engleski

Identification of geomorphological units and hazardous processes in the Vinodol Valley

Vinodol Valley, situated in western Croatia in the Primorsko-Goranska County, represents an area of wide range of different landform types, each characterized by specific processes and materials which create them. Necessity of study of geological hazards in the Vinodol Valley arises from the continual direct damaging impact of different hazardous processes on public roads and private material properties. Sliding and erosion processes thus cause great economic losses for the local government and residents. Study of past and recent hazardous processes in the Vinodol Valley has been conducting with the aim to create susceptibility and hazard maps depicting potential for all processes causing slope instabilities. In this respect, the essential step for reliable landslide susceptibility assessment is to select an appropriate terrain subdivision, i.e., creating individual mapping units based on the certain criteria (Van den Eeckhaut et al., 2009). Delineated mapping unit thus represents a homogeneous portion of the land surface characterized by a set of ground conditions that differ the unit from the adjacent ones across definable, closed boundary (Evans, I., 2012). Methodology of research of hazardous processes in the Vinodol Valley is based on the geomorphological approach which implies delineation of geomorphological units on the basis of identification of topographical landform characteristics, materials which create them and its past and recent landslide and erosion processes and phenomena. Current study of the Vinodol Valley presents extension of the preliminary investigations of landforms and geomorphological processes at the area of Dubračina River Basin, where different geomorphological units were outlined characterized by typical types of landslides and erosion phenomena (Bernat et al., 2014). Dubračina River Basin of 43, 5 km2 covers nearly the half of the territory of the Vinodol Valley, i.e., its northwestern and central part. Vinodol Valley, with its length of approximately 22 km and maximum width of 4 km, has pronouncedly elongated shape and characteristically asymmetrical cross section in which the prominence of longer northeastern and shorter southwestern slopes is present. Moreover, three different geomorphological zones exist along the valley. The first zone extends from the Križišće settlement in the northwestern part to the Janjevalj and Pećca setllements in the southeastern direction. The length of this zone is approximately 7, 5 km and the width ranges from 950 m to 3, 50 km. The second zone, with length of about 6, 5 km and maximum width of 4 km, extends from Janjevalj and Pećca settlements to the Saftići and Kričina settlements. The third zone is characterized by mostly uniform width of about 2 km and extends from Saftići and Kričina settlements to the city of Novi Vinodolski situated at the sea coast at the end of the valley. For identification of geomorphological units and hazardous processes in the Vinodol Valley high resolution airborne LiDAR-derived imagery of resolution 1 x 1 m was primarily used. Visual interpretation was undertaken to identify all the types of sliding processes and sliding and erosion phenomena. Field investigations were conducted to identify the types of materials of which the area of Vinodol Valley was built and to additionally identify sliding phenomena which were recognized with uncertainty on the LiDAR-derived imagery. The criteria adopted for identification of specific geomorphological unit were morphological characteristics and internal relief, types of material defined by lithology of base rock mass and superficial deposits, and types of identified geomorphological processes and phenomena. Identified processes causing slope instabilities in the Vinodol Valley can be generally categorised into two main groups: erosion and sliding processes. Among erosion phenomena planar erosion, gully erosion and excessive erosion can differ. Identified sliding phenomena encompass rock falls, topples, landslides, mud flows and instabilities in scree deposits. Features of historical debris flow were also identified. In the paper types and spatial extent of all types of hazardous phenomena per geomorphological unit type were analysed together with possibilities of visual identification of the phenomena from high-fidelity DEM.

geomorphological units; geomorphological processes; hazardous phenomena; landslide susceptibility

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