Outer Banks Coastal Research – Building Up
Music; Ambience Ocean waves, wind
We often hear about the erosion of coastlines, but beaches can also rebuild and grow. I’m Jim Metzner, and this is the Pulse of the Planet.
“One of the things, in fact, that goes on over the long term is when the beach is not eroding, when there’s not a storm causing erosion to occur, the beach is rebuilding.”
Bill Birkemeier is director of the Army Corps of Engineers Field Research Facility on North Carolina’s Outer Banks.
“We always hear how erosive things are and how things are washing in to the ocean, but in between those events the sand’s returning to the beach. It’s a slow, steady, bit by bit, grain by grain process, so it’s not as dramatic as an event from a storm. But we wouldn’t have beaches if the movement of sand was only one direction, erosional. We wouldn’t have beaches at all. They would’ve long ago disappeared.”
So how does a beach recover?
“If you can imagine a particle of sand, which has a certain size, our beach has a mix of sand size grains and also gravel size grains, and that sand is pulled up into the water column by a breaking wave, and then as it falls back-waves are orbital, so there’s a forward motion and a backward motion in every wave that goes by. And so, if that grain of sand falls on the forward motion, it moves toward the beach. If it falls on the backward motion, it moves offshore. When storms are coming in, we tend to have strong backwards motion, and the finer sands are up higher in the water column so that it takes them longer to fall, and they fall on the backward side. Now, what’s interesting is that we can have a storm event with the right kinds of waves. The perfect storm of 1991 had waves so long that we were actually moving gravel toward the beach as the finer sand was moving offshore. We had large deposit of gravel on the beach, very unusual for the east coast.”
We’ll hear more about coastline research in future programs. Pulse of the Planet is made possible by the National Science Foundation. I’m Jim Metzner.