Water

20 pages, 4978 KB

Open AccessArticle

Optimization of Concurrent Seawater and Freshwater Pumping from Coastal Aquifers

by Konstantinos L. Katsifarakis, Dimitrios K. Karpouzos, Ioakeim Rompis, Yiannis N. Kontos and Nikolaos Nagkoulis

Water 2026, 18(10), 1221; https://doi.org/10.3390/w18101221 (registering DOI) - 18 May 2026

Abstract

Covering water demand for secondary uses with resources of inferior quality is already an established practice. In coastal aquifers, saline groundwater can serve as an alternative source. In this paper, we examine concurrent optimization of freshwater and seawater pumping from a coastal aquifer, [...] Read more.

Covering water demand for secondary uses with resources of inferior quality is already an established practice. In coastal aquifers, saline groundwater can serve as an alternative source. In this paper, we examine concurrent optimization of freshwater and seawater pumping from a coastal aquifer, which may lead to more efficient overall solutions. The particular objective is to determine well locations and pumping rates that meet specified freshwater and saline water demands while preventing seawater intrusion into freshwater wells. A genetic algorithm code is used as an optimization tool, combined with a groundwater flow simulation model based on the Boundary Element Method (BEM). The BEM scheme has a relatively low computational cost and can be efficiently incorporated into the genetic algorithm’s fitness evaluation. Validity of the resulting optimal solutions is further investigated using two, more detailed, groundwater flow and mass transport models: (a) A combination of BEM with a particle-tracking (moving point) technique to simulate seawater movement from the coast towards the wells, and (b) the MODFLOW 6 computational package, including the Groundwater Transport (GWT) model for solute transport. The procedure is illustrated through its application to a synthetic coastal aquifer. Full article

(This article belongs to the Special Issue Groundwater Resources: Their Protection, Restoration and Optimal Development)

30 pages, 2181 KB

Open AccessArticle

Accelerating Multi-Objective Evolutionary Algorithms for Cascade Hydropower Scheduling via a Physics-Embedded TCN

by Yaxin Liu, Junhuai Liu, Zhiyun Guo, Jia Lu and Qi Deng

Water 2026, 18(10), 1220; https://doi.org/10.3390/w18101220 - 18 May 2026

Abstract

Cascade hydropower scheduling is a high-dimensional, tightly constrained multi-objective optimization problem in which classical genetic and evolutionary algorithms struggle to find feasible solutions. Under random initialization, algorithms such as the Non-dominated Sorting Genetic Algorithm II (NSGA-II), the Non-dominated Sorting Genetic Algorithm III (NSGA-III), [...] Read more.

Cascade hydropower scheduling is a high-dimensional, tightly constrained multi-objective optimization problem in which classical genetic and evolutionary algorithms struggle to find feasible solutions. Under random initialization, algorithms such as the Non-dominated Sorting Genetic Algorithm II (NSGA-II), the Non-dominated Sorting Genetic Algorithm III (NSGA-III), and the Constrained Two-Archive Evolutionary Algorithm (C-TAEA) rarely produce any feasible solution when the feasible region occupies a vanishingly small fraction of the search space. This paper presents a three-phase framework that combines physics-guided deep learning with evolutionary computation to accelerate both NSGA-II and NSGA-III. The method trains a Physics-Embedded Temporal Convolutional Network (PeTCN) as a differentiable surrogate model that explicitly incorporates physical constraints, applies gradient-based inverse optimization to obtain a feasible or near-feasible solution of high quality, and warm-starts NSGA-II or NSGA-III with that solution for efficient Pareto front exploration. Experiments on a real-world six-station cascade system show that, under a 1500 s fixed-time budget across 20 independent runs, Boosted NSGA-II and Boosted NSGA-III both find feasible solutions in all runs. Boosted NSGA-II and Boosted NSGA-III both reach the first feasible solution within roughly 50–60 generations of Phase 3 search on average, whereas standard NSGA-II produces no feasible run within the same budget and standard NSGA-III requires thousands of generations among its successful runs. The mean final hypervolume reaches

43.84 \times 10^{6}

for Boosted NSGA-II and

46.52 \times 10^{6}

for Boosted NSGA-III, and both boosted algorithms reach a target hypervolume of

35.00 \times 10^{6}

in all 10 target-hypervolume runs. These results demonstrate that coupling physics-embedded surrogates with gradient-based initialization is an effective strategy for constrained multi-objective problems in which feasible solutions are extremely sparse. Full article

(This article belongs to the Section Water-Energy Nexus)

20 pages, 4464 KB

Open AccessArticle

Water Quality Monitoring and Spatiotemporal Mapping of Water Quality in the Mae Kha Canal, Chiang Mai, Thailand

by Vongkot Owatsakul, Suttipong Kawilapat, Phonpat Hemwan and Damrongsak Rinchumphu

Water 2026, 18(10), 1219; https://doi.org/10.3390/w18101219 - 18 May 2026

Abstract

Urban canals in rapidly growing cities often experience water quality deterioration from wastewater inputs and stormwater runoff, with impacts that vary across space and time. This study aimed to quantify five-year spatiotemporal patterns of key water quality indicators in the Mae Kha Canal, [...] Read more.

Urban canals in rapidly growing cities often experience water quality deterioration from wastewater inputs and stormwater runoff, with impacts that vary across space and time. This study aimed to quantify five-year spatiotemporal patterns of key water quality indicators in the Mae Kha Canal, Chiang Mai, Thailand, and to identify persistent degradation hotspots to support management. Monthly longitudinal data (2020–2024) for dissolved oxygen (DO), biochemical oxygen demand (BOD), pH, and water temperature (WT) were collected at 18 monitoring stations and analyzed using locally estimated scatterplot smoothing (LOESS) for trend exploration, repeated-measures correlation for association between parameters, and Geographic Information Systems-based spatiotemporal mapping using inverse-distance-weighted interpolation. Results showed that DO remains very low across much of the canal, while BOD was persistently high; pH was relatively stable near neutral and WT exhibited clear seasonal variability. Spatial mapping indicated that upstream sections generally had better quality, whereas the urban middle reaches repeatedly exhibited hotspots of low DO and high BOD. BOD and DO levels positively correlate with pH level (p < 0.001). In conclusion, the Mae Kha Canal has sustained impairment over 2020–2024, highlighting the need for strengthened wastewater control, stormwater management, and targeted remediation guided by hotspot-based monitoring. Full article

(This article belongs to the Special Issue Water Pollution Assessment, Control, and Resource Recovery)

25 pages, 12523 KB

Open AccessArticle

An Externally Validated Event-Window Framework for Short-Term Hypoxia Early Warning in Receiving Waters

by Jiabin Gao, Zhuolun Li and Yongwei Gong

Water 2026, 18(10), 1218; https://doi.org/10.3390/w18101218 - 18 May 2026

Abstract

Hypoxia episodes in receiving waters near estuarine outlets pose persistent challenges to water-environment management because operational early warning is often hindered by noisy observations, class imbalance, and inter-annual distribution shifts. This study proposes an externally validated Event-Window early-warning framework that bridges high-frequency monitoring [...] Read more.

Hypoxia episodes in receiving waters near estuarine outlets pose persistent challenges to water-environment management because operational early warning is often hindered by noisy observations, class imbalance, and inter-annual distribution shifts. This study proposes an externally validated Event-Window early-warning framework that bridges high-frequency monitoring data and management-oriented decision support. An explainable gated recurrent unit model with temporal attention (GRU-Attn) was developed and evaluated using a strict External-Year test in 2025. To better reflect operational needs, model performance was assessed not only at the daily classification level but also at the event-window level. The model achieved a PR-AUC of 0.9138 for day-level prediction, while Event-Window aggregation further increased PR-AUC to 0.9723, reduced false alarms by 59% (from 22 to 9), and provided a median lead time of 2.0 days for severe events. To improve deployment transparency, a governance diagnostic layer integrating population stability index analysis, threshold reliability assessment, and attention-based temporal attribution was further introduced. The results show that combining External-Year validation with event-scale evaluation and transparent diagnostics can substantially improve the robustness and practical interpretability of hypoxia early warning under real-world distribution shifts. Full article

(This article belongs to the Special Issue Applied Artificial Intelligence and Advanced Sensing for Real-World Water Quality Monitoring)

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20 pages, 2002 KB

Open AccessArticle

Impact of Vineyard Inter-Row Management in Estimated Soil Erosion Under Actual and Future Rainfall Scenarios

by Matteo Giganti, Massimiliano Bordoni, Antonio Gambarani, Valerio Vivaldi, Tommaso Frioni, Alberto Vercesi, Matteo Gatti, Stefano Poni and Claudia Meisina

Water 2026, 18(10), 1217; https://doi.org/10.3390/w18101217 - 18 May 2026

Abstract

Sloping vineyards are highly susceptible to soil erosion driven by intense rainfall. Evaluating the impact of different soil management practices is crucial for implementing conservation strategies to mitigate this process. This study aims to estimate soil erosion under various inter-row management systems (permanent [...] Read more.

Sloping vineyards are highly susceptible to soil erosion driven by intense rainfall. Evaluating the impact of different soil management practices is crucial for implementing conservation strategies to mitigate this process. This study aims to estimate soil erosion under various inter-row management systems (permanent grass cover, alternating tillage, and different combinations of sown mixtures and termination methods) using a modeling procedure based on the Revised Universal Soil Loss Equation (RUSLE). The research was conducted in the Oltrepò Pavese (Northern Italy), a representative hilly vineyard area with medium steepness and clayey soils. Soil erosion was modeled at an annual scale, considering current conditions and three future climate projections (CMCC-CM2-VHR4, MPI-ESM1.2-XR, and EC-Earth3P-HR). Results indicate that annual soil loss is strongly influenced by inter-row management across all rainfall scenarios. Conservative practices—specifically cereal-based cover crops combined with rolling and sub-row mulching—significantly reduced erosion compared to alternating tillage, with average rates dropping from 1.85–3.30 Mg/ha/yr to 0.02–0.04 Mg/ha/yr. These findings underscore the importance of optimized interrow management in reducing soil degradation on sloping terrains. Full article

(This article belongs to the Special Issue Water-Induced Geo-Disaster Reduction in the Context of Climate Change: Hydrology, Management Strategies, and Ecological Geological Engineering)

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20 pages, 5263 KB

Open AccessArticle

Spatiotemporal Variability of Water Quality Along an Altitudinal Gradient in a Tropical River Basin: The Chiriquí Viejo River (Panama)

by Dalys Rovira, Guillermo Branda, Mauricio Vega-Araya, Hermes De Gracia, Victoria Serrano and Benedicto Valdés-Rodríguez

Water 2026, 18(10), 1216; https://doi.org/10.3390/w18101216 - 18 May 2026

Abstract

This study evaluated spatial and seasonal patterns of physicochemical water quality in the Chiriquí Viejo River basin (western Panama), a tropical watershed characterized by strong seasonal variability. A total of 90 water samples were collected at ten stations during the rainy season (May [...] Read more.

This study evaluated spatial and seasonal patterns of physicochemical water quality in the Chiriquí Viejo River basin (western Panama), a tropical watershed characterized by strong seasonal variability. A total of 90 water samples were collected at ten stations during the rainy season (May to October 2024) and dry season (January to March 2025). Dissolved oxygen (DO), turbidity, potential of hydrogen (pH), apparent color, total dissolved solids (TDS), and electrical conductivity (EC) were analyzed following ISO/IEC 17025:2017 accredited methods, and precipitation patterns were characterized using spatial interpolation of meteorological data. Spatio-temporal variability was assessed using linear mixed-effects models, with season and basin position as fixed effects and sampling site as a random factor. Results showed a spatial and seasonal structuring of water quality, with the upper basin exhibiting high and stable DO concentrations and low turbidity and apparent color. In contrast, the middle and lower basin showed rainy-season increases in turbidity and apparent color, supported by a significant season × basin interaction, indicating that precipitation driven impacts are heterogeneous along the basin. EC and TDS displayed spatial gradients, while DO remained relatively stable across seasons and basin levels. These findings highlight turbidity and apparent color as sensitive indicators of precipitation-driven impacts. Full article

(This article belongs to the Special Issue Advanced Data Analytics for Water Quality and Public Health)

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16 pages, 2868 KB

Open AccessArticle

Prediction of Water-Conducting Fracture Zone Height in the Mines of Binchang Mining Area Based on Data-Driven Modeling

by Bingchao Zhao, Feixiang Liu, Jingbin Wang, Wei Wang and Yongsheng Tuo

Water 2026, 18(10), 1215; https://doi.org/10.3390/w18101215 - 18 May 2026

Abstract

Given the severe water hazard in the coal seam roof of the Binchang mining area, existing research methods still primarily rely on traditional approaches such as empirical formula and numerical simulation—resulting in insufficient accuracy and convenience in predicting the height of the water-conducting [...] Read more.

Given the severe water hazard in the coal seam roof of the Binchang mining area, existing research methods still primarily rely on traditional approaches such as empirical formula and numerical simulation—resulting in insufficient accuracy and convenience in predicting the height of the water-conducting fracture zone (WCFZ). By comprehensively considering three influencing factors—mining thickness, mining depth, and working face length—a data-driven approach was employed to construct a multiple nonlinear regression prediction model and a Convolutional Neural Network (CNN) prediction model based on 27 sets of measured data. Both models were subsequently applied to the ZF1403 and ZF1405 working faces in the Yadian coal mine. The results indicate that when considering only single factor of mining thickness, the coefficient of determination (R²) value of the multiple nonlinear regression model was 0.64. When considering all influencing factors, R² improved to 0.84. The mean absolute percentage error (MAPE) of multiple nonlinear regression model was 7.52%. The established CNN model achieved a R² of 0.97, a root mean square error (RMSE) of 9.78, and a MAPE of 4.67%. Compared to the Back Propagation Neural Network model, the prediction accuracy of the CNN model was significantly improved. The relative prediction errors of the developed height of WCFZ in the ZF1403 and ZF1405 working faces at Yadian mine were 6.30% and 2.54% for the multiple nonlinear regression model, respectively, and 0.97% and 3.15% for the CNN model, respectively. Both models met practical engineering requirements. This paper can provide reliable technical support for the prediction of water-conducting fracture zone height under mining conditions similar to the Binchang mining area. Full article

(This article belongs to the Section New Sensors, New Technologies and Machine Learning in Water Sciences)

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25 pages, 2551 KB

Open AccessArticle

Risk Assessment of Water Hazard in Karst Metal Underground Mines Based on an Improved Fuzzy Comprehensive Evaluation Model Integrating AHP and Normal Distribution Confidence

by Rong Liu, Gaofeng Yang, Yuqi Huang, Yang Wen, Jian Ou and Ying Huang

Water 2026, 18(10), 1214; https://doi.org/10.3390/w18101214 - 17 May 2026

Abstract

Hidden disaster-causing factor investigation is a fundamental task for safety production in mines. Water hazards in karst metal underground mines are characterized by complex disaster-forming mechanisms, strong suddenness, and high risk, while traditional assessment methods are prone to expert subjective bias and cannot [...] Read more.

Hidden disaster-causing factor investigation is a fundamental task for safety production in mines. Water hazards in karst metal underground mines are characterized by complex disaster-forming mechanisms, strong suddenness, and high risk, while traditional assessment methods are prone to expert subjective bias and cannot meet the demand for precise prevention and control. This study proposes an improved fuzzy comprehensive evaluation model by integrating the analytic hierarchy process (AHP) and normal distribution-based expert confidence weighting. A three-level assessment index system consisting of 3 first-level indicators and 11 s-level indicators is established for karst metal mine water hazard risk. The normal distribution function is used to quantify expert confidence weights so as to reduce subjective deviation. A three-level fuzzy comprehensive evaluation is performed to achieve quantitative risk grading, and the model robustness is verified through sensitivity analysis. Furthermore, three-dimensional geological modeling and seepage–stress coupling numerical simulation are conducted using COMSOL 6.0 software to validate the reliability of assessment results. The Mao’erling Gold Mine in Hunan Province is taken as a case study. The evaluation yields a comprehensive membership vector of (0.103, 0.130, 0.184, 0.351, 0.232), which is strongly consistent with numerical simulation results and field water inrush records. The results demonstrate that the improved model features strong objectivity and favorable robustness, and can provide a scientific basis for water hazard investigation, risk assessment, and prevention engineering in karst metal underground mines. Full article

(This article belongs to the Special Issue Evaluation and Monitoring of Hydrogeological Hazards in Underground Engineering)

17 pages, 2408 KB

Open AccessArticle

The Effect of Water Treatment Processes on the Performance of Proton Exchange Membrane Water Electrolysis

by Dongkyu Kang, Juhyeong Kim, Dongkeon Kim and Suhan Kim

Water 2026, 18(10), 1213; https://doi.org/10.3390/w18101213 - 17 May 2026

Abstract

This study investigates performance variation and cell degradation in proton exchange membrane water electrolysis (PEMWE) systems depending on feed water quality. In commercial PEMWE designs, simplified water treatment configurations focusing primarily on electrical conductivity (EC) control are sometimes adopted instead of conventional full [...] Read more.

This study investigates performance variation and cell degradation in proton exchange membrane water electrolysis (PEMWE) systems depending on feed water quality. In commercial PEMWE designs, simplified water treatment configurations focusing primarily on electrical conductivity (EC) control are sometimes adopted instead of conventional full ultrapure water production processes. To evaluate the impact of different water treatment processes on cell degradation, permeates from various processes were used as feed water, and cell voltage patterns were analyzed based on EC and total organic carbon (TOC) levels. The experimental results demonstrated that both the two-pass reverse osmosis (RO) and mixed-bed polisher (MBP) permeates achieved an EC below 1 μS/cm, meeting the minimum required standard. Although the cell voltage increase trends for both permeates were similar, the MBP permeate exhibited a higher TOC level despite its lower EC. The elevated TOC level observed in the MBP permeate is attributed to the low organic matter rejection rate of the RO membrane used in the preceding process. This highlights that in simplified water treatment processes for PEMWE, implementing a two-pass RO configuration is essential for effective TOC control. However, simply introducing this configuration is insufficient; it must be accompanied by strategic RO membrane selection to ensure stable operation of PEMWE systems. Full article

(This article belongs to the Special Issue The Application of Electrochemical Methods in Water Treatment, 2nd Edition)

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23 pages, 5037 KB

Open AccessArticle

Landscape Controls on Coupled Water–Air Pollution in an Urbanized Watershed: A GeoSHAP Analysis of the Liaohe River Basin, China

by Sixue Shi, Tingshuang Zhang and Miao Liu

Water 2026, 18(10), 1212; https://doi.org/10.3390/w18101212 - 17 May 2026

Abstract

Landscape pattern is closely associated with pollution in rapidly urbanizing watersheds, but most studies still focus on single pollutants or single environmental media. This study developed a watershed-based framework to compare coupled water and air pollution in the Liaohe River Basin, China. A [...] Read more.

Landscape pattern is closely associated with pollution in rapidly urbanizing watersheds, but most studies still focus on single pollutants or single environmental media. This study developed a watershed-based framework to compare coupled water and air pollution in the Liaohe River Basin, China. A total of 156 hydrologically connected sub-basins were used as common spatial units. Landscape metrics were calculated for 2000, 2010, and 2020. Total nitrogen and total phosphorus loads were simulated using the Soil and Water Assessment Tool, while annual mean PM_2.5 and O₃ concentrations were aggregated from gridded products to the same sub-basin scale. Coupling coordination degree was used to identify relative co-pollution patterns within the aquatic and atmospheric systems. GeoXGBoost with spatial block cross-validation was used to evaluate predictive performance, and GeoSHAP was used to interpret model-based predictor contributions. The aquatic coupled pollution index was predicted more accurately than the atmospheric index, indicating a stronger landscape association with nutrient coupling. Cropland proportion was the most stable predictor of aquatic coupling, whereas forest proportion was the most stable predictor of atmospheric coupling. These results suggest that water-oriented management should focus on cropland structure and ecological buffering, while air-oriented management should emphasize forest continuity and fragmentation control. The framework provides a spatially explicit basis for differentiated watershed management and territorial spatial planning. Full article

(This article belongs to the Section Urban Water Management)

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17 pages, 9763 KB

Open AccessArticle

Land Use Impacts on Sediment Nutrients in a Major Tributary of the Upper Yangtze River: Management Implications for Watershed Remediation

by Linlin Bao, Xiaocong Liu, Yao Wei, Wenliang Xiang, Lahai Jiang and Ye Du

Water 2026, 18(10), 1211; https://doi.org/10.3390/w18101211 - 16 May 2026

Abstract

Massive nutrient inputs from different land uses have caused eutrophication in the Yangtze River. River sediment, as a sink for terrestrial nutrients, can sustain eutrophication for a long time. To further improve water quality, sediment organic carbon (TOC), nitrogen (TN), phosphorus (TP), and [...] Read more.

Massive nutrient inputs from different land uses have caused eutrophication in the Yangtze River. River sediment, as a sink for terrestrial nutrients, can sustain eutrophication for a long time. To further improve water quality, sediment organic carbon (TOC), nitrogen (TN), phosphorus (TP), and the impact of land use composition were investigated in the Tuojiang River watershed, once the most polluted tributary of the Upper Yangtze River. Results showed that the average TOC, TN, and TP contents were, respectively, 11.4 g/kg, 1078 mg/kg, and 1170 mg/kg higher than the local soil background value or the ecologically safe level limit. Due to the spatial layout of agriculture and industry, sediment nutrients were higher in the tributaries and the upper reaches of the main stream of the Tuojiang River. Regression analysis identified that TN was primarily affected by the composition of the dry-farm field within the 500 m zone along the river system, and TOC was affected by 1000 m of dry-farm field and 100 m of paddy field, while TP was related to the distribution of the phosphate chemical industry. It also enhances the urgency of reducing nutrient loss from agricultural non-point sources and mitigating residual nutrients in river sediment. Full article

(This article belongs to the Section Water Quality and Contamination)

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16 pages, 2042 KB

Open AccessArticle

Chromosomally Encoded Resistance and Virulence Determinants Are Selectively Enriched in Hospital Wastewater Effluent Despite Reduced Total ARG Abundance

by Lin Liu, Danyang Shi, Tianjiao Chen, Junwen Li and Min Jin

Water 2026, 18(10), 1210; https://doi.org/10.3390/w18101210 - 16 May 2026

Abstract

Hospital wastewater treatment efficacy is conventionally assessed by total antibiotic resistance gene (ARG) abundance; however, whether this metric accurately reflects biosafety risk remains poorly defined. Using a one-year longitudinal metagenomic survey (bimonthly sampling; n = 18 per group), we simultaneously profiled the resistome, [...] Read more.

Hospital wastewater treatment efficacy is conventionally assessed by total antibiotic resistance gene (ARG) abundance; however, whether this metric accurately reflects biosafety risk remains poorly defined. Using a one-year longitudinal metagenomic survey (bimonthly sampling; n = 18 per group), we simultaneously profiled the resistome, virulome, and mobilome of hospital wastewater influent and effluent; stratified functional gene abundances by genomic origin; quantified ARG–mobile genetic element (MGE) colocalization; and characterized multicategory gene cocarriage across the 15 most abundant pathogenic species. Although the abundance of total strict ARGs decreased significantly in the effluent (p = 0.038), the abundances of metal resistance genes and virulence factors increased concurrently (both p < 0.01), and 8 of the 20 ARG subtypes were enriched rather than removed. This decline was driven exclusively by a reduction in the number of plasmid-encoded ARGs (p < 0.001), whereas genes encoding chromosomal virulence factors, metal resistance genes, biocide resistance genes, and MGEs were significantly enriched in the effluent (all p < 0.05). The normalized ARG–MGE colocalization rate was significantly greater in the effluent (p = 0.028), with a concurrent shift toward transposase-mediated chromosomal mobilization. Pathogen-associated metagenomic assemblies of clinically relevant species exhibited synchronous multicategory resistance coenrichment in the effluent, which is consistent with coselection under antibiotic, biocide, and metal pressures. Total ARG abundance is fundamentally decoupled from biosafety risk in treated hospital wastewater, warranting integrated surveillance beyond ARG-centric metrics. Full article

(This article belongs to the Special Issue Evaluation of Microbiological Indicators for Water and Wastewater Treatment and Reuse, 2nd Edition)

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31 pages, 3417 KB

Open AccessArticle

Surface and Groundwater Quality in the Tula Valley, Mexico

by Adrián Pedrozo-Acuña, Norma Ramírez-Salinas, Marco Rodrigo López-López, Juan Carlos Bustos-Montes and Edgar Yuri Mendoza-Cázares

Water 2026, 18(10), 1209; https://doi.org/10.3390/w18101209 - 16 May 2026

Abstract

Water security in rapidly urbanising river basins is increasingly threatened by untreated city effluents, industrial discharges, and legacy agricultural contamination. The Tula River basin in central Mexico illustrates this issue, absorbing the majority of Mexico City’s effluent while sustaining a heavily exploited aquifer [...] Read more.

Water security in rapidly urbanising river basins is increasingly threatened by untreated city effluents, industrial discharges, and legacy agricultural contamination. The Tula River basin in central Mexico illustrates this issue, absorbing the majority of Mexico City’s effluent while sustaining a heavily exploited aquifer beneath one of the nation’s largest irrigation districts. This study provides an integrated assessment of surface water and groundwater quality throughout the basin, including the Endhó Dam and its associated aquifer. Water quality analysis revealed severe surface water contamination (WQI > 300), driven by untreated sewage and inadequate sanitation infrastructure. Elevated COD, BOD, and nutrient concentrations indicate significant organic loading and eutrophication risk. Near Tula City, arsenic, copper, and zinc were detected at levels posing direct risks to human health. Groundwater quality was comparatively favourable, with 71% of wells recording WQI < 100; however, arsenic exceeded permissible limits more than twentyfold in select wells, attributed to geological sources. The detection of SVOCs in both hydrological compartments confirms cross-compartment contamination. Point-source reduction alone is insufficient for aquifer recovery; comprehensive sanitation strategies and long-term monitoring are urgently required. These findings carry direct relevance for water governance in megacity-dependent basins globally, where urban, agricultural, and geological stressors demand integrated management approaches. Full article

(This article belongs to the Section Water Quality and Contamination)

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11 pages, 903 KB

Open AccessArticle

Effects of Ocean Surface-Water Salinity on Osmotic Potential and Water-Vapor Emission Potential

by Thomas A. Cochrane and Thomas T. Cochrane

Water 2026, 18(10), 1208; https://doi.org/10.3390/w18101208 - 16 May 2026

Abstract

Studies have shown that oceanic surface-water salinity varies across the globe and changes over time, while atmospheric water-vapor levels have also increased in recent decades. Evaporation from ocean and inland waters is controlled primarily by meteorological forcing, but the thermodynamic state of the [...] Read more.

Studies have shown that oceanic surface-water salinity varies across the globe and changes over time, while atmospheric water-vapor levels have also increased in recent decades. Evaporation from ocean and inland waters is controlled primarily by meteorological forcing, but the thermodynamic state of the water body also matters. In saline waters, dissolved solutes reduce water activity and thereby reduce the equilibrium tendency of water molecules to enter the vapor phase. In this study, the authors’ coefficient-less aqueous osmotic potential equation was used to examine the thermodynamic effect of representative oceanic salinity differences on evaporative tendency. Calculations were made for recorded surface-water salinities ranging from 31 to 38 kg·m⁻³ of dissolved solutes at an average temperature of 20 °C. Computed osmotic potentials ranged from −2.257 to −2.708 MPa. The corresponding semi-permeable membrane interface pressures ranged from 8.935 to 8.484 MPa, indicating an approximately 5% difference across the selected oceanic salinity range. The interface pressure calculated for solute-free water (11.192 MPa) was more than 24% higher than for the seawater cases considered. These results suggest that salinity acts as a secondary thermodynamic modifier of evaporation potential, whereas radiative, aerodynamic, humidity, and temperature controls remain dominant in determining actual evaporation fluxes. The results also indicate that freshwater bodies and changing land-based evaporative sources may contribute differently to atmospheric water vapor than saline ocean waters. The framework presented here is intended to complement, rather than replace, established evaporation formulations by clarifying how salinity-related osmotic effects can modify the water-side boundary condition. Full article

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20 pages, 5255 KB

Open AccessArticle

Regionalized Rainfall Disaggregation Coefficients for the Rio de Janeiro Metropolitan Region, Brazil

by Pedro Henrique Garcia de Souza Façanha, Marcelo de Miranda Reis and Igor da Silva Rocha Paz

Water 2026, 18(10), 1207; https://doi.org/10.3390/w18101207 - 16 May 2026

Abstract

This study estimates rainfall disaggregation coefficients for the State of Rio de Janeiro and for the Rio de Janeiro Metropolitan Region (RMRJ) based on automatic rain gauges from the CEMADEN network. A Python-based workflow collected time series, selected stations according to record length, [...] Read more.

This study estimates rainfall disaggregation coefficients for the State of Rio de Janeiro and for the Rio de Janeiro Metropolitan Region (RMRJ) based on automatic rain gauges from the CEMADEN network. A Python-based workflow collected time series, selected stations according to record length, extracted annual extreme events (10 min to 48 h), and calculated sub-daily to daily rainfall ratios for return periods of 2–100 years. The formulations proposed by Pfafstetter and Chen were evaluated through a case study to guide the model selection. In the RMRJ, 109 stations were analyzed and aggregated by municipality, resulting in the metropolitan mean disaggregation coefficient (COERM). The COERM values are close to those proposed by CETESB up to the 30 min–1 h duration range. However, the coefficients were up to 18.8% higher in the duration range between 1 h and 3 h relative to the 24 h rainfall, indicating a stronger temporal concentration of precipitation precisely in durations critical for urban drainage design. Full article

(This article belongs to the Section Hydrology)

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25 pages, 8051 KB

Open AccessArticle

Experimental Investigation of Unfrozen Water Content, Pore Structure, and Mechanical Properties of Remolded Warm Frozen Soil from the Ili River Valley

by Yue Qi, Zizhao Zhang, Lilong Cheng, Jianhua Zhu, Xveye Wang and Peizhi Liu

Water 2026, 18(10), 1206; https://doi.org/10.3390/w18101206 - 16 May 2026

Abstract

The Ili River Valley is a typical seasonally frozen region in which slope instability frequently occurs during the warm frozen-soil stage, generally at temperatures ranging from approximately −1.5 to 0 °C. In this context, changes in unfrozen water content play an important role [...] Read more.

The Ili River Valley is a typical seasonally frozen region in which slope instability frequently occurs during the warm frozen-soil stage, generally at temperatures ranging from approximately −1.5 to 0 °C. In this context, changes in unfrozen water content play an important role in controlling the pore structure and mechanical behavior of warm frozen soil, yet the links among these factors remain insufficiently understood. This study investigates warm frozen soil from the Ili River Valley, with particular emphasis on the role of unfrozen water content in regulating pore-structure characteristics and mechanical response under low-temperature conditions. Low-field nuclear magnetic resonance (NMR), low-temperature triaxial shear tests, scanning electron microscopy (SEM), and quantitative image analysis were employed to examine the relationships between unfrozen water content, pore structure, and macroscopic mechanical properties under different temperatures, initial water contents, and confining pressures. The results show that unfrozen water content decreases markedly with decreasing temperature, especially within the range of −1.5 to −5 °C, and increases with increasing initial water content. These changes are accompanied by significant variations in porosity, pore abundance, and pore fractal dimension, reflecting freezing-induced reorganization of the pore system. Lower temperatures and higher initial water contents promote ice-crystal growth and the formation of larger ice-cemented aggregates, thereby modifying the pore framework. Meanwhile, peak strength and cohesion increase with decreasing temperature and increasing initial water content, whereas the internal friction angle shows a decreasing trend. In addition, porosity, pore abundance, and pore fractal dimension are closely correlated with peak strength and cohesion. The results indicate that unfrozen water content governs the freezing-induced reorganization of pore structure, which in turn controls the strength evolution of warm frozen soil. These findings improve understanding of the role of unfrozen water in low-temperature soil structure and strength evolution and provide a basis for evaluating slope instability in the Ili River Valley. Full article

(This article belongs to the Special Issue Advances in Hydro-Thermal–Mechanical Coupling Geotechnical Engineering)

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23 pages, 28331 KB

Open AccessArticle

Physics-Coupled and Message-Transferred Inverse Modeling for Subsurface Flow with Very Sparse Supervision

by Haibo Cheng, Jiahao Qiao, Xian’e Xiong, Xiaodi Zhang and Wenke Wang

Water 2026, 18(10), 1205; https://doi.org/10.3390/w18101205 - 16 May 2026

Abstract

Inverse modeling for subsurface flow represents a fundamental scientific challenge in hydrogeology and geotechnical engineering, which seeks to reconstruct critical hydrogeological parameters from sparse observational constraints. The marked spatial heterogeneity of subsurface formations, combined with the prohibitively high costs of data acquisition, renders [...] Read more.

Inverse modeling for subsurface flow represents a fundamental scientific challenge in hydrogeology and geotechnical engineering, which seeks to reconstruct critical hydrogeological parameters from sparse observational constraints. The marked spatial heterogeneity of subsurface formations, combined with the prohibitively high costs of data acquisition, renders parameter inversion, especially with very sparse supervision, inherently ill-posed and susceptible to non-uniqueness and instability. Numerical simulation-based iterative inversion methods are computationally expensive and time-consuming. Purely data-driven approaches require extensive labeled data, whereas the existing physics-informed methods lack an explicit architecture-level information transfer channel between parameter and response fields. Under sparse supervision, this prevents hydraulic head observations from effectively constraining hydraulic conductivity identification, resulting in weak parameter identifiability. In this work, we propose a physics-coupled and message-transferred inverse modeling method for transient subsurface flow problems with very sparse supervision. Specifically, the static parameter field estimated by the inversion network is explicitly incorporated into the dynamic response prediction network, and the static inversion and dynamic prediction networks are physics-coupled by the governing equations in parallel. This method enables accurate hydraulic conductivity inversion under extremely limited supervision. Experiments on multiple parameter fields, label scales, and noise levels demonstrate accurate and stable inversion performance under very sparse supervision, with ensemble-based uncertainty analysis, further confirming the reliability of the proposed method. Full article

(This article belongs to the Special Issue Application of Machine Learning in Hydrologic Sciences, 2nd Edition)

17 pages, 11073 KB

Open AccessArticle

Enhancing Salmonid Reproduction in a Natural River System: A Case Study of the Ina River (Baltic Sea Catchment)

by Adam Tański, Adam Brysiewicz, Agata Korzelecka-Orkisz, Beata Więcaszek, Małgorzata Bonisławska and Krzysztof Formicki

Water 2026, 18(10), 1204; https://doi.org/10.3390/w18101204 (registering DOI) - 16 May 2026

Abstract

Salmonid fish only reproduce in habitats that meet specific environmental requirements, including appropriate gravel–cobble substrate, suitable flow velocity, and adequate oxygenation. Long-term drainage practices and river channel regulation have led to substantial alterations of river systems, particularly affecting bed structure. The aim of [...] Read more.

Salmonid fish only reproduce in habitats that meet specific environmental requirements, including appropriate gravel–cobble substrate, suitable flow velocity, and adequate oxygenation. Long-term drainage practices and river channel regulation have led to substantial alterations of river systems, particularly affecting bed structure. The aim of this study was to assess habitat conditions in the Ina river catchment and to restore spawning grounds for salmon and sea trout through the construction of artificial redds, as well as to evaluate the effectiveness of these measures over subsequent years. The number of fish nests recorded prior to the implementation of the restoration project in 2011 was significantly lower (3 ± 1, mean ± SD) compared to post-restoration periods in 2013 (23 ± 11) and 2015 (21 ± 14). Spawning nests were predominantly located in areas characterized by high flow velocity and elevated water conductivity, hardness, and alkalinity. During the spawning migrations in 2013–2015, a total of 4593 individuals were recorded using a fish scanner. Despite a gradual decline in water levels from pre-restoration to post-restoration periods, the number of nests remained consistently high. The results indicate that ongoing environmental and climatic changes necessitate continued efforts to improve spawning conditions for anadromous salmonids. Currently (2024–2025), the potential for natural reproduction in the Ina River catchment remains comparable to the study period (89 redds), largely determined by the availability of gravel habitats and river discharge enabling upstream migration. Full article

(This article belongs to the Section Biodiversity and Functionality of Aquatic Ecosystems)

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25 pages, 16761 KB

Open AccessArticle

Influence of DEM Spatial Resolution on the Accuracy and Computational Efficiency of HEC-RAS 1D and 2D Flood Inundation Modelling: A Case Study of the Cimanceuri Basin, Indonesia

by Rijal Muhammad Fikri, Henny Herawati and Wati Asriningsih Pranoto

Water 2026, 18(10), 1203; https://doi.org/10.3390/w18101203 - 15 May 2026

Abstract

Digital Elevation Model (DEM) resolution plays a critical role in hydraulic flood modelling by influencing inundation accuracy, spatial precision and computational efficiency. However, limited studies have simultaneously evaluated both inundation accuracy and computational performance across multiple DEM resolutions in event-based urban flood modelling. [...] Read more.

Digital Elevation Model (DEM) resolution plays a critical role in hydraulic flood modelling by influencing inundation accuracy, spatial precision and computational efficiency. However, limited studies have simultaneously evaluated both inundation accuracy and computational performance across multiple DEM resolutions in event-based urban flood modelling. This study aims to evaluate the impact of DEM spatial resolution on the performance of HEC-RAS 1D and 2D models in simulating an event-based urban flood that occurred on 3 March 2025. A 1 m LiDAR-derived DEM was resampled to 2 m, 5 m, 8 m, 10 m, 20 m, 25 m, and 30 m resolutions to assess the effects of terrain generalization on hydraulic response. Simulated inundation extents were validated against observed flood areas derived from aerial imagery, and computation time was recorded for each scenario. Results reveal a clear trade-off between spatial accuracy and computational demand. In the 1D simulations, deviation from observed inundation increased from 0.76 ha at 1 m to 2.50 ha at 30 m, while computation time remained relatively stable. The 2D simulations were more sensitive to DEM resolution, with deviation increasing from 0.33 ha to 3.12 ha and longer runtimes at finer resolutions. Among the evaluated scenarios, the 10 m DEM provided the most balanced performance in both 1D and 2D models. For rapid assessment and operational flood management, where computational efficiency and timely decision-making are critical, a 1D modelling approach combined with a 10 × 10 m DEM is recommended as a practical and efficient solution. Full article

(This article belongs to the Section New Sensors, New Technologies and Machine Learning in Water Sciences)

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