Can Storage Coefficient Be Neglected in the Estimation of Unconfined Aquifer Parameters?

Abstract

Unlike the Neuman solution (1974), the Dagan solution (1967) neglects elastic storage of unconfined aquifers. Whereas theformer has been commonly used in the analysis of aquifer pumpingtests, application of the latter to determination of aquiferparameters are rare. This article evaluates the reliabilityof the Dagan solution (1967) for the determination of the horizontaland vertical hydraulic conductivity Kr and Kz and specific yieldSy by neglecting the role of aquifer storage coefficient S.To be consistent in the analysis of aquifer test data, the Dagansolution was combined with an inverse computational procedureso that Kr, Kz, and Sy can be automatically calculated. Computationsconverge relatively fast because evaluation of the Dagan solutionis mathematically simpler than is the Neuman solution. Datafrom three pumping tests conducted in alluvial aquifers in thePlatte and Republican River valleys, Nebraska, were analyzed.Earlytime drawdown data from the site in the Platte River valleyare scarce, but plenty of early-time drawdowns were collectedfrom the two sites in the Republican River valley. Comparisonof the results from the Dagan and the Neuman solution indicatesthat the Dagan solution provides aquifer parameter values veryclose to those of the Neuman solution in most situations. Formost practical purposes, the Dagan solution is as good as theNeuman solution for aquifer test analysis.