Natural Hazards and Earth System Science www.nat-hazards-earth-syst-sci.net 1561-8633 1684-9981 9 1 2009 10.5194/nhess-9-197-2009 http://www.nat-hazards-earth-syst-sci.net/9/197/2009/ http://www.nat-hazards-earth-syst-sci.net/9/197/2009/nhess-9-197-2009.html http://www.nat-hazards-earth-syst-sci.net/9/197/2009/nhess-9-197-2009.pdf 197 209 2009-02-19 Hazard index maps for woody material recruitment and transport in alpine catchments B. Mazzorana bruno.mazzorana@provinz.bz.it A. Zischg A. Largiader J. Hübl Department of Hydraulic Engineering, Autonomous Province of Bolzano/Bozen South Tyrol, Bolzano, Italy Institute of Mountain Risk Engineering, University of Natural Resources and Applied Life Sciences, Vienna, Austria Abenis AG, Chur, Switzerland Abenis Alpinexpert srl, Bolzano, Italy A robust and reliable risk assessment procedure for hydrologic hazards deserves particular attention to the role of transported woody material during flash floods or debris flows. At present, woody material transport phenomena are not systematically considered within the procedures for the elaboration of hazard maps. The consequence is a risk of losing prediction accuracy and of underestimating hazard impacts. Transported woody material frequently interferes with the sediment regulation capacity of open check dams and moreover, when obstruction phenomena at critical cross-sections of the stream occur, inundations can be triggered. The paper presents a procedure for the determination of the relative propensity of mountain streams to the entrainment and delivery of recruited woody material on the basis of empirical indicators. The procedure provided the basis for the elaboration of a hazard index map for all torrent catchments of the Autonomous Province of Bolzano/Bozen. 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