# iMOD User Manual version 4.4 (html)

#### 12.9STO Storage coefficients

The storage coefficient (for confined conditions) or specific yield (for unconfined conditions) of each modellayer is defined by one IDF (or a constant value). The value depends on the lithology of the modellayer. The storage coefficient in confined aquifers varies between 1x10${}^{-}$${}^{5}$ to 1x10${}^{-}$${}^{3}$. The specific yield ranges between $0.02$ for clay to $0.25$ for gravel. The STO storage coefficient corresponds with the SF1 variable specified in the MODFLOW BCF package and the SS and SY variable specified in the MODFLOW LPF package.