Hydrology

10 pages, 2722 KiB

Open AccessArticle

Stable Isotope Investigations of Icicle Formation and Evolution

by Thomas Brubaker and R. V. Krishnamurthy

Hydrology 2025, 12(2), 30; https://doi.org/10.3390/hydrology12020030 - 9 Feb 2025

Icicles are elongated structures formed from water flowing over hangings and crystallizing in sub-freezing conditions. These features are ubiquitous in several parts of the world that experience severe to moderate winter seasons. It has been suggested that they could be a source of [...] Read more.

Icicles are elongated structures formed from water flowing over hangings and crystallizing in sub-freezing conditions. These features are ubiquitous in several parts of the world that experience severe to moderate winter seasons. It has been suggested that they could be a source of recharge to groundwater. Icicles are presumed to affect groundwater quality via incorporation of atmospheric and roof top contaminants. Relatively little attention has been paid to these wintry features, insofar as only a few theoretical models have attempted to describe their formation. Stable isotope measurements (δ¹⁸O and δ²H) of icicles that were melted stepwise into fractions are presented as support for the models that invoke the rapid formation of icicles. Icicles exhibit minimal fraction to fraction isotope variation, suggesting a lack of isotope equilibrium and that kinetic effects dominate the freezing process. Deviations from the Global Meteoric Water Line (GMWL), which is similar to the Local Meteoric Water Line (LMWL), indicate that post-depositional processes, namely sublimation, may occur throughout the freezing process. Isotopic evidence lends support to a “growth-cessation-growth” variation of the already proposed methods of rapid icicle formation, where a cessation period occurs between pulses of rapid freezing during icicle growth. Full article

(This article belongs to the Special Issue Isotope Hydrology in the U.S.)

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19 pages, 6000 KiB

Open AccessArticle

Policy Measures to Lead Sustainable Development of Agriculture Catchment: Socio-Hydrology Modeling Insights

by Mahendran Roobavannan, Jaya Kandasamy and Saravanamuthu Vigneswaran

Hydrology 2025, 12(2), 29; https://doi.org/10.3390/hydrology12020029 - 9 Feb 2025

Abstract

Achieving sustainable development in agricultural catchments requires well-designed policy measures. This study examines the intricate interactions between social dynamics and hydrological processes within agricultural systems to propose targeted policy interventions. By employing socio-hydrology models that integrate socio-economic and hydrological data, the research provides [...] Read more.

Achieving sustainable development in agricultural catchments requires well-designed policy measures. This study examines the intricate interactions between social dynamics and hydrological processes within agricultural systems to propose targeted policy interventions. By employing socio-hydrology models that integrate socio-economic and hydrological data, the research provides valuable insights into the feedback loops and interdependencies that influence catchment sustainability. In this study, we find that policies on population management should aim to balance natural growth rates with the carrying capacity of the basin. Strategies such as education, healthcare access, and family planning can help manage demographic pressures. Migration policies should consider the economic and environmental impacts of population influx and support balanced regional development to distribute the demographic pressures more evenly. Wage growth should be aligned with economic productivity to prevent unemployment and inequality. Policies that promote equitable wage structures and enhance labor mobility between sectors can mitigate disparities. The findings emphasize the necessity of adaptive policies that address both environmental and societal factors, advocating for interdisciplinary approaches in water resource management and agricultural policy development. This study also highlights the pivotal role of technological innovations and the societal values and norms that shape sustainability and resilience in agricultural catchments. Full article

(This article belongs to the Special Issue Hydrological Processes in Agricultural Watersheds)

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21 pages, 4960 KiB

Open AccessArticle

Evaluating Expert Opinion-Based Reservoir Operation in Cfa/Csa Climatic Conditions

by Mahdi Sedighkia and Bithin Datta

Hydrology 2025, 12(2), 28; https://doi.org/10.3390/hydrology12020028 - 6 Feb 2025

Abstract

This study evaluates the application of an expert opinion-based fuzzy method for reservoir operation in humid subtropical climate/hot-summer Mediterranean climatic classes (Cfa/Csa in the Köppen–Geiger climate classification system), which are characterized by humid subtropical to Mediterranean conditions with ample rainfall and seasonal water [...] Read more.

This study evaluates the application of an expert opinion-based fuzzy method for reservoir operation in humid subtropical climate/hot-summer Mediterranean climatic classes (Cfa/Csa in the Köppen–Geiger climate classification system), which are characterized by humid subtropical to Mediterranean conditions with ample rainfall and seasonal water availability challenges. Effective reservoir management in these regions is critical for balancing water storage and downstream release and maintaining ecosystem health under variable hydrological conditions. The performance of the fuzzy method was compared to two meta-heuristic algorithms: gravitational search algorithm (GSA) and shuffled frog leaping algorithm (SFLA). System performance was assessed using key indices such as the reliability index as a measure of meeting water demands. The fuzzy method achieved the highest reliability index of 0.690, outperforming GSA (0.677) and SFLA (0.688), demonstrating its superior ability to ensure consistent water supply downstream. The fuzzy method, leveraging expert knowledge, not only enhanced downstream water supply reliability but also reduced computational time compared to the meta-heuristic approaches. The incorporation of expert opinions provides a practical, robust, and efficient framework for reservoir management in challenging climate conditions such as Cfa/Csa classes. Additionally, the fuzzy solution demonstrated superior adaptability to diverse hydrological conditions, balancing ecological and water supply needs effectively. These findings highlight the potential of using expert opinions to support sustainable reservoir operations by achieving optimal trade-offs between competing objectives and addressing challenges in water resource management under varying climatic conditions. Full article

(This article belongs to the Special Issue Natural or Artificial Water Reservoirs' Impacts on Mitigating the Intensities of Floods and Droughts)

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20 pages, 5362 KiB

Open AccessArticle

Investigating the Water, Ecosystem, and Agriculture Nexus in Three Inland River Basins of the Arid Hexi Corridor, China, Using Integrated Hydrological Modeling

by Yuan Chen and Yong Tian

Hydrology 2025, 12(2), 27; https://doi.org/10.3390/hydrology12020027 - 6 Feb 2025

Abstract

The Water–Ecosystem–Agriculture (WEA) relationship is pivotal to the sustainable development of arid and semi-arid areas. The WEA nexus in these areas is essential for making policies towards sustainable development. This study aims to explore the WEA nexus in three large inland river basins [...] Read more.

The Water–Ecosystem–Agriculture (WEA) relationship is pivotal to the sustainable development of arid and semi-arid areas. The WEA nexus in these areas is essential for making policies towards sustainable development. This study aims to explore the WEA nexus in three large inland river basins (Heihe River Basin, Shiyang River Basin, and Shule River Basin) in the Hexi Corridor, Northwest China, using an integrated hydrological modeling approach. The integrated model was calibrated and validated against observed streamflow data, achieving Nash–Sutcliffe Efficiencies ranging from 0.83 to 0.94 in the validation period. The major findings are as follows. First, altering the amount of irrigation water significantly affects hydrological and ecological processes in both midstream and downstream areas, influencing the WEA nexus. For example, a 20% reduction in irrigation demand led to a 0.46 billion m³/year recovery in midstream groundwater storage and a 4.3% increase in downstream ecosystem health, but resulted in a 5.4% decrease in midstream agricultural productivity. Second, intense trade-offs among agricultural productivity, ecosystem health, and groundwater sustainability were identified. These trade-offs are highly sensitive to water management strategies, particularly those affecting groundwater sustainability. Third, implementing stricter groundwater-level drawdown constraints significantly improved groundwater sustainability and ecosystem health. Fourth, this study highlighted unique WEA nexus characteristics in each of the three basins. This study provides insights into the understanding the complex WEA nexus, and the quantitative results underscore the trade-offs and synergies within the WEA nexus, providing a foundation for informed decision-making in water resource management. Full article

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16 pages, 4882 KiB

Open AccessArticle

Effects of Inconsistency in Drought Event Definitions on Drought Characteristics

by Frank Joseph Wambura

Hydrology 2025, 12(2), 26; https://doi.org/10.3390/hydrology12020026 - 5 Feb 2025

Abstract

Drought, as one of the hazards exacerbated by climate change, has attracted the attention of many scientists. Many drought studies have used different drought event definitions (DEDs). However, little is known about the effects of these definitions on drought characteristics. This study investigated [...] Read more.

Drought, as one of the hazards exacerbated by climate change, has attracted the attention of many scientists. Many drought studies have used different drought event definitions (DEDs). However, little is known about the effects of these definitions on drought characteristics. This study investigated the effects of DEDs on drought characteristics using the standardized precipitation evapotranspiration index (SPEI) in the Upper Pangani Basin in northeast Tanzania. First, rainfall and air temperature data from the Climatic Research Unit database were used to compute the SPEI. Then, four different types of DEDs were used to identify drought events in the SPEI time series. The identified drought events were examined for agreements and correlations using Kappa and Phi coefficients, respectively, and finally characterized. The findings show that different DEDs produced different types and frequencies of drought events. The patterns of drought events for these DEDs had agreements ranging from 52 to 78% and correlations ranging from 79% to 95%. Different DEDs also led to different drought intensities, ranging from mild to extreme, although the overall drought intensities were either mild or moderate. From this study, we can infer that using suitable DEDs is essential for identifying drought events, as they enable accurate comparisons of droughts across regions and periods, consequently reducing errors and biases in evaluating drought hazards. Full article

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41 pages, 24123 KiB

Open AccessArticle

Coupling HEC-RAS and AI for River Morphodynamics Assessment Under Changing Flow Regimes: Enhancing Disaster Preparedness for the Ottawa River

by Mohammad Uzair Anwar Qureshi, Afshin Amiri, Isa Ebtehaj, Silvio José Guimere, Juraj Cunderlik and Hossein Bonakdari

Hydrology 2025, 12(2), 25; https://doi.org/10.3390/hydrology12020025 - 4 Feb 2025

Abstract

Despite significant advancements in flood forecasting using machine learning (ML) algorithms, recent events have revealed hydrological behaviors deviating from historical model development trends. The record-breaking 2019 flood in the Ottawa River basin, which exceeded the 100-year flood threshold, underscores the escalating impact of [...] Read more.

Despite significant advancements in flood forecasting using machine learning (ML) algorithms, recent events have revealed hydrological behaviors deviating from historical model development trends. The record-breaking 2019 flood in the Ottawa River basin, which exceeded the 100-year flood threshold, underscores the escalating impact of climate change on hydrological extremes. These unprecedented events highlight the limitations of traditional ML models, which rely heavily on historical data and often struggle to predict extreme floods that lack representation in past records. This calls for integrating more comprehensive datasets and innovative approaches to enhance model robustness and adaptability to changing climatic conditions. This study introduces the Next-Gen Group Method of Data Handling (Next-Gen GMDH), an innovative ML model leveraging second- and third-order polynomials to address the limitations of traditional ML models in predicting extreme flood events. Using HEC-RAS simulations, a synthetic dataset of river flow discharges was created, covering a wide range of potential future floods with return periods of up to 10,000 years, to enhance the accuracy and generalization of flood predictions under evolving climatic conditions. The Next-Gen GMDH addresses the complexity and limitations of standard GMDH by incorporating non-adjacent connections and optimizing intermediate layers, significantly reducing computational overhead while enhancing performance. The Gen GMDH demonstrated improved stability and tighter clustering of predictions, particularly for extreme flood scenarios. Testing results revealed exceptional predictive accuracy, with Mean Absolute Percentage Error (MAPE) values of 4.72% for channel width, 1.80% for channel depth, and 0.06% for water surface elevation. These results vastly outperformed the standard GMDH, which yielded MAPE values of 25.00%, 8.30%, and 0.11%, respectively. Additionally, computational complexity was reduced by approximately 40%, with a 33.88% decrease in the Akaike Information Criterion (AIC) for channel width and an impressive 581.82% improvement for channel depth. This methodology integrates hydrodynamic modeling with advanced ML, providing a robust framework for accurate flood prediction and adaptive floodplain management in a changing climate. Full article

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19 pages, 4538 KiB

Open AccessArticle

The Use of Fluorescent Organic Matter as a Natural Transit Time Tracer in the Unsaturated Zone of the Fontaine De Vaucluse Karst System

by Leïla Serène, Naomi Mazzilli, Christelle Batiot-Guilhe, Christophe Emblanch, Milanka Babic, Julien Dupont, Roland Simler and Matthieu Blanc

Hydrology 2025, 12(2), 24; https://doi.org/10.3390/hydrology12020024 - 1 Feb 2025

Abstract

The fluorescence index called the Transit Time index (TTi) is based on the fluorescence of natural organic matter in order to qualitatively assess the transit time of karst groundwater, using springs affected by human activities. This study aims to further evaluate the potential [...] Read more.

The fluorescence index called the Transit Time index (TTi) is based on the fluorescence of natural organic matter in order to qualitatively assess the transit time of karst groundwater, using springs affected by human activities. This study aims to further evaluate the potential of fluorescent compounds as a natural tracer of transit time when applied to unsaturated zone flows with natural catchments, in contrast to the first study. For this purpose, a bi-monthly sampling of one year of monitoring for organic matter fluorescence, TOC, major elements and water-stable isotopes was performed. A conceptual model of the sources and fates of fluorescent compounds is built, emphasizing the allochthonous origin of humic-like C compounds, and the autochthonous production of humic-like M and protein-like compounds within the unsaturated zone. Fluorescent compound intensity interpretation according to this model reveals consistent relative transit times with flow behavior and also provides complementary information. The results also show the TTi’s ability to summarize fluorescent compounds, its consistency with relative transit time, and its higher sensitivity as compared to other natural tracers. However, prior to its use, a thorough assessment of soil organic matter, microbial activity, and potential anthropogenic contamination is required, encouraging interdisciplinary collaboration between hydrogeologists, microbiologists and soil scientists. Full article

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18 pages, 1162 KiB

Open AccessArticle

Modelling Hydrological Droughts in Canadian Rivers Based on Markov Chains Using the Standardized Hydrological Index as a Platform

by Tribeni C. Sharma and Umed S. Panu

Hydrology 2025, 12(2), 23; https://doi.org/10.3390/hydrology12020023 - 31 Jan 2025

Abstract

The standardized hydrological index (SHI) is the standardized but not normalized (normal probability variate) value of the streamflow used to characterize a hydrological drought, akin to the standardized precipitation index (SPI, which is both standardized and normalized) in the [...] Read more.

The standardized hydrological index (SHI) is the standardized but not normalized (normal probability variate) value of the streamflow used to characterize a hydrological drought, akin to the standardized precipitation index (SPI, which is both standardized and normalized) in the realm of the meteorological drought. The time series of the SHI can be used as a platform for deriving the longest duration, L_T, and the largest magnitude, M_T (in standardized form), of a hydrological drought over a desired return period of T time units (year, month, or week). These parameters are predicted based on the SHI series derived from the annual, monthly, and weekly flow sequences of Canadian rivers. An important point to be reckoned with is that the monthly and weekly sequences are non-stationary compared to the annual sequences, which fulfil the conditions of stochastic stationarity. The parameters, such as the mean, standard deviation (or coefficient of variation), lag 1 autocorrelation, and conditional probabilities from SHI sequences, when used in Markov chain-based relationships, are able to predict the longest duration, L_T, and the largest magnitude, M_T. The product moment and L-moment ratio analyses indicate that the monthly and weekly flows in the Canadian rivers fit the gamma probability distribution function (pdf) reasonably well, whereas annual flows can be regarded to follow the normal pdf. The threshold level chosen in the analysis is the long-term median of SHI sequences for the annual flows. For the monthly and weekly flows, the threshold level represents the median of the respective month or week and hence is time varying. The runs of deficit in the SHI sequences are treated as drought episodes and thus the theory of runs formed an essential tool for analysis. This paper indicates that the Markov chain-based methodology works well for predicting L_T on annual, monthly, and weekly SHI sequences. Markov chains of zero order (MC0), first order (MC1), and second order (MC2) turned out to be satisfactory on annual, monthly, and weekly scales, respectively. The drought magnitude, M_T, was predicted satisfactorily via the model M_T = I_d × L_c, where I_d stands for drought intensity and L_c is a characteristic drought length related to L_T through a scaling parameter, ɸ (= 0.5). The I_d can be deemed to follow a truncated normal pdf, whose mean and variance when combined implicitly with L_c proved prudent for predicting M_T at all time scales in the aforesaid relationship. Full article

(This article belongs to the Section Statistical Hydrology)

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23 pages, 4334 KiB

Open AccessArticle

Evaluation and Adjustment of Historical Hydroclimate Data: Improving the Representation of Current Hydroclimatic Conditions in Key California Watersheds

by Andrew Schwarz, Z. Q. Richard Chen, Alejandro Perez and Minxue He

Hydrology 2025, 12(2), 22; https://doi.org/10.3390/hydrology12020022 - 22 Jan 2025

Abstract

The assumption of stationarity in historical hydroclimatic data, fundamental to traditional water resource planning models, is increasingly challenged by the impacts of climate change. This discrepancy can lead to inaccurate model outputs and misinformed management decisions. This study addresses this challenge by developing [...] Read more.

The assumption of stationarity in historical hydroclimatic data, fundamental to traditional water resource planning models, is increasingly challenged by the impacts of climate change. This discrepancy can lead to inaccurate model outputs and misinformed management decisions. This study addresses this challenge by developing a novel monthly data adjustment approach, the Runoff Curve Year–Type–Monthly (RC-YTM) method. The application of this method is exemplified at five key California watersheds. The RC-YTM method accounts for the increasing variability and shifts in seasonal runoff timing observed in the historical data (1922–2021), aligning it with the contemporary climate conditions represented by the period from 1992 to 2021 at the study watersheds. This method adjusts both annual and monthly streamflow values using a combination of precipitation–runoff relationships, quantile mapping, and water year classification. The adjusted data, reflecting current climatic conditions more accurately than the raw historical data, serve as valuable inputs for operational water resource planning models like CalSim3, commonly used in California for water management. This approach, demonstrably effective in capturing the observed climate change impacts on streamflow at monthly timesteps, enhances the reliability of model simulations representing contemporary conditions, which can lead to better-informed decision-making in water management, infrastructure investment, drought and flood risk assessment, and adaptation strategies. While focused on specific California watersheds, this study’s findings and the adaptable RC-YTM method hold significant implications for water resource management in other regions facing similar hydroclimatic challenges in a changing climate. Full article

(This article belongs to the Special Issue Runoff Modelling under Climate Change)

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20 pages, 8692 KiB

Open AccessArticle

Forecasting Model for Danube River Water Temperature Using Artificial Neural Networks

by Cristina-Sorana Ionescu, Ioana Opriș, Daniela-Elena Gogoașe Nistoran and Constantin-Alexandru Baciu

Hydrology 2025, 12(2), 21; https://doi.org/10.3390/hydrology12020021 - 21 Jan 2025

Abstract

The objective of this paper is to propose an artificial neural network (ANN) model to forecast the Danube River temperature at Chiciu–Călărași, Romania, bordered by Romanian and Bulgarian ecological sites, and situated upstream of the Cernavoda nuclear power plant. Given the temperature increase [...] Read more.

The objective of this paper is to propose an artificial neural network (ANN) model to forecast the Danube River temperature at Chiciu–Călărași, Romania, bordered by Romanian and Bulgarian ecological sites, and situated upstream of the Cernavoda nuclear power plant. Given the temperature increase trend, the potential of thermal pollution is rising, impacting aquatic and terrestrial ecosystems. The available data covered a period of eight years, between 2008 and 2015. Using as input data actual air and water temperatures, and discharge, as well as air temperature data provided by weather forecasts, the ANN model predicts the Danube water temperature one week in advance with a root mean square deviation (RMSE) of 0.954 °C for training and 0.803 °C for testing. The ANN uses the Levenberg–Marquardt feedforward backpropagation algorithm. This feature is useful for the irrigation systems and for the power plants in the area that use river water for different purposes. The results are encouraging for developing similar studies in other locations and extending the ANN model to include more parameters that can have a significant influence on water temperature. Full article

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23 pages, 5265 KiB

Open AccessArticle

High-Resolution Flow and Phosphorus Forecasting Using ANN Models, Catering for Extremes in the Case of the River Swale (UK)

by Elisabeta Cristina Timis, Horia Hangan, Vasile Mircea Cristea, Norbert Botond Mihaly and Michael George Hutchins

Hydrology 2025, 12(2), 20; https://doi.org/10.3390/hydrology12020020 - 21 Jan 2025

Abstract

The forecasting of river flows and pollutant concentrations is essential in supporting mitigation measures for anthropogenic and climate change effects on rivers and their environment. This paper addresses two aspects receiving little attention in the literature: high-resolution (sub-daily) data-driven modeling and the prediction [...] Read more.

The forecasting of river flows and pollutant concentrations is essential in supporting mitigation measures for anthropogenic and climate change effects on rivers and their environment. This paper addresses two aspects receiving little attention in the literature: high-resolution (sub-daily) data-driven modeling and the prediction of phosphorus compounds. It presents a series of artificial neural networks (ANNs) to forecast flows and the concentrations of soluble reactive phosphorus (SRP) and total phosphorus (TP) under a wide range of conditions, including low flows and storm events (0.74 to 484 m³/s). Results show correct forecast along a stretch of the River Swale (UK) with an anticipation of up to 15 h, at resolutions of up to 3 h. The concentration prediction is improved compared to a previous application of an advection–dispersion model. Full article

(This article belongs to the Special Issue Hydrodynamics and Water Quality of Rivers and Lakes)

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17 pages, 15530 KiB

Open AccessArticle

Exploring Seasonality Indices for Low-Flow Analysis on Tibagi Watershed (Brazil)

by Alexandre Sokoloski de Azevedo Delduque de Macedo and Michael Männich

Hydrology 2025, 12(1), 19; https://doi.org/10.3390/hydrology12010019 - 17 Jan 2025

Abstract

This study investigated the seasonality of low-flow discharges in the Tibagi watershed, Paraná, Brazil, through the analysis of three indices: Seasonality Ratio (

S R

), Seasonality Index (

S I

), and Seasonality Histogram (

S H

). The indices were computed [...] Read more.

This study investigated the seasonality of low-flow discharges in the Tibagi watershed, Paraná, Brazil, through the analysis of three indices: Seasonality Ratio (

S R

), Seasonality Index (

S I

), and Seasonality Histogram (

S H

). The indices were computed and compared using previously calculated low-flow discharge data (

Q_{95}

) and physiographic information on sub-watersheds. A ‘Seasonality Calendar’ was developed, illustrating the period and intensity of low-flow discharge occurrences in the watershed. The results indicate that, despite the watershed not presenting a strong seasonality, there is a tendency for low-flow discharges to concentrate in certain months, notably in August, September, and October. Spatial analysis reveals varied patterns with a certain trend of increased seasonality intensity (parameter r) towards downstream (north) and as the watershed area increases. These indices emerge as valuable tools for water resource management, aiding decision-making for allocation and hydrological regionalization, such as optimizing granting water resource distribution during dry seasons based on the identified low-flow patterns and establishing different reference low-flow values throughout the year. Full article

(This article belongs to the Section Statistical Hydrology)

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17 pages, 10357 KiB

Open AccessArticle

Performance Assessment of a Permeable Reactive Barrier on Reducing Groundwater Transport of Nitrate from an Onsite Wastewater Treatment System

by Charles P. Humphrey Jr., Guy Iverson and Mike O’Driscoll

Hydrology 2025, 12(1), 18; https://doi.org/10.3390/hydrology12010018 - 17 Jan 2025

Abstract

Elevated concentrations of nitrate in potable water supplies have been linked to negative health outcomes such as methemoglobinemia and various cancers. Groundwater can become contaminated with nitrate from sources including onsite wastewater treatment systems (OWTSs). A groundwater well down-gradient from an OWTS serving [...] Read more.

Elevated concentrations of nitrate in potable water supplies have been linked to negative health outcomes such as methemoglobinemia and various cancers. Groundwater can become contaminated with nitrate from sources including onsite wastewater treatment systems (OWTSs). A groundwater well down-gradient from an OWTS serving an elementary school in Eastern North Carolina USA had 15 consecutive water samples collected over a 5-year period that exceeded the maximum contaminant level of 10 mg/L for nitrate. Corrective actions were required. A permeable reactive barrier (PRB) filled with woodchips was installed between the OWTS drainfield and the contaminated well. The concentration of nitrate in groundwater from the well steadily decreased after the PRB was installed, and a significant (p = 0.001) inverse correlation (−0.859) was observed between the mean annual nitrate concentration and years after the PRB. The nitrate concentration in groundwater from the well has been below 10 mg/L for the last 17 consecutive sampling events. The median nitrate concentration in the well was significantly lower (p = 0.007) post (6.93 mg/L) relative to pre (12.66 mg/L) PRB. The PRB has not required any maintenance over the past 10 years. The implemented PRB directly influences the sampling results from a monitoring well, but it is not necessarily confirmed that it intercepts the entire groundwater flow or fully prevents aquifer contamination. To confirm this, additional monitoring wells would need to be installed. This research has shown that PRBs can be an effective, low-maintenance, best-management practice to reduce the groundwater transport of nitrate. Full article

(This article belongs to the Special Issue Novel Procedures and Methodologies for Surface and Underground Water Quality Analysis: Theory and Application)

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23 pages, 25140 KiB

Open AccessArticle

Flood Risk Assessment and Zoning for Niamey and Lokoja Metropolises in Niger and Nigeria

by Youssoufa Doulla Nouhou, Martins Yusuf Otache, Salamatou Abdourahamane Illiassou, Olasunkanmi Habeeb Okunola, Appollonia Aimiosino Okhimamhe and Thanh Thi Nguyen

Hydrology 2025, 12(1), 17; https://doi.org/10.3390/hydrology12010017 - 15 Jan 2025

Abstract

With the increasing frequency of floods in recent decades, particularly in West Africa, many regions have faced unusual and recurrent flooding events. Communities in flood-prone areas experience heightened insecurity, loss of property, and, in some cases, serious injuries or fatalities. Consequently, flood risk [...] Read more.

With the increasing frequency of floods in recent decades, particularly in West Africa, many regions have faced unusual and recurrent flooding events. Communities in flood-prone areas experience heightened insecurity, loss of property, and, in some cases, serious injuries or fatalities. Consequently, flood risk assessment and mitigation have become essential. This comparative study between Niamey and Lokoja employs Geographic Information Systems (GIS) and the Analytical Hierarchy Process (AHP) to delineate flood susceptibility, vulnerability, and risk zones. The study utilized a comprehensive range of thematic layers, with weight percentages assigned to each parameter as follows: 29% for elevation, 24% for slope, 15% for the Topographic Wetness Index (TWI), 9% for drainage density, 9% for distance from rivers, 4% for both precipitation and the Normalized Difference Water Index (NDWI), and 2% each for the Normalized Difference Vegetation Index (NDVI) and soil type. To validate these weightings, a consistency ratio was calculated, ensuring it remained below 10%. The findings reveal that 32% of the Niamey study area is at risk of flooding, compared to approximately 15% in Lokoja. The results highlight a very high flood potential, particularly in areas near the Niger River, with this potential decreasing as elevation increases. Given the current prevalence of extreme weather events in West Africa, it is crucial to employ effective tools to mitigate their adverse impacts. This research will assist decision-makers in quantifying the spatial vulnerability of flood-prone areas and developing effective flood risk assessment and mitigation strategies in the region. Full article

(This article belongs to the Section Water Resources and Risk Management)

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18 pages, 4329 KiB

Open AccessArticle

Integrating Nature-Based Solutions for Increased Resilience to Urban Flooding in the Climate Change Context

by George Radu, Maria Ilinca Chevereșan, Sorin Perju and Alina Bărbulescu

Hydrology 2025, 12(1), 16; https://doi.org/10.3390/hydrology12010016 - 15 Jan 2025

Abstract

As climate change intensifies with more frequent and severe flood events, urban areas face increasing challenges to protect population wellbeing. Amid urban development challenges, political uncertainty, and socioeconomic pressures, finding sustainable solutions to enhance urban resilience has become urgent and complex. This article [...] Read more.

As climate change intensifies with more frequent and severe flood events, urban areas face increasing challenges to protect population wellbeing. Amid urban development challenges, political uncertainty, and socioeconomic pressures, finding sustainable solutions to enhance urban resilience has become urgent and complex. This article explores the limitations of traditional drainage systems in an urban zone of Bucharest, Romania, and the integration of nature-based solutions for flood mitigation. We compare the existing situation with those simulated in a climate change scenario before and after implementing green solutions. The imperviousness of parking lots was set at 60%, that of green roofs at 65%, and that of parking lots at 85%. A hydraulic model was used for this purpose. The results demonstrate that the current stormwater systems struggle to meet the demands of increasing rainfall intensity and highlight how sustainable strategies can effectively address extreme weather challenges while contributing to the restoration of natural environments within the city. In the case of using ‘gray’ solutions, only 10–20% of the area affected by floods is reduced. In comparison, a combination of gray and green infrastructure achieved an average reduction in peak water levels of 0.76 m. Full article

(This article belongs to the Special Issue Sustainable Urban Water Resources Management)

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23 pages, 9846 KiB

Open AccessFeature PaperArticle

Assessing Groundwater Connection/Disconnection to Waterholes Along the Balonne River and in the Barwon–Darling River System in Queensland and New South Wales, Australia, for Waterhole Persistence

by Harald Hofmann and Jonathan Marshall

Hydrology 2025, 12(1), 15; https://doi.org/10.3390/hydrology12010015 - 14 Jan 2025

Abstract

Waterholes in semi-arid environment are sections of rivers that fill during high river flows or floods and keep water once flow ceases. They are essential water sources for rive ecosystems. Some waterholes remain even during prolonged droughts. The resilience of ecosystems in these [...] Read more.

Waterholes in semi-arid environment are sections of rivers that fill during high river flows or floods and keep water once flow ceases. They are essential water sources for rive ecosystems. Some waterholes remain even during prolonged droughts. The resilience of ecosystems in these environments depends on the persistence of the waterholes. While most semi-arid, ephemeral river systems are disconnected from regional groundwater and losing in most parts there may be some sections that can be connected to localised groundwater or parafluvial areas. To assess the persistence of waterholes the groundwater contribution to the water balance needs to be addressed. This study assesses groundwater connectivity to waterholes in a part of the Murray-Darling Basin, one of the largest watersheds in the world, using environmental tracers radon and stable isotopes. Approximately 100 samples were collected from 27 waterholes along the Narran, Calgoa, Barwon and Darling rivers, as well as 8 groundwater bore samples. The assessment of groundwater connectivity or the lack of is necessary from water balance modelling and estimation of persistence of these waterholes. As expected, the results indicate consistently low radon concentrations in the waterholes and very small deviation in stable isotopes

δ^{18}

O and

δ^{2}

H. In general, most of these waterholes are losing water to groundwater, indicated by low salinity (EC values) and low radon concentrations. While radon concentrations are small in most cases and indicative of little groundwater contributions, some variability can be assigned to bank return and parafluvial flow. It indicates that these contributions may have implications for waterhole persistence in ephemeral streams. The study demonstrates that in some cases local bank return flow or parafluvial flow may contribute to waterhole persistence. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Integrated Surface Water and Groundwater Resources Management)

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44 pages, 6676 KiB

Open AccessReview

Advancing Slope Stability and Hydrological Solutions Through Biocementation: A Bibliometric Review

by Armstrong Ighodalo Omoregie, Tariq Ouahbi, Fock-Kui Kan, Qurratu Aini Sirat, Hafsat Omolara Raheem and Adharsh Rajasekar

Hydrology 2025, 12(1), 14; https://doi.org/10.3390/hydrology12010014 - 13 Jan 2025

Abstract

Biocementation is an innovative and sustainable technique with wide-ranging applications in slope stabilization, watershed management, and erosion control. Despite its potential, comprehensive evaluations of its use in hydrology and geotechnical engineering are limited. This study addresses this gap through a bibliometric analysis of [...] Read more.

Biocementation is an innovative and sustainable technique with wide-ranging applications in slope stabilization, watershed management, and erosion control. Despite its potential, comprehensive evaluations of its use in hydrology and geotechnical engineering are limited. This study addresses this gap through a bibliometric analysis of 685 articles (2013–2023) from the Scopus database, employing VOSviewer and RStudio to explore global research trends, key contributors, and emerging themes. The analysis reveals that China, the United States, and Japan are leading contributors to this field, with significant advancements in microbial-induced (MICP) and enzyme-induced calcium carbonate precipitation (EICP) techniques. These methods have demonstrated effectiveness in improving soil strength, reducing erosion, and enhancing hydrological properties such as infiltration, runoff control, and water retention. Co-occurrence analysis identifies interdisciplinary connections between geotechnics and hydrology, highlighting research clusters focused on biomineralization, erosion resistance, and durability. The findings underscore biocementation’s pivotal role in addressing sustainability challenges by providing environmentally friendly alternatives to traditional soil stabilization techniques. This study not only maps the current research landscape but also offers valuable insights into the practical implications of biocementation for slope stability and hydrological management, laying the foundation for future advancements in sustainable engineering practices. Full article

(This article belongs to the Section Soil and Hydrology)

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19 pages, 11754 KiB

Open AccessArticle

Assessing the Impacts of Climatic and Water Management Scenarios in a Small Mountainous Greek River

by Angeliki Mentzafou, Anastasios Papadopoulos and Elias Dimitriou

Hydrology 2025, 12(1), 13; https://doi.org/10.3390/hydrology12010013 - 11 Jan 2025

Abstract

The water resource management of transboundary mountainous river basins under climate change is expected to be challenging. In order to contribute to the better understanding of climate change effects on the water resources of the mountainous and transboundary Prespa Lakes basin, a hydrological [...] Read more.

The water resource management of transboundary mountainous river basins under climate change is expected to be challenging. In order to contribute to the better understanding of climate change effects on the water resources of the mountainous and transboundary Prespa Lakes basin, a hydrological model of the Agios Germanos River, one of the main rivers discharging to Great Prespa Lake, was developed, and two water management plans under two different climate scenarios were examined. Based on the results, the impact of climate change on surface water resources was evident in all climate change scenarios examined, even under the most favorable water abstraction practices. Nevertheless, sensible water management can moderate the impact of climate change by up to 10% in an optimistic scenario in both the near- and long-term, and by up to 6% and 1% for the near- and long-term, respectively, in a pessimistic scenario. Integrated water management practices that moderate the impact of climate change on the water ecosystem services should be prioritized. Nature-based approaches could provide solutions regarding climate change adaptation and mitigation. Transboundary cooperation, data exchange mechanisms, common policy frameworks, and monitoring, reporting, and evaluation systems, could reduce human and ecosystems’ vulnerabilities and improve the water security of the area. Full article

(This article belongs to the Special Issue Runoff Modelling under Climate Change)

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22 pages, 14251 KiB

Open AccessArticle

The Development of Drawdown Dolines and Subsidence Dolines with the Comparison of Their Bedrock Resistivities—A Case Study

by Márton Veress

Hydrology 2025, 12(1), 12; https://doi.org/10.3390/hydrology12010012 - 10 Jan 2025

Abstract

The effect of the epikarst on the development of drawdown dolines and subsidence dolines is described. For this, the resistivity values of the bedrock determined by Vertical Electrical Sounding (VES) measurements were used. The higher resistivities below drawdown dolines are explained by the [...] Read more.

The effect of the epikarst on the development of drawdown dolines and subsidence dolines is described. For this, the resistivity values of the bedrock determined by Vertical Electrical Sounding (VES) measurements were used. The higher resistivities below drawdown dolines are explained by the deeper position of the piezometric surface, while the low resistivity values below subsidence dolines can be traced back to the more elevated position of the piezometric surface. Resistivities increasing towards the centre of drawdown dolines refer to cavity heterogeneity increasing towards the centre and increasing vertical percolation rate, while decreasing resistivity values indicate an increasing degree of cavity fill above the piezometric level. At their asymmetrical variety, the bedrock of their opposite slope is of asymmetric resistivity, which is explained by the different elevations of the piezometric surface and the latter by different infiltration that took place on slopes with different inclinations. The same resistivity values of the doline with a flat floor indicate the homogeneous cavity formation of the epikarst. This latter results in homogeneous vertical infiltration, which favours horizontal dissolution. The piezometric surface is not deflecting below the subsidence dolines because resistivity differences are small between the bedrock below the doline and the bedrock of its environment. Below subsidence doline, above the piezometric surface, cavities develop (the resistivity is higher relative to the resistivity of the environment), and then the cavities become filled by suffosion (therefore, the resistivity below the doline is lower relative to its environment). The passage below the doline develops into a shaft as a result of its concentrated water supply and the epikarst is separated into parts. Full article

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