Abstract
Results of landslide monitoring undertaken between 1998–2010 on the north-eastern slope of the central part of Rjecina 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 Rjecina riverbed are formed in siliciclastic sedimentary rocks with flysch 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 sliding bodies. It occurred in December 1996 by displacement of an initial landslide body where movement had been registered in the 19th 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 flysch 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 Rjecina Valley from the Valici Dam to the Pasac Bridge was selected as a pilot area in the framework of the Croatian-Japanese 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.
Highlights
The Rječina River flows through three different geomorphological zones
The results indicate the formation of a complex landslide with thirteen sliding bodies
Combined casings for an inclinometer and a deformeter were installed in two boreholes (G-4 and G-6), in the central part of the landslide, Piezometers were installed into another five boreholes to facilitate observation of changes in groundwater levels (Fig. 7)
Summary
The Rječina River flows through three different geomorphological zones. The first occupies the area from the river source at the foot of the Gorski kotar Mountains to the Lukeži Village. The second zone extends from Lukeži Village to the canyon entrance near the Pašac Bridge, while the third stretches from the entrance of the canyon and the alluvial plain near the river mouth in the centre of Rijeka City. Different types of mass movements can be distinguished including the slippage of slope deposits over the flysch bedrock, rockfalls from limestone cliffs and the slippage of rocky blocks larger than 200 m3. These phenomena prevail on the northeastern slopes, but are relatively rare on the southwestern slopes of the Rječina – Sušačka Draga and Bakar Bay – Vinodol Valleys morphostructural unit (BENAC et al, 2009)
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