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These properties are storativity (S), specific storage (S s) and specific yield (S y). According to Groundwater , by Freeze and Cherry (1979), specific storage, S s {\displaystyle S_{s}} [m −1 ], of a saturated aquifer is defined as the volume of water that a unit volume of the aquifer releases from storage under a unit decline in hydraulic head.
Another kind of specific quantity, termed named specific quantity, is a generalization of the original concept. The divisor quantity is not restricted to mass, and name of the divisor is usually placed before "specific" in the full term (e.g., "thrust-specific fuel consumption"). Named and unnamed specific quantities are given for the terms below.
The fraction of water held back in the aquifer is known as specific retention. Thus it can be said that porosity is the sum of specific yield and specific retention. Specific yield of soils differ from each other in the sense that some soil types have strong molecular attraction with the water held in their pores while others have less.
Specific yield (S y) is also a ratio between 0 and 1 (S y ≤ porosity) and indicates the amount of water released due to drainage from lowering the water table in an unconfined aquifer. The value for specific yield is less than the value for porosity because some water will remain in the medium even after drainage due to intermolecular forces.
Specific storage or storativity: a measure of the amount of water a confined aquifer will give up for a certain change in head; Transmissivity The rate at which water is transmitted through whole thickness and unit width of an aquifer under a unit hydraulic gradient. It is equal to the hydraulic conductivity times the thickness of an aquifer;
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Dividing through by the specific storage (S s), puts hydraulic diffusivity (α = K/S s or equivalently, α = T/S) on the right hand side. The hydraulic diffusivity is proportional to the speed at which a finite pressure pulse will propagate through the system (large values of α lead to fast propagation of signals). The groundwater flow ...
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