TY - JOUR
T1 - Effects of Unsaturated Flow on Salt Distributions in Tidally Influenced Coastal Unconfined Aquifers
AU - Luo, Zhaoyang
AU - Kong, Jun
AU - Yu, Xiayang
AU - Lu, Chunhui
AU - Werner, Adrian D.
AU - Barry, David A.
PY - 2023/6
Y1 - 2023/6
N2 - Unsaturated flow influences both the seawater extent under steady-state conditions and the propagation of tides in coastal aquifers. However, its effects on salt distributions in tidally influenced coastal aquifers are little investigated. The present study used numerical simulations and data from laboratory experiments to analyze the effects of unsaturated flow on density-dependent solute transport in coastal unconfined aquifers. The effects of the inland boundary condition (i.e., constant-head or constant-flux) were tested. Compared to a stable sea level, the results show that unsaturated flow has a more pronounced influence on salt distributions in coastal unconfined aquifers when tides are considered, regardless of the type of inland boundary condition. Neglect of unsaturated flow effects leads to expansion of the upper saline plume (USP), shrinkage of the saltwater wedge (seaward movement of saltwater wedge), and overestimation of water and salt exchange across the aquifer-ocean interface. This is caused by a lower head in the nearshore area during high-tide periods with the unsaturated zone effects removed. Thus, without the unsaturated zone, stronger head gradients within the nearshore aquifer occur at high tide, leading to stronger tidally driven seawater infiltration and hence a larger USP. Counterintuitively, ignoring unsaturated flow effects leads to greater average inland head over a tidal period, which shifts the saltwater wedge seaward. It is concluded that unsaturated zone effects should not be neglected for modeling tide-affected seawater intrusion, especially if quantification of near-shore conditions is important.
AB - Unsaturated flow influences both the seawater extent under steady-state conditions and the propagation of tides in coastal aquifers. However, its effects on salt distributions in tidally influenced coastal aquifers are little investigated. The present study used numerical simulations and data from laboratory experiments to analyze the effects of unsaturated flow on density-dependent solute transport in coastal unconfined aquifers. The effects of the inland boundary condition (i.e., constant-head or constant-flux) were tested. Compared to a stable sea level, the results show that unsaturated flow has a more pronounced influence on salt distributions in coastal unconfined aquifers when tides are considered, regardless of the type of inland boundary condition. Neglect of unsaturated flow effects leads to expansion of the upper saline plume (USP), shrinkage of the saltwater wedge (seaward movement of saltwater wedge), and overestimation of water and salt exchange across the aquifer-ocean interface. This is caused by a lower head in the nearshore area during high-tide periods with the unsaturated zone effects removed. Thus, without the unsaturated zone, stronger head gradients within the nearshore aquifer occur at high tide, leading to stronger tidally driven seawater infiltration and hence a larger USP. Counterintuitively, ignoring unsaturated flow effects leads to greater average inland head over a tidal period, which shifts the saltwater wedge seaward. It is concluded that unsaturated zone effects should not be neglected for modeling tide-affected seawater intrusion, especially if quantification of near-shore conditions is important.
KW - laboratory experiment
KW - numerical simulation
KW - saltwater wedge
KW - tidal fluctuation
KW - upper saline plume
UR - http://www.scopus.com/inward/record.url?scp=85162147107&partnerID=8YFLogxK
U2 - 10.1029/2022WR032931
DO - 10.1029/2022WR032931
M3 - Article
AN - SCOPUS:85162147107
SN - 0043-1397
VL - 59
JO - Water Resources Research
JF - Water Resources Research
IS - 6
M1 - e2022WR032931
ER -