Specific Storativity
Specific storativity of a porous medium is defined as the volume of water released or added into a unit volume of the aquifer under unit declination in the piezometic head (Φ). Thus it can be written as,
|
(7.1) |
Where, S0 is the specific storativity of the aquifer, ΔVW is the amount of water release or added into the aquifer, V is the total volume of the aquifer and ΔΦ is the change in the piezometric head.
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| Fig. 7.1 Sketch to explain aquifer storativity of confined aquifer |
Aquifer storativity
Consider a confined aquifer of horizontal area A and depth D as shown in Fig. 7.1. The initial piezometric head is at C. VW is the amount of water withdrawn from the aquifer. As a result of pumping, the piezometric head is dropped down by an amount of ΔΦ. In this case, the equation (7.1) can be written as,
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(7.2) |
Or,
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(7.3) |
Or,
|
(7.4) |
Where Ss is the aquifer storativity.
Thus storativity for a confined aquifer is defined as the volume of water released from storage or added to the aquifer per unit horizontal area under unit declination or rise of peizometric head (Φ). It may be noted that like transmissivity (T) of
an aquifer, the storativity is also an aquifer property. In case of confined aquifer, when Dupuit assumption of essentially horizontal flow in an aquifer is considered, the parameter T and Ss should be used.
However, in the case of three dimensional flow,
the hydraulic conductivity (K) and specific storativity (S0)
need to be used.