## Description

After the keyword $PERMEABILITY_TENSOR the intrinsic permeability, which is a measure of the ability of a porous material to allow fluids to pass through it, is defined. Both, isotropic and anisotropic systems are supported. This keyword can be used in the processes such as groundwater flow and liquid flow.

## Parameters

The first parameter (char) distinguishes between ISOTROPIC ORTHOTROPIC and ANISOTROPIC.

In isotropic cases (ISOTROPIC), one permeability value (double) is used for all directions.

The orthotropic case (ORTHOTROPIC) requires the entry of three values (double double double) for the X,Y,Z direction.

The anisotropic case (ANISOTROPIC) allows to define a 3x3 permeability tensor,

P11 P12 P13

P21 P22 P23

P31 P32 P33

i.e. 9 values written in one row P11 P12 P13 P21 P22 P23 P31 P32 P33

The unit for permeability is m^{2}.

Attention: For groundwater flow processes (GROUNDWATER_FLOW), the hydraulic conductivity in m/s is used instead of the permeability but the keyword stays $PERMEABILITY_TENSOR. The following example shows an isotropic case with a hydraulic conductivity of 5.7870370e-4 m/s.

## Example

### Theis_2D

#MEDUIM_PROPERTY . . . $PERMEABILITY_SATURATION 1 1.0 $PERMEABILITY_TENSOR ISOTROPIC 5.787037037037e-4 . . . . #STOP