Channel Migration

Channel Migration

The Oregon Department of Geology and Mineral Industries (DOGAMI) maps historic stream channels to determine future channel migration hazards.

Channel migration is the natural process by which streams move laterally over time. This process includes bed and bank erosion, sediment deposition, and channel avulsion, an event in which the stream abruptly moves to an entirely new location on the floodplain.

Channel migration can occur gradually across thousands of years or rapidly, usually associated with flood events. It can undermine buildings, roads, levees, and other infrastructure. It can erode land, redirect flooding to new areas, cut off evacuation routes during floods, and, in rare cases, endanger lives. The process of channel migration is not considered in FEMA Flood Insurance Studies and, as a result, channel migration may impact homes outside of the 1%-annual-chance flood zone.

To interact with DOGAMI channel migration zone (CMZ) maps, please see links to individual publications at the bottom of this page or review the Channel Migration Zone Storymap.

Channel Migration Zones

Channel migration zone (CMZ) maps define the area in which a given stream is likely to move laterally and change its channel course within a defined period of time. The components that comprise DOGAMI CMZ maps are the active channel (AC); historical migration area (HMA); 30-year high, 30-year medium, and 100-year low erosion hazard areas (EHAs); avulsion hazard area (AHA); and flagged streambanks. The method primarily based on the interpretation of historical aerial photographs, high-resolution lidar topography, geologic maps, and flood inundation maps.

CMZ maps are designed to aid in community planning, raise awareness of riverine flood and erosional hazards, and to inform decisions about environmental and emergency management and land use. The maps may be used to identify which buildings, critical facilities, transportation infrastructure, and utility lines are potentially at risk from channel migration and to prioritize areas for pre-disaster risk reduction. These hazard maps provide a valuable resource for Tribal, county, and community planning efforts, including during the development of emergency plans and updates to Natural Hazard Mitigation Plans (NHMPs). DOGAMI often partners with the Oregon Department of Land Conservation and Development to identify strategies that communities can use to reduce risk. 

Please note that the maps in these studies do not replace a site-specific analysis by a land surveyor, geologist, engineer, or some combination thereof.

Lidar reveals historic channel patterns in ways never before possible. We have created a series of landscape maps to highlight the evolution of channel configurations in the Willamette Valley and beyond.