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Transmissivity From Specific CapacityThe following equation, based on the Cooper-Jacob (1946) solution for flow to a well in a confined aquifer, computes the specific capacity, Q/Sw, of a well:
where Q is constant discharge rate [L3/T], rw is pumped well radius [L], S is storativity [dimensionless], sw is drawdown in the well [L], T is transmissivity [L2/T] and t is time [T]. Approximate Formulas for Estimating Transmissivity from Specific CapacityUsing equation (1), Driscoll (1986) assumed the following values to develop approximate formulas for estimating transmissivity from specific capacity in confined and unconfined aquifers: T = 30,000 US gal/day/ft S = 0.001 (confined) or 0.075 (unconfined) rw = 0.5 ft t = 1 day Given these assumed values, Driscoll (1986) estimates transmissivity given the specific capacity of a well as follows: T = 2000(Q/sw) confined aquifer T = 1500(Q/sw) unconfined aquifer where T is transmissivity [US gal/day/ft], Q is constant discharge rate [US gal/min] and sw is drawdown in the pumped well after 1 day [ft]. If we express Q in m3/day and sw in m, the equations for computing T in m2/day are (Batu 1999): T = 1.385(Q/sw) confined aquifer T = 1.042(Q/sw) unconfined aquifer You also may convert specific capacity to transmissivity using equation (1).
Transmissivity From Specific Capacity Calculator developed by Glenn M. Duffield, HydroSOLVE, Inc. |
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