ADVANCES IN CHANNEL MIGRATION ZONE MAPPING METHODOLOGY IN OREGON

Channel migration describes the lateral movement of a stream across its floodplain due to channel erosion and sediment deposition. This movement includes both gradual erosion and rapid avulsions. The goal of channel migration zone (CMZ) mapping is to identify the areas that a stream has historically occupied and may occupy in the future. Identifying these areas leads to a more complete understanding of flood hazards, flood risk, and conservation opportunities and can inform planning, land management, and emergency management decisions.

The Oregon Department of Geology and Mineral Industries has developed a CMZ mapping methodology for rivers in Oregon based on a review of CMZ literature and approaches utilized across the United States. This method is relatively rapid and primarily based on remotely sensed data including lidar-derived topography, relative elevation models, surficial geologic maps, historical aerial imagery, hydrologic records, infrastructure and historical maps, and local knowledge. The resulting map units include the active channel, historical migration area, erosion hazard area, avulsion hazard area, and stream banks flagged for additional site inspection. We present a summary of the new CMZ mapping methodology and examples of the maps for several streams within Oregon.