Activated by mining activities in 1963, the Kostanjek landslide is the largest in the Republic of Croatia. Located in the hilly capital city of Zagreb, it is a reactivated, deep-seated, large translational landslide with an area of about a square kilometer.
Despite extremely low landslide movement over the past 50 years, the risk surrounding the landslide is still high. Since 2011, scientists have been working to estimate these risks by acquiring new knowledge about landslide movements. Displacements, velocities and accelerations are analyzed by the influence of precipitation and groundwater level changes. With these observations, the goal is to better predict displacement based on meteorological precipitation forecasts that could lead to landslides and to provide an early warning in the case of a threatening slide.
There are several unique characteristics of the Kostanjek landslide that made monitoring challenging including: finding adequate positions to monitor within the landside, providing adequate electrical power supply, and gaining permission from local citizens and city authorities. Other solutions providing 3D displacement information, such as optical total stations, were not an option because landslide morphology challenges the line-of-sight visibility between a total station and prisms.
Between 2011 and 2014, landslide scientists from Croatia, Japan, Geomatika Smolčak Ltd. and Trimble Inc. developed and implemented a real-time monitoring system to monitor and predict the movement of the landslide that got around the problem of line-of-sight by installing GNSS receivers and various types of geotechnical sensors. All movement sensors are connected to the core of the monitoring system – Trimble 4D Control monitoring software. Trimble 4D Control visualizes and analyzes the monitoring data in real-time, issuing alarms automatically whenever the system detects a predefined movement. A versatile monitoring software, it is also used worldwide for other monitoring applications such as mines, dams and construction-related monitoring.
In total, 15 Trimble NetR9 TI-2 GNSS reference receivers with Trimble Zephyr Geodetic 2 antennas have been installed on site. Working with Trimble 4D Control software, multiple GNSS processing options can operate in parallel. Using 60-minute and 24-hour post-processing intervals, as well as 1 Hz RTK results, the monitoring team also calculated the precision of GNSS measurements proving they correspond to Trimble specifications. This means the measurements at the Kostanjek landslide provide reliable data about antenna positions. Additionally, daily monitoring of movement with high precision enables measurements of small displacements, which is particularly important for the analysis of slowly moving landslides, such as the Kostanjek landslide.
According to Dr. Martin Krkač, assistant professor at the Faculty of Mining, Geology and Petroleum Engineering of the University of Zagreb, “The donation of monitoring equipment by the Japanese Government through the Science and Technology Research Partnership for Sustainable Development (SATREPS) scientific project made it possible for the Kostanjek landslide to be equipped by densely spaced GNSS stations, comparing to other world-wide known landslide monitoring systems. Geomatika Smolčak, together with Trimble, helped to setup the GNSS monitoring system, and even now, five years after deployment of the solution, they help to solve different kinds of issues that arise related to data measurements and data transmission, which has been a tremendous asset.”
Read the complete account of developing the Kostanjek landslide forecasting and protective monitoring system using Trimble Monitoring Solutions in GIS Resources.