Flooding (copy)

As Charleston looks to update its Century V City Plan, rising sea levels, flooding and traffic loom as major concerns. Above, Morrison Drive during a recent high tide. Grace Beahm/Staff/File

The sea keeps coming in faster and faster.

Within 50 years, the sea off Charleston will be rising about one inch every five years — twice as fast as it was rising about a century ago and one-third faster than it was in 2000.

The number of days Charleston floods will go from 40 per year to as many as 70 per year, with progressively more ground flooding.

Charleston is combating sea rise flooding with projects that include raising the Low Battery walls at Charleston Harbor, as well as drainage and other improvements. That's designed to stave off an estimated 2½ feet of sea rise.

It won't be enough, said James Morris, a University of South Carolina civil and environmental engineering professor at the Baruch Institute for Marine & Coastal Research near Georgetown.

The improvements under way are necessary and will help in the short run "but going forward they will need to do more," he said.

Morris' findings will be in a study he plans to publish shortly.

"Sea level is now rising at an exponential rate," Morris said. "When you extrapolate that into the future, and even at the present exponential rate not allowing for acceleration, the rise is significantly greater than what a linear extrapolation would predict."

In other words, we'll be going under more quickly than simple-progression predictions indicated — and it will keep getting worse. Within a century, the seas will be rising an inch every four years.

As the creep and flooding speed up, so does the cumulative damage to infrastructure like buildings and roads.

Morris' findings — using tide gauge and other factors on the South Carolina coast — were specific to South Carolina. He says the numbers are likely conservative.

Mark Gould, of the Citizens Climate Lobby in Charleston, agreed those numbers are more conservative than other studies.

"Several reports indicate that sea levels in Charleston will rise faster in relation to land levels than the global average, due to subsidence and other factors," Gould said.

Morris' results echo recent findings by researchers at Tulane University, whose study of tidal gauges in the Mississippi Delta indicates the gauges were not sinking with the mud, not accounting for the fact that the land is subsiding or collapsing under the weight of rising sea.

"Around the world, communities in low-lying areas may be more vulnerable to flooding than we realized," said Tulane researcher Molly Keogh.

"This has implications for coastal management, city planners and emergency planners. They are planning based on a certain timeline, and if sea level is rising faster than what they are planning on that's going to be a problem," she said.

The South Carolina coast doesn't have that muddy layer, Morris said. But previous sea rise predictions haven't fully taken into account the acceleration of the rise, or haven't factored in the water seeping from polar ice melting in the ground. 

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Reach Bo Petersen at @bopete on Twitter or 843-937-5744.

Science and environment reporter. Author of Washing Our Hands in the Clouds.