VODNA GLADINA V NOTRANJSKEM IN PRIMORSKEM KRASU SLOVENIJE (S 14 SLIKAMI) WATER TABLE IN SLOVENE KARST OF NOTRANJSKO AND PRIMORSKO (WITH 14 FIGURE$) PETER HABIC SPREJETO NA SEJI RAZREDA ZA NARAVOSLOVNE VEDE SLOVENSKE AKADEMIJE ZNANOSTI IN UMETNOSTI DNE 31. OKTOBRA 1985 Vsebina Izvleček - Abstract UVOD ..... . IZHODIŠČE VODNA GLADINA V IZVIRIH LJUBLJANICE PRI VRHNIKI VODNA GLADINA V ZALEDJU PRIMCOVEGA STUDENCA . VODNA GLADINA MED LJUBLJANSKIM BARJEM TER LOGAŠKIM IN PLANINSKIM POLJEM . . . . . . . . . . . . . . . . . . KRAŠKA VODA MED PLANINSKIM POLJEM IN RAKOVIN ŠKOCJANOM Planinska jama . . . . . . . . . . . . . . . . . . . . . . . KRAŠKA VODA MED RAKOVIM ŠKOCJANOM IN CERKNIŠKIM JEZE- ROM ................ , .......... . KRASKA VODA NA CERKNIŠKEM POLJU IN NJEGOVEM OBROBJU VODNA GLADINA V POSTOJNSKEM KRASU ....... . VODNA GLADINA NA ZGORNJI PIVKI IN POD JAVORNIKI. PODZEMNE VODE V MATIČNEM KRASU ....... . KRAŠKA VODA V ZALEDJU RIZANE IN OSAPSKE REKE . VODA V KRASU MED IDRIJCO IN VIPAVO . RAZPRAVA IN SKLEPI . . . . . . . . . . . . . . . . LITERATURA . . . . . . . . . . . . . . . . . . . WATER TABLE IN SLOVENE KARST OF NOTRANJSKO AND PRIMORSKO 39 ( 3) 39 ( 3) 40 ( 4) 41 ( 5) 45 ( 9) 48 (12) 48 (12) 49 (13) 51 (15) 52 (16) 54 (18) 56 (20) 61 (25) 63 (27) 63 (27) 67 (31) 72 (36) (Summary) ................•.... . . . . . 75 (39) Naslov - Address Dr. Peter HABIC, znanstveni svetnik Inštitut za raziskovanje krasa ZRC SAZU Titov trg 2 66230 Postojna Jugoslavija Acta carsologica XIII (1984), 37-78, Ljublja'1a, 198:; Izvleček UDK 556.32(497.12-13/-14 551.491.54( 497.12-13/-14) Habič Peter: Vodna gladina v Notranjskem in Primorskem krasu. Po razpoložljivih speleoloških podatkih sta prikazana razporeditev in nihanje vod- ne gladine v krasu v porečju Ljubljanice, Idrijce, Vipave, Notranjske Reke in Ti- mava ter Rižane. Nakazani so vzroki različnega nihanja in ocenjen je praktični pomen poznavanja razporeditve voda v krasu. Podčrtana je potreba po boljši regi- straciji niha'Ilja vode vsaj v speleološko dostopnem podzemlju. Abstract UDC 556.32(497.12-13/-14) 551.491.54( 497 .12-13/-14) Habič Peter: Water table in Slovene karst of Notranjsko and Primorsko. According to available speleological data distribution and osaillation of water table in karst of river basin of Ljubljanica, Idrijca, Vipava, No'ranjska Reka, Timava and Rižana are presented. The reasons for different oscilations are shown and practicali significance of water distribution in karst is assed. The need for better registration of water oscillation at l~ast in s•peleologically accessible underground is emphasised. UVOD Medzrnska poroznost v grobozrnatih naplavinah omogoča sklenjeno vodno gladino, ki različno niha glede na dotok, prepustnost in odtok v posameznih vodonosnikih. Razpoklinske pore in kraške votline v karbonatnih kamninah so lahko povezane ali nepovezane. Razporeditev in nihanje vodne gladine v njih je zaradi tega ponekod skladno na večje razdalje, drugod pa ločeno in neod- visno že v bližnjih izvirih in podzemeljskih rovih. Zaradi večje heterogenosti kraškega vodonosnika se vodne razmere v krasu od predela do predela razli- kujejo, zato ni čudno, da so se v začetnem obdobju preučevanja kraških pod- zemeljskih voda porajale različne predstave in razlage. Vznikle so različne hipoteze in teorije, ki so slonele na omejenih spoznanjih in ugotovitvah iz raz- ličnih kraških predelov (A. Grund, 1903; F. Kat z er, 1909; J. Cvijic, 1918; O. Le hm a n n, 1932). Postopno pa se je znanje iz;popolnjevalo in tako so se dopolnile tudi teorije o razporeditvi in povezanostih kraških voda (F. Jen- k o, 1959; B. Geze, 1958, 1965; A. Mangi n, 1975). Zaradi različne prevot- ljenosti in prepustnosti so torej vode v krasu zelo različno razporejene, zato krajevno veljajo lahko tudi povsem nasprotne teorije. V tem prispevku želim predstaviti razporeditev vodne gladine v No- tranjskem in Primorskem krasu, kakor smo jo sodelavci Inštituta za raziskova- nje krasa ZRC SAZU lahko spoznali na podlagi občasnih in nepovezanih opa- zovanj. Škoda je, ker ni bilo mogoče opraviti sistematičnih meritev hkrati v različnih predelih in ob različnih vodnih razmerah. Tako ne poznamo nihanja vodne gladine ob postopnem praznjenju ali naglem polnjenju podzemlja, ne v bližnjih, še manj v bolj oddaljenih delih istega kraškega povodja. 39 Acta carsologica XIII, 1984 (1985) IZHODišCE Položaj in nihanje podzemeljskih kraških voda v povodju Ljubljanice in Notranjske Reke ter v delu visokega krasa med Idrijco in Vipavo smo občasno opazovali ob kraških iz;ririh in ob ponorih ter v dostopnih vodnih jamah v letih od 1963 do 1984. Položaj kraških izvirov je odvisen predvsem od geološke zgradbe in geo- morfološkega razvoja, ki skupno opredeljujeta hidrogeološke značilnosti njiho- vega zaledja. Z geološko zgradbo je dana razporeditev propustnih, delno pre- pustnih in nepropustnih kamnin. Te kamnine pa so bile izpostavljene podneb- nim silam, oziroma geomorfološkim procesom, ki so jim vtisnili svoj pečat, v nekraških predelih predvsem na površju, v prepustnih kraških predelih pa tudi v podzemlju. Iz kraškega podzemlja se prelivajo vode na površje v višini abso- lutnih ali lokalnih kraških erozijskih baz, ki jih predstavlja morje ali najnižja vrzel v nepropustnem obrobju krasa. Voda pa se v krasu pretaka sifonsko tudi precej globlje. Način iztekanja vode iz kraškega podzemlja je odvisen od položaja izvira in od hidrogeoloških značilnosti njegovega zaledja, to je predvsem od prevot- ljenosti in prepustnosti kamnin. Od razporeditve in stopnje prepustnosti je namreč odvisen tudi način podzemeljskega pretakanja vode v krasu. Neposredno spoznavanje kraškega podzemeljskega pretakanja je omejeno, ker večina podzemeljskih vodnih poti ni dostopnih. To pomeni, da lahko kraški vodni sistem le delno spoznamo in to posredno na različne načine. Znanje o pretakanju in razporeditvi vode v krasu se le počasi izpopolnjuje. Kljub bogati tradiciji hidroloških in speleoloških preučevanj našega krasa so le redka ob- močja zadovoljivo preučena, saj so za zahtevnejše raziskovalne postopke po- trebna znatna sredstva, ki so na voljo le ob izgradnji večjih energetskih ali drugih vodnogospodarskih objektov. Pretežni del krasa pa je prepuščen bolj slučajnemu raziskovanju, pri katerem imajo pomemben delež tudi člani jamar- skih organizacij. Kraška vodna gladina predstavlja jasno mejo med zalitim in nezalitim de- lom krasa. Ker je voda v razpokani kamnini z omejeno prepustnostjo neena- komerno razporejena, meja med zalitim in nezalitim krasom ni ne sklenjena, ne ravna ploskev. Voda zaliva le votline in pore v kamnini, zato je njena po- vršina razčlenjena v mrežo bolj ali manj povezanih prostih gladin in pritis- njenih vodnih površin v razpokah in špranjah, rovih in drugih votlinah ter v vmesnih kamninah. Tako so vodne ploskve tudi po višini različno razporejene. V splošnem je gladina kraške podzemeljske vode stopnjasta ali rahlo nagnjena k izvirom. Znotraj zakrasele kamnine pa je lahko krajevno stopnjasta in nag- njena od manj prevodnih k bolj prevodnim žilam in tokovom. Izviri in pogla- vitne vodne žile predstavljajo lokalne hidrografske baze, h katerim so usmer- jene razpoklinske in kraške vode. Proste in pritisnjene vode so v medsebojni tlačni ali piezometrski zvezi, če so žile v kamnini dovolj razvejane in prevodne. Povezanost kraških vodnih gladin se odraža v skladnem nihanju prostih gladin. Te lahko primerjamo le v dostopnih vodnih jamah in breznih, posredno pa jih dosežemo z vrtinami. Naravni dostopi do podzemeljskih voda v krasu so razmeroma redki, poleg tega pa so odvisni tudi od stopnje speleološke raziskanosti terena ter jamarske 40 P. Habič, Vodna gladina v Notranjskem in Primorskem krasu Slovenije izurienosti in opremljenosti. V Sloveniji imamo dolgo tradicijo v raziskovanju kraškega podzemlja. Doslej je med 5000 znanimi jamami komaj 9 % vodnih jam, od tega nekaj več kot ena tretina izvirnih, ena četrtina ponornih in le v dobri četrtini, to je v 140 jamah, pridemo do podzemeljskih voda (P. Habič, I. Kenda, 1981). Opazovanja nihanja voda v teh jamah so še posebej dragocena, saj z raz- meroma skromnimi sredstvi spoznavamo pomembne vodne razmere v kraškem podzemlju. Seveda moramo pri tem upoštevati omejeno natančnost in zanes- ljivost. številna opazovanja niso povezana, podatki veljajo le za določene tre- nutke ob slučajnih jamarskih obiskih. Le redko so ti sistematično organizirani. Praksa kaže, da je vsaj občasno sodelovanje z jamarskimi organizacijami pri spremljanju vodnih razmer v krasu lahko zelo uspešno. Na ta način so bili zbrani v porečju kraške Ljubljanice in Notranjske Reke zanimivi podatki o položaju vodne gladine v različnih hidroloških situacijah, predvsem v najbolj sušnih razmerah, pa tudi ob katastrofalnih poplavah. Podatki o razporeditvi in nihanju kraške vodne gladine so delno že ob- javljeni, nekaj pa jih je ostalo v terenskih zapisnikih po opazovanjih in me- ritvah, opravljenih tudi v okviru Inštituta za raziskovanje krasa ZRC SAZU v Postojni, bodisi po rednem programu, ki ga financira Raziskovalna skupnost Slovenije, ali pa po posebnih pogodbenih nalogah različnih naročnikov. Vsem, ki so pomagali zbirati podatke, se na tem mestu še posebej zahvaljujem. Zbrano gradivo nam vkljub pomanjkljivosti omogoča vsaj približno pred- stavo o vodnih razmerah v raznih delih Notranjskega in Primorskega krasa. S tem prispevkom želim tudi vzpobuditi natančnejša opazovanja kraških pod- zemeljskih voda. Vodomerna služba je namreč preveč omejena samo na površje, v kraškem podzemlju pa nimamo nobene stalne opazovalne postaje, čeprav že dalj časa skušajo hidrologi in hidrotehniki razvozlati kraške vodne uganke. Sistematične hidrološke raziskave so bile zastavljene le na obrobju Planinskega polja (M. Brezni k, 1962) in na območju matičnega Krasa (P. Kri vic, 1982, 1983), ki so dale prav zanimive rezultate. Na podoben način bi s sodobno me- rilno opremo in opazovalno tehniko lahko zbrali bolj zanesljive in dragocene podatke, ki jih potrebujemo ne le v strogo teoretičnem, temveč še bolj v prak- tičnem pogledu. Poznavanje vodnih razmer v kraškem podzemlju postaja vse pomembnejše zaradi naraščajoče izrabe kraških voda in njihove onesnaženosti. VODNA GLADINA V IZVIRIH LJUBLJANICE PRI VRHNIKI Kraški izviri Ljubljanice so razporejeni na razdalji 4 km ob zahodnem robu Ljubljanskega barja v predelu med Vrhniko in Bistro. Podzemeljske kra- ške vode se prelivajo na površje v treh poglavitnih skupinah, ki napajajo izvire Velike in Male Ljubljanice, Lubije in Bistre. Na zahodni strani so še izviri Hribskega potoka ter Primcov in Bečkajev studenec, ki se skupaj s površinsko Belo izlivajo v Malo Ljubljanico. Izviri Male Ljubljanice so razporejeni v iz- raziti zatrepni dolini Malega in Velika Močilnika pri Vrhniki, izviri Velike Ljubljanice pa v zatrepni dolini Retovje pri Verdu. Izviri Lubije so razvrščeni v Verdu na razdalji 500 m, in sicer od Smukovega in Gradarjevega brezna do Ceglarjevega potoka. V Bistri so ob vznožju strme rebri Pokojiške planote tri 41 "'" t-:1 - mite bottom of Cerknica polje which otherwise controls the water table in Javor- niki. A special hydrogeological unit with higher karst water table lies east :kom Cerknica lake, from Slivnica towards BlOlke and Racna gora. There the karst water table does not lower under 560 m, shown by the springs of Zerovnica, Stebrščica and by water in Mrzla and Križna jama. TJ1e hydro-contour line 550 m extends under Loško polje presumably as in Golobina near Dane the low water is on 542 m, continuing on the other side of Idrija fault zone into Snežnik massif. The karst water table in Javorniki near the springs of Unica and Malenščica is a bit above 450 m a.s.l. Rega,rding the water conditions in Postojnska jama, Pla- ninska jama, Rakov Škocjan and in Karlovicčl as well in Svinjska jama we infer that under Javorniki there are two or even three outflow directions. The karnt water table is possibly tightened up in the central part of Javorniki and lowered on both sides towards Pivka and towards Cerknica polje. At these bovders the level lowers under Javorniki, but it is not yet cle11r whether the springs in Malni are fed by two streams, from Postojna and Cerknica, or by the uniform stream from Javorniki. Peak-flow towards Pivka and lower flow towards Cerknica remain pos- sible. A special outflow system of karst water is presented by Postojnska jama and Pivka branch in Planinska jama where separated flow is formed wi hout direct connection with Javorniki flow towards Malni as far is now known. The data on water table in Kobilje griže, near Stara vas, ž;eje and in Matijeva jama on Palško jezero show that the karst water table along P,ivka lowers for more thar. 20 m under the outflow border at the valley of Upper Pivka and thus near Zag,orje it remains on Hill 550 m only. Between Zagorje and Knežak there is underground wa,tershed, a part of waters being directed towards Pods,terrjšček and a pa,rt towa,rds Bis rica where the karst water table lowers for more than 100 m. We suppose that in the cen~ral Javorniki ridge and in Snežnik the water table remains on 650 m. Unfort- unately this part is speleologically not yet explored as far as to reach the under- ground karst water. The distribution of karst waters in neighbour river basins is interesting too. On watershed between Notranjska Reka and Vipava there is special hydrogeological unit of Slavina karst with Košana valley and Vremščica. Near Neverke the wacer lowers :under the Sušica valley for more that 100 m and we find in the c'aV!e Gabranca under 292 m a.s.l. At high waters Sušica spnng flows from it lin the 75 40 Acta carsologica XIII, 1984 (1985) a1titude of 415 m. In Škocjanske jame and in Kačna jama the water level lowers to 150 or 100 m above the sea level, while at floods it increases in Kačna jama up to 260 m and in Škocjanske jame even to 344 m. In Labodnica near Trebče the lowest level is 12 m above the sea, and the high- est 110 m. In the background of Timavo springs, where the influence of high tide is already felt, near Brestovka the level does not lower under 2 m, but increases near Klariči up to 7 m and near Brestovica to 16 m. As the low water table in Doberdob is higher than near Brestovica we suppose that the lake is fed by Soča groundwater through the Kras. Chemical and temperature properties of springs between Mošče­ nice and Doberdob lake correspond as well. In this region also Vipava contributes to karst underground water inflitrating into Kras between Miren and Sovodnje. In the background of Sežana and Osapska reka the water conditions are rela- tively badly known. In Rižana spring the discharges have greater oscillations than the level, being on the altitude about 70 m, in Osapska jama the water decreases for more than 50 m, when the spring on the altitude about 100 m dries up; small are the oscillations in Boljunec too. In Matarski kras the underground waters are accessible in caught siphons of Brkini s.inking streams in different altitudes bet- ween 280 and 500 m. Permanent flow is accessible in Dimnice only on the altitude 470-450 m, and the karst water table probably gradually lower;; under Slavnik to- wards Rižana. The watershed between Timavo and Rižana in Kozina karst is not yet explained but partial overflowing of Brkini and Slavnik waters towards La- bodnica and Timavo and towards Rižana is possible. About the karst water distribution in the background of Vipava under Nanos and Hrušica there are no useful data. Probably the karst water table gradually in- creases from Vipava springs, where it is on the altitude about 100 m to the 400 m on the ponor edge near Predjama. According to water conditions in Predjama and Jama v Grapi the karst water increases towards Belsko. The ponor cave Lokve ha:s a siphon in the altitude 427 m but probably the water is caught there. In Jama v Grapi the sinking stream lowers from 506 m near the entrance to 492 m in the out- flow siphon. In Sever Hall in Predjama the permanent brook flows on 456 m (F. Habe, 1970, 1976). The karst water table increases steeply towards the Zagora dolomite where the unknown watershed between Vipava and Ljubljanica wacers is above 550 m at least. · The underground watershed in Hrušica is not clearly defined. The real waters- hed role plays flysch zone probably extending from Col, Podkraj and Vodice to- wards Lom (L. Placer, J. Car, 1974). The flysch is permeable there and waters sink into kars.tifi.ed limestones. The karst water leve! is somewhat higher in the dolomite of fourth nappe where above črni vrh smaller outflow springs are found. Karst water in the region of črni vrh plateau is directed towards Divje jezero and Pod- roteja where the Idrijca valley restrains it in the ,altitude above 300 m, but even towards Hubelj. proved by water tracing (P. Habič, 1984). The karst water table remains under the Zala valley loosing the water in its own river bed there where it is cut into Cretaceous limestones. From dolomite karst around Godovič and Ho- tedršica all the brooks sink when reaching the Cretaceous limestones, underlying the Triassic dolomites and shales. In the limestones under dolomitic nappe the watershed between Idrijca and Ljubljanica was proved by water tracing (SUWT, 1976). In the region among Hotedršica, Rovte and Logatec there is peculiar karst area where one part of waters superficially flows to the main ponors, while the other part sink directly into karstified base. The karst water table is in this region somewhere in dolomite, elsewhere in limestones thus it probably exists even in more branches than in the neighbour, mostly limestone rocks. The altitude of the table is not known, but we suppose that it is a bit higher than under the Logatec plateau. In the karst between Idrijca and Vipava, that means the background of Hu- belj, Lijak and Mrzlek springs, the underground water 1s not accessible. The pre- cipitations and springs, distributed differently high on the con"act of limestone and flysch, are controlling it. Hubelj and Mrzlek have probably separated catchment areas, Lijak is active after heavy rains only when the water table in Mrzlek back- ground increases to the outflow border in the alti,tude of about 100 m. After the 76 P. Habič, Vodna gladina v Notranjskem in Primorskem krasu Slovenije 41 water tracing of Cepovan brook, when the dyes were found in the springs of Hoteš- ček near Idrijca, in Avšček on west and in Mrzlek on south we conclude, that the low karst water table in the center of Trnovski gozd and on Banjšice plateau so- mewhere in the altitude between 200 and 300 m can flow to three different di-rec- tions. General hydrological properties, dictated by the size and situation of the catch- ment area and by distribution of springs on karst border are controlling the distri- bution and karst water oscillations. But interna!, local, partial or complete dams, posed by lithological and structural units, specially if they are tectcmically displa- ced, are important. In smaller degree but not without temporary important effects, even the secundary karst phenomena as are collapses and breakdowns in under- ground channels influence to distribution and oscillation of karst waters. An im- portant role is played by alluvial sediments transported by superficial waters from impermeable vicinity and deposited in the karst underground decreasing the trans- missivity and permeability of karst. Artificial daming and controlling of karst waters regime is rather modest in the karst of Notranjsko and Primorsko. Formerly local dams of karst springs, 1-2 m high were popular for water power exploitation. Experiments by daming the ponors on Cerknica polje are more recent. Intervention of man on springs or ponors cannot essentially influence to the entire water con- ditions in karst (P. Habič, 1974). Speleological researches among Postojna, Planina and Cerknica (I. Gams, 1965; R. G.Yspodarič, 1976), but also on Cerknica lake (R. Gospodarič & P. Habič, 1979) and on Planina polje (R. Gospodarič, 1982; F. Šušteršič, 1982), in Škocjanske jame (R. Gospodarič, 1984) and elsewhere on Notranjsko and Primorsko karst contributed valuable data on distribution of water table and illustrated the caves development and speleological going on in Quaternary. In geological past the water conditions in the ka.,,t u;1derg:r~und changed several times. Temporary the actual dry caves were flooded and thick layers of flood loams or even gravel were deposited. Other- wise some ac;ual act1ve channels were at least for some tirne dry and flowstones were deposited in them. Somewhere the actual waters reach older spacious chan- nels. In them the waters stay still and suspend material but we could expect that they flow through quickly. Thus older channels do not oontribute to bigger karst permeability, they render possible bigger periodical underground accumulafr:ms o"lly. The limited permeability or maximisation of the karst underground water flow (I. Gams, 1970) does not correspond to bigger karst cavernosity in higher lying zones. Permeability of other spacious channels is partly limited by breakdowns, as we can ascertain along the underground Pivka, Rak and Notranjska Reka. The main reason for changes in the kars,t underground permeabilitiy probably lies in young differentiated tectonic dynamics of structural units being reflected in the relief too (P. Habič, 1982 a, 1984 a). Neotectonics produces in the karst underground always new hydrogeological conditions to which the underground waters differently react. Among the blocks the waters force their way above the old channels which are somewhere filled up by sediments. In lifted karst units waters choose new fissures and cracks or deepen their old river beds. Unconcordant big gradients on the spring side of karst and other tectonic basins and more leve11ed gradients on the ponor side correspond well. Where the underground water ways are not yet adapted to actual hydrologic conditions, bigger oscillations of water table occur, either at springs or at ponors but even in interjacent regions locally. Undeveloped underground water flows are found in the regions where the underground waters runoff is diverted into other river basin because of intesive erosion of impermeable karst border. Such conditions are found specially on Black Sea - Adriatic watershed. ln karst with gradually distributed water table, being the results of limited karst and fissure permeability, the possibilities for efficaceous static and dynamic water reserves by pumping wells are diminished. But the dynamic water reserves are not distributed only in the phreatic zone of water table oscillations but also in vadose karst above the permanent leve!, where through fissures and joints pre- cipitations percolate from the surface, feeding karst water permanently. 77