At the Time of the Study, the Tunnel Was in the Final Stages of Construction
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1.4.2. Tunnel Fatničko polje and Beleća reservoir (FP->BR) At the time of the study, the tunnel was in the final stages of construction. The tunnel is much longer than DP->FP and has a steeper slope (S= 0.00166 or 0.166%) thus, when it is not surcharged (the flow in it is free surface), the regime is supercritical (FROUDE number larger than 1). Temporarily, the tunnel is not lined throughout its whole length and only the parts which are more susceptible to high leakage are lined with concrete. The roughness will therefore vary along its lined and unlined reaches. For the hydraulic analysis of its capacity, we have used an equivalent roughness value (i.e. average over its entire length). The plan view and cross section of this tunnel is presented in Figure 8. 461.50 457.17 28.89% 0.00166 0.00425 418.59 450.40 427.48 398.00 47.67 13560 2090 224.38 6.50 5.40 7.10 6.10 2.2 0 -13560 13560 - 15650 Figure 8. Longitudinal section of the tunnel between Fatničko polje and Beleća reservoir Its capacity function will again consist of two parts: 1. Free surface flow in the tunnel: When the flow in the FP-BR tunnel is free surface, the flow regime in the tunnel is supercritical (FROUDE Number bigger than 1) and therefore water level in the tunnel will not affect the water level upstream from its entrance - inlet. Additionally, since the slope of the approaching channel is higher than critical, water level in it will not determine the stage-discharge relationship. The control section (with Froude number equal to 1) will be formed at downstream most part of the sedimentation tank, where there is an elevated channel invert, a sort of brad crested weir. The lower portion of the flow – discharge curve is calculated for both the control section (critical depth) and for the section a few meters upstream (which was used as a cross section for the stage measurement that were calculated and presented in Figure 9), by taking into account the gradually varied flow in the inlet channel with the normal depth in the tunnel as the downstream boundary condition (two different values for the friction factor in the tunnel were taken into account). 2. Tunnel surcharged: When the tunnel is surcharged its capacity is determined by its friction losses and it depends on the water level in Fatničko polje. Before the tunnel is made fully operational, it is suggested to perform a measurement of the friction of the tunnel in order to establish the real values which determine it capacity. Since this data was not yet 25 available, the analysis was again performed with two hypothetical Manning roughness factors (n= 1/60 m-1/3s and n= 1/80 m-1/3s, whereas K=1/n). The results are shown in Figure 9 and have been used in the modelling work (following chapters). Z Zcr 461.5 459.5 Rating Curves FP-BR 485 480 475 Z[m asl] 470 465 460 0 50 100 150 200 250 Q[m3/s] Ks60 Ks80 Zcr Z Figure 9. Capacity of the tunnel between Fatničko polje and Bileća reservoir 26 It is planned that the channel will have a flow regulation gate at is downstream end. Under the present operational management framework it is to be kept opened at all times. 1.5. Preceding studies and data sources relevant to this project In addition to the references cited in the individual reports of modelling groups, in elaboration of the present study the following documents have been used: a. documents relevant to data and modelling - HIS-HET data base, i.e. data base containing data sets made available by HET Trebinje. In this data base the results of monitoring of hydrological, meteorological, hydrogeological and data related to operational management of the power plants that were kept in paper files have been compiled and digits by the Jaroslav Černi Institute from Belgrade. - Additional data obtained form HET Trebinje (for the period between the years 2000 – 2003) - Additional meteorological data obtained from the focal point for implementation of the UN convention on climate change b. Projects, studies, published papers and proceedings In elaborating this study the following reports and publications were available to the authors: - Water Management Master plan for Trebišnjica catchment (Kraška polja Istočne Hercegovine, Vodoprivredna osnova, izvod, Trebinje 1967 ) - Hydrological study (Knjiga 1. Hidrološka obrada podataka) for the Project – Study on the possibilities of the utilisation of the unused and diverted water by increasing the installed capacity of PHE Čapljina or by building HE Dubrovnik II (Studija mogućnosti iskorištenja neiskorištenih i prevedenih voda povećanjem instalacija PHE Čapljina ili izgradnjom HE Dubrovnik II, Sveska 1. Kraška polja: Nevesinjsko, Dabarskio i Fatničko) Energoinvest, Energonženjering, Sarajevo, 1992 - Multipurpose use of the Upper Horizons waters of the river Trebišnjica (Višenamjensko korišćenje voda Gornjih Horizonata r. Trebišnjice) clients: SOUR Elektroprivreda BiH, RSIZ Vodoprivreda BiH, SOUR APRO Mostar), Study performed in accordance with the request of the Executive Council of the Parliament of SR BiH (Izvršno vijeće Skupštine SR BiH), Trebinje, 1984 - Effect of the Energy system Trebišnjica on the development of the adjacent region (Uticaj izgradnje energetskog sistema Trebišnjica na razvoj gravitirajućeg područja) , Institute of Economy, Faculty of Economy, Sarajevo 1973 - Study on the effects of diversion of Dabarsko polje water on the regime of Bregava river. (Uticaj prevodjenaj voda Dabarskog polja na režim voda r. Bregave) Institute for use and protection of water resources in karst Trebinje 1985 - Study on the effects of the Diversion of river Zalomka waters on water regime of Buna and Bunica, (Uticaj prevodjenja voda r Zalomke na režim voda r. Bregave) Institute for use and protection of water resources in karst Trebinje 1985 - River Bregava – Possibilities for low flow augmentation (Rijeka Bregava Mogućnosti povećanja malih voda), Institute for use and protection of water resources in karst Trebinje 1986 - Tunnel Dabar – Fatnica, Hydraulic Analyses, (Tunel Dabar – Fatnica – Hidrauličke analize), Energoinvest, OOUR Higrainženjering, Sarajevo 1985 27 - Excerpts from the project Tunnel Fatničko polje and Beleća reservoir, Energoinvest, Sarajevo - Proceedings of USA-Yugoslav Symposium Karst Hydrology and Water Resources, held in June 2-7 1975. in Dubrovnik, Published by WRP – Water Resources Publication, Fort Collins, Colorado, Edited by V. Yevjevich -1976, Library of Congress Catalogue card Number 76-012972 Since the present study was conceived to be independent and unbiased, no direct comparison has been made with the results of the previous studies. However, the comparison can be made simply by comparing the synthesis results (for example the duration curve) with the equivalent functions obtained from earlier work. Such a legacy diagram is enclosed in the Appendix. 1.6. Water Management issues relevant to this project In this section we shall concentrate only on the part of water resources management which are relevant to this project. The basis for establishing the tunnel operation rules were following two documents: • BUILDING PERMIT (Vodoprivredna saglasnost) No.UP-I-06-337-180/86 of 27.05.1986, for building the tunnel Fatnica – Bileća issued by the Committee for Agriculture, Forestry and Water Resources of the Republic Bosnia and Herzegovina. (Republički Komitet za Poljoprivredu, Šumarstvo i Vodoprivredu) uprava za vodopriverdu) BiH, Sarajevo, Deputy Chairman of the Committee Božo Knežević. • BUILDING PERMIT (Vodoprivredna saglasnost) No.UP-I-03-78-1/69 of 29.7.1969, for water transfer from Dabarsko polje to Fatničko polje issued by the Water Resources Administration of the Republic (Republička uprava za vodopriverdu) BiH, Sarajevo, Director Abdulah Huzbašić. Provisions of the latter permit require the holder of the permit to build manage – operate the tunnel pursuant to the following rules (Figure 10): • Whenever the water level in Dabarsko polje is lower than 472 m asl. low flow to Ponikve ponor should not be changed and water is allowed to flow to Hrgud spring (tunnel DP->FP closed) • When the water level is between 472 and 490 m asl, access to Ponikve ponor is closed and water is transferred to Fatničko polje (tunnel open). When water level in Fatničko polje is higher than in Dabarsko polje, the tunnel closes and remains closed until the level in Fatničko polje becomes lower. • When the water level in Dabarsko polje is higher than 490 m asl both the Ponikve ponor access and the tunnel are open. In addition to the above rules, which deal with water levels and flow regulation, the Building permit, has several other provisions dealing with compensation to the farmers should the duration of he flood be longer than prescribed. These aspects have not been dealt with in this study in detail, because they do no affect the water regime in the Bregava catchment. 28 490 WLDP < 472 472 SWALLOW DABARSKO POLJE HOLE TUNNEL PONIKVE DP-FP QFP=0 TO BREGAVA 490 472 < WLDP < 490 472 WLFP < WLDP SWALLOW DABARSKO POLJE TO HOLE TUNNEL FATNIČKO PONIKVE DP-FP POLJE WLFP > WLDP QFP=0 QB=0 490 < WLDP 490 472 WLFP < WLDP SWALLOW DABARSKO POLJE TO HOLE TUNNEL FATNIČKO PONIKVE DP-FP POLJE WLFP > WLDP QFP=0 QB Figure 10. Conditions for flow regulation - operation of the tunnel 29 1.7. Interactions with the Inter-Entity Committee Before this study was contracted it had been agreed between the relevant ministries of both entities in BiH (Republic Srpska and Federation of BiH) to create an expert team (herein called Inter-Entity Committee) consisting of 5 water experts from each entity. The Committee was tasked with re-examining the results of the previous studies and giving recommendation to the relevant governments on the viability and robustness of the findings and results obtained in the previous projects.