When reporting on last week’s sewage spill from Haverhill, Mass., I queried Woods Hole for an expert on the likelihood of polling leaving the Merrimack River and going north along the coast, affecting New Hampshire beaches.
Rocky Geyer, an emeritus professor in the Applied Ocean & Engineering Department at Woods Hole Oceanographic Institution, got back to me but too late for any stories; Haverhill had put in a diversion pipe and the immediate problem was over.
Here’s what I learned from a short conversation: Due to the rotation of the earth and its effect on winds as well as the shape of the (relatively shallow) estuary at Newburyport and the shape of the coast, fresh water leaving the Merrimack River into the ocean virtually always goes south toward Plum Island.
“The tidal currents aren’t very strong. It kind of does whatever it wants to do, mostly affected by the western Maine coastal current” which travels south along the coast – as the term “downeast” reflects.
It is possible for southwest winds to push it north toward Hampton Beach but that’s a rarity, he said.
Geyer also discounted pollution concerns once the sewage plum reached the ocean because of dilution.
The situation was different in the river itself, as shown by testing by the Merrimack River Watershed Council that detected high levels of E. Coli bacteria for days even after the diversion pipe was installed.
