For transient simulations of groundwater systems, the elasticity of the aquifer needs to be defined. The elasticity is not due to the elasticity of the individual grains that make up the aquifer, but rather reflects primarily the rearrangement of the individual grains as the fluid pressure in the aquifer changes. There is also an elastic effect due to the elasticity of water (water expands a little with a decrease in pressure), but it is minor relative to the impact of grain rearrangement. In MAGNET, we represent this elasticity in terms of aquifer storage (specific yield or specific storage). By default, a specific yield of 0.1 and a specific storage of 10-5 m-1 is applied throughout the model domain; but again, you can use zones to represent local heterogeneities (localized effective values or interpolation of scatter points).