Officials want to repair valve
County officials want to repair a valve at the bottom of North Park Lake that could help prevent a flood in the event of a catastrophic rainstorm or dam breach at the lake.
An aging valve that plugs the lake is surrounded by so much silt from runoff that if it were opened, officials are unsure whether it could close again.
In addition, wooden components near the entrance to the valve gates have deteriorated and need to be replaced, said Eugene Vaskov, an engineer with the Allegheny County Department of Public Works.
“If there was an emergency, we’d get (the valve) open, but there would be consequences,” Vaskov said. “There’s so much sediment built up there, we don’t know if we’d be able to shut it.”
The 75-acre lake is held back by a dam along Babcock Boulevard, one of 29 in the county classified as a high potential hazard because of its proximity to development and residential housing.
The classification does not reflect a lack of structural integrity. The dam is considered safe, according to recent inspection reports.
The valve, submerged in 15 feet of water, connects to a conduit that runs 500 feet from the lake to an emergency spillway into Pine Creek.
The valve is an integral part of the safety design of dammed lakes like North Park Lake, said Don Martino, chief of the state’s safety division covering dams.
“If there would be an emergency at the lake and they want to drain it, they’ve got to be able to open up the valve,” Martino said.
Lakes need to be drained periodically for maintenance, for structural emergencies such as dam leaks and breaks or to prepare for catastrophic rainstorms, officials said.
“It’s just like if you had to fix your swimming pool. The easiest way to do it is drain it, fix it, then fill it back up,” Martino said.
Had Hurricane Isabel threatened to wash out Pittsburgh, the lake could have been drained to create extra runoff capacity to prevent flooding, Vaskov said.
He estimated the repair project would run several hundred thousands of dollars and would include improvements to the spillway into Pine Creek.
Although the dam is considered safe, worries about the valve make it a priority for repair, Martino said.
North Park Lake is the only dammed lake for which the county is responsible.
Martino said the state recommends valves be opened every year for about 30 minutes.
Vaskov said he does not know the last time the valve at North Park Lake was opened.
He said the repairs could coincide with a $7.69 million Army Corps of Engineers dredging project that is expected to begin in 2005. If the Army Corps decides to drain the lake, the repairs could be done fairly easily.
If the lake is not drained, however, the county could surround the valve with a coffer dam, a sealed room that could be pumped dry to allow open air access to the lake bottom.
The dredging project will restore aquatic habitat to the lake, which has seen its water levels cut in half by silt runoff from suburban development.
Vaskov said the county had initially hoped the Army Corps of Engineers would make repairs to the damn and valve, but the corps’ project is limited to restoring habitat, not structural repair.