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Study: Floods more common at Beach

Colonial Beach, Lewisetta and Gloucester Point are among the sites in the United States flooding more frequently—even during regular high tides—because of climate-related sea-level rise, according to a report from the National Oceanic and Atmospheric Administration.

“It no longer takes a strong storm or a hurricane to cause flooding,” said the report’s lead author, William Sweet.

Sweet, an oceanographer at NOAA’s Center for Operational Oceanographic Products and Services, said the effects of rising sea levels along most of the continental U.S. coastline are going to become more noticeable and much more severe in the coming decades, probably more so than any other climate-change related factor.

He said the report is meant to help communities understand the impacts of more frequent minor flooding events that exceed elevation thresholds set by the National Weather Service, called nuisance flooding. Coastal communities at or below the thresholds are particularly susceptible to flooding.

“The rare extremes, the direct hurricane strikes are catastrophic; they’re deadly. These are awful events for communities,” said Sweet. “They recover, they rebuild, they respond.

“But these lesser events will have a cumulative toll in time and I don’t think this is widely recognized or understood by people living in those areas.”

Nuisance flooding causes road closures, overflowing storm drains and compromises infrastructure, the report said. Recent storms in the Fredericksburg area have caused flash flooding.

Stephen Gill, chief scientist at the NOAA Center who also worked on the report, said a variety of factors are affecting the Virginia region, but the mix of rising waters and sinking land is most noted for its impact on islands disappearing out on the bay.

Scientists believe the ancient impact crater at the mouth of the Chesapeake Bay, where a comet or asteroid hit the earth some 35 million years ago, is filling in. NOAA data show water around the Chesapeake Bay Bridge–Tunnel is rising at about 6 millimeters each year, and nearly 2 feet every 100 years, the fastest of the seven stations.

Lewisetta waters are rising 1.63 feet every 100 years at a rate of 4.97 millimeters annually, while Colonial Beach waters rise 1.57 feet every 100 years at 4.78 millimeters annually. That’s about 2 inches every 10 years.

NOAA has been collecting data at 45 stations throughout the United States. In Virginia, from the Chesapeake Bay Bridge–Tunnel up along the western shores of the bay to Colonial Beach, there are seven stations, some dating back to 1935. Colonial Beach had a station since 1972 but it was knocked out by Hurricane Isabel. This year it’s being replaced by a new location at the Navy base at Dahlgren.

Scientists said the extent of nuisance flooding depends on multiple factors, including topography and land cover. Sweet said the sites studied were chosen with the aid of local weather forecasters, who use elevations on tide gauges at certain stations to issue flood warning and forecasts.

The study used historical data from the 45 stations and compared that to reports of numbers of days of nuisance floods. They also relied on anecdotal evidence from communities.

“The living memory of these communities will recognize that things have changed,” said Sweet. “That’s a first step to being prepared and to facilitate a discussion that needs to be had about adaptation.”