TY - JOUR

T1 - Effect of cut-off wall on freshwater storage in small islands considering ocean surge inundation

AU - Yang, Jie

AU - Graf, Thomas

AU - Luo, Jian

AU - Lu, Chunhui

N1 - Funding Information: The files and data to reproduce the modelling results were uploaded separately to HydroShare ( Yang, 2020 ). This research was supported by the National Natural Science Foundation of China (52009032, 51879088) and the Fundamental Research Funds for the Central Universities (B210202019). C. Lu acknowledges the financial support from the Fundamental Research Funds for the Central Universities (B200204002) and the Natural Science Foundation of Jiangsu Province (BK20190023). We thank the editorial board of Journal of Hydrology for handling our manuscript, especially two anonymous reviewers, whose constructive comments helped improve the manuscript.

PY - 2021/12

Y1 - 2021/12

N2 - Freshwater lenses (FWL) underneath islands are often unique freshwater resources. Constructing cut-off walls in coastal islands to increase the FWL size has been proposed and tested effective. Meanwhile, seawater inundation induced by ocean surges on low-lying islands can cause the vertical intrusion of saltwater and salinization of FWL. Constructing cut-off walls can influence the post-inundation recovery once the FWL is salinized during the inundation. This influence has not been investigated and considered when discussing the feasibility of cut-off walls. In this study, we numerically simulated an ocean-surge inundation on a 2D, vertically oriented island constructed with a cut-off wall, using a coupled surface–subsurface approach. We varied the aquifer permeability and the depth of the cut-off wall. The effect of the cut-off wall on FWL was quantitatively assessed in terms of FWL volume and flushing time. The results show that the cut-off wall can significantly increase the volume of FWL, confirming previous studies, especially when it is constructed in high-permeability (>10−10.5 m2) islands and deeper. In addition, the cut-off wall can significantly reduce seawater infiltration by up to 40% during the inundation. Therefore, the recovery tends to be accelerated in the early stage, and in islands of low & intermediate permeability. However, the average recovery in high-permeability islands can be slowed down, because the cut-off wall reclaims larger and deeper space that is harder for flushing. As a first attempt to assess the feasibility of the cut-off wall construction from the perspective of FWL recovery, our study is important for the management of freshwater on islands facing the risk of ocean-surge inundation.

AB - Freshwater lenses (FWL) underneath islands are often unique freshwater resources. Constructing cut-off walls in coastal islands to increase the FWL size has been proposed and tested effective. Meanwhile, seawater inundation induced by ocean surges on low-lying islands can cause the vertical intrusion of saltwater and salinization of FWL. Constructing cut-off walls can influence the post-inundation recovery once the FWL is salinized during the inundation. This influence has not been investigated and considered when discussing the feasibility of cut-off walls. In this study, we numerically simulated an ocean-surge inundation on a 2D, vertically oriented island constructed with a cut-off wall, using a coupled surface–subsurface approach. We varied the aquifer permeability and the depth of the cut-off wall. The effect of the cut-off wall on FWL was quantitatively assessed in terms of FWL volume and flushing time. The results show that the cut-off wall can significantly increase the volume of FWL, confirming previous studies, especially when it is constructed in high-permeability (>10−10.5 m2) islands and deeper. In addition, the cut-off wall can significantly reduce seawater infiltration by up to 40% during the inundation. Therefore, the recovery tends to be accelerated in the early stage, and in islands of low & intermediate permeability. However, the average recovery in high-permeability islands can be slowed down, because the cut-off wall reclaims larger and deeper space that is harder for flushing. As a first attempt to assess the feasibility of the cut-off wall construction from the perspective of FWL recovery, our study is important for the management of freshwater on islands facing the risk of ocean-surge inundation.

KW - Coupled surface–subsurface modelling

KW - Cut-off wall

KW - Freshwater lens

KW - Ocean surge inundation

KW - Seawater intrusion

UR - http://www.scopus.com/inward/record.url?scp=85118973001&partnerID=8YFLogxK

U2 - 10.1016/j.jhydrol.2021.127143

DO - 10.1016/j.jhydrol.2021.127143

M3 - Article

AN - SCOPUS:85118973001

VL - 603

JO - Journal of hydrology

JF - Journal of hydrology

SN - 0022-1694

M1 - 127143

ER -