Rising seas hamper flood-control efforts

Sea levels play a large role in coastal flooding and stormwater drainage, issues that have been causing problems on the Charleston peninsula for hundreds of years.

As the city said in an explanation of why the peninsula regularly is flooded, “The height of the tide has one of the greatest impacts on how quickly stormwater will drain from the city.”

That’s because streets and pipes drain into tidally influenced rivers and the harbor, where the water level can rise 7 feet or more from low tide to high.

“At high tide, much of the stormwater collection system is already full of sea water, leaving little room for the stormwater runoff,” said the city’s paper on drainage problems.

It’s a problem that has been getting worse with rising sea levels.

According to the National Oceanic and Atmospheric Administration, the number of high tides in Charleston with the potential for flooding has increased greatly.

For example, from 1960 through 1990, there were only four years with more than 10 flood-level high tides.

From 1990 through 2010, all but two years had at least 10 flood-level high tides.

The sea level around Charleston increased at least 9 inches during the last century. Intermediate-range scenarios for sea-level rise in the United States by 2100 range from 19 inches to 3.6 feet, NOAA reported in December.

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