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Featured articles from Cave & Karst Science Journals
Characterization of minothems at Libiola (NW Italy): morphological, mineralogical, and geochemical study, Carbone Cristina; Dinelli Enrico; De Waele Jo
Chemistry and Karst, White, William B.
The karst paradigm: changes, trends and perspectives, Klimchouk, Alexander
Long-term erosion rate measurements in gypsum caves of Sorbas (SE Spain) by the Micro-Erosion Meter method, Sanna, Laura; De Waele, Jo; Calaforra, José Maria; Forti, Paolo
The use of damaged speleothems and in situ fault displacement monitoring to characterise active tectonic structures: an example from Zapadni Cave, Czech Republic , Briestensky, Milos; Stemberk, Josef; Rowberry, Matt D.;
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 porous-medium (Keyword) returned 28 results for the whole karstbase:
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Recession curves contain information on storage properties and different types of media such as porous, fractured, cracked lithologies and karst. Recession curve analysis provides a function that quantitatively describes the temporal discharge decay and expresses the drained volume between specific time limits (Hall 1968). This analysis also allows estimating the hydrological significance of the discharge function parameters and the hydrological properties of the aquifer. In this study, we analyze data from perennial springs in the Judean Mountains and from others in the Galilee Mountains, northern Israel. All the springs drain perched carbonate aquifers. Eight of the studied springs discharge from a karst dolomite sequence, whereas one flows out from a fractured, slumped block of chalk. We show that all the recession curves can be well fitted by a function that consists of two exponential terms with exponential coefficients alpha(1) and alpha(2). These coefficients are approximately constant for each spring, reflecting the hydraulic conductivity of different media through which the ground water flows to the spring. The highest coefficient represents the fast flow, probably through cracks, or quickflow, whereas the lower one reflects the slow flow through the porous medium, or baseflow. The comparison of recession curves from different springs and different years leads to the conclusion that the main factors that affect the recession curve exponential coefficients are the aquifer lithology and the geometry of the water conduits therein. In normal years of rainy winter and dry summer, (Xi is constant in time. However, when the dry period is longer than usual because of a dry winter, (X, slightly decreases with time
The current conceptual model of the unconfined karstic aquifer in the Yucatan Peninsula, Mexico, is that a fresh-water lens floats above denser saline water that penetrates more than 40 km inland. The transmissivity of the aquifer is very high so the hydraulic gradient is very low, ranging from 7-10 mm/km through most of the northern part of the peninsula. The computer modeling program AQUIFER was used to investigate the regional groundwater flow in the aquifer. The karstified zone was modeled using the assumption that it acts hydraulically similar to a granular, porous medium. As part of the calibration, the following hypotheses were tested: (1) karstic features play an important role in the groundwater-flow system; (2) a ring or belt of sinkholes in the area is a manifestation of a zone of high transmissivity that facilitates the channeling of groundwater toward the Gulf of Mexico; and (3) the geologic features in the southern part of Yucatan influence the groundwater-flow system. The model shows that the Sierrita de Ticul fault, in the southwestern part of the study area, acts as a flow barrier and head values decline toward the northeast. The modeling also shows that the regional flow-system dynamics have not been altered despite the large number of pumping wells because the volume of water pumped is small compared with the volume of recharge, and the well-developed karst system of the region has a very high hydraulic conductivity
The geothermal reservoir in Tianjin can be divided into two parts: the upper one is the porous medium reservoir in the Tertiary system; the lower one includes the basement reservoir in Lower Paleozoic and Middle-Upper Proterozoic. Hot springs are exposed in the northern mountain and confined geothermal water is imbedded in the southern plain. The geothermal reservoir is incised by several fractures. In recent years, TIDS of the geothermal water have gone up along with the production rate increasing, along the eastern fracture zone (Cangdong Fracture and West Baitangkou Fracture). This means that the northern fracture system is the main seepage channel of the deep circulation geothermal water, and the reservoir has good connection in a certain area and definite direction. The isotopic research about hydrogen and carbon chronology indicates that the main recharge period of geothermal water is the Holocene Epoch, the pluvial and chilly period of 20 kaBP. The karst conduits in weathered carbonate rocks of the Proterozoic and Lower Paleozoic and the northeast regional fracture system are the main feeding channels of Tianjin geothermal water. Since the Holocene epoch, the geothermal water stayed at a sealed warm period. The tracer test in WR45 doublet system shows that the tracer test is a very effective measure for understanding the reservoir's transport nature and predicting the cooling time and transport velocity during the reinjection. 3-D numerical simulation shows that if the reinjection well keeps a suitable distance from the production well, reinjection will be a highly effective measure to extract more thermal energy from the rock matrix. The cooling of the production well will not be a problem
For more than a century, hydrologists and hydrogeologists have been investigating the processes of stream and spring baseflow recession, for obtaining data on aquifer characteristics. The Maillet Formula [Librairie Sci., A. Hermann, Paris (1905) 218], an exponential equation widely used for recession curve analysis, is an approximate analytical solution for the diffusion equation in porous media whereas the equation proposed by Boussinesq [C. R. Acad. Sci. 137 (1903) 5; J. Math. Pure Appl. 10 (1904) 5], that depicts baseflow recession as a quadratic form, is an exact analytical solution. Other formulas currently used involve mathematical functions with no basis on groundwater theory. Only the exact analytical solutions can provide quantitative data on aquifer characteristics. The efficiency of the two methods was compared on the basis of recession curves obtained with a 2D cross-sectional finite differences model that simulates natural aquifers. Simulations of shallow aquifers with an impermeable floor at the level of the outlet show that their recession curves have a quadratic form. Thus, the approximate Maillet solution largely overestimates the duration of the 'influenced' stage and underestimates the dynamic volume of the aquifer. Moreover, only the Boussinesq equations enable correct estimates of the aquifer parameters. Numerical simulations of more realistic aquifers, with an impermeable floor much deeper than the outlet, proves the robustness of the Boussinesq formula even under conditions far from the simplifying assumptions that were used to integrate the diffusion equation. The quadratic form of recession is valid regardless of the thickness of the aquifer under the outlet, and provides good estimates of the aquifer's hydrodynamic parameters. Nevertheless, the same numerical simulations show that aquifers with a very deep floor provide an exponential recession. Thus, in that configuration, the Maillet formula also provides a good fit of recession curves, even if parameter estimation remains poor. In fact, the recession curve appears to be closer to exponential when flow has a very important vertical component, and closer to quadratic when horizontal flow is dominant. As a consequence, aquifer permeability anisotropy also changes the recession form. The combined use of the two fitting methods allows one to quantify the thickness of the aquifer under the outlet. (C) 2003 Elsevier Science B.V. All rights reserved
The evolution of permeability and flow in a karst aquifer is studied by numerical simulations. The aquifer considered consists of a large central fracture, a network of finer fissures, and a porous rock matrix. Enlargement of both the central fracture and the fissures by chemical dissolution is possible, hence the conductivities in the fracture and the fissure system can increase with time. No dissolution is allowed in the porous rock matrix, which has a constant conductivity. How is driven by a simple fixed head boundary condition representative for the initial phase of karstification. A systematic parameter study is carried out by varying the initial width of the fissure network and the conductivity of the rock matrix, while keeping the initial width of the central fracture fixed. Key parameters such as flowrates, breakthrough times, and conductivities for the different models are compared. If either the conductivity of the rock matrix is high enough or the initial width of the fissures is large enough to carry flow, breakthrough times of the aquifer are significantly reduced, when compared to a model with low matrix conductivity and small fissures. However, due to the dissolutional widening of fissures the evolution of the aquifer is distinctively different for models with rock matrix simulated by a porous medium or a fissure network. (C) 2003 Elsevier B.V. All rights reserved
Various approaches can be used to simulate groundwater flow in karst systems, including equivalent porous media distributed parameter, lumped parameter, and dual porosity approaches, as well as discrete fracture or conduit approaches. The purpose of this study was to evaluate two different equivalent porous media approaches: lumped and distributed parameter, for simulating regional groundwater flow in a karst aquifer and to evaluate the adequacy of these approaches. The models were applied to the Barton Springs Edwards aquifer, Texas. Unique aspects of this study include availability of detailed information on recharge from stream-loss studies and on synoptic water levels, long-term continuous water level monitoring in wells throughout the aquifer, and spring discharge data to compare with simulation results. The MODFLOW code was used for the distributed parameter model. Estimation of hydraulic conductivity distribution was optimized by using a combination of trial and error and automated inverse methods. The lumped parameter model consists of five cells representing each of the watersheds contributing recharge to the aquifer. Transient simulations were conducted using both distributed and lumped parameter models for a 10-yr period (1989-1998). Both distributed and lumped parameter models fairly accurately simulated the temporal variability in spring discharge; therefore, if the objective of the model is to simulate spring discharge, either distributed or lumped parameter approaches can be used. The distributed parameter model generally reproduced the potentiometric surface at different times. The impact of the amount of pumping on a regional scale on spring discharge can be evaluated using a lumped parameter model; however, more detailed evaluation of the effect of pumping on groundwater levels and spring discharge requires a distributed parameter modeling approach. Sensitivity analyses indicated that spring discharge was much more sensitive to variations in recharge than pumpage, indicating that aquifer management should consider enhanced recharge, in addition to conservation measures, to maintain spring flow. This study shows the ability of equivalent porous media models to simulate regional groundwater flow in a highly karstified aquifer, which is important for water resources and groundwater management. (C) 2003 Elsevier Science B.V. All rights reserved
One of the more advanced approaches for simulating groundwater flow in karstic and fractured porous media is the combination of a linear and a nonlinear model. The paper presents an attempt to determine outflow influencing parameters in order to simulate aquifer outflow. Our approach in this study is to create a productive interaction system between expert, mathematical model, MERO,. and artificial neural networks (ANNs). The proposed method is especially suitable for the problem of large-scale and long-term simulation. In the present project, the first objective is to determine aquifer outflow influencing parameters by the use of MERO model, which gave a good results in a fissured and chalky media, and then introduce these parameters in neural network (NN). To determine outflow influencing parameters, we propose to test the NN under fourth different external input scenarios. The second objective is to investigate the effect of temporal information by taking current and past data sets. The good found results reveal the merit of ANNs-MERO combination and specifically multilayer perceptron (MLP) models. This methodology provided that the network with lower, lag and number hidden layer, consistently produced better performance. (C) 2003 Elsevier Science Ltd. All rights reserved
[1] The salinity of an inland coastal brackish karstic spring is modeled on the basis of a simple concept of fluid exchange through head differences between a continuous porous matrix and a karst conduit. The coastal aquifer is reduced to an equivalent porous medium ( matrix) naturally invaded by seawater, crossed by a single karst conduit where fresh water and brackish water mix in variable proportions and flow up into the spring. A new numerical model with an upwind explicit finite difference scheme, called salt-water intrusion in karst conduits (SWIKAC), was developed and successfully applied to the Almyros spring of Heraklio ( Crete, Greece). The good fit of the model to the observed salinity in the spring validates the proposed conceptual model of salinization. It provides a quantitative description of the seawater intrusion inside the karst conduit. The results open up new perspectives for managing the fragile and precious fresh water resources in karstic coastal zones
This paper presents a method for characterizing flow systems in karst aquifers by acquiring quantitative information about the geometric and hydraulic aquifer parameters from spring hydrograph analysis. Numerical sensitivity analyses identified two fundamentally different flow domains, depending on the overall configuration of aquifer parameters. These two domains have been quantitatively characterized by deducing analytical solutions for the global hydraulic response of simple two-dimensional model geometries. During the baseflow recession of mature karst systems, the hydraulic parameters of karst conduits do not influence the drainage of the low-permeability matrix. In this case the drainage process is influenced by the size and hydraulic parameters of the low-permeability blocks alone. This flow condition has been defined as matrix-restrained flow regime (MRFR). During the baseflow recession of early karst systems and fissured systems, as well as the flood recession of mature systems, the recession process depends on the hydraulic parameters and the size of the low-permeability blocks, conduit conductivity and the total extent of the aquifer. This flow condition has been defined as conduit-influenced flow regime (CIFR). Analytical formulae demonstrated the limitations of equivalent models. While equivalent discrete-continuum models of early karst systems may reflect their real hydraulic response, there is only one adequate parameter configuration for mature systems that yields appropriate recession coefficient. Consequently, equivalent discrete-continuum models are inadequate for simulating global response of mature karst systems. The recession coefficient of equivalent porous medium models corresponds to the transition between matrix-restrained and conduit-influenced flow. Consequently, equivalent porous medium models yield corrupted hydrographs both in mature and early systems, and this approach is basically inadequate for modelling global response of karst aquifers. (c) 2004 Elsevier B.V. All rights reserved
[1] Fracture dissolution in the early stages of karstification under hypogene conditions is investigated using a coupled numerical model of fluid flow, heat transfer, and reactive transport. Dissolution of calcite in the H2O-CO2-CaCO3 system along a cooling flow path is investigated using both equilibrium and kinetic models. During the very early stages of fracture growth, there is a positive feedback between flow, heat transfer, and dissolution. In this stage the dissolution rate is largely controlled by the retrograde solubility of calcite, and aperture growth is relatively uniform along the fracture length. There is a period of slow continuous increase in the mass flow rate through the fracture, which is followed by an abrupt rapid increase. We refer to the time when this rapid increase occurs as the maturation time. As the flow rate continues to increase after maturation, forced convective effects lead to higher fluid temperatures in the fracture, resulting in a negative feedback that slows the rate of fracture growth. The behavior of aperture growth before the maturation time can be described by a simple ordinary differential equation. The solution of this differential equation provides an estimate of the maturation time, in terms of the initial aperture, hydraulic and thermal gradients, and the change in solubility with temperature. The behavior before maturation in two-dimensional variable aperture fractures is investigated using a simplified model. The maturation time is shown to decrease with the degree of aperture variability due to highly selective growth along preferential flow paths
Carbonate aquifers typically have complex groundwater flow patterns that result from depositional heterogeneities and post-lithification fracturing and karstification. Various sources of information may be used to build a conceptual understanding of flow in the system, including drilling data, well tests, geophysical surveys, tracer tests, and spring gaging. These data were assembled to model flow numerically in Germany's Malm Formation, at a site where water disappears from the beds of ephemeral stream valleys, flows through conduit systems, and discharges to springs along surface water features. Modeling was performed by using a finite-difference approach, with drain networks, representing the conduit component of flow, laced throughout the porous medium along paths inferred on the basis of site data. This approach represents an improvement over other karst models that attempt to represent a conduit by a single, specialized model node at the spring location or by assigning a computationally problematic extremely high permeability to a zone. By handling the conduit portion of this mixed-flow system with drains, a realistic, interpretive flow model was created for this intricate aquifer
In southeastern Minnesota, Paleozoic bedrock aquifers have typically been represented in groundwater flow simulations as isotropic, porous media. To obtain a more accurate hydrogeologic characterization of the Ordovician Prairie du Chien Group, a new approach was tested, combining detailed geologic observations, particularly of secondary porosity, with hydraulic data. Lithologic observations of the depositional and erosional history of the carbonate-dominated bedrock unit constrained characterization of both primary (matrix) and secondary porosity from outcrops and core. Hydrostratigraphic data include outcrop and core observations along with core plug permeability tests. Hydrogeologic data include discrete interval aquifer tests, borehole geophysics, water chemistry and isotope data, and dye trace studies. Results indicate that the Prairie du Chien Group can be subdivided into the Shakopee aquifer at the top, consisting of interbedded dolostone, sandstone and shale, and the underlying Oneota confining unit consisting of thickly bedded dolostone. The boundary between these two hydrogeologic units does not correspond to lithostratigraphic boundaries, as commonly presumed. Groundwater flow in the Shakopee aquifer is primarily through secondary porosity features, most commonly solution-enlarged bedding planes and sub-horizontal and vertical fractures. Regional scale preferential development of cavernous porosity and permeability along specific stratigraphic intervals that correspond to paleokarst were also identified, along with a general depiction of the distribution of vertical and horizontal fractures. The combination of outcrop and core investigations, along with borehole geophysics, discrete interval aquifer tests, water chemistry and isotope data and dye trace studies show that the Prairie du Chien Group is best represented hydrogeologically as heterogeneous and anisotropic. Furthermore, heterogeneity and anisotropy within the Prairie du Chien Group is mappable at a regional scale (> 15,000 km2)
Carbonate aquifers provide important sources of potable water but are known to be particularly prone to pollution owing to rapid transfer of pollutants from the surface to springs or boreholes. Source protection zones and groundwater vulnerability maps are commonly used to mitigate against the pollution hazard but cannot be applied simplistically to carbonate aquifers, which are usually highly heterogeneous with overlapping groundwater divides that may vary with water levels. Divergent flow and disjunct contributory areas provide further complexity. Under these conditions, water-tracing experiments, repeated under different flow conditions, are the only tool capable of identifying those areas that contribute recharge to a particular source. Examples of water pollution affecting disjunct and overlapping source contributory areas are presented from the Waitomo area (New Zealand), Cuilcagh Mountain (Ireland) and the Peak District (UK). Source protection zones (SPZ), that have been defined by the Environment Agency in the Buxton area of the Peak District using equivalent porous medium models, are shown to be deficient. Further water-tracing experiments are essential if carbonate aquifers are to be adequately protected from pollution
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