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Enviroscan Ukrainian Institute of Speleology and Karstology

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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 troglophile is 1. "cave lover." an animal that can complete its life cycle in caves, but may also do so in suitable habitats outside caves [23].?

Checkout all 2699 terms in the KarstBase Glossary of Karst and Cave Terms

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What is Karstbase?



Browse Speleogenesis Issues:

KarstBase a bibliography database in karst and cave science.

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;
See all featured articles from other geoscience journals

Search in KarstBase

Your search for modeling (Keyword) returned 235 results for the whole karstbase:
Showing 211 to 225 of 235
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Shaw Faulkner M. G. , Stafford K. W. , Bryant A. W.

The Fort Hood Military Installation is a karst landscape characterized by Cretaceous-age limestone plateaus and canyons in Bell and Coryell Counties, Texas. The area is located in the Lampasas Cut Plain region of the Edwards Plateau and is stratigraphically defined by exposures of the Fredericksburg Group. Spatial interpolation of 105 km2 of the Fort Hood Military Installation provided depression data that were delineated and classified using geoanalytical methods. Most of the karst features within the study area are predominantly surficial expressions of collapse features, creating windows into karst conduits with surficial exposures of epikarst spatially limited.The increasing capabilities of GIS (Geographic Information Systems) and accuracy of geographically referenced data has provided the basis for more detailed terrain analysis and modeling. Research on terrain-related surface features is highly dependent on terrain data collection and the generation of digital models. Traditional methods such as field surveying can yield accurate results; however, they are limited by time and physical constraints. Within the study area, dense vegetation and military land use preclude extensive traditional karst survey inventories. Airborne Light Detection and Ranging (LiDAR) provides an alternative for high-density and high-accuracy three-dimensional terrain point data collection. The availability of high density data makes it possible to represent terrain in great detail; however, high density data significantly increases data volume, which can impose challenges with respect to data storage, processing, and manipulation. Although LiDAR analysis can be a powerful tool, filter mechanisms must be employed to remove major natural and anthropogenic terrain modifications resulting from military use, road building and maintenance, and the natural influence of water bodies throughout the study area.

Hydrodynamic modeling of a complex karst-alluvial aquifer: case study of Prijedor Groundwater Source, Republic of Srpska, Bosnia and Herzegovina, 2013,
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Polomčić Dušan, Dragišić Veselin, Živanović Vladimir

Middle Triassic fractured and karstified limestone and dolomite form a karst aquifer in the Sana River Valley near the town of Prijedor. As a result of intensive tectonic movements, carbonate rocks are mostly below the Sana River level, covered by younger Pliocene and alluvial deposits. The main source of groundwater recharge is infiltration from the Sana River through its alluvium over most of the aquifer. The main objective of the research reported in this paper was to evaluate the hydraulic relationships of the alluvial, Pliocene and karst aquifers in order to better understand the water supply potential of the karst aquifer. Although the use of hydrodynamic modeling is not very common with karst aquifers, the developed model provided significant and useful information on the groundwater budget and recharge type. The influence of fault zones and spatial anisotropy of the karst aquifer were simulated on the hydrodynamic model by varying permeability on the xand y­axes of the Cartesian coordinate system with respect to the fault, the main pathway of groundwater circulation. Representative hydraulic conductivities were Kx

 = 2.3·10­3

 m/s and Ky

 = 5.0·10­3

 m/s in the faults of Nw to SE direction, and Kx

 = 2.5·10­3

 m/s and Ky


 m/s in the faults of Sw to NE trend. Model research showed that the karst aquifer can be used in the long term at maximal tested capacities and that current groundwater exploitation is not compromised in dry periods when the water budget depends entirely on recharge from the Sana River.

Biological Control on Acid Generation at the Conduit-Bedrock Boundary in Submerged Caves: Quantification through Geochemical Modeling, 2013,
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Herman Janet S. , Hounshell Alexandria G. , Franklin Rima B, Mills Aaron L.

No-mount Cave, located in wekiwa Springs State Park in central Florida, USA, is an aphotic, submerged, freshwater cave in which large colonies of sulfur-oxidizing bacteria live in filamentous microbial mats. Upwardly discharging groundwater enters the cave from the Upper Floridan aquifer, specifically the Eocene-aged Ocala Limestone. we undertook a combined field, laboratory, and modeling study in which we sought to determine the amount of calcite dissolution attributable to the generation of protons by microbially mediated sulfide oxidation. The chemical compositions of groundwater within the limestone formation collected through a newly designed sampling device and of water in the cave conduit were used in geochemical modeling. we used the reaction-path model PHREEqCI to quantify the amount of calcite dissolution expected under various plausible scenarios for mixing of formation water with conduit water and extent of bacterial sulfide oxidation. Laboratory experiments were conducted using flow-through columns packed with crushed limestone from the study site. Replicate columns were eluted with artificial groundwater containing dissolved HS- in the absence of microbial growth. without biologically mediated sulfide oxidation, no measurable calcite dissolution occurred in laboratory experiments and no additional amount of speleogenesis is expected as formation water mixes with conduit water in the field. In contrast, significant calcite dissolution is driven by the protons released in the biological transformation of the aqueous sulfur species. Although a range of results were calculated, a plausible amount of 158 mg Ca2+ released to conduit water per liter of groundwater crossing the formation-conduit boundary and mixing with an equal volume of conduit water was predicted. Our modeling results indicate that significant cave development can be driven by microbially mediated sulfide oxidation under these hydrogeochemical conditions

Early-stage hypogene karstification in a mountain hydrologic system: A coupled thermohydrochemical model incorporating buoyant convection, 2013,
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Chaudhuri A. , Rajaram H. , Viswanathan H

The early stage of hypogene karstification is investigated using a coupled thermohydrochemical model of a mountain hydrologic system, in which water enters along a water table and descends to significant depth (_1 km) before ascending through a central high-permeability fracture. The model incorporates reactive alteration driven by dissolution/ precipitation of limestone in a carbonic acid system, due to both temperature- and pressuredependent solubility, and kinetics. Simulations were carried out for homogeneous and heterogeneous initial fracture aperture fields, using the FEHM (Finite Element Heat and Mass Transfer) code. Initially, retrograde solubility is the dominant mechanism of fracture aperture growth. As the fracture transmissivity increases, a critical Rayleigh number value is exceeded at some stage. Buoyant convection is then initiated and controls the evolution of the system thereafter. For an initially homogeneous fracture aperture field, deep well-organized buoyant convection rolls form. For initially heterogeneous aperture fields, preferential flow suppresses large buoyant convection rolls, although a large number of smaller rolls form. Even after the onset of buoyant convection, dissolution in the fracture is sustained along upward flow paths by retrograde solubility and by additional ‘‘mixing corrosion’’ effects closer to the surface. Aperture growth patterns in the fracture are very different from those observed in simulations of epigenic karst systems, and retain imprints of both buoyant convection and preferential flow. Both retrograde solubility and buoyant convection contribute to these differences. The paper demonstrates the potential value of coupled models as tools for understanding the evolution and behavior of hypogene karst systems.

Permeability evolution due to dissolution and precipitation of carbonates using reactive transport modeling in pore networks, 2013,
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A reactive transport model was developed to simulate reaction of carbonates within a pore network for the high-pressure CO2-acidified conditions relevant to geological carbon sequestration. The pore network was based on a synthetic oolithic dolostone. Simulation results produced insights that can inform continuum-scale models regarding reactioninduced changes in permeability and porosity. As expected, permeability increased extensively with dissolution caused by high concentrations of carbonic acid, but neither pH nor calcite saturation state alone was a good predictor of the effects, as may sometimes be the case. Complex temporal evolutions of interstitial brine chemistry and network structure led to the counterintuitive finding that a far-from-equilibrium solution produced less permeability change than a nearer-to-equilibrium solution at the same pH. This was explained by the pH buffering that increased carbonate ion concentration and inhibited further reaction. Simulations of different flow conditions produced a nonunique set of permeability-porosity relationships. Diffusive-dominated systems caused dissolution to be localized near the inlet, leading to substantial porosity change but relatively small permeability change. For the same extent of porosity change caused from advective transport, the domain changed uniformly, leading to a large permeability change. Regarding precipitation, permeability changes happen much slower compared to dissolution-induced changes and small amounts of precipitation, even if located only near the inlet, can lead to large changes in permeability. Exponent values for a power law that relates changes in permeability and porosity ranged from 2 to 10, but a value of 6 held constant when conditions led to uniform changes throughout the domain

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Covington M. , Myre J.

Numerical models of speleogenesis typically simulate flow and dissolution within single fractures or networks of fractures. Such models employ fracture flow and pipe flow equations to determine flow rates and only consider average velocities within each fracture segment. Such approximations make large scale simulations of speleogenesis tractable. However, they do not allow simulation of the formation and evolution of micro- or meso-scale cave passage morphologies. Such morphologies are frequently studied within a field setting and utilized for the interpretation of the speleogenetic processes that formed the cave. One classic example is the formation of scallops in cave streams with turbulent flow. Scallops are used to interpret past flow velocities and directions. However, a recent analysis of the theory of limestone dissolution in turbulent flow conditions suggests a discrepancy between theory and reality concerning the formation of limestone scallops (Covington, in review). Similarly, the only attempt to numerically simulate flute formation in limestone found that the flute forms were not stable (Hammer et al., 2011). Motivated by these puzzles, we are developing a computational fluid dynamics (CFD) framework for the simulation of the evolution of dissolution morphologies.

While this project was initially conceived to better understand dissolution in turbulent flow, the tools being developed are particu­larly well-suited to examine a variety of other questions related to cave morphology on the micro- and meso-scales. There has been significant recent discussion about the interpretation of features that are diagnostic of hypogenic or transverse speleogenesis, such as the morphological suite of rising flow defined by Klimchouk (2007). Other authors have suggested that such forms can be found in a variety of settings where confined flow is not present (Mylroie and Mylroie, 2009; Palmer, 2011). We propose that simulation of such forms using a CFD speleogenesis code will allow a more complete understanding of the connections between process and form, because in such simulations the processes occurring are well-known, well-defined, and also can be adjusted within controlled numeri­cal experiments, where relevant parameters and boundary conditions are systematically varied.

The CFD framework we are developing is based on the Lattice Boltzman method (Chen and Doolen, 1998), which is a popular tech­nique for modeling the mechanics of complex fluids, including fluid mixtures, reactive transport, porous media flow, and complex and evolving domain geometries. With this framework it is straightforward to simulate many of the processes occurring in hypogene settings, including complex fluid flows, dissolution, solute and heat transport, and buoyancy-driven flow. Furthermore, this modeling framework allows these processes to be coupled so that their interactions and feedbacks can be explored. With the suite of capabili­ties provided by this framework, we can begin to numerically simulate the processes occurring in hypogene speleogenesis, including the driving mechanisms and the role of buoyancy-driven flow and its relationship with the morphological suite of rising flow. In the spirit of a workshop, this work is presented as in-progress, in the hopes that it will stimulate discussion on potential applications of the model being developed.

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Rosaleslagarde L. , Boston P. J.

Conspicuous brackish sulfidic springs have been described at the northern Sierra the Chiapas, Mexico. These springs are produced by a mixture between regional and local groundwater flow paths. The regional groundwater has an average Total Dissolved Ions of 3081 mg/L so it has a brackish composition. This brackish water is saturated with respect to calcite and dolomite but undersaturated with respect to gypsum, anhydrite and halite. The mass balance and the discharge rate are used to quantify the mass and volume of minerals that are dissolved by the brackish spring water following Appelo and Postma (1993). This quantification will allow comparing the various speleogenetic mechanisms in the area. This is considering the composition of the spring water is relatively constant over time, as it is suggested by periodic measurements at the Cueva de Villa Luz springs during the last 10 years.
Sulfur isotopes in the water are consistent with anhydrite dissolution as the main source of the sulfate to the brackish spring water. Thus, the average 6 mol/L of sulfate in the brackish springs are produced by dissolution of 6 mol of anhydrite after subtracting the sulfate that could result from evapotranspiration of rainwater. Each liter of brackish water dissolved an average of 882 mg of anhydrite, which are equivalent to dissolving 0.36 cm3 of this mineral considering a density of 2.981 g/cm3. Additionally, using the average brackish water discharge rate of 144 L/s, an average of 57 g of anhydrite are being dissolved each second per every liter of brackish water. This is a minimal value because some of the sulfate in the water is used by sulfate-reducing bacteria in the subsurface to produce the hydrogen sulfide in the spring water. The anhydrite subject to dissolution is found interbedded in the Cretaceous carbonates, either from the subsurface at 4,000 m below sea level to the carbonate outcrops.
Similarly, we can calculate the volume of halite that is being dissolved by the brackish springs, considering chloride is a conservative element and subtracting the chloride concentration from the rainwater from that of the spring water following Appelo & Postma (1993). The 22 mol/L of chloride in the brackish water can result from dissolution in the subsurface of 22 moles or 1.3 g of halite per liter of brackish water. This mass of halite dissolved is equal to 0.59 cm3 considering a density of 2.168 g/cm3. Alternatively, 118 g of halite are dissolved per second per each liter of brackish water if we use the average discharge rate of 144 L/s.
Even when the brackish springs are oversaturated with respect to calcite and dolomite, their dissolution is still possible due to the common ion-effect of calcium after anhydrite dissolution and by mixing of waters with different compositions. A range of 10 to 80 % of brackish water from the regional aquifers mixes with fresh water from the local aquifer based on their water chemistry. Additionally, sulfuric acid speleogenesis occurs due to the oxidation of hydrogen sulfide to sulfuric acid.
Finally, the increase in the chloride concentration of the fresh water springs with respect to the concentration in rainwater was used to estimate that from the 4000 mm/y of annual precipitation, only 4%, 158 to 182 mm/y, recharge the aquifers. This low percentage is slightly higher than the 3.3% recharge in marls, marly limestone, silts and clays (Sanz et al., 2011), probably because of the relatively small area of carbonate outcrops over the entire region and the lack of recharge in altitudes higher than 1500 m above sea level.
Sulfuric acid is the most obvious speleogenetic mechanism occurring in the caves of the northern Sierra de Chiapas, Mexico due to the high hydrogen sulfide concentration in the spring water. In addition, the location of the springs at a zone of regional and local discharge where waters from different composition converge and mix, and the amount of mixing calculated suggests mixing is also an important speleogenetic mechanism. However, the depth and the time constrains at which these two hypogenic mechanisms occur is still unknown. The relatively low rainwater recharge rate suggests epigenesis is limited. Most likely, the porosity created by dissolution of anhydrite and halite in the subsurface is occluded by the precipitation of calcite. Chemical modeling and petrography will help to elucidate the order of the reactions occurring in the subsurface.

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The theory of gravity-driven regional groundwater flow was first proposed in 1962/3 based on the Laplace equation. Hydraulic-head patterns were calculated for a two dimensional trapezoidal and homogeneous flow domain with flow lines drawn by hand. The flow region was intended to represent one flank of a stream basin with a periodically undulating water table. At the dawn of numerical modeling the results generated international interest. Numerical models began to be produced with progressively increasing complexity of basin geometry, types and distributions of permeability and time dependent flow. One of the most important results of the first analyses was the birth of the flow-system concept. In a flow system groundwater moves from relatively highly elevated recharge areas, through medium high mid-line regions to relatively low lying discharge areas where it may resurface. Because flow systems are associated with topographic elements of different scale, they are self-organized in hierarchically nested geometric patterns.
The understanding of the systematized structure of basinal groundwater flow soon resulted in the recognition that flow systems act like subsurface conveyor belts. They mobilize and remove matter and heat from the recharge area, pick up more or/and emplace some of it en route, and deposit them in the discharge region. In short: flowing groundwater is a general geologic agent. The original „Theory of regional groundwater flow” became thus expanded into a bimodal umbrella theory with two component theories: i) „The hydraulics of basin-scale groundwater flow” and ii) „The geologic agency of regional groundwater flow”. More than half a century after its conception the theory is extensively analyzed and continues to be applied to a growing number of groundwater related disciplines

Evaluation of the US DOE’s conceptual model of hydrothermal activity at Yucca Mountain, Nevada, 2014,
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A unique conceptual model describing the conductive heating of rocks in the thick unsaturated zone of Yucca Mountain, Nevada by a silicic pluton emplaced several kilometers away is accepted by the US Department of Energy (DOE) as an explanation of the elevated depositional temperatures measured in fluid inclusions in secondary fluorite and calcite. Acceptance of this model allowed the DOE to keep from considering hydrothermal activity in the performance assessment of the proposed high-level nuclear waste disposal facility. The evaluation presented in this paper shows that no computational modeling results have yet produced a satisfactory match with the empirical benchmark data, specifically with age and fluid inclusion data that indicate high temperatures (up to ca. 80 _C) in the unsaturated zone of Yucca Mountain. Auxiliary sub-models complementing the DOE model, as well as observations at a natural analog site, have also been evaluated. Summarily, the model cannot be considered as validated. Due to the lack of validation, the reliance on this model must be discontinued and the appropriateness of decisions which rely on this model must be re-evaluated.A unique conceptual model describing the conductive heating of rocks in the thick unsaturated zone of Yucca Mountain, Nevada by a silicic pluton emplaced several kilometers away is accepted by the US Department of Energy (DOE) as an explanation of the elevated depositional temperatures measured in fluid inclusions in secondary fluorite and calcite. Acceptance of this model allowed the DOE to keep from considering hydrothermal activity in the performance assessment of the proposed high-level nuclear waste disposal facility. The evaluation presented in this paper shows that no computational modeling results have yet produced a satisfactory match with the empirical benchmark data, specifically with age and fluid inclusion data that indicate high temperatures (up to ca. 80 _C) in the unsaturated zone of Yucca Mountain. Auxiliary sub-models complementing the DOE model, as well as observations at a natural analog site, have also been evaluated. Summarily, the model cannot be considered as validated. Due to the lack of validation, the reliance on this model must be discontinued and the appropriateness of decisions which rely on this model must be re-evaluated.

Karst water resources in a changing world: Review of hydrological modeling approaches, 2014,
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Karst regions represent 7–12% of the Earth’s continental area, and about one quarter of the global population is completely or partially dependent on drinking water from karst aquifers. Climate simulations project a strong increase in temperature and a decrease of precipitation in many karst regions in the world over the next decades. Despite this potentially bleak future, few studies specifically quantify the impact of climate change on karst water resources. This review provides an introduction to karst, its evolution, and its particular hydrological processes. We explore different conceptual models of karst systems and how they can be translated into numerical models of varying complexity and therefore varying data requirements and depths of process representation. We discuss limitations of current karst models and show that at the present state, we face a challenge in terms of data availability and information content of the available data. We conclude by providing new research directions to develop and evaluate better prediction models to address the most challenging problems of karst water resources management, including opportunities for data collection and for karst model applications at so far unprecedented scales

Hydrogeological and Environmental Investigations in Karst Systems, 2014,
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Karst is the result of climatic and geohydrological processes, mainly in carbonate and evaporite rocks, during geological periods of Earth history. Dissolution of these rock formations over time has generated karst aquifers and environments of significant water and mineral resources. In addition, beautiful landscapes have been created which constitute natural parks, geosites, and caves. Due to their origin and nature, karstified areas require investigation with special techniques and methodology. International collaboration and discussions on advances in karst research are necessary to promote Karst Science. The International Symposium on Karst Aquifers is one of the worldwide events held periodically to specifically address karst environments. The symposium constitutes an ongoing international forum for scientific discussion on the progress made in research in karst environments. The first and second symposiums were organized in Nerja (near Malaga, Spain), in 1999 and 2002; the third and fourth symposiums were held in Malaga city in 2006 and 2010. The 5th International Symposium on Karst Aquifers (ISKA5) occurred in Malaga on during October 14–16, 2014. It was organized by the Centre of Hydrogeology University of Málaga (CEHIUMA) and the Spanish Geological Survey (IGME), in cooperation with UNESCO and the International Association of Hydrogeologists (IAH) Karst Commission. More than 100 contributions were received from 30 countries on five continents. Presentations made during the symposium and published in this book are a compendium of 70 of these manuscripts. Papers submitted by April 2014, were peer-reviewed and subsequently accepted by the Scientific Committee. Contributions are grouped into five sections:

• Methods Utilized to Study Karst Aquifers.

• Karst Hydrogeology.

• Mining and Engineering in Karst media.

• Karst Cavities.

• Karst Geomorphology and Landscape.

A large part of the contributions, 30 %, is related to Methods Utilized to Study Karst Aquifers. Several issues are addressed: methods for groundwater recharge assessment, dye tracer and stable isotope applications, analysis of hydrodynamic data and hydrochemistry, among others. Most contributions, 40 %, however, are on Karst Hydrogeology. These are primarily in connection with various topics such as numerical modeling in karst, floods, karst groundwater flow, protection of karst aquifers or pollution, and vulnerability in karst. Five percent of the published papers deal with Mining and Engineering in Karst Media. These papers are about tunnels, hydrogeological risks, and karst risk assessment in mining and civil engineering. Another section concerning Karst Cavities encompasses 15 % of the contributions. These chapters deal with corrosion and speleogenetic processes, speleothems, CO2 sources, the global carbon cycle in endokarst, and the study of past climate. Karst Geomorphology and Landscape constitutes the remaining 10 % of the contributions. These papers are related to karst features, wetlands, hypogene speleogenesis, geodiversity, and karstic geosites. The results of project work performed by karst specialists worldwide are described in the book. Included in it are experiences from pilot sites, methodologies, monitoring, and data analyses in various climatic, geological, and hydrogeological contexts. Material presented may be utilized for activities such as teaching and technical-professional applications particularly as they apply to the increasingly multidisciplinary nature of karst studies. Information provided may also be useful to decisions makers in making critical decisions regarding development in karst regions. Scientists and engineers and many of the lay public interested in karst environments will benefit from the contents

Transferring the concept of minimum energy dissipation from river networks to subsurface flow patterns, 2014,
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Hergarte Stefan, Winkler Gerfried, Birk Steffen

Principles of optimality provide an interesting alternative to modeling hydrological processes in detail on small scales and have received growing interest in the last years. Inspired by the more than 20 years old concept of minimum energy dissipation in river networks, we present a corresponding theory for subsurface flow in order to obtain a better understanding of preferential flow patterns in the subsurface. The concept describes flow patterns which are optimal in the sense of minimizing the total energy dissipation at a given recharge under the constraint of a given total porosity. Results are illustrated using two examples: two-dimensional flow towards a spring with a radial symmetric distribution of the porosity and dendritic flow patterns. The latter are found to be similar to river networks in their structure and, as a main result, the model predicts a power-law distribution of the spring discharges. In combination with two data sets from the Austrian Alps, this result is used for validating the model. Both data sets reveal power-law-distributed spring discharges with similar scaling exponents. These are, however, slightly larger than the exponent predicted by the model. As a further result, the distributions of the residence times strongly differ between homogeneous porous media and optimized flow patterns, while the mean residence times are similar in both cases.

Hydrogeological Characteristics of Carbonate Formations of the Cuddapah Basin, India, 2014,
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Farooq Ahmad Dar

Karst hydrogeology is an important field of earth sciences as the aquifers in carbonate formations represent vital resource of groundwater that feeds a large part of the world population particularly in semi-arid climates. These unique aquifers posses peculiar characteristics developed by dissolutional activities of water. Karst aquifers possess a typical hydrogeological setup from surface to subsurface. The aquifers are governed by slow groundwater flow in matrix porosity, a medium to fast flow in fractures and rapid flow in conduits and channels. This large variability in their properties makes the prediction and modeling of flow and transport very cumbersome and data demanding. The aquifers are vulnerable to contamination as the pollutants reach the aquifer very fast with little or no attenuation. The geomorphological and hydrogeological properties in these aquifers demand specific techniques for their study. The carbonate aquifers of the semi-arid Cuddapah basin were characterized based on geomorphological, hydrogeological and hydrochemical investigations. All the formations are highly karstified possessing one of the longest and deepest caves of India and few springs along with unique surface features. Karstification is still in progress but at deeper levels indicated by growing speleothems of different architectural size. Model of karstification indicates that lowering of base level of erosion resulted in the dissolution of deeper parts of the limestone as represented by paleo-phreatic conduits in the region. Moist conditions of the past were responsible for the karst development which has been minimized due to the onset of monsoon conditions. Karst has developed at various elevations representing the past base levels in the region.

The recharge processes in these aquifers are complex due to climatic and karst specificities. Point recharge is the major contributor which enters the aquifer as allogenic water. It replenishes the groundwater very rapidly. Diffuse recharge travels through soil and epikarst zone. Average annual recharge of semi-arid Narji limestone aquifer is 29% of the rainfall which occurs during 5-7 rain events in the year.

The hydrogeochemical characteristic of karst aquifers is quite varaible. A significant difference is observed in hydrochemistry. High concentrations of SO42-, Cl-, NO3- suggests the anthropogenic source particularly from agriculture. Local Meteoric Water Line of δ2H and δ18O isotopes of rain and groundwater shows a slope of 7.02. Groundwater isotope data shows more depletion in heavy isotopes -a result of high evaporation of the area. Groundwater samples show a trend with a slope of 4 and 3.1 for δ2H and δ18O respectively. Groundwater during dry months gets more fractionated due to higher temperature and little rainfall. The irrigated water becomes more enriched and then recharges the aquifer as depleted irrigation return flow. The isotopes show large variation in spring water. Few springs are diffuse or mixed type and not purely of conduit type in the area. Tracer results indicate that the tracer output at the sampling location depends on the hydrogeological setup and the nature of karstification.

The study has significantly dealt with in disclosing the typical characteristics of such aquifer systems and bringing out a reliable as well as detailed assessment of various recharges to the system. The groundwater chemistry has been elaborated to establish the nature of possible hydrochemical processes responsible for water chemistry variation in semi-arid karst aquifer. Such study has thrown light on the aquifers that are on one hand very important from social and strategic point of view and on the hand were left unattended from the detailed scientific studies.

Caractérisation et modélisation hydrodynamique des karsts par réseaux de neurones. Application à l’hydrosystème du Lez , 2014,
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Virgile, Taver

Improving knowledge of karst hydrodynamics represents a global challenge for water resources because karst aquifers provide approximately 25% of the world population in fresh water. Nevertheless, complexity, anisotropy, heterogeneity, non-linearity and possible non-stationarity of these aquifers make them underexploited objects due to the difficulty to characterize their morphology and hydrodynamics. In this context, the systemic paradigm proposes others methods by studying these hydrosystems through input-output (rainfall-runoff) relations.

The approach proposed in this thesis is to use information from field measurement and from systemic analyses to constrain neural network models. The goal is to make these models interpretable in terms of hydrodynamic processes by making model functioning to be similar to natural system in order to obtain a good representation and extract knowledge from model parameters.

This work covers the association of information available on the hydrosystem with correlation and spectral analyses to develop a temporal multiresolution decomposition of variables and to constrain neural network models. A new method for variable selection, adapted to represent long term hydrodynamics of the system, has been proposed. These constrained models show very good results and allow, through their parameters, to study the temporal contribution of inputs variables to the output.

Modeling nonlinear and non-stationary hydrosystems with neural network has been improved by a novel implementation of data assimilation. More precisely, when non-stationarity is attributed to the catchment, data assimilation is used to modify the model parameters. When the inputs are non-stationary, data assimilation can be used to modify the inputs.

The modification of inputs opens considerable scope to: i) fill gaps or homogenizing time series, ii) estimate effective rainfall.

Finally, these various analyses and modeling methods, mainly developed on the karst hydrosystem Lez, can improve the knowledge of the rainfall-runoff relationship at different time scales. These methodological tools thus offer perspectives of better management of the aquifer in terms of floods and resources. The advantage of these analyses and modeling tools is that they can be applicable to other systems.

On the applicability of geomechanical models for carbonate rock masses interested by karst processes, 2015,
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Rock mass classification and geomechanical models have a particular importance for carbonate rocks, due to their peculiar fabric, variability of the main features, and scarce availability of experimental data. Carbonates are particularly sensitive to syn-depositional and post-depositional diagenesis, including dissolution and karstification processes, cementation, recrystallisation, dolomitisation and replacement by other minerals. At the same time, as most of sedimentary rocks, they are typically stratified, laminated, folded, faulted and fractured. The strength and deformability of carbonate rock masses are, therefore, significantly affected by the discontinuities, as well as by their pattern and orientation with respect to the in situ stresses. Further, discontinuities generally cause a distribution of stresses in the rock mass remarkably different from those determined by the classical elastic or elasto-plastic theories for homogeneous continua. Goal of this work is the description of the difficulties in elaborating geomechanical models to depict the stress–strain behavior of karstified carbonate rock masses. Due to such difficulties, a high degree of uncertainty is also present in the selection of the most proper approach, the discontinuum one or the equivalent continuum, and in the numerical model to be used within a specific engineering application as well. The high uncertainty might cause wrong assessments as concerns the geological hazards, the design costs, and the most proper remediation works. Even though recent developments in the application of numerical modeling methods allow to simulate quite well several types of jointed rock masses, as concerns carbonate rock masses many problems in representing their complex geometry in the simulation models still remain, due to peculiarity of the structural elements, and the presence of karst features. In the common practice, the improper use of the geomechanical models comes from a superficial geological study, or from the lack of reliable geological and structural data that, as a consequence, bring to erroneous evaluations of the influence of the geological-structural features on the in situ stress state and the stress–strain rock mass behavior.

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