Role of geological structures in seepage from Lar dam reservoir
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ORIGINAL PAPER
Role of geological structures in seepage from Lar dam reservoir S. Nayeb Asadollah 1 & A. Aalianvari 2 & H. Hajialibeigi 1 Received: 7 April 2018 / Accepted: 1 October 2018 # Saudi Society for Geosciences 2018
Abstract The main objective of this paper is to estimate the water seepage from Lar dam reservoir based on a combination of the geological structure study results and identification of the flow conduits in the right bank of the reservoir. From the beginning of impounding the dam in 1980, heavy seepage was observed at two karstic springs, Haraz and Galugah, located about 9 km downstream of the dam. During the first impounding, the discharge of the Haraz spring abruptly increased from 0.5 m3/s to around 5 m3/s. The results of piezometers and dye tests indicate that seepage occurs mainly through the right abutment of the dam where there is a structural wedge between the north dipping North Tiz Kuh and the south dipping Lar Valley faults. F1, F2, and F3 faults are the most important faults in vicinity of the structural wedge. Based on the dye test results, the North Tiz Kuh and F3 faults along which caves No. 1 and 2 are formed are regarded as two isolated conduits for seepage and conveyance into Lar Valley Fault at downstream of Lar dam. After identifying the conduits, water seepage from the Lar dam reservoir has been calculated using finite element method. According to the results of numerical method, when the reservoir water level is at 2485 m a.s.l, the average of water seepage is around 8.51 m3/s (this amount of water is related to the seepage along the Lar Valley Fault). The average discharge of springs downstream of the dam has been used to verify the numerical method. The results show a very close relation between estimated and observed discharge. Keywords Lar dam . Structural wedge . Karstic conduit . Seepage
Introduction The karst nature presents a great variety of risks associated with any kind of human activities. Construction of large structures in karst as dams, reservoirs, and hydropower tunnels is particularly sensitive and risky task (Milanović 1997). Seepage from dams has been reported in numerous dams in karst areas (Zou et al. 2017). Solution activity forms conduits of unpredictable dimensions and geometry whose permeability is often measured in centimeters or meters per second (Zhao et al. 2014). In most cases, the seepage occurs during the first impounding and reservoirs may fail to fill despite an extensive investigation program and sealing treatment (Karimi et al. 2005). The main causes of seepage at karst dam sites are the non-homogeneous
* A. Aalianvari [email protected] 1
Department of Geology, ShahidBeheshti University, Tehran, Iran
2
Department of Mining Engineering, Faculty of Engineering, University of Kashan, Kashan, Iran
nature of the karst formations, inadequate data, and limited investigation due to time and cost limitations(Raeisi and Kowsar 1997). The high permeability zones are local, representing a small percentage of the total karst area. T
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