Potential Flow Paths Research Articles

Utilizing high-resolution 3D Voronoi meshing to analyze field data from the Brine Availability Test in Salt (BATS)

Salt is an attractive disposal medium for radioactive waste because intact salt is essentially impermeable and non-porous. However, upon drift or borehole excavation a damaged region develops surrounding the excavation which causes increased permeability and porosity creating potential flow paths for brine. Brine leads to corrosion of waste forms and waste packages and is a possible transport vector for radionuclides, so it is important to better understand the early-time behavior and evolution of brine flow in a salt. As a result, this study is part of Task E of DECOVALEX-2023 which focuses on understanding the evolution of thermal, two-phase hydrological, and mechanical processes in the excavation damaged zone in salt. Field measurements from The Brine Availability Test in Salt (BATS) 1a heater experiment are analyzed by implementing a high-resolution three-dimensional numerical model. This salt heater experiment consists of 28 days of heating and 13 days of cooling in a central borehole within bedded salt at the Waste Isolation Pilot Plant (WIPP). Here, the flow simulator PFLOTRAN is utilized; simulations are run on a Voronoi mesh, with temperature-dependent thermal conductivity, permeability and porosity decay away from excavations. The temperature-dependency of permeability is done to match field measurements. Results from the simulation match temperature measured in the field within + /- 0.1 °C and the total brine inflow over the 41-day experiment. This study illustrates that the accuracy of the temperature evolution within salt is critically important when analyzing and modeling experimental data by simulating three heating scenarios of the BATS 1a experiment showing that temperature has a direct effect on total brine inflow.

Water Content Evolution in the EDZ of Opalinus Clay: A Methodic Approach for a Comparative Interpretation of Measurements and Modelling

In the Mont Terri Rock Laboratory (Switzerland), an interdisciplinary examination program is carried out to increase knowledge about coupled hydro-mechanical effects in Opalinus Clay, which are of significant interest regarding the stability and integrity of a potential storage facility for high-level radioactive waste. This article focuses on the characterization of the claystone in the near field of excavations and related hydraulic effects due to excavation and ventilation. Electrical resistivity tomography (ERT) is applied to characterize the OPA: Several open fractures correlate with regions of high resistivity values, indicating potential preferential flow paths that are relevant for transport processes. Due to the combined interpretation of ERT long-term monitoring and seasonally repeated nuclear magnetic resonance (NMR) measurements, a relationship between electrical resistivity and water content can be established, resulting also in a time-dependent map of the water content around excavations with different climatic conditions. The statistical interpretation of these measurements indicates the existence of small-scale singularities in contrast to dominating, more homogeneous zones. The presented approach leads to a better process understanding of these heterogeneous near field effects and provides a valuable basis for a pragmatic approach to safety assessment.

Modelling of debris flow-boulder-barrier interactions using the Coupled Eulerian Lagrangian method

The impact load of boulders transported by debris flow is crucial in designing protective structures constructed along the potential flow paths. In this study, the Coupled Eulerian-Lagrangian (CEL) method is applied to establish a three-dimensional model for analysing debris flow, boulders, and barrier interactions in various scenarios, with an Australian rivulet serving as a case study. The proposed CEL method was verified by simulating the runout and impact behaviour based on experimental granular and debris flow tests. Subsequently, a comprehensive series of numerical simulations explores the impacts of transported boulders on a rigid tooth barrier, encompassing various boulder shapes and sizes. The results indicate a direct correlation between boulder size and impact force, while the influence of boulder shape on peak impact force is minimal. Nevertheless, boulder shape affects the arrival time, as noted with increased boulder size. Although boulder dimensions remain the primary factor affecting impact force, variations in the geometry are observed to influence the overall dynamics of debris flow-boulder interactions. This study proposes a procedure for assessing barrier impact forces through simulations combining debris flow and boulder transport with the CEL method. The research presents the effectiveness of the CEL method in estimating the impact force of media transported by debris flows in intricate 3D terrains. The findings contribute significantly to the existing measures for assessing the risk of debris flows.

Imaging hydrological dynamics in karst unsaturated zones by time-lapse electrical resistivity tomography

The hydrodynamics of karst terrain are highly complex due to the diverse fractures and reservoirs within limestone formations. The time delay between rainfall events and subsequent flow into reservoirs exhibits significant variability. However, these hydrological processes are not easily visualized in karst topography. Subsurface geophysics, specifically 2D time-lapse electrical resistivity tomography (ERT), provides an effective method for studying the relationships between hydrological and geophysical features. In our research, we adopted ERT in the Karst Critical Zone (KCZ) to visualize specific karstic zones, including cave galleries, water storage reservoirs, wetting fronts, soil layers, and potential preferential flow paths down to a depth of 20 m. To capture spatial and seasonal variations in resistivity, we presented a comprehensive approach by combining sixteen inversion models obtained between February 2020 and September 2022 above the Villars Cave in SW-France—a well-known prehistoric cave. We used a multi-dimensional statistical technique called Hierarchical Agglomerative Clustering (HAC) to create a composite model that divided the synthetic ERT image into eight clusters representing different karst critical zones. The ERT image clearly visualized the cave gallery with high resistivity values that remained consistent throughout the seasons. Our analysis revealed a close seasonal relationship between water excess and resistivity variations in most infiltration zones, with time delays increasing with depth. The karst reservoirs, located at significant depths compared to other clusters, displayed sensitivity to changes in water excess but were primarily affected by fluctuations in water conductivity, particularly during summer or dry periods. These findings have significant implications for predicting rainwater infiltration pathways into caves, thereby assisting in the conservation and preservation of prehistoric caves and their cultural heritage.

Seismic imaging of reservoir heterogeneity using a network with high station density at The Geysers geothermal reservoir, CA, USA

We analyze results of high-resolution seismic imaging at The Geysers geothermal reservoir in northern California, USA, using a dense seismic network to image the spatial heterogeneity of the reservoir structure and flow paths. The project uses 92 seismic stations spaced at approximately 500 m over a 5 km × 5 km study area. Microseismic data for more than 17,000 earthquakes have been acquired over a period of 13 months and automatically processed for P- and S-wave phase arrival times. The data are subsequently inverted using a joint inversion approach to image the spatial heterogeneity of the reservoir including the 3D P- and S-wave velocity structure and [Formula: see text]/[Formula: see text] ratio, and to locate earthquake hypocenters. The resulting tomographic images are appraised by integration into The Geysers’ 3D reservoir model and by a spatial correlation to the injection and production wells. Spatial correlation of P-wave velocity images to water injection and steam production wells reveal higher velocities below injection wells, due to higher water saturation, and lower velocities in the vicinity of steam-producing wells, due to the presence of steam in the surrounding reservoir rocks. The spatial correlation of [Formula: see text]/[Formula: see text] to steam in the reservoir indicates decreased estimates in the vicinity of steam production wells. In contrast, the [Formula: see text]/[Formula: see text] ratio reveals high values in the reservoir for regions near water injection wells and along the potential flow path of water through the reservoir. The estimates of shear modulus indicate high values in a region of competent graywacke, which is known for a lack of fractures and steam production, and low values in a region that is dominated by water flow, suggesting that fractured rock created a pathway for the water through the reservoir. The heterogeneity observed in the S-wave velocities indicates a compartmentalized reservoir, which correlates spatially with fault projections in the 3D reservoir model.

Characterizing the performance of node-aware strategies for irregular point-to-point communication on heterogeneous architectures

Supercomputer architectures are trending toward higher computational throughput due to the inclusion of heterogeneous compute nodes. These multi-GPU nodes increase on-node computational efficiency, while also increasing the amount of data to be communicated and the number of potential data flow paths. In this work, we characterize the performance of irregular point-to-point communication with MPI on heterogeneous compute environments through performance modeling, demonstrating the limitations of standard communication strategies for both device-aware and staging-through-host communication techniques. Presented models suggest staging communicated data through host processes then using node-aware communication strategies for high inter-node message counts. Notably, the models also predict that node-aware communication utilizing all available CPU cores to communicate inter-node data leads to the most performant strategy when communicating with a high number of nodes. Model validation is provided via a case study of irregular point-to-point communication patterns in distributed sparse matrix–vector products. Importantly, we include a discussion on the implications model predictions have on communication strategy design for emerging supercomputer architectures.

Hydrodynamic Hysteresis and Solute Transport in Agglomerated Heaps under Irrigation, Stacking, and Bioleaching Controlling

Hydrodynamic hysteresis exists widely in agglomerated heaps with well-developed intra-pores, and it directly affects solute transports and bioleaching reaction. In this paper, the dynamic liquid retention behavior under different heap porosity and irrigation condition is quantified via a novel real-time, in-situ liquid retention characterizing system (RILRCS), and the potential effects of initial liquid retention on solute transport and leaching reaction are carefully discussed. The results show that the immobile liquid is dominant in agglomerated heaps. The ratio of immobile and mobile liquid (η) dynamically changes due to mineral dissolution and new flow path appearances. The η normally increases and mobile liquid occupies a higher proportion due to acidic leaching reactions, especially at a smaller Rg (10.32 mm) and a larger u (0.10 mm/s). The dynamic liquid retention is more sensitive to the diameter of packed feeds (Rg) and superficial flow rate (u) instead of leaching reactions. This might be because the damage of leaching reaction on minerals pores/voids is limited and cannot extensively change the potential pore channels or fluid flow paths. Based on pulse tracing and conductivity tests, we reveal that the solute resides longer under a slower u and smaller packed Rg condition, which corresponds well with desirable copper leaching efficiency. Specifically, the liquid hysteresis behavior is more obvious at a lower u (0.01 mm/s) and smaller Rg (10.32 mm). This paper gives a good reference to ascertain the liquid retention and hydrodynamic hysteresis and promote mineral leaching performance.

Characteristics of hydraulic conductivity in mountain block systems and its effects on mountain block recharge: Insights from field investigation and numerical modeling

The process wherein groundwater flowing from mountain bedrock into lowland and adjacent alluvial aquifers, known as mountain-block recharge (MBR), is found across various climatic and geological settings. An understanding of the potential groundwater flow paths in mountain block systems is necessary for comprehending MBR spatial distribution. However, poorly characterized mountain block hydraulic properties, and especially a lack of direct measurements of hydraulic conductivity (K) at depths > 200 m, limit the characterization and quantifications of the MBR processes. In this study, we analyze hydraulic data set, namely 555 in-situ K measurements at various depths from two borehole sections extending from mountain block to mountain front in a potential disposal site for high-level radioactive waste. The K dataset was categorized into two groups: one for bedrock and another for fault zones, which was further classified into fault core K, damage zone K, and general fault zone K. Using a permeability conceptual model and multiple scenarios numerical modelling, this study examined the potential flow paths of MBR processes, mainly focusing on the characteristics of K in bedrocks and the hydraulic role of fault zones in mountain block systems. The distribution of Bedrock K supports the assumption of decreased trend with depth. A logarithmic fit through Bedrock K and depth pairs resulted in Log(K) = −1.62*Log(z) − 6.52, with low predictive power. This study illustrated the localized effects and spatially variable roles of fault zones in MBR within this particular hydrogeological configuration in Beishan, China. Our results provide insights into the MBR process in crystalline mountain block systems. Additionally, the hydraulic conductivity presented here provides data on the subsurface properties of mountain block systems in a crystalline area, and further facilitates the characterization and quantification of mountain-block recharge.

Managed aquifer recharge site assessment with electromagnetic imaging: Identification of recharge flow paths

AbstractSurface spreading recharge, the intentional flooding of the ground surface to replenish a groundwater system, is one approach used to mitigate groundwater overdraft in California's Central Valley (CV). Choosing appropriate sites for surface spreading recharge, in regard to the sites’ ability to convey water from the ground surface to the desired recharge depth, can be challenging because of limited knowledge of the properties of the subsurface. In this study, we present an approach for using a towed time‐domain electromagnetic (tTEM) imaging method to develop three‐dimensional (3D) models of sediment type, map potential flow paths through the subsurface, and evaluate sites for surface spreading. We began with tTEM data from seven sites in the CV along with an existing resistivity‐to‐sediment type transform. We leveraged geostatistical methods to generate multiple 3D models of binary (flow and no‐flow) sediment type from the tTEM data. We then developed two metrics to assess the quality of sites for recharge: (a) the depth to the shallowest no‐flow unit beneath each point at the surface and (b) preferential flow paths lengths measured by finding the shortest distance through connected flow units between surface points and the desired depth. We explored how these metrics can be used to identify optimal areas within a site, then developed a way to compare and assess the relative suitability of each site using the decay in the number of vertical flow paths as a function of depth. Our methods can be used to rapidly identify potential sites for surface spreading recharge.

Evaluation of Electrical and Electromagnetic Geophysical Techniques to Inspect Earthen Dam and Levee Structures in Arkansas

Within the State of Arkansas, there is an increasing number of aging dams and levees that have little to no documentation concerning their construction or composition. Surface geophysical surveys offer a non-intrusive method for investigating these structures to describe their lithologic makeup, evaluate the materials constructed upon, and identify potential flow paths through them. Techniques such as electrical resistivity tomography, seismic refraction, and electromagnetic induction have been used to image dams and levees. They require additional information from geologic outcrops, geotechnical borings, or drill cores to make informed geologic interpretations of the geophysical models. These geologic models then allow the owners of these structures to make more informed decisions about their operation and maintenance. Between 2011 and 2018, the U.S. Geological Survey conducted geophysical and geotechnical investigations of three earthen structures in Arkansas. Electrical and electromagnetic geophysical data were used to develop lithologic models of these structures and characterize the underlying geology. Self-potential surveys were utilized to detect the movement of water through these structures and identify any possible seepage pathways. Geotechnical methods such as electric and hydraulic direct-push well logs and cores acted as a control on the geophysical interpretations and a confirmation of anomalies. This integrated approach detected the lack of an impermeable core within a levee, imaged a change in lithology of the bedrock forming the seal beneath a gravity dam, and identified a potential seepage feature within the core of an earthen dam. These results further support that this method of extending known lithologic features via surface and borehole geophysics is a useful approach for characterizing earthen water-control structures.

Fluid Flow Concentration on Preferential Paths in Heterogeneous Porous Media: Application of Graph Theory

AbstractFluid flow through geological formations is often concentrated on distinct preferential flow paths owing to the presence of fractures or large‐scale permeability structures. However, the existence of such structures is not a mandatory condition of preferential paths formation. Pore‐scale spatial fluctuations of pore size and/or pore connectivity in statistically stationary porous media, if sufficiently large, can also lead to the concentration of fluid flow on distinct pathways. In this paper, we attempted to establish the conditions of formation of preferential flow paths in heterogeneous porous media in terms of pore‐size heterogeneity and pore connectivity. We simulated steady‐state flow through stochastically constructed two‐ and three‐dimensional pore networks, in which the width of the pore radius distribution and the pore coordination number (a measure of pore connectivity) were varied. We developed new techniques based on graph theory to identify potential preferential flow paths and characterize them. We observed a gradual transition from approximately uniform flow fields in low heterogeneity/high connectivity networks to flow localization on preferential paths with increasing pore‐size heterogeneity and decreasing connectivity. The transition occurred at lower heterogeneity levels in three‐dimensional than in two‐dimensional simulations and was less influenced by pore connectivity variations. These results were summarized in a phase diagram in pore‐size heterogeneity/pore connectivity parameter space, which we found consistent with relevant real rocks data.

Hydro-mechanical continuum modelling of fluid percolation through rock salt

Salt caverns for storing renewably produced hydrogen underground pose a promising option to reduce CO2 emissions by improving the utilization of volatile renewable energy sources. Rock salt limits the infiltration of hydrogen into the storage cavern walls due to its favourable low permeability. However, pressure-driven percolation may create discrete pathways for the fluid and damage the cavern. Depicting this effect accurately in simulations may be crucial for assessing the long-term stability and integrity adequately. By introducing an extension to a deformation-dependent permeability model by Alonso, Olivella and Arnedo (2006) we can capture the non-linear feedback between salt deformation, permeability development and fluid migration using continuum models. Based on a quasi-isotropic arrangement of potential flow paths the model is able to reproduce pressure-driven percolation of hydrofrac experiments on rock salt specimens in terms of breakthrough pressure as well as preferential path orientation and locality. The model is implemented in the scientific open-source framework OpenGeoSys.

Design of seepage control system around a large-scale underground powerhouse: A case study of Baihetan Hydropower Station

Located at the lower reach of Jinsha River, the Baihetan Hydropower Station is the world’s second largest hydropower station. It consists of a double-curvature arch dam with a maximum height of 289 m and two large-scale underground cavern systems on each side of the bank, which is the largest underground cavern system of hydropower project in the world. The construction site is characteristic of complex geological conditions, and multiple interlayer staggered zones are developed between different strata. Based on the results of on-site packer tests, the interlayer staggered zones generally have a higher hydraulic conductivity than the surrounding rocks, and therefore may act as the potential seepage flow path. Since the underground powerhouse is close to the upstream reservoir and these is a large difference of water level between the upstream and downstream reservoirs, the control of groundwater flow in the surrounding rocks of the underground caverns becomes one of the key technological issues. A large-scale seepage control system including grout curtains and drainage curtains was designed around the underground powerhouses. Besides, the hydraulic conductivity of the interlayer staggered zones was systematically characterized and several anti-seepage tunnels were designed and constructed specifically for the control of seepage flow through the interlayer staggered zones. On this basis, numerical simulation of seepage field was conducted, and the results show that the designed seepage control system is effective in lowering the groundwater level and reducing the amount of seepage around the powerhouse.

Temporal Temperature Distribution in Shallow Sediments of a Large Shallow Lake and Estimated Hyporheic Flux Using VFLUX 2 Model

Identifying and quantifying exchange flux across sediment-water interface is crucial when considering water and nutrient contributions to a eutrophic lake. In this study, observed temporal temperature distributions in shallow sediment of Lake Taihu (Eastern China) based on three-depth sensors at 14 sites throughout 2016 were used to assess temporal water exchange patterns. Results show that temporal temperature in shallow sediments differed with sampling sites and depths and the temperature amplitudes also clearly shrunk as the offshore distance increasing. Exchange fluxes estimated using the VFLUX 2 model based on temperature amplitude show that alternating-direction temporal flow exists in the eastern zone of Lake Taihu with averages of −13.0, −0.6, and 3.4 mm day−1 (negative represents discharging into the lake) at three nearshore sites (0.5, 2.0, and 6.0 km away from the shoreline, respectively). Whereas downwelling flow occurred throughout almost the entire year with averages of 37.7, 23.5, and 6.6 mm day−1 at the three southern nearshore sites, respectively. However, upwelling flow occurred throughout almost the entire year and varied widely in the western zone with averages of −74.8, 45.9, and −27.0 mm day–1 and in the northern zone with averages of −76.2, −55.3, and −51.1 mm day−1. The estimated fluxes in the central zone were relatively low and varied slightly during the entire year (−15.1 to 22.5 mm day−1 with an average of −0.7 mm day−1). Compared with the sub sensor pair (at 5 and 10 cm), the estimated hyporheic fluxes based on the top sensor pair (at 0 and 5 cm) varied within wider ranges and exhibited relatively larger values. Effects of upwelling flow at the western and northern zones need to be paid attention to on nearshore water quality particularly during winter and spring seasons. Estimated flow patterns at the four zones summarily reflect the seasonal water interaction near the sediment surface of Lake Taihu and are beneficial to improve its comprehensive management. Thermal dispersivity usually used for estimating the thermal diffusivity is more sensitive for upward hyporheic flux estimating even if with a low flux. Temperature amplitude ratio method can be used to estimate the exchange flux and suitable for low flux conditions (either upwelling or downwelling). A better evaluation of the exchange flux near inclined nearshore zones might need an optimized installation of temperature sensors along with the potential flow path and/or a vertical two-dimensional model in the future.

Effect of leaf distribution pattern on the interception storage capacity of leaf litter under simulated rainfall conditions

AbstractRainwater interception by leaf litter is an important part of forest hydrological processes. The objective of this study was to investigate the interception storage capacity (ISC) of woodland leaf litter for three leaf distribution patterns, one flow path, two flow paths, and three flow paths, manually simulated via one‐by‐one leaf connection in the top leaf litter layer. A random pattern served as the control. Three different slopes (0°, 5° and 25°, representing flat, gentle and steep slopes, respectively) and two contrasting leaf litters (needle‐leaf litter, represented by P. massoniana leaves, and broad‐leaf litter, represented by C. camphora leaves) with a biomass of 0.5 kg/m2 per unit area were applied, at a rainfall intensity of 50 mm/h. Results suggested that leaf distribution pattern greatly impacts litter drainage and hence affects leaf litter ISC. The delaying capacity of litter drainage initiation and ISC of broad‐leaf litter were higher than those of needle‐leaf litter under the same slope conditions. The maximum ISC (Cmax) and minimum ISC (Cmin) of leaf litter at flat and gentle slopes were higher than those at steep slope. Cmin of the broad‐leaf litter was two times higher than that of needle‐leaf litter on average. When raindrops reached the litter layer, some were temporarily intercepted by the top litter layer while others infiltrated leaf litter sublayer along leaf edges, and in the process, some rainwater flowed through litter layer and contributed to lateral litter drainage along the potential flow path formed by leaves. The lateral litter drainage of broad‐leaf litter was higher than that of needle‐leaf litter, and the partitioning of rainwater into lateral litter drainage increased with increases in slope. The difference in leaf litter Cmax among different slopes and leaf shapes decreased with flow path increasing. Therefore, leaf distribution pattern notably impact leaf litter ISC, which is similar to leaf shape and slope impacts. On inclined slopes, avoiding leaf accumulation to form flow path is helpful for improving ISC.

Toward a new conceptual model for groundwater flow in merokarst systems: Insights from multiple geophysical approaches

AbstractMerokarst aquifers — relatively thin (<1–2 m) karstified carbonate units interbedded between mudstone, shale, or sandstone — constitute a significant proportion of carbonate terrain and underlie a large portion of the west‐ and south‐central USA, yet few advances have been made in our understanding of porosity development and flow‐path generation in these complex systems in decades. Toward this end, we used a multi‐geophysical approach at the well‐studied Konza Prairie Biological Station (KPBS), a part of the larger Flint Hills (25,734 km2), underlain by thin limestone units (1–2 m thick) interbedded with mudstone/shale units (2–4 m thick), to elucidate hydrologic connectivity and potential controls on known groundwater flow directions. We combined electrical resistivity tomography (ERT), surface and borehole nuclear magnetic resonance (NMR), and ground penetrating radar (GPR) measurements across a low order catchment where over 25 boreholes and groundwater wells sampling perched aquifers could be used to constrain interpretation of lithology, potential flow paths, and permeability. Data revealed that groundwater export may be an unappreciated component of lateral‐flow‐dominated models used to represent merokarst in that: (a) potentiometric surfaces from two limestone units showed groundwater flows toward a hydrologic depression, opposite the direction of stream flow, in the upstream portion of the catchment, (b) long term measures of groundwater levels revealed a greater variance and overall water storage in this same upstream area compared to wells near the outlet, and (c) ERT and NMR results indicate pronounced lateral heterogeneity within a given unit, suggestive of a greater degree of vertical hydrological connectivity than usually considered for horizontally‐layered merokarst. Our data suggest vertical connectivity can shunt water to depth in these “sandwiched” merokarst aquifers, yielding atypical groundwater flow directions and unrealized deep export of weathering solutes and carbon.

A multidisciplinary approach for delineating wastewater flow paths in shallow groundwater aquifers: A case study in the southeastern part of the Nile Delta, Egypt

Groundwater pollution is a global issue in highly populated areas, the Eastern Nile Delta region is a typical example; especially around artificial wastewater drains. In the present work, a multidisciplinary approach using hydrogeochemical, geostatistical, microbiological and geophysical data was applied to determine the vulnerability conditions and to identify potential pathways through which contaminants could potentially percolate to shallow aquifers in the southern boundary of the Eastern Nile Delta. An organized groundwater sampling was conducted for hydrogeochemical investigation in rural areas along the Belbies unlined drain. This drain is known of being heavily polluted by agricultural and municipal wastewater.The hydrogeochemical analysis reveals high pollution levels by Pb, Cd, and Cr for most of the collected shallow groundwater samples nearby the drain. Additionally, NO3−, fecal and total coliform bacteria were observed in many samples with high concentrations. Six factors were distinguished on the basis of principal component analysis and varimax rotation, with total variance more than 78%. These factors reflected sewage contamination, lithogenic and anthropogenic effects on the shallow groundwater. Hierarchical cluster analysis revealed two main clusters of groundwater groups. Accordingly, Electrical Resistivity Tomography (ERT) was carried out in the areas of the distinguished clusters to locate potential preferential flow paths and horizons of lateral flow around the drain. The obtained resistivity models illustrate breakthrough behavior in parts of the measured profiles due to the presence of permeable paths close to the drain.The applied integrative approach is valuable for understanding the ambiguities during the interpretation process and for characterizing water quality and the aquifer vulnerability conditions. Additionally, it may guide to understand the surface water-groundwater links in order to supply the growing population with safe water.

Connectivity evaluation of fracture networks considering the correlation between trace length and aperture

Connectivity evaluation of fracture networks is important in the design, assessment, and development of reservoirs in various engineering applications involving geothermal exploitation and the petroleum industry. By employing nonhomogeneous Poisson distribution and annealing arithmetic, this study generates fracture networks that fit well with actual outcrop fracture data. Based on Allard's definition of the connectivity index, a weighted factor is introduced, and an extended connectivity evaluation method is proposed to consider the effects of the aperture and its correlation with trace length. The results of the analysis show that the extended method improves the accuracy and reliability of connectivity evaluation compared with the traditional method. Moreover, the extended method is effective and accurate at predicting potential preferential flow paths in a practical example of the Dragon and Tiger Mountain (Jiangxi, China), and can better show the anisotropy with a change in the aperture. Hence, the proposed method extends the function of connectivity analysis and can benefit well location optimization in geothermal or petroleum exploration.

Visualization of flow behavior in ore-segregated packed beds with fine interlayers

Ore particles, especially fine interlayers, commonly segregate in heap stacking, leading to undesirable flow paths and changeable flow velocity fields of packed beds. Computed tomography (CT), COMSOL Multiphysics, and MATLAB were utilized to quantify pore structures and visualize flow behavior inside packed beds with segregated fine interlayers. The formation of fine interlayers was accompanied with the segregation of particles in packed beds. Fine particles reached the upper position of the packed beds during stacking. CT revealed that the average porosity of fine interlayers (24.21%) was significantly lower than that of the heap packed by coarse ores (37.42%), which directly affected the formation of flow paths. Specifically, the potential flow paths in the internal regions of fine interlayers were undeveloped. Fluid flowed and bypassed the fine interlayers and along the sides of the packed beds. Flow velocity also indicated that the flow paths easily gathered in the pore throat where flow velocity (1.8 × 10−5 m/s) suddenly increased. Fluid stagnant regions with a flow velocity lower than 0.2 × 10−5 m/s appeared in flow paths with a large diameter.

The hydrogeological situation after salt-mine collapses at Solotvyno, Ukraine

Study regionThe study site is located in the south-western part of the Ukraine, in the area of the historical rock-salt mining town Solotvyno. The former mining area is situated in close vicinity to the River Tisza, the main tributary of the Danube River, the largest river in Europe. Study focusAfter uncontrolled flooding of several salt mines, a one month advisory mission was launched by the European Commission to estimate the impact of the abandoned salt mines (containing large quantities of salt water) on the environment. As a consequence of the flooding, dozens of sinkholes formed and sinkhole forming processes are ongoing, with sinkhole diameters reaching 250 m. As river contamination by the release of large quantities of saltwater would lead to an international disaster, hydrogeological measurements were taken on-site to study the system. New hydrological insights of the regionAt the study site, saturated (hyper-saline) water as well as fresh surface and groundwater were encountered in close vicinity to each other. Electrical conductivity, as a proxy for salinity, and temperature were measured on-site and water samples taken from surface-, ground- and mine waters were analyzed for chemistry and stable isotopes, providing new insights into groundwater flow dynamics. A conceptual model shows the salt dome, and potential flow paths from the mining area to the Tisza River, in the context of the mines and associated sinkholes potentially impacting the river water quality.