Forest Falls Debris Flows and Potential Hazard to Residents

SMSU Event Center BC

Debris flows present an ongoing threat to life and property for residents in the San Bernardino Mountain community of Forest Falls, California. Previous studies focused on the Snow Creek channel which produces the largest and most frequent flows. This study analyzed six channels that flow across the bajada on which the town exists: Camp, Summit Dr., Rattlesnake, Snow, Slide, and Bridal Veil Creeks. Using LIDAR and Google Earth imagery, historic aerial photographs, geologic maps and USGS topographic maps, this study mapped changes in channel patterns over time. The volume of debris coming out of the 6 canyons has produced enough sediment to cause flow deformations in the main stem drainage of Mill Creek. This finding indicates that the rate of deposition from debris flows is frequent enough and has enough volume to disrupt the natural flow of Mill Creek and, at least locally, these tributary inputs overpower the rate at which sediment is carried down the main stem of Mill Creek. Although there appeared to be no correlation between tributary canyon length or width and sediment volume, there did appear to be a correlation between the radii measurements of the tributary debris fan and the volume of debris flow accumulations. The larger the radii, the larger and more prevalent the accumulations were in the canyon. By mapping past debris flows we were able to recognize where future channels may be directed; and how these debris flows will affect the redirection of Mill Creek.