engleski

Landslides in the area of Zagreb city

Activities of Working group 3 titled ‘Hazard mapping and development of guidelines for the application in urban planning’ will be implemented at the pilot area in the Zagreb city with the purpose of development of methodologies for indirect landslide mapping, landslide hazard assessment and application of results of scientific investigation into system of urban planning and construction. In this paper geological settings, geomorphological and hydrogeological conditions of hilly area of the Zagreb city are presented aimed at understanding conditions for landslide formation. The main objective is to make overview of landslide types and their characteristics, as a preliminary research for the purpose of planning of landslide mapping and hazard zonation. The Zagreb City is located in the north-west part of Croatia, i.e. in the western part of Panonian Basin. Total area of the Zagreb city is 220 km2 and it is placed between forest area of Mt. Medvednica (on the north) and roundabout road of the city in flood plane of the Sava River (on the south). Approximately 45% of the urban area is placed in the hilly area in which landslides are main geological hazard. Preparatory causal factors of slope instabilities in this zone are the following: ground conditions related to engineering properties of soils ; geomorphological processes (fluvial erosion of the slope toe) ; physical processes (intense, short period rainfall) ; and man-made processes of different types (mainly loading of the slopes, defective maintenance of drainage systems, water leakage from service, vegetation removal etc.). The most often triggering causal factors are rainfalls or man-made processes. Landslides are dominant geomorphological process in all catchments of Mt. Medvednica streams. Pilot area of Croatian-Japanese project encompass middle and lower part of catchments located in the area composed of Upper Miocene and Quaternary sediment. Upper Miocene deposits are stratified engineering soils (marls, silts and sands) with moderately to slightly inclined bedding (10-20°), overlain by younger deposits or deposits from weathered zone. Quaternary deposits are heterogeneous mixtures of fine grained soils without foliation, mostly impermeable. Geological contact between Miocene sandy silt soils and Quaternary clayey soils is highly susceptible to sliding. Landslides in the hilly area of the city of Zagreb are dominantly small and shallow movements of superficial deposits along contacts with unweathered soils. Despite this, they cause significant economic losses by damaging houses and urban infrastructure. Local authorities (i.e. the City of Zagreb) introduced measures for managing landslide risk caused by intensive construction activities and increase of density of population. Current practice of landslide risk prevention in the City of Zagreb will be shortly presented in this paper.

Zagreb City; landslides; hazard mapping

nije evidentirano