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Dewatering Well Yield Calculator (Dupuit-Forchheimer)

Estimate the steady-state pumping rate a dewatering well can sustain in an unconfined aquifer, using the Dupuit-Forchheimer equation.

Computed in your browser — nothing you enter is uploaded. Figures are presented in United States units and terminology, and each formula’s basis is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax
330 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Estimated well yield

5.97 CFM

Check your inputs

This is a steady-state estimate assuming a fully penetrating well in a homogeneous, isotropic unconfined aquifer — real dewatering systems are affected by partial penetration, aquifer boundaries, and non-steady flow, and should be verified with an actual pump test.

Equivalent in m³/day
243.51 m³/day
Equivalent in US gallons per minute
44.67 gpm

Running these inputs gives 5.97 CFM as the estimated well yield. Expect some drift against the real job; the calculation is solid but conditions on site are not. Currently reading for United States — pick a different market above and the figures re-cast accordingly.

Add the equipment this sizes

This result is a specification — 5.97 CFM — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.

Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Regulatory standards & verification citations

  • Dupuit-Forchheimer equation for steady radial flow to a well in an unconfined aquifer: Q = pi x K x (h1² − h2²) / ln(r1/r2)

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Frequently asked questions

What is the Dupuit-Forchheimer equation used for?
It's a classic well hydraulics formula for estimating steady-state groundwater flow to a pumping well in an unconfined aquifer, widely used for early dewatering and water supply well planning.
Why does the answer depend on ln(r1/r2) rather than a simple ratio?
Radial groundwater flow toward a well isn't uniform — flow lines converge, and the logarithmic term correctly captures how the hydraulic gradient increases as flow approaches the well, a signature feature of radial flow problems.
How accurate is this compared to real dewatering performance?
It's a reasonable planning-level estimate for a single well in ideal conditions — real systems (especially well fields with multiple wells) benefit from an actual pump test and, for complex sites, numerical groundwater modeling.