Ashjari, Javad

Koch, Manfred

Sohi, Seyed Mohammad Hosseiny

English

Hydraulic Engineering Repository

Conference Paper, Published VersionSohi, Seyed Mohammad Hosseiny; Koch, Manfred; Ashjari, JavadConstruction Effects of the Karun 4 Dam, Iran, on theGroundwater in the Adjacent Karstic AquiferZur Verfügung gestellt in Kooperation mit/Provided in Cooperation with:Kuratorium für Forschung im Küsteningenieurwesen (KFKI)Verfügbar unter/Available at: https://hdl.handle.net/20.500.11970/99416Vorgeschlagene Zitierweise/Suggested citation:Sohi, Seyed Mohammad Hosseiny; Koch, Manfred; Ashjari, Javad (2014): ConstructionEffects of the Karun 4 Dam, Iran, on the Groundwater in the Adjacent Karstic Aquifer. In:Lehfeldt, Rainer; Kopmann, Rebekka (Hg.): ICHE 2014. Proceedings of the 11thInternational Conference on Hydroscience & Engineering. Karlsruhe: Bundesanstalt fürWasserbau. S. 65-74.Standardnutzungsbedingungen/Terms of Use:Die Dokumente in HENRY stehen unter der Creative Commons Lizenz CC BY 4.0, sofern keine abweichendenNutzungsbedingungen getroffen wurden. Damit ist sowohl die kommerzielle Nutzung als auch das Teilen, dieWeiterbearbeitung und Speicherung erlaubt. Das Verwenden und das Bearbeiten stehen unter der Bedingung derNamensnennung. Im Einzelfall kann eine restriktivere Lizenz gelten; dann gelten abweichend von den obigenNutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte.Documents in HENRY are made available under the Creative Commons License CC BY 4.0, if no other license isapplicable. Under CC BY 4.0 commercial use and sharing, remixing, transforming, and building upon the materialof the work is permitted. In some cases a different, more restrictive license may apply; if applicable the terms ofthe restrictive license will be binding.1 INTRODUCTION When it comes to the construction of dams and reservoirs in karsts, which are known for their high pervi-ousness due to dissolution faults and conduits, the prevailing risk is water loss, while the risk of stability is considered to be considerably lower (Milanović, 2004). The term Karst is generally defined as a terrain underlain by rocks that are highly soluble (such as limestone) with well-developed secondary porosity, and a terrain that exhibits a distinctive hydrology and landforms such as sink holes, sinking streams, springs and caves (Ford & Williams, 2007). Water loss through basements and abutments of the dams constructed in karst areas leads to considerable costs and non-productivity of the dams. Although the con-struction of a grout curtain is the most common method to reduce or prevent the water loss, it can solve the problem only partly and in some cases this operation is even fruitless.  For example, the Lar Dam in Iran has used less than half of its conceived capacity, because of continu-ous leakage - about 10 m3/s - through the dam foundations and abutments, since its construction in 1980 (Uromeihy, 2000). Although efforts, such as water injection into the fault, lining of parts of the bottom  of the reservoir by thick blankets of clay, or the construction of cut off walls, have been made in recent times to prevent or, at least, to reduce the water leakage, successes to that regard have been very limited. The main paths of water loss underneath dams and reservoirs in karst are the dissolution conduits and the main cause of this problem then is the poor identification of such conduits as being responsible for the leakage. The generation and development of karst conduits within a rock mass is not completely random, but is somehow guided by various chemical pre-requisites which drive the dissolution processes (Wright, Construction Effects of the Karun 4 Dam, Iran, on the Groundwater in the Adjacent Karstic Aquifer  S.M. Hosseiny Sohi & M. Koch  Department of Geohydraulics and Engineering Hydrology, University of Kassel, Germany J. Ashjari Geosciences Department, Tehran University, Iran  ABSTRACT: The Karun 4 concrete dam is with a maximum dam height above foundation of 230m the highest dam of Iran. It has been in operation since July 2011. It was constructed over a karst limestone and water leakage has been, and continues to be, one of the most important problems of this dam. The ge-ological formations around the dam site consist of carbonate layers of the Asmari formation and marl-stone and marly limestone of the impervious Pabdeh formation, upstream of the dam site. The object of this study is to determine the dam construction effects on the groundwater levels in the adjacent aquifer. Thus, before the dam construction, the natural groundwater levels at both banks were recorded to be 5-8m higher than the river stage. This indicates that the natural groundwater gradient at that time was from the banks towards the river, i.e. the latter was an effluent stream before the construction of dam. At that time no important springs were identified at the dam site., other than a minor spring with a discharge <5 lit/sec that emanated at the contact interface between the permeable Asmari- and the impermeable Pabdeh for-mation (perching aquifer conditions) on the left bank, upstream of the dam. A Lugeon test that was car-ried out at that time indicated that the permeability of the adjacent limestone is high, as it varies from 25 to 55 Lu in the layers above the river level, but it decreases gradually to 3 Lu in the formations below. Af-ter dam impounding, some changes in the borehole's water levels were observed. Thus it has been found, in particular, that the leakage from the reservoir has induced groundwater level rises between 12 to 17 meters. Keywords: Karun 4 dam, Iran, Water seepage, Karst, Hydrogeology ICHE 2014, Hamburg - Lehfeldt & Kopmann (eds) - © 2014 Bundesanstalt für Wasserbau ISBN 978-3-939230-32-865Table 1. Some Karun 4 dam technical specifications Dam type  Concrete double arc Height from foundation 230 m Crest length /width 440 m / 7m Foundation width 37 to 52 m Total volume of concrete placement 1.65 million m3 Total volume of the reservoir  2190 million m3 Power Plant Type Ground Spillway  Chute, orifice types and free  The dam is located in the tectonically folded belt of the Zagros Mountains within a canyon that is located in the southwestern flank of the Kuh-Sefid anticline which has a NW-SE trend. Most of the reservoir is situated on Cretaceous to Miocene limestone and marly limestone (Haghnejad et al., 2014). The geologi-cal formations around the dam site consist of carbonate layers of the Asmari formation (As) which can be divided into lower (As1), middle (As2) and upper (As3) units and marlstone and marly limestone of im-pervious Pabdeh formation (Pd) on upstream of dam site (see Figs.2 and 3). The lower unit (As1) com-prises limestone, porous limestone and some marly limestone with some marlstone, generally thick to very thickly bedded and highly karstic. The measured mean RQD (rock-quality designation) index (Deere, 1964) ranges between 55% and 83%. The middle unit (As2) is located downstream of the dam and comprises alternating limestone, dolomitic, marly limestone and marl. Karstification is limited and the RQD is between 53% and 84%. The upper part (As3) consists of alternating layers of limestone, marly limestone and marl with slight karstification and an RQD between 45% and 78%. These RQD-values indicate a fair to good quality rock in all three units (Koleini, 2012). As1 outcrops in the dam val-ley abutments are highlighted in the cliff around the site. The strike of the beddings is northwest to south-east, and southern limb slopes to the south with a dip of 70-80 degrees. The AS1 unit, with an apparent thickness of about 200 m in normal direction to the bedding, constitutes the foundation rock of the dam.  The geology of the dam site is affected by many faults, 122 major joints and 4 discontinuities sets. The strongly dipping reverse Monj fault, with a length of 14 km, is located at a distance of about 500 m down-stream of the dam. The joint openings along the bedding at the ground surface range from 1 to 100 mm and decrease with increasing depth.  2.2 Hydrogeology  Before dam construction in year 2002, the natural groundwater level at both banks was recorded to be 5-8m higher than that of the river water level. This indicates that the natural gradient of groundwater at that time was from the banks toward river, i.e. the river was an effluent stream, which is the normal situation for most rivers in the world. In fact, the phreatic levels in the left and right banks of the river were meas-ured as 848 and 845m NN, respectively.  In fact, at that time, before 2002, no important springs were identified at the dam site. The only minor spring, with a discharge of less than 5 lit/sec, emanated at the contact interface between the permeable Asmari Formation and the impermeable Pabdeh formation, upstream of the left abutment of the dam. In the Asmari Formation dissolutional surface features such as vugs and small cavities along the dis-continuities with infilling were observed. Some larger cavities (1 to 2m in diameter) were encountered during the excavation of the galleries. A porous limestone layer was identified, which had a vuggy feature and was recognized as a key bed underneath the dam site.  Lugeon tests were carried out at that time (2002), which resulted in a rather high permeability between 25 to 55 Lu in the limestone  layers above the river level, but which decrease gradually to 3 Lu, as one goes towards the formations below the river water.  After dam impounding in 2010, some changes in the borehole water levels were observed and it was found that the leakage probability from the grout curtain had increased. This was corroborated by the studies of Shabab (2011) and Kamali and Ashjari (2012) who proved the existence of increased leakage, but these authors could neither specify nor identify the pathways of the leaking waters. 67tional network, so that any instability- or safety problems with this dam would result in irrecoverable losses to the country as a whole. REFERENCES Bakalowicz, M. (2005). Karst groundwater: a challenge for new resources, Hydrogeol J., 13,148–160 Deere, D U (1964). Technical description of rock cores, Rock Mechanics Engineering Geology, 1, 16-22. Ford, D. and Williams, P. (2007). Karst Hydrogeology and Geomorphology. Wiley Ltd, England. Haghnejad, A., Ahangari, K., Noorzad, A. (2014).  Investigation on various relations between uniaxial compressive strength, elasticity and deformation modulus of Asmari formation in Iran. Arab. Journ. Science and Engineer., 39, 4, 2677-2682. Kamali, M. and Ashjari, J. (2012). Determination of efficiency of grout curtain of Karun 4’s Dam by dye tracing test. Report to IWPC (Iran Water & Power resources development Company), 124 p. Kiraly, L. (1975). Rapport sur l'état actual des connaissances dans le domaine des caractères physiques des roches karstiques, in: Bueger and Dubertret (Eds.), International Union Geol. Sci., Series B. 3, pp.53-67. Koleini, M. (2012). Engineering geological assessment and rock mass characterization of the Asmari formation (Zagros range) as large dam foundation rocks in southwestern Iran. Ph.D thesis, University of Pretoria, South Africa. Mahab Ghods Consulting Engineering Co. (2002). Karun 4 dam project. Final engineering geological report (phase 2). Milanović, PT. (2004). Water resources engineering in karst. CRC Press, Boca Raton. Scanlon, B.R.,  Mace, R.E.,  Barrett, M.E.,  Smith, B. (2003). Can we simulate regional groundwater flow in a karst system us-ing equivalent porous media models? Case study, Barton Springs Edwards aquifer, USA. J. Hydrol., 276, 137–158. Shabab Boroujeni, B. (2011).  Determination of effective factors on permeability in karstic dams in west of Zagros. M.Sc. the-sis, Tehran University, Iran.  Teutsch, G., Sauter, M. (1998). Distributed parameter modelling approaches in karst-hydrological investigations. Bull. d’Hydrogeologie,  16, 99–109. Urumeihy, A. (2000). The Lar Dam; an example of infrastructural development in a geologically active karstic region. Journal of Asian Earth Sciences. 18, 25-31. Wright, V.P. (1991). Palaeokarst types, recognition,controls and associations, in: Wright,  V.P., Esteban, M., Smart, P.L. (Eds.), Palaeokarsts and Palaeokarstic Reservoirs, Reading: P.R.I.S. Occasional Publication Series 2, pp.56-88.   73

Construction Effects of the Karun 4 Dam, Iran, on the Groundwater in the Adjacent Karstic Aquifer

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Construction Effects of the Karun 4 Dam, Iran, on the Groundwater in the Adjacent Karstic Aquifer

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