Estimation of aquifer parameters using tide-induced groundwater level measurements in a coastal confined aquifer

Aquifer parameters are useful for modeling sea water intrusion and other groundwater management issues in coastal areas. Oscillations in tide-induced groundwater levels contain important information of the properties of coastal aquifers and measurements of tidal effects can be employed to estimate the aquifer parameters. The solution to the transient groundwater flow model in a coastal confined aquifer with a sinusoidal fluctuation of the tide shows that the amplitude of groundwater levels is smaller than the tide, the tidal efficiency decreases exponentially with distance from the coast and the time lag increases linearly with distance from the coast. The aquifer property described by the ratio of storativity to transmissivity can be estimated if the amplitude (or tidal efficiency) and the time lag of groundwater levels are obtained based on filed measurements of tidal effects. Principle of these tidal methods is presented in this article, including those with one observation well and two observation wells. Hourly observations of the tide and groundwater levels at 14 observation wells in the coastal aquifer near Beihai, China are used to illustrate the application of these methods. The estimated ratio of storativity to transmissivity of the confined aquifer ranges from 1.66 x 10(-7) to 4.84 x 10(-7) d/m(2). For a given transmissivity of 750 m(2)/d, the storativity of the aquifer is in the range 1.245 x 10(-4) to 3.63 x 10(-4).