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Groundwater Flow (Darcy) Calculator

Work out groundwater flow (darcy) instantly with clear inputs, formula shown and shareable results.

About Groundwater Flow (Darcy) Calculator

Darcy's law makes groundwater discharge proportional to hydraulic conductivity, gradient and area: Q = KiA. A 3.5 m head drop over 250 m gives a gradient of 0.014, so with K = 2e-4 m/s across 400 m2 the flow is 1.12e-3 m3/s, about 97 m3 a day. The Darcy velocity is a flux, not the actual pore water speed.

Formulas

Darcy's law

Q = K x i x A, with i = head difference / path length

Darcy velocity

v = K x i

Worked example

With the default values below, Groundwater Flow (Darcy) Calculator returns Groundwater Flow Rate of 1.12000 × 10⁻³. Change any input above and every figure here is recalculated in your browser.

Inputs used

Hydraulic conductivityminimum 0 m/s
0.0002 m/s
Head difference
3.5 m
Flow path lengthminimum 0 m
250 m
Cross-sectional areaminimum 0 m2
400 m2

Results

Groundwater Flow Rate
1.12000 × 10⁻³ m3/s
Hydraulic Gradient
1.4000 × 10⁻²
Darcy Velocity
2.8000 × 10⁻⁶ m/s
Flow Per Day
96.768 m3/day

Step by step

  1. 1Values used
  2. 2Darcy's law
  3. 3Darcy velocity
  4. 4Groundwater Flow Rate= 0.00112 m3/s
  5. 5Hydraulic Gradient= 0.0140
  6. 6Darcy Velocity= 0.0000 m/s
  7. 7Flow Per Day= 96.768 m3/day

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is the Darcy velocity not the real water speed?

Because water only moves through the pores. Dividing by porosity gives the higher seepage velocity that a tracer would actually show.

What conductivity values are typical?

Gravel 1e-2 to 1 m/s, sand 1e-5 to 1e-2, silt 1e-8 to 1e-5, and clay below 1e-9 m/s.

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