Groundwater Interactions Research Articles

Analysis of natural and technological factors of changes in exogeodynamic conditions of mine No. 2 of the Stebnytsky potassium deposit as a consequence of self-rehabilitation flooding

The Stebnytsy deposit of potash salts is located in the foothills of the Ukrainian Carpathians. The engineering-geological and hydrogeological conditions of the field’s operation due to the development of a thick layers of loose and water-soluble rocks are difficult of loose and water-soluble rocks are complex and therefore sensitive to mining-technological influences, extraction of rocks, deformation of the surface, hydrographic network, activation of the interaction of surface and groundwater. The most threatening situation was at mine No. 2, where in 1978, due to too intensive blasting, violation of waterproof layers, loosening and increase of water permeability, reduction of rock strength, an emergency breakthrough of super-saline waters occurred in the spent chambers of the first horizon. The total inflow of brines during the years of existence of the flow here constantly increased and reached up to 1700 m³/day, in 2002, the outflow of suprasaline waters developed in 22 points and acquired an irreversibly negative character, suffusion-diffusion processes began to develop actively. During the operation of the mine, ore extraction was carried out for a long time without laying out spent cavities, as a result of which more than 15 million m³ of unlined cavities were formed at the mine, the deformations of which disturbed the geodynamic regime of the salt-bearing massif with the subsequent development of sedimentary and karst-failure processes. In 2004, a comprehensive project for the conservation of mine No. 2 and the reclamation of disturbed lands was approved in order to restore the ecological balance in this area. Mine conservation works were carried out behind the design schedule, which led to the failure of the main provisions of the project and increased the danger due to the expansion of existing karst cavities and the formation of new ones. It can be argued that the works on the conservation of mine No. 2, including: preparation of brines, feeding them to underground mine workings, laying of chambers, etc., were carried out in a timely and incomplete manner, which does not ensure the cessation of negative consequences for the natural environment and ecological safety. The results of our research can be used in the future in the development of projects for the conservation or liquidation of salt mines.

Patterns of nitrate load variability under surface water-groundwater interactions in agriculturally intensive valley watersheds

Nitrate pollution is a significant environmental issue closely related to human activities, complicated hydrological interactions and nitrate fate in the valley watershed strongly affects nitrate load in hydrological systems. In this study, a nitrate reactive transport model by coupling SWAT-MODFLOW-RT3D between surface water and groundwater interactions at the watershed scale was developed, which was used to reproduce the interaction between surface water and groundwater in the basin from 2016 to 2019 and to reveal the nitrogen transformation process and the evolving trend of nitrate load within the hydrological system of the valley watershed. The results showed that the basin exhibited groundwater recharge to surface water in 2016-2019, particularly in the northwestern and northeastern mountainous regions of the valley watershed and the southern Beishan Reservoir vicinity. Groundwater recharge to surface water declined by 20.17% from 2016 to 2019 due to precipitation. Nitrate loads in the hydrologic system of the watershed are primarily derived from human activities (including fertilizer application from agricultural activities and residential wastewater discharges) and the nitrogen cycle. Nitrate loads in surface water declined 16.05% from 2016 to 2019. Nitrate levels are higher in agricultural farming and residential areas on the eastern and northern sides of the watershed. Additionally, hydrological interactions are usually accompanied by material accumulation and environmental changes. Nitrate levels tend to rise with converging water flows, a process that becomes more pronounced during precipitation events and cropping seasons in agriculturally intensive valley watersheds. However, environmental changes alter nitrogen transformation processes. Nitrogen fixation, nitrification, and ammonification intensify nitrogen inputs during river pooling, enhancing nitrogen cycling fluxes and elevating nitrate loads. These processes are further enhanced during groundwater recharge to surface water, leading to evaluated nitrate load. Enhanced denitrification, dissimilatory nitrate reduction to ammonium (DNRA), anaerobic ammonia oxidation, and assimilation promote the nitrogen export from the system and reduce the nitrate load during surface water recharge to groundwater.

Key point of desert riparian forest development in the arid area: The response of phreatic water table depth to ecological water supply

Desert riparian forest vegetation maintains the fragile balance of ecosystems in extreme arid areas. Raising the phreatic water table through efficient ecological water supply is the key to the desert riparian forests in extreme arid areas. The main objective of this study is to explore an innovative framework in which the response of phreatic water table depth (PWTD) to ecological water supply flow (EWSF) can be effectively reflected. The framework is based on the computationally efficient integrated surface water - groundwater model (ISGWM), through which surface water processes, groundwater recharge and discharge processes, and PWTD changes under different EWSF can be accurately simulated. A large number of simulations were conducted to reflect the response of PWTD to EWSF, and to explore the suitable EWSF and its intra-annual process considering the efficiency of PWTD reduction. The applicability and advantages of ISGWM were evaluated for the Tarim River Basin (TRB), a typical inland river basin, northwest China. The response of PWTD to EWSF was studied in 55 gate control areas in the mainstream of TRB. The formulas of suitable EWSF of 55 gates with different initial PWTDs were fitted. It is more beneficial to concentrate the ecological water supply in flood season (Jun.-Oct.). Overall, the ISGWM can accurately describe the multi-process of surface water and groundwater interactions. This study can provide scientific support for water resources management and allocation in the TRB and other similar inland river basins.

Interaction of shallow and deep groundwater with a tropical ocean: Insights from radiogenic (87Sr/86Sr) and stable isotope cycling and fluxes

Interaction of shallow and deep groundwater with a tropical ocean: Insights from radiogenic (87Sr/86Sr) and stable isotope cycling and fluxes

Hydrochemistry and surface water - groundwater interactions in an anthropically disturbed mountain river (Sierras Pampeanas, central Argentina)

The surface water - groundwater interactions in a small anthropically affected mountain watershed (Salsipuedes River) in the Sierras Pampeanas (central Argentina) were analyzed and quantified by means of 222Rn mass balance modeling, and its implications in hydrochemistry and water quality were examined. Surface waters, springs and groundwater were sampled during the 2021–2022 hydrological year, and the major dissolved composition was determined. The studied waters are alkaline, showing an evolution from medium mineralized (1.5 < ∑+ < 3 meq L−1) to mineralized type (3 < ∑+ < 6 meq L−1) downstream. In general, waters are of the bicarbonate - calcium type with no spatial or seasonal variations. This composition is mainly controlled by silicates weathering. 222Rn modeling indicates that near the headwaters the Salsipuedes River recharges the aquifer, losing 1.2% and 2.4% of its discharge during the dry and wet seasons, respectively. Downstream, the system changes its hydrological behavior and the river acts as a gaining stream; i.e, it receives groundwater inflow. The magnitude of this inflow varies seasonally, being greater in the wet season (1.5–2.2% of the total flow) than in the dry season (less than 0.25%) due to a rise in the water table level as a result of direct recharge of the phreatic aquifer. Anthropic influence is noticeable in nitrate and chloride concentrations, which are derived from domestic wastes and septic tanks. The highest concentrations of these ions in surface waters are found in the urbanized area, where the river stretch corresponds to a gaining stream, reflecting that even small amounts of groundwater inputs can alter the chemical composition of streams. A temporal analysis also showed a variable response of the system to the increasing anthropic pressure and climatic events such as ENSO, which affect not only water availability but also its quality, highlighting the vulnerability of small mountain watersheds.

Shallow Groundwater Quality Assessment and Pollution Source Apportionment: Case Study in Wujiang District, Suzhou City

Groundwater serves as a crucial resource, with its quality significantly impacted by both natural and human-induced factors. In the highly industrialized and urbanized Yangtze River Delta region, the sources of pollutants in shallow groundwater are more complex, making the identification of groundwater pollution sources a challenging task. In this study, 117 wells in Wujiang District of Suzhou City were sampled, and 16 groundwater quality parameters were analyzed. The fuzzy synthetic evaluation method was used to assess the current status of groundwater pollution in the study area; the principal component analysis (PCA) was employed to discern the anthropogenic and natural variables that influence the quality of shallow groundwater; and the absolute principal component scores–multiple linear regression (APCS-MLR) model was applied to quantify the contributions of various origins toward the selected groundwater quality parameters. The results indicate that the main exceeding indicators of groundwater in Wujiang District are I (28%), NH4-N (18%), and Mn (14%); overall, the groundwater quality is relatively good in the region, with localized heavy pollution: class IV and class V water are mainly concentrated in the southwest of Lili Town, the north of Songling Town, and the south of Qidu Town. Through PCA, five factors contributing to the hydrochemical characteristics of groundwater in Wujiang District were identified: water–rock interaction, surface water–groundwater interaction, sewage discharge from the textile industry, urban domestic sewage discharge, and agricultural non-point source pollution. Additionally, the APCS-MLR model determined that the contributions of the three main pollution sources to groundwater contamination are in the following order: sewage discharge from the textile industry (10.63%) &gt; urban domestic sewage discharge (8.69%) &gt; agricultural non-point source pollution (6.26%).

Longitudinal Investigation of Groundwater and Surface Water Interaction of Two Gravel Pit Lakes in Central Texas: Chemical and Flow Implications

Two gravel pit lakes in central Texas were examined over the course of two years with upgradient and downgradient piezometer installations. Groundwater and lake water were sampled bimonthly for nutrients, water levels, and groundwater chemistry, and in addition, rain and lake gauges and mini-piezometers were installed, depth surveys were conducted, and a simple 2D flow model was constructed. The project goal was evaluating and examining flow dynamics and chemical effects as groundwater flows to surface water and back to groundwater with the intent to understand the effects that gravel pit lake systems have on connected shallow groundwater. Both lake systems were shown to be flow-through systems that influence the water quality by decreasing the dissolved nutrients in the groundwater in their vicinity while oxygenating the water and altering the pH. However, the lakes are also prone to high levels of evaporation, meaning that minor improvements to water quality come at the cost of decreasing the quantity of water in storage within the aquifer. Similar groundwater and mine lake systems may show comparable tendencies, providing new information for water managers, regulators, and stake-holders about the potential roles that non-remediated gravel pit lakes may play in local ecosystems and aquifer dynamics.

Integrated modeling of surface water and groundwater interactions in the Eastern Mitidja Plain, North Algeria: investigating the impact of human activities and climate change

ABSTRACT The interaction between surface water and groundwater is a crucial factor in understanding water resources' dynamics and in promoting sustainable groundwater development, particularly in regions affected by human activities and climate change. This work aims to investigate dynamic interactions between El Hamiz river and Eastern Mitidja alluvial aquifer (North Algeria) using a regional three-dimensional groundwater numerical model (MODFLOW 6). A typical scenario analysis approach was conducted using historical and projected climate data from CMIP5 and CMIP6 models, as well as current and projected groundwater abstraction rates. The findings demonstrate major shifts in the flow dynamics over time. In 1982, the aquifer replenished the river at a rate of 2.59 m3/s. However, in 2019 a new state was observed in which the aquifer was recharged by the river at a rate of 0.73 m3/s. This decrease in flow rate can be linked to over-pumping and decreased recharge rates, which are expected to continue in the future. Future forecasts show that groundwater misuse affects groundwater dynamics more than climate change. However, the Algerian government's projected saltwater desalination and upgraded irrigation methods could provide a substantial contribution to the sustainable growth of groundwater resources, with a potential increase of up to 14 meters.

Hydrogeochemical dynamics under saltwater-freshwater mixing in a mangrove wetland over tidal cycles

Seawater and groundwater interactions shape the hydrogeochemical profile of mangrove aquifers, revealing how biogeochemical processes adapt to saline-freshwater mixing via the fluctuating patterns of key hydrochemical indicators and primary biogenic elements. This study, utilizing a multi-level monitoring profile spanning the entire submerged aquifer within a mangrove wetland, analyzed the spatiotemporal dynamics of DO, ORP, pH, alkalinity and biogenic elements (C, N, S). The results revealed that among the basic hydrochemical parameters, total alkalinity showed the most stable spatiotemporal distribution and was positively correlated with salinity. pH demonstrated a significant negative correlation with salinity, whereas the correlations of ORP and DO with salinity were not substantial. The discharge of terrestrial freshwater into the mangrove wetland is marked by hydrogeochemical reactions favoring the input of Mg2+ and DIC, with potential iron mineral precipitation within the aquifer. Spatial distribution of biogenic elements in the groundwater showed no apparent pattern across sampling periods. DOC concentrations ranged from 0.3 to 1.3 mmol/L. Three components of dissolved organic matter were identified using three-dimensional fluorescence spectroscopy, with high molecular weight components (C1 + C2) accounting for an average of 47 to 73 %. Both elevated DOC concentrations and high molecular weight component ratios were primarily found in shallow layers of dense mangrove areas, decreasing with depth. Concentrations of ammonia, nitrite, and nitrate varied dynamically, reflecting active biochemical processes in the shallow to mid-layers of the aquifer. Furthermore, sulfate and sulfide concentrations, ranging from 0 to 26 mmol/L and 0.4 to 576.8 μmol/L, respectively, underscore the interplay of biogeochemical reactions, especially sulfate reduction. These findings highlight valuable insights into the complex biogeochemical processes within mangrove aquifers and provide theoretical guidance for protecting the ecological health of mangrove wetlands.

Assimilation of Sentinel‐Based Leaf Area Index for Modeling Surface‐Ground Water Interactions in Irrigation Districts

AbstractVegetation‐related processes, such as evapotranspiration (ET), irrigation water withdrawal, and groundwater recharge, are influencing surface water (SW)—groundwater (GW) interaction in irrigation districts. Meanwhile, conventional numerical models of SW‐GW interaction are not developed based on satellite‐based observations of vegetation indices. In this paper, we propose a novel methodology for multivariate assimilation of Sentinel‐based leaf area index (LAI) as well as in‐situ records of streamflow. Moreover, the GW model is initially calibrated based on water table observations. These observations are assimilated into the SWAT‐MODFLOW model to accurately analyze the advantage of considering high‐resolution LAI data for SW‐GW modeling. We develop a data assimilation (DA) framework for SWAT‐MODFLOW model using the particle filter based on the sampling importance resampling (PF‐SIR). Parameters of MODFLOW are calibrated using the parameter estimation (PEST) algorithm and based on in‐situ observation of the GW table. The methodology is implemented over the Mahabad Irrigation Plain, located in the Urmia Lake Basin in Iran. Some DA scenarios are closely examined, including univariate LAI assimilation (L‐DA), univariate streamflow assimilation (S‐DA), and multivariate streamflow‐LAI assimilation (SL‐DA). Results show that the SL‐DA scenario results in the best estimations of streamflow, LAI, and GW level, compared to other DA scenarios. The streamflow DA does not improve the accuracy of LAI estimation, while the LAI assimilation scenario results in significant improvements in streamflow simulation, where, compared to the open loop run, the (absolute) bias decreases from 75% to 6%. Moreover, S‐DA, compared to L‐DA, underestimates irrigation water use and demand as well as potential and actual crop yield.

Interaction of pans and groundwater: A case study in the Khakhea- Bray Transboundary aquifer portion in South Africa

Understanding the groundwater-surface water interaction is important for the sustainable management of water resources and ecology. Most of the studies on groundwater-surface interactions are confined to aquifer-river and aquifer-lake interactions. The interactions of water pans and groundwater have not received much attention. The study aims to provide insights into the interaction of the pans and groundwater at a case study in the Khakhea-Bray dolomite Transboundary Aquifer (TBA) shared by Botswana and South Africa. The study uses field observations, geology, hydrogeophysics, and stable isotopes complimentary tools. Complimentary tools provide several evidence to corroborate the findings. The hydrogeophysics taps into the recently developed Telluric Electric Frequency Selection Method (TEFSM). Groundwater discharge zones/springs were delineated at the geological contact of the boundary of the Khakhea-Bray dolomite transboundary aquifer and the granite of the Kalahari group. 4 of the 33 research pans are in the groundwater discharge zone and are classified as groundwater dependent. The findings highlight the benefits of complimentary approaches to corroborate the findings on groundwater-surface water interactions. The TEFSM hydrogeophysics can be able to delineate groundwater discharge zones, aquifer boundaries, and the mapping of TBAs. More studies are recommended to test the TEFSM hydrogeophysical approach to study groundwater-surface water in different hydrological environments.

Forest catchment structure mediates shallow subsurface flow and soil base cation fluxes

Hydrologic behavior and soil properties across forested landscapes with complex topography exhibit high variability. The interaction of groundwater with spatially distinct soils produces and transports solutes across catchments, however, the spatiotemporal relationships between groundwater dynamics and soil solute fluxes are difficult to directly evaluate. While whole-catchment export of solutes by shallow subsurface flow represents an integration of soil environments and conditions but many studies compartmentalize soil solute fluxes as hillslope vs. riparian, deep vs. shallow, or as individual soil horizon contributions. This potentially obscures and underestimates the hillslope variation and magnitude of solute fluxes and soil development across the landscape. This study determined the spatial variation and of shallow soil base cation fluxes associated with weathering reactions (Ca, Mg, and Na), soil elemental depletion, and soil saturation dynamics in upland soils within a small, forested watershed at the Hubbard Brook Experimental Forest, NH. Base cation fluxes were calculated using a combination of ion-exchange resins placed in shallow groundwater wells (0.3 – 1 m depth) located across hillslope transects (ridges to lower backslopes) and measurements of groundwater levels. Groundwater levels were also used to create metrics of annual soil saturation. Base cation fluxes were positively correlated with soil saturation frequency and were greatest in soil profiles where primary minerals were most depleted of base cations (i.e., highly weathered). Spatial differences in soil saturation across the catchment were strongly related to topographic properties of the upslope drainage area and are interpreted to result from spatial variations in transient groundwater dynamics. Results from this work suggest that the structure of a catchment defines the spatial architecture of base cation fluxes, likely reflecting the mediation of subsurface stormflow dynamics on soil development. Furthermore, this work highlights the importance of further compartmentalizing solute fluxes along hillslopes, where certain areas may disproportionately contribute solutes to the whole catchment. Refining catchment controls on base cation generation and transport could be an important tool for opening the black box of catchment elemental cycling.

Coupled Modelling of Brine Availability in Salt-Based Disposal Facilities - Learning from DECOVALEX 2023

Salt is a potential host rock or caprock for deep geological disposal facilities for radioactive waste and has several favourable properties compared to other candidate rock types. In particular, intact salt has an extremely small porosity and permeability, which limits water availability and transmissivity. This has tended to lead to disposal concepts in salt being considered as ‘mostly dry’ and hence ideally suited to limiting groundwater interactions that could otherwise lead to corrosion of waste packages and mobilisation of radionuclides over isolation timescales (10 5 -10 6 years). However, there is plentiful experimental evidence to suggest that excavations in bedded salt can exhibit non-trivial inflows. These inflows often increase on heating and are thought to arise due to complicated interactions between thermal, hydrogeological and mechanical processes in the salt. Task E in the international collaborative DECOVALEX 2023 programme was established to attempt to better understand how these coupled processes affect brine availability in bedded salt. A summary of the UK team's learning from the task is given in this paper that may be of relevance when constructing models to inform future safety cases for radioactive waste disposal in salt, and other energy geoscience applications where brine interactions are a potentially complicating factor.

Consistent solutions for simultaneous dynamic water, solute, stable isotope and radon balances to estimate average exchange fluxes between surface water bodies and groundwater

Many papers show that water, conservative solute, stable isotope and radon balances can be applied to the study of surface water – groundwater interaction. When undertaken simultaneously, such analysis provides an even more powerful method for estimating groundwater inflows and outflows, i.e. the exchange fluxes that for most people are hardest to estimate. The overarching objective of this paper is to provide practitioners with a consistent conceptual and simulation modelling framework with which to achieve a rapid initial understanding of surface water – groundwater interaction, as well as to guide the efficient and targeted acquisition of field data. This paper makes several important contributions. First, after an introduction that explains the complexities of groundwater flow patterns near surface water bodies, a set of general balance equations is developed using consistent terminology and notation. Second, after focusing on a simple conceptual model with steady groundwater inflow I, groundwater outflow O, precipitation P and ever-present evaporation E, analytical solutions are developed for transient and steady state conditions: one water balance solution is found to apply in all situations; solutions for the solute balance equation are developed for 23 different subcases; a transient balance equation for stable isotopes written in terms of 1+δ is found to apply in all situations; and a new transient solution for radon is found in terms of the upper incomplete gamma function. On the path towards developing the isotope balance equation, we present a rigorous approach, based on coupled nonlinear balance equations for abundant and rare isotope pairs (1H and 2H, then 16O and 18O), using isotope ratios and the fractions of each isotope. Third, we describe a Lake Water Balance Calculator (LWBC) written using GoldSim simulation software, a tool to help others to conduct the simultaneous analyses that we promote; we use GoldSim’s numerical methods to solve the general balance equations, we implement the analytical solutions to demonstrate that both GoldSim’s numerical methods and the analytical solutions are correct, and we also show that the 1+δ approximation is equivalent to the rigorous coupled equations, at least for heavy stable isotopes with very low abundance. Fourth, we describe field studies: we provide three examples of applications of LWBC to short-term studies of Perry Lakes East, Lake Jasper and Georgetown Billabong in Australia; we then describe WSIBal, a simulation model based on the same balance equations and describe its application to Lake Jasper over a 19-year period; finally, we describe R-WSIBal, which evolved from WSIBal, and explain its application to 2500 km of the Murray River in Australia.

Geochemical-hydromechanical couplings during water-serpentinized harzburgite interactions at 20°C and 30 bars

Interaction of groundwater with the serpentinized harzburgites of the upper mantle plays an important role in the geologic carbon cycle and serpentinization processes. In this study, an intact serpentinized harzburgite with more than 60% lizardite from the Semail ophiolite in Oman was reacted with water at near neutral pH and low PCO2 to observe its dissolution behavior and reaction path within the CaO-MgO-SiO2-CO2-H2O system at 20 °C and 30 bars. In the experiment, mass (i.e. H2O, ions) transfer is by diffusion and the selected temperature and pressure conditions mimic water-rock interactions at the shallow portions of most ultramafic rock hosted aquifers. Equilibrium activity-activity diagrams and thermodynamic data were used to compare the experimentally determined reaction path with the theoretical stability boundaries for minerals involved to investigate the evolution of bulk chemical composition, mineralogy, and water composition. The experiments demonstrated that (i) the water-rock interactions increased the pH of the aqueous phase from 5.9 to 7.5 over a period of 18 weeks; (ii) the dissolution of lizardite, orthopyroxene (enstatite), and clinopyroxene (diopside and augite) increased the concentration of Mg, Ca, and Si in the aqueous phase; (iii) the dissolution was incongruent with respect to Mg and Si, favoring Si release at pH > 6 due to (a) breaking of more reactive cation‑oxygen bonds that is consistent with the stoichiometry of magnesium for proton exchange reaction which favors a surface that is enriched in Mg at basic conditions, and (b) preferential dissolution of clinopyroxene Mg1.30Ca0.52Fe0.06Si2O6; (iv) the aqueous phase was undersaturated with respect to carbonate (e.g. calcite, magnesite, and hydromagnesite) and hydrous (e.g. lizardite, chrysotile, brucite, and talc) minerals; (v) the bulk chemical composition and mineralogy of the intact serpentinized harzburgite matrix did not change; (vi) the thermodynamic data can successfully predict water-intact serpentinized harzburgite behavior if the water chemical composition can be constrained; and (vii) no detectable macroscopic form of damage (e.g. microcracks forming as a result of differential stress fields due to changes in volume during chemical reaction) was observed.

High-accuracy and low-disturbance approach for identifying surface water and groundwater interactions in wetlands

Comprehending the hydrological conditions in wetlands is a critical aspect of successfully enhancing wetland conservation. The interaction between wetland surface water and groundwater is a complex process, requiring detailed onsite hydrological and soil surveys, laboratory experiments, and modeling to clarify this relationship. However, conventional investigation methods often cause significant disruptions and thus may affect the natural environment and compromise data reliability. In this study, a high-accuracy and low-environmental-disturbance (LED) approach was proposed involving modified falling head permeability and modified seepage meter tests to elucidate the groundwater characteristics in an ecological reserve. A water balance (WB) calculation method was employed to examine the performance of the proposed LED approach. The results revealed that the LED performed better than conventional methods in hydraulic conductivity and seepage velocity exploration, thereby improving the accuracy of quantifying groundwater flow. Moreover, the experimental findings and ecohydrological observations were used to assess the groundwater flow regime, and the data were consistent with the field survey results. The contradiction between conducting research and protecting ecological reserves can pose difficulties in the sustainable and effective management of wetlands. The LED approach can be applied broadly, especially in areas where significant disturbance should be avoided. The water budget model can thus be developed to help deduce the interaction between groundwater and surface water. We suggest that these innovative methods are effective tools and can assist both scientists and authorities in formulating corresponding habitat management strategies.

Estimation of Surface and Groundwater Interaction by Stable Isotopic Techniques – A Case Study of Chengalpattu District, OMR Region

Isotopes are atoms of an element having the same atomic number but different mass numbers. Isotopes in hydrology and water resources are used for identifying its occurrence, movement, residence times, recharge, and discharge process. Stable isotopes of hydrogen(δ2H) and oxygen(δ2O) are used for identifying the surface and groundwater interactions as they constitute hydrogen and oxygen. In this study oxygen and hydrogen stable isotopes are used to identify surface and groundwater interaction in Old Mahabalipuram Road (OMR) regions of Chengalpattu district. The precipitation, lake, surface, and groundwater were collected during pre-monsoon, monsoon, and post-monsoon seasons. The collected sample is analyzed for stable isotopic compositions of oxygen and hydrogen seasonal-wise. The measured stable isotopic compositions during pre-monsoon season of stable oxygen are -4.29 to -2.00 and stable hydrogen are -29.39 to -24.67. The isotopic compositions during monsoon season range from -4.72 to -4.00 and for hydrogen ranges from -29.39 to -23.50. During monsoon season the depletion of isotopic composition is seen and the enrichment of isotopic composition is observed during pre-monsoon season. The variation in stable isotopic composition of oxygen and hydrogen are observed. A Groundwater Water Meteoric Water Line (GMWL) is developed for the study area, and it is compared with a Local Meteoric Water Line (LMWL) for better interpretation of the results. A slight deviation is observed from that of GMWL to LMWL mostly due to isotopic depletion and evaporation effects. From the analysis, a good correlation exists between precipitation and surface water in the study area indicating about recharge mechanism existing in the study area. The groundwater recharge is observed during monsoon seasons and discharge is more towards the pre-monsoon seasons.

Investigating the impact of irrigation practices on hydrologic fluxes in a highly managed river basin

Irrigation practices and sources can have significant impacts on water resources and the hydrologic fluxes that control these resources. To better manage water resources and future water supply, the influence of irrigation practices and management on these hydrologic fluxes should be quantified in time and space at varying scales, under potential irrigation management practices. To fulfill this objective, a surface-subsurface modeling approach was applied to simulate watershed-scale hydrologic processes in the Cache la Poudre River Basin, Colorado, USA (4824 km2), in which both surface water irrigation and groundwater irrigation are prevalent. The model chosen for this study is the watershed model SWAT+, using the spatially distributed, physically based groundwater module gwflow, in which unconfined groundwater storage, flows, and interaction with land surface features are simulated using a collection of grid cells that represent control volumes of the aquifer. Major groundwater inflows and outflows include pumping, recharge, groundwater-channel exchange, groundwater-lake exchange, and tile drainage outflow. To investigate the impact of irrigation practices, detailed surface and groundwater irrigation routines and canal-aquifer interactions were added to the SWAT+ source code, requiring information of irrigation sources and irrigation canal locations throughout the river basin. Model calibration and testing was performed using monthly stream discharge and groundwater head. The calibrated model is used to quantify the impact of surface water and groundwater irrigation scenarios on water availability and hydrologic fluxes within the river basin. A total of 22 scenarios were conducted and grouped into five main groups: irrigation source, irrigation amount, irrigation type, canal bed thickness, and partial or full sealing of earthen irrigation canals. Using groundwater as the only irrigation source decreases groundwater discharge to streams (by 14 %) due to lowering groundwater levels; converting flood irrigation to sprinkler irrigation throughout the basin decreases surface runoff by 22 %; and sealing earthen canals leads to a lowering of groundwater levels, which decreases groundwater discharge to streams by 9 %, leading to an overall decrease in streamflow in the Cache la Poudre River and changes to temporal patterns in streamflow. Overall, irrigation amount and type and canal sealing have a small impact on total groundwater storage, compared to changes in the percent of fields irrigated by groundwater pumping. Results are helpful for informed decision-making in agriculture water management and can lead to sustainable, efficient, and equitable use of water resources, helping to address the challenges posed by water scarcity and environmental conservation.

Assessing the impact of surface water and groundwater interactions for regional-scale simulations of water table elevation

Groundwater flow models are increasingly considered for the regional scale simulation of hydraulic heads and water table elevation. In the most complete configuration, models explicitly simulate two-way interactions between surface water (SW) and groundwater (GW) to reproduce and forecast both SW and GW water levels. In most regional scale groundwater models, however, SW-GW interactions are represented by simplified boundary conditions that only allow one-way interaction from SW to GW, neglecting most of the dynamic exchange fluxes between SW and GW. To evaluate the potential consequences of such simplifications on the simulation of regional GW levels, we compare two models on a 36,900 km2 regional aquifer system in Southern Quebec. One model explicitly simulates both SW and GW flow with two-way SW-GW feedback and the other model only simulates GW flow with a surface boundary flux to represent a one-way interaction with the land surface. Both models are developed with the same numerical code to ensure that the only differences are the representation of SW water flow and SW-GW feedback. The one-way model simulates overall deeper water tables because it removes all exfiltrated groundwater from the system once it exits the subsurface, therefore not allowing exfiltrating groundwater to re-infiltrate. This effect is most pronounced in areas where the water table is close to the surface and for low-flow periods. The inclusion of two-way feedback also reduces the sensitivity of simulated GW levels to the magnitude of the hydraulic conductivity. This result highlights the need for additional data on other system states to improve the calibration of regional scale models that explicitly simulate two-way SW-GW interactions.

Quantifying the Impacts of Density-Dependent Flow on Surface Water–Groundwater Interaction in a Riparian Setup

Surface Water–Groundwater (SW–GW) interaction is a crucial aspect of the hydrological cycle and requires accurate modeling for reliable predictions. In many basic hydrological models and calculations, it is common to assume that the water density is constant. However, density-dependent flow, which accounts for changes in water density, plays a significant role in various hydrological processes. This study aims to quantify the effects of density-dependent flow on SW–GW interaction and evaluate the sensitivity of dominant hydrological drivers to density-dependent flow. Our simulations using the HydroGeoSphere model revealed that neglecting density-dependent flow in SW–GW interaction can lead to inaccurate estimations of water and solute balances. In particular, including density-dependent flow in the model yielded more realistic salinity distributions under gaining river scenarios and captured the gradual expansion of freshwater lenses under losing river scenarios. The results also indicated that under non-density-dependent flow, more saline groundwater is exposed to evapotranspiration, resulting in higher solute mass storage and a more saline unsaturated zone. Further, surface recharge and pumping rates played crucial roles in salinity distribution. This study highlights the critical importance of incorporating density-dependent flow in simulations, providing valuable insights for improving the accuracy of predictions and effectively managing water and solute balances in floodplain aquifers.