National Seashore Trying to Understand, Adapt to Erosion Hotspots

Visitors to the Cape Cod National Seashore this summer will likely notice changes at some of the beaches. At Nauset Light in Eastham, there is now a long path down to the beach, instead of a staircase. And at Marconi in Wellfleet, there’s a brand new staircase for the second year in a row.

Both beaches seem to be hotspots for erosion right now. And the Seashore is trying to adapt.

Mark Adams’ office, in North Truro, is full of maps.

“If you look at Cape Cod, it’s this beautiful curve. It’s almost like a mathematical curve,” he said. “That’s the sum total of all this wave energy, all of these forces that are consistent enough to make a beautiful shape.”

Adams, the long-time geographer for the National Seashore, said that beautiful shape is proof that over the long-term — a 100 or 200-year time span — the Outer Cape is eroding pretty consistently, about 3 feet a year, all up and down the coast.

“But in the short term those forces are chaotic, and so waves come from all directions.”

So if you were to zoom in on that curve of the Outer Cape over a much shorter time span, maybe five or ten years, it would be more jagged.

Those are “what are called hotspots,” said Karst Hoogeboom, the chief of facilities and maintenance at the National Seashore. “Where we’ll have a lot of erosion in one area, and then all of a sudden from one year to the next we might not have any erosion.”

Hoogeboom is very aware of where some of those hotspots are, such as Nauset Light, and, more recently, Marconi. Places where the dunes lose closer to 15 feet a year, or sometimes even more.

But these erosion hotspots aren’t fixed; they shift around.

And after five years in a row of having to replace the staircase down to the beach at Nauset Light, Hoogeboom said, now “the erosion seems to be slowing down just a little bit and we may no longer have a hotspot there, but we don’t know yet.”

How often the hotspots shift, and why, is still somewhat of a mystery. One that Mark Adams says they’re getting closer to solving, in part by observing waves.

Not far from his office in North Truro is one of the highest spots on the Outer Cape — a steep, jagged dune 130 feet above the beach.

Just back from the edge, looking out over a wide expanse of blue, is a tiny moveable wooden shack with a sign that says “wave observation lab.” A volunteer comes here every other day to count waves.

“When we measure erosion we measure the results of the waves. When we count waves, we’re measuring the forces that created the erosion,” Adams said. “And so they’re two ways of looking at the same question. Hopefully together they give us a more complete picture of what’s driving our erosion.”

One thing driving erosion hotspots is underwater sandbars, and the channels that form between them, perpendicular to shore.

And sometimes, Adams said, pointing out at the surface of the water, “at some of the hotspots, you might see a big plume of sand where the water’s carrying the sand back out beyond the bars.”

That’s also where you’d likely find a rip tide. Where there’s nothing offshore to break the energy of waves rushing in — or back out.

In the places where these hotspots are occurring near buildings or stairs or parking lots, the National Park Service is trying to get ahead of nature, Hoogeboom said. “The park is sort of at the forefront of pulling back from the shoreline wherever we can.”

They’ve already pulled back at Nauset Light. During the off-season, they tore down the bathrooms, which were getting dangerously close to the edge of the dune, and abandoned the wooden staircase altogether, in favor of a long, winding path to the beach. And at Herring Cove Beach, in Provincetown, the recently-built bath house and snack bar were designed specifically to be easily moveable, when the ocean gets too close.

Then there’s the north parking lot at Herring Cove, which, at the moment, is one of the hottest spots for erosion at the National Seashore.

And it’s obvious, when you drive up. There’s a tell-tale double yellow line — a dead giveaway that years ago, this parking lot was a road — that now leads straight into the sand, and the edge of the pavement is curled and crumbling.

“Several hundred cars used to park here,” Adams said. “The parking lot extended out to where the beach chairs are now on sand.”

But in just the last two years, he said, much of it has been claimed by the ocean. The National Seashore is planning to move the parking lot back, to where the road is.

And since this spot — for now at least — is eroding so fast, the plan is to pave it with gravel, instead of asphalt, because there’s a good chance it won’t be long before at least part of the new lot also winds up in the ocean.

“The legislation that made the Seashore tells us what our mission is here,” Adams said. “In essence, the Seashore was created for the enjoyment and use of everyone. And also to allow natural processes to take place.”

That means letting erosion happen, instead of trying to fight it. And it also means finding new ways to keep these beaches — and all their shifting natural beauty — accessible to everyone.