UD K 551.444.5 Nastanek zaslanjenih kraških izvirov in njihova sanacija Marko Breznik Vsebina 1. UVOD .........................84 2. RAZLAGA POMEMBNIH IZRAZOV, UPORABLJENIH V RAZPRAVI 86 3. LITERATURA O ZASLANJEVANJU IZVIROV.........87 3.1. Pregled del o zaslanjenih izvirih.............87 3.2. Razlage zaslanjevanja v zrnatih sedimentih.........88 3.3. Razlage zaslanjevanja v zakraselih sedimentih........89 4. OPIS NEKATERIH ZASLANJENIH IZVIROV.........94 4.1. Brojnica pri Trstu...................94 4.2. Izviri v Sečovljanski dolini...............95 4.3. Izvir Blaž v Istri...................100 4.4. Izviri južno od Senja.................. 4.5. Izviri v zalivu Poljice blizu Trogira............103 4.6. Izvir Pantan pri Trogiru................104 4.7. Izvir Pištica pri Komiži na otoku Visu...........106 4.8. Postirska dolina na Braču................107 4.9. Zrnovica pri Gradacu................. 4.10. Izviri v Morinjskem zalivu v Boki Kotorski.........110 4.11. Brojnice pri La Mortoli na italijansko francoski meji.....116 4.12. Brojnice pri Tarantu v Italiji..............I17 4.13. Brojnica Cadimare pri Speziji v Italiji...........117 4.14. Izvir in brojnice Ayios Georgios pri Kiveriju v Grčiji.....117 4.15. Morski požiralniki na otoku Kefalonija..........117 4.16. Izvir Almyros Irakliou v Grčiji..............118 5. ZASLANJEVANJE KRAŠKIH IZVIROV IN NJIH KLASIFIKACIJA 121 5.1. Zaslanjevanje zaradi večje gostote morske vode........121 5.11. Brojnice z zaslanitvijo v ustju izvira..........121 5.12. Zaslanjeni izviri v izotropno prepustnem kraškem vodonosniku 122 5.13. Zaslanjeni izviri v anizotropno prepustnem kraškem vodonosniku .....................I22 5.131. Zaslanjeni izviri v anizotropno prepustnem kraškem vodonosniku s plitvim razcepom.............125 5.132. Zaslanjeni izviri v anizotropno prepustnem kraškem vodonosniku z globokim razcepom............125 5.2. Zaslanjevanje s srkanjem morja zaradi hidrodinamičnega učinka 126 5.3. Kombiniran način zaslanjevanja.............128 6. SANACIJA ZASLANJENIH IZVIROV.............129 6.1. Sanacija izvirov, ki se zaslanjujejo zaradi večje gostote morske vode ...................... i .jo 6.11. Sanacija brojnic, ki se zaslanjujejo v ustju izvira . . 6.12. Sanacija zaslanjenih izvirov v izotropno prepustnem kraškem vodonosniku .................. 6.13. Sanacija zaslanjenih izvirov v anizotropno prepustnem kra škem vodonosniku................ 6.131. Sanacija z dvigom gladine izvira........ 6.132. Sanacija s tesnitvijo spodnje žile........ 6.133. Sanacija z zajetjem sladke vode v notranjosti krasa . 6.2. Sanacija izvirov, zaslanjenih s srkanjem morja zaradi hidrodina-mičnega vpliva................... 6.3. Sanacija izvirov, zaslanjenih s kombinacijo vplivov večje gostote morske vode in hidrodinamičnega učinka......... 7. GOSPODARNOST SANACIJ ZASLANJENIH KRAŠKIH IZVIROV 7.1. Cena vode saniranih izvirov.............. 7.2. Cena sladke vode, pridobljene iz morja ali somornice .... 7.3. Primerjava načinov preskrbe s sladko vodo........ 8. SKLEP......... 9. ZAHVALA 10. Slovstvo 1. UVOD Kraški izviri odvodnjavajo večji del zakraselega hribovja v zaledju. Zaradi prodora morske vode v notranjost krasa se pogosto zaslanijo in njihova voda potem ni uporabna. Ker pa sladke vode v primorju močno primanjkuje, je sanacija teh izvirov izrednega pomena za prebivalstvo in gospodarstvo. Ameriški hidrogeolog K oh out (1966) je preučeval vpliv prodora morske vode v vodonosne zrnate sedimente na Floridi. Po njegovih podatkih do zadnjih let niso posvečali dovolj skrbi izvirom na morskem dnu, saj je bilo na vsem svetu izvedenih samo 15 znanstvenih raziskav tega pogostnega pojava. Poskusi zajetja pa niso mnogo napredovali od dobe Feničanov, ki so pokrivali take izvire s svinčenimi lijaki, jih zasuli in po ceveh speljali vodo iz lijakov. Večji del jugoslovanske obale in širok pas zaledja sestoji iz zakraselih karbonatnih sedimentov. Sistematične raziskave slanih izvirov pri nas so se pričele pred drugo svetovno vojno (I. Kuščer, 1946), njihovo delovanje pa je bilo pojasnjeno v petdesetih letih (G j u r a š i n , 1942, 1943; I. Kuščer, 1950). Obsežne raziskave in poskusi sanacij so delo zadnjih 15 let (si. 1). Istočasno so v manjšem obsegu raziskovali v Libanonu, Španiji, Franciji in Italiji ter v večjem v Grčiji, kjer sem sodeloval. Za raziskave v zadnjem desetletju je značilno, da so bile vodene iz določenih centrov in da med seboj niso bile koordinirane. Izmenjave izkušenj skoraj ni bilo, večina rezultatov še ni objavljena. SI. 1. Zaslanjeni in sanirani kraški izviri na jadranski obali in otokih, omenjeni v razpravi Fig. 1. Brackish and desalted karstic springs along the Adriatic coast and islands mentioned in the paper Naša razprava vsebuje detajlni opis raziskav in sanacij več kot 20 slanih izvirov. Poleg tega podaja kriterij za njihovo klasifikacijo, oceno možnosti za sanacijo v različnih hidrogeoloških razmerah, pregled sanacijskih stroškov in primerjavo cene pitne vode, pridobljene iz morja in somornice s ceno vode saniranih zaslanjenih izvirov. 2. RAZLAGA POMEMBNIH IZRAZOV, UPORABLJENIH V RAZPRAVI Izotropno prepusten kraški vodonosnik vsebuje množico razpok, manjših kanalov in votlinic, ki so dobro povezani v vseh smereh. Pretakanje vode je možno v vseh smereh, ni privilegiranih smeri cirkulacije. Takšna je površinska zakrasela cona, kadar je potopljena. Primer takšnega vodo-nosnika je zakrasel peščenjak na izraelski obali. Pretok vode je podoben pretoku podtalnice v zrnatih sedimentih. Anizotropno prepusten kraški vodonosnik je karakteriziran s posameznimi zakraselimi conami in vmesnimi malo zakraselimi bloki. Voda se pretaka po posameznih žilah, ki imajo veliko prepustnost v vzdolžni smeri in majhno v prečni. Pretok je podoben pretoku po sistemu cevi, ki niso na gosto razporejene. Vodonosnik. Plast, zaporedje plasti ali del plasti s porami, zapolnjenimi z vodo, ki ni kemično ali fizikalno vezana. Ustreza tujemu izrazu aquifer. Kraška podtalnica. Voda, ki zapolnjuje kraške pore in žile v potopljeni coni, in ki ni kemično ali fizikalno vezana. Prezračena cona. V tej coni so kraške pore zapolnjene z zrakom in vodo. Skozi njo pronica ali se pretaka voda v globino proti potopljeni coni. Potopljena ali zasičena cona. V njej so pore zapolnjene z vodo. Sladkovodna cona je vodonosnik s sladkovodno podtalnico. Somorniška cona je vodonosnik s somornico. Morska cona je vodonosnik z morsko vodo. Ta cona se od obale proti celini spušča v globino. Mejna ploskev je ploskev, ki razmejuje sladko in morsko podtalnico v izotropno prepustnem kraškem ali zrnatem vodonosniku. Ta meja je včasih ostra, navadno pa je bolj ali manj široka in se imenuje prehodna cona ali cona mešanja. Peta mejne ploskve je v globini, kjer se priključi mejna ploskev na neprepustne plasti pod vodonosnikom. Ravnotežna ploskev je namišljena ploskev, ki povezuje v anizotropno prepustnem kraškem vodonosniku tiste točke žile in razcepa, kjer sta vodna pritiska s sladkovodne in morske strani v ravnotežju. Peta ravnotežne ploskve je v globini, kjer se priključi ravnotežna ploskev na neprepustne plasti pod vodonosnikom. Ravnotežni pretok sladkega izvira imenujemo pretok tik pred njegovo zaslanitvijo. Zaslanjen izvir je splošen pojem, ki obsega tudi izvirajočo vodo, žilo in kraj, kjer voda izvira. Brojnica je izvir na morskem dnu s sladko ali zaslanjeno vodo. Ustreza hrvaškosrbskemu izrazu vrulja. Morski požiralnik je odprtina na morskem dnu, ali ob obrežju, ki občasno ali stalno požira morje. Morska estavela je brojnica, ki se v suši spremeni v morski požiralnik. 2ila je splošen pojem za cono, ki je močno prepustna v smeri toka in malo prepustna v prečni smeri. Po žilah se pretaka podtalnica v anizo-tropno prepustnem kraškem vodonosniku. Oblika žile ni definirana, to je lahko kraški rov, prepustna razpokana cona, splet razpok in votlinic itd. Razcep žile ali kratko razcep je mesto, kjer se cepi dovodna žila v spodnjo žilo, ki ima zvezo z morjem, in zgornjo žilo, ki vodi do izvira. Morje pomeni tudi morsko vodo. Voda pomeni tudi sladko, svežo vodo kraške podtalnice. Brakična voda ali somornica pomeni zmes sladke in morske vode. Varen pretok črpanja je količina vode, ki jo lahko črpamo iz vodonos-nika in s tem ne povzročimo nezaželenih posledic, npr. zaslanjenja ali stalnega znižanja piezometrične gladine. Slanost je količina soli v vodi. Morska voda vsebuje predvsem NaCl, MgS04 in CaC03. Slanost podajamo s količino klorovih ionov v miligramih na liter tekočine. Voda Sredozemskega morja ima okrog 21000 mg/l C1 . Dopustna slanost je količina soli v vodi, ki še ne vpliva škodljivo na ljudi in živali ali na rastlinstvo. Za pitno vodo je jugoslovanska norma 250 mg/l Čl" Norma za pitno vodo se v svetu stalno povečava, nekateri menijo, da 500 mg/l ne škoduje, posebno v suhem podnebju. Mnogo vasi v Sredozemlju pije vodo, ki vsebuje prek 500 mg/l, beduini v Sahari do 2000 mg/l Čl" Slanost do 300 mgA nima vpliva na okus, voda s 300 do 1000 mg/l je »plehka« in prek 1000 mgA je slana. Od rastlin so občutljive pomaranče, ki zahtevajo vodo z manj kot 100 mgA CI" V kmetijstvu je možno uporabiti za nekatere rastline še vodo s 1000 mgACl- (Tunis, Izrael). Važno pa je, da je zemlja prepustna, da se v času deževja izpere in da se sol v njej ne nabira. 3. LITERATURA O ZASLANJEVANJU IZVIROV 3.1. Pregled del o zaslanjenih izvirih Presenetljivo dobro predstavo o zaslanjevanju izvira je imel Lau-rentis de Monacis že leta 1364 (Patakis, 1968). Opisal je izvir Almyros s slano vodo poleti in sladko pozimi »iz jame... izvira z veliko močjo slana rečica. Izliva se v morje, s katerim je povezana s podzemeljskimi kanali... pozimi voda ni slana, ker se dež s hribov zliva v dolino in jamo ter osladi izvir...« (Anno Domini 1364, sexti Mai... Et spelunca vero, quae est penes radicem dieti Strumbuli (gora nad izvirom op. av.) a dicta parte Orientali exit cum impetu magnus globus salsarem aquarum, quae vementes a man per subterraneos anfractus emittuntur per ora dietae speluncae; a salsedine vero locus ille dicitur Almiro. Inhieme vero non sunt ita salsae; nam a pluviis de contiguis montibus in valles defluentibus et penes illam speluncam cadentibus aliquantulum dulciorantur). V prejšnjem in sedanjem stoletju so vzbudili največje zanimanje morski požiralniki pri Argostolionu. Brown (1835) je domneval, da je gladina morja ob požiralnikih višja kakor v ostalem delu zaliva. Po Stricklandu (1835) naj bi voda, ki ponira, izparevala na kon- taktu z velikansko maso, ter se v globini ponovno kondenzirala in izvirala v toplih izvirih. Davy (1836) je mislil, da glina in lapor vpijata to vodo, nabrekata in povzročata potrese. P tickler (1841) je je veroval v odtok v morje z nižjo gladino. Po Moussonu (1858) se voda v veliki globini ogreje, postane zato lažja in se dviga ter ponovno izvira. Unger in Ansted sta menila, da se ponikla voda dviga s ka-pilarnimi silami in na površju izpareva (Glanz, 1965). Prvi teoriji, ki sta fizikalno sprejemljivi, sta Fouquejeva in Wieblova. Fou qu 6 (1867) je trdil, da izvira ponikla voda v zaslanjenih izvirih v zalivu Livadi. Gladina v morskih ponorih je nižja zaradi večje specifične teže slane vode. W i eb el (1874) je opazoval izvire na otoku. Po njegovem mišljenju je sesalni učinek v rovih, ki odvajajo sladke vode, vzrok po-niranja morja. Pravilno je sklepal na zvezo z izviri v zalivu Sami, ker mu je bil pretok izvirov v Argostolskem zalivu premajhen. Lehman (1933) je dopolnil Wieblovo teorijo s potrebnimi zožitvami rovov. Badon-Ghyben (1888) in Herzberg (1901) sta postavila za zrnate sedimente teorijo o mešanju morja z vodo zaradi različnih prostor-ninskih tež. Za tekočo podtalnico je to teorijo dopolnil H u b b e r t (1940), za razmere, kjer je med vodo in morjem večja prehodna cona, pa sta jo prikrojila Cooper (1959) in Luscynski (1961). Za zaslanjene kraške izvire je Gjurašin (1942 in 1943) uporabil teorijo različnih prostorninskih tež, ki jo je K u š č er (1950) podal v bolj splošni obliki in dodal možen vpliv sesanja. Mijatovič (1966) je izdelal model vdora morja na podlagi različnih prostorninskih tež. Glanz (1965) je z modelom skušal dokazati, da je kinetična energija vode v rovih, usmerjenih k izvirom, v zalivu Sami vzrok za podtlak v kraškem kanalu in vtok morja v požiralnike pri morskih mlinih pri Argostolionu. 3.2. Razlage zaslanjevanja v zrnatih sedimentih Ghyben-Herzbergovo pravilo o odnosih med morsko in sladko vodo temelji na njunih različnih prostorninskih težah (de W i e s t, 1965). Pogoja za njegovo veljavnost sta, da se tekočini ne mešata med seboj in da mirujeta. Pravilo je možno uporabiti v primeru, ko se podtalnica morske vode ne giblje, gibanje podtalnice sladke vode pa je počasno; tak primer imamo tedaj, ko je gladina podtalnice le malo napeta. G h y b e n -Herzbergova razlaga zaslanjevanja ne upošteva cone mešanja. Hubbert je ugotavljal mejno ploskev med morjem in vodo za hidro-dinamične pogoje in pokazal na omejeno uporabnost Ghyben-Herz-bergovega pravila ter na poenostavitve, ki jih vsebuje. Ob obali, kjer se podtalnica izliva v morje, se mora razviti taka strujna mreža, kjer se tokovnice dvigajo proti izviru, istočasno pa se gladina podtalnice spušča proti morski gladini. Globina mejne ploskve je večja kakor izračunana po Ghyben-Herzbergovi enačbi. Razlika je majhna za položne gradiente, napake pa so velike za strme gradiente. Luscynski je računal z gibanjem podtalnice in upošteval tudi obstoj cone mešanja. Vpeljal je nove pojme pri merjenju piezometričnih višin. Po njegovi metodi lahko računamo globino cone mešanja. Bossy (1970) je pokazal na primeru vodnjaka Bosse Crau, da je pri majhnem strmcu gladine podtalnice sladke vode in imobilni podtalnici morske vode možno uporabiti Ghyben-Herzbergovo pravilo za določitev globine mejne ploskve. Prehod iz sladke v morsko cono je bil nenaden, prehodna cona je bila tanjša od 2 m. Dreyfus in Vailleux (1970) sta preučevala veljavnost navedenih treh razlag na območju Wateringues ob Rokavskem prelivu. Edino metoda Luscynskega je dala dobre rezultate, vendar zahteva zelo precizna terenska merjenja in številne korekture rezultatov, kar omejuje njeno praktično uporabo. Rezultatov po Ghyben-Herzbergovi metodi sploh nista mogla uporabiti. Glavni vzrok je bil, da je piezometrični nivo v morski coni 2,80 m nad srednjo gladino morja, s katero računa ta metoda. Tudi rezultati računa po Hubbertovi metodi niso bili sprejemljivi. Hubbertova metoda podaja fiktivno mejno ploskev znotraj cone mešanja. Če pa zavzema cona mešanja 50% celotne višine, kakor v tem primeru, potem je seveda takšen rezultat preveč nedoločen. G h y -ben-Herzbergova in Hubbertova metoda naj bi bili uporabni le v primeru, kjer je cona mešanja tanka, kjer je podtalnica mirna in reagira malo na padavine in na sezonske spremembe. 3.3. Razlage zaslanjevanja v zakraselih sedimentih Lehmann (1932) je utemeljeval Wiebelovo razlago zaslanjevanja kraških izvirov po principu Venturijeve cevi. Dovodni rov je močno zožen na mestu, kjer se priključi spodnja žila, ki ima ustje pod morsko gladino. Po Lehmannovi razlagi bi moral biti izvir ob visokih vodah slan, ob nizkih pa sladek. V naravi pa je obratno, zato se G j u r a š i n ne strinja z Lehmannovo razlago. Po Gjurašinu je različna specifična teža morske in sladke vode vzrok, da morje vdira v izvire ob obali. Dovodni rov se cepi v večjo zgornjo žilo in manjšo spodnjo žilo, katere ustje mora biti pod morjem. Nadmorski izviri so slani le v primeru, če je izpolnjena naslednja neenačba: y kjer je y — specifična teža sladke vode, ym — specifična teža morske vode, hs — globina razcepa žil pod morsko gladino, kv — višina izvira nad morsko gladino. V odvisnosti od pretoka izvira lahko nastopijo naslednji trije primeri: 1. sladka voda izvira na zgornji in spodnji žili, 2. na zgornji žili izvira sladka voda, v spodnji pa miruje, 3. morje vteka na spodnji žili, na zgornji pa izvira somornica. Gjurašin je podal tudi grafikone za različna razmerja pretokov morske in sladke vode. Po njegovem mišljenju delujejo tudi morski mlini pri Argostolionu na principu različnih specifičnih tež in ne na hidro-dinamičnem principu, kakor je domneval L e h m a n n. Kuščer je s sodelavci (I. Kuščer, 1950; I. Kuščer in D. Kuščer, 1962) detajlno raziskal 4km obale južno ob Senja, kjer so izviri vod Like in Gacke. Opazovali so na desetine zaslanjenih izvirov in brojnic. Odkrili so morske požiralnike in morske estavele. Z barvanjem so ugotovili zvezo med morskim požiralnikom in zaslanjenimi izviri na obali. Najenostavnejši zaslanjeni izvir ima dovodno žilo, ki se cepi na spodnjo žilo, po kateri priteka morje, in na zgornjo (glavno) žilo, ki vodi k izviru (si. 2). Vzroka za dotok morja sta lahko dva: 1. hidrostatični zaradi večje specifične teže — če je razcep dovolj globoko — in 2. hidrodinamični zaradi ožine v razcepu. V prvem primeru požiralnik morje požira, v drugem pa sesa. Predstavljajmo si na si. 2, da je spodnja žila zaprta s pregradama A in B in da je vmesni prostor zvezan z izvirkom po umetni cevi C. Delovanje sistema je odvisno od tlačnih razlik P in S ob obeh pregradah. P = p' — p" = [p0 + Qm g (hm — hr)] — [p0 + qv g (ht — hr)] P = (Qm — 9v) g (hi — hr) ~omg (hi — hm) (a) Požiranje je možno le, če je P pozitiven, za kar mora biti Qm hi —hr>--. (hi — hm) = 36,4 . (ht — hm) (b) Qm — Qc S = P" - p"' = (1 _ fc)--&--1 . = C Qr2 (C) L2 Qr2 2 qč J kjer je: hidrostatični tlak v spodnji žili (m) p' hidrostatični tlak v umetni cevi (C) p" hidrostatični tlak v zgornji žili (s) p"' tlačna razlika med m in i p tlačna razlika med i in s S tlačna razlika zaradi trenja ws zračni tlak p0 gostota (g/cms) g pospešek prostega pada g višina nad določenim začetnim nivojem h višina gladine morske vode hm ploščina preseka žile q pretok, jakost vodnega toka Q hitrost v zastojni tlak ^L 2 pri znakih p, h, q, Q pomenijo indeksi: i izvirek, v sladko vodo v dovodni žili ali dovodno žilo, s somoirnico v zgornji žili ali zgornjo žilo, m morsko vodo v spodnji žili ali spodnjo žilo. m Po v- - x-=\ v=- SI.2. Skica zaslanjenega izvira (po I. Kuščerju, 1950) Fig. 2. Sketch of a brackish spring (after I. K u š č e r, 1950) Dovodna 211a Primary vein Razcep 211e Vein branching Spodnja žila Lower vein Zgornja žila Upper vein Zračni tlak Atmospheric pressure Hidrostatični tlak v spodnji Žili (m) Hydrostatic pressure of lower vein (m) Hidrostatični tlak v umetni cevi (C) Hydrostatic pressure of imaginary auxiliary tube (C) Hidrostatični tlak v zgornji žili (s) Hydrostatic pressure of upper vein (s) Višina nad določenim začetnim nivojem Height above some reference level Presek žile Cross section of the vein Vodni tok Water flow poprečna hitrost Mean velocity Enačba (c) je le aproksimativna rešitev za visoko Reynoldsovo število in kaže, da je S sorazmeren kvadratu pretoka. Konstanta k{—l 0, toda ni dovolj ozek, S< 0. Izvir je zaslanjen samo pri gibkem pretoku. Slanost pojema z rastočim tokom in preneha pri pretoku Q*=]/-| (d) kadar je P + S = 0. Ce se pretok Se poveča, vdere sladka voda v spodnjo žilo. Tip S: Nasprotno deluje izvir z ozkim razcepom S> 0, ki ne leži dovolj globoko, P<0. Izvir je zaslanjen samo pri velikem pretoku, ko pretok preseže vrednost Q0. Tip N: Ce sta P < 0 in S < 0 se izvir seveda ne more zaslaniti. Splošno veljavne formule za odvisnost slanosti od pretoka ni. Pri zelo šibkem toku se slanost približa naslednji hidrostatično določeni mejni vrednosti , Qm (hi — hm) p o0 = 1 —--= „__(e) (&m — ev) (hi — hr) — g (hi — hr) Opazovanja so pokazala, da so izviri ob veliki vodi sladki, ob suši pa slani in da slanost raste s pojemanjem pretoka. To se ujema s hidrostatično razlago; zato trdi Kuščer, da sili morje v zaslanjene izvire zaradi večje specifične teže pri dovolj globokem razcepu. Hidrodinamična razlaga ne drži, ker bi morali biti izviri bolj slani ob veliki vodi, opazovanja pa kažejo, da niso. Potem ko sta Mauri n in Zotl dokazala, da morje, ki ponira pri Argostolionu, izvira v zaslanjenih izvirih v 15 km oddaljenem zalivu Sami, je G1 a n z preučeval hidravlični mehanizem morskih mlinov pri Argo^ stolionu. Zagovarjal je hidrodinamično teorijo in trdil, da sesanja morja ne moremo razložiti z obliko podzemeljskih kanalov po sistemu Ven-tunjeve cevi. Vtok morja v Argostolionu je tako velik (l,7m8/s) da bi si težko predstavljali tako veliko Venturijevo cev. Ce pa naj bi bilo več vzporednih Venturijevih cevi, si je zopet težko predstavljati njihovo sin-hronizirano delovanje, ker bi priključek enega rova z morsko vodo na mestu, kjer je v glavnem rovu majhna hitrost, lahko uničil sesalni učinek več Venturijevih cevi. V pleistocenu je bil sedanji zaliv Argostolion kraško polje s podzemeljskim odtokom v zaliv Sami. Plasti krednega apnenca glavnega gorstva na otoku vpadajo proti vzhodu, torej proti zalivu Sami, in glavni kraški kanali, ki odvajajo padavine s tega območja, vpadajo tudi proti vzhodu. Ce sedaj rov s tekočo vodo zadene na pleistocenski talni rov, napolnjen z morjem, bo pognal morsko vodo v smeri svojega gibanja. Svojo kinetično energijo, oziroma komponento impulza, usmerjeno v smeri talnega rova (spodnje žile), bo oddal morski vodi. To je princip črpalke s curkom ali ejektorske črpalke. Impulzi se lahko vzdolž talnega rova poljubno seštevajo; vsak nov curek sladke vode, ki se izliva v talni rov, pospeši v njem gibanje somornice. Curek deluje neodvisno od zračnega pritiska. ♦ * * t Ui * * * * m SI.3. Strujne mreže po Edelmanu (1966) Fig.3. Flow net on an island after the Dutch hypothesis (after Edelman, 1966) a) Strujna mreža naravnega toka podtalnice Flow net of the natural ground water flow b) Strujna mreža črpanja Flow net of pumping c) Kombinirana strujna mreza Combined flow net tno Morje Sea v Sladka voda Fresh water m Morska voda Sea water mm Mirujoča morska voda Stagnant sea water i. Napajanje podtalnice s padavinami 1 Recharge of ground water by preclpl-* tations Edelman (1966) je obravnaval problem hitre zaslanitve pri črpanju iz leče sladke vode, ki plava na morski vodi. V naravnih pogojih, ko padavine napajajo lečo sladke vode na otoku in se ta voda preceja proti izvirom na obali, pride med vodo in morjem do dinamičnega ravnotežja, ki je karakterizirano z zakrivljeno mejno ploskvijo (si. 3 a). Mejna ploskev med dvema tekočinama različne specifične teže, ki mirujeta, je horizontalna, pri dinamičnem ravnotežju pa je pogojena z enakomernim tokom vode proti izvirom na obali in z mirovanjem morja. Če pričnemo črpati iz podtalnice, ki ima povsod enako specifično težo, potekajo strujnice iz vseh smeri proti vodnjaku (si. 3b) ali drenažnemu rovu. Po metodi superpozicije dobimo kombinirano strujno mrežo tako, da v vsaki točki seštejemo fizikalne lastnosti osnovnih strujnih mrež. Pri črpanju iz plavajoče leče sladke vode potekajo zato nekatere strujnice tudi iz globljih plasti — iz morske cone — in zaslanijo vodnjak (si. 3c). v mo SI. 4. Zaslanjevanje po Baturiču (1961 in 1969) Fig. 4. Fresh water contamination after B a t u r i č (1961 and 1969) mo Morje Sea v Sladka voda Fresh water m Morska voda Sea water pr Neprepustna pregrada Impervious barrier s Somornica Brackish water gp Gladina podtalnice Ground water surface Po Baturiču (1959, 1961 in 1969) je razpokanost in drobna kaver-noznost apnenca tolikšna, da se kraška podtalnica normalno preceja po vsej kamenini in le izjemoma po kanalih. Pogoji precejanja v bližini obale so podobni precejanju v peščenih sedimentih, z izjemo, da so v apnencu možne neprepustne cone, ki tvorijo skoraj neprepustne vertikalne bariere. Te bariere so nekakšne viseče zavese (si. 4), prek katerih se voda preliva ali se pod njimi »podliva«. Morje ali somornica se »podliva« pod pregradami proti notranjosti zaradi razlike v prostorninski teži po Herzbergovem zakonu. Po Man delu (1971) prodira morska voda v vodonosno plast zaradi spremenjene porazdelitve potencialov, ki je posledica močne anizotropnosti apnenca. Stefanon (1971) trdi, da se vse brojnice zaslanjujejo v ustju. Brojnica izvira nekaj km zahodno od Trsta pod vasjo Sv. Križ. V italijanski literaturi je znana pod imenom »Le sorgenti d'Aurisina« (Boe-g a n, 1906). Izvir je na kraju, kjer se neprepustna flišna pregraja spusti malo pod gladino morja. Tu je na dolžini okrog 100 m 7 brojnic; ob oseki so nekatere nad gladino morja. Pri izviru je numulitni apnenec pod gladino morja, na obeh straneh pa ga loči od morja neprepustni fliš. Prve izvire so zajeli okrog leta 1860. Leta 1865 zajetje zaradi suše en mesec ni imelo dovolj vode, leta 1868 pa celo tri mesece. V letu 1867 je bilo vode malo in je bila slana. Po Boeganu (1906) je bilo temu vzrok 4. OPIS NEKATERIH ZASLANJENIH IZVIROV 4.1. Brojnica pri Trstu SI. 5. Gradnja pregrade v Brojnici pri Trstu leta 1901 (po B o e g a n u , 1906) Fig. 5. Dam construction at Brojnica near Triest in 1901 (after Boegan, 1906) nepopolno zajetje. Ostali izviri niso bili zajeti in so se izlivali v morje, ki je ob črpanju skozi nje tudi lahko prodrlo v zajetje. V tem času so ocenili zajetje kot neuspešno. Ko so potrebe Trsta po vodi narasle, so izvir leta 1901 dokončno zajeli (si. 5). 4.2. Izviri v Sečovljanski dolini Bujska antiklinala sestoji iz terciarnega in krednega apnenca, ki je važen kolektor podzemeljskih voda v severozahodni Istri. Večji del voda odteka proti jugu, kjer sta v Mirenski dolini zajeta izvira Mirna in Gra-dole. Njeno severovzhodno krilo vpada pod kotom 10° proti NE in se odvodnjava proti Sečovljanski dolini, kjer so izviri Bužini in Gabrieli oddaljeni 4, oziroma 3 km od morja (si. 6). Zaradi pomanjkanja pitne vode v Slovenskem primorju so se zanimali za vodne vire v Sečovljanski dolini že kmalu po vojni, posebno pa še po vdoru vode v premogovnik Sečovlje leta 1954. Jugovzhodni revir premogovnika Sečovlje (Breznik, 1956) so odkopavali v letih 1953 in 1954 v globini okrog 230 m. Dotok iz krovnine je bil 17 l/s in je leta 1954 v enem tednu narastel na 65 l/s, ko je krovnina počila. Takrat se je pretok iz vrtine S 7/2 v jamo zmanjšal in se je zopet normaliziral, ko so ta del jame potopili. Ob začetku raziskovalnih del decembra 1955 so kopali v 1. jugovzhodnem revirju. Mali potopljeni revir in 2. jugovzhodni revir sta bila zaprta in potopljena. Celoten dotok v jamo je bil 160 do 1901/sek in slanost 420 do 520 mgA Cl~ Dotok v 1. jugovzhodni revir je bil 120 do 150 l/s, od tega iz vrtine S 7/2 60 do 65 l/s in iz počene krovnine blizu vrtine 8/2 okrog 65 l/s. Voda tega revirja je vsebovala okrog 80 mg/l Cl", tudi njena bakteriološka analiza je bila ugodna. Kompaktni paleogenski apnenec v krovnim produktivnih plasti z jamskimi rovi je delno razpokan zaradi rudarskih del, ni pa zakrasel in tudi le malo naravno razpokan. Njegova neprepustnost je za apnenec nenavadna, kar dokazujejo tudi razmere pri čepu Malega potopljenega revirja v globini 227 m, kjer je bil na vodni strani pritisk 20 atm. Na zračni strani v razdalji 5 m vode ni bilo; apnenec je bil samo vlažen. Analiza podatkov je pokazala, da je globina zakraselosti omejena, ker je bil kredni apnenec, ki je sicer kolektor podzemeljskih voda v Bujski antiklinali, v jami vedno suh. Iz krednega apnenca, ki je talnina produktivnih plasti, ni bilo v jami nobenega dotoka vode. Slanost vode v 1. jugovzhodnem revirju 80 mgA Cl- je mnogo ugodnejša od norme za pitno vodo 250 mg/l. Tudi slanost vode iz celotne jame 420 do 520 mg/l kaže, da je vdor morske vode v rudnik kljub ogromni depresiji —230 m majhen. Ker so v teh letih nadaljevali odkopavanje v premogovniku, je bilo sklenjeno, da naj se preiščejo hidrogeološke razmere v dolini in da naj se poskuša s površja zajeti vodo, ki je dotekala v 1. jugovzhodni revir. Vrtanje štirih vrtin je pokazalo (Breznik, 1958), da so mlajše naplavine debele okrog 90 m in so povečini zaglinjene. Tudi del prodnatih plasti je bil slabo prepusten, kar na eni strani dokazuje, da v mlajših naplavinah ni podtalnice, ki bi jo bilo vredno zajeti, na drugi pa, da so mlajše naplavine kot celota slabo prepustne in da skozi nje morje ne doteka v apnenec. Morska voda delno prodira v Bujsko antiklinalo vzdolž njenega severovzhodnega roba, ki sestoji iz apnenca. Profil vrtine V-5, locirane v bližini stare vrtine S-7/2 na območju večjih dotokov v jamo je naslednji (ustje vrtine 0,0m je na koti okrog 6 m): 0,0— 89,0 m Meljnata peščena glina 89,0 — 90,8 m Preperel razpokan apnenec 90,8 —182,5 m Kompakten foraminiferni apnenec 182,5 —185,0 m Razpokan apnenec 185,0 — 190,0 m Kompakten apnenec Voda je pritekala v vrtino le v globini 182,5 do 185,0 m. Pri črpalnem poskusu 1958. leta je bil pretok 6,2 l/s, depresija 3,9 m in slanost 38,2 mgA Cl*". Vrtina je imela premer 10 cm, pretok je bil omejen z zmogljivostjo črpalke. Črpalni poskus leta 1959 je pokazal pretok 16 l/s, depresijo 13,16 m in temperaturo 16 °C. Kaptažna vrtina večjega premera, oddaljena od vrtine V-5 samo 7 m in enako globoka, ni našla nobene vodonosne plasti. Tudi z večkratnim torpediranjem vrtine z brizantnim Vitezitom 3 v količini od 5 do 200 kg nismo uspeli dobiti zveze z vodonosno plastjo, ki je bila navrtana v vrtini V-5 v globini 182,5 m. Kaptažne vrtine ni bilo možno poglobiti do jame v globini 225 m, kjer bi dobila zvezo z vodonosno plastjo, ki se je K SI. 6. Situacija izvirov, vrtin in premogovnika v Sečovljah Fig. 6. Situation of springs, bore holes and coal mine at Sečovlje i Izvir Spring i Jašek Morje Sea Kredni apnenec Cretaceous limestone PS Kozinski skladi Kozina beds E,_2 Eocenski apnenec Eocene limestone Ej2 Eocenski fliš Eocene flysch Q Mlade naplavine Recent deposits Shaft 1. JVR Prvi jugovzhodni revir First southeastern field 2. JVR Drugi jugovzhodni revir Second southeastern field S 7/2, V-5 Vrtine Bore holes drenirala v jamo, ker so takrat še kopali premog. Danes bi bilo možno navrtati to plast, ker je premogovnik opuščen. Vrtanja v letu 1959 so pokazala, da bi bilo možno zajeti izvir Bužini, ki se mu je pretok poleti močno zmanjšal, v večji globini. V letih 1962 do 1965 je bil zajet izvir Bužini z vodnjakom, globokim 15 m, in s 4 vrtinami, globokimi 50 m. Izvori šče Gabrieli je bilo zajeto s 650 m dolgo drenažno cevjo, napeljano v črpalni vodnjak, globok 5 m. Zmogljivost vodnjaka Bužini je bila 54 Vs pri depresiji 13 m, vodnjaka Gabrieli pa 37 l/s pri depresiji 2,75 m. Za oba vodnjaka so uredili čistilno napravo in ju obenem z vrtino V-5 priključili na vodovod Sečovlje—Portorož. 7 — Geologija 18 T—-vk Smer dotoka sladke vode —^ Direction of fresh water flow -40 — Smer vdora morske vode Direction of sea water intrusion Predlagana injekcijska zavesa Proposed situation of the impervious screen Plastnica Elevation contour line Crta enake slanosti 11. do 31. okt. 1970 JUU Line of equal salinity October 11—31, 1970 f Zaslanjen izvir Brackish spring Brojnica Submarine spring n: Glavni izvir z jezerom y1 Main spring with pool ®B f. Raziskovalna vrtina D 0 Exploration borehole Q„, Obalne naplavine al Coastal deposits Zakrasel zgorajekredni apne-1^2 nec IV 2 Karstified Upper Cretaceous limestone ^ Smer in vpad plasti " Strike and dip of beds SI. 7. Izvir Blaž v Istri (po Krznar in Franič, 1970) Fig. 7. The Blaž spring in Istria (after Krznar and F r a n i č , 1970) 4.3. Izvir Blaž v Istri Izvir Blaž leži na zahodni obali Raškega kanala pod vasjo Rakalj (Krznar, Franič, 1970). V uvali Blaž je vzdolž obale na dolžini 500 m okrog 20 izvirov. Večina jih je na obali v nivoju morja, nekaj je brojnic, glavni izvir z majhnim jezerom pa je oddaljen od obale okrog 30 m (si. 7). Nasip med morjem in tem izvirom je vsaj delno umeten, ker so vode Blaža nekdaj izkoriščali mlini, ki so mleli tudi za otoka Cres in Lošinj. Po cenitvah je minimalni pretok glavnega izvorišča okrog 170 1/sek, ostalih izvirov 30 do 50 1/sek, kar znese skupno 200 do 220 1/sek. Srednji letni pretok je 1,6 do 1,8 mVsek, maksimalni je bil 1970. leta 2,6 m3/sek. Glavni izvir Blaž je imel v času opazovanja 1969—1970 vse leto 1969 in do konca septembra 1970 slanost pod 100 mgA CI". V začetku oktobra, ko je nivo pri odprtem bočnem prelivu padel na 0,54 m nad morjem, se je izvir nenadoma zaslanil; voda je vsebovala 12000 mgA Cl~ (si. 8). Slanost ostalih izvirov je večja, kar je razumljivo, ker večina izvira v nivoju morja. Naloga raziskav v letih 1968 do 1970 je bila, najti cone dotoka sladke vode na širšem in ožjem območju ter locirati kaptažni objekt tako, da bi zajel Čim večji del voda tam, kjer še niso zaslanjene. V prvem delu raziskav so skušali najti podzemeljski vodni tok v širšem zaledju. Po starejših podatkih naj bi se obarvana voda ponora Fojbe pri Pazinu pojavila na izvirih Blaž. Tudi geofizika je nakazovala sorazmerno ozko prepustno cono od Barbana prek Beloviča proti Blažu. Ce bi raziskave to potrdile, bi kopali kaptažni rov od morja proti podzemeljskemu toku. Vrtina B-l, ki je oddaljena od zaliva Blaž 7 km, je pokazala, da so razpoke in manjše kaverne v rudistnem apnencu zapolnjene s kalcitom in meljem. Ker je tudi barvanje vrtin B-l in B-2 ter jame Rebiči pokazalo, da je dotok vode pahljačast, kar potrjuje tudi množica izvirov ob vsej obali južnega dela Istre, so nadaljnje raziskave v tej smeri opustili. V drugem delu raziskav so izvrtali nad 20 vrtin v ožjem zaledju Blaža z namenom, da bi našli cone glavnega dotoka in vdora morja. V vseh vrtinah so merili prepustnost, slanost in temperaturo ter iskali smer toka z barvanjem. Rezultat raziskav je bil, da teče voda h glavnemu izviru skozi 40 do 50 m širok pas med vrtinami B-6a—B-24 ter B-l7—B-15. V neposredni bližini glavnega izvira je prepustnost v navpični in prečni smeri različna. SI.8. Izvir Blaž. Padavine, gladina, pretok in slanost 1970 (po Krznar in Franič, 1970) Fig. 8. Blaž spring. Precipitations, level, discharge, and salinity 1970 (after Krznar and Franič, 1970) P Dnevne padavine Gladina izvira v metrih nad mor- Daily precipitations jem Q Pretok izvira Spring level in metres above sea Discharge of spring level CI- Slanost v mg/l CI" Salinity in mg/l of Cl- Večina vrtin v tem delu je pokazala prepustne dele apnenca plitvo, v vrtinah B-18, B-16 in B-23 pa so ugotovili prepustne dele še v globini 40 m pod morjem in globlje. Barvanja v vseh teh vrtinah so pokazala zvezo z glavnim izvirom. Navidezne hitrosti gibanja barve so bile naslednje: Raziskovalci mislijo, da niso našli glavne dovodne žile glavnega izvira, ker so navidezne hitrosti gibanja barve sorazmerno majhne in ker je pretok izvira mnogo večji kakor pretok iz smeri vrtin, ki so bile obarvane. Umetno reguliranje gladine v glavnem izviru hitro vpliva na vrtine v zaledju izvira in le deloma ter počasi na vrtine v severnem in južnem območju. To nam dokazuje, da teče sladka voda h glavnemu izviru z območja vrtine B-6a—B-24, čeprav glavne dovodne žile tam še niso našli. Med glavnim izvirom in morjem je v vrtini B-l9 močno prepusten interval v globini 12 do 18 m pod morjem, v vrtini B-21 pa med 49 in 69 m. Ker je ostala ta vrtina ob močni zaslanitvi glavnega izvira malo slana tudi v globini, naj bi bila njena direktna zveza z morjem dvomljiva. Zato mislijo, da žile, po kateri morje doteka v glavni izvir, tudi še niso odkrili. Zvezo glavnega izvira z morjem dokazuje plimovanje gladine in sprememba pretoka glavnega izvira. Amplituda nihanja gladine izvira je 22 °/o amplitude plimovanja morja. V severnem delu zaliva med vrtinama B-22 in B-28 so prepustne cone plitve, največ 10 m pod gladino morja. Vendar tudi tukaj prodira morje v notranjost vsaj lokalno. Podobno prodira morje tudi južno od glavnega izvira vzdolž prepustne cone med vrtinami B-8 do B-14. V vseh vrtinah so merili tudi gladino in slanost v različnih globinah. Po spremembah slanosti ločimo dva tipa vrtin. V vrtinah v severnem in južnem območju ter v vrtinah med glavnim izvirom in morjem je slanost stalno naraščala v času meritev, to je od avgusta do oktobra 1970, ko je bila zaslanitev največja. V teh vrtinah je slanost tudi v globini večja kakor na površju. Vrtine imajo najnižje piezometrične nivoje in so blizu morja. Te vrtine se stalno zaslanjujejo v direktnem kontaktu z morjem. V ostalih vrtinah slanost do oktobra ni naraščala ali pa le malo. V oktobru pa je nenadoma narasla. Takrat se je zaslanil glavni izvir prej in močneje kot vrtina. Avtorja mislita, da je glavni izvir zaslanil tudi vrtine v zaledju in predlagata, da naj bi izkoristili sedanji glavni izvir kot glavno zajetje, zgradili drenažne rove proti severnemu in južnemu izvorišču ter celotno območje izolirali proti morju z injekcijsko zaveso dolgo 500 m (si. 7). V prvi etapi bi zgradili le 300 m injekcijske zavese. Dalje mislita, da bi z dre-nažnim rovom v zaledju glavnega izvira zaradi razbitosti dotočnih žil zajeli lahko le del voda, njegova varnost proti zaslanitvi pa bi bila odvisna od oddaljenosti od morja. Investitor se je leta 1971 na priporočilo prof. Bat urica odločil za izkop drenažnega rova proti vrtini B-24 v zaledju glavnega izvira. Rov B-l 5 B-16 B-23 B-25 19 m/uro 134 m/uro 60 m/uro 40 m/uro je v razdalji 70 m od vhoda zadel na kaverno z večjim dotokom vode v zimskem času, ki pa se je poleti 1972 močno zmanjšal. Izkop ter meritve pretoka in slanosti se bodo nadaljevale v sušni dobi. 4.4. Izviri južno od Senja Izvire in brojnice južno od Senja v dolžini 4 km so podrobno raziskali I. in D. K'uščer ter D. Leskovšek (Kuščer, 1950; I. in D. Kuščer, 1962). Najznačilnejši so morda »izviri pri žagi« 0,5 km južno od Jurjevega. Na obali dolgi 300 m je 70 studencev in 30 brojnic (si. 9). Izviri so razdeljeni na 6 podskupin, katerih vsaka ima približno enako slanost. Brojnica KEa v Kolih je v globini 9 m in bruha do 1 mVsek vode, ob suši pa požira več 1001 morske vode na sekundo. Izviri pri žagi so v medsebojni zvezi in odvisnosti. Na sliki 9 je I. Kuščer označil razvrstitev razcepov rj do r4 in podal kvalitativen prikaz spodnjih žil A do Y, ki dovajajo morje ali somornico k posameznim skupinam izvirov. V deževni dobi imajo vsi izviri neslano vodo. Ob koncu pomladi, ko se pretok zmanjšuje, usahne brojnica KF in vdere morje najprej po žili X v razcep r*. Brojnica KE v Kolih se zaslani do 700 mg/l Cl" in studenci KC in KD podobno. Pozneje (navadno v pričetku julija) priteče morje še po žili Y in zaslani izvire KA in KB ter za enako vrednost poviša slanost Kol in izvirov KC in KD. V suhih poletjih usahnejo še Kola in prično požirati morje, slanost izvirov KB naraste na 9000 mgA Cl~. Brojnica pri Kolih se zelo hitro spremeni v požiralnike — v 1 do 2 dneh — in tudi slanost izvirov KB naraste hitro. Jeseni ob nastopu deževja se vsi izviri osladijo in ostanejo sladki vso zimo. Končni dokaz o pretoku morja po spodnjih žilah je dalo barvanje s 300 g fluoresceina, ki so ga izlili 30. 7. 1947 v najmočnejši požiralnik KEa. Po 5 urah se je prikazala barva v izvirih KB, dosegla največjo koncentracijo po 1 uri, nakar je koncentracija polagoma padala. Po 6 in pol urah so se obarvali tudi izviri KA, vendar z 2- do 3-krat slabšo koncentracijo. Zanimiva so bila opazovanja v zalivu 2rnovnica dne 24. 8. 1940, ki jih je opisal I. Kuščer (1950): »Po morskem površju odteka cela reka somornice. Obratno smer ima morski tok na dnu zaliva. Studenčnica se meša z dotekajočim morjem, mešanica se dviga na površje in odteka. Ta pojav dobro ponazoruje delovanje morskih požiralnikov in zaslanjenih izvirov. Kar se dogaja tam v podzemeljskih žilah, se godi tu v morju samem in je opazovanju neposredno dostopno. V obeh primerih poganja studenčnica krožni tok morske vode.« 4.5. Izvili v zalivu Poljice blizu Trogira Kakor poroča Jevremovič (1966), narašča slanost izvirov v zalivu Poljice z naraščanjem pretoka. Tako je bila v času suše septembra 1957 slanost 1500 do 1900 mgA Cl", v času visokih gladin podtalnice aprila 1962 pa 6620 do 6700 mgA Cl". Pri gornjih podatkih moti petletni časovni interval med merjenjem. Mi j at o vi č (1969) navaja za izvire v zalivu Poljice samo minimalno in maksimalno slanost in ne omenja časa meritev. 4.6. Izvir Pantan pri Trogiru Zakrasel apnenec Kozjaka je proti Kaštelanskemu zalivu zaprt z laporjem in peščenjakom flišne sinklinale. V zahodnem delu zaliva, tam kjer se apnenec najbolj približa obali, je izvir Pantan. Izvir je tik pod Jadransko magistralo, oddaljen od morja 500 m, v katerega se izliva po 1 km dolgi rečici. V neposrednem zaledju izvira je eocenski apnenec, v oddaljenosti 300 m pa pas krednega apnenca širok 2 km in povezan z glavnim apnenim masivom. Apnenec je narinjen na flišne sedimente E2_s, ki so med izvirom in morjem pod kvartarno preperino. Na izvirnem območju tik pod narivnim robom je več izvirov, ki so združeni v umetno jezerce za zidano pregrado, zgrajeno pred 200 leti zaradi izkoriščanja voda za mlin (M i j a t o vi č , 1972). Gladina v jezercu niha med 2,5 in 4 m nad morjem, pretok doseže 10 mVs in se zmanjša poleti na 1,3 do 2 mVs. Pozimi je slanost 500 mg/l CI", poleti pa se poveča do 10 000 mg/l Cl~ Počasno naraščanje slanosti ob upadanju pretoka (si. 10) je analogno istemu pojavu pri izviru Almyros, tako da lahko tudi tukaj sklepamo na globok spodnji kanal in precej velik podzemeljski rezervoar nad razcepom. Druga dva značilna pojava na tem območju sta izvir Slanac, ki je oddaljen od Pantana 1,5 km, in dve brojnici (Alfirevič, 1966, 1960) v Kaštelanskem zalivu, prva 800 m od Divulj in druga 800 m od Slatine. Brojnici sta od Pantana oddaljeni 900 oziroma 2500 m. Slanac teče okrog 2 meseca ob času večjih padavin pozimi s pretokom okrog 0,5 mVs in slanostjo 800 mg/l Cl~ Preseneča višina izvira 27 m nad morjem. Brojnici bruhata v zimskih mesecih somornico, poleti pa mirujeta. Raziskave dna Kaštelanskega zaliva s sonarji in neposredne okolice brojnic S1 Pu P^C1 S(> pokazale> da sta brojnici lijaka v apnencu z dnom na globini 39 oziroma 32 m, medtem ko je dno zaliva v globini 15 m Po Alfirevič u (1969) naj bi bili brojnici vrtači, ki sta nastali v kontinentalni fazi, ko je bilo dno Kaštelanskega zaliva kopno in sta bili potopljeni pn postpleistocenski transgresiji morja. Alfirevič misli da SI. 9. Izviri pri žagi pri Jurjevem in njihove domnevne podzemeljske zveze (I. K u š c e r, 1950, 1962) Fig. 9. Springs of the saw-mill at Jurjevo and their supposed underground connections (after I. Kuščer, 1950, 1962) ^ Zaslanjen obalni izvir Brackish coastal spring O o Podmorski izviri Submarine springs A — Y Domnevna podzemeljska zveza Supposed underground connection r. — r Razcepi podzemeljskih zvez 4 Branchings of underground connections KA — KD Skupine izvirov s podobnimi lastnostmi Subgroups of springs with similar characteristics KE Podmorske estavele Submarine estavelles o 50 100m r\ i—,—.—,—,—i—.—i—.—.—i '1 \ mtysec. mg./I (after M i j a t o v i č, 1967) Q Pretok Discharge Cl- Slanost Salinity sta brojnici estaveli v zvezi z izvirom Pantan, vendar tega niso mogli dokazati, ker ob ponovnih poizkusih z barvanjem brojnici nista požirali fluoresceina. Tudi po M i j a t o v i č u sta izvira in brojnici v medsebojni zvezi. Raziskovalna vrtanja v zaledju izvira Pantan (Mijatovič, 1972) leta 1971 so imela nalogo poiskati dovodne cone k izviru, da bi nato zajeli vodo z rovom. Sladko vodo so našli v vrtini B-l, oddaljeni 1,5 km od Pantana, dve vrtini sta zadeli na somornico, ena pa v apnencu ni dobila zveze z glavno kraško podtalnico. 4.7. Izvir Pištica pri Komiži na otoku Visu Po Baturiču (1961) je bil izvir Pištica pozimi 1956. leta bolj slan kakor poleti tega leta, kar naj bi bilo odvisno od količine padavin. Maksimalni pretok izvira je bil 12 l/s. Leta 1953 so pričeli z izkopom kaptažnega rova, ki je zadel na »ka-verno« z vodo. Pozimi 1956 je bil pretok iz kaverne 60 l/s in slanost je narasla na 3600 mg/l. Decembra 1956 so zgradili v kaptažnem rovu čep z odvodno cevjo 0 150 mm in zasunom, tako da so pretok lahko regulirali. V letu 1958 ni slanost nikoli presegla 635 mg/l Cl". Pri posebnem poskusu, ko so odprli ventile, je narastel skupni pretok na 37 l/s in slanost Pištice od 580 na 635 mg/l Cl". Podatke o slanosti in gladini kaže tabela 1 za suho (avgust 1957) in mokro (april 1958) obdobje. Tabela 1. Table L Podatki o gladini in slanosti izvira PiŠtica (po Baturiču, 1959) Data on the water level and salinity of the PiStica spring (after Baturic, 1959) Vrtina K-1A »kaverna« Pištica 8,15 4,0 1,3 520 580 (?) 15,2 7,0 Avgust 1957 April 1958 Gladina nad Gladina nad Kraj opazovanja Observation locality morjem v m Water level in meters above sea level Slanost Salinity mg/1 Cl- morjem v m Water level in meters above sea level Slanost Salinity mg/1 CI" 320 524 684 4.8. Postirska dolina na Braču Otok Brač ima površino 100 km2 in sestoji večidel iz gornjekrednega apnenca in dolomita v obliki antiklinale s smerjo vzhod—zahod. Teme antiklinale je bliže južnemu robu otoka. V sredini otoka je 90 km2 velika planota na višini 300 m z letnimi padavinami 1450 mm. Površje otoka je zakraselo. Površinskih odtokov ni, razen nekaterih hudournikov, ki pa tečejo le ob neurjih. Na osrednji planoti je več ponorov, katerih brezna so bila raziskana do globine 300 m. Obalni in podmorski izviri kažejo, da se otok v glavnem drenira proti severu. V zalivu Prvlja in Postire je več izvirov; zato so dolino Postire—Dol, ki je v zaledju, izbrali za kraj raziskav (Bakič, 1966 in Kom at in a, 1968). S kartiranjem in vrtanjem so odkrili štiri vzporedne zdrobljene cone, ki so jih imeli za glavne kolektorje. To so potrjevali tudi stalni izviri ob obali. Od štirih vrtin sta dve zadeli kompakten, v glavnem neprepusten apnenec, po ena pa slano oziroma sladko vodo. Po geofizikalnih meritvah naj bi segal vpliv morja 600 do 700 m daleč v notranjost. Zajetje KI, oddaljeno 800m od morja, je presekalo samo kolektorsko cono II. V letih 1961 in 1962 je bil minimalni nivo 0,48 m in maksimalni 5,74 m nad gladino morja. Pri poskusnem črpanju se je voda hitro za-sJanila. Zato je eksploatacijska kapaciteta zajetja, omejena z dopustno slanostjo, pozimi okrog 281/sek in poleti največ 3,51/sek. Gladina vode v zajetju redno plimuje. Amplituda znaša okrog 0,1 m, kar je 30 do 40°/» amplitude morja. Plimovanje v zajetju zaostaja za okrog 1 1/4 ure za plimovanjem morja. Da bi se izognili neugodnemu vplivu morja, so zgradili zajetje K2, oddaljeno 1800 m od morja. Zajetje K2 ima 55 m globok jašek, katerega dno je 2 m pod morjem, vendar je ta del jaška zabetoniran. Horizontalni rov z dnom na koti 5 m je 470 m dolg in je presekal 6 zdrobljenih con s kolektorji. V letih 1961 in 1962 je bila najnižja gladina 2,61 m, najvišja pa 12,14 m. Vpliva plimovanja ni opaziti. V coni IV/1 je bilo odkrito kraško brezno, globoko 75 m, z dnom 36 m pod gladino morja. Slanost vode pred črpanjem je bila 17,8 do 26,2 mg/l Cl~ na površini vode, 17,6 mgA v coni JV/1 in 24,8 mgA na dnu brezna. Črpalna poskusa sta bila izvedena v letih 1961 in 1962. Leta 1961 so črpali 21178 m3 in leta 1962 4 512m\ poprečna slanost je bila 437 oz. 415 mgA Cl- Med posameznimi kolektor-skimi conami so bile razlike v slanosti; zato avtorji sklepajo-, da so med seboj slabo povezane. Slanost je narasla takoj v začetku Črpanja, čeprav se je znižala gladina samo za nekaj cm. Medsebojna odvisnost med količino črpanja in slanostjo obstaja, vendar je niso mogli izraziti z enačbo. B a k i č misli, da plava v zajetju K2 sveža voda na morski ali zaslanjeni vodi in da Ghyben-Herzbergov zakon pri pogojih tečenja ne velja. Pri slanosti, ki naj bi bila v dopustnih mejah do 250 mg/1 Cl-, je bil določen dopusten pretok črpanja iz zajetja K2, in sicer pozimi 28,7, spomladi 16,8 in poleti 19,7 do 3,5 1/sek v odvisnosti od padavin. Zmogljivost zajetja je pod pričakovano, zato so predlagali kot naslednjo fazo sanacije kopanje zajetja K3, oddaljenega od morja 2,7 km, ali za-tesnitev kolektorskih con pod nivojem morja v zajetju K2 z namenom, da bi zmanjšali izgube sladke vode, z dvigom gladine zmanjšali vpliv morja ali ga v najugodnejšem primeru povsem izolirali. Injiciranje od kote + 5 do —70 m je bilo predlagano v kolektorski coni IV/2. Posebno zanimiva so bila v Postirah opazovanja o pretakanju kraških voda. Površinska zakrasela cona sega do globine 20 m pod površjem hribine. V njej je mnogo razpok, manjših kanalov in dimnikov, manjših votlin itd. Vse te odprtine so med seboj povezane; zato je cirkulacija vode v vzdolžni, prečni in navpični smeri dobra. Ta tip zakrasovanja sledi reliefu pokrajine. Tam, kjer je ta cona v višjem položaju, je to prezračena cona s pronicanjem navzdol; ob morju, kjer je ta cona potopljena, se po njej podzemeljske vode izlivajo v morje. Poroznost in prevodnost te cone sta veliki. V globino napreduje zakrasovanje vzdolž prelomov in tektonsko porušenih con. V zajetju K2 je bilo 6 takih con pri dolžini rova 470 m. V njih se podzemeljske vode pretakajo v vzdolžni smeri proti morju. Zveze v prečni smeri pa so slabe, kar dokazujeta različno reagiranje in različna slanost posameznih kolektorskih con ob črpanju. 4.9 2rnovica pri Gradacu Izvir Zrnovica (Komat ina, 1968; Krznar in dr., 1970) leži na meji apnenca in dolomita le 1 km južno od flišnega pasu Makarskega primorja. Flišni pas ob morju je skupaj z dolomitom usmeril podzemeljske tokove, ki drenirajo Biokovo in Rilič planino proti severozahodu v izvire D. Brela in delno proti jugu na izvir Žrnovico ter izvire v BaČinskih jezerih. Tabela 2. Table 2. Meritve slanosti in gladin izvira Zrnovica maja 1970 (po Krznar in dr. 1970) Salinity and plezometric surface of Zrnovica spring in May 1970 (after Krznar a. ot. 1970) Mesto meritve Observation locality Slanost Salinity mg/l Cl" Gladina v metrih nad morjem Piezometric surface in meters above sea level Glavni izvir 4800 0,84 Main spring Vrtina 2-2 72 1,62 Borehole Vrtina 2-3 32 2,89 Borehole Vrtina 2-9 116 0,34 Borehole Vrtina 2-15 16 1,81 Borehole Vrtina 2-16 12 1,50 Borehole Vrtina 2-17 124 1,54 Borehole Vrtina 2-18 20 2,18 Borehole Vrtina 2-19 60 1,53 Borehole Vrtina 2-20 2720 1,41 Borehole Vrtina 2-21 40 1,11 Borehole Vrtina 2-32 48 1,98 Borehole Vrtina 2-34 32 1,97 Borehole Vrtina 2-35 24 1,26 Borehole Vrtina 2-42 32 3,39 Borehole Vrtina 2-43 16 2,41 Borehole Vrtina 2-44 20 2,45 Borehole Vrtina 2-45 28 2,88 Borehole Vrtina 2-46 84 2,21 Borehole Vrtina 2-47 28 2,15 Borehole Vrtina 2-48 224 2,26 Borehole Izviri Zrnovica bi bili pomembni za vodno preskrbo južnega dela Makarske riviere. V raziskavo izvira so bila vložena že znatna sredstva. Glavni izvir (si. 11) na bregu, imenovan Mlinica, je ograjen z zidom. Njegova gladina je dvignjena za 1 m nad morje; vodni padec izkorišča mlin, ki je tik ob morju. Ostali izviri so na obeh straneh zaliva. V morju so še 3 brojnice, najmočnejša, ki teče samo ob deževju, je oddaljena od mlina 120 m. Pretok vseh izvirov je ocenjen na 0,5 do 1 m3/sek v suši in 2 do 3 mVsek ob deževju. Izvir št. 1 na zahodni obali je stalno sladek, vsi ostali pa so ob suši slani s 3000 do 11 000 mg/l Cl~. Ob deževju se nekateri izviri oslade na okrog 50 mg/l, ostali pa na 3000 do 3500 mg/l Cl". Cilj raziskav v letih 1968 do 1970 (Krznar in dr., 1970) je bil, poiskati v neposrednem zaledju izvirov glavne dovodne kanale, po možnosti na krajih, kjer voda še ni zaslanjena. Geoelektrično sondiranje je pokazalo glavni vpliv morja v zaledje v ozkem pasu vzdolž preloma med dolomitom in apnencem, geoelektrično profiliranje pa anomalije v dolomitu. Prva vrtina je zadela na slabo prepusten dolomit. Nato so usmerili vrtanje v apnenec na vzhodni strani zaliva. Tudi v apnencu niso našli glavnih vodnih žil. Zato so v letu 1970 sistem raziskav spremenili in začeli iskati glavne vodne žile v neposrednem zaledju glavnega izvira z vrtanjem in barvanjem. Z nadaljnjimi vrtinami so se od izvira odmikali. Glavne žile so našli v kompaktnem dolomitu. Za prelom mislijo, da je zaglinjen. Podatke o barvanju kaže slika 11, o občasnih meritvah slanosti pa tabela 2. Velike razlike v slanosti med skupinama vrtin Z-47 in Z-48 ter Z-19, Z-20 in Z-21 s podobnimi piezometričnimi nivoji in majhno medsebojno oddaljenostjo nam kažejo, da se voda zaslanjuje vzdolž omejenih med seboj ločenih con. Rezultati govore tudi za to, da se voda zaslanjuje v malo oddaljenem zaledju. 4.10. Izviri v Morinjskem zalivu v Boki Kotorski Gore Orjen, Lederica in Lovčen v zaledju Boke Kotorske sestoje večidel iz zakraselega apnenca. Pripadajo coni Visokega krasa (Radulovič, 1971), narinjeni proti morju na cono Cukali, ki je kot celota prečno na SI. 11. Barvanje raziskovalnih vrtin v zaledju izvira Zrnovica (po Krznar ju in dr., 1970) Fig. 11. Tracer experiments carried out in the hinterland of the Zrnovica spring (after Krznar and others, 1970) si Gl Sladek Izvir Fresh water spring Glavni zaslanjen izvlr Main brackish spring Vrtina Bore hole 11 Zaslanjeni izviri Brackish springs Mlin Water mill Bazen Pool pgl Piezometrična gladina podtalnice v vrtinah maja 1870 (v metrih nad morjem) Piezometric head of ground water in bore holes in May 1970 (in meters above sea level) s Slanost v maju 1970 Salinity in May 1970 t Cas od barvanja vrtine do pojava barve v izviru Time between introduction of the tracer into bore hole and its appearance in the spring \fi) 16 Z-1 (m)(mg/l CO i pgl S mg/l Cl 2.89 32 Z"3 2,88 28 Ž-4 5 V 4 2.21 84 Z-46 3,39 32 2-42 2.45 20 t" 2,4i is Z-43 2,18 20 .V Z-18 .96 1,97 32 1.26 24 Z" z-: Z-2 2.26 2 24 Z-48 Z-47 2.15 281 \o. 154 124 U.41 \27201 / MORJE SEA SI 100 m smer plasti neprepustna. V Kotorskem in Risanskem zalivu so na meji teh tektonskih enot močni obmorski izviri. Nastali so zato, ker velike padavine (do 4000 mm) v gorovju napajajo apnenec, odprt proti morju. Morinjske in Kostanjiške izvire, ki imajo srednji letni pretok 5,5m8/sek in srednji nizki pretok okrog 0,5m3/sek, so raziskovali v letih 1968 do 1970 (Pavlin, Biondič, 1971). Hidrogeološko kartiranje je pokazalo, da tečejo vode k izvirom od zahoda skozi turonsko-senonski apnenec z globotrunkanami K22>3. Na južni strani apnenca sta slabo prepusten cenomansko-turonski ploščasti apnenec z roženci in spodnjekredni silificirani apnenec in radiolariti K/, na severni strani pa je slabo prepusten senonski ploščasti apnenec s tenkimi vložki laporja in rožencev Kz3. Slabo prepustne plasti so usmerile pretok skozi turonsko-senonski apnenec z globotrunkanami K/-3, ki je zakrasel (si. 12). N 15 E S 1SW SI. 12. Hidrogeološki profil Morinj (po Pavlinu in B i o n d i č u , 1971a) Fig. 12. Hydrogeological section Morinj (after Pavlin and Biondič, 1971a) Pobočni grušč Scree Naplavina Alluvium Eocenskl fllS, kot celota neprepusten Eocene flysch, impervious Apnenec Kt*+Pc, dobro prepusten Limestone K^+Pc, highly permeable Ploščasti apnenec z roženci, malo prepusten Platy limestone with chert, poorly permeable Apnenec z globotrunkanami Kaa'», dobro prepusten Limestone with globotruncanas K,1'5, highly permeable Ploščasti apnenec z roženci Kj1«1, malo prepusten Platy limestone with chert Kg1", poorly permeable Silificirani apnenec in radiolarit Ki, malo prepusten Silicified limestone and radiolarite K,, poorly permeable Apnenec in dolomit T + J, dobro prepustna Limestone and dolomite T+J, highly permeable Morinjski in Kostanjiški izviri (si. 13) tečejo vse leto, poleti so za-slanjeni s 1000 do 12 600 mg/l Cl~ Pozimi in poleti po močnem deževju so sladki. Pozimi tečejo »Zimski izviri«, ki so oddaljeni od obale 700 m, poleti je imela voda v njih 1300 mg/l Cl— Izvrtali so 10 raziskovalnih vrtin in dva vodnjaka. Situacija je podana na sliki 13, slanost in gladina vode pa na tabeli 3. Prva štiri barvanja v zaledju izvirov (tabela 4) so pokazala, da gravitirajo v tem delu podzemeljski tokovi proti Morinjskim izvirom. Glavni dovodi h Kostanjiškim izvirom, ki so močnejši, so nekoliko bolj južno. SI. 13. Situacija Morinjskih izvirov in raziskovalnih del (po Pavlin u in Biondiču, 1971b) Fig. 13. Situation of Morinj springs and exploration works (after Pavlin and B i o n d i č , 1971b) KB Vrtina Pr Prelom Bore hole Fault BN vodnjak I—IV Kraj barvanja Water well Site of tracer introduction M1-M3 Morinjski izviri Močno obarvano Morinj springs High concentration of the tracer K1-K6 Kostanjiški izviri — Sledovi barvila Kostanjica springs Very poor concentration of the tracer Zimski izviri Springs flowing during winter Tabela 3. Table 3. Slanost in drugi podatki o izvirih, vrtinah in vodnjakih v Morinjskem zalivu (po Pavlino In Biondiču, 1971b) Salinity and other data of springs, boreholes and wells in Morlnj bay (after Pavlin and Blond i č, 1971b) Mesto meritve Observation locality Dno vrti- ne ali Razdalja vodnjaka od obale m pod metrov morjem Distance Bottom of from sea borehole/ shore in /well in meters meters below sea level Gladina vode Pi ezo metric surface Datum Date ob meritvi slanosti during salinity measurements najnižja 1969-1970 the lowest m nad morjem in meters above sea level Slanost Salinity na površju vode at water surface v globini 12 m at 12 meters depth mg/1 CI- Izvir Spring M 1 25 26. 8. 69 1,07 2970 M 1 25 29. 8. 69 120 KI 250 26. 8. 69 1,90 2960 K 1 250 29. 8. 69 0 K 3 270 26. 8. 69 1,14 3120 K 3 270 29. 8. 69 0 K 5 260 26. 8. 69 1,70 3070 K5 260 29. 8. 69 0 K 6 200 26. 8. 69 0,5 12600 K 6 200 29. 8. 69 880 Vrtina Borehole KB 1 740 58 26. 8. 69 KB 1 740 58 26. 8. 69 KB 1 740 58 14. 8. 70 KB 2 460 16 28. 8. 69 KB 2 460 16 16. 8. 70 KB 3 680 46 8. 69 KB 3 680 46 16. 8. 70 KB 8 840 14 16. 8. 70 KB 9 800 23 14. 8. 70 KB 10 680 25 14. 8. 70 Vodnjak Water well BN1 900 12 31. 8. 70 BN1 900 12 30. 9. 70 BN 2 880 18 19. fl. 70 Rezultati barvanja so podani v tabeli 4 in sliki 13. 3,0 800 1520 3,33 3,33 660 1080 1,98 2250 1,94 1,94 260 1170 1,30 1000 3,14 3,14 — 810 2,38 2,38 80 80 3,71 2,51 80 80 3,06 3,06 1350 1650 7,0 4,5 290 280 4,5 ■8,0 5 4000 ob črpanju during pumping Tabela 4. Stev. barvanja Number of tracer test I II III IV Morinjski izviri. Iskanje vodnih zvez z barvanjem Morinj springs. Determination of ground water connections by tracers Table 4. Kraj barvanja Site of tracer introduction Vrtina KB-2 Bore hole KB-2 Vrtina KB-3 Bore hole KB-S Prepustno korito Suhega potoka, nad vrtino KB-8 Pervious bed of Suhi potok creek above bore hole KB-8 Pobočje nad Zimskimi izviri Slope above Zimski izviri Uvala Mokri ne nad Igalom Razdalja 11 km Uvala Mokrine above Igalo Distance 11 km Kraj vzorčevanja Sampling site Intenzivno obarvano High concentration M-l, M-2, M-3 Zimski izviri M-l, M-2, M-3 K-l—K-6 Sledovi barvila Very poor concentration Izviri M-l, M-2, M-3 Springs M-l, M-2, M-3 KB-2 M-l, M-2, M-3 K-l—K-6 KB-2 Opomba Remark pri visoki vodi at high water konec zime 1971 at the end of winter 1971 Pavlin in Biondič (1971b) mislita, da se voda zaslanjuje vzdolž kraških kanalov, ki vodijo k Morinjskim in KostanjiŠkim izvirom. To naj bi dokazovalo zmanjševanje slanosti z oddaljevanjem od morja ter večja slanost v globljih delih vrtin. Območje zimskih izvirov naj bi sanirali s kaptažnimi vodnjaki in z injekcijsko zaveso pod izviri. Zavesa, dolga 360 m in globoka 100 m, do kote — 85 m, naj bi presekala pas zakraselega apnenca z globotrunkanami in preprečila vtok morja. Zgradili naj bi jo iz raziskovalno kaptažnega rova. 4.11. Brojnice pri La Mortoli na italijansko francoski meji Brojnice pri La Mortoli so raziskovali v letih 1960 do 1962. C a 1 v i n o in Stefanon (1963) poročata, da so 600 m od obale 3 brojnice; največja, imenovana Rovereto, je v globini 39 m. Brojnice so ob podaljšku preloma, ki na bregu razmejuje zgornjekredni glinasti apnenec s plastmi laporja in čisti kompaktni jurski apnenec. Raziskave s sonarjem in potapljači septembra 1961 so odkrile v peščenem dnu več lijakov. Na dnu treh lijakov so močni izviri sveže vode. Dva sta med seboj oddaljena 5 m ter imata odprtino 1,0X0,25 in 0,5X0,1 m. Pretok je bil ocenjen na 0,1 m3/sek, slano&t pa med 45 in 75 mg/l Cl"~. C al vino in Stefanon (1969) sta predlagala italijanskemu Narodnemu odboru za raziskave (Consiglio Nazionale delle Ricerche), da bi izvire pokrili z valjem, ki bi bil z gibljivo cevjo zvezan z ladjo, kjer bi merili pretok vode in njeno slanost. Raziskovalca menita, da bi s tem začasnim zajetjem v 3 letih zbrala dovolj podatkov za projektiranje stalnega zajetja. 4.12. Brojnice pri Tarantu v Italiji O teh brojnicah poročata Cerruti (1948) in Stefanon (1971). Stefanon meni na podlagi raziskav, da se morje in sladka voda mešata v ustju podvodnega izvira. Da bi mešanje preprečili, so se odločili, da pokrijejo ustje izvira z zvonom, podaljšanim v sifon. 4.13. Brojnica Cadimare pri Speziji v Italiji Znano brojnico Cadimare so zajeli v globini okrog 6 m in dvignili njeno gladino na + 3,5 m. Vendar so valovi konstrukcijo kmalu porušili. Tudi brojnica ni več aktivna (Calvin o, Stefanon, 1963), ker je pokopana pod ruševinami. 4.14. Izvir in brojnice Ayios Georgios pri Kiveriju v Grčiji Sredina Peloponeškega polotoka sestoji iz apnencev in je povečini brez površinskega odtoka. Planota pri mestu Tripolis, dolga okrog 50 km in široka okrog 15 km, je tipično kraško polje s ponori ob pobočjih. Tritij, ki so ga zlili v ponor Nestani na vzhodnem robu polja Tripolis, se je pokazal po 8 dneh v največji koncentraciji v 27 km oddaljenem izviru Ayios Georgios. Na morski obali pri izviru Ayios Georgios je bilo več izvirkov, ki so vsebovali 177 in 184 mg/l C1-. Glavni izvir pa je bil v globini 10 m in v razdalji 10 m od obale. Slanost brojnic je bila 3000 do 4000mgACl~ (Slander, 1971). Načrt za izkoriščanje voda v letu 1964 je predvideval izgradnjo akumulacije v notranjosti polotoka in zajezitev teh vod pred ponornimi področji. Pripomniti je treba, da bi tako zajeli le del voda, ki povečini tečejo direktno proti izvirom ob morski obali in ne prek kraških polj. Prof. W. Stander je meril slanost, gladino in pretok na tem izviru in predlagal njegovo sanacijo z izgradnjo polkrožne pregrade. 4.15. Morski požiralniki na otoku Kefalonija Morski požiralniki na otoku Kefalonija so znani v literaturi že 150 let pod imenom »morski mlini pri Argostolionu«. Gladina v morskih požiralnikih je 0,75 do 1,25 m pod gladino morja, maksimalni pretok je v izko- panem kanalu okrog 1,7 mVsek. Žitni mlin, ki je bil zgrajen leta 1834, je potres leta 1953 porušil. Maurin in Z o ti sta 1963 leta z barvanjem dokazala, da morje, ki ponira pri mlinih, zaslanjuje 15 km oddaljene izvire v zalivu Sami. Skupen pretok teh izvirov je okrog 10 m8/sek., temperatura 15 °C, vsebujejo pa 10 do 12 °/o morske vode. 4.16. Izvir Almyros Irakliou v Grčiji Almyros pomeni v novi grščini slan izvir. To ime so dali več izvirom in rečicam. Almyros Irakliou je na severni obali otoka Kreta, 8 km zahodno od glavnega mesta otoka Irakliona (Heraklion). Voda izvira na vznožju zakrasele planote Keri na skrajnem severovzhodnem delu gorstva Psiloritis. Od morja je izvir oddaljen 1 km in se vanj izliva kot rečica Almyros potamos, dolga 1,5 km. Ob izviru je jezero, široko 60 m, tipično kraško »oko«, ki je umetno povečano z nasipom. Na njem je bilo pet mlinov, vendar danes stoji le še eden. Glavni dotok v jezero je v globini 20 m po kraškem rovu s presekom okrog 5 m2. Pri pretokih nad 8 mVsek. deluje še zgornji izvir iz sifonskega jezera, dvignjenega za 1 m nad gladino jezera. Zgornji izvir je v manjši votlini na robu glavnega jezera. Srednji pretok je okrog 8 mVsek., minimalni 4 in maksimalni do 30 ms/sek. VeČino leta je voda zaslanjena do 5500 mg/l Cl—, pozimi pa je sladka zaradi večjih pretokov (Burdon, Papakis, 1964). Padavinsko območje meri okrog 300 km2. Letna količina padavin je odvisna od nadmorske višine pokrajine in se povečuje od 600 mm pri izviru nad 1400 mm v višini nad 1500 m. Padavinsko območje izvira je pogorje Psiloritis, zgrajeno v zahodnem delu iz ploščastega apnenca z roženci, verjetno permske starosti, in v vzhodnem iz apnenca serije Tripolitza, ki je jurske do eocenske starosti (Papadopoulos, Skanvic, 1968). Oba apnenca sta močno zakrasela. Psiloritis je omejen na vzhodu in jugu vzdolž preloma ob tektonskem jarku Irakiion-Festos z neprepustnim flišem in neogenskim laporjem. Odtok proti zahodu preprečuje neogenski lapornati apnenec, ki je transgresivno odložen prek vznožja Psiloritisa. Severni rob meji na slabo metamorfoziran skrilavec in delno na fliš. Najvišji vrh pogorja Psiloritis Timios Stavros, visok 2456 m je na zahodu. Pogorje se proti severovzhodu polagoma znižuje proti izviru Almyros. Skrajni severovzhodni izrastek Psiloritfsa je planota Keri, visoka 300 m (si. 14 in 15). Zanimanje za ta izvir se je v zadnjem desetletju močno povečalo, ker so narasle potrebe po pitni in namakalni vodi. Vzrok zaslanitve so različno razlagali. Nekateri so napak domnevali, da je slanost posledica izluževanja sedimentov in da je v globini pod izvirom sladka voda. Kot dokaz so navajali vrtino Khavrohori, oddaljeno od izvira samo 160 m. Z njo so zadeli na manj slano vodo (600 mg/l Cl~), ki jo uporabljajo za vodovod v vasi Gazi. V letih 1968 do 1971 sem sodeloval pri raziskavah Almyrosa po projektu grške vlade in Združenih narodov o »Oceni in možnosti izkoriščanja podzemeljskih voda v vzhodnem delu Krete« (Gov. of Greece, UNDP FAO 1968—1971). Leta 1968 so bili predlagani (Re, Breznik, 1968) naslednji načini canacije izvira: a) dvigniti gladino izvira in s tem odriniti morsko vodo, b) z injekcijsko zaveso presekati spodnjo žilo, po kateri doteka morska voda, c) zajeti vodo iz dovodne žile še preden se zmeša z morsko vodo. Raziskave za varianti b in c so v glavnem končane. Poskus z dvigom gladine, ki je zelo drag, je prenesen v drugo fazo raziskav. Mezozojski apnenec planote Keri je narinjen na metamorfni skrilavec na severu. Narivni rob je 500 m oddaljen od izvira. Na vzhodu in jugovzhodu je planota Keri omejena s subvertikalnim prelomom, ob katerem se je vzhodni in jugovzhodni del pogreznil za več kot 500 m. Tektonski jarek Heraklion-Festos, ki je pri tem nastal, so zapolnili slabo prepustni neogenski pesek, melj, lapor in apnenec organskega izvora. Območje med izvirom in morjem, prekrito s hudourniškim vršajem, je bilo posebno zanimivo za raziskave, ki naj bi ugotovile smer prodora morja proti pogorju Psiloritis. Razdalja med morjem in zakraselim apnencem je samo 1 km. Poleg tega je blizu izvira izdanek apnenca. Raziskave so pokazale, da se ta pas apnenca, ki je okrog 300 m širok in 50 do 180 m globok, razteza 500 m daleč proti morju. Tam je odrezan z glavnim prelomom. Apnenec je močno zakrasel do globine 80 m pod morsko gladino, vendar ni znakov, da bi morje skozenj prodiralo proti glavnemu apnenemu pogorju. Morska voda verjetno prodira po nekaj kilometrov dolgi poti jugovzhodno od glavnega preloma. Območje med izvirom in morjem leži nizko in drenira več podtalnic. Podzemeljski tok iz zakraselega mezozojskega apnenca, ki je večji del leta zaslanjen, ima glavni izliv v izviru Almyros. Majhen del voda se morda drenira v vršaj hudournika. Na novo je bil odkrit podzemeljski tok v neo-genskih sedimentih, predvsem v organskem apnencu, ki je malo zaslanjen zaradi izluževanja soli iz neogenskih sedimentov in bolj zaradi prodora morja. Slanost tega toka se ne spreminja, je pa manjša od poletne slanosti glavnega izvira. Za razumevanje hidravličnega mehanizma izvira so posebno važne covisnice med pretokom, gladino gornjega izvira in slanostjo, ki so podane za leto 1970/1971 na sliki 16 (Gov. of Greece, UNDP, FAO, 1968 do 1971). Za izvir je značilno, da slanost počasi in stalno narašča v času upadanja pretoka v sušni dobi, a se hitro zmanjša, kadar pretok močno naraste. Na sliki 16 je za fazo oslajevanja izvira označena prva meritev s količino klorida pod 50 oziroma 100 mg/l s »kon 50« oziroma »kon 100«. Analogno pomeni v fazi zaslanjevanja »zač 50« oziroma »zač 100« prvo meritev, ko je bila količina klorida nad 50 oziroma 100 mg/l. Količina klorida v vodi kraške podtalnice, ki ni pomešana z morjem, je okrog 35 mg/l. Količino 50 mg/l Cl~ smo privzeli za mejo, kadar ugotavljamo, ali se morje meša s podtalnico ali ne. Ob zmanjševanju pretoka se začne zaslanjevanje (Cl" več od 50 mg/l) ko se pretok zmanjša pod 13 do 14m3/sek. Pri pretoku okrog 12m3/sek. naraste slanost nad 100 mg/l in pri pretoku pod 11 m3/sek. prek 300 mgA Tabela 5. Table 5. Dischar«ea„d ^^^ *** Almyr°S (GoV' 0f Greece' FAO, 1968-1971) Discharge and salinity of the Almyros Irakliou spring during increase of the salt content (Gov. of Greece, UNDP, FAO, i»oa—1971) Prejšnje stanje Previous conditions Slanost prek 50 mg/l cr Salinity above Slanost prek 100 mg/l Cl" Salinity above Slanost prek 300 mg/l Cl" Salinity above Datum q Date m'/s bi-hr m Cl- Datum mg'l Date Q h| — h„ m'/s m Cl- Datum mg'l Date 9. 14. 11. 12. 22. 9. 2. 3. 68 12. 68 2. 69 3. 70 1. 71 2. 71 3. 71 16,48 12,99 13,84 18,60 12,71 17,38 15,00 4,48* 4,21* 4,32 4,73 3,71 4,06 4,05 35 35 35 35 38 14. 3. 16. 12. 12. 2. 13. 3. 23. 1. U. 2. 3. 3. 14,42 14.42 15.43 13,27 12,15 12,43 13,56 4,38* 4,38* 4,46 4,27 3,64 3,72 3,82 89 55 53 70 78 88 59 15. 3. 17. 12. 14. 2. 14. 25. 12. 1. 7. 3. Q m'/s h| — hm m Cl-mg/l Datum Date Q m'/s hi — hm m Cl" mg/l 13,56 4,26* 248 16. 3. 12,99 4,21* 355 10,80 3,93* 140 18. 12. 10,67 3,91* 370 13,27 4,28 142 19. 2. 11,88 4,10 302 11,34 4,05 142 16. 3 9,51 3,66 500 14,42 3,88* 29. 1. 11,48 3,58* 497 11,74 3,49 195 13. 2. 11,07 3,54 355 10,80 3,53 106 8. 3. 10,28 3,42 639 Ocenjeno po merjeni gladini v jezercu. Estimated according to level measurements in the pool. SI. 14. Pogled od izvira Almyros proti morju. Levo od jezu je viden izdanek mezozojskega apnenca, ki se vleče proti morju Fig. 14. View from the Almyros spring towards the sea. Mesozoic limestone crops out on the left side of the weir and extends seawards SI. 15. Pogled z morja proti planoti Keri in izviru Almyros pod njo. Desno od izvira je soteska Keri in nad njo hrib Stroumboulas. Hribovje na desni četrtini slike sestoji iz metamorfnih skrilavcev Fig. 15. View from the sea towards the Keri plateau and the Almyros spring below it. On the right side of the spring Keri gorge and Stroumboulas hill can be seen. Metamorphic schists build the hills in the right Gladina gornjega izvira, v metrih nad morjem Water level of the upper spring, in meters above sea level Pretok sladke vode v »/« od celotnega pretoka Discharge of fresh water in per-cents of total discharge Qv + Qm Celotni pretok Total discharge CI- Slanost Izvira v mg/l Cl- Salinity of spring in mg/1 Cl-zač 50 Prva meritev izvira s slanostjo nad 50 mg/l Cl- The first measurement of the spring with salinity above 50 mg/1 Cl- kon 50 Prva meritev izvira s slanostjo pod 50 mg/l Cl— The first measurement of the spring with salinity below 50 mg/1 Cl- hj—hm Qv SI. 16. Pretok, gladina in slanost izvira Almyros 1D70—1971 (Gov. of. Greece, UNDP, F AO, 1968—1971) Fig. 16. Water level, discharge and salinity of Almyros spring 1970—1971 (Gov. of Greece, UNDP. FAO, 1968—1971) Qv+Qm Celotni pretok Total discharge CI- Slanost v mg/l Cl- Salinity in mg/l Cl-fci—hm Gladina gornjega Izvira, v metrih nad morjem Water level of the upper spring, in meters above sea level SI. 17. Sovisnice med gladino, pretokom in slanostjo izvira Almyros (Gov. of Greece, UNDP, FAO, 1968—1971) Fig. 17. Relation between discharge, water level and salinity of Almyros spring (Gov. of Greece, UNDP, FAO, 1968—1971) Cl— Podatki so zbrani v tabeli 5 in na sliki 17. Na sliki vidimo, da se prične vtok morja pri pretoku okrog 13,5 m3/sek. Slanost se nato neenakomerno povečuje do pretoka okrog 9,5 m3/sek. in se pri nadaljnjem zmanjševanju pretoka enakomerno povečuje. Krivulja Cl~ = f(Qv + Qm) nakazuje domnevo, da mehanizem, ki regulira dotok pri pretokih med 13,5 in 9,5 m3/sek., postopoma odpira več spodnjih žil v različnih globinah. Vsi ti kanali verjetno skupno dovajajo morje pri pretokih pod 9,5 m3/sek. Pri naraščanju pretoka se zmanjša slanost pod 50 mgA Cl- šele pri pretokih nad 20m3/sek. Velika razlika v pretokih za enako slanost (50 mg/l Cl-) ni nastala zaradi različnega delovanja mehanizma, ki regulira dotok morja, ampak zaradi somornice, akumulirane v zgornji žili že takrat, ko se je dotok morja ustavil. To somornico mora sladka voda najprej izplakniti iz podzemeljske akumulacije, šele nato se lahko izvir osladi. 5. ZASLANJEVANJE KRAŠKIH IZVIROV IN NJIH KLASIFIKACIJA 5.1. Zaslanjevanje zaradi večje gostote morske vode Ako sta v določeni globini v stiku sladka in morska voda in imata enak piezometrični nivo, tedaj morska izpodriva sladko zaradi večjega tlaka, ki je posledica večje gostote morske vode. 5.11. Brojnice z zaslanitvijo v ustju izvira To so brojnice, pri katerih je voda v zgornji žili še sladka, se pa za-slani v ustju izvira, ki je bolj ali manj globoko v morju. Morska voda zaradi večjega tlaka vdira v tok sladke vode. Pri mešanju nastane somor-nica, ki je lažja od morske vode in se dviga proti površju. Pojav je podoben konvekcijskemu toku zraka nad segretim telesom. Tok somornice ima obliko stožca, ki se proti površju širi in je pod morsko gladino dobro viden, ker je zaradi migotic bolj ali manj moten. Migotice so posledica neenakomernega lomljenja svetlobe v vrtincih, nastalih pri mešanju morja s sladko vodo. Primeri takih izvirov so Brojnica (Sorgenti d'Aurisina) pri Trstu, Ca-dimare pri Speziji, La Mortola in Mar Piccolo pri Tarantu v Italiji ter Ayios Georgios v Grčiji. Brojnica, Cadimare in Ayios Georgios so v plitvem morju, 1 do 2, 6 in 10 metrov globoko. Pri La Mortoli je globina morja 39 m, v Mar Piccolo pa 19 m. Brojnice pri La Mortoli, Cadimare in v Mar Piccolo imajo po en glaven izvir, v Brojnici in Ayios Georgios pa je na precejšnji površini več izvirov podobne jakosti. Izvire, ki se zaslanjujejo v ustju, identificiramo na ta način, da čim globlje v ustju izmerimo slanost, ki mora biti manjša od približno 100 gA Cl— Najlaže določimo slanost z merjenjem električne prevodnosti. Utripanje kazalca amperometra, ki je posledica vrtincev sladke in morske vode, pove, da je elektroda aparata še v coni mešanja in da je treba izmeriti slanost globlje. Indikacija za izvorišče takšnega tipa je to, da je eden izmed več izvirkov sladek. 5.12. Zaslanjeni izviri v izotropno prepustnem kraškem vodonosniku Za izotropno prepusten kraški vodonosnik je značilno, da so razpoke in votlinice enakomerno porazdeljene v vseh smereh, tako da je poroznost podobna poroznosti zrnatih sedimentov. Sladka voda se torej zaslanjuje v celotni porozni masi in ne samo v posameznih kraških kanalih ali žilah. V porozni masi obstojita sladkovodna in morska cona. Med njima je cona mešanja, v kateri se voda zaslanjuje. Sladka voda se zaslanjuje delno zaradi difuzije morske in sladke vode, v glavnem pa zaradi mehaničnega mešanja pod vplivom plimovanja, sezonskega nihanja gladine in razlike v hitrosti sladke vode, ki teče proti morju, ter morske vode, ki miruje ali teče proti celini. Debelina cone mešanja je odvisna predvsem od gradienta podtalnice. Pri majhnih gradientih znaša le nekaj metrov, pri večjih gradientih in predvsem ob obali pa naraste na prek 50 %> višine vodonosne plasti. Delce morja, ki se mešajo z vodo v coni mešanja, odnaša tok vode in somornice proti izvirom. Zato nastane majhna razlika v gostoti in nadomestitev odnesenih delcev povzroči počasen tok morja proti celini. Tak tok je bil dokazan na Floridi (Chow, 1964), opazoval pa ga je tudi Ku š č er (1950). Ravnotežje med vodo in morjem se vzdržuje zaradi različnih gostot. V primerih, kjer je cona mešanja tanka, bi bilo možno računati globino mejne ploskve po Ghyben-Herzbergovi enačbi ali po Hubbertovi enačbi, pri debelejši coni mešanja pa po enačbi Lusczynskega (glej pogl. 3.2. Takšen tip izvirov identificiramo z vrsto izvirov vzdolž obale, ki niso mnogo dvignjeni nad morsko gladino. V več vrtinah merjene slanosti, piezometrične gladine in globine morske vode ali somornice je možno povezati v ploskve bolj ali manj pravilne oblike. Na ta način se zaslanjuje podvodni tok v Postirski dolini na Braču in v dolini Marina-Stupin ter obalni vodonosnik Izraela. 5.13. Zaslanjeni izviri v anizotropno prepustnem kraškem vodonosniku V anizotropno prepustnem kraškem vodonosniku se vodni tokovi združujejo. Dokaz za to je centralno dinarski kras, kjer je na površini 17 500 km2 samo 55 večjih izvirov. To pomeni, da se na vsakem izviru srednje izdatnosti 7 do 9m8/sek. praznijo podzemeljske vode kraškega terena površine 320km2 (Komatina, 1968). Podobno je na otoku Kreti, kjer tri ločena pogorja Dikti, Psiloritis in Lefka Ori sestoje iz apnenca. Zakrasele površine teh pogorij znašajo 150, 300 in 400 km2. Njihove podzemeljske vode se v glavnem praznijo v posamezne zaslanjene kraške izvire s srednjim pretokom 2, 6 in 8 mVsek. Tudi kaptažni rovi Postire, Dubrava, Zaton, Gustirna in Blaž kažejo, da se voda pretaka po posameznih privilegiranih poteh. To so lahko raz-pokane oone, splet majhnih votlinic, lahko pa tudi pravi kraški kanali. Zaradi enostavnosti jih bomo imenovali s skupnim imenom žila. Takšen pretok pa seveda v glavnem ni več podoben laminarnemu pretoku skozi več ali manj homogene sedimente enakomerno poroznega krasa ampak se približuje pretoku po ceveh. Tudi način zaslanjevanja ne more biti enak zaslanjevanju v zrnatih sedimentih in v izotropno prepustnem kraškem SI. 18. Shema kraških žil v bližini obale Fig. 18. Scheme of karstic veins near the coast mo Morje Sea gm Gladina morja Sea level i zaslanjen izvir Brackish spring v Dovodna žila s sladko vodo Primary vein with fresh water r Razcep žil Vein branching m Spodnja žila z morsko vodo Lower vein with sea water s Zgornja žila s somornico "Upper vein with brackish water u Ustje spodnje žile Mouth of the lower vein h Višina nad določenim začetnim nivojem Height above some reference level Srednja gladina morja Mean sea level Primerjalni nivo Reference level Tlačna linija dovodne in zgornje žile Plezometric head line of the primary and upper veins Tlačna Unija spodnje žile, izražena s stebrom sladke vode Piezometric head line of the lower vein expressed through the head of fresh water Linija energije dovodne in zgornje žile Energy head line of the primary and upper veins Linija energije spodnje žile Energy head line of the lower vein vodonosniku z laminarnim tokom vode s kolikor toliko regularnimi struj-nicami in kontinuirano cono mešanja velike vzdolžne in prečne razsežnosti. V anizotropno prepustnem kraškem vodonosniku se voda zaslanjuje v razcepu dovodne žile, kjer se mešata sladka in morska voda (G j u r a -šin, 1943; I. Kuščer, 1950). Najenostavnejši sistem kraških kanalov v bližini obale je shematično podan na sliki 18. Na desni strani razcepa ob priključku spodnje žile je pritisk P = Po + (hm~hr — ~--Tni) gQm (i) l 2 g I Tm = f(Qm) in na levi strani razcepa na dnu zgornje žile je pritisk P" = Po + ^h, — hr — ^ + Ts j g0s (2) T* = f(Qs) Tm in Ta sta poprečji tlačnih izgub v spodnji in zgornji žili, Qm je gostota morske vode v spodnji žili in — "m— (hi - hm) + J*I±L.Q*2± _ ^»-^g«. 6m P« — Qs 2 g (0m — 9s) V gornji neenačbi pomenijo imenovalci desnih členov razliko gostot vode v spodnji in zgornji žili, števec prvega člena višino izvira nad morsko gladino, števec drugega vsoto tlačnih izgub v spodnji in zgornji žili ter števec tretjega razliko hitrostnih višin v obeh žilah. Mnogi zaslanjeni izviri postanejo sladki ob visokih vodah, ko se poveča višina izvira nad morsko gladino. Ko pa pretok pojema in se višina izvira zniža, se zopet zaslanijo. ^ Imenujmo pretok sladkega izvira tik pred njegovo zaslanitvijo ravnotežni pretok Qeq. Tedaj je spodnja žila že napolnjena z morsko vodo, ki pa še ne teče v razcep. Sladka voda se ne izgublja v spodnjo žilo. Pritiska spodnje in zgornje žile sta v razcepu v ravnotežju. Skozi gornjo žilo teče samo sladka voda. Tedaj je: Qm = 0 Tm = O —-- =0 = QV = 1,0 Qm = 1,028 2 9 hi — hr= — (hi — hm) + —^— (5) {?>*— i?« — \ 2gJ - vs2 Ts^fiQev) — = /(Q«) 2g Na terenu je možno meriti pretok, gostoto vode in višino izvira. Meritev povprečnih tlačnih izgub in hitrostne višine v zgornji žili pa bi bila možna le izjemoma, če bi prodrli do razcepa potapljači ali Če bi zadeli razcep z vrtino. Predstavo o globini razcepa bo dal račun z ocenjenim Ts in Vs2 2 g V naravi lahko pričakujemo, da ima posamezni izvir po več dovodnih žil in več razcepov. Postopno zaslanjevanje izvira Almyros (glej si. 17), ko se pretok zmanjšuje od 13 na 9,5 m3/sek., kaže na več razcepov v različnih globinah. Obratno pa kaže nenadna zaslanitev izvira Blaž na en razcep (glej si. 8). Glede na globino razcepa žil delimo te izvire na dve skupini. 5.131. Zaslanjeni izviri v anizotropno prepustnem kraškem vodonosniku s plitvim razcepom Razcepe do 100 m globine pod gladino morja označujemo kot plitve. Pri tej globini je še možna sanacija izvira s tesnenjem spodnje žile, pri globljih pa večinoma ne. Izvire v anizotrozno prepustnem kraškem vodonosniku s plitvim razcepom spoznamo po tem, da so to posamezni koncentrirani izviri, katerih gladina je lahko do 2,5 m dvignjena nad morsko gladino takrat, ko so zaslanjeni. Podatki o slanosti in o globini morske vode ali somornice iz več vrtin v zaledju izvira se medsebojno razlikujejo, kar je razumljivo, če pomislimo na sterilne cone in priviligirane cone pretoka. S pojemanjem pretoka se slanost povečuje. Možno je tudi, da se slanost nenadoma poveča, kadar vleče spodnja žila morsko vodo kot natega, ko se primerno zniža pritisk v zgornji žili zaradi zmanjšanja dotoka sladke vode. Tak pojav so opazovali na izviru Blaž v Istri v oktobru 1970. Podoben pojav je hitra sprememba brojnice v morski požiralnik, kar so opazovali v brojnicah Kola pri Jurjevem in Gurdič pri Kotoru. Če bi gladino izvira dvignili naravno ali z zajezitvijo na ustrezno ko. Voda se izgublja po spodnji žili proti morju če je Qm i « • , . , že izgubili ves ali večji del pretoka sladke vode skozi razcep n in spodnjo žilo mi. Vse vmesne možnosti pomenijo delni uspeh sanacije. Izkušnje o sanacijah z dvigom gladine so dokaj skromne. V letih 1951 do 1953 je prof. Šegvic v Postiri na Braču preizkušal svojo napravo na podvodnem izviru s pretokom 5 do 7 l/s. Izvir je bil v globini 2 m in oddaljen 20 m od obale. Ustje izvira je bilo pokrito s teleskopsko povezanimi plastičnimi cevmi. Najvišja cev je s pomočjo plavača vzdrževala gladino izvira okrog 0,3 m nad gladino morja. V suši se je slanost znižala od 1200 na 440 mg/l Cl" (Šegvic, 1955). Uspeh je bil zaradi premajhnih sredstev in hidrogeoloških razmer le skromen, ker ni bilo možno dovolj dvigniti gladine v izviru. Izvir Pištica na otoku Visu se je leta 1956 zaslanil na 3600 mgA Cl", potem ko so s kaptažnim rovom zadeli na kaverno in znižali gladino. Po Tabela 6. Table 6. Delovanje zaslanjenega Izvira z dvema spodnjima žilama pri postopnem dviganju gladine izvira Brackish spring with two lower veins during a gradual artificial rise in spring level Umetni dvig gladine Artificial rise in spring level Ah; 0 A hi 1 A hi 2 A hi 3 A hi 4 Ravnotežna ploskev Equilibrium plane Razcep 1 Razcep 2 Izvir Vein branching 1 Vein branching 2 Spring Vtok morja Inflow of sea water heq 0 heg 1 heq 2 heg 3 hon 4 da yes ne no ne no ne no ne no Izgube sladke vode Losses of fresh water ne no ne no da yes da yes da yes Vtok morja Inflow of sea water da yes da yes da yes ne no ne no Izgube sladke vode Losses of fresh water ne no ne no ne no ne no da yes Pretok Slanost Disc- Salinity harge 5 Q S« Q Si < So Qiek mil,, m vot^ Structure Develop- gation Yearly ^arty Annual ^ Structure P and ma,nte- flow Water method develop- cost cu.m secm milho" . cfsts ment million c.°?ts cu- din/cu. m. costs din m^l!on meters million din din Gotovi objekti — Completed structures Marina rov 0,300 0,0218 0,0015 0,0035 0,11 0,265 gallery Dubrava I rov 0,600 0,0435 0,003 0,037 1,17 0,050 gallery Kovča- rov 2,600 0,1887 0,013 0,030 0,95 0,266 Zaton gallery Dubrava II rov 1,000 0,0726 0,005 0,015 0,47 0,206 gallery Gustirna I rov 0,600 0,0435 0,003 0,060 1,89 0,0302 gallery A. Georgios izolacija 34,000 2,178 0,150 12,0 378,4 0,0076 Kiveri isolation Izdelan projekt sanacije — Design of development completed Mojdež izolacija 6,000* 0,435 0,030 0,2** 6,30 0,0925 isolation Almyros II izolacija 33,600* 2,440 0,168 0,3** 9,45 0,345 isolation Almyros I dvig 8,500* 0,616 0,043 1,0** 31,54 0,0261 raise in spring level * Stroški ocenjeni po ponudbah izvajalcev. Costs estimated according to preliminary constructor bids. ** Pretok je ocenjen kot % pretoka izvira. The discharge estimated as percent of brackish spring discharge. je gradnja 150 m dolge in 10 m visoke zemeljske pregrade s prelivom in zapornico, s katero bo možno dvigniti gladino izvira na koto 10 m. Letni stroški kapitala in odplačila so računani pri 6-odstotnih obrestih in odplačilni dobi 30 let. Letni stroški vzdrževanja so ocenjeni kot 0,5 °/o investicije. Za nedograjene objekte je bil pretok ocenjen kot odstotek pretoka nesaniranega izvira. V ceni vode so stroški kapitala in vzdrževanja računani na 80°/» izkoriščanje letnega pretoka. Stroški eventualnega črpanja in napeljave vodovoda do potrošnika niso upoštevani. Cena vode velja za odvzem iz kaptaž-nega rova ali zajezitvenega jezerca. 7.2. Cena sladke vode, pridobljene iz morja ali somornice Osnovni podatki objektov in cena vode so zbrani v tabeli 11. Tabela 11. Table 11. Cena vode, pridobljene iz morja ali somornice Cost of desalted water Stev. Objekt Number Structure Način desalinizacije Method of desalinization Leto gradnje Year of construction Letna zmogljivost milj. m3/leto Annual capacity million cu. meters Cena vode Water cost din/ma din 'cu. m. 1 Shuwaik C + D Kuwait destilacija distillation 1957 0,87 4,76 2 Shuwaik E Kuwait destilacija distillation 1960 1,66 2,97 3 Buckeye Arizona elektrod iali za electrodialysis 1962 0,90 3,10 4 Curacao Cuba destilacija distillation 1963 2,21 4,81 5 Atomska elektrarna Izrael Nuclear pover station Israel destilacija distillation projekt design 120,0 1,7—2,25 6 Benghazi Libija elektrodializa* electrodialysis* 1969— 1971 6,9—16,4 1,71** Elektrarna na pogon z jedrskim reaktorjem v Izraelu naj bi imela moč 200.000 kW, del toplote bi porabili za destilacijo vode. Podatki za objekte št. 1—4 po United Nations 1969, in št. 6 po Water and Water Engineering 1969. * Iz somornice z 6500 mg/l Cl". From the brackish water with 6500 mg 1 Cl- ** Cena velja za večjo zmogljivost naprave. The cost valid for a big plant capacity. 7.3. Primerjava načinov preskrbe s sladko vodo Voda sladkih izvirov, prečiščena rečna ali jezerska voda in sladka podtalnica so gotovo najcenejši viri preskrbe s sladko vodo. Poprečne cene te vode ni možno podati, ker se spreminja v odvisnosti od morfoloških, hidroloških in geoloških razmer. Kjer obstajajo naravne možnosti, se je treba usmeriti na preskrbo s sladko vodo s kopnega. Na drugem mestu je sanacija zaslanjenih kraških izvirov. Voda iz saniranih izvirov je mnogo cenejša kakor voda, pridobljena iz morja ali somornice. Za umetno desalinizacijo bi se odloČili samo tam, kjer ni drugih možnosti. Cena take vode je še zelo visoka. Z intenzivnimi raziskovanji poskušajo odkriti cenejše postopke. 8. SKLEP Zaslanjeni izviri so pogost in v splošnem dovolj pojasnjen pojav na kraških obalah. Vedeti pa moramo, da ima vsak izvir svoje posebnosti, ki otežujejo raziskave in sanacijo. Vsakega zaslanjenega izvira ni možno sanirati, zato je treba izbirati tiste, kjer so orientacijske raziskave nakazale največ možnosti za uspeh. V detajlne raziskave moramo vključiti tudi večji del sanacijskih ukrepov: izolacijo, dvig gladine, tesnitev spodnje žile in kopanje raziskovalno-kaptažnega rova. Samo poizkus s sanacijskimi ukrepi lahko popolnoma razjasni način zaslanitve in nakaže uspeh sanacije. Največja težava sanacije zaslanjenih izvirov je v tem, da je treba vložiti v raziskave z vključenimi sanacijskimi poskusi mnogo truda in denarja. Druga težava je dolga doba raziskav in sanacijskih del ter negotovost, da bodo dela uspešna. Razmere so podobne kakor pri iskanju novih rudnikov ali mineralnih surovin. Zato lahko prevzamejo financiranje raziskovalnih in sanacijskih del večje teritorialne enote, ki so sposobne prevzeti stroške in riziko, sicer večje sanacije ne bodo izvedljive. V nekaterih delih Dalmacije so prešli na gradnjo dragih regionalnih vodovodov ravno zaradi tega, ker je bil pri teh delih končni uspeh zagotovljen že v naprej. Zaradi dragih raziskav in sanacij in izgub sladke vode, s katerimi moramo računati, se je treba usmeriti na velike izvire, od majhnih pa le na tiste, katerih uspešna sanacija bi bila zelo pomembna. S pravilnim planiranjem potreb po vodi bo možno pričeti z raziskavami in sanacijami pravočasno. Računati moramo, da trajajo raziskave in sanacija tri do pet let. Cena vode saniranih zaslanjenih izvirov je sicer višja od cene sladke vode, zajete na kopnem v bližini potrošnje, je pa mnogo nižja od cene sladke vode, pridobljene iz morja ali somornice. Dosedanji uspehi sanacij zaslanjenih kraških izvirov opravičujejo in spodbujajo k nadaljevanju teh del. 9. ZAHVALA Prof. dr. J. Baturič, ing. V. Cule, ing. D. Franič, ing. J. Krznar, dr. B. Mijatovič, ing. B. Pavlin, Prof. Dr. W. Stander in Dr. A. Stefanon so mi dali na razpolago neobjavljene podatke o najnovejših sanacijskih delih. Vladi Grčije in Malte, Organizacija Združenih narodov za kmetijstvo in prehrano — Rim, Geološki zavod — Ljubljana, Geotehnika — Zagreb, in Zavod za geološka i geofizička istraživanja — Beograd so mi dovolili uporabo njihovih neobjavljenih poročil. Sklad Borisa Kidriča — Ljubljana je financiral raziskavo in Laboratorij za mehaniko tal FAGG Univerze v Ljubljani mi je nudil vso pomoč pri izdelavi študije. Vsem se najlepše zahvaljujem. The Origin of Brackish Karstic Springs and Their Development Marko Breznik Contents Abstract..........................157 1. INTRODUCTION.....................158 2. GLOSSARY OF THE TERMS USED IN THE PAPER.......158 3. EXPLANATIONS OF THE COASTAL SPRINGS CONTAMINATION 160 3.1. Review of references..................160 3.2. Sea water intrusion into karstic aquifers...........160 4. DESCRIPTION OF SOME BRACKISH SPRINGS........163 4.1. Brojnica springs near Triest...............163 4.2. Springs in the Sečovlje valley in Slovene littoral.......163 4.3. Blaž spring in Istria..................163 4.4. Springs to the south of Senj in Croatian littoral........164 4.5. Springs in the Poljice bay near Trogir...........165 4.6. Pantan spring near Trogir................165 4.7. Pištica spring on the Vis island..............166 4.8. Springs near Postire on the Brač island...........166 4.9. 2rnovica spring near Gradac...............167 4.10. Springs in Morinj bay of Boka Kotorska..........167 4.11. Submarine springs near La Mortola on the Italian-French border 168 4.12. Submarine spring at Mar Piccolo near Taranto in Italy.....168 4.13. Submarine spring Cadimare at Spezia in Italy........168 4.14. Ayios Georgios spring near Kiveri in Greece.........168 4.15. Sea swallov holes on the Kephallinia island in Greece .... 169 4.16. Almyros Iraldiou spring in Greece............169 5. THE ORIGIN AND CLASSIFICATION OF BRACKISH KARSTIC SPRINGS........................170 5.1. Springs contaminated due to the greater density of sea water . . . 170 5.11. Submarine springs contaminated in their mouths.....170 5.12. Springs in the karst aquifer showing isotropic permeability . 171 5.13. Springs in the karst aquifer showing anisotropic peremability 171 5.2. Springs contaminated by sucking of sea water due to hydrodinamic effect........................173 5.3. Springs contaminated by the combination of greater density and hydrodynamic effect..................174 6. THE POSSIBILITIES FOR THE DEVELOPMENT OF BRACKISH KARSTIC SPRINGS.................... 6.1. The development of springs contaminated on the density principle 6.11. Submarine springs contaminated in their mouths..... 6.12. The development of brackish springs of the karst showing isotropic permeability................ 6.13. The development of brackish springs in the karst showing anisotropic permeability............... 6.131. Development by raising in the spring level..... 6.132. Development by sealing the lower vein....... 6.133. Development by the interception of fresh water before the contamination............... 6.2. The development of brackish springs contaminated due to the hy-drodinamic effect................... 6.3. The development of brackish springs contaminated by the combination of density and hydrodinamic principles......... 7. ECONOMICAL ASPECTS OF BRACKISH SPRINGS DEVELOPMENT 8. CONCLUSION...................... 9. ACKNOWLEDGMENTS .................. 10. References........................ Abstract Brackish karstic springs are a regular phenomenon of every sea shore made of limestone. They are known in almost all Mediterranean countries but are especially frequent on the coasts of Yugoslavia and Greece. Development of karstic springs contaminated by sea water would be of great human and economic importance for these areas short of fresh water. Field investigations of many brackish springs in Yugoslavia, and of the Almyros and other springs in Greece and the elaboration of data concerning about thirty springs in the Mediterranean Sea were the basis for the dissertation. The explanation of sea water intrusion is discussed briefly. One important conclusion of the study is that there are some different ways of contamination. Consequently the brackish karstic springs are classified as follows: a) Springs contaminated due to the greater density of sea water. 1. Submarine springs contaminated at the mouth of the spring. 2. Springs in the karst aquifer of isotropic permeability. 3. Springs in the karst aquifer of anisotropic permeability with either shallow or deep vein branching. b) Springs contaminated due to the hydrodinamic effect. c) Springs contaminated by a combination of greater density and hydrodinamic effect. 174 174 174 175 176 176 179 180 181 181 181 182 183 183 The way in which springs could be developed, the chance to remove the salt from brackish water and to prevent the karstic fresh water from mixing with sea water are discussed for each group. The economical aspect of development is also discussed. The price of the water of developed springs is higher than the price of fresh ground water but much lower than the price of the water produced from brackish or sea water in desalinisation plants. The successes already achieved justify and stimulate the development of brackish springs. 1. INTRODUCTION Brackish karstic springs are a regular phenomenon of every sea shore consisting of limestone or dolomite. Fresh water from the calcareous karstic aquifer is contaminated by the intrusion of sea water which renders the spring water useless. Development of brackish springs would be of great human and economic importance for these areas short of fresh water. Kohout (1966) pointed out that only a few scientific investigations of these phenomena had been made and that the development technique had not improved much since the time of the Phoenicians who covered the submarine springs with lead funnels and fed fresh water into the leather bags. The greater part of the Yugoslav coast and a large belt of the hinterland are made of carbonate sediments. The first systematic investigation of brackish karstic springs started in the late thirties (Kuščer, 1946/1947), the mechanism of the springs was explained in the forties (Gjurašin, 1942, 1943; Kuščer, 1950). Intensive investigations and development on the Adriatic coast are a result of the last 15 years (Fig. 1). At the same time some investigations were carried out in Lebanon, Libya, Malta, France, and Italy, and large ones in Israel and Greece. The author participated in part of the investigations in Greece and Yugoslavia. A review of the possibilities for development, of the favorable natural conditions and of the investigations necessary was the main aim of the study. The investigation and development costs and the price of water of developed springs were discussed either. 2. GLOSSARY OF THE TERMS USED IN THE PAPER Karst aquifer of isotropic permeability. Karst region with many solution fissures, small channels which are well connected in all directions. Movement of water is possible in all directions and is analogous to the ground water movement in granular sediments. Karst aquifer of anisotropic permeability. Karst region with isolated karstified zones and not karstified blocks between them. Ground water moves along veins that means along well karstified zones. The aquifer is highly permeable in the direction of veins whereas poorly permeable or impermeable in the transverse direction. Ground water movement is similar to the movement of water in a system of pipes which are not densely disposed. Aquifer. A formation, group of formations or part of a formation that bears water which is not bound chemically or physically to the rock. Karstic ground water. Water which fills karstic pores and veins in the drowned zone and is not bound physically or chemically to the rock. Aerated zone. Zone above ground water surface in which karstic pores are filled partially with air and partially with water. Drowned zone. Zone below ground water surface in which karstic pores are saturated with water. Fresh water zone. Part of aquifer saturated with fresh water. Brackish water zone (also called zone-of-mixing or transition zone). Part of aquifer saturated with brackish water. Sea water zone. Part of aquifer saturated with sea water. Interface. The surface bordering the fresh water and sea water in an aquifer of isotropic permeability. This border could be sharply defined but is usually a transition zone. Toe of the interface is the place where the interface reaches the impermeable layers below the aquifer. Equilibrium plane. Nominal plane connecting in the karst of anisotropic permeability those points of veins and branchings where the water pressures from the fresh water and sea water sides are equal. Toe of the equilibrium plane is the place where the equilibrium plane reaches the impermeable layers below the aquifer. Storage coefficient of the Karst is the volume of water which a karstic aquifer release from storage or takes into storage. Brackish spring. General term which means a spring with brackish water but also the vein and place of such a spring. Submarine spring. A spring with either fresh or brackish water rising from the sea bottom. Sea swallow hole. Hole in the sea bottom or seashore which swallows sea water. Sea estavelle. A submarine spring which stops to flow in every dry season and starts to swallow sea water. Vein. General term for a zone which is highly pervious in the flow direction and poorly permeable or impervious in the transverse direction. Ground water moves through veins in the karst of anisotropic permeability. The form of the vein is undefined, it could be a solution channel, a pervious fissured zone, a system of small connected cavities etc. Vein branching or shortly branching. The place where the primary vein branches off into a lower vein connected with the sea and an upper vein leading to the spring. Sea means the sea water too. Fresh water. Sweet fresh ground water unmixed with sea water. Brackish water. A mixture of fresh and sea waters. Salinity. Quantity of salts in water. In this paper expressed as content of chlorine ions (Cl~) in mg/1. The salinity of the Mediterranean Sea is about 21 000 mg/1 of C1-. Admissible salinity. The quantity of salts in drinking or irrigation water which is harmless to people, animals or vegetation. Yugoslav standard for drinking water is 250 mgA of Cl~. In dry areas a drinking water with 500 mg/1 of Cl" is considered as harmless. Many villages in the Mediterranean use water with more than 500 mgA of Cl~, the Bedouins of Sahara up to 2000 mgA of Cl" 3. EXPLANATIONS OF THE COASTAL SPRINGS CONTAMINATION 3.1. Review of references The Almyros spring with fresh water in winter and brackish water in summer was explained in a surprisingly clear way by Laurentis de Monacis from Venice in the year 1364 (According to P a t a k i s , 1968): Anno Domini 1364, sexti Mai. Et spelunca vero, quae est penes radicem dicti Strumbuli (mountain above the spring, author's remark) a dicta parte Orientali exit cum impetu magnus globus salsarem aquarum, quae vementes a mari per subterraneos anfractus emittuntur per ora dictae speluncae; a salsedine vero locus ille dicitur Almiro. Inhieme vero non sunt ita salsae; nam a pluviis de contiguis montibus in valles defluentibus et penes illam speluncam cadentibus aliquantulum dulciorantur. Many speculations have been established during the last 150 years in order to explain the phenomenon of the sea mills near Argostolion on Kephallinia island in Greece. The speculations of Brown (1835), Strickland (1835), Dawy (1836), Piickler (1841), Mousson (1858), Unger and Ansted (Glanz, 1965) are not physically acceptable. According to the first well explained theory originated from Fouque (1867) the swallowing of sea water flowing towards the Livadi springs is due to the greater density of sea water which mixes with fresh water in the deep vein branching. The W i e b e 1' s explanation suggesting the flow of swallowed sea water towards the Sami springs and aspiration of sea water due to hydrodynamic effects is acceptable too. The brackish springs from grained sediments were interpreted by Eadon-Ghyben (1888), Herzberg (1901), H u b b e r t (1940), Cooper (1959) and Luscynski (1961). The brackish springs in karst were explained by Fouque (1867), Wiebel (1874), Lehmann (1932), Gjurašin (1942, 1943), I. K u-ščer (1947, 1950), I. and D. K u š č e r (1962), Man del (1971), E delni an (1966) and Stefan on (1971). 3.2. Sea water intrusion into karstic aquifers Lehmann (1932) explained the Wiebel's theory (1874) by a Venturi tube effect due to the natural contraction of a karstic channel. Fouqu6 (1867) first expressed the opinion that the greater density of sea water generates the inland flow of sea water towards the brackish springs. Gjurašin's (1943) theory is based on a good knowledge of the underground morphology of the karst. The intrusion of sea water occurs in veins branchings due to its greater density. The seasonal changes of the spring salinity could be explained by the change in the pressure of fresh and sea waters in the branching. A more general form of this theory was given by I. KušČer (1950). Figure 2 will help to show some quantitative relations. Let us suppose that the lower vein is closed near the branching by two plugs and the space between them connected with the spring outlet by an imaginary auxiliary tube. The behaviour of the system is determined by the pressure differences P and S upon both plugs: P = p' — p" = [Po + Qm 9 (hm — for)] — [Po + Qv 9 {hi — M] ^ p = {om — qv) g (hi — hr) — Qm g (Ji,- — h„<) Hydrostatic overpressure from the sea side P is positive only if the branching is situated sufficiently deep, i. e. if h. _ hr > —- (hi — hm) = 36,4 . [h; — M (b) {.'«? — Qv S — p" — p" - (1-k)- {>r - Ws] . Qr2 = C Qr* (c) L 2 Qr2 2 q,* J where it means: p — hydrostatic pressure, p0 — atmospheric pressure, q — density (g/cms), g — gravity acceleration, h — height above some reference level, q — cross-section of a vein, Q — flux of water, v = Q: q mean velocity. The notations p, o, hy q, Q, v are more closely determined by the adjoined indices i, r, v, s, m. These refer as follows: i to the upper opening, r to the branching, v to fresh water or to the primary vein, m to sea water or to the lower vein, s to brackish water or to the upper vein. The equation c is only an approximation for high Reynolds' numbers. The constant k (— 1 < /c < 1) depends on the configuration of the branching. The coefficient c, which may be called the sucking coefficient is positive only if the vein is narrowed just at the branching. Let us again close the auxiliary tube and remove the plugs A and B. The overpressure p' — p" = P + S determines whether or not sea water will flow in. According to the signs of P and S four cases are possible which I. K u š č e r denotes as types PS, P, S and N. Type PS: The branching is situated sufficiently deep and is narrow enough, so that both P and S are positive. At any discharge the spring remains brackish. Type P: The branching is situated deep enough (P > 0), but is not narrow enough so that S is negative. The spring is brackish only at low flux, and its salinity disappears when the flux of fresh water reaches the value Qo - ]/— at which P + S = 0. When this limit is surpassed, fresh water will penetrate into the lower vein. Type 5: At P < 0, but S > 0, the behavior of the spring is just inverse. It becomes brackish only at high flux, after the limit Q0 has been surpassed. 11 — Geologija 16 Type N: A spring with P< 0 and S < 0, can never become brackish. Gjurašin gives for the type P formulae and diagrams representing the dependence of the salinity upon the flux. The limit value of the salinity at a very weak current is: ( 0) should exist, as the two rushing currents would soon erode and widen the narrow passage. Man d el (1971) states that the solution process has enlarged the hydraulic conductivity in the flow direction and rendered the aquifer strongly anisotropic. The pattern of potential distribution is changed in a way which induces an upwards and inland displacement of the interface. Under the prevailing conditions of anisotropy sea water penetrates into the aquifer and mixes with fresh water. G lan z (1965) studied the hydraulic mechanism of the sea-mills of Argostolion after the connection with Sami springs at a distance of 15 km had been proved. The inflow of sea water (1,7 m3/sec) is too big for only one Veneturi tube, but it is nearly impossible to synchronize a simultaneous action of many parallel Venturi tubes. A jet of fresh water reaching a vein of sea water will produce a movement of sea water in the direction of the fresh water impulse. The addition of the effects of many impulses is possible. E d el m a n (1966) treated the influence of pumping out of a lense of fresh water floating on sea water. The flowlines of the ground water movement are directed towards the springs on the sea shore during the state of natural conditions when the precipitations recharge the ground water (Fig. 3a). Pumping out of a well changes the flow pattern. The flowlines of sea water rising towards the pumping well out of the lower part of the aquifer contaminate the well (Fig. 3c). Bat uri č (1961, 1969) considers that the karst is uniformly porous except some rare veins. Ground water movement near the sea shore is similar to the movement in grained sediments but is influenced by the existence of impermeable or nearly impermeable barriers (Fig. 4). Ground water flows seawards over these barriers and sea water moves inland under these barriers due to its greater density. Between the barriers there are zones with different salinity which increases as they approach the sea. Stefan on (1971) considers that the contamination of submarine springs occurs in the mouth of the spring. 4. DESCRIPTION OF SOME BRACKISH SPRINGS 4.1. Brojnica springs near Triest These springs are also known by the name Sorgenti d'Aurisina (B o e -g an, 1906). The water issues from the karst limestone, where there the overlying flysch has been removed by sea. There are 7 submarine springs near the coast in a line of 100 metres. The two largest springs were tapped in 1860 but were dry in the years 1865 and 1868 and brackish in the year 1867. The development was considered unsuccessful at that time. Thirty years later when the needs of the Triest town for water had increased all the 7 springs were successfully developed (Fig. 5). 4.2. Springs in the Sečovlje valley in Slovene littoral The calcareous anticline of Buje is an important collector of ground water in the Istria peninsula which is short of water. The aquifer is partly drained towards the Sečovlje valley. The interest in developing these waters for water supply increased after a large intrusion of ground water into the Sečovlje coal mine 4 kilometres distant from the sea at a depth of 230 metres below the sea level (Fig. 6). In December 1955 the total inflow into the mine was 160—190 litres per second with a salinity of 420—520 mg/1 of Cl~ (Breznik, 1956) and the inflow into the second southeastern field 120—150 1/sec with 80 mgA of Cl~ Later this water was partially developed with a borehole above the second field (Breznik, 1958) and many boreholes near Bužini and Gabrieli springs. Now when the mine is abandoned and drowned it would be possible to capture all the water with deep boreholes penetrating into the second mine field. An important experience is that the sea water zoine does not reach the area of the mine which was proved by the small salinity of the intruding water inspite of an enormous depression in the mine. 4.3. Blaž spring in Istria The Blaž bay is 10 to 20 metres deep. Along the calcareous coast there are about 20 springs in a line of 500 metres. Most of them are coastal and some submarine springs. The main spring however forms a pool at a distance of 30 metres from the shore (Fig. 7). The minimum discharge of the main spring is about 150 litres per second and of other springs about 40 litres. Mean discharge is about 1,6 cubic metres per second and the maximum was 2,6m3/sec in the year 1970. The salinity of the main spring was below 100 mg/1 of CI" during the observation period from 1969 to September 1970. In October 1970 the salinity had increased quickly to 12 000 mg/1 of Cl~ when the level in the pool had dropped to 0,54 m above sea level when the side sluice was open (Fig. 8). The salinity of the other springs is higher because their altitudes equal sea level. The aim of the investigations in the years 1968—1970 was to find the zones of fresh water inflow both near and far from the spring. The desire was to find a location where a collecting structure could intercept the biggest quantity of fresh water. The tracer tests performed in boreholes B-l, B-2 and the cave Rebiči at a distance of 3 kilometres from the springs have shown a fan-shaped direction of ground water flow towards the sea. During the second phase of the investigations 20 boreholes were drilled in the near vicinity of the spring. The aim was to find the main zones of fresh water flow towards the springs and the zones of sea water intrusion. Permeability pressure tests, salinity and temperature measurement were performed in all boreholes and the flow direction determined with tracer tests. The main quantity of fresh water flows through a 40 metres wide belt between boreholes B-6a — B-24 and B-17—B-15 towards the spring (Fig. 7). Most of the boreholes in this belt showed a high permeability of the rocks at shallow depths and boreholes B-18, B-16 and B-23 at a depth of 40 metres below sea level and deeper. The velocity of the tracer movement between boreholes B-15, B-16, B-23, B-25 and the main spring were 19, 134, 60 and 40 metres per hour. The researchers consider these velocities as moderate and conclude that the main inflow vein was not revealed by boreholes. Water remained fresh in boreholes until the end of September 1970 and the salinity increased simultaneously with that of the main spring. Salinity in the boreholes to the north and south of the main spring and between the main spring and the sea increased continuously during the year 1970 and did not change during the high contamination of the spring in October 1970. It is considered that the sea water vein which contaminates the spring was not detected by boreholes. The development design anticipated capturing the water in the main spring and to construct a grouting screen 500 metres long and about 40 m deep situated along the coast which should prevent the inflow of sea water (Fig. 7). In the first stage only 300 metres of the screen should be constructed. The largest quantities of fresh water could be captured in this way. Later an investigation gallery was excavated in the direction of the borehole B-24 where the highest ground water surface was observed. At a distance of 70 metres a cave with fresh water was found. The explorations are not completed yet. 4.4. Springs to the south of Senj in Croatian littoral There are some hundreds of coastal and submarine springs and some sea estavelles along a four kilometres long coast south of Senj. These springs were examined in detail by I. K uš čer and his colleagues in the years from 1937 to 1940 and from 1946 to 1947 (I. Kuščer, 1946/47, 1950; I.and D. Kuščer, 1962). The best investigated is the group of springs at the sawmill near Jurjevo, where 70 coastal and 30 submarine springs and some estavelles are on a 300 metres long coast (I. Kuščer, 1950). The largest of these springs are the estavelles (KE) on the western side (Fig. 9) called "Kola" ("the wheels"). The whole group may be divided into subgroups (KA, KB,... KF). There were no differences in salinity between the springs of the same subgroup. The relations between the subgroups have been investigated to some extent. Figure 9 shows qualitatively the connections and the succession of the branchings r2t r3, r4, but cannot tell anything about the length and directions of the underground veins and other details. In the rainy season fresh water flows from all springs. After the rain ceases the springs begin to weaken, and sea water first penetrates through X to r4 and the springs KF disappear. The springs KE then become brackish to about 700 mg/1 of Cl~ which means that sea water starts to penetrate throug the vein X. Later sea water penetrates also into vein Y, so that the springs KA and KB become brackish too, all to the same degree of 1700 mgA of CI". At the same time and by the same amount, the salinity of KE increases. This was observed at the end of July 1940. Finally but only in dry summers, the Kola KE stops and starts to swallow sea water. This causes the salinity of KB to increase up to about 9000 mgA of CI- while that of KA decreases a little, presumably because of the slight increase in pressure at rv The swallowing of Kola was directly observed. KEa swallowed some hundred litres per second. The researchers performed a tracer test on 30 July 1947 in order to obtain a proof of the connection with the springs on the other side of the bay. A solution of 300 grams of fluoresceine was poured into the estavelle KEa. Five hours later, the first trace, some lO-^g/cm3, appeared in the springs KB. For 1 hour the concentration progressed, up to some 3.10-8g/cm3, and then fell off very slowly. Unexpectedly, with a delay of six and a half hour the colour appeared in KA, though in a concentration 2 or 3 times less. The rainfalls in autumn reverse the above changes in succesion until the initial state of fresh water flow is restored. 4.5. Springs in the Poljice bay near Trogir Jevremovic (1966) reports that the salinity of springs in the Poljice bay increases with the increase in the discharge. During the dry period in September 1957 the salinity was 1500 to 1900 mgA of CI" and during the high discharges in April 1962 6620 to 6700 mgA of CI". 4.6. Pantan spring near Trogir Karstified limestone beds of the Kozjak mountain are thrust over the flysch syncline of the Kašteli bay and closed against the sea. The limestone is drained by the Pantan spring issuing 500 metres from the sea. An artificial weir forms a pool around the spring. An old mill is driven by the spring water. The level in the pool fluctuates between 2.5 and 4 metres above sea level. The winter discharge reaches lOmVsec and in the dry period drops to 1,3—2 mVsec. The salinity in winter is 500 mgA of Cl~ and in summer rises up to 10 000 mg/1 of CI" The increase in the salinity is slow and proportional with the decrease in the discharge (Fig. 10). One and a half kilometre away is the Slanac ("salty") spring which flows for only two months during the winter. The discharge of the spring is 0,5 mVsec and the salinity 800 mg/1 of CI" The elevation of 27 metres above the sea level is surprising. Two submarine springs at a distance of 900 and 2500 metres from the Pantan spring rise from the sea floor of the Kaštela bay during the winter time. Investigation drilling in the hinterland of the Pantan spring found fresh water in borehole B-l at a distance of 1.5 kilometres from the spring (Mijatovič, 1972). 4.7. Pištica spring on the Vis island In winter 1956 the salinity of the Pištica spring increased to 3600 mg/1 of Cl~ after the increase of the discharge to 601/sec during the excavation of the water capturing gallery. Later the gallery was closed with a plug and a regulating valve installed. In 1958 the maximum of the regulated discharge was 37 1/sec and the salinity did not increase beyond 635 mg/1 of Cl"(Baturic. 1961). 4.8. Springs near Postire on the Brae island Extensive hydrogeological, geophysical and development works were performed on that island between the years 1958 and 1962. Island Braf with a surface of 400 square kilometres is mainly built of Upper Cretaceous limestone and dolomite which forms an anticline in the west-east direction. In the middle of the island there is a plateau 300 metres high with swallow holes. The island is mainly drained towards the north. The main investigations were made in the hinterland of the springs near Postire. Four parallel fissured zones directed towards the main springs were revealed and were supposed to be the main collectors of ground water. The investigation gallery K1 is 800 metres from the sea. In 1961 and 1962 the ground water level fluctuated between 0.48 and 5.74 metres above sea level. During the pumping test, water quickly became brackish. The exploitation discharge had to be intentionally decreased to 281/sec in winter and 3,51/sec in summer in order to keep the salinity within acceptable limits. The investigation gallery K2 is at a distance of 1800 metres from the sea. The shaft is 55 metres deep and the gallery 470 m long with the bottom 5 metres above sea level. Six fissured zones with ground water and a karstic chimney with a bottom 36 metres below sea level were found. Ground water level fluctuated between 2.61 and 12.14 metres in 1961—1962. Before the pumping the salinity was between 17.8 and 26.2 mg/1 of Cl~ and increased quickly to about 430 mgA of Cl~ when the pumping started inspite of a very small drawdown of some centi- metres. The exploitation discharge adjusted to the salinity of 250 mg/1 of CI" would be between 19.7 and 3.5 1/sec in summer depending on the rate of precipitations. The researchers consider that fresh water is floating above sea water in the area of both galleries. They have proposed closing the fissured zones in the gallery K2 with a grouting screen against the influence of sea water or excavating a new gallery at a distance of 2.7 kilometres from the sea. 4.9. Žrnovica spring near Gradac The Biokovo calcareous mountain is closed towards the sea with a long flysch syncline and a belt of dolomite. The development of the Žrnovica spring which drains the south-eastern part of the mountain would be important for the water supply of Makarska littoral. The main spring which rises in a small artificial pool is 1 metre above sea level. There are smaller coastal springs along the bay and two submarine springs at a distance of 120 m. A small spring on the western shore is fresh. The aim of the investigations in the years 1968—1970 (Krznar e. al., 1970) was to find the main channels in the hinterland of the main spring. Geophysical sounding has shown the greatest sea water intrusion to be along the fault betweeen the dolomite and limestone. Anomalies in the dolomite were also revealed. The first borehole in the dolomite found a poorly pervious rock and the boreholes in the limestones on the eastern side of the bay were not much better. The system of investigations was later changed. A row of boreholes was drilled just behind the main spring. The direction and velocity of the flow were determined by tracer tests. Two additional rows of boreholes were drilled at distances of 100 and 150 metres. Salinity and piezometric surface were also measured. The results are presented in Fig. 11 and table 2. The salinity decreasses quickly when mowing away from the sea. The researchers consider that the main active channels are in the dolomite and the fossilized ones following the main fault are closed by clay deposits. The development design proposes the exploitation of the present main spring. Sea-water intrusion should be blocked by a grouting screen constructed along the coast. A water collecting gallery in the area of the borehole 2-42, which has revealed the highest piezometric surface and fresh water, would have good chances of a successful development. 4.10. Springs in Morinj bay of Boka Kotorska The calcareous mountain of Orjen with the very high rate of yearly precipitation of 4000 mm is thrust over the Cukali zone. This zone of a very complicated lithostratigraphic composition (Fig. 12) is mostly impervious in the transverse direction, and closes the massif along its southern border against the sea. In the east where the Orjen is open to the sea, there are springs with a large discharge in the Morinj and Risan bays. The minimum discharge of the Morinj springs is 0.5 mVsec and the mean discharge about 5.5 mVsec. The salinity is 1000 to 12 000 mg/1 of Clin summer. Water is fresh during the winter and after the heavy rains in the summer. Ten boreholes and two wells were made and many tracer tests performed. The results are given in Fig. 13 and tables 3 and 4. The main channels are supposed to be in karstified limestone with Globotruncanae. The design of the development is based on the discovery of a location where the limestone is only 350 m wide due to a transverse fault. A grouting screen 360 metres long and 100 metres deep should be constructed out of a gallery. The screen should prevent the intrusion of sea water and permit a small rise of fresh water. Water collecting shafts should be excavated on the fresh water side of the gallery (Pavlin, B i o n d i č , 1971b). The excavation of the access gallery started recently! 4.11. Submarine springs near La Mortola on the Italian-French border Six hundred metres from the shore there are three submarine springs at a depth of 39 metres. The discharge of the springs is about 1001/sec and salinity below 75 mg/1 of CI- The design of a preliminary development proposes to cover the springs with a bell connected by a tube with a boat where salinity and discharge measurement would be made (Calvin o and Stefanon, 1969). 4.12. Submarine spring at Mar Piccolo near Taranto in Italy The spring rises at a depth of 19 metres from the sea bottom. Stefanon (1971) considers that it is contaminated with sea water inside the spring mouth. The spring was covered with a fibreplast bell. Pumping at different rates combined with salinity measurements should determine the exploitation discharge. 4.13. Submarine spring Cadimare at Spezia in Italy The spring rises from a depth of 6 metres. It was closed against the sea by a cylinder shaped structure. The level of the spring was raised to 3.5 metres above sea level. But the construction soon collapsed in rough sea (Crema, 1915; Calvino and Stefanon, 1963). 4.14. Ayios Georgios spring near Kiveri in Greece This spring drains the karstified plateau of the central part of the Peloponnesus peninsula. There were some small coastal springs with salinity of 177—184 mg/1 of CI" and a row of large submarine springs with 3000-4000 mg/1 of Cl" (S Under, 1971) and a discharge of about 10 mVsec. Springs were developed by a construction of a semicircular dam around the spring area. 4.15. Sea swallow holes on the Kephallinia island in Greece The level in swallow holes is 0.75 to 1.25 metres below sea level and the maximum inflow about 1.7 mVsec. A tracer test has shown the connection with the Sami springs 15 kilometres away. The discharge of these springs is about lOmVsec and the salinity 2100 to 2500 mgA of Cl~ (Maurin, Zotl, 1967). 4.16. Almyros Irakliou spring in Greece The spring is situated on the northern shore of the island of Crete iS kilometres from Iraklion (Heraklion). It is at the foot of the Keri plateau the extreme northeastern part of the Psiloritis (Ida) mountain at a distance of 1 km from the sea. The spring has a typical form "oko" of a rising karstic spring and forms a pool 60 metres in diameter. The main inflow into the pool is through a karstic channel at a depth of 20 metres. The cross section of the channel is about 5 m2. The upper spring in a cave besides the pool starts to flow at a discharge of over 8 mVsec. The minimum discharge is 4 mVsec, the mean 8 and the maximum about 30 mVsec. Water is fresh in the winter and brackish up to 5500mg/1 of CI" during the other seasons (Burdon, Papakis, 1964). The Psiloritis mountain is the catchment area of a surface of 300 square kilometres. The western part of the Psiloritis consists of platy limestone of the Permian period and the eastern of the Tripolitza limestone of Jurassic to Eocene period (Papadopoulos, Scanvic, 1968) (Figs. 14, and 15). The interest in the development of this spring has increased during the last ten years due to the increased needs for drinking and irrigation water. During the years from 1968 to 1971 extensive investigations of the spring were made by the Project of Greek Government and United Nations ' Study of Water Ressources and Their Exploitation for Irrigation in Eastern Crete". In the year 1968 a scheme of investigations was established (R e , Breznik, 1968) taking into account three possible ways of the spring development: a) Raising the level of the spring. b) Construction of a grouting screen to close the lower channels where sea water intrudes. c) Interception of the fresh water before the contamination. Investigations under b and c are partly carried out. Preparations for the test by raising the spring level are progressing. Mesozoic limestone of the Keri plateau is thrust over the impervious metamorphic schists. The front of the nappe is 500 metres towards the north from the spring. The Keri plateau is bordered on the eastern and southeastern sides by a subvertical fault with a dip separation of over 500 metres. The subsided part i. e. the Iraklion-Festos graben, is filled with Neogene sand, sandstone, silt, marl and organic limestone. The area between the spring and the sea is covered with an alluvial torrent fan. The distance between the spring and the sea is about 1 km and the exposure of limestone directed towards the sea is on the left side of the spring (Fig. 14). This area, where sea water could penetrate the limestone, was thoroughly examined. A 300 metres wide and 50 to 180 metres deep block of limestone extends towards the sea to a distance of 500 metres where it is cut off by the main fault. The limestone is strongly karstified to a depth of 80 metres below sea level. No signs of sea water intrusion were found here. Now we suppose that sea water penetrates the karst through the channels in the Mesozoic limestone below the Neogene deposits of the Iraklion-Festos graben. These channels should be some kilometres long. The discharge, the elevation of the upper spring and the salinity (Fig. 16) (Greek Gov., UNDP, FAO 1968—1971) help us to understand the mechanism of the spring. A slow and constant increase in the salinity during the decrease of the discharge is characteristic (Table 5). The salinity decreases quickly however when the discharge increases rapidly. The salinity : discharge curve (Fig. 17) shows that the mechanism which regulates the inflow of the sea water gradually opens many lower channels which are at different depths when the discharge decreases from 13.5 to 9.5 m3/sec. Sea water penetrates through all these channels at discharges smaller than 9,5 mVsec. The following special investigations were performed in the area of the spring: measurement of the discharge, salinity, piezometric surface and the temperature of the spring and boreholes; drilling with rock sampling and permeability tests; geoelectrical geophysical investigations; sampling and chemical analyses of water from boreholes; analyses of environmental isotopes: tritium and l®0, influence of sea tidal movement on the piezometric surface in the spring and boreholes; influence of the rise of the spring level for 1 metre on the salinity and piezometric surface of the spring and boreholes; drilling of two deep boreholes with measurement of salinity, temperature and piezometric surface. These boreholes are in the hinterland of the spring at distances of 3.4 and 9.3 kilometres from the sea. (Breznik, 1971). 5. THE ORIGIN AND CLASSIFICATION OF BRACKISH KARSTIC SPRINGS 5.1. Springs contaminated due to the greater density of sea water 5.11. Submarine springs contaminated in their mouths These are submarine springs where water is still fresh in the upper vein but is contaminated at the mouth of the spring. Sea water penetrates into the current of fresh water due to its greater density and mixes with it. Brackish water rises upwards due to a smaller density than sea water. The phenomenon is similar to the convectional movement of a gas above a warm object. The current of brackish water has the form of a cone which extends upwards. The cone is untransparent and could be observed by divers. Examples of this type of springs are submarine springs Brojnica (Sorgenti d'Aurisina), Cadimare, La Mortola, Mar Piccolo in Italy and Ayios Georgios in Greece. These springs can be identified by the electrical measurement of the salinity deep in the mouth of the spring. The salinity should not exceed 100 mg/1 of CI". One indication is also a fresh water spring among a group of brackish springs. 5.12. Springs in the karst aquifer showing isotropic permeability The porosity and ground water movement in the isotropically permeable karst aquifer and in granular sediment aquifer are similar. Like that is the contamination occurring in the isotropic rock mass. The contamination takes place in the zone-of-mixing where denser sea water mixes with fresh water. The mixing process is partly the result of diffusion but mostly of hydraulical mixing due to the different velocities of fresh and sea water. The thickness of the zone-of-mixing depends upon the velocity of ground water movement and upon the fluctuation of the sea. Ghyben-Herzberg and Hubbert rules can be used for the calculations. A row of small brackish springs which are submarine or only a little elevated above sea level indicates this type of the contamination. Examples are the lower part of the Postire valley and Marina-Stupin valley in Yugoslavia and the coastal aquifer in Israel. 5.13. Springs in the karst aquifer showing anisotropic permeability In the depth of the karst, the ground water circulation trends to concentrate along some rare well karstified zones. This is proved by the concentration of drainage in the direction of a few large springs. The karst of the Central Dinaric Alps with the surface of 17 500 square kilometres has only 55 large springs. Every spring with a discharge of 7—9 mVsec drains a surface of 320 square kilometres (Komatina, 1968). A similar situation is found on the island of Crete. Each of the three separated karstic regions Dikti, Psiloritis and Lefka Ori with the surfaces of 150, 300 and 400 km2 is drained by a single large spring with the discharges of 2, 6 and 8m3/sec. Water collecting galleries Postire II, Du-brava, Zaton, Gustirna, and Blaž all in Yugoslavia have also shown a concentration of ground water circulation. In the anisotropic karst aquifer the ground water moves through veins. The form of the veins is undefined; it could be a solution channel, a pervious fissured zone, a system of small tied-up cavities etc. The way of contamination cannot be the same as in the karst of isotropic permeability or in grained sediments with the uniform porosity and semi-laminar ground water movement. In the karst of anisotropic permeability the contamination occurs in the vein branching. This was proved by Gjurašin (1943) and I. K uš čer (1950). The simplest scheme of karstic veins near the coast is given in Fig. 18. The following notations will be used in figures and equations: Hydrostatic pressure P Atmospheric pressure Po Density (g/cm8) o Gravity acceleration 9 Height above some reference level h "Point-water head" h' Discharge Q Cross-section of a vein {h. _ hm) + emTm + Q,T, _ t^fr-lVp« — Qm — Qs 2 g(gm — Qs) All the denominators in the right part of the in-equation are the differences in the densities. The first numerator is the height of the spring above sea level, the second the head losses in the upper and lower veins and the third the difference of the velocity heads in both veins. Many karstic springs are fresh during high discharges. When the discharge is decreasing the contamination begins. Let us suppose the discharge just before the beginning of the contamination is an equilibrium discharge Q,iq. The lower vein is already filled with sea water which has not yet penetrated the vein branching. There are no losses of fresh water through the lower vein as well. The pressures in the lower and upper veins are equal at the vein branching. Hence It is possible to measure the discharge, density and elevation of the spring. But the measurement of head losses and of velocity heads can succeed only exceptionally if the branching is reached by a borehole or by divers. We can get an idea of the depth of the branching by taking estimated values of head losses and of velocity heads into account. It is expected that most of the springs will have more veins and more branchings and are thus more complicated as explained by the above equations. A gradual contamination of the Almyros spring during the decrease in the discharge from 13,5 to 9 mVsec indicates the presence of many lower veins and many branchings (Figs. 16, 17). On the other hand shows a sudden contamination of the Blaž spring a single branching (Fig. 8). These springs are divided into two groups according to the depth of the vein branching. To the first group belong the springs contaminated in shallow branchings occurring in the depth up to 100 metres. This depth was selected for practical reasons as it represents an economic limit to the construction of a grouting screen. These springs could be recognized as single springs collecting the water from a larger area and issuing at the elevation of the spring level up to 2.5 metres during the flow of brackish water. The springs of Blaž, Jurjevo, Zrnovica and Gurdič all in Yugoslavia are some examples. In the second group are the springs contaminated in the branchings deeper than 100 metres. The springs could be identified as single concentrated springs with an elevation of the spring level above 2.5 metres when brackish. The examples are Pantan and Pištica springs in Yugoslavia, Almyros Irakliou, Almyros Yeoryoupolis in Greece, Nahal Hatan-ninim and Na'aman in Israel and others. 5.2. Springs contaminated by sucking of sea water due to hydrodinamic effect Hydrodinamic effects are possible only in the karst region showing anisotropic permeability as the flow through veins is essential. The sucking of the sea water in the narrow of the primary vein requires a connection of the lower vein exactly at the narrow. It is only a small probability that such complicated Venturi tubes exist in the nature. Contamination of a fresh water jet submerged in brackish or sea water is a more likely explanation (Fig. 19). A jet of fast flowing fresh water loses its velocity if submerged in stagnant or slowly flowing sea Qm Qs = Qv (5) water. This means a loss of its kinematic energy. In accordance with the law of energy preservation, the sea water starts moving. The flux of the jet increases when its velocity decreases. The flux could increase only if some sea water is admixed. Small whirls along the plane of different velocities cause the process of the lateral mixing which increases when moving away from the mouth of the jet. The extent of the mixing depends on the capacity of the lateral flow and on the difference between the jet and the neighbouring fluid. The same degree of mixing could be obtained by a strong lateral current which is active on a short longitudinal distance as well as by a weak lateral current active on a long longitudinal distance. The process of mixing takes place at every change of the vein section. Large velocities in the current are not necessary. Only the difference between the velocity of the current and that of the neighbouring fluid is essential. Figure 20 shows a spring which is hydrodynamically contaminated. It could become fresh again when all the underground, including the lower vein, is flooded with fresh water during a big increase in the discharge. It is obvious that the majority of the springs are contaminated by the principle of greater density. Also a hydrodinamical principle with a jet or current action is not so complicated that it could not exist in nature. Venturi tube systems are complicated and could hardly be formed by nature. An increase in the salinity during the increase in the discharge is the best identification sign for a hydrodynamic system of contamination. Another less reliable indication is the very high position of a brackish spring. It is hard to explain the very high elevation of some brackish springs by the density principle of contamination. An example could be the Slanac spring in Yugoslavia with an elevation of 27 metres above sea level and 15 metres deep sea in the Kašteli bay. 5.3. Springs contaminated by the combination of greater density and hydrodynamic effect The spring is contaminated by the density principle during the low discharge and in addition by the hydrodinamic effect during the highest discharge. An example is the Bilan spring in Yugoslavia whose salinity increased considerably after heavy rains in November 1971 (Mijatovič, 1972). 6. THE POSSIBILITIES FOR THE DEVELOPMENT OF BRACKISH KARSTIC SPRINGS 6.1. The development of springs contaminated on the density principle 6.11. Submarine springs contaminated in their mouths The method of development is very simple. The spring area should be isolated against the sea water. The discharge of pumping should not exceed the fresh water inflow. Two large similar developments were successfully completed. The Brojnica (Aurisina) springs have been isolated by a 100 metres long and 7 metres high dam constructed in 1901 (Fig. 5). The dam was built on flysch sediments. The artificial pool level was 1.4 metres above sea level before the pumping. The discharge was 0.36 mVsec and the level 0.45 to 0.05 metres below sea level during the pumping test. There is no available data on the salinity but the water should have been fresh. The spring was connected to the Triest water supply system (Boegan, 1906). A 180 metres long semicircular dam was constructed around the coastal and submarine springs Ayios Georgios at Kiveri in Greece in 1970. The dam was built on a calcareous breccia at a depth of 10 metres below sea level. The top of the dam is 4 metres above sea level (Fig. 21). The artificial pool level was 0.3 metres above sea level during our visit in November 1970. The salinity was not measured but could not have exceeded 300 mg/1 of CI- as water tasted fresh. A small river was flowing through the openings of the dam into the sea. According to Prof. Stander (1971) the water was entirely fresh (probably with about 30 mg/1 of CI", author's remark) when the level inside the pool had been raised to 3 metres above sea level. The discharge had been 12 m3/sec. The main development was achieved by the isolation of the spring area and the salinity decreased to 200—300 mgA of CI-*. The second phase of the development was completed by the rise of the pool level to 3 metres above sea level. An inflow of sea water with a discharge of about 0.1 m8/sec was stopped by this rise. This discharge is calculated on the basis that such an inflow could contaminate a 12 m3/sec spring to the salinity of 200 mgA of Cl~ recorded in the coastal spring before the development. The mouth of the submarine spring in Mar Piccolo in Italy is already closed with a bell and connected to the pumps. Pumping will be restricted to the quantity of fresh water inflow in order to prevent a sea water intrusion (Stefanon, 1971). A similar solution has been proposed for La Mortola submarine springs. A rise in level of 3.5 metres was achieved inside the cylinder which isolated the Cadimare submarine spring in Italy. Required explorations. The main exploration aim is to ascertain that the contamination occurs in the mouth of the spring only. Salinity measurements should be made deep in the mouth of the spring. Measurement has to be made electrically and recorded on a tape, if possible, for a long period. The second aim is to determine the safe yield which should not exceed the fresh water inflow. A long pumping test with salinity registration should be performed. 6.12. The development of brackish springs of the karst showing isotropic permeability The ground water flow in karst of isotropic permeability is similar to the flow in the granular sediments and so is the development technique. A lense of fresh water is floating on sea water near the coast. Fresh water partially contaminated in the zone-of-mixing flows towards the sea and is lost. Fresh water oould be intercepted in the fresh water lense either by a row pumping wells or by a water-collecting gallery. Pumping will move the interface inland and reduce the fresh water losses. The pumping rate has to be carefully regulated in accordance with the salinity in order to avoid a contamination. One example is the development of the coastal aquifers in Israel. The length of the aquifers is over 100 km and the width about 15 km. The yearly losses of fresh water were about 300 millions cubic metres. The main layers of a 130 metres thick aquifer are karstified calcareous sandstone and sand (Bear, Dagan, 1964). The pumping out of numerous wells in the inland part of the aquifer has greatly reduced the fresh water losses. The interface was gradualy moved inland for about 2 km. A coastal collector consisting of shallow wells situated in a row which is 200 to 600 metres from the sea, was constructed (Fig. 22). The collector is able to intercept 50°/o of the residual flow towards the sea. It is possible to intercept 75 to 80 % of previous fresh water flow by pumping out of all wells situated inland and along the coast (K a h a n a , 1964). The salinity, piezometric surface and the position of the interface are constantly observed and the pumping rate adapted correspondingly (Schmorak, 1967). Separate pumping out of the fresh water and sea water zones performed by two pumps (Fig. 23) should stabilize the interface of a fresh water lense floating on sea water. Such a system of development of a karstic aquifer on the island of Malta was proposed by E d e 1 m a n (1966) and has been in sueeesfull operation in a well in grained sediments in Holland. A similar development by pumping out of zone-of-mixing and out of fresh water zone (Fig. 24) was proposed by M i j a t o v i č (1967). An experimental project in grained sediments in Ventura country USA has been operating using this extraction type of barrier. The first results were encouraging (Task Committee, 1969). Development by a grouting screen which should prevent sea water intrusion is not economically acceptable due to a very long front which chould be sealed. The construction of a fresh water barrier with a row of recharge wells situated along the coast poses similar economical problems. An 8 km long fresh water barrier was constructed near Tel Aviv with the aim of protecting an existing well field. A similar fresh water barrier 9 miles long in grained sediments is in operation in California (Task Committee, 1969). 6.13. The development of brackish springs in the karst showing anisotropic permeability 6.131. Development by raising in the spring level An artificial rise of the spring level prevents sea water intrusion due to the increase of the pressure in the upper vein. Kuščer (1950) and ft eg vič (1955) first intended to raise the spring level. The sea water inflow was treated in article 5.13. The equation 6 explains the conditions when sea water does not penetrate the vein branching but also fresh water is not lost through the lower vein. hi + Ahi - hr = —{hi + Ahi - hm) + (is - — ) (6) Qm — Qs Qvi — Qs \ 2 g J In addition to notations given in article 5.13. and Fig. 18 is Ahi artificial rise of the spring level. If the pressure on the fresh water side in the lowest point of the lower vein exceeds that on the sea water side, the fresh water is lost through the lower vein into the sea. The inequation 7 expresses such conditions: T — p T hi + Ahi — hm.miK < gm (hi + Ahi — hm) + -—- — Qm — Qs Qm — Qs vs~ Qs-U/tt2 Qm ^ijj 2 g (Qm-Qs) Fresh water is not lost, however, if the value of the left part of the inequation is higher. The form of the lower vein has apparently an important influence on the direction of its flow. During a gradual artificial rise in the level of a brackish spring where the lowest point of the lower vein is deeper than the vein branching, the following phases can be distinguished: a) The inflow of sea water is stopped when the pressure of the upper vein in the branching exceeds that of the lower one. The springs become fresh but fresh water is not lost (eq. 6). b) The spring is fresh but loses fresh water when pressure on the fresh water side exceeds that of the sea water side at the lowest point of the lower vein (ineq. 7). c) The springs is fresh but losses of fresh water are increasing when the raising of the level continues. All fresh water can be lost through the lower vein if the rise is high enough. A fresh spring without losses of fresh water could be the most favorable solution (eq. 6 and ineq. 7). A brackish spring with a rising lower vein (Fig. 25) is less favorable as it starts to lose fresh water when the salinity decreases. The above mentioned phase b does not exist. The technique explained above could give the wrong impression that every brackish spring could be developed by raising the spring level and larger or smaller losses of fresh water have to be taken into account. The real possibilities are not so bright. First single isolated springs are an exception only, springy areas are more frequent. The rise in the level cf a single spring could turn over the flow to other springs and it is possible that the required increase in the pressure will not reach the branching. Secondly single branching are a rare exception. Every spring or a group of springs have usually many lower and upper veins and 12 — Geologija 16 branchings lying at different depths. During the pumping test in the water-collecting gallery Postire II the increase in the salinity was different in several upper veins which were found. This proved the existence of many branchings situated at different depths. The salinity increase curve of the Almyros spring (Fig. 17), also indicates the existance of many branchings at different depths. Hydraulic conditions will be thereafter more complicated during the rise of level and cannot be expressed analytically. The conception of the equilibrium depth of a branching or a single vein and of the equilibrium plane were introduced to follow the influence of the rise in level at least qualitatively. The equilibrium depth heq is that depth at which the pressures on the fresh water and sea water sides are equal. The equilibrium depth changes in accordance with discharge and the spring level. Head losses and velocity heads in veins are taken into account in the calculation. Equilibrium plane is a nominal plane connecting the equilibrium depths of many branchings and veins. Drilling in the hinterland of a brackish springs in the karst showing an anisotropic permeability would probably reveal the rocks outside the main circulation of ground water. A vein would rarely be detected and even more rarely a branching. Interface on the contrary is a real boundary of fresh water and sea water. Every borehole in the hinterland of a brackish spring in the karst of isotropic permeability or granular sedimentary aquifer would find a moving ground water and a more or less sharp interface. In veins which are below the equilibrium plane the pressure on the sea water side exceeds that of the fresh water side and the opposite in veins above the plane. The flow direction in a vein is determined by the pressure relations in the characteristic points of the vein. They are the mouth, the lowest and highest points, and the branching. A full success of development would be a fresh spring without losses of fresh water, and a practical failure a spring with unacceptable salinity and big losses of fresh water. All the combinations of these extreme cases are possible. Developing experience resulting from spring level rising is still modest. S eg vie (1955) achieved partial success in his Postire experiments in 1951—1953. A clear influence of the changes of spring level on the salinity was observed in Pištica, Blaž and Jurjevo springs. An inflow of about 0.1 mVsec of sea water was blocked by the rise in the level of Ayios Georgios spring (art. 6.11). Hydrogeologic conditions. Development by the raising in spring level is attractive as it seems simple and inexpensive. In reality it can only succeed in very favorable hydrogeologic conditions. heq = (hi + Ahi) - (hi + Ah-, — hm) — Qm Tm + Qs Ts Qm-Qs + V* Qs — Vm2 Qm 2 9 (Qm-Qs) Qm —Qs (8) Only concentrated springs permit the construction of a dam at a reasonable expense. The discharge has to be high as fresh water losses through the lower vein and below the dam could be expected. The benefit of possible successfull development should correspond to the expenses involved. The spring should become fresh during high discharges what indicates the great influence of a higher level on the salinity. A spring with a falling lower vein which has the lowest point deeper than the branching, offers better possibilities for development by raising. Almyros spring could have such a falling lower vein if it passes below the Neogene sediments as supposed (art. 4.16). Investigations. Piezometric level, discharge and salinity measurements are the basic observations. The influence of sea tidal movement is instructive. The determination of the level at which the contamination starts could give an idea on the depth of the branching. But all these investigations cannot answer the question whether the raising in the spring level would be successful. Only a real rise in the level can provide the necessary data. This rise has to be considered as a part of the investigations. The decision to perform such test is difficult. The test is expensive and the result not known in advance. 6.132. Development by sealing the lower vein The idea of development is clear. Sea water intrusion should be blocked by sealing the lower vein. The technique of sealing a karstified rock is known as a result of the construction of storage basins in the Dinaric karst. But it is hard to find the lower vein. The distance between sea-swallow holes at Jurjevoand related brackish springs is 70—100 metres but the length ov the lower vein has to be some hundreds of metres (I. Kuščer, 1950). The sea-swallow holes at Argostolion are 15 kilometres away from the related springs near Sami (Glanz, 1965). Extensive investigations in the area of Zrnovica, Blaž, Morinj and Almyros did not reveal the position of the lower vein. The lower vein should be sealed with a grouting screen. The technique of successeful grouting works in Dinaric karst should be used. In exceptional cases a concrete diaphragm could be used to seal a very shallow lower vein. The sealing of submarine or coastal swallow-holes cannot be successful as all holes and small fissures could not be revealed and sealed. A similar technique proved unsuccessful at Nikšič and Cerknica Polje in Yugoslavia. It seems that there are no examples of development achieved by sealing the lower vein. Such developments were proposed for Blaž, Žrno-vica and Morinj springs. The preparatory works started at Morinj. Exploratory works at Almyros did not confirm the supposition of the sea water intrusion through a limestone block lying between the spring and the sea. This limestone could have been sealed by a grouting srceen of a reasonable size. Development by sealing should be combined with a small rise in the spring level in order to prevent leaking of sea water through the unsealed parts of the screen. Field conditions. This technique is not suitable for springs with a deep branching. First it is hard to find a deep lower vein and secondly the grouting screen should be deep. Brackish springs where the contamination occurs in the near vicinity of the spring could be suitable for this type of development. The advantage is that the fresh water losses are the smallest if this type of development is applied. Investigation. A tracer test should be performed out of sea-swallow holes if found or out of boreholes in order to determine the direction of the intrusion and the position of the grouting screen. 6.133. Development by the interception of fresh water before the contamination This method of development has mostly been used on the Adriatic coast during the last ten years. The data on development structures and expenses are given in table 7. Hydrogeologic data of the nearest brackish spring and water-collecting gallery are in table 8 and the success of the development in table 9. The fact that all galleries found ground water should not give a wrong impression that this was an easy task. The situations of all galleries were determined on the base of extensive studies. Besides this, only a small section of the galleries was productive. In a 540 metres long Kovča-Zaton gallery there were only 3 water collecting zones (5 metres long). The length of 6 water-collecting zones in Postire II gallery is about ten percent of the length of the whole gallery. In the galleries Pištica, Postire II, Gustirna, Blaž and Koromačno found cavities delivering the main part of the discharge were found. The contamination of fresh water during pumping was the reason for a semi-successful development of Pištica, Marina and Zuljana galleries and an unsuccessful development of Postire I, II, Trpanj and Koromačno galleries. Fresh water is likely floating on brackish water or sea water in all of these galleries. The brackish or sea water zones situated below or near the gallery are a potential danger of contamination when pumping starts. A short analysis of successful developments shows that in Slatina an unkarstified dolomite lies below the limestone, and that wells at Korita and galleries Dubrava I, II and Kovča are distant from the sea and out of its influence. The sea influence is minimal in the structures Sečovlje and Gustirna. Today as the Sečovlje mine is abandoned, the exploitation of the underground water storage of 140 000 cubic meters (Breznik, 1956) is possible. Field conditions. In places where fresh water is in the near hinterland of the spring the development by interception is suitable. The Zrnovica spring offers such possibilities. Interception is suitable in places where other methods of development cannot be applied. We could say that the interception technique could be applied everywhere. But we have to realize that it requires a lot of previous investigations, that success cannot be ascertained in advance and that only a small part of the discharge of the involving spring can be intercepted. The devflopment can succeed only if the gallery is outside the present and future brackish or sea water zones. This distance from the spring on the other hand decreases the possibility of intercepting a large quantity of water. Investigations. The first aim is to find out the fresh water inflow and the second is to determine the extent of the sea water influence. Investigations should be made in the hinterland of a large spring. Regional hydrogeological investigations could determine the general flow direction. But the determination of a detailed location of ground water flow is difficult. Geophysically determined fissured zones at Dubrava and Zaton galleries are sealed with clay deposits now. A longer fault revealed by aerial photos is a good collector zone in Gustirna gallery. The extent of sea water intrusion can be sometimes revealed by geophysical measurements (Poljice). Piezometric surface, salinity measurements and tracer tests should be performed in boreholes. The movement of the piezometric surface induced by the sea tidal movement indicated the presence of the sea water zone. 6.2. The development of brackish springs contaminated due to the hydrodinamic effect The development by interception of fresh water inside the karstic l egion seems to be the only possible method of development. The necessary investigations are the same as explained in art. 6.133. It would be difficult, however, to carry out the investigations, as they should be made during the period of high discharge, which is very short. The development of these springs is difficult but they are rare. 6.3. The development of brackish springs contaminated by the combination of density and hydrodinamic principles All the difficulties of development and investigation as explained above are also valid for these springs. The investigations should be made during low and high discharges. Spring Bilan in Yugoslavia was investigated during low discharges only. The development by a water-collecting gallery had seemed successful as water with 290 mgA of Cl~ was found but the salinity increased up to 1800 mg/1 of CI- during a high discharge (Mijatovič, 1972). The development and investigation of these springs are difficult. 7. ECONOMICAL ASPECTS OF BRACKISH SPRINGS DEVELOPMENT Price of fresh water from developed springs is given in table 10. The investigations and development costs were calculated according to 1971 prices. Almyros I is the proposal for development by the construction of dam 150 metres long and 10 metres high which will enable the spring level to rise to an elevation of 10 metres above sea level. Almyros II would be the construction of a 3 km long access gallery and 1.5 long water-coPecting gallery; the cost was estimated by a competent contractor.* The yearly payment of instalments of the credit is calculated for a 6 percent interest rate and a 30 year period. Yearly maintenance costs are 0.5 percent. The fresh water discharge of incomplete developments is an estimate on the base of an assumed percentage of the brackish spring discharge. The utilisation of 80 percent of the developed springs discharge was taken into account in the calculation. The price of water does not include the cost of eventual pumping. The basic data on desalinization plants and the price of water are given in table 11. A comparison of the prices of fresh water shows that the water from fresh springs, of treated water from rivers or lakes and fresh ground water is the cheapest way of water supply. But fresh water from developed brackish springs is much cheaper than fresh water acquired from brackish or sea water in desalinisation plants. 8. CONCLUSION Brackish karstic springs are a general and adequately explained phenomenon of the calcareous coasts. The springs are contaminated by sea water. There are some different mechanisms of contamination and the investigations should reveal them and prepare a development plan. The development technique includes these works: isolation of the spring from sea water, rise in the spring level, sealing of the lower vein and interception of fresh water before the contamination. It will not be possible to develop all the springs. The detailed investigations should be performed at most favorable places revealed by preliminary investigations. A test by the selected development technique should be included in the investment. Only such a test could show us the mechanism of con-tanvnation and indicate a prospective development. The main difficulty of the development is that great efforts and considerable expenses are required, but the final result cannot be known in advance. The conditions are similar to the prospecting for mineral resources; the difference is that the investors for fresh water are ussually poor communities. The other difficulty is the long period required for investigations and development. The construction of expensive regional water supply using river water started on the Adriatic coast due to the fact that the final success of these works was ascertained in advance. Larger territorial units should carry out the works and take over the expenses and the risk. Only large and very important smaller springs should be explored and developed. The planning of water needs, well in advance, will enable the investigations and development to start in time. About three to five years are required for investigation and development of a spring. * OGP "Učka" Labin, Yugoslavia. The price of the water from developed brackish springs is higher than the fresh water captured at a corresponding distance but much lower than the fresh water produced from brackish or sea water in desalinization plants. The success in developments already achieved justify and stimulate the continuation of these works. 9. ACKNOWLEDGMENTS Thanks are due — to Messr: Prof. Dr. J. Baturič, V. Cule, Dipl. Eng., D. F r a -nič, Dipl. Eng., J. Krznar, Dipl. Eng., Dr. B. Mi j ato vič , B. P a v -lin, Dipl. Eng., Prof. Dr. W. Stander and Dr. A. Stefanon who gave their unpublished data on the newest development works at the disposal. — to the Governments of Greece and Malta, the Food and Agriculture Organization of the United Nations Rome, Geološki zavod Ljubljana, Geotehnika Zagreb, and Zavod za geološka i geofizička istraživanja Belgrade which granted permission for the use of their unpublished reports. — to Sklad Borisa Kidriča Ljubljana which suported the research and the Soil Mechanics Laboratory of the University Ljubljana for assistance in the preparation of the study. 10. Slovstvo References Albertson M. L., Dai, Y. B, Jensen, R. A., Rouse, H. 1950, Diffusion of Submerged Jets. ASCE Transactions 1950. Alfirevič, S. 1966, Les sources sous-marines de la bale de Kaštela, Acta Adriatica, Vol. X. No. 12, Split. Alfirevič, S. 1969, Jadranske vrulje u vodnom režimu Dinarskog pri-morskog krša i njihova problematika. Krš Jugoslavije, knj. 6, Zagreb. *B a d o n Ghyben, W. 1888—1889, Nota in verband met de vorrgenomen putboring nabij Amsterdam. Tijdschrift van het Koninklijk Instituut van In-genieurs. The Hague, 1901. Bakič, M. 1966, Hydrogeological Importance of Results of Prospecting for Water on the Isle of Brač. Mčmoires 6, Reunion de Belgrade, Ass. Int. des Hydrogčologues, Belgrade. Baturič, J. 1959, Hidrološka istraživanja na otoku Visu u god. 1957 i 1958. Neobjavljeno poročilo Zavoda za rudarska mjerenja i geofizička istraživanja, Zagreb. Baturič, J. 1961, Neki rezultati ispitivanja cirkulacije vode u obalnom području. Drugi Jugoslovenski speleološki kongres Split i Dalmatinska Zagora, 1958, Zagreb. Baturič, J. 1969, Application de la g£o physique & la hydrogčologie du karst. Sbornik II Symposium scientifique international e sur la gčodšsie de mines, la gčologie de mines et la geometrie des gisement, Prague. Bear, J., D a g a n, G. 1964, Intercepting Fresh Water Above the Interface in a Coastal Aquifer. Int. Ass. of Scientific Hydrology, Publ. No. 64, Gentbrugge. Boegan, E. 1906, Le sorgenti d'Aurisina. Rassegna bimestrale della Societa Alpina delle Giulie, Trieste. Bossy, G. 1970, Intrusion d'eau salee dans une nappe d'eau douce. Verification des lois theoriques, Bull. B.R.G.M. sec. Ill, No. 2, Paris. Breznik, M. 1956, Vodovod Koper, Geološki in hidrološki opis rudnika Sečovlje s predlogom raziskav za kaptažo vode. Neobjavljeno poročilo Geološkega zavoda, Ljubljana. Breznik, M. 1958, Rižanski vodovod Koper, Skrajšano hidrogeološko poročilo o podzemnem zajetju v Sečovljah. Neobjavljeno poročilo Geološkega zavoda, Ljubljana. Breznik, M. 1971, Geology and Hydrogeology of the Almyros Spring Area. Neobjavljeno poročilo Organizacije Združenih narodov za prehrano in kmetijstvo vladi Grčije. Unpublished report of the Food and Agriculture Organization of the United Nations to the Government of Greece, Iraklion. ♦Brown, C. 1835, Lt. Lawrence and Mr. Stefens on the streams of sea-water. which flow into the land in Cephalonia. Quat. Journ. Geol. Soc. 2, London. Bur d on. D. J., Papakis, N. J. 1964, Preliminary Note on the Hvdro-geology of the Almyros spring Iraklion — Crete. Inst, for Geology and Subsurface Research, Atene. Calvino, F., Stefanon, A. 1963, Osservazioni geologice sulla polla Rovereto e le altre sorgenti sottomarine della Mortola (Riviera di Ponente). Atti dell'Istituto di geologia della Universita di Genova, vol. I., fasc. 1. Calvino, F., Stefanon, A 1969, The submarine springs of fresh water and problems of their capture. Rapport et proc&s-verbaux des reunions de la Commission internationale pour l'exploration scientifique de la mer Mediterranče. Vol. XTX. fasc. 4. Monaco. *C e r r u t i, A, 1948. Ulteriori notizie sulle sorgenti sottomarine (citri) del Mar Grande e del Mar Piccolo di Taranto e sulla loro eventuale utilizzazione. Bol, Pešca Piscic. Idrobiol. Min. Agr. For. anno XXTV. 3 (1). Chow, Ven Te 1964, Handbook of Applied Hydrology, 13-50. New York. *Cooper, H.. H.. Jr. 1959, A hypothesis concerning the dynamic balance of fresh water and salt water in coastal aquifer. J. Geophys. Res., U. S. A., 64, no. 4. *Crema, C 1915, Alcune notizie sulla polla di Cadimare, sulla sprugola della Spezia e sui tentativi fatti per captare le acque. Boll. R. Com. Geol. It,, XLV. Roma. *C r e m a. C. 1922. Arcora sulla polla di Cadimare. Boll. Soc. Geol. Ital. XLT. Davis, S N.. DeWiest, R. 1967, Hydrogeology. New York. *Davy, J. 1836. On a curios phenomenon observed in the Island of Cefalo-nia. and on the proximate cause of the Earthquakes in the Ionian Islands. Edinb, New. Philos. Journ., 20, Edinburgh. Dreyfus, A., Vaileux, Y. 1970, Localisation de l'interface. Comparison des lois de Ghyben-Herzberg, Hubbert, et Lusczynski. Bull. B.R.G.M. sec. Ill, no. 2, Paris. Edelman. J. H. 1966, Salinity Problems in the Extraction of Groundwater. Neobjavljeno poročilo Organizacije Združenih narodov za prehrano in kmetijstvo vladi Malte Unpublished report of the Food and Agriculture Organization of the United Nations to the Government of Malta. Rome. F AO 1964. Karst Ground Water Investigations — Greece. Rim. F r a n i c , D. 1966, Conditions hydrog£ologiques de rile de Hvar et la solution de son alimentation en eau. Memoires AIH. Reunion de Belgrade 1963, Beograd. Fouque, F. 1867, Rapport sur le tremblement de terre de Cčphalonie et de Metelin en 1867. Arch., des miss, scientifique s, 4, 445, Paris. Gjurašin, K. 1942, Prilog hidrografiji primorskog krša. Tehnički viesnik, 59, 107—112, Zagreb. Gjurašin, K. 1943, Prilog hidrografiji primorskog krša. Tehnički vjesnik, 60, 1—17, Zagreb. G1 a n z, T. 1965, Das Phanomen der Meermuhlen von Argostolion. Stei-rische Beitrage zur Hydrogeologie, Graz. Gov. of Greece, UNDP, F A 0, 1968—1971, Study of Water Resources and Their Exploitation for Irrigation in Eastern Crete. Neobjavljeni podatki o terenskih meritvah. Unpublished data of field measurements, Iraklion. Herak, M., Bahun, S., Magdalenič, A. 1969, Pozitivni i negativni utjecaji na razvoj Krša u Hrvatskoj. Krš Jugoslavije 6, Zagreb. *Herzberg, B. 1901, Die Wasserversorgung einiger Nordseebader. Zeit. Gasbeleuchtung und Wasserversorgung, Vol. 44, Miinchen. *Hubbert, M. K. 1940, The theory of ground water motion. J. Geol., U. S. A., 48, no. 8. . ^ , ... .. _ Jevremovič, M. 1966, Hydraulic Characteristics and classification of Brackish Springs in the Adriatic Zone of the Dinaric Karst. AIH, Memoires, pp. 293—297, 1963, Belgrade. _ Kahana, Y. 1964, Coastal Groundwater Collector as a Means of Intensifying Exploitation of Groundwater. Int. Ass of Scientific Hydrology, Pub. No. 64, Gentbrugge. ^ . _ _ . Kneževič, B. 1962, Hidraulički problemi Karsta. Saopstenja, st. 25, Inst. za vodoprivredu »J. Cerni«, Beograd. * K o h o u t, F. A. 1966, Submarine Springs. A Neglected Phenomenon of Coastal Hydrology. Symp. on Hydrology and Water Resouces, Ankara. Koma tin a, M. 1968, Karst i hidrogeološke mogučnosti racionalnijeg zahvatanja podzemnih voda. Vesnik Zav. za geol. i geof. ispt, knj. VIII, ser. B, str. 83—121, Beograd. . Krznar, J., Franič, D. 1970, Vodoistražni radovi 1968—1970 izvonšte Blaž. Poročilo Geotehnika Zagreb (neobjavljeno), Zagreb. Krznar, J., Skaberna, I., Franič, D. 1970, Elaborat o vodoistraž-nim radovima u Zrnovici kod Gradca n/m 1968—1970. Neobjavljeno poročilo, Geotehnika, Zagreb. , v , • KušČer, I. 1946, Čemu smo se potapljali. Proteus 1946/47, st. 2. Ljubljana. KuŠČer, I. 1950, Kraški izviri ob morski obali. Razprave SAZU, Ljub- l3aiKušČer, I.. KuŠčer, D. 1962, Observation on Brakish Karst Sources and Swallow-Holes in the Yugoslav Coast. Mčmoires de l'Association Internationale des Hydrogeologues, Tome V, Reunion d'Athenes. Lehmann, O. 1932, Die Hydrographie des Karstes, Enz. d. Erdkunde, 6b, Leipzig—Wien. , ^ M ... Luscynski, N. J. 1961. Head and flow of ground water of variable density. J. geophys. Res. U. S. A., 66. no. 12. Mandel. S. 1971, The Mechanism of Sea-Water Intrusion into Calcareous Aquifers Publ. no. 64 of the I. A. S. H., Commission of Subterranean Waters. Maurin, V., Zotl, J. 1967. Salt Water Encroachment in the Low Altitude Karst Water Horizons of the Island of Keohallonia (Ionian Islands). Actes du colloque de Dubrovnik. Octobre 1965. AIHS-Unesco. Gentgrugge-Paris. Mij a to vie, B. 1967. Hidraulički mehanizam kraških izdani u niskim primorskim kolektorima. Vesnik Zav. za geol. i geof. istr., knj. VII, ser. B, Beograd M i .1 a t o v i č , B. 1969a. Hidrodinamički režim i kvantitativna ocena eksplo-atacionih rezervi kraške izdani u dolini Kovča-Zaton kod Sibenika. Vesnik Zav. za geol. i geof. istr.. knj. IX. ser. B, Beograd. Mi j at o vič, B. 1969b, Uloga geofizičkih ispitivanja pri kompleksnim hidroeeološkim istraživanjima. Vesnik Zav. za geol. i geof. istr., knj. IX, ser. B, Beosrad. .» yi Mijatovič, B. 1970, Kompleksna hidrogeološka istraživan.ia terena Gu-stirna-Poljice kod Trogira. Mogučnost korištenja podzemnih voda za vodo-snabdevanje. Neobiavljeno poročilo Fonda strokovne dokumentacije Zavoda za geol. i geof. istr., Beograd. Mijatovič, B. 1971, Prikaz hidrogeoloških uslova šire okoline Herceg Novog i usvojenog reSenja problema vodosnabdevanja koriščenjem kraških izdanskih voda. I. Jug. simp, o hidrogeologiii i inž. geol. Herceg Novi, Beosrad. Mijatovič, B. 1972, Kompleksna hidrogeološka istraživania u području izvora Pantan. Slanac i Kaštelanskih vrulja. Neobjavljeno poročilo. Fond strokovne dokumentacije Zavoda za geol. i geof. istr., Beograd. *Mousson, A. 1858, Ein Besuch auf Corfu und Cefalonia lm September 1858, Zurich. Papadopoulos N., Scanvic, Y., 1968, Esquisse geologique de rile de Cr£te. Rapport inedit, Paris. P a t a k i s, E. K. 1968, Almyros Irakliou. Kritika kronika, Vol. 19, Iraklion Kritis. Pavlin, B., Biondič, B. 1971a, Istražni radovi na kraškim izvorima Kotorsko-Risanskog basena. Zbornik radova 1. jug. simp, o hidrog. i inž geol Hercegnovi, Beograd. Pavlin, B., Biondič, B. 1971b, Kaptaža izvorišta Morinj-Kostanjica sa zaštitom od upliva mora, Idejni projekt, knj. 1. Neobjavljeno poročilo, Geotehnika, Zagreb. Petri k, M. 1961, Mjerenja na vruljama. Drugi jug. speleološki kongres, Zagreb. *Puckler- Muskau 1841, Sudostlicher Bildersaal 3. Teil, Munchen. Radulovič, V. 1971, Hidrogeološki vodič kroz terene Bokokotorskog zaliva i masiva Lovčena. Hidrogeološke ekskurzije, 1. jug. simp, o hidrog. i inž. geol., Herceg Novi, Beograd. Re, R., Breznik, M. 1968, Le probleme des sources d'Almyros-I raki ion. Neobjavljeno poročilo Organizacije Združenih narodov za prehrano in kmetijstvo vladi Grčije. Unpublished report of the Food and Agriculture Organization of the United Nations to the Government of Grecce, Iraklion. Rižanski vodovod Koper, 1966, Vodovod Sečovlje, Projektiranje in izgradnja, Koper. Roglič, J. 1961, Odnos morskog nivoa i cirkulacije vode u kršu. II jugosl. speleol. kongres, Zagreb. Rouse, H. 1950, Engineering Hydraulics, New York. Schmorak, S. 1967, Salt Water Encroachment in the Coastal Plain of Israel. Int. Ass. of Scientific Hydrology, Publ. 72, Symposium of Haifa, Gent-brugge. Stander , W., 1971, pismeno sporočilo. Stefan on, A., 1971 (?), Notes on Submarine Springs, XXII Congr^s — Assemblee Pleniere de la Commission Internationale pour l'Exploitation Scien-tifique de la Mer Mediterranee. ♦Strickland, H. E., 1835, On currents of sea-water flowing into the land near Argostoli in the Island of Cephalonia, Quat. Journ. Geol. Soc 2 London. ' S eg vič, B., 1955, Način zajetja in razsolitev obmorskih izvirov. Gradbeni vestnik št. 37-38, Ljubljana. Task Committee on Saltwater Intrusion, 1969, Saltwater Intrusion in the United States, Jour, of the Hydraulic Div., Proc. ASCE. Todd, D. K., 1967, Ground Water Hydrology, Willey and Sons, New York United Nations 1969, First United Nations Desalination Plant Operation Survey. UN Publication, New York. Water and Water Engineering 1969, World's Largest Electro-dialysis Plant. Benghazi Contract for William Boby & Co Lt, št May 1969 London. * W i e b e 1, K. W. M., 1874, Die Insel Kephalonia und die Meermiihlen von Argostoli, Hamburg. Wiest, R. De, 1965, Geohydrology, Willey & Sons, New York. Wiest, R. J. M. De, 1970, Invasion marine dans les aquiffcres cotiers Bulletin du B. R. G. M. Section III, no. 2, Paris. * Z zvezdico označena dela mi niso dostopna, poznam jih le do drugih avtorjih.