- The Washington Times - Tuesday, July 25, 2017

Virginia officials are testing the stability of an ancient landmark — Natural Bridge in Rockbridge County — amid concerns about the arch’s sturdiness after decades of supporting part of U.S. Route 11 (Lee Highway).

The Virginia Department of Transportation is beginning its tests of Natural Bridge as the land around the massive limestone arch officially has become a state park.

Lynn Crump, environmental planner at the Virginia Department of Conservation and Recreation, says the bridge’s transition to an official state park brings with it a great deal of responsibility.

“We have to make sure the resources of the park are there in perpetuity for all generations to come,” Ms. Crump told The Washington Times. “Natural processes happen, and arches like this have been crumbling around the world.

“Some significant arches — like Stony Man in New Hampshire, the Azure [Window] arch in the Mediterranean — have actually fallen already, and our concern is that the geological processes may be exacerbated by the continuous traffic on top,” she said.

A naturally formed limestone arch, the Azure Window in Malta collapsed into the sea after a strong storm in March.

According to VDOT spokeswoman Sandy Myers, the stability testing of Route 11 could begin as early as this week. Geologists will use ground-penetrating radar, which can produce images of subsurface structures, to search for weaknesses in the highway’s roadbed.

Natural Bridge currently supports some 2,000 vehicles on a daily basis, and often is subject to even heavier use.

“Route 11 is the primary alternative route if there is any closure on [Interstate 81], so there could be hundreds of cars going over it when there’s a closure to 81,” Ms. Crump said.

That’s why, she said, a park planning committee recently discussed the possibility of closing the bridge to traffic and building an alternative highway route along Natural Bridge State Park’s northern end.

But the committee’s more immediate concern is the danger of loosened rocks falling from the 215-foot-tall arch — the remnant of a tunnel through which Cedar Creek flowed that is estimated to be about a million years old.

Louise Cathy, a tourist from Georgia, was killed in 1999 after being struck in the head by a rock at Natural Bridge. Her death prompted an evaluation of the arch’s structural integrity the following year, but the investigation concluded that any falling rocks were merely part of natural erosion and not caused by highway vibrations.

The evaluation, however, did note that “common sense would indicate that any vibration” from highway traffic could have the tendency to loosen the arch’s rocks.

According to Skip Watts, a geology professor at Radford University, that report provided nothing concrete in terms of evidence for long-lasting stability.

“The question is how much [vibration] is enough over time to cause some deterioration, and that’s a question we never got a very good answer to,” he told The Roanoke Times.

The 17-year-old evaluation remains the most recent of the bridge’s stability, but as the potential of eventually closing the bridge to traffic becomes more likely, the need for a new evaluation has become more pressing, Ms. Crump said.

“If we are looking at rerouting Route 11 off of the bridge at some future date, that whole process can take decades,” said Ms. Crump. “So if a study is needed before an alternative route is considered, we need to get started on it.”

 

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