Attributes:

UNTE [meters above reference datum] (element wise),

UNTK [meters above reference datum] (node wise), (horizontal models only)

The lower boundary of the aquifer is required to calculate the horizontal free/phreatic surface, or the initial and maximum thickness of the aquifer in conjunction with the upper aquifer boundary (OBER), initial potential heads (EICH) or the surface elevation (GELA).

It is essential to specify the lower boundaries in order to iterate the aquifer thickness.