Sustainable Utilization Of Groundwater Resources Research Articles

Sustainable Groundwater Management Through Micro Irrigation: A Critical Review on Challenges and Solutions

Abstract Groundwater plays a vital role in global water resources, supporting agricultural, industrial, and domestic water supply systems. However, the long-term sustainability of groundwater is increasingly threatened due to the widespread adoption of irrigation systems especially micro irrigation. Micro irrigation is a widespread agricultural technique that involves water application to crops through drip irrigation and sprinkler systems. This method has gained widespread adoption due to its ability to deliver water efficiently to crops. This review paper examines the impacts of micro irrigation on groundwater sustainability, focusing on its effects on groundwater quantity, quality, and overall sustainability. The findings reveal that micro irrigation can significantly contribute to groundwater conservation by reducing water losses. However, improper management practices, such as over-irrigation or incorrect application rates, can lead to excessive groundwater extraction, depletion of aquifers, and declining water tables. Applying fertilizers and pesticides in micro irrigation systems may lead to groundwater pollution, thereby affecting water quality and posing a risk to human health. This review article emphasizes the significance of appropriate design, installation, and upkeep of micro irrigation systems to minimize potential adverse effects on groundwater. Furthermore, regulatory frameworks, policies, and educational programs are crucial in promoting sustainable groundwater management practices in micro irrigation. The present review highlights the significance of adopting balanced water use practices, enhancing water management techniques, and implementing relevant regulations to ensure the sustainable utilization of groundwater resources in micro irrigation systems.

Estimating groundwater recharge rates in the Upper Awash Basin, Ethiopia under different combinations of model complexity and objective functions

Abstract This study addresses the critical need for reliable groundwater recharge quantification by investigating the uncertainty associated with recharge estimation based on various combinations of model complexity and objective functions. Focusing on the Hombele catchment in the upper Awash Basin, Ethiopia, the research aims to analyze parameter sensitivity under different model complexities and objectives while estimating groundwater recharge for the period 1986–2013. Employing a Monte-Carlo-based calibration scheme, the study fine-tunes model parameters using objective functions like KGE, NSE, LogNSE, R2, and VE across 10 combinations of model complexity and objective functions. Results identify FC, LP, and BETA as highly sensitive parameters, while UZL, K0, and MAXBAS show limited influence in all model complexity and objective function scenarios. The semi-distributed HBV-light model achieves calibration, validation, and overall period KGE (NSE) values of 0.89 (0.80), 0.80 (0.73), and 0.87 (0.77), respectively. Sensitivity analyses reveal significant impacts on model parameters and recharge estimation based on the chosen objective function and model complexity levels. Average annual recharge rates range from 185.9–280.5 mm when the HBV-light model is semi-distributed, contrasting with 185.3–321.7 mm under lumped model conditions, emphasizing the importance of considering these factors in groundwater resource assessments.

Hazards and influence factors of arsenic in the upper pleistocene aquifer, Hetao region, using machine learning modeling

The Hetao region is one of the regions with the most serious problem of the greatest measured arsenic concentrations in China. The enrichment of arsenic in groundwater may poses a great risk to the health of local residents. A comprehensive understanding of the groundwater quality, spatial distribution characteristics and hazard of the high arsenic in groundwater is indispensable for the sustainable utilization of groundwater resources and resident health. This study selected six environmental factors, climate, human activity, sedimentary environment, hydrogeology, soil, and others, as the independent input variables to the model, compared three machine learning algorithms (support vector machine, extreme gradient boosting, and random forest), and mapped unsafe arsenic to estimate the population that may be exposed to unhealthy conditions in the Hetao region. The results show that nearly half the number of the 605 sampling wells for arsenic exceeded the WHO provisional guide value for drinking water, the water chemistry of groundwater are mainly Na-HCO3-Cl or Na-Mg-HCO3-Cl type water, and the groundwater with excessive arsenic concentration is mainly concentrated in the ancient stream channel influence zone and the Yellow River crevasse splay. The results of factor importance explanation revealed that the sedimentary environment was the key factor affecting the primary high arsenic groundwater concentration, followed by climate and human activities. The random forest algorithm produced the probability distribution of high arsenic groundwater that is consistent with the observed results. The estimated area of groundwater with excessive arsenic reached 38.81 %. An estimated 940,000 people could be exposed to high arsenic in groundwater.

Simulation of spatial and temporal variation of nitrate leaching in the vadose zone of alluvial regions on a large regional scale

Excessive use of fertilizers presents a significant threat to groundwater safety. To mitigate nitrate leaching and ensure the sustainable utilization of groundwater resources, it is crucial to quantify the spatial heterogeneity of nitrogen leaching and its drivers. Therefore, accurate modeling of deep nitrate leaching at large regional scales is necessary. In this study, we have created a computational framework to analyze the transport of unsaturated zone water and nitrate at a regional scale. The framework is based on a process-oriented, watershed-scale computational model that segments the study area into a grid system, with each grid modeled using Richards-based advection-diffusion equations for water and solutes. The research model estimated nitrate nitrogen leaching, accumulation, and denitrification in the vadose zone of agricultural fields in the Baiyangdian watershed, which is a typical agricultural region with complex land use and soil deposition conditions in the North China Plain. The results showed that there were significant spatial differences in nitrate N leaching, denitrification and accumulation with values of 0–388 kg/ha/year, 30–177 kg/ha/year and 75–4778 kg/ha. Groundwater recharge in the wheat/maize, vegetable, and cotton area exhibited a negative correlation with nitrate N accumulation while showing a positive correlation with nitrate N leaching. Nitrate nitrogen distribution indicated spatial heterogeneity, attributable mainly to the heterogeneity in soil texture, structure, and land use. With nitrate nitrogen leaching and denitrification levels reaching 327–388 kg/ha/year and 133–175 kg/ha/year, respectively, vegetable fields pose a direct threat to groundwater. Meanwhile, wheat/maize fields showed the greatest nitrate nitrogen accumulation, ranging from 624 to 4778 kg/ha. This excessive buildup of nitrate in these fields presents a potential hazard to groundwater quality. Soil texture in the root zone had a greater influence on the amount of nitrate leaching and denitrification than soil texture below the root zone. Deeper soil texture (>2 m) was found to mainly control total nitrate accumulation in the vadose zone. To assess nitrate leaching, denitrification, and accumulation at a regional scale within the deep vadose zone, a process-oriented model was developed, considering the intricate associations among land usage, soil texture, and biochemical reactions.

Controlling Factors of Groundwater Salinization and Pollution in the Oasis Zone of the Cherchen River Basin of Xinjiang

Groundwater is a vital resource for local human life and production in the oasis zone of the Cherchen River Basin of Xinjiang. Understanding the controlling factors of groundwater salinization and pollution is of great significance for the sustainable utilization of groundwater resources and protection of the ecological environment in desert oasis areas. In light of this, a total of 36 single structure unconfined groundwater samples and 54 multi-layered structure unconfined and confined groundwater samples were collected from the oasis zone of the Cherchen River Basin and evaluated for the distribution characteristics and pollution status of major ions. Hydrogeochemical methods (e.g., Piper diagram, multivariate statistics, Gibbs model, and relationships among ions) were used to determine the main controlling factors of groundwater salinization and pollution. Differences in hydrogeochemical zonation were found from the single structure unconfined aquifers in sloping plains of piedmont areas to the multi-layered structure unconfined and confined aquifers in alluvial-proluvial plain areas, and Cl-Na (87.8%) was the main hydrochemical type in the groundwater of the study area. The quality of single structure unconfined groundwater was starkly better than that of the multi-layered unconfined and confined groundwater, which was mainly caused by Na+ (mean value of 9 969 mg·L-1), Cl- (13 687 mg·L-1), and SO42- (5 840 mg·L-1). Moreover, the natural hydrogeochemical process was the main reason for the deterioration of groundwater quality. The hydrochemistry was mainly controlled by the water-rock interaction and evaporation processes. The mineral dissolution of silicates and evaporites was an important source of chemical ions in the groundwater. Furthermore, the chemical weathering of evaporites combined with the processes of evaporation and cation exchange had a significant influence on the salinization of multi-layered unconfined and confined groundwater in alluvial-proluvial plain areas. In addition, synthetic fertilizers were the main pollution sources of NO3- in groundwater in the intensive agricultural zones.

A New Socio-Hydrology System Based on System Dynamics and a SWAT-MODFLOW Coupling Model for Solving Water Resource Management in Nanchang City, China

To address the issue of seasonal water resource shortages in Nanchang City, a multi-system coupling socio-hydrology simulation method was proposed. This approach involves dynamically integrating a centralized socio-economic model with a distributed surface water groundwater numerical model to explore the intricate relationships between the socio-economic system, the surface water–groundwater integrated system, and the outcomes related to seasonal water resource shortages. Taking Nanchang City as an example, this study conducted research on the water resource supply and demand balance, as well as the groundwater emergency supply, using the multi-system coupling model. Three scenarios were established: status quo, developing, and water-saving. The results show that with the increasing total water demand of social and economic development, the severity of the water resource shortage will be most pronounced in 2030. The minimum water resources supply and demand ratios for the status quo, developing, and water-saving scenarios are projected to be 0.68, 0.52, and 0.77, respectively. To meet residents’ water needs during drought conditions, emergency groundwater supply efforts are investigated. According to the simulation results, groundwater emergency supply would increase the total population by 24.0 thousand, 49.4 thousand, and 11.2 thousand people, respectively, in the status quo, developing, and water-saving scenarios. In the water-saving scenario, the Youkou and Xiebu water sources can serve as suitable emergency water sources. In the status quo scenario, the Youkou water source is the most viable emergency water source. However, in the developing scenario, relying solely on any single water source for emergency supply could have an irreversible impact on the aquifer. Therefore, considering the simultaneous use of multiple water sources is recommended, as it can fulfill water demands while ensuring the sustainable utilization of groundwater resources.

Responses of plant sap flow rate to epikarst water availability under different karst water-bearing media

The water supply capacities of epikarst zones play an essential role in the restoration of vegetation and sustainable utilization of groundwater resources in karst areas. The permeability and water storage capacity of karst water-bearing media directly determines prospective water acquisition for plants. However, the degree to which karst water-bearing systems influence plant transpiration remains unclear. Consequently, this study selected three common karst water-bearing structures (pore and fissure (L1), fissure and conduit (L2), dissolution seam and pore (L3), to examine the sap flow rate (SF), infiltration rate, meteorological factors, soil water, and groundwater depth (GD) associated with the growth of Toona sinensis. The results revealed that: (1) Marked differences in the SF based on long term monitoring (2016/1–2022/6) were observed in three sample plots with the order of L2 > L1 > L3. Similar trends in the rock permeability coefficient were also found. (2) Groundwater depth and soil water are the major factors that determine the SF. (3) The threshold of GD (2.54 m for L1, 0.96 m for L2, and 3.56 m for L3) was identified, wherein the sensitivity of SF to GD (λn) was weakened with greater GD. (4) The fissure and conduit sample plot with a shallower GD and higher rock permeability provided more plant-available water, resulting in a larger SF. In contrast, the dissolution seam and pore sample plot with a more stable GD and media rock permeability hindered the absorption of water by plants, which translated to a lower SF. These results highlighted that the structures of karst water-bearing media determined the overall SF. This study provides useful information toward guiding the restoration of vegetation in subtropical karst areas with abundant rainfall and shallow groundwater reservoirs.

Spatial-temporal variations of groundwater storage in China: A multiscale analysis based on GRACE data

Groundwater storage (GWS) plays a key role in the freshwater supply in China. Revealing the changes in GWS in China is critical for realizing sustainable utilization of groundwater resources. We used Gravity Recovery and Climate Experiment (GRACE) satellite data as well as HydroSHEDS datasets to quantify the variation of GWS in China from 2003 to 2020 at multiple scales. We found that GWS was decreasing at a rate of -2.09 mm/a in China. Three hot-spot areas with dramatic GWS decrease, located in Northwest, Southwest and North China, accounted for 55.52% of the total GWS decrease in China, and the reduction in GWS in these areas was driven primarily by human activities. Additionally, more than half of the urban agglomerations in China potentially impacted by the declining GWS. Therefore, it is suggested that targeted measures should be taken according to local conditions to strengthen the scientific management of groundwater.

Integrated Geospatial and Geophysical Approaches for Mapping Groundwater Potential in the Semi-Arid Bukombe District, Tanzania

The rapid growth of civil societies coupled with population influx due to the artisanal mining industry in the Bukombe district (BD) has triggered a high demand for water resources. The daily consumption of water resources in the district surpasses the supply from available surface water sources. Thus, the situation has raised the demand for groundwater resources as an alternative. Despite the importance of groundwater resources, no current studies have spatially assessed groundwater potential to locate optimal points for borehole development. This study intended to investigate and map the groundwater potential areas (GWPAs) in the semi-arid BD using remote sensing (RS), the geographic information system (GIS), and the analytic hierarchy process (AHP) to help local communities access clean and safe water. Rainfall, geology, slope, drainage density, land use/land cover and lineament density were prepared to delineate the map of GWPAs. The map was categorized into poor (0.21%), moderate good (51.39%), good (45.70%) and very good (2.70%). Finally, the GWPA map was validated using Vertical Electrical Sounding (VES), 2-D sections and a drilled borehole. The validation results confirmed that the applied approach provides significant results that can help in planning the sustainable utilization of groundwater resources.

Hydrogeochemical studies of groundwater in semi-arid areas of northern Ethiopia using geospatial methods and multivariate statistical analysis techniques

The present study focused on evaluating the groundwater hydrogeochemical of shallow aquifers in the semi-arid areas of northern Ethiopia, using geospatial modelling and multivariate statistical techniques. Physico-chemical parameters, including pH, major ions, electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH), pollution index (PI) and other parameters, from 22 samples have been used to assess water quality, sources of various ions, water types and factors controlling groundwater chemistry. Results showed that the spatial distribution of major ions, EC, TDS, TH and PI values in these samples significantly differ from one location to another due to geological variations and anthropogenic activities of the area. The quality of most groundwater is generally unfit for drinking due to their PI, EC, TH, calcium, potassium, total iron and bicarbonate (HCO3−) values that found to be above the permissible limits of WHO and Ethiopian standards. The parameters like sodium percentage, sodium adsorption ratio (SAR), residual sodium bicarbonate, permeability index, magnesium hazard and Kelly’s ratio revealed good quality of groundwater for irrigation utilization, whereas EC of irrigation water (ECiw), combined effects of ECiw − SAR and bicarbonate hazard values indicated that majority of groundwater are not suitable for irrigation use. Piper trilinear diagram classified majority of samples under temporary hardness with Ca–Mg–HCO3 type. Further, Gibbs diagram reveals that water–rock interaction is the major hydrogeochemical processes governing the water chemistry of the study area. Therefore, it is recommended to perform a constant water quality checking program and improvement of tangible management practices for sustainable utilization of groundwater resources.

GRACE Satellite-Based Analysis of Spatiotemporal Evolution and Driving Factors of Groundwater Storage in the Black Soil Region of Northeast China

Clarifying the evolution pattern of groundwater storage (GWS) is crucial for exploring the amount of available water resources at a regional or basin scale. Currently, the groundwater resources of Northeast China have been extensively exploited, but only limited studies have assessed the extent of GWS depletion and its driving mechanisms. In this study, the groundwater storage anomaly (GWSA) in the black soil region of Northeast China was explored based on the Gravity Recovery and Climate Experiment (GRACE) satellite combined with the Global Land Data Assimilation System (GLDAS) hydrological model. The results show that from 2002 to 2021, the overall GWSA decreased (−0.4204 cm/a), and specifically, the average rates of decrease in Heilongjiang, Jilin, and Liaoning Provinces were −0.2786, −0.5923, and −0.6694 cm/a, respectively, with the eastern, southern, and central parts of Heilongjiang, Jilin, and Liaoning Provinces losing seriously. Especially the GWSA deficit trend can reach −0.7471 cm/a in southern Jilin Province. The GWSA deficits in the three provinces from April to September were greater than 0.40 cm/a, while the deficit values from January to March and from October to December were less than 0.40 cm/a. This study is the first to quantitatively analyze the GWSA and its influencing factors in Northeast China for 2002–2021. The results of the study help clarify the differences in the spatial and temporal distribution of groundwater resources and their driving mechanisms in the northeastern black soil regions and provide a reference for the conservation and sustainable utilization of groundwater resources in the black soil region.

Hydrochemical characteristics and processes of groundwater in the Cenozoic pore aquifer under coal mining.

Mining activities considerably affect groundwater quality and resources. It is crucial to investigate water chemistry and hydrochemical processes under coal mining settings for water environment protection and sustainable utilization of groundwater resources. In this study, 36 groundwater samples from the Cenozoic pore aquifer in the Gubei coal mine in Huainan (Anhui Province, China) were analyzed using hydrochemical, multivariate statistical methods, and inverse geochemical modeling. Results revealed a hydrochemical boundary around 100m below the ground surface, forming two flow zones participating in different hydrological cycles. In the shallow (circulation) zone above the boundary, the main hydrochemical processes are silicate dissolution and cation exchange, followed by evaporite dissolution. In this zone, the Na+ + K+, Cl-, and SO42- concentrations are low and stable, forming low-salinity water (total dissolved solids [TDS] < 1g/L) dominated by Na*Ca*Mg-HCO3 and Na*Ca-HCO3 types. At greater burial depths, the pH, TDS, Na+ + K+, Cl-, and SO42- concentrations in the groundwater gradually increase, while the HCO3- concentration gradually decreases, which is mainly due to the enhanced evaporite dissolution and decarbonation in the deep (circulation) zone below the hydrochemical boundary. In this zone, the Na+ + K+, Cl-, and SO42- concentrations are high and variable, forming high-salinity water (TDS > 1g/L) dominated by Na-Cl and Na-Cl*SO4 types. A hydrochemical evolution model of the Cenozoic aquifer was finally established, which advances our understanding of the evolutionary processes of groundwater chemistry under mining drainage.

Origin and Implications of Pollution in Coastal Groundwater of the Guangdong Province

The groundwater resource is crucial to the urbanization and industrialization in the Guangdong coastal area; the rapid development of Daya Bay has presented a challenge for the management of the groundwater quantity and quality. Therefore, a novel approach to hydrochemical analysis, which, combined with the health risk model and the water quality index (WQI), was used to explain the hydrochemistry characteristics and risks to human health of groundwater in the Guangdong coastal areas in addition to investigating the factors controlling groundwater quality. The results showed that the average concentration of total dissolved solids (TDS) in groundwater was 1935.26 mg/L and the quality of water was weakly alkaline. The dominant hydrochemical types of groundwater were identified to be Mg-HCO3 and Na-Cl·HCO3. The main factor influencing the hydrochemical composition was rock weathering, while the result of principal component analysis (PCA) shows seawater intrusion and anthropogenic inputs also have an effect on the water quality. The conclusions of the water quality assessment indicated that most of the groundwater samples were acceptable for drinking. However, both WQI and the non-carcinogenic hazard quotient (HQ) values indicated unacceptable risks in any area of Maoming, Zhanjiang and Shantou, and, according to the hazard index (HI) value, children in the study area are at more danger to health risks than adults. It is suggested that both groundwater salinization and nitrate pollution should be paid attention to when improving groundwater quality and exploring the sustainable utilization of groundwater resources.

Application of remote sensing and GIS to assess groundwater potential in the transboundary watershed of the Chott-El-Gharbi (Algerian–Moroccan border)

Remote sensing (RS) and Geographic Information Systems (GIS) have become widely used in various fields around the world in recent years. In this paper; we attempt to delineate the groundwater potential zone in the transboundary watershed of Chott-El-Gharbi using the integration of RS, GIS methods. Eight influencing thematic layers viz. geology, rainfall, water table level, lineaments density, slope, drainage density, elevation, and land use/land cover were used. Afterward, Analytical Hierarchy Process technique, which offers good functionality for mapping the groundwater potentiality was used, where ranks and weights, assigned to each factor are computed statistically, based on their relative importance in terms of groundwater potential. Then, groundwater potential zones are classified into five categories namely excellent, high, medium, low, and very low zone, which represent 964.48 km2 (7.33%), 1467.30 km2 (11.15%), 7969.51 km2 (60.57%), 2639.52 km2 (20.06%), and 116.19 km2 (0.88%) of the study area, respectively. The very low potential region is found in the southern region of the study area, which is covered by mountains. Moreover, excellent groundwater potential zones are located at the central part of the region of Chott, which has quaternary formations where the infiltration is high. On the other hand, moderate and poor groundwater potential zones cover by the bare lands in the study area. Finally, the results were carefully validated with the yields data of various boreholes in the study area, which reveals an accuracy achievement of 72.41%. The finding of this research constitutes a valuable contribution towards the water resources management, and it forms a significant decision support tool for equitable and sustainable utilization of groundwater resources in the transboundary watershed of Chott-El-Gharbi. The study's findings will also serve as a benchmark for future research and studies, such as hydrogeological modeling.

Groundwater recharge mechanisms on the Loess Plateau of China: New evidence for the significance of village ponds

Numerous studies have been conducted to understand the mechanism of groundwater recharge for water resources management. But the roles of wide-spread village ponds on the Chinese Loess Plateau on groundwater recharge remains uncertain. Here, to evaluate the groundwater recharge under village ponds, we measured environmental tracers (2H, 18O, Cl-) in rainwater, groundwater, and pore waters of the deep unsaturated zone under three land-cover types (cropland, a village pond, and two apple orchards with stand ages of 10 and 27 years). The results show that shallow groundwater is recharged by both diffusive recharge and focused recharge. Specifically, diffusive recharge occurs beneath farmlands, grasslands, orchards and similar land-cover types, but diminishes in old orchards due to deep root water uptake. The diffusive recharge beneath crop field had an infiltration velocity of 10.3–12.5 cm yr−1; the resulting recharge rate was 30–33 mm yr−1, accounting for 5–6% of the annual precipitation. However, focused recharge occurs mainly beneath village ponds with low-lying terrain, and had an infiltration velocity of 26 cm d−1 during the rainy season; the resulting mean recharge rate was 134 mm yr−1 in the catchment of the pond, accounting for 23.1% of the annual precipitation. Given that the water table is generally more than 30 m below the soil surface, it takes hundreds of years for rainwater to reach the water table via the diffusive recharge but only days to months via the focused recharge. Diffusive recharge contributed 55–68% to the total recharge while focused recharge contributed 32–45%. However, the conversion of croplands to apple orchards and the decrease in the number of village ponds are occurring, which diminishes diffusive recharge, and reduces focused recharge, respectively. These findings are critical to understanding hydrological processes and protecting groundwater resources. We should preserve, reclaim, and construct village ponds to ensure groundwater recharge, in addition to optimizing areal ratio of large farmland to apple orchards in the region for the sustainable utilization of groundwater resources.

Groundwater quality assessment and hydrogeochemical processes in typical watersheds in Zhangjiakou region, northern China.

It is of significance to elucidate the groundwater quality and hydrogeochemical processes for sustainable utilization of groundwater resources in water shortage regions. A total of 256 groundwater samples were collected in typical watersheds in Zhangjiakou, northern China. The hydrochemical parameters, conventional ions, and trace elements were measured, and δD and δ18O data were collected to delineate the groundwater quality and hydrogeochemical processes. The results showed that 32.91% of the groundwater could be directly used for drinking water sources in the Bashang Plateau, north of the study area. The F- and NO3--N were the main parameters above the standard threshold for drinking water. In contrast, the groundwater quality in the Baxia River Basins, south of the study area, was of a better scenario. Nonetheless, high concentrations of F-, total hardness, and SO42- were still observed. Most samples in the Bashang Plateau had relatively higher salinity than the Baxia River Basins. Both surface water and groundwater in the study area originated from local meteoric water with considerable hydraulic connections. The high-fluoride groundwater was primarily formed by dissolution of fluoride-rich minerals under conditions of high pH and Na+, low Ca2+, and rich in HCO3-. The dissolution of carbonate and silicate minerals accompanied by strong cation exchange and weak evaporation was the dominant water-rock interaction affecting the hydrochemical composition of groundwater, and anthropogenic NO3- input had an extra influence on hydrochemical process. This study provides a scientific guideline for the protection and allocation of local groundwater resources.

Development of Seawater Intrusion Vulnerability Assessment for Averaged Seasonality of Using Modified GALDIT Method

Climate change and anthropogenic activities are necessitating accurate diagnoses of seawater intrusion (SWI) to ensure the sustainable utilization of groundwater resources in coastal areas. Here, vulnerability to SWI was assessed by classifying the existing GALDIT into static parameters (groundwater occurrence (G), aquifer hydraulic conductivity (A), and distance from shore (D)) and dynamic parameters (height to groundwater-level above sea-level (L), impact of existing status of seawater intrusion (I), and aquifer thickness (T)). When assessing the vulnerability of SWI based on observational data (2010–2019), 10-year-averaged data of each month is used for GALDIT dynamic parameter for representing the seasonal characteristics of local water cycles. In addition, the parameter L is indicated by the data observed at the sea-level station adjacent to the groundwater level station. The existing GALDIT method has a range of scores that can be divided into quartiles to express the observed values. To sensitively reflect monthly changes in values, the range of scores is divided into deciles. The calculated GALDIT index showed that the most vulnerable month is September, due to relatively low groundwater level. The proposed method can be used to apply countermeasures to vulnerable coastal areas and build water resources management plan considering vulnerable seasons.

Application of a Surrogate Model for a Groundwater Numerical Simulation Model for Determination of the Annual Control Index of the Groundwater Table in China

The Chinese government hopes to implement groundwater table control to realize the sustainable utilization of groundwater resources based on controlling the current groundwater exploitation amount. In this study, a method to determine the control index of the groundwater table is proposed. In the method, the reasonable relationship between the groundwater table and groundwater exploitation amount is ensured using the groundwater numerical simulation model. The operability of the index determination is improved using a surrogate numerical model, and the annual hydrological dynamic is simplified to three scenarios of dry, flat, and wet. To verify this method, the Minqin Basin in Northwest China was chosen as a typical study area. It is assumed that the control index of groundwater exploitation in 2020 is 85,000 × 103m3. Then, the preset annual water table index is calculated as [−0.70, 0.62, 1.13, −1.25, 1.36, 3.09] m [−0.77, 0.53, 1.05, −1.33, 1.27, 2.96] m, and [−0.83, 0.46, 0.99, −1.40, 1.20, 2.85] m for the chosen six monitoring wells, varying over the years with wet, flat, and dry scenarios. This method can ensure high precision, operability, and dynamic management when determining the control index of the groundwater table and satisfy the demand of managers.

Numerical groundwater flow modeling of the Kombolcha catchment northern Ethiopia

Intensive groundwater extraction is a changing groundwater system. It is also the main challenge for future groundwater availability. In this study, numerical groundwater flow model was developed in Kombolcha catchment, Ethiopia by using MODFLOW-OWHM. To address this concern, the conceptual model was built by analyzing the hydrogeological data. The groundwater model was calibrated under the steady-state condition to produce the best match between the simulated and observed hydraulic head. The simulated outflow of the MODFLOW model was 358,221.09 m3/day which is nearly equal to 358,221.08 m3/day of groundwater inflow with a difference 0.01 m3/day and zero discrepancies. The subsurface inflow covers the most percentage (76%) in the budget and surface outflow contributes about 66% of the total groundwater outflow. The model result shows that the Kombolcha aquifer system is highly sensitive to change of hydraulic conductivity. Prediction of this aquifer behavior for increasing well withdrawal and decreasing recharge scenarios has been carried out. The effect of increasing withdrawal by 25, 50 and 100% results in a decline of groundwater level by 6.77, 12.15 and 24.37 m, respectively, whereas the effect of decreasing groundwater recharge by the same percentage of withdrawal results in a decline of groundwater level by 4.27, 6.34 and 11.25 m, respectively. This model can be as a tool to understand the aquifer system and sustainable utilization of groundwater resources.

Solute geochemistry and groundwater quality for drinking and irrigation purposes: a case study in Xinle City, North China

Xinle City is located in the upper reaches of the Daqing River basin, north China. Influenced by intense and extensive industrial and agricultural activities, sodium and nitrate pollution of the groundwater is becoming more and more serious in the study area. With an effort to quantitatively describe the present situation of groundwater and analyze the specific sources of the main ingredients, 32 well samples were collected and analyzed for understanding the hydrochemical characteristics and the suitability for drinking and irrigation purposes. Gibbs diagrams, Piper diagrams, solubility diagram, and ionic correlation analysis were used to assess the groundwater formation process. Drinking water quality index (DWQI) based on TDS, pH, K+, Ca2+, Na+, Mg2+, Cl−, HCO3−, SO42− and NO3− was used to evaluate the quality for drinking, while irrigation water quality index (IWQI) based on EC, Na%, permeability index (PI), sodium adsorption ratio (SAR), residual sodium bicarbonate (RSBC) and magnesium (MH) were used to assess the water quality for irrigation. The results demonstrated that the groundwater hydrochemical type in Xinle City is mainly dominated by the typical Ca∙Na-HCO3 and Ca-HCO3. Groundwater in the study area was found to be suitable for long-term drinking and irrigation. The abundances of ions are Ca2+>Na+>Mg2+>K+ for cations, and HCO3−>SO42−>NO3−>Cl−>F− for anions. The concentrations of Na+ and NO3− in groundwater are high in the study area. Particularly, the value of NO3− in some water samples far exceeds the WHO and Chinese standard limits. Na+ and NO3− are mainly of anthropogenic source, and they are from industrial pollution and agricultural pollution, respectively. Therefore, reducing the concentrations of Na+ and NO3− in groundwater is essential for the sustainable utilization of groundwater resources in the study area. The recommendations suggested in this research may provide insights for decision makers to make sound groundwater quality policies, and thus could be helpful to prevent further groundwater pollution in the study area.