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.
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.