Determining the hydraulic properties of coastal aquifer systems using groundwater response to tidal fluctuations: applicability and limitations

Abstract

Determination of the hydraulic properties of a coastal aquifer system with lower cost and acceptable accuracy has practical implications. Although many theoretical solutions have been developed over recent decades, most of them assume that an aquifer system extends inland and subjected a single-frequency tidal fluctuation on coastline boundary. In addition, only one hydraulic parameter, i.e., the hydraulic diffusivity, of an aquifer can be obtained in most cases. In this paper, the solution of groundwater response in a leaky confined coastal aquifer to dual frequency tidal fluctuations has been established. The new solution was then used as an example to discuss the applicability and limitations of using tidal fluctuations for determining coastal aquifer hydraulic properties. Our study illustrated that ocean tides could only transport to a limited distance towards inland depending on the coastal aquifer hydraulic properties. The tidal method is applicable only when changes in the hydraulic head within in a monitoring well can be detected with an acceptable accuracy. Both the hydraulic diffusivity and leakage can be identified from the monitored hydraulic heads. By incorporating the use of aquifer thickness, the transmissivity and storage coefficient of a perfectly confined aquifer can also be simultaneously estimated.

A generalized analytical solution of groundwater head response to dual tide in a multi‐layered island leaky aquifer system

“…In addition, it is known that the real-world ocean tides consist of multiple constituents, whose amplitudes, frequencies and phases are functions of geographic location (Kvale, 2012). In fact, in view of the linearity of Equations ( 1a)-( 1c), the multi-frequency analytical solution can be basically obtained by superposition principle (Trefry & Bekele, 2004;Yang et al, 2020).…”