Consideration of early warning system on the Grohovo Landslide

The Grohovo Landslide, the largest active landslide along the Croatian part of the Adriatic coast, is located on the north-eastern slope of the Rječina Valley. In 2009 the Croatian-Japanese research joint project “Risk identification and Land-Use Planning for Disaster Mitigation of Landslides and Floods in Croatia” was initiated and the Grohovo Landslide was chosen as a pilot area for monitoring system development. A comprehensive monitoring system will be consisted of geodetical and geotechnical monitoring. Installation of monitoring equipment started in March 2011 and will be complete to the end of 2011. Integrated monitoring system will be consisted of surveying system using GPS and robotic total station, so as geotechnical monitoring using pore pressure gauges, inclinometers, extensometers and seismographs. In the automated integrated monitoring system until December 2011 are included observation of geodetic prisms with robotic total station and system of 10 GPS rovers. Immediately after starting on of the system, the measurement data from the GPS and robotic total station observations were starting to collect, and it was possible to analyze initial landslide monitoring data. One of most important aim of the Grohovo Landslide monitoring system is establishment of the early warning system. In designing of early warning system it is necessary: to identify real hazard of further sliding and possible direct and indirect threats, to identify possible movements and landslide widening with high hazard, to select appropriate equipment relating to position in the field and measurement accuracy and to define critical limit values that indicating new sliding appearance and start up alarm. Analyses of the past and prediction of the future landslide behavior are the most important steps in early warning system consideration, while equipment selecting should depend on measurements of appropriate values with required accuracy. In this paper we will present consideration of early warning system establishment on the Grohovo Landslide analyzing all previously mentioned requirements.