Can storage coefficient be neglected in the estimation of unconfined aquifer parameters?

Unlike the Neuman solution (1974), the Dagan solution (1967) neglects elastic storage of unconfined aquifers. Whereas the former has been commonly used in the analysis of aquifer pumping tests, application of the latter to determination of aquifer parameters are rare. This article evaluates the reliability of the Dagan solution (1967) for the determination of the horizontal and vertical hydraulic conductivity K_r and K_z and specific yield S_y by neglecting the role of aquifer storage coefficient S. To be consistent in the analysis of aquifer test data, the Dagan solution was combined with an inverse computational procedure so that K _r, K_z, and S_y, can be automatically calculated. Computations converge relatively fast because evaluation of the Dagan solution is mathematically simpler than is the Neuman solution. Data from three pumping tests conducted in alluvial aquifers in the Platte and Republican River valleys, Nebraska, were analyzed. Early-time drawdown data from the site in the Platte River valley are scarce, but plenty of early-time drawdowns were collected from the two sites in the Republican River valley. Comparison of the results from the Dagan and the Neuman solution indicates that the Dagan solution provides aquifer parameter values very close to those of the Neuman solution in most situations. For most practical purposes, the Dagan solution is as good as the Neuman solution for aquifer test analysis.