5.1.2. Precipitation.....................................................................................................215 5.1.2.1. Seasonal variation.......................................................................................215 5.1.2.2. Short term variation...................................................................................218 5.1.3. Altitude Effect................................................................................................220 5.1.4. Long-term observation..................................................................................221 5.1.4.1. Altitude of the catchment........................................................................221 5.1.4.2. Mean residence time..................................................................................225 5.1.5. Short term observation.................................................................................227 5.1.5.1. Vipava spring...............................................................................................228 5.1.5.2. Hubelj spring...............................................................................................231 5.1.5.3. Additional karst springs.............................................................................233 5.1.5.4. Results...........................................................................................................235 5.2. Dissolved Inorganic Carbon Isotope Composition of Waters (J. Urbane, B. Trcek, J. Pezdic, S. Lojen)................................................236 5.2.1. Carbon Isotope Composition In Individual Parts Of The Researched System........................................................................................237 5.2.1.1. Characteristics of carbon isotope composition of soil CO^..............237 5.2.1.2 Carbon isotope composition of carbonate rocks..................................242 5.2.1.3. Isotope composition of the total dissolved inorganic carbon in the outflow...............................................................................242 5.2.2. Reconstruction of Initial CO^ Isotope Composition..............................251 a) The Open System Model..................................................................................251 b) The Closed System Model................................................................................251 5.3. Short-term Investigations during a heavy Snowmelt Event (V. Armbruster, C. Leibundgut)...................................................................256 5.3.1. Introduction.....................................................................................................256 5.3.2. Methods............................................................................................................256 5.3.3. Results and Interpretation...........................................................................256 5.3.4. Conclusions......................................................................................................259 6. TRACING EXPERIMENTS.............................................................................260 6.1. Organisation, Injection and Sampling (A. Kranjc, J. Kogovšek, R. Benischke, B. Reichert, M. Zupan, M. Heinz-Arvand)...................260 6.1.1. First Combined Tracing experiment in October 1993 ..........................263 6.1.2. Second Combined Tracing experiment in April 1994...........................265 6.1.3. Third Combined Tracing Experiment, August 1995 ..............................268 6.1.4. Fourth Combined Tracing experiment, October 1995 ...........................273 6.2. Description of the Hydrological Situations during the Tracing Experiments (N. Trišič & J. Polajnar)........................................................274 6.2.1. The Hubelj Spring in the Time of the First Tracing Experiment (October 14 to December 31, 1993)...................274 6.2.2. The Hubelj Spring in the Time of the Second Tracing Experiment (April 16 to July 31, 1994)...................................276 6.2.3. The Hubelj Spring in the Time of the Third Tracing Experiment (August 1 to December 31, 1995).......................277 6.2.4. The Vipava Spring in the Time of the Fourth Tracing Experiment (October 26 to December 31, 1995)...................278 6.3. Results with Fluorescent Tracers...................................................................280 6.3.1. Analytical Procedures (R. Benischke, B. Reichert, M. Zupan)..........280 6.3.2. Results of the Hubelj - Mrzlek- Podroteja Area (M. Zupan, B. Reichert).............................................................................283 6.3.2.1. First Tracing Experiment in October 1993...........................................283 6.3.2.2. The Second Tracing Experiment in April 1994 ..................................285 6.3.2.3. Third Tracing Experiment in August 1995...........................................288 6.3.2.4. Summary.......................................................................................................292 6.3.3. Results of the Vipava Area........................................................................295 6.3.3.1. The Second Tracing Experiment in Spring 1994 (H. Behrens, R. Benischke, W. Käss, M. Zupan).............................295 6.3.3.2. The Fourth Tracing Experiment in Autumn 1995 (M. Zupan)......302 6.3.4. The decomposition of tracers in the spring waters (M. Zupan).......304 6.3.5. The Background Concentrations of the Used Fluorescent Dyes (M. Zupan).........................................................305 6.4. Results with Phages (M. Bricelj).......................,..........................................307 6.4.1. Introduction.....................................................................................................307 6.4.2. Injection data..................................................................................................307 6.4.3. Results..............................................................................................................308 6.4.4. Conclusions......................................................................................................312 6.5. Results with Salts (W. Käss)..........................................................................315 6.5.1. Lithium Tracing Test at Zavrhovc (April 16, 1994)..............................315 6.5.2. Strontium Tracing Test at Mrzli log (April 16, 1994)..........................318 6.6. Mathematical modeling with the Multi-Dispersion-Model (A. Werner & P Maloszewski).....................................................................321 6.6.1. Introduction.....................................................................................................321 6.6.2. The Multi-Dispersions-Model (MDM)......................................................322 6.6.3. The Tracer Tests of the Injection Place Belo Brezno..........................323 6.6.3.1. The First Tracer Test (1993)...................................................................323 6.6.3.2. The Second Tracer Test (1994)...............................................................325 6.6.3.3. The Third Tracer Test (1995)..................................................................327 6.6.4. Conclusion.......................................................................................................328 7. CONCLUSIONS REGARDING THE INVESTIGATION AREA..........329 7.1. Underground connections in dependency to hydrogeological conditions (J. Janež)........................................................................................329 7.2. Underground water connections dependent on hydrometeorological conditions (P. Habič).................................................332 7.2.1. The aim of water tracing by artificial tracers........................................332 7.2.2. Hydrometerological conditions during water tracing tests....................335 7.2.3. Underground water connection Belo Brezno - Hubelj.........................336 7.2.4. Underground connection Belo Brezno - Mrzlek....................................337 7.2.5. Underground connection Belo Brezno - Lijak.......................................338 7.2.6. Underground connection Zavrhovc - Hubelj...........................................339 7.2.7. Underground connection MrzU Log - the Podroteja and Divje Jezero....................................................................................................340 7.2.8. Underground connection Malo Polje - the Podroteja and Divje Jezero....................................................................................................341 7.2.9. Underground connection Lokva (Predjama) - the Vipava (P Habič, V. Armbruster)...........................................................................341 7.2.10. Underground connection Slapenski Ledenik (Nanos Mt.) - the Vipava........................................................................342 7.3. Water Protection measures (J. Janež)..........................................................343 7.3.1. Introduction.....................................................................................................343 7.3.2. Physico-chemical and biological threat to karst superficial and underground waters.......................................................................................344 7.3.2.1. General criteria...........................................................................................344 7.3.2.2. Vulnerability.................................................................................................344 7.3.3. Overview of way and degree of protection.............................................345 7.3.3.1. General criteria...........................................................................................345 7.3.4. Verifying the protection areas related to recent water tracing tests.....346 8. GENERAL CONCLUSIONS............................................................................347 8.1. Methodological aspects of water-tracing experiments (H. Behrens, R. Benischke, W. Käss).........................................................347 8.1.1. Degradation of Uranine during tracer tests............................................348 8.2. Methodological aspects of investigations of single events - The use of the natural tracer silica (V. Armbruster).............................351 8.3. Future aspects (P Habič)................................................................................351 9. BIBLIOGRAPHY................................................................................................354 10. POVZETEK (J. Kogovšek).............................................................................365 10.1 Osnovni podatki...............................................................................................365 10.2 Cilji in potek raziskav....................................................................................366 10.3 Rezultati raziskav.............................................................................................367 10.4 Sledenja v zaledju Mrzleka, Hublja in Lijaka..........................................372 10.5 Sledenja v zaledju Vipave..............................................................................374 10.6 Sklepi..................................................................................................................375 LIST OF THE AUTHORS....................................................................................377 MEMBERS OF ASSOCIATION OF TRACER HYDROLOGY (ATH)....382 1. PREFACE (A. KRANJC) During the 6th SWT at Karlsruhe (1992) the proposal of the participants from Slovenia to organise the next, the 7th SWT in Slovenia, was generally approved. In the autumn of the same year was organised a meeting in Slovenia; a group of experts visited the karst plateau Tmovsko-Banjška Planota conducted by the Slovene specialists who provided appropriate explanations. The final decision to accept the Slovenian proposal passed in Ljubljana. Immediately three committees were designed: the preparatory one (consisting of the members of ATH), the research council (for the research project at Tmovsko-Banjška Planota), and the organising committee. Research activities required for the symposium were carried out in the frame of the international project "Transport of pollutants in karst: tracers and models in different aquifers - field research on Tmovsko-Banjška Planota 1992-1995". Project was mainly financed by the Slovene Ministry of Science and Technology and Ministry of Environment and Physical Planning and, occasionally, by communes and water organisations in the surroundings of Tmovsko-Banjška Planota. The research work including both the field and the laboratory work of the research associates not living in Slovenia, was financed by their organisations or by themselves. More than 50 researchers of various professional profiles from 16 organisations from Austria, Germany and Slovenia co-operated at the research work of the mentioned project. Due to finances, to large number of participants, to their fluctuations, and to questions, opened during the investigations, the course of the research as well as some aims and targets had to be changed, but the essential of the initial plan was kept all the same. To minimise co-ordination questions regular "Preparatory Meetings" were held twice a year in different countries and places, where about 30 researchers gathered every time. As the editor of Acta carsologica and as the Organising Secretary of the 7th SWT I am very glad that both the Classis IV of the Slovene Academy of Sciences and Arts with Editorial Board and the ATH decided that the results of Tmovsko-Banjška Planota investigations will be published in Acta carsologica, with special title "Karst Hydrogeological Investigations in south-western Slovenia". Due to vast number of very different researches, of large amount of data gathered, of great number of authors and of various ways and methods of data interpretation, the preparation of the material for this volume was hard and complicated. But the results prove that it was worth the work and troubles. The editor is deeply grateful, and owes a great debt of thanks to the 7th SWT Editorial Board and to the colleagues from the Karst Research Institute. Map. 1: Visoki Kras (The High Karst) plateaux in western Slovenia (p. 12). Map 2: Tmovsko-Banjška Planota, an overview map (Inštitut za geodezijo in fotogrametrijo FGG, Ljubljana) (p. 13). Merilo 1:450.000 © Geografski inštitut ZRC SAZU o CO > o oc H < LU ^ Z Q LU ILI ^ Ü ^ LU Z CC < CL OQ O CO > O O O Q- i ^ Q_ rf < 0C>(/5 LU o Z Z LU < O m o o o Ui «M Oi- fSo §i cri— m" y LU (C lU s < LUZ ncd 0_j l-CL tr Nl-QZ N — O) m (O s. C 3 (T NJ > < O S "So ^ CE ^ N n 13 CC o. t/) o fO o: ro g ^ I s i C 0) o m o > ™ N § I _ ^ >(0 ro Q^ ^ -J ™ d § C3 >0 LL ns o C « I •S « h» O) fi ^ s oj ca P g g C >o il o s 's > 5 0) M O) ^ d) ■a 5 5 C5 C3 ~ .'A "o ^ OJ ffl tr* (U E 5) o N (D T3 O Q) O) ns N £ o ^ ^ g = o .m 5. 5 SS ^ ■a ® 2. NATURAL BACKGROUND 2.1. PHYSICAL GEOGRAPHY OF TRNOVSKO-BANJSKA PLANOTA (P. HABIČ) The test area of the 7"' Symposium on Water Tracing includes a part of High Dinaric Karst in the western Slovenia; it is bounded by the valleys of the rivers Soča, Idrijca, Vipava and Pivka. From the Soča river in the north-west up to the sinking karst rivers Pivka and Ljubljanica in the south-east, there are, within otherwise uninterrupted landscape of the High Karst, morphologically slightly different areas as for example Banjšice, Trnovski Gozd, Črnovrška Planota, Hrušica and Nanos. This area of the High Karst is usually referred to as Trnovsko-Banjška Planota (TBP). The belt of the High Karst between the northern border of the Adriatic Sea and eastern foot-hills of the Southern Limestone Alps narrows the most in the western Slovenia. A block of carbonate rocks belonging structurally to the Dinaric Mountains, is from 10 to 15 kilometres wide and about 50 km long, covering roughly 700 km^ of the surface. Deeply karstified Cretaceous and Jurassic limestones and Triassic dolomites prevail; towards the north-west they underhe younger, mostly Eocene flysch rocks. Flysch encompasses karstified limestones of Trnovski Gozd and neighbouring plateaux in the southern and eastern side thus acting as a partial, hanging hydrogeological barrier. In the north the High Karst is surrounded by mostly impermeable Middle and Lower Triassic, partly also Permian and Carboniferous rocks. The valleys of the Belca, Idrijca, Trebuša, Hotenka, Kanomlja and Zala rivers are cut into these rocks. In their river basins, specially on the Vojsko Plateau, there are some sinking streams, caves and karst springs. For several reasons this final edge of the High Dinaric Karst between the Vipava valley and the foot-hills of the Julian Alps dissected by the valleys of the Idrijca and Soča rivers was chosen as a test area of Association of Tracer Hydrology for the preparation of the 7"' International Symposium on Water Tracing. From a physiographic and hydrogeological point of view this is a relatively well-confined mountainous karst area bounded by lower, non-karstic margin regions from almost all the parts. The rainfall from this entire area sinks into deep karst aquifer feeding abundant karst springs located at its foot along the tributaries of the Idrijca, Vipava, Soča and Ljubljanica rivers. Smaller sinking streams may only be found in the western and eastern side of Trnovski Gozd. In the valleys on its border major karst springs are distributed, such as Mrzlek, Avšček, Kajža and Vogršček along the Soča; Lijak, Hubelj and Vipava along the Vipava; and Divje Jezero, Podroteja and Hotešk along the Idrijca. The rivers Idrijca, Soča and Vipava belong to the Adriatic water system, and Ljubljanica to the Black Sea basin. Thus the underground watershed between the Adriatic and Black Sea is found within the High Karst. Karst springs in the border of the High Karst are captured for water supply of villages in Vipava valley, on Goriško and along the Soča and Idrijca. As these are the only abundant sources of drinking water in western Slovenia their karst background must be protected against pollution. Due to hydro-graphical complexity within this karst aquifer, it has not yet been possible to define the extent, size and capacity as well as threat to each karst spring separately. For the same reason, protection measures were not introduced separately but for the area as a whole. Previous hydrological and geological researches indicated the main drainage directions of karst waters, but a series of unsolved hydrological questions remained. To solve these would provide better exploitation and better protection of water resources. Intensive karstification is evidenced by solution channels, runnels and karren on bare rocky surfaces. There are numerous, karst dolines and ouvalas, more than 100 m deep, and many caves and shafts, some more than 300 m deep. In the ice-cave Velika Ledena Jama v Paradani cavers have reached a depth of almost 700 m. This external image of intensive karstification is complemented by hydrological indicators. After rainfall the discharge in springs increases rapidly and also decreases relatively fast. Deep karstification is shown also by the location of karst springs in the bottom of the valleys and by their deep siphon outflow passages; at Mrzlek they are below the Soča riverbed, in Divje Jezero cave divers reached more than 100 m below the Idrijca valley without getting to the end of this typical Vauclusian spring. Karst relief dominates over the entire area. Among the elevations typical cone-shaped features prevail; isolated peaks are distributed in levels over the central ridge but they appear also on lower, more flattened borders. Between the elevations there are deep dry valleys with dolines. Such a relief neutralises the superficial watershed. Deep fluvial valleys are cut on the border of the High Karst plateau only. The bottoms of river valleys are from 50 to 300 a.s.l. and this is also the altitude where are the lowest probable free surface springs. Central karst plateaux reach altitudes from 600 to 1500 m a.s.L; the slopes of the valleys are steep and high. The south-western edge of the High Karst from Razdrto past Vipava and Ajdovščina up to Gorica is nearly vertical and at the foot of limestone walls there are recent and fossil scree slopes above the Vipava valley. Carbonate rubble and breccia on the flysch base represent smaller porous aquifers. Calcarenite, breccia and conglomerate inliers of carbonates in Eocene flysch along the Soča to the western border of Banjška Planota represent aquifers of karst and fissure porosity of local importance. In the eastern and western side of Trnovski Gozd, specially on Banjšice, along northern border of Nanos, near Črni Vrh and on Pivka they contribute a part of waters to the central karst aquifer which is seen also in the hydrochemical properties of related springs. Orographic properties of the surface are controlled by geological structure and by younger tectonic movements and by geomorphologic development from the Middle Pliocene onwards. The main ridge of the High Karst trends from north-west to south-east, but it is slightly displaced towards the north-east border. The highest elevations in the central part of Trnovski Gozd are the peaks named Veliki Golak (1495 m) and Mah Golak (1480 m). On the southern and western border of the main ridge of Trnovski Gozd there are some marginal shelves preserved as remains of former, broader planations. There were found the remains of fluvial gravel deposited by waters from neighbouring Pre-alpine valleys when the rivers flowed over the actual High Karst towards the Adriatic Sea. Transverse and also longitudinal dry valleys are downcut into an old, levelled surface. The most expressive is the valley of Čepovan, 20 km long and more than 300 m deep. It widens in its southern part and passes into a smaller karst margin polje near Grgar (280 m). The lowest exit of Grgar lies in the continuation of a dry valley on Preval, 336 m a.s.l. between Sveta Gora (681 m) and Škabrijel (546 m) which is almost 300 m above the present riverbed of the Soča near Gorica. The bottom of the dry valley reaches the highest point in the north of Čepovan, at 620 m and it lowers to 540 m in its northern border near Vrata to remain hanging in a steep edge, 270 m above the Idrijca riverbed. The valley of Čepovan is a natural border between Banjšice to the west and Trnovski Gozd to the east. The highest main ridge of Trnovski Gozd between Paradana, Mala and Velika Lazna and Krnica is cut by a transverse dry valley. Similar are transverse valleys in the south-eastern side of Trnovski Gozd between Mala Gora and Kovk and between Črni Vrh and Col. Transverse dry valleys are important for traffic and they are used for local and forest roads. However, main traffic roads lead along the High Karst by the valleys of the Idrijca and Vipava. An important cross traffic road passes along the western border of the High Karst by the Soča valley between Gorica and Tolmin. There is little soil on the karstified hmestones of Trnovski Gozd (The Wood of Trnovo) and wood prevails there as its name indicates. The rather humid mountainous climate is favourable for fir and beech trees. These two species comprise Vast fir-beech forests. On the highest ridge of Trnovski Gozd the trees are exposed to strong wind, the bora, and therefore the trees are lower with typically shaped branches bent and blasted by the wind. The highest Golaki displays the features of upper tree limit. Instead of beech, dwarf pines appear there. This species may also be found at the bottom of deep karst dolines where cooler air accumulates. In these frost-places the vegetation belts are inversely distributed. A belt of beech is followed downwards by a belt of spruce and at the bottom of doline there is a belt of dwarf pines; in the deepest karst dohnes, in particular at the entrance to ice-caves, a belt of mountainous meadows without trees may even appear. These vegetation specialities of Trnovski Gozd very early aroused the attention of experts. Forest management, that is regulation and protection of karst woods accompanied by a suitable exploitation, has a several hundred years long tradition. From a climatic point of view the High Karst is a typical transitional area between the Mediterranean climatic influences of the Adriatic and the continental and Alpine climatic region of inner Slovenia. The high karst ridge is a sort of barrier against the frequent south-western wind that brings the humidity from Mediterranean. As humid air lifts over the first mountainous barrier it releases heavy precipitation. Thus the central part of Trnovski Gozd receives annually more than 3000 mm, and the maximal daily rainfall may even surpass 300 mm. The mean annual temperature varies from 7 to 9° C. The mean air temperature in January is about -2° C, and in July about 16° C. On Golaki where the upper tree limit is at 1440 m a.s.l. the mean air temperature in July is about 12° C. In the cold half of the year cool air from the south-eastern side frequently passes from the High Karst towards the Mediterranean; this occurs as a strong wind in gusts, called the bora, which may reach more than 200 km/h in the Vipava valley and in dry transverse valleys. Relatively early in autumn snow falls on the peaks of Trnovski Gozd and in spite of some thawing during the winter it may be found in deep dolines up to May, and in caves with large entrances throughout the summer. In many ice caves the local people used to cut out the ice and transport it to the valley and to Triest and Gorica to chill food and drink in times when electric refrigerators did not yet exist. On the border of Trnovsko-Banjška Planota and on Nanos the trees were cut down. At first the land was used for pastures, and later permanent settlements grew. The most dense population is found on Banjšice as far as Grgar to the south and Čepovan and Lokovec to the north. On flysch rock there is more soil which favours agriculture. On Lokovec north from Čepovan and around Trnovo, Voglarji and Lokev south from the Čepovan valley there are less cultivated surfaces. Slightly more soil is provided by disintegrated cherts that occur as lens-shaped inhers in Cretaceous and Jurassic limestones. The same may be said for the inhabited south-eastern part of Trnovski Gozd where modest farms are scattered on the border of the plateau from Predmeja, over Othca, Kovk, Gozd and Križna Gora to Col, Podkraj and Vodice. Some scattered farms may also be found to the north of the main ridge of the High Karst near Zadlog, Črni Vrh and Lomi. In the western border of Nanos the former Vast pastures are more and more overgrown by vegetation and only two farms remain there. Sparse population and low agricultural activity are relatively favourable to protecting the karst aquifer. But, together with endeavours to protect karst waters, there exists a wish to increase the economic development of these villages. In the past they mostly survived by cattle breeding and forestry. Later local people travelled to work in the valleys, and in factories in Gorica, Ajdovščina, Vipava and Idrija; in recent years they try to get work at home in craft and smaller industries. Former rainwater reservoirs are replaced by piped water supply; water is pumped from lower lying springs and increased quantities of waste water flow mostly untreated, underground. The economic development on Trnovsko-Banjška Planota must as soon as possible be co-ordinated with protection of this important karst aquifer which is capable of supplying the larger and more inhabited valley area of the High Karst around Vipava, Gorica and Idrija with drinking water. 2.2. HYDROLOGY (N TRIŠIČ) 2.2.1. Basic description of the area The area of the Trnovski Gozd, the Banjšice, the Nanos, and a part of the Hrušice plateaux hydrologically belongs to the Soča river basin extending over approx. 2000 km^ in Slovenia, which is almost one tenth of Slovenian territory (Fig. 2.1). The river basin stretches from the central part of the JuUan Alps over the pre-Alpine mountains, the territories of Cerkljansko and Idrijsko, the high karst area of the Nanos and the Trnovsko-Banjška Planota, the flysch area of the Vipavska Dolina, to the level gravel-sand accumulation of the Soča and its tributaries on Italian side. In Slovenia, the Soča river basin borders on the Upper Sava river basin, and the Ljubljanica and the Timava river basins, and on Itahan side, on the Taghamento river basin (Fig. 2.1). The strongest tributaries of the Soča are two left tributaries, the Idrijca and the Vipava, which drain the area of Idrijsko and Cerkljansko, the high karst area of the Trnovsko-Banjška Planota, the Nanos, a part of the Hrušica, and the flysch area of the Vipavska Dolina valley. The entire area can be studied as two separate hydrological units, one of which as the catchment area of the karstic springs of the Vipava, and the other one as the catchment area of the karstic springs at the rims of the Trnovsko-Banjška Planota. POREČJE SOČE V SLOVENIJI - SOČA RIVER BASIN , LEGENDA - LEGEND Avtomatske fxtetage 1961-1990 XI XII Fig. 2.5: The average monthly precipitation in the catchment area of the Idrijca and the mean monthly discharges (1961-1990). Tab. 2.4: The 1961-90 data for the Idrijca - LP Podroteja profile. F Precipitation Evaporation Precipit. runoff Q, difference km^ Q (mVsec) (mVsec) (mVsec) (mVsec) (mVsec) 112.84 9.20 2.21 6.99 9.75 +2.3 Tab. 2.5: The characteristic discharges of the 1961-90 period at the Idrijca- Podroteja, and their ratio (m^tsec). ^min ^me;in ^max Q : Q ^min mean 0.84 9.29 306 1 : 11 : 364 The ratio between the maximum and the minimum discharges of the Idrijca at the LP Podroteja gauging profile is so high exactly due to the surface part of the catchment area (Tab. 2.5). Tab. 2.6: The average annual precipitation in the catchment area of the Idrijca (mm). Črni Vrh Idrijska Bela Mrzla Rupa Vojsko 2589 2623 2784 2450 Lijak - Šmihel In the gauging profile at the Lijak - Šmihel station discharges are registered of the periodically active springs, which are only an overflow of high waters from the catchment area of the Mrzlek spring. The hydrauHc Unk between these two springs has been confirmed. At low waters, the water level of the Lijak oscillates parallel to the oscillation of the water level in the Solkan hydropower-plant reservoir, and the gradient towards the Soča is minimal. When the spring Lijak is active, the water table in its karstic catchment area rises even more than by 40 m. There were no continuous observations of the spring in the 1961-90 period, therefore, the characteristic data for that period are missing. The highest registered discharge is 32.6 mVsec, but a greater part of a year the spring is dry. The catchment area of the Lijak can also be considered as a bifurcation area since the high waters of the spring also gravitate towards the Vipava, and when the spring is not active, all the waters from the catchment area gravitate towards the spring Mrzlek, i.e., to the Soča. The regime of the Lijak spring demands a special interpretation of water balance, since the high water waves exert impacts on the discharge regime of the lower section of the Vipava, but the size of its belonging catchment area cannot be defined. The correlation with the Hubelj spring was studied for the Lijak spring; it shows a strong dependence between the regimes of both springs (MUZIC 1986). Hubelj - Ajdovščina The gauging station is located less than 2 km downstream of the Hubelj spring. At the spring itself, water is tapped for the water supply, which reduces the volume by 50 to 150 1/sec. The orographically determined size of the catchment area (F = 85.25 km^) for the gauging station on the Hubelj is too big, therefore the calculation of water balance gives so great a difference between the calculated and the gauged runoffs (Tab. 2.7). The theoretically calculated size of the belonging catchment area measures approx. 50 km^ (STAHL 1994). Tab. 2.7: The 1961-90 data for the Hubelj - VP Ajdovščina profile. F Precipitation Evaporation Precip. runoff Q. difference km^ Q (mVsec) (mVsec) (mVsec) (mVsec) (mVsec) 85.25 6.64 1.76 4.89 3.03 -1.9 Tab. 2.8: The characteristic discharges of the 1961-90 period at the Hubelj - VP Ajdovščina, and their ratio (m^/sec). Q Q mean Q ^max Q . mm : Q mean : Q 0.185 3.03 59.5 1 : 16 : 322 The coefficient is high and speaks in favour of the fact that in the case of the Hubelj spring its maximum discharge is not suppressed (Tab. 2.8). Tab. 2.9: The average annual precipitation heights in the catchment area of the Hubelj (mm). Ajdovščina Lokve Otlica Podkraj 1553 2381 2409 2179 The largest quantity of precipitation in the catchment area of the Hubelj spring falls in November, on average, while the mean monthly discharges of the Hubelj are the highest in April when snow begins to melt (Fig. 2.6 and 2.7, and Tab. 2.9). The distribution of the maximum discharges in all three discussed gauging profiles do not offer any law; but from the distribution of the minimum discharges, the influence is clearly visible of the water reserves from the snow cover, even on the minimum discharges in the summer months. The minimum discharges of the Hubelj and the Vipava occur in February, and in September or October, and they are practically equal, while the autumn minimum discharges of the Idrijca are essentially lower than those in February (Fig. 2.8). The quoted basic hydrological conditions of the discussed area and the springs already represent the hydrological problems which are typical of the karstic hydrological systems (Fig. 2.9). Besides the inaccurately determined sizes of the catchment areas and the directions of water streams in the system, an additional uncertainty occurs in the area of the Trnovski Gozd and the DISCHARGES HUBELJ-AJDOVSCINA PRECIPITATIONS PODKRAJ 3.5 3 I" V VI VII Wll IX mounttily average 1961-1990 Fig. 2.6: Mean monthly discharges of the Hubelj and mean monthly precipitation in the 1961-90 period. Hubelj - AjdovSčin« 1961 • 1990 20 2S "min ~"max-*-™sre(J. Fig. 2.7: The lines of the 1961-90 discharge duration of the Hubelj at the VP Ajdovščina gauging station. DISTRIBUTION OF MINIMAL MOUNTHLY DISCHARGES (1961-1990) IDRIJCA-PODROTEJA III IV VI VII VIII IX XI XII Fig. 2.8: The distribution of the minimum monthly discharges in the 1961-90 period. HIDROGRAFSKA IN HIDROLOŠKA MREŽA HYDROGRAPHYC AND HYDROLOGICAL NETWORK 8610 o LEGENDA - LEGEND SlPRA VODOTOK - POSTAJA CODE RIVII! - CAUGCTG STATION BISO 83-16 B630 64S0 8456 84130 B500 854 S 6647 8849 85«0 8565 8590 SBOD 8808 8603 8SI0 8630 8640 8BD0 8S60 8670 Soča - Solkan Idrijce ■ Petnar Idrijca - Podrotejn Mrljoa - Hotescek Cerknica - Cerkno Trebuse - Dol.TrebuSa Be6a - Baea pri Madnjju Bel&£tcB ~ Sukovj« Lokva - PredjBma Pod (aronera " Vipava Vipava ~ Vipava Vipava - Planino Vipava - Dornbark Vipava ~ Miren Bela - Saaabor Bela - Vipava MaÄilniii -- Podnanos Hubelj - Ajdovseina Branlca ~ Branik UJak - Smiliel Ujak - Volčja Draga VogrfiCak - Baiovljak Fig. 2.9: Hydrographie and hydrologieal network. Banjšice, which further aggravates the comprehension of hydrological conditions. These are the unspecified discharges of the Mrzlek spring which flows into the Soča in the area of the Solkan HPP reservoir and, thus, cannot be directly gauged. 2.3. THE CLIMATE OF THE TRNOVSKO-BAN JŠKA PLANOTA (J. PRISTOV) 2.3.1. Meteorological conditions The Trnovski Gozd, the Banjšice and the Nanos are the first mountain barrier (the altitudes of peaks between 1000 and 1500 m above sea level) on the way from the Mediterranean, or the Northern Adriatic, towards the north and the north-east. Naturally, there is the Kras plateau before it, yet, it mainly does not exceed the altitude of 600 m. Therefore, the orographic precipitation are modest on the Kras, but they already become rather abundant at the barrier running from the Banjšice to the Nanos, and they are the most abundant at the southern part of the Julian Alps. There, the altitudes of the peaks already reach approximately 2000 m, and the average annual precipitation already amounts to 4000 mm, which is the highest value in the Alps. This barrier represents a divide between the Mediterranean and the Alpine climates. The Vipavska Dolina and Goriško region, both located at the southern rims of the Trnovski Gozd, are under the intense influence of the Mediterranean climate. Yet, the Trnovski Gozd, the Banjšice and the Nanos already have the real Alpine climate with the abundant snow during the rather cold winters. The precipitation are abundant all year round, with the explicit maximum in October and November. In the heart of the Trnovski Gozd, i.e. the area of Golaki, they exceed the precipitation average over the period of 30-years, which is 3000 mm, and also the entire area of the Banjšice, the Trnovski Gozd and the Nanos, annually receives over 2000 mm of precipitation, on the average. The most intense precipitation very often occur in October, up to 900 mm (Vojsko 888 mm; Mrzla Rupa 855 mm; Otlica 702 mm), but on the average, October is not the wettest month. Namely, oscillations of precipitation quantity are extremely sharp in this month: on the one hand, the monthly precipitation extremes occur with heavy precipitation, and on the other, this month often receives the minimum precipitation and sometimes - although it happens rarely -they do not fall at all (in 1965). November is the month with the largest average quantity of precipitation, yet the oscillations are not as sharp as in October, and therefore, the annual extremes do not occur in this month. Although rarely, but very heavy precipitation also occur in the month of September. It is typical of autumn precipitation that they are very intense in shorter periods, and they are often unevenly distributed over the discussed area. It happens that the intensity of precipitation in individual areas differs a lot (the ratio of 1:5), which is not the case with the convective precipitation, but with the orographic precipitation related to the front system. For determining the quantities of precipitation by individual precipitation situations, a rather dense network of precipitation gauging stations would be necessary, or, great errors could occur due to the intensely agitated precipitation area. The Trnovski Gozd receives the majority of precipitation in autumn, when the sea is still rather warm, and the very warm and humid air, driven by the SW winds, flows in from above the Mediterranean. When on its way during the precipitation situation this air reaches the first higher mountain barrier, it must ascend to pass it, which results in the orographic precipitation. Such situations often occur during the generation of secondary cyclones in the Genoa bay or above the Northern Adriatic. It is in autumn and spring when the secondary cyclones are most frequent, only that the warm air in autumn contains quite a lot of humidity. The humidity of air is considerably lower in spring due to the cooler northern Mediterranean, and therefore, the orographic precipitation are not so abundant. The monthly quantity of precipitation considerably exceeds the evaporation. July is the least wet month, and even then, more than 160 mm of precipitation fall; concurrently, it is also the month with the most intense evaporation, when the potential evapotranspiration (ETP) on the Nanos amounts to 130 mm, and Ce at Cepovan, to 122 mm (Fig. 2.10 and 2.11). Since the monthly precipitation, on the average, always exceed the ETP, it is assumed that the actual evapo- Fig. 2.10: Mean monthly values of potential evapotranspiration (ETP), precipitation (RR) and corrected precipitation (CRR) on the station Cepovan. 250 ■ ETP(iTm) BRR(mm) Fig. 2.11: Mean monthly values of potential evapotranspiration (ETP), precipitation(RR) and corrected precipitation (CRR) on the station Nanos-Ravnik. transpiration (ET) equals to the potential evapotranspiration (ETP); therefore, in the continuation of this paper, only the term evaporation is used and is equalised with the ETP. On the average, more than 300 mm of precipitation fall in November at Vojsko and Mrzla Rupa, but only 15 mm evaporate. In October, the same area receives more than 250 mm of precipitation, but only about 35 mm evaporate. On the average, the greatest discharges occur in October, although the greatest quantity of precipitation fall in November. The air in the inland of Slovenia is already so cold in this month that the higher altitudes of the Trnovski Gozd are already covered with snow, which is immediately manifested in the reduced discharges. The secondary maximum of discharges occurs in the spring months when the snow cover is melting. As it has already been mentioned, the Trnovski Gozd and Nanos represent the divide between the Mediterranean and the Alpine climates. When the inland of Slovenia is filled with the cold air from the north or the Northeast, great temperature differences originate at the foregoing barrier, as well as great pressure gradients. When the air descends from above the Trnovski Gozd and the Nanos towards the Vipavska Dolina and the Kras, it is adiabatically warmed, yet, it is still cooler than the air above the northern Adriatic. The result of this temperature difference is that the cold air cascades down the slopes, and reaches great velocities, while due to the agitated landforms, violent turbulences are generated. This strong wind is known under the name of bora, and reaches the velocities of up to 200 km/h with individual gusts. Relatively frequent occurrence of the bora, of smaller velocity of course, is also the cause that the air above the Kras and the Vipavska Dolina is dryer than the air above the other regions of Slovenia. Such relatively dry atmosphere provides for the natural drying of ham which is famous as a speciality under the name kraški pršut (i.e. the karstic crude ham). 2.3.2. The water balance The equation of water balance P = Q + E + N* + R (1) expresses that in a specified area the precipitation, P, equal the sura of water discharges, Q, evaporation, E, the changes in water reserve, N*, and the water captured for the biological and industrial consumption, which is pumped from the studied area, R. In our case, the amount of the pumped water is small in comparison to the possible errors at precipitation gauging and making the precipitation maps, and therefore, it is not directly taken into consideration. For the longer periods it can be assumed that the changes in water reserves in an average year are negligible, and the equation is reduced to the following items only: P = Q + E (2) which means that the precipitation in a specified area equal the sum of discharges and evaporation. For the needs of evaluating tracing experiments we wished to obtain water balance for the short periods, i.e., for the individual precipitation situations, or, at least for the periods of several months during which the individual tracing experiments were performed. The results of water balance for the shorter periods were not encouraging although we tried to do our best when making the basic maps. For the precipitation map of wider area of the Nanos and the Trnovsko-Banjška Planota, the data were made use of from 40 precipitation stations where daily precipitation were gauged at 7 hrs (Archives of the Hydrometeo-rological Institute, Slovenia). In individual precipitation situations, very explicit minor precipitation cells occurred, which were impossible to be correctly presented through such low density of precipitation gauging station network. During the relatively stationary precipitation situations, the differences of precipitation between individual areas (from the north towards the south, or, from the west towards the east), even reached the ratio of 10:1. At such sharp precipitation changes, errors occur in the making of precipitation maps, especially at the determining of precipitation for the relatively small contributing areas, particularly if the watersheds are not strictly defined. The equation of water balance in which the precipitation are equal to the sum of water runoff and evaporation, apply only in case when the changes in the water reserve N* are negligible, which is almost impossible to expect at precipitation situations. With heavy precipitation the water reserve in the ground considerably increases. In the late autumn months, the higher altitudes of the Trnovski Gozd are already under the snow covcr which can contain quite large water quantities. To avoid all these troubles, the 30-year water balance was taken as a basis. Let it be assumed in this case, that the water reserve at the end of the period equals to that at the beginning, sincc the difference in an average year is minimal in so long a period, thus, it means N* = 0. Also at the gauging of precipitation, the casual errors arc eliminated by averaging; however, the systematic errors remain, which can be considerably reduced by applying supplementary procedures (precipitation correction due to wind, etc.). Due to the considerable oscillation of annual precipitation in the 30-year period, the water balances were determined also for the 5-year and the 2-year periods, and it was also assumed that N* was negligible. Although this is a rough premise, yet, it is acceptablc were the accuracy taken into consideration, of the precipitation gauging, which is particularly problematic at the higher altitudes due to wind, while the terrain configuration does not allow that the vertical precipitation gradients be directly applied. Precipitation determining Precipitation are gauged with a gauge of Hellmann type which collects too little precipitation in windy weather. The experiments proved that, at wind speed of more than 5 m/scc, only 22 % of the actual snow precipitation are gauged, and 87 % of the actual rain precipitation (YANG et al. f994). Experiments on precipitation gauging in wind conditions were not carried out in Slovenia; therefore, we assumed the WMO intercomparison results. For the stations registering wind observations, force of wind was reduced for each precipitation day, to the altitude of Hellmann's gauge, and then, the adequate coefficient or the anticipated precipitation quantity was calculated. On the basis of gauge locations and direct obstacles, the precipitation stations were ranked into classes. For each class, the monthly and annual coefficients for the correction of precipitation were specified, on the basis of data from the stations with wind observations. By means of these coefficients, the quantities of precipitation were also corrected for the stations without wind observations. Because the precipitation in Slovenia are heavier than in the places where the experiments were performed, it is assumed that also the rain drops and the snow flakes, on average, are shghtly greater and heavier, respectively. Therefore, we reduced the corrective coefficients by 20 % for the places at the altitudes between 1000 m and 1500 m, and by 35 % for the places lying higher than 1500 m. Thus, the corrective coefficients amount to between 1.01 and 1.05; for the very exposed locations only, between 1.05 and 1.08; for the exposed locations above 1000 m in the area of the Nanos and the Trnovsko-Banjška Planota, up to 1.14. Besides the increase of precipitation due to wind, we also toolc into account the increase of precipitation due to the gauge moistening. Whenever the gauge is emptied, a slight amount of water remains on the bottom and the sides of container. Following the results of laboratory testing, we took for the precipitation days with more than 1 mm of precipitation, the correction of 0.3 mm for a rainy day, and the correction of 0.15 mm for a day with snow precipitation. For all the precipitation maps, the corrected precipitation data were made use of. In the making of precipitation maps (Fig. 2.12), the vertical precipitation gradients were not taken into account (a rather even increase of precipitation with the altitude), but the distribution was assessed subjectively, depending on the terrain configuration and precipitation data. Namely, it turned out that certain lower-lying places had received more precipitation than the higher-lying ones (Mrzla Rupa, 930 m above sea level - 2940 mm; Vojsko, 1070 m above sea level - 2800 ram; similar situation occurs in some other stations). Fig. 2.12: The 1961-90 period precipitation map (mm).