Temple U Refines Pennypack Floodplain

Study refines and updates floodplain lines, bearing on home prices and ownership costs Updated Floodplain lines in Pennsyvania’s Pennypack Creek watershed (map excerpted from the one at the Philadelphia Inquirer)(click to enlarge) “God willing and the creek don’t rise”, goes a certain expression of hope passed on to us by our elders…

Study refines and updates floodplain lines, bearing on home prices and ownership costs

Updated Floodplain lines in Pennsyvania’s Pennypack Creek watershed (map excerpted from the one at the Philadelphia Inquirer)(click to enlarge)

“God willing and the creek don’t rise”, goes a certain expression of hope passed on to us by our elders. While tinged with folksy charm, it does recognize one crucial fact: occasionally, the creek do, indeed rise. When it does, we have to cope with it or, better, we hope to know in advance where the creek is willing to be when it tries to come up to meet us.

To try to anticipate the vagaries of storm water, we typcially turn to Federally-produced floodplain maps. Much depends on these maps; everything from property values to mortgages to insurance costs to potential maintenance and repair bills can be assayed using these maps as sources. Nothing, of course, is as constant as change, so even floodplains can move and change, especially given the gradual development of small urban watersheds, decreasing permeable land which serves as a natural ’shock absorber’ during periods of heavy weather; the fewer places for the water to go, the more water will go straight into the watercourse and the quicker that stream will fill and flood.

Recently a team from Temple University completed a resurvey of the the Pennypack Creek basin, a suburban watershed just north of and adjacent to Philadelphia. Performed by Temple’s Center for Sustainable Communities and partially funded by FEMA, who produces the standard floodplain maps, the new lines fall in somewhat different places than the standard: they take in land that the FEMA maps don’t and include numerious new dendrites illustrating tributaries that enlarge during minor floods.

Good work…too good!

The work improved on the standard by using up to the minute information (the basic information on the Federal floodplain maps is said to be around 20 years old) and satellite imagery. The result is a map that details, on a property-by-property basis, where the waters are most likely to rise.

Ironically, though the Government laudes the work, they won’t be using it; it turns out that it’s toogood. Diane Mastrull and Anthony R. Wood, writing in the Philadelphia Inquirer:

The researchers’ work was done in such exacting detail - literally house by house - that it was far and above FEMA’s longtime standards for floodplain mapping, said Martin Frengs, an official at the agency’s regional headquarters in Philadelphia. The maps’ quality, he explained, must be uniform across the country because they are the foundation of the National Flood Insurance Program, which FEMA administers.

Though the team is complying with FEMA’s requests to modify the maps, they are making them available in unaltered form to municipalities in the basin, with the aim of giving those organizations vital information to make planning decisions.