The Philadelphia area was affected by the remnants of Tropical Storm Allison on 16 – 17 June 2001 with heavy rains and isolated (but significant) flash flooding of the smaller river basins in the area. While the rains were not nearly so heavy as the 30"+ that resulted in extensive flooding in the Houston, TX area, rainfall in this region was characterized by persistent development and maintenance of convective cells in small areas.
The Neshaminy Creek watershed north of the city of Philadelphia in particular was hard hit. Because of increasing development and the resulting reductions in vegetation and soils to retain runoff, this watershed has become increasingly flood-prone. The last serious flooding occurred in September 1999 in association with Hurricane Floyd. In that event, eight people lost their lives in the Philadelphia area, and total property damage reached into the hundreds of millions of dollars!
The Neshaminy Creek basin is shown in the graphic below, in bright green. For reference, the city of Philadelphia is shown in bright blue.
By Dr. Bill Bua, UCAR/COMET
Thanks to:
