Articles | Volume 15, issue 12
Nat. Hazards Earth Syst. Sci., 15, 2597–2604, 2015
https://doi.org/10.5194/nhess-15-2597-2015
Nat. Hazards Earth Syst. Sci., 15, 2597–2604, 2015
https://doi.org/10.5194/nhess-15-2597-2015

Research article 02 Dec 2015

Research article | 02 Dec 2015

Laboratory tests for the optimization of mesh size for flexible debris-flow barriers

C. Wendeler1,a and A. Volkwein1 C. Wendeler and A. Volkwein
  • 1WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Zuercherstr. 111, 8903 Birmensdorf, Switzerland
  • anow at: Geobrugg AG Protection Systems, Aachstr. 11, 8590 Romanshorn, Switzerland

Abstract. Flexible barriers can be used within channelized riverbeds as an effective and efficient alternative to protect from debris flows. Their retention capability strongly depends on the size of the mesh openings and the gap between the lower barrier edge and the channel's floor. The question is now whether there is a relation between the grain size distribution of the debris material and the openings of a flexible barrier. Small-scale laboratory tests were performed to study these loading aspects of flexible debris-flow barriers for the Milibach river (Canton Berne, Switzerland). In situ debris material has been used to quantify the influence of different mesh sizes and the gap between the lower barrier edge and the riverbed compared to the d90 grain size and the flow height, where d90 is the maximum diameter of 90 % of the grains. It was possible to study the filling process and the retaining behaviour of the barriers as a function of the mesh size. A reasonable retention was reached with the net having a mesh size and a basal gap smaller than or equal to d90. These relations could be transferred to the field. A dimensional analysis reveals possible dimensionless numbers that can be used to scale the laboratory results. The findings are supported by the results of similar laboratory tests using debris material from different locations and by the available field measurements.

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Short summary
Laboratory tests were performed with natural debris material to study the loading aspects of flexible debris-flow barriers and to quantify the influence of different mesh sizes and the lower gap between barrier and the riverbed. A reasonable retention was reached with a net mesh size and a basal gap smaller than 90% of the grains. By scaling the laboratory tests to the field using Froude similarity, a recommendation is given for the best net mesh size and the gap under natural conditions.
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