Well Pump Drawdown & Recovery Rate Calculator
Calculate the drawdown in a pumping well and estimate aquifer recovery rate using the Theis equation and specific capacity method. Useful for well design, pump sizing, and aquifer characterization.
Pumping Test Parameters
Recovery Test Parameters
Formulas Used
Drawdown: s = Hpumping − Hstatic (ft)
Residual Drawdown: s' = Hrecovery − Hstatic (ft)
Recovery Rate: RR = (s − s') / trecovery (ft/min)
Recovery Percentage: RP = [(s − s') / s] × 100 (%)
Specific Capacity: SC = Q / s (GPM/ft)
Transmissivity (Theis, 1963 approximation): T ≈ SC × 192.5 (ft²/day)
Hydraulic Conductivity: K = T / b (ft/day), where b = saturated aquifer thickness
Casing Storage Volume: Vcasing = π × r² × Δh (ft³)
Assumptions & References
- Drawdown is measured as the difference between static and pumping water levels at the end of the pumping period.
- Recovery rate is assumed approximately linear for the elapsed recovery period (conservative estimate).
- Transmissivity is estimated using the Theis (1963) single-point approximation: T ≈ SC × 192.5 ft²/day, valid for confined aquifers with full penetration.
- Hydraulic conductivity assumes uniform aquifer thickness (homogeneous, isotropic aquifer).
- Aquifer contribution percentage compares actual drawdown to theoretical casing-storage-only drawdown.
- Full recovery time is a linear extrapolation and may underestimate actual recovery in low-yield aquifers.
- References: Theis, C.V. (1935); Cooper & Jacob (1946); Driscoll, F.G. (1986) Groundwater and Wells, 2nd ed.; USGS Techniques of Water-Resources Investigations.
- 1 US gallon = 0.13368 ft³; 1 GPM/ft ≈ 192.5 ft²/day transmissivity (Theis approximation).