Salt domes are considered potential host rocks for nuclear waste disposal. Therefore, it is of particular interest to characterize nearby groundwater flow, which is driven by density differences from salt and temperature gradients. Thermohaline convection and radionuclide transport in fractured-porous media are investigated near a salt dome using 2D numerical simulations. A fractured thermohaline convection problem near a salt dome was defined using random fracture networks consisting of horizontal and vertical fractures. The basal temperature boundary condition (constant temperature or constant heat flux) was identified as a key methodological assumption that strongly influences thermal-only convection near a salt dome. The presence of fractures can enhance thermohaline convection strength. Matrix diffusion, porosity, and hydraulic conductivity significantly affect convection and radionuclide migration. Fracture networks with longer fractures or higher fracture density show stronger thermohaline convection and further radionuclide transport. Thermohaline convection and radionuclide transport depend highly on the particular realization of the fracture network. Individual fracture positions, lengths and orientations critically influence thermohaline convection strength and radionuclide migration. Fractures aligned with the dominant flow direction strengthen convection and enhance advective transport, whereas fractures orthogonal to the flow direction suppress convective strength and limit radionuclide migration. These findings suggest that fractures may introduce substantial uncertainty when simulating thermohaline convection and radionuclide transport near salt domes, which must be considered in the safety assessment of potential nuclear waste repositories.

Geothermal reservoir modeling often focuses on fractured or single-layer systems, even though multilayer porous aquifers offer an additional opportunity for geothermal energy extraction. This study examines how specific modeling assumptions influence the flow field and thermal evolution in stratified geothermal systems. It focuses on a representative multilayer aquifer of the Bückeberg Formation in the North German Basin. The targeted interval contains stacked sandstone units separated by claystone between depths of 1200 and 1400 m with reservoir temperatures around 70 °C and injection rates of several tens of litres per second.A three dimensional numerical model is developed in the open source software OpenGeoSys to evaluate groundwater flow and heat transport in this layered system. As the fluid viscosity is temperature-dependent, the resulting flow field evolves over time. To investigate the associated water distribution around the well, injection and extraction are represented using three numerical approaches. First, a pipe based implementation is used to explicitly model the flow through the wells so that the distribution of injected and produced water between the sandstone layers is not prescribed but governed by the geological and hydraulic properties of the multilayer aquifer. Further, two imposed injection concepts are applied for comparison: a line based source term and a source term defined on a cylindrical borehole surface. Moreover, the approximation of constant viscosity is assessed by comparison with simulations using both constant and temperature-dependent viscosity for the three well implementations. Preliminary results show that temperature-dependent viscosity noticeably alters the flow field and affects the evolution of production temperature. These tendencies confirm the relevance of viscosity formulation when analysing thermal behaviour in multilayer geothermal systems. The ongoing comparison of injection and extraction well approaches extends these findings by including the influence of inflow and outflow patterns on the flow field near the wells, where flow paths in multilayer aquifers are inherently more complex. This highlights the importance of choosing appropriate inflow and outflow conditions for modeling the thermo-hydraulic response of stratified reservoirs.

Leakage from aging sewer and stormwater pipes into the subsurface poses significant environmental risks and threatens the integrity of urban infrastructure, primarily through the degradation of groundwater quality and the alteration of urban water balances. While the presence of defects within pipe networks is well-documented, accurately quantifying volumetric exchange fluxes remains a challenge due to the complex, nonlinear interactions between the pipe, the surrounding variably saturated soil, and the fluctuating groundwater level. Current modeling approaches often overlook the threshold behaviors of these systems, leading to potential inaccuracies in leakage estimation. In this study, we show for the first time that leaky pipes can become hydraulically disconnected from the underlying groundwater, a phenomenon analogous to well-known river-groundwater interactions that include disconnection. In a sewer-groundwater context, hydraulic disconnection is restricted to point sources and is strongly influenced by colmation/clogging. Through numerical modeling of a hypothetical case study, we show that the leakage flux from the pipe (in absolute terms) initially increases with declining groundwater levels, until a critical depth below the leaky pipe is reached. After this point, the hydraulic communication from the groundwater to the leaky pipe stops and the leakage flux can be considered constant. In a sensitivity analysis, we demonstrate the impact of the individual hydraulic parameters of the leaky-pipe-groundwater system on the hydraulic disconnection. We further modify the properties of the aquifer material, resulting in a hydraulic disconnection depth of 0.89 m, 1.77 m and 4.00 m below pipe for sand, loamy sand and sandy loam aquifers, respectively. This insight has important implications for leakage modeling: once hydraulic disconnection occurs, the leakage flux becomes independent of groundwater dynamics. The present study provides a proof-of-concept for the mechanism by which leaky sewers hydraulically disconnect from groundwater.

Peatlands acquire only 3% of the terrestrial earth's surface; however, they store up to 30% of the global soil carbon. These peatlands also dominate the northern Hemisphere, which is covered by more than 25% of permafrost. An accelerating trend in the rate of permafrost degradation due to climate warming has been observed in most regions of the Northern Hemisphere. An indicator of permafrost degradation is the active layer depth, which is situated in the variably saturated zone. The hydraulic properties of the peatland top soil layer are influenced by its unstructured porous media, high organic matter, and high porosity. The water content in the variably saturated zone in cold regions is influenced by both drying-wetting and freezing-thawing cycles. The soil water characteristic curves (SWCC) define the relationship between unfrozen water content and matric potential. The soil freezing characteristic curves (SFCC) define the relationship between unfrozen water content and temperature around 0°C. The SWCC, SFCC, and the similarities between them have been intensively investigated for mineral soils in comparison to organic soils. The three main goals of the study for peatland permafrost mires are as follows: (i) Determine the SWCC using inverse modeling of transient evaporation experiments. (ii) Estimate the SFCC using field-based volumetric water content measurements using a simple empirical function. (iii) Compare and develop a relationship between the SWCC and SFCC. The lowland permafrost mires in the Abisko region, located in the northern part of Sweden, were investigated. For the SWCC evaporation experiments, 12 soil samples at six locations and two depths (10 and 25 cm) were taken. Inverse numerical modeling was used to fit and compare the three pressure-saturation functions: (i) Van Genuchten model. (ii) Peter Durner Iden (PDI)-variant of the Van Genuchten model (iii) PDI-variant of the bimodal van Genuchten model. The goodness of fit was checked by Root Mean Square Error and Akaike Information Criterion. It was observed that the PDI-variant of the bimodal van Genuchten model was most suitable for all the soil samples. 12 soil moisture sensors were also installed at the six locations and five depths (10 to 50 cm). An exponential logarithmic function with two parameters (transition temperature and temperature dispersion) was fitted to individual freezing and thawing curves from the soil moisture sensor data. The function showed a very good fit, and it was observed that the two fitting parameters were higher for thawing curves compared to freezing curves. A new SFCC function was developed based on the PDI variant of the bimodal van Genuchten model. This function was compared with the fitted SFCC logarithmic function. Reasonable differences were identified, which could be attributed to the field-installed soil moisture sensors and laboratory-conducted evaporation experiments. It is one of the few hydrological studies that has investigated the effects of bimodal behavior in organic soils on soil freezing and thawing. The measured parameters and datasets provide the necessary functions for developing cryohydrogeological models. The cryohydrogeological models can be used to assess the impacts of climate change on permafrost.

We carried out laboratory experiments of free thermal and thermohaline convection in homogeneous isotropic media using a laboratory-scale two-dimensional tank filled with glass beads representing a porous medium. Glass beads of different diameter were used in different experiments to achieve different permeabilities of the porous medium. Density and viscosity of the fluid were changed by initially introducing a salt (NaCl) solution, and by applying a heating device placed inside the tank. Fluid temperature inside the tank was measured over time on multiple thermocouples placed inside the tank on the inner glass walls. The fluid was dyed with two color tracers in order to visualize the emerging free convective flow pattern. The convective flow pattern was captured using a digital camera for the tracer distribution, and an IR camera for the temperature distribution. In subsequent numerical simulations, the experiments were successfully simulated numerically including density/viscosity variations and heat loss of the tank to the laboratory air across the back and front glass panes. Flow and transport parameters were calibrated using the results of the experiments with constant salinity. The set of calibrated parameter values was applied to successfully validate a thermohaline experiment with no need for further calibration. The processes of salt (NaCl) transport and heat transfer were both very accurately simulated in a single simulation. Analysis of flow velocities and streamlines showed that flow packages in a convection cell mostly follow a closed path such that there is little radial mixing. The approaches and results presented here can be used for interpretation, testing, and analysis of other simulation software of free thermohaline flow and transport.

Density-driven flow caused by concomitant differences in temperature and salinity, known as thermohaline convection, is important in understanding the circulation of deep geofluids, e.g., in geothermal energy production. We carried out experiments of free thermal and thermohaline convection in homogeneous isotropic media using a laboratory-scale two-dimensional tank filled with glass beads representing a porous medium. Glass beads of different diameter were used in different experiments to achieve different permeabilities of the porous medium. Density and viscosity of the fluid were changed by initially introducing a salt (NaCl) solution and by applying a heating device placed inside the tank. Fluid temperature inside the tank was measured over time on multiple thermocouples placed inside the tank on the inner glass walls. The fluid was dyed with two color tracers in order to visualize the emerging free convective flow pattern. The convective flow pattern was captured using a digital camera for the tracer distribution and an IR camera for the temperature distribution. In subsequent numerical simulations, the experiments were successfully simulated numerically including density/viscosity variations and heat loss of the tank to the laboratory air across the back and front glass plates. Flow and transport parameters were calibrated using the results of the experiments with constant salinity. The set of calibrated parameter values was applied to successfully validate a thermohaline experiment with no need for further calibration. The processes of salt (NaCl) transport and heat transfer were both very accurately simulated in a single simulation. The approaches and results presented here can be used for interpretation, testing and analysis of other simulation software of free thermohaline flow and transport. Analysis of flow velocities and streamlines showed that flow packages in a convection cell mostly follow a closed path such that there is little radial mixing.

Numerical modeling of permafrost dynamics requires adequate representation of atmospheric and surface processes, a reasonable parameter estimation strategy, and site-specific model development. The three main research objectives of the study are: (i) to propose a novel methodology that determines the required level of surface process complexity of permafrost models by conducting parameter sensitivity and calibration, (ii) to design and compare three numerical models of increasing surface process complexity, and (iii) to calibrate and validate the numerical models at the Yakou catchment on the Qinghai-Tibet Plateau as an exemplary study site. The calibration was carried out by coupling the Advanced Terrestrial Simulator (numerical model) and PEST (calibration tool). Simulation results showed that (i) A simple numerical model that considers only subsurface processes can simulate active layer development with the same accuracy as other more complex models that include surface processes. (ii) Peat and mineral soil layer permeability, Van Genuchten alpha, and porosity are highly sensitive. (iii) Liquid precipitation aids in increasing the rate of permafrost degradation. (iv) Deposition of snow insulated the subsurface during the thaw initiation period. We have developed and released an integrated code that couples the numerical software ATS to the calibration software PEST. The numerical model can be further used to determine the impacts of climate change on permafrost degradation.

Interactions between thermally driven seawater circulation and sub-seafloor basalt play an important role in global geochemical cycles, influencing the nutrient supply to deep-sea ecosystems and the formation of mineral deposits. In the off-axis area of ridge flank hydrothermal systems, low-permeability sediments may overlie the permeable basalt. However, seamounts protruding from the seafloor and faults provide hydraulic connections, giving rise to so-called hydrothermal siphons, in which one outcrop acts as a recharge and the other as a discharge site. Temperature measurements in bottom sediments have confirmed the occurrence of such circulation systems in the study area. Previous numerical models either used coarse numerical grids or were only able to show the general principles of such systems, e.g. by using pre-conditioned pressure fields. A numerical model with high grid resolution showed that flow is dominated by convection cells, which move horizontally at around 0.21 m/a, although the internal velocity distribution is large. Local recirculation cells form at both the recharge and the discharge sites.

Potash mining to obtain potassium generates large quantities of solid waste composed mainly of sodium chloride, accompanied in lesser quantities by magnesium sulfate and magnesium chloride, as well as insoluble clay minerals. The solid waste is disposed off on the ground surface to form tailings piles. In central Germany, there are dozens of potash tailings piles, some of which are more than two hundred meters high and form a unique landscape due to their appearance and lack of vegetation. Potash tailings are therefore exposed to climatic conditions such as rainfall, which may potentially dissolve salt, thus affecting the surrounding ecosystem including surface water bodies and groundwater. The environmental impact can likely be mitigated by applying soil covers over the potash tailings to limit and, in the best case, prevent the contact of the percolating water with the saline core of a pile. The efficiency of the soil covers is increased by applying a perennial vegetation layer to reduce the amount of water infiltration by interception, evaporation and plant transpiration. Therefore, the design of a cover system is based on the hydrological processes of the site, which include precipitation, surface runoff, evapotranspiration, in- and exfiltration and the water storage capacity of the soil. In addition, the type of soil cover and thus its hydraulic characteristics, the number of layers, the thickness of each layer, as well as the angle of slope of the layers can significantly influence the long-term efficiency of the cover. In conclusion, understanding the synergy between the soil cover and the potash tailing is essential to determine the effects caused on the surrounding environment, in particular on groundwater. The objective of this research work focuses on the numerical simulation of variably saturated water fluxes, in particular the creation of a water balance between surface runoff, in- and exfiltration and evaporation loss to the atmosphere in the soil cover. For this purpose, different configurations of vegetation covers are investigated and the capillary barrier effects are analyzed for each of them. The water flow through the potash tailing produced by the remaining infiltration through the vegetation cover is modeled for a hypothetical geometrical setting of a representative tailings pile.

In the overburden of salt domes, salt is dissolved by groundwater, resulting in groundwater flow under highly variable water densities. Density-dependent flow is therefore important in assessing potential migration pathways for radionuclides accidentally released from high-level nuclear waste repositories located in salt domes. Groundwater life expectancy has been established as a safety indicator for radionuclide travel times and is therefore of particular interest. The objective of this study is to numerically investigate and understand the effects of uncertain transport parameters on density-dependent flow above a salt dome. The effects of density-dependent flow and salt transport, along with the transport parameters on the groundwater life expectancy are investigated numerically using the FEM code Saltflow. Groundwater life expectancy can be directly simulated using an advection-dispersion equation. The life expectancy depends on the transport parameters in two ways, first via the flow velocities calculated in the density-dependent flow simulation which depend on the dispersion terms, and second directly for the calculation of the life expectancy. This suggests a strong and also highly non-linear dependence of life expectancy on the transport parameters. Preliminary results support this interpretation. Longitudinal macrodispersivity shows a considerable influence on groundwater life expectancy. Strongly non-linear results are also obtained depending on the transverse vertical dispersivity. Increasing the transverse dispersivity up to a certain threshold leads to an increase of the maximum life expectancy in the model domain. Above this threshold, which depends on the longitudinal dispersivity, the maximum life expectancy decreases. Life expectancy also strongly increases with a decreasing diffusion coefficient. These results highlight the importance of considering uncertainty in the transport parameters when numerically evaluating groundwater life expectancy in density-dependent flow in the context of nuclear waste disposal.

Soil shrinkage significantly alters hydraulic and thermal properties in peatland-dominated permafrost regions. This study examines the impact of shrinkage on soil water characteristic curves and thermal conductivity drying curves in Storflaket Mire, Sweden. Seven peat samples were collected at three depths close to the surface. The HYPROP and WP4C devices determined the soil water characteristic curve parameters. The HYPROP device is a transient evaporation experiment that measures soil water potential heads and corresponding volumetric water content. The WP4C measures the dry-range soil water potential and the corresponding volumetric water content. The VARIOS device was used to determine the thermal conductivity drying curves of the peat samples. The shrinkage effects were accounted for by measurements taken with a vernier caliper, followed by validation using a three-dimensional structured light scanner under air-dried conditions. The results from the hydrological experiments showed that shrinkage effects were most pronounced in the deepest layers. Comparing cases with and without shrinkage revealed a 40% reduction in volume under air-dried conditions. The hydraulic conductivity curves showed minimal changes between the cases with and without shrinkage, assuming that tortuosity remains constant with shrinkage. Including dry-range measurements was essential for a more reliable soil water characteristic curve representation. Shrinkage alongside dry-range measurements showed that the pore size distribution shifts from macropores (300–3000 μm) to micropores (3–30 μm), indicating reduced bimodality with depth. This change likely explains the higher matric potential in the deepest layers. The results from the thermal experiments revealed near-linear thermal conductivity drying curves, with dry surface peat exhibiting lower conductivity than saturated deeper layers. Empirical models based solely on volumetric water content outperformed traditional parameter-based models in predicting thermal conductivity.

Groundwater flow above deep geological repositories in salt domes may lead to the transport of radionuclides into the biosphere. To mitigate this risk, groundwater age is used as an exclusion criterion for repository site selection, and groundwater life expectancy is an established measure for radionuclide travel times. Complexities arise in computing age since groundwater flow above salt domes is highly density-dependent due to the presence of brines. Groundwater flow and solute transport are therefore strongly coupled and are also affected by mixing processes, including diffusion and mechanical dispersion, which are aquifer-specific and highly uncertain. Numerical simulations have been carried out to address this uncertainty for 2D topography-driven and density-dependent groundwater flow above salt domes. Simulation results show that the components of longitudinal and transverse dispersion have a strong influence on the density-dependent flow system and therefore, along with diffusion, significantly affect groundwater age and life expectancy. Underestimation of the associated parameters may lead to overestimation of life expectancy and the critical overestimation of repository safety. Selecting appropriate parameter values and consideration of their uncertainty for mixing processes is therefore critical when modeling life expectancy in the safety assessment of repository sites.

Modeling peatland hydraulic processes in cold regions requires defining near-surface hydraulic parameters. The current study aims to determine the soil freezing and water characteristic curve parameters for organic soils from peatland-dominated permafrost mires. The three research objectives are as follows: (i) Setting up an in situ soil freezing characteristic curve experiment by installing sensors for measuring volumetric water content and temperature in Storflaket mire, Abisko region, Sweden; (ii) Conducting laboratory evaporation experiments and inverse numerical modeling to determine soil water characteristic curve parameters and comparing three soil water characteristic curve models to the laboratory data; (iii) Deriving a relationship between soil freezing and water characteristic curves and optimizing this equation with sensor data from (i). A long-lasting in situ volumetric water content station has been successfully set up in sub-Arctic Sweden. The soil water characteristic curve experiments showed that bimodality also exists for the investigated peat soils. The optimization results of the bimodal relationship showed excellent agreement with the soil freezing cycle measurements. To the best of our knowledge, this is one of the first studies to establish and test bimodality for frozen peat soils. The estimated hydraulic parameters could be used to better simulate permafrost dynamics in peat soils.

AbstractIn natural environments, fluid density and viscosity can be affected by spatial and temporal variations of solute concentration, for example, due to saltwater intrusion in coastal aquifers, leachate infiltration from waste disposal sites, and upconing of saline water from deep aquifers. Potentially unstable situations may arise in which a dense fluid overlies a less dense fluid. This situation can produce instabilities manifested by dense plume fingers moving vertically downwards counterbalanced by vertical upward flow of the less dense fluid. The resulting free convection increases solute transport rates over large distances and times relative to constant-density flow. Unstable brine flow is further complicated if the porous medium is variably saturated. The results from a laboratory experiment of variably saturated variable-density flow and solute transport from Simmons et al. (2002) are used as the physical basis to define a new mathematical benchmark. This benchmark aims at realistically reproducing the experimental fingering patterns. Random hydraulic conductivity fields were used in the simulations as a numerical perturbation method to realistically mimic the observed dense plume fingering. The HydroGeoSphere code coupled with PEST are used to calibrate the parameter set that defines the benchmark. A grid convergence analysis is performed to obtain the adequate spatial and temporal discretizations. The new mathematical benchmark is useful for model comparison and testing of variably saturated variable-density flow in porous media. Simmons CT, Pierini ML, Hutson JL (2002) Laboratory investigation of variable-density flow and solute transport in unsaturated–saturated porous media. Transp Porous Media. 47(2): 215–244, 10.1023/A:1015568724369.

In natural environments, fluid density and viscosity can be affected by spatial and temporal variations of solute concentration, for example, due to saltwater intrusion in coastal aquifers, leachate infiltration from waste disposal sites, and upconing of saline water from deep aquifers. Potentially unstable situations may arise in which a dense fluid overlies a less dense fluid. This situation can produce instabilities manifested by dense plume fingers moving vertically downwards counterbalanced by vertical upward flow of the less dense fluid. The resulting free convection increases solute transport rates over large distances and times relative to constant-density flow. Unstable brine flow is further complicated if the porous medium is variably saturated. The results from a laboratory experiment of variably saturated variable-density flow and solute transport from Simmons et al. (2002) are used as the physical basis to define a new mathematical benchmark. This benchmark aims at realistically reproducing the experimental fingering patterns. Random hydraulic conductivity fields were used in the simulations as a numerical perturbation method to realistically mimic the observed dense plume fingering. The HydroGeoSphere code coupled with PEST are used to calibrate the parameter set that defines the benchmark. A grid convergence analysis is performed to obtain the adequate spatial and temporal discretizations. The new mathematical benchmark is useful for model comparison and testing of variably saturated variable-density flow in porous media. Simmons CT, Pierini ML, Hutson JL (2002) Laboratory investigation of variable-density flow and solute transport in unsaturated–saturated porous media. Transp Porous Media. 47(2): 215–244, 10.1023/A:1015568724369.

The Tibetan Plateau (TP) is also called the “Third pole” because its aquifers constitute the origin for several major rivers, which are the water supply for millions of people all over Asia. Groundwater is the most important fresh water resource, however population is continuously growing, resulting in an increasing need of water supply. Due to the remote character of the TP, hydrogeological aquifer information is scarce, which leads to uncertain water resource management. To ensure future sustainable water supply, aquifer characterisation is therefore an important issue on the TP. This study is motivated by the need of increasing hydrogeological knowledge on the TP and provides the physical and numerical hydrogeological characterisation of the Zhagu subcatchment, which is a subcatchment of the third largest lake on the TP: the Nam Co Lake. This project is part of the International Research Training Group “Geoecosystems in transition on the Tibetan Plateau” (TransTiP), funded by the DFG. Multiple interdisciplinary geophysical (electrical resistivity tomography, ERT), lithological (grain size analysis) and hydrogeological methods (observed hydraulic heads, hydraulic conductivity and recharge estimation) followed by numerical groundwater flow modeling (OpenGeoSys6, OGS6) were applied in order to hydrogeologically characterize the Zhagu subcatchment. The interdisciplinary results reveal the existence of a Quaternary hydrostratigraphic unit (Zhanongtang-Ganmanong aquifer). Furthermore, the results show three hydraulic conductivity zones in the Zhagu subcatchment. Monsoonal recharge in 2018 ranged between 108 and 242 mm and covered 30% to 67% of monsoonal precipitation. The physical results were interpreted into a conceptual model, which was prerequisite for the numerical groundwater flow model. For model calibration, the parameter estimation code PEST was coupled to OGS6. The model was successfully calibrated against hydraulic heads. The simulation results reveal that hydraulic head distribution ranged between 4691 and 5043 m and groundwater fluxes flow from the Zhagu subcatchment into the Nam Co lake by 0.03 m3m-2s-1. This study provides an overall insight into the hydrogeological conditions of the remote Nam Co catchment on the TP. The new insights of the hydrostratigraphic unit and numerical groundwater flow modeling results are helpful in order to improve current hydrological water balances, which neglect and/or assume groundwater inflow fluxes. In future, the calibrated model can be used for different water extraction and/or climate change scenarios in order to evaluate anthropogenic and climate change influences on the regional aquifer. This study and further future physical and numerical hydrogeological analyses can help to develop a sustainable water management on the TP.

EDITORIAL article Front. Water, 04 May 2022Sec. Water and Hydrocomplexity https://doi.org/10.3389/frwa.2022.913844

Urban flood warning systems need fast response times between the rainfall forecast and the flood alarm. Flood forecasts from physically based numerical models usually need much computation time. Flood forecasts based on databases from previous events or pre-simulated events can speed up the process of decision making. This work introduces and compares four distance metrics for temporal rainfall patterns used in a nearest neighbour based forecast system for dynamic water levels and velocities during pluvial floods. The system uses a database of 960 pre-calculated flood events. The performance of each metric is evaluated by analysis of time-series of flow variables. For the error quantification,a procedure to find a small number of representative locations in an urban catchment is described. A new approach to quantify the similarity of dynamic flow fields is introduced, which makes use of particle transport tracking. The four distance metrics are tested on forecast for four exemplary pluvial flood events resulting from rainfall of durations between 15 and 50 min and return-periods between 10 and 100 years. The best metric is based on the temporal precipitation pattern and takes the response time of the drainage system into account. If the pattern has a very short duration, a simpler characterisation-metric can be used, which takes the total volume, peak intensity and peak position into account.

Climate change and pollution are posing additional unprecedented threats to existing water resources, especially to water supply from karst aquifers in Mediterranean and semi-arid regions. A numerical model considering the most important key hydraulic parameters can forecast the impact of any given input on model quality and quantity output. In this work, we propose to model flow and transport using Comsol multiphysics in a synthetic model and to apply it to a simplified real case study (Jeita spring in Lebanon supplying water to 1.5 million inhabitants). The model geometry consists of a 5300 m long variably saturated horizontal conduit portrayed as 1) 2-D continuum and/or 2) a channel draining a porous equivalent matrix (400 m thick). Flow is simulated using the Richards Equation in both saturated and unsaturated medium. Recharge is applied vertically as both diffuse and point source in a shaft linked to the conduit. Percentages of fast infiltration rates are obtained from the analysis of event time series recorded at the spring (electrical conductivity and discharge). Flow rates at the outlet are used for transient model calibration. Mean velocities, dispersivities, and phreatic conduit diameters obtained from tracer experiments under various flow periods are used for transport validation in the channel. The aim is to test the validity of a functional simplified flow model on a complex real case and to identify based on a sensitivity analysis the key parameters that allow an optimal calibration of such a model.