Excavation Dewatering Pump Rate

Pump rate to draw an open excavation down in a target time and hold it against a steady inflow.

Run the calculator

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

Details, formula, and sources

With a safety-margined selection rate. Defers head to the pump total dynamic head calculator.

drawdown_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).

First-principles volume and pumping-rate arithmetic by name; defers total dynamic head to the pump-tdh tile.

The 7.48 gal/ft^3 constant is exact and public. The inflow must be estimated from a pumping test.

Estimate. AHJ and licensed professional govern.

Field names used by the API: pit_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