Our shifting coastline
Outer Cape Cod is eroding. We often hear the question: What can be done to control the erosion? There are many temporary and partial answers of varying complexity and practicality, but the single final answer is very simple: nothing. Nothing can be done to prevent the erosion of the shores of Cape Cod.
- Graham Giese, Center for Coastal Studies, Provincetown
The Outer Cape is eroding. The National Seashore has for fifty years had a policy against sand nourishment. But in areas not under the control of the seashore, a cottage industry of consultants has sprung up to answer the the call to action. Countermeasures ranging from drift fences, coir rolls and erosion blankets to sacrificial sand and “biomimicry” have been deployed to stave off the inexorable creep of sea level rise and the pounding surf. But all the efforts of the erosion-industrial complex cannot forestall the steady and sometimes dramatic shape-shifting of the little spit of land we call home.
Graham Giese, a founder of the renowned Center for Coastal Studies in Provincetown, came into prominence for having predicted the dramatic punch-through storm that turned Monomoy Point, off the elbow of Chatham, into Monomoy Island. Dr. Giese’s article on coastal erosion, first published in 1974, and re-released in 1994, is as insightful, elegant and timely as it was fifty years ago. I have never read a more lucid, even literary, explanation of the coastal geology of the Outer Cape, and the dynamics of wind and wave that shape it from year to year. I recommend it to you.
I was blown away, for instance, to learn that Georges Bank, New England’s most celebrated fishery, was once a giant island. As sea levels rose after the last Ice Age, swallowing it whole, the Outer Cape lost an important buffer from the open ocean. The currents in Cape Cod Bay shifted at that point, with Wellfleet as the dividing line: North of Wellfleet, the coastal rip carried sand up the Truro coastline, eventually to form Provincetown’s spiral. Sand flowed to the south below Wellfleet, contributing to the tidal flats you see on your right as you drive off Cape, near Eastham.
It is that littoral flow of sand, parallel to the beach, along with the onshore wave action that jackhammers away at the toe of the coastal bank, that are the primary causes of coastal erosion. Sand either gets carried North, up to P-town, or joins the shifting sandbar that hovers offshore. Sea level rise, in progress since the last Ice Age and accelerating in our new “Anthropocene” era, intensifies both of these phenomena. In a few thousand years, the sandy heights of Truro will be exhausted, leaving Provincetown as an Island and all of Cranberry Hill underwater. (The least P-town could do is give us free parking!)
Giese takes a persuasive stance, one adopted by the National Park Service since the mid-1970s, on the futility of trying to control these coastline processes. We see an example of the National Seashore’s “managed retreat” strategy in the newly constructed parking lot complex at Herring Cove Beach. The planned revisions to Cranberry Hill’s beach access, and accompanying restoration of native vegetation toward the top of the coastal bank, are in line with this pragmatic and environmentally sensitive approach.
Mind you, Truro will be here for a long time - so let’s appreciate this fragile and unique land form while we can. We should all take to heart Professor Giese’s advice to “enjoy the magnificence of ever changing natural shoreline forms: towering cliffs, long sweeping beaches, reaches that change from hour to hour with the changing tides and winds.”
Originally published June 11, 2022