GROUNDWATER HEAD FLUCTUATION IN A COASTALCONFINED AQUIFER OVERLAIN BY A SEMI-PERMEABLELAYER WITHSTORAGE EXTENDINGINFINITELY UNDER THE SEA

摘要

Analytical studies are carried out to investigate groundwater head changes in a coastal aquifer system in response torntidal fluctuations. The system consists of an unconfined aquifer, a leaky confined aquifer and a semi-permeable layer between them.rnThe leaky confined aquifer and its semi-permeable roof extend under the sea infinitely. An exact analytical solution is derived torninvestigate the influences of both leakage and elastic storage of the semi-permeable layer on the tide-induced groundwater headrnfluctuation in the semi-confined aquifer. Given the head fluctuation amplitude and phase shift at the coastline, the head fluctuation inrninland aquifer behaves exactly the same as that by Li and Jiao [2001b, Advances in Water Resources, p565-573]. Hence the solutionrnanalysis focuses on the impacts of the loading effect, the leakage and elastic storage of the roof on the groundwater head fluctuationrnat the coastline. The head at the coastline fluctuates with an amplitude approximately half of that, and with a phase shiftrnapproximately the same as that in the sea sufficiently far from the coastline. The tidal loading on the roof tends to increase therngroundwater head fluctuation at the coastline. Leakage from the roof's offshore part enhances the head fluctuation at the coastline.rnThe roof’s elastic storage tends to reinforce the tidal loading effect within the roof and damp the vertical, downward tidal wavernpropagation due to the direct hydraulic connection of the pore water in the roof with the tidal water at the seabed boundary. The finalrnimpact of the roof’s elastic storage is determined by the superposition of these two factors of opposite effects, which leads to arncomplicated, non-monotone dependence of the head fluctuation at the coastline on the roof’s elastic storage.