Officials: Landslide locations are tricky to predict
May 18, 2014 11:30 PM
Construction workers place steel posts for a new retaining wall along the Norfolk Southern Railroad tracks along West Carson Street at the site of an April 8 landslide that blocked the tracks.
By Kaitlynn Riely / Pittsburgh Post-Gazette
A landslide, unlike a hurricane, is not a phenomenon whose location forecasters can pinpoint.
They can be predicted, because heavy rains are often triggers for landslides that are caused by geology and slope, said engineer Michael Edwards, a vice president for the Pittsburgh-headquartered Paul C. Rizzo Associates Inc. engineering and consulting firm.
But saying exactly when, and exactly where, a landslide will occur is difficult to do.
"It's like an earthquake," he said. "You're not going to know where it will surface."
One surfaced last week, after heavy rains from Thursday into Friday caused a small mudslide that closed a section of McArdle Roadway on Mount Washington for a few hours Friday as crews cleaned it up.
Pennsylvania's geology and geography, especially in the southwestern portion of the state, contribute to frequent landslides, said Helen Delano, senior geologic scientist for the Pennsylvania Geological Survey under the state Department of Conservation and Natural Resources.
But there is no formal statewide monitoring program for landslides, she said. Instead, communities tend to pay attention to areas that previously have been prone to landslides and keep an eye on slopes with similar characteristics.
"It's a lot more complicated when you actually sit down to do it," she said.
In Pittsburgh, the Public Works Department uses a "three-tiered system" to oversee hillsides that are on city property, spokesman Tim McNulty said in an email.
The city has a two-page "watch list" of all hillsides known to have the possibility of landslide issues. And then it has an immediate list of hillsides that engineers have determined could be at risk of landslides or other problems, Mr. McNulty said. For those hillsides, the city will pre-emptively close the surrounding streets to stabilize them.
The city also heeds citizen complaints, 311 calls and observation by Public Works supervisors to alert officials to problems with hillsides, which are then added to the city's watch list, he said.
On Mount Washington, one of the hillsides in the city that has been prone to landslide issues, staff with Mount Washington Community Development Corporation are among those keeping watch, said Ilyssa Manspeizer, the development group's director of park development and conservation.
"We keep an eye on all of the hillside in Emerald View Park so that we can tell the city if we notice any change in the landscape and alert them to the location," she said.
The landslide lookout is not just happening in the city.
Within Allegheny County's Public Works Department, employees visually inspect hillside areas on a regular basis, and are aware of problem spots, in some cases using fences or retaining walls to prevent debris from potential landslides from reaching the road, county spokeswoman Amie Downs said.
Maintenance managers for the Pennsylvania Department of Transportation also are on the lookout for vulnerable hillsides, said Steve Cowan, spokesman for District 11. The agency attempts to mitigate inevitable landslides using approaches such as installing fencing and steel netting to protect roadways, he said.
Even with those precautions, he said, "It's nearly impossible to know when or where a landslide is actually going to occur."
Still, the state agency can look to historical patterns to get a sense of where the landslides will occur. Landslides have happened on Route 28, Interstate 79 between Bridgeville and I-376, Route 65, Route 51 in the West End and the Boulevard of the Allies, he said.
In some cases, the agency takes action to prevent larger landslide problems after small ones occur. A good example came in March along Freeport Road in O'Hara. There was a minor landslide that shifted a large rock. PennDOT crews went to the hillside and removed it, with the hope that they prevented a future, more damaging slide caused by the weight shift from the earlier one, Mr. Cowan said.
Kaitlynn Riely: firstname.lastname@example.org or 412-263-1707.
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