Groundwater response to tidal fluctuations in wedge-shaped confined aquifers

Abstract

Most of the analytical solutions to describe tideinduced head fluctuations assume that the coastal aquifer has a constant thickness. These solutions have been applied in many practical problems ignoring possible changes in aquifer thickness, which may lead to wrong estimates of the hydraulic parameters. In this study, a new analytical solution to describe tide-induced head fluctuations in a wedge-shaped coastal aquifer is presented. The proposed model assumes that the aquifer thickness decreases with the distance from the coastline. A closed-form analytical solution is obtained by solving a boundary-value problem with both a separation of variables method and a change of variables method. The analytical solution indicates that wedging significantly enhances the amplitude of the induced heads in the aquifer. However, the effect on time lag is almost negligible, particularly near the coast. The slope factor, which quantifies the degree of heterogeneity of the aquifer, is obtained and analyzed for a number of hypothetical scenarios. The slope factor provides a simple criterion to detect a possible wedging of the coastal aquifer.

Tide‐induced head fluctuations in coastal aquifers of variable thickness

“…Near the coast, a decreasing thickness (negative wedging parameter) produces a slope factor greater than 1. Similar results are reported by Cuello et al (2017) for an aquifer whose thickness decreases to zero. Conversely, an increasing thickness (positive wedging parameter) produces a slope factor smaller than 1 near the coast.…”

“…The solution is obtained by solving a boundary‐value problem combining the separation of variables and change of variables methods. This solution is a generalization of the solution obtained by Cuello et al (2017) for an aquifer whose thickness decreases with the distance to the coast. The effect of widening or thinning of the aquifer on the induced head fluctuations is analysed in terms of a wedging parameter.…”

“…The proposed analytical solution is a generalization of the solution obtained by Cuello et al (2017). Note that for b L = 0 ( α = − 1/ L ) the thickness of the aquifer defined by Equation ) becomes b ( x ) = b 0 (1 − x / L ) 2 , which is the same expression proposed by these authors for an aquifer thickness that decreases to zero with the distance to the coast.…”

“…Hantush proposed linear and exponential laws to describe variations of the aquifer thickness (Hantush, 1962a,b,c). To the authors' knowledge, Cuello, Guarracino, and Monachesi (2017) derived the first analytical solution for tide‐induced fluctuations that considers spatial variations in the aquifer thickness. This solution also provides a simple criterion to predict a possible thickness variation of the aquifer based on the computation of the slope factor introduced by Trefry and Bekele (2004).…”

Hydrogeological Characterization of Coastal Aquifer on the Basis of Observed Sea Level and Groundwater Level Fluctuations: Neretva Valley Aquifer, Croatia

“…Confined aquifer thickness has been shown to have a crucial role in the determination of groundwater signals. Hereby, Cuello et al [30] demonstrated that the wedging drastically increases the amplitude of the groundwater piezometric head inland. In 2007, Xia et al [26] presented an analytical solution of piezometric head inland, which incorporated several parameters in tidal methods: (i) subsea roof length extension, (ii) permeability of the outlet capping, (iii) outlet capping thickness, (iv) variable loading efficiency (LE), and (v) partial effects of the leakance within the offshore and inland sub-domains.…”