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.
Highlights
Industrial development and population growth are accompanied by increases in water demand, for which groundwater plays a significant source
The time to reach a steady state varies depending on the experimental conditions, it represents the time reach a steady state varies depending on the experimental conditions, it represents the time when when changes the groundwater the coastal and the saltwater-freshwater interface changes in the in groundwater level oflevel the of coastal aquiferaquifer and the saltwater-freshwater interface rarely rarely occur for an extended period
We investigate the groundwater flow in the coastal aquifer, pore water pressure distribution, and the formation process of the seawater–freshwater equilibrium interface under the practical condition for scale, which could not be verified in the scale model experiment
Summary
Industrial development and population growth are accompanied by increases in water demand, for which groundwater plays a significant source. The Navier-Stokes solver based on the Porous Body Model (PBM) was introduced, the latter of which can directly analyse the groundwater flow while accounting for fluid resistance according to the characteristics (particle diameter, porosity, shape) of the coastal aquifer. This is a departure from conventional methods that depend on hydraulic conductivity. We analyse the groundwater level distribution, groundwater flow, and pressure gradient according to seawall construction in the coastal aquifer to investigate the mechanism of the formation of the seawater–freshwater equilibrium interface. This study seeks to understand the hydraulic characteristics of groundwater in a coastal aquifer with a seawall
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