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Chesapeake Region Leads East Coast In Sea-Level Rise

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The Chesapeake Bay has areas which are experiencing among the highest rates of sea-level rise on the East Coast. This is because the ground in many areas is sinking.
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The Chesapeake Bay has areas which are experiencing among the highest rates of sea-level rise on the East Coast. This is because the ground in many areas is sinking.

Towns are starting to see the effects and they're bracing for it. But there's more than just climate change behind the rising tide.

The beach in Ocean City is a major tourist draw, it stretches hundreds of feet from the board walk, with giant dunes studded with grasses a little farther south.

This beach would probably not be here right now if it weren't for the fact that tons of sand are brought in every few years to replenish it, especially after major storms.

"Beach replenishment serves as storm protection for the town of Ocean City. It's the equivalent of the levees in New Orleans for us," says Terry McGean, the Ocean City beach engineer. "They dredge sand from a couple miles offshore, and we pump that material onto the beach and basically bring the beach back."

Storms and erosion aren't new, but there's something else going on here, that's making every storm a little more serious: Tidal gauges here have measured an increase in sea level. It's gone up seven inches over 30 years -- that's 5.5 millimeters per year, and almost two feet per century.

Dr. John Boon, a professor emeritus with the Virginia Institute of Marine Science, says the sea level is rising throughout this region, and some parts have it particularly bad.

"We have relative sea-level rise rates that are the highest on the U.S. East Coast," he says.

You may wonder why or how sea level rise might be any different here versus anywhere else.

"The ocean circulation moves water masses to different parts of the globe, and gravity changes as ice masses at the polar regions melt, there's differential heating in the oceans," Boon says.

But in our region there's an extra factor: The ground is sinking. It's called "subsidence," and Boon says it's been going on for a while now.

"Ninety-thousand years ago, we had a very large ice mass to the north of us, an ice sheet of almost a mile thick. This placed a great load over the earth's surface up there, and in adjustment to that we had what is called a glacial forebulge," he says.

It's somewhat like stepping into a mud puddle.

"You notice around your foot where it sinks in there's a little bit of a bulge that arises...The land is the same way," Boon says.

So when the glaciers melted, the weight to the north lifted and our area started sinking back down like a seesaw. As if that wasn't enough, towns in the southern Bay are paying the price for an asteroid that hit 35 million years ago.

"That crater has created some regions in the southern Bay that seem to have higher subsidence rates than elsewhere," Boon says.

And then, on top of all of that, we have sea-level rise caused by global warming -- something that many scientists expect will accelerate here.

The National Oceanic and Atmospheric Administration predicts sea level could rise in our region by as much as three feet over the next century. But the combination of all the different factors means the water is already rising everywhere in this region, and certain areas are seeing it more than others.

"People have noticed it with their piers and certainly...with storms over the last decade," says John Carlocke, a city planner for Hampton Roads, Va.

In Hampton roads, the rate of sea-level rise is currently about 1.5 feet over a century, if things stay the same -- let alone what's predicted with climate change.

"If we see a one-meter rise in sea level...considerable areas will flood...and you add a storm on top of that, and it's pretty ugly," he says.

Carlocke says they are starting to plan for it. Detailed studies are underway to figure out how to address flooding in certain neighborhoods, either with better drainage or pumping or barriers.

Back in Ocean City, engineer Terry McGean says building codes have been tightened to keep new construction and redevelopment higher up or further in from the water. But flooding has already become a problem around the bay separating Ocean City from the mainland.

"That's a tough one for us because, you know, the houses are where the houses are," he says.

If water levels keep rising the way scientists expect them to, at some point those houses won't be anywhere at all.

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