Stream Depletion in a Two-Layer Leaky Aquifer System

A new semianalytical stream-depletion solution is obtained for pumping from a well beside a stream in a two-layer leaky aquifer system. The well abstracts water from an upper unconfined aquifer underlain by an aquitard and a second semiconfined aquifer. The governing equations reduce to the equations that describe flow in a Hantush-Jacob leaky aquifer, in which the bottom aquifer has zero drawdown for all time, when the storativity of the bottom aquifer becomes infinite. This allows a Hantush-Jacob leaky aquifer solution to be compared with the solution for a bottom aquifer with finite storativity, and this comparison shows that the Hantush-Jacob approximation significantly underestimates stream depletion at larger values of time. In addition, comparison of the two-aquifer solution with a stream-depletion solution for a single aquifer shows that a single-aquifer solution closely approximates the two-aquifer solution when the single-aquifer transmissivity is replaced with the sum of transmissivities for the two-layer system. This suggests that a similar approximation might be used in a previously obtained solution to obtain a very general stream depletion model for multiaquifer systems.