Seawater Intrusion Research Articles

Groundwater quality and hydrogeochemical analysis for assessing saltwater intrusion in coastal aquifers of Eastern Odisha, India

Climate change has intensified hydro-climatic variability worldwide, altering rainfall patterns, soil moisture dynamics, and freshwater availability. Across Africa, these changes undermine ecosystem resilience and threaten livelihoods dependent on rain-fed agriculture and wetlands. Within this broader frame, the Tana Delta in coastal Kenya is increasingly vulnerable to climate-driven stresses. This study examined rainfall and temperature trends, their influence on soil–water systems, and implications for community resilience. A mixed-methods design combined household surveys (n=382), focus group discussions, key informant interviews, meteorological records (1990–2020), and remote sensing techniques, including the Normalized Difference Vegetation Index, the Normalized Difference Water Index, and Geographic Information Systems were used for this study. Results show a statistically significant decline in rainfall (p < 0.05) and average warming of +1.2 °C. Wetland extent declined by 21% between 2017 and 2023, with more severe losses and salinity intrusion in lower-delta zones. Communities reported increased reliance on boreholes. Communities reported increased reliance on boreholes, rivers and canals, though many water sources are increasingly saline. Soil degradation and reduced moisture retention have intensified water scarcity, thus undermining agriculture, pastoralism, and fishing. Household surveys confirmed that 76% of respondents experienced declining crop yields, with about 64% reporting livestock losses and 58% noted the reduction of fish catches. These findings demonstrate that hydro-climatic variability has significantly undermined soil and water security in the Tana Delta. Effective adaptation strategies such as wetland restoration, salinity management and climate-smart agriculture are urgently needed to sustain livelihoods and ecosystem services. Strengthening community-based water governance will also be critical in enhancing resilience to future climate stresses.

The comprehensive, accurate, and rapid acquisition of large-scale surface deformation using Interferometric Synthetic Aperture Radar (InSAR) technology provides crucial information support for regional eco-geological safety assessments and the rational development and utilization of groundwater resources. The Linfen-Yuncheng Basin in Shanxi Province is one of China’s historically most frequented regions for geological hazards in plain areas, such as land subsidence and ground fissures. This study employed the coherent point targets based Small Baseline Subset (SBAS) time-series InSAR technique to interpret a dataset of 224 scenes of 5 m resolution RADARSAT-2 satellite SAR images acquired from January 2017 to May 2024. This enabled the acquisition of high-resolution spatiotemporal characteristics of surface deformation in the Linfen-Yuncheng Basin during the monitoring period. The results show that the area with a deformation rate exceeding 5 mm/a in the study area accounts for 12.3% of the total area, among which the subsidence area accounts for 11.1% and the uplift area accounts for 1.2%, indicating that the overall surface is relatively stable. There are four relatively significant local subsidence areas in the study area. The total area with a rate exceeding 30 mm/a is 41.12 km2, and the maximum cumulative subsidence is close to 810 mm. By combining high-resolution satellite images and field survey data, it is found that the causes of the four subsidence areas are all the extraction of groundwater for production, living, and agricultural irrigation. This conclusion is further confirmed by comparing the InSAR monitoring results with the groundwater level data of monitoring wells. In addition, on-site investigations reveal that there is a mutually promoting and spatially symbiotic relationship between land subsidence and ground fissures in the study area. The non-uniform subsidence areas monitored by InSAR show significant ground fissure activity characteristics. The InSAR monitoring results can be used to guide the identification and analysis of ground fissure disasters. This study also finds that due to the implementation of surface water supply projects, the demand for groundwater in the study area has been continuously decreasing. The problem of ground water over-extraction has been gradually alleviated, which in turn promotes the continuous recovery of the groundwater level and reduces the development intensity of land subsidence and ground fissures.

Saltwater intrusion adversely affects both agriculture and mental health, yet its impact on quality of life (QoL) is underexplored. To understand the profound implications of saltwater intrusion on mental health and quality of life (QoL), especially when combined with other stress factors. The study aims to explore this underexplored relationship in saltwater intrusion-affected zones of Thailand. We investigated the QoL of 417 Thai agriculturists in saltwater-affected areas using the WHOQOL-BREF survey and multiple linear regression. Results indicated that a majority, 61.63%, experienced a moderate QoL, and a significant 83.69% reported tasting salinity in their water. A key finding was that individuals aware of their water’s salinity had notably lower QoL scores. Influential factors on QoL included gender, age, household size, education, and occupation. Specifically, the detection of salinity in drinking water was linked to a 3.16-point reduction in QoL scores (Adjusted Mean Difference: -3.16, 95% CI: -5.08 to -1.25). Furthermore, those with an awareness of water salinity saw an additional QoL decrease of 4.40 points (Adjusted Mean Difference: -4.40, 95% CI: -6.84 to -1.96). The findings underscore the urgency for targeted government interventions to address the repercussions of saltwater intrusion. Strategies including the implementation of real-time alert systems and the establishment of protected freshwater reserves are vital for preserving agricultural productivity, ensuring water security, and enhancing the well-being of affected communities.

Women’s livelihoods, particularly those residing in coastal areas, are vulnerable due to their reliance on climate-sensitive occupations and limited adaptive capacities. Sagar Island in India is one such region, which is often affected by cyclonic storms, coastal flooding, and saltwater intrusion. This study explores the factors driving occupational changes and the coping strategies adopted by married women of reproductive age in Sagar Island. A cross-sectional survey design was employed to explore the occupational challenges and coping mechanisms among 420 purposely selected married women. Primary data were collected during June and July 2024. Bivariate and multivariate logistic regression models were employed for statistical analysis. Findings indicated that approximately 43% of the sampled women had been compelled to change their primary occupation over the past 3 years due to climate-related hazards. Among these women, those engaged in labor and cultivation are more likely to experience occupational shifts due to climatic hazards. Logistic regression revealed that their occupations were significantly affected by cyclonic storms, coastal flooding, and saltwater intrusion. In addition, factors such as social category, housing type, economic status, the wealth index, and husband’s occupation were significantly associated with occupational shifts. The study showed that women resorted to adopting numerous coping strategies to address the challenges to their livelihoods. The study underscores the need to address socio-economic disparities to improve livelihood resilience. It also highlights the importance of targeted interventions for affected women to raise awareness about climate change, provide credit facilities for taking adaptative measures, and enhance women capacity in the face of climate change.

Abstract Constructing underground structures in coastal regions poses significant challenges, particularly due to seawater intrusion, which can cause corrosion and threaten the safety and stability of the caverns and surrounding facilities. A crucial aspect of preventing seawater intrusion lies in accurate mapping of the geological structure of the reservoir area and its proximity to the coastline. This study uses reflection seismic data, borehole ultrasonic imaging, and core samples to identify geological features that influence subsurface stability. The seismic profile revealed a V-shaped or concave-down structure associated with faults, suggesting a down-dropped block within the subsurface. Seismic facies analysis identified chaotic, high-amplitude reflections within basement rocks, indicating highly fractured and faulted zones, possibly including mylonitic rocks. A novel approach is proposed that combines borehole ultrasonic imaging with fractal theory, integrating core photos, seismic attributes, and geophysical analysis. A functional relationship was established between the joint surface density and the joint information dimension within the borehole. Additionally, a relationship was established between fault information dimension and borehole joint surface density. Results showed that the joint information dimensions within the identified fault zones consisttently exceeded 1.775. By applying a threshold of joint information dimension greater than 1.775, 15 small-scale structural prediction zones were identified. Subsequent analysis of core photos from the predicted regions confirmed the presence of relatively long fractured zones, demonstrating the high accuracy of the proposed method in identifying small-scale structures. This study presents a comprehensive method for mapping geological structures in coastal areas, providing an essential reference for the identification and management of small-scale features in underground engineering projects.

Abstract. Saltwater intrusion is an increasing concern for coastal ecosystems. While groundwater models have made progress in simulating aquifer salinization, their boundary conditions – potentially informed by ocean model simulations in shallow water systems and intertidal zones – remain constrained. Here we presented a 3D unstructured-grid model that covers the Gulf of Maine and the Mid-Atlantic Bight, and most areas of the South-Atlantic Bight along the North American Atlantic Coast (“NAAC”) for 2 decades, with a focus on the salinity simulations. This model resolves detailed geometric features of tidal tributaries down to 100 m while maintaining a resolution of 6.5 km in the coastal ocean. The two-decadal simulations from 2001 to 2020 were evaluated using a comprehensive observational dataset of elevation, temperature, and salinity. The mean absolute error in the M2 amplitude across the NOAA tidal gauges within the domain is 0.11 m. The root-mean-square deviation for salinity and temperature measurements are 0.27 PSU and 0.12 °C, respectively. The model reasonably captured the currents and circulations. For the first time, we extended a regional continental scale ocean model to the tidal wetlands to include compound flooding process. The two-decade of simulations of hydrodynamic and hydrological connectivity along the Atlantic Coast have significantly addressed numerous observational gaps in many systems. Specifically, saltwater intrusion patterns in major estuaries of the Mid-Atlantic, such as Chesapeake Bay, Delaware Bay, and other tributaries within the same hydrologic unit, exhibit significant correlations. The seamless cross-scale capability of this model facilitates future applications to land-sea interactions, such as carbon fluxes.

We employ a time series of ERS-1/2, ALOS-1/2 PALSAR, Sentinel-1, COSMO-SkyMed, and RCM differential synthetic-aperture radar interferometry data from 1996 to 2023 to document the short and long-term migrations of the grounding line (GL) of Berry Glacier, West Antarctica, a tributary of Getz Ice Shelf that controls 10% of its ice discharge. In 2019–2021, we detected a short-term GL migration of 18.0 ± 0.9 km, which is exceptionally long and implies that the glacier bed is up to 1300 m deeper than previously known. On short time scales, the GL migrates between three states controlled by bed topography. The observed flexing of the glacier suggests that seawater is trapped in the newly formed ice shelf cavity in an irregular fashion during the tidal cycle. From 1996 to 2021, the most inland position of the GL retreated by 18.1 ± 0.4 km, or 0.7 km/year, the ice thickness decreased by 11 ± 1 m/year, the ice sped up by 64 ± 5%, and the glacier lost a total mass of 131 ± 23 Gt. We attribute the rapid retreat to an enhanced ocean heat flux from warm Circumpolar Deep Water (CDW) reaching the grounding line through favorable bathymetry channels, combined with km-sized seawater intrusions beneath the glacier that cause rapid melting of basal ice.

Coastal Bangladesh faces severe drinking water scarcity due to salinity intrusion. To address this challenge, the study assesses the socio-technical and economic factors shaping the performance of small-scale reverse osmosis (RO) desalination plants through field audits, household surveys, stakeholder interviews, and water quality analysis. Community acceptance was evaluated using the Theory of Planned Behavior (TPB). Feedwater was highly contaminated, with average TDS 3732.63 mg/L, hardness 636.36 mg/L, iron (Fe) 3.23 mg/L, and turbidity 14.63 NTU. Despite this, RO systems demonstrated strong performance, achieving removal efficiencies of 95.15% for salts, 95.95% for hardness, and 91.67% for alkalinity, with an average recovery rate of 37.25% (range: 20–60%). Treated water met WHO and Bangladesh standards, with mean concentrations of TDS (195.54 mg/L), Fe (0.21 mg/L), arsenic (0.0085 mg/L), and turbidity (1.09 NTU). However, inadequate operator training and a lack of maintenance threaten sustainability. Energy consumption increased by 0.1 kWh/m3 per 1000 mg/L rise in salinity, while financial constraints hinder membrane replacement. TPB analysis revealed positive attitudes and perceived behavioral control as key adoption drivers. Untreated brine discharge (mean TDS 12,900 mg/L) posed significant environmental risks. This study provides micro-level insights to inform policy and strengthen the sustainability of decentralized RO systems in climate-vulnerable coastal regions.

Abstract. Local characterization of groundwater systems is critical for managing and protecting vulnerable resources. Geophysical methods can provide dense imaging of subsurface parameters to delineate lithological boundaries and water tables for hydrogeological investigation, though using a single geophysical method for determining lithologies can yield erroneous interpretations as different lithologies can have similar properties. By using several geophysical methods, it is possible to reduce this risk and better assign likely lithologies to subsurface units. We present two case studies where transient electromagnetics (TEM) and surface nuclear magnetic resonance (SNMR) are used in combination to delineate hydrogeological structures. Novel spatially constrained inversion in SNMR was used to provide horizontal consistency between soundings. Three coincident parameters, resistivity from the TEM measurements and water content and relaxation time from the SNMR measurements, were used in a K-means clustering scheme to resolve subsurface structures. The K-means clustering was evaluated with a silhouette index to pick the number of clusters. After clustering, each cluster was assigned a hydrogeological description based on the distinct features in the three parameters; e.g., a low resistivity, high water content, and high T2∗ are assigned as saltwater-saturated sand. In the first case study, the clusters enabled improved resolution of a regional water table in an unconfined aquifer setting with the multi-geophysical approach. The water table estimates were positively evaluated against multiple boreholes within 500 m of coincident geophysical models. The second case study illustrates how clustering, of SNMR and TEM models, can delineate saltwater intrusion in an island coastal aquifer, which would not be possible with any of these methods individually. Additionally, the clustering resolved the main shallow aquifer on the island. Our work illustrates how the combination of geophysical data can be used to improve the identification of hydrogeological layers and reduce interpretational bias.

In the North China region, measures such as restricting groundwater extraction and promoting cross-basin water diversion have effectively alleviated the problem of excessive groundwater exploitation. Nevertheless, the continuous rise in groundwater levels may alter the mechanical properties of foundation soil layers, potentially leading to geotechnical hazards such as foundation instability and the uneven settlement of structures. This study employs FLAC3D software to simulate the displacement, deformation, and stress–strain behavior of buildings and their surrounding strata during the dynamic recovery of groundwater levels, aiming to assess the impact of this process on structural integrity. Research findings indicate that the maximum building settlement within the study area reaches 54.8 mm, with a maximum inter-column differential settlement of 8.9 mm and a peak settlement rate of 0.16 mm/day. In regions where differential settlement aligns with the interface between the floor slab and walls, tensile stress concentrations are observed. The maximum tensile stress in these zones increases progressively from 1.8 MPa to 2.19 MPa, suggesting a potential risk of tensile cracking in the concrete structures. The influence of groundwater level recovery on buildings exhibits distinct phase characteristics, and the response mechanisms of different lithological strata vary significantly. Therefore, particular attention should be given to the physical properties and mechanical behavior of strata that are highly sensitive to variations in moisture content. These findings hold significant reference value for the sustainable development and utilization of underground space in the North China region.

ABSTRACT Seawater intrusion (SWI) is the most important hydrological problem in the highly populated coastal regions. SWI in the coastal aquifers is caused by the intense withdrawal of groundwater and reversal of the natural hydraulic gradient. The study focuses on geophysical and geochemical analysis to identify areas contaminated by saline water intrusion. Resistivity survey and groundwater analysis were conducted in 33 locations in the study area to identify the extent of SWI. Geochemical analysis indicated that the groundwater quality was not suitable for drinking and irrigation purposes in 64% and 85% of the study area, respectively. The areas with low resistivity and high values of water quality parameters, such as electrical conductivity, chloride, and low values of Na/Cl, indicate SWI. Resistivity study was verified by geochemical studies, and the results indicated high salinity prevailed up to 13.7 km, moderate salinity up to 16.5 km, and freshwater was present beyond 16.5 km from the coast. The study found that geophysical methods offer a valuable alternative to laborious geochemical approaches for estimating aquifer parameters and detecting saline water intrusion. The study indicated the need for proper management of coastal aquifers to control SWI.

This study aims to evaluate the spatial variation of water quality in three short rivers on Penang Island in relation to tidal dynamics and seawater intrusion from the Strait of Malacca. Sungai Tukun, located within a national park, served as a reference site. Ten sampling stations were established across upstream, midstream, and downstream segments of the rivers, with an additional site in Sungai Batu Ferringhi to capture anthropogenic influences. Water sampling and in situ measurements were conducted during spring and neap tides and analysed using the standard method (APHA, 2017). The Kruskal-Wallis H test revealed significant spatial variations (p < 0.05) in multiple parameters, including pH, total dissolved solids, salinity, Secchi depth, ammonium, nitrate, chlorophyll-a, orthophosphate, and discharge. The Mann-Whitney U test showed significant differences (p < 0.01) in water temperature, pH, salinity, total dissolved solids, ammonium, discharge, and euphotic depth between high and low tides at downstream stations. Significant vertical stratification in salinity and Secchi disk depth was also observed at downstream segments (p < 0.01). Principal component analysis (PCA) indicated that PC1, dominated by salinity, water temperature, and total dissolved solids, accounted for 28.80%, 30.88%, and 27.02% of the total variance in Sungai Batu Ferringhi, Sungai Tukun, and Sungai Keluang, respectively, indicating tidal influence. PC2 was mainly associated with nutrient-related variables. The findings revealed distinct spatial variation in water quality and nutrient distribution among the three short rivers of Penang Island, with tidal dynamics contributing to these patterns and informing sustainable freshwater management in tidal-influenced catchments.

Groundwater salinization poses a critical threat to freshwater security in coastal regions, particularly under intensified extraction and evolving hydroclimatic conditions. This study examines the spatial and temporal evolution of salinity in the lower Chao Phraya River Basin during 2008 and 2020 using a multi-method machine learning framework. SHAP-based feature attribution analysis identified groundwater extraction as the most influential driver of salinity dynamics. A Gaussian copula model was employed to quantify the conditional probability of salinity threshold exceedance under varying extraction pressures, capturing nonlinear dependence structures between total dissolved solids (TDS) and groundwater extraction. A Graph Neural Network (GNN) model was developed to simulate TDS concentrations at 212 monitoring stations, demonstrating high predictive performance across both periods. To translate model outputs into actionable insights, a scenario-based Decision Support System (DSS) was implemented, enabling interactive visualization of salinity risk zones under 20% and 40% increases in groundwater withdrawal. Results reveal a pronounced expansion of high-salinity areas over time, largely driven by anthropogenic factors. By fusing explainable machine learning with probabilistic analysis and decision support, this framework provides a novel, scalable tool for real-time groundwater salinity risk assessment and supports evidence-based management in data-scarce coastal aquifers.

Implications of waterfowl impoundments as a response to sea-level driven saltwater intrusion.

Land subsidence is widely present across the globe and brings catastrophic hazards. The well-acknowledged mechanism of subsidence is groundwater pumping, which leads to the reduction of hydraulic head and hence increases the effective stress, resulting in the vertical compaction of unconsolidated sediment. Here, we propose a hypothesis that subsidence in the coastal areas might be caused by osmotic effects, given the presence of seawater intrusion. The hypothesis is corroborated by simulating fluid flow, solute transport, and elastic deformation of multi-layered aquifer-aquitard systems. The simulations potentially cover a variety of natural environments by varying concentration, hydraulic head, thickness of aquitard, and hydraulic conductivity. We find that osmotic effects due to seawater intrusion play a non-negligible role in controlling subsidence in our studied cases, suggesting that future work on subsidence in areas impacted by seawater intrusion should fully incorporate osmotic effects to improve our understanding and prediction of subsidence.

This study aims to evaluate key parameters of groundwater quality and associated health risks in three coastal aquifers of Cox's Bazar, Bangladesh, with a focus on manganese contamination and geochemical processes. A total of 288 groundwater samples from 36 monitoring wells were analyzed to assess physicochemical parameters and calculate the Water Quality Index (WQI). Hydrogeochemical facies revealed distinct water types, with the Dupi Tila aquifer containing predominantly fresh Ca-HCO₃ type water, while the Tipam and Bokabil aquifers exhibited Na-Cl-SO₄ facies, indicating seawater intrusion and water-rock interactions. To predict WQI and identify key influencing parameters, four machine learning (ML) models, Random Forest (RF), Gradient Boosting Regressor (GBR), XGBoost, and Artificial Neural Network (ANN) were employed. Among these, XGBoost achieved the highest prediction accuracy (R2 = 0.947, RMSE = 12.2, MAPE = 9.6%), followed by GBR and RF, while ANN showed lower performance. Feature importance analysis highlighted manganese (Mn), total dissolved solids (TDS), sodium (Na⁺), and chloride (Cl⁻) as dominant predictors. Health risk assessments using Hazard Quotient (HQ) analysis identified manganese as a significant threat, particularly for children, with over 50% of samples exceeding safe limits. The findings emphasize the need for regular monitoring and targeted mitigation in vulnerable aquifers. This study is novel in its integration of ML algorithms with geochemical analysis in a refugee-impacted coastal region, offering a predictive framework for sustainable groundwater management. The outcomes are broadly applicable to similar hydrogeological settings affected by salinization and trace metal contamination.

Located on the Loess Plateau, the Yan’an New District (YND) has experienced significant geological instability due to large-scale mountain excavation and city construction (MECC). This study applied the Small Baseline Subset Interferometric Synthetic Aperture Radar (SBAS-InSAR) technique to 66 ascending Sentinel-1A SAR images acquired between January 2017 and May 2022 to investigate ground deformation patterns and influencing factors. Results show that the maximum subsidence rate reached −86 mm/year, with a maximum cumulative deformation of 400 mm. Groundwater storage was identified as the key natural driver, exhibiting a significant positive correlation (r = 0.4–0.8) with cumulative deformation with a two-month lag. Fill thickness emerged as the dominant anthropogenic factor, controlling the duration of soil consolidation and thus the deformation rate. Regulating groundwater extraction and improving recharge can effectively reduce subsidence risks. These findings provide scientific guidance for geological hazard early warning and urban planning in YND.

Hydrogeochemical characterization and human health risk assessment for heavy metal contamination in coastal aquifers: A case study in Satkhira District, Bangladesh.

Mangrove ecosystems are remarkable coastal environments that thrive at the interface between land and sea, playing a crucial role in maintaining ecological balance and safeguarding coastal agricultural and fisheries productivity through erosion control, nutrient cycling, and salinity buffering. The physicochemical properties of mangrove soils underpin the health of these ecosystems, particularly for Avicennia marina, a keystone species critical to coastal resilience and habitat provisioning. However, anthropogenic disturbances threaten their sustainability and compromise their ability to deliver vital ecosystem services. Soil samples from undisturbed (Southern Corniche, Jeddah) and disturbed (Masturah) mangrove sites were analyzed for physicochemical characteristics to assess potential anthropogenic impacts along Saudi Arabia’s Red Sea coast. From six locations (undisturbed: Jeddah, n=3; disturbed: Masturah, n=3) soil samples were analyzed for texture, pH, electrical conductivity (EC), total dissolved solids (TDS), water content (%WC), total nitrogen (TN), phosphorus (TP), organic carbon (TOC), macronutrients (Na+, Ca²+, Mg²+, K+), and cation exchange capacity (CEC). Undisturbed soils exhibited significantly higher moisture, TN, TP, and TOC—key indicators of nutrient retention and carbon sequestration capacity—while disturbed soils were more alkaline, a condition linked to diminished nutrient cycling and plant stress. Macronutrient distribution (Na+ &amp;gt; Mg²+ &amp;gt; Ca²+ &amp;gt; K+) remained consistent across sites, suggesting salinity-driven nutrient imbalances may limit mangrove recovery. These findings highlight how soil degradation in disturbed mangroves reduces their ability to stabilize sediments, mitigate saltwater intrusion, and sustain fisheries nurseries, directly impacting coastal communities. Moreover, these soil changes reduce mangrove capacity to buffer adjacent farmland from salinization and erosion, threatening agricultural productivity and undermining carbon sequestration goals central to climate mitigation. To enhance ecosystem resilience, we recommend the application of soil organic amendments and the strategic conservation of high-carbon mangrove zones, in alignment with Saudi Arabia’s Vision 2030 sustainability framework. This study highlights the critical importance of safeguarding mangrove soils as foundational natural infrastructure for climate adaptation and food security in arid coastal environments.