Specific Capacity, Coefficient of Storage

Specific Capacity:  Specific capacity of a well is the rate of flow from a well per unit of drawdown. It should be determined for the fall of the first meter, as it is not the same for all the drawdowns.

Coefficient of Storage or Storage Coefficient or Specific Storage or Storativity (S):  In general, storage coefficient (S) is defined as the volume of water that an aquifer releases or stores per unit surface area per unit decline or rise of water table.

                                                     Where, S = Storage Coefficient
                                                                        y_w = unit weight of water
                                                                 H = confine aquifer thickness
                                                                1/E_s = compressibility of aquifer, where E_s = elasticity of                                                                                   aquifer
                                                                1/E_w = compressibility of water, where E_w = elasticity of                                                                                    water = 2.1 x 10^-6 KN/m³ at 10°C

                                                 Typical Values of Elasticity (E_s) of Aquifer Material

Sl. No.	Aquifer Material	Elasticity (Es)
1.	Loose sand	104 to 2 x 104
2.	Dense sand	5 x 104 to 8 x 104
3.	Dense sandy gravel	105 to 2 x 105
4.	Loose clay	103 to 5 x 103
5.	Stiff clay	104 to 105