Flood no surprise

Once again development itself was the cause of destruction. The flooding over the weekend can be directly attributed to decreased permeable surfaces in the the three rivers? watersheds. It?s expected that when six inches of rain fall in a day there will be some flooding; it?s practically inevitable. But with rivers cresting at six or eight feet above flood stage, sprawl is to blame.
As development occurs upriver of Pittsburgh, impermeable macadam surfaces prevent water from draining ? as it would naturally ? into the ground. The water quickly runs off into streams instead, filling those and increasing their speed until they flow into the larger bodies.
I was in Downtown on Saturday, looking with hundreds of others at the damage caused by Friday?s rain. While Friday had the largest 24-hour rainfall in Pittsburgh?s recorded meteorological history, it was relatively light over the several days. Yet the Point was completely overwhelmed, and boats were moored ?inland? of its fountain. Perhaps the strangest scene, though, was the boat washed up on a ramp to the Ft. Duquesne Bridge as a refrigerator floated down the Tenth St. Bypass, which was under eight or ten feet of water.
Pittsburgh has seen bad flooding before, sometimes with less rain than Friday?s. Probably the worst was the St. Patrick?s Day flood. In March 1936, the Ohio River crested at 46 feet ? 21 feet over flood stage. A sign near the Post-Gazette?s building at Commonwealth and the Boulevard of the Allies shows the high-water mark at seven feet above street level. Damage was devastating, with 200 people dead, 500 injured, and thousands more with no power, water, or mobility. Many of the existing dam structures were in place in 1936 already, including both Allegheny Lock and Dam 2 (Highland Park) and Monongahela Lock and Dam 2 (Braddock).
The fact that the flooding was so bad with the same flood control devices in place is attributable to the fact that in March the ground was still frozen, and the surface water had nowhere else to drain. Days of rain ran straight into moving ? and therefore liquid ? streams and flooded the city and much of the upper Ohio and Potomac valleys.
As sprawl worsened, the potential for catastrophic floods increased. In June 1972, when Hurricane Agnes pushed through central Pennsylvania and New York and deluged the Allegheny Valley, flooding was relatively less than in 1936, but by then there had been several Army Corps of Engineers flood-control projects built upstream. If not for them, there would have been two more feet of water at the Point than in 1936. The average rainfall caused by the storm was estimated by the National Oceanic and Atmospheric Administration (NOAA) at eight inches ? water had fewer places to drain to groundwater in the region, but the dams kept the region ultimately salvageable.
Additional problems created by sprawl occur when streams are forcibly rerouted into culverts: small pipes or channels running underneath roads and paved lots. Debris dragged by raging floodwaters can jam at culvert entrances, creating dams which flood the surrounding area, often including the lot the culvert was supposed to protect. Weak zoning laws also increase damage when developers are allowed to build in drained wetlands and flood plains, the areas first hit and worst damaged by severe flooding.
Today more than ever, sprawl is the cause of environmental problems. People driving ever farther to and from work spew extra pollution from their increased fuel usage. Parks and open land are ?reclaimed? for use as asphalt fields and residences.
All things equal, Friday?s flooding was not that severe. To curb future flooding disasters, people in western Pennsylvania should think twice before continuing to build further and more. The more they pave, the more potential there is for destruction.