storage coefficient

   1. The volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in head [22].

   In a confined aquifer, the water is derived from storage with decline in head resulting from an expansion of the water and compression of the aquifer. Similarly, water added to storage with a rise in head is accommodated partly by compression of the water and partly by expansion of the aquifer. In an unconfined aquifer, the amount of water so released or accepted is generally negligible compared to the amount involved in gravity drainage or filling of pores, hence, in an unconfined aquifer, the storage coefficient is virtually equal to the specific yield.

   2. The volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in head (virtually equal to the specific yield in an unconfined aquifer.) 3. The volume of water a confined hydrogeologic unit releases from or takes into storage per unit subsurface area of the hydrogeologic unit per unit change in head.