History of Jones Falls makes inevitable inundations worse

Flooding

Storm Recovery

July 09, 2004|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

Rain fell so fast during Wednesday's storms - what a forecaster called a "monumental pace" - that flooding was inevitable. But history made the problem much worse in the neighborhoods along the Jones Falls in Baltimore.

Development of mills, small shops and houses along the stream in the 18th and 19th centuries set the stage for flash flooding because the paved roads and parking lots that came later leave little space for quick-moving storm water to seep into the earth. Many areas developed in the 20th century have set aside easements in such flood plains.

"Basically, urban streams have what we call flashy responses," said Ralph Scott, a geography professor at Towson University. "They fill up quickly, and the Jones Falls is an urban stream."

Scott said Baltimore, like most U.S. cities, was built along a network of streams, which attracted mills that were built to harness the water's power. In Baltimore, many of those streams feed into the Jones Falls.

As the mills were replaced by power plants, developments sprang up around them, bringing with them asphalt, concrete and brick that have hampered the drainage of storm water ever since.

"We call it impervious surface," said Wendy McPherson, a hydrologist for the U.S. Geological Survey.

The storms arrived Wednesday afternoon as a sticky, humid air mass moved up from the Southeast, then smashed into cooler air pushing its way into Central Maryland from the Midwest.

The result was storms that in some areas dumped rain at a rate of 6 inches an hour, what the forecaster termed a "monumental pace."

"No matter what you have on the ground, with that kind of rainfall, you're going to have flooding," said Andy Woodcock, a National Weather Service meteorologist in Sterling, Va.

The intensity of the storms and the flooding they brought stunned some experts.

"My office has been monitoring these storms for 15 years, and that's the worst I've seen," said William Stack, chief of Baltimore's water quality division, who oversees the flood warning system.

Rainfall varied widely

Moisture in the humid air, when chilled, provided rain that drenched some areas and brought a sprinkling elsewhere.

Rainfall ranged from 4.5 inches in the Westview area of Baltimore County to an inch in Fallston. At Baltimore-Washington International Airport, 1.3 inches fell.

Contrasting rainfall amounts are a common phenomenon during summer storms. Unlike hurricanes that sweep up the East Coast each fall, summer storms can hit small, isolated areas hard and leave nearby communities unscathed.

"The key ingredient to that kind of storm is high humidity," said Todd Minor, a meteorologist with the Penn State Weather Communications Group. "Once you have that, a lot of things can happen."

Stream levels jumped 7 feet in three hours Wednesday afternoon along the Jones Falls near the Baltimore County line, according to the U.S. Geological Survey.

Water rose fast

A stream gauge showed that water levels rose from 3 feet about 2 p.m. to 10 feet by 5 p.m. That was far short of the record of 18 feet set by Tropical Storm Agnes in 1972.

City officials said the steep slopes and low-lying areas along much of the Jones Falls make certain communities vulnerable to flooding, including Mount Washington and the Meadow Mill area in Woodberry.

Felled trees and limbs often make their way into the Jones Falls, further clogging the stream, particularly near bridges in Mount Washington and the Meadow Mill area.

"Once logs start tumbling down, it can jam everything up," said city Department of Public Works spokesman Kurt L. Kocher.

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