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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 imbibition is 1. the absorption of a fluid, usually water, by a granular rock or other porous material, under the force of apillary attraction, and in the presence of pressure. 2. fluid displacement in porous media as a result of capillary forces only [16]. 3. absorption of water by plants. synonym: capillary percolation.?

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Featured articles from Cave & Karst Science Journals
Chemistry and Karst, White, William B.
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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 dam site (Keyword) returned 23 results for the whole karstbase:
Showing 1 to 15 of 23
Observations of karst hydrology in the Waga Valley, Southern Highlands District, Papua, New Guinea, 1975, Jacobson G. , Michael Bourke R.

In the neighbourhood of a possible dam site in the Waga Valley, Southern Highlands District, Papua New Guinea, there is little surface drainage apart from the Waga River itself. However, many nearby features - streamsinks, springs, estavelles, dry valleys, dolines and caves - are indicative of the marked development of karst drainage. Loss of river water by entry underground is not balanced by the known local outflows, and larger resurgences must be sought further afield to complete an understanding of the karst hydrology relevant for the engineering proposal.


Karstification at Be:_konak dam site and reservoir area, southern Turkey, 1993, Degirmenci M,

HYDRODYNAMIC CONTROL OF INORGANIC CALCITE PRECIPITATION IN HUANGLONG RAVINE, CHINA - FIELD-MEASUREMENTS AND THEORETICAL PREDICTION OF DEPOSITION RATES, 1995, Liu Z. H. , Svensson U. , Dreybrodt W. , Yuan D. X. , Buhmann D. ,
Hydrochemical and hydrodynamical investigations are presented to explain tufa deposition rates along the flow path of the Huanglong Ravine, located in northwestern Sichuan province, China, on an altitude of about 3400 m asl. Due to outgassing of CO2 the mainly spring-fed stream exhibits, along a valley of 3.5 km, calcite precipitation rates up to a few mm/year. We have carried out in situ experiments to measure calcite deposition rates at rimstone dams, inside of pools and in the stream-bed. Simultaneously, the downstream evolution of water chemistry was investigated at nine locations with respect to Ca2 Mg2, Na, Cl-, SO42-, and alkalinity. Temperature, pH, and conductivity were measured in situ, while total hardness, Ca-T, and alkalinity have been determined immediately after sampling, performing standard titration methods. The water turned out to be of an almost pure Ca-Mg-HCO3 type. The degassing of CO2 causes high supersaturation with respect to calcite and due to calcite precipitation the Ca2 concentration decreases from 6 . 10(-3) mole/l upstream down to 2.5 . 10(-3) mole/l at the lower course. Small rectangular shaped tablets of pure marble were mounted under different flow regimes, i.e., at the dam sites with fast water flow as well as inside pools with still water. After the substrate samples had stayed in the water for a period of a few days, the deposition rates were measured by weight increase, up to several tens of milligrams. Although there were no differences in hydrochemistry, deposition rates in fast flowing water were higher by as much as a factor of four compared to still water, indicating a strong influence of hydrodynamics. While upstream rates amounted up to 5 mm/year, lower rates of about 1 mm/year were observed downstream. Inspection of the marble substrate surfaces by EDAX and SEM (scanning electron microscope) revealed authigeneously grown calcite crystals of about 10 mu m. Their shape and habit are indicative of a chemically controlled inorganic origin. By applying a mass transfer model for calcite precipitation taking into account the reaction rates at the surface given by Plummer et al. (1978), slow conversion of CO2 into H and HCO3-, and diffusional mass transport across a diffusion boundary layer, we have calculated the deposition rates from the hydrochemistry of the corresponding locations. The calculated rates agree within a factor of two with the experimental results. Our findings confirm former conclusions with respect to fast flow conditions: reasonable rates of calcite precipitation can be estimated in reducing the PWP-rate calculated from the chemical composition of the water by a factor of about ten, thus correcting for the influence of the diffusion boundary layer

Early evolution of karst aquifers in limestone: Models on two-dimensional percolation clusters, 1997, Dreybrodt W. , Siemers J.
Two-dimensional nets of initial fractures are constructed on a square-lattice by occupying the lines between nearest neighbour sites by a water leading fissure of width a"SUBo" and length l with an occupation probability p. For p > 0.5 percolating nets occur which lead water. To simulate cave genesis we calculate the water flow rates driven by the hydraulic head h through all fissures. By employing nonlinear dissolution rates of the type F=k"SUBn"(l-c/c"SUBeq")'"SUPn" the widening of the fractures is obtained. At the onset of karstification flow is evenly distributed on all fractures. As the system develops solutional widing creates preferred pathways, which attract more and more flow, until at breakthrough both widening and flow increase dramatically. We discuss the evolution of karst aquifers for natural conditions and also upon human impact at dam sites where steep hydraulic gradients may generate water leading conduits below the dam in times comparable to the lifetime of the structure.

Special speleothems in cement-grouting tunnels and their implications of the atmospheric CO2 sink, 1998, Liu Z. H. , He D. B. ,
Based on the analyses and comparisons of water chemistry, stable carbon isotopes and deposition rates of speleothems, the authors found that there are two kinds of speleothems in the tunnels at the Wujiangdu Dam site, Guizhou, China, namely the CO2-outgassing type and the CO2-absorbing type. The former is natural, as observed in general karst caves, and the product of karst processes under natural conditions. The latter, however, is special, resulting from the carbonation of a cement-grouting curtain and concrete. Due to the quick absorption of CO2 from the surrounding atmosphere, evidenced by the low CO2 content in the air and the high deposition rate of speleothems (as high as 10 cm/a) in the tunnels, the contribution of the carbonation process to the sink of CO2 in the atmosphere is important tin the order of magnitude of 10(8) tons c/a) and should be taken into consideration in the study of the global carbon cycle because of the use of cement on a worldwide scale

Les karsts littoraux des Alpes-Maritimes : inventaire des mergences sous-marines et captage exprimental de Cabb, 2002, Gilli, ric
Inventory of coastal and submarine springs in the Alpes-Maritimes (France) - Experimental catchment at the Cabb spring. Several submarine freshwater springs are present on karst shore in the Alpes-Maritimes (France). Salinity and conductivity measuring coupled with GPS location has permitted to inventory these springs. Three main springs have an average flow around 500 l/s. A balance on inland and offshore springs allows to explain the deficit observed on karst units of Arc de Nice area. A dam was built in the submarine karst spring of Cabb Massolin (Roquebrune-Cap-Martin, France) to study the effects of an artificial augmentation of the pressure on the salinity of a karst aquifer. Trials in low and high water levels show the impossibility to increase the pressure. The presence of several springs and the important jointing of limestone dont allow a sufficient impermeability of the dam site. Nevertheless, the salinity decreases, due to the physical separation between the two kinds of water.

Karstification below dam sites: a model of increasing leakage from reservoirs, 2002, Dreybrodt, Romanov, Gabrovsek,

Dam sites in soluble rocks: a model of increasing leakage by dissolutional widening of fractures beneath a dam, 2003, Romanov D. , Gabrovsek F. , Dreybrodt W. ,
Water flowing through narrow fissures and fractures in soluble rock, e.g. limestone and gypsum, widens these by chemical dissolution. This process, called karstification, sculptures subterranean river systems which drain most of their catchment. Close to dam sites, unnaturally high hydraulic gradients are present to drive the water impounded in the reservoir downstream through fractures reaching below the dam. Under such conditions, the natural process of karstification is accelerated to such an extent that high leakage rates may arise, which endanger the operation of the hydraulic structure. Model simulations of karstification below dams by coupling equations of dissolutional widening to hydrodynamic flow are presented. The model scenario is a dam 100 in wide in limestone or gypsum. The modelling domain is a two-dimensional slice 1 m wide directed perpendicular to the dam. It extends 375 in vertically and 750 in horizontally. The dam is located in its center. This domain is divided by fractures and fissures into blocks of 7.5 x 7.5 x 1 m. The average aperture width of the fractures is 0.02 cm. We performed model runs on standard scenarios for a dam site in limestone with the height H of impounded water 150 in, a horizontal impermeable apron of width W=262 m and a grouting curtain reaching down to a depth of G=97 m. In a second scenario, we changed these construction features to G=187 m and W=82 m. To calculate widening of the fractures, well-established experimental data on the dissolution of limestone and gypsum have been used as they occur in such geochemical settings. All model runs show similar characteristic behaviour. Shortly after filling, the reservoir exhibits a small leakage of about 0.01 m(-3) s(-1), which increases steadily until a breakthrough event occurs after several decades with an abrupt increase of leakage to about 1 m(3) s(-1) within the short time of a few years. Then, flow in the fractures becomes turbulent and the leakage increases to 10 m(3) s(-1) in a further time span of about 10 years. The widths of the fractures are visualized in various time steps. Small channels propagate downstream and leakage rises slowly until the first channel reaches the surface downstream. Then breakthrough occurs, the laminar flow changes to turbulent and a dense net of fractures which carry flow is established. We performed a sensitivity analysis on the dependence of breakthrough times on various parameters, determining breakthrough. These are the height of impounded water H, the depth G of grouting, the average aperture width a(0) of the fractures and the chemical parameters, which are c(eq) the equilibrium concentration of Ca with respect to calcite and the Ca-concentration c(in) of the inflowing water. The results show that the most critical parameter is a(0). At fracture aperture widths of 0.01 cm, breakthrough times are above 500 years. For values of a(0)>0.02 cm, however, breakthrough times are within the lifetime of the structure. We have also modelled dam sites in gypsum, which exhibit similar breakthrough times. However, after breakthrough, owing to the much larger dissolution rates of gypsum, the time until unbearable leakage is obtained, is only a few years. The modelling can be applied to complex geological settings, as phreatic cave conduits below the dam, or a complex stratigraphy with varying properties of the rock with respect to hydraulic conductivity and solubility. A few examples are given. In conclusion, our results support the assumption that increasing leakage of dam sites may be caused by dissolutional widening of fractures. (C) 2003 Elsevier Science B.V. All rights reserved

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

Evolution of Karst Aquifers in Natural and Man Made Environments: A Modeling Approach. Ph.D. thesis, 2003, Romanov, Douchko

The evolution of karst aquifers under various hydrological and chemical boundary conditions is studied.
In the first part the influence of exchange flow from a prominent fracture into a two-dimensional network of fissures is compared to the evolution of a fracture isolated from this net. The modeling domain is 742.5 m long and 375 m wide dissected by fractures into 100 by 51 blocks. The wide prominent fracture extends along its center, thus constituting a part of the network. Under constant head conditions between the left and the right hand side of the domain it looses flow into the network. We have studied the influence of the fracture widths of the fine net to the breakthrough time (BT) of the system. Because of loss of flow from the central fracture to the net, aggressive solution from the input enhances dissolution and breakthrough times are reduced. This effect is most effective, when the aperture width of the fine net is only smaller by about 1% than the widths of the prominent fracture, such that a large amount of water can flow into the net. To obtain further information on the processes involved, an isolated one-dimensional fracture with an additional single point of outflow from it, is investigated.
As an application of the results above, the evolution of a karst aquifer below dam sites is studied. The modeling domain is a 2D, 1 m wide vertical section of soluble rock (gypsum and limestone), perpendicular to the dam. The block extends 750 m horizontally and 375 m vertically. It is divided by fractures and fissures into blocks of 7.5 m x 7.5 m x 1m. The chemical composition of the inflowing water is equal at all input points. Because of dissolution along the fractures, a large zone of increasing permeability is created below the structure, causing high unbearable water losses from the dam site and also endangering the mechanical stability of the dam. The dependence of BT on the basic parameters - the height of the impounded water, the depth of the grouting curtain, the initial aperture widths of the fractures and the fissures, and the chemical parameters of the inflowing water (equilibrium concentration with respect to calcite and input concentration) is investigated. For fracture aperture widths larger than 0.02 cm breakthrough occurs within the lifetime of the structure.
In the second part the effect of chemical boundary conditions on the evolution of a karst aquifer is studied. The model domain is 500 m x 225 m, divided into blocks of 5 m x 5 m x 1 m by fracture network. There are two input points at constant head (25 m) at the inflow side of the block. The outflow side is open at constant head – 0 m. The hydrological boundaries are equal for all simulated scenarios. The chemical composition of the inflowing water at both inputs is varied, and the reaction of the aquifer is studied. Mixing corrosion is the reason for zones of increased permeability deep inside the aquifer along the boundary, where the solutions mix. The influence of mixing corrosion for various values of the input Ca concentration is studied. The results show two types of evolution. Breakthrough (BT) governed evolution – for values of cin<0.96?ceq, and mixing corrosion (MC) - governed evolution for values of cin>0.96?ceq. The BT - type is characterized by enlarged pathways connecting an inflow point with the outflow boundary. For increasing values of the input concentrations the effect of MC becomes stronger. For high Ca concentrations, MC is dominating. There is no considerably widened connection between the inflow points and the out flow boundary. but an enlarged channel along the mixing zone is observed. The timescale for this type of evolution is considerably longer. For solutions saturated with respect to calcite, the mixing zone is the only area of widening inside the aquifer.


Modeling the evolution of karst aquifers and speleogenesis. The step from 1-dimensional to 2-dimensional modeling domains, 2004, Romanov D. , Gabrovsek F. , Dreybrodt W.

First models of karst evolution considered a single isolated fracture with no loss of flow along its entire length. Under conditions of constant head dissolution of limestone creates a positive feedback-loop of increase of aperture widths and flow until at breakthrough the flow and aperture width are enhanced dramatically. If a second dimension is added to this model domain, in the simplest case by an exit-tube connected to the isolated channel, water loss from the isolated channel occurs. We have investigated the influence of the water loss on the breakthrough time of the single channel. In all cases, when water loss is present, more aggressive solution enters at the input. The aggressive solutional activity penetrates deeper along the conduit. Therefore dissolutional widening at the exit is enhanced and breakthrough times are reduced. This is discussed in detail by investigating the profiles of hydraulic head, flow rates, aperture widths, and calcium concentrations along the conduit as they evolve in time and comparing them to those of the isolated 1-D conduit.
In a further step the 1-D conduit is embedded into a net of fractures with smaller aperture widths. The conduit is located in the center of the rectangular domain and connected to the 2-D net at equally spaced nodes. By this way exchange flow from the conduit into the net can arise. But also flow from the net to the conduit is possible. We have studied the evolution of this aquifer considering dissolution also in the network of the narrow fissures. Flow from the main central fracture into the net again reduces breakthrough times. After breakthrough, however, a complex exit fan evolves in the net, which later on is overprinted by a net of entrance fans propagating down flow. These fans are related to flow from the net into the central fracture. The evolution of these fans resulting finally in a maze-like structure is significant for high hydraulic gradients (i0.1) as they exist at artificial dam sites. For such situations realistic modeling has to include dissolutional widening in the net. For low hydraulic gradients, i<0.03, the evolution in the net is slow compared to that of the central conduit and therefore the aquifer is dominated by the evolution of the central fracture.


Karst geology and engineering treatment in the Geheyan Project on the Qingjiang River, China, 2004, Xu Ruichun, Yan Fuzhang,
The Geheyan Hydropower Project is located in a highly karstified limestone area. The Shilongdong limestone of the foundation bedrock is strongly karstified. Over 600 karst caves of different sizes were discovered in the project area, with a total volume of more than 60,000 m3. Faults parallel to the river are quite developed and karstification is intensified along the faults and their intersections. Exploration adits following the fault zones show a linear karstification ratio of 50%. Therefore, the potential karst leakage under the dam foundation and around both dam abutments is potentially problematic. Thanks to a proper investigation program and a large amount of geological investigations and analysis the karst conditions and major karst zones in the dam site had been identified before the construction commenced. Accordingly, the optimum grouting route was chosen and appropriate seepage control measures were adopted. During the construction, the pre-construction investigation results were well confirmed. Up to now, the project has been in good operation for nine years and the engineering treatment are proved to be very effective

Processes of Speleogenesis: a Modeling Approach, 2005, Dreybrodt W. Gabrovsek F. , Romanov D.

This book draws together the major recent advances in the modeling of karst systems. Based on the dissolution kinetics of limestone, and flow and transport processes in its fractures, it presents a hierarchy of cave genetic situations that range from the enlargement of a single fracture to the evolution of cavernous drainage patterns in confined and unconfined karst aquifers. These results are also applied to the evolution of leakage below dam sites in karst. The book offers a wealth of information that helps to understand the development of cave systems. It addresses geologists, hydrologists, geomorphologists, and geographers. It is also of interest to all scientists and engineers who have responsibilities for groundwater exploration and management in karst terrains.

?Processes of Speleogenesis: a Modeling Approach is an exciting book that brings together and displays the products of the first and second generations of karst cave and aquifer computer modeling in a succinct fashion, with excellent illustrations and stimulating contrasts of approach. It is a ?benchmark? publication that all who are interested in speleogenesis should read. It will be a very useful volume for teaching, not only in karst and hydrogeology, but for others who use computer modeling in the physical and spatial sciences.? (From the foreword by D.C. Ford)

?This book is an extraordinary achievement that warrants close attention by anyone interested in speleogenesis??This book is ideal for researchers in speleogenesis who have a solid grasp in technical aspects. Most of the necessary background information is outlined in the first chapter, but subtle aspects will be clear only to those who already have a good background in geochemistry and computer modeling especially when interpreting the figures. This book is not aimed at groundwater hydrologists, although the results would be eye-opening to anyone in that field who denies the importance of solution conduits in carbonate aquifers.? (From book review by A.N. Palmer, JCKS, Volume 67, No.3, 2005)

?To specialists the book is very helpful and and up-to-date, providing many ideas and answering many questions.? (From book review by P. Hauselmann, Die Hohle, Volume 56, 2005)

CONTENTS

  1. Introduction
  2. Equilibrium chemistry and dissolution kinetics of limestone in H2O-CO2 solutions
  3. The evolution of a single fracture
  4. Modeling karst evolution on two-dimensional networks: constant head boundary conditions
  5. Unconfined aquifers under various boundary conditions
  6. Karstification below dam sites
  7. Conclusion and future perspectives
  8. Bibliography

GUEST CHAPTER by Sebastian Bauer, Steffen Birk, Rudolf Liedl and Martin Sauter
Simulation of karst aquifer genesis using a double permeability approach investigation for confined and unconfined settings

GUEST CHAPTER by Georg Kaufmann
Structure and evolution of karst aquifers: a finite-element numerical modeling approach


Hydrogeological uncertainties in delineation of leakage at karst dam sites, the Zagros Region, Iran, 2007, Mohammadi Z. And Raeisi E.
Leakage from dam reservoirs has been reported in different karst regions of the world. Water leakage occurs through the karst features directly or indirectly. The estimation of leakage locations, path(s), and quantity are subject to error due to uncertainties in the non-homogenous nature of a karst formation, method of study, and limited investigation due to time and cost factors. The conventional approaches for study on the karst development are local boring at the dam site and geological mapping. In this paper, uncertainties associated with conventional hydrogeological approaches are addressed from both qualitative and quantitative points of view. No major solution cavities were observed in boreholes and galleries of some dam sites in the Zagros Region, Iran, but huge karst conduits were discovered during the drilling of a diversion tunnel. This inconsistency is due to the point character of boreholes and the inherent nonhomogeneity of karst. The results of dye tracing tests in boreholes may be significantly affected by location of the injection and sampling points, as tests executed at the Saymareh and Tangab Dam sites in the Zagros Region, Iran show. The quantitative uncertainty of leakage is analyzed for diffuse and conduit flow systems for cases with and without any grout curtain, under the combined effect of input uncertainties at the Tangab Dam site, southern Iran. Assuming a diffuse flow system, the mean leakage at 95% confidence interval for both strategies is estimated at less than 5% of the mean annual discharge of the river. Accordingly, the dam can be constructed without the necessity of a grout curtain. However, assuming a conduit flow system, the results reveal a significant uncertainty. A small diameter conduit can convey significant amounts of water under high reservoir pressure heads. The leakage of a 4 m diameter conduit (cross section area of 12.5 m2) is 163 times more than the leakage of 0.5 m diameter conduit (cross sectional area of 0.2 m2) while the cross sectional area ratio is 60. The uncertainty may be decreased if a detailed study is carried out on the stratigraphic and tectonic settings, karst hydrogeology, geomorphology, speleogenesis, and by performing several dye tracing tests, especially outside the proposed grout curtain area.

Interaction between a dam site and karst springs: The case of Supramonte (Central-East Sardinia, Italy), 2008, De Waele Jo, Forti Paolo

Sardinia is one of the Italian regions with the greatest number of dams per inhabitants, almost 60 for a population of only 1.5 million people. Many of these dam sites are located on non-carbonate rocks along the main rivers of the Island and their waters are used for irrigation, industrial, energy supply, drinking and flood regulation purposes.  The Pedra 'e Othoni dam on the Cedrino river (Dorgali, Central-East Sardinia) is located along the threshold of the Palaeozoic basement on the Northern border of the Supramonte karst area, where water is forced to flow out of the system through several resurgences, the most famous of which is the Su Gologone vauclusian spring, used for drinking water supply. The other main outflows of the system, Su Tippari and San Pantaleo springs, are at present almost permanently submerged by the high water level of the Pedra 'e Othoni dam. In the near future water will be supplied also to other communities with a possible increase of water taken from the spring.

The dam, originally meant to regulate the flooding of Cedrino river but actually used for all sorts of purposes (electricity supply, drinking water, irrigation of farmlands, industrial uses), has a maximum regulation altitude of 103 m a.s.l., only slightly less than a meter below the Su Gologone spring level (103.7 m), and 4 and 9 m respectively above the submerged Su Tippari and San Pantaleo springs.

During floods of the Cedrino river, occurring on average twice a year, also the Su Gologone spring becomes submerged by the muddy waters of the lake for a time ranging between a couple of hours up to several days, making water supply impossible. 

The analysis of the available meteorological and hydrogeological data relative to the December 2004 flood, one of the severest of the past 100 years, suggests that the reservoir is filled in a few days time. Several flooding scenarios have been reconstructed using digital terrain models, showing that backflooding submerges most of the discharge area of the aquifer, having important repercussions also on the inland underground drainage system. The upstream flood prone areas prevalently comprise agricultural lands with some sparse houses, but also highly frequented tourist facilities. Fortunately flooding occurs outside the tourist season, thus limiting risk to a limited number of local inhabitants. Massive discharge at the dam site, instead, determines a more hazardous situation in the Cedrino coastal plain, where population density in low lying areas is much higher. To avoid flooding hazard upstream the water level in the lake should be regulated, keeping it low in the flood prone seasons, and having it filled from the end of the winter in order to have enough water stocked before the beginning of the summer. Discharge at the dam site, instead, should be done cautiously, preventing severe flooding of the coastal Cedrino plain.


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