On Sept. 1-2, 2021, the remnants of Hurricane Ida dumped up to eight inches of rain in just a few hours on parts of the Brandywine Creek watershed in Delaware and Pennsylvania, breaking a 75-year record for the volume of water discharged at Wilmington, and causing some $45 million in damage to private property and public infrastructure throughout the region.
The storm, which also memorably flooded a stretch of interstate highway in central Philadelphia, was one of 10 high-precipitation events to flood the watershed and cause widespread damage and disruption in only 18 years between 2003 and 2021. Those floods followed dozens of others in the 19th and 20th centuries.
The growing frequency and force of this century’s storms, and the flooding that accompanied them, are consistent with climate-change forecasts for more and bigger rain events, higher temperatures, and – without careful control mechanisms now -- even more flooding.
Now, three organizations that represent many stakeholders in the watershed have produced a plan that’s designed to reduce flooding and help communities withstand bigger rainstorms in future.
The Brandywine Flood Study, from the nonprofit Brandywine Conservancy, the University of Delaware’s Water Resources Center, and Pennsylvania’s Chester County Water Resources Authority, advocates a massive program that would rebuild, repair or remove “structural” features such as roads, bridges, dams and culverts that worsen flooding by restricting the flow of flood waters. The analysis also calls for upgrades to “non-structural” measures such as policy, planning, public education and emergency management that would be modified to allow for the bigger storms that are coming with climate change, and do a better job of protecting the 265,000 residents of the watershed, 43,000 of whom live in Delaware.

Dr. Jerry Kauffman, director of UD’s Water Resources Center, said the cost of implementing all items on the long list could be as high as “nine digits” – hundreds of millions of dollars – and so would have to attract significant federal funding as well as that raised from state and local sources. Funding from the outgoing Biden administration is still available for such projects, and as bridges, for example, need replacing, advocates for flood control are urging highway departments to rebuild them bigger and stronger, he said.
Kauffman acknowledged that the report calls for huge work. “It is a massive list but the magnitude of the flooding was equally as massive,” he said. “There’s certain to be another flood, maybe not as intense as Ida but we know that lesser floods like Agnes are certain to happen again. It is a comprehensive look at the flooding, and we think we have identified the causes and the solutions.”
The study urged towns to install more ‘green infrastructure’ like rain gardens to absorb rainfall before it becomes runoff, and ensure that underserved communities are not neglected. Other measures would include preserving open space in the areas around the headwaters of the creek’s main stem and its eastern and western branches so that the land is better able to absorb heavy rainfall. More zoning codes also need to be written to control the addition of new pavement that worsens flooding, the report said.
And it called for the acquisition of flood-plain land, either in public open space or in privately owned conservation easements, because those lands represent some 17 billion gallons of flood storage that could at least diminish storm waters flowing into Delaware.
“The results of this storm were catastrophic for many communities in the central and lower portions of the watershed,” the 56-page report said, referring to Ida. “In some cases, individual recovery efforts are still ongoing. These impacts were the catalyst for this study, to provide recommendations for communities to be better protected and prepared for future storms.”

After being researched and written over about a year and a half, the document was publicly announced on Thursday at a conference in Chadd’s Ford, Pa. on conserving and protecting the watershed, as well as creating conditions that would allow it to better-survive future floods. The study is a draft which will be released on Friday for a 45-day public-comment period, and then finalized in April.
Dustyn Thompson, director of the Delaware Sierra Club, welcomed the report but said it didn’t pay enough attention to the needs of environmental justice communities such as those in some parts of Wilmington, and said that may reflect the relative wealth of people who live in the Brandywine watershed. He called for a statewide assessment of flood risk that would look at the exposure of all sectors of society including those that are disproportionately affected by environmental harms.
“You have the more affluent areas around the Brandywine that have resources to call attention, and then you have lower-income areas, where you haven’t seen anything saying ‘This is how we’re going to avoid the next one,’” Thompson said.

Any new federal funding for flood control will likely be stopped or, if it’s money left over from the Biden administration, will likely be made harder to obtain under the new Trump administration, Thompson predicted. But the flood study will at least help state and local governments identify projects that could be implemented with their own funds, he said.
The Brandywine watershed is no stranger to flooding, or to measures designed to curb it. Between 1920 and 1973, six flood-control mechanisms were installed, together representing 5.5 billion gallons of flood-control capacity, or enough to fill Lincoln Financial Field, home of the Philadelphia Eagles, seven times over, the report said. But those measures are not enough to prevent the kind of flooding that came with Ida, and is expected to worsen with climate change in future.
“As storms become more frequent and intense, and development continues throughout the watershed, the challenge of flooding continues,” the report said.
It produced what it called an “actionable suite” of flood-mitigation recommendations. For example, it identified bridges, culverts, and dams throughout the watershed that may raise flood elevations for 10-, 50-, 100-, and 500-year floods, mostly because their openings may be too small to convey dramatically increased volumes of water. In many cases, flood levels may increase upstream, covering bridge decks, and taking main roads out of service. Addressing inadequately sized infrastructure generally requires rebuilding the structures with larger waterway openings, or removing them entirely, the report said.
The analysis examined 291 bridges, culverts and dams along the mainstem, East and West Branches of the Brandywine, of which, 172, or 60%, were found to be undersized and/or insufficient. On the mainstem creek in Delaware, a third of 25 bridges, dams and culverts were identified as undersized. In upstream areas of Pennsylvania, some reservoirs should be expanded to hold more water during storms, the report said.
It also urged municipal governments to reduce their stormwater flows by using measures including detention basins and wet ponds that would hold and absorb heavy rainfall so that it doesn’t swell downstream flooding. “These features convey, reduce peak flowrates and quantity, and control stormwater runoff before it is released to surface waters throughout the drainage area,” the report said. “Stormwater infrastructure is typically constructed during land development and is regulated by local municipalities in accordance with state law.”
The study urged local governments to reduce the amount of impervious surface such as parking lots that generate runoff and worsen downstream flooding. Removing that surface and replacing it with either natural vegetation or pervious pavement can help curb runoff, it said.
In areas where even pervious surfaces may not be effective in absorbing heavy rains because of, for example, the underlying geology, towns should consider adding underground stormwater storage.
Improved public education about flooding during extreme rain events is also among the report’s recommendations. To remind people about the magnitude of Ida’s flooding, for example, that could be achieved by installing high-water-mark signs at places like the US Route 13 bridge in northeast Wilmington where the waters rose up to 9.7 feet during the storm.
State Rep. Debra Heffernan (D. Brandywine Hundred), chair of the House Natural Resources & Energy Committee, welcomed the report.

“There is certainly value in the flood study report, especially as it increases our understanding of what can be done to mitigate future flooding risks, even as we acknowledge that the exact solutions and how they will be funded haven't been decided yet,” Heffernan said.
While working to prevent or divert floods, the report also advised towns to step up their planning to protect people and property from the waters. It urged local emergency planners to pay special attention to roads that may be cut off by flood waters, preventing access by emergency services; to identify bridge crossings and low-lying roads, and to determine communities that are bisected by a waterway, and which therefore night need two emergency-response plans.
For each municipality, the study also calculated how much land was developed in an area that would be flooded by a 100-year storm -- that which is deemed to have a 1 percent chance of happening in a given year. In New Castle County, it found 528 acres containing 52 structures were in that zone; in Wilmington, there were 434 acres and 270 structures that would be flooded by a 100-year storm. It said the amount of impervious surface in Wilmington increased by 45 percent from 2001 to 2021, far more than in the two other main urbanized areas of the watershed: West Chester, Pa. and the Route 30 corridor in the Great Valley region of Pennsylvania.
To protect themselves from flood waters, buildings can opt to elevate above the expected flood height, or install ‘dry’ or ‘wet’ flood proofing, the report said. Owners of properties that are already subject to repeated flooding, and can expect worse conditions in future, might be covered by buyout programs under which the state or local government buys houses from willing sellers, then demolishes them and leaves the resulting open space as a barrier to future floods.
“Where structures have been repeatedly damaged, eventually the solution will be moving away,” Kauffman said.
But such programs may drive people away, diminishing the local tax base. “Many residents may be unwilling to participate, and those who do may choose to move out of the municipality, which has potential ramifications for the tax base and overall fabric of the community,” the report said.
Read the full draft report here: