# Darcy's law

From AMS Glossary

## Darcy's law

The relationship for movement of fluids through permeable or porous media, such as soil, which states that at low Reynolds numbers the flow velocity The hydraulic head where

*V*is proportional to hydraulic gradient*dh*/*dl*, where the constant of proportionality*K*is the hydraulic conductivity:*h*is the height of fluid in a manometer, which is proportional to the fluid pressure, while*l*is the slant length in the medium along the flow streamline. The velocity*V*is really a specific discharge (volume flow rate of fluid per unit cross-sectional area of medium), and is sometimes called the Darcy velocity or Darcy flux. The hydraulic conductivity depends both on the permeability*k*of the medium (e.g., sand vs clay), and on the kinematic viscosity ν of the fluid:*g*is gravitational acceleration.Freeze, R. A., and J. A. Cherry 1979. Groundwater. 15–18.