Also in: Disaster Response and Recovery
Excavation Dewatering Pump Rate
Pump rate to draw an open excavation down in a target time and hold it against a steady inflow.
Example
You enter
- Pit length at water surface (ft) 20
- Pit width at water surface (ft) 12
- Drawdown depth (ft) 3
- Time to draw down (min) 30
- Steady inflow / seepage (gpm) 40
- Pump-sizing margin (%) 25
You get
- Gallons to remove 5386 gal
- Pump rate (draw down + hold) 219.5 gpm
- Safety-sized pump rate 274.4 gpm
Checked against published worked examples from: Indigo Water Group (Sidney Innerebner, PhD, PE).
Details, formula, and sources
ScopeWith a safety-margined selection rate. Defers head to the pump total dynamic head calculator.
Formula or tabledrawdown_gal = pit_len x pit_wid x drawdown x 7.48052; pump_gpm = drawdown_gal / drawdown_min + inflow; sized_gpm = pump_gpm x (1 + safety/100).
Source and editionFirst-principles volume and pumping-rate arithmetic by name; defers total dynamic head to the pump-tdh tile.
Free accessThe 7.48 gal/ft^3 constant is exact and public. The inflow must be estimated from a pumping test.
What governsEstimate. AHJ and licensed professional govern.
API field namespit_len_ft, pit_wid_ft, drawdown_ft, drawdown_min, inflow_gpm, safety_pct, drawdown_gal, pump_gpm, sized_gpm
- Volume constant 7.48052 gal per ft^3 (exact)physical fact
- Safety margin 25% pump-sizing margin (default)pump-selection practice