Simulation Of Groundwater Flow Research Articles

Groundwater head uncertainty analysis in unsteady-state water flow models using the interval and perturbation methods

In the numerical simulation of groundwater flow, uncertainties often affect the precision of the simulation results. Stochastic and statistical approaches such as the Monte Carlo method, the Neumann expansion method and the Taylor series expansion, are commonly employed to estimate uncertainty in the final output. Based on the first-order interval perturbation method, a combination of the interval and perturbation methods is proposed as a viable alternative and compared to the well-known equal interval continuous sampling method (EICSM). The approach was realized using the GFModel (an unsaturated-saturated groundwater flow simulation model) program. This study exemplifies scenarios of three distinct interval parameters, namely, the hydraulic conductivities of six equal parts of the aquifer, their boundary head conditions, and several hydrogeological parameters (e.g. specific storativity and extraction rate of wells). The results show that the relative errors of deviation of the groundwater head extremums (RDGE) in the late stage of simulation are controlled within approximately ±5% when the changing rate of the hydrogeological parameter is no more than 0.2. From the viewpoint of the groundwater head extremums, the relative errors can be controlled within ±1.5%. The relative errors of the groundwater head variation are within approximately ±5% when the changing rate is no more than 0.2. The proposed method of this study is applicable to unsteady-state confined water flow systems.

Tracing Bank Storage and Hyporheic Exchange Dynamics Using 222Rn: Virtual and Field Tests and Comparison With Other Tracers

AbstractDynamic hydrologic exchange flows in river beds and banks are important for many ecosystem functions throughout river corridors. Here we test whether the exchanges and the associated mixing between a flooding river and groundwater within the river’s bank can be effectively traced by Radon‐222 (222Rn), a naturally occurring, inert, radiogenic, and radioactive gas that can be analyzed and monitored in situ. The assessment was done by simulation of groundwater flow and reactive transport of 222Rn in the bank following a single, relatively rapid (hours long) flood wave and auxiliary field observations of 222Rn, temperature and total dissolved solids (a surrogate for any ionic conservative tracer). Results illustrate that 222Rn is more effective than temperature and total dissolved solids in tracing dynamic hyporheic exchange. 222Rn variations in space and time are larger than the analytical uncertainty of common measurement methods. The individual effects of aquifer hydraulic conductivity, dispersivity, river water 222Rn concentration, and bank topography were analyzed through sensitivity analysis. Larger hydraulic conductivity and dispersivity, lower 222Rn concentration in river water relative to groundwater, and gentler bank slopes resulted in a more prominent and traceable 222Rn signal. The transport and residence time of exchanged water may be estimated and interpreted using reactive transport models such as those implemented here. However, such application is sensitive to fluctuations in river water 222Rn, requiring it to be well characterized. The assessment provides guidance for using 222Rn as a tracer for groundwater and surface water interactions in dynamic settings.

Simulation of groundwater flow using meshfree collocation method with Cubic Spline function

Groundwater is a long term reservoir of the natural water cycle. India is the largest user of groundwater in the world. There are many areas in the country facing scarcity of water primarily due to unplanned groundwater development resulting in fall of water levels. If measures to ensure sustainable groundwater usage are not taken consequences may include a collapse of shortages of potable water, conflict and suffering. Therefore it is necessary to identify the groundwater resources and predict the groundwater flows at different locations in the aquifers. Numerical methods can simulate the groundwater flows for the delineated aquifers. In this study, the simulation of groundwater flow is carried out using Meshfree Collocation Method (CM) with Cubic Spline (CS) function and moving support domains. The results are compared with the analytical solution and found satisfactory. The sensitivity analysis is carried out for Courant number, simulation scheme, spatial and temporal variation.

Enhancement of sustainable agricultural production system by integrated natural resources management framework under climatic and operational uncertainty

Constant decline of freshwater reserve poses a major challenge for coastal agricultural systems. The present study focuses on the integrated land and water resources management framework under operational and climatic uncertainties to achieve sustainable agricultural production in a tropical coastal river basin. To capture the operational and climatic uncertainties, Grey Linear Programming (GLP) and Acceptability Constrained Linear Programming (ACLP) optimization models were developed. GLP can consider both climatic and operational uncertainties. However, ACLP can accommodate operational uncertainty only. Groundwater model was coupled within the optimization models (GLP and ACLP) by a grey response matrix. The SWAT estimated recharge rates were utilized in the MODFLOW model as the groundwater flux. The calibrated (R2 = 0.80) and validated (R2 = 0.84) groundwater flow simulation model was utilized to generate the grey response matrix. The eight plausible scenarios were tested for GLP (Scenarios I, II, III, IV, V, VI, VII, VIII) and ACLP (Scenarios Ia, IIa, IIIa, Iva, Va, VIa, VIIa, VIIIa) with groundwater table fluctuation (GWTF) method and grey response matrix as drawdown constraint. A reduction in net annual return was observed in Scenarios III and IV (with grey response matrix) in comparison to Scenarios I and II (with groundwater table fluctuation) under any change in crop yield. Decrease was more prominent for Rabi (winter) season compared to Kharif (monsoon) season. Futuristic Scenarios (V, VI, VII, VIII) considering crop yield reduction showed a possible change required in cropping pattern (specifically rice area reduction in Kharif Season). ACLP model results showed similar trends. Results suggest that the GWTF method overestimates the groundwater availability compared to the physically based simulation model. Obtained land and water resources management plans were cross-validated for the safe yield limit using MODFLOW simulation model.

Scale-dependent spatial variabilities of hydrological exchange flows and transit time in a large regulated river

Hydrological exchange flows (HEFs) across the river-aquifer interface and the associated transit time of river water in the aquifer have important implications for contaminant plume migration and biogeochemical processes in the river corridor. HEFs and transit time are influenced by both subsurface physical features and hydrologic forcing related to the transport process, which can exhibit complex spatial and temporal variations. In this study, we used a massively parallel subsurface flow model and a particle-tracking model to study the influences of different control factors on spatial variability of HEFs and transit time distributions in the Hanford Reach of the Columbia River in Washington State. 100 million particles were randomly injected in time and space and then tracked in a model domain that covers a 51-km2 area (15.1million model cells). We used hourly river stages and groundwater levels to drive the model to provide dynamic velocity fields for the particle tracking in the two + -year simulation period. The groundwater flow simulation and particle-tracking results provide a comprehensive assessment of the spatial distribution of HEFs and transit time in a large, complex river corridor. Our results show that the aquifer hydrogeological structure has strong correlations with the extent and magnitude of exchange flux. The transit time exhibits complex patterns that are affected by all the river geomorphologic, hydrodynamic, and hydrogeologic factors and are strongly correlated with the downwelling ratio of exchange flux. The new insights gained through this study can be used to support the development of reduced-order models of HEFs and transit time distributions for large complex river systems.

Analytical Solution of Saltwater Intrusion in Costal Aquifers Considering Climate Changes and Different Boundary Conditions

Groundwater contamination due to saltwater intrusion (SWI) has an extreme effect on freshwater quality. Analytical and numerical models could be used to investigate SWI. This study aims to develop an analytical solution to investigate SWI into coastal aquifers which was applied to a real case study at the Middle Nile Delta aquifer (MNDA). The study presented a new formula to predict the difference in depth of freshwater to seawater interface due to a change in boundary conditions. A Computer Program for Simulation of Three-Dimensional Variable-Density Ground-Water Flow and Transport (SEAWAT) is used for groundwater flow simulation and SWI and the results compared with the developed analytical solution. Four scenarios are considered in the study, including; the sea-level rise (SLR), reduction in recharge, over abstraction, and combination after 50 years (2070). The analytical solution gave good results compared to the numerical one where Equiline 1 intruded to 103 and 101.66 km respectively at the base case. The results also gave a good agreement between numerical and the analytical solution for SLR due to climate changes by 52.80 cm where the Equiline 1 reached to 105 and 103.45 km. However, the reduction in aquifer recharge by 18.50% resulted in an intrusion for the Equiline-1 to 111 and 108.25 km from the shoreline. Over pumping due to the increase in population by 89% has increased the SWI to reach 121,110.31 km, while it reached 131 and 111.32 km at a combination of the three scenarios, which represents the highest threatening scenario. Also, the difference between the two solutions reached 1.30%, 1.48%, 2.48%, 8.84%, and 15.02%, respectively for the base case and four scenarios. For the current case study, the analytical model gave good results compared to the numerical one, so that the analytical solution is recommended for similar studies, which could save the time and capabilities of computer required for the numerical solutions.

An Attempt to Boost Posterior Population Expansion Using Fast Machine Learning Algorithms.

In hydrogeology, inverse techniques have become indispensable to characterize subsurface parameters and their uncertainty. When modeling heterogeneous, geologically realistic discrete model spaces, such as categorical fields, Monte Carlo methods are needed to properly sample the solution space. Inversion algorithms use a forward operator, such as a numerical groundwater solver. The forward operator often represents the bottleneck for the high computational cost of the Monte Carlo sampling schemes. Even if efficient sampling methods (for example Posterior Population Expansion, PoPEx) have been developed, they need significant computing resources. It is therefore desirable to speed up such methods. As only a few models generated by the sampler have a significant likelihood, we propose to predict the significance of generated models by means of machine learning. Only models labeled as significant are passed to the forward solver, otherwise, they are rejected. This work compares the performance of AdaBoost, Random Forest, and convolutional neural network as classifiers integrated with the PoPEx framework. During initial iterations of the algorithm, the forward solver is always executed and subsurface models along with the likelihoods are stored. Then, the machine learning schemes are trained on the available data. We demonstrate the technique using a simulation of a tracer test in a fluvial aquifer. The geology is modeled by the multiple-point statistical approach, the field contains four geological facies, with associated permeability, porosity, and specific storage values. MODFLOW is used for groundwater flow and transport simulation. The solution of the inverse problem is used to estimate the 10 days protection zone around the pumping well. The estimated speed-ups with Random Forest and AdaBoost were higher than with the convolutional neural network. To validate the approach, computing times of inversion without and with machine learning schemes were computed and the error against the reference solution was calculated. For the same mean error, accelerated PoPEx achieved a speed-up rate of up to 2 with respect to the standard PoPEx.

Comparison of three types of fiber optic sensors for temperature monitoring in a groundwater flow simulator

Different fiber optic sensors have been used for groundwater temperature monitoring and the question is which one to choose for a particular study. In the field conditions it is sometimes difficult to determine how much error is introduced by the sensor placement technique, packaging or cross-sensitivity between temperature and strain. These factors were studied in a laboratory groundwater simulator during a heat tracing experiment. The performance of three fiber optic technologies was evaluated – distributed temperature sensing, fiber Bragg gratings and continuous fiber Bragg gratings. All sensors had comparable accuracy of around 0.2 °C and resolution smaller than 0.1 °C. Therefore, factors which need to be considered when choosing a sensor for groundwater temperature monitoring are spatial resolution, sampling frequency and possibility to measure absolute/relative temperature. The experiment also showed that strain effects can be introduced even when fibers have a loose tube packaging.

Uncertainty in soil hydraulic parameters: A review of basics and methods

The paper is a review article on the basics of uncertainty, necessity of its quantification and a comparative study of various methods of uncertainty estimation. The paper primarily focusses on uncertainty estimation of soil hydraulic parameters as of their pivotal importance in groundwater flow and transport simulations, soil moisture modelling techniques etc. The deterministic and probabilistic approaches of uncertainty quantification are studied and an understanding of uncertainty based on field scale measurements, empirical methods and pedotransfer functions is established. A comparative analysis of the basic methods of uncertainty analysis Monte Carlo, Bayesian, FORM/SORM and GLUE is done and the preferential use based on the importance is suggested. Bayesian approach was most suitable for evaluating parametric uncertainty, Monte Carlo was one of the most powerful tools but computationally expensive, FORM was applicable to both numerical and analytical solutions but didn’t guarantee a global convergence and GLUE was conceptually simple but gave only a statistical measure.

Simulation of Groundwater Flow in Fractured-Karst Aquifer with a Coupled Model in Maling Reservoir, China

A coupled model has been developed to simulate groundwater flow in fractured karst systems according to the complex geological and karst hydrogeological conditions of the dam site, where a 3D mathematical model based on Boussinesq equation was used to describe the movement of groundwater flow in fractured medium, and a 1D conduit model for karst medium. The model was solved with the continuous hydraulic heads at the common boundaries. The hydraulic conductivities of karst medium were determined by geometrical parameters and flux of pipes. Furthermore, the permeability parameters for fractured medium were calibrated by the measured and calculated groundwater levels. The calibrated model was employed to predict the variation of groundwater flow field and leakage from the karst pipes and underground powerhouse during the reservoir operation. The simulated results showed that the groundwater level of the powerhouse had decreased by about 2–5 m. The water level of conveyance pipeline had risen by 10–20 m, and the water level on both banks had risen by 15–25 m. The leakage of karst conduits for impervious failure was larger than that for normal seepage control. In addition, the leakage of the powerhouse was estimated to be about 1000–3000 m3/d, and the seepage control of karst pipes had little influence on the leakage of underground powerhouse.

Modeling the behavior of shallow groundwater system in sustaining arid agroecosystems with fragmented land use

Shallow groundwater often presents multiple behaviors in supporting the sustainability of arid agroecosystems. The behaviors are especially important and complicated for the arid irrigated areas with fragmented land-use types. In the view of understanding the role of shallow groundwater in such areas, the MODFLOW and MT3DMS (with the assistance of HYDRUS-1D) were used to simulate groundwater flow and salt transport in a typical observation site of the arid upper Yellow River basin (YRB). The original MODFLOW was modified with introducing a variable expression of specific yield, aiming to improve the modeling accuracy in shallow groundwater environments. The model was calibrated and validated using the observation data of groundwater depth and drainage in 2013 and 2012, respectively. Groundwater evapotranspiration and lateral water-salt exchange among different land-use types were simulated and analyzed; meanwhile, the dry drainage effect of non-cultivated natural land was quantitatively interpreted. Results indicated that the fragmented land-use/planting pattern (with different irrigation scheduling) resulted in significant lateral groundwater flow and water/salt redistribution among different land-use fields during irrigation. The groundwater evapotranspiration ranged at about 160–220 mm for different land-use types, reaching to 0.30–0.45 of plant evapotranspiration (ETpt) during the growing seasons. This effectively supplemented the plant water use in arid climate, especially for the unirrigated cultivated land (during some stages) and the non-irrigated natural land. Meanwhile, the lateral groundwater flow drove salt migrating from the cultivated land to the natural land. The natural land accumulated 27–40% of salts introduced by irrigation, playing a significant role in accommodating salts (i.e. the dry drainage effect). Moreover, our modeling work further implied that the reliable groundwater modeling in arid and shallow groundwater areas required a more detailed model conceptualization and more accurate information of land-use distribution, irrigation scheduling, and local microrelief than the general understanding in the past.

Hyperbolic Reformulation Approach to Enable Efficient Simulation of Groundwater Flow and Reactive Transport

We apply Cattaneo's relaxation approach to the one-dimensional coupled Boussinesq groundwater flow and advection-diffusion-reaction equations, commonly used in engineering applications to simulate ...

Determination of optimal well locations and pumping/injection rates for groundwater heat pump system

Groundwater heat pump (GWHP) system enables to exploit additional value of groundwater as a promising renewable energy resource. This study suggested a simulation-optimization approach to find optimal installation and operation strategy for sustainable GWHP system, which aims at maximizing performance and efficiency, maintaining operational stability, complying with legal regulation on water injection, and minimizing possible costs and environmental impacts at the same time. A groundwater flow and heat transport simulation model was linked with a genetic algorithm as optimization technique and, particularly, this model can determine optimal well locations and pumping/injection rates together or apart. Assuming a hypothetical GWHP model, it was shown that the consideration of thermal recycling and value of land available for installation is important for determining optimal well configuration and resulting well distance. Results also demonstrated that simultaneous optimization of well location and flow rate can provide a better design than optimization of only well location for given flow rate. By applying the developed model to a GWHP facility in Korea, the capability of this model that can account for site-specific conditions in planning stage was proven, which must be critical to sustainable operation of GWHP system.

Microfluidic pore model study of precipitates induced by the pore-scale mixing of an iron sulfate solution with simulated groundwater

Precipitates induced by the pore-scale mixing of iron sulfate solutions with simulated groundwater were investigated using a microfluidic pore model to assess the environmental impacts of the infiltration of acid mine drainage into a shallow aquifer. This model was employed to visualize the formation of precipitates in a porous network and to evaluate their physicochemical influences on pore flow. Four types of groundwater (Na–HCO3, Na–SO4, Na–Cl, and Ca–Cl) were evaluated, and precipitation rates were calculated by processing images of precipitates in the pores captured via microscopy. The results showed that all groundwater types formed a yellow-brownish precipitate at the interface of the iron solution and simulated groundwater flow. Microscopic X-ray analyses demonstrated that precipitate morphology varied with groundwater type. Faster precipitation was observed in the following order by groundwater type: Na–HCO3 > Na–Cl > Na–SO4 > Ca–Cl, which was attributed to the different stability constants of the major anions in each simulated groundwater with Fe ions. Chemical equilibrium models suggested that precipitates were Fe minerals, with FeOOH as the predominant form consistent with the results of X-ray photoelectron spectrometry. The presence of FeOOH implies that precipitates may serve as an effective sorption barrier against some nutrients and heavy metals for the underlying groundwater. However, dye-flow experiments suggested that the precipitates may clog aquifer pores, thereby altering hydrogeological properties in the aquifer.

Simulation of Groundwater Flow in an Aquiclude for Designing a Drainage System during Urban Construction: A Case Study in Madrid, Spain

A detailed hydrogeological study was carried out due to the recent occurrence of unexpected problems associated with the flooding of the water table during excavations in the area of a major urbanization work in Madrid. The numerous exploratory drilling excavations carried out allowed for the development of a conceptual model of the complex hydrogeological functioning in clay formations in an urban area. The clays have very little natural recharge, and the underground flow is highly conditioned by the topography and a fold-fault. Modelling with MODDFLOW confirmed and quantified this conceptual model and also allowed for the design of an efficient network of 1.5 km-long drainage trenches. The design of this drainage network was influenced by the difficult balance that must be respected in order not to contaminate the water with sulphates from the nearby gypsum substrate. This is to guarantee the quantitative and qualitative sustainability of the groundwater. The follow-up and monitoring of the water tables and the quality of the groundwater for more than a year after the excavation of the drainage trenches guaranteed the results of the research.

Multi-objective groundwater management using genetic algorithms in Kerbala desert area, Iraq

Kerbala desert is one of the most important areas in Iraq, due to the large number of groundwater aquifers in the region. Based on this, many agricultural investment projects have been established in this area recently, with multiple new wells being drilled in the desert. All such wells penetrate the Dammam confined aquifer to a depth of 260 to 300 m, and uncontrolled use of these wells, and the additional wells expected as the area develops, is likely to lead to problems with groundwater sources, including depletion of water levels, well interference, and groundwater pollution. This study introduces a multi objectives groundwater management model based on an integrated simulation-optimisation (S/O) model. The simulation of groundwater flow was developed using a finite-difference numerical model, MODFLOW, under GMS software for various conditions, and evaluation of calibration of the transient model was determined by observing the measured and calculated aquifer heads. A multi-objective optimisation model was applied to maximise the pumping rate and minimise pumping costs, and this was solved using a genetic algorithm method supported by two further mechanisms, Pareto optimality ranking and fitness sharing. A set of Pareto optimal solutions as determined in the final generation was thus created for the multi-objective function (maximum pumping rate and minimum pumping cost) to help decision-makers (DM). Based on the Pareto solutions set, a DM or the designer may thus choose a preferred solution, or a compromise solution may be derived by considering the full set of Pareto optimal solutions.

Conceptual and Mathematical Modeling of a Coastal Aquifer in Eastern Delta of R. Nestos (N. Greece)

In this paper, the development of the conceptual and groundwater flow model for the coastal aquifer system of the alluvial plain of River Nestos (N. Greece), that suffers from seawater intrusion due to over-pumping for irrigation, is analyzed. The study area is a typical semi-arid hydrogeologic environment, composed of a multi-layer granular aquifers that covers the eastern coastal delta system of R. Nestos. This study demonstrates the results of a series of field measurements (such as geophysical surveys, hydrochemical and isotopical measurements, hydro-meteorological data, land use, irrigation schemes) that were conducted during the period 2009 to 2014. The synthesis of the above resulted in the development of the conceptual model for this aquifer system, that formed the basis for the application of the mathematical model for simulating groundwater flow. The mathematical modeling was achieved using the finite difference method after the application of the USGS code MODFLOW-2005.

An insight into the hydrological aspects of landslides of 2018 in Kodagu, South India

The goal of the work has been to assess the factors that led to the series of landslides, which ravaged the District of Kodagu situated in the mountainous Western Ghats, in 2018. The work has been accomplished through field investigations and analysis of field data. While commonly, studies in India lay emphasis on the geological aspects and anthropogenic factors associated with landslides, the present work intended to study in detail the hydrological aspects of the disaster, which wreaked havoc in the region characterised by deep soils, very heavy rainfall and a dense vegetation cover. All the slides of significant magnitude along a 25-km stretch of the Payaswini valley, draining the western slopes of the Madikeri hill range, were identified, and their land characteristics delineated using field surveys and maps. Soil characteristics of the region were determined through tests on samples collected from ten slide sites. Results from tests on texture, density and permeability were used to learn about the part played by subsurface water. Characteristics of rainfall during the year were investigated using field data from the worst affected region. Studies on progress of the Monsoon rain, an analysis of probability of extreme values and establishment of intensity–duration relationships were accomplished. A variable source area watershed model incorporating MODFLOW, the popular ground water flow simulation model, has been applied on a typical micro-catchment in order to study the growth of the saturated zone during rains. It has been inferred from the investigations that an unprecedented combination of extremely wet catchment and a very heavy spell of rainfall, rather than any commonly attributed factor, has been the primary cause of the disaster in the district. It is concluded that it would be a futile exercise working on this natural phenomenon devoid of extensive field studies, because of the uniqueness of the region.

Methods for verification of groundwater flow simulators (case study: Jakarta groundwater basin in the urban villages of Jatiluhur and Jatirangga, Bekasi City)

Limited access to clean water leads to residents extracting groundwater through dug wells or boreholes, which in turn results in groundwater becoming contaminated. Groundwater flow simulation of the Jakarta basin, which has been previously modeled with the Groundwater Modeling System 10.3, can be used as a basis for simulating groundwater flow pollution. Before simulating the groundwater flow pollution, the groundwater flow simulator needs to be verified to examine whether simulators and conditions in the field correspond to the water table level. This study demonstrated the methodology used for verification of the simulator in research. Verification was done using the Chi-square method. The results revealed that calculated Chi-square values were larger than Chi-square table values for the two urban villages of Jatiluhur and Jatirangga. The value of calculated Chi-square value for Jatiluhur was 17.3, whereas it was 7.81 in the Chi-square table. In Jatirangga, the calculated Chi-square value was 37.23, whereas it was 14.1 in the Chi-square. Results indicated that the simulation was not in accordance with the actual water table level. This discordance can occur since it necessary to update the data on groundwater flow simulation results with bore log data or to verify the hydrodynamic conditions of the study area.

Modeling the Impact of Fertilizers on Groundwater Quality in Hormat-Golina Sub-basin, Golina-Basin, Ethiopia

Groundwater, in many parts of the world, is under risk as a result of excessive withdrawal, mismanagement and contamination. A number of studies have been carried out in this respect, but most of them have not predicted groundwater quality concerning anthropogenic stress. As opposed to this, in this study, groundwater fluctuation with respect to human pressure was investigated in Hormat-Golina Sub-basin of the Golina-Basin of Ethiopia. Visual MODFLOW Flex 5.1 model was used to simulate groundwater flow in response to different stress periods in the study area. The study showed that the initial concentration values were measured in each nutrient chemical species. The impacts of climate change and human pressure on groundwater have been the greatest threats in those supply wells. Decreased in pumping rate with increased recharge rate has accomplished to restore and protect the groundwater resources which is the best option for groundwater restoration and monitoring. Anthropogenic pressures including the application of fertilizers were a considerable cause of degraded groundwater quality in relation to Nitrate and Phosphate concentration with series of time. The groundwater quality has deteriorating with the applied Urea and DAP fertilizes in the selected wells of Hormat-Golina Sub-basin. Farmers have encouraged using practices that minimize the risk of groundwater pollution by carefully controlling and timing of the use of fertilizers to avoid over application.