Latest in wave of storms brings extensive damage

Hill among areas hardest hit by Jeanne

by JAMES STURDIVANT

When the tropical system called Jeanne brought its vicious swan song to Southeastern Pennsylvania last week, it hit the entire region hard, but dumped the greatest amount of rain in two areas: Chester County near the Delaware border, and Northwest Philadelphia and its immediate suburbs.

Chestnut Hill, Mt. Airy and environs escaped the deadly floods that plagued lower-lying areas along the Schuylkill River, but suffered the effects of torrential runoff caused by as much as 10 inches of rain.

In West Mount Airy, flooding made many roads impassable. Along the Wissahickon and Cresheim Creeks, swiftly rising water collapsed banks, undermined bridges, washed away parked cars and caused an already-damaged portion of Cresheim Valley Drive to collapse.

The RittenhouseTown National Historic Landmark District along Lincoln Drive saw severe flood damage, as did parts of Whitemarsh Township, where officials declared a disaster emergency.

"It took a beating," Tom Pelikan, executive director of the Friends of the Wissahickon, said of the creek valley. The numbers tell the tale: according to data from a USGS sensor that monitors the rate of water flow near the creek's mouth, close to 17,000 cubic feet of water per second was flowing at the height of the storm. The normal rate is 40-70 cubic feet of water per second.

That was enough to undermine the piers supporting the Bell's Mill Bridge through a process called scouring, said Philadelphia Streets Department chief surveyor Joseph Syrnick. Earth supporting the piers was washed away during the storm and had to be replaced with truckloads of stone, he said. The bridge was reopened to traffic the next day.

Cresheim Valley Drive, closed since an Aug. 1 storm caused cracks and depressions to develop along the edge of the road, fared much worse. An entire section of the drive has now collapsed into Cresheim Creek.

"It's very serious. It's certainly exacerbated what was already a problem," Syrnick said. "We had thought it would be open on a temporary basis in one or two directions within a week; all that we needed to do was put up barricades and post a detour in one direction.

"Both our highway people and our traffic people are [now] adamant that this is not safe to be reopened at all ...  until it's at least back to where it was before the storm," he said.

Syrnick said that the original estimate for repairs of $800,000 has now jumped to close to a million.

"That's a lot of money when you don't have two pennies to rub together," he said, referring to the Street Department's repair budget.

The collapse occurred at the point where the creek takes a sharp turn and flows under the road. Syrnick said that repair work would require installing gabions -- rock baskets -- to rebuild the banks and contain the stream.

"Reestablishing the bank with gabions would be the most expensive thing," he said.

At RittenhouseTown, floodwaters from the Monoshone Creek inundated the 1707 Nicolas Rittenhouse Home, leaving several feet of water within the historic building, according to a press release. Large ruts were cut through roads and potions of the creek's bank were eroded.

At the Morris Arboretum, floodwaters from Paper Mill Run inundated the fields adjacent to Northwestern Avenue, flooding the stone pump house "up to the eaves," according to physical facilities director Robert Anderson. The storm also exacerbated earlier damage to the gardens caused by the Aug. 1 storm, most seriously in the Swan Pond and along stream banks.

"The Swan Pond is basically silted in, which will create a problem for the swans in the wintertime with the water being only a foot and a half deep," Anderson said. He said that the arboretum would try to dredge the pond before the water freezes.

No foot bridges in the gardens are closed, but the pond and log cabin exhibit are currently fenced off, Anderson said.

The storm's effects varied elsewhere in the Wissahickon Valley. The covered bridge "held up nicely," according to Pelikan. Valley Green Inn also escaped any major problems, although the parking lot saw severe erosion.

"The amazing thing about these storms is, wherever we -- the Fairmount Park Commission and the restoration volunteers -- improved the trails, damage wasn't nearly as bad as it could have been," Pelikan said. He added that recent forest management projects, such as replanting native undergrowth, might have helped to cut down on slope and gulley erosion.

"It's unusual to have two six-inch-plus storms within two months. But the scary part is, the hurricane storm season doesn't end until the end of October," Pelikan said.