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HIDROELEKTRANA O M BLA

PROJEKT ZA ENERGETSKO KORITENJE PODZEMNIH VODA U KRAKOM TERENU

THE OMBLA HYDRO ELECTRIC POWER PLANT

PROJECT FOR POWER UTILIZATION OF UNDERGROUND WATERS IN KARST AOUIFER

DUBROVNIK, DECEMBER 1989.

Ovu publikaciju HIDROELEKTRANA OMBLA - PROJEKT ZA ENERGETSKO KORI:jTENJE POD-ZEMNIH VODA U KRA:jKOM TERENU, na osnovi rezultata do sada zavrenih istraivanja, te elaborata i projekata izraenih od: ELEKTROPROJEKT A- ZAGREB, ENERGOPROJEKTA - BEO-GRAD, HIDROELEKTRANE NA TREBI:jNJICI, INSTfTLJT - TREBINJE, GEORZIKOG INSTITUT A - BEOGRAD, GEOFIZIKE- ZAGREB, GEOLO:jKOG ZAVODA LJUBLJANA- LJUBLJANA i dru-gih, pripremio je i izradio PAVI:jA TOMISLAV, dipl. ing. gra., HIDROELEKTRANA DUBROVNIK - DUBROVNIK.

This publication, THE OMBLA HYDRO-ELECTRIC POWER PLANT PROJECT FOR POWER UllU-ZATION OF UNDERGROUND WATERS IN KARST AQUIFER, on the basis of the results obtained in research work completed by now, and elaborates and projects elaborated by: ELEKTROP-ROJEKT- ZAGREB, ENERGOPROJEKT- BEOGRAD, HYDRO-ELECTRIC POWER PLANTS ON TREBI:jNJICA - THE INSTITUTE OF TREBINJE, GEOPHYSICAL INSTITUTE - BEOGRAD, GEOFIZIKA - ZAGREB, GEOLOGICAL INSTITUTE OF LJUBLJANA - LJUBLJANA, and others, has been prepared and elaborated by TOMISLAV PAVI:jA, civil engineer, HEPP DUBROVNIK -DUBROVNIK

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SADRLAJ

SALET AK 5 UVOD................................................... ........................................ .... ............... 6 PRIRODNE KARAKTERISTIKE SLIVNOG PODRUJA .. . . . . . . . .. . .. . . .. .. . .. .. . . . .. . . . .. . . .. . . . .. . .. . 7 Hidroloke karakteristike . .. .. .. . . . . . .. . . . . . . . . .. .. . .. . . . . . .. . . . . . . . .. .. .. . .. . . .. . .. . .. .. . . . . . . . .. . . .. . .. . . .. . . 8

Geoloke i hidrogeoloke karakteristike . . .. . .. .. .. . .. . .. . .. .. . . . . . . . .. .. .. . . . . . .. . . .. . . . . .. .. . . . .. . . . .. . . . 9

ISTRALNI RADOVI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 o PREOLOtENO RJEENJE HE OMBLA .. .. .. .. .. .. .. .. .. .. . .. .. .. .. .. .. .. . .. .. .. .. .. . .. .. . .. .. .. . . . 11 ENERGETSKO-EKONOMSKE VELIINE IZGRADNJE ..... , .. . .. .. . . .. . . . .. . .. . .. . . . .. . . . .. . .. .. . . . . . 14 ZAKLJUAK .................................... ................................................................. 15 PRILOZI .... .. ............................. ... ............................... .. ......... ...... ..... ............... .

TABLE OF CONTENST

SYNOPSIS ..................................... .. ................................................................ INTRODUCTION ............................................................................................... . NATURAL CHARACTERISTICS OT THE ORA/NAGE AREA ............... .. ...................... .. Hydrological Characteristics ............................................................................... . .. Geological and Hydrogeological Characteristics ... .... .. ........... ........... ...... .................. . RESEARCH$ WORKS ....................................... ................................................ . PROPOSEO SOLUTION FOR HEPP OMBLA .......................................................... . POWER-ECONOMIC CONSTRUCTION VALUES ................................................... .. . CONCLUSION .................................................................................................. . MUPS ..................................................... ... ........................................... .... ..... .

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UVOD Izvor OMBLA postaje predmet znaajnijeg interesa ireg kruga specijalista koji se bave problema-tikom voda u kru, poetkom ezdesetih godina, kada je odabirana osnovna koncepcija hidrosi-stema TREBINJICA. Nepoznavanje hidrolokih i hidrogeolokih karakteristika ovog podruja na-metnuli su potrebu provedbe vrlo opsenog programa istraivanja. Nakon njihovog zavretka stvo-rena je ideja o mogunosti hidroenergetskog iskoritenja vodnog potencijala OMBLE sa koncep-cijom kakva se danas analizira. Dosad izraene studije i projekti nivoa idejnog rjeenja pokazale su da je ovo neuobiajeno rjee-nje za energetsko iskoritenje voda krakog podzemlja, tehniki ostvarivo i da je izgradnja ovog objekta ekonomski opravdana. Recenzione komisije sastavljene od jugoslavenskih eksperata potvrdile su dosadanje navedene osnovne zakljuke, ime je omoguen nastavak istraivanja do zavretka idejnog projekta. Ovaj saeti prikaz osnovnih rezultata istraivanja i odabrane koncepcije rjeenja ima za cilj upoznati sve zainteresirane sa ovim dosta neuobiajenim ~eenjem za energetsko koritenje podzemnih voda kra, o kojem se izvan uih strunih krugova vrlo malo zna, a ija iskustva mogu biti vrlo korisna za ostale zemlje koje imaju vee povrine krakih terena.

INTRODUCTION With the beginning of 60-s the OMBLA spring appears as a subject of interest in a wider circle of experts dealing with karst water problems. At the time main concept for the TREBINJICA hydro-system was being chosen. Lack of information about hydrological and hydrogeological characteristics of this region imposed a need for implementation of an extensive research prog-ramme. Upon completion of the research the idea of the possible power utilization of the OMBLA water capacity took shape under conception that is now being analysed. The studies elaborated until now and the projects at a preliminary design level have indicated that this unusual solution for power utilization of karst underground waters is technically feasible and that construction of this plant is economically justified. Review committees formed by Yugoslav experts approved the above stated main conclusions, enabling thus continuation of the research until completion of the feasibility study. This short review of the main research results and the selected conception is intended to clarify to everyone concemed this rather unusual solution for power utilization of karst underground waters since outside the narrow circle of specialists there is hardly anyone familiar with it and, moreover, the experience gained here can be very useful for other countries with larger karst areas.

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PRIRODNE KARAKTERISTIKE SLIVNOG PODRUJA Izvor OMBLA je tipian priobalni kraki izvor veoma znaajne izdanosti. U prirodnim uvjetima, prije izgradnje objekata hidrosistema Trebinjica, on je bio kao i svugdje u kru prirodni drenani sistem, koji je omoguavao odvoenje vode najkraim putem do mora. Tu su ponori du vodotoka Trebinjica bili ulaz a izvor OMBLA izlaz, kako je prikazano na slici 1, iz priloga. Naravno pored ovih voda izvor se prihranjivao i vodama iz vlastitog slivnog podruja. Ovaj izvor ire promatrano pripada slivu Trebinjice, jednom od najveih i sigurno po bogatstvu prirodnih obiljeja najinteresantnijih krakih podruja u Jugoslaviji. Ovo podruje najveim dijelom obuhvaa regiju Istona Hercegovina, sa uom priobalnom zo-nom Dubrovnik. Izgradnjom objekata hidrosistema Trebinjica, deavaju se neminovne promjene koje pNenstveno mijenjaju prirodni reim voda kako na irem podruju tako i na izvoru OMBLA.

NATURAL CHARACTERISTICS OF THE DRAJ NAGE AREA The OMBLA spring is a typical coastal karst spring abundant with water. Under its natural condi-tions, prior to construction of the TREBISNJICA hydro-system plants, it was a natural drainage system characteristic for karst areas which enabled drainage of water through the shortest way into the sea. The swallow-holes along the water flow of the river TREBISNJICA were the entrance and the OMBLA spring was the exit, as picture 1 of the enclosure illustrates. Naturally, besides these waters the spring was recharging from its own catchment. Seen from a broader point of view, this spring belongs to the TREBISNJICA drainage area, one of the largest and with its rich natural characteristics certainly one of the most interesting karst regions in Yugoslavia. Most of this area belongs to the region of Eastern Herzegovina and includes the narrow coast belt of Dubrovnik. The construction of the TREBISNJICA hydro-system plants originated some unavoidable changes which have primarily influenced the natural water regime in both the wider area and the OMBLA spring

Hidroloke karakteristike Za itavo podruje obuhvaeno projektom hidrosistema Trebinjica uoljiva je osnovna zakonitost hidrolokih ciklusa koju karakteriziraju: - bogatstvo vodom u periodu od kasne jeseni do ranog proljea i - izraziti nedostatak za vodom u ostalom dijelu godine. Ljudi na ovom podruju oduvijek su vodili borbu protiv vode - branei plodne povrine od popla-va, i za vodu -osiguravajui neophodne koliine za osobne potrebe i za navodnjavanje minimalnih obradivih povrina na kojima su proizvodili hranu. Ovo podruje obiluje kiama Prosjeno godinje ovdje padne od 1400 mm u priobalju do preko 2200 mm u planinskom dijelu ovog slivnog podruja Potpuno suno razdoblje moe potrajati i preko 90 dana

Za potrebe projekta HE OMBLA bilo je neophodno utvrditi reim voda u novonastalim uvjetima, nakon zavretka izgradnje objekata hidrosistema Trebinjica Izgradnjom ovih objekata dolo je do smanjenja ukupne bilance voda, dok su minimalne i maksimalne protoke ostale nepromijenje-ne.

Karakteristine vrijednosti dananjeg reima voda su Osr = 24.4 m3/sec Omax11oo = 138.3 m3/sec Om.n 3.0 m3/sec Karakteristini pokazatelji, hidrogram za karaktenstinu godinu i dijagram godinje raspodjele pro-toke, dati su na slici iz priloga.

Hydrological Characteristics For the whole region included in the TREBINJICA hydro-system project a basic pattern in hyd-rological cycles dynamics can be obseNed, characterized by abundance of water during the late autumn - early spring period and a considerable lack of it during the rest of the year. ln this region men had always !ought against water, protecting the fertile land from floods, and for water, saving the minimum quantities for their own needs and for inrigation of the few cultivable areas kept for production of food. This region is a rich precipitation area Mean annual precipitation here is 1400 mm in the coastal belt and over 2200 mm in the mountains of the catchment area. On the other hand, a completely dry period can last over 90 days. For the HEPP OMBLA project purposes it was imperative to determine the water regime under the newly formed conditions upon completion of construction of the TREBINJICA hydro-system plants. The construction of these plants caused a decrease in total water reseNes with the minimum and maximum water flows remaining the same. Distinctive values of the present discharge are:

Oav = 24.4 m3/sec omax/100 = 138.3 m3/sec Omon 3.0 m3/sec

Specific indicators, hydrogram for a specific year and annual ftow distribution diagram are all shown on the drawing enclosed.

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Geoloke i hidrogeoloke karakteristike Podruje koje je obuhvaeno projektom hidrosistema Trebinjica izraeno je od sedimentnih sti-jena, trijasa, jure, krede, eocena i kvartara. Na cijelom prostoru dominiraju vapnenci i dolomiti, trijaske, jurske i kredne starosti. Eocenski sedimenti sastoje se od flinog kompleksa u kome dominiraju laporovito-glinovite komponente (lapor, glina, pjeari, konglomerati i laporoviti vapnen-ci). Sedimenti kvartara pokrivaju dna krakih polja i vrtaa, gdje je terra-rosa najzastupljenija forma-cija. Osnovne strukturne i stratigrafske jedinice izduene su u smjeru pruanja Dinarida. Kao posljedica intenzivne neotektonske aktivnosti formirana su kraka polja koja se kaskadno sputaju sa visine od 1 000 m do nivoa mora. Glavnu i iroko rasprostranjenu litostratigrafsku jedinicu ine sedimenti karstificiranih vapnenaca koji u hidrogeolokom smislu predstavljaju vodopropusne stijene. Znatno manje susreemo sedi-mente dolomita, koji spadaju u kategoriju slabo propusnih do vodonepropusnih stijena. Najmanje su zastupljeni sedimenti flia, koji predstavljaju vodonepropusnu barijeru. Prema niim horizontima voda otie putem brojnih veih ili manjih ponora. Najvei imaju kapacitet preko 50 m3/sec. Ukupni kapaciteti ponorskih zona u pojedinim krakim poljima iznose 100-200 m3/sec. Promjene razine podzemne vode su vrlo brze (do 90 m/24h), a ukupne razlike izmedu minimalne i maximalne razine podzemne vode iznose preko 300 m. Podzemni vodni tokovi od ponora prema izvoru nieg horizonta mogu biti dui od 30 km. Brzine u koncentriranom toku kroz krake kanale variraju izmedu 2,0 i 55 cm/sec. Karstifikacija je duboka - generalno dubine stijenske mase koje su zahvaene procesom okravanja iznose 200-250 m.

Geological and Hydrogeological Characteristics The region covered by the TREBINJICA hydro-system project is compcsed of sedimentary rocks, Triassic, Jurassic, Cretaceous, Eocene and Ouartemary sediments. Typical for the whole area are limestones and dolomites of T riassic, Jurassic and Cretaceous formations. The Eocene sediments consist of a flysch complex dominated by marly-clayish components (marl, clay, sandstone, conglomerates and marly limestones). Ouarternary sediments cover the bottoms of karst fields and sinkholes where terra-rosa is the primary formation. Basic structural and stratographic units stretch in a belt following the extension of the Dinarides. As a consequence of an intensive neotectonic activity karst fields have been formed cascading from an altitude of 1 000 m down to the sea level. The main and wide-spread lithostratographic unit consists of karstified limestone sediments which in hydrogeological terms represent water permeable rocks. However, dolomite sediments are to be found much rarer and they are in the cathegory of low permeable to impermeable rocks. Flysch sedi ments appear in the least quantities and they represent a water impermeable barrier. T awards lower levels the water goes underground through numerous larger or smaller swallow-holes. The largest ones have a capacity of over 50 m3/sec. Total capacities of the swallow-hole zones in separate karst fields read 100-200 m3/sec. Level fluctuations of the underground water come very quickly (to 90 m/24h), and total differences between the minimum and maximum underground water levels reach over 300 m. Underground water circulations from a swallow-hole towards a lower leveled spring can sometimes be more than 30 km long. Flow rates in a concentrated flow through karst channels vary from 2,0 to 55 cm/sec. Karstification is deep, mostly the depths of the rock volume affected by karstfication reach 200-250 m.

Geoloke i hidrogeoloke karakteristike na uplivnom podruju sliva OMBLE kao i u zoni podzemne akumulacije i buduih objekata HE OMBLA, u potpunosti su sukladne sa prethodnim opisom regionalnih geolokih i hidrogeolokih karakteristika ovog podruja. Svi osnovni geoloki i hidro-geoloki inioci koji su utjecali na formiranje ovog krakog izvora prikazani su na hidrogeolokoj karti koja se daje u prilogu.

ISTRNN RADOVI Postojanost ideje o mogunosti izgradnje ovog specifinog hidroenergetskog postrojenja ovisi ponajvie o realnosti i ekonominosti tehnikih ~eenja objekata za usporavanje vode u krakom

zaleu izvora OMBLA, odnosno o mogunosti formiranja podzemne akumulacije. Zbog toga su skoro sva istraivanja bila usmjerena na prostor podzemne akumulacije i na pregradni profil budu-

e podzemne brane. Izraene su detaljne geoloke analize litostratigrafskih, tektonskih, hidrogeolokih pojava te rezul-tata geoelektrinog sondiranja u prostoru podzemne akumulacije OMBLA i na djelovima slivnih povrina susjednih izvora Zaton i Zavrelje. lzbuene su duboke piezometarske buotine. u pojedi-nim karakteristinim djelovima podzemne akumulacije na kojima se kontinuirano biljee satne vri-jednosti razine vode. Na izvoru OMBLA i na susjednim izvorima Zaton i Zavrelje, gdje postoje

mogunosti da se u njihov sliv povremeno prelije dio voda iz sliva OMBLE, kontinuirano se regi-striraju satne vrijednosti protoke. Stalnim praenjem ponaanja razine vode u podzemnoj akumu-laciji, koja se povremeno formira u dananjim prirodnim uvjetima i njihovom usporedbom sa veli-inama protoka na OMBU i susjednim izvorima mogue je sa dovoljno preciznosti odrediti razinu vode u akumulaciji kada dolazi do prelijevanja prema susjednim izvorima.

Geological and hydrogeological characteristics in the catchment area of the OMBLA spring as well as in its underground storage reseNoir and the future HEPP OMBLA installations zone, are fully congruent with the preliminary description of the regional geological and hydrogeological characteristics. All the basic geological and hydrogeological factors that influenced formation of this karst spring are illustrated on the hydrogeological map herewith enclosed.

RESEARCH WORKS Perseverance of the idea about the possibility of constructing this specific hydro-power plant depends mostly on the reality and economic feasibility of the technical solutions for water retar-dation installations in the OMBLA spring hinterland, i. e. on the possibility of forming underground water reseNes. This was the reason for concentrating of almost all research works on the under-ground water storage reseNoir and on the partition profile of the future underground dam. Detailed geological analyses of lithostratographic, tectonic, hydrogeological factors have been elaborated as well as of the geoelectric prospecting in the OMBLA underground storage basin and in some parts of the neighbouring springs ZATON and ZAVRELJE catchments. Deep piezometric boreholes have been drilled in some characteristic parts of the underground storage area for continuous recording of the water level values every hour. At the OMBLA spring and its neighbouring springs ZATON and ZAVRELJE, where there are possibilities for periodical percola-tion of some of the water from OMBLA aquifer into their respecitve aquifers, values of the water discharge are continuously being registered. By the continuous obseNation of the water level fluctuations in the underground storage basin, periodically being formed under present natural conditions, and their contrasting with the values of the OMBLA and its neighbouring springs discharge, it is possible, pretty accurately, to determine the storage basin water level at the time of the water overflow into the neighbouring catchments.

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Svi dosadanji rezultati ukazuju da se prelijevanje prema izvoru Zaton dogaa kada razina vode u akumulaciji naraste iznad kota 120-130 m. n. m. Prema izvoru Zavrelje ovo prelijevanje poinje neto ranije kada se voda popne do kota 90-100 m. n. m. Porastom akumulacije do kota 120 - 130 m. n. m. ukupna protoka na izvoru Zavrelje kree se od 4,0-4,2 m3/sec. U zoni budue podzemne brane izvreno je detaljno geoloko kartiranje, izraen istrani potkop duine 700 m, te izbueno 30 buotina ukupne duine 3,400 m koje su rasporeene du dna i oba boka pregradnog profila. Sva provedena istraivanja izvrena su s ciljem da se detaljno utvrde odnosi izmedu pojedinih tektonskih blokova, odnosno utvrdi prostorni poloaj vodonepropusnih stijena (fli), nepropusnih do slabo propusnih (dolomit) te vodopropusnih (vapnenci). Mjerenjem vodopropusnosti du svih buotina dobijeni su kvantitativni podaci o vodopropusnosti svih slojeva unutar istraivanog profila. Svi ovi radovi omoguili su da se utvrde dimenzije poprenog profila na mjestu podzemne brane, kako je prikazano na slici iz priloga. Iz istranog potkopa i buotina koje su iz njega izvedene izvrena su geoloka, opsena geofizika, te speleoloka i ronilako-speleoloka istraivanja da se utvrdi prostorni poloaj fosilnih i danas aktivnih, piljskih kanala. Do danas otkriveni piljski prostori nekadanjih kanala i danas aktivni dovodni kanali OMBLE prikazani su na slikama iz priloga.

PREDLOLENO RJEENJE HE OMBLA Iz prethodnog prikaza hidrolokih analiza koje su obavljene za potrebe izrade Idejnog projekta ovog hidroenergetskog objekta moe se konstatirati da raspoloiva srednja protoka OMBLE iznosi Osr = 24,4 m%ec, to je vie od srednje protoke koja je usvojena pri izradi Idejnog ~eenja (Osr = 23,3 m3/sec).

All the results so far obtained indicate that the water overflow towards the ZATON spring occurs when the level of water in the aquifer is above an elevation of 120-130 a. s. l. Towards the ZAVRELJE spring this overflow starts somewhat earlier when the aquifer reaches an elevation of 90-1 OO a. s. l. By an increase of the storage water to an elevation of 120-130 a. s. l. total discharge at the ZAVRELJE spring oscillates from 4,0-4,2 m3/sec. Detailed geological mapping in the future underground dam zone has been performed, gallery 700 m long has been escavated for investigation purposes and 30 boreholes drilled with total length of 3,400 m positioned along the bottom and both sides of the partition profile. All explora-tions carried out by now have been performed with an intention to have the relations between separate tectonic blocks specifried in detail, i. e. to specify the spaciallocations of water imperme-able rocks (flysch), impermeable to low permeable (dolomite) and water permeable rocks (limes-tones). By measuring the water permeability near all boreholes, quantitative data have been ob-tained of water permeability of all strata within the profile under exploration. All these works helped to determine the dimensions of the cross profile at the underground dam locality, as illustrated on the drawing enclosed. From the gallery and the boreholes drilled from it. geological, extensive geophysical, speleological and diving-speleological research have been conducted to locate the fossil as well as the still active conduits. The former conduits located until now and the still active OMBLA feeding chan-nels are illustrated on the drawings in the enclosure.

PROPOSED SOLUTION FOR HEPP OMBLA From the previous review of hydrological analyses performed for elaboration purposes of this hydro-power plant conceptual design it can be concluded that the actual OMBLA mean dis-charge reads Oav = 24.4 m3/sec, what is more than the mean discharge adopted during elabora-tion of the conceptual design (Qav = 23,3 m3/sec).

-Iz analize geolokih i hidrolokih uvjeta krakog podruja ireg zalea izvora OMBLA i do sada provedenih istraivanja moe se sa dovoljno sigurnosti konstatirati da je u zaleu OMBLE mogue formirati podzemnu akumulaciju sa kotom uspora 1 OO m. n. m., kako je prikazano u shemi iz priloga. Sve analize ukazuju da je mogue formirati akumulaciju sa veom kotom uspora od 120-130 m. n. m., s tim da se na osnovu tehniko-ekonomske analize daje ~eenje za iskoritenje onog malog dijela voda koje se prelijevaju prema izvoru Zavrelje, kako je prikazano na slici iz priloga. Pored prirodno stvorenih uvjeta koji osiguravaju vododrivost lijevog i desnog boka akumulacije,

kljuni objekt kojim se postie ovo usporavanje vode u podzemlju jest objekt podzemne brane koji je smjeten u brdskom masivu iza izvora OMBLE. Ovaj se objekt bono vee za debele naslage vodonepropusnih stijena (fli), a u dnu na slabopro-pusne naslage dolomitskih stijena. Samo rjeenje ove podzemne brane bit e potpuno definirano nakon detaljne analize rezultata svih istraivanja, a za sada se moe rei da e njezin gornji dio (do kote + 1 OO m. n. m.) biti injekcijska zavjesa dok e donji dio (do kote - 1 OO m. n. m.) biti izveden kao injekcijska zavjesa i posebne betonske konstrukcije za zatvaranje veih krakih kanala i piljskih upljina. Sa uzvodne strane ove podzemne brane bit e iskopana posebna galerija za zahvat vode kojom e se osigurati uredna vodoopskrba Dubrovnika kako za vrijeme gradnje svih objekata tako i za vrijeme eksploatacije ovog energetskog postrojenja. Nato nizvodnije i blie brani bit

e iskopani objekti za zahvat vode, koja e se dalje tlanim cjevovodom dovesti do turbina. Svi ostali objekti koji su prikazani na priloenom crteu su klasini podzemni objekti.

Analysing the geological and hydrogeological conditions in a wider hinterland of the OMBLA karst spring and research works carried out until now, it can be concluded with enough certainty that in OMBLA hinterland it is possible to form a storage basin at an elevation of 1 OO a. s. 1., as the scheme in the enclosure indicates. All analyses indicate the possibility of forming a storage basin with a higher elevation of 120-130 a. s. 1., under presumption that on the basis of a technical-economic analysis a solution be given for utilization of the small part of waters that outflow towards ZAVRELJE spring, as shown on the picture enclosed. Besides the natural conditions which ensure impermeability on both sides of the storage basin, the key project which will ensure water retardation in the underground is the underground dam project placed in the hill massif behind the OMBLA spring. This project is tied sidewise to the thick stratum of impermeable rocks {flysch), and at the bottom to low permeable dolomite rocks. The very solution for the underground dam is to be fully defined upon a detailed analysis of all investigations results. Nevertheless, at this moment we can say that its upper part (up to an elevation of + 1 OO a. s. 1.) will be an grouting curtain while at the same time its lower part (up to an elevation of 1 OO a. s. 1.) will be constructed as an grouting curtain and special concrete constructions for closing up of bigger karst counduits and cave holes. Upstream from the underground dam a separate gallery is to be dug for collecting the water that will ensure regular water supply of the city of Dubrovnik, both during the construction of all installations and during exploatation of this power plant. Somewhat downstream and closer to the dam, water collectors will be dug from where through pressure pipeline the water will be brought to the turbines. All other installations, as shown on the drawing enclosed, are standard

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ENERGETSKO-EKONOMSKE VELIINE IZGRADNJE Na osnovi Idejnog rjeenja, HE OMBLA je predloena kao pribransko postrojenje sa slijedeim osnovnim veliinama izgradnje: - srednja protoka - instalirana protoka - maksimalni brutto pad - instalirana snaga - prosjena godinja proizvodnja

Osr = Oi =

23,3 m3/sec 70,0 m3/sec H= 100 m P=60MW

W = 156 GWh Proraun mogue proizvodnje proveden je za uvjete da je rad elektrane protoni. Procjena trokova izgradnje iznosi:

Graevinski radovi Hidromehanika i elektrostrojarska oprema Ostali trokovi

UKUPNO:

POWER-ECONOMIC CONSTRUCTION VALUES

30,100.000 21,600.000 13 9()().000' 65,600.000

On the preliminary design basis the HEPP OMBLA has been offered as a plant with the power station immediately below the dam, with following construction values: - mean discharge - installed discharge - maximum gross head - installed power capacity

Oav = 23,3 m3/sec oi = 70,0 m3/sec

H= 100 m P= 60MW

- mean annual production W = 156 GWh Estimate for the possible production has been made under the assumption that the power plant functions under free-flow conditions.

Estimate for the construction expenses reads:

Construction works Hydro-machanical and electro-mechanical expenses Other expenses

TOTAL:

(in USA $) 30,100.000 21,600.000 13,900.000'

65600.000

~L~----------~------------------~--~

ZAKLJUAK Svi do sada dobiveni rezultati istraivanja pokazuju da je predloeno tehniko ~eenje ovog hi-droenergetskog postrojenja, izraeno sa realnim osnovnim elementima. Ukupna koliina vode, koja se u prosjeno vlanoj godini danas pojavljuje na izvoru OMBLA iznosi O= 24.4 m%ec, to je vie od koliine koja je usvojena kod izrade Idejnog ~eenja (0 = 23,3 m3/sec). Geoloka, hidrogeoloka, geofizika istraivanja i posebno analiza ponaanja razine vode u prirod-noj podzemnoj akumulaciji OMBLA pokazuju da je mogue ostvariti maksimalnu kotu izmedu 120-130 m. n. m. Idejno ~eenje je razraeno sa kotom maksimalnog uspora od 1 OO m. n. m. lako za konanu ocjenu postojanosti predloenih tehnikih ~eenja pojedinih objekata, a posebno za ocjenu ekonominosti ovog hidroenergetskog postrojenja, moramo saekati zavretak kom-pletnog programa istranih radova, odnosno zavretak idejnog projekta, danas moemo rei da dosadanji rezultati istraivanja potvruju osnovne postavke idejnog rjeenja i da su dobiveni re-zultati pozitivno ocijenjeni od komisije jugoslavenskih eksperata.

Cijenei sloenost objekta koji smo postavili kao konani cilj, prisiljeni smo dobivene rezultate uvijek ponovo provjeravati. Etape istraivanja koje su za nama, te posebno dobiveni rezultati istra-ivanja, omoguuju nam da kod dananje ocjene realnosti predloene ideje za energetsko isko-ritenje voda krakog podzemlja, budemo realni optimisti.

CONCLUSION All the investigation results so far obtained indicate that the suggested technical solution for this hydro-power plant has been worked out based on realistic fundamental elements. Maximum discharge of the OMBLA spring in an average wet year amounts to O = 24,4 m3/sec, which happens to be a larger quantity than the one adopted at working out the preliminary design (0 = 23,3 m3/sec). Geological, hydrogeological, geophysical explorations and particularly the analysis of water level fluctuations in the OMBLA karst aquifer indicate that it is possible to obtain a maximum elevation of 120-130 a. s. l. The preliminary design has been elaborated on the basis of a maximum elevation of 1 OO a. s. l. Although for final evaluation whether the offered technical solutions for separate plants stand, and especially for evaluation of the economic feasibility of this hydro-power plant, it is necessary to wait for the complete research works to be finalized, i. e. for the preliminary design to be completed, we shan't be wrong if we now say that the investigation results obtained support the basic concepts of the preliminary design and that these results have gained favourable opinions from the Yugoslav experts committee. Appreciating the complexity of the project set as our final goal, we are obliged to recheck all the results obtained. All the stages of the research that are now behind us, and particularly the results obtained, having in mind the present evaluation of the feasibility of the offered idea for power utilization of karst underground waters, justify our attitude of realistic optimis.

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IZDAVA/EDITOR: ELEKTROPRIVREDA HRVATSKE HIDROELEKTRANA DUBROVNIK - DUBROVNIK

RPREVODILAC/ TRANSLATION: NIVES BORE CRTELI/MUPS: SLOBODAN VUKOVI dipl ing arh

REALIZACIJA/REALIZATION: SPORTING- ZAGREB TISAK/ PRINTED BY: TISKARA VARTFI

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UNDERGROUND STORAGE BASIN - HYOROGEOLOGICAL PROFILE

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