Western Pa. Region Facing 'A Flood of Record'

Experts say rain, quick thaw raise water and anxiety

Pittsburgh Post-Gazette
21 February 2010
By Don Hopey,

It's not a good thing when Werner Loehlein -- who has overseen the U.S. Army Corps of Engineers' 16 flood-control dams and reservoirs in the upper Ohio River watershed since 1991 -- starts a conversation using the words "flood" and "record" in the same sentence. Not with 3 to 5 feet of snow already on the ground throughout the region and more on the way.

And when the chief of the Corps' water management branch in Pittsburgh says he's getting "real uncomfortable" with what's going to happen when all that deep snow melts, maybe it's time to move the washer and dryer out of the basement, haul up the magazine collection and find the paddles for the canoe. Just in case.

According to Mr. Loehlein, the near-record snowfall blanketing the region, combined with an extended winter storm cycle now predicted to blow into March, is increasing the risk that a record flood could occur in Pittsburgh when the weather breaks.

"Come the end of the month or the beginning of March when the temperatures jump up, well, we could see some excitement," Mr. Loehlein said. "We are going to see some high water when the snow melts for sure. The question is, how high?"

Just for the record, the biggest flood to hit Pittsburgh in the last 100 years occurred in March 1936, when heavy rains on top of a huge snow pack caused the rivers to crest at 46 feet at the Point -- 21 feet above the flood stage of 25 feet. Sixty-two people died, 500 more were injured, 135,000 were driven from their homes at least temporarily and water filled Downtown streets from the Point past Smithfield Street.

That was before the dams were built.

As a result of that St. Patrick's Day tragedy, the Corps built a flood-control system that today includes nine dams in the Allegheny River watershed, three in the Monongahela River watershed and four in the Beaver River drainage. Together the dams control drainage on about 40 percent of the Upper Ohio River watershed -- about 26,000 square miles in Western Pennsylvania, Eastern Ohio, West Virginia and Maryland.

That system reduces the number and severity of flooding in Pittsburgh and along the region's rivers but doesn't eliminate it. In June 1972, flooding brought on by Hurricane Agnes caused the rivers in Pittsburgh to crest at 36 feet, 11 feet above flood stage at the Point. But Mr. Loehlein said the dams "knocked 12 feet off the top" of the crest by holding back water that otherwise would have flowed into the rivers.

In January 1996, the region was under 9 to 24 inches of snow that melted in two days. Then came a storm that dumped 2 inches of rain. The rivers crested at 34.6 feet around the Point in Pittsburgh. But the crest would have been 13.3 feet higher without the dams -- higher than the 1936 flood.

In 2004, after Hurricane Ivan spawned heavy rainstorms, the rivers crested in Pittsburgh at 31 feet, 6 feet above the flood stage.

Mr. Loehlein said there now is more snow on the ground throughout the region than there was in 1996, especially south of Pittsburgh in the Youghiogheny, Cheat, Tygart and Monongahela river watersheds. And the dense, heavy snowpack is holding more water -- the equivalent of 3.2 inches of rain, compared with 2.5 inches in 1996.

"We will have a flood of record if we have a quick thaw and rain on top of it," Mr. Loehlein said. "If we have a slow thaw, with temperatures climbing above freezing during the day and falling below freezing at night, flooding will be less. But as we move into March, temperatures could warm quickly and the risk of a quick melt will increase."

To make room for all that water, Mr. Loehlein said the reservoirs behind the dams have been lowered as much as possible to ensure maximum flood-water storage.

The Corps has also been meeting over the last week with state and local government agencies, emergency response managers and police to review preparations. It also is urging the public, especially folks in flood-prone areas, to make what preparations they can.
"We tried to get word out about the flooding potential last week, but people weren't listening.

They were still digging out," Mr. Loehlein said. "Now we're telling everyone to think about the flood in 1996, and figure out a plan for what you would do if it happened again. If you weren't here in 1996, talk to a neighbor who was."

According to AccuWeather, the weather forecasting service in State College, Centre County, daytime temperatures through the end of February will climb to slightly above freezing during the day and fall to around 20 degrees overnight through the end of the month. That could be a recipe for a systematic, gradual thaw that would minimize flooding.

But it's also predicting a continuing winter storm cycle stretching into March. A significant storm that originated in the Pacific Ocean will roll into the area on Monday into Tuesday.

Alex Sosnowski, AccuWeather senior meteorologist, said that storm has the potential for putting down a "wintry mix" of rain and 3 to 6 inches of slushy snow over the Pittsburgh area.

Some areas in the Laurel Highlands could get more.

Don Hopey: dhopey@post-gazette.com or 412-263-1983.