Transmissivity from Specific Capacity

The following equation, based on the Cooper and Jacob (1946) solution for flow to a well in a confined aquifer, computes the specific capacity, Q/S_w, of a well:

$$\frac{Q}{s_w}=\frac{T}{0.183\text{log}\left(\frac{2.25Tt}{r_w^{2}S}\right)}\text{(1)}$$

where Q is constant discharge rate [L³/T], r_w is pumped well radius [L], S is storativity [dimensionless], s_w is drawdown in the well [L], T is transmissivity [L²/T] and t is time [T].

We can rearrange equation (1) to find an expression for T as follows:

$$T=0.183\frac{Q}{s_w}\text{log}\left(\frac{2.25Tt}{r_w^{2}S}\right)\text{(2)}$$

Because T also appears in the logarithm term of equation (2), we can use a technique such as successive approximation to solve for T.

You also may convert specific capacity to transmissivity using approximate formulas.

Transmissivity from Specific Capacity Calculator
Q/sw =	[L3/T/L]
t =	[T]
rw =	[L]
S =	[dimensionless]
Use consistent units for the above input parameters. For example, enter Q/sw in m3/day/m, t in days and rw in m to compute T in m2/day.