What Ida Taught Chester County About Flooding (and How to Prepare for the Next One)

The remnants of Hurricane Ida on September 1–2, 2021 pushed Brandywine Creek to a record 21.04-foot crest at Chadds Ford, beating the 17.15-foot mark set by Floyd in 1999. Downingtown and Coatesville were hit hard, and Goose Creek flooded West Chester streets. The lesson: big floods recur here, and small creeks can be as dangerous as the main stem.

By West Chester Flood Cleanup Editorial Team · Published 2026-11-05

Chester County's own hazard planning calls flooding the county's most significant hazard (chesco.org/flood). This guide looks back at what happened, why it happened and what homeowners can do before the next big storm.

Ida's record at Chadds Ford

Ida arrived as a tropical remnant, not a hurricane, but it carried an enormous amount of rain in a short time. Much of it fell on ground that was already wet.

According to reporting by the Philadelphia Inquirer, the Brandywine at Chadds Ford crested at 21.04 feet, the highest on record there. The previous record, 17.15 feet, came from Hurricane Floyd in September 1999 (Inquirer). Beating a record by nearly four feet is unusual. It shows how much the rain from one storm can exceed what people living along the creek had come to expect.

The same reporting describes severe damage in Downingtown and Coatesville, both upstream towns on branches of the Brandywine. In Downingtown, the East Branch runs close to homes, businesses and roads in the center of the borough.

West Chester's experience was different. Contemporary reporting in the Delco Times says the borough's street flooding came mainly from Goose Creek, a much smaller stream, and that there were water rescues (Delco Times). That detail matters: you don't have to live next to the Brandywine to be in the path of fast-rising water.

What Ida showed homeowners:

• Records are not ceilings. The previous record was beaten by a wide margin.
• Upstream towns flood too. It's not only the lower Brandywine near the Delaware line.
• Small creeks flash flood. Streams that look like a trickle most of the year can fill streets in an hour.
• Basements fill from many directions. Creek water, runoff, groundwater and sewer backups often arrive in the same storm.

Major floods: 1920 to 2021

Ida wasn't the first. The Brandywine Flood Study, a watershed review, lists major floods in 1920, 1933, 1942, 1955, 1972 (Agnes) and 1973, followed by Floyd in 1999 and Ida in 2021 (Brandywine Flood Study summary, PDF).

A few patterns stand out:

• Tropical systems cause many of the worst floods. Agnes in 1972, Floyd in 1999 and Ida in 2021 were all tropical storms or their remnants. Late summer and early fall are peak risk.
• Floods come in clusters. 1972 and 1973 hit back to back. A wet period can mean several high-water events in a short span.
• The landscape has changed. Since the early floods, much of the watershed has gone from farms and woods to roads, rooftops and parking lots. Paved surfaces send rain into streams faster.
• Memory fades. Decades can pass between major floods. Many homeowners in the area today weren't here for Floyd, and few remember Agnes.

If you own an older home near a stream, there's a good chance it has flooded before, even if the current owners don't know it. Look for clues in the basement: old water lines on stone walls, rusted lower stair stringers and replaced mechanicals.

The upstream flood-control dams and their limits

The Brandywine watershed has five upstream flood-control facilities, including the Marsh Creek and Struble dams, according to the Brandywine Flood Study.

What these dams do:

• They hold back part of the runoff from the areas upstream of them during a storm.
• They release that water more slowly afterward.
• They can lower peak water levels downstream compared with what would happen without them.

What they can't do:

• They only control water from above the dam. Rain that falls below them, on tributaries and town streets, goes straight into the creek.
• They have a fixed capacity. In a storm as large as Ida, the volume of rain can exceed what storage can absorb.
• They don't stop flash flooding on small creeks. Streams like Goose Creek in West Chester aren't controlled by these dams at all.
• They don't stop basement flooding from groundwater or storm sewer backups.

The dams reduce risk; they don't remove it. Planning as if the dams will keep every flood away is the mistake that catches people off guard.

Flash flooding on smaller creeks

For many homes in West Chester, West Goshen, Downingtown and Kennett Square, the more likely threat is a smaller creek or storm drain rising fast during a cloudburst.

Why small creeks are dangerous:

• Very fast rise. A small watershed can go from normal to flood in less than an hour in intense rain.
• Little warning. There may be no official river forecast for that stream.
• Water in unexpected places. Culverts under roads clog with debris and send water over streets and into yards.
• Driving risk. The National Weather Service warns that many flood deaths happen in vehicles. Water over a road is deeper and faster than it looks.

Summer thunderstorms can cause this kind of flooding even when there's no named storm. If your street has flooded before, assume it will again.

What homeowners can do

You can't stop a creek from rising, but you can reduce how much damage it does.

Know your mapped and real risk

Check your property on FEMA's flood map, ChescoViews and the PA Flood Risk Tool. Our guide to the Chester County flood zone map walks through each one. Remember that small-creek and runoff flooding often happens outside mapped zones.

Get the right insurance

Standard homeowners policies don't cover flood. If water from a creek or runoff could reach your home, ask your agent about NFIP or private flood insurance, and buy it well before storm season because NFIP has a waiting period (pa.gov flood insurance).

Protect the basement

• Keep the sump pump tested and add a battery backup.
• Clean gutters and extend downspouts.
• Move valuables, papers and photos off the basement floor and onto shelves or upstairs.
• Raise the furnace, water heater and electrical panel when replacing them, if possible.
• Consider a backwater valve if sewer backups are a concern.

Have a plan to leave

Know two ways out of your neighborhood that don't cross low roads or creeks. Keep a go-bag with medications, documents and chargers.

Photograph your home now

A photo inventory of your basement and belongings, taken before a storm, makes a flood claim much easier.

Stream gauge alerts

The Chester County Water Resources Authority's Flood Tool covers 19 USGS stream gauges and lets you sign up for text or email alerts when a gauge rises (chesco.org water maps). Picking the gauge nearest you, and knowing what level means trouble for your street, gives you time to move cars and belongings. Our step-by-step guide to setting up Chester County stream gauge alerts shows how.

Five lessons to keep

1. Plan for a bigger flood than the last one. Ida beat the old record by almost four feet.
2. Watch the small creek near you, not only the Brandywine.
3. Insure for flood separately, and do it before the season starts.
4. Keep the basement ready: tested pump, raised valuables, clear drains.
5. Sign up for alerts now, while skies are clear, so a warning reaches you in time to act.

After the water goes down

Creek water is treated as contaminated (Category 3 under the industry's IICRC S500 standard). It carries mud, sewage and chemicals. That changes cleanup:

• Wet drywall, insulation and carpet that floodwater touched usually need to be removed, not dried.
• Hard surfaces need cleaning and disinfecting.
• The structure then needs drying with dehumidifiers and moisture readings to prevent mold.
• Everything should be photographed for your flood claim before it goes to the curb.

Stay out of floodwater, and don't turn on power in a flooded basement until it's been checked. Our flood damage cleanup team handles extraction, removal, sanitizing and drying for creek and storm flooding. If you're along the East Branch, see our Downingtown page for local service details.

FAQ

What was the Brandywine's highest crest at Chadds Ford?

Ida's crest of 21.04 feet in September 2021, according to the Inquirer, beating Floyd's 17.15 feet in 1999.

Will the flood-control dams prevent another Ida?

They help reduce peaks on the main stem, but they can't control rain that falls below them, on small creeks or in town. A storm like Ida can still cause major flooding.

Is West Chester borough in the Brandywine floodplain?

Most of the borough sits away from the Brandywine's main stem, but smaller creeks such as Goose Creek and runoff can flood streets and basements. Check your specific address.

When is flood season in Chester County?

Floods can happen any time, but many of the largest have come from tropical systems in late summer and early fall, and from heavy spring rain on wet ground.

Flooded by a creek or storm?

Call (555) 000-0000 for flood cleanup, sanitizing and drying. (555) 000-0000 · Get a Free Quote