Numerical Groundwater Model Research Articles

Numerical groundwater modelling under changing water abstraction in Weyib watershed, Ethiopia

Numerical groundwater modelling under changing water abstraction in Weyib watershed, Ethiopia

The hidden consequences of sea level rise: assessing vulnerability of buried infrastructure to groundwater inundation in American Samoa

Abstract To island nations, sea level rise (SLR) is an existential threat. An insidious and often hidden consequence of SLR is groundwater inundation (GWI), which reduces the unsaturated zone causing flooding, enhanced corrosion, and reduced service life of buried utilities. In the Pacific, SLR may reach 0.6–2.5 m by the end of century, and on Tutuila, American Samoa (AS), apparent SLR is five times the global average, making adaptation planning critically important. This study addresses the climate impact-knowledge-gap regarding AS's infrastructure by combining a numerical groundwater model with buried and surface utility data to map where adaptation efforts should be prioritized. Rigorous studies of GWI are few, and this study is the first to model this phenomenon in the South Pacific. The model estimates that 70 km or 45% of the buried water, electrical, and sewer lines will be inundated, and 28% of present-day roads, 13.6% of buildings, and 20% of water-booster stations will be permanently flooded under a 2.4-m SLR scenario with projected recharge in 2100. These effects are often overlooked by or unknown to policy and decision makers; therefore, building awareness of GWI will help managers in AS and in other island communities to prioritize holistic adaptation actions.

A New Socio-Hydrology System Based on System Dynamics and a SWAT-MODFLOW Coupling Model for Solving Water Resource Management in Nanchang City, China

To address the issue of seasonal water resource shortages in Nanchang City, a multi-system coupling socio-hydrology simulation method was proposed. This approach involves dynamically integrating a centralized socio-economic model with a distributed surface water groundwater numerical model to explore the intricate relationships between the socio-economic system, the surface water–groundwater integrated system, and the outcomes related to seasonal water resource shortages. Taking Nanchang City as an example, this study conducted research on the water resource supply and demand balance, as well as the groundwater emergency supply, using the multi-system coupling model. Three scenarios were established: status quo, developing, and water-saving. The results show that with the increasing total water demand of social and economic development, the severity of the water resource shortage will be most pronounced in 2030. The minimum water resources supply and demand ratios for the status quo, developing, and water-saving scenarios are projected to be 0.68, 0.52, and 0.77, respectively. To meet residents’ water needs during drought conditions, emergency groundwater supply efforts are investigated. According to the simulation results, groundwater emergency supply would increase the total population by 24.0 thousand, 49.4 thousand, and 11.2 thousand people, respectively, in the status quo, developing, and water-saving scenarios. In the water-saving scenario, the Youkou and Xiebu water sources can serve as suitable emergency water sources. In the status quo scenario, the Youkou water source is the most viable emergency water source. However, in the developing scenario, relying solely on any single water source for emergency supply could have an irreversible impact on the aquifer. Therefore, considering the simultaneous use of multiple water sources is recommended, as it can fulfill water demands while ensuring the sustainable utilization of groundwater resources.

Neural network predictions of drawdown from groundwater abstraction in the Egebjerg catchment, Denmark

Results from numerical simulations play a vital role in the decision process of everyday groundwater management. However, these simulations can be time-consuming for large-scale investigations, and it can be necessary to apply approximate methods instead. This study investigates the abilities of a neural network to replicate simulated drawdown from groundwater abstraction in a numerical groundwater model of the Egebjerg catchment, Denmark. We follow a generalised methodology that uses the information within the deterministic numerical model to create a training set for the neural network to learn from and extend the method to work in a 3D Danish groundwater model case. We compare the abilities of the trained neural network with the results of conventional computations in terms of speed and accuracy and argue that this approach has the potential to improve decision support for decision-makers within groundwater management.

Hydrogeological characterization of the Silala River catchment

AbstractThis article reviews hydrogeological studies carried out between 2016 and 2018 in the Silala River basin, a catchment shared by Chile and Bolivia. These were conducted in the context of the Case Concerning the Status and Use of the Waters of the Silala River, submitted to the International Court of Justice in 2016, and contributed to multidisciplinary science to demonstrate that this system is an international watercourse. In 2016, the hydrogeological understanding of the Silala River basin was poor. The studies reviewed here filled many knowledge gaps, providing a solid hydrogeological baseline, and establishing new monitoring infrastructure to collect relevant aquifer data. The most important hydrogeological units were identified as the fluvial deposits, alluvial deposits, and the Cabana ignimbrite. The latter is highly heterogeneous, weathered and fractured, and exhibits a high permeability. It is the most important unit in terms of productivity, and is the major regional aquifer providing spring flows to Bolivian wetlands and groundwater flow across the international border. The studies provided a preliminary understanding of the main aquifers in Chile and their properties, which underpinned the development of a robust hydrogeological conceptual model of the system, reviewed elsewhere in this special issue. Subsequent refinements are also summarized. This work confirmed that both surface water and groundwater flows from Bolivia to Chile, and thus confirms the status of the Silala River as an international watercourse and provided the basis for a basin‐scale groundwater numerical model, used to investigate the impact of wetland channelization on surface water/groundwater partitioning.This article is categorized under: Science of Water > Hydrological Processes

An integrated framework for examining groundwater vulnerability in the Mekong River Delta region.

The Mekong River provides water, food security, and many other valuable benefits to the more than 60 million Southeast Asian residents living within its basin. However, the Mekong River Basin is increasingly stressed by changes in climate, land cover, and infrastructure. These changes can affect water quantity and quality and exacerbate related hazards such as land subsidence and saltwater intrusion, resulting in multiple compounding risks for neighboring communities. In this study, we demonstrate the connection between climate change, groundwater availability, and social vulnerability by linking the results of a numerical groundwater model to land cover and socioeconomic data at the Cambodia-Vietnam border in the Mekong River Delta region. We simulated changes in groundwater availability across 20 years and identified areas of potential water stress based on domestic and agriculture-related freshwater demands. We then assessed adaptive capacity to understand how communities may be able to respond to this stress to better understand the growing risk of groundwater scarcity driven by climate change and overextraction. This study offers a novel approach for assessing risk of groundwater scarcity by linking the effects of climate change to the socioeconomic context in which they occur. Increasing our understanding of how changes in groundwater availability may affect local populations can help water managers better plan for the future, leading to more resilient communities.

Simulation of lake-groundwater interaction under unsteady-state flow using the sloping lakebed method

Water exchange between lakes and aquifers directly affects the water balance in lakes, which is a challenging problem in groundwater numerical models. The refined characterization of the lake bottom in popular lake models often results in computational instability. In this article, a new method, namely, the groundwater-sloping lakebed method (SLM), is proposed for simulating unsteady-state flow in lakes and groundwater coupling. The SLM is based on the definition of lake units and the lake bottom setting method, which have been introduced in an article on stable flow coupling simulation. This method offers several advantages, which have been recognized in previous studies. In this article, we provide a detailed explanation of the equation to obtain the fully coupled exchange flux between lakes and groundwater for lake units with different water accumulation states. A modified calculation equation for the water storage term (confined storage coefficient and unconfined specific yield) and the hydraulic conductance of lake units is also presented based on the variation characteristics of the groundwater level. This equation can be used for unsteady-state numerical simulation of lake–groundwater coupling. Supported by the fully coupled lake–groundwater equation, the lake water level can be calculated based on strict equilibration of the lake water volume during each simulation period. Finally, the rationality of the SLM is verified through examples. The results indicate that the SLM coupled with lake–groundwater numerical simulation calculations is strict and stable. Therefore, this approach can be applied in regions with similar conditions and research requirements.

Comprehensive uncertainty analysis for surface water and groundwater projections under climate change based on a lumped geo-hydrological model

Sustainable management of aquifers requires long-term predictions of their aquifer-scale groundwater balance under climate change with meaningfully quantified uncertainty. In our analysis, we account for uncertainty in model parameters, measured data, model errors, stochastic model inputs (e.g., rainfall, potential evapotranspiration), and climate scenarios. To afford this analysis, we rely on an extension of lumped hydrological models that includes groundwater flow and storage, called lumped geohydrological model (LGhM). It shows good model performance and is three orders of magnitude faster than 2D or 3D numerical groundwater models. We use Markov chain Monte Carlo (MCMC) for Bayesian inference on a calibration period to quantify posterior parameter uncertainty and lumped data-and-model error. Then, we perform Monte Carlo forward runs with stochastic weather inputs under three different climate scenarios to quantify uncertainty in long-term predictions up to the year 2040. We apply our approach on a virtual reality representation of the Wairau Plain aquifer, New Zealand. We hypothesize that the variability in future climate is the most important impact factor. To test this hypothesis, we disentangle the overall uncertainty between data/model, parameters, weather, and climate inputs. We expect our approach to be highly useful for arbitrary types of catchments because the LGhM model structure can easily be adapted.

Groundwater pollution source identification using Metropolis-Hasting algorithm combined with Kalman filter algorithm

Increasing the precision of groundwater pollution source identification (GPSI) is crucial for groundwater pollution control and risk management. Bayesian theory based on the Markov Chain Monte Carlo (MCMC) method is a useful strategy of solving the GPSI problem. However, because of the nonlinear and uncertainty characteristics of GPSI, the Metropolis-Hasting (MH) algorithm, one of the most well-known MCMC algorithms, has the disadvantage of relatively low precision and is time-consuming. To address this problem, the Kalman filter (KF) algorithm was combined with the MH algorithm and referred to as the Kalman filter Metropolis-Hasting (KF–MH) algorithm. The algorithm generates a new initial distribution that is close to the true value through a prior distribution, and the new initial distribution is used to perform subsequent iterations of the calculation. The viability and superiority of the proposed KF-MH algorithm were assessed in three hypothetical GPSI cases under different conditions. In the inversion process, a surrogate model was constructed using a temporal convolutional network (TCN) to reduce the computational pressure imposed by the numerical simulation model. The results of the TCN surrogate model in the cases illustrate the high accuracy of the TCN surrogate model in fitting the groundwater numerical model. In the three cases, the normalized errors between the identification results and the true values of the source features obtained with the KF–MH algorithm were significantly lower than those of the MH algorithm. The results indicate that the proposed KF–MH algorithm has higher inversion accuracy than the MH algorithm.

Examining the change in groundwater flow patterns: A case study from the plain area of the Baiyangdian Lake Watershed, North China

Examining the evolution of groundwater flow patterns is critical to understanding the hydrological cycle and plays an important role in the sustainable management of water resources and ecosystems. In this study, the plain area of the Baiyangdian Lake Watershed (PBW) was chosen as a typical area for severe water scarcity and ecological crisis in the North China Plain. We investigated the temporal and spatial variability in groundwater flow patterns from a holistic view of the water cycle in the PBW and explored more sustainable water resources management using multiple methods, including field surveys, historical data review, statistical analysis, and numerical groundwater modelling. The results show that the groundwater storage decreased by 494 × 108 m3 across the PBW from 1965 to 2019, while the groundwater level presented a decreasing trend for most of the period, which resulted in changes of Baiyangdian Lake and groundwater interactions. Human factors, such as groundwater extraction and water transfer projects, significantly influenced the evolution of groundwater flow patterns by generating a greater contribution of human factors to groundwater balance (54.23%) than that of climate change (45.77%). The hydrodynamic simulations imply that the interaction between groundwater and Baiyangdian Lake was dominated by groundwater recharging the river under natural conditions, and the influence depth of the interaction zone was within about 80 m underground; however, under anthropogenic disturbance, their interaction was altered to the lake recharging groundwater, with a maximum influence depth up to 135 m. Furthermore, considering the systematicity and zoning of the water cycle, we proposed a combination of different strategies, including restricted groundwater exploitation, increased water diversion and water use efficiency, and managed aquifer recharge, which could restore groundwater levels and groundwater storage over a 20-year period to realize sustainable groundwater development. This study highlights the spatiotemporal groundwater flow patterns in a changing environment and the associated hydrogeological processes and provides insights towards the development of more effective water management strategies.

Climate scenarios, groundwater models, and uncertainties in long-term safety

Abstract. Assessing future climate scenarios plays a fundamental role in evaluating the long-term safety of a repository for high-level radioactive waste (HAW). Over the assessment period of 1 million years, the repository is affected by various processes and developments that must be considered in the design of the repository. Predictions are complicated by the dynamics of the climate and are subject to uncertainties. The aim of this study is to evaluate uncertainties for various climate-induced processes that are relevant for the safety assessment of a repository for HAW. This research addresses fundamental questions concerning the impact of future cold stages on different regions of Germany, the differences between past and future cold stages, the transfer of future climate developments to stylized climate models, and the uncertainties resulting from these models. The study identifies the primary climate processes that could potentially affect the evolution of a HAW repository, including the formation of glaciers or ice sheets, the development of permafrost conditions, fluctuations in sea level, erosion, and isostatic adjustment. These processes can be represented in numerical groundwater models through parameter variations. In this project, these parameter variations and the impact of climatic states on different processes will be modeled for a sensitivity study. Finally, the results will be analyzed with respect to uncertainties, and possible improvements to dealing with uncertainties will be discussed. The focus of the presentation is on the climate impacts and the implementation in the model.

Wellfield optimization to minimize contaminant migration from a surficial to a semi‐confined aquifer using numerical modeling

AbstractThe shallow, Memphis, and Fort Pillow aquifers are the three major water‐bearing strata beneath Memphis, Tennessee, where the Memphis aquifer serves as the primary groundwater source. The upper Claiborne confining unit (UCCU) separates shallow and Memphis aquifers across the majority of Shelby County, acting as an upper protective layer for the Memphis aquifer. However, hydrogeologic breaches within the UCCU create a hydraulic connection and provide an avenue for potential contaminant migration from the shallow to the Memphis aquifer. This research aims to minimize contaminant migration, mitigate risks, extend existing wells' life that may face water contamination, and find suitable locations for future well construction. Several strategies are developed addressing well depth, seasonal well operation, and mapping no‐drilling or red zones to provide practical solutions. A numerical groundwater modeling technique is developed for each strategy that includes stochastic simulation–optimization and customized simulation models depending on the strategy. The models result in thousands of numerical simulations for each scenario to identify recurring patterns of contaminant movement to and through the Memphis aquifer. The results indicate that optimum well positions (spatially and vertically) and modification to pumping can increase the life expectancy of wellfields, offer sustainable management of the Memphis aquifer, and reduce contaminant migration through 2050.

Simulation of groundwater dynamic conditions in the Baiquan spring region under optimal groundwater resource allocation

Abstract Xingtai, once been famous city for its spring groups in history, has become one of the regions in the country where water resources are in high demand due to long-term over-exploitation in groundwater resource. In the region where the springs in the area have dried up and been cutting-off over the years, including Baiquan and Dahuo. In order to allocate the amount of water diverted from the Middle Section of South-North Water Diversion Project reasonably, to effectively make the springs re-rushing and restore the groundwater level, this research established a numerical groundwater model based on the hydrogeological conditions of the study area. The calculate model is used to discuss the hydrodynamical patterns changes and predict the flowrate of spring groups under different allocation of supplement diversion schemes quantifiably. It was found that the scheme of using the amount of river diversion to rehabilitate the Xingtai urban funnel was most conducive to the recovery of groundwater levels in the spring groups, which is due to the reduction in groundwater extraction has reduced the influence range of the urban funnel and improved the hydrodynamic conditions in the northern preferential runoff zone. The results have demonstrated the feasibility of re-rushing the spring groups.

The development of a hydrogeological conceptual model of groundwater and surface water flows in the Silala River Basin

AbstractFrom 1999 a dispute between Bolivia and Chile concerning the status and use of the Silala River developed. In 2016 it was taken before the International Court of Justice. Over time, a key disagreement between the parties emerged, concerning artificial channels in the headwater wetlands of the Silala River in Bolivia and their impact on the river and groundwater discharge from Bolivia to Chile. To quantify this, a numerical groundwater model was developed by Chile, requiring a hydrogeological conceptual model of the Silala River Basin, reviewed here. This focussed on understanding the groundwater system and its interactions with the Silala River. The data and information used to gain this understanding included geological mapping, drilling, satellite imagery interpretation, geophysical surveys, hydrogeochemical analyses, groundwater level monitoring, surface flow monitoring, and groundwater pumping tests. These were focussed along the course of the river and wetlands. A three‐dimensional geological model of the Silala Basin was based on these investigations. The groundwater model area covers the topographic catchment, plus three adjacent closed (endorheic) topographical catchments to the northeast, which together form the groundwater catchment of the Silala River. The main deep regional aquifer is found in ignimbrite pyroclastic rocks and an interbedded alluvial deposit, but secondary perched aquifers on the flanks of the Silala River ravine contribute to the complexity. Although uncertainty remains, the hydrogeological conceptual model describes the main observed features of the system in a scientifically sound and coherent manner, with appropriate detail to support a credible numerical model.This article is categorized under: Science of Water > Hydrological Processes Engineering Water > Sustainable Engineering of Water

Simulation of present and future land subsidence in the Rafsanjan plain, Iran, due to groundwater overexploitation using numerical modeling and InSAR data analysis

In the Rafsanjan plain, Iran, the excessive use of groundwater for pistachio irrigation since the 1960s has led to a severe water level decline as well as land subsidence. In this study, the advantages of InSAR analyses and groundwater flow modeling are combined to improve the understanding of the subsurface processes causing groundwater-related land subsidence in several areas of the region. For this purpose, a calibration scheme for the numerical groundwater model was developed, which simultaneously accounts for hydraulic aquifer parameters and sediment mechanical properties of land subsidence and thus considers the impact of water release from aquifer compaction. Simulation results of past subsidence are calibrated with satellite-based InSAR data and further compared with leveling measurements. Modeling results show that land subsidence in this area occurs predominantly in areas with fine-grained sediments and is therefore only partly dependent on groundwater level decline. During the modeling period from 1960 to 2020, subsidence rates of up to 21 cm year−1 are simulated. Due to the almost solely inelastic compaction of the aquifer, this has already led to an irreversible aquifer storage capacity loss of 8.8 km3. Simulation results of future development scenarios indicate that although further land subsidence cannot be avoided, subsidence rates and the associated aquifer storage capacity loss can be reduced by up to 50 and 36%, respectively, by 2050 through the implementation of improved irrigation management for the pistachio orchards.

Numerical modeling as a support tool for groundwater permits in the state of Bahia, Brazil

The western region of Bahia State is an important agricultural frontier in Brazil, generating a large increase in requests for groundwater usage in the last decades, mainly through large capacity water wells tapping the Urucuia Aquifer System (UAS). This study aims to develop a groundwater numerical model using the Visual MODFLOW software and the additional packages MODPATH and ZONEBUDGET to evaluate the effects of intensive groundwater pumping in eight possible scenarios of two areas (Central and Eastern) in the Alto Grande - São Desidério rivers sub-basin. Drawdown ranging from 4 to 20 m was observed in the different areas and scenarios. The analysis of the local flow path lines showed that the wells have an area of influence that captures part of the groundwater flow. The water balance indicated that the total volume pumped in the sub-basin did not reach 10% of the recharge in any scenario, considering the entire model domain. The high concentration of irrigation pumping wells in restricted areas resulted in a significant impact on the aquifer, reaching up to 84.6% of the local recharge, a value that is far above what is considered sustainable for the region. Results show that the eastern area is more susceptible to drawdown and changes in flow path lines by pumping. The applied method has proven to be useful to predict the effects of water abstraction on the aquifer before the implementation of projects, improving water resources management. Long-range forecasts and taking into account possible climate changes are also some of the advantages of the method, though it depends on reliable field hydrological and climate data.

A probabilistic assessment of surface water-groundwater exchange flux at a PCE contaminated site using groundwater modelling

Polluted groundwater discharge at a chlorinated solvent contaminated site in Hagfors, Sweden, is affecting a nearby stream flowing through a sparsely populated area. Because of difficulties related to source zone remediation, decision makers recently changed the short-term site management objective to mitigating discharge of polluted groundwater to the stream. To help formulating targeted remediation strategies pertaining to the new objective, we developed a groundwater numerical decision-support model. To facilitate reproducibility, the modelling workflow was scripted. The model was designed to quantify and reduce the uncertainty of surface water-groundwater (SW-GW) exchange fluxes for the studied period (2016–2020) through the use of history-matching. In addition to classical observations, thermal anomalies detected in fiber optic distributed temperature sensing (FO-DTS) measurements were used to inform the model of groundwater discharge. After assessing SW-GW exchange fluxes, we used measurements of surface water chemistry to provide a probabilistic estimation of mass influx and spatio-temporal distributions of contaminated groundwater discharge. Results show 1) SW-GW exchange fluxes are likely to be significantly larger than previously estimated, and 2) prior estimations of mass influx are located near the center of the posterior probability distribution. Based on this, we recommend decision makers to focus remediation action on specific segments of the stream.

Integrated Three‐Dimensional Geological and Numerical Groundwater Model Development

AbstractConceptual site model (CSM) development is a foundational step for numerical groundwater model construction. Tools for reviewing and combining disparate data to develop a CSM have been furthered through software that efficiently integrates multiple data streams, especially when a large amount of information is available at complex sites. Three‐dimensional (3D) interfaces for data visualization and geological modeling are becoming commonly used to compile data, support development of a robust CSM, and create effective visuals that enable project stakeholders to understand site complexity. This article describes a 3D interface workflow applied to a geological and numerical groundwater modeling case study where numerical modeling (i.e., MODFLOW family of codes) was used to assess remedy effectiveness. Specifically, the numerical model was used to overview an in situ solidification (ISS) application, where soil mixing will be conducted with cement, for possible adverse effects to an existing groundwater treatment system. 3D geological modeling allowed for the existing numerical groundwater flow model to be reconstructed to include previously overlooked data on buried infrastructure, which led to a detailed depiction of high‐permeability channels and a more accurate representation of site conditions. Modeling showed that the ISS remedy would not adversely impact the existing groundwater treatment system. Integration of existing data within a 3D interface led to hydrogeological insights that would have been difficult to obtain from two‐dimensional visualization of information, improved numerical modeling efficiency, and informed site remedy decisions. Additionally, the 3D interface created effective visuals that increased internal and external project team conceptual understanding.

Groundwater modeling of the Silala basin and impacts of channelization

AbstractA key issue in the legal case before the International Court of Justice between Bolivia and Chile concerned artificial channels in the headwater wetlands of the Silala River in Bolivia, and their impact on the river and groundwater flow rates across the international border into Chile. In pleadings before the Court, Bolivia had claimed up to 40% changes in river flow, whereas Chile had maintained that these were much smaller. This paper reviews construction of a numerical groundwater model to quantify this impact, based on the hydrogeological conceptual model presented earlier in this volume. The groundwater model domain covers the Silala River topographical catchment, plus three adjacent closed (endorheic) topographical catchments to the northeast, which together form the groundwater catchment of the Silala River. The geometry was based on a 3D geological model, constructed based on knowledge gained from several geological mapping investigations. Surface water flows were simulated within a margin of error less than the range of uncertainty associated with the flow measurements. The resulting calibrated groundwater model was used to simulate scenarios corresponding to (a) the removal of channels in the Bolivian wetlands and (b) backfilling of the channels and a small increase in ground elevation (postulated by Bolivia due to long term peat accumulation). The results of these scenarios indicate that the measures would result in a small reduction to the surface water flow over the border to Chile; for Scenario A less than 1% change in surface flows, and for Scenario B less than 3%.This article is categorized under: Human Water > Rights to Water Science of Water > Hydrological Processes Human Water > Water Governance

Urbanization effects on the groundwater potential recharge of the aquifers in the southern part of the Basin of Mexico

Abstract Collection, processing, and analysis of GIS and satellite data were performed in this work to estimate temporal groundwater recharge changes, which are needed as input in numerical groundwater-flow models. Layers of geological alignments, land use, drainage network, lithology, topography, and precipitation were collected. This information was spatialized, then layer importance was calculated using an Analytic Hierarchy Process (AHP) based on infiltration capacity to define Potential Recharge (PR) regions. A water budget equation was used to calculate PR volumes. The analysis was done every five years from 1970-19, considering average urban area changes. For all study periods, an increase in urban area was calculated from 16 to 28% of the total study area, while potential recharge decreased from 23 to 19% of the mean precipitation values for each 5-year period. The most significant urban expansion was from 1980-94 and 2010-19, which match periods of potential recharge decrease. However, a slight increase in PR from 2000-09, unrelated to urban area change, may be due to temperature variations. The results account for the spatial and temporal dynamics of the recharge in the study area and can be used as input data to calibrate the actual recharge in a groundwater numerical model.