Poiseuilles Law for simple structures.
Hydraulic conductivity for a flow in a tube
For a tube, with smooth border, saturated with a given fluid
of viscosity 
, we
can compute the flux q of fluid generated by a difference of pressure
at the extremity of the tube using poiseuille law. For a tube of radius r
and length l, the flux is given by:
Hydraulic conductivity for a flow between parallel plates
For a fracture, with smooth border, saturated with a given fluid
of viscosity , we
can compute the flux q of fluid generated by a difference of pressure
at the extremity of the fracture using poiseuille law. For a fracture of width
a, aperture l and length L, the flux is given by:
