Use of Properly Designed Flexible Barriers to Mitigate Debris Flow Natural Hazards

Several natural debris flow events in the USA and around the world have demonstrated that a flexible barrier properly designed to handle the complex forces present in a fluid/slurry torrent can be effective at stopping debris flows and/or mitigating such hazards. Intensive research has been conducted to identify the appropriate design parameters for such barriers and to identify specific engineering criteria necessary for use in debris flow applications. Such research has included 1:1 laboratory testing with small-scale, artificially generated debris flows, real-scale 1:1 field-testing as well as computer simulations modeling the behavior of barriers during such events. A design model for debris flow barriers (based on a finite element software program, but not included in the paper) has been calibrated and verified by real-scale field-testing, under supervision/involvement of the Swiss Federal Institute for Forest Snow and Landscape (WSL) and is the only known valid model for tested barrier type ((GB) ring-net barriers) in debris flow applications. During the model's development, it become clear that each application site where a debris flow barrier would be considered requires specific dimensioning be completed for each barrier as no "one-size-fits-all" criteria exists for a properly designed solution. This research has led to an initial dimensioning model for flexible barriers to be used for debris flow mitigation, which is currently being applied in numerous cases. In California, this concept has been applied to one project case involving 10 debris flow sites along a short distance of highway in the San Bernardino Mountains of Southern California. These barriers have been installed and impacted by actual debris flows. The subsequent observations have provided invaluable information regarding performance, design assumptions, and maintenance requirements including cleanout.