Hydrogeological characterization of groundwater storage anddrainage in an alpine karst aquifer (theKaninmassif, JulianAlps)
Janez Turk,1,2* Arnauld Malard,3 Pierre-Yves Jeannin,3 Metka Petrič,1 Franci Gabrovšek,1
Nataša Ravbar,1,4 Jonathan Vouillamoz,3 Tadej Slabe1 and Valentin Sordet31 Karst Research Institute, Research Centre of the Slovenian Academy of Sciences and Arts (ZRC SAZU), Postojna, Slovenia
2 Slovenian National Building and Civil Engineering Institute (ZAG), Ljubljana, Slovenia3 Swiss Institute for Speleology and Karst Studies (SISKA), La Chaux-de-Fonds, Switzerland
4 Urban Planning Institute of the Republic of Slovenia, Ljubljana, Slovenia
Globally speaking, the needs for water are increasingfor several reasons: growth of the population, thedevelopment of industry and tourism, climate changeswhich result in additional needs for irrigation inagriculture, etc. Most groundwater is exploited fromalluvium (i.e. inter-granular) aquifers. Along withalluvium, karstified carbonate rock formations are themost important aquifer formations in the world(Bakalowicz, 2005; Ford and Williams, 2007). Despiteintensive exploitation of karst groundwater in somecountries (including Slovenia and Italy, to which thiscase study refers), these aquifers are still considered asfuture groundwater resources (Doerfliger et al., 2009).
orrespondence to: Janez Turk, Slovenian National Building and Civilgineering Institute (ZAG), Dimičeva ulica 12, 1000 Ljubljana,venia.ail: [email protected]
There are two main explanations for this. Firstly, karstaquifers have various types of porosity. This meansthat, in comparison with other aquifers, karst aquifersare extremely heterogeneous and anisotropic and thattheir characterization (i.e. understanding of undergrounddrainage and storage) is a difficult task, especially on aregional scale. The second reason involves theirvulnerability. They are more vulnerable to pollution dueto rapid infiltration, the high permeability of karst rocks andrapid transport along a conduit system over long distances(Ravbar and Goldscheider, 2009; Pardo-Igúzquiza et al.,2012; Hartmann et al., 2013). The management ofgroundwater and the maintenance of its quality can bedifficult if there is a lack of an exact understanding about thefunctioning of karst aquifers (Perrin and Luetscher, 2008).For this reason, it is very important to find a
methodology for the construction of a good conceptualmodel which could provide a satisfactory overview ofhow the system functions (Bredehoeft, 2005). In karstsystems, it is crucial to take into account the geological
J. TURK ET AL.
and tectonic structures, which play a major role ingroundwater flow and storage (Goldscheider andNeukum, 2010; Ballesteros et al., 2013). In this study, anovel conceptual model was applied, which could be usedas a basis for detailed investigations, including numericalmodelling. Such a conceptual model could be tested andimproved by using field data. This is the KARSYSapproach, which was applied in order to characterizegroundwater storage and underground drainage within analpine karst massif exhibiting a complex geologicalstructure. The approach was developed by scientists ofthe Swiss Institute for Speleology and Karst Studies. Ithas already been successfully applied in Swiss karst areas(Malard et al., 2012; Jeannin et al., 2013). Collaborationbetween Swiss and Slovene institutes has led to theapplication of the KARSYS approach to karst aquifers inSlovenia. Application of the KARSYS worldwide(Ballesteros et al., 2013; Turk et al., 2013) hasdemonstrated the high degree of practical applicabilityof this novel approach in the field of karst groundwatercharacterization.In the present study, the KARSYS approach was
applied to the Kanin high alpine massif. Among karstaquifers in the Alps, that of the Kanin massif is probablyone of the most studied, according to the results ofsurveys performed in recent decades (Casagrande et al.,1999; Audra, 2000; Benedetti and Mosetti, 2000; Cucchiet al., 2000a, b; Komac, 2000; Semeraro, 2000;Casagrande and Cucchi, 2007; Muscio et al., 2011).The site has fascinated generations of cavers andscientists in the field of karst hydrology and speleology.However, the results of past surveys have not yet beenable to provide a clear and easily comprehensible pictureof the functioning of the aquifer (i.e. a consensualoverview). Various hypotheses have been suggested(Čar and Janež, 1992; Komac, 2000; Casagrande andCucchi, 2007; Muscio et al., 2011), but because of thelack of data, none of them has been properly validated.Nevertheless, hydrogeological characterization withsome higher degree of certainty is needed to enablethe long-term and sustainable management planning ofthe Kanin water reserves. The goal of this study wastherefore to fulfil this requirement. By application ofthe KARSYS approach, the results of previous surveyswere assembled, combined, compared and re-applied insuch a way that a completely new insight into theinterior of the massif was obtained.
THE STUDIED AREA
The Kanin massif [approximately 135 km2, the highestpeak being at 2587m above sea level (a.s.l.)], is a trans-boundary aquifer, located along the border between
Slovenia and Italy (the Western Julian Alps). It is oneof the most characteristic high-altitude karst areas of theAlps (Semeraro, 2000) (Figure 1). The massif exhibitscomplex geological and tectonic structures that conditiongroundwater drainage and storage. Groundwater emergesfrom the massif in the form of a number of karst springs(Table I), which are mostly situated in the southernfoothills of the massif. The total discharge of all thesprings in this area has been estimated to amount to about5–8m3/s at low-flow conditions, whereas at high-flowconditions, it can be at least 20 or 30 times greater(Komac, 2000; Muscio et al., 2011). Estimates and(rarely) punctual measurements have indicated that themaximum discharges of the biggest springs can exceed50m3/s. The aquifer is only recharged by precipitationand melted snow. The mean annual precipitation on theKanin massif is around 3000mm or more (Komac, 2000).The groundwater within the massif has, potentially,
great economic potential. Up until now, this water hasonly been partly exploited. The alpine region is rich withwater sources, which also come from neighbouringmassifs, and is sparsely populated, so there has been noneed for greater exploitation of this water source fordrinking purposes (Petrič, 2004). It could, however, alsoact as a source of drinking water not only for the directsurroundings but also, in the future, for more denselypopulated lowlands, such as the Friuli Plain (Italy) whichis located 30 km away. The water could also be used forthe production of electricity (by means of hydroelectricpower plants) and for the production of artificial snow(for use at the ski resort which is located near the top ofthe massif).In addition to these activities, the massif is especially
interesting from the speleological point of view. Severalvertical caves in the Kanin massif are among the deepestin the world. The difference in height between the highestpeaks and that of the springs in the surrounding valleysreaches up to almost 2 km. Currently there are sevencaves deeper than 1 km, the deepest, known as Čehi II,being over 1.5 km deep. The longest cave system, knownas Col del Erbe, has more than 40 km of galleries (Muscioet al., 2011).
Geological context of the massif
The Kanin massif has been interpreted as an anticlinewhich is formed of carbonate rocks that mainly belong to theUpper Triassic (Main dolomite and Dachstein limestone).TheDachstein limestone (up to 1200m thick) lies on a seriesof massiveMain dolomite (Norian and Rhaetian), which hasa thickness of approximately 1000m.In contrast with the Main dolomite, the Dachstein
limestone is well-stratified and highly karstified (Cucchiet al., 1997; Casagrande et al., 1999; Telbisz et al., 2011).
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Figure 1. (a) Aerial view of the Kanin massif, showing the locations of the most important springs – see also Table I. (b) The tectonic units which wereincorporated into the KARSYS model of the Kanin massif are shown. Eight cross-sections were defined based on the hydrogeological model of the
Kanin massif in 2D. Their locations and extents are indicated
Table I. The main springs and some minor springs which emerge from the Kanin massif and their characteristics. The perennial springsare indicators of a permanently saturated zone just upstream of the spring (inside the massif). On the other hand, the springs, which areperched and are activated only seasonally, are indicators of the elevation of the groundwater table at high-flow conditions. High-flow
conditions are not discussed in detail in this paper
SpringCoordinatex (m) D48
Coordinatey (m) D48
Elevation(m a.s.l.)
Minimumdischarge(m3/s)
Maximumdischarge(m3/s) Type
Tomažek* 391 093 135 092 ~520 a few 0.001? ? presumably perennialGlijun 385 692 133 400 425 0.15 >40 perennialŽvika 384 674 131 904 370 0.15 0.8 perennialMala Boka or Sušec 384 186 131 886 383 0 >10 seasonalBoka 383 440 132 016 730 0.2 >40 perennialBočič 383 883 131 344 350 0.1 0.5 perennialMožnica** 389 476 138 688 740 0.25 25 perennialGoriuda 380 084 139 808 868 0.01 10 perennialFontanone Sotto il Monte Sart 376 044 137 523 810 0.03 10 perennial, according to the literatureRio del Lago springs* 384 530 140 076 ~1111 0 0.2 seasonalSpring below Sella Nevea* 382 659 139 761 ~1150 0.02 0.5 perennial
*Springs of minor importance.**The coordinates refer to the average position of the seven springs of the Možnica, which are located at elevations of between 740 and 670m a.s.l.(Čar and Janež, 1992).
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The transition between the Dachstein limestone andthe Main dolomite is not well-defined. It is probablygradual, with several metres or several tens of metresof alternation of limestone and dolomite (Muscioet al., 2011).Jurassic and Cretaceous rocks have been eroded from
the Kanin massif, except at some locations, where theylocally outcrop. The Jurassic rocks (micritic and ooliticlimestones) are also highly karstified, whereas Cretaceousrocks (Scaglia Rossa and flysch) are very scarce (Muscioet al., 2011) and presumably not karstified. Thestratigraphy of the Kanin massif is presented in Figure 2,where the hydrogeological characteristics of each facieshave been interpreted.The carbonate rocks of the Kanin massif are thrust over
the Cretaceous rocks (flysch and marls) which form theBovec basin. The basin is covered, on its surface, byQuaternary sediments. The thickness of the flyschformations can amount up to 600m, whereas that of theQuaternary sediments can amount up to 320m (Kuščer,1974; Komac, 2000).
Hydrogeological characteristics
The stratified and sub-vertically faulted Dachsteinlimestone is well-karstified, and thus highly permeable.The Jurassic rocks that outcrop locally on the surfaceof the Kanin massif are also highly permeable. Thedolomite is generally considered to be ‘less’ karstified,fracture porosity being dominant (Cucchi et al., 2000a),so it can, to some extent, be considered as a basementfor the karst groundwater flows (Figure 2) (Manca,1997; Komac, 2000) because the contrast between the
Figure 2. The stratigraphic units of the Kanin massif. The porosity andpermeability of the individual units has been interpreted from theliterature. Note that the thickness of these units is not shown to scale
permeability of the dolomite and that of the Dachsteinlimestone is large.The location and characteristics of the springs in the
foothills of the Kanin massif depend on the geologicalstructure. The springs at the lowest elevations, just abovethe Bovec basin (Glijun, Bočič and Žvika), emerge alongthe thrust contact between the high-permeability carbon-ate rocks of the Kanin massif and the low-permeabilityflysch of the Bovec basin. Other springs emerge mainly atthe contact between the high-permeability limestone andthe relatively low-permeability dolomite (which are understratigraphic or tectonic control).
METHODOLOGY
The KARSYS approach was developed in order toprovide a conceptual model of the karst aquifers anddrainage systems of a massif, which could be used as apreliminary model for the planning of further investiga-tion (geophysics, dye tracing, boreholes, survey stations)and/or to support further analysis (hydrological, hydraulicand transport simulation, resource vulnerability, collapsemapping hazards, etc.). It is based on a geologicalstructural approach which combines a 3D model of theaquifer geometry with hydraulic principles. The applica-tion of KARSYS is systematic and pragmatic and may besummarized in four steps (Jeannin et al., 2013; Malardand Jeannin, 2013) (Figure 3).
Step 1: data inventory and identification of the forma-tions that are potentially karstified (aquifers) and theirboundaries (aquicludes);
Step 2: construction of a 3D geological model focusedon the aquifer geometry;
Step 3: implementation of the hydrological features andmodelling of the groundwater table within the aquifer byassuming a low hydraulic gradient (even zero) during low-flow conditions (Figure 4a). The unsaturated/saturated andconfined/unconfined zones of aquifers are then identified;
Step 4: identification of the main drainage axes assumingthe following principles: (i) vertical flow through theunsaturated zone, (ii) down-dip flow on the top of theaquiclude formations and (iii) a pseudo-horizontal flowtowards a spring or group of springs in the saturatedzone (Figure 4b). At this time the catchment area of thesystem can be delineated, but its final delineationdepends on how the system functions during high-flow conditions.
Depending on the type of application (further investi-gations or analysis), the model may be improved byfurther iterations.
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Figure 3. Flowchart of the KARSYS approach; four basic steps are required to build the conceptual model of karst aquifers and flow systems
FvcFphf
Fplf
Fvv
imp.
vadosezone
phreatic zone
epiphreatic zone
imp.
Permanent spring
Seasonal spring
b).a).
Figure 4. The KARSYS approach is based on the principles presented in the figure. Adopted from Malard (2013)
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The geological model
Several different types of software that are dedicated to3D geological modelling are available. In the case of thepresent study, the Geomodeller® software was used (seewww.geomodeller.com).The geological and structural model was assembled
based on several geological maps and sets of profiles. Asa primary source, the 1:50 000 scale map of Muscio et al.(2011) was used. Additionally the 1:100 000 scale basicgeological map of Slovenia (Buser, 1986) and thegeological map of Friuli, at a scale of 1:100 000 (Fabianiet al., 1937), were used for comparisons, and for somemarginal areas not covered by Muscio’s map. Compar-ison of the above-listed maps revealed a number ofinconsistencies. After careful consideration of suchinconsistencies, preference was given either to interpre-tations of Muscio et al. (2011) or those of Buser (1986).Geological cross-sections form a crucial part of the
geology is to be reconstructed. Several cross-sectionswere found in the literature (Kuščer, 1974; Gasparo,1982; Antonini and Squassino, 1992; Casagrande, et al.,1999; Anselmi et al., 2000; Audra, 2000; Muscio et al.,2011). However, they are not evenly distributed or aligned.Most of the cross-sections concern the west and east parts ofthe massif and are aligned north–south. All the cross-sections are interpretations that are based on surfacegeological and structural mapping, which have, in somecases, been supplemented by the observations of cavers. Theinterpretations are non-unique, and divergence increaseswith depth. As the cross-sections proposed by differentauthors differ, the decision was taken to use the mostconsistent cross-sections, which are distributed across thestudied area. Altogether nine cross-sections were applied forthe construction of the 3D geological model. In general,recent cross-sections were preferred to older ones, whereascross-sections that contradicted the selected geologicalmaps were excluded.
Some additional geological information was obtainedfrom cave surveys, e.g. about lithological contactsbetween the limestone (i.e. the aquifer formation) andthe dolomite (considered to be an aquifer basement).Unfortunately there is a lack of seismic, borehole andmore precise geological data in the studied area, which, ifavailable, would have been most helpful for theconstruction of a more consistent model.The model of the Kanin massif includes the main
stratigraphic units which are present in the area (Figure 2).Additional tectonic data are also needed for theconstruction of a reliable model. During the first stage,two major thrusts and three regional faults wereincorporated into the 3D geological model. In the secondstage, some other faults were taken into consideration inorder to achieve a more consistent interpretation of themodel. The most characteristic tectonic unit in the area isthe Julian thrust, which is generally orientated west–east(Figure 1). It divides the Kanin massif (i.e. the carbonateplatform) from the flysch of the Bovec basin (Kuščer,1974; Semeraro, 2000; Muscio et al., 2011). The Julianthrust dips towards the north, with an inclination of up to70° (Muscio et al., 2011).Another important tectonic unit is the Rezija-Koritnica
thrust, which has a west–east alignment (Figure 1). Thisthrust fault crosses the Kanin massif and then stretchesalong the Možnica valley in the east. The inclination ofthis thrust fault is between 60° and 80°. It dipssouthwards, leading to a tectonic contact between theMain dolomite and the Dachstein limestone. This regionalthrust fault divides the two opposite monoclines of theKanin into two parts, the northern and the southern parts.The northern part dips towards the north, whereas thesouthern part dips towards the south (Cucchi et al., 1997;Casagrande et al., 1999; Semeraro, 2000; Muscio et al.,2011).Vertical strike-slip faults, with the northwest–southeast
direction, show lateral dextral displacements of severaltens to several hundred metres (Komac, 2000). In the firstmodelling stage, three of the most important faults wereincluded: the Ravne fault, the Polovnik fault and the Idrijafault (Figure 1), all of which are considered to be stillactive. The Ravne fault consists of individual northeastdipping fault planes with different dip angles (Kastelicet al., 2008). The Idrija fault is the most important fault inwestern Slovenia, with an orientation of 75° towards thenortheast. The Polovnik fault is an accompanying fault ofthe Idrija fault.The model (which has a size of 21 × 13 × 4 km) was
prepared on the basis of data from the 1:50 000 and1:100 000 geological maps. The precision of the modeldecreases from the surface (1:50 000) downwards, todepths where geological information becomes rare anduncertain. The spatial resolution of the obtained model
was limited by the size of the studied area and by theaccuracy of the maps and cross-sections implemented inthe model. The mesh resolution was 150 × 150m for xy(latitude and longitude) and 50m for z (altitude).
The hydrogeological model
The 3D geological model, which was obtained asdescribed earlier, provides the main framework for 3Dhydrogeological interpretation. At this stage, all the otheravailable data, which are related to hydrological orhydraulic information, are added to the model as physicalobjects (e.g. the locations of the main springs and theelevations of groundwater tables obtained from deepcaves). To do this, an appropriate tool for 3D animationis needed. Cinema 4D® software was applied (cf. Szabo,2012).The geometry of the karst aquifer and its boundaries is
then described. In the case of the Kanin massif,groundwater reserves are preferentially developed withinthe high-permeability limestone. The bottom of theaquifer consists of the relatively low-permeability dolo-mite and/or flysch. It should be mentioned that thecontrast in the hydraulic conductivity of the limestonewith triple porosity (including conduits) and the lesskarstified dolomite with double porosity reaches up to afactor of 1000:1 (Lewis et al., 2006; Worthington andFord, 2009).The geological and hydrogeological data are combined
with the basic principles of karst hydraulics (the aquifervolume below the main perennial springs is watersaturated and the hydraulic gradient in the phreatic zoneis almost flat under low-flow conditions and confined bythe impervious formations – Figure 4a) in order to locatethe potential groundwater bodies (i.e. phreatic zones), asalready mentioned. These basic principles make itpossible to delineate the extent of phreatic zones underlow-flow conditions.Once the locations of the groundwater bodies have
been identified, the underground drainage axes aredetermined, taking into account the principles describedin Figure 4b.It frequently occurs that the application of the KARSYS
approach leads to the identification of water exchangebetween adjacent karst systems (springs), depending onwatertable fluctuations (Malard et al., 2012). It can thus be used toshow the boundaries of systems and their interactions.Data from tracing experiments can also be integrated intothe model as a control; but some caution needs to be takenas these results and interpretations may be affected bytechnical difficulties and the quality of the survey. Forthese reasons, the accuracy of the dye-tracing results isoften questionable; moreover, proved connections de-pend also on the current hydrological conditions which
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are not always documented. Underground drainage in theKanin massif was previously studied by several tracertests (Cucchi et al., 1997; Audra, 2000; Cucchi et al.,2000a; Muscio et al., 2011).
RESULTS AND DISCUSSION
The obtained 3D model is quite complex due to thepresence of numerous faults and displaced units. Severalfaults that were not incorporated into the 3D geologicalmodel were added later, as it was realized that they couldstrongly affect the geometry of the massif. Suchcorrections make visualization of the 3D model evenmore difficult. In order to improve visualization of themodel, the results are represented in 2D cross-sections (bymeans of fence diagrams), which directly and typicallyreflect the 3D model (Figure 5).
Hydrogeological overview
The results provide a first overview of the geometry ofthe studied karst aquifer (within the limestone formation)and its basement (dolomite and flysch formations), as wellas the regional organization of the flows.The results for low-flow conditions are presented in
Figures 5 and 6. The model indicates that, within the Kaninmassif, a phreatic zone occurs all along the flysch barrier atthe southeastern foothills of the massif (just above the Bovecbasin). Groundwater emerges at several springs which aresituated at different altitudes. The elevation of these springsdecreases in cascades from the northeast (the Tomažek
Figure 5. Hydrogeological interpretation of the Kanin massif, shown in 2D (uthe cross-
spring, ~500ma.s.l.) towards the southwest (the Bočičspring, 350ma.s.l.) (Figure 5). Also, the hydraulic head ofthe groundwater decreases gradually from the northeast tothe southwest along the thrust contact between the carbonateblock and the flysch barrier. What is involved is basically acontinuous groundwater body (Figure 5) that is divided bydiscontinuities (faults). Such are the regional Ravne andIdrija faults (both orientated in a predominantlysoutheastern–northwestern direction) and the local thrustswhich intersect themassif (Figure 1). At least under low-flowconditions, these discontinuities seem to act, to some extent,as hydrogeological barriers (or thresholds which create astepped water table). However, water drainage does occur inthe direction from the upper to the lower groundwater bodies(drainage from the northeast towards the southwest), asshown by the results of tracer tests (Muscio et al., 2011).Such underground overflows can be significant at relativelyhigh-flow conditions (storm events and/or snow melting).The extent of the phreatic zones upstream of the
discussed springs, which occur in the southern foothills ofthe Bovec basin, and also of the phreatic zone upstream ofthe Možnica spring, appears to be relatively well-defined,irrespective of the limitations of the model. However, theextent of this zone cannot be precisely defined in the caseof the Boka spring, which is perched at 730m a.s.l. (onthe Slovenian side), nor in the case of the springs in thenorthwest part of the massif (on the Italian side), i.e. theGoriuda and the Fontanone Sotto il Monte Sart springs. Inthe latter (northwest) area, the quality of the geologicaldata is poor, which means that in this case, theapplicability of the proposed approach is limited.
sing fence diagrams – see Figure 7). See Figure 1 for the exact location ofsections
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Figure 6. Location of (a) the identified groundwater bodies in the Kanin massif and (b) the catchment areas of the main springs. The drainage axes in thephreatic zones point towards the springs. The drainage axes in the vadose zones are also indicated. The division between the Boka and the Glijun springs
has been defined only approximately
J. TURK ET AL.
Any misinterpretation of geological data can lead tosignificant errors in the constructed model. For this reason,interpretation of the groundwater body upstream of theFontanone Sotto il Monte Sart spring is not possible, on thebasis of the existing data set. The Goriuda spring is differentfrom other springs in the area, because it emerges visiblyfrom the dolomite sequence, so that its functioning istherefore more difficult to interpret. Confusion also existsregarding the geological context of the Boka spring asseveral geological interpretations have been proposed.The model also indicates the existence of several perched
groundwater bodies. One occurs in the underground area
between the Goriuda and Fontanone Sotto il Monte Sartsprings (Figure 5). Its interpretation is partly question-able, due to the abovementioned problems (uncertaintiesin the geological data which were applied to construct themodel). Another groundwater body occurs below the areaof ‘Kaninski podi’ (which is a karren field area). Thisgroundwater body belongs to the underground catchmentarea of the Boka spring (Figures 5 and 6). The existence ofboth of these perched groundwater bodies is interpreted asbeing due to the syncline structuring of the stratigraphiclayers. These two supposed groundwater bodies areformed along the axis of the dolomite syncline which
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surrounds the groundwater stored in the limestone(Figure 7, cross-section 7).
The role of tectonics
As discussed earlier, in the Kanin massif, there are twomain tectonic structures that play a fundamental role ingroundwater drainage and storage, i.e. the Julian thrustand the Rezija-Koritnica thrust. Such regional thrustfaults, as well as strike-slip faults, can have a significanteffect on the organization of flows and the extent ofgroundwater bodies because they result in the lifting ofimpermeable blocks above more permeable ones. Thiscan create ‘reservoirs’ where underground groundwaterbodies lie and/or have an effect on the privileged drainageaxes (i.e. on the development of conduits).In the case of the Julian thrust fault, the springs which
are located above the Bovec basin are actually situated atthe surface contact between aquifer rocks (limestone) andimpermeable flysch (Figure 1). However, in the case ofthe Rezija-Koritnica thrust fault, which intersects themassif in the west–east direction, dividing it into asouthern and northern part, the situation is different. Thelithological boundary between the Main dolomite and theDachstein limestone in the southern block of thecarbonate sequence is relatively uplifted (in comparisonwith this boundary in the northern block), which meansthat the lithological contact is near the surface or thedolomite outcrops on the surface (Figure 7, cross-sections1–4). Dolomite is considered to be an aquiclude, and forthis reason, underground drainage from the northernblock to the southern block is at least greatly diminished.This back-thrust is also the main division between thecatchment areas of the northern (Možnica, Goriuda andFontanone Sotto il Monte Sart) and southern springs(Boka, Glijun and all the other springs above the Bovecbasin).With regard to regional strike-slip faults (in this case
the Ravne fault and the Idrija fault, together with thelatter’s accompanying faults), they probably have a strongeffect on the underground drainage conditions. Thesefaults cross the massif, in its eastern part, in the generaldirection southeast–northwest (Figure 1) and may facil-itate the flow’s drainage towards the Boka spring.
Description of the investigated karst hydrogeologicalsystems
• The Glijun spring and other springs just above theBovec basin (Bočič and Žvika)
Glijun is the largest spring in the area of thesoutheastern foothills of the Kanin massif (just abovethe Bovec basin). It seems that the groundwater body ofthe Glijun spring (which is located at 425m a.s.l.) collects
the great majority of groundwater flows from theneighbouring groundwater body which is located towardsthe northeast (Figure 6). This groundwater body onlyfeeds some minor springs (of very low abundance). Mostof the groundwater presumably flows over a threshold(fault) that separates this groundwater body from theGlijun groundwater body. Another threshold separatesthe groundwater body of the Glijun spring from those of theŽvika and Bočič springs, but groundwater connectionbetween both groundwater bodies still exists (Figure 6).
• The Boka spring
The emergence of the Boka spring is interpreted asbeing due to a contact between high-permeabilitylimestone and the relatively low-permeability dolomitebeneath it (Kuščer, 1974; Cucchi et al., 2000a) eventhough there is no consensus among different authorsabout the presence of dolomite at this location (cf. Muscioet al., 2011). Based on field verification work, the authorsconsider that, at this location, the dolomite is shiftedrelatively high above the valley along the strike-slipPolovnik fault (Figure 1). The extent of the phreatic zonejust upstream of the Boka spring remains unknown. Inorder to solve this problem, a higher-resolution (local-scale) model would be needed, with the integration ofadditional geological and hydrogeological data.According to the model, a relatively large and perched
groundwater body should exists further upstream in theunderground catchment area – below the abovementionedkarrenfield area of ‘Kaninski podi’ (Figure 6). Speleologicalsurveys of the ‘Renejevo brezno’ shaft have also indicatedthe existence of a phreatic zone in this part of the area.Groundwater from this body may flow down towards theBoka spring via phreatic conduits within a layer oflimestone that is laterally presumably surrounded byrelatively low-permeable dolomite (Figure 7, cross-section8). This could be a good explanation of the permanency ofthe Boka spring, but it needs to be evaluated by futurespeleological surveys, geological mapping and/or tracertests. If confirmed, the groundwater flow between perchedgroundwater body and the Boka spring could represent apotential significant future energy resource.
• The Možnica spring
The model indicates that the phreatic zone upstream ofthe Možnica spring extends relatively far to the west, tothe Italian side of the massif. Such an observation is quitenovel. In the model, the extension of the groundwaterbody is strictly confined by the topography of the Maindolomite (Figure 7, cross-section 5). The phreatic zone,which develops in the Dachstein limestone block, issurrounded by relatively low-permeability dolomite.
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Figure 7. Overview of the cross-sections which were based on the hydrogeological model. For their locations, see Figure 1
HYDROGEOLOGICAL INTERPRETATION OF KANIN KARST MASSIF
Towards the south, it is confined by the dolomite series,which is uplifted towards the surface along the line of theeast–west thrust which divides the massif into two parts(Figures 1 and 7, cross-sections 1–4).
• The Goriuda spring
The Goriuda spring emerges from a large phreaticconduit that is formed in the dolomite series. Thegeometry of the aquifer indicates that a groundwaterbody is perched inside the limestone. The groundwater isdrained by conduits inside the dolomite so that it reachesthe Goriuda spring (Figure 7, cross-section 3). However,data from nearby caves (Benedetti and Mosetti, 2000)indicate that the assumed water table of the phreatic zoneprobably decreases stepwise towards the spring.
• The Fontanone Sotto il Monte Sart spring
The scale of the model is not optimal for the depictionof spring systems that are relatively small. In this part ofthe studied area, the available geological data are not veryreliable, which makes it impossible to provide a reliableinterpretation for this spring.
Catchment areas and drainage axes
One of the main goals of the study was to perform acatchment delineation of the main springs in a systematicway. The catchment areas (Figure 6b and Table II) of thediscussed springs have been defined based on theorganization of the drainage axes in the 3D model(Figure 6a). The catchment areas were delineated basedon low-flow conditions only. It is presumed that, in high-flow conditions, the hydraulic head rises significantlywithin the system (>50m), leading to an increase in thesize of the phreatic zone, and possible divergence. In sucha case, the catchment delineation would need to bemodified, and overlapping catchment areas might appear.The catchment area for all of the springs above the
Bovec basin (Glijun, Boka, Žvika and Bočič) is defined as
Table II. The catchment areas of the main springs
SpringCatchment area
(km2)
Možnica ~16.5Glijun and Boka ~53.5Springs above the Bovec basin (Glijun, Boka,Žvika and Bočič)
~57
Goriuda ~9.5Fontanone Sotto il Monte Sart ~7Divergent area between Goriuda and FontanoneSotto il Monte Sart springs
a whole (Figure 6); it extends over the Slovenian/Italianborder. An attempt was made to define the catchmentdivision between the Boka perched spring and the Glijunspring. The proposed catchment division is interpreted bydextral movement of the carbonate sequence along thesoutheast–northwest faults and by movement along otherthrust faults that occur in the area. But this is only apresumption that needs to be verified.The catchment areas for the Možnica, Goriuda and
Fontanone Sotto il Monte Sart springs were also delineated(Figure 6). That of the Možnica spring is larger thanpreviously thought (e.g.Čar and Janež, 1992; Muscio et al.,2011). The catchment area stretches far to the Italian side ofthe massif; it goes as far as the area of the Rifugio Gilbertialpine hut and the Sella Nevea ski-resort area, which couldmake protection of this resource quite difficult. Significantcooperation with the Italian ski resort managers would beneeded. For example, a hypothetical contamination on thearea of Sella Nevea ski resort would reach groundwaterbody of the Možnica spring. It would then reach also theSoča River, south of the massif (Figure 5).The results of old tracer tests do not indicate any
bifurcation between the Goriuda and Možnica catchmentareas (Muscio et al., 2011), but these data may beuncertain. The common border of these two catchmentareas is delineated by a local thrust fault, which isindicated on the geological map of Muscio et al. (2011)(Figure 7, cross-section 6). This hypothetical delineationshould be verified by additional surveys (tracer tests), asthe offset of the fault is not clear.A diffluent area between the Goriuda and Fontanone
Sotto il Monte Sart springs has been suggested in thisresearch, but its existence needs to be proved by tracertests performed at high-flow conditions. The model(which is not precise in this region) indicates primarydrainage towards the Goriuda spring (low-flow condi-tions) and probably towards both springs under relativelyhigh-flow conditions.Based on the results presented here, a division of
groundwater flows to the northern (Italian) and thesouthern (Slovenian) side could be performed. The resultsof the research confirmed that the great majority of themassif (80%) drains to springs on the Slovenian side of thetrans-boundary aquifer (cf. Komac, 2000; 85% vs 15%).
CONCLUSIONS
The proposed results, which are based on the KARSYSapproach, have provided a new insight into the interior ofthe Kanin massif. They synthesize existing interpretationin a more consistent way and include some newinterpretations of the hydrogeological functioning of themassif. The system of underground drainage and
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J. TURK ET AL.
groundwater storage within the Kanin massif has beencharacterized in a novel way. Groundwater bodies areindicated, some with high certainty (those above theBovec basin and the Možnica spring), some with relativecertainty (the perched groundwater body upstream ofBoka) and some with less certainty (Goriuda). Thedetermined directions of underground drainage and thedelineations of the spring catchment areas appear to bereliable. Based on the findings of the model, it should bepossible to solve some remaining questions by futuredetailed tracer tests. The advantage of this approach (andthe model) is that it points out the areas wheregeological/hydrological source information is poor ornon-consistent. Moreover, it is a support for furtherinvestigations as it will be easier to anticipate new tracertests and to interpret their results in terms of functioning.The drilling of boreholes will also be assisted by themodel in the case when groundwater resources are beingsearched for. The most important findings of the surveyare in connection with the catchment area of the Možnicaspring, together with an explanation of the functioning ofthe Boka spring, which has been a challenge for severaldecades. These questions are not completely solved, buthypotheses can now be validated by focusing investiga-tions on a precise part of the model.
(i) The catchment area of the Možnica spring seems toextend far to the Italian side, as far as the area of theRifugio Gilberti alpine hut. This finding could be easilyvalidated, e.g. by a tracer test. If such a confirmation ismade, good bilateral cooperation will be needed in orderto ensure protection of theMožnica groundwater reserve.
(ii) The model also offers explanation about the function-ing of the Boka spring (which is a natural asset on thenational level). What is new is the indication ofexistence of a perched groundwater body upstream ofthe system. The groundwater seems to be perchedalong the dolomite syncline below the area of‘Kaninski podi’. The exact elevation of the water tableof this groundwater body seems to be around 1000m a.s.l., but not higher than 1050m a.s.l., taking intoaccount also the data from the ‘Renejevo brezno’ shaft(at low-flow conditions). The elevation of the watertable should be controlled by the lowest lithologicalcontact between the dolomite (i.e. the aquiclude) andthe limestone (i.e. the aquifer) on the southern edge ofthis groundwater body, where underground drainagetowards the Boka spring takes place.
Future work should focus on the interpretation of high-flow conditions, which were only discussed in outline inthis paper (due to the lack of reliable data). Thus,additional measurements of high-flow data and theirimplementation in the model would be needed. Integra-
tion of the high-flow dynamics could change the bordersof the systems as well as the extent of their catchmentareas. Another challenging task is the estimation ofgroundwater reserves. After that, the model can bevalidated with a water balance.
Limitations of the model
In reality, the division between aquifer formations andthe aquifer basement does not strictly follow the narrowstratigraphic contact between the limestone and thedolomite. It is just a simplification of the model. In thereality, the transition between these two lithological units isgradual (the thickness of the contact could amount to asmuch as approximately 100m). This simplification mayhave some slight effects on the extent and location ofgroundwater bodies as they are defined in the model. Thedegree of karstification of the upper part of the dolomitesequence could have a much more important effect,because dolomite with conduit porosity can also beconsidered as an aquifer formation (see the case of theGoriuda spring). Karstification is not, however, uniformthroughout the study area. The thickness of karstifieddolomite could be studied in some of the deep caves, whichcould be a future challenge. Non-uniform karstification ofthe dolomite is probably the model’s most importantlimitation, so that some caution should be used whenmaking hydrogeological interpretations in this area.
ACKNOWLEDGEMENTS
The authors are grateful to the Swiss Contribution for thefinancing of the research and to Joško Pirnat andGiacomo Casagrande for data obtained from cavesurveys. They are also grateful to Peter Sheppard forcareful editing of the text.
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