Equations of Hydrogeology


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