The article discusses the peculiarities of the use of combined technologies in monitoring on the example of the Simferopol reservoir, namely low-frequency electromagnetic field (VLF) technology and numerical modeling of dangerous structural violations. It is possible to detect decompression of the soil base of the structure. When the field finds an object in the ground that conducts electricity, it detects the hydraulic structure’s own magnetic field, namely decompaction and subsidence. On the basis of the studies carried out, numerical simulation of the dam of the Simferopol reservoir was carried out with various dangerous structural defects and defects acquired over a long period of operation. It should be noted that during the period of operation at the complex of hydraulic structures of the Simferopol reservoir, no major repairs and reconstruction were carried out. The design features of the tooth in the body of the dam were numerically calculated. Stress and strain diagrams were obtained. Based on the calculations, in order to reduce water losses for filtration in the left side of the dam, the installation of a cementation curtain is envisaged. It has been established that the height of the cementation curtain is different depending on the depth of occurrence of water-resistant rocks. Based on the materials of the reconnaissance survey and calculations, field work and laboratory tests, it is possible to conclude that the structure is stable, while maintaining the current intensity of operation