Groundwater Flow Research Articles

SWAT Model Performance Using Spatially Distributed Saturated Hydraulic Conductivity (Ksat) and Varying-Resolution DEMs

Saturated hydraulic conductivity (Ksat) is a hydrologic flux parameter commonly used to determine water movement through the saturated soil zone. Understanding the influences of land-use-specific Ksat on the model estimation error of water balance components is necessary to advance model predictive certainties and land management practices. An exploratory modeling approach was developed in the physically based Soil and Water Assessment Tool (SWAT) framework to investigate the effects of spatially distributed observed Ksat on local water balance components using three digital elevation model (DEM) resolution scenarios (30 m, 10 m, and 1 m). All three DEM scenarios showed satisfactory model performance during calibration (R2 > 0.74, NSE > 0.72, and PBIAS ≤ ±13%) and validation (R2 > 0.71, NSE > 0.70, and PBIAS ≤ ±6%). Results showed that the 1 m DEM scenario provided more realistic streamflow results (0.315 m3/s) relative to the observed streamflow (0.292 m3/s). Uncertainty analysis indicated that observed Ksat forcings and DEM resolution significantly influence predictions of lateral flow, groundwater flow, and percolation flow. Specifically, the observed Ksat has a more significant impact on model predictive confidence than DEM resolution. Results emphasize the potential uncertainty of using observed Ksat for hydrological modeling and demonstrate the importance of finer-resolution spatial data (i.e., 1 m DEM) applied in smaller watersheds.

Numerical model with Moving Particle Method coupling groundwater and surface water flow

Numerical model with Moving Particle Method coupling groundwater and surface water flow

Combining groundwater and game-theoretical models for determining the sustainable yield in a heavily stressed aquifer system

Sustainable groundwater abstraction is nowadays widely debated and the application of criteria available in the literature is not easy depending on site-specific features of the systems. In the Tivoli Plain (Rome, Italy) the same groundwater resource is exploited by an important thermal plant for therapeutic purposes and is subject to dewatering for the extraction of travertine by numerous quarries, thus representing a significant case of conflict among different resources users. The study proposes a new approach in defining the sustainability of groundwater exploitation by matching the results of groundwater flow model with those of a game model. From the conceptual hydrogeological model and the numerical flow simulations, the sustainability conditions for the groundwater withdrawals are obtained and the hydrodynamic interferences between the different users are assessed. The results of numerical simulations were encapsulated in the game-theoretical model in order to find conceptual solutions to maximize the profit related to quarry’s economy and, at the same time, to limit the quantitative and qualitative decline of the thermal waters. Assuming that the sustainability of the groundwater abstraction from the quarry area depends on ensuring residual groundwater flow to the thermal springs and the river, a cooperative game among the different players has been developed. The strategy of a player is bound by the influence of dewatering on the springs and the river and the player’s utility is proportional to the total quantity of travertine extracted. Results indicate that the “price of sustainability” would be around a 23% reduction of the total exploited travertine volume, driven by an overall reduction in dewatering of about 31%, if compared to that necessary to reach the maximum depth of excavation. For the different groups of quarries the reduction of the pumping flow is not homogeneous but varies according to the position of the pumping center in the groundwater flow net and its distance from boundaries to be captured. Therefore, the combination of the flow model with the game model solutions appears to be a valuable tool to achieve sustainable groundwater management in a conflicting situation among different users. In addition, the game model allows to introduce other players and/or to find out other, non-cooperative solutions.

Hydrological responses to historical and predicted land use/land cover changes in the Welmel watershed, Genale Dawa Basin, Ethiopia: Implications for water resource management

Study regionWelmel watershed, Genale-Dawa Basin, Ethiopia. Study focusThis study aimed to analyze the hydrological impacts of land use/land cover (LULC) changes in the Welmel watershed for 1990–2020 and to predict the LULC change impact on the hydrological status in the year 2050. The hybrid land use classification technique for classifying Landsat images; Cellular-Automata Markov (CA-Markov) for prediction of the 2035 and 2050 LULC; and the Soil and Water Assessment Tool (SWAT) for hydrological modeling were employed in the analyses. New hydrological insights for the regionThe findings revealed that from 1990 to 2020, significant alterations in the hydrological regime occurred due to historical LULC changes in the Welmel watershed, which are expected to continue in the 2035 and 2050 periods. Forest cover loss and expansion of agricultural areas, which occurred from 1990 to 2020, have resulted in increased annual flow (6.18%), wet seasonal flow (10.21%), and surface runoff (25.32%), and reduced dry seasonal flow (6.34%), groundwater flow (17.17%, and evapotranspiration (0.36%). The 2035 and 2050 LULC indicate further increased annual flow, wet seasonal flow, and surface runoff, and reduced dry seasonal flow, groundwater flow, and evapotranspiration. The study also stated the hydrological impacts of the LULC changes at the sub-watershed scales. More noticeable changes in hydrological components have been observed at the sub-watershed scale, mainly associated with the uneven spatial distribution of LULC changes. The findings provide valuable insights for policymakers, water resource managers, and local communities in formulating strategies to enhance water resource management practices in the Welmel watershed and similar regions. It could also be for researchers and Academia who can be benefited and it can be used to supplement global goals like Sustainable Development Goal 6 (SDG 6): ensure the availability and sustainable management of water and sanitation for all.

Geophysical investigation of aquifer flow unit characteristics in northern parts of Akwa Ibom State, Southern Nigeria

The heterogeneous nature of the aquifer system poses significant challenges to both aquifer delineation into hydraulic flow units (HFUs) and the assessment of groundwater flow efficiency. This heterogeneity leads to changes in aquifers’ hydraulic parameters, which include porosity, flow and storage capacities, permeability, flow Zone Indicator (FZI) and aquifer quality index (AQI). Thus, the key aim of this study is to examine aquifer flow unit characteristics in Ikot Ekpene and Obot Akara municipalities by categorizing the units into distinctive HFUs via the combined application of the electrical resistivity technology (ERT), Stratigraphic Modified Lorenz Plot (SMLP) and Flow Zone Indicator (FZI) techniques. The area is shown to comprise successions of three to four sandy layers with minor clay interbeddings at few locations from the ERT results. The aquifer units are found in layers two and three respectively at depths of between 1.6 and 30.2 m with 30.2–89.0 m thickness. The results of the FZI technique identify two distinct HFUs in the area with respective discrete rock typing (DRT) values of 14 and 15 whereas that of the SMLP method reveal 5 unique HFUs, each characterised by similar flow characteristics. The delineated flow units from the SMLP results are classified as conductors with a fair efficiency ranking. This ranking seems to correlate with the DRT results for the delineated unconsolidated sandy and gravelly sand aquifers, which are shown to be perfectly heterogeneous. These findings from this maiden study in the area are very promising and provide useful insights on groundwater flow characteristics in the area to assist groundwater resource regulating authorities and policy makers in making decisions on appropriate location of new water boreholes to satisfy the mushrooming water needs of the local population.

Using natural gas content of groundwater to improve the understanding of complex thermo-mineral spring systems

The varied gaseous composition of thermo-mineral waters emerging in a non-active zone reflects the diversity and complexity of groundwater pathways and provides important insights into their hydrogeological behaviours. The investigated geochemical content of complex thermo-mineral springs revealed the need to use dissolved gas contents as part of a multi-tracer approach to discriminate processes, geogenic (water–gas-rock interactions), abiotic (geological confinement, flow paths) and biotic activity influencing geochemical of groundwater along regional pathways. Irrespective of the dissolved element content or the water type, examining the overall concentration of dissolved gases enables an effective delineation of regional groundwater flow paths. Using dissolved gas content further contributed to the circumvention of some analytical challenges associated with conventional isotopic or geochemical techniques, often linked to the high concentration of elements such as iron, sulfate, sulfide or other naturally occurring elements content. The primary objectives are to analyse the gas composition of individual springs, to identify the origin of these gases in the groundwater, and to use this gas composition to improve the understanding of the flow patterns contributing to the geochemical diversity observed at the surface. From field investigations in a geologically and structurally complex area of Eastern Corsica (France), three types of gas contents are identified: (type 1) CH4 & H2S-rich, (type 2) N2-rich and (type 3) CO2-rich. The study of these dissolved gases highlights that the wide geochemical diversity of thermo-mineral waters observed here is not only related to the mineralogical composition of the local aquifer but also involves strong and cumulative interactions along deep regional circulation pathways. This approach also reveals a common deep crustal gaseous influence characterised by N2 production, which interacts during up flow with groundwater and then with the local metamorphic or sedimentary rock matrix. The groundwater’s isotopic and geochemical contents are then altered by local lithologies encountered through both abiotic and biotic interactions. Finally, at shallow depths, phreatic groundwater can add its geochemical and isotopic footprint and dilute this complex mixture before groundwater emerges as mineral spring. This paper answers the primary objectives yet further demonstrates that using dissolved gas as a tracer of groundwater flow paths allows a deeper interpretation of surface geochemical and isotopic observations, distinguishes local from regional flow paths, and provides information about processes at the origin of groundwater diversity.The combination of tools presented in this paper (i.e., geochemical, dissolved gas, and isotopic tools) allows the establishment of a reliable regional groundwater flow scheme for thermo-mineral waters in a non-active zone. This scheme is essential to improve thermo-mineral water management, and protection to ensure their sustainable quality in front of increasing anthropogenic and climatic pressures.

Influence of karst conduit’s geometry and morphology on 3D flow and transport processes: Insights from 3D tracer tests and numerical modelling

In karst, the characterization of subsurface solute and contaminant transport is a major issue that has been widely investigated due to the high vulnerability of these hydrosystems. In former studies, several researchers addressed these needs with different approaches such as laboratory experiments, field experiments, or groundwater flow and transport simulations. The objective of such approaches is to improve knowledge of transport processes in karst hydrosystems, and propose solutions to limit the downstream hydrogeological risks (contamination of water resources). In this study, we performed the 3D mapping of the karst conduit, which outlet is the Lez spring (southern France) to get the precise geometry and morphology of this fully water-filled karst conduit. Then we injected a dye in the water-filled karst conduit and performed a continuous monitoring of dye tracer recovery at three different cross-sections located downstream the injection spot, at a distance of 40 m, 90 m and 160 m, respectively. In each cross-section, five submersible fluorometer probes were positioned at different locations (top, right, down, left and central parts) along the cross-section of the karst conduit. Experimental data allowed to reconstruct the transient spatial distribution of concentration for each cross-section, which allowed assessing the propagation and evolution of solute plume over time. Monitored data also provided information about dye mixing along the karst conduit and were used to investigate the effect of karst conduit geometry, flow turbulences and velocity profiles on the mixing processes and propagation of solute plume along the conduit with numerical models. Modelling results showed that the consideration of 3D mapped karst conduit geometry and morphology allows a much better reproduction of observed transport processes and breakthrough curves, than the one obtain when considering simplified conduit geometry and morphology.

Coupled hydro-thermal flow and radionuclide transport driven by spatial variation of heat-generating radioactive wastes in shale formations

Deep geologic disposal of multiple nuclear waste packages with various heat sources can induce nonuniform hydro-thermal behaviors in the near-field of the repository, consequently influencing the long-term radionuclide transport in the far-field once waste form breach initiates. This study looks into three cases with variation in the spatial order of six groups of heat sources (10th, 50th, 75th, 90th, 95th, and 99th percentiles of heat outputs generated from 1,981 as-loaded dual-purpose canisters in the field site) in a shale-hosted repository with respect to the uni-directional groundwater flow (from west to east): (1) cooler waste packages from west to east, (2) hotter waste packages from west to east, and (3) hottest waste packages in the middle of the repository. Our field-scale PFLOTRAN simulation represents heat-driven multiphysics coupled mechanisms, including multiphase flow, heat transfer, and chemical/radioactive transport, and also, calculates the onset of waste form breach based on temperature-dependent canister vitality. The results from this sensitivity study will quantify the short- (less than 1 × 103 years) and long-term (up to 1 × 106 years) impacts of sporadic heat pulses from waste package on the spatio-temporal perturbation in hydro-thermal flow quantities and the rate of radionuclide transport in both near- and far-field of the repository system.

Hydraulic containment of TCE contaminated groundwater using pulsed pump-and-treat: Performance evaluation and vapor intrusion risk assessment

Remedial actions for groundwater contamination such as containment, in-situ remediation, and pump-and-treat have been developed. This study investigates the hydraulic containment of Trichloroethylene (TCE) contaminated groundwater by using pulsed pump-and-treat technology. The hypothetical research site assumed the operation of pulsed pump-and-treat to manage groundwater contaminated with 0.1 mg/L of TCE. at the pump-and-treat facility. Numerical models, employing MODFLOW and MT3DMS for groundwater flow and contamination simulations, were used for case studies to evaluate the performance and risks of pump-and-treat operation strategies. Evaluation criteria included capture width, removal efficiency, and contaminant leakage. Health risks from TCE leakage were assessed using a vapor intrusion risk assessment tool in adjacent areas. In the facility-scale case study, the capture width of the pump-and-treat was controlled by pumping/injection well operations, including schedules and rates. Pumping/injection well configurations impacted facility efficiencies. Pulsed operation led to TCE leakage downstream. Site-scale case studies simulated contaminant transport through pump-and-treat considering various operation stages (continuous; pulsed), as well as various reactions of TCE in subsurface environment (non-reactive; sorption; sorption and biodegradation). Assuming non-reactive tracer, TCE in groundwater was effectively blocked during continuous operation stage but released downstream in the following pulsed operation stage. Considering chemical reactions, the influences of the pump-and-treat operation followed similar trends of the non-reactive tracer but occurred at delayed times. Groundwater contamination levels were reduced through biodegradation. Cancer and non-cancer risks could occur at points of exposure (POEs) where the contamination levels approached or fell below TCE groundwater standards.

Multi-gauge calibration comparison for simulating streamflow across the Major River Basins in Madagascar: SWAT + Toolbox, R-SWAT, and SWAT + Editor Hard calibration

Abstract This paper aims to improve the Soil and Water Assessment Tool (SWAT) model performance across the Major River Basins in Madagascar (MRBM), specifically for SWAT simulation in the Manambolo, Onilahy, Mananara, and Mandrare basins. A multi-gauge calibration was carried out to compare the performance of SWAT+ Toolbox, and R-SWAT, SWAT+ Editor Hard calibration on a monthly time step for the periods 1982–1999. We found that the SWAT+ model generated greater surface runoff, while the SWAT model resulted in higher groundwater flow in both CSFR and CHIRPS datasets. It has been demonstrated that the SWAT+ Toolbox had more potential in calibrating runoff across the MRBM compared to R-SWAT. Calibration in both methods led to a reduction in surface runoff, percolation, water yield, and curve number but increased the lateral flow, evapotranspiration (ET), and groundwater flow. The results showed that the multi-gauge calibrations did not significantly enhance simulation performance in the MRBM compared to single-site calibration. The performance of the SWAT+ model for runoff simulation within the SWAT+ Toolbox and R-SWAT was unsatisfactory for most basins (NSE < 0) except for Betsiboka, Mahavavy, Tsiribihina, Mangoro, and Mangoky basins (NSE = 0.40–0.70; R2 = 0.45–0.80, PBIAS≤ ±25), whether considering the CHIRPS or CSFR datasets. Further study is still required to address this issue.

Ammonium enrichment, nitrate attenuation and nitrous oxide production along groundwater flow paths: Carbon isotopic and DOM optical evidence

Dissolved organic matter (DOM) plays a crucial role in the biogeochemical processing of reactive nitrogen in groundwater systems. However, the impacts of DOM on release of geogenic ammonium and transport and transformation of reactive nitrogen including nitrate attenuation under dynamics in groundwater level characteristic for floodplain environments remain unclear. In this study, we have identified the influence of riparian water level fluctuations on changes in the redox conditions, groundwater geochemical composition including the DOM mobilization in the piedmont recharge and the discharge area along groundwater flow paths. We have also evaluated the pivotal roles of DOM degradation in transport and transformation of nitrogen species including geogenic ammonium enrichment, nitrate attenuation, and dissolved nitrous oxide (N2O) production combining the stable carbon isotopic signatures and the optical characteristics of DOM. Along groundwater flow paths, the seasonal amplitudes of surface water levels were higher in the piedmont recharge area than those in the plain discharge area, and four DOM fluorescent components were identified through the parallel factor analysis (PARAFAC), with two terrestrial humic-like components (C1 and C2) in the piedmont recharge area, and two microbial humic-like components (C3 and C4) in the plain transition-discharge area. A positive correlation between stable dissolved inorganic carbon isotopic signatures (δ13C-DIC) and ammonium-nitrogen concentrations indicated that microbial degradation processes of DOM concomitantly promote the release of geogenic ammonium into groundwater. Ammonium enrichment and nitrate attenuation trend in groundwater was noted as one moved from the recharge area to the discharge area. Evidently, a clear correlation emerged where elevated dissolved N2O concentrations were linked to diminished ammonium-nitrogen levels and elevated nitrate-nitrogen levels. Additionally, groundwater exhibited higher dissolved N2O levels in the piedmont recharge area compared to the plain discharge area. These findings revealed that the impacts of groundwater DOM degradation on nitrate attenuation and dissolved N2O production in similar geogenic ammonium-affected Quaternary alluvial aquifers along groundwater flow paths, and established the theoretical basis for ensuring the security of local groundwater supply.

Origin of Fracture-Controlled Conduits in Calcite-Rich Highly Productive Aquifers Impregnated with Diagenetic Silica

The origin of highly permeable flow paths in carbonate-siliciclastic rocks, such as large-aperture fractures in aquifers in the Eastern Bohemian Cretaceous Basin (EBCB), is poorly understood. The karst potential was assessed from the rock carbonate content and the degree of disintegration after leaching in HCl. Surprisingly, dissolution of calcite in EBCB usually did not lead to rock disintegration until calcite > 78%. Instead, porosity increased significantly. High-porosity rock is held together by microns-thick secondary silica cement with a foam-like structure and considerable tensile strength. Three types of conduits occur in the EBCB: (i) bedding-parallel conduits associated with calcite-rich layers, (ii) subvertical fracture swarm conduits that develop on damaged zones of fracture swarms, and (iii) conduits formed by dissolution of calcite veins by groundwater flow. These are ghost-rock karst features where calcite is leached from the rock in the first phase and the residue is washed out by conduits under steep hydraulic gradients in the second phase. Very similar features have been described in Minnesota and Wisconsin, USA. Research has shown that fractures with sharp-edged walls that give the impression of an extensional tectonics origin may actually be ghost-rock karst features in which dissolution and piping have played an important role in their enlargement.

Impacts of hydrofacies geometry designed from seismic refraction tomography on estimated hydrogeophysical variables

Abstract. Understanding the critical zone processes related to groundwater flows relies on subsurface structure knowledge and its associated parameters. We propose a methodology to draw the patterns of the subsurface critical zone at the catchment scale from seismic refraction data and show its interest for hydrological modelling. The designed patterns define the structure of a physically based distributed hydrological model applied to a mountainous catchment. With that goal, we acquired 10 seismic profiles covering the different geomorphology zones of the studied catchment. We develop a methodology to analyse the geostatistical characteristics of the seismic data and interpolate them over the whole catchment. The applied geostatistical model considers the scale variability of the subsurface structures observed from the seismic data analysis. We use compressional seismic wave velocity thresholds to identify the depth of the soil and saprolite bottom boundaries. Assuming that such porous compartments host the main part of the active aquifer, their patterns are embedded in a distributed hydrological model. We examine the sensitivity of classical hydrological data (piezometric heads) and geophysical data (magnetic resonance soundings) to the applied velocity thresholds used to define the soil and saprolite boundaries. Different sets of hydrogeological parameters are used in order to distinguish general trends or specificities related to the choice of parameter values. The application of the methodology to an actual catchment illustrates the interest of seismic refraction in constraining the structure of the critical zone subsurface compartments. The sensitivity tests highlight the complementarity of the analysed hydrogeophysical data sets.

Providing Enhanced Insights into Groundwater Exchange Patterns through Downscaled GRACE Data

The measurement of groundwater exchange between neighboring regions is a critical topic in water resource management and can usually be achieved through a combination of field investigations and the use of groundwater flow models. In this study, we employed the water balance and Darcy’s law methods, utilizing downscaled Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow On (GRACE-FO) data to assess groundwater exchange patterns in the Beijing-Tianjin-Hebei (BTH) region of China. Additionally, we determined the contributions of human activities and climate factors to the observed variations via residual analysis. The results revealed a consistent decrease in groundwater storage in the study area since 2008, especially in the spring and summer months. The groundwater exchange rates calculated by 1° and 0.05° groundwater storage anomalies (GWSAs) were basically consistent, and the downscaled GWSAs could better reflect the small-scale groundwater exchange characteristics. The groundwater exchange rate showed a decreasing trend from the Piedmont plain to the coastal areas. A notable trend of declining groundwater exchange between the Taihang Mountains and Piedmont plains was observed, and the downward trend gradually intensified from north to south between 2003 and 2007. After 2008, there was an increasing trend, and coastal areas exhibited the smallest amount of groundwater exchange. Human activities emerged as the predominant factor accounting for more than 90.9% of the overall reduction in groundwater storage, while climate change imposed a minimal influence on groundwater storage variations. The insights obtained in this study hold significant implications for groundwater resource planning and management in the region.

Estimation of groundwater recharge from groundwater level fluctuations and baseflow rates around Mount Meru, Tanzania

Estimating groundwater recharge, direct runoff and baseflow is essential for understanding groundwater resource availability and managing groundwater systems. This study estimates groundwater recharge, direct runoff and baseflow on two slopes of Mount Meru: the northern and southern slopes using the water-table fluctuation (WTF) method and baseflow separation technique. High-frequency groundwater level measurements in five shallow wells over three hydrological years from 2018 to 2021 were analysed, while streamflow data in four gauging stations over nine hydrological years from 2010 to 2019 were used. The results of the WTF method show that the aquifer undergoes an average recharge of 544 mm/year and 90 mm/year on the south-western and north-eastern slopes, respectively. On average, this recharge is about 53% and 13% of the annual rainfall on each slope. The baseflow results show that the aquifer on the south-eastern and north-western slopes recharges an average of 88 mm/year and 54 mm/year, respectively, which is on average about 12% and 7% of annual rainfall, respectively. In general, the high recharge on the south-western slope is attributed to the high rainfall, and the high hydraulic conductivity and high hydraulic diffusivity of the pyroclastic deposits compared to the debris avalanche deposits on the north-eastern slope. In addition, debris avalanche deposits show homogeneous recharge conditions, while pyroclastic deposits show heterogeneous recharge conditions. The WTF method can be useful to identify areas of preferential recharge so that preferential groundwater flow paths can be mapped for focused recharge of surface runoff during the rainy season.

A dynamic modeling approach to predict water inflow during tunnel excavation in relatively uniform rock masses

Karst landforms are widely distributed all over the world. With the continuous improvement of infrastructure construction, tunnelling in mountainous karst areas is inevitable. Due to the complex hydrogeological conditions in karst areas, groundwater inflow during tunnelling is usually difficult to predict and can cause huge economic losses and casualties. Therefore, finding better ways to improve the prediction of tunnel water inflow is of great significance to ensure the safety of tunnelling. In this study, three commonly used modules (CHD, DRAIN and CFPM1) in MODFLOW are selected and compared to predict the water inflow of tunnels. We find that the CFPM1 module performs better in terms of considering both tunnel size and actual water inflow dynamics during tunnel excavation, which is a continuous process rather than an instantaneous process. Secondly, we build a hypothetical case and predict the tunnel water inflows using above three different modules. We find that the CHD module yields the largest initial and stable water inflow, followed by the DRAIN module, and the CFPM1 yields the least. Besides, as the most sensitive factor in the CFPM1 module, the influence of tunnel diameter on water inflow is discussed. Finally, taking the Shizishan Tunnel as an actual field example, we compare the simulation results of different modules with the measured tunnel inflow. In general, the prediction of the CFPM1 module is the closest to the measured value, and the prediction accuracy is the highest during the conventional tunnel construction process. However, when water-saturated karst features such as underground rivers, caves or faults are exposed during tunnelling, the water level may change instantaneously, which is more consistent with the principle of CHD module. In summary, this study provides theoretical and numerical support for the safe construction of relatively uniform rock mass tunnels in karst areas.

Comparison of three recent discrete stochastic inversion methods and influence of the prior choice

Groundwater flow depends on subsurface heterogeneity, which often calls for categorical fields to represent different geological facies. The knowledge about subsurface is however limited and often provided indirectly by state variables, such as hydraulic heads of contaminant concentrations. In such cases, solving a categorical inverse problem is an important step in subsurface modeling. In this work, we present and compare three recent inverse frameworks: Posterior Population Expansion (PoPEx), Ensemble Smoother with Multiple Data Assimilation (ESMDA), and DREAM-ZS (a Markov chain Monte Carlo sampler). PoPEx and ESDMA are used with Multiple-point statistics (MPS) as geostatistical engines, and DREAM-ZS is used with a Wasserstein generative adversarial network (WGAN). The three inversion methods are tested on a synthetic example of a pumping test in a fluvial channelized aquifer. Moreover, the inverse problem is solved three times with each method, each time using a different training image to check the performance of the methods with different geological priors. To assess the quality of the results, we propose a framework based on continuous ranked probability score (CRPS), which compares single true values with predictive distributions. All methods performed well when using the training image used to create the reference, but their performances were degraded with the alternative training images. PoPEx produced the least geological artifacts but presented a rather slow convergence. ESMDA showed initially a very fast convergence which reaches a plateau, contrary to the remaining methods. DREAM-ZS was overly confident in placing some incorrect geological features but outperformed the other methods in terms of convergence.

On the computation of the Basal Envelope Surface of Talwegs using the Analytic Element Method

The stream network is a major feature of a landscape, conveying water, sediment, and solute from hillslopes to the ocean. Noticeably, from a large-scale point of view, the elevation of the talwegs of perennial streams is an important head boundary condition for both surface and groundwater flow originating from hillslopes. Assuming a wireframe (1D) representation of talweg lines, the problem of interpolating elevation between talwegs has received attention for applications such as flood mapping using Height Above Nearest Drainage (HAND, [Nobre et al., 2011]), or groundwater level interpolation in low-conductivity aquifer systems. In this study we propose an alternate definition of this large-scale base level concept introduced by [Wyns et al., 2004], namely the Basal Envelope Surface of Talwegs (BEST) and the associated Height Above the Basal Envelope Surface of Talwegs (HABEST), along with a procedure to compute it using the Analytic Element Method (AEM). It can be defined as the head distribution satisfying Laplace equation (Darcy flow with vanishing divergence), with stream segments set as Dirichlet boundary conditions. The BEST is thus the real part of a complex analytic (holomorphic) function which can be modeled using analytic slit elements, with very low computational requirements and without the need for kriging, as it is often seen in the literature. This analytic model is extended to the case of a non-zero, uniform divergence flow (head distribution satisfying a Poisson equation) which can be useful to analyse groundwater levels at catchment scale.

Is subsurface geophysics as seismic and acoustic investigations a rescue to groundwater flow inversion?

Is subsurface geophysics as seismic and acoustic investigations a rescue to groundwater flow inversion?

Modeling the influence of climate on groundwater flow and heat regime in Brandenburg (Germany)

This study investigates the decades-long evolution of groundwater dynamics and thermal field in the North German Basin beneath Brandenburg (NE Germany) by coupling a distributed hydrologic model with a 3D groundwater model. We found that hydraulic gradients, acting as the main driver of the groundwater flow in the studied basin, are not exclusively influenced by present-day topographic gradients. Instead, structural dip and stratification of rock units and the presence of permeability contrasts and anisotropy are important co-players affecting the flow in deep seated saline aquifers at depths >500 m. In contrast, recharge variability and anthropogenic activities contribute to groundwater dynamics in the shallow (<500 m) freshwater Quaternary aquifers. Recharge fluxes, as derived from the hydrologic model and assigned to the parametrized regional groundwater model, reproduce magnitudes of recorded seasonal groundwater level changes. Nonetheless, observed instances of inter-annual fluctuations and a gradual decline of groundwater levels highlight the need to consider damping of the recharge signal and additional sinks, like pumping, in the model, in order to reconcile long-term groundwater level trends. Seasonal changes in near-surface groundwater temperature and the continuous warming due to conductive heat exchange with the atmosphere are locally enhanced by forced advection, especially in areas of high hydraulic gradients. The main factors controlling the depth of temperature disturbance include the magnitude of surface temperature variations, the subsurface permeability field, and the rate of recharge. Our results demonstrate the maximum depth extent and the response times of the groundwater system subjected to non-linear interactions between local geological variability and climate conditions.