Abstract
Abstract. The groundwater fluctuations due to tidal variations at an observation well in a coastal aquifer can be used to determine the tidal characteristics and aquifer parameters without conducting an aquifer test. In this study, a method, comprised of Jeng et al.'s solution (2005) and simulated annealing (SA) algorithm, is developed to determine the coastal aquifer parameters (hydraulic diffusivity, beach slope, and aquifer thickness) as well as the tidal characteristics (bichromatic-tide amplitudes, bichromatic-tide wave frequencies, and tidal phase lag) from the analysis of the tide-induced well-water-level (WWL) data. The synthetic WWL data generated from Jeng et al.'s solution (2005) with assumed parameter values and field data obtained from Barrenjoey beach, Australia, are analyzed. The estimated parameter values obtained from analyzing synthetic WWL data by the present method show good agreements with the previously assumed parameter values. The parameter estimation procedure may however fail in the case of a large shallow water parameter which in fact violates the constraint on the use of Jeng et al.'s solution (2005). In the analysis of field WWL data, the results indicate that the aquifer parameters estimated from the present method with single or multiple well data are significantly different from those given in Nielsen (1990). Inspecting the observed WWL data and the WWL data predicted from Jeng et al.'s solution (2005) reveals that the present method may provide better estimations for the aquifer parameters than those given in Nielsen (1990).
Highlights
IntroductionGroundwater levels of an aquifer fluctuate with tidal variations. The coastal aquifer parameters can be estimated from analyzing the well-water-level (WWL) data at an observation well without conducting conventional aquifer tests
In coastal areas, groundwater levels of an aquifer fluctuate with tidal variations
The CPU time listed in the right column is the computing time for parameter estimation in each case using a personal computer with Genuine Intel CPU 2140 @ 1.60 GHz and 1 GB RAM
Summary
Groundwater levels of an aquifer fluctuate with tidal variations. The coastal aquifer parameters can be estimated from analyzing the well-water-level (WWL) data at an observation well without conducting conventional aquifer tests. Nielsen (1990) used a perturbation technique to obtain an analytical solution up to the secondorder of amplitude parameter (α = A/D) for tidal dynamics in sloping sandy beaches In his model, the shoreline boundary condition at the interface of the beach and the ocean was allowed to vary with the tide height; it was invalid in the situations of flat beach and/or large tidal range that may cause a seepage point deviated from the shoreline. Li et al (2000) overcame this conflict by introducing a moving shoreline condition and considered the tides to be bichromatic, namely, tides can be represented by two different wave frequencies Both models treated the beach slope as a part of the perturbation parameter, which restricts the applicability of the models to the case of aquifers with large beach slopes. On the other hand, Teo et al (2003) developed a higher-order analytical solution based on the shallow water expansions for the water table fluctuations induced by the monochromatic tide in a sloping coastal aquifer. Jeng et al (2005) further considered the effect of bichromatic tide in the development of solution for WWL fluctuations in a sloping coastal aquifer
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