MWH Global

Enviroscan Ukrainian Institute of Speleology and Karstology

Community news

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 branchwork cave pattern is 1. a cave system that has been formed by the intersection of tubular or canyon-like conduits as tributaries in the down-flow direction. 2. a dendritic cave system of subterranean watercourses having many incoming branches and no visible outgoing ones [10].?

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

What is Karstbase?

Search KARSTBASE:

keyword
author

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 exploitation (Keyword) returned 62 results for the whole karstbase:
Showing 16 to 30 of 62
Overview of the Human Use of Caves in Virginia: A 10,500 Year History, 1997, Barber, M. B. , Hubbard Jr. , D. A.
The human utilization of caves within the Commonwealth of Virginia began early in prehistoric times and has extended to the present. Such use often has focused on the exploitation of removable resources; knappable lithic materials for the production of stone tools is an important prehistoric example. During historic times, the mining of saltpetre dominates although other natural resources also were removed. The human interaction with caves, however, extends well beyond raw material extraction into the realm of ceremonialism and supernaturalism. Within a Virginia context, Native American use of caves includes both human interments and the codification of symbols. Cave burials have long been known and appear to include attitudes of elaborate ceremonialism as well as less intricate body disposal systems. The mud glyph cave phenomenon has been recorded in Virginia with incised designs and anthropomorphic figures apparently mediating between the sacred and the mundane. Such symbols have roles in rites of passage. Historic use usually is framed in a more functional light. While resource extraction is an obvious utilization realm, the historic use of caves for other purposes is prevalent and includes resort recreation, scientific study, aesthetics, and general exploration. Caves can be discussed in terms of modern symbols and ceremonialism

Environmental and legal aspects of karst areas, 1997, Lamoreaux P. E. , Powell W. J. , Legrand H. E. ,
Environmental impacts on karst settings are common as they are more sensitive than those of other rock terrains. Regulatory procedures that are effective in other rock terrains are not necessarily applicable to karst settings. Development and exploitation by man that affect the karst hydrology regime can trigger catastrophic events and result in numerous legal actions where the effects of changes go beyond property boundaries. A great variety of regulations and examples of litigation exist for karst areas

Optimum well design to avoid salt water pollution of a coastal karst aquifer, 1997, Dermissis V,
The maximum freshwater well pumping flowrate, from an underground karst channel, is defined as function of the channel length, between the well and the submarine spring, in which the channel is terminated. The differential equations that describe the phenomenon of saltwater intrusion into the channel have been analytically solved. The derived dimensionless graphs are suitable for practical applications. Their use can lead to a freshwater exploitation up to 90% of the submarine spring discharge without brackishnesh of the well freshwater

Hydrogeologue versus speleologue, ou de qui releve I'etude et I'exploration des eaux souterraines karstiques ?, 1997, Bakalowicz M.
Tracing tests and sometimes investigations such as exploration of karst conduits for instance, are done by cavers in France in the aim of defining protection areas for karst water supply or exploitation conditions of karst groundwater. The cavers who promote such investigations over all consider that the only direct approach, that of the cave explorer, gives the real knowledge about karst and allows to understand, to exploit and to protect karst groundwater. After defining the originality of karst and its function as an aquifer, one explains the part of the potential actors of its knowledge, of its exploration and of its management, and especially the part of cavers and of hydrogeologists. That paper tries to define the boundaries of the domain in which the actors take a part. It also indicates to decision makers and to managers that their responsability is directly engaged when defining the conditions of each other contributions. Investigations and management of groundwater in karst areas absolutely need an obvious definition of the part plaid by cavers and by hydrogeologists. Cavers should not play a direct part in hydrogeological investigations, as it occurs sometimes, but they should contribute to them, in co-operation with hydrogeologists. Proposals are made about cave and karst feature data base and about tracing test experiments.

Lutilisation des rserves hydrauliques karstiques : lexemple de la commune de Penne-de-Tarn, 1999, Bou, Claude
Water collecting in the commune of Penne was meant to offer an option to the polluted and scarce water resources of the liasic limestone aquifer layer through a planned and reasonable exploitation of the Jurassic reserves. Three underground streams actually supply the whole commune territory - the largest in the Tarn department - with good water which does not suffer any summer depletion. The civil engineering work, the electro-mechanical fittings, the proper fixtures which followed the preliminary surveys were made by unpaid amateur cavers from several clubs of the caving district committee gathered in the ATEK (Association Tarnaise d'Etudes Karstiques). Different methods and techniques have been used to collect water on the following three sites: - the underground stream of Cabeou and the building of a storage dam of 500 m3 which was put into service in 1984 on the limestone plateau of the Garrigue; - the undergroung stream of Amiel where a 25 meter deep well was drilled through hard rock and which has supplied the village with water since 1985; - and the underground stream of Madeleine whose pumping station protected by a dam has increased the water resources of the right bank of the Aveyron river since 1989.

Agricultural use and water quality at karstic Cuban western plain, 1999, Castillo Juan Reynerio Fagundo, Hernandez Patricia Gonzlez
In the paper some results of studies on the karstic aquifers of the western plain of Cuba are presented and discussed. The intensive exploitation of these aquifers for agriculture use and drinking water supply induces an increase of marine water intrusion, water salinisation and a progressive increase of chemical corrosion with a greater dissolution of carbonates. During the period of study (1983-1998) a trend in the deterioration of water quality was observed by means of a chronological series of hydrochloride content.

Karst and agriculture in Australia, 1999, Gillieson David, Thurgate Mia
Much of the development and degradation of karst lands in Australia has occurred in the last two centuries since European settlement. Recent prolonged El Nino events add further climatic uncertainty and place real constraints on sustainable agriculture. The lower southeast of South Australia is perhaps the one area in Australia where karst, and particularly karst hydrology, impinge on the daily lives of the community in that pollution and overexploitation of the aquifer are readily apparent to the local population. Effluent from intensive dairy farms, piggeries and cheese factories enters the karst and has caused concern over pollution of water supplies. Human impacts on the Mole Creek karst of Tasmania have been well documented. The principal recent impacts on the karst arc associated with land clearance for farmland, forest cutting for timber, road building, refuse disposal and associated hydrological change. There is similar evidence of agricultural impacts un karst in central New South Wales, with clear evidence of vegetation clearance and soil stripping on the limestones at Wellington, Orange and Molong.

Exploitation of massif fracturation by karstification: example of the Causse de I'Hortus (Herault, France), 1999, Boinet N,
The Causse de l'Hortus is a particularly well adapted massif to the survey of the fracturation and to its interdependences with karstification. The on-going realisation of a hydrogeological and speleological monograph of the massif, as well as the existence of more than twenty kilometers of prospected channels belonging to the active networks, provide new data which can be compared with previous surveys carried out in this field. The comparison of the directions of fracturation, visible on aerial photographs with directions currently exploited by the karstic channels on the whole Causse, show the effect of the greater fractures and the influence of the hydraulic gradient on the exploitation of the fracture spectrum. To sum up, the display of the relationships between the dextral disconnecting faults and the temporary emergences of the 'boulidou' type, results in concrete applications for speleological and hydrogeological aspects. The survey of these 'boulidous' provides new information about the vertical structuration of the karst. (C) Elsevier, Paris

Water quality impacts and palaeohydrogeology in the Yorkshire Chalk aquifer, UK, 2001, Elliot T, Chadha Ds, Younger Pl,
A large hydrochemical data-set for the East Yorkshire Chalk aquifer has been assessed. Controls on the distribution of water qualities reflect: water-rock interactions (affecting especially the carbonate system and associated geochemistry); effects of land-use change (especially where the aquifer is unconfined); saline intrusion and aquifer refreshening (including ion exchange effects); and overexploitation (in the semi-confined and confined zones of the aquifer). Both Sr and I prove useful indicators of groundwater esidence times, and I/Cl ratios characterize two sources of saline waters. The hydrochemical evidence clearly reveals the importance both of recent management decisions and palaeohydrogeology in determining the evolution and distribution of groundwater salinity within the artesian and confined zones of the aquifer. Waters encountered in the aquifer are identified as complex (and potentially dynamic) mixtures between recent recharge waters, modern seawater, and ancient seawater which entered the aquifer many millennia ago

Environmental problems caused by gypsum karst and salt karst in Great Britain., 2001, Cooper A. H.
In Great Britain, gypsum karst is widespread in the Late Permian (Zechstein) gypsum of north-eastern England. Here and offshore, a well-developed palaeokarst with large breccia pipes was formed by dissolution of the underlying Permian gypsum. Farther south, around Ripon, the same rocks are still being dissolved, forming an actively evolving phreatic gypsum-maze cave system. This is indicated by the presence of numerous active subsidence hollows and sulphate-rich springs. In the English Midlands, gypsum karst is locally developed in the Triassic deposits south of Derby and Nottingham. Where gypsum is present, its fast rate of dissolution and the collapse of overlying strata lead to difficult civil-engineering and construction conditions; these can be further aggravated by water abstraction. Salt (halite) occurs within British Permian and Triassic strata, and has a long history of exploitation. The main salt fields are in central England and the coastal areas of northwest and northeast England. In central England, saline springs indicate that rapid, active dissolution occurs that can cause subsidence problems. In the past, subsidence was aggravated by shallow mining and the uncontrolled extraction of vast amounts of brine. This has now almost stopped, but there is a legacy of unstable buried salt karst, formed by both natural and induced dissolution. The buried salt karst occurs at depths ranging from about 40 m to 130 m; above these depths, the overlying strata are foundered and brecciated. In the salt areas, construction and development are hampered by both abandoned mines and by natural or induced brine runs, with their associated unstable ground.

Lunan "Shilin" (Stone Forest), human impact and protection of (eventual) World Heritage Site (Yunnan, China), 2001, Kranjc Andrej, Liu Hong

The Chinese expression "shilin" (stone forest) is becoming an international term meaning megakarren, that is a Čforest« of intensively corroded limestone pinnacles. The best known is Shilin near the town of Lunan. The first known description of Shilin is from 1382. Shilin is very important tourist site. Modern tourism began to develop in 1980, in 1999 the number of visitors reached over 2 million. In 1981 the whole area (350 sq. km) was protected. Under the auspices of the National Ministry of Construction material is being collected for an application to inscribe Shilin into the list of World's Natural Heritage at UNESCO. Related to human impact the most important threats are: exploitation (destruction) of limestone pinnacles as a source of rock material; the pressure of population towards the protection zone due to their increase (need for new building plots); agriculture (farming and stockbreeding) connected to soil erosion and underground water pollution (use of fertilisers); fast growth of visitor numbers. The Shilin administration introduced different protection measures: ban on rock (limestone pinnacles) exploitation in the protection zone (orientation towards afforestation); construction of new tourist facilities out of the core zone (and demolition of some of them in that zone); establishment of a special protection department within Shilin management (18 person); education of "special voluntary rangers" - recruited among highly respected persons of villages and towns in the region.


Le karst et les carrires souterraines du Barrois : un sicle et demi de relations Hommes / Milieu, 2002, Jaillet Stphane, Depaquis Jeanpierre, Herbillon Claude
The karst and the underground quarries of Barrois: 150 years of relationship Man/Nature - The exploitation of the Savonnires stones in Barrois area (Lorraine/Champagne) was made during the last 150 years by underground quarries. The development of these quarries is estimated between 300 and 350 km today. During this exploitation the cutting of a paleokarst (viailles) and an active karst (pits), disturb the exploitation obliging the quarrymen to fill or to avoid the karst. Karst water added a supplementary constraint but gave a good contribution for the exploitation of the quarry. In the final, karst and waters are for the quarry a minor set of constraints and potentialities, which structure a spatial organisation of this anthropological underground space. Quarry, karst, geology, fauna constitute a unique underground patrimony in Lorraine which would deserve interest and adapted protection.

Coastal karst springs in the Mediterranean basin : study of the mechanisms of saline pollution at the Almyros spring (Crete), observations and modelling, 2002, Arfib B, De Marsily G, Ganoulis J,
Variations in salinity and flow rate in the aerial, naturally salty spring of Almyros of Heraklion on Crete were monitored during two hydrological cycles. We describe the functioning of the coastal karstic system of the Almyros and show the influence of the duality of the flow in the karst (conduits and fractured matrix) on the quality of the water resource in the coastal area. A mechanism of saltwater intrusion into this highly heterogeneous system is proposed and validated with a hydraulic mathematical model, which describes the observations remarkably well. Introduction. - Fresh groundwater is a precious resource in many coastal regions, for drinking water supply, either to complement surface water resources, or when such resources are polluted or unavailable in the dry season. But coastal groundwater is fragile, and its exploitation must be made with care to prevent saltwater intrusion as a result of withdrawal, for any aquifer type, porous, fractured or karstic. In karstic zones, the problem is very complex because of the heterogeneous nature of the karst, which makes it difficult to use the concept of representative elementary volume developed for porous or densely fractured systems. The karstic conduits focus the major part of the flow in preferential paths, where the water velocity is high. In coastal systems, these conduits have also an effect on the distribution of the saline intrusion. As was shown e.g. by Moore et al. [1992] and Howard and Mullings [1996], both freshwater and salt-water flow along the fractures and conduits to reach the mixing zone, or the zone where these fluids are superposed in a dynamic equilibrium because of their differences in density ; but the dynamics of such a saltwater intrusion are generally unknown and not represented in models. Such coastal karstic systems are intensely studied at this moment in the Mediterranean region [Gilli, 1999], both as above sea-level or underwater springs, for potential use in areas where this resource would be of great value for economic development. This article discusses the freshwater-saltwater exchange mechanisms in the karstic aquifer of the Almyros of Heraklion aquifer (Crete) and explains the salinity variations observed in the spring. First, the general hydrogeology of the study site is described, then the functioning of the spring : a main conduit drains the freshwater over several kilometres and passes at depth through a zone where seawater is naturally present. The matrix-conduit exchanges are the result of pressure differences between the two media. These processes are represented in a mathematical model that confirms their relevance. General hydrogeology of the studied site. - The karstic coastal system of the Almyros of Heraklion (Crete) covers 300 km2 in the Ida massif whose borders are a main detachment fault, and the Sea of Crete in the north, the Psiloritis massif (highest summit at 2,456 m) in the south and west, and the collapsed basin of Heraklion filled in by mainly neo-geneous marl sediments in the east. The watershed basin consists of the two lower units of characteristic overthrust formations of Crete (fig. 1) : the Cretaceous Plattenkalk and the Cretaceous Tripolitza limestones. The two limestone formations are locally separated by interbedded flysch or phyllade units that form an impervious layer [Bonneau et al., 1977 ; Fassoulas, 1999] and may lead to different flow behaviour within the two karstic formations. Neo-tectonic activity has dissected these formations with large faults and fractures. The present-day climate in Crete is of Mediterranean mountain type, with heavy rain storms and snow on the summits in winter. Rainfall is unevenly distributed over the year, with 80 % of the annual total between October and March and a year-to-year average of 1,370 mm. The flow rate of the spring is high during the whole hydrologic cycle, with a minimum in summer on the order of 3 m3.s-1 and peak flow in winter reaching up to 40 m3.s -1. The water is brackish during low flow, up to a chloride content of 6 g.l-1, i.e. 23 % of seawater, but it is fresh during floods, when the flow rate exceeds 15 m3.s-1. During the 1999-2000 and 2000-2001 hydrologic cycles, the water was fresh during 14 and 31 days, respectively. The water temperature is high and varies very little during the year (see table I). In the areas of Keri and Tilissos (fig. 1), immediately south of the spring, the city of Heraklion extracts water from the karstic system through a series of 15 wells with depth reaching 50 to 100 m below sea level. Initially, when the wells were drilled, the water was fresh, but nowadays the salinity rises progressively, but unequally from well to well (fig. 2). The relatively constant temperatures and salinities of the wells, during the hydrological cycle, contrast with the large salinity variations at the spring (fig. 2 and table I). They show that the karstic system is complex and comprises different compartments, where each aquifer unit reacts to its individual pressures (pumping, rainfall) according to its own hydrodynamic characteristics [Arfib et al., 2000]. The Almyros spring seems disconnected from the surrounding aquifer and behaves differently from that which feeds the wells (upper Tripolitza limestone). It is recharged by fresh water from the mountains, which descends to depths where it probably acquires its salinity. The spring would thus be the largest resource of the area, if it was possible to prevent its pollution by seawater. A general functioning sketch is proposed (fig. 3), which includes the different geological units of interest. Identification of the functioning of the Almyros spring through monitoring of physical and chemical parameters. - The functioning of the aquifer system of the Almyros spring was analysed by monitoring, over two hydrological cycles, the level of the spring, the discharge, the electric conductivity and the temperature recorded at a 30 min time interval. In the centre of the watershed basin, a meteorological station at an altitude of 800 m measures and records at a 30 min time interval the air temperature, rainfall, relative humidity, wind velocity and direction ; moreover, an automatic rain gauge is installed in the northern part of the basin at an altitude of 500 m. The winter floods follow the rhythm of the rainfall with strong flow-rate variations. In contrast, the summer and autumn are long periods of drought (fig. 7). The flow rate increases a few hours after each rainfall event ; the water salinity decreases in inverse proportion to the flow rate a few hours to a few days later. Observations showed that the water volume discharged at the Almyros spring between the beginning of the flow rate increase and the beginning of the salinity decrease is quite constant, around 770,000 m3 (fig. 4) for any value of the flow rate, of the salinity and also of the initial or final rainfall rates. To determine this constant volume was of the upmost importance when analyzing the functioning of the Almyros spring. The lag illustrates the differences between the pressure wave that moves almost instantaneously through the karst conduit and causes an immediate flow rate increase after rainfall and the movement of the water molecules (transfer of matter) that arrives with a time lag proportionate to the length of the travel distance. The variation of the salinity with the flow rate acts as a tracer and gives a direct indication of the distance between the outlet and the seawater entrance point into the conduit. In the case of the Almyros, the constant volume of expelled water indicates that sea-water intrusion occurs in a portion of the conduit situated several kilometres away from the spring (table II), probably inland, with no subsequent sideways exchange in the part of the gallery leading up to the spring. As the lag between the flow rate and the salinity recorded at the spring is constant, one can correct the salinity value by taking, at each time step, with a given flow rate, the salinity value measured after the expulsion of 770,000 m3 at the spring, which transforms the output of the system so as to put the pressure waves and the matter transfer in phase [Arfib, 2001]. After this correction, the saline flux at the spring, equal to the flow rate multiplied by the corrected salinity, indicates the amount of sea-water in the total flow. This flux varies in inverse proportion to the total flow rate in the high-flow period and the beginning of the low-flow period, thereby demonstrating that the salinity decrease in the spring is not simply a dilution effect (fig. 5). The relationship that exists between flow rate and corrected salinity provides the additional information needed to build the conceptual model of the functioning of the part of the Almyros of Heraklion aquifer that communicates with the spring. Freshwater from the Psiloritis mountains feeds the Almyros spring. It circulates through a main karst conduit that descends deep into the aquifer and crosses a zone naturally invaded by seawater several kilometers from the spring. The seawater enters the conduit and the resulting brackish water is then transported to the spring without any further change in salinity. The conduit-matrix and matrix-conduit exchanges are governed by the head differences in the two media. Mathematical modelling of seawater intrusion into a karst conduit Method. - The functioning pattern exposed above shows that such a system cannot be treated as an equivalent porous medium and highlights the influence of heterogeneous structures such as karst conduits on the quantity and quality of water resources. Our model is called SWIKAC (Salt Water Intrusion in Karst Conduits), written in Matlab(R). It is a 1 D mixing-cell type model with an explicit finite-difference calculation. This numerical method has already been used to simulate flow and transport in porous [e.g. Bajracharya and Barry, 1994 ; Van Ommen, 1985] and karst media [e.g. Bauer et al., 1999 ; Liedl and Sauter, 1998 ; Tezcan, 1998]. It reduces the aquifer to a single circular conduit surrounded by a matrix equivalent to a homogeneous porous medium where pressure and salinity conditions are in relation with sea-water. The conduit is fed by freshwater at its upstream end and seawater penetrates through its walls over the length L (fig. 6) at a rate given by an equation based on the Dupuit-Forchheimer solution and the method of images. The model calculates, in each mesh of the conduit and at each time step, the head in conditions of turbulent flow with the Darcy-Weisbach equation. The head loss coefficient {lambda} is calculated by Louis' formula for turbulent flow of non-parallel liquid streams [Jeannin, 2001 ; Jeannin and Marechal, 1995]. The fitting of the model is intended to simulate the chloride concentration at the spring for a given matrix permeability (K), depth (P) and conduit diameter (D) while varying its length (L) and its relative roughness (kr). The spring flow rates are the measured ones ; at present, the model is not meant to predict the flow rate of the spring but only to explain its salinity variations. Results and discussion. - The simulations of chloride concentrations were made in the period from September 1999 to May 2001. The depth of the horizontal conduit where matrix-conduit exchanges occur was tested down to 800 m below sea level. The diameter of the conduit varied between 10 and 20 m, which is larger than that observed by divers close to the spring but plausible for the seawater intrusion zone. The average hydraulic conductivity of the equivalent continuous matrix was estimated at 10-4 m/s. A higher value (10-3 m/s) was tested and found to be possible since the fractured limestone in the intrusion zone may locally be more permeable but a smaller value (10-5 m/s) produces an unrealistic length (L) of the saline intrusion zone (over 15 km). For each combination of hydraulic conductivity, diameter and depth there is one set of L (length) and kr (relative roughness) calibration parameters. All combinations for a depth of 400 m or more produce practically equivalent results, close to the measured values. When the depth of the conduit is less than 400 m, the simulated salinity is always too high. Figure 7 shows results for a depth of 500 m, a diameter of 15 m and a hydraulic conductivity of 10-4 m/s. The length of the saltwater intrusion zone is then 1,320 m, 4,350 m away from the spring and the relative roughness coefficient is 1.1. All the simulations (table II) need a very high relative roughness coefficient which may be interpreted as an equivalent coefficient that takes into account the heavy head losses by friction and the variations of the conduit dimensions which, locally, cause great head losses. The model simulates very well the general shape of the salinity curve and the succession of high water levels in the Almyros spring but two periods are poorly described due to the simplicity of the model. They are (1) the period following strong freshwater floods, where the model does not account for the expulsion of freshwater outside the conduit and the return of this freshwater which dilutes the tail of the flood and (2) the end of the low-water period when the measured flux of chlorides falls unexpectedly (fig. 5), which might be explained by density stratification phenomena of freshwater-saltwater in the conduit (as observed in the karst gallery of Port-Miou near Cassis, France [Potie and Ricour, 1974]), an aspect that the model does not take into account. Conclusions. - The good results produced by the model confirm the proposed functioning pattern of the spring. The regulation of the saline intrusion occurs over a limited area at depth, through the action of the pressure differences between the fractured limestone continuous matrix with its natural saline intrusion and a karst conduit carrying water that is first fresh then brackish up to the Almyros spring. The depth of the horizontal conduit is more than 400 m. An attempt at raising the water level at the spring, with a concrete dam, made in 1987, which was also modelled, indicates that the real depth is around 500 m but the poor quality of these data requires new tests to be made before any firm conclusions on the exact depth of the conduit can be drawn. The Almyros spring is a particularly favorable for observing the exchanges in the conduit network for which it is the direct outlet but it is not representative of the surrounding area. To sustainably manage the water in this region, it is essential to change the present working of the wells in order to limit the irreversible saline intrusion into the terrain of the upper aquifers. It seems possible to exploit the spring directly if the level of its outlet is raised. This would reduce the salinity in the spring to almost zero in all seasons by increasing the head in the conduit. In its present state of calibration, the model calculates a height on the order of 15 m for obtaining freshwater at the spring throughout the year, but real tests with the existing dam are needed to quantify any flow-rate losses or functional changes when there is continual overpressure in the system. The cause of the development of this karstic conduit at such a great depth could be the lowering of the sea level during the Messinian [Clauzon et al., 1996], or recent tectonic movements

Environmental problems caused by gypsum karst and salt karst in Great Britain, 2002, Cooper Ah,
In Great Britain, gypsum karst is widespread in the Late Permian (Zechstein) gypsum of north-eastern England. Here and offshore, a well-developed palaeokarst with large breccia pipes was formed by dissolution of the underlying Permian gypsum. Farther south, around Ripon, the same rocks are still being dissolved, forming an actively evolving phreatic gypsum-maze cave system. This is indicated by the presence of numerous active subsidence hollows and sulphate-rich springs. In the English Midlands, gypsum karst is locally developed in the Triassic deposits south of Derby and Nottingham. Where gypsum is present, its fast rate of dissolution and the collapse of overlying strata lead to difficult civil-engineering and construction conditions; these can be further aggravated by water abstraction. Salt (halite) occurs within British Permian and Triassic strata, and has a long history of exploitation. The main salt fields are in central England and the coastal areas of northwest and northeast England. In central England, saline springs indicate that rapid, active dissolution occurs that can cause subsidence problems. In the past, subsidence was aggravated by shallow mining and the uncontrolled extraction of vast amounts of brine. This has now almost stopped, but there is a legacy of unstable buried salt karst, formed by both natural and induced dissolution. The buried salt karst occurs at depths ranging from about 40 m to 130 in; above these depths, the overlying strata are foundered and brecciated. In the salt areas, construction and development are hampered by both abandoned mines and by natural or induced brine runs, with their associated unstable ground

Modeling the hydraulical behavior of a fissured-karstic aquifer in exploitation conditions, 2002, Debieche Th, Guglielmi Y, Mudry J,
A 5-year daily measurement of the dynamic level in a borehole was plotted versus cumulative yield since the beginning of exploitation. Eighty percent of the experimental curve is explained by a linear function (h = aQ(c) h(0)) by intervals. Only floods, which follow heavy storms and non-pumping cannot be taken into account. The slopes of the straight lines are spread around two constant values of the slope: a(r) = .35 x 10(-3) m m(-3), which characterizes the part which is controlled by recharge, and a(p) = -0.14 x 10(-3) m m(-3), which characterizes the draining part of the aquifer fractures. This linear fitting demonstrates that the borehole -aquifer system can be considered as an equivalent continuous medium, where the linear relationship between dynamic head and pumped yield are defined by the values of ar and a, Thus the hydraulic behavior of the aquifer differs according to the pumping rate: equivalent continuous medium for a low rate, dual permeability for a high one. This work demonstrates that the long-term behavior of an exploited fissured aquifer can be described by a simple model, if the duration of the aquifer test is long enough (1-3 months). It also shows that the production phase must include repetitive head measurements in order to refine the exploitation yield and the management conditions. (C) 2002 Elsevier Science B.V. All rights reserved

Results 16 to 30 of 62
You probably didn't submit anything to search for