Buzzotta house and the seven houses that were washed away or had to be moved in 2013 were immediately downstream of the jetties, and that the 2013 damage happened along the entire groinfield – not in just one particular hotspot.
But having stated my skepticism that the 25 to 40 year hotspot cycle is not as definitive as presented, I am also impressed with the implications of this theory.
The theory means that the south jetty works in tandem with the groins to create a perfect storm of erosion. The jetty pushes the erosion complex south where the groins pin it in place so it can wreck its havoc on Newbury’s beach homes.
So instead of hiring a former Army Corps engineer to lobby to have the jetty repaired, Newbury homeowners should have lobbied to have the Army Corps take the time to design a shorter more effective jetty and remove the groins.
So I applaud these geologists for switching their attention away from what happened thousands of years ago, to what is happening today. It takes guts to step out of your comfort zone and help solve real world problems.
It is this kind of local focused research that the North Shore will also need if it buys its own dredge. Such research will allow local communities to bypass the cumbersome Corps of Engineers and find and use their own sinks and sources of sand to build berms and dunes to protect their beaches while also keeping their rivers open for boating and navigation.
Bill Sargent is a North Shore science writer and contributing columnist. His most recent book, North of Boston, Living on the Edge of a Warming World is available in local bookstores and through http://plumislandoutdoors.org, and at www.ingramcontent.com.