Combined Effect of Tides and Varying Inland Groundwater Input on Flow and Salinity Distribution in Unconfined Coastal Aquifers

• Main Authors: Gibbes, B. (Author), Jin, G. (Author), Kuan, W.K (Author), Li, L. (Author), Robinson, C.E (Author), Xin, P. (Author)
• Format: Article
• Language: English
• Published: Blackwell Publishing Ltd 2019
• Subjects: Aquifers; atmospheric forcing; atmospheric tide; coastal aquifer; Coastal unconfined aquifers; coastal water; coastal water quality; Coastal water quality; Discharge (fluid mechanics); estuary; experimental study; flow measurement; freshwater input; groundwater; Groundwater resources; groundwater-seawater interaction; Hydrochemistry; Hydrogeology; intertidal environment; Nonlinear interactions; oceanic oscillations; oscillation; salinity; Salinity distributions; Salt water intrusion; saltwater intrusion; seawater; Seawater; spatial distribution; submarine groundwater discharge; Submarine groundwater discharge; Submarines; subterranean environment; subterranean estuary; Subterranean estuary; Tides; unconfined aquifer; Unconfined coastal aquifers; underwater environment; water exchange; water quality; Water quality
• Online Access: View Fulltext in Publisher; View in Scopus
• ISBN: 00431397 (ISSN)
• ISSN: 00431397 (ISSN)
• DOI: 10.1029/2018WR024492

Tides and seasonally varying inland freshwater input, with different fluctuation periods, are important factors affecting flow and salt transport in coastal unconfined aquifers. These processes affect submarine groundwater discharge (SGD) and associated chemical transport to the sea. While the individual effects of these forcings have previously been studied, here we conducted physical experiments and numerical simulations to evaluate the interactions between varying inland freshwater input and tidal oscillations. Varying inland freshwater input was shown to induce significant water exchange across the aquifer-sea interface as the saltwater wedge shifted landward and seaward over the fluctuation cycle. Tidal oscillations led to seawater circulations through the intertidal zone that also enhanced the density-driven circulation, resulting in a significant increase in the total SGD. The combination of the tide and varying inland freshwater input, however, decreased the SGD components driven by the separate forcings (e.g., tides and density). Tides restricted the landward and seaward movement of the saltwater wedge in response to the varying inland freshwater input in addition to reducing the time delay between the varying freshwater input signal and landward-seaward movement in the saltwater wedge interface. This study revealed the nonlinear interaction between tidal fluctuations and varying inland freshwater input will help to improve our understanding of SGD, seawater intrusion, and chemical transport in coastal unconfined aquifers. ©2019. American Geophysical Union. All Rights Reserved.