Groundwater response to dual tidal fluctuations in a peninsula or an elongated island

Abstract

SUMMARY Groundwater flow in a peninsula or an elongated island is influenced by tidal fluctuations on both sides of the peninsula or island, which is named as dual tidal fluctuations. In this study, semianalytical solutions of transient groundwater flow in response to dual tidal fluctuations in an aquifer–aquitard system were presented for cases with and without the aquitard storage. These solutions were first derived using the Laplace transform and subsequently computed by the Fourier series numerical inverse Laplace transform. The derived solutions were found to agree very well with the results of numerical simulations by MODFLOW. The solution ignoring the aquitard storage approached the quasi‐steady state solution quickly when the mean sea level initial condition was used. The solutions with and without the aquitard storage were nearly the same at the early time and were separated from each other during the intermediate time, and the difference of solutions became constant at late time for small aquifer/aquitard storativity ratio and large tidal frequency. The propagation bias, which is the departure from the theoretical ratio of tidal attenuation to tidal lag, was enhanced not only with increase of the dimensionless specific leakage (aquitard/aquifer hydraulic conductance ratio) but also with decrease of the aquifer/aquitard storativity ratio and with the increase of the dimensionless tidal frequency. The solution with the aquitard storage was more sensitive to these three parameters. The newly developed solutions were capable of handling realistic initial conditions that might be approximated by piecewise linear functions. Copyright © 2012 John Wiley & Sons, Ltd.

Analysis of Tide and Offshore Storm‐Induced Water Table Fluctuations for Structural Characterization of a Coastal Island Aquifer

“…Aquifer characterization techniques have been developed to estimate aquifer properties (e.g., diffusivity D ) based on analysis of water table response to external forces (e.g., barometric fluctuations, tides) (e.g., Carr & Van Der Kamp, ; Ferris, ). These methods have been widely implemented (e.g., Alcolea et al, ; Rotzoll et al, ; Slooten et al, ; Trefry & Bekele, ; Wang et al, ) as they are often less‐resource intensive relative to other investigative methods (e.g., boring, pumping tests) and can provide information over large length scales. Independent estimates of D can be derived from calculating the rates of tidal attenuation ( D amp , amplitude‐resolved D ) and phase lags ( D pha ; phase‐resolved D ) as the signal propagates inland.…”

Two‐dimensional flow response to tidal fluctuation in a heterogeneous aquifer‐aquitard system

“…Secondly, the storage of the aquitard can be ignored. Thirdly, the tidal effect to the head in the unconfined aquifer is very small and can be negligible, compared with the effect of the confined aquifer (Jiao and Tang, ; Wang et al ., ). Volker and Zhang () pointed out that the second and third assumptions were too simplified, and might cause unacceptable errors when the leakance from the aquitard was greater than 1 day −1 .…”