Most recent flooding in Prince George's County has been flash flooding from short, intense storms that overwhelm drainage and small creeks, usually outside the mapped floodplains. Water runs to the lowest point of a lot and enters through a window well, a door, a bulkhead or a floor drain, so a basement can flood without any river rising.
Key takeaways
- The county reports that most flooding in the past decade has been flash flooding, not floodplain flooding.
- Flash floods overwhelm drainage and small creeks, often outside the mapped floodplains.
- Water enters at the lowest point of a lot: window wells, doors, bulkheads and floor drains.
- Grading, downspouts and gutters decide how much water reaches the foundation.
- Tidal flooding on the Potomac and Patuxent is a separate risk, and it is a different claim.
- The county's flood maps are not a guarantee of safety, because flash water often falls outside them.
What is a flash flood, and why does it flood a basement with no river nearby?
A flash flood is water that arrives faster than the ground and the storm drains can absorb it. In Prince George's County, short intense storms often produce it, and the water runs off the land toward the lowest point of a lot. A basement can flood from that runoff even when no stream nearby has risen.
The county's own flood guidance says that most flooding in the past decade has been flash flooding from intense local storms that overwhelm drainage and small creeks, usually outside the mapped floodplains. The flood maps track streams and rivers. Water that never reaches a mapped stream can still fill a basement.
When runoff reaches the foundation faster than the soil and the drains can take it, the water finds the first way in, and the lowest level takes it.
Where does the water enter a basement in a storm?
Water usually enters at the lowest openings: window wells, doors, bulkhead hatches, cracks at the slab joint and floor drains. Finding the entry points is the first job, because drying a floor does nothing while water is still coming in.
A window well that drains poorly can fill to the sill and pour through the window. A bulkhead or a basement door that sits below grade is a common entry point in heavy rain. The slab joint and the cracks in the foundation wall carry water in from the soil, and a floor drain can push water up when the sewer or the drain line is full.
A technician checks each opening and the grading near it before opening up the walls. The line of water on the walls shows how high the water rose, and that tells you which openings were under it.
| Entry point | How it fails | What to check |
|---|---|---|
| Window well | Fills with rain and pours through the window | Drainage in the well, and the cover |
| Door or bulkhead | Runoff flows down the steps or under the door | Threshold height and the grade outside |
| Slab joint or foundation crack | Water wicks in from saturated soil | Staining on the wall at the floor line |
| Floor drain | Pushes water up when the drain line is full | Whether the water rose only at the drain |
Do gutters, downspouts and grading change the risk?
Yes. Downspouts that discharge near the foundation, gutters that overflow, and ground that slopes toward the house all add water to the spot where the foundation is weakest. Directing roof runoff away from the house and grading the soil away from the wall lower the risk before the next storm.
A downspout that empties at the foundation can send the whole roof's runoff into the soil beside the basement. A short extension that carries the water several feet away changes that. Gutters that are full of leaves overflow in the first heavy rain, and the water pours down the wall.
Grade is the longer-term fix. Soil that slopes toward the house holds water against the wall, while soil that slopes away lets it drain. Changing grade is building work, so ask a contractor and check the county permit requirements first.
- Clear the gutters before the storm season.
- Extend the downspouts so the roof water lands well away from the foundation.
- Look at the grade around the window wells and the bulkhead, not just the main walls.
How is flash flood water different from tidal flooding?
Flash flood water comes from heavy local rain over the land, and it usually enters through the doors, windows and low openings. Tidal flooding comes from the Potomac and the Patuxent, which are tidal near the county, and it rises from the bottom of a house upward through the floor drains. The two leave different marks and raise different questions with an insurer.
The county's flood guidance notes that coastal and tidal flooding affects the tidal Potomac and Patuxent. The Patuxent is tidal up to the confluence of the Western Branch. A house near tidal water can see both kinds of flooding, which is why the cause should be recorded before cleaning.
Insurance treats the two differently. A standard homeowners policy generally excludes flood, and river or tidal water is a flood matter. Keep photographs of the water line and of the outside grading so the source is clear.
What should a homeowner check before the next heavy rain?
Before the next heavy storm, clear the gutters, check that the downspouts discharge well away from the foundation, look at the window wells and the bulkhead for drainage, and move valuables off the lowest floor. These steps cost little and reduce the water that reaches the basement.
Check the sump pump, if there is one, by pouring water into the pit and watching it run. Keep the power to the pump on a circuit that is not in the flood path, and know where the breaker is before the water arrives.
If water begins to enter during a storm, move people and pets out of the room, shut off power to the wet area only if the panel is dry, and call (833) 490-5225 once the storm has passed. Do not walk through standing water to reach the panel.
- Clear gutters and extend downspouts.
- Test the sump pump before the storm.
- Move valuables off the floor of the lowest level.
Frequently asked questions
Is my basement flood-prone if it is outside a mapped floodplain?
Not necessarily. The county reports that most recent flooding has been flash flooding that happens outside the mapped floodplains. A house outside a mapped zone can still take water, so the flood map does not settle the risk for a specific basement.
Will my policy pay for flash flood water in the basement?
Water that comes in from outside during a storm is usually treated as flood, which a standard homeowners policy generally excludes. Check whether you hold flood coverage through an endorsement, a private policy or the National Flood Insurance Program, which has a 30-day waiting period.
How do I tell whether water came in through a window well or a drain?
Look at where the water line is on the walls and where the stain begins. A window well or door usually leaves water at the openings and a line across the wall, while a drain leaves water rising from the floor. A technician records both before cleaning.
Who do I call when a storm floods the basement?
Call (833) 490-5225 once the storm has passed and it is safe to enter. Keep out of standing water, and do not run the drains until the sewer side has been checked.
Sources
- Prince George's County Government - Local Flood Hazards
- Maryland Insurance Administration - Water Back Up
- Maryland Insurance Administration - Flood Insurance FAQs
This guide is general information for Prince George's County homeowners, not a substitute for an on-site inspection. Prices are estimates. See our disclaimer.