How this calculator works
Darcy discharge is proportional to bulk area and hydraulic driving gradient. Intrinsic permeability describes the medium, while hydraulic conductivity also includes fluid density, viscosity and gravity. The pressure form used here assumes horizontal flow; use total hydraulic head when elevation changes matter. Darcy flux Q/A is not pore-water speed. The latter also depends on effective porosity. The model assumes a saturated medium and sufficiently slow viscous flow.
Formula
Horizontal pressure form: Q = k A delta p/(mu L). Head form: Q = K A i, with K = k rho g/mu and i = delta h/L. Collected volume V = Qt.
Worked example
With k = 1e-12 m2, A = 1 m2, delta p = 10000 Pa, mu = 0.001 Pa s and L = 1 m, Q = 1e-5 m3/s. In 100 s this collects 0.001 m3.
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Frequently asked questions
Is permeability the same as conductivity?
No. Permeability has units of area and describes the pore structure; conductivity has units of speed and also depends on the fluid.
What area should I use?
Use the entire bulk cross-sectional area perpendicular to flow, including solids and pores.
Does this include unsaturated flow?
No. Unsaturated hydraulic conductivity depends strongly on water content and requires a separate model.