The need for increased attention to the reliability and safety of hydraulic structures in the water management complex of southern Russia is determined by the scale of the socio-economic consequences of their accidents. During the long-term operation of the low-pressure earthen dam of the Varnavinsky reservoir, various hidden defects and damages were formed. Which in the future can lead to a man-made disaster. The threat of catastrophic floods with the formation of hidden defects and damage will lead to natural disasters, namely the destruction of the dam body. The identification of these hidden defects and damages is a priority task in assessing the technical condition of the body of an earthen dam. The article considers only two methods of non-destructive testing for the detection of hidden defects and damage. Methods of electrocontact dynamic sounding and seismic exploration. They make it possible to obtain the electrical resistivity of soils when subdividing a section according to a lithological feature. As a result of data processing and interpretation, the geoelectric section of the electrical resistivity of soils was obtained. Applied hardware and methodological complex allowed to solve the tasks. The advantage of the complex is its methodological mobility. After a short experimental and methodological work and express processing, it is possible to clearly orient and combine the capabilities of the instrumentation complex and the engineering-geological situation in order to obtain the maximum quality and at the lowest cost of time and money. Studies of low-pressure earth dams should be carried out in the monitoring mode at various water levels in the reservoir. As can be seen from the results of processing, the geophysical complex of non-destructive testing makes it possible to study earth dams with the determination of soil parameters. To determine the physical and mechanical properties of soils, a greater amount of work should be carried out using reference drilling wells and identifying correlation dependencies of parameters.