Posted by: coastlinesproject | August 17, 2015

Plum Island; The Next Folly, Shoveling Sand Against the Tide

The Latest Folly




On August 7, 2015 the Army Corps of Engineers presented a plan to dredge 370,000 cubic yards of sediment out of the Piscataqua River and dump it off Plum Island. The idea was that waves would winnow sand out of the mixture of mud and rocks and wash it ashore to protect Plum Island’s homes.


It was the latest in a series of Plum Island debacles. Groins built in the 1960’s created a hotspot of erosion in the Annapolis Way- Southern Boulevard neighborhood. An illegal seawall built in 2012, failed in 2013, 2014 and 2015. Merrimack River’s South Jetty, repaired in 2014. put 80 homes at risk on North Point.


All of the projects were done without proper sand transport studies and apparently even without reference to previous research. If a proper literature search had been done, the Corps would have discovered a nugget of shiny research amongst all the dreck.


In 1976 Dennis Hubbard wrote a paper for the Corps that explained that 90% of the time, during calm weather, longshore currents carry sand from the center of Plum Island north. It is only during those relatively few days when you have 8 foot high waves coupled with Northeast winds that sand gets torn off Salisbury Beach and by-passes the mouth of the Merrimack River to flows as far north as Annapolis Way.


The problem with the groins and jetties is that they interfere with this flow of sand that wants to repair the beach naturally. Until you let sand flow through the landward end of these structures any sand pumped onto the beach will simply be jettisoned out to sea near the Merrimack River and by-pass Annapolis Way. We will have flushed $1.5 Million dollars down the drain in another vain attempt to protect half a dozen houses which would be better off raised on pilings or be moved to less vulnerable locations.




Dr. Hubbard will be presenting his research on Plum Island as part of the Storm Surge lecture series 7:30, October 21st, at the Parker River Wildlife refuge.




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