hydrogeology

When groundwater moves through an aquifer, pressure head is dissipated as it flows. Viscous friction produces drag, in the direction of flow. The force that transfers energy from water to soilid particles is known as the seepage force. In the subsurface, both gravity and seepage forces can act on a given soil particle. Under certain hydraulic conditions, seepage forces can cancel gravitational forces, leading to the condition known as quicksand.