Also in: Disaster Response and Recovery
Flooded Basement Staged Pump-Down Schedule
Pumping a flooded basement dry in one go can collapse its walls or heave its floor.
Example
You enter
- Basement floor area (sq ft) 1200
- Water depth (ft) 6
- Daily drawdown after the test days (ft, 2 to 3) 2.5
- Pump rate (gpm) 50
You get
- Gal per ft 8977
- Total (gal) 53860
- Days 4 days if every drawdown holds
- Largest day (gal) 22442
- Largest day run (min) 449
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeBecause the saturated soil outside is still pushing and the water inside is holding the walls up. FEMA's guidance is a staged schedule: mark the water, pump down 1 ft, and wait overnight; if the level held, pump 1 ft more and wait again; then 2 to 3 ft every 24 hours until empty. If the water came back up after a test, the ground is still saturated, and the schedule stops rather than pushing through. The calculator turns that into days, gallons, and pump hours. A basement holds 7.48 gallons per square foot per foot of depth, so a 30 x 40 ft basement with 6 ft of water holds 8,977 gallons per foot and 53,860 gallons in all. At 2.5 ft per day after the tests the schedule is 1 ft, 1 ft, 2.5 ft, and 1.5 ft -- four days, not an afternoon -- and the largest day's 22,442 gallons keep a 50 gpm pump running 449 minutes, about 7.5 hours, well within a day. A drawdown above 3 ft per day is refused with the FEMA limit, and a pump that cannot move the largest day in 24 hours is flagged. Electrical and gas hazards in a flooded basement come first and are not addressed. It does not assess wall or floor condition, size a pump for head, treat Category 3 water, or plan drying. FEMA guidance, the restoration contractor, and a structural engineer where walls have moved govern.
Formula or tableday 1: 1 ft, wait 24 h; day 2: 1 ft more if the level held; then the daily rate (2-3 ft) until empty; days = number of steps (2 + ceil((depth - 2) / rate) for depths over 2 ft); gallons per ft = area x 1,728 / 231; pump minutes = largest day's gallons / gpm.
Source and editionFEMA, Mitigation and Basement Flooding (pumping out a flooded basement), with University of Nebraska-Lincoln Extension disaster education guidance. The restoration contractor, and a structural engineer where walls show movement, govern.
Free accessFEMA and university extension guidance are free public documents.
What governsEstimate. AHJ and licensed professional govern.
API field namesfloor_area_sqft, water_depth_ft, daily_drawdown_ft, pump_gpm, gal_per_ft, total_gal, days, largest_day_gal, largest_day_run_min
- Staged schedule 1 ft, wait; 1 ft, wait; then 2 to 3 ft per 24 hFEMA basement pump-down guidance
- Volume 1,728 / 231 = 7.4805 gal per cu ft, flat floor, no contents displacementexact conversion
- Failed test water returning after a drawdown stops the scheduleFEMA and UNL Extension guidance