CHANNELIZED DEBRIS FLOW INVENTORY DATA IN OREGON

Channelized debris flows (CDF) are a complicated landslide process. Many of the historic CDF initiation sites (points) in the Statewide Landslide Information Database of Oregon were located on the ground using GPS or drawn on paper maps. To calibrate a new CDF susceptibility model for Western Oregon, these historic CDF points were used; however, it was immediately evident that most of the point locations did not align with the now-prevalent high-resolution lidar topography. An exception are the ~155 CDF locations mapped by Coe and others (2011), which were located on orthophotos and corrected to match the lidar topography. We remapped 680 historic CDF initiation sites by placing a new point in the central portion of the initiation area for each historic CDF site, as observed and verified in orthophotos. These 680 CDF initiation points, including the ~155 CDF points by Coe and others (2011), were used to select adjacent, downslope transport channel segments that experienced channelized debris flow transport. All 680 historic events displayed transport in a channel. Topographic spatial statistics were evaluated at the initiation sites and channel segments, including slope, curvature, and distance to channel at initiation sites, and gradient and confinement along channels. Channels with debris flow activity were divided into 100 ft segments. Each of the channel segments were examined visually using orthophotos, and classified as primarily transport and/or erosion, or primarily deposition. The CDF channel dataset contains 10,253 transport and/or erosion segments and 1,534 deposition segments, totaling 11,787 100-ft segments. The initiation sites’ mean slope angle is 39° (1 SD = 4.6°). The initiation sites’ mean curvature is −1.0 (1 SD = 0.67), and there are no sites with a value above 1.2. The initiation sites’ mean distance to the channels is 48 ft. The mean gradient of the channel segments that displayed transport is 20° (1 SD = 10°). The histogram of channel gradient has an abrupt increase in frequency above approximately 5°. The channels classified as having CDF deposition have a mean of 9°, and the greatest frequency was 6°. The mean of the channel segment confinement is 60 ft vertical per 100 ft horizontal (1 SD = 20ft). The remapping of CDF inventory was a critical step towards the new CDF susceptibility model for Western Oregon.