Groundwater Quantity Research Articles

The state of knowledge of freshwater resources in the U.S. Virgin Islands: Data scarcity and implications

AbstractLike many small island communities, the U.S. Virgin Islands (USVI), an unincorporated territory of the U.S., is naturally freshwater scarce. In recent decades, rapid land development in the USVI has increased water demand considerably, exerting extra pressure on freshwater resources. Freshwater quantity and quality data for the USVI are very scarce and scattered, which limits freshwater management capabilities. We draw attention to this information deficit and discuss its implications by reviewing the current state of knowledge of surface and groundwater quantity and quality for the USVI. Our review confirms that long‐term records of surface and groundwater quantity and quality are limited and unreliable. For example, streamflow was most recently monitored in 2006, and the most extensive surface water quality records are from the 1960s and 1980s. Since 2016, mean groundwater levels have been recorded daily, but only for three wells (one on each island of the USVI). Importantly, this lack of information threatens water security for the territory and limits our understanding of how development has impacted water quality and availability over time. This could be addressed using models, such as a groundwater recharge model, in combination with remote sensing and updated field data (i.e., streamflow, groundwater, and ecohydrological characterizations of land use change).

A Systematic Review of the Current State of Numerical Groundwater Modeling in American Countries: Challenges and Future Research

In arid and semi-arid regions, groundwater is often the only available water source. However, overexploitation and pollution have led to a decrease in groundwater quantity and quality. Therefore, the proper management of groundwater resources is essential to promote sustainable development. Numerical simulation models (NSMs) have emerged as a valuable tool to address these challenges due to their ability to accurately and efficiently model groundwater systems. This study provides a comprehensive systematic review to evaluate the current knowledge on using numerical groundwater flow models for planning and water resource management in countries in the American region. A total of 166 research articles were published between the years 2000 and 2024. We analyzed and summarized details such as the study regions, numerical simulation methods and applied software, performance metrics, modeling units, modeling limitations, and prediction scenarios. In addition, we discuss alternatives to address the constraints and difficulties and suggest recommendations for future research. The continued research, improvement, and development of numerical groundwater models are essential to ensure the sustainability of groundwater resources.

Visual MODFLOW, solute transport modeling, and remote sensing techniques for adapting aquifer potentiality under reclamation and climate change impacts in coastal aquifer

Global environmental changes, such as climate change and reclamation alterations, significantly influence hydrological processes, leading to hydrologic nonstationarity and challenges in managing water availability and distribution. This study introduces a conceptual underpinning for the rational development and sustainability of groundwater resources. As one of the areas intended for the development projects within the Egyptian national plan for the reclamation of one and a half million acres; hundreds of pumping wells were constructed in the Moghra area to fulfill the reclamation demand. This study investigates the long-term impacts of exploiting the drilled pumping wells under climate change. The approach is to monitor the groundwater levels and the salinity values in the Moghra aquifer with various operational strategies and present proposed sustainable development scenarios. The impact of global warming and climate change is estimated for a prediction period of 30 years by using satellite data, time series geographical analysis, and statistical modeling. Using MODFLOW and Solute Transport (MT3DMS) modules of Visual MODFLOW USGS 2005 software, a three-dimensional (3D) finite-difference model is created to simulate groundwater flow and salinity distribution in the Moghra aquifer with the input of forecast downscaling (2020–2050) of main climatic parameters (PPT, ET, and Temp). The optimal adaptation-integrated scenario to cope with long-term groundwater withdrawal and climate change impacts is achieved when the Ministry of Irrigation and Water Resources (MWRI) recommends that the maximum drawdown shouldn’t be more significant than 1.0 m/ year. In this scenario, 1,500 pumping wells are distributed with an equal space of 500 m, a pumping rate of 1,200 m3/day and input the forecast of the most significant climatic parameters after 30 years. The output results of this scenario revealed a drawdown level of 42 m and a groundwater salinity value of 16,000 mg/l. Climate change has an evident impact on groundwater quantity and quality, particularly in the unconfined coastal aquifer, which is vulnerable to saltwater intrusion and pollution of drinking water resources. The relationship between climate change and the hydrologic cycle is crucial for predicting future water availability and addressing water-related issues.

Urban Water Management in Milan Metropolitan Area, a review

The increasing rate of urbanisation and extreme climatic events represent a constant threat for urban water resources management. In recent decades, Milan Metropolitan Area (Lombardy Region, Northern Italy) has been affected by a) frequent extreme rainfall events, responsible for the flooding of major surface water courses, and b) groundwater management problems, both from a quantitative (i.e. interaction with underground infrastructures) and qualitative point of view. Moreover, the increasing use of groundwater geothermal systems also requires further considerations. This work analyses the literature available in the area regarding surface floods, groundwater quantity, quality, and temperature. Finally, a discussion is provided to understand a) which approaches could promote an effective management of both surface water and groundwater resources b) which points of contact emerge between these two aspects of the urban water cycle, and c) which possible urban interventions could contribute to an integrated and functional management of water resources, also reducing some current issues.

Urban Groundwater in the cities of Europe: hidden challenges in a changing climate

In European cities, groundwater remains an issue of significant concern, largely because it is “out of sight and out of mind.” The general public, and even decision-makers, possess only a limited understanding of the state and characteristics of this vital resource. As a consequence, problems related to groundwater quality or changing water tables/piezometric surfaces may persist for years, or even decades, without being adequately addressed-or worse, without being noticed at all before resulting in land subsidence,saltwater intrusion, deep migration of persistent organic contaminants like PFAS (Le monde, 2023) or other irreversible consequences. The urban water cycle is central to ensuring the supply of clean, safe drinking water, effective sanitation, and wellfunctioning drainage systems for millions of residents. The impacts of human activities, such as land use change, excessive water abstraction and mismanagement, and the discharge of wastewater can exert a far greater influence on groundwater systems and hydrogeology than climate change. These activities alter the quantity and quality of both surface and groundwater, raising complex scientific, technical, socio-economic, cultural, and ethical challenges in urban water management. It is important to address the many challenges associated with ensuring water security and safety in cities (Quevauviller et al., 2024), as well as for development of effective climate change mitigation and adaptation strategies for urban areas (IPCC, 2024). Groundwater plays a critical role in the green transition and is an integral component of most climate change mitigation and adaptation strategies (Ingemarsson et al., 2022), and for meeting the increasing demand for freshwater in cities due to accelerating urbanization (United Nations, 2022). Many urbanized areas in Europe already face poor chemical and quantitative status (EEA, 2024; Sentek et al., 2024), and global change including increasing populations and sea level rise pose a tremendous challenge for safe and secure water supply especially in coastal European cities. Open access to digital subsurface data e.g. through the European Geological Data Infrastructure supports societal needs and UN sustainable development goals (Hinsby et al., 2024). This special issue demonstrates some of the important issues that the water supply of European cities are facing in times of increasing competing use of the subsurface (Volckko et al., 2020), projected climate change impacts on the hydrological cycle (Henriksen et al., 2023) and with freshwater now being among the transgressed planetary boundaries (Richardsson et al., 2023). [...]

GROUNDWATER CONDITION AND VULNERABILITY IN THE ATHABASCA AND COLD LAKE OIL SANDS REGIONS: GAPS, OPPORTUNTIES AND CHALLENGES

Oil sands development in the Athabasca and Cold Lake oil sands regions of Alberta has raised concerns about potential impacts to groundwater and groundwater dependent ecosystems. This review summarizes the current state of understanding as to how oil sands mining and in situ activities can affect groundwater systems using a stressor-mechanism-response framework. Specific oil sands activities and practices are reviewed, and where possible, described in terms of how they can impact hydraulic head, the hydraulic properties of aquifers, recharge and transport of constituents of concern and linked to observed or potential impacts to groundwater quantity and quality. Groundwater is an important component of the water balance in boreal ecosystems, and specific vulnerabilities related to development are reviewed, including water use, landscape disturbance, groundwater withdrawals, tailings pond seepage, deep well disposal and thermal impacts. Knowledge gaps include lack of baseline data and monitoring of the quantity and quality of groundwater discharge to rivers, lakes and wetlands. One key monitoring challenge is attribution of hydrogeologic responses to specific oil sands stressors given the range of other natural and anthropogenic factors contributing to their variability. Quantitative groundwater exchange mapping, regional-scale isotope mass balance assessment, and broader incorporation of isotopic and geochemical tracers for fingerprinting water sources and incorporation of Indigenous Knowledge appear promising for improved effectiveness of monitoring.

Optimizing Irrigation Systems for Water Efficiency and Groundwater Sustainability in the Coastal Nile Delta

This study investigates the replacement of traditional surface irrigation methods with modern irrigation systems (MIS) including horizontal sprinkler, central pivot, surface drip, and subsurface drip aimed at improving water efficiency in the Nile Delta, Egypt. The primary objectives were to determine the optimal agricultural area for implementing MIS and to assess the effects of these systems on groundwater quantity and quality in the region. To achieve this, the LINDO software was employed to optimize land allocation for each irrigation method. At the same time, the SEAWAT code was utilized to simulate saltwater intrusion (SWI) in the Nile Delta aquifer. The transition from traditional surface irrigation to MIS resulted in significant water savings, reaching 2.15 × 10^9 m³. However, groundwater modeling indicated a decrease in groundwater levels, leading to an 8 % increase in aquifer salinity due to reduced infiltration of recharge water. These findings underscore the urgent need to revise outdated irrigation practices and enhance water management strategies in the Nile Delta to mitigate salinity issues in coastal aquifers. This research's outcomes are crucial for decision-makers and stakeholders in selecting appropriate irrigation methods, particularly in arid and semi-arid regions, to ensure sustainable water use and agricultural productivity.

GIS-based multi-criteria approach for ranking suitable areas for the implementation of PV-Powered MCDI desalination plants in the Rheris Watershed, Southeast Morocco

In Morocco's oases, which rely heavily on surface water from mountain sources, the threat of decreasing rainfall presents a significant challenge, leading to a decline in surface water availability. This study focuses on the Rheris Watershed in Southeast Morocco, where brackish water desalination emerges as a viable alternative to ensure sustainable water supply for agriculture. Prior to the deployment of a pilot plant integrating a desalination unit, selecting an optimal site for PV-powered MCDI desalination plants was critical. This selection was based on a range of criteria, including Groundwater Quantity, Global Horizontal Irradiation, Temperature, Evaporation, Water Salinity, Water Quantity, Well Density and Slope. These criteria were evaluated using a combination of the Analytical Hierarchy Process (AHP), and geospatial data obtained from Remote Sensing (RS) and Geographic Information System (GIS) techniques.This case study in the Rheris watershed identified potential sites for future Membrane Capacitive Deionization (MCDI) desalination projects, High suitability areas encompass 280.45 km² (30.91 %), located west of Tinejdad, Khettarat Moulay Hachem, north of Goulmima, and south of Tinghir. Low suitability areas cover 63.75 km² (7.02 % of the study area), including regions south of Tadighoust and Tinejdad. Moderate suitability areas span 562.86 km² (62.05 %), involving central regions of Goulmima, Tadighoust, Tinejdad, and Tinghir. Based on the results of the study, the recommendations include focusing on areas identified as highly suitable for MCDI technology for sustainable agriculture, refining selection criteria based on local data, exploring brine management strategies, and adopting integrated water management approaches to ensure sustainable resource use.

Quantifying recharge mechanisms in low-hilly areas of a loess region: Implications for the quantity and quality of groundwater

Groundwater plays a crucial role in sustaining water supply and irrigation in arid regions with thick vadose zones; however, the recharge mechanisms and their impact on water quality remain contentious. For flood-irrigated areas, irrigation water amount is not well known to evaluate the effect of irrigation on the recharge. In this study, we employed multiple tracers to investigate recharge mechanisms in a low-hilly region with some flood-irrigated areas, where irrigation water recharge was estimated by the chloride mass balance method combined with the tritium peak method. Deep soil samples from irrigated lands in vadose zone and groundwater from unconfined aquifers were collected to determine the contents of the water isotopes (2H, 18O, and 3H), chlorides (Cl-), and nitrates (NO3−). The findings revealed unique tritium peaks preserved in the loess vadose zone, where the recharge rate under the non-irrigated site was estimated to be only 8.6 mm yr−1, 2.4 % of the average annual precipitation. According to the estimated irrigated recharge rates, irrigation water dominates the potential diffuse recharge in vadose zone. For the aquifer recharge, we then quantified diffuse recharge (62.2 ± 4.7 %, piston flow) and focused recharge (37.8 ± 4.7 %, preferential flow) via the line-conditioned excess (lc-excess) balance method. Focused recharge occurred in low depressions, where surface runoff carrying sediments with high solutes converged in large rainfall events during wet season. Subsequently, focused mode rapidly recharges groundwater with NO3− and Cl- elevated, deteriorating water quality of phreatic aquifer. Finally, we concluded focused recharge does not dominate aquifer recharge, but significantly affects groundwater quality. These findings underscore the implications for the sustainability of agricultural water and soil resources management, emphasizing the potential impacts of soil conservation on groundwater quality in low-hilly regions.

Spatial Distribution of Wells in the Eastern Side of Nineveh Governorate – Iraq

Groundwater is an important resource, especially in areas where water resources do not meet the requirements of life. Therefore, population centers in areas far from rivers are linked to the quantity and quality of groundwater available. The study area represents a large part of the eastern part of Nineveh Governorate, which is dotted with small cities and villages with population and agricultural activity. The quantity and quality of groundwater are related to the nature of the reservoir rocks in the region, which are mainly represented by the Pila Spi Formation, composed of dolomite limestone, the Fat’ha Formation, composed of periodic successions of marl, limestone, and gypsum, and the Injana Formation, composed of periodic successions of sandstone, siltstone, and clay. The quality of the rocks exposed in the study area, especially at the feet of the Bashiqa and Ain Al-Safra mountains, and the ability of the minerals that make up them to dissolve in conditions of weathering and erosion also affect the water content of dissolved salts. The water quality index (WQI) was calculated to determine its suitability for civil use based on the physical (pH, E.C, T.D.S and T.H) and chemical (Ca2+, Mg2+, Na+, K+, HCO3-, SO42-, Cl- and NO3-) specifications. In light of this, the distribution of wells was determined according to their specifications. In general, there were six regions; The first in the northern part has excellent water, the second in the south has good water, the third in the south has unsuitable water, and the fourth area, which represents the area confined between the city of Mosul and Mount Bashiqa, has poor water quality, while the area adjacent to Ain Al-Sufra Mountain is classified as having good water quality, while The area located to the southwest towards the Tigris River is of very poor quality. There are sites for wells whose specifications vary according to the type of activity there.

Hydrochemical and Formation Mechanism Studies of Groundwater in Quaternary Aquifer in a Northern Plain of China: An Example of Beijing Plain

Beijing Plain is a very active part of Beijing city regarding the socio-economic and human activities of the region. Over the past four decades, Beijing’s economic development and the continuous drought for nearly 10 years in the 2000s have negatively impacted the groundwater quantity and quality. Therefore, it is necessary to investigate the present situation of groundwater chemistry in this region to develop a comprehensive database and orientation for future research on groundwater quality evaluation. Mathematical statistics, Piper’s trilinear diagram, Gibbs plots, the ion ratio method and PHREEQC software 3.7.3 were used to analyze the groundwater hydrogeochemical characteristics and formation mechanisms of the quaternary aquifers of the Beijing Plain area. Hydrogeochemical results indicated that the groundwater is slightly alkaline, with pH values ranging from 6.76 to 8.65 and an average value of 7.92. The order of major cations in groundwater was Ca2+ > Na+ > Mg2+ > K+ with average values of 66.54 mg/L, 50.58 mg/L, 23.78 mg/L, and 1.81 mg/L, respectively, while the order of major anions was HCO3− > SO42− > Cl− with average values of 284.89 mg/L, 52.1 mg/L and 35.5 mg/L, respectively. The groundwater chemical types are Mg-Ca-Cl-HCO3, Na-Ca-HCO3, Mg-Ca-HCO3 and Mg-Na-HCO3. Research on the main influencing factors and PHREEQC hydrogeochemical inverse simulations results along the four pathways selected confirmed that rock weathering with sulfate, silicate and carbonate rock mineral dissolution and Na+, Mg2+ and Ca2+ ion reaction exchange influenced groundwater hydrogeochemical characteristics of the quaternary aquifers of the Beijing Plain area. Understanding the formation mechanisms of hydrogeochemistry in quaternary plains provides guidance for future studies and, through suggestions and case studies, facilitates decision-making by policy-makers on the sustainable management of groundwater resources.

Estimating natural groundwater recharge taking into consideration temporal and spatial variability for arid unconfined aquifer

ABSTRACT Water scarcity is one of the major critical affecting arid climate countries. In addition, population growth and climate change are threatening the sustainable development of water resources in the upcoming decades. Therefore, managing groundwater can solve water scarcity such that sustainable development is ensured for future generations. Hence, it is crucial to assess the current quantity of groundwater by analyzing groundwater variables. Thus, natural groundwater recharge could be utilized as an indicator to assess groundwater quantity conditions. This study aims to estimate natural groundwater recharge in an arid unconfined aquifer. El-Qaa plain in Sinai, Egypt was chosen as a case study. Recharge was estimated taking into consideration spatial and temporal variability. To accomplish this, the WetSpass (Water and Energy Transfer between Soil, Plants, and Atmosphere under quasi-Steady State) model was applied. The model was run using morphological, landuse – land cover and climate data from 1986 to 2015 with a monthly time step. To calibrate the model, the isotope signature of δ18O and δ2 H of water was analyzed to determine the natural groundwater recharge of the aquifer. The obtained recharge value was utilized as a reference value for the calibration process. The results were validated using a finite-difference groundwater flow model (MODFLOW). The recharge values were imported to MODFLOW followed via a transient run from 2000 to 2011. The validation was conducted by comparing the simulated groundwater level with the observed ones. After validation process, the inter-annual and seasonal variability of recharge were determined, and a relationship between recharge and other hydrological parameters was deduced. In addition, the recharge distribution was mapped to depict the recharge spatial variability. The results show that the current recharge rate ranges from approximately 8.10 to 16.62 mm/yr, with a mean annual recharge rate of nearly 12.36 mm/yr. The study might be useful for hydrogeologists for determining potential recharge in the study area, groundwater modelers for developing a reliable groundwater flow model, and decision-makers for planning appropriate future sustainable development through water resources management.

Shortage Analysis and Strategies for the Water Resource in Saudi Arabia under the Rapid Development of the Tourism Industry

This study evaluates water sustainability in Saudi Arabia amid expanding tourism using a mixed-methods approach. Primary data were collected through surveys targeting 150 stakeholders in water management and tourism, while secondary data were sourced from official reports. Quantitative analysis revealed significant challenges, with an average daily per capita water consumption of 299 liters and severe stress in regions like Riyadh and Jeddah. Groundwater quantity for 2022 was recorded at 1.48 km³, and desalinated water production totaled 1.95 km³, revealing a supply-demand gap of 1.82 km³. The correlation analysis indicated a significant positive relationship (r=0.440) between tourism growth and water demand. Survey results showed 70% of respondents reported no difficulties in accessing clean water during Hajj, while 30% indicated occasional issues. Stakeholders emphasized the need for integrating renewable energy with desalination to reduce operational costs and carbon emissions. The study recommends enhancing Reverse Osmosis (RO) technology with solar energy to improve sustainability and efficiency, aligning with Saudi Arabia's Vision 2030. These findings highlight the necessity for sustainable water management strategies to balance economic growth with resource sustainability, guiding policymakers in developing effective practices for future water security.

ECONOMIC FEASIBILITY AND ENVIRONMENTAL IMPLICATIONS OF PERMEABLE PAVEMENT IN PALESTINE

Permeable pavement is considered one of the sustainable management options for roadway networks, which mitigates a number of problems associated with stormwater, ground water pollution, and traffic safety. In this study, the economic feasibility, vehicle operation, and environmental implications of implementing permeable pavement in Nablus, Palestine have been determined by selecting the local roadways that satisfy the permeable pavement requirement, such as low traffic volume, grade less than 5%, speed limit up to 50 km/h, and subgrade with good permeability. The total costs of construction and maintenance for both conventional asphalt and permeable pavement have also been compared based on the life cycle cost analysis (LCCA). Finally, the environmental implications such as the expected increase in the amount of ground water and the reduction in water pollutants have been investigated. The results of the analysis show that the permeable pavement is applicable for the local roadways that have satisfied the requirements, which are 61 roadways. Furthermore, it could lead to an annual significant increase in ground water by 107,404.7 m3 and slightly reduce the cost of construction and maintenance by up to 1,912,000 ILS during its life period compared to conventional asphalt pavement. Moreover, applying porous asphalt could enhance vehicular traffic safety by improving skid resistance.

Unravelling the impact of microclimatic changes on coastal aquifer of multiple land use through integrated techniques: A comparative study using two decadal data

Regional climatic changes reflect the microclimatic variations and these affect the water resources of a region. Urbanization and population growth significantly influence microclimates, impacting groundwater resources and Land Surface Temperature (LST). The climatic variables (rainfall and temperature) interplay with geospatial parameters such as Land Use Land Cover (LULC), LST influence the quality and quantity of groundwater. Hence, this current approach employs geospatial techniques to explore the interrelationship between these variables by studying the long-term variation for a period of 20 years (1997–2018) to assess the microclimate variation and its impact on groundwater resources of a coastal aquifers with complex lithology. Results reveal a notable increase in minimum and maximum temperatures, with an average annual rise of 0.5°C predominantly along the western part. Spatial rainfall variation for the study period was higher in the northern region influenced by urban heat islands. The change in LULC reflected a 12% increase in agricultural areas and a 1.7% expansion in habitation, accompanied by a decline in surface water bodies in 2018. Maximum increase in electrical conductivity(EC) is observed along the southern coastal region, indicating rise in ionic concentration due contamination from sea water, urban and agricultural sources, witnessed by the isotopic signatures. Comparison of the depth to groundwater between the different study periods indicate a maximum depletion of 49m in northeastern and western regions due to extraction for domestic water supply, agriculture and mining. Further, a maximum rise of 14m in the regions adjacent to the reservoirs was observed, during 2018. The current study reveals the relationship between microclimate and groundwater (quality and the quantity) is predominantly observed in the northern and western parts of the study area. Our findings suggest that managing groundwater extraction and improving land use practices are essential for sustainable development, primarily through policy and governance.

Groundwater quality vs. groundwater quantity. Combining information on irrigator concerns with past water use and cropping behavior.

The effectiveness of groundwater in fulfilling crop water deficits depends on its quality and quantity. This paper examines the relationship between irrigators’ stated concerns over groundwater quality and groundwater quantity and their past water use and cropping decisions. Information on irrigator concerns over groundwater quality and quantity is obtained from 626 survey responses of agricultural producers in the Kansas portion of the High Plains Aquifer. We combine 20 years of field-level water use and cropping data with each of the 626 survey responses. We find that irrigators indicating elevated concern over either groundwater quality or groundwater quantity correlates with less total water use, fewer total irrigated acres, and fewer acres of irrigated corn. Additionally, concerns over groundwater quantity generally correlate with a greater reduction in water use along multiple water use margins compared to equal concerns over groundwater quality.

Exploring available water resources in Bahraich district of Uttar Pradesh: A comprehensive study

Present study was carried out during 2018–22 at Bahraich, Uttar Pradesh focusing on groundwater, runoff, and canal water suggesting that a sizable database is essential for effectively managing water resources. Groundwater quantity was estimated using water level fluctuation (WLF), runoff using GIS coupled with curve number and canal water volume using equivalent length factor methods. This study revealed that the contribution of groundwater was more than 52.5%, whereas runoff (45.61%) and canal water (1.89%). Higher amounts of total available water observed in Mihipurwa (305.3 million cubic meter, MCM), Mahsi (211.6 MCM), Chittaura (189.3 MCM) and Nawabganj (184.4 MCM) blocks due to denser vegetation cover and moderate to low curve number values, while Risia (96.5 MCM) had the lowest amounts of available water in juxtaposition with the other blocks due to high industrial draft, higher drop down in the depth of post-monsoon groundwater level and minimal canal water irrigation. The sandy soil predominant in Jarwal had the lowest annual runoff (117.54 mm) while Nawabganj had the highest (359.84 mm) followed by Balha and Huzoorpur due to having a higher elevation over the other blocks. The runoff ratio was found to be larger in Nawabganj (27.74%), followed by Balha (23.06%) and lowest in Mihipurwa (14.89%) followed by Chittaurah (14.91%). Kaisarganj (11.6 MCM) had the highest amount of canal water resources accessible, followed by Mahsi (6.8 MCM) and Huzoorpur (6.1 MCM), while Balha and Nawabganj had the lowest amounts of canal water resources at 0.1 MCM.

Analysis on unconfined groundwater availability during dry and rainy season using dynamic approach in Ngemplak, Sleman, Yogyakarta, Indonesia

Groundwater is a natural resource with disparity across the different regions throughout time. In comparison to surface water, the groundwater in unconfined aquifers is easily accessible and generally of good quality. Groundwater macro zoning is classified into three, namely water catchment areas, transition areas, and groundwater discharge areas. Based on the macro zoning, previous research has mostly been carried out in catchment areas and discharge areas with a focus on groundwater potential and temporary groundwater conditions. The dynamics of groundwater availability, especially in the water transition zone, has not been studied much, even though the dynamics of groundwater availability in the transition zone plays a vital role for areas in the discharge zone. This study identified the availability of groundwater during rainy and dry seasons in groundwater transition zone. Groundwater availability was assessed through a dynamic discharge approach. The study variables included the hydraulic conductivity of the aquifer, the hydraulic gradient, and the cross-sectional area of the aquifer. Dynamic discharges were analysed during the rainy and dry seasons. The results showed that the availability of groundwater during the rainy season was 4,333,906.1 liters/day and 3,898,850.4 liters/day during the dry season. Based on the calculation of the dynamic discharge (Q), the decrease in the quantity of groundwater is affected by the variable hydraulic gradient (I) and cross-sectional area of the aquifer (A). The numbers of these two variables are smaller during the dry season than the rainy season. The decrease in the quantity of groundwater during the dry season is of course closely related to reduced rainfall which is a source of infiltration and percolation. Reduced rainfall causes the groundwater level to decrease, then technically reduces the groundwater hydraulic gradient (I) and aquifer cross-sectional area variable (A). There was no indication of groundwater scarcity in the study area. This study can serve as a reference related to the application of dynamic discharge theory to assess groundwater availability. Periodic monitoring of groundwater quantity, rainwater harvesting, and intensification of water infiltration wells can be carried out as a recommendation to anticipate problems related to groundwater availability in the study area. This study can serve as a reference related to the application of dynamic discharge theory to assess groundwater availability.

Estimating groundwater resources in an equatorial forested basin using geographic information system and remote sensing techniques (case of Nyong, South Cameroon)

ABSTRACT This article aims to produce a groundwater potential zone (GWPZ) map of the Nyong basin using an integrated analytical hierarchy process driven in a geographic information system (GIS) environment. For this, seven parameters (rainfall, geology, slopes, drainage density, land use and land cover, lineament density, and soil) known to influence the availability of groundwater were considered. The results obtained show that the Eastern part of the basin holds the largest quantities of groundwater. The produced map shows that this region includes high and very high GWPZs (yield > 6 l/s). It is essentially characterized by abundant rainfall (on average 135–136 and 131–134 mm), low slopes, significant drainage and lineament densities, and significant forest cover. On the other hand, the opposite region (west), which includes the low and very low GWPZs, is characterized by less abundant precipitation (on average 121–125 and 125–128 mm), significant slopes, lower drainage and lineament densities, and greater impervious areas. With a success rate of 80%, confidence deserves to be placed in the GWPZs map produced. It can be considered in water supply projects in this basin. Such work has never been done in this basin before.

Enhancing hydrological insight: isotopic methods revealing groundwater–surface water interactions in the Lower Quang Tri River Group, Vietnam

ABSTRACT The Lower Quang Tri River Group, situated in central Vietnam, faces a myriad of challenges, notably the decline in groundwater levels and the salinisation of both groundwater and surface water, significantly impacting water availability for domestic, agricultural, and industrial purposes. To address these pressing concerns, this study adopts a comprehensive methodology integrating hydrogeological measurements, isotopic techniques, and chemical analyses of various water sources, including local precipitation, surface water bodies, reservoirs, and groundwater samples. Utilising the deuterium and oxygen-18 signatures (δ 2H and δ 18O) in water molecules as environmental tracers for the assessment of base flow and water sources enables a nuanced understanding of the intricate interaction between surface water and groundwater. Research findings elucidate that during the dry season, groundwater recharge primarily stems from water in the reservoirs over approximately seven months. Base flow contributes between 80 and 85 % of streamflow during the rainy season, escalating to 100 % during the dry season. The mean travelling time of the base flow is estimated at 120 ± 10 days using the sine curve model developed by Rodgers et al. The insights gleaned from this study are poised to play a pivotal role in guiding the local water resources managers in licensing for the exploitation of a right quantities of groundwater as sustainable management strategies in the region.