Student Study Backs Pa. Residents’ Claims of Development Effect on Flooding

A doctoral student says his examination of two small streams in eastern Pennsylvania appears to back up what inundated residents have long suspected: flooding along small creeks and streams is worsened when land is paved over.

Joshua Galster watched the Little Lehigh and Sacony creeks in eastern Pennsylvania for months last year, taking measurements at certain points along each one during periods of significant rainfall. The streams are similar in almost every respect, but there is a lot more development along the Little Lehigh, which cuts through Allentown, than along the Sacony, which lies farther west in Berks County.

Galster found that discharge — the amount of water flowing past a certain point in a certain period in time — increased at a much greater rate as he moved downstream along the Little Lehigh than along the Sacony, heightening the potential for flooding along the former.

Precipitation, climate and geology can all play a role in discharge, but Galster, a doctoral candidate in environmental sciences at Lehigh University, said his research has largely accounted for those factors — leaving development as a likely explanation for all that water.

“If I had to say now, preliminarily, all those caveats, I would say the difference is development,” Galster said. “It seems that the difference in those two streams is caused by land use.”

Lehigh professor Bruce Hargreaves, one of Galster’s advisers, said paved, or impervious, surfaces cause more runoff, which in turn contributes to stream discharge.

Bill Muehler, who works in the planning division of the Army Corps of Engineers, said one rule of thumb is that when at least 10 percent of a given land mass is developed, runoff into nearby streams is increased significantly.

Many waterlogged residents along the Delaware River blame their flooding problems on development. But researchers say the latest round of flooding — which forced thousands of people to evacuate in New Jersey, New York and Pennsylvania and caused millions in property damage — was more likely caused by other factors, including back-to-back soaking rainstorms, melting snow and oversaturated ground that could not absorb the water.

Development may have a greater effect on smaller streams and creeks such as the Little Lehigh, which flooded in September in the wake of Hurricane Ivan, Muehler said.

The Lehigh Valley Planning Commission has attempted to mitigate the effects of development in Lehigh and Northampton counties by developing storm water management plans for each of the 12 watersheds within its jurisdiction. Now, developers are often required to install detention basins and take other steps to reduce runoff.

The commission measured the effectiveness of the Little Lehigh’s storm water plan in 1996. Based on eight years of data, “we were not seeing increases in flood heights,” even though development along the stream had increased, said Geoff Reese, the commission’s assistant director.

But while detention basins, which catch runoff and allow it to slowly infiltrate into the ground, are a help, they are not a panacea, Muehler said.

“Even the best plans, the best technology, the best everything, you’re going to have some problem or potential for problems,” he said.

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