Coastal agriculture is increasingly affected by salinization as sea-level rise, subsidence, river regulation, and water withdrawals combine with more frequent drought and heat extremes. In recent years, a key advance has been the ability to link seawater intrusion (SWI) to crop impacts by integrating satellite observations with targeted field measurements.

At the global scale, cropland distribution and low-elevation coastal metrics reveal a clear mismatch between where impacts are reported and where exposure is likely. Documented hotspots include the Mediterranean, South and South-East Asia, and the Bohai Sea region, while extensive low-lying coastal croplands remain weakly monitored. A screening based on coastal proximity and elevation indicates ~87 Mha of cropland potentially vulnerable to SWI-related salinization (Ghirardelli et al. 2025). This estimate is useful to guide monitoring and prioritization. The global synthesis also highlights recurring combinations of drivers—drought and low flows, pumping, subsidence, and saline surface-water incursions—that promote salt accumulation in soils.

At the regional scale, results from the Po River Delta (Italy) illustrate how drought can trigger rapid salinity increases and measurable crop impacts (Luo et al. 2024). Sentinel-2 time series of vegetation greenness and salinization-sensitive spectral information, interpreted alongside measurements of soil electrical conductivity and moisture, provide spatially explicit identification of vulnerable areas and seasons. This approach supports early warning during extreme dry summers and provides benchmarks to evaluate management actions.

Mitigation is moving from single measures to combined strategies. Current evidence supports integrated portfolios that couple nature-based buffers (e.g., wetlands/mangroves that limit saline intrusion while sustaining ecosystem services) with water and soil management (rainwater harvesting and storage, efficient irrigation including precision and subsurface drip systems, and drainage improvement) and, where needed, salt-tolerant crops enabled by breeding and bioengineering (Tarolli et al. 2024).

Remaining challenges include: (1) AI-enabled prediction for short-term forecasting and early warning, especially during drought and low-discharge periods; (2) process-coupled models that translate seawater intrusion into root-zone salinity, including irrigation water quality, evaporaton-driven salt concentration, capillary rise, and drainage; (3) stronger monitoring with denser networks and higher-frequency data, integrating in situ salinity/EC measurements with remote sensing; (4) a practical management protocol for coastal agriculture linking observations to irrigation, drainage, and water allocation decisions; and (5) progress in salt-tolerant crops (breeding and bioengineering), tested and deployed together with soil–water management under real coastal conditions.

References

• Ghirardelli et. al. (2025). Environmental Research Letters, doi:10.1088/1748-9326/ad9bcd.
• Luo et al. (2024). International Soil and Water Conservation Research, doi:10.1016/j.iswcr.2023.09.009.
• Tarolli et al. (2024). iScience, doi:10.1016/j.isci.2024.108830.

How to cite: Tarolli, P.: Seawater Intrusion and Soil Salinization in Coastal Agriculture: Global Hotspots, Remote-Sensing Evidence, and Mitigation Pathways, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14654, https://doi.org/10.5194/egusphere-egu26-14654, 2026.

Storm surge increases the salinity of coastal aquifers through subsequent vertical seawater intrusion. Climate change is expected to reduce the frequency of storm surges while increasing their intensity, raising complex challenges for the recovery of coastal aquifers to pre-surge conditions. Using integrated surface–subsurface numerical simulations of a generalized coastal aquifer, we examine how the shifts in storm-surge frequency and intensity control long-term salinization. The results show the emergence of two regimes: full recovery, where the aquifer returns to pre-surge conditions, and a shifted equilibrium, characterized by salt accumulation and reduced fresh groundwater availability. The transition between the regimes is captured by a dimensionless number E, linking recurrent storm-surge characteristics and aquifer properties to salt loading. This framework provides an efficient basis for assessing climate-change impacts on vulnerable coastal groundwater systems.

How to cite: Tajima, S., Therrien, R., and Brunner, P.: Post-surge recovery of coastal aquifers under climate change, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8522, https://doi.org/10.5194/egusphere-egu26-8522, 2026.

Coastal salinisation is frequently attributed to contemporary anthropogenic and climatic drivers, such as upstream freshwater withdrawal, land-use change, and sea-level rise. However, these explanations often overlook the fundamental role of offshore bathymetry and continental shelf geometry in regulating tidal dynamics and saltwater retention. We argue that these deeper geological and oceanographic controls govern where salinisation is spatially persistent, structurally organised, and resistant to reversal.

Across many large deltas, offshore geometry exerts first-order control on inland flushing efficiency. While wide, gently sloping shelves typically support large tidal ranges, the narrow and steep shelves—such as those found in the western Bengal Delta—generate tidal ranges approximately  1m lower than in the eastern delta. This reduction in tidal energy supports the development of dense, intricate tidal creek networks, while the accompanying weaker vertical mixing promotes the persistence of saline water. These networks distribute saline water laterally across the landscape and facilitate the formation of persistent, density-driven salinity wedges in underlying shallow aquifers. The lateral prevalence of these high-density wedges, coupled with relict salinity from the geological past, renders groundwater salinity a ubiquitous feature of the coastal region.

We illustrate this structural vulnerability using the Bengal Delta, where a pronounced east–west hydro-salinity divide is dictated by the "Swatch of No Ground"- a 1-km deep Pleistocene submarine canyon. This NNE-SSW deep-water feature on the narrow western shelf fundamentally influences creek-induced salinity patterns. While the eastern delta remains comparatively fresh due to higher-magnitude tidal ranges that promote the mixing and flushing of fluvial and saline water, the south-western delta exhibits persistent salinisation despite similar climatic forcing.

Leveraging a two-decade spatio-temporal dataset from 54 stations, we reveal a sharp asymmetry in salinisation rates: the Western Estuarine System is experiencing rapid increases averaging 111 ± 28 µS/cm yr^-1. To explain this variability, we introduced the Offshore Controlled Estuarine and Aquifer Nexus (OCEAN) Salinisation Framework. Our findings indicate that while declining river discharge and polderisation are critical accelerating factors, they operate within a system already structurally predisposed to salinity. Notably, similar anthropogenic forcing in the eastern delta has not produced comparable salinity responses, reinforcing the primacy of underlying structural controls.

Recognising that contemporary drivers function primarily as accelerants of existing vulnerabilities, rather than root causes, is essential for realistic adaptation planning and water security strategies. Interventions targeting only recent drivers risk underestimating the persistence of salinity in systems where offshore-controlled geometry imposes long-term constraints on freshwater recovery. This reframing has global relevance for the management and health-oriented water security of low-lying coastal deltas.

How to cite: Hoque, M., Feist, S., Tsai, C., Aurthy, M., Belesova, K., Dewan, A., and Butler, A.: Reframing Deltaic Salinisation: Why Offshore Controls are Primary Drivers and Anthropogenic Factors are Accelerants, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11313, https://doi.org/10.5194/egusphere-egu26-11313, 2026.

Sustaining groundwater resources in coastal and island aquifers is increasingly challenged by seawater intrusion driven by groundwater abstraction, land-use change, and climate-related shifts in recharge. Freshwater lenses are particularly vulnerable, and their response is strongly conditioned by subsurface heterogeneity, although many conceptual and analytical approaches still assume homogeneous conditions. The role of layered heterogeneity in controlling freshwater-lens development and saltwater upconing is investigated through an integrated framework combining controlled laboratory experiments, density-dependent numerical modelling with FEFLOW, and comparisons with classical analytical solutions.

Sandbox experiments are conducted under homogeneous and stratified configurations to examine lens evolution under steady recharge and during pumping. The heterogeneous setting, characterized by contrasts in vertical hydraulic conductivity, markedly altered lens geometry by reducing its maximum thickness, laterally extending the mixing zone, and promoting preferential flow pathways. Numerical simulations successfully reproduced the observed system behavior and enabled further exploration of pumping scenarios beyond the limitations of the physical model.

Results indicate that stratification accelerates and intensifies saltwater upconing, effectively lowering sustainable pumping rates and increasing vulnerability to salinization under human impacts. Analytical solutions are shown to overestimate lens stability and delay the predicted onset of upconing in layered systems, highlighting limitations when applied to heterogeneous coastal aquifers.

The findings provide quantitative evidence that layered heterogeneity exerts a first-order control on seawater-intrusion dynamics relevant to integrated water resources management. The combined physical–numerical approach supports improved assessment of pumping sustainability, monitoring design, and adaptation strategies to enhance resilience to salinization under changing climate and extraction pressures.

How to cite: Tinjacá, N., Rodrigo-Ilarri, J., and Rodrigo-Clavero, M. E.: Influence of layered heterogeneity on freshwater lens development and seawater upconing in island aquifers: insights from integrated physical and numerical modelling., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13477, https://doi.org/10.5194/egusphere-egu26-13477, 2026.

Coastal aquifers are critical freshwater resources that are increasingly threatened by seawater intrusion driven by the combined impacts of climate change and intensive human activities. The introduction of harmful substances, rising sea levels and groundwater overextraction increase salinization processes. Coastal Groundwater contamination is a complex environmental challenge that requires robust, scalable tools for reliable assessment and prediction. This talk presents recent advances in data-driven approaches for groundwater contamination analysis, with a particular focus on the application of probabilistic, supervised and unsupervised learning techniques in coastal aquifer systems. Drawing on case studies from arid to semi-arid regions of Mexico and Peru, the presentation demonstrates how Bayesian networks, clustering algorithms and random forest models can be applied to multi-parameter hydrogeological and hydrochemical datasets to identify sources of salinization and improve the characterization of seawater intrusion processes. These approaches have proven effective in handling data scarcity and uncertainty. By incorporating artificial intelligence and probabilistic frameworks into hydrogeological assessments, the proposed methods enhance contaminant source identification, support the development of early-warning tools, and enable more informed decision-making. The talk concludes with recommendations for advancing groundwater sustainability through interdisciplinary, data-driven strategies.

How to cite: Mahlknecht, J., Torres-Martinez, J. A., and Mora, A.: Data-Driven Assessment of Seawater Intrusion and Salinization in Coastal Aquifers under Climate and Human Pressures, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16171, https://doi.org/10.5194/egusphere-egu26-16171, 2026.

Climate change-induced sea level rise (SLR) is widely perceived as one of the main reasons for increased saltwater intrusion (SWI) in coastal aquifers. However, past research using analytical and numerical models that predict the effects of SLR in coastal aquifers shows contrasting SWI responses depending on the choice of inland freshwater boundary conditions. While simulations employing a head-controlled (HC) freshwater boundary condition show considerable additional SWI, those that use a flux-controlled (FC) freshwater boundary condition show negligible additional SWI. Both confined and unconfined aquifers exhibit this contrasting behaviour; however, the difference is more pronounced in confined aquifers, which show no additional SWI under FC conditions. Past research has identified that FC systems limit additional SWI through a natural ‘head-lift’ effect wherein inland freshwater heads rise in proportion to SLR. The current understanding of the mechanism that explains the enhanced SWI response observed under HC conditions is the decrease in the hydraulic gradient between the two boundaries. However, decrease in the hydraulic gradient will induce a decline in the freshwater flux through the coastal aquifer. The hydrological ramifications of this boundary condition have not been sufficiently explored. Here we perform laboratory-scale physical experiments, and computational numerical simulations using the SEAWAT model to i) show that HC systems enhance SWI through a ‘flux-decline’ effect which reduces upstream freshwater boundary flux in response to SLR. Consequently, regional groundwater fluxes decrease, altering the aquifer system’s overall water balance. On the other hand, FC systems maintain the freshwater boundary fluxes and do not suffer from this effect. However, the head-lift effect in FC systems can lead to flooding in low-lying areas where the aquifer extent is constrained by topography. This study provides a comprehensive assessment of the mechanisms driving SWI and highlights the broader hydrological consequences of selecting different inland boundary conditions when evaluating the impacts of SLR.

How to cite: Sadhasivam, R. and Srinivasan, V.: Influence of inland boundary conditions on coastal aquifer response to sea-level rise, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17728, https://doi.org/10.5194/egusphere-egu26-17728, 2026.

Worldwide, sandy coastal dune systems form a substantial part of the global shoreline. Global assessments show that approximately one-third of the world’s ice-free coastline consists of sandy beaches, many of which host coastal dune systems with fresh groundwater lenses that are crucial for drinking water supply and ecosystem functioning. These fresh groundwater resources are increasingly exposed to saltwater intrusion driven by intensified human water use, land subsidence, and sea-level rise and changes in recharge. These processes make them highly relevant case studies for integrated water resources management in coastal aquifers.

In this study, we quantify the response of fresh groundwater lenses in coastal dune systems to sea-level rise and human pressures, using the Netherlands as a well-monitored and modelled example. We apply a high-resolution 3D variable-density groundwater flow and salt transport model (iMOD-WQ which is similar to SEAWAT), calibrated against observed hydraulic heads and salinity distributions, to simulate present and future conditions. Scenario simulations include sea-level rise of 0.5 m and 1.0 m by 2100, and an extreme scenario of 3.0 m by 2150, combined with land subsidence, climate-induced changes in recharge, and ongoing groundwater extractions for domestic use.

The simulations explicitly resolve key seawater intrusion processes such as lateral saline groundwater intrusion, saline upconing under extraction wells, shifts in groundwater divides, and storm-driven saline inundation. Results indicate that under moderate sea-level rise scenarios, fresh groundwater lenses in dune systems remain relatively in a relative sense, largely due to sufficient recharge from managed aquifer recharge (MAR) practices that maintain hydraulic gradients. However, absolute freshwater volumes decline gradually, and localized risks of salinization increase near production wells. Under the extreme sea-level rise scenario of 3.0 m by 2150, several low-lying dune systems show pronounced freshwater volume losses and increased vulnerability to saltwater intrusion.

Our results demonstrate that coastal dune aquifers can be resilient to sea-level rise when supported by integrated management strategies, but also reveal clear thresholds beyond which freshwater availability rapidly deteriorates. We illustrate that high-resolution modelling can inform sustainable management of coastal aquifers worldwide under a changing climate with increasing human pressures.

How to cite: Oude Essink, G. H. P. and Nogueira, G. E. H.: Effects of sea-level rise on fresh groundwater resources in coastal dune areas – a case-study in the Netherlands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17440, https://doi.org/10.5194/egusphere-egu26-17440, 2026.

 Traditionally coastal aquifers have been monitored and modelled by restricting the spatial extent of observations and simulations to the inland portion of the aquifer. As a result, most hydrogeological studies and numerical models focus on the terrestrial part of the system, assuming that the key marine processes affecting hydrogeological dynamics are adequately captured at the coastline interface. However, important hydrological processes take place offshore, and may significantly influence the inland aquifer behaviour.

Offshore processes such as tides, sea storms, and even groundwater discharge can generate rapid variations in pressure and salinity in the submerged part of coastal aquifers. These processes operate at temporal scales typically shorter than those governing inland groundwater flow, which is mainly controlled by seasonal fluctuations. Consequently, aquifer dynamics and behaviour may not be fully captured when observations are limited to the terrestrial domain.

In this contribution, we show how offshore monitoring data, such as salinity measurements or geophysical observations can improve the understanding of inland aquifer behaviour. Offshore data provide direct information on marine-driven dynamics that cannot be inferred from inland observations alone and help to better constrain the conceptualisation of coastal aquifer systems.

We further demonstrate that integrating offshore observations into hydrogeological numerical models improves their representativity and ability to reproduce observed inland aquifer responses, including seawater intrusion dynamics. This integrated terrestrial–offshore perspective is particularly relevant for improving the assessment and management of coastal aquifers, including seawater intrusion and submarine groundwater discharge.

Aknowledgements: This research has been supported by the project MUCHOGUSTO (PID2022-140862OB-C21 and PID2022-140862OB-C22 funded by MCIN/AEI/10.13039/501100011033/ and “FEDER Una manera de hacer Europa”) anf SecuCoast financed for the European Commission and Spanish Research Council (AEI)  under the 2023 Joint call of the European Partnership 101060874 — Water4All.

How to cite: Folch, A., Tur, J., Almillategui, B., Jin, J., Diego-Feliu, M., Rodellas, V., Grifoll, M., Espino, M., Fernàndez-Garcia, D., Ledo, J., and Carrera, J.: Beyond the Coastline: The Role of Offshore Data in Understanding Coastal Aquifers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13458, https://doi.org/10.5194/egusphere-egu26-13458, 2026.

Patterns of seawater intrusion (SWI) over most of the coastal aquifers in Lebanon have been noticed since more than 5 decades. This hazard is now assessed over the entire Lebanese coast through field measurements and sampling of available groundwater resources. The results show elevated salt content present in several zones and ongoing salinization to variable extents in others. Porous non-consolidated aquifers show the most permanent and growing patterns of SWI along the coast, while fractured and karstic aquifers appear to be more resistant to the intrusion spread. Comparison with previous SWI studies confirms early salinization signs detected at several points of the coast, and well-established salinization over the recent years in many other coastal zones.

The largest impact on SWI comes from a mix of anthropogenic factors essentially related to urbanization including change in land use, modification of natural flow, along with growth in excessive groundwater abstractions related to a failing water-resources development and management. For example, flood control and land management plans of two major coastal rivers implemented since the 1960s are now associated with two of the sharpest SWI patterns of the entire coast. Climate-related and other natural SWI drivers do not appear to play important roles in the observed coastal groundwater salinization so far. However, integrated water resources management covering the entire watersheds of coastal river basins and aquifers is needed to forecast and mitigate longer term climatic effects especially those related to the snowmelt driven recharge of more inland aquifers and the availability of water resources outside the coastal aquifer areas. Mitigating SWI hazard at national scale requires 1) appropriate policy for water resources management to be adopted at national governmental level, 2) continuous awareness and education campaigns on water resources and water use, 3) implementing a monitoring plan for groundwater quality in all coastal aquifers and 4) undertaking detail hydrogeological studies in key coastal areas to better understand the mechanisms and amplitude of seawater intrusion.      

Reference: Ata Elias, Wisam M. Khadra & Michel A. Majdalani (2025) Saltwater intrusion in coastal Lebanon: evolution of patterns, and database for groundwater quality monitoring and management, Hydrological Sciences Journal, 70:6, 975-993, DOI: 10.1080/02626667.2025.2468839

How to cite: Elias, A. R.: Seawater Intrusion in the Coastal Aquifers of Lebanon: the Importance of Reducing the Anthropogenic Factors., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11684, https://doi.org/10.5194/egusphere-egu26-11684, 2026.

Major land reclamation using polders took place along the southern coastal area of Bangladesh during the mid‑20th century. These polders, located in the Ganges–Brahmaputra–Meghna Delta, are protected by earth embankments approximately 2 metres high. While the embankments restrict tidal ingress of saline water, they can be breached or overtopped by storm surges produced by tropical cyclones in the Bay of Bengal. These surges, in turn, cause large volumes of saline water to enter and remain trapped within the polders, adversely affecting both shallow groundwater and surface water sources. Many communities continue to rely on these sources for drinking water despite sodium concentrations exceeding 200 mgNa/L. Epidemiological studies have linked long‑term exposure to such levels with adverse cardiovascular, renal, and pregnancy‑related health outcomes. Enhanced ocean warming due to climate change is expected to result in more frequent and intense tropical cyclones and associated storm surges. Consequently, there is a need for improved understanding of the impacts of, and recovery from, such storm‑surge events to support long‑term adaptation and improved health outcomes. This, however, is challenging due to the combined and interacting nature of surface‑water and groundwater processes.

To address these challenges, the hydrodynamic and salinity responses of a low‑lying coastal aquifer in Dacope, southwestern Bangladesh, were investigated using two‑dimensional (2D) and three‑dimensional (3D) numerical models developed in HydroGeoSphere. Field observations and hydrogeological data were integrated to simulate surface‑water and groundwater responses under ambient and storm‑surge conditions. The 3D simulations revealed interacting mechanisms controlling both the persistence and spatial heterogeneity of storm‑surge‑induced salinization. Comparison with 2D simulations showed that omitting lateral storage and cross‑sectional flow leads to rapid surface drainage and systematic underestimation of near‑surface salt accumulation and recovery timescales. The results provide important insights into the long‑term impacts of storm‑surge inundation, the identification of salinity‑vulnerable zones, and contribute to a large‑scale joint UK–Bangladesh project on multi‑sectoral interventions aimed at improving access to low‑salinity drinking water for health protection in the coastal areas of Bangladesh.

How to cite: Butler, A., Tsai, C., Hoque, M., Khan, A., Vineis, P., Costopoulos, E., and Ahmed, K. M.: Impacts of tropical cyclone induced storm surges on water resources in coastal Bangladesh and implications for population health, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19056, https://doi.org/10.5194/egusphere-egu26-19056, 2026.

In coastal aquifers, one of the most common processes is seawater intrusion, which is the incursion of seawater towards the continent, displacing and mixing with the fresh groundwater, causing multiple difficulties in drinking and agricultural coastal water supply systems.

In the peninsula of Yucatán, a karstic platform in the southeast of Mexico, seawater intrusion is frequently found along the coast. However, the extension of the saline water mass is still undetermined as well as its temporal variations. Particularly, the lack of deep (> 100 m) sampling sites in the central and western part of the peninsula, hinders a general understanding of the groundwater system dynamics.

Sea level is one of the main drivers of seawater intrusion, therefore, by analyzing the effect of tidal oscillations on groundwater levels a better understanding of the aquifer connectivity and seawater intrusion can be achieved.

In previous studies, tidal oscillation analysis in lakes and sinkholes water levels have suggested that the central region of Yucatán is heavily connected to the sea. This has been explained by the high porosity and fracturing of the local lithology. Nevertheless, the geological settings in the peninsula are exceptionally variable, which is the result of many karstic processes involved and the existence of the Chicxulub crater.

In the present contribution, groundwater levels were measured in different wells and sinkholes from the coast across the west Yucatán through the Ring of Cenotes (a highly hydrogeological connected area) and its surroundings. We compare the groundwater signals to atmospheric pressure and sea level time series, by performing cross spectral analysis and coherence tests. Sea level measurements were collected from the National Mareograph Service, and the atmospheric pressure was registered by the National Meteorological Service.

The data show a similar response in all the sites: a very clear tidal effect on groundwater levels near the coast (10 km from the beach at Celestún), which is strongly attenuated inland and absent inside the Ring of Cenotes. On the other hand, the cross spectra between groundwater level and barometric pressure, suggests a strong influence at diurnal, semidiurnal (similar frequencies to tidal oscillations) and low frequencies at all sites. In other words, there is a major influence on the groundwater levels in the aquifer produced by the atmospheric variations. These results suggest that the link between the ocean and the groundwater in this area is relevant close to shore, but not as relevant inland as was previously suggested. This opens more inquiries about the complexity of the geological settings, the extension and temporal variability of the seawater intrusion in the zone, and the implications of the atmospheric variations in the groundwater flow pattern.

How to cite: Salas-Barrena, C., Mariño-Tapia, I., Neri-Flores, I., Morales-Casique, E., and Núñez-Fernández, T.: Influence of ocean tides and atmospheric pressure on a coastal karstic aquifer, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14580, https://doi.org/10.5194/egusphere-egu26-14580, 2026.

Groundwater is often the only drinking water resource of many small marine islands. The fresh water lenses underneath these islands are highly restricted in their extent and vulnerable to salt water intrusion caused by groundwater extraction or other factors. An example is the barrier island of Langeoog located off the North German coast. The drinking water supply of this island is exclusively provided by groundwater extracted from its fresh water lens. Since several of the drinking water wells exhibit strong salinity variations, a long-term sustainable drinking water management requires knowledge of the factors driving these variations.

To identify the reasons for the salinity variations in the drinking water wells on Langeoog, long-term data series on chloride concentrations, groundwater and sea water levels, pumping activity, climate data, soil moisture and dune locations were analyzed for the period of 1993-2023.  Measured and from measurements derived data were investigated using time series analysis, multivariant regression and artificial intelligence approaches to determine the relevance of different driving factors for the observed salinity variations and the ability to predict such variations.

The results of the study show that individual drinking water wells differ not only in the magnitude of the salinity variations but also regarding the reasons for these variations. In general, the salinity in individual wells is not driven by the present conditions and their short term variability but reflects the response of the groundwater system to factors integrated over periods of several years. Relevant factors include the water balance of the well field (groundwater recharge vs. extraction) as well as the storm flood frequency and the associated variations in the location of barrier dunes. Without detectable influence on salinity are groundwater levels, sea water levels and the operation intensity of individual wells. A limited prediction of the salinity based on the entire set of collected data is possible for selected wells.

How to cite: Thullner, M., Doll, F., Wetzel, M., Kunz, S., Hüske, K., Broda, S., Liesch, T., and Houben, G.: Factors driving varying salinity of a fresh water lens underneath a coastal barrier island, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19851, https://doi.org/10.5194/egusphere-egu26-19851, 2026.

Cheniers are sandy or shelly sediment ridges that are formed, often parallel to the shore, on silty and clay-rich coastlines. We will investigate Chenier plains in Suriname’s low-lying coastal region to quantify their hydrogeological potential to function as a medium for sustainable drinking water supply and irrigation in rural areas, where people lack access to reliable water supply for now and in the future.

In the study area, the cheniers are of Quaternary age and occur as elongated sandy depositions surrounded by clayey swamps and tidal deposits (Augustinus, 1989; Groen 2000,2002). Substantial research has been conducted on the depositional environments, formation processes, and internal structure of cheniers, but large knowledge gaps remain regarding their hydro(geo)logical potential. Previous hydro(geo) logical investigations indicate that the saline groundwater originally entrapped during deposition, has been completely flushed out through sustained recharge from abundant precipitation. This study will therefore focus on understanding the hydro(geo)logy of the cheniers in the study area. We will investigate to what extend cheniers interact with underlaying stratigraphy and surrounding sedimentary layers, the relationship between the geomorphology and their water bearing capacity, and the current groundwater quality.  Additionally, we will determine the impact of climate variability, climate change and groundwater extraction on chenier groundwater availability and quality.   

We will use hydrogeological and geophysical methods (electrical resistivity and electromagnetic methods) to characterize the subsurface by understanding their hydrogeology and groundwater occurrence in relation with geology and depositional environment. We will install piezometers to monitor groundwater levels and hydraulic heads variations and to assess the impact of seasonal changing weather conditions on recharge and groundwater levels, while water samples will be collected to assess water quality and determination of the chemical composition of major ions and stable isotopes. In addition, we will take chenier sediment samples  to determine hydraulic parameters together with pumping test analysis.

We will use the field data acquired to develop conceptual and numerical models for the study area mimicking groundwater flow and salinity patterns within and around the cheniers. We will make projections of groundwater availability and quality under future groundwater extractions, sea level rise and climate change scenarios. The variable-density groundwater flow and salt transport model will also be used to evaluate different management scenarios in order determine management practices for protection and sustainable groundwater use of the cheniers containing freshwater lenses.

How to cite: Verwey, O. S., OudeEssink, G., and Bierkens, M.: Assessing the hydrogeological potential of shallow coastal cheniers in Suriname. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5544, https://doi.org/10.5194/egusphere-egu26-5544, 2026.

Safe drinking water in the Sundarbans, a UNESCO world heritage site, is increasingly at risk as coastal aquifers are repeatedly impacted by salinity intrusion, tidal influence, cyclones, and anthropogenic stresses such as population growth, urbanization, and over-extraction. Consequentyly, this ecologically vulnerable delta-front region is experiencing growing groundwater stress, threatening about 4.5 million people. Therefore, this study aimed to assess groundwater vulnerability in the Sundarbans using stable water isotopes (δ²H and δ¹⁸O) and hydrochemistry to apprehend SW-GW mixing processes and salinity pathways from coastal shoreline to further inland across four zones (I, II, III, and IV). Results revealed that despite an increasing rainfall trend, groundwater levels (GWL) and salinity (Cl⁻) have shown a decreasing trend over the past decade. Groundwater salinity and δ¹⁸O values varied widely in Zone I (salinity: 0.7–4 PSU, δ¹⁸O: −2.3 to +0.5‰) and Zone II (0.7–9 PSU, δ¹⁸O: −2.8 to −0.5‰), while Zones III and IV exhibited narrow ranges (Zone III: salinity 0.8–1.2 PSU, δ¹⁸O: −2 to −0.6‰; Zone IV: salinity 0.7–1.2 PSU, δ¹⁸O: −1.6 to −1.1‰). Groundwater in zones I and IV closely aligns with the Global and Local Meteoric Water Line (GMWL and LMWL), indicating direct meteoric recharge. In contrast, groundwater zones II and III slightly deviates, suggesting evaporative enrichment prior to recharge. This is further supported the by average d-excess in zones I, II, III, and IV are 4.5 ± 3‰, -2. ± 1.7‰, -2 ± 1‰, and 5 ± 6‰, respectively. River water, with high salinity (10 and 24 PSU in Zones I and II, respectively), appears to be a major source of saline intrusion, and seawater near coast (salinity: 33 PSU, zone IV)  elevating groundwater salinity suggesting the potential pathways of SW-GW interaction and solute mobilization contributing to groundwater vulnerability in the study area. Consequently, it is evident that the inland groundwater is more depleted indicating monsoonal rainfall recharge with very less maritime influence while the delta-front groundwater near shoreline suggest enriched isotopic signature indicates possible vertical mixing which raise concern for water security. Therefore, this study emphasizes for implying immediate and effective groundwater management strategies for sustainable drinking-water management in the Sundarbans.

Keywords: Groundwater; Coastal aquifers; Stable isotopes; δ²H; δ¹⁸O; Sundarbans; Salinity intrusion; Drinking water security

How to cite: Mondal, M. and Das, K.: Insight into surface water-groundwater interaction derived solute mobilization using stable isotopes in Sundarbans delta front aquifer: An implication to drinking water sustainability, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-475, https://doi.org/10.5194/egusphere-egu26-475, 2026.

Assessing groundwater vulnerability is a tenet of sustainable groundwater management. As a result, developing new practical approaches is an ongoing task that needs to be improved over time, considering growing knowledge and getting new evidence regarding groundwater contamination and risk. In this regard, the DATASET project (Groundwater salinization and pollution assessment tool: a holistic approach for coastal areas) aims to introduce an innovative framework for evaluating groundwater vulnerability and risk related to agricultural products and to salinization phenomenon in coastal aquifers.  The proposed methodology integrates the most relevant influencing factors identified in literature, including ground elevation (slope), hydraulic conductivity, soil texture (clay/sand/silt composition), depth to groundwater, vertical and lateral recharge, hydraulic resistance, and pollution probability. These parameters are systematically incorporated into a flexible assessment framework supported by an open-access database. To enhance applicability, the approach introduces two complementary levels of implementation. The first, the Automatic Dataset Index (ADI), relies solely on freely available open-source data to provide an initial assessment of aquifer vulnerability, with a focus on specific pressures such as agricultural pollution and salinization. The second, the Improved Dataset Index (IDI), allows users to incorporate local knowledge and modify parameters, thereby improving accuracy and tailoring the assessment to site-specific conditions. Case studies conducted in Morocco, Italy, and Poland illustrate the robustness of the approach, demonstrating its ability to identify agricultural pollution hotspots and areas at risk of salt accumulation with high reliability. The results highlight the adaptability of the framework across different hydrogeological and climatic contexts. Overall, this methodology offers a practical and scalable tool for the evaluation and management of coastal aquifer systems, supporting both scientific research and decision-making for sustainable groundwater use worldwide.

How to cite: Ez-zaouy, Y., Busico, G., Jaworska-Szulc, B., Jovanovic, N., Chalikakis, K., Hirata, R., and Mastrocicco, M.: Application of an Automated and Enhanced Dataset Index for Agricultural Leaching Assessment in Coastal Areas: Insights from the Mediterranean and Baltic Seas, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1111, https://doi.org/10.5194/egusphere-egu26-1111, 2026.

Flood management through drainage infrastructures effectively removes inundated water yet creates a critical hydrogeological trade-off. By artificially altering hydraulic gradients, these systems can accelerate saltwater intrusion into freshwater aquifers—particularly in regions where land subsidence from groundwater extraction has increased flooding vulnerability. In this study, we used a coupled surface–subsurface flow model to assess how land subsidence and drainage infrastructure affect shallow groundwater salinization in subsided estuarine zones. Comparison of simulated groundwater salinities with field measurements indicates that the model captures relatively well the primary spatial patterns in salinity distributions. However, agreement with 1D resistivity inversion results varied across locations, with some sites showing close correspondence while others exhibited marked discrepancies—likely reflecting spatial heterogeneity and complexity beyond the model's representation. The results showed that although pumping stations effectively reduce surface inundation, they alter hydraulic gradients by removing surface water, thereby promoting the inland transport of high-salinity water. These findings demonstrated that conventional flood-management strategies can exacerbate aquifer salinization in subsided coastal areas. While land subsidence is often a localized phenomenon, the mechanisms identified here may have broader relevance to coastal regions under sea-level rise globally, as both subsidence and sea-level rise reduce relative land elevation and intensify the hydraulic gradient driving saltwater intrusion. This suggests the need for coupled surface–groundwater assessment frameworks that account for alterations to both flooding patterns and subsurface salinity transport in vulnerable coastal regions.

How to cite: Tsai, C. S., Liu, J., Ito, Y., and Tokunaga, T.: Impact of land subsidence and drainage infrastructure on estuarine aquifer salinization, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6065, https://doi.org/10.5194/egusphere-egu26-6065, 2026.

Based on an analysis of available data combined with new observations, we propose a steady-state model of the freshwater lens of Petite Terre island in Mayotte. The hydrological balance of the airport's meteorological station allows us to estimate the annual recharge using Turc formula. This recharge is on the order of two million cubic meters per year, a portion of which could be extracted for the drinking water supply. Simple modeling under the Dupuit Boussinesq approximation enables to characterise the form of the lens and estimate its volume. We show that the model accords with available data. These results suggest the existence of a significant resource and call for the implementation of further monitoring and analysis, coupled with a review of the groundwater extraction strategy by public authorities in a socially and politically tense island context.

How to cite: Metivier, F., Groleau, A., Frere, J., Levagueresse, L., Jézequel, D., Magali, A., and Deves, M.: Hydrological budget of Mayotte: groundwater flow and water resources of Petite Terre Island, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8301, https://doi.org/10.5194/egusphere-egu26-8301, 2026.