Temple completes Pennypack Creek floodplain mapping
Study finds flood danger zones have changed significantly in Bucks, Montgomery and Philadelphia counties
Last week, hundreds of homeowners in the Pennypack Creek Watershed became aware that their homes are in danger of being flooded. Other learned that their homes are now out of danger’s way.
To help protect the safety of residents within the floodplain, the Center for Sustainable Communities at Temple University embarked on a four-year study of the Pennypack Creek Watershed to develop the most accurate floodplain maps possible.
“There are hundreds of people in the Pennypack Creek Watershed living in high-risk flood zones,” said Jeffrey Featherstone, director of the Center for Sustainable Communities. “Because of inaccurate or outdated FIRMs [Flood Insurance Rate Maps], one can only guess the actual number. Many municipalities are using 1920 to 1960 precipitation data to determine the likely impacts of a 100-year flood.
|About 12 Temple students at all levels — undergraduate, graduate and doctoral — assisted the Center for Sustainable Communities in the Pennypack Creek Watershed project over four years. Above, Jeff Ham, a geology major who graduated in 2005, gathers creek data in the field.
(Photo courtesy the Center for Sustainable Communities)
“They are 15 to 20 percent lower than today’s reality — seven inches in 24 hours compared to today’s nine inches. In the more dramatic events that have taken place in recent years, it drives the numbers up dramatically.”
The Pennypack Creek Watershed study was a four-year project designed to completely map and provide updates to the floodplains of the watershed, suggest stormwater best management practices to avoid flooding in the future, provide recommendations for open space preservation, and analyze water quality in an 11-municipality region.
The research team consisted of Temple University faculty members, experts and students from disciplines including landscape architecture, horticulture, geology, geography, geographic information systems, urban and suburban studies, land use policy and planning, environmental justice and civil engineering. (See a complete list of the watershed study research team.)
The Pennypack Creek Watershed comprises a 12-municipality, 56-square-mile area with a population of 640,000 people. Townships and boroughs involved include Abington, Bryn Athyn, Hatboro, Horsham, Jenkintown, Lower Moreland, Rockledge, Upper Dublin, Upper Moreland, Upper Southampton and Warminster. A portion of northeast Philadelphia is also in the watershed, but was not part of this study.
The study was funded by a $330,000 grant from the William Penn Foundation, a $192,500 grant from the Federal Emergency Management Agency, $70,000 from participating municipalities ($100,000 pledged), and $95,000 from the Center for Sustainable Communities.
According to Md. Mahbubur Meenar, senior GIS design specialist at the CSC, the updated floodplain maps that CSC researchers have developed are likely to raise several new issues and concerns for the region and the affected municipalities.
“The preliminary maps produced by the study have identified about 130 additional buildings within the 100-year floodplain boundaries that were not indicated on the existing FIRMs,” he said. “Other families will be facing the reverse situation — their property was within the 100-year floodplain boundary on the existing FIRMs, but the new study shows that they are now out of the flood danger zone,” added Meenar, who also is an adjunct assistant professor in the department of community and regional planning.
According to Meenar, the study consists of several components: hydrologic modeling to determine new floodplain boundaries, geographic information system mapping and data, inventory creation, water-quality studies, evaluation of existing stormwater facilities, assessment of open space and corridor alternatives, and recommendations to the municipalities.
Richard Nalbandian, a research associate professor in the department of community and regional planning who conducted the bulk of the ground mapping reconnaissance, said homeowners’ reactions to the study have been mixed.
“Some never even knew they were in the floodplain and didn’t know about the Federal Flood Insurance Program. We found others that are now out of the floodplain, and still others that are squarely mapped within the new floodplains and will be eligible for federal flood insurance that don’t want to admit that they are,” he said. “People in some cases don’t want to admit that they will suffer an economic loss. Others are grateful to know what the situation is and what they can do about it.”
Floodplains do change over time, for both natural and manmade reasons, Nalbandian said. Many of the existing floodplain maps have become obsolete due to recent changes in land development, unplanned urban land use, increased volumes of stormwater run-off, poor stormwater management, raised sea level, natural changes, siltation, and even flood mitigation efforts like drainage systems and levees, he said.
“The smaller, but more frequent, storms actually are the principal shapers of the stream channels. They produce the most erosion and cause sedimentation as well as non-point source pollution [polluted runoff],” Nalbandian said. “Some of the municipalities within the watershed are doing a good job of stormwater management and enforcement; others with good ordinances in place still aren’t enforcing them to the best of their ability. Public-owned land such as schools, which are often 10- to 15-acre sites, are ideal candidates for new stormwater management methods.”
With the Watershed Study complete, Center for Sustainable Communities Director Featherstone said the center is now recommending that municipalities enact “stormwater districts” and create them using best management practices.
“We are asking the municipalities to enact the new floodplains are their official maps — FEMA will eventually require it. Floodplain re-mapping requires multi-municipal coordination and management,” he said. “A watershed study like Pennypack is a good example of how and why municipalities should work together. If they are not working toward a common goal, the same problems are just going to keep reappearing.”
Updating floodplain maps will not fix everything, he added.
“Communities need to focus on land use patterns and stormwater management systems. The flooding issue simply cannot be addressed in isolation from water quality, stormwater, land use and other related issues,” he said. “The Pennypack Creek Watershed Study can serve as a model for how to resolve — on a watershed basis — complicated multi-jurisdictional problems that have been addressed in a piecemeal and fragmented manner in the past.”
For more information on the center’s Pennypack Creek Watershed Study, call
267-468-8312 or visit the study Web site at www.temple.edu/ambler/csc/projects/projects_pennypack.htm.
— James Duffy
The watershed study research team
Principal investigator: Jeffrey Featherstone, director of the Center for Sustainable Communities, was responsible for project oversight.
Co-principal investigators: Michel Boufadel, civil and environmental engineering department, oversaw all modeling; and Laura Toran, geology department, oversaw water quality research.
The project also included coordinating faculty researchers Richard Nalbandian, community and regional planning department, and Jonathan Nyquist, geology department; geographic information systems specialists A.S.M. Bari and Md. Mahbubur Meenar; consultants Aero 2 Inc. and Andropogon Associates; and graduate and undergraduate student assistants.