A new approach for estimating transmissibility from specific capacity

Transmissibility estimated from specific capacity is subject to error, because the effects of duration of pumping and specific yield are not evaluated. Rearrangement of the Theis equation provides a mathematical relation for evaluating drawdown during nonequilibrium conditions and delayed yield from storage at any time after pumping begins. This relation is obtained from type curves of u plotted against u [ W ( u )] where u [ W ( u )] is equal to 1.632 × 10 −2 [( S y ) r 2 s / Qt ]. The only term that needs to be assumed is specific yield. The error of the estimated transmissibility will be 30 to 40% of the error made in assuming the apparent specific yield for u = 10 −2 and 10 to 15% for u less than 10 −4 . The curves presented in the paper were used to construct a transmissibility map of the valley‐fill aquifer in the Arkansas River valley of Colorado. The map was the foundation for an analog‐model analysis of the aquifer system. The transmissibilities estimated from the type curves correlate well with transmissibilities determined from aquifer tests and estimated from test‐hole logs.