Following heavy rain, Conemaugh River Lake crest gates opened for 1st time since 2010

The recent rainfall that has caused flooding across the Pittsburgh region filled the Conemaugh River Lake to 74% of its capacity.

To bring the lake’s level down, the U.S. Army Corps of Engineers started opening the dam’s crest gates Thursday, said Megan Gottlieb, water management lead engineer.

It’s the first time since 2010 that the gates have been opened for daily operations.

“It’s a way to pass a lot of flow quickly,” she said. “It’s totally safe. It’s how the dam is designed.”

The National Weather Service measured 3.78 inches of rain from 8 p.m. Sunday to 2 p.m. Thursday at Pittsburgh International Airport, but some areas got more.

In Blairsville, up the Conemaugh River from the dam, 4.7 inches of rain was measured, according to the weather service.

The Conemaugh River Lake’s depth increased to 68 feet. That’s 58 feet over its normal depth of 10 feet, Gottlieb said.

Getting the lake back to its normal level will take up to two weeks.

At the gates’ opening on Friday, about 123,000 gallons of water were being released each second.

“We’re trying to get rid of this water,” Gottlieb said.

Kiski River affected …

That water will flow to the Kiski River before reaching the Allegheny River. It takes water leaving the Conemaugh Dam a day to get to The Point at Pittsburgh, Gottlieb said.

Also impacting the Kiski River is the Loyalhanna Lake, which, while much smaller than Conemaugh, rose 35 feet. It is 48% full, Gottlieb said. Its crest gates are not in use, but water is being released from its lower gates, which operate every day.

“The Kiski River will be seeing higher than usual river levels because they are getting a lot of water from Conemaugh and Loyalhanna,” Gottlieb said.

The releases are timed to be made after the rivers crest and to not create any new crests or cause any flooding, she said.

The dams were functioning well with no problems reported, Gottlieb said.

While saying Conemaugh is 74% full sounds like a lot, it does not make its top five highest levels, Gottlieb said.

Its highest pool was during Hurricane Agnes in 1972, when it reached 88% of its capacity at 62.8 feet deep. That was 4.8 feet deeper than now.

Conemaugh and Loyalhanna are two of 16 flood damage reduction projects in the U.S. Army Corps of Engineers Pittsburgh District. They, and several others, were authorized by the flood control acts of 1936 and 1938, following the St. Patrick’s Day flood of March 1936.

… and at The Point, too

The Ohio River crested at The Point at 28.4 feet between 6 and 6:30 a.m. Thursday.

Without the reservoirs on the Allegheny and the Monongahela rivers, the crest at The Point would have been 6 feet higher, at 34.4 feet, Gottlieb said.

That would not have been far below the Agnes crest, which was 35.8 feet.

Conemaugh alone is largely responsible for keeping water levels lower at The Point, Gottlieb said.

“Conemaugh is one of the best reservoirs,” she said. “It provides so many benefits that most don’t understand.”