Total Recharge Research Articles

Evaluation of Groundwater Resources in the Middle and Lower Reaches of Songhua River Based on SWAT Model

The SWAT model primarily investigates sources of water pollution and conducts ecological assessments of surface water in contemporary hydrology and water resources research. To date, there have been limited accomplishments in the study of groundwater resources in China. The MODFLOW model currently primarily simulates groundwater levels and the migration of water quality, depending on the hydrological surface water data in the relevant area. This study aims to investigate the groundwater distribution characteristics of the middle and lower reaches of the Songhua River, a significant agricultural and grain production region in China. The research focuses on the middle and lower reaches of the Songhua River basin in Northeast China and employed the SWAT distributed hydrological model to simulate runoff. The monthly recorded runoff at Tongjiang Station in Jiamusi City was utilized to calibrate the model parameters. Consequently, the MODFLOW model was introduced to compare and assess the simulation outcomes of the SWAT model, ultimately ascertaining the distribution characteristics of shallow groundwater, groundwater recharge, recoverable volume, and groundwater levels in the Songhua River Basin. The findings indicate that: (1) The SWAT model demonstrates efficacy in the study region, achieving R2 and NS values of 0.81 and 0.76, respectively, thereby fulfilling the fundamental criteria for scientific research. The MODFLOW model exhibits strong performance in the study region, achieving a periodic R2 of 0.98 and a verification R2 of 0.97, with the discrepancy between simulated and actual groundwater levels confined to 0.6 m, thereby satisfying the criteria for scientific research. (2) In 2011, 2014, and 2016, the groundwater recharge in the middle and lower sections of the Songhua River was 24.33 × 108 m3, 30.79 × 108 m3, and 32.25 × 108 m3, respectively, aligning closely with the SWAT simulation results, while the average annual groundwater level depth was 8.17 m. (3) In the research area, groundwater recharging occurs primarily by atmospheric precipitation, while drainage predominantly transpires via groundwater as base flow, constituting 81.46%. Secondly, the recharge of shallow groundwater to deep aquifers is around 7.14%, with a minimal share attributed to vadose zone loss, constituting merely 2.1%. (4) From 2010 to 2016, the average groundwater runoff modulus of the middle and lower reaches of the Songhua River basin was 1.005 L/(s·km²), with a total recharge of 216.58 × 108 m3 and a total recoverable amount of 105.11 × 108 m3. The mean yearly supply was 25.11 × 108 m3. The total groundwater recharge was 26.54 × 108 m3 in the driest year (2011) and 33.25 × 108 m3 in the year of most ample water (2016).

Influence of Spring Water Residence Time on the Irrigation Water Stability in the Hani Rice Terraces

The stability of irrigation water is critical for the sustainability of alpine agriculture. Based on monthly precipitation and terraced field water and spring water samples obtained between 2015 and 2016, the study used the mean residence time and isotope mixing model to analyze the influence of spring water residence time on irrigation water stability in the Hani Rice Terraces. The results indicate that: (1) The mean residence time of precipitation and terraced field water in spring water was 2.46 years and 1.55 years, respectively, implying that the terraced field’s irrigation water source could be refilled by spring water recharged 1.5–2.5 years ago. (2) The mean residence time of precipitation in ascending and descending springs was 2.73 years and 1.95 years, respectively. The mean residence time of terraced field water in ascending and descending springs was 1.54 years and 1.04 years, respectively. The ascending spring’s recharge water residence time is 0.5–0.8 years longer than that of the descending spring, indicating that the spring water exhibits intra-seasonal and inter-seasonal staggered peak recharging. At the same time, the total recharge period of the ascending–descending spring is extended to 1–3 years, which means the terraced fields have a drought resistance of three years. (3) The mean residence time of precipitation and terraced field water at higher altitudes in the ascending spring is 2.52 times and 3.73 times, respectively, while in the descending spring, it is 3.36 times and 6.49 times to the lower altitude region. This means that the mean residence time of the recharge water source in the lower terraced fields was shorter, and the elevation difference between ascending and descending springs was smaller, thereby regulating the spatial homogeneous distribution of recharge water sources in the terraced fields.

Assessment of the impact of rainfall uncertainties on the groundwater recharge estimations of the Tikur-Wuha watershed, rift valley lakes basin, Ethiopia

Spatial recharge estimation uncertainty is directly proportional to uncertainty in input precipitation data Thus, the main objective of this study was to investigate the recharge uncertainty by using improved spatial rainfall observations. The physically based fully distributed hydrological model WetSpa was used to simulate 20,000 possible combinations of parameters for two model setup. The M1 model setup was developed based on the rainfall measurements obtained from rain gauge stations scattered in and around the Tikur-Wuha watershed in Ethiopia, while M2 model setup was developed using bias-corrected satellite rainfall estimates (SREs) based on Climate Hazards Group InfraRed Precipitation (CHIRP) merged with relevant ground station records. The required parameter combinations were generated using Monte Carlo simulation stratified by applying Latin Hypercube Sampling (LHS). One hundred best performing parameter combinations were selected for each model to generate spatial recharge statistics and assess the resulting uncertainty in the recharge estimates. The results revealed that enhanced spatial recharge estimates can be produced through improved CHIRP-based SREs. The long-term mean annual recharge (218.29 mm) in the Tikur-Wuha watershed was estimated. Model parameter calibration performed using discharge measurements obtained from the Wosha rain gauge station located in the subcatchment area of the Tikur-Wuha watershed had a Nash-Sutcliffe efficiency of 0.56. Seventy percent of the watershed showed a coefficient of variation (Cv) < 0.15 for M2, while 90 % of the area exhibited a Cv < 0.15 for M1. Furthermore, the study findings highlighted the importance of improving evapotranspiration data accuracy to reduce the uncertainty of recharge estimates. However, the uncontrolled irrigation water uses and the total recharge coming from the irrigation fields scattered across the Tikur-Wuha watershed were not considered in the study, which is a limitation of the study. Future studies should consider the contribution made by irrigation water to the total recharge of the watershed.

Hydrodynamic Groundwater Modeling and Hydrochemical Conceptualization of the Closure Mining Area of the WuMa River Watershed of China.

The WuMa River (WMR) watershed is located in Renhuai City, Guizhou Province of China, which is a first-class tributary of the Chishui River. The geochemical investigation mainly included the determination of groundwater pH, total hardness, total dissolution solid, major cationic and anionic, and the geochemical groundwater modeling. The principal component analysis (PCA) and Gibbs model were used to analyze the pollution type and geochemical composition. The geochemical investigation results show that the cations of groundwater are dominated by Ca2+ and the anions are dominated by HCO3-; therefore, two main hydrochemical types in the study area are identified as Ca2+-Mg2+-HCO3- and Ca2+-Mg2+-SO42-. The chemical composition of groundwater in this area is mainly controlled by weathering of the carbonate rocks. The ion concentration of groundwater in the study area exhibited significant spatial variability between dry and wet seasons, while temporal changes of cationic and anionic concentrations exhibited irregularities. In PCA and FA analysis, PC1, PC2, and PC3 were extracted, which could explain 51.92, 26.98, and 12.61% of the total information, respectively. F1 explained 67.44% of the total variance, among which Ca2+, Mg2+, K+, SO42-, and Cl- contributed the most among the factors and were the main factors controlling the chemical composition of groundwater. The relative error between the measured water level and the simulated water level is less than 2%, which meets the requirements of simulation accuracy. During the simulation period of the model, a total recharge of 339.05 × 104 m3 was observed in the simulated area, primarily attributed to infiltration from rainfall. The total excretion amounted to 330.78 × 104 m3, primarily through evaporation, with a minor amount of lateral outflow. The migration pathway of pollutants in groundwater primarily follows the direction of groundwater flow while diffusing vertically. The migration range of the pollutant is in accordance with the direction of groundwater flow and extends along the larger hydraulic gradient, demonstrating consistency. The findings of this study serve as a reminder that the closure of coal mines can constitute a significant source of water pollution. Simultaneously, they offer empirical data and theoretical references for the simulation and prediction of groundwater contamination in enclosed coal mines.

Optimizing groundwater pumping in small island groundwater lenses: An analytical approach

For residents living on small islands, groundwater serves as their primary source of freshwater, which exists in the form of a freshwater lens floating above denser seawater. Previous research on optimizing pumping strategies in freshwater lenses focused on pumping from fixed wells using numerical models, and optimal well locations have not been explored. In this study, we analyze pumping optimization for both fixed well cases and moving well cases in a rectangular island using an analytical approach. This approach allows for a clear understanding of the relationship between hydrogeological parameters and optimization results. For fixed well cases, we provide an analytical solution for the critical pumping rate of each well. For moving well cases, Bayesian optimization is employed to efficiently search the extensive space of possible well locations and identify the critical pumping rate. Our results reveal that the well location has a substantial impact on the critical pumping rate in the fixed well cases, indicating that investigating the optimization of well placement is essential. In the discussion of the moving well cases, the maximum total pumping rate of a pumping well network is independent of hydraulic conductivity, and the critical pumping percentage relative to total recharge is independent of both hydraulic conductivity and recharge. The distribution of optimized well locations for islands with a fixed aspect ratio but different sizes follows the same pattern. In the moving well cases, different solutions can achieve the same maximum pumping rate, especially when multiple wells are involved. In addition, our approach is applicable to scenarios where new wells are added to an existing well system. Our solutions and findings significantly contribute to a deeper understanding of the hydraulic performance of pumping activities from freshwater lenses and offer valuable insights for developing more sustainable and robust groundwater management strategies in small islands.

Quantifying groundwater recharge in the Venetian high plain between the Brenta and Piave Rivers through integrated surface–subsurface hydrological modeling

Study regionVenetian high plain between the Brenta and Piave Rivers, Northeast Italy. Study focusGroundwater recharge is the process by which aquifers, i.e., the groundwater reservoirs, are replenished. In many regions, recharge fluxes are currently declining due to more frequent hydroclimatic extreme events and unsustainable land use management. In this study, CATHY (CATchment Hydrology), an integrated surface–subsurface hydrological model (ISSHM), is used to estimate current and future recharge fluxes in a study area that represents an important source of drinking water supply for the Treviso province (Veneto Region, Northeast Italy). In particular, we aim to evaluate the impacts on recharge of a scenario with changed irrigation management, planned in compliance with European directive indications, to decrease water withdrawals from the Piave River and preserve its ecological flow. The model was first calibrated through a combination of FePEST and the Shuffled Complex Evolution algorithm, whereby both the bottom of the unconfined aquifer and the hydraulic conductivity field were tuned. After a validation step, the resulting model was used to simulate a scenario in which the flood irrigation method, currently the most widespread in the study area, is fully replaced by sprinkler irrigation. New hydrological insights for the regionOur results show that, in response to a 50 % decrease in water withdrawn from the Piave River, the total recharge decreases by about 10 %, with a local reduction in groundwater head, mainly limited in wells located in the area directly affected by the conversion of the irrigation technique. The model suggests that most of the recharge fluxes occur in irrigated areas where the hydraulic conductivity is higher. Overall, this work resulted in the development of an ISSHM capable to reproduce groundwater dynamics and its drivers at high resolution and large scale. Although it can still be improved, the model represents a useful tool to investigate possible responses of the considered hydrosystem to future land use and climate change.

Effects of various land utilization types on groundwater at different temporal scales: a case study of Huocheng plain, Xinjiang, China

Different land utilization types have unignorable impacts on adjacent aquifers, so studying the effects of varying land utilization types on groundwater balance and groundwater table in arid and semi-arid areas is crucial to facilitate the rational development of territorial space and groundwater resource management. This study investigated the relationship between land utilization type variations and groundwater dynamics from spatial and temporal scales in Huocheng plain, Xinjiang, China, via taking advantage of different land utilization maps provided by remote sensing techniques in 1990, 2000, and 2015. Based on the analysis of results, the findings can be summarized as follows. First, the cultivated and construction land has expanded significantly in the past 25 years. The migration of the regional center of cultivated land was insignificant, as it is still located almost in the center of the entire study area. However, the transfer span of the location center of construction land was more prominent, and its moving direction was mainly from south to northeast, directly affecting the groundwater balance state and groundwater table. Second, the total amount of groundwater storage exhibited a remarkable reduction, from a recharge in 1990 to a continuous discharge in 2000–2015, during which the total recharge and discharge had both continuously declined. Meanwhile, recharging and discharging elements were also changed profoundly as less groundwater recharges from ambient aqueous environments and more groundwater extraction. Thus, human activities were the fundamental driving terms causing the changes in groundwater sources. Third, the groundwater table gradually and continuously dropped from south to northeast in the study area over time. The drawdown of spatially averaged groundwater tables was positively correlated with construction and cultivated area extension. In addition, compared to the former literature, this study offers an alternative approach for groundwater protection and optimization of territorial space development and utilization in arid and semi-arid areas.

Numerical analysis of surface hydrogeological water budget to estimate unconfined aquifers recharge

Under changing climate, groundwater resources are the main drivers of socioeconomic development and ecosystem sustainability. This study assessed the contribution of two adjacent watersheds, Muse Street (MS) and West Wood (WW), with low and high urban development, to the Memphis aquifer recharge process in central Jackson, Tennessee, USA. The numerical MODFLOW model was created using data from 2017 to 2019 and calibrated using reported water budget components derived from in-situ data. The calibrated MODFLOW model was then used to investigate the impact of high and low urban developments on the recharge rate. The hydraulic parameters and recharge rates were optimized by adjusting the groundwater level based on the observed water level using PEST. The stochastic modeling was also carried out using the Latin Hypercube approach to reduce the uncertainty. The calibration results were satisfactory, with RMSE of 0.124 and 0.63 obtained in the WW and MS watersheds, respectively, indicating accurate estimation of the input parameters, precisely the hydrodynamic coefficients. The study results indicate that, per unit area, the MS watershed contributes 119% more to recharge and 186% more to riverbed leakage compared to the WW watershed. However, regarding total recharge and riverbed leakage, the WW watershed contributed more than the MS watershed. The results of this study have enhanced the knowledge of the impact of urbanization on hydrology and the recharge process in watersheds with diverse land uses.

Study on the simulation of reservoir water environment and the optimization of ecological water replenishment effect: Taking Luhun Reservoir as an example

Abstract With global climate change and extreme weather events, water scarcity and environmental degradation are becoming increasingly prominent. Ecological replenishment is one important measure to enhance water quality in reservoirs. To address the severe pollution and ecological degradation problems of the Luhun Reservoir, this paper uses MIKE21 software to construct a coupled hydrodynamic-water quality model. Six recharge scenarios were designed to compare and explore the enhancement of reservoir water quality for these scenarios. The water quality status of these options was evaluated using the single-factor index method and the combined pollution index method. The results show that due to the ecological replenishment, the pollutant concentration leads the phenomenon of gradient diffusion to the center of the reservoir, and the average improvement rate of water quality is up to 40.22%. Schemes 2 and 5 have the lowest integrated pollution index. The most significant improvement in water quality was achieved at the same total recharge conditions, using 0.5 times the flow rate and two times the recharge time of the actual recharge project. The study results provide theoretical and technical support for the future management of the reservoir water environment.

Water budget study for groundwater recharge in Indus River Basin, Punjab (Pakistan)

Abstract Assessing groundwater recharge is crucial for managing and governing water resources in any region. Indus River Basin (IRB) is an area that relies heavily on canal and groundwater irrigation. The replenishment of groundwater is largely dependent on surface water supplies. The purpose of this research is to determine the amount of groundwater recharge from various sources in Rachna Doab. The study employed the water budget method to calculate seasonal groundwater recharge during the Rabi (October–March) and Kharif (April–September) (Summer) periods from 2005 to 2011. The main components of the recharge were rainfall, water conveyed through channels, and irrigation water applied to cultivated fields. Conversely, the extraction of water from private and public tube wells was the discharge component of the study. Groundwater levels increased during the Kharif season but decreased during the Rabi season. Average recharge contribution from rainfall was 45 and 14% during the Kharif and Rabi seasons, respectively. The total annual recharge from watercourses and irrigation fields was estimated to be approximately 33% of the total recharge. Rainfall was the most significant source of long-term seasonal recharge, followed by watercourses and irrigation fields. In general, the average depletion of the reservoir was 94 million cubic meters per season.

Climate Change Implication on Palestine: A Case Study Jenin Governorate

Climate change negatively affects sustainable development in Palestine, especially Jenin Gover-norate, which is the food basket for Palestine. This study identified climate change variables in Jenin Governorate for more than 100 years, especially temperatures and precipitation, derived from historical data to study the manifestations of climate change and its impact on water re-sources and the agricultural sector. The impact of climate change on groundwater wells is an un-derstatement. The majority of Jenin’s water wells, which number about 66 (including 22 agricul-tural wells), are located in the northeastern basin. By analyzing the data for the average annual total recharge of this basin, it was evident that the recharge had decreased from about 151 million cubic meters/year from 1976-1992 to about 134 million cubic meters/year during 1993-2009. (about 11.3%). This is because of the general solid decrease in rainfall in the Jenin area due to the effects of climate change. The decrease in recharge, coupled with increased groundwater pump-ing, has drained the reservoir stock and deteriorated the groundwater quality. The other source of water in Jenin Governorate is springs. Jenin Governorate has 42 streams largely used for small-scale agricultural and household needs. The research showed that the discharge of the springs increases from 2014 to 2020 (average discharge 0.48 MCM/yr.) compared to the period 2001 to 2011 (average discharge 0.48 MCM/yr.). years) due to the increase in the amounts of discharge from the springs and the start of relying on them more, as Jenin governorate is facing water scarcity recently. In the future, climate change will considerably impact water resources, altering surface and underground water supplies for residential and commercial purposes, irriga-tion, in-stream ecosystems, and aquatic leisure.

Based on the Numerical Simulation Analysis of the Impact of Coal Mining in the Land Conservation Area

As China pays more attention to the protection of water resources, there are overlapping areas between the planned reservoir conservation area and planned coal mine field. In the coal mining process, a water-conducting fracture zone is formed after the roof of the goaf is damaged, and cracks also generated on the surface of the mining area. In order to study the effect of coal mining on the recharge of surface water into the reservoir in the land conservation area, FLAC3D and Visual MODFLOW are used to simulate the development law of water-conducting fracture zone and surface subsidence cracks in the roof of the coal seam after coal mining in the land conservation area of the reservoir. Prediction and analysis on the change of the reservoir recharge capacity after coal mining in the land reserve are conducted. The results show that the maximum growth height of the water-conducting fracture zone in the overlying strata of the goaf after coal mining in the secondary land conservation area of the reservoir is not connected with the surface subsidence fracture. However, coal mining induces partial aquifer drainage in the roof of the coal seam, increasing the amount of surface water flowing to groundwater. Therefore, the maximum drop in the water level of the reservoir is 0.19 m, and the maximum recharge of the reservoir is 52,900 m33/a, accounting for 0.89% of the total recharge. It demonstrates that coal mining in the secondary land conservation area has little effect on the recharge of the reservoir. On the basis of good ecological compensation, water saving and comprehensive utilization of mine water, coal mines need to further carry out research on mitigating the adverse effects of coal mining on the reservoir’s land conservation area.

Influence of intensive agriculture and geological heterogeneity on the recharge of an arid aquifer system (Saq–Ram, Arabian Peninsula) inferred from GRACE data

Abstract. This study assesses the detailed water budget of the Saq–Ram Aquifer System (520 000 km2) over the 2002–2019 period using satellite gravity data from the Gravity Recovery And Climate Experiment (GRACE). The three existing GRACE solutions were tested for their local compatibility to compute groundwater storage (GWS) variations in combination with the three soil moisture datasets available from the land surface models (LSMs) of the Global Land Data Assimilation System (GLDAS). Accounting for groundwater pumping, artificial recharge, and natural discharge uniformly distributed over the Saq–Ram domain, the GRACE-derived mass balance calculation for water yields a long-term estimate of the domain-averaged natural recharge of (2.4±1.4) mm yr−1, corresponding to (4.4±2.6) % of the annual average rainfall (AAR). Beyond the regional-scale approach proposed here, spatial heterogeneities regarding the groundwater recharge were identified. The first source of heterogeneity is of anthropogenic origin: chiefly induced by irrigation excess over irrigated surfaces (about 1 % of the domain), artificial recharge corresponds to half of the total recharge of the aquifer. The second source of recharge heterogeneity identified here is natural: volcanic lava deposits (called harrats on the Arabian Peninsula) which cover 8 % of the Saq–Ram aquifer domain but contribute to more than 50 % of the natural recharge. Hence, in addition to this application on the Arabian Peninsula, this study strongly indicates a major control of geological context on arid aquifer recharge, which has been poorly discussed hitherto. Due to large lag times of the diffuse recharge mechanism, the annual analysis using this GRACE–GLDAS approach in arid domains should be limited to areas where focused recharge is the main mechanism, while long-term analysis is valid regardless of the recharge mechanism. Moreover, it appears that about 15 years of GRACE records are required to obtain a relevant long-term recharge estimate.

Considerations on the water supply of the aquifer-wetland systems in Colombia from the GRACE satellites data interpretation

[Introduction]: Thanks to the recent data provided by the GRACE satellites, it is possible to establish a prelimi- nary estimate of changes in groundwater storage (GWS), thus offering a new and unprecedented tool for studying the dynamics of aquifer-wetland systems. [Objective]: As a result of the trends observed in GRACE for the Magdalena-Cauca basin in Colombia, this study investigates the water availability of the aquifer-wetland systems. [Methodology]: For this purpose, a map overlay analysis was performed using GRACE data to estimate ground- water recharge and discharge for different basins and aquifer-wetland systems. [Results]: Considering the trends in groundwater storage (GWS), we obtained water volumes and translated these into recharge and discharge esti- mates of the aquifer-wetland systems identified in the Magdalena-Cauca basin. These values show a total recharge between 2002 and 2010 of 284.65 mm, followed by a loss of 490.68 mm between 2011 and 2017. Furthermore, good correspondence was observed between the ENSO and GWS events, especially during the strong 2010-2011 La Niña and 2015-2016 El Niño events, which caused severe impacts in the country and that were particularly evi- dent in the Mojana wetland area located in the north of the basin. [Conclusions]: Although these results have yet to be validated with continuous monitoring data, the results presented in this study raise questions on the formulation of better policies and management of water resources that promote future water security.

Jointly estimating recharge and groundwater withdrawals of the NWSAS by inverting GRACE/GRACE-FO gravity data

A new approach is proposed for estimating groundwater recharge and withdrawals in North Western Sahara Aquifer System (NWSAS) by inverting 18-years of Gravity Recovery And Climate Experiment (GRACE/GRACE-Follow-On) data. In this study, only groundwater component was found contributing to GRACE-based terrestrial water storage change. By considering the inter-zone heterogeneity of potential recharge and water withdrawals in the groundwater balance equation, total recharge and water output rates are estimated at both cell-grid and the whole of NWSAS scale levels. 1.9 and 5.2 km3/year were determined for total recharge and water-output rates, respectively, corresponding to -3.3 km3/year of depletion. After subtracting from the total recharge both artificial and assumed-quaternary recharges, 1 km3/year was found for actual recharge, similarly as reported elsewhere. For water withdrawal, the estimated rate is 4.75 km3/year, higher than those published in other studies. The agreement found between our results with other authors have served to validate our approach.

Probability Distribution for Water Fluxes in a Heterogeneous Unsaturated Zone Using an Ensemble of 1D Simulations

Groundwater recharge plays an important role in water resource management. In arid and semi-arid areas, the groundwater recharge under agricultural fields constitutes a large portion of the total recharge. Estimating the agricultural recharge is important for groundwater management and assessing contamination risk. However, estimations of the recharge fluxes are difficult due to the soil heterogeneity and the complex nature of the flow processes in the soil. Here, we suggest a new method for estimating the recharge flux probability distribution that accounts for the soil heterogeneity. The method is demonstrated using a unique data set of long-term continuous measurements of water content under an agricultural field. The measurements are used to assign weights to a large ensemble of hydraulic parameter sets. The weights are then used to derive the probability distribution of flux under different agricultural practices. We found that the distribution of the recharge fluxes varies considerably between one annual crop and a cycle of three crops over 2 years. However, the distribution of the fraction of the input water that infiltrates does not vary much between the two practices. Under natural conditions, with no irrigation, the recharge flux is much smaller, and its distribution is narrower. Our approach provides the full probability distribution of fluxes rather than a single expected value of the flux or its mean.

Spatial assessment of groundwater potential using Quantum GIS and multi-criteria decision analysis (QGIS-AHP) in the Sawla-Tuna-Kalba district of Ghana

Study regionSawla-Tuna-Kalba (4226 km2). Study focusThis study employed QGIS to assess the groundwater potential in the Sawla-Tuna-Kalba district of Ghana with some selected surficial factors while estimating the groundwater recharge from 1981 to 2021. New hydrological insightsAmong the classification algorithms tested, Random Forest (RF) yielded the highest overall accuracy with 93.63% while Support Vector Machine (SVM) and Gaussian Mixture Model (GMM) had 90.22% and 84.73% respectively. From the AHP model, geology had the highest weight of 0.279. It was found that low potential regions comprise 229.53 km2, moderate zones comprise 1700.62 km2, high potential zones comprise 2135.04 km2, and excellent potential areas were found to be 152.14 km2. The groundwater recharge due to rainfall computed from the Chaturvedi formula indicates that an average of 2.85% of the total annual rainfall goes to groundwater recharge with a variation of ± 0.35 mm. The total recharge for 2021 was found to be 30.18 ± 0.35 mm but between 1981 and 2021 the total recharge was 1191.18 ± 0.35 mm. Also, from the soil analysis, it was found that 56.21% of the study area would allow infiltration. In conclusion, it was observed that the groundwater potential in the study area was high and can be attributed to the recharge and present surficial conditions.

Hydrologic and Cost–Benefit Analysis of Multiple Check Dams in Catchments of Ephemeral Streams, Rajasthan, India

Investment in the small-scale enhancement of groundwater recharge through check dams and other recharge structures in rural India is on the order of USD 1 billion/year. However, for any catchment, the optimal capacity of check dams is unknown, and the impacts on downstream flows are rarely determined. This paper describes a method that can be applied to plan recharge augmentation in catchments that have at least one monitored check dam. It was applied in the Dharta catchment of the Aravalli Hills in Udaipur district, Rajasthan, India, where four check dams in an ephemeral stream were monitored by farmers over seven years. For the last three years of this study, the hydrology of two of these check dams was affected by 19 new check dams established upstream. A basic hydrologic model, WaterCress, was calibrated on monitored check-dam storages and used to assess the impacts of the new structures on recharge from those downstream. Then, the model was rerun with a range of capacities of upstream check dams to determine the effects of check-dam capacity on (1) the recharge from the downstream check dam, (2) the total recharge from all check dams, and (3) the frequency of spill from the downstream check dam. Using the available economic information, the benefit–cost ratio was calculated for a range of check-dam capacities. This showed a decline in economic efficiency with each new check dam and defined the optimal capacity. Monsoon size was found to be consequential to results, and longer hydrological records yield more reliable results. The study showed that monitoring check dams, rainfall, and groundwater levels is key to deciding whether additional check dams are economically beneficial.

Analyzing Recharge Dynamics and Storage in a Thick, Karstic Vadose Zone

AbstractKarst vadose zone heterogeneity creates complex transmission and storage dynamics that affect the timing and magnitude of aquifer recharge. Young, high‐matrix permeability eogenetic karst aquifers may have significantly higher matrix storage than older, lower matrix permeability counterparts. In vulnerable and water‐limited karst regions, the timescales of storage may be important for seasonal and sub‐seasonal water resource management. We create a framework to quantify storage dynamics in karst aquifers using high‐resolution precipitation and groundwater levels from the Northern Guam Lens Aquifer in the US territory of Guam. We estimate recharge using the Water Table Fluctuation method, and then develop transfer functions between precipitation and recharge to quantify storage and release of water from the vadose zone. The transfer functions are partitioned into different flow pathways including conduit, conduit/matrix, and slowly draining matrix. Probability distributions are fit to each pathway to determine the average travel times of infiltrated waters. The results show that aquifer recharge through secondary porosity features typically occurs within a few hours of a rainfall event, but this rapid recharge accounts for only 12%–28% of total recharge. The majority of aquifer recharge (&gt;70%) occurs within a month of a contributing storm event. An additional 10% of recharge, on average, took longer than a month to reach the water table. The framework established can help improve the hydrological modeling and freshwater management for karst aquifers.

HYDROGEOCHEMICAL CHARACTER AND GROUNDWATER POTENTIAL IN TERNATE BASIN, NORTH MALUKU, INDONESIA

Ternate Basin is located a small volcanic island in the archipelago of North Maluku, Indonesia. This island has very limited water resources and prone to seawater intrusion. This study aims to determine and analyze the distribution of hydrogeological interest points, determine patterns and directions of groundwater flow, and analyze hydrogeochemical quality and groundwater facies. Determination of the free aquifer zone was carried out by geoelectric measurements in 37 points, while the interpretation of confined aquifers was carried out in 17 drill log points. The quality of groundwater was analyzed in the study area, 126 samples were collected and analyzed. The piper diagram was adopted to identify groundwater facies. The determination of groundwater basin with a total recharge of 54,155 million m3/year. The saturated zone of groundwater flow reaches 1.237 million m3/day or 451.712 million m3/year. The quality of groundwater laboratory results indicates that the water from the two aquifer sources is suitable as a source of drinking water with moderate permeability and has met the quality standards. There were three groundwater facies in the study sites consisting of calcium magnesium bicarbonate (C4H4-Ca-MgO12), calcium magnesium chloride (CaCl2-MgCl2) and sodium potassium chloride (NaCL-KCL). Bicarbonate facies type in the groundwater basin indicated localized flow systems. This means the groundwater in the study site has a recharge area close to its groundwater source. Meanwhile, chloride facies type in the groundwater basin indicates a long process of flow pattern and allows the groundwater to interact with seawater or magmatic matters. These results can be used for policymakers to determine the appropriate and accurate location for groundwater exploitation for the public purposes. Determination of the location must be carried out by considering the flow, quantity, and quality of groundwater.