High Groundwater Research Articles

Mapping of Groundwater Potential Zones in the Kuzhithuraiyar Sub Basin of Kodayar River, Kanniyakumari District, Tamilnadu: Using Analytic Hierarchy Process (AHP) and GIS


 
 
 Groundwater plays a very important role for all living beings. It is decisive to have a scientific understanding of groundwater management since, with careful use and replenishment, groundwater may help solve issues. The distribution of groundwater tables, slope, land-form, drainage pattern, lithology, topography, geological structure, fracturing density, opening and connectivity of fractures, secondary porosity, and landuse landcover all affect the occurrence and efficiency of groundwater in an aquifer system. An essential tool for assessing, tracking and protecting groundwater resources is the integration of geospatial techniques such as Remote Sensing and Geographic Information System for the identification of groundwater potential zones. This study aims to find the groundwater potential zones using Analytical Hierarchy Process (AHP) and managing the resources by creating different thematic layers such as rainfall, geology, geomorphology, drainage density, soil, slope, lineament and landuse landcover (LULC) of the Kuzhithuraiyar sub basin of the Kodayar river in Tamilnadu using the application of geospatial technologies. The thematic maps for all the thematic layers have been prepared using tools such as Interpolation, contour lines, Classification in ArcGIS 10.8. Theme weight and class rank were assigned to different thematic layers in weighed overlay analysis. The results were validated through field work and groundwater potential map was created. The groundwater potential zonation mapping was done by the overlay analysis in ArcGIS 10.8 software. The obtained map was classified into four categories namely very high groundwater potential zone, high groundwater potential zone, medium groundwater potential zone and low groundwater potential zone. The North Eastern part of the basin is considered as low groundwater potential zone while the Southern portion has high groundwater potentiality. The low groundwater potential zone covers an area of 10.58 sq.km and high groundwater potential zone covers an area of about 388.37sq.km.This study will be helpful for useful groundwater management for different tenacities.
 
 

Characterization of subsurface geology and hydrogeology in Kribi -Cameroon using electrical resistivity soundings and 3D-Implicit modelling: Baseline for groundwater resource management

This scientific article aims to characterize the geology and hydrogeology of Kribi, Cameroon for the purposes of water resources management, infrastructure development, and environmental protection. The specific objectives include mapping the subsurface electrical resistivity structure, identifying groundwater potential zones, and constructing a hydrogeological model for groundwater modelling. The study employed the Schlumberger method to map the electrical resistivity structure of the 3D subsurface and utilized 3D implicit modelling techniques to delineate groundwater potential zones. The study revealed that Kribi exhibits a highly complex geology, characterized by three-layered electrical resistivity models, typical of sedimentary and metamorphic formations. The major lithologies identified include laterite, clay, sand, quartz, and granite. The region encompasses areas with low water potential and brackish zones alongside high groundwater production areas. The study established the presence of aquifers within Kribi, with the unconfined aquifer found at depths ranging from 2 m to 13 m, and the confined aquifer extending from 14 m to 40 m. The aquifers are notably thick and productive, indicating substantial groundwater resources. Static groundwater volumes were estimated at 50,179,381 m3 and 317,118,946 m3 for the unconfined and confined aquifers respectively. Despite this potential, water resources management in the area is non-existent. The study recommends the implementation of Integrated Water Resources Management (IWRM) to improve water resource management, with a primary focus on groundwater modelling. The northern and southern regions of Kribi exhibit high permeability, which is advantageous for groundwater recharge and storage projects but also poses challenges for environmental remediation efforts. Consequently, safeguarding the delineated area for groundwater provision is of utmost importance.

Spatial distribution, sources, and human health risk assessment of elevated nitrate levels in groundwater of an agriculture-dominant coastal area in Hainan Island, China

In order to comprehend the groundwater nitrate contamination in Hainan Island, which is recognized as China's sole “tropical agricultural production base,” the distribution characteristics of nitrate in different aquifers and land-use types were elucidated through hydrochemical and geostatistical analysis methods. Principal component analysis (PCA), hierarchical cluster analysis (HCA), and absolute principal component score-multiple linear regression (APCS-MLR) were employed for qualitative and quantitative analysis of the nitrate source. The results showed that NO3−-high (>88.57 mg/L) groundwater accounted for about 10 % of the total distribution area of the western coastal area in Hainan Island. Moreover, the proportions of NO3−-high groundwater in pore water and fissure water were 10 % and 7 %, respectively. The order of groundwater nitrate concentration in different land-use types was as follows: bare land, cultivated land, construction land, grassland, and woodland. The main sources of elevated nitrate concentrations in pore water were animal feces and nitrogen/potassium fertilizers, accounting for 45.4 % of the overall contribution. These substances infiltrated through the vadose zone, leaching out and mobilizing selenium within this zone, ultimately leading to the characteristic enrichment patterns observed in pore water, including nitrate, arsenic, potassium, and selenium. Furthermore, the occurrence of high nitrate in fissure water was mainly attributed to the leaching of cultured manure, septic tank leakage, and infiltration of domestic sewage, accounting for a contribution rate of 32.9 %. Simultaneously, under oxidizing conditions, selenium became activated and entered groundwater through water flow, thereby exhibiting common enrichment characteristics with nitrate and potassium in fissure water. In addition, the assessment of human health risks revealed that 16 % and 40 % of groundwater samples posed unacceptable non-carcinogenic risks to adults and children respectively, with a higher risk for local children. The study recommends the reasonable application of chemical fertilizers, as well as the strengthening of sewage treatment capacity and standardized disposal of manure and feces, to reduce nitrate contamination of groundwater at source and ensure the safety of drinking water.

The estimation of infiltration and inflow in a sewage network by combining continuous monitoring of hydrological parameters, flow and temperature with stable isotopes of oxygen and hydrogen

The failure of sewage network systems can lead to the introduction of external water, impacting the capacity, performance, and environmental sustainability of urban infrastructures. This study examined methods for identifying and quantifying external water in a sewage system in cold climate conditions through the analysis of stable isotope of oxygen (δ18O) and hydrogen (δ2H) from samples, and continuous temperature monitoring, followed by the simulation of the network's hydraulics and temperature profile. The assessment was conducted during periods of low and high groundwater levels, specifically during dry weather flow. In comparison, the yearly trends of infiltration and inflow rates were assessed utilizing the moving minimum method. Using δ18O as a tracer, daily infiltration rates of 5.8 % and 35 % were estimated for periods of low and high groundwater levels, respectively. Using the outputs of the thermodynamic model, temperature was used as a tracer and the daily infiltration rates were found to be 1.5 % and 21.9 % for the same periods. The infiltration and inflow rate for the year in question was estimated to be 23 % using the moving minimum method. The findings of this study demonstrate the temporal variability of infiltration in networks and highlight the need for, as well as the potential of, a multi-faceted approach and continuous monitoring for the accurate estimation of external water before sewage network renovations are carried out.

Inhibiting effects of humic acid on iron flocculation hindered As removal by electro-flocculation on air cathode iron anode

Activated carbon air cathode combined with iron anode oxidation-flocculation synergistic Arsenic (As) removal was a new groundwater purification technology with low energy consumption and high efficiency for groundwater with high As concentration. The presence of organic matter such as humic acid (HA) had ambiguous effects on formation of organic colloids in the system. The effects of the particle size distribution characteristics of these colloids on the formation characteristics of flocs and the efficiency of As purification was not clear. In this work, we used five different pore size alumina filter membranes to separate mixed phase solutions and studied the corresponding changes in iron and arsenic concentrations in the presence and absence of humic acid conditions. In the presence of HA, the arsenic concentration of < 0.05 µm particle size components was 1.01, 1.28, 3.07, 7.69, 2.85 and 1.24 times of that in the absence of HA. At the same time, the arsenic content in 0.05–0.1 µm and 0.1–0.45 µm particle size components was also higher than that in the system without HA, which revealed that the presence of HA hindered the flocculation behavior of As distribution to higher particle sizes in the early stage of the reaction. The presence of HA affected the flocculation rate of iron flocs from small to large particle size fractions and it had limited effect on the behavior of large-size flocs in adsorption of As. These results provide a theoretical basis for targeted, rapid, and low consumption synergistic removal of arsenic and organic compounds in high arsenic groundwater.

Mapping coastal groundwater potential zones using remote sensing based AHP model in Al Qunfudhah region along Red Sea, Saudi Arabia

Due to the increases in agriculture and industry sector as well as high population, lack of water is becoming a major problem in the Middle East especially in arid regions. Saudi Arabia needs more groundwater research and explorations because of its higher water use and no source of freshwater. Assessing groundwater zonation in semi-arid locations is essential due to the significant degree of variation in groundwater depth, aquifer features, topographical characteristics, and insufficient precipitation. Mapping prospective groundwater zones in Al Qunfudhah region of southwestern Saudi Arabia has utilized the capability of the multi-criteria decision approaches (MCDA), and the Geographic information system (GIS). We have used the analytical hierarchy process (AHP) as one of the MCDA that is applied to achieve the objective of the current study by integrating twelve controlling factors. These factors are represented by the thematic layers; slope, precipitation, soil type, land use/cover (LULC), drainage density (DD), normalized difference vegetation index (NDVI), curvature, topographic position index (TPI), Terrain Ruggedness Index (TRI), drainage density (DD), and Lineament Density (LD). These thematic layers are combined with GIS to delineate the zones of groundwater potentialities. All factors were classified and weighted according to their importance and its effect on groundwater zones. Their normalized weights were evaluated using a pairwise comparison matrix. The present study shows that the groundwater potential zones (GWPZs) map is represented by five groups ranging between a very high zone with an area of 23781.06 Km2 that represents 4.04 % of the studied area, and a very poor GWPZ with an area of 182944.4 Km2 that represents 31.09 % of the studied area. The AHP model suggests that lineament density, slope, and drainage density are more important for determining the groundwater potentiality than other physiographic factors. The study's findings will be helpful in developing practical strategies for the region's groundwater supply. This analysis shows how the methodology may be used to study a broad coastal groundwater basin. The current study will give the decision makers to select suitable sites with a high groundwater potential.

Groundwater spring potential mapping: Assessment the contribution of hydrogeological factors

Groundwater, a fundamental asset, isn't effectively accessible in some parts of the world. The current research work pointed toward obtaining precise maps of potential groundwater zones. This study aimed for potential groundwater modeling and extracting the precise maps using four new advanced hybrid ML models (Dagging-HP, Bagging-HP, AdaBoost-HP, Decorate-HP) and one single model Hyperpipes (HP) in the Doji Watershed, situated in the eastern part of Golestan province, Iran. Among the selected models, the AdaBoost-HP model is the most efficient, with an AUC - ROC of 0.972, accuracy (0.922), sensitivity (0.906), and specificity (0.938), which gives the most promising values, when determining the collinearity between the 14 training factors, which are, in descending order of significance, LULC, Distance to stream (DtS), Topography wetness index (TWI), HAND, Distance to the road (DtR), Geomorphology, Topography position index (TPI), Lithology, Drainage density (DD), Elevation, Slope, Rainfall, and Clay (%). The AUC-ROC approach was employed to assess the model's performance along with Accuracy, Specificity, and Sensitivity. This model revealed that 7.37% has very high groundwater potential in the eastern and south-western parts of the study, whereas 36.8% has a very low groundwater potential in the north-western and south-eastern parts of the study. It can be said from this assessment that results obtained from this investigation are better and more reliable, which gives essential encouragement for further study put on this method for groundwater potential mapping of other areas of the world along with other areas of hydrogeological investigations.

GROUNDWATER VULNERABILITY MAP OF BASARA BASIN, SULAIMANI GOVERNORATE, IRAQI KURDISTAN REGION

The Basara basin which is one of the most promising hydrogeological basin in Iraqi Kurdistan Region, located in north east of Iraq, 25 km west of Sulaimani city, between the 496652 - 537752 East and 3911038 - 3951906 North in Universal Transverse Mercator (UTM) and lie in Zone 38N. The basin has a rectangular shape and covering an area of 571 km². The present hydrogeological investigations have revealed three inhomogeneous and anisotropic water bearing formations: Eocene Karstic Fissured Aquifer (EKFA), Intergranular Aquifer represented by Alluvium and Pliocene (AIA) &amp; (PIA), as well as Miocene Complex Aquifer (MCA).For the first time, not only in Kurdistan but also in Iraq, Groundwater Vulnerability Map has been constructed in this study, using DRASTIC method with the assistance of Geographic Information System (GIS) to show zonation area of high and low groundwater susceptibility to pollution. Accordingly, vulnerability classes of the study area were classified into four classes. Most of the basin shows the highest extension of the zones with very low and low vulnerability zones, in contrast the zones with high vulnerability are distributed mainly in the mountain areas, solely in the eastern Uloblagh and Kuwaik mountains, in addition to that small zones in the farthest northern corner and south western corner of the area have less or no human activity.

Analysis of the chemical characteristics and causes of high total hardness of groundwater in Jianghan Plain, China.

Familiarity with the chemical characteristics of regional groundwater can provide important guidance and reference for the development of regional groundwater exploitation. Jianghan Plain has been reported to have high groundwater total hardness (TH), resulting in the inability of local groundwater to be directly used as drinking water. In order to explore the causes of high TH, the paper analyzed the hydrochemical characteristics of shallow groundwater in Jianghan Plain combined with software of SPSS, JMP, and PHEEQC. The results showed that the cations in the groundwater in the area were mainly Ca2+, while the anions were mainly HCO3-. 20% of groundwater exceed the China national guideline for TH (i.e., 450mg/L). The groundwater chemistry in the study area was controlled by three main factors of dissolution of carbonate rocks, human activities, and redox conditions, among which the interaction between water and rock had the greatest impact. The water carbonate rock interaction within Jianghan Plain was affected by various factors such as water flow and aquifers and showed a gradually weakening trend from west to east. This work not only strengthened the understanding of the causes of the high TH of groundwater in the region, but also provided reference value for regional groundwater environmental management.

Hydrogeochemical characteristics, stable isotopes, positive matrix factorization, source apportionment, and health risk of high fluoride groundwater in semiarid region

Chronic exposure to high fluoride (F-) levels in groundwater causes community fluorosis and non-carcinogenic health concerns in local people. This study described occurrence, dental fluorosis, and origin of high F-groundwater using δ2H and δ18O isotopes at semiarid Gilgit, Pakistan. Therefore, groundwater (n = 85) was collected and analyzed for F- concentrations using ion-chromatography. The lowest F- concentration was 0.4 mg/L and the highest 6.8 mg/L. F- enrichment is linked with higher pH, NaHCO3, NaCl, δ18O, Na+, HCO3-, and depleted Ca+2 aquifers. The depleted δ2H and δ18O values indicated precipitation and higher values represented the evaporation effect. Thermodynamic considerations of fluorite minerals showed undersaturation, revealing that other F-bearing minerals viz. biotite and muscovite were essential in F- enrichment in groundwater. Positive matrix factorization (PMF) and principal component analysis multilinear regression (PCAMLR) models were used to determine four-factor solutions for groundwater contamination. The PMF model results were accurate and reliable compared with those of the PCAMLR model, which compiled the overlapping results. Therefore, 28.3% exceeded the WHO permissible limit of 1.5 mg/L F-. Photomicrographs of granite rocks showed enriched F-bearing minerals that trigger F- in groundwater. The community fluorosis index values were recorded at > 0.6, revealing community fluorosis and unsuitability of groundwater for drinking.

Determining land subsidence potential using the evidential belief function model: A case study for the Bardaskan Aquifer, Iran

AbstractIn this study, we employed the evidential belief function model (EBF) to evaluate the potential for land subsidence in the primary aquifer of Bardaskan. Through field visits, we recorded GPS coordinates for 174 land subsidence points. Factors considered in assessing land subsidence potential included well density, groundwater extraction rate, geological characteristics, proximity to faults, vegetation cover, distance from the river, slope, and land use. To develop and validate the model, 70% of the recorded points were randomly selected for training and implementation, while the remaining 30% were reserved for model validation. The number and percentage of land subsidence points in the different classes of the corresponding layers were determined by integrating the training points with influential variables maps such as distance from the river, distance from the fault, land use, and extraction volume. The EBF model rate was calculated for different layer classes. For modeling, all rates of the EBF model in each cell were summated, and the ‎potential of land subsidence was calculated.‎ Finally, the map of land subsidence potential based on the EBF model was determined with GIS. The results showed that most of the subsidence points were located in alluvial sediment of the Holocene period, in areas with high groundwater harvesting, a distance of at least 3000 m from a river, a distance of at least 6000 m from a fault, low‐density rangelands, slopes of at least 0%–2%, and farmlands and gardens. A receiver operating characteristic curve analysis of the EBF model showed that it could accurately predict land subsidence in 87.5% of cases using 30% of the validation data. This suggests that the model can be used for practical applications.

Mapping groundwater potential zone using groundwater potentiality index in Sulamu, Central Fatuleu and West Fatuleu, Kupang, East Nusa Tenggara

Water scarcity often occurs during the dry season in Kupang Regency, which is a semi-arid area. The drought limits surface water availability during the dry season, thus making groundwater one of the reliable solutions for fulfilling the need for water from springs and wells. Therefore, mapping the potential of groundwater in the research area becomes the aim of this study, which has never been conducted before. The method used in this research is the Groundwater Potentiality Index, which uses five parameters to identify groundwater potential areas: fracture, lithology, topography, drainage, and rainfall. Field observation and secondary data collection were conducted to provide those parameters. The results are groundwater potential index classified into five groundwater potential zones, resulting in very low (17.07% and 20.39% of total area), low (51.16% and 48.94% of total area), moderate (26.9% and 27.05% of total area), high (4.09% and 3.1% of total area), and very high (0.77% and 0.53% of total area). Zones of very high are found along major fault areas. Areas with high groundwater potential zones indicated favorable conditions for wells positioning at groundwater exploration. These results can be a basis for action related to groundwater resource development in the research area.

Investigation of fluoride concentrations, water quality, and non-carcinogenic health risks of borehole water in bongo district, northern Ghana

Access to potable water is a significant concern due to the increasing global threat posed by fluoride contamination in groundwater sources. This study investigated the concentrations of fluoride (F−), the suitability of groundwater for human consumption, the physicochemical characteristics affecting the water quality, and non-carcinogenic adverse health risks to both children and adults in the Bongo district in Northern Ghana. The findings revealed that the groundwater had a mean pH, salinity, TDS, conductivity, and turbidity below the WHO guideline values with a mean fluoride concentration of 1.76 mg/L above the guideline limit of 1.5 mg/L. The study also found that there was no strong relationship between fluoride and the measured water parameters, which may be attributed to poor control of distribution, transport mechanisms, and sources. The WQI scores ranged from 42.62% to 70.72%, indicating that all borehole water samples were of good and excellent quality. The average chronic daily intake showed that children are often more exposed to the harmful impact of fluoride than adults. The average HQ > 1 indicates the probability of dental and skeletal fluorosis after continuous exposure over time in adults and children. The study recommends taking immediate action to mitigate high groundwater fluoride concentrations, implementing appropriate water management strategies, and raising public awareness of the health risks. These measures can guide future groundwater management practices and help policymakers address contamination and protect local communities.

Determination of priority areas for the development of groundwater utilization in Pangandaran Regency

This research has the goal of determining priority areas in the Pangandaran Regency, which are the main priority in developing groundwater utilization. This research uses the Groundwater Potential Index (GPI) method, which is modified to suit the research area, and adds aspects of groundwater utilization parameters to find priority areas for developing groundwater utilization. In determining groundwater development priority areas, data from remote sensing and Geographic Information Systems (GIS) are needed, which are processed using the GPI and Analytic Hierarchy Process (AHP) method. This study uses eight parameters, including fracture (F), lithology (L), drainage (D), topography (T), rainfall (R), water utilization, land use, and population. The results of the analysis show that in areas with moderate levels of drought, there is still the possibility of groundwater potential, and it can be developed according to the level of water utilization. It was also found that the relationship between areas with very high groundwater potential and groundwater utilization will have the highest priority value in developing groundwater utilization. The estimated areas are divided into five zones: very high is 21.92 km2; high is 161.83 km2; medium is 407.87 km2; low is 502.45 km2; and very low is 7.07 km2.

Geological exploration of coal mine burnt rock and waterlogged area boundary based on transient electromagnetic and high-density electrical resistivity

The water-rich burnt rock may threaten the safe production of coal mines. Identifying the boundaries of burnt rock and the water-rich area is of great practical significance for the ensuring the safety of mining operations. Transient electromagnetic and high-density resistivity methods are commonly employed in geophysical exploration, such as for investigating the presence of groundwater or delineating boundaries of altered rocks. These methods are non-invasive and provide detailed information about subsurface conditions without the need for drilling or excavation. The Jiangjun Gobi No. 1 open-pit coal mine is situated in the Kalamaili fault zone and is characterized by a high groundwater content. In certain mining sites within the study area, the inflow of water reaches tens of thousands of cubic meters per day, which significantly impacts production and presents major risks. To accurately determine the boundaries of burnt rock and water accumulation areas in the Jiangjun Gobi No. 1 open-pit coal mine, this paper uses different geophysical prospecting methods based on the depth of the strata. The middle and deep parts are investigated using the high-resolution transient electromagnetic method, while the shallow parts are examined using the high-accuracy high-density electric method. Through analyzing the electrical characteristics of the study area, it is inferred that the low-resistivity area in the northwest represents a shallow surface water-rich region. This area extends continuously towards the northwest, is not trapped, and is supplied by surface water. The deep low-resistivity zone primarily consists of sandstone and coarse sandstone. It is inferred that the low-resistance area in the southern part of the study area is also a shallow surface water-rich region, extending towards the east and west sides, not trapped, and supplied by surface water. The deep low-resistivity zone mainly comprises a combination of sandstone, coarse sandstone, and burnt rock, with intermittent layers of mudstone and argillaceous sandstone. The boundary line of burnt rock (coal-bearing strata) is located in the south of the study area. The resistivity of burnt rock (coal-bearing strata) is higher than that of the surrounding rocks, and the resistivity of coal seams is slightly higher than that of sandstone with larger porosity. Estimating the boundaries of groundwater and altered rocks serves to prevent geological disasters and provides valuable information for mineral development and ecological protection.

Spatial Assessment of Groundwater Salinity and Its Impact on Vegetation Cover Conditions in the Agricultural Lands of Al-Ahsa Oasis, Saudi Arabia

This study investigated the complex relationship among groundwater salinity, soil texture, and vegetation health in Al-Ahsa Oasis, Saudi Arabia. Utilizing vegetation condition index data from 5 years of satellite imagery, alongside ground measurements of groundwater salinity and soil analysis, the study unveiled significant spatial heterogeneity. The vegetation health and groundwater salinity in the study area ranged from 27 to 70% and from 1.7 to 9.6 dS m−1, respectively, and exhibited contrasting patterns, with a high vegetation condition index (healthy vegetation) in the north and east versus high salinity in the southwest. The applied cross-tabulation statistics revealed a strong negative correlation between the vegetation condition index and salinity, with “good” and “normal” vegetation health primarily coinciding with “slightly saline” groundwater. Soil texture further modulated the vegetation response, as “Silt loam” soils corresponded with “good” VCI, while “silty clay loam” only supported “dry” and “normal” conditions. The applied spatial autocorrelation analysis confirmed this, showing low vegetation clustering with “silt” texture and high salinity in the mid-west of the study area (p &lt; 0.05). Outlier districts hint at local factors beyond simple salinity–vegetation health relationships. Finally, a conditional plot, applied as a spatial statistical approach, revealed that low vegetation health spatially correlates with high groundwater salinity (&gt;5 dS m−1) on “silt loam” in the mid-west, while a higher vegetation condition index aligned with lower groundwater salinity in the east and north. These findings highlight the critical role of spatial variability and the need for advanced modeling and data integration to understand and predict the responses of vegetation to environmental challenges, and will be crucial for optimizing water management to ensure the long-term sustainability of Al-Ahsa Oasis.

Evaluating groundwater resources trends through multiple conceptual models and GRACE satellite data.

In this research, three numerical groundwater flow models, developed and calibrated from three equally plausible conceptual models over the Nasia Basin, have been used to assess groundwater resources variations over a transient period. The use of multiple numerical models reduces the effect of uncertainties in conceptual model formulation. All the three calibrated numerical models indicate an increasing trend of groundwater recharge and storage over the period of the groundwater level monitoring. This suggests that the prevailing erratic climatic conditions in the area are conducive for increasing groundwater recharge and storage in the terrain. The high-intensity, short duration rainfall patterns, attending climate change in the basin, enhance high levels of infiltration and percolation, leading to steadily increasing groundwater recharge. Groundwater recharge estimates from each of the models over the transient period appear to reflect the pattern of seasonal variations in rainfall in the region. Data from the models indicates a significant role of baseflow in sustaining perennial streamflow in the area. This presents a significant development in terms of groundwater-based adaptation projects, especially in agriculture. The trend of groundwater recharge in the Nasia Basin is in sync with regional groundwater storage variations estimated from the Gravity Recovery and Climate Experiment (GRACE) satellite data collected and processed over the Volta Basin. At the Volta Basin level, groundwater storage variations indicate a strong positive trend of increasing groundwater recharge from 2002 (beginning of the GRACE mission) to 2022 (end point of the data used for this research). Analysis of the GRACE data suggests that there is a cumulative increase in groundwater storage by 30cm, representing approximately 120 km3 of groundwater over the period in the basin. This translates into approximately 15mm/year of groundwater storage increase. Thus, at both the regional and local levels, groundwater appears to be responding positively to the impacts of erratic rainfall patterns observed in the area recently. The high-intensity, short duration rainfall patterns appear to favor significant groundwater recharge, resulting in a strong positive groundwater storage signal. The high positive groundwater storage signal suggests increasing groundwater resources potential in the area, indicating promising opportunities for groundwater-based climate change adaptation interventions.

Identification of Deep and Shallow Groundwater Potential Zones using GIS Techniques; Case Study: Monaragala District, Sri Lanka

One of the most crucial steps in the management of groundwater sources sustainably is the delineation of the zones with potential for groundwater. However, in addition to taking a lot of time and money, groundwater investigations can be difficult and complex in many locations. To get sufficient results, it needed to demarcate shallow and deep groundwater potentiality separately. Sri Lankan districts have various problems due to a lack of water. With population growth and urbanization, surface water is insufficient to meet the water requirement. This study focused on groundwater potential mapping in Monaragala district covered with the total are 5708 km2 in Sri Lanka. The fuzzy overlay and weighted overlay method integrated with GIS were mainly used to determine potential zones for deep and shallow groundwater. The final results from the two overlaying methods were compared to identify most accurate locations. Six parameters, namely aquifer type, soil depth, soil group, rainfall, proximity to surface water bodies, and slope, were evaluated for the shallow groundwater studies. Proximity to lineament, geology and shallow groundwater parameters were assessed for profound groundwater potentiality. The final output resulting maps were categorized into five main categories such as extremely low, low, moderate, high and extremely high by considering obtained potential values. The deep groundwater potential map demonstrates that the high groundwater potential areas are located around the lineaments, prominently areas having mountain ranges. Therefore the effect of the lineament is very high for deep groundwater availability. High shallow groundwater potential areas are located in smaller regions from Katharagama, Thanamalwila and Siyambalanduwa. Obtained results were validated using existing 220 tube well data and 100 dug well data. &#x0D; Keywords: Fuzzy overlay, Geology, GIS, Groundwater, Weighted overlay

Surface water-groundwater interactions drive the spatial variability of dissolved heavy metals and interfacial fluxes in mangrove intertidal zones

The intertidal aquifer is a crucial area that significantly influences the transport of heavy metals and the health of coastal environment. In this study, we used a 3-dimensional sampling method to analyze the spatial variability of heavy metals in the groundwater of the mangrove intertidal zone in China. The pollution level of heavy metals and their release processes into coastal waters through groundwater discharge were also explored. Our findings revealed high spatial heterogeneity of heavy metals occurred along the cross-shore, parallel-shore, and depth directions. Specifically, heavy metals exhibited inconsistent variation trends between the seawater infiltrated zone and groundwater discharge zone along the cross-shore direction. Fe, Cr, Cu, Zn, and Pb exhibited a similar variation trend along the cross-shore direction, but were opposite to that of Hg and As. In addition, most heavy metals showed higher concentrations in mangrove groundwater compared to inland pond water and coastal seawater, indicating that mangrove intertidal zone played a crucial role in sequestering heavy metals. The spatial variability of heavy metals can be attributed to different exchange types and magnitudes between the surface water and groundwater, as well as the complex biogeochemical reactions. Our study also identified a slight pollution level of Zn and Hg, and high groundwater discharge-derived fluxes of Hg and As compared with other study sites in the world. In addition, this study highlights the importance of considering different groundwater end-member, especially for redox sensitive heavy metals, when determining groundwater discharge-derived fluxes into the surface water in mangrove intertidal zone.

Aquifers Recharge Potentiality Evaluation using Bivariate and Multivariate Statistical Analysis: A Case Study in Malwathu Oya River Basin

An aquifer is a body of porous rock or sediment saturated with groundwater that plays a vital role in the hydrological cycle. Due to rapid population growth and urbanization, these valuable resources face threats like climate changes, pollution, and over-exploitation. Overdraft, where extraction exceeds recharge, can lead to groundwater depletion. Although Sri Lanka is not considered a water- scarce country, it faces rising water demands due to rapid population growth. Especially in dry zones, groundwater is crucial for drinking and agriculture; unauthorized agro-wells exacerbate groundwater issues. Therefore, this research aims to assess groundwater recharge potential zones in Malwathu Oya river basin using Bivariate and Multivariate statistical analysis. Comparing these techniques will lead to the precise identification of potential recharge areas. And this study primarily focuses on the implementation of GIS to find solutions for this kind of challenge without performing field investigations. Therefore, eight conditioning factors; water level, electrical conductivity, lithology, soil, slope, lineament density, drainage density and land use were selected as groundwater recharge influencing factors. The well inventory database consisted of 380 well locations and, out of these, 70% was considered as the training dataset, and the remaining 30% was taken as the testing data set. Groundwater recharge potential maps (GRP) were developed in ArcGIS 10.8, based on the results obtained from Frequency Ratio (FR), Logistic Regression (LR) and their ensemble method. For testing the accuracy of the FR model, test well locations were cross tabulated with the GRP map, and the highest well percentage was achieved in high groundwater recharge potential zone (37.39%). In the LR model, cross-tabulation results showed that 62.61% of testing wells were in the very high potential zones. The ensemble method of FR and LR revealed that 53.04% of test wells fall into the very high potential class. Hence, it can be assumed that LR predictions are more reliable than the FR model. To further validate the LR model and ensemble model, Receiver Operating Characteristics curve method was used. The Area Under the Curve (AUC) values for Success rate curve (SRC) and prediction rate curve (PRC) in LR method were 63% and 57% respectively. In ensemble method, the AUC values for SRC and PRC were 89% and 75%. These results indicate that the LR model is relatively poor estimator, whereas FR and LR ensemble method is relatively good estimator to evaluate groundwater recharge potential in Mulwathu Oya river basin.&#x0D; &#x0D; Keywords: Area under curve, Frequency ratio, GIS, Groundwater recharge, Logistic regression&#x0D;