Analytical studies of groundwater-head fluctuation in a coastal confined aquifer overlain by a semi-permeable layer with storage

Analytical studies are carried out to investigate groundwater-head changes ill a coastal aquifer system in response to tidal fluctuations. The system consists of an unconfined aquifer, a semi-confined aquifer and a semi-perme able confining unit between them. An exact analytical solution is derived t o investigate the influences of both leakage and storage of the semi-permea ble layer on the tide-induced groundwater-head fluctuation in the semi-conf ined aquifer. This solution is a generalization of the solution obtained by Jiao and Tang (Water Resource Research 35 (1999) 747-751) which ignored th e storage of the semi-confining unit. The analytical solution indicates tha t both storage and leakage of the semi-permeable layer play an important ro le in the groundwater-head fluctuation in the confined aquifer. While leaka ge is generally more important than storage, the impact of storage on groun dwater-head fluctuations changes with leakage. With the increase of leakage the fluctuation of groundwater-head in the confined aquifer will be contro lled mainly by leakage. The study also demonstrates that the influence of s torativity of the semipermeable layer on groundwater-head fluctuation is ne gligible only when the storativity of the semi-permeable layer is comparabl e to or smaller than that of the confined aquifer. However, for aquifer sys tems with semi-permeable layer composed of thick, soft sedimentary material s, the storativity of the semi-permeable layer is usually much greater than that of the aquifer and its influence should be considered. (C) 2001 Elsev ier Science Ltd. All lights reserved.