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From practical experience to national guidelines for debris flow mitigation measures in Austria
Huebl, Johannes Nagl, Georg
Huebl, Johannes
Nagl, Georg
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2019
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Abstract
In the second half of the 19th century a lot of torrential disasters occurred in the Alps causing substantial damage. These catastrophes may be traced back to non-sustainable land-use management with inadequate alpin pasture farming, leading to forests in a poor condition, large denuded areas and steep incised channels. Starting with an analysis of these disasters, political decisions were made to implement mitigations measures, including forestry, agricultural and structural measures. Additional financial regulations were established to facilitate mitigations measures even for poor rural communities. The technological background for the design of structural measures was founded in forestry, because of the experience with construction of log driving. Basic hydraulic models were used for designs, sometimes empirical values were added to consider bedload or the impact of point loads. The structures served to stabilize the channel bed, to deposit bedload upstream of settlements, to restrict sedimentation or inundation on the fan or to redirect the flow to areas of low interest. In the early years of torrent control in the Alps, structures were usually built as dry masonry walls, later cement mortar masonry walls and concrete gravity walls were favoured. New static concepts and the use of reinforced concrete formed the basis of a colloquium in Vienna (1973), where load models and static concepts were discussed. In practice, the multiplier of the static load of the Lichtenhahn-model was used within a broad range, leading to different structural design of check-dams. In the beginning of the 21th century, based on the design concept of EUROCODE, new technical guidelines for barrier design (ONR-Series 248xx) were developed. The load cases include flood and debris-flow and combination of events for all kind of torrential structures. The experience in the application of these guidelines is currently being evaluated and will lead to a new national standard.
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