ORIGINAL PAPER Electrical resistivity imaging for investigation of seepage paths in the Yukari Gökdere Dam, Isparta, Turkey Sedat Yilmaz 1 & Mahmut Okyar 1 & Mustafa Gurbuz 2 Received: 29 November 2019 /Accepted: 7 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract Upon completion of the Yukarı Gökdere Dam, designed as a clay-cored rock fill dam for irrigation purpose, in Eğirdir district of Isparta, the water started to accumulate in the reservoir. Following this, reservoir’s water level has dropped sharply, and it was completely empty. In the winter season, the dam has accumulated water again; however, two water leakage areas were observed on the downstream side of the dam. Three different survey data were utilized to investigate the seepage paths of the dam. The first data set, before the construction phase, involves the lithological units and rock quality designation indexes in the cores recovered from boreholes, and the in-situ ground water table characteristics and Lugeon’s tests applied in the boreholes. The second data set, electrical resistivity, was collected in three campaigns performed in June 2017, August 2017, and February 2018. Resistivity data were measured using dipole-dipole electrode array with electrode spacing of 1.7 m and 2.5 m in the reservoir, and 3 m on the crest. The last data set includes benchmark readings. With the evaluation of resistivity, geotechnical, and survey data, the leakage in the dam is interpreted to be due to damaged parts in the clay fill material forming the main body of the dam. Keywords Dam . Leakage . Seepage . Electrical resistivity imaging Introduction The dams are the most important components of the economic development and human quality of life. By diverting water for power, navigation, flood control, and irrigation, dams support economic development. Similarly, drinking water from the dams is the indispensable requirement for improving human quality of life. The seepage is one of the most important criteria to be considered in the dam’s design and construction. It is defined as the interstitial movement of water that may take place through a dam, its foundation or its abutments (DEC 1987). From this definition, it is clear that all dams have some seepages, but the important point is that the seepages should be kept to a minimum as much as possible as excessive seep- ages compromise the dam’ s safety and serviceability. According to a study of the ICOLD (1973), about 38% of all embankment or fill dam failures are caused by seepage or piping. Although many seepage detection and investigation methods are available, geophysical methods are most often used. The effectiveness of this method has been well established in various electrical resistivity (e.g., Butler and Llopis 1990; Gourry and Moldoveanu 1997; Titov et al. 2000; Panthulu et al. 2001; Brosten et al. 2005; Cardarelli et al. 2010, 2014, 2018), self-potential (e.g., Davenport et al. 1983; Corwin 1989; Butler and Llopis 1990; Al-Saigh et al. 1994; Titov et al. 2000; Panthulu et al. 2001; Brosten et al. 2005), electromagnetic profiling/conductivity (e.g., Butler and Llopis 1990; Brosten et al. 2005; Blais et al. 2007), ground penetrating radar (e.g., Butler and Llopis 1990; Gourry and Moldoveanu 1997; Blais et al. 2007), and seismic refraction (e.g., Davenport et al. 1983; Krishnaiah et al. 2000; Cardarelli et al. 2010, 2018) studies. In Turkey, the number of large dams (i.e., dams with a height of 15 m or more from the foundation, or dams that are between 5 and 15 m high and have a storage volume more than 3 million m 3 , as defined by the ICOLD) is reported to be 856 (TRCOLD 2014). In addition to this, there are 657 small dams in the country, based on DSI (2009). However, in spite of the existence of vast numbers of dams in Turkey, our * Sedat Yilmaz sedatyilmaz@sdu.edu.tr 1 Department of Geophysics, Engineering Faculty, Süleyman Demirel University, 32260 Isparta, Turkey 2 General Directorate of State Hydraulic Works, 18. Regional Directorate, 32240 Isparta, Turkey Bulletin of Engineering Geology and the Environment https://doi.org/10.1007/s10064-020-01952-2