Groundwater Variations Research Articles

Watershed groundwater level multistep ahead forecasts by fusing convolutional-based autoencoder and LSTM models

The development of deep learning-based groundwater level forecast models can tackle the challenge of high dimensional groundwater dynamics, predict groundwater variation trends accurately, and manage groundwater resources effectively, thereby contributing to sustainable water resources management. This study proposed a novel ConvAE-LSTM model, which fused a Convolutional-based Autoencoder model (ConvAE) and a Long Short-Term Memory Neural Network model (LSTM), to provide accurate spatiotemporal groundwater level forecasts over the next three months. The HBV-light and LSTM models are chosen as benchmarks. An ensemble of point data and the corresponding derived images concerning the past (observations) and the future (forecasts from a conceptual model) of groundwater levels at 33 groundwater wells in Jhuoshuei River basin of Taiwan between 2000 and 2019 constituted the case study. The findings showcase the effectiveness of the ConvAE-LSTM model in extracting crucial features from both point and imagery datasets. This model successfully establishes spatiotemporal dependencies between regional images and groundwater level data over diverse time frames, leading to accurate multi-step-ahead forecasts of groundwater levels. Notably, the ConvAE-LSTM model exhibits a substantial improvement, with the R-squared values showing an increase of more than 18%, 22%, and 49% for the R1, R2, and R3 regions, respectively, compared to the HBV-light model. Additionally, it outperforms the LSTM model in this regard. This study represents a noteworthy milestone in environmental modeling, offering key insights for designing sustainable groundwater management strategies to ensure the long-term availability of this vital resource.

Elevated arsenic concentrations in groundwater of the Upper Indus Plain of Pakistan across a range of redox conditions

Groundwater of the Ravi River floodplain is particularly elevated in arsenic (As) on both sides of the Pakistan-India border. To understand this pattern, 14 sites were drilled to 12–30 m depth across floodplains and doabs of Pakistan after testing over 20,000 wells. Drill cuttings were collected at 1.5 m intervals, 132 of which were sand overlain by 77 intervals of clay and/or silt. Radiocarbon dating of clay indicates deposition of the aquifer sands tapped by wells 20–30 kyr ago. Most (85 %) of the sand samples were gray in color, indicating partial reduction to Fe(II) oxides, whereas most (92 %) of the clay and/or silt samples were orange. Associations between groundwater electrical conductivity, dissolved Fe, sulfate, and nitrate suggest that wells can be elevated (>10 μg/L) in As in the region due to either reductive dissolution of Fe oxides, evaporative concentration, or alkali desorption. In the Ravi floodplain, 47 % of 6445 wells tested contain >10 μg/L As compared to only 9 % of 14,165 tested wells in other floodplains and doabs. The As content of aquifer sands in the Ravi floodplain of Pakistan averages 4 ± 4 mg/kg (n = 66) and is higher than the average of 2 ± 2 mg/kg (n = 51) for aquifer sands outside the Ravi. Synchrotron spectroscopy and column-based speciation indicate predominance of As(V) over As(III) in both aquifer sands and groundwater. Whereas multiple processes may be responsible for elevated levels of As in groundwater across the region, spatial heterogeneity in groundwater As concentrations in the Ravi floodplain seems linked to variations in As concentrations in aquifer sands. Regulation by the solid phase may limit variations in groundwater As over time in response to natural and human-induced changes in hydrology. This means spatial heterogeneity could be taken advantage of to lower the exposure across the region with more testing and targeted drilling.

Isotopic variations in surface waters and groundwaters of an extremely arid basin and their responses to climate change

Abstract. Climate change accelerates the global water cycle. However, the relationships between climate change and hydrological processes in the alpine arid regions remain elusive. We sampled surface water and groundwater at high spatial and temporal resolutions to investigate these relationships in the Qaidam Basin, an extremely arid area in the northeastern Tibetan Plateau. Stable H–O isotopes and radioactive 3H isotopes were combined with atmospheric simulations to examine hydrological processes and their response mechanisms to climate change. Contemporary climate processes and change dominate the spatial and temporal variations of surface water isotopes, specifically the westerlies moisture transport and the local temperature and precipitation regimes. The H–O isotopic compositions in the eastern Kunlun Mountains showed a gradually depleted eastward pattern, while a reverse pattern occurred in the Qilian Mountains water system. Precipitation contributed significantly more to river discharge in the eastern basin (approximately 45 %) than in the middle and western basins (10 %–15 %). Moreover, increasing precipitation and a shrinking cryosphere caused by current climate change have accelerated basin groundwater circulation. In the eastern and southwestern Qaidam Basin, precipitation and meltwater infiltrate along preferential flow paths, such as faults, volcanic channels, and fissures, permitting rapid seasonal groundwater recharge and enhanced terrestrial water storage. However, compensating for water loss due to long-term ice and snow melt will be a challenge under projected increasing precipitation in the southwestern Qaidam Basin, and the total water storage may show a trend of increasing before decreasing. Great uncertainty about water is a potential climate change risk facing the arid Qaidam Basin.

Geomorphic understanding of loess landslides activity on the loess tableland:A case study in the Bailu Tableland, China

Loess landslides, predominantly triggered by human activity and precipitation, dominate the geomorphological evolution of extensive regions of the Chinese Loess Plateau. Tablelands constitute a large proportion of this Loess Plateau. Although the area has a long history of human occupation, the Bailu Tableland is relatively poorly studied. Recent landslide events along the edge of the tableland significantly affected lives and livelihoods. To develop a better understanding of geomorphological evolution and develop appropriate hazard management and mitigation strategies, we characterized recent landslide activity and determined whether there are discernable trends in activity. We used Unmanned Aerial Vehicle (UAV) observations, Interferometric Synthetic Aperture Radar (InSAR) monitoring, and Digital Terrain Analysis (DTA) to observe significant differences in the position, shape, and magnitude between old and new landslides. The geomorphological evolution of the tableland was initially driven by large landslides, while current and future morphological development is more likely affected by small landslide events. We demonstrate the successful application of InSAR to investigate potential landslides in well-vegetated loess landscapes and show that loess landslides tend to develop on slopes with high relative relief and high topographic wetness associated with gully erosion. Unlike landslides induced by groundwater variations in the Heifangtai and South Jingyang tablelands, precipitation and infrastructure construction form the main controls on landslide activity in the Bailu Tableland. We propose two geomorphological evolution models that describe loess tableland recession caused by landslides. The results from this research contribute to a better understanding of the reactivation behavior of landslides along loess tablelands, provide a scientific foundation for landslide hazard and risk management, and supplement understanding of the geomorphological evolution of loess tableland landscapes.

Assessing Terrestrial Water Storage Variations in Southern Spain Using Rainfall Estimates and GRACE Data

This paper investigates the relationship between rainfall, groundwater and Gravity Recovery and Climate Experiment (GRACE) data to generate regional-scale estimates of terrestrial water storage variations in the Andalucía region of southern Spain. These estimates can provide information on groundwater depletion (caused by periods of low rainfall or droughts) and groundwater recovery. The spatial distribution of groundwater bodies in southern Spain is complex and current in situ groundwater monitoring methods are deficient, particularly in terms of obtaining representative samples and in implementing and maintaining groundwater monitoring networks. The alternative approach proposed here is to investigate the relationship between precipitation time series and changes in the terrestrial water storage estimated from GRACE observations. The results were validated against the estimated fluctuation in regional groundwater. The maximum correlation between the mean groundwater level and the GRACE observations is 0.69 and this occurs at a lag of one month because the variation in gravity is immediate, but rainfall water requires around one month to travel across the vadose zone before it reaches the groundwater table. Using graphical methods of accumulated deviations from the mean, we show that, in general, groundwater storage follows the smooth, multi-year trends of terrestrial water storage but with less short-term trends; the same is true of rainfall, for which the local trends are more pronounced. There is hysteresis-like behaviour in the variations in terrestrial water storage and in the variations of groundwater. In practical terms, this study shows that, despite the abnormal dryness of the Iberian Peninsula during the 2004–2010 drought, the depleted groundwater storage in Andalucía recovered almost to its pre-drought level by 2016. In addition, groundwater storage and terrestrial water storage show very similar trends but with a delay in the groundwater trend.

Seasonal scour and siltation induced spatiotemporal variations in riverbed sediment leakage coefficients as measured via the thermal tracer method

Riverbed scour and siltation can change the hydraulic conductivity and thickness of sediments, leading to notable spatiotemporal variations of groundwater–surface water interaction. However, correlated quantitative research on the dynamic leakage coefficient (LC) remains lacking under riverbed scour and siltation. Based on dynamic monitoring and analysis of sediment medium properties, river-groundwater levels, and temperature profiles in the section of Liao River, this study compared the applicable conditions of different thermal analytical models and identified spatiotemporal variations in the LC values induced by riverbed scour and siltation. The results showed that: (1) The thermal tracer method combined with river-groundwater level monitoring can effectively quantify spatiotemporal variations in the LCs of riverbed sediment. Based on the sediment temperature presents diurnal fluctuations and gradient characteristics in different seasons, the LCs in summer, spring, and autumn compared to winter in seasonally frozen regions should be calculated using transient and steady-state analytical solution models, respectively. (2) The LCs ranged from 0.47 to 24.90 × 10-6 s−1, showed larger temporal variability than spatial, increased from the river bank to the center, and had larger values in autumn and winter. (3) Distinct from previous findings, the riverbed underwent a scouring process associated with reductions in the incoming sediment coefficient as the river stage shifted from high to low, eroding the surface 4–8 cm of sediment. During this process, the LC increased by 40 to 420%. Further, the influence of riverbed scour and siltation on the LC varied by river section. Near the riverbank, the sediment LC was primarily controlled by hydraulic conductivity related to the coarsening of sediment lithology; however, it was influenced by variations in both sediment thickness and hydraulic conductivity near the riverbed center. Collectively, these results further understand the mechanisms underlying changes in the sediment LC induced by riverbed scour and siltation, as well as provide a scientific basis for ensuring the sustainable development of riverside water sources under such changes.

Perceptions and attitudes of farmers and landowners on soil salinity management and use of elemental sulphur in Oman

AbstractSoil salinity threatens agricultural sustainability globally and is a significant challenge in Oman. Previous studies in Oman focused on examining the causality and spatiotemporal variation of groundwater and soil salinity, neglecting farmers' perceptions and attitudes towards salinity management. Therefore, this study evaluates (i) perceptions and attitudes of landowners and farmers towards soil salinity and its management, and (ii) determinants of willingness to use elemental sulphur to alleviate soil salinity in Oman. A questionnaire survey (122 responses) assessed perceptions, attitudes and knowledge using Likert scales and qualitative questions. Binary Logistic Regression analysed determinants of willingness to use elemental sulphur. Results reveal variations in perceptions, attitudes, knowledge and management practices. Most of the respondents were aware of adequate nutrient and water requirements for crops (p < .05). Respondents rely on social media (38.5%), fellow farmers (32.1%) and personal experiences (11.5%) for knowledge acquisition about soil salinity management. Half of the respondents did not monitor soil salinity, while the other half relied primarily on visual observation. A substantial number (62.6%) of the respondents did not implement any techniques to alleviate soil salinity, while among those who acted, a majority preferred cultivating date palms (55%) or fodders (29.4%). Awareness of the national salinity management strategy and commercial products is lacking. However, when introduced to elemental sulphur as a soil amendment for salinity, 74.8% of the respondents demonstrated a willingness to utilize it. Most (82.4%) preferred elemental sulphur products within the lowest price range. Being a full‐time farmer, owning a farm, awareness of the national strategy and low‐price preferences were positive determinants, while <1 year of farming experience was a negative determinant of willingness to use elemental sulphur. These findings inform future research on socio‐economic perceptions of salinity in Oman, the Gulf region and similar arid areas facing food production limitations.

Numerical Example to Estimate Groundwater Level Changes using Time-lapse Microgravity Data

The study using time-lapse microgravity (TLM) data can be helpfull to understand near surface variation caused by hidrological variation. Shallow groundwater variation can be highly correlated with density variation as time-lapse microgravity source, because the changes are very close to the surface. For several days (or weeks or months), we can observe density variation in the near surface caused by the changes of water saturated zones. The time-lapse of density variation for several days can be simplified as groundwater table changes. The purpose of this work is to study time-lapse microgravity application for groundwater level estimation. Using numerical example, we utilize lateral variation of time-lapse microgravity signal and also surface topography. In order to do the estimation groundwater level for second TLM survey, we need the groundwater level data from first survey (and vice versa). After numerical example, we applied the algorithm in the study area of (5 × 5) km square in the Blora regency. The shallow groundwater level (0 to 14 meters below the surface) are observed after the second (2016) microgravity survey. From this work, we constrained the model using second groundwater level data. After iterative calculation of using TLM anomaly (value in the range of -80 to +80 microGal) with surface topography variation (in the range 90 to 230 meters), we get the estimation the first (2014) groundwater level variation in the range of -7 to 7 meters from the second (2016) groundwater level data.

Groundwater Depletion Rate Over China During 1965–2016: The Long‐Term Trend and Inter‐annual Variation

AbstractMany countries have experienced the increase of groundwater depletion rate (GWDR), posing great challenges to the environment and society. Given the slow variation of groundwater, long‐term estimation of GWDR at high‐resolution is critical for sustainable managements of regional water resources and risks of hydrological extremes in a changing climate. However, limited in‐situ and satellite observations and uncertainties from hydrological model simulations prohibit reliable estimation of the long‐term trend and inter‐annual variation of GWDR. Using survey‐based water withdrawal and water availability datasets, this study provided a spatially distributed estimation of annual GWDR over China at the 0.25° × 0.25° grid scale for the period 1965–2016 using a flux‐based approach. The estimated GWDR has higher spatial resolution and longer temporal coverage than previous products. With the newly compiled data, we found that groundwater over China was depleted at an average rate of 20.4 km3 year−1 during 1965–2016, especially in the arid and semi‐arid areas of northern China. The GWDR showed a significant increasing trend during 1965–2016, but such trend slowed down from 0.66 km3 year−1 during 1965–2001 to 0.06 km3 year−1 during 2001–2016, which was mainly attributed to the deceleration in human water withdrawal. Further analysis showed that over 40% of the inter‐annual variability of GWDR could be explained by precipitation variability, and the climate control increased over time. This study suggested a growing control of climate variations on GWDR over China as the human water withdrawal has been decelerating, and a need for climate change adaptation for a sustainable groundwater management.

ANALISIS DEFORMASI DAN STABILITAS LERENG DENGAN VARIASI GEOMETRI DAN PERKUATAN GEOTEKSTIL PADA PROYEK GEDUNG FAKULTAS HUKUM UII

Indonesian Islamic University (UII) is a private university located in Sleman, Special Region of Yogyakarta. As an educational institution, UII must be able to fulfill the infrastructure to carry out the teaching and learning process for its students, namely the lecture building. At present UII has campuses spread across Kaliurang (integrated campus), Condongcatur (Faculty of Economics), and student parks (Faculty of Law). The process of building a law faculty building UII is on the road Kaliurang km14.5 which is just below the foot of Mount Merapi and has contours of mountainous land. The contours of mountainous land have different levels of land up and down. In mountainous areas can cause problems, namely landslides. In the construction of the UII law faculties building, a suitable slope design is needed, so to solve the problem, slope stability analysis is used. This method is carried out by analyzing the deformation and slope stability by strengthening the geotextiles using the Plaxis 8.2 program. Slope modeling is designed with variations in geometry and variations in water level. Geometry variations used are geometry 70 °, 60 °, and 50 ° while variations in water level with dry water conditions, depth of water conditions 3.8 m, and saturated water conditions. In carrying out the analysis using structural loads and earthquake loads. Deformation analysis is seen from horizontal point X deformation, vertical point X deformation and horizontal deformation of Y-Y pieces. The results of this study are that slope with geotextile reinforcement have large safety factor and small deformations. A more slope geometry variation (50°) result in a larger safety factor and has a small deformation than steep geometry (70°). Groundwater variation have an influence on the results of the safety factor and deformation. The face of saturated ground water has a low safe value and large deformation due to having more water content.

Removal of Manganese and Iron from Groundwater by using Chlorination and Rapid Sand Filtration: A Case Study

The average groundwater extraction from Murunkan well field, Mannar, is around 3.4 MCM/year, and it was triggered by extensive development projects and resettlements that took place in the last decade. Manganese and Iron variations in Murunkan groundwater reported during some periods created various operational and aesthetic issues in the potable water supply. This study is focused on treating iron and manganese in groundwater using chlorination and Rapid Sand Filtration (RSF) techniques. Pebble layers, height of 205 mm with the particle sizes ranging from 2-25 mm, were filled at the bottom of RSF model filter. Filter media, height of 700 mm with 0.45 mm effective size (D10) and a uniformity coefficient (Cu) of 1.33, was placed above the pebble layers. The filter was operated continuously for 15 days, and influent and effluent water samples were collected from 15 trials. Filter backwashing was performed after every two trials to maintain a consistent filtration rate. Raw water pH values ranged from 6.74 – 7.48. Chlorine solution (1.08-1.26 ppm) was added at the inlet point, and a 2.88 m water column was maintained, allowing adequate mixing and oxidation time. The results revealed that average removals of iron and manganese as 60% and 73%, respectively, while maximum removals of 93% and 91% were observed for iron and manganese, respectively.

Laboratory development of TDR automatic distributed settlement sensing for land subsidence monitoring

Recognizing land subsidence to reduce the risk is critical in complex alluvial-basin aquifers and the subsidence profiling requires multi-leveling techniques. However, the manual magnetic ring sampling is limited with low temporal resolution. This study adopted Time Domain Reflectometry (TDR) for automatic and high-accuracy instrumentation with designs of subsidence sensor and data reductions. A physical model was included to examine measurement accuracy and standard deviation due to the groundwater variation. The water fluctuates in the unconfined aquifer scenario affected the measurement accuracy to −1.52 cm/m by the Maximum point method. Additionally, the Maximum point accuracy is 0.84 mm/m with a stable water level as the confined aquifer case, proofing the measurement feasibility but limited measurement range due to signal attenuation. Thus, a novel TDR multi-sections schema was provided to solve the signal attenuation, resulting in the measurement range extending to 150 m with a standard deviation ≤ 1 mm.

Effect of Moisture Sources on the Isotopic Composition of Precipitation in Northwest China

Stable isotopes (18O/16O and 2H/1H) are fingerprints of water molecules and thus can be used to gain insight on water circulation. Especially, the factors controlling the isotopic composition of precipitation should be identified because they act as baseline determinants of the isotopic variations of surface water and groundwater. Here, using the HYSPLIT model, we attribute observed isotope variations to different moisture sources and characterize the isotopic composition of meteoric precipitation in Northwest China. Results show that the westerlies play a dominant role across the region throughout the year, while other moisture sources only affect some parts of the region during a specific season, i.e., Arctic airflow only affects the Altay Mountains as far as the Middle Tianshan Mountains; the East Asia Monsoon only affects the region east of 100° E longitude during the summer; and summer rainfall of local origin may contribute to the precipitation budget of basin areas. Given the different moisture sources across Northwest China, a local meteoric water line (NWMWL) of δ2H = 6.8δ18O − 1.6 is observed. Our findings not only can provide valuable insights into the mechanism of precipitation isotope fractionation in Northwest China but also can contribute to a better understanding of regional climate and hydrological studies.

Assessing groundwater storage anomalies in Beijing based on the new multifactor-quantitative joint prediction model

Water shortages and groundwater depletion are critical issues in the world, leading to unsustainable agricultural production and adverse ecological impacts. Here, the new Multifactor-Quantitative joint Prediction Model (MQPM) is developed to quantitatively predict the Groundwater Storage Anomalies (GWSA), which includes an annual multifactor module and a monthly quantitative module. The correlative coefficients from two modules between simulated GWSA and observed GWSA reach up to 0.98 and 0.87, respectively. Taking Beijing as an example, results show that GWSA trends before South-to-North Water Diversion (SNWD) (2005–2014) and after SNWD (2015–2018) are at a rate of −3.00 × 108 m3/yr and 1.95 × 108 m3/yr, respectively, which reflects the effectiveness of water diversion. Additionally, the predicted results show that GWSA from the multifactor module will increase to 45.97 × 108 m3 by 2028. The quantitative module designs four scenarios under different climate changes and policies, from which the predicted GWSA with values ranging from 28.49 × 108 m3 to 63.06 × 108 m3. For the latter module, the groundwater level will recover to ∼8.9 m up to 2028, combining multiple favorable conditions. Finally, factors consisting of water diversion, climate change, and water-saving policies have a vital influence on groundwater variations, and contributions of these factors to the GWSA account for 46%, 27%, and 27%, respectively.

Ideas and perspectives: Land–ocean connectivity through groundwater

Abstract. For millennia, humans have gravitated towards coastlines for their resource potential and as geopolitical centres for global trade. A basic requirement ensuring water security for coastal communities relies on a delicate balance between the supply and demand of potable water. The interaction between freshwater and saltwater in coastal settings is, therefore, complicated by both natural and human-driven environmental changes at the land–sea interface. In particular, ongoing sea-level rise, warming and deoxygenation might exacerbate such perturbations. In this context, an improved understanding of the nature and variability of groundwater fluxes across the land–sea continuum is timely yet remains out of reach. The flow of terrestrial groundwater across the coastal transition zone and the extent of freshened groundwater below the present-day seafloor are receiving increased attention in marine and coastal sciences because they likely represent a significant yet highly uncertain component of (bio)geochemical budgets and because of the emerging interest in the potential use of offshore freshened groundwater as a resource. At the same time, “reverse” groundwater flux from offshore to onshore is of prevalent socio-economic interest, as terrestrial groundwater resources are continuously pressured by over-pumping and seawater intrusion in many coastal regions worldwide. An accurate assessment of the land–ocean connectivity through groundwater and its potential responses to future anthropogenic activities and climate change will require a multidisciplinary approach combining the expertise of geophysicists, hydrogeologists, (bio)geochemists and modellers. Such joint activities will lay the scientific basis for better understanding the role of groundwater in societally relevant issues such as climate change, pollution and the environmental status of the coastal oceans within the framework of the United Nations Sustainable Development Goals. Here, we present our perspectives on future research directions to better understand land–ocean connectivity through groundwater, including the spatial distributions of the essential hydrogeological parameters, highlighting technical and scientific developments and briefly discussing the societal relevance of that connectivity in rapidly changing coastal oceans.

The Generalized Method of Wavelet Moments with eXogenous inputs: a fast approach for the analysis of GNSS position time series

The global navigation satellite system (GNSS) daily position time series are often described as the sum of stochastic processes and geophysical signals which allow to study global and local geodynamical effects such as plate tectonics, earthquakes, or ground water variations. In this work, we propose to extend the Generalized Method of Wavelet Moments (GMWM) to estimate the parameters of linear models with correlated residuals. This statistical inferential framework is applied to GNSS daily position time-series data to jointly estimate functional (geophysical) as well as stochastic noise models. Our method is called GMWMX, with X standing for eXogenous variables: it is semi-parametric, computationally efficient and scalable. Unlike standard methods such as the widely used maximum likelihood estimator (MLE), our methodology offers statistical guarantees, such as consistency and asymptotic normality, without relying on strong parametric assumptions. At the Gaussian model, our results (theoretical and obtained in simulations) show that the estimated parameters are similar to the ones obtained with the MLE. The computational performances of our approach have important practical implications. Indeed, the estimation of the parameters of large networks of thousands of GNSS stations (some of them being recorded over several decades) quickly becomes computationally prohibitive. Compared to standard likelihood-based methods, the GMWMX has a considerably reduced algorithmic complexity of order mathcal {O}{log (n) n} for a time series of length n. Thus, the GMWMX appears to provide a reduction in processing time of a factor of 10–1000 compared to likelihood-based methods depending on the considered stochastic model, the length of the time series and the amount of missing data. As a consequence, the proposed method allows the estimation of large-scale problems within minutes on a standard computer. We validate the performances of our method via Monte Carlo simulations by generating GNSS daily position time series with missing observations and we consider composite stochastic noise models including processes presenting long-range dependence such as power law or Matérn processes. The advantages of our method are also illustrated using real time series from GNSS stations located in the Eastern part of the USA.

Multiscale Variability of Hydrological Responses in Urbanizing Watershed

Anthropically-induced land-use/land cover (LULC) changes create an imbalance between water and energy fluxes by affecting rainfall-runoff partitioning. This alters the catchment’s flow regime, generating increased highs and reduced low flows, triggering socio-economic and environmental damages. The focus of this study is two-fold (i) to quantify the hydrological changes induced in the urbanizing watershed and (ii) to analyze changes in streamflow variability and generation of extremes (high- and low-flow), using the soil and water assessment tool (SWAT) for Peachtree Creek, USA. The results indicate that the change in LULC significantly influences the availability of soil moisture, ET, and contribution to groundwater flow. It is observed that the variations in these processes regulate the water availability from the surface and sub-surface sources, thus affecting the generation of extreme flows. The spatio-temporal analysis, in response to LULC changes, indicates that (i) urbanization significantly affects baseflow, and its variability depends on the degree of urbanization and the predominant land-use class of the subwatersheds, and (ii) the seasonal variations in the baseflow contribution to the streams depend on ET and the timing and magnitude of groundwater outflow to streams. These variations in ET and groundwater lead to water excess/deficit regions, thus increasing the susceptibility to floods during heavy precipitation events and reducing the reliability of streams during dry periods. Thus, in an urbanizing watershed, the hydrological regime of the watershed may not always be a function of changes in the surface runoff, but will be modified by ET and groundwater dynamics. Further, the study shows that the changes in model parameters can provide insight into the implications of LULC changes on hydrological processes and flow regimes. Evaluating the implications on the basin water balance is paramount for deriving any management operations and restoration activities. The study also outlines the significance of analyzing the spatial and temporal scale streamflow variations for managing water resources to reduce damage to lives and properties.

Geophysical and Remote Sensing Assessment of Chad’s Groundwater Resources

Because of climate change and human activity, North and Central Africa are experiencing a significant water shortage. Recent advancements in earth observation technologies have made widespread groundwater monitoring possible. To examine spatial and temporal mass fluctuations caused by groundwater variations in Chad, gravity solutions from the Gravity Recovery and Climate Experiment (GRACE), climatic model outputs, and precipitation data are integrated. The results are as follows: (1) The investigated region experienced average annual precipitation (AAP) rates of 351.6, 336.22, and 377.8 mm yr−1, throughout the overall investigation period (04/2002–12/2021), Period I (04/2002–12/2011), and Period II (01/2012–12/2021), respectively. (2) Using the three gravity solutions, the average Terrestrial Water Storage Variations (ΔTWS) values are estimated to be +0.26 ± 0.04, +0.006 ± 0.10, and +0.64 ± 0.12 cm yr−1, for the overall study period, periods I, and II, respectively. (3) Throughout the full period, periods I, and II, the groundwater storage fluctuations (ΔGWS) are calculated to be +0.25 ± 0.04, +0.0001 ± 0.099, and +0.62 ± 0.12 cm yr−1, respectively after removing the soil moisture (ΔSMS) and Lake Chad water level trend values. (4) The country receives an average natural recharge rate of +0.32 ± 0.04, +0.068 ± 0.099, and +0.69 ± 0.12 cm yr−1, throughout the whole period, Periods I, and II, respectively. (5) The southern mountainous regions of Erdi, Ennedi, Tibesti, and Darfur are receiving higher rainfall rates that may recharge the northern part of Chad through the stream networks; in addition to the Lake Chad and the higher rainfall over southern Chad might help recharge the central and southern parts of the country. (6) A preferred groundwater flow path from the Kufra (Chad and Libya) to the Dakhla basin (Egypt) appears to be the Pelusium mega shear system, which trends north-east. The findings suggest that GRACE is useful for monitoring changes in groundwater storage and recharge rates across large areas. Our observation-based methodology provides a unique understanding of monthly ground-water patterns at the state level, which is essential for successful interstate resource allocation, future development, and policy initiatives, as well as having broad scientific implications for arid and semiarid countries.

Groundwater Investigation Using Electrical Resistivity Method at New Borg El-Arab City, Alexandria, Egypt

New Borg El-Arab is a city located on the northwestern coast of Egypt, where the increasing anthropogenic activities have led to an increase in water demand. Groundwater is the main source of water in this area, but it is seriously affected by the Mediterranean saltwater intrusion. This causes a substantial impact on the water quality of the coastal aquifer. In this study, the electrical resistivity method was applied to delineate the shallow groundwater aquifer and its quality. Twenty vertical electrical soundings (VES) distributed along 6 profiles were measured. To observe the seasonal groundwater variations, 14 VES points were measured at the end of the rainy season, while the measurements of 6 VES points were repeated at the end of the dry season. The results revealed 4 geoelectrical layers; the first layer is a surface dry zone with variable resistivity values, followed by a water-bearing layer; while the third is a limestone layer, followed by a clay deposits zone. In comparison to the winter season, the water-bearing layer records lower resistivity values at the end of summer. Optimal locations to drill new groundwater wells have also been determined with a depth varying from 1.8 m north to about 30 m south.

Safety analysis of near surface nuclear waste repository constituting an aquifer in proximity

Probabilistic safety assessment involves the calculation of risk associated with possible radioisotope contamination of Groundwater. The overall scenario and the consequences that may occur on the failure of the external barriers are identified using an Event Tree analysis to be the multi-barrier failure due to rainwater intrusion into the near-surface disposal site and leaching out of radionuclides into groundwater which is extracted as drinking water by critical groups present around the repository. A program is developed in Python 3.0 for such a scenario to assess necessary parameters such as radioactive release rate, groundwater radionuclide concentration, dose ingested by members and total risk associated with each radioisotope. The initiation is with the assessment of the failure density function of the multi-barrier system operating in redundancy, using the failure density functions. The radionuclide concentrations of the near-surface disposal facility are necessary to be calculated to know the probable release rate of each radionuclide into groundwater. The concentration depletion with Spatio-temporal variance is also considered a factor for radioisotope concentration variation in groundwater. The concentration of radionuclides in groundwater when ingested at a rate of 2.2 L/day helps us to calibrate the Radiation dose to humans through this pathway by using the Ingestion dose coefficient for each isotope fixed by International Atomic Energy Agency [IAEA]. The final risk assessment is accomplished by multiplying the radiation dose ingested by members of the critical group with a risk factor for fatal or non-cancers and critical hereditary effects by the International Commission on Radiological Protection. In the present work, a subjective analysis is done to calibrate the dosage of radiation, of five radioisotopes (3H, 60Co, 59Ni, 90Sr, 129I) for disposal. Radioactive Iodine delivered maximum risk despite a low concentration in the inventory of radioactive waste. However, much lower than the permissible dosage suggested by ICRP i.e.,1 mSv in a scenario where an exclusion zone is considered to be existing, and a drinking water well is established at a distance of 1.6 km from the repository and the risk is computed over a period of 150 years since the multi-barrier failure.