Performance of Flexible Debris Flow Barriers in Fire Burned Areas, State Route 18, San Bernardino County, CA

摘要

As presented at the 55th Annual Highway Geology Symposium in 2004, various flexible debris flow barriers were installed near San Bernardino, CA in the summer of 2004 in anticipation of debris flows originating from fire burned slopes. These debris flow barriers were installed in ten distinct debris flow channels upslope from and opening onto state route 18. Each of the barriers was dimensioned based on a unique dimensioning model using data provided by Caltrans including anticipated debris volumes and velocities, and a broad characterization of the expected debris flow compositions, channel geometry and barrier orientations. Each site required a unique barrier design with differing barrier heights, capacities and support infrastructure. Construction of these barriers was completed in June, 2004. As anticipated, heavy rains in October and winter of 2004/2005 resulted in significant debris flows in all the identified channels. During the October events, all the barriers were impacted to various degrees. The barriers performed exactly as intended, and were subsequently cleaned of debris. As a result of these events, some aspects of designs were identified that could be adjusted to better facilitate cleanout maintenance and improve performance in general. In the winter of 2004/2005, the barriers were impacted again by debris during storm events. Some barriers were completely filled with debris and even somewhat overtopped, and some damage to the barriers was evident due to the greater than expected debris volumes. However, the drainage culverts immediately below the barriers remained clear and effective as intended, thus channeling water flow underneath rather than over the road. Ironically, this protected section of road was now used as a detour for other sections of road that were closed due to problems created by debris flow and rockfall; an opposite scenario from one year earlier.