Predicting landslides through continuous GNSS monitoring
Discover how University of Zagreb engineering geologists rely on Trimble GNSS and Trimble 4D Control to overcome complex terrain challenges, predict landslide behavior and establish early warnings.
High frequency meteorological, hydrogeological and movement data obtained by continuous monitoring enabled us to establish a new, more accurate method to predict landslide movements.
— Dr. Martin Krkač
Assistant Professor, Faculty of Mining, Geology and Petroleum Engineering, University of Zagreb
Background
Predicting movements on Croatia's largest landslide
Activated by mining activities in 1963, the Kostanjek landslide is the largest landslide in the Republic of Croatia. Located in a populated hilly area of the capital city of Zagreb, it is a reactivated, deep-seated, large translational landslide spanning about 1 square kilometer. Despite extremely slow landslide movements over the past 50 years, the risk surrounding the landslide remains high, as more than 300 homes and associated infrastructure sit directly on the moving land mass.
The dynamic nature and complex terrain of the Kostanjek landslide presented several unique monitoring challenges. Finding adequate positions to install monitoring equipment, providing a stable electrical power supply, and gaining permissions from local residents and city authorities were critical obstacles. Traditional total station solutions were not viable because the landslide morphology blocked line-of-sight visibility between total stations and prisms. Additionally, scientists needed real-time data integration across rainfall, groundwater levels and displacement to accurately forecast movements 24 hours in advance.
Solution
Establishing continuous real-time GNSS monitoring
To overcome line-of-sight constraints, landslide scientists from Croatia and Japan worked with Geomatika Smolčak Ltd. and Trimble to deploy an automated, real-time monitoring system. The project installed 15 Trimble NetR9 TI-2 GNSS reference stations equipped with Trimble Zephyr Geodetic 2 antennas across the landslide area, along with a base station placed in a stable area 7 kilometers south. The network was supplemented by geotechnical sensors, including short- and long-span extensometers, pore pressure gauges, well water level gauges, and a rain gauge weather station.
All movement and environmental sensors deliver data via wireless internet routers to Trimble 4D Control (T4D) monitoring software running on a server at the University of Zagreb. Trimble 4D Control visualizes and analyzes monitoring data in real time, calculating 60-minute and 24-hour post-processing intervals alongside 1 Hz RTK results. The software automatically issues alarms whenever movement exceeds predefined thresholds, while a web portal allows city authorities and scientists to observe landslide movement behavior remotely.
Results
Enhanced public safety and early warning capabilities
The Trimble monitoring solution successfully established a high-precision, continuous monitoring network with an average data loss of only 3% due to transmission. High-density GNSS coverage provided the spatial and temporal resolution required to measure small displacements, identifying both slow and fast movement patterns corresponding to precipitation and groundwater fluctuations. Between 2013 and 2018, the system successfully tracked multiple reactivations and identified maximum displacements of up to 70 centimeters in the central landslide area.
By integrating real-time displacement data with meteorological predictions, scientists developed an empirical model capable of predicting landslide displacement 24 hours in advance. This forecasting window gives civil protection authorities the critical time needed to issue early warnings and execute evacuation plans if threatening movements occur. Furthermore, the continuous data stream supports the Kostanjek Landslide Observatory in evaluating long-term disaster risk factors and guiding future slope stabilization efforts.
