PROTOCOL FOR CHANNELIZED DEBRIS FLOW SUSCEPTIBILITY MAPPING IN OREGON

Since 2007, the Oregon Department of Geology and Mineral Industries (DOGAMI) has developed and published protocols which detail methods for creating next-generation landslide hazard maps. Landslide protocols, published as DOGAMI Special Papers (SP), include lidar-based landslide inventory (SP-42), shallow landslide susceptibility (SP-45), deep landslide susceptibility (SP-48), and a tool for semi-automatic landslide mapping (SP-52). In 2022, DOGAMI published a new protocol for channelized debris flow (CDF) susceptibility mapping (SP-53).

The SP-53 CDF susceptibility mapping protocol is a geomorphic empirical method, developed based on a CDF inventory dataset consisting of 680 debris flow events throughout western Oregon. This inventory was used to calibrate the CDF susceptibility mapping protocol to local Oregon conditions and to define four relative CDF susceptibility zones (none-very low, low, moderate, high). Each of the process subdivisions: initiation, transport and inundation are individually evaluated and then combined for an overall assessment of the project area. Initiation uses slope steepness, curvature, and distance to channel. Transport uses channel gradient and confinement. Overall basin susceptibility is a combination of initiation and transport. Inundation susceptibility uses a multi-point LAHARZ model developed at the USGS. DOGAMI’s SP-53 methods will be the basis for completing future CDF mapping projects where needed to assist in landslide risk reduction. Project follow-up includes appending of data into our statewide landslide database for Oregon (SLIDO).