You’ve probably seen it before. A heavy rainstorm moves through town and suddenly water is ponding at intersections, collecting along curbs, or temporarily covering parts of the street.
It’s a common question:
“If we have storm drains, why does my street still flood?”
The answer is that stormwater systems are designed to manage rainfall—but they aren’t designed to prevent all flooding during every storm.
Storm Drains Have Limits
Stormwater infrastructure is designed to handle a certain amount of rainfall over a specific period of time.
Most storms are relatively small and pass through the system without issue. During larger storms, however, rain can fall faster than storm drains, pipes, ditches, and channels can carry it away.
Think of it like pouring water into a funnel.
Pour slowly, and the water flows through easily.
Pour too quickly, and water temporarily backs up until the funnel can catch up.
Stormwater systems work much the same way.
Rain Doesn’t Fall Evenly
Not every storm is the same.
Some storms produce light rain over several hours. Others deliver large amounts of rain in a short period of time.
When intense rainfall occurs, water can accumulate faster than it can enter storm drains.
This can create temporary ponding in:
- Streets
- Intersections
- Low-lying areas
- Parking lots
- Roadside ditches
In many cases, the water disappears shortly after the rain slows or stops.
Urban Areas Create More Runoff
Before development, much of the rain that fell on the landscape soaked into the ground.
Today, rooftops, streets, driveways, sidewalks, and parking lots prevent water from infiltrating.
Instead, rain becomes runoff.
The more impervious surfaces an area contains, the more stormwater must be carried by the drainage system.
This is one reason communities invest in both traditional drainage infrastructure and green infrastructure practices that help water soak into the ground.
Leaves, Debris, and Sediment Can Reduce Capacity
Storm drains work best when water can flow freely into and through the system.
Leaves, grass clippings, litter, and sediment can partially block storm drains and reduce the amount of water they can carry.
Residents can help by:
- Keeping leaves and debris away from storm drains
- Sweeping instead of hosing debris into the street
- Properly disposing of yard waste
- Reporting blocked storm drains when they are observed
Even small obstructions can affect drainage during heavy rainfall.
Some Streets Are Designed to Store Water Temporarily
This surprises many people.
In some situations, streets provide temporary storage during large storms.
Allowing water to pond in roadways for a short period can help protect homes, businesses, and other structures from flooding.
While temporary street flooding may be inconvenient, it is often preferable to water entering buildings.
As stormwater moves through the system, these areas typically drain once capacity becomes available downstream.
Why Doesn’t the City Just Build Bigger Pipes?
It’s a reasonable question.
Designing a system large enough to eliminate all flooding during every possible storm would require extremely large infrastructure and significant costs.
Instead, communities balance:
- Public safety
- Cost
- Available space
- Environmental impacts
- Expected storm frequency
Stormwater systems are generally designed to manage common and moderately severe storms while reducing risk during larger events.
Even the largest systems have limits during extreme rainfall.
What You Can Do
Residents play an important role in reducing localized flooding.
You can help by:
- Keeping storm drains free of leaves and debris
- Directing downspouts toward vegetated areas when appropriate
- Maintaining rain gardens and other infiltration practices
- Reporting blocked inlets or drainage structures
- Avoiding dumping grass clippings, leaves, or trash into streets and ditches
Small actions across the community can improve drainage and help stormwater systems function more effectively.
Why It Matters
Flooding is not always a sign that something is broken.
Often, it is a result of intense rainfall exceeding the temporary capacity of the stormwater system.
Understanding how stormwater moves through our community helps residents recognize the challenges of managing runoff while protecting homes, businesses, roadways, and local waterways.
As our community grows and weather patterns change, reducing runoff and improving stormwater management will continue to play an important role in building resilience.
Our Water, Our Responsibility.