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Monitoring of Geomorphological Processes on Steep Slopes by Using TLS: Case Studies from Dalmatia, Croatia

In the few last decade monitoring of landscape changes (including potential instabilities) became ever so popular, and necessary. Even though remote sensing became more frequently used and affordable, there are some situations in which, (i.e. for small to medium scale slopes, and very steep slopes and cliffs), these methods are still not sufficiently precise (or possible to use). Therefore, usage of ground based measuring techniques, such as Terrestrial Laser Scanning, or lately airborne photogrammetry, in those situations is still the best way to go. As Dalmatian coastline is mostly rocky and with very steep slopes, mostly consisting of interchanging Cretaceous limestones and Eocene flysch, rockfalls, landslides and erosion of steeps slopes are very common (Miščević and Vlastelica, 2014.). For that particular reason TLS was selected as a main tool for activities in the Work Group 4 of the SATREPS “Project on Risk Identification and Land- use Planning for Disaster Mitigation of Landslides and Floods in Croatia” (Marui et al., 2016.), which was conducted in Croatia from 2009 to 2013. WG4 consisted mainly of researchers from Niigata University and University of Split, and all the activities were conducted in Central Dalmatian County (Vlastelica et al., 2012.). Key points of the research of WG4 during the project was to monitor two pilot locations in Duće county and slopes above town of Omiš for potential rockfalls, possibly to detect movements and elaborate environmental conditions prior to a rockfall event (Vlastelica et al., 2013.). Fortunately for the inhabitants in that area, those locations were selected for governmental financing of the remediation measures which are now implemented. Unfortunately for the project, this meant that the long-term post project activities could not carried out. Therefore, the project timespan of couple of years (when the actual monitoring was made) was not sufficient for general conclusions. As one of the main goals of the whole project was to create a „template“ for hazard mapping in this region, it can be presumed that the project motivated the government to take some actions at pilot sites of the WG4. More important, at least for the researchers at University of Split, is that methodology for future monitoring on other locations was defined, and some key issues were addressed when dealing with slope monitoring in Eocene flysch formations (Vlastelica, Miščević and Fukuoka, 2016a.). It is important to note that prof. Fukuoka's contribution in this period is not only the scientific one. Looking from perspective of an young researcher and PhD student, more important part was to see his devotion to scientific way of thinking and motivation that he provided as a true sensei to (at that time) a young researcher, even though he wasn’t his official mentor. During the last year of the project (2012-13) almost 20 pilot locations (mostly manmade cuts in flysch, and coastal cliffs) were selected as a part of independent research (institutional project at University of Split) which was the basis of doctoral thesis titled: The Influence of Weathering on Durability of Cuts in Soft Rock Mass (Vlastelica, 2015, main parts of the thesis later published Vlastelica et al., 2016b. and Vlastelica et al., 2018b.). This monitoring is conducted to this day on most of the pilot locations, providing more than total of 6 years of monitoring. Part of results is published as a preview, or explaining methodological approach on local and regional conferences (Vlastelica, Miščević and Fukuoka, 2014. ; Vlastelica, 2016. ; Vlastelica, Miščević and Fukuoka, 2016a. ; Vlastelica et al., 2016c. ; Vlastelica and Miščević 2017. ; Vlastelica et al., 2017. and Vlastelica and Miščević 2018.), and two journal papers are currently in preparation. Results of the monitoring (i.e. detection of erosion rates) were also used in a project for local community as well: “Geomechanical aspects of remediation of quarries in the flysch: Case study of abandoned quarry in Majdan, Croatia.” (Vlastelica et al., 2018a.). In this case a low cost solution for protection measures was made, therefore European funding for a public recreation project was ensured, which local community otherwise could not afforded. Therefore, aside the methodological approach to monitoring of steep slopes by using TLS, this presentation will consist of series of examples from both published and unpublished case studies from Dalmatia, Croatia.

Soft rock, Erosion, TLS, Slope stability, Cooperation

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