As I See It: ‘All Models Are wrong; Some Are Useful’, Bill Sargent Mar 20, 2023


In 1976, the British statistician George Box wrote, “All models are wrong; some are useful.”

The father of today’s generation of coastal geologists, Orrin Pilkey, did him one better, saying historical data is always more useful than a model when you want to determine what will happen when you alter a beach.

We have several historical examples on Plum Island. In the late 1960s, the Army Corps of Engineers fortified the Merrimack River’s south jetty, which cut off the natural flow of sand. This initiated 100 feet of erosion off Plum Island Point’s Reservation Terrace.

By 1969, the erosion was threatening the Coast Guard Station, then off 69th Street, so the engineers added a spur to the jetty. But the spur simply speeded up the erosion so the station had to be demolished in 1970.

In the following years, Newburyport built concrete walls and constructed huge sand berms that were immediately washed away, leading then-Mayor Byron Matthews to note, “All the dunes were leveled. It has been like we couldn’t do anything to stop it.”

But then nature intervened, and the Blizzard of ’78 disheveled the south jetty, creating a natural weir. The weir allowed sand to flow through the jetty, causing the beach to grow again at the rate of a hundred feet a year.

This happened until 2012 when models and politics were used to convince the Corps to fortify the jetty once more, and as happened only 20 years earlier, the beach returned to eroding a hundred feet a year.

Now, some residents are pushing the Corps to produce a model to show that fortifying the spur will work this time. Experience, however, should tell us that history will just repeat itself.

Any coastal geologist will tell you that this plan will not succeed and that rather than spending valuable time, money, and effort fortifying the spur, we should keep our eye on the prize and work with the Corps to cut a weir in the jetty which is often done in these situations.

The Town of Sandwich is working with the Corps to build a weir in the jetty, stabilizing the Cape Cod Canal. It is the only solution that will work in either case.

Right now, the Corps has less than five weeks to complete dredging their 15-foot deep channel in open water at the mouth of the Merrimack River. Long-term weather reports forecast that our present cold, windy weather will continue through March because the polar vortex has herniated out of the north.

We can only hope that the wind, tides, and storms will hold off, giving the Corps the narrowest of windows to pump the dredged sand on the beach to protect the Reservation Terrace houses through the end of this year’s erosion season.

One bright spot in this situation is that the owners of the Captain’s Lady have offered Newburyport close to 100 truckloads of sand that the city can put in front of the homes on Reservation Terrace.

This would be considered a “dry sand borrow” that has already been permitted by city, state, and federal officials. It also shows how much faster such local initiatives can be than waiting for a slow-moving federal bureaucracy like the Corps.

The other bright spot is that nature may solve the problem for us. Part of the jetty has settled almost 3 feet and that area seems to have widened this year.

To date, more sand has flowed through this natural weir than has been pumped onto the beach by H&L, the contractor that provided the lowest bid on the project.

The situation brings up the issue that what Massachusetts really needs is its own coastal geologist to help coastal residents decide what will and won’t work to slow down erosion.

He or she should not be part of a permitting agency like the DEP but be like a public defender there to offer help and guidance to residents facing the dual threat of coastal erosion and sea level rise.

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