Periodic Monitoring of the Kostanjek Landslide using UAV

The Kostanjek landslide is located in the western residential area of the City of Zagreb. The landslide was activated in 1963 and the main cause of sliding was excavation of the marl at the foot of slope. Since 1976 a several different projects of landslide displacement measurements were done. In the period from 1976 to 1994, geotechnical investigations, geodetic surveys and aerial photogrammetric surveys were carried out in order to determine an engineering-geological model of the Kostanjek landslide. In 2012, real time monitoring system of the landslide was established which consists of 15 GNSS sensors for displacements monitoring. In order to obtain more detailed information about landslide displacements, two UAV surveys (April 2017 and May 2019) of the landslide were carried out. Since landslide velocities have been changing over the last 50 years, ranging from extremely slow to very slow, in this paper we wanted to analyze suitability of UAV for monitoring of slow-moving landslide. The accuracy of UAV survey was examined by comparison of the point coordinates and displacements determined by UAV survey with coordinates and displacements determined by GNSS RTK method. Also, determined displacements were compared with displacements determined by GNSS sensors from monitoring system.