标题：Hochwasser- und Rutschungsereignissen in ausgewählten Gemeinden Vorarlbergs = 22nd and 23rd August 2005 - Analysis of flooding events and mass movements in selected communities of Vorarlberg.
摘要：Extreme disasters (flooding, debris-flows, landslides) were caused by Vb-like weather conditions with extreme precipitation (i.e. 244 mm within 24 hours in Innerlaterns - Vorarlberg) at 22nd and 23rd of August 2005 inWestern Austria. The BFW - Institute of Natural Hazards and Alpine Timberline was charged by the Federal Ministry of Agriculture and Silviculture, Environment and Water Management (BMLFUW, department IV/5) with the analysis of the inundations by the Höllbach near Schnepfau, the Züsbach near Lech a.Arlberg and the documentation of the landslides in the communities of Au/Schnepfau, Mittelberg/Zürs and Laterns/Düns/Dünserberg/Viktorsberg/Zwischenwasser in Vorarlberg. This work was done in intensive contact with the local authorities of the Austrian Avalanche and Torrent Control Service in Bregenz and Bludenz. Analysis of precipitation data from January to August 2005 provided by the Hydrological Service of the District Government in Vorarlberg shows that runoff behaviour and infiltration characteristics of the soils during the extreme events mainly was influenced by antecedent precipitation from 19th to 22nd August and the intensive persistent rain from 22nd to 23rd August 2005. For the Höllbach brook peak runoff was calculated with approx. 12 m³ sec-1 by use of the hydrological model ZEMOKOST. Due to jamming, temporarily overlay of surface runoff from different parts of the catchment and intensive contributions of interflow from both the upper soil and the deeper underground in the watershed areamaximumrunoff in fact might have been higher, especially in periods with high intensity of precipitation (18 mm h-1). For the Zürsbach model calculations delivered peak values between 30 and 50 m³ s-1. Because of blockages (breaking of dams caused by debris from washout of the banks with volumes up to 8000 m³) and bedload transport temporary higher runoff peaks seem realistic. During the torrential rain events in August 2005 postglacial sediments have been activated in the catchments primarily. Landslides were dominantly translational slides, in second term slump slides. Due to geological predisposition slides often concentrated along a small band between 1100 and 1300 m sea level and on slopes of 25 to 40° inclination. The majority of the slides occurred in open land (meadows, grassland, swards, and marsh areas). Significantly fewer slides are documented in forests. Sliding activity in forests is strongly related to forest condition. Often mass movements were observed in gaps, in and under grassland in forests, areas which had been formerly under agrarian utilization, now suffering from an uncontrolled succession to new vegetation forms and in forests with loose structure. Abrupt discontinuation of agricultural utilization of formerly intensively used agricultural land is an eminent factor of landslide release. In open land, e.g. on loamy alpine grassland soil, several times hints for surface runoff processes due to limited infiltration capacity of the soils were found. During the intensive rain event on 22nd of August 2005 (90 mm within 5 hours = 18 mm*h-1 at Laterns) especially on alpine grassland and swards a high amount of the precipitation immediately formed surface runoff and contributed to runoff in the brooks and the receiving rivers within a short time.
关键词：Cultivation, flooding, forest, inundation, land use, mass movement, runoff, vegetation
