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Speleology in Kazakhstan

Shakalov on 04 Jul, 2018
Hello everyone!   I pleased to invite you to the official site of Central Asian Karstic-Speleological commission ("Kaspeko")   There, we regularly publish reports about our expeditions, articles and reports on speleotopics, lecture course for instructors, photos etc. ...

New publications on hypogene speleogenesis

Klimchouk on 26 Mar, 2012
Dear Colleagues, This is to draw your attention to several recent publications added to KarstBase, relevant to hypogenic karst/speleogenesis: Corrosion of limestone tablets in sulfidic ground-water: measurements and speleogenetic implications Galdenzi,

The deepest terrestrial animal

Klimchouk on 23 Feb, 2012
A recent publication of Spanish researchers describes the biology of Krubera Cave, including the deepest terrestrial animal ever found: Jordana, Rafael; Baquero, Enrique; Reboleira, Sofía and Sendra, Alberto. ...

Caves - landscapes without light

akop on 05 Feb, 2012
Exhibition dedicated to caves is taking place in the Vienna Natural History Museum   The exhibition at the Natural History Museum presents the surprising variety of caves and cave formations such as stalactites and various crystals. ...

Did you know?

That wall slab is a thin but large block of rock, which has fallen outward from the wall of a cave in limestone in which the dip is nearly vertical [10]. see also cave breakdown.?

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Featured articles from Cave & Karst Science Journals
Chemistry and Karst, White, William B.
See all featured articles
Featured articles from other Geoscience Journals
Karst environment, Culver D.C.
Mushroom Speleothems: Stromatolites That Formed in the Absence of Phototrophs, Bontognali, Tomaso R.R.; D’Angeli Ilenia M.; Tisato, Nicola; Vasconcelos, Crisogono; Bernasconi, Stefano M.; Gonzales, Esteban R. G.; De Waele, Jo
Calculating flux to predict future cave radon concentrations, Rowberry, Matt; Marti, Xavi; Frontera, Carlos; Van De Wiel, Marco; Briestensky, Milos
Microbial mediation of complex subterranean mineral structures, Tirato, Nicola; Torriano, Stefano F.F;, Monteux, Sylvain; Sauro, Francesco; De Waele, Jo; Lavagna, Maria Luisa; D’Angeli, Ilenia Maria; Chailloux, Daniel; Renda, Michel; Eglinton, Timothy I.; Bontognali, Tomaso Renzo Rezio
Evidence of a plate-wide tectonic pressure pulse provided by extensometric monitoring in the Balkan Mountains (Bulgaria), Briestensky, Milos; Rowberry, Matt; Stemberk, Josef; Stefanov, Petar; Vozar, Jozef; Sebela, Stanka; Petro, Lubomir; Bella, Pavel; Gaal, Ludovit; Ormukov, Cholponbek;
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Your search for numerical models (Keyword) returned 28 results for the whole karstbase:
Showing 1 to 15 of 28
Hydrogeology of the Umm Er Radhuma aquifer, Saudi Arabia, with reference to fossil gradients, 1982, Bakiewicz W, Milne Dm, Noori M,
Much of North Africa and the Arabian peninsula, lying in the Saharan climate zone, are underlain by huge tabular sandstone and carbonate aquifers, ranging in age from Cambrian to Tertiary. These are often saturated with water of reasonable quality and form very valuable resources in an area often desperately short of water. The Palaeocene Umm Er Radhuma carbonate aquifer is one such formation which has been the subject of intensive recent investigation. The formation contains groundwater of a reasonable quality, has adequate transmission and storage characteristics and hence considerable potential for future development. The origin of the water in such aquifers is the subject of continuing controversy. It is not disputed that the water is moving under the influence of regional groundwater gradients but origins of these gradients are the subject of considerable argument. On the one hand, there are those who hold that the presently observed gradients are fossil remnants of conditions created by a much wetter climatic regime prevalent some thousands of years ago. Against this are those who maintain that the gradients, at least in part, reflect a present day system with groundwater discharge in approximate dynamic equilibrium with recharge. This paper examines the hydrogeology of a typical Middle Eastern formation of the disputed kind, the Umm Er Radhuma aquifer in Saudi Arabia, and, with the aid of analytical and numerical models, attempts to resolve the problem of the origin of the observed groundwater gradients and to discover the extent to which the past must influence present day plans for future development

Principles of early development of karst conduits under natural and man-made conditions revealed by mathematical analysis of numerical models., 1996, Dreybrodt W.

Principles of early development of karst conduits under natural and man-made conditions revealed by mathematical analysis of numerical models, 1996, Dreybrodt W,
Numerical models of the enlargement of primary fissures in limestone by calcite aggressive water show a complex behavior. If the lengths of the fractures are large and hydraulic heads are low, as is the case in nature, dissolution rates at the exit of the channel determine its development by causing a slow increase of water flow, which after a long gestation time by positive feedback accelerates dramatically within a short time span. Mathematical analysis of simplified approximations yields an analytical expression for the breakthrough time, when this happens, in excellent agreement with the results of a numerical model. This expression quantifies the geometrical, hydraulic, and chemical parameters determining such karat processes. If the lengths of the enlarging channels are small, but hydraulic heads are high, as is the case for artificial hydraulic structures such as darns, it is the widening at the entrance of the flow path which determines the enlargement of the conduit. Within the lifetime of the dam this can cause serious water losses, This can also be explained by mathematical analysis of simplified approximations which yield an analytical threshold condition from which the safety of a dam can be judged. Thus in both cases the dynamic processes of karstification are revealed to gain a deeper understanding of the early development of karst systems. As a further important result, one finds that minimum conditions, below which karstification cannot develop, do not exist

The applicability of numerical models to adequately characterize ground-water flow in karstic and other triple-porosity aquifers, 1996, Quinlan J. F. , Davies G. J. , Jones S. W. , Huntoon P. W.

Structure et comportement hydraulique des aquifers karstiques, DSc thesis, 1996, Jeannin, P. Y.

This thesis aims to provide a better knowledge of karst flow systems, from a functional point of view (behaviour with time), as well as from a structural one (behaviour in space). The first part of the thesis deals with the hydrodynamic behaviour of karst systems, and the second part with the geometry of karstic networks, which is a strong conditioning factor for the hydrodynamic behaviour.
Many models have been developed in the past for describing the hydrodynamic behaviour of karst hydrogeological systems. They usually aim to provide a tool to extrapolate, in time and/or space, some characteristics of the flow fields, which can only be measured at a few points. Such models often provide a new understanding of the systems, beyond what can be observed directly in the field. Only special field measurements can verify such hypotheses based on numerical models. This is an significant part of this work. For this purpose, two experimental sites have been equipped and measured: Bure site or Milandrine, Ajoie, Switzerland, and Holloch site, Muotathal, Schwyz, Switzerland. These sites gave us this opportunity of simultaneously observe hydrodynamic parameters within the conduit network and, in drillholes, the "low permeability volumes" (LPV) surrounding the conduits.
These observations clearly show the existence of a flow circulation across the low permeability volumes. This flow may represent about 50% of the infiltrated water in the Bure test-field. The epikarst appears to play an important role into the allotment of the infiltrated waters: Part of the infiltrated water is stored at the bottom of the epikarst and slowly flows through the low permeability volumes (LPV) contributing to base flow. When infiltration is significant enough the other part of the water exceeds the storage capacity and flows quickly into the conduit network (quick flow).
For the phreatic zone, observations and models show that the following scheme is adequate to describe the flow behaviour: a network of high permeability conduits, of tow volume, leading to the spring, is surrounded by a large volume of low permeability fissured rock (LPV), which is hydraulically connected to the conduits. Due to the strong difference in hydraulic conductivity between conduits and LPV, hydraulic heads and their variations in time and space are strongly heterogeneous. This makes the use of piezometric maps in karst very questionable.
Flow in LPV can be considered as similar to flow in fractured rocks (laminar flow within joints and joints intersections). At a catchment scale, they can be effectively considered as an equivalent porous media with a hydraulic conductivity of about 10-6 to 10-7 m/s.
Flow in conduits is turbulent and loss of head has to be calculated with appropriate formulas, if wanting any quantitative results. Our observations permitted us to determine the turbulent hydraulic conductivity of some simple karst conduits (k', turbulent flow), which ranges from 0.2 to 11 m/s. Examples also show that the structure of the conduit network plays a significant role on the spatial distribution of hydraulic heads. Particularity hydraulic transmissivity of the aquifer varies with respect to hydrological conditions, because of the presence of overflow conduits located within the epiphreatic zone. This makes the relation between head and discharge not quadratic as would be expected from a (too) simple model (with only one single conduit). The model applied to the downstream part of Holloch is a good illustration of this phenomena.
The flow velocity strongly varies along the length of karst conduits, as shown by tracer experiments. Also, changes in the conduit cross-section produce changes in the (tow velocity profile. Such heterogeneous flow-field plays a significant role in the shape of the breakthrough curves of tracer experiments. It is empirically demonstrated that conduit enlargements induce retardation of the breakthrough curve. If there are several enlargements one after the other, an increase of the apparent dispersivity will result, although no diffusion with the rock matrix or immobile water is present. This produces a scale effect (increase of the apparent dispersivity with observation scale). Such observations can easily be simulated by deterministic and/or black box models.
The structure of karst conduit networks, especially within the phreatic zone, plays an important role not only on the spatial distribution of the hydraulic heads in the conduits themselves, but in the LPV as well. Study of the network geometry is therefore useful for assessing the shape of the flow systems. We further suggest that any hydrogeological study aiming to assess the major characteristics of a flow system should start with a preliminary estimation of the conduit network geometry. Theories and examples presented show that the geometry of karst conduits mainly depends on boundary conditions and the permeability field at the initial stage of the karst genesis. The most significant boundary conditions are: the geometry of the impervious boundaries, infiltration and exfiltration conditions (spring). The initial permeability field is mainly determined by discontinuities (fractures and bedding planes). Today's knowledge allows us to approximate the geometry of a karst network by studying these parameters (impervious boundaries, infiltration, exfiltration, discontinuity field). Analogs and recently developed numerical models help to qualitatively evaluate the sensitivity of the geometry to these parameters. Within the near future, new numerical tools will be developed and will help more closely to address this difficult problem. This development will only be possible if speleological networks can be sufficiently explored and used to calibrate models. Images provided by speleologists to date are and will for a long time be the only data which can adequately portray the conduit networks in karst systems. This is helpful to hydrogeologists. The reason that we present the example of the Lake Thun karst system is that it illustrates the geometry of such conduits networks. Unfortunately, these networks are three-dimensional and their visualisation on paper (2 dimensions) is very restrictive, when compared to more effective 3-D views we can create with computers. As an alternative to deterministic models of speleogenesis, fractal and/or random walk models could be employed.


Structure et comportement hydraulique des aquifers karstiques, DSc. Thesis, faculte des Sciences de l'Universite de Neuchatel., 1998, Jeannin Py.
This thesis aims to provide a better knowledge of karst flow systems, from a functional point of view (behaviour with time), as well as from a structural one (behaviour in space). The first part of the thesis deals with the hydrodynamic behaviour of karst systems, and the second part with the geometry of karstic networks, which is a strong conditioning factor for the hydrodynamic behaviour. Many models have been developed in the past for describing the hydrodynamic behaviour of karst hydrogeological systems. They usually aim to provide a tool to extrapolate, in time and/or space, some characteristics of the flow fields, which can only be measured at a few points. Such models often provide a new understanding of the systems, beyond what can be observed directly in the field. Only special field measurements can verify such hypotheses based on numerical models. This is an significant part of this work. For this purpose, two experimental sites have been equipped and measured: Bure site or Milandrine, Ajoie, Switzerland, and Holloch site, Muotathal, Schwyz, Switzerland. These sites gave us this opportunity of simultaneously observe hydrodynamic parameters within the conduit network and, in drillholes, the "low permeability volumes" (LPV) surrounding the conduits. These observations clearly show the existence of a flow circulation across the low permeability volumes. This flow may represent about 50% of the infiltrated water in the Bure test-field. The epikarst appears to play an important role into the allotment of the infiltrated waters: Part of the infiltrated water is stored at the bottom of the epikarst and slowly flows through the low permeability volumes (LPV) contributing to base flow. When infiltration is significant enough the other part of the water exceeds the storage capacity and flows quickly into the conduit network (quick flow). For the phreatic zone, observations and models show that the following scheme is adequate to describe the flow behaviour: a network of high permeability conduits, of tow volume, leading to the spring, is surrounded by a large volume of low permeability fissured rock (LPV), which is hydraulically connected to the conduits. Due to the strong difference in hydraulic conductivity between conduits and LPV, hydraulic heads and their variations in time and space are strongly heterogeneous. This makes the use of piezometric maps in karst very questionable. Flow in LPV can be considered as similar to flow in fractured rocks (laminar flow within joints and joints intersections). At a catchment scale, they can be effectively considered as an equivalent porous media with a hydraulic conductivity of about 10-6 to 10-7 m/s. Flow in conduits is turbulent and loss of head has to be calculated with appropriate formulas, if wanting any quantitative results. Our observations permitted us to determine the turbulent hydraulic conductivity of some simple karst conduits (k',turbulent flow), which ranges from 0.2 to 11 m/s. Examples also show that the structure of the conduit network plays a significant role on the spatial distribution of hydraulic heads. Particularity hydraulic transmissivity of the aquifer varies with respect to hydrological conditions, because of the presence of overflow conduits located within the epiphreatic zone. This makes the relation between head and discharge not quadratic as would be expected from a (too) simple model (with only one single conduit). The model applied to the downstream part of Holloch is a good illustration of this phenomena. The flow velocity strongly varies along the length of karst conduits, as shown by tracer experiments. Also, changes in the conduit cross-section produce changes in the (tow velocity profile. Such heterogeneous flow-field plays a significant role in the shape of the breakthrough curves of tracer experiments. It is empirically demonstrated that conduit enlargements induce retardation of the breakthrough curve. If there are several enlargements one after the other, an increase of the apparent dispersivity will result, although no diffusion with the rock matrix or immobile water is present. This produces a scale effect (increase of the apparent dispersivity with observation scale). Such observations can easily be simulated by deterministic and/or black box models. The structure of karst conduit networks, especially within the phreatic zone, plays an important role not only on the spatial distribution of the hydraulic heads in the conduits themselves, but in the LPV as well. Study of the network geometry is therefore useful for assessing the shape of the flow systems. We further suggest that any hydrogeological study aiming to assess the major characteristics of a flow system should start with a preliminary estimation of the conduit network geometry. Theories and examples presented show that the geometry of karst conduits mainly depends on boundary conditions and the permeability field at the initial stage of the karst genesis. The most significant boundary conditions are: the geometry of the impervious boundaries, infiltration and exfiltration conditions (spring). The initial permeability field is mainly determined by discontinuities (fractures and bedding planes). Today's knowledge allows us to approximate the geometry of a karst network by studying these parameters (impervious boundaries, infiltration, exfiltration, discontinuity field). Analogs and recently developed numerical models help to qualitatively evaluate the sensitivity of the geometry to these parameters. Within the near future, new numerical tools will be developed and will help more closely to address this difficult problem. This development will only be possible if speleological networks can be sufficiently explored and used to calibrate models. Images provided by speleologists to date are and will for a long time be the only data which can adequately portray the conduit networks in karst systems. This is helpful to hydrogeologists. The reason that we present the example of the Lake Thun karst system is that it illustrates the geometry of such conduits networks. Unfortunately, these networks are three-dimensional and their visualisation on paper (2 dimensions) is very restrictive, when compared to more effective 3-D views we can create with computers. As an alternative to deterministic models of speleogenesis, fractal and/or random walk models could be employed.

The initiation of hypogene caves in fractured limestone by rising thermal water: investigation of a parallel series of competing fractures, 1999, Dumont K. A. , Rajaram H. , Budd D. A.
Integrated cave systems can either form at or near the surface of the earth (epigenic) or at some depth below the earth's surface (hypogenic)For caves that form in fractured limestone, the two most common types of cave-system morphologies are branchwork and mazeworkBranchwork caves are composed of tributaries that coalesce in the downstream direction, similar to surface streamsMazework caves exhibit two or more sets of parallel passages intersecting in a grid-like patternThe majority of epigenic caves exhibit branchwork morphologies, which represent the dominance of individual flow pathsIn contrast, mazework caves develop when dissolution occurs along numerous flow pathsWhereas most epigenic caves are related to surficial meteoric flow systems, some mazework caves are thought to have formed in hypogene environments where rising thermal water cools in response to the geothermal gradientOur objective is to examine the fundamental cause for the difference in morphology between epigenic and thermal hypogenic cave systems using numerical modelsIn particular, we are examining the competition between different flow paths in fractured limestone undergoing dissolutional enlargementAs noted in previous numerical studies, epigenic systems are characterized by the dominance of a single flow path, which is consistent with the structure of epigenic cavesSo, in order to explain the structure of maze caves, one has to explain why no single flow path attains dominanceThe retrograde solubility of calcite coupled with heat transfer from the fluid to the rock is hypothesized to provide the mechanism by which dissolutional power is distributed among all competing flow pathsNumerical models of fluid flow, heat transfer, and calcite dissolution chemistry are integrated to develop a model of hypogene cave initiation in fractured limestoneFlow is assumed to occur in the presence of a spatially variable rock temperature field that is constant through timePreliminary numerical modeling results for a system of parallel fractures demonstrate the differences in the nature of competition between flow paths in epigenic (constant temperature) and hypogenic systems (flow in the presence of a negative thermal gradient)Differences in results using various kinetic models for calcite dissolution are also presentedThe role of aperture variation and distribution in a parallel set of fractures is also examined

Infiltration measured by the drip of stalactites, 2000, Sanz E. , Lopez J. J. ,
The hydrodynamic processes and mechanisms involved in rain infiltration and recharge in local areas of karst terrain can be identified and quantified by using measurements of the seepage of cave stalactites, Detailed measurements of the seepage of stalactites in seven caves located in an area close to the land surface, or the subcutaneous area of the karst, show a diversity of complex factors involved in infiltration: type of precipitation (rain or snow), air temperature, soil type and thickness, etc., which give rise to larger or smaller variations of flow in the espeleothem hydrographs, In some cases, no explanation can be found for the response of stalactites to rainfall, while in others there is a relationship between outer atmospheric parameters and the recharge represented by the stalactite drip. Romperopas Cave (Spain) has both a rapid and a basic flow, with hydrograph recessions similar to those observed in other caves. Water seepage in this cave varies greatly both in space and in time. The infiltration in Altamira Cave (Spain) was calculated and a multiple regression was found between infiltration, rain and outside air temperature. In other cases, the balance of the water on the soil is responsible for the seepage, Thus, a precipitation runoff numerical model that simulated the stalactite hydrographs could be applied to the Baradla and Beke Caves (Hungary), The complex properties of the ground, which are required for other flow numerical models for the unsaturated zone, were not taken into consideration

Influence of fracture roughness on karstification times, 2000, Dreybrodt W. , Gabrovsek F.
Karst aquifers develop along water-transmitting fractures which are rough by nature. Most numerical models on the evolution of the widths of those fractures by limestone dissolution, however, approximate such rough fractures by two parallel smooth planes. Here we investigate the influence of fracture roughness on the breakthrough time of conduits. All results show that even when the flow through a fracture is reduced by its roughness by a factor of ten in comparison to a corresponding smooth fracture, breakthrough time is increased only by a factor of 4. This gives a first answer to the influence of natural fracture roughness on the evaluation of karst and shows that extreme roughness, unlikely in nature, is necessary to exert significant influence on karstification time.

Genesis of a large cave system: the case study of the North of Lake Thun system (Canton Bern, Switzerland), 2000, Jeannin Py. , Bitterli T. , Hauselmann P.
The genesis of the cave system in the region Hohgant-Sieben Hengste-Lake of Thun (more than 250 km of surveyed passage) has been reconstructed based on speleomorphological observations (mainly by observing where the morphology changes from vadose to phreatic). Eight flow systems (phases) and their respective conduit networks have been distinguished so far. The oldest had a phreatic level at an altitude of 1950 m a.s.l. The last corresponds to today's phreatic zone located at 658 m a.s.l. Between each system, the water table dropped several hundred meters. This appears to be a consequence of changes in boundary conditions, mainly the springis position, which moved down as a tectonic uplift and deepening of the nearby valleys occured. Observations demonstrate that phreatic conduits are sometimes developed close to the ancient water table, but often much deeper, down to 200 to 400 m below this level. The change from one phase to the next seems to have been quick. This stepwise evolution is compatible with the results of computer models which give durations of 10'000 to 30i000 years for conduits systems to develop. Analysis of the conduit networks of each flow system shows that their geometry is mainly influenced by the hydraulic gradients and the overall geometry of the aquifer. The orientation of discontinuity surfaces (fractures and bedding planes) and/or their intersections, play a subordinate role. This is also supported by numerical models found in the literature. As, despite a high fracture density, we observe deep rather than shallow phreatic loops, we assume that the heterogeneity of the discontinuity openings plays a more important role in the depth of karstification than the frequency of the discontinuities.

On flow and transport of miscible tracers in the vadose zone, 2000, Loboferreira J. P. , Leitã, O Teresa, Quigley Seá, N P. , Theves Thomas

The paper presents a synthesis of LNEC's contribution to the European Commission (DGXII) Contract n° CI1*-CT94-0014 (DG 12 HSMU), based on the results reported by Lobo-Ferreira et al. (1998). The main contribution of LNEC to the project was the development of flow and transport experiments, for different flow type conditions (i.e. saturated and unsaturated). These included experiments at: (1) different scales (two scales in the laboratory and one in a medium scale - artificial aquifer), (2) different saturation conditions, and (3) different tracers (MgCl2, CaCl2, NO3-, Ni, Cd). The goals of the experiments were threefold: (1) analysis and quantification of the physical parameters that control circulation in this zone (hydraulic conductivity correspondent to the degree of saturation etc.); (2) determination and quantification of the more important processes that control the chemical behaviour of heavy metals and nitrate, and (3) to obtain data for calibrating the numerical models.


HJWFTAC: software for Hantush-Jacob analysis of variable-rate, multiple-extraction well pumping tests, 2002, Fleming Sw, Ruskauff Gj, Adams A,
Analytical well test solutions are a powerful approach to aquifer characterization and the parameterization of comprehensive numerical models. In addition, wellfield drawdown tests, which consist of coordinated pumping and data collection at a suite of monitoring and operating production wells, are of growing significance due to increasing pressures upon groundwater resources and the consequent management and planning requirement for superior hydrogeologic characterization of existing production wellfields. However. few pumping test analysis codes accommodate the multiple extraction wells involved, particularly for more sophisticated analytic aquifer test solutions. We present and demonstrate here a FORTRAN code for analysis of drawdown at a monitor well due to simultaneous variable-rate pumping at multiple independent production wells, which we developed in response to a need to refine an existing numerical, coupled groundwater/surface water resource management model, Spatial and temporal superposition are used to accommodate the typical operational properties of wellfield pumping tests, The software invokes the well-accepted Hantush-Jacob method for semiconfined or 'leaky' aquifers in a forward simulation procedure and effectively assumes homogeneity in applicable aquifer parameters (transmissivity, coefficient of storage, and leakance). Intended for both professionals and students, the code is widely applicable and straightforward to use as written. However, it can be modified with relative ease to use alternative well test solutions and/or formal inverse modeling techniques, or to accommodate spatial hydrogeologic variability. An application to a pumping test conducted in a karst limestone aquifer at the Cross Bar Ranch wellfield in Tampa Bay, Florida, demonstrates the utility of the software. (C) 2002 Elsevier Science Ltd. All rights reserved

Analytical 1D dual-porosity equivalent solutions to 3D discrete single-continuum models. Application to karstic spring hydrograph modelling, 2002, Cornaton F, Perrochet P,
One-dimensional analytical porosity-weighted solutions of the dual-porosity model are derived, providing insights on how to relate exchange and storage coefficients to the volumetric density of the high-permeability medium. It is shown that porosity-weighted storage and exchange coefficients are needed when handling highly heterogeneous systems-such as karstic aquifers-using equivalent dual-porosity models. The sensitivity of these coefficients is illustrated by means of numerical experiments with theoretical karst systems. The presented ID dual-porosity analytical model is used to reproduce the hydraulic responses of reference 3D karst aquifers, modelled by a discrete single-continuum approach. Under various stress conditions, simulation results show the relations between the dual-porosity model coefficients and the structural features of the discrete single-continuum model. The calibration of the equivalent 1D analytical dual-porosity model on reference hydraulic responses confirms the dependence of the exchange coefficient with the karstic network density. The use of the analytical model could also point out some fundamental structural properties of the karstic network that rule the shape of the hydraulic responses, such as density and connectivity. (C) 2002 Elsevier Science B.V. All rights reserved

Karst aquifer evolution in a changing water table environment - art. no. 1090, 2002, Kaufmann G. ,
[1] A vertical cross section through a karst aquifer is modeled by means of the finite element method to study the evolution of fractures and flow in the aquifer. The karst aquifer receives a constant recharge along the top boundary by precipitation and drains toward a resurgence assumed to be the base level in a valley. Flow is allowed both in the permeable rock matrix and the fracture network, and the fractures are enlarged with time by chemical dissolution. Hence during the early evolution of the karst aquifer the conductivity increases over several orders of magnitude, and the initially high water table drops to a steady state base level niveau. As a consequence, fractures above the final water table change from phreatic to vadose flow conditions. A systematic parameter study is carried out to investigate the aquifer evolution over a wide range of parameters, such as recharge rate, initial fracture width and density, and initial calcium concentration. The numerical models cover a wide range of drainage patterns, from phreatic water table caves to deep bathyphreatic caves to vadose river caves. The models suggest that a single theoretical approach is capable of explaining most common cave passage patterns

Numerical models for mixing corrosion in natural and artificial karst environments, 2003, Kaufmann G. ,
[1] The enlargement of initially small fractures in a karst aquifer by chemical dissolution is studied. Flow in the aquifer is driven by head differences between sinks and resurgences, and flow depends on the permeability of small fissures and fractures in the aquifer. Enlargement of fractures is controlled by the chemical composition of the recharge, as water undersaturated with respect to calcite is able to dissolve material from the fracture walls. As fractures are enlarged with time, permeability within the aquifer increases significantly, and flow becomes very heterogeneous. Two different processes are considered: enlargement due to normal corrosion, where water is undersaturated with respect to calcite, and enlargement due to mixing corrosion, where two solutions saturated with respect to calcite but with different carbon dioxide concentrations mix and the resulting solution becomes undersaturated again. The importance of mixing corrosion is discussed for two boundary conditions: A natural karst aquifer is modeled with fixed recharge boundary conditions representing sinking streams, and an artificial karst aquifer is simulated with fixed head boundary conditions representing a reservoir. In both cases, mixing corrosion is important, especially if recharge is characterized by an almost saturated chemistry. Mixing corrosion significantly changes the evolving passage pattern, as dissolution due to mixing of solutions is possible deep in the aquifer. Mixing corrosion also reduces breakthrough times of the aquifer and can result in dramatic leakage underneath dam sites, even if the impounded water is almost saturated with respect to calcite

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