Abstract
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.
Highlights
Flexible debris-flow barriers derived from rockfall and snowslide protection systems are an innovative protection measure against small- and medium-sized debris flows
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
The tests were started with a mesh size equal to the d90 grain size in order to see whether the debris is retained or not
Summary
In the study presented here the opening sizes are investigated for a flexible debris-flow barrier in the Swiss Milibach river (Monney et al, 2007; Schatzmann, 2006; Roth et al, 2006). Six laboratory tests with debris-flow material taken from the river Milibach were carried out with net barriers of different mesh sizes and with basal gaps between the lower net edge and the channel bed in relation to the grain size distribution. Oratory chute of the Swiss Federal Research Institute WSL (Weber, 2000) enables tests with artificial debris flows from natural debris material impacting different barrier systems. Relevant dimensionless numbers are explained and their range is found for laboratory tests and field measurements as shown
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