Attributes: SPEI [-] (element wise) or KSPE [-] (node wise)
Meaning in horizontal models:
In case of a transient calculation, you can define a storage coefficient S [-] at each element (SPEI) or rather at each node (KSPE) of an unconfined aquifer. In a confined aquifer, the default storage coefficient S0 = S / thickness = 3.3 10-6 is used. The value can be changed in the file sitr.
Meaning in 3D models and vertical models:
Usually, the calculation of the specific pressure-storativity in the transient pressure equation :
uses for the variable n [-] the specified porosity (PORO). For the case either SPEI or KSPE is defined, this value is used instead of the porosity, otherwise, the porosity is initialized with 0.2.
For the transient flow computation the user has to decide which calculation module to use. The module SITRA requires node wise storage coefficients or the porosity. For SITRA, it is better to define the attribute KSPE. Otherwise, the element wise attribute SPEI must be averaged to node wise values. In contrast to SITRA the module INSTAT uses element wise storage coefficients or the porosity. Therefore, it is preferable to use SPEI.