Many subsurface rock formations are most accurately conceptualized and modelled as being fractured-porous media. The hydrological behavior of fractured-porous rocks has been studied extensively since the 1960s and 1970s, with early major contributions by researchers such as Barenblatt, Snow, and Witherspoon, among others. This field is now sufficiently mature that several monographs have been written on the topic of fluid flow and transport in fractured rocks, including Fractured Porous Media, by Adler, Thovert, and Mourzenko (Oxford University Press, 2013) and Fluid Flow in Fractured Rocks, by Zimmerman and Paluszny (Wiley, 2024). Nevertheless, a few key issues in this field are still not fully resolved, and perhaps deserve further consideration. For example, (1) the Reynolds lubrication approximation for flow through a single fracture reduces the problem to a 2D “effective medium” problem, eventually allowing the transmissivity of a fracture to be expressed as a function of mean aperture, standard deviation of the aperture, and contact area fraction, but it is known that the geometry of many fractures are too irregular for the lubrication approximation to apply. The question then arises as to whether the full Stokes equations will permit the transmissivity to be expressed in terms of simple geometrical parameters. (2) The Darcy-like relationship between pressure gradient and flowrate breaks down as the Reynolds number increases, after which the flow can be modelled with the Forchheimer equation. However, a robust correlation between the Forchheimer coefficient and aperture geometry is not yet available. (3) Dual-porosity models require a “shape factor” parameter that controls flow between the fractures and matrix blocks. Although the relationship between shape factors and matrix block geometry is well understood for discrete, clearly-defined blocks, the appropriate shape factor for a sparsely-fractured rock mass has not received much study. (4) A key ingredient in models for solute transport through fractured rocks is the Taylor-Aris relation between “effective diffusivity” and Peclet number. Yet even for the simplest possible geometry, a rectangular channel, two different “exact” expressions can be found in the literature. Furthermore, the results for narrow elliptical channels and narrow rectangular channels are completely inconsistent with each other. These facts seem to call for a re-investigation of the Taylor-Aris conceptual model.
How to cite: Zimmerman, R. W.: Unresolved Issues in Fractured Rock Hydrology, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20969, https://doi.org/10.5194/egusphere-egu25-20969, 2025.
In the coming years, we face many challenges related to groundwater flow in bedrock, including climate change and the ambition to increase Europe’s mineral supply. In crystalline bedrock, groundwater flow mostly occurs in fractures. Therefore, it is important to understand how individual fractures can affect groundwater flow. Simulating groundwater flow in a discrete fracture network is challenging, and the availability of analytical models is limited. This presentation introduces an analytical model for modeling groundwater flow in interconnected three-dimensional fracture networks. The presented model is based on the analytic element method and can manage random fracture networks [1].
The analytical model consists of planar circular fractures. The flow within each fracture plane is assumed to be two-dimensional. Intersecting fractures form an intersection line where the flow between the fractures is redistributed. Along the intersection line, the hydraulic head and flow are continuous. The analytical model uses a combined direct and iterative solver, and the solution can be used to calculate, among other things, equipotentials, streamlines, and flow velocities.
A unique feature of this model is that it does not require a computational mesh. This means that both the hydraulic head and flow velocity are known everywhere in the fracture network. The model also has no theoretical limit on the number of fractures that can be included or how large or small they can be. Therefore, the model is excellent for managing a combination of flow on both large and small scales simultaneously.
This presentation covers the basic concepts, the model’s properties, and application examples. We demonstrate that it is possible to include fractures at both kilometer and meter scales within the same model, while maintaining analytical accuracy. Furthermore, we will present particle tracking for multiscale models and discuss the influence scales on flow paths.
[1] Otto D.L. Strack, Erik A.L. Toller, An analytic element model for flow in fractured impermeable rock, Journal of Hydrology, Volume 643, 2024, 131983, ISSN 0022-1694, https://doi.org/10.1016/j.jhydrol.2024.131983.
How to cite: Toller, E. and Strack, O.: An analytic element model for groundwater flow in multiscale discrete fracture networks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7348, https://doi.org/10.5194/egusphere-egu25-7348, 2025.
Typically, the available information for the characterization of sub-surface formations is very limited, inducing significant uncertainties. This challenge is particularly pronounced in fractured formations and complicates predictive numerical simulations of flow and transport. For instance, isolated fractures can act as long-range highly conductive flow pathways, thus significantly influencing flow and transport. Since fractures may extend over lengths comparable to the domain of interest, homogenization approaches often yield unsatisfactory results. A common alternative is fracture-resolving Monte Carlo simulation (MCS), but there the high computational cost limits the inclusion of numerous fractures, which compromises the representation of realistic formations.
Alternatively, the Sid-FM approach offers a different methodology by bypassing fracture-resolving descriptions. Instead, it directly determines the ensemble-averaged flow field by incorporating non-local effects of extended fractures through fracture kernels. The present study demonstrates that suitably chosen kernel functions can effectively capture the influence of diverse fracture distributions, shapes, and connected fracture clusters. Numerical experiments compare Sid-FM results to fracture-resolving Monte Carlo simulations and demonstrate that Sid-FM provides accurate flow estimates at very low computational cost.
How to cite: Stalder, D., Cao, S., Meyer, D., and Jenny, P.: Sid-FM: A Statistical Integro-Differential Fracture Model for Efficient Flow Simulations in Fractured Sub-Surface Formation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9342, https://doi.org/10.5194/egusphere-egu25-9342, 2025.
How to cite: Cao, S., Stalder, D., Meyer-Massetti, D., and Jenny, P.: A new effective flow model for formations with spatially varying fracture statistics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8325, https://doi.org/10.5194/egusphere-egu25-8325, 2025.
Karst water resources play a vital role in global water supply, providing drinking water to 10–25% of the world´s population. Karst systems exhibit complex hydrological behavior, with fast-flow pathways and highly variable storage capacities. Hydrological models are essential for effective water resource management. However, modelling of karst systems is still a difficult task due to the heterogeneity of these systems and the uncertainties in karst structure.
LuKARS, a semi-distributed hydrological model for karst systems, addresses some of these challenges by allowing the consideration of multiple hydrotopes (i.e. distinct landscape units characterized by similar land use and soil types and thus by homogeneous hydrological properties) within a catchment. Despite its low computational cost, LuKARS faces challenges in the context of sensitivity analysis and uncertainty quantification due to its large number of parameters. Compared to the original LuKARS version developed by Bittner et al., (2018), the newly developed version of LuKARS 3.0 presented in this study allows much faster computational times with reduction in runtime of approximately 99.39% (from 1.14 seconds per test run down to 7 milliseconds), for the same model structure. In addition, LuKARS 3.0 allows an easy implementation of the model on clusters and a flexible model structure characterized by an arbitrary number of hydrotopes as well as by the possibility of activating/deactivating different model compartments, i.e., epikarst, matrix and conduit.
In this study, we leverage the low computation time of LuKARS 3.0 to apply Morris’ sensitivity analysis method, demonstrating its comparability to dimensional reduction techniques like the active subspace method. The efficient runtime also facilitates the investigation of combined parameter and structural uncertainties. We calibrate different model structures for the Kershbaum spring in Austria, with parameter estimation and uncertainty quantified via the GLUE method. The best-performing model structure is then coupled with PHREEQC to create an initial solute transport model based on the complete mixing assumption accounting for the posterior distributions of the parameter of the selected model structure of LuKARS 3.0.
Reference
Bittner, D., Narany, T.S., Kohl, B., Disse, M., and Chiogna, G. (2018). Modeling the hydrological impact of land use change in a dolomite-dominated karst system. Journal of Hydrology 567:267–279.
How to cite: Richieri, B., Sivelle, V., Hartmann, A., Labat, D., and Chiogna, G.: Simulation of Flow and Transport Processes in Karst Systems: LuKARS 3.0 Unveiled, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3776, https://doi.org/10.5194/egusphere-egu25-3776, 2025.
Extensive karstification and speleogenesis in carbonates can be induced by the rise of hydrothermal fluids. However, the contribution of different geochemical and hydrogeological mechanisms to this process remains unclear, and a variety of reactivity sources, as well as hydrogeological mechanisms, were suggested. These include renewed reactivity by mixing of different solutions or condensation corrosion above the groundwater table [1-4]. However, the role of cooling and retrograde solubility of carbonates as a major hypogene speleogenesis mechanism was often considered negligible (e.g., [1] & [2]) or attributed to the development of diffuse karst [3]. Here, using mathematical modeling, we study speleogenesis induced by upwelling thermal flow, enriched by deep CO2 fluxes, that upon cooling leads to large retrograde solubility and extensive dissolution. The conceptual model we suggest, consistent with our case study of hypogene caves [5], considers upwelling of focused channelized thermal flow through faults. Upon approaching an impermeable caprock this flow is diverted sideways and flows radially along permeable bedding planes and fractures in limestone strata (inception horizons). Radially dispersed hot flow then cools rapidly via heat transfer to the surrounding rock, leading to focused dissolution and, over time-scales of 10 000 - 100 000 yrs, to speleogenesis near the inlet. Because the caves are isolated and breakthrough to the surface is not achieved during speleogenesis, the overall permeability and fluid flux do not appreciably change, so that dissolution remains localized, forming a cave. The model also predicts that maximal fluid cooling and dissolution are attained slightly downstream from the inlet, for which corresponding field observations are presented. These findings show that geothermal heat loss by upwelling of thermal fluids, in conjunction with deep CO2 fluxes, may shape and extensively karstify carbonate aquifers in the upper crust, with the formation of sizable speleological structures [6].
[1] Palmer, A.N., Geol. Soc. Am. Bull., 103(1), 1-21, 1991
[2] Klimchouk, A.B., In: White, W.B., Culver, D.C. (Eds.), 2nd ed. Academic Press, New York, 748–765, 2012
[3] Andre, B.J. and Rajaram, H., Water Resour. Res., 41, W01015, 2005
[4] Dreybrodt, W., Gabrovsek, F., Romanov, D., Processes of Speleogenesis: A Modeling Approach, ZRC Publishing, 2005
[5] Frumkin, A. et al., Geol. Soc. Am. Bull., 129(11-12), 1636-1659, 2017
[6] Roded, R., Aharonov, E., Frumkin, A., Weber, N., Lazar, B., and Szymczak, P. , Commun. Earth Environ., 4, 465, 2023
How to cite: Szymczak, P., Roded, R., Aharonov, E., Frumkin, A., Weber, N., and Lazar, B.: Upwelling geothermal flow and retrograde solubility lead to hypogene speleogenesis in carbonate aquifers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17039, https://doi.org/10.5194/egusphere-egu25-17039, 2025.
Tracer tests are the key technique to characterize karst conduits. Hundreds of thousands tracer tests done worldwide showing typical flow velocities in conduits in km/day. In contrast slow flow in fractions of m/day is typical for porous aquifers. This study reports surprisingly slow flow velocity obtained from karst conduit in small metamorphosed carbonate occurrence in Czech Republic. Factors responsible for exceptionally slow flow are discussed.
Chýnov Karst is formed by several km long but few hundred meters wide carbonates strip inside gneiss in slightly undulated landscape. It hosts karst conduit traversed by small subterranean stream (5-13 L/s, observation since 2001), fed by diffuse recharge, no sinking streams occur in area. Karst conduit is accessible at two places: Chýnov Cave and 1200 m distant spring Rutice. The carbonate strip is traversed perpendicularly by two small streams, which valleys contain Miocene Mydlovary Formation. The river network and karst conduit could be dated back at least to Miocene, as demonstrated by Miocene sediments below the recent streams. There are no signs of hypogenic origin. Cave is formed by deep phreatic loops indicating low density of fractures available for conduit forming. No transport of sediment was ever observed, the water remains limpid and flow in conduit is nearly constant.
Tracer tests from 1960 indicated residence time in days, but individual results strongly differed, therefore new tracer test was performed using uranine in 2021. Uranine concentration has been monitored by field fluorometers GGUN-30 (Albilia, Switzerland) and laboratory fluorimeter Perkin Elmer LS55 for more than 3 years (continues). Breakthrough curve was analyzed by Qtracer2 code. New tracer test demonstrated residence time 1.4 year between cave and Rutice spring, which is equal to mean flow velocity 3.6 m/day. Volume of mobile water in conduit is 252000 m3 which is equal to average cross section of conduit 140 m2 . Tracer recovery is currently 25%. Tracer did not arrive to any other spring or stream in wider surrounding. Large conduit volume and low flow rate are responsible for extremely slow flow and long residence time. Large volumes are probably primarily caused by deep phreatic loops in cave. Phreatic loops disable under gentle landscape the transport of sediment from streams to cave.
Therefore, the localized sinks can never develop in the area. As a consequence, the corrosion over more than 20 million years ever increases the conduit volume and no sediment is transported inside to infill it. Existence of this conduit indicates that low fracture density resulting in deep phreatic loops can in combination with gentle morphology over long time period result in evolution voluminous conduits with very slow flow. If Chýnov cave is not known in the area the long residence time of water and low flow fluctuation will be considered as indication of non-existence of karst conduits.
Funded by the GAUK No. 171624.
How to cite: Koutník, J., Mareš, J., Bruthans, J., and Krejča, F.: Extremely slow flow in voluminous karst conduit developed in metamorphosed carbonates: Result of long-term evolution and lack of sediment transport, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12298, https://doi.org/10.5194/egusphere-egu25-12298, 2025.
Granite forms a hardrock hydrogeological environment, characterized by a shallow permeable zone and relatively low transmissivity. Cold springs from granite mostly do not exceed a few L/s. Interestingly, hot springs with yield up to tens of L/s are not uncommon (e.g. Idaho batholith, USA). However, little is known about the character and origin of these high-permeability features in granite. The Karlovy Vary Spa (western Czech Republic) is fed by a large hot spring granite with a temperature of 73 °C and yields 30 L/s. Since the 1970s, > 70 boreholes have been drilled in the area to capture water for the spa. This provides a unique opportunity to study the characterization of the granite and its alteration by well logging techniques, to investigate conduits by borehole camera, to analyze cores, and to perform the tracer test from conduits captured by boreholes into a hot spring.
The Karlovy Vary Spa is located on the outskirts of the Eger Graben structure. One major spring, Vřídlo, (30 L/s) and tens of small springs occur in area (total yield < 3 L/s). The water has a TDS of 6.4 g/L and is classified as a Na-HCO3-SO4-Cl type, probably derived from water of high-TDS tertiary paleolakes. The water is enriched with CO2 (water-to-gas ratio 1:3). Granite is capped by a 10-16 m thick aragonite shield precipitated from hot water. Open conduits in granite filled by hot water were observed. In 1980, the geophysical log probe (1050 mm long and 36 mm in diameter) was incidentally lowered into an open conduit feeding the Vřídlo spring from the base of a 133 m deep borehole. The probe reached a depth of 370 m. It follows that hot spring conduits have a considerable diameter. Flow velocity in this conduit exceeds 0.3 m/s, as water carries granite grain fragments up to 2 mm in diameter to the surface.
Four tracer tests using Na-fluorescein were conducted under a constant injection rate of 0.9–1.1 L/s. The tracer was injected into boreholes in close surroundings of the Vřídlo hot spring (tens of meters, depth up to 160 m) and monitored in boreholes feeding the Vřídlo spring. Flow velocities varied between 100–400 m/day (first arrival) and 50–140 m/day (mean residence time). Mean flow cross-sections derived from tracer tests were 5–10 m2, recovery was 8–15 %. In one test, where the tracer was injected directly below the aragonite shield, the tracer did not arrive to the Vřídlo spring or boreholes as close as 20 m away, despite injecting 500 m³ of water to mobilize the tracer. This indicates a very high effective porosity of strongly weathered granite in shallow depth, which can accommodate hundreds of m3 of water without allowing any tracer to reach the monitored boreholes.
Hot water enriched with CO2 can create highly permeable conduits in granite transmitting flow of tens of L/s. Granite is weathered into disintegrating residuum in places. It is likely that the high flow velocity >0.3 m/s emptied some fracture zones into high permeability conduits.
Funded by the GAUK No. 164524.
How to cite: Landa, D.-A., Koutník, J., Mareš, J., Bruthans, J., Vylita, T., and McCann, C.: Characterization of high-permeability feeding conduits of thermal springs in fractured crystalline rocks (Karlovy Vary Spa, Czech Republic), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4763, https://doi.org/10.5194/egusphere-egu25-4763, 2025.
The aim of this study is to understand the relationships between surface and underground flows of Kibounda karstic system, near Madingou town, in the southwest of the Republic of Congo. This karst system developed within the carbonated formations of the Neoproterozoic Schisto-Calcaire Group, and is characterized by a distinctive landscape featuring cone and pinnacle reliefs typical of tropical karst terrain. Surface flows appear rare and are influenced by seasonal rhythms. Structural studies and chemical analyses of the water were carried out in order to understand how the network operates according to seasonal variations.
Surface and groundwater samples were collected, and major ions were analysed to understand the geochemical processes controlling the water chemistry in Kibounda. High concentrations of Ca, Mg, and HCO₃ indicate the dissolution of limestone and dolomite rocks. The observed SiO₂ concentrations in these waters suggest the widespread presence of silicates in the soils and rocks of the carbonate reservoir. Significant concentrations of sulfates in the rivers would indicate contamination of the water by anthropogenic activities. Other major ions are present in marginal concentrations, with Sr detected in trace amounts.
Structural measurements realized at key sites in the area show two dominant fracture orientations, NE-SW and NW-SE, along which water flows preferentially. These fractures are the fundamental drivers in the genesis of multiple karstic sites in the region.
The study determined the hydraulic connections between different sites following on their hydrochemical characteristics. It provides the information needed to understand the hydrochemical functioning of the Kibounda karstic system, contributing to the sustainable management of water resources of this area.
Keywords: Kibounda, Hydrokarst System, hydrochemical characteristics, Structural control, Congo Republic.
How to cite: Samba, P., Bazebizonza, N., Nkodia, H., Boudzoumou, F., Arfaoui, I., and Lahogue, P. and the Prefina Samba: Chemical signature and structural study of a Madingou hydrokarst system, southwest of the Republic of Congo., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-716, https://doi.org/10.5194/egusphere-egu25-716, 2025.
The role that fractures play for karst development has been widely described, most particularly for the generation of preferential flow pathways. The alignments between fractures and karst features, such as conduits and dolines, occur in various regions where the rock is prone to diaclase or where the tectonic history imprints fracture patterns that facilitate rock dissolution. However, most studies specifically linking the orientation of fractures and karst features are largely descriptive. A quantitative analysis of the geometries and their interconnection is required before modeling any discrete karst network model (DKN).
In order to analyze the relationship between structural geology and karst development, we propose a novel quantitative approach, in between description and modeling. This approach is applied on the karst aquifer system of Tsanfleuron in the Helvetic domain of the western Alps. We check if the fracture and conduit orientation is similar, by statistically comparing their azimuths. The aim is to quantify and identify which fracture families have the highest influence in the development of karst features.
We interpret fracture alignments on a scale 1:2.500, based on a set of data acquired from an uncrewed aerial vehicle with 10 cm/px resolution, consisting of a digital elevation model and an orthomosaic image. Fracture interpretation was verified in the field. Karst surveys were previously acquired by the Groupe de Spéléologie Rhodanien, Société Spéléologique Genevoise, Spéléo-Club Jura, and Groupe Spéléo Lausanne. We calculate the azimuths from the fracture interpretation and karst surveys. We identify the dolines by the circular and ellipsoidal shape as depressions on the DEM, and their alignments are detected with the application of the Hough transform.
The superposition of structural and karstic features on maps and the plot of their direction in rose diagrams show that some fracture sets coincide with the orientation of most of the conduits in the study area. We apply the chi-square test to verify how similar are the distributions of the fractures and conduit azimuths. The null hypothesis (H0) is that the distributions are similar, and the alternative hypothesis (H1) is that the distributions are significantly different. If the chi-square test yields a value under the selected p-value = 0.05, we reject the null hypothesis.
Comparison of all azimuths ranging from 0° to 180° shows that hypothesis H0 cannot be rejected; therefore, the distributions of fractures and karst conduits are similar. Testing more specific direction ranges indicates that fractures and conduits are strongly aligned especially in the NE-SW, ENE-WSW, and E-W directions (with high p-values). The alignments of the dolines are based on fewer measurements, but show a preferential NE-SW orientation.
We conclude that the fracture and karst conduit azimuth distributions are similar. Therefore, fractures, helped by the gentle dip of the bedding, controlled the development of the karst in Tsanfleuron, mainly in the NE-SW, ENE-WSW, and E-W directions. This result will be used for the construction of a DKN model in future work.
How to cite: Burgoa Tanaka, A. P., Trunz, C., Trottet, M., Racine, T., and Renard, P.: Detecting fracture networks and karst features alignments similarities in the aquifer system of Tsanfleuron, Swiss Alps., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11154, https://doi.org/10.5194/egusphere-egu25-11154, 2025.
The objective of this work is to investigate infiltration processes, flows on both saturated and unsaturated zones, and quantify their contributions to spring discharge, in a binary karst aquifer (recharged by the karst massif, as well as sinking streams). The study site is the Verneau karst aquifer located in the Jura Mountains (France). The recharge area covers 15 km², with half consisting of marl outcrops, where water enters through five losses (localized infiltration), and the other half consisting of limestone massif covered by a soil layer (diffuse infiltration).First, to analyze the spatial variability of flows generated by diffuse and localized infiltration at various depth, we performed hydrochemical analyses in soil lysimeters, caves and at the spring, conducting to characterize the physico-chemical end-members of the various compartments: soil layer, unsaturated zone in the karst massif and in the conduit network, saturated zone. Second, we used continuous high-frequency (1hour) time series (3 years) of semi-conservative tracers (electrical conductivity and nitrate concentrations) to characterize discharge response throughout the seasonal cycle. A End-Member Mixing Analysis (EMMA) was conducted on 40 flood events to determine the contribution of the infiltrations types to spring discharge. Our results show that the localized infiltration shows a relatively homogeneous spatial signal, characterized by low values of electrical conductivity and nitrate content. Diffuse infiltration is spatially variable due to anthropogenic activities and contrasted residence time within the massif. Results of the EMMA method reveal that during flood events, approximately 1/3 of spring discharge comes from localized infiltration, while the majority comes from diffuse infiltration and pre-event water stored in the massif. A seasonal variability is evidenced in link with lower stream losses and storage in the unsaturated zone. A hydrogeological conceptual model is finally proposed, allowing us to discuss the origin of spring waters, given new elements on drivers controlling infiltration modalities, and the role of transfer and storage in the unsaturated zone.
How to cite: Durand, L., Charlier, J.-B., Champollion, C., Idoux, A., Ladouche, B., Mexler, J., Tourenne, D., and Vallet, A.: What is the contribution of localized recharge to spring flows in a binary karst aquifer? A response using a multi-scale physico-chemical approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8835, https://doi.org/10.5194/egusphere-egu25-8835, 2025.
The objective of this work is to understand the mechanism of seawater intrusion and nature of water components supplying the slightly brackish Te Waikoropupū Springs (TWS) in New Zealand (Stewart and Thomas, 2008; Williams, 2023). Seawater intrusion in karst has special features due to flow being in conduit networks below sea level, very different from seawater inflow to porous aquifers (Fleury et al., 2007). Three mechanisms of seawater intrusion in karst have been identified (venturi suction effect, head balance process, and freshwater dilution of a near-constant brackish water flow, Arfib & Charlier, 2016). This work proposes a fourth mechanism at TWS – near-constant freshwater flow with increasing brackish water contribution as spring discharge increases following rainfall in the catchment.
The salinity of TWS Main Spring ranges between 0.02 and 0.23 g/L varying accurately with discharge, with a mean of 0.18 g/L. It is believed that two distinct water stores, designated Fresh Component (FC) and Brackish Component (BC), combine to produce the springs’ outflow. At low flow (low salinity) the discharge is almost all FC, then flow and salinity increase as BC is added. Chemical data over 50 years shows that the FC contribution has been near-constant and the salinity of BC has not changed in that time. While the positive relationship between salinity and discharge rate might suggest seawater intrusion by venturi suction, the nature of the system suggests otherwise.
Fleury et al., 2007 classed the TWS coastal karst aquifer as Type 3 (i.e. ‘a system with well-developed karstification below sea level, partially or totally closed to the sea’). This is exemplified by relatively slight brackishness of the spring water and no clear offshore outlets, although it is clear that freshwater escapes to the sea. A conceptual model of the system will be presented.
References
Arfib, B., Charlier, J.-B. Journal of Hydrology 540, 148–161, 2016.
Fleury, P., Bakalowicz, M., de Marsily, G. A review. Journal of Hydrology 339, 79–92, 2007.
Stewart, M.K., Thomas, J.T. Hydrology and Earth System Sciences 12(1), 1-19, 2008.
Williams, P.W. Carbonates and Evaporites 38:44, 2023.
How to cite: Stewart, M., Moreau, M., Morgenstern, U., and Thomas, J.: Seawater intrusion mechanism in coastal karst (TWS brackish spring in New Zealand), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7611, https://doi.org/10.5194/egusphere-egu25-7611, 2025.
Karst aquifers, characterised by extensive and intricate conduit networks, serve a critical role in groundwater flow and contaminant transport. These natural systems exhibit complex geometrical features, including branching conduits, variations in cross-sectional shape, and significant wall roughness (k/D≈10-1). Such heterogeneity makes it challenging to understand and predict flow patterns, friction losses, and the onset of turbulent behaviour in karst environments. Accurate characterisation of flow dynamics at the conduit scale is therefore essential for developing robust numerical models and reliable management strategies.
This study aims to investigate flow behaviour within representative karst conduits to determine key geometrical and fluid mechanical parameters, such as average cross-sectional areas, cave centrelines, friction factors, and velocity distributions by means of direct numerical simulations in a wide range of flow conditions (Re=1-104). These parameters are fundamental inputs for upscaling methodologies that aim to describe entire karst networks without resolving every conduit in detail. A combination of finite-volume and spectral element methods is employed, each chosen to capture specific flow regimes. At lower Reynolds numbers, a finite-volume approach is used to accurately resolve laminar flows, while at higher Reynolds numbers, a spectral element method is implemented to better capture the full range of turbulent flow scales.
The conduit geometries used in the simulations are reconstructed from high-resolution LiDAR scans of real karst formations. The provided STL files preserve critical features such as irregular walls, branching geometries, and variable cross-sections. To ensure accurate resolution of the boundary, an immersed boundary technique is applied in conjunction with a ray-tracing algorithm. This combined approach precisely identifies the conduit walls, thereby facilitating the correct imposition of boundary conditions in these complex geometries.
Preliminary results for low Reynolds number flows show that laminar assumptions can hold in certain portions of the conduit, leading to streamlined centreline velocities and predictable head losses. However, irregular conduit shapes disrupt the flow field, causing spatial variations that deviate significantly from classical smooth-channel results. As also observed in a previous wavy-channel investigation, transitional flows can occur much earlier than predicted by standard empirical correlations (Re ≤ 1500), suggesting that conventional methods for estimating friction factors may be insufficient for karst-specific conditions and to account for the marked heterogeneity of the systems.
The implications of this study are crucial not only for single conduits but also for the better understanding of network-scale flow dynamics, which enables more accurate prediction of groundwater movement and contaminant dispersion in karst aquifers. Furthermore, the hydraulic parameters identified in this investigation are highly valuable for upscaling models, as they allow for their incorporation into comprehensive karst network simulations, thereby improving the assessment of these systems.
How to cite: El Mellas, I., Racine, T., Hidalgo, J. J., Renard, P., and Dentz, M.: Direct numerical investigation of turbulent and laminar flow in karst conduits, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16662, https://doi.org/10.5194/egusphere-egu25-16662, 2025.
The Buda Castle Cave, consisting of natural limestone formations and artificial corridors, lies under the Buda Castle Hill. The landscape of the area above the cave is part of the UNESCO World Heritage Sites. In the area of the Great Labyrinth – part of the Castle Cave – the infiltrating water seems to have reached an amount, that has never been experienced before, and it has also caused more intense weathering and rock falls, especially on the roof of the cave. The main motivation of the research was to preserve the condition of the Castle Cave and the priceless historical and cultural values of the Buda Castle District above by determining the origin of cave waters. In order to achieve this goal, a detailed study of the water conditions in the cave was necessary. Data on the cave system's current water conditions were limited, as the latest measurements were carried out between 2008 and 2010. The monitoring started again in October 2023, and several measurements were carried out to quantify the water conditions and to determine the origin of the cave waters. In addition to measuring the water level in the cave wells and conducting pumping tests, the amount of drip water was measured using self-made tipping bucket gauges and ad hoc field tests. The temporal resolution of the measurements was much more detailed than in previous studies. After processing the data, statistical analyses were performed on the measured data. The precipitation in the area was correlated to well water level and drip water intensity time series. The precipitation data were shifted by different numbers of days, and the maximum correlation coefficients were determined using linear regression. The correlation analyses indicated only a weak relationship, so other – presumably anthropogenic – effects may be present. Although strong linear relation between daily precipitation and daily average water levels and drip water intensities was not revealed, some assumptions could be made. In one of the wells, there was found a weak connection to the precipitation about three months prior and two drip locations in the Castle Cave had very similar correlation coefficient values. However, further measurements are essential to draw more accurate conclusions about the origin of the cave waters.
How to cite: Gazda, F., Farkas, D., Hajnal, G., and Négyesi, K.: Effect of precipitation on well water levels and drip water intensity in the Buda Castle Cave, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13427, https://doi.org/10.5194/egusphere-egu25-13427, 2025.
In active petroleum systems, hydrocarbon charging and leakage often occur simultaneously. Establishing the relative relationship between reservoir charging and leakage is crucial for hydrocarbon exploration and reserve assessment. This study investigates the dynamic equilibrium between gas charging and leaking in a sandstone reservoir using high-resolution seismic, wireline logging, and well testing data from the LD10 gas field in the Yinggehai Basin, South China Sea. Fluid migration pathways, including top seal breaches, are depicted by utilizing attribute extraction and volume rendering. The fluid pressure distribution is characterized through measured and predicted pressure data. The charging episodes are identified by carbon isotope compositions. Our results show that gas-bearing fluids were charged from source rocks into the channel sandstone reservoirs in the Upper Miocene Huangliu Formation through positive flower faults The fluids subsequently migrated to higher sandstone intervals via hydraulic fractures. Leakage occurred through normal faults developed at the top of the channels, penetrating the seal of the upper Huangliu Formation. Our findings provide insights into fluid migration mechanisms in deep overpressured environments in sedimentary sequences.
How to cite: Yang, B., Meng, Q., Hao, F., Zong, Z., and Guo, Z.: Dynamic equilibrium in hydrocarbon charging and leakage of an intensively overpressured reservoir, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10526, https://doi.org/10.5194/egusphere-egu25-10526, 2025.
Preferential flow (PF) is the rapid, irregular movement of water through soil channels. In permafrost regions, it is triggered by rainfall, snowmelt, and other hydrometeological factors, and affected by environmental and soil factors. With climate change, permafrost is degrading, especially in boreal areas such as the Da Xing’anling Mountains and along the China-Russia Crude Oil Pipelines (CRCOPs). This study focuses on silty clay from the right of way of CRCOPs. Using indoor color tracers and comparative testing, six PF types were simulated in the samples and compared to a control.
The results show that soil columns with microfracture PF and randomly distributed macroporous PF experienced extended cooling (by 65% and 87%) and warming (by 57% and 39%) periods. Their average minimum temperatures were 0.4 to 2.5°C lower than those of the control, and took 1.9 to 2.4 times longer to reach stable temperatures. Microfracture and funnel PF samples had 18% to 25% higher minimum water content compared to the control. The coloration rate was 15% to 56% higher, and the preferential flow index in PF soil columns was over 48% higher during the first freeze-thaw cycle. Overall, PF type and related factors are crucial for the thermal and moisture characteristics of silty clay. These findings provide valuable insights for pipeline operation and permafrost engineering, contributing to enhanced foundation stability in a changing climate.
Key words: preferential flow; freeze-thaw cycles; hydrothermal effects; color tracing; silty clay; northern Da Xing’anling Mountains
How to cite: Cheng, Y. and Jin, H.: Experimental study on hydrothermal effects of preferential flows in silty clay specimens from the Da Xing’anling Mountains using a color tracer under freeze-thaw cycles, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2333, https://doi.org/10.5194/egusphere-egu25-2333, 2025.
The coupled flow, transport, and hydro-chemo-mechanical processes in fractured porous media have great relevance for numerous applications including underground water management, hydrocarbon recovery, CO2 sequestration, and geological waste disposal. We developed a novel experimental setup designed to investigate these coupled processes. The setup uses fully matched transparent rectangular fracture blocks. These blocks are created by molding a granite fracture surface with resin. The design of the experimental setup provides controlled shear and normal stresses with simultaneous measurement of the resulting stresses and displacement in both the normal and shear directions. The fluid is injected from the center and flows radially toward the outputs. There are nine discrete outlets per side to provide high-resolution measurements of the redistribution of flow and permeability anisotropy at various flow and stress conditions. Moreover, we utilize high-resolution imaging and fluorescent tracers to visualize real-time flow.
The results of shear-flow experiments showed that shear displacement enhances the permeability in the direction perpendicular to the applied shear stress. This anisotropic behavior results from the development of preferred flow paths due to the dilation and changes in the geometry of fractures caused by shear. This result was supported by high-resolution fluorescent tracer imaging, which likewise showed the changes in flow paths during shear-flow tests.
This experimental setup enables us to study coupled hydraulic, mechanical, and chemical processes, with precise evaluation of permeability anisotropy under a wide range of conditions. In the next step, we will utilize this setup for two-phase flow studies, as it has often been a challenging complexity in fractured porous media.
How to cite: Sheikhi, S., Ortín, J., and Aquino, T.: Investigating Permeability Anisotropy in a Rough Fracture: A Novel Shear-Flow Setup, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3568, https://doi.org/10.5194/egusphere-egu25-3568, 2025.
The complexity of karst aquifers hampers the assessment of groundwater recharge processes in the upper vadose zone. Consequently processes governing water flow in the soil and epikarst into the vadose zone remain poorly understood. This study aims to explore spatial differences of water recharge, storage, and movement through the upper vadose zone on a field scale at the Hochschwab karst massif (Eastern Alps, Austria).
To achieve this, we combined multiple approaches such as geophysical, hydrological, pedological, and structural geological methods to distinguish spatial variability in infiltration processes. Data were collected at Hirschgruben cave (1896 m above sea level) for dry and wet conditions in winter and summer providing a seasonal comparison of infiltration dynamics in regard to snowmelt and precipitation. Monitoring included cave drip water (discharge, electrical conductivity and temperature) along with soil moisture measurements at depths of 5 to 30 cm, and electrical resistivity tomography (ERT) utilizing 96 electrodes between the cave ceiling and the surface to produce resolved 2D images. A structural geological survey of the fracture density classes and fault characteristics was carried out.
The results show different infiltration processes for snowmelt and precipitation; deep saturation with slow water percolation after snowmelt and rapid transit of water and quick responses at the cave weir after heavy precipitation events. Spatial differences in the ERT images indicate differences in water saturation in the epikarst, bedrock and the frost-weathered cave ceiling. The ERT images show the greatest increase in saturation in the bedrock during snowmelt, while rain events with rapid and heavy water flow show a continuous increase in water saturation in the epikarst and preferential flow paths. The structural geological characterisation of the catchment area enables the interpretation of differences in the spatial distribution of water saturation. These results underline that the integration of multiple sensors and methods is crucial to understand the variability of water fluxes in Alpine karst systems under different meteorological conditions.
How to cite: Kaminsky, E., Funk, B., Michtner, R., Nagl, M., Flores-Orozco, A., Decker, K., and Plan, L.: Characterisation of structural and water flow processes in the upper vadose karst zone using a multi-method approach in a cave, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4282, https://doi.org/10.5194/egusphere-egu25-4282, 2025.
Heat transport in fractured media concerns various hydrogeology and subsurface engineering applications, such as heat transfer in enhanced geothermal systems (EGS), thermal energy storage in fractured rocks, or the effect of heat on rock properties near nuclear waste repositories. The main factors influencing heat transport in fractured media are the thermal and hydraulic properties of the rock matrix and the presence and magnitude of fluid flow, which depends on the connectivity, geometry, and hydraulic properties of the fracture network.
This study analyzes coupled flow and heat transport processes at fracture intersections based on numerical simulations and laboratory experiments. The numerical simulations are conducted with OpenFoam, solving the mass, momentum, and energy conservation equations in the fractures coupled to heat conduction in the impermeable rock matrix. The numerical simulations are complemented by high-resolution temperature measurements in quasi-two-dimensional fracture intersection geometries. This is accomplished by the phosphor thermometry measurement technique. Phosphor particles are seeded into the fluid and act as tracers for the fluid temperature thanks to their temperature-dependent luminescence. The simulations and experiments are conducted under different volumetric flow rates to vary the thermal Péclet number.
Coupled flow and thermal transport in the numerical simulations and laboratory experiments are analyzed from the thermal breakthrough curves, the thermal front in the fractures, and the overall heat transfer coefficient between the fractures and the rock. The results characterize the effect of the fracture aperture, the angle under which the fractures intersect, and the thermal conductivity of the matrix on the heat transport at fracture intersections.
How to cite: Ringel, L. M., Rashed, A., Fond, B., Méheust, Y., and Klepikova, M.: Numerical and Experimental Analysis of Heat Transport at Fracture Intersections, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5741, https://doi.org/10.5194/egusphere-egu25-5741, 2025.
We present a newly developed flow and transport simulator for karst systems, designed to model complex flow dynamics and tracer transport in large-scale networks. The simulator is based on the Saint-Venant equations and integrates advanced hydraulic modeling and particle tracking algorithms to study the interplay between the physical properties of karst conduits, their large-scale network structure, and the resulting flow and transport behavior. The simulator accommodates both steady-state and transient flow scenarios under free-surface and pressurized conditions. Turbulent flows are modeled using the Darcy-Weisbach equation, supported by classical friction models such as the Churchill and Colebrook-White equations. Validation against a broad range of analytical solutions and flow dynamics in one of the largest cave systems in the world, the Ox Bel Ha cave, confirms the robustness of the approach.
Using field data obtained from 3D lidar scans of cave systems, we extract geometries to build high-resolution network models and investigate how resolution impacts flooding signals. Specifically, we analyze how downscaling to lower resolutions, resulting in fewer conduits with averaged properties such as diameter, hydraulic radius, and roughness, alters critical features like bottlenecks and their influence on flow propagation. Bottlenecks, which play a significant role in controlling flow rates and local hydraulic gradients, can disappear or be muted when the geometric complexity of the network is reduced. This smoothing process effectively reduces the spatial variability in conduit dimensions and frictional resistance, leading to changes in the timing, magnitude, and spatial distribution of flooding signals. The disappearance of bottlenecks at lower resolutions may result in a more homogenized flow regime, potentially masking the true hydrodynamic behavior of the original network. Understanding these impacts is critical for accurately modeling flow dynamics in karst systems and assessing the trade-offs between computational efficiency and the complexity of hydrological predictions.
How to cite: Kordilla, J., Dentz, M., and Hidalgo, J.: openKARST: A novel computational modeling tool for flow and transport in complex karst conduit networks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9802, https://doi.org/10.5194/egusphere-egu25-9802, 2025.
The effects of global warming have already been recorded in many decorated caves located in karst systems, and some prehistoric paintings are already deteriorating. Modeling the microclimate of caves under various climate change scenarios will enable to adapt the conservation strategy for rock art heritage. In this study, we consider the first step in this modeling approach: the simulation of water and heat transfers from the soil surface to the cave through the soil/epikarst/karst system.
Water transfer is modeled using a double-permeability approach. A sensitivity analysis was conducted to assess the influence of various parameters on the model's behavior. Calibration of the model was achieved by comparing the simulated water flux at the model's exit with the observed drip rates from stalagmites.
For heat transfer modeling, the thermal rock characteristics are calibrated using sensor data taken at various depths in the soil and in the karst over a few years, and in the cave thanks to long-term monitoring. To provide long-term climate forcing, a transfer function is established between meteorological data measured at a height of 2 meters by Météo France and the temperature measured at the ground surface.
Then, this heat and water transfer model is fed with projections from regional climate downscaling models. This modeling approach, which integrates both current data and climate projections, will be a significant step towards the effective management and conservation of decorated caves, which are not only exceptional geological sites but also hold important historical and archaeological significance.
How to cite: Artigue, C., Mugler, C., and Genty, D.: Water and heat transfer modeling in karst environments to study the impact of climate change on the future of decorated caves: Application to the Villars Cave (Dordogne), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9955, https://doi.org/10.5194/egusphere-egu25-9955, 2025.
Synthetic rough-surfaced fractures have been successfully generated using methods founded on self-affine principles, which can be based on properties obtained from fracture surface measurements. In order to generate fractures using self-affine methods, a function describing the correlation between the upper and lower surfaces is required, as well as two key parameters, the Hurst exponent H and a scaling parameter Sp. In current literature, there are several methods for determining H and Sp which are primarily adopted for measurements of 1-dimensional fracture traces. There are however comparatively few studies using these methods with measurements of surface scans and applying them to generate realistic fractures. In this work, we evaluate two methods commonly used, the root-mean-square correlation function (RMS-COR) and the Fourier Power Spectrum (FPS) approach, each with several variations of possible implementation when applied to measurements of fracture surfaces.
To obtain an accurate representation of the aperture field and rough surfaces we use high resolution surface scans of a natural fracture sample. For each method variation 100 realisations of the aperture fields are generated and their respective ensembles are evaluated against the measured aperture distribution. The most accurate method for obtaining H and Sp in terms of its ability to generate apertures that correspond with the measured fracture sample studied was the RMS-COR method. We show a linear relationship between H and Sp that provides a best fit of synthetically generated fractures when compared with the measured fracture sample. We also introduce an improved approach for representing the correlation function between two rough surfaces. Finally, using a restricted subsection of the sample, we demonstrate the developed model can successfully generate upscaled fractures. Thus, aperture fields generated using this method can be used for representing and modelling larger fractures or multiple fractures in a network, allowing for numerical flow simulations to include realistic representations of aperture internal heterogeneity based on measurements obtained from a natural rock fracture.
How to cite: Stock, B. and Frampton, A.: Rough-surfaced fracture generation with variable aperture using self-affine methods, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13698, https://doi.org/10.5194/egusphere-egu25-13698, 2025.
Fractured rock aquifers pose challenges for flow system characterization due to the complex nature of fracture networks controlling the bulk hydraulic conductivity within and across hydrologic units. The distinct depositional characteristics of mud-rich carbonate facies as well as the post-depositional alteration of material via diagenesis often result in highly anisotropic flow systems. The lithostratigraphic properties and sequence stratigraphic surfaces in sedimentary bedrock are known to affect fracture development and connectivity. The objective of our study is to build a robust geologic model to inform fracture network connectivity influencing vertical and horizontal flow of groundwater and creosote DNAPL in a shallow Silurian limestone aquifer located on the island of Gotland, Sweden.
Previous consulting studies using conventional wells showed widespread presence of dissolved phase creosote constituents and occasional presence of non-aqueous phase components near and away from the historical operations area. The current research investigation aims to use recently advanced high-resolution methods to build a robust, hydraulically-calibrated geologic framework. It began with six ODEX air-rotary boreholes, drilled 30m below the top of rock around the perimeter of known contamination at the site. Four additional boreholes were cored using GeoBore-S diamond bit wireline drilling within the contaminated zone to provide continuous core for lithology and fracture feature logging. These four cores were also used to inform sample locations near and away from fractures for contaminant concentrations and rock physical properties. All 10 new boreholes were geophysically logged to inform the placement of temperature and pressure transducers in the boreholes, which were then sealed in place using flexible, impermeable fabric liners (FLUTe™) for depth-discrete dynamic hydraulic head monitoring.
Lithology and fracture-feature logs were collected and confirmed the sitewide presence of limestone-marl alternations with a high propensity for laterally extensive, bedding plane fractures dipping south-southeast. Depth-discrete rock samples for VOC and PAH contaminant analyses confirmed that: 1) matrix diffusion of PAH compounds from hydraulically active fractures was limited due to low aqueous solubilities, low porosity and high sorption, 2) downward migration of creosote through vertical fractures was likely inhibited by the lack of vertical connectivity between fine-grained limestone facies imparting strong anisotropy, the near neutral density of the creosote as a NAPL and the high sorption of low solubility solutes in the organic-rich marlstone units. Downhole geophysics and core logs also confirmed that a weathered bedrock zone at the overburden-bedrock interface exists sitewide and contained the highest contaminant concentrations. This sediment-bedrock interface may serve as a preferential pathway for the lateral migration of the marginally dense creosote oil. In combination, these data provide a process-based conceptual site model that can be used to accurately model fluid flow and plume mobility, improving risk assessment and remediation efficacy.
How to cite: Walker, Z., Parker, B., Arnaud, E., Chapman, S., Pehme, P., Kroeker, R., and Kennel, J.: Development of a Robust Geological Model to Explain Creosote Flow and Transport in a Sole-Source Carbonate Aquifer , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14065, https://doi.org/10.5194/egusphere-egu25-14065, 2025.
Shallow biogenic gas fields are widely distributed in the world, but their development is limited due to their smaller scale and lower reservoir pressure compared to conventional gas fields. However, as the discovery of new reservoirs becomes increasingly challenging and the demand for gas as a clean energy source continues to rise, the development of shallow biogenic gas fields is necessary. Specially, the total biogenic gas reserves in Indonesia are around 152.9 TCF, and the contribution of biogenic gas to the total reserves is only around 7.2 TCF (4.7%). In this study, we conducted reservoir and geomechanical simulation studies for the enhancement of gas recovery and analysis of the geomechanical stability in Indonesian biogenic shallow gas field. Geomechanical analysis is essential because many shallow gas fields are consisted of unconsolidated sandstone.
How to cite: Lee, T., Park, S., and Lee, W.: Reservoir and geomechanical simulation study of CO2 EGR at the shallow biogenic gas reservoir in Indonesia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14594, https://doi.org/10.5194/egusphere-egu25-14594, 2025.
Karst aquifers provide approximately 9.2 % of the global population with drinking water (Stevanović, 2019), and therefore, their proper water resource management is an important task. The assessment of available water resources requires both, the identification of the structure of the aquifer geometry including phreatic and vadose zone and the characterization of hydraulic parameters. However, the heterogeneity of karst systems poses a challenge for the accurate characterization based on numerical modeling approaches and obstructs risk assessment efforts. Highly conductive features within the vadose zone offer a domain for rapid infiltration via preferential pathways that may not be accurately recovered by classical instruments, e.g., the Richards equation, since gravity-driven flow regimes may prevail. Hence, we propose a distributed dual-domain modeling approach that accounts for both the diffuse infiltration through a porous matrix and film-flow on fracture surfaces. Phreatic flow, including flow within a porous matrix, flow in conduits, and an exchange between these domains, is realized by the numerical modeling framework implemented in MODFLOW-CFPv2. Furthermore, this study presents compartment-specific parameter sensitivities during infiltration events in a synthetic karst model and methodology to determine film-flow parameters based on field data, i.e., precipitation time series and water table fluctuations. The global sensitivity analysis highlights the influence of film-flow parameters, i.e., the limiting fracture facial area along the z-axis, Flim, and an activation threshold, qthr, while a recharge pulse persists. The delay between the commencement of infiltration and the hydraulic response at the water table, tlag, may be site-specific and relies on the availability of observation data with proper temporal and spatial resolution.
How to cite: Noffz, T., Kordilla, J., Reimann, T., Kavousi, A., Liedl, R., and Sauter, M.: Dual-domain modeling of infiltration dynamics in the vadose zone of karst systems using film-flow theory – Investigation of compartment-specific parameter sensitivities and film-flow parameters , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17671, https://doi.org/10.5194/egusphere-egu25-17671, 2025.
We investigate infiltration into a single fracture embedded in an initially unsaturated sandstone with homogeneous matrix properties (doi: 10.1029/2023WR036323).
To outline the control of dual-porosity mechanisms, a classical analytical framework developed by Nitao (doi: 10.1029/91WR01369) was applied to model the observed infiltration behavior. Our study considered flow dynamics in terms of penetration depth, dominating flow regime (matrix- or fracture-dominated) related to applied flow rates, wetting front propagation in both domains, and the interference of matrix imbibition with the lateral boundary of the system. The employed model accounts for the matrix imbibition effect on fracture flow propagation.
Most interesting, matrix imbibition affected the observed discontinuous, partially saturated fracture flow (a combination of slugs and films) to behave, on average, like plug flow. Within the range of applied flow rates above a critical threshold, we found the model's plug flow assumption is not a relevant precondition for its applicability. Corresponding to the matrix imbibition state, fluid propagation in the fracture exhibits three characteristic scaling regimes (FP1-3). Only two scaling regimes are established for flow rates below a critical threshold, hence required to recover bulk infiltration for the chosen geometry. Furthermore, wetting fronts switch from fracture- to matrix-dominated at moderate to high flow rates, indicating a flow-rate-dependent limitation of fracture-dominated infiltration depth (source-responsive). While the scaling regimes agree with experiments for applied flow rates above the critical threshold, the model underestimates the initial penetration depth below. Here, we observe the direct onset of flow regime FP2 and the delayed transition into FP3.
How to cite: Rüdiger, F., Dentz, M., and Kordilla, J.: Revisiting Nitao's Analytical Model with Laboratory Experiments of Partially Saturated Fracture-Matrix Infiltration, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17825, https://doi.org/10.5194/egusphere-egu25-17825, 2025.
Posters virtual: Mon, 28 Apr, 14:00–15:45 | vPoster spot A
EGU25-4107 | ECS | Posters virtual | VPS8
Sequential Gaussian Mixtures for Transient Hydraulic Tomography Inversion in Fractured AquifersMon, 28 Apr, 14:00–15:45 (CEST) | vPA.17
Fractured aquifer parameters are expected to have complex non-Gaussian spatial distributions. Gaussian Mixture Models, known for their effectiveness in representing non-Gaussian distributions, present a promising alternative for capturing the complex heterogeneity of fractured geologic settings however their usage in the fractured geologic settings is unexplored. In this study we extended the application of Gaussian mixtures to transient hydraulic tomography on laboratory-based fractured geologic settings using sequential Gaussian Mixture Model (GMM). We further examined the impact of the number of Gaussian components, sampling strategies and the amount of pumping data on the performance of the sequential GMM. Results demonstrate that GMM with an optimal number of Gaussian components effectively identifies high and low conductivity regions, fracture connectivity, and reasonably predicts drawdowns (R² = 0.61) pumping from validation ports. Stratified sampling of GMM parameters (R2 = 0.74, average RMSEmedian= 9.89 mm) outperforms other sampling strategies like random (R2 = 0.61, average RMSEmedian= 20.64 mm ), uniform (R2 = 0.64, average RMSEmedian= 11.70 mm) and quasi-random sampling (R2 = 0.67, average RMSEmedian= 11.40 mm) techniques in mapping the fracture connectivity and parameter distribution. Stratified sampling with reduced and information-based pumping data maintains commensurable accuracy (R2 = 0.75, average RMSEmedian= 11.34 mm). Overall, our findings suggest that the sequential GMM combined with stratified sampling technique effectively captures the spatial variability of aquifer parameters in fractured media.
How to cite: Muraharirao, P. C. and Kbvn, P.: Sequential Gaussian Mixtures for Transient Hydraulic Tomography Inversion in Fractured Aquifers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4107, https://doi.org/10.5194/egusphere-egu25-4107, 2025.
