Water Losses from the Ričice Reservoir Built in the Dinaric Karst

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Water losses from the Ričice reservoir built in the Dinaric karst

Article in Engineering Geology · June 2008 DOI: 10.1016/j.enggeo.2007.11.014

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Ognjen Bonacci Tanja Roje-Bonacci University of Split University of Split

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Engineering Geology 99 (2008) 121–127 www.elsevier.com/locate/enggeo

Water losses from the Ričice reservoir built in the Dinaric karst ⁎ Ognjen Bonacci , Tanja Roje-Bonacci

Faculty of Civil Engineering and Architecture, University of Split, 21000 Split, Matice hrvatske str. 15, Croatia

Accepted 14 November 2007 Available online 13 February 2008

Abstract

The Ričice reservoir was built in 1987 in the central part of the bare Dinaric karst region in Croatia, on the border with Bosnia and Herzegovina. The reservoir water level rise rapidly after rainfall, but due to high water-loss rates the water remains impounded for a very short time. The reservoir volume at the spillway altitude is 18.4 × 106 m3. Due to water losses, the mean annual water volume in the 1989–1995 period was 6.5 × 106 m3. Interdisciplinary analyses and investigations of geological, hydrological and hydrogeological factors which caused water losses from the Ričice reservoir have been carried out. Water losses from the reservoir are defined using a water budget equation. An assessment of the calculation of hydraulic conductivity, and a definition of the groundwater level below the Ričice reservoir, using Darcy's equation for vertical flow, is carried out. It may be concluded that the water losses from the Ričice reservoir are mainly controlled by the water level in the reservoir. © 2008 Elsevier B.V. All rights reserved.

Keywords: Dinaric karst; Croatia; Ričice reservoir; Water losses; Hydraulic conductivity, Lugeon unit

1. Introduction dissolution widening of initially narrow fractures. They showed that the structure of the karst rocks below the dam site is of high Living conditions for man in many karst regions are not relevance for the stability of the dam, as well as for the water favourable. This is especially through in bare Dinaric karst region. leakage from the reservoir. The main reason for this is specific annual water regime (Bonacci, Natural lakes and artificial reservoirs may lie directly within 1987). In autumn and winter excessive precipitation results in the carbonate rocks, but may also be present where unconsolidated flooding, which frequently last a long time. Immediately after the deposits overlie limestone strata (Winter, 2004). Many bodies of floods end, long dry periods began. These facts have forced man water in karst terrains, especially those lying on bare limestone, to build dams and storage water in karst. are intermittent, but may also be perennial. Motz (1998) found Karst is not static but a highly dynamic system. Scale issues are that vertical leakage from 11 natural karst lakes to the upper particularly important for understanding and modelling karst water Floridian aquifer averages 0.12–4.27 m yr− 1. circulation, and especially water losses from reservoirs. Conditions The above mentioned characteristics of karst water circulation for water circulation in a karstified medium are strongly dependent present a great variety of risks associated with the construction of on space and time scales (Bonacci et al., 2006). Ford and Williams dams and reservoirs. The most frequent problems are related to (2007) state that the direct exposure of karst terrains facilitates the caverns at dam sites, land subsidence at reservoir bottoms, water initiation of karst drainage and its later evolution through sinkholes leakage at dam sites and from reservoirs, induced seismicity as a of different sizes at the main points of water infiltration. consequence of water storage, endangerment of endemic fauna, Dreybrodt et al. (2002) and Romanov et al. (2003) presented and the changing of the local groundwater-surface water balance a model of karstification below dam sites and have demonstrated (Milanović, 2004a,b; Waltham et al., 2005). Milanović (2004a) that leakage from these hydraulic structures can be caused by stresses that due to the fact that each karst region is different, individual situations are very seldom, if ever, repeated. ⁎ Corresponding author. Fax: +385 21 465117. The main problem for the construction of the surface reservoirs E-mail address: [email protected] (O. Bonacci). in karst is ensuring water tightness. There are great numbers of

Fig. 1. Location map of the study area with state border between Croatia and Bosnia and Herzegovina, hydrographic networks, position of main discharge gauging stations and supposed groundwater flow directions. successfully performed reservoirs in karst all over the world region. Fig. 1b shows a study area, with the locations of surface (Bonacci and Roje-Bonacci, 2003; Milanović,2004betc), but streamflows, significant natural karst water phenomenon (the there are also some failures (Turkmen 2003; Milanović, 2004b; Prološko Blato natural retention, the Red Lake and the Blue Ahmadipour, 2005; Unal et al., 2007 etc). In this paper problems of Lake), the locations of three reservoirs (Rastovača, Tribistovo water losses from the Ričice reservoir developed in bare Dinaric and Ričice), the positions of five discharge gauging stations karst region will be discussed. (designated A, B, C, D and E), supposed groundwater flow directions, directions of flow in superficial watercourses, and 2. Basic characteristic of the Ričice reservoir and the state border between Croatia and Bosnia and Herzegovina. its catchment The relief is morphologically well-developed and non-uniform, as can be seen from two cross-sections given in Figs. 2 and 3. Fig. 2 The Ričice reservoir is located in Croatia (Fig. 1a) between presents cross-section α–α, marked in Fig. 1b. It can be seen at the 43°29′ and 43°31′N and 17°04′ and 17°08′E. The whole study position of the Red Lake, the world's deepest collapsed karst area is located in the central part of bare and deep Dinaric karst doline (Bögli, 1980) in which water permanently exists. The water

Fig. 2. Cross-section α–α (see Fig. 1) with indicated position of the Red Lake. O. Bonacci, T. Roje-Bonacci / Engineering Geology 99 (2008) 121–127 123

Fig. 3. Cross-section β–β (see Fig. 1) with indicated position of the Ričice reservoir and the Vrljika River. level in the Red Lake fluctuates from about 250 to 275 m above sea existence of many uncontrolled swallow holes through which level (a. s. l.). The investigated depth of its bottom is at 6m below surface water quickly infiltrates underground. For example, the sea level (b. s. l.). Detailed speleological investigations of the Red number of days on which the Ričina River at station A (Fig. 1b) Lake proved that the lake is connected directly to two karst dried up in the period 1979–1995 varies from between 285 conduits through which water constantly flows in and out from the (1979) and 350 (1994), with an average of 327 days. The flow at upper to the lower part of the karst aquifer. The Red Lake is a this location exists only 10% of the year, and appeared after natural piezometer directly connected to the large karst conduits, heavy rainfall. and its water level fluctuations very probably follow the ground- The average annual discharge in the period 1989–2001 and water level oscillations in that part of the karst aquifer. Because of topographic catchment areas of five discharge gauging stations the difficulty in measuring the water level in the Red Lake only designated in Fig. 1b are given in Table 1. The topographic isolated measurement is available. catchment area for the location of the Ričice dam (gauging station The study area is located at the periphery of the Mediterra- BinFig. 1b), defined in accordance with surface morphology and nean climate belt, with a strong influence of continental climate. directions of flow in open watercourses is 190 km2, while the The Ričice reservoir is located only 20 km from the Adriatic Sea, mean annual measured discharge is 0.26 m3 s− 1.UsingTurc but it is separated from the sea by the Biokovo Mountain chain, (1954) equation and the methodology developed by Bonacci which has a maximum altitude of 1762 m a. s. l. (1999), for the definition of catchment areas, the mean annual The average annual air temperature in the catchment varies discharge for station B should be about 5 m3 s− 1, which means from 12 °C (northern higher part) to 14 °C (southern lower part) that more than 4.7 m3 s− 1 or about 95% of water from the with a minimum daily temperature in January below 0 °C, and a topographic catchment flow is groundwater. Clear evidence for maximum daily temperature in July and August higher than this is given by the gauging station E on the Vrljika River which 35 °C. The annual rainfall ranges from 750 to 2350 mm with an has a topographic catchment of about 25 km2 and a mean annual average of about 1500 mm. The maximum rainfall occurs in discharge in the analysed period of 6.62 m3 s− 1. It is obvious that October and November, and the minimum in July and August. most of the flowing water into the underground in the upper part In spite of relatively numerous geological, hydrogeological of the Ričina River appears at the springs of the Vrljika River. This (especially groundwater tracing) and hydrological (Bonacci and fact is partly confirmed by a dye tracing test made in 1997. Test Roje-Bonacci, 2000) investigations in study area, it has not been results are shown in Fig. 4. It should be stressed that only less than possible to define either the catchment boundaries or the direc- 10% of injected dye (fluorescein), appeared after eleven days, at tions of groundwater circulation in different hydrological situations during different regional groundwater levels. The reason for Table 1 this is the extremely complex surface and underground karst Mean annual discharges Q for the 1989–2001 period and topographic morphology that can be only partly seen in Figs. 1b, 2and3. catchment areas A for five discharge gauging stations designated in Fig. 1b č č The Ri ina River that inflows into the Ri ice reservoir Station Station name Mean annual discharge Topographic catchment changes name in the downstream section to the Suvaja River, number in Fig. 1b Q (m3 s− 1) area A (km2) the Sija River and finally the Vrljika River. The reason for this is 1 A 0.22 66 the hydrological situation typical for deep and bare Dinaric karst 2 B 0.26 190 region. The groundwater level is, generally in the whole area 3 C 0.06 222 and for most of the time, beneath the bottom of the river courses. 4 D 0.45 250 ≈ All the above mentioned rivers are intermittent due to the 5 E 6.62 25 124 O. Bonacci, T. Roje-Bonacci / Engineering Geology 99 (2008) 121–127 the Opačac Spring, which is one of the permanent karst springs of the Vrljika River. The Ričice reservoir was impounded by construction of a 45 m high earth dam on the intermittent Ričina river course situated in the central part of the bare Dinaric karst region, on the border between Croatia and Bosnia and Herzegovina. The dam is constructed in a dolomite bedrock canyon. Fig. 5 represents a schematized geological–hydrogeological map of the area of the Ričice reservoir. The flooded area mostly consists of low permeable marls, marl limestone and sandstone. Designers believed that these impervious clastic layers would have been able to prevent water losses from the reservoir. Despite this, there are considerable water losses from the reservoir. Per- meable limestone and limestone breccia outcrop at several places along the right valley flank, near the dam and in some upstream of the reservoir. Tectonic fractures, fissures, joints, caverns and other karst features contribute to increase the permeability of the carbonate deposits. The carbonate rocks of the area are predominantly limestones, and only partly dolomites of Tertiary and Cretaceous Fig. 5. Simplified geological and hydrogeological map of the study area. formations. The dolomites do not considerably obstruct groundwater flows. Lower Cretaceous dolomites and thin bedded limestones make underground barriers to groundwater flow. The rock mass is practically tight if at this pressure less than Water table in the limestone, as well as in the broader area of the 1 Lu of water is absorbed. The permeability of 10 Lu indicates Ričice reservoir only after extremely intensively precipitations, the existence of water seepage through rock mass, while 100 Lu rises up to the surface. or more means that open joints exist in the rock mass through which water can quickly penetrate. 3. Water pressure test Under a laminar flow regime, 1 Lu is approximately equal to the velocity of 0.015 m day− 1 (Nonveiller, 1989). Nonveiller The permeability of rock masses has been determined by (1989) gives the next approximate relationship between hydraulic means of water pressure tests (WPT) or Lugeon tests (Lugeon, conductivity K in cm s− 1 and Lugeon: 1933). The amount of water injected in isolated borehole sections is a measure describing the absorption capacity of the rock Kc1:5 10 5 Lu: ð1Þ and, under certain assumptions, the permeability. One Lugeon (1 Lu) is defined as one litre-per-meter-and-minute at a reference The WPT was measured at the Ričice reservoir, in five bore- pressure of 10bar, approximately. holes (M1, M2, M3 and B1, in Fig. 5). A total of 118 Lugeon tests were made from the surface to the 65 m depth. The measured values vary between boreholes and with depth from 0.0 to 14.86 Lu, with an average of 2.21 Lu. Using Eq. (1) the values of hydraulic conductivity vary from 0.0 to 223 × 10− 6 cm s− 1, with an average value of 33.2 cm s− 1. It should be stressed that the number of boreholes as well as their position in the reservoir was not ideal. Nonveiller (1989) reports the permeability of a similar karst rock mass in the region of Dinaric karst at the Buško Blato reservoir, only 15 km away from the Ričice reservoir. In this case, a few hundreds measured values of permeability vary from 0.0 to 180 Lu, with an average of 10 Lu. Günay and Milanović (2005) report that the permeability of limestone at the Akkopru reservoir (southwest Turkey) varies from 0.0 to 50 Lu.

4. Determination of water losses

The reservoir volume at a spillway altitude of 393.62 m a. s. l. is 18.4 × 106 m3. Due to water losses, the mean annual water volume in the 1989–1995 period was 6.5 × 106 m3, which cor- Fig. 4. Results of dye tracing test from piezometer B2. responds to an altitude of 383.94 m a. s. l. O. Bonacci, T. Roje-Bonacci / Engineering Geology 99 (2008) 121–127 125

Fig. 6. Time series of mean monthly water losses from the reservoir G* expressed in m3 for the period January 1989–December 1995 (84 months).

Daily water losses G from the Ričice reservoir in the 1989– Daily water losses in the analysed period varied between 1995 period have been calculated using the water budget 0.030 and 0.970 m3 s− 1. Mean monthly and annual water losses equation: varied between 0.076 and 0.667 m3 s− 1, and 0.138 (1990) and 0.452 (1994) m3 s− 1, respectively. Fig. 7 presents the ratio G ¼ I þ P O EFDV ð2Þ − between mean monthly water losses G expressed in m3 s 1 and where I is the surface water inflow to the reservoir controlled by the mean monthly reservoir water level H for 84 months. Fig. 8 two discharge gauging stations, P is the rainfall on the reservoir presents the ratio between mean annual water losses G ex- surface, O is outflow from the reservoir through the spillway pressed in m3 s− 1 and the mean annual reservoir water level H and bottom outlet, E is free water surface evaporation, and ΔV for 7 years. The coefficients of the linear correlations are 0.889 is the change in the volume of the water stored in the reservoir at (for monthly values) and 0.971 (for yearly values). Since they the beginning and at the end of the time interval of calculation. are very high (close to 1) it may be concluded that the water The six mentioned components of the budget are expressed as losses from the Ričice reservoir are mainly controlled by the m3 and as m3 s− 1. water level in the reservoir. The calculated values of the mean monthly water losses G* for the period January 1989–December 1995 (84 months), 5. Assessment of groundwater level below the expressed as m3, are plotted in Fig. 6. The trend line shows a Ričice reservoir slight increase of water losses during the analysed period. Due to the short monitoring time it is not possible to make strong Two boreholes, B1 and B2 shown in Fig. 5, were drilled with conclusions but it is possible that the leakage from the Ričice the main aim of taking continuous groundwater measurements reservoir is increasing. in order to discover the regional or at least local behaviour of the

Fig. 7. The ratio between mean monthly water losses G expressed in m3 s−1 and the mean monthly reservoir water level H for the period January 1989–December 1995 (84 months). 126 O. Bonacci, T. Roje-Bonacci / Engineering Geology 99 (2008) 121–127

Fig. 8. The ratio between mean annual water losses G expressed in m3 s−1 and the mean annual reservoir water level H for the period of 1989–1995 (7 years). groundwater level around the Ričice reservoir. The piezometers experimental area in the vicinity of Montpellier (France), made are only 120 m apart. Fig. 9 presents the relationship between continual measurements of the groundwater levels and water the water level in the Ričice reservoir H and the groundwater temperatures at 19 piezometers. The study showed that ground- level measured in piezometers B1 and B2. The groundwater water levels in piezometers that were close to one another level in piezometer B2 was continuously higher than in piezo- responded differently to rainfall, primarily because of varying meter B1 (between 20 and 30 m) and higher (except for two connections with the main karst conduits and subsurface karst days at the beginning of the measurements) than the water level features. He proved that the groundwater level reacts more in the reservoir. In piezometer B1 the groundwater oscillated in rapidly in piezometers connected to main karst conduits com- a large range of 13 m, between 354 and 367 m a. s. l., while in pared with piezometers connected to a system of small fractures, piezometer B2 oscillations were in narrow range of 2 m, although they are close (only 5 to 10 m) to one another. between 384 and 386 m a. s. l. Oscillations in both piezometers The loss of water from the bottom of a water body to the are correlated with the water level in the Ričice reservoir. underlying karst aquifer G, or vertical leakage, can be described Different groundwater behaviour in two (or more) close in terms of Darcy's equation written for vertical flow (Motz, piezometers is not a surprise for the karst areas. Drogue (1980, 1998): 1985), in studying the geometry of a karst aquifer over a 1000 m2 G ¼ DH A ðÞKv=b ð3Þ

where Kv is the vertically averaged hydraulic conductivity of the hydrogeological units between the bottom of the water body and the top of the underlying karst aquifer, A is the surface of the reservoir, b is the thickness of hydrogeological units between the bottom of the water body and the top of the karst aquifer, and ΔH is the difference between the water level in the analysed water body and the hydraulic head of the underlying karst aquifer. In the case of the Ričice reservoir it is realistic to

Table 2 Values of pairs of averaged hydraulic conductivity of the hydrogeological units between the bottom of the Ričice reservoir and the top of the underlying karst

aquifer Kv, and the thickness of hydrogeological units between the bottom of the Ričice reservoir and the top of the karst aquifer b calculated by Eq. (3) −1 b (m) Kv (cm s ) Altitude of groundwater level — H (m a. s. l.) 160 28×10− 4 200 85 25×10− 4 275 Fig. 9. The ratio between the water level in the Ričice reservoir H and the 60 23×10− 4 300 groundwater level measured in piezometers B1 and B2 designated as HB1 and 35 19×10− 4 325 HB2. Dashed lines represent relationship during groundwater level (GWL) 66×10− 4 354 rising (W.R.), while full lines represent relationship during GWL falling (W.F.). O. Bonacci, T. Roje-Bonacci / Engineering Geology 99 (2008) 121–127 127 suppose that there does not exist a confined karst aquifer, which In many cases the improvement of the strengthening of the means that: rock mass is also a desired effect of the injection, together with the removal or decrease of water losses from the reservoir. Ford DH ¼ H þ b ð4Þ and Williams (2007) stress that experience has shown that re- where H is the depth of water in the analysed water body. The medial measures after a dam and reservoir have been completed ratio (Kv/b) is the vertically averaged vertical conductance of the and tested are much more costly than dense grouting during units between the bottom of the analysed water body and the construction. underlying karst aquifer. In Eq. (3) the two values of variables Kv and b are unknown References while the values of water losses G have been calculated in the previous section. Using the known values of G and Eq. (3), in Ahmadipour, M., 2005. The effect of sinkholes on leakage of water from the Table 2 we can calculate pairs of values for the averaged hydraulic Sarabchenar dam, Southwest Iran. Journal of Environmental Hydrology 13, 1–5. Bögli, A., 1980. Karst Hydrology and Physical Speleology. Springer Verlag, conductivity of the Kv, and the thickness of hydrogeological units between the bottom of the Ričice reservoir and the top of the karst Berlin, Germany. Bonacci, O., 1987. Karst Hydrology with Special References to the Dinaric aquifer b. The last column in the Table 2 gives the groundwater Karst. Springer Verlag, Berlin, Germany. level in m a. s. l. Bonacci, O., 1999. Water circulation in karst and determination of catchment It should be stressed that the values of horizontal hydraulic areas: example of the River Zrmanja. Hydrological Sciences Journal 44 (3), conductivity K, as defined by the Lugeon test, are not identical 373–386. with the values of the vertical hydraulic conductivity K but some Bonacci, O., Roje-Bonacci, T., 2000. Interpretation of groundwater level moni- v toring results in karst aquifers: examples from the Dinaric karst. Hydrological similarities should exist. It is very probably that the groundwater Processes 14 (14), 2423–2438. level below the Ričice reservoir varies from between 275 and Bonacci, O., Roje-Bonacci, T., 2003. The influence of hydrotechnical development 325 m a. s. l., which corresponds to the averaged vertical hydrau- on the flow on the karstic river Cetina. Hydrological Processes 17, 1–15. − 4 − 1 Bonacci, O., Ljubenkov, I., Roje-Bonacci, T., 2006. Karst flash floods: an example lic conductivity Kv of 19 and 25 × 10 cm s ,respectively. from the Dinaric karst (Croatia). Natural Hazards and Earth System Scien- ces 6 (2), 195–203. 6. Conclusion Dreybrodt, W., Romanov, D., Gabrovšek, F., 2002. Karstification below dam sites: a model of increasing leakage from reservoirs. Environmental Geo- The main objective of the paper was to prove, by an actual logy 42 (5), 518–524. example and a complex case from the bare Dinaric karst region, Drogue, C., 1980. Essai d'identification d'un type de structure de magasins that the water circulation processes in karst can be explained, at carbonates fissurés. Mémoire Hydrogéologique Série Société Géologique de France 11, 101–108. least partly, with classical climatological and hydrological data. Drogue, C., 1985. Geothermal gradients and ground water circulation in fissured At the same time it presents the need for interdisciplinary ana- and karstic rocks: the role played by the structure of the permeable network. lyses incorporating several approaches and techniques in the Journal Geodynamics 4, 219–231. study of water losses from the reservoirs built in karst. From an Ford, D.C., Williams, P.W., 2007. Karst Hydrogeology and Geomorphology. John Wiley, Chichester, UK. interdisciplinary standpoint, the paper gives an explanation of the ć č Günay, G., Milanovi , P., 2005. Karst engineering studies at the Akkopru processes of water losses from the Ri ice reservoir built in deep reservoir area, SW of Turkey. Proceedings of the International Conference and bare Dinaric karst. and Field Seminars “Water Resources and Environmental Problems in Due to extreme heterogeneity of the karst, it is very hard Karst”, Belgrade and Kotor, Serbia and Montenegro, pp. 651–658. to obtain reliable local and regional information, parameters Lugeon, M., 1933. Barrages et Geologie. Dunod, Paris, France. ć and conclusions on water circulation processes. A good under- Milanovi , P., 2004a. Dams and reservoirs on karst. In: Gun, J. (Ed.), Encyclopedia of Caves and Karst Science. Fitzroy Dearborn, New York, USA, pp. 277–279. standing of the mechanisms of water losses from the reservoirs Milanović, P.T., 2004b. Water Resources Engineering in Karst. 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