A complex landslide in the Rječina Valley: results of monitoring 1998-2010

AB STRA CTResults of landslide monitoring undertaken between 1998-2010 on the north-eastern slope of the central part of Rječina Valley in front of Grohovo village (north-eastern coastal part of Adriatic Sea, Croatia) are presented.This is the largest regional active landslide.The slopes around the Rječina riverbed are formed in siliciclastic sedimentary rocks with fl ysch characteristics.The bedrock is mostly covered with unstable slope formations.A limestone rock mass is visible on the cliffs around the top of the river valley.The landslide is complex and retrogressive, with 13 slid ing bodies.It occurred in December 1996 by displacement of an initial landslide body where movement had been registered in the 19 th century.The limestone mega-blocks and separated rocky towers on the top of the slope have also moved, which is an atypical phenomenon of the fl ysch slopes in the area of Rijeka.After initial sliding ceased, and major movements subsided, monitoring of benchmark movements from 1998 until 2010 determined further maximum displacements on the upper part of the slope, and minimum movement in the lower part.The area of the Rje čina Valley from the Valići Dam to the Pašac Bridge was selected as a pilot area in the framework of the Croatian-Ja panese bilateral joint research project.Monitoring results provided the basis of establishing an early warning system for possible landslide occurrence and estimating the degree of landslide risk.