Groundwater Flow Model Research Articles

Mathematical Modeling of Groundwater Flow: A Case Study of Foundation Piles in the Vicinity of Danube River

This study investigated the interaction of groundwater flow and foundation piles located in the vicinity of the Danube River. The piles represent an obstacle to the groundwater flow, causing a backwater effect upstream whilst increasing the local flow velocity. On the other hand, a high flow velocity around the piles can cause suffusion of the surrounding soil in the long term, thus significantly reducing the shaft resistance of the piles. A 3D model of groundwater flow and its impact on the piles was developed in the software 10.3 package GMS based on MODFLOW 2005. The model was calibrated by comparing the calculated results with the measured values in the control well for different values of the filtration coefficients. In the calibration process, foundation piles were not applied in the model. After the calibration process, the piles were implemented into the model and the underground flow was simulated in the study area for the calibrated year 2006. The impact analysis was carried out by comparing the groundwater level change over time in the pile zone at three control points, in cases with and without the piles, along with the flow net analysis at the piles’ location. The results indicate no influence of the piles on the groundwater flow in the study area, both in terms of critical flow velocities and a possible backwater effect upstream.

Developing a cost-effective emulator for groundwater flow modeling using deep neural operators

Current groundwater models face significant challenges in their implementation due to heavy computational burdens. To overcome this, our work proposes a cost-effective emulator that efficiently and accurately forecasts the impact of abstraction in an aquifer. Our approach uses a deep neural operator (DeepONet) framework to learn operators that map between infinite-dimensional function spaces via deep neural networks. The goal is to infer the distribution of hydraulic heads in a confined aquifer in the presence of a pumping well. We successfully tested the DeepONet framework on multiple problems, including forward time-dependent problems, an inverse analysis, and a nonlinear system. Additionally, we propose a novel extension of the DeepONet-based architecture to generate accurate predictions for varied hydraulic conductivity fields and pumping well locations that are unseen during training. Our emulator’s predictions match the target data with excellent performance, demonstrating that the proposed model can act as an efficient and fast tool to support a range of tasks that require repetitive forward numerical simulations or inverse simulations of groundwater flow problems. Overall, our work provides a promising avenue for developing cost-effective and accurate groundwater models.

Three-dimensional inter-basin groundwater flow toward a groundwater-fed stream: Identification, partition, and quantification

Inter-basin groundwater flow (IGF), defined as groundwater flows across the topographic divides, occurs in nature as a common phenomenon, and seriously affect water balance and solute transport in a basin. Although the existence of IGF has been checked in drainage basins with indirect methods, such as using information of hydrogeochemistry, few studies are conducted to directly identify and quantify the IGF in the three-dimensional (3D) space using numerical modeling of groundwater flow. In this study, we identify, partition and quantify IGF based on a regional-scale 3D groundwater flow model covering several traditional surface water basins. The investigation is focused on the Hailiutu River, a groundwater-fed stream in the Ordos Plateau, China. It is the first time that the source zones and 3D paths of IGF as well as its contribution to the streamflow are fully captured for a groundwater-fed stream. Results indicate that the IGF contributes 36%∼59% to the baseflow and 32%∼52% to the streamflow of the Hailiutu River, through different groups of circulation paths with the maximum depth up to ∼ 1000 m. Uncertainty analyses of the model show that the contribution of IGF to the streamflow is positively correlated to the infiltration recharge and hydraulic conductivities of the aquifer media. Several indirect methods are also checked for comparison, but they could only be used to assess the potential contribution of IGF, not the IGF paths. This study will facilitate in deeply understanding the evolution mechanism of the inter-basin groundwater circulation and the interaction between surface water and groundwater.

Status and Prospects for Development of Groundwater Flow and Transport Modeling Techniques to Address the Long-Term Radiation Safety Issues

Status and Prospects for Development of Groundwater Flow and Transport Modeling Techniques to Address the Long-Term Radiation Safety Issues

Impact of increasing vegetation coverage on gaining and losing streams in an arid endorheic river watershed

AbstractTo improve the ecology in northern China, the Chinese government has launched a series of revegetation projects. However, the impact of increasing vegetation coverage on gaining and losing streams remains largely unexplored, particularly in arid endorheic watersheds with frequent exchanges of water and other materials between surface water and groundwater. To address this, we modified the vegetation growth module of the soil and water assessment tool (SWAT) to simulate the vegetation coverage change proposed for the middle and lower reaches of the Bayin River. We then coupled the modified SWAT to a modular finite‐difference groundwater flow model to simulate the surface and subsurface water exchange. Hydrological, meteorological, and hydrogeological observation data were then used to build and calibrate the coupled model for the period 2001–2019. We set two vegetation coverage scenarios (non‐revegetation and vegetation) and two irrigation variants (non‐irrigation and irrigation) to investigate the impact of changes in vegetation coverage and the related irrigation variant on gaining and losing streams. The results showed that the vegetated land area and annual leaf area index both increased significantly between 2019 and 2001. The groundwater discharge to the gaining streams was more strongly affected by revegetation and related irrigation than the groundwater recharge from the losing streams. Irrigation related to revegetation emphasizes the effect of revegetation on streamflow. We suggest that in arid endorheic river basins, because of the related irrigation, revegetation has a substantial impact on groundwater level and streamflow, which is mainly composed of baseflow. Therefore, the irrigation efficiency of newly planted vegetation must be improved to stabilize the groundwater level and related ecological conditions.

Groundwater Flow Model Part Of Sokoto-Rima Hydrological Basin, Northwestern Nigeria

The aim of this work is to model the groundwater system of Zamfara part of Sokoto-Rima hydrological basin, under three objectives which are to evaluate the water budget, assess the interaction between surface water and groundwater, and to predict the temporal and spatial distribution of groundwater head and groundwater flow. MODFLOW-NWT, which is a Newtonian formulation for MODFLOW-2005, was used in the study. The result of sensitivity analysis revealed groundwater (RCH), evapotranspiration (EVT) and hydraulic conductivity (HKZ) had the highest composite scales. The water budget of the calibrated model showed that groundwater recharge was 5,571,293 m3 d-1, contributing 65.7% of total inflow (8,478,903 m3 d-1) to the aquifer. Inflow from river seepage represented 30.7% of the total inflow to the aquifer by 2,597,995 m3 d-1 while seepage from the general head boundary contributed 3.7% of the inflow to the aquifer by 309,615 m3 d-1. The outflow quantification of the aquifer showed that 75.8% (6,428,824 m3 d-1) of the total outflow was accounted to by evapotranspiration, the remaining 15 % (1,273,747 m3 d-1) outflow represented the river recharge, 8.6% (730,656 m3 d-1) to general head boundary (GBH), and 0.5% (45,678 m3 d-1) by pumping wells from the aquifer. Simulated groundwater level ranges between 202.9 m. asl and 688.5 m. asl, with an average level of 414.14 m. asl. Groundwater Flow model results indicated that the topography and geologic structures control groundwater flow in the study area and that base flow to river is an important factor moderating groundwater movement. This implies that the study area currently has sufficient groundwater resources to meet the demand, despite its fragile climate condition.

Quantifying aquifer interaction using numerical groundwater flow model evaluated by environmental water tracer data: Application to the data-scarce area of the Bandung groundwater basin, West Java, Indonesia

Study Region:Bandung groundwater basin, Indonesia. Study focus:Groundwater abstraction of various magnitudes, pumped out from numerous depths in a multitude of layers of aquifers, stimulates different changes in hydraulic head distribution, including ones under vertical cross-sections. This generates groundwater flow in the vertical direction, where groundwater flows within its storage from the shallow to the underlying confined aquifers. In the Bandung groundwater basin, previous studies have identified such processes, but quantitative evaluations have never been conducted, with data scarcity mainly standing as one of the major challenges. In this study, we utilize the collated (1) environmental water tracer data, including major ion elements (Na+/K+, Ca2＋, Mg2+, Cl−, SO42−,HCO3−), stable isotope data (2H and δ18O), and groundwater age determination (14C), in conjunction with (2) groundwater flow modeling to quantify the aquifer interaction, driven mainly by the multi-layer groundwater abstraction in the Bandung groundwater basin, and demonstrate their correspondence. In addition, we also use the model to quantify the impact of multi-layer groundwater abstraction on the spatial distribution of the groundwater level changes. New hydrological insights for the region:In response to the limited calibration data availability, we expand the typical model calibration that makes use of the groundwater level observations, with in-situ measurement and a novel qualitative approach using the collated environmental water tracers (EWT) data for the model evaluation. The analysis in the study area using EWT data and quantitative methods of numerical groundwater flow modeling is found to collaborate with each other. Both methods show agreement in their assessment of (1) the groundwater recharge spatial distribution, (2) the regional groundwater flow direction, (3) the groundwater age estimates, and (4) the identification of aquifer interaction. On average, the downwelling to the deeper aquifer is quantified at 0.110 m/year, which stands out as a significant component compared to other groundwater fluxes in the system. We also determine the unconfined aquifer storage volume decrease, calculated from the change in the groundwater table, resulting in an average declining rate of 51 Mm3/year. This number shows that the upper aquifer storage is dwindling at a rate disproportionate to its groundwater abstraction, hugely influenced by losses to the deeper aquifer. The outflow to the deeper aquifer contributes to 60.3% of the total groundwater storage lost, despite representing only 32.3% of the total groundwater abstraction. This study shows the possibility of quantification of aquifer interaction and groundwater level change dynamics driven by multi-layer groundwater abstraction in a multi-layer hydrogeological setting, even in a data-scarce environment. Applying such methods can assist in deriving basin-scale groundwater policies and management strategies under the changing anthropogenic and climatic factors, thereby ensuring sustainable groundwater management.

Groundwater flow modeling and recharge estimation of heterogeneous aquifer: Applied to Matmata aquifer, southeastern, Tunisia

Groundwater is an important source of water supply for several socioeconomic sectors. In particular, heterogeneous carbonate aquifers are an important potential reservoir of groundwater resources. The Matmata carbonate aquifer, located in southern Tunisia, suffers from over abstraction and severe anthropogenic pressure. This study aims to estimate diffusive recharge rates using climate and soil datasets, and proposes a combination of CMB techniques and numerical simulation methods. Groundwater chloride mass balance and numerical simulations were best practices for achieving these goals. The Hydrus-1D model was applied, calibrated and validated with soil water content measured at different depths and using long-term, diurnal-scale field and climate data. The results highlight that Richard's retention parameters give a close correlation with the observed saturated moisture content with RMSE of 0.07. The calculated evaporation is around 22.5 mm for the entire study period, and the contribution of rainfall to infiltration, which was estimated at 9.8 mm as 8.4%. The CMB model shows a recent recharge rate 4.83 mm. yr−1, corresponding to a groundwater recharge rate of 5.84 % of precipitation. Groundwater recharge estimation is one of the most important concepts of water balance, and its assessment is crucial for groundwater management and protection.

Investigating Multilayer Aquifer Dynamics by Combining Geochemistry, Isotopes and Hydrogeological Context Analysis

Geochemical tracers have the potential to provide valuable insights for constructing conceptual models of groundwater flow, especially in complex geological contexts. Nevertheless, the reliability of tracer interpretation hinges on its integration into a robust geological framework. In our research, we concentrated on delineating the groundwater flow dynamics in the Innisfil Creek watershed, located in Ontario, Canada. We amalgamated extensive hydrogeological data derived from a comprehensive 3D geological model with the analysis of 61 groundwater samples, encompassing major ions, stable water isotopes, tritium, and radiocarbon. By seamlessly incorporating regional physiographic characteristics, flow pathways, and confinement attributes, we bolstered the efficiency of these tracers, resulting in several notable findings. Firstly, we identified prominent recharge and discharge zones within the watershed. Secondly, we observed the coexistence of relatively shallow and fast-flowing paths with deeper, slower-flowing channels, responsible for transporting groundwater from ancient glacial events. Thirdly, we determined that cation exchange stands as the predominant mechanism governing the geochemical evolution of contemporary water as it migrates toward confined aquifers situated at the base of the Quaternary sequence. Fourthly, we provided evidence of the mixing of modern, low-mineralized water originating from unconfined aquifer units with deep, highly mineralized water within soil–bedrock interface aquifers. These findings not only contribute significantly to the development a conceptual flow model for the sustainable management of groundwater in the Innisfil watershed, but also offer practical insights that hold relevance for analogous geological complexities encountered in other regions.

Quantitative analysis and modeling of groundwater flow using visual MODFLOW: a case from subtropical coal mine, northwest Bangladesh

Quantitative analysis and modeling of groundwater flow using visual MODFLOW: a case from subtropical coal mine, northwest Bangladesh

Comparison of different pilot point parameterization strategies when measurements are unevenly distributed in space

The parameterization of spatially distributed hydraulic properties is one of the most crucial steps in groundwater modeling. A common approach is to estimate hydraulic properties at a set of pilot points and interpolate the values at each model cell. Despite the popularity of this method, several questions remain about the optimum number and distribution of pilot points, which are determining factors for the efficiency of the method. This study proposes a strategy for optimal pilot point parameterization that minimizes the number of parameters while maximizing the assimilation of an observed dataset unevenly distributed in space. The performance of different pilot point distributions has been compared with a synthetic groundwater model, considering regular grids of pilot points with different spacings and adaptive grids with different refinement criteria. This work considered both prior and iterative refinements, with a parameter estimation step between successive refinements. The parameter estimation was conducted with the Gauss–Levenberg–Marquardt algorithm, and the strategies were ranked according to the number of model calls to reach the target objective function. The strategy leading to the best fit with the measurement dataset at the minimum computational burden is an adaptive grid of pilot points with prior refinement based on measurement density. This strategy was successfully implemented on a regional, multilayered groundwater flow model in the south-western geological basin of France.

Simulation of the impact of sea level rise groundwater flooding along the south-eastern coast of India

Sea-level rise affects low-lying coastal regions that jeopardize superficial infrastructure through groundwater flooding, which also impacts near-surface artificial structures, inhumed networks, and near-shore ecosystems. In the present study, groundwater flow modeling has been utilized to simulate different scenarios of sea level rise to evaluate the groundwater level changes and predict possible vulnerable zones to groundwater inundation along the coast of the Nagapattinam district. The model has been simulated for ten years (2010–2019) under the transient condition with MODFLOW-2000 engine in Visual MODFLOW. Calibration and validation of the simulated model have been performed by trial-and-error method considering groundwater heads of selected observations well data, which results in a root mean square value of 1.765 m, 0.941 as correlation coefficient, and a value of 0.687 m as the standard error. Groundwater flooding due to a 0.6 m sea level rise is forecasted to cause significant flooding, covering 23.83% of the study area. A 1.0 m rise in sea level impacts 26.2% of the study region. The sea level rise scenarios evaluate that the coastal groundwater heads will reduce as they are restricted by topography from rising landward. The present study suggests groundwater in the coastal regions is influenced by sea level rise due to climate change impacting the coastal ecosystems.

Stable Isotopes and Water Level Monitoring Integrated to Characterize Groundwater Recharge in the Pra Basin, Ghana

In the Pra Basin of Ghana, groundwater is increasingly becoming the alternative water supply due to the continual pollution of surface water resources through illegal mining and indiscriminate waste discharges into rivers. However, our understanding of hydrogeology and the dynamics of groundwater quality remains inadequate, posing challenges for sustainable water resource management. This study aims to characterize groundwater recharge by determining its origin and mechanism of recharge prior to entering the saturated zone and to provide spatial estimates of groundwater recharge using stable isotopes and water level measurements relevant to groundwater management in the basin. Ninety (90) water samples (surface water and groundwater) were collected to determine stable isotope ratios of oxygen (δ18O) and hydrogen (δ2H) and chloride concentration. In addition, ten boreholes were installed with automatic divers to collect time series data on groundwater levels for the 2022 water year. The Chloride Mass Balance (CMB) and the Water Table Fluctuation (WTF) methods were employed to estimate the total amount and spatial distribution of groundwater recharge for the basin. Analysis of the stable isotope data shows that the surface water samples in the Pra Basin have oxygen (δ18O) and hydrogen (δ2H) isotope ratios ranging from −2.8 to 2.2‰ vrs V-SMOW for δ18O and from −9.4 to 12.8‰ vrs V-SMOW for δ2H, with a mean of −0.9‰ vrs V-SMOW and 0.5‰ vrs V-SMOW, respectively. Measures in groundwater ranges from −3.0 to −1.5‰ vrs V-SMOW for δ18O and from −10.4 to −2.4‰ vrs V-SMOW for δ2H, with a mean of −2.3 and −7.0‰ vrs V-SMOW, respectively. The water in the Pra Basin originates from meteoric source. Groundwater has a relatively depleted isotopic signature compared to surface water due to the short residence time of infiltration within the extinction depth of evaporation in the vadose zone. Estimated evaporative losses in the catchment range from 51 to 77%, with a mean of 62% for surface water and from 55 to 61% with a mean of 57% for groundwater, respectively. Analysis of the stable isotope data and water level measurements suggests a potential hydraulic connection between surface water and groundwater. This hypothesis is supported by the fact that the isotopes of groundwater have comparatively lower values than surface water. Furthermore, the observation that the groundwater level remains constant in months with lower rainfall further supports this conclusion. The estimated annual groundwater recharge in the catchment ranges from 9 to 667 mm (average 165 mm) and accounts for 0.6% to 33.5% (average 10.7%) of mean annual precipitation. The total estimated mean recharge for the study catchment is 228 M m3, higher than the estimated total surface water use for the entire Pra Basin of 144 M m3 for 2010, indicating vast groundwater potential. Overall, our study provides a novel insight into the recharge mechanism and spatial quantification of groundwater recharge, which can be used to constrain groundwater flow and hydrogeochemical evolution models, which are crucial for effective groundwater management within the framework of the Pra Basin’s Integrated Water Resources Management Plan.

Regional Groundwater Flow Modeling Using Improved Isogeometric Analysis: Application and Implications in Unconfined Aquifer Systems

Regional Groundwater Flow Modeling Using Improved Isogeometric Analysis: Application and Implications in Unconfined Aquifer Systems

Numerical Study on the Influence of Aquitard Layer Distribution and Permeability Parameters on Foundation Pit Dewatering

Evaluating the influence of geologic features on dewatering efficiency, particularly within strata of varying permeability, is critical to optimizing dewatering designs for deep excavations. In river valley areas, river sedimentation results in a discontinuous distribution of relatively aquitard layers (clay layers). The evaluation and calculation of the distribution and permeability parameters for foundation pit dewatering are very important when on-site geological data are insufficient. For this purpose, the deep excavation pit on the right bank and floodplain of Chongjiang River is taken as an example in this article. A three-dimensional groundwater flow model was constructed using the Unstructured Grid (MODFLOW-USG) software package version 1. The model was carefully calibrated using hydrogeologic features and observed groundwater levels to ensure its reliability. The simulation results effectively reproduce actual dewatering processes. The study reveals the following findings: (1) Increased aquitard layers (clay layer) enhance the barrier effect, thereby improving dewatering efficiency. (2) Increased clay layer permeability and storage coefficients reduce dewatering efficiency, while the specific yield of the clay layer has less pronounced effects. (3) Due to the discontinuous nature of the clay layer, dewatering rates are higher when the clay layer is below the riverbed than when it is in the flow boundary area (foothills).

Numerical simulation of different pollutant control measures around an old landfill contaminated site: A field scale study

The remediation of contaminated soils is a great challenge for global environmental sciences and engineering. The landfill was a kind of infrastructure to deal with waste from different sources while it would also cause the threat to groundwater. Cut-off walls and pumping wells were usually applied in the landfill to prevent the spread of pollutants to wider areas. However, the combination of using both of methods was rarely analyzed, especially using field data for calibrating and fitting groundwater flow and pollutant transport. 7 monitoring wells were arranged in the study area to survey the subsurface seepage. The pollution monitoring was carried out for a period of 50 days, covering 31 types of inorganic and organic pollutants. The concentration of 2,4,6-trichlorophenol (TCP) was 556.7 times greater than the standard concentration. A coupled numerical model of groundwater flow and pollutant transport was developed to assess the effectiveness of various control methods. Three options were tested, including the implementation of a single cut-off wall as well as a combination of a cut-off wall and a pumping well, for preventing the discharge of pollutants from landfills. The combination of a cut-off wall and a pumping well is the best strategy for removal of TCP. The combination approaches lead to a reduction of pollution plumes by a factor of 11 compared to the case without pollution control measures. The research findings may provide a basis and reference for the application of cutoff walls and pumping well in landfill sites or contaminated groundwater.

Rock core VOC profiles diagnostic of aquitard occurrence and integrity in a multi-layered sedimentary rock aquifer flow system

Aquitard assessment poses a challenge for practitioners and researchers managing dense non-aqueous phase liquid (DNAPL) contaminants in sedimentary rock aquifer systems. Within these systems, DNAPL migration and bulk hydraulic properties are controlled by fracture networks which are difficult to characterize at relevant scales with conventional methods. A previous study at a DNAPL contaminated site used contrasts in high-resolution vertical gradients to delineate four aquitards and two surfaces with poor vertical connectivity within a thick (>200 m) sedimentary rock aquifer system primarily composed of layered sandstones. In this study, we corroborate that method by using the existing DNAPL contamination as a tracer to identify and characterize the aquitards in the sequence and assess aquitard integrity. Closely spaced samples of rock from four continuous cores were collected and analyzed for volatile organic compounds (VOCs). The cores were collected along a transect perpendicular to groundwater flow and 75 m downgradient of the DNAPL source zone. Dissolved phase contaminant concentrations were collected using high-resolution multilevel systems placed along the plume centerline, downgradient from the source. The rock core and groundwater VOC concentration profiles suggest a primary aquitard limits vertical migration of both DNAPL and the associated dissolved phase contaminants, despite relatively large, downward gradients across its lower boundary. A calibrated, three-dimensional numerical groundwater flow model indicates an anisotropy factor of 1,000 for this aquitard. The Kv values for all four aquitards are only slightly lower than the values for the aquifers. However, the aquitard Kv values are 1–3 orders of magnitude less than their Kh values, and the aquitard Kh values are often similar to or even greater than the Kh values for the aquifers. Therefore, large anisotropy, rather than exceptionally low Kv values, distinguish the aquitards from the aquifers in this system. Fracture network characterization of nearby outcrops showed the anisotropy of the aquitards can be attributed to laterally extensive, bedding parallel partings coupled with short, frequently terminating, and poorly connected vertical fractures. In addition, the rock VOC profiles combined with fracture network data show that fracture termination surfaces can be powerful inhibitors of downward DNAPL migration providing additional evidence for the importance of these features in sedimentary rock flow systems. Ultimately, this study reveals the important influence of anisotropic aquitards on DNAPL migration, accumulation, and persistence, as well as associated plume migration. Furthermore, it demonstrates that subtle contrasts critical to aquitard integrity may be easily missed with long screened wells and other conventional, low resolution site characterization methods.

Transport of pollutants in groundwater of domestic waste landfills in karst regions and its engineering control technologies

Domestic waste produces leachate with a high concentration of pollutants in the landfill process due to biochemical degradation stages like compaction and fermentation. A large number of cases show that anti-seepage membranes widely used in refuse landfills tend to rupture under long-term tension and corrosion, causing leachate to enter the groundwater system and pollute the environment. To reveal the phenomenon of groundwater contamination in refuse landfills, typical domestic waste landfills in karst regions were examined, on the basis of a summary of hydrogeological conditions and hydrochemical characteristics, a three-dimensional groundwater flow model and solute transport model were constructed to analyze the pattern of pollutant diffusion, and its controlling factors, under the current conditions and massive rupture of anti-seepage membrane. The results show that with a minor rupture of the anti-seepage membrane, the area of the low pollution region increases first and then decreases while that of the slight pollution region continuously increases; When a massive rupture of the anti-seepage membrane appears, the ranges of heavy pollution region and total pollution regions continue to grow; Pollutant migrates along the same direction as the groundwater flow and diffuse from high concentration region to low concentration regions under the differential concentration effect. Based on the temporal-spatial distribution characteristics of groundwater pollutants, two engineering control schemes, namely, curtain grouting blocking and group well pumping, were established. A comparison of the two control schemes shows that group well pumping stably maintains water quality safety over the long term, pollutants overflow from both sides of the curtain after they have accumulated to a certain point of concentration, causing damage to the groundwater environment in the conservation area.

Conditional Karhunen–Loève regression model with Basis Adaptation for high-dimensional problems: Uncertainty quantification and inverse modeling

We propose a methodology for improving the accuracy of surrogate models of the observable response of physical systems as a function of the systems’ spatially heterogeneous parameter fields, with applications to uncertainty quantification and parameter estimation in high-dimensional problems. Practitioners often formulate finite-dimensional representations of spatially heterogeneous parameter fields using truncated unconditional Karhunen–Loève expansions (KLEs) for a certain choice of unconditional covariance kernel and construct surrogate models of the observable response with respect to the KLE coefficients. When direct measurements of the parameter fields are available, we propose improving the accuracy of these surrogate models by representing the parameter fields via conditional Karhunen-Loève expansions (CKLEs). CKLEs are constructed by conditioning the covariance kernel of the unconditional expansion on the direct measurements of the parameter field via Gaussian process regression, and then truncating the corresponding KLE.We apply the proposed methodology to constructing surrogate models via the Basis Adaptation (BA) method of the stationary hydraulic head response, measured at spatially discrete observation locations, of a groundwater flow model of the Hanford Site, as a function of the 1000-dimensional representation of the model’s log-transmissivity field. We find that BA surrogate models of the hydraulic head based on CKLEs are more accurate than BA surrogate models based on unconditional expansions for forward uncertainty quantification tasks. Furthermore, we find that inverse estimates of the hydraulic transmissivity field computed using CKLE-based BA surrogate models are more accurate than those computed using unconditional BA surrogate models.

Conceptual model of groundwater flow in a volcanic-sedimentary aquifer system of the Andean region of Chimborazo, Ecuador

The Chimborazo volcano is located in Ecuador's northern Andes and is one of the world's tallest mountains. The central valley of Riobamba's morphology, structure, and groundwater flow networks are all influenced by the evolution of this stratovolcano. Both the urban and rural populations in this area rely on groundwater extracted from volcano-sedimentary aquifers. This study presents a conceptual model of the groundwater flow system in the lower Chambo River basin (LCRB) based on the interpretation of geological, hydrogeological, hydrochemical, and stable isotope (δ18O and δ2H) data from 23 wells, 10 springs, two sources of surface water, and rainwater. The Tertiary-Quaternary volcanic-sedimentary infill of the Inter-Andean Valley, that overlies the Jurassic-Cretaceous metamorphic bedrock of the Eastern and Western cordilleras, gave rise to three multilayer aquifers (Llo-Guano, Riobamba, and Yaruques). In these aquifers, groundwater flows from the recharge of Chimborazo glaciers to deep circulation zones of low-elevation lands in Riobamba. In this pathway, groundwater evolves from acidic - low temperature - low electric conductivity bicarbonate waters to alkaline - high temperature - high electric conductivity sulfate waters discharged in the Chambo River. The stable isotope data confirmed the hypothesis of different types of water changing and interacting in the flow direction, demonstrating a dynamic hydrogeological system that evolves from the recharge area in Chimborazo, Igualata, and Altar volcanoes to the discharge area in the Chambo River.