Recharge Efficiency Research Articles

A Review on Integrating Smart Aquifer Recharge Systems into Urban Road Networks: A Sustainable Approach to Water Management and Urban Resilience

This literature review examines the integration of Smart Aquifer Recharge Systems (SARS) into urban road networks to address groundwater depletion, urban flooding, and water scarcity. The SARS approach involves innovative techniques such as collecting runoff water from roads using perforated medians and corner drainage systems and directing it through sedimentation tanks for pre-treatment before infiltration. Studies highlight the significance of managing stormwater in urban areas, where impervious surfaces limit natural recharge, contributing to the decline of flooding and the water table decline. Key findings reveal the potential of advanced filtration systems, permeable pavements, and GIS-based site selection to enhance recharge efficiency. Challenges such as maintenance, space constraints in urban areas, and irregular rainfall patterns are also discussed. Existing research underscores the need for real-time monitoring and adaptive management to optimize recharge efforts. This review identifies gaps in long-term system performance and scalability in high-density urban regions. By focusing on integrating SARS into road infrastructure, the study aims to contribute to sustainable urban water management and align with global sustainability goals. The findings are a foundation for implementing cost-effective and innovative solutions in cities like Bangalore, addressing critical water challenges while improving urban resilience.

Analysis of Recharge Efficiency Under Barrier Effects Incurred by Adjacent Underground Structures

Analysis of Recharge Efficiency Under Barrier Effects Incurred by Adjacent Underground Structures

IoT-Enhanced Decision Support System for Real-Time Greenhouse Microclimate Monitoring and Control

Greenhouses have taken on a fundamental role in agriculture. The Internet of Things (IoT) is a key concept used in greenhouse-based precision agriculture (PA) to enhance vegetable quality and quantity while improving resource efficiency. Integrating wireless sensor networks (WSNs) into greenhouses to monitor environmental parameters represents a critical first step in developing a complete IoT solution. For further optimization of the results, including actuator nodes to control the microclimate is necessary. The greenhouse must also be remotely monitored and controlled via an internet-based platform. This paper proposes an IoT-based architecture as a decision support system for farmers. A web platform has been developed to acquire data from custom-developed wireless sensor nodes and send commands to custom-developed wireless actuator nodes in a greenhouse environment. The wireless sensor and actuator nodes (WSANs) utilize LoRaWAN, one of the most prominent Low-Power Wide-Area Network (LPWAN) technologies, known for its long data transmission range. A real-time end-to-end deployment of a remotely managed WSAN was conducted. The power consumption of the wireless sensor nodes and the recharge efficiency of installed solar panels were analyzed under worst-case scenarios with continuously active nodes and minimal intervals between data transmissions. Datasets were acquired from multiple sensor nodes over a month, demonstrating the system’s functionality and feasibility.

Physical experiment and pore-scale investigation of the clogging of polydisperse particles in saturated porous media during artificial groundwater recharge

Groundwater recharge engineering practices are usually accompanied by the migration and deposition of polydisperse particles. Solid particles may be retained in the pore space leading to clogging of the porous media and reducing groundwater recharge efficiency. However, the mechanism behind this clogging phenomenon remains poorly understood. Specifically, the relation of particle clogging at pore-scale and macroscale is unclear. Here, the influence of polydisperse particle size on clogging development patterns was studied utilizing a series of laboratory-scale column experiments in conjunction with pore-scale scanning electron microscopy (SEM) experiments. Particles with median particle sizes (dp50) of 0.66, 4.05, 11.83 μm were injected separately into the sand column to simulate particle clogging that occurs during groundwater recharge. SEM was used to directly observe particles deposition on porous media grain surface after the column experiments. By counting the size distribution of the particles on the media grain surface, the response of the particle deposition to the surface morphology of the media grains was analysed. Compared to dp50 of 4.05 and 11.83 μm, the spatial distribution of particles deposited in the sand column was more uniform at dp50 of 0.66 μm. The smallest particles (dp50 = 0.66 μm) used in the experiments ultimately formed mixed clogging, which was the result of the combined effects of particle deposition and aggregation. The particle deposition with dp50 = 4.05 and 11.83 μm ultimately exhibited hyper-exponential distribution and formed mixed and superficial clogging, respectively. At the same time, the concave region of the media grain surface played a dominant role in particle deposition. For dp50 = 4.05 μm, 69.41 % of the particles were deposited in the concave region, and for dp50 = 11.83 μm, the proportion was 90.1 %. The results help to better manage particle clogging in groundwater recharge and other engineering applications (e.g., groundwater source heat pump, and filtration project). In addition, these findings provide a theoretical reference for the development of numerical models to help recognize the probability of particles of different sizes to be captured in porous media.

The Mechanism of the Influence of Different Irrigation Methods on Groundwater Recharge

In the Yinchuan Plain, the main source of water supply for agricultural crops is irrigation infiltration. Therefore, the irrigation process, method, and time are crucial for the rational planning and utilization of water resources in the region. In this study, the effects of different irrigation methods on groundwater recharge were investigated through irrigation quadrat tests combined with numerical simulations. The water content at depths of 10–50 cm had a more significant response to irrigation than that at 80 and 100 cm in the intelligent irrigation quadrat. The water content change at depths of 10–50 cm was smaller than that at 80 and 100 cm in the flood irrigation quadrat. The flood irrigation method had a greater impact on the water content in the deep vadose zone. The water content of intelligent irrigation was concentrated at depths of 30–50 cm, with weak groundwater recharge. The water content of the flood irrigation quadrat was concentrated at depths of 50–80 cm, with a significant impact in the vertical direction. The simulation results indicated that flood irrigation had the best effect on groundwater recharge, with an infiltration recharge coefficient of 0.73, compared to intelligent irrigation, which had an infiltration recharge coefficient of 0.41. When the groundwater depth range was 0.65–3.8 m, the infiltration recharge efficiencies of intelligent and flood irrigation were the highest at groundwater depths of 1.3 and 1.8 m. Our findings provide a scientific basis for methods of rational irrigation, which could help save water resources in the study area.

Areal artificial recharge has changed the interactions between surface water and groundwater

Artificial groundwater recharge is increasingly utilized globally for addressing regional groundwater issues due to its effectiveness and ease of application. However, due to the complexity of the interaction of groundwater systems with the external environment and its inherent latency, governance effects are difficult to quantify and are not fully understood yet. In this study, the efficiency of areal artificial groundwater recharge was determined and the interactions with surface water were analyzed by field surveys, sample analysis, water balance reconstruction, and model simulation. A typical groundwater recharge region in the Beijing-Tianjin-Hebei region, China, was focused. Additionally, the response of groundwater flow and water quality to areal artificial groundwater recharge was quantified. Results showed that areal artificial groundwater recharge changes the relationship between surface water and groundwater, with an efficiency of 70 % under high recharge and fluctuation, and decreasing to 20–30 % after the groundwater level was stabilized. The impact on the hydrodynamic field were primarily manifested as the formation of water mounds near river channels, which expand laterally up to 9.2 km from the recharging river channel one year after implementation.Then the impact increases to 14.9 km and continues to expend a year after cessation. The areal artificial groundwater recharge has simultaneously improved the water quality by 23 % in monitoring wells within a 10 km distance from the river channel. The results of this study quantify the impacts of area artificial recharge on groundwater and provide references for the improvement of water resources and water environment in those similar regions.

Electrochemical Analysis of Charge Overpotentials in Non-Aqueous Lithium and Sodium Oxygen Batteries

Aprotic metal-oxygen batteries, especially Li-O2 and Na-O2 batteries, could afford theoretical specific energies of more than 500 Wh/kg. However, while not compromising on rechargeability, the practical realization of the theoretically possible high specific energies has been elusive. A better understanding of the differences and similarities between Li–O2 and Na–O2 battery systems in terms of charge-discharge mechanisms and parasitic chemistry will be meaningful in solving these challenges. Here, we explore the differences between the two systems using a combination of galvanostatic charge-discharge measurements, Differential Electrochemical Mass spectrometry (DEMS), and Potentiostatic Electrochemical Impedance Spectroscopy (PEIS) analysis. The discharge profiles of these battery chemistries are similar in terms of overpotential and have been widely studied. But the origins of the differences in charge overpotentials are not clear. Using in-situ pressure decay measurements during discharge, we calculated the number of electrons/oxygen (e-/O2) to be 2.02 and 1.01 for Li-O2 and Na-O2 cells, respectively. Further, DEMS analysis during charge has shown that the ideal 2 e-/O2 is attained only during the initial phases of charging for Li-O2 cells. However, for Na-O2, the ideal 1 e-/O2 is achieved during a signification portion of the galvanostatic charge step. We corroborate these findings with PEIS and distribution of relaxation times (DRT) analysis to develop a mechanistic view of the processes that lead to poor coulombic and oxygen evolution efficiencies in metal-oxygen cells. Based on DRT analysis, we identify a lower time constant process that is common to both Li-O2 and Na-O2 cells. Interestingly, we observed that voltage polarization is preceded by the observation of this lower time constant peak. In the case of Li-O2 cells, this lower time constant process was observed at the end of discharge and throughout the recharge process, while for the Na-O2 cells, this was only observed after about 70% of recharge. We discuss the possible origins of this low time-constant process and its implications for recharging metal-oxygen batteries. We will also discuss the role of singlet oxygen, if any, in the recharge efficiencies of these two aprotic metal-oxygen batteries. Our results imply that the identification of the origins of this lower time constant process and possible suppression of this process will be key for rechargeable metal-oxygen batteries.

Estimating the impact of vadose zone heterogeneity on agricultural managed aquifer recharge: A combined experimental and modeling study

Agricultural managed aquifer recharge (Ag-MAR) is a promising approach to replenish groundwater resources using flood water and cropland as spreading grounds. However, site selection, particularly the layering of sediment deposits in the subsurface, can greatly influence Ag-MAR efficacy as it controls water flow and solute transport in the vadose zone. In this study, we use the HYDRUS-1D software to simulate water flow and solute transport from the land surface to the groundwater table in three vadose zone profiles (LS, MS, HS) characterized by differing fractions of sand (44 %, 47 %, and 64 %). For each profile, the single- and dual-porosity models (i.e., considering or not nonequilibrium water flow and solute transport) were calibrated using observed surface ponding, soil water content, and KBr breakthrough data. Water flow and bromide transport in the profile with the lowest sand fraction (LS) were best captured using the model that considered both preferential flow and nonequilibrium bromide transport. Water flow and bromide transport in the profile with the highest sand fraction (HS) was best simulated with the model that considered preferential flow and equilibrium bromide transport. Uniform water flow and nonequilibrium bromide transport provided the best fit for the third profile (MS). The degree of preferential flow was highest in the profile with the largest sand fraction (HS), which also showed the largest flow velocities compared to the profiles with lower sand amounts (LS and MS). Preferential flow did not significantly impact the overall water balance (within 3 %), but caused a significant decrease in vadose zone travel times (bromide) by up to 38 %, relative to a single-porosity model fit. Recharge efficiency varied between 88 % and 90 %, while the average travel times from the soil surface to groundwater varied up to 119 % (from 3.6 to 7.9 days) between the three sites. This study demonstrates that similar recharge efficiency can be achieved at sites with differing soil texture profiles, but subsurface heterogeneity can substantially affect contaminant transport processes and their travel times.

Influencing parameters of recharge efficiency and well types optimization in middle-deep sandstone geothermal reservoir

ABSTRACT Recharge efficiency is of importance to ensure the sustainable utilization of geothermal resources. However, there are still challenges for reinjection work of porous sandstone in North China. The present work aims at optimizing reinjection parameters and well types based on the high recharge efficiency, and it was studied by establishing a numerical model of geothermal production-reinjection and designing an indoor reinjection experiment. It is observed that the effects of skin coefficient, daily reinjection amount, well diameter, well inclination angle, and water layer thickness ratio on the recharge efficiency are decreased in turn. In order to ensure the high efficiency of reinjection work, the mode of two reinjectors and one producer should be selected, preferentially considering around 60° directional well or horizontal well. The skin coefficient should be controlled about 1, the well diameter is greater than 81/2 in, the daily reinjection amount is greater than 2320 m3, and the water layer thickness ratio is about 1:3. The present results can provide helpful references for optimal selection of reinjection parameters and well types of Sandstone Geothermal Reservoir.

Flow Cell for Simultaneous In Situ Analysis of Local Electrolyte Distribution and Porous Morphology within the Negative Electrode in a Lead-Acid Battery

While lead-acid is without doubt the oldest battery technology still in use and despite continuous research over many years, mystery still surrounds certain key aspects of its operation. A complex relationship exists between the characteristics of the electrolyte and those of the solid lead sulfate that is alternately deposited and removed during discharge-charge. A premature mode of failure is the often-cited “plate sulfation” that affects the negative electrode and this was investigated by forcing electrolyte flow through the electrode to probe structural changes. A new design of Flow cell that measures flow through the porous electrode has been developed. Under forced electrolyte flow, the discharge capacity and recharge efficiency both increased significantly confirming that local sulfuric acid concentration has a strong effect. Also contributing to decreased electrolyte flow was the production of hydrogen gas during charging, which may make this technique useful in studies of fast-charging. Beyond this, the Flow cell can be used to investigate types of duty where the deposition of lead sulfate triggers catastrophic loss of performance. The ability to monitor electrolyte flow accurately provides an important additional operating parameter that will help characterize modes of electrode failure that until now have remained opaque.

Charging Protocol for Partially Rechargeable Mobile Sensor Networks.

Wireless sensor networks (WSNs) have wide applicability in services used in daily life. However, for such networks, limited energy is a critical issue. The efficiency of a deployed sensor network may be subject to energy supply. Wireless rechargeable sensor networks have recently been proposed and discussed. Most related studies have involved applying static rechargeable sensors to an entire rechargeable environment or having mobile chargers patrol the environment to charge sensors within it. For partially rechargeable environments, improving the recharge efficiency and extending the lifetime of WSNs are considerable challenges. Scientists have devoted attention to energy transmission technologies and mobile sensor network (MSN) applications. In this paper, we propose a flexible charging protocol in which energy can be transmitted from certain energy supply regions to other regions in an MSN. Mobile rechargeable sensors are deployed to monitor the environment. To share energy in a certain region, the sensors move to replenish their energy and transmit energy to sensors outside the energy supply region. The efficiency of the proposed protocol is also discussed in the context of various situations. The evaluation results suggest that the flexible protocol is more efficient than other charging protocols in several situations.

Controls on flood managed aquifer recharge through a heterogeneous vadose zone: hydrologic modeling at a site characterized with surface geophysics

Abstract. In water-stressed regions of the world, managed aquifer recharge (MAR), the process of intentionally recharging depleted aquifers, is an essential tool for combating groundwater depletion. Many groundwater-dependent regions, including the Central Valley in California, USA, are underlain by thick unsaturated zones (ca. 10 to 40 m thick), nested within complex valley-fill deposits that can hinder or facilitate recharge. Within the saturated zone, interconnected deposits of coarse-grained material (sands and gravel) can act as preferential recharge pathways, while fine-textured facies (silts and clays) accommodate the majority of the long-term increase in aquifer storage. However, this relationship is more complex within the vadose zone. Coarse facies can act as capillary barriers that restrict flow, and contrasts in matric potential can draw water from coarse-grained flow paths into fine-grained, low-permeability zones. To determine the impact of unsaturated-zone stratigraphic heterogeneity on MAR effectiveness, we simulate recharge at a Central Valley almond orchard surveyed with a towed transient electromagnetic system. First, we identified three outcomes of interest for MAR sites: infiltration rate at the surface, residence time of water in the root zone and saturated-zone recharge efficiency, which is defined as the increase in saturated-zone storage induced by MAR. Next, we developed a geostatistical approach for parameterizing a 3D variably saturated groundwater flow model using geophysical data. We use the resulting workflow to evaluate the three outcomes of interest and perform Monte Carlo simulations to quantify their uncertainty as a function of model input parameters and spatial uncertainty. Model results show that coarse-grained facies accommodate rapid infiltration rates and that contiguous blocks of fine-grained sediments within the root zone are >20 % likely to remain saturated longer than almond trees can tolerate. Simulations also reveal that capillary-driven flow draws recharge water into unsaturated, fine-grained sediments, limiting saturated-zone recharge efficiency. Two years after inundation, fine-grained facies within the vadose zone retain an average of 37 % of recharge water across all simulations, where it is inaccessible to either plants or pumping wells. Global sensitivity analyses demonstrate that each outcome of interest is most sensitive to parameters that describe the fine facies, implying that future work to reduce MAR uncertainty should focus on characterizing fine-grained sediments.

A Review of Managed Aquifer Recharge Potential in the Middle East and North Africa Region with Examples from the Kingdom of Saudi Arabia and the United Arab Emirates

Groundwater extraction in most Middle East and North Africa (MENA) countries far exceeds its renewability, which ranges from 6% to 100%. Freshwater resources to support food production are very limited in this region. Future climate predictions include more consistent and longer wet periods with increasing surplus rainfall, which will enhance flood and flash flood occurrences in the MENA. Demand management of groundwater resources and managed aquifer recharge (MAR, also called groundwater replenishment, water banking, and artificial recharge, is the purposeful recharge of water to aquifers for subsequent recovery or environmental benefits) represent essential strategies to overcome the challenges associated with groundwater depletion and climate change impacts. Such strategies would enable the development of groundwater resources in the MENA region by minimizing the stress placed on these resources, as well as reducing deterioration in groundwater quality. Groundwater augmentation through recharge dams is a common practice in different countries around the globe. Most dams in the MENA region were built to enhance groundwater recharge, and even the few protection dams also act as recharge dams in one way or another. However, the operating systems of these dams are mostly dependent on the natural infiltration of the accumulated water in the reservoir area, with limited application of MAR. This review presents analyses of groundwater renewability and the effectiveness of recharge dams on groundwater recharge, as well as the potential of MAR technology. This study indicates that the recharge efficiency of dam’s ranges between 15 to 47% and is clustered more around the lower limit. Efficiency is reduced by the clogging of the reservoir bed with fine materials. Therefore, there is a need to improve the operation of dams using MAR technology.

Threshold Recognition of Water Turbidity for Clogging Prevention during Groundwater Recharge Using Secondary Effluent from Wastewater Treatment Plant

The recharge efficiency during artificial groundwater recharge (AGR) is reduced primarily by clogging that is triggered by suspended particles. However, there are loopholes in the current standards of recharge-water quality for clogging control during AGR, and the threshold values of turbidity to prevent clogging have not been reasonably determined. In this study, secondary effluents from wastewater treatment plants (WWTPs) were injected into saturated sand columns to simulate the process of AGR. Batch experiments under different turbidity conditions were conducted, and the numerical modeling of particle transport and deposition was performed to assess the clogging processes. Theories of single-collector contact and interfacial interaction energy were applied to elucidate possible microcosmic mechanisms. The results showed that the diluted secondary effluent (SE) with turbidities of 0.540 ± 0.050, 1.09 ± 0.050, and 1.84 ± 0.060 NTU caused considerable clogging in the porous media, which decreased the relative hydraulic conductivities (K/K0) by 13.2%, 17.6%, and 83.6%, respectively. The filtered SE with a turbidity of 0.160 NTU did not cause clogging, and K/K0 was reduced by only 1.70%. The clogging was attributed to the deposition of suspended particles in the sand matrix because they have a high collision efficiency (0.007–1.98) and attachment efficiency (0.029–0.589 kBT). Finally, this paper recommends that the turbidity of the recharge water should not exceed 0.500 NTU during AGR practices.

Near constant groundwater recharge efficiency under global change in a central European catchment

AbstractThe fraction of precipitation that infiltrates soils and subsequently becomes recharge is one of the principle components of an unconfined aquifer's water budget (this fraction is here termed recharge efficiency). Here we tested how recharge efficiency will respond to climate change including a possible plant physiological response to climate change (e.g., stomatal closure; increasing leaf area) in a catchment used for drinking water production in western Germany. To this end we used a soil water model (HYDRUS‐1D) forced with climate data spanning the time period from 1971 to 2099. Three different vegetation types were considered: turf grass representing the primary infiltration sites within residential areas; maize representing the main crop on agriculturally used land; and beech representing the forested parts of the catchment. We found that, the positive effects of climate change on recharge efficiency (more rain during the main recharge season in winter, less crop water demand due to faster plant ripening in spring and summer, increased plant water use efficiency, reduced global radiation as cloud density increases) were not completely compensated by the negative effects (less precipitation, higher leaf area index and increasing vapour pressure deficit in summer season) at our study site. Because total annual precipitation increased slightly until the end of the 21th century, changes in the amount of total annual recharge were also positive, though moderate (up to +20% change in the period 2071–2099 as compared to 1970–2000). The results of this study will be helpful for water authorities managing water rights under the perspective of a changing climate. In the future, our study site is expected to receive sufficient recharge from precipitation to maintain current rates of groundwater withdrawal for public water supply and irrigation. Thus, the region's agriculture sector may become a ‘global warming winner,’ when cropping in other regions in Europe may increasingly suffer from drying conditions during the growing season.

Study of leachate recharge model and vertical well design method for bioreactor landfills.

Leachate recharging not only solves the leachate treatment problem but also has tremendous environmental and engineering benefits. In this study, a recharge model was developed based on consideration of the inhomogeneous characteristics of the pile and the degree of clogging of the leachate collection and removal system (LCRs), and a design diagram of the maximum injection pressure Ps and the minimum setback distance ds was given. The following conclusions are obtained: the rate of diffusion in the horizontal and burial depth directions depends on anisotropy coefficient A, and the rate of development of the blocked water level on the LCRs depends on the degree of blockage h1. The development rate of the region affected by the recharging is low at the beginning of the recharging and increases rapidly when the moment Tb is reached, which decreases with the injection pressure P, and the degree of blockage h1. The safety factor of slope Fs decreases at a slower rate when the anisotropy coefficient is 0 < A < 1 and 15 < A < 20, and at a faster rate when 1 < A < 15. When the LCRs is blocked, the injection pressure P and anisotropy coefficient A increase the degree of influence on the recharge efficiency and slope stability, and when the blocked water level h1 > 30m, recharge is not recommended. This model and the vertical well design method can well simulate the recharging process and its effect on the slope stability and provide a reference for the design of vertical wells.

Study on Unblocking and Permeability Enhancement Technology with Rotary Water Jet for Low Recharge Efficiency Wells in Sandstone Geothermal Reservoirs

In China, sandstone geothermal reservoirs are large in scale and widely distributed, but their exploitation is hindered by low recharge efficiency. In this paper, an unblocking and permeability enhancement technology using a rotary water jet for low recharge efficiency wells in sandstone geothermal reservoirs is proposed to solve this problem. This paper presents a series of studies about the proposed technology, including experiments, simulation and field application. Firstly, an experiment was carried out to verify the scale removal effect of a high-pressure water jet on the inner wall of the screen tube and its impact on sandstone. Secondly, the numerical models of the rotary jet flow field in the wellbore were established by ANSYS Fluent to study the influence of parameters. Finally, based on the simulation and experiment results, a rotary jet tool applicable to unblocking and descaling low-efficiency wells was designed, and a field application for low-efficiency wells in sandstone thermal reservoirs was conducted. The study results show that the unblocking and permeability enhancement technology using a rotary water jet is effective in removing the blockages and improving the permeability near the well. In conclusion, the presented technology can solve the problem of low efficiency during the reinjection of cooled thermal waters back into sandstone geothermal reservoirs and has great effectiveness in field application.

Application of GIS Techniques in Identifying Artificial Groundwater Recharging Zones in Arid Regions: A Case Study in Tissamaharama, Sri Lanka

Groundwater resources are severely threatened not only in terms of their quality but also their quantity. The availability of groundwater in arid regions is highly important as it caters to domestic needs, irrigation, and industrial purposes in those areas. With the increasing population and human needs, artificial recharging of groundwater has become an important topic because of rainfall scarcity, high evaporation, and shortage of surface water resources in arid regions. However, this has been given the minimum attention in the context of Sri Lanka. Therefore, the current research was carried out to demarcate suitable sites for the artificial recharging of aquifers with the help of geographic information system (GIS) techniques, in one of the water-scarce regions in Sri Lanka. Tissamaharama District Secretariat Division (DSD) is located in Hambanthota district. This region faces periodic water stress with a low-intensity seasonal rainfall pattern and a lack of surface water sources. Hydrological, geological, and geomorphological parameters such as rainfall, soil type, slope, drainage density, and land use patterns were considered to be the most influential parameters in determining the artificial recharging potential in the study area. The GIS tools were used to carry out a weighted overlay analysis to integrate the effects of each parameter into the potential for artificial groundwater recharge. The result of the study shows that 14.60% of the area in the Tissamaharama DSD has a very good potential for artificial groundwater recharge, while 41.32% has a good potential and 39.03% and 5.05% have poor and very poor potential for artificial groundwater recharge, respectively. The southern part of the DSD and the Yala nature reserve areas are observed to have a higher potential for artificial groundwater recharge than the other areas of Tissamaharama DSD. It is recommended to test the efficiency and effects of groundwater recharge using groundwater models by simulating the effects of groundwater recharge in future studies. Therefore, the results of the current research will be helpful in effectively managing the groundwater resources in the study area.

Multiyear ENSO Dynamics as Revealed in Observations, Climate Model Simulations, and the Linear Recharge Oscillator

Abstract El Niño–Southern Oscillation (ENSO) events occasionally recur one after the other in the same polarity, called multiyear ENSO. However, the dynamical processes are not well understood. This study aims to elucidate the unified mechanisms of multiyear ENSO using observations, phase 6 of the Coupled Model Intercomparison Project (CMIP6) models, and the theoretical linear recharge oscillator (RO) model. We found that multiyear El Niño and La Niña events are roughly symmetric except for cases of multiyear La Niña following strong El Niño. The composite multiyear ENSO reveals that anomalous ocean heat content (OHC) in the equatorial Pacific persists beyond the first peak, stimulating another event. This prolonged OHC anomaly is caused by meridional Ekman heat transport counteracting geostrophic transport-induced recharge–discharge process that otherwise acts to change the OHC anomaly. A meridionally wide pattern of sea surface temperature anomalies observed during multiyear ENSO is responsible for the Ekman heat transport and multiple factors such as decadal variability, subtropical processes, and ENSO diversity modulate the ENSO meridional structure. CMIP6 multimodel ensemble shows a significant correlation between the ENSO meridional width and the occurrence ratio of multiyear ENSO, supporting the aforementioned mechanism. A multiyear ENSO-like oscillation was simulated using the linear RO model that incorporates a seasonally varying Bjerknes growth rate and a weak recharge efficiency representing the effect of Ekman transport. When the recharge efficiency parameter was estimated using reanalysis data based on geostrophic transport alone, a multiyear ENSO rarely occurred, confirming the importance of Ekman transport in retarding the recharge–discharge process.

Predictive geospatial model for arsenic accumulation in Holocene aquifers based on interactions of oxbow-lake biogeochemistry and alluvial geomorphology

The identification of arsenic-contamination hotspots in alluvial aquifers is a global-scale challenge. The collection and inventory of arsenic concentration datasets in the shallow-aquifer domain of affected alluvial basins is a tedious and slow process, given the magnitude of the problem. Recent research demonstrates that oxbow-lake biogeochemistry in alluvial plains, mobilization of geogenic arsenic, and accumulation in geomorphologically well-defined areas are interacting processes that determine arsenic-contamination locations. This awareness provides a tool to identify potential arsenic-hotspots based on geomorphological similarity, and thus contribute to a more robust and targeted arsenic mitigation approach. In the present study, a conceptual predictive geospatial model is proposed for the accumulation of dissolved arsenic as a function of interaction of oxbow-lake biogeochemistry and alluvial geomorphology. A comprehensive sampling campaign in and around two oxbow lakes in the Jamuna River Basin, West Bengal (India) provided water samples of the oxbow-lake water column for analysis of dissolved organic matter (DOM) and microbial communities, and groundwater samples from tube wells in point bars and fluvial levees bordering the oxbow lakes for analysis of the geospatial distribution of arsenic in the aquifer. Results show that abundant natural and anthropogenic (faecal-derived) recalcitrant organic matter like coprostanols and sterols in clay-plug sediment favours microbial (heterotrophs, enteric pathogens) metabolism and arsenic mobilization. Arsenic concentrations in the study area are highest (averaging 505 μg/L) in point-bar aquifers geomorphologically enclosed by partially sediment-filled oxbow lakes, and much lower (averaging 121 μg/L) in wells of levee sands beyond the oxbow-lake confinement. The differences reflect variations in groundwater recharge efficiency as result of the porosity and permeability anisotropy in the alluvial geomorphological elements, where arsenic-rich groundwater is trapped in point-bars enclosed by oxbow-lake clays and, by contrast, levee ridges are not confined on all sides, resulting in a more efficient aquifer flushing and decrease of arsenic concentrations.