Flood Study Calls for Wide-Ranging Measures to Control Bigger Storms Coming With Climate Change

The outlook for more climate-related flooding in a southeastern Pennsylvania watershed has prompted a new call for measures to contain heavy rains, allow raging waters to pass downstream and help the public anticipate bigger and more frequent storms.

The Brandywine Flood Study, prepared by the nonprofit Brandywine Conservancy, the University of Delaware Water Resources Center and a local flood-control agency, says more land should be set aside for open space that could absorb rains before they become floods. The report also calls for more bridges, dams and culverts to be repaired, removed or enlarged to cope with increased water flows that would otherwise flood the area and urges the construction of more green infrastructure such as rain gardens to absorb heavy rains.

The recent study was prompted in part by the remnants of Hurricane Ida in September 2021. The storm triggered record flooding and water flows in the Brandywine Creek in Pennsylvania and Delaware, causing some $45 million in property damage and taking one life.

The study, a draft that will be finalized in April, was also driven by the Brandywine watershed’s long history of flooding and by the outlook for more and bigger storms fueled by the warming planet. Ida was just one—albeit the most severe—of 10 high-precipitation storms to hit the watershed between 2003 and 2021. It followed dozens of others in the 19^th and 20^th centuries.

“The results of this storm were catastrophic for many communities in the central and lower portions of the watershed,” the report said, referring to Ida. “These impacts were the catalyst for this study, to provide recommendations for communities to be better protected and prepared for future storms.”

Ida’s flooding temporarily closed hundreds of roads across Pennsylvania, including two interstate highways. Some eight inches of rain fell on tiny Modena Borough, Pennsylvania, about a dozen miles north of the Delaware state line. That’s twice the area’s average rainfall for the entire month of September the prior decade, dumped in just a few hours.

At Chadds Ford, about 12 miles to the southeast, Brandywine Creek rose by 21 feet during Ida, seven feet more than expected and four feet higher than the previous record, said Grant DeCosta, director of community services at the Brandywine Conservancy and one of the report’s authors. 

That was the equivalent of an 800-year storm, he said: an event with a chance of occurring in a given year of one eighth of one percent. A warming world, experts warn, is upping those odds.

“Ida was historic but there is more work to do to anticipate climate change and precipitation,” DeCosta said. “We’re seeing some of these things happening now that we already need to start preparing for.”

Summer storms are becoming more intense and more frequent, while three days of rain last winter produced the kind of flooding in the Brandywine watershed that normally results from tropical storms, showing that the threat now exists year round, DeCosta said.

More than 90 percent of that watershed is in Pennsylvania, with the remainder in Delaware. The report’s recommendations were based on what DeCosta called a “pessimistic” scenario of a 1,000-year storm hitting the watershed in 2100 and 150,000 additional residents living there, or about 50 percent more than now.

But even the ambitious program of infrastructure improvements and emergency planning measures wouldn’t fully protect the region from flooding by the increased rains, argued Kate Hutelmyer, water resources planner at Pennsylvania’s Chester County Water Resources Authority, which contributed to the report.

“That theoretical storm is massive; there’s not enough money or space in the watershed to hold back all of those flood waters and prevent anyone from flooding ever again,” she said. “At some point, we have to turn to preparedness, to outreach and education, and other measures that will reduce harm even when we can’t eliminate the risk of it. Communities everywhere can work on this today, and they do have very tangible benefits for the protection of life and property.”

Preparedness by the Brandywine watershed’s approximately 250,000 current residents is among the “non-structural” flooding remedies recommended by the report. The authors called, for example, for signage to be installed to remind people how high the waters rose during Ida, such as a 9.7-foot surge recorded at a bridge in northeast Wilmington, an environmental justice community in Delaware’s biggest city. 

The non-structural elements of the plan, such as continuing to conserve open space and installing early warning systems, can be implemented more quickly and less expensively than work such as bridges and culverts, the team said.

For the structural work, the report noted, “the lowest hanging fruit is to work with those that are already slated to be upgraded due to their age or existing condition.” 

The study examined 291 bridges, culverts and dams along the Brandywine Creek’s main stem and east and west branches. They found that 60 percent were not big enough to take the anticipated volume of water, which would flood the surrounding land. 

Who Will Pay for Flood-Control Work?

Together, the structural and non-structural work may cost up to “nine digits”—hundreds of millions of dollars—from federal, state, local or private sources, said Jerry Kauffman, director of the University of Delaware’s Water Resources Center, another of the report’s authors. 

Although the effort may face new cuts in federal funding from the Trump administration, much of the money is already in place because of historic infrastructure spending by the Biden administration, Kauffman said. During a video call with Inside Climate News, he pushed back against the idea that the long list of projects would have to be pared back because of money shortages.

“We had some unprecedented infrastructure funding passed by the prior administration. Much of those funds will still be there,” he said.

But Dustyn Thompson, director of the Delaware Sierra Club, predicted that federal funding for flood control left over from the Biden administration won’t be easy to get under its successor. “Just because those buckets of money are sitting there doesn’t mean they are going to let anybody access it,” he said. Flood-protection measures on the Brandywine may now be more dependent on state spending, he said.

Indeed, this week the Trump administration told agencies to freeze payments on a broad range of federal spending, including for infrastructure. 

Potential sources of money for flood-control work include transportation funds, watershed rehabilitation cost-share programs, environmental restoration grant programs and hazard mitigation grants, all of which exist at the state and federal levels, the report team said in a statement. There may also be opportunities to use local funds or access private foundation dollars.

“We had some unprecedented infrastructure funding passed by the prior administration. Much of those funds will still be there.”

— Jerry Kauffman, University of Delaware’s Water Resources Center

DeCosta of the Brandywine Conservancy added that state and local governments in the watershed may not have to choose which projects to implement because they are funded from diverse sources, and some of that money is already in place.

“On many of these, we don’t have to prioritize,” he said. “We have such a wide breadth of options. We have structural and we have non-structural. Other things that do have a cost, such as preserving more land, are not competing for the same resources that have a structural element. The operation and maintenance of existing stormwater basins do not compete for dollars.”

And the proposed projects would build on existing flood-control programs, such as the acquisition of open space or upgrades to municipal storm sewer systems, that are ongoing. “We just need to increase the pace and remain focused on doing a lot of these things again,” DeCosta said.

The report, which cost $374,000, is the result of extensive discussions with lawmakers in Pennsylvania and Delaware, DeCosta said. The authors met with staff and elected officials in every municipality, had five public meetings to discuss the study and went to about 30 other public meetings where the report was mentioned. “One of our major goals was to have as much public engagement as we could,” he said.

Pennsylvania’s Department of Environmental Protection said it is reviewing the document. Spokesman Neil Shader said the agency already has several flood-reduction programs, some of which are cited in the study.

The report is now subject to a public comment period that ends March 1 and is due to be finalized in early April.