Name: Channel Migration Areas
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Description: Conventional flood hazard maps, like the FEMA Flood Insurance Rate Map (FIRM) series, examine only the hazard posed by standing floodwaters on a given floodplain. Damage from bank erosion as river channels naturally migrate may be far greater locally and may occur even in the absence of major flooding. To address this hazard, channel migration hazard maps were created to identify areas susceptible to future channel movement and erosion. Following the methodology of Rapp and Abbe (2003) and Abbe and others (2008), lidar-derived digital elevations models and serial aerial photography were examined to map the position of the channel over time. Localized erosion rates, potential avulsion sites, areas where erosion may be prevented, and areas where infrastructure is at risk from erosion were identified from these data. The resulting Channel Migration Zone and its subzones represent best estimates of the likely hazard projected 100 years into the future. The analysis area is mostly within the geologic floodplain of the river, with some exceptions where forecasted erosion boundaries intersect active landslides. In these locations, the Channel Migration Zone may include the landslide toe. The channel hazard maps should be used as a guide for local governments, land owners, and infrastructure managers to identify assets potentially at risk and to develop effective mitigation measures. For more information on methodologies, see DOGAMI OFR O-11-09, Channel Migration Hazard Maps, Coos County, Oregon.
Copyright Text: John T. English, Daniel E. Coe, and Robert D. Chappell
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