HGS RESEARCH HIGHLIGHT – The effects of land subsidence and its mitigating measures on shallow groundwater salinization in the low-lying coastal plain of East Japan
Tsai, C., Ito, Y., Liu, J., & Tokunaga, T. (2024). The effects of land subsidence and its mitigating measures on shallow groundwater salinization in the low-lying coastal plain of East Japan. In Environmental Research Communications. IOP Publishing. https://doi.org/10.1088/2515-7620/ad5951
“A 2D cross-section (A’B’) across the lower reach of Nabaki river (Figure 1(d)) was chosen as it extends through the subsided area and is parallel to the coastline. The cross-sectional model was developed by using HydroGeoSphere (HGS).”
Fig. 3. The groundwater head distributions of the four cases. (a) The assumed surface topography around 1960s with no pumping stations and (b) with two pumping stations. (c) The current surface topography with no pumping stations including surface water head distribution, and (d) with two pumping stations including surface water head distribution (Tecplot 2018).
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The research investigates how land subsidence and mitigation measures, specifically pumping stations and ditch systems in Shirako Town, Japan's lower Nabaki River region, interact.
Land subsidence, caused by natural and human factors, heightens flood risks in coastal areas, challenging infrastructure stability and environmental sustainability. While pumping stations and ditches aim to manage surface water levels and reduce floods, their impact on groundwater salinity near tidal rivers is unclear. Using a coupled surface-subsurface model, the study reveals potential risks like saline water intrusion into groundwater.
Pumping stations near riverbanks are often implemented to manage flooding, but they can lower the groundwater table, worsening subsidence and increasing saltwater intrusion risk. Lower groundwater tables enhance seawater flow into freshwater aquifers, accelerating groundwater salinization.
The study uses numerical modelling to investigate this issue. By simulating various scenarios, including different topographies and the presence of pumping stations, to understand their effects on groundwater dynamics. Results indicate that pumping stations, while effective for flood management, can induce saline water intrusion from tidal rivers into surrounding groundwater. Using HydroGeoSphere (HGS), a sophisticated modelling platform known for simulating coupled surface water-groundwater interactions, the researchers investigate how these factors influence groundwater salinity near tidal rivers. HGS's versatility allowed the researchers to model various scenarios and gain insights into the impact of subsidence and flood mitigation strategies on groundwater salinization.
By exploring the dynamics of land subsidence and its mitigation strategies concerning shallow groundwater salinization in East Japan's low-lying coastal plain. Land subsidence, influenced by both natural geological processes and human activities such as excessive groundwater extraction and infrastructure development, heightens the vulnerability of coastal areas to flooding during high tides. To counteract these risks, coastal regions often implement mitigation measures such as pumping stations and ditch systems aimed at managing surface water levels and preventing inundations.
However, the effectiveness of these mitigation strategies in relation to their impact on groundwater salinity near tidal rivers remains a topic of significant concern and study. Using a coupled surface-subsurface modelling approach, this research focuses on the lower Nabaki River region in Shirako Town, Japan. Their simulations reveal that while pumping stations are essential for flood control, they can inadvertently exacerbate the intrusion of saline water from tidal rivers into the adjacent groundwater aquifers. This unintended consequence highlights a critical trade-off: while these infrastructures help manage surface water levels and protect against flooding, they may simultaneously increase the vulnerability of coastal aquifers to saltwater contamination.
Despite the inherent limitations of 2D modelling approaches in capturing the full complexity of three-dimensional groundwater flow dynamics, this study provides valuable insights into the interactions between coastal groundwater systems and the processes driving salinization; by integrating field data with numerical modelling, they aim to contribute to a deeper understanding of how land subsidence and associated mitigation measures influence groundwater quality in coastal environments.
By leveraging HydroGeoSphere (HGS), a sophisticated modelling platform known for simulating coupled surface water-groundwater interactions, researchers were able to develop a 2D cross-sectional model of the river estuary. The study revealed that while pumping stations effectively manage surface water levels, they also inadvertently alter groundwater flow patterns, leading to increased vulnerability to saltwater intrusion.
A key advantage of HGS is its ability to simulate complex hydrological processes accurately. By leveraging this platform, the researchers were able to assess the adverse effects of pumping stations, which, while designed to prevent floods, may inadvertently induce saline water intrusion from tidal rivers into surrounding groundwater. This study provides critical information for policymakers and land managers, helping them understand the consequences of flood mitigation strategies on groundwater quality in vulnerable coastal areas.
Abstract:
Land subsidence in low-lying coastal regions results from geological and human factors, causing inundation during high tides. Mitigation measures, like pumping stations and ditch systems, aim to address this challenge. However, their impact on groundwater salinity near tidal rivers is understudied. Using a coupled surface-subsurface model, we investigate this issue in the lower Nabaki River region, Shirako Town, Japan. The simulation reveals adverse effects of pumping stations that induce intrusion of saline water from the tidal river into surrounding groundwater. While they are designed to prevent floods, these stations and ditches may inadvertently raise groundwater vulnerability to saltwater contamination. Despite 2D model limitations, it offers valuable insights into coastal groundwater dynamics and salinization. This study provides important information for policymakers and land managers to better understand the consequences of flood mitigation strategies on groundwater quality in vulnerable coastal areas.
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