Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)

Bohyně in Děčín district - the largest landslide area in the Czech Republic

 

Oldřich Krejčí, Vladimíra Krejčí, Petr Kycl, Martin Paleček, Jan Rybář

Geoscience Research Reports 50, 2017, pages 227–234
Map sheets: Děčín (02-23)

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Published online: 31 October 2017

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Abstract

Bohyně, a countryside affected by several landslides is located about 5 km southwest of the Děčín city. The “Bohyně” name was historically used for the entire group of landslides. The aim of the project was remapping of the whole locality and link together up to now isolated landslides in a single complex of landslides. The relief rises from the Labe River in the East (150 m a.s.l.) to over 520 m a.s.l. in the West. The studied area is part of the České středohoří Highlands, and is typical with special characteristics such as steep slopes, geological setting including fractured volcanic and soft sedimentary rocks and deeply incised valley of the Labe River. These are essential features contributing to the particularly high intensity and wide-spread occurrence of the slope deformation phenomena.
Upper Cretaceous sediments in this area were deposited mostly almost horizontally in a shallow synclinal basin and reach thickness of up to 400 m. The surface morphology results from Tertiary and Quaternary denudation and accumulation. The current relief consists of structural plains, river terraces, and deep canyon-like valleys, e.g. that of the Labe River. Saxonian tectonic movements segmented the originally uniform basin to a series of plates uplifted to different elevations and forming a highly dissected landscape. Basin is marked by scattered clean-cut monadnocks, mostly formed as denudation fillings of volcanic chimneys and various types of dykes. Slope deformations known in the study area are mainly typical landslides, earth or debris flows and vast, complex slope deformations up to many hundreds of meters in length.
As concerns the landslide activity, we differentiate currently moving active landslides, and inactive landslides, which have not moved within the last 12 month. Inactive landslides are further subdivided in two groups. Calmed landslides are inactive landslides which are no longer affected by its original causes and relict landslides are inactive landslides developed under climatic or geomorphological conditions considerably different from those of present day.
To recognize the landslide structures, we used geomorphological mapping and LiDAR-based digital elevation model (DMR 5G, ČÚZK) interpretation. The deep-seated landslides can be observed in the LiDAR data as characteristic geomorphologic features. We focused on establishing dimensions, mechanics and possible future development of several different typical slope failures.
Based on the input data quasihomogeneous zones were delineated and the susceptibility of landslide hazard was evaluated. District area maps in a scale of 1:10 000 provide information on hazard areas of possible occurrence of landslide phenomena. The maps display, presently quiescent slope deformations in black and presently active in red colour.
With its total 12,456 km2 this locality is the largest landslide area in the Czech Republic which forms a unique organic complex. Along with the results of our new research, the whole area will be registered in a geodatabase of the Register of Ground Instabilities. This Register has been since long ago (founded in 1962) one of the cornerstones of factual databases in geology. Information about slope instabilities is available online on the Internet portal: geology.cz/map_applications/ground_instabilities.