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Sea level rise in Southern Maryland is too gradual for most people to notice. But a Solomons Island tidal gauge records that it has been creeping up 3 millimeters a year.

A University of Maryland study released last month calls on the state government to plan for the sea level to rise by 2 feet along the state’s shoreline by 2050 and up to 4 feet within the next 100 years, if not more, based on global warming, the melting of ice sheets and the sinking of land, called subsidence.

In St. Mary’s County, any significant rise in sea level would put areas of Scotland and Point Lookout underwater in the future, said Sue Veith, environmental planner with the St. Mary’s County Department of Land Use and Growth Management.

A rise in the Potomac River threatens much of St. George Island and areas of Piney Point. The White Point area of Leonardtown and sections of the Golden Beach neighborhood in northern St. Mary’s would be affected.

A sea level rise of 2 feet could affect 461 homes in St. Mary’s County. A rise of 4 feet could touch 1,055 homes, according to an analysis by the St. Mary’s County Department of Emergency Services and Technology.

Already “St. Mary’s County is within an area that has experienced nearly 8 inches of subsidence in the last century. This subsidence combined with rise in tidal waters has resulted in 1.08 feet of sea level rise reported by the National Oceanic and Atmospheric Administration for the tidal gauge in Solomons Island measured between 1937 and 1999,” says the St. Mary’s County Multi-Jurisdictional Hazard Mitigation Plan.

Throughout the state, the rise in sea level may impact 3,100 miles of tidal shoreline and other low-lying lands within 37 years, according to the University of Maryland Center for Environmental Science. Maryland has 7,700 miles of shoreline, according to the Maryland Geological Survey.

The Chesapeake Bay is rising at a rate two to three times faster than the worldwide rate, according to reports by the Capital News Service. While sea level throughout the world rose by an average of 4 to 8 inches during the 20th century, it came up by a foot in the Chesapeake region.

The land is sinking because of vertical movement of the continental tectonic plate and locally, by the pumping of water out of underground aquifers. “Aquifers compress when you don’t have water in them,” Veith said.

According to the Federal Emergency Management Agency’s coastal flood plain maps, there are 2,331 properties in St. Mary’s in the flood zone. “Most of them are coastal shoreline,” Veith said.

St. Mary’s County has 536 miles of shoreline, according to the Maryland Geological Survey, more than any other county on the western shore of the Chesapeake Bay.

Even a rise of “6 inches makes a huge difference,” Veith said, as marshland expands into more low-lying areas. Wet land threatens the viability of septic systems, which the majority of households in St. Mary’s use.

Maryland law already heavily regulates development on the water through the Chesapeake Bay Critical Areas Program, which affects lands within 1,000 feet of tidal waters. Adding impervious surface is limited and clearing vegetation is mitigated.

New lots cannot be created in floodplains, Veith said, and depending on how close a new house would be built to the water, it would have to be elevated above the potential wave action during a storm surge. “They have to do it. It’s not an option,” she said, if the home is to be covered by federal flood insurance.

In the future, to comply with FEMA floodplain regulations, disclosure to a home buyer may be required if a home is in a storm surge area or prone to sea level rise. “A lot of realty people don’t want us to do that — that’s going to kill a lot of waterfront” sales, she said.

Veith said she looked initially at buying a property herself on St. George Island, where elevations range from sea level and up to 8 feet at isolated points. She ended up in Hollywood in a house 16 feet above sea level, which is still susceptible to storm surge, she said.

“I wouldn’t buy one, personally,” she said of houses on the island. “If not all, then 95 percent of it” is in the flood plain.

“We got a captive audience down here on St. George Island,” said Jack Russell (D), president of the St. Mary’s commissioners and a resident of the island since 1970.

He lives on Island Creek, on property 2.7 feet above the water. Over the years, he said, he’s noticed changes. “The tides seem like they’re much higher now. It seems like it’s more extremes now,” with more erratic weather, he said.

Several sections of roads on the island go underwater during high tides or storm surges. In some sections, the only solid ground is the road, flanked by marshland.

Russell said he would be interested in getting an estimate to elevate portions of the roads prone to flooding, perhaps establishing taxing districts to pay for the work. “It would be a tremendous bill, but one worth knowing,” he said. A native of nearby Piney Point, Russell recalls his mother telling him of ballfields and orchards on one side of the state road, now claimed by the Potomac during decades of erosion.

Already 13 islands have disappeared in the Chesapeake Bay. Smith Island, home to a community of watermen, could be gone by 2025, according to the Capital News Service.

Off the shoreline of St. Mary’s, Heron Island is now gone, washed into the Potomac. Erosion gnawed St. Clement’s Island down from around 400 acres in 1634 to its current 62 acres. St. Catherine Island was 180 to 200 acres in 1634 and is now just 30 to 40 acres, wrote Jefferson Glassie in his history of the island, “My Love Affair with an Island.”

jbabcock@somdnews.com