Yesterday's Levees as Cause of Today's Floods

After Lee, towns in Pennsylvania question previous efforts to control rivers

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Thousands are returning to homes and surveying damage in central Pennsylvania after the flooding triggered by Hurricane Lee. Some of them are wondering if the damage they are facing now was made worse by the mitigation efforts that followed previous generations' floods and storms. What if the levees that saved some cities created the floods that have now inundated neighboring towns?

That's the verdict from some small towns in today's Philadelphia Inquirer.

When the U.S. Army Corps of Engineers called in 1979 for raising levees in Wilkes-Barre by three to five feet after Tropical Storm Agnes, it cited the nearly $3 billion in damage that storm had caused to justify the expense. In essence, shoring up the flood-control system in the city of 42,000 in the heart of Pennsylvania coal country would cost less than would repairing houses and businesses after another catastrophic flood, engineers said.
But in a handful of smaller neighboring communities on the river's west bank - West Pittston, Plains, and low-lying Jenkins Township - the figures didn't add up.
It was there Friday that agitated murky water crept to the rooftops, National Guardsmen launched rescue efforts from second-story windows, and the torrent rose much higher than anyone predicted as the remnants of another tropical storm - Lee - pummeled one of the most flood-prone regions in the United States.
Though it will take weeks to fully assess Lee's damage to the Wyoming Valley, these waterlogged, levee-less communities couldn't help but think the flood-control improvements that spared Wilkes-Barre from disaster may have caused their own.
"All that water not flowing into the city has to go somewhere," West Pittston resident Keith Englehardt said. "It came here."
The problem is simple physics. Levees channel a larger than usual body of water into smaller space, backing up water upstream. Within the confines of the walled-in river, the The Citizens' Voice of Wilkes-Barre (Pa.) notes, "the flowing water has less friction and more force behind it, so the river gains velocity. Downstream, the pent up water is freed from the girdle of the levee, and pours forward and outward, like a pitcher spilled on a table."
The table, in this case, is the lower reaches of the Wyoming Valley.

After the Wyoming Valley levee was raised an additional three to five feet in 2003, the U.S. Army Corps of Engineers said the modified levee would protect from an Agnes-level flood, estimated to be a once every 345-year event. Friday morning the Susquehanna River in Wilkes-Barre crested at 42.66 feet, about 1.5 feet higher than Agnes.

How could a 345-year flood happen twice in a half century?

Part of the answer may be sprawl and development in outlying areas that drain into the Susquehanna River. Wetlands and forests act as a sponge, soaking up and consuming water. Every rooftop, roadway, driveway, parking lot and piece of concrete robs the land beneath it from its absorbency. Rather than being retained in the ground, the runoff water is swiftly carried to gorged rivers and streams.

But Konrad said he's not sure if development made a difference in Northeastern Pennsylvania's recent flooding. While homes, roads and patios make the ground underneath impervious to water, saturated ground can be just as impervious. For that reason, development is more likely to promote flash flooding.

"We know development exacerbates flooding, but it tends to be greater on small events that normally wouldn't cause flooding," he said. "When the ground is already saturated and has no storage capacity, its acts as though it is impervious, so development doesn't make a difference."

So the problem may be levee building, and the often unsuccessful efforts of humans to guide a river's course. (Just ask those who would presume to steer the Big Muddy.) But it may also be how society has been building on land, with little regard to the way all that hard surface would respond to something inevitable: a hard rain.

This article is from the archive of our partner The Wire.