8.5 Parameters of Groundwater Storage

Water storage is a term used within agriculture to define locations where water is stored for later use. These range from natural water

stores, such as groundwater aquifers, soil water and natural wetlands to small artificial ponds, tanks and reservoirs behind major dams.

The parameters usually concern the geometry of and distances in the domain to be modeled and those physical properties of the

aquifer that are more or less constant with time but that may be variable in space.

Some parameters may be influences by changes in the groundwater situation, like the thickness of a soil layer that may reduce when

the water table drops and the hydraulic pressure is reduced.

8.5.1: Specific Yield (Sy)  Specific yield, also known as the drain-able porosity, is a ratio, less than or equal to the effective porosity, indicating the volumetric fraction of the bulk aquifer volume that a given aquifer will yield when all the water is allowed to drain out of it under the forces of gravity.  It can be simplified as a volume of water released from storage per unit area per unit change in water level (for unconfined aquifer) . Value of Specific yield will be refer the table below from Johnson (1967) based on the type of soil and it in ranges from 0.01 to 0.3.