Darcy’s Law (linear flow):

q is flux (flow/area)

K is hydraulic conductivity

H is total head (hydraulic head + pressure head)

q is water content

Richard equation (unsaturated flow):

h is hydraulic or pressure head

z is gravity head (elevation)

D is soil diffusivity ( )

Fick’s law (mass transport by diffusion):

First Law

J is the solute flux

D is the molecular diffusion coefficient

c is concentration of the solute (solute/unit mass of liquid)

Second Law

van Genuchten model (water content):

y is capillary pressure head

M=1-1/N