Analytical and Experimental Investigation of the Impact of Land Reclamation on Steady‐State Seawater Extent in Coastal Aquifers

Abstract

Previous studies of the effects of land reclamation on the extent of seawater in coastal aquifers have assumed that the reclaimed area penetrates to the impermeable base of aquifer, and that the seawater in the aquifer is entirely contained within reclaimed sediments. The current study extends previous research into the effects of reclamation on groundwater levels and seawater extent by developing new analytical expressions for the steady‐state heads and non‐dispersive freshwater‐seawater interface for situations where reclaimed soils overly permeable aquifer material. Situations involving reclaimed soils that are more permeable or less permeable than the original aquifer are explored. Sand‐tank experiments and associated numerical simulations (in 2D cross section) were undertaken to evaluate assumptions adopted in developing the solutions, which include an empirical correction to account for dispersion effects. Sand tank solute distributions are well matched to numerical modeling results, and provide validation of analytical solutions and the associated simplifications. Application of the new solution demonstrates that both the water level rise and the seaward shift of seawater extent caused by reclamation are modified with the inclusion of the underlying permeable layer, depending on permeability contrasts and the reclaimed area size. For example, if the reclaimed soil is less permeable than the original aquifer, water level rise and the seawater extent shift are reduced with the inclusion of an underlying permeable layer. The analytical solution developed in this study can provide rapid guidance on the changes to seawater extent and groundwater levels caused by land reclamation in otherwise permeable substrate.

Time Scale of the Formation of Fresh Groundwater Lens on an Atoll Island under the Influence of Land Reclamation

“…In the study of atoll island groundwater systems, these islands are often represented as symmetrical models with homogeneous aquifer features. This approach aids in facilitating sand-tank experiments and numerical simulations. , However, the actual structure of atolls is more complex, typically featuring a dual-aquifer system. Land reclamation projects are often executed on one side of these islands.…”

Groundwater Response to Tide Fluctuation and Rainfall in Coastal Reclamation Area

“…However, it overlooks environmental factors such as tides and natural disasters [26]. Zhang et al (2021) developed new analytical solutions for the steady-state heads and nondispersive SFI, which considered extended situations where reclaimed soils were more permeable than the original aquifer. However, it neglects number of real-world characteristics in a real reclamation site such as tides, spatiotemporal recharge, and aquifer heterogeneities [27].…”

“…Recently, Zhang et al (2019) considered the short-term variations of GWL [14]. Sheng et al (2021) and Zhang et al (2021), respectively, used new analytical solutions and a combination of various methods to study the response of GWL change to land reclamation in coastal areas. However, new analytical solutions ignore the real characteristics of the actual reclamation site and the combination of various methods overlookes the impact of tidal fluctuations [25,27].…”

Effects of Land Reclamation on a Subterranean Estuary

“…For example, during 1985–2015, the average rate of shoreline extension in Bohai Sea (China) was 188.47 m per year (Ding et al., 2019). Subsequently, the shifted shoreline may lengthen the groundwater flow path toward the ocean, raise the groundwater level, and move the freshwater‐seawater interface seaward (Hu et al., 2008; Zhang, Lu, Werner, 2021). In certain situations, the higher groundwater level may lead to water‐logging of soils inland of the reclaimed area (Hu & Jiao, 2010).…”