Bulk Movement of Water between Phreatic and Confined Aquifers Induced by Pumping

From a water management perspective, the bulk quantity of water moved and where it has been sourced from are more important than simply estimating drawdown effects due to pumping. This note considers the problem of estimating the total quantity of water discharged between each aquifer in a multilayer aquifer model of Dudley Ward and Falle. Direct formulas are obtained in terms of the storativities and leakage coefficients. Assuming a typical disparity of scale between storativities of the phreatic aquifer and confined aquifers, type curves show that over time the vast majority of extracted water is sourced from the overlying phreatic aquifer.