A draft of Brandywine Conservancy’s Flood Study Report is now available online for public scrutiny. Grant DeCosta, the conservancy’s director of community services made the announcement on Jan. 16, saying there is a 45-day window for comment that will close on March 1.
As previously reported, it was the devastation from Hurricane Ida on Sept. 1, 2021, that instigated the need for the study. Properties — businesses and homes — were damaged or destroyed from Coatesville south into Wilmington. Hank’s Place at Creek Road and Route 1 in Chadds Ford Township was destroyed and the rebuild still isn’t complete. The Conservancy incurred more than $10 million in damages, with 10 buildings damaged to one extent or another. Some of those buildings need to be demolished. The meeting room on the ground level of the Brandywine Museum of Art remains unusable.
The U.S. Geological Survey flood gauge along the Brandywine at the museum reported the flood level reached more than 21 feet. The next highest flood level was 17 feet from Hurricane Floyd in 1999.
DeCosta didn’t go into great detail about the study’s findings, which include a review of mitigation procedures, but said 95 percent of the people surveyed said they’re worried about increased frequency or possible intensity of flooding. In addition, 79 percent said flooding affected their ability to travel; 51 percent had property damage. Only 28 percent had flood insurance.
“Historic flooding,” he said. “It was here; it was awful, and we’re probably going to have more. Flooding is not new to us; it’s a legacy challenge for the Brandywine.”
The report, he said, reviews land use, and population growth that could result in more impervious surfaces, and questions how more intense storms might affect the Brandywine Valley and how to prepare. 
“Ida was the worst of record. What might be coming?”
He said conducting the study involved talking with municipalities, “robust engagements” DeCosta called them. “We talked to their folks on the ground, public works crews, asking them what the conservancy needed to know from them.
The study team looked at the Chester County hazard mitigation plan and reviewed that with all the municipalities. But he also said the county is about to update it again. The team also looked at municipal stormwater management systems
In terms of public engagement, DeCosta said “I hope we did a good job. We attended more than 35 public meetings…We reached over 1,500 individuals…There are people who are still out of their homes. We needed to hear from them.”
DeCosta also said the team looked at structural and nonstructural solutions. The structural solutions included five dams in the area to determine how well they functioned. He said the Marsh Creek dam did a good job, reducing water coming into the reservoir from 4,160 cubic feet per second to an outflow of 369 cfs.
Would more dams such as the one at March Creek be beneficial in the face of another Ida-like storm?
“We don’t see the opportunity to build more large solutions in the watershed for various reasons. If we wanted to contain Ida, we would have to build five more Marsh Creeks,” he said. “That’s not feasible.”
There was also more localized flooding in smaller streams which was also a problem.
DeCosta said both situations need to be addressed but require different solutions.
He said the floodplains in the region are doing a good job in mitigation.
“When we look at the flow at Pocopson before it gets to Chadds Ford, gets beyond Chadds Ford before it gets into the city of Wilmington, in the 15 miles of the Brandywine, we have over 16.5 billion gallons of flood storage in our flood plains. They’re doing a lot for us, but we need more.”
He added that without municipal ordinances in place for open space, for preventing building in a flood plain, “That 16.5 billion gallons would have gone from catastrophic in Wilmington, Coatesville, and Chadds Ford to cataclysmic.”
More can be done with the flood plains, DeCosta said. They contain about 300 years of legacy sediment built. Maybe clearing out the sediment would allow for more flood storage, and the conservancy is looking at areas in Chadds Ford for just that.
“Locally, that can do a lot. That’s in a good pilot project that’s going to deliver downstream benefits as well as local benefits. More work is needed on that and it’s not a small undertaking, but it’s something that we intend to begin hitting the road on right away.”
Drafts of the 169-page technical report and the summary can be found here. The final flood study will be released in April, he said.
About Rich Schwartzman
Rich Schwartzman has been reporting on events in the greater Chadds Ford area since September 2001 when he became the founding editor of The Chadds Ford Post. In April 2009 he became managing editor of ChaddsFordLive. He is also an award-winning photographer.
