Effects of Land Reclamation on a Subterranean Estuary

Submarine groundwater discharge via coastal aquifers is an important pathway for land-derived chemicals to enter the oceans. While previous studies have mostly focused on natural coastal aquifers, little attention has been paid to those modified by land reclamation. This study used laboratory experiments and numerical simulations to investigate the effects of land reclamation on flow and mixing processes in a nearshore subterranean estuary. The results show that, regardless of the permeability, the addition of reclamation soil will shift the tide-driven upper saline plume (USP) seaward and reduce the USP size. When the aquifer is reclaimed by low-permeability soil, the seawater intrusion length is reduced for small tidal amplitudes but extended as tidal amplitude further increases. Depending on the tidal amplitude, high- and low-permeability reclamation soils prolong or shorten the average particle travel time in the USP, the freshwater discharge zone, and the saltwater wedge. Compared to the case without reclamation, high-/low-permeability reclamation soil enhances/weakens the water discharge rate across the aquifer-ocean interface, narrows/expands the freshwater discharge zone, and increases the tide-/density-driven recirculation percent. Findings from this study highlight the complexity of nearshore groundwater systems subject to human activities, and have significant implications for better understanding the fate of terrestrially sourced chemicals in subterranean estuaries before discharging into the coastal water.

Automated summary

Submarine groundwater discharge is a crucial pathway for land-derived chemicals to enter the oceans. This study investigates the effects of land reclamation on flow and mixing processes in a nearshore subterranean estuary through laboratory experiments and numerical simulations. The study finds that reclamation soil alters the tide-driven upper saline plume and affects the freshwater discharge zone and saltwater wedge.