Experimental and Numerical Analysis on Hydraulic Characteristics of Coastal Aquifers with Seawall

Abstract

In this study, hydraulic model experiments were conducted to measure the saltwater–freshwater equilibrium interface in a coastal aquifer with underground obstructions such as an impermeable seawall. To analyse the hydraulic characteristics inside the coastal aquifer, numerical analysis was conducted using a non-hydrostatic Navier-Stokes solver based on the Porous Body Model (PBM), which can directly analyse groundwater flow. A unique saltwater–freshwater equilibrium interface that does not appear in typical coastal aquifer analyses was observed in a sandy tank experiment. In the experiment, the rise of the groundwater level behind the seawall increased the pressure gradient and groundwater flow rate, causing the saltwater–freshwater interface to move towards the sea and a freshwater region to form on the seabed in front of the seawall. The numerical analysis enabled close examination of the groundwater level distribution, groundwater flow, seawater–freshwater interface, and pore water pressure characteristics of the coastal aquifer with underground obstructions. The sandy tank experiment also provided an understanding of the hydraulic characteristics of groundwater in the coastal aquifer with a seawall, which previously could not be accurately analysed. The experimental and analytical results demonstrated that the rise of groundwater level due to underground obstructions in the coastal aquifer increased the pressure gradient and groundwater flow rate and slowed seawater intrusion. This principle can be employed to sufficiently reduce seawater intrusion of coastal aquifers.

Experimental and Numerical Investigation of Self-Burial Mechanism of Pipeline with Spoiler under Steady Flow Conditions

“…As suggested by Brorsen and Larsen [34], the flux density of the flow generation source in the momentum equation (Equation (3)) is gradually increased for three seconds at the beginning of the current generation [35], and is shown in Equation (5).…”

The impact of aquifer stratification on saltwater intrusion characteristics. Comprehensive laboratory and numerical study

“…Sandbox laboratory setups have been extensively utilized to study the fundamental mechanisms of saltwater intrusion in coastal aquifers (Abdoulhalik et al, 2017; Armanuos et al, 2019; Goswami & Clement, 2007; Konz et al, 2008; Kuan et al, 2012; Liu et al, 2017; Robinson et al, 2016; Stoeckl & Houben, 2012; Takahashi et al, 2018; Zhang et al, 2002). The majority of laboratory studies have recreated SWI in homogeneous synthetic aquifers (Abdelgawad et al, 2018; Abdoulhalik & Ahmed, 2018a, 2018b; Q. Chang et al, 2019; Guo et al, 2019; Kuan et al, 2019; Lee et al, 2019; Levanon et al, 2019; Memari et al, 2020; Na et al, 2019; Noorabadi et al, 2017; Shen et al, 2020; Stoeckl et al, 2019; Yu et al, 2019). Nevertheless, sandbox setups have been successfully employed to study freshwater—saltwater interface in aquifers with structured—sedimentary heterogeneity (Houben et al, 2018), in freshwater lenses, located in heterogeneous island aquifers (Dose et al, 2014; Stoeckl et al, 2015), as well as inside fractured porous media (Etsias et al, 2021).…”

“…The majority of laboratory studies have recreated SWI in homogeneous synthetic aquifers (Abdelgawad et al, 2018;Abdoulhalik & Ahmed, 2018a, 2018bQ. Chang et al, 2019;Guo et al, 2019;Kuan et al, 2019;Lee et al, 2019;Levanon et al, 2019;Memari et al, 2020;Na et al, 2019;Noorabadi et al, 2017;Shen et al, 2020;Stoeckl et al, 2019;Yu et al, 2019). Nevertheless, sandbox setups have been successfully employed to study freshwater-saltwater interface in aquifers with structuredsedimentary heterogeneity (Houben et al, 2018), in freshwater lenses, located in heterogeneous island aquifers (Dose et al, 2014;Stoeckl et al, 2015), as well as inside fractured porous media (Etsias et al, 2021).…”

2-D Characteristics of Wave Deformation Due to Wave-Current Interactions with Density Currents in an Estuary

“…The mechanism and hydrodynamic characteristics of the interactions between waves and currents were analyzed accounting for the densities of freshwater and seawater. For this purpose, a 3-D numerical analysis model [47,48] based on the existing 3-D numerical wave tank (NWT), LES-WASS-3D [49][50][51] was introduced to analyze density currents in this study.…”

“…Figure 4 presents the computed water surface profiles in the numerical water basin during one wave period. Figure 3 shows that the wave spatial envelope is gradually attenuated in both of the added damping zones by the numerical dispersion caused by the coarse grid system and the wave For the boundary condition of the impermeable slope in a quadrilateral mesh system according to spatial discretization based on finite difference method, the impermeable condition is adopted in the normal direction and slip condition is adopted in the tangential force for the inclined structure by applying the reasonable boundary [48,51] based on Petit et al [71]. Figure 4 presents the computed water surface profiles in the numerical water basin during one wave period.…”