Behind Ida’s destruction along the Brandywine: A 1,000-year downpour, a ‘choke point,’ and a record crest

After terrorizing neighborhoods from Coatesville to Downingtown, the Brandywine’s floodwaters reached a crescendo at Chadds Ford. By then, they were two stories high and rampaging at an incredible 33,000 cubic feet per second, a ferocity beyond anything in the period of record.

The waters crashed into the Brandywine River Museum — home of some of the region’s most significant artworks, including Andrew Wyeth paintings that famously captured the valley’s tranquil and mystical sides — filling the lower level to the ceiling and damaging all 10 buildings in the complex.

Ten weeks after the historic floods incited by the remnants of Ida, and with the peak holiday season now imminent, the museum remains closed and it is unclear when it will reopen.

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Although no one was injured and all the Wyeth paintings and other artworks were spared, the museum complex suffered at least $6 million in structural and equipment damage and counting, said Virginia A. Logan, executive director of the Brandywine Conservancy & Museum of Art.

“We’ve never seen anything like this,” she said.

No one else has, either, according to a hydraulic analysis of the Brandywine at Chadds Ford completed last week by Gerald Kauffman Jr., director of the University of Delaware’s Water Resources Center. The U.S. Geological Survey “never anticipated this extreme of flooding,” nor had any other government agency, he said.

A wave of floodwater two stories high — triple the depth of the creek at Chadds Ford — overwhelmed the stream banks, and of all the record Ida-related crests verified by the National Weather Service, that one evidently was No. 1 in terms of exceeding the previous record.

What was captured at the USGS gauge right at the museum was a dramatic encapsulation of the ferocity and unprecedented nature of the Ida-related flooding. The conspirators identified by experts included topography, enhanced rains associated with climate change, a once-in-1,000-years downpour 18 miles upstream, a cascade of water from 1,000 feet above sea level, and a fateful 19th-century engineering decision.

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This probably wasn’t what Wyeth had in mind when he said: “I don’t think that there is anything that is really magical unless it has a terrifying quality.”

The Brandywine watershed covers 38% of Chester County and all or part of 41 towns, according to the Stroud Water Research Center’s Return on Environment report. In a tuning-fork shape, the West and East Branches of the Brandywine Creek in western Chester County join the main stem near Lenape, and it becomes seriously pinched as it approaches Chadds Ford.

The banks at the museum site are about 80 feet apart, less than half the separation just a few hundred yards upstream, says Kauffman.

Population in the watershed has risen 10% this century, and with it paving and other hard surfaces have increased, according to his analysis. Between 1996 and 2010, the watershed added nine square miles of developed land, or more than 5,000 football fields’ worth.

Perhaps surprising given that the Brandywine flows through both the Routes 30 and 1 corridors, just under 6% of the watershed is hard-covered, according to Kauffman’s report. That’s because so much of the acreage is “protected.”

Development did make some contribution to Ida’s havoc, said Seung Ah Byun, executive director of the Chester County Water Resources Authority.

Nevertheless, Stroud Center director Charles Dow believes Ida’s rains probably trumped everything else. When rain overwhelms even a meadow, he said, it can take on the character of a paved surface in that additional rains run right off of it.

And while the overall rain amounts in Chester County were prodigious, the speed with which they came was catastrophic.

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At Modena, on the Brandywine’s West Branch, 7.02 inches of the 8.18 total fell in a six-hour period ending at 8 p.m. Sept. 1 — a downpour that would be expected only once every 1,000 years — according to a Chester County Water Resources Authority analysis.

“My grandmother used to say, ‘It’s raining cats and dogs,’” Kauffman said. “This is higher than that.”

Six hours later, the consequences had rippled to Chadds Ford, 18 miles downstream.

The museum has a standing disadvantage in its battle with nature, said Dow: “It was built in a floodplain.”

Occupying a building that housed a mill dating to 1859, it opened in 1971. A year later, it endured what was then a record flood from the remnants of Agnes, a record topped when Floyd visited in 1999 and the Chadds Ford gauge reached 17.15 feet. Ida, at 21.04 was a full 20% higher.

The museum is still tallying the damage, Logan said. She added that neither insurance nor disaster assistance will come close to covering the costs. The Brandywine Conservancy has set up a relief fund.

Kauffman says the museum’s flooding woes have a whole lot to do with human activity, and not just increases in greenhouse gases or development.

At some point in the 19th century, a decision was made to “channelize” the Brandywine’s banks from Route 1, near the current site of the museum, for several hundred yards eastward to make way for a railroad bridge, he said. Shrinking the banks provided land for planting the trestle supports.

“I think that’s the choke point,” he said.

Kauffman is confident that can be fixed, federal money willing, adding it would cost about $500,000 to widen the banks. He is part of a bistate, intergovernmental task force that is looking at the basin and what can be done to mitigate the flood hazards.

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”This group, I’m hoping, is going to move quickly, so that malaise doesn’t set in, and we’re not ready for the next big one,” he said. “We’re trying to avert that.

“We call this the hydro-illogical cycle,” he said, “not the hydrologic cycle.”