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Open-File Report O-11-09, Channel Migration Hazard Maps, Coos County, Oregon, by John T. English and Daniel E. Coe.

Order publication DVD, $25, from Nature of the Northwest. DVD includes 18 p. PDF text report and PDF map plates.

Lidar-based maps; actual plate size: 44 x 34 inches. All plates are 1:6,000 scale except plates 18, 19 and 20, which are 1:12,000 scale. Preview Plate 5.

Plate 1
Plate 1. Channel migration hazard map for the Isthmus Slough, river miles 0 through 2, Coos County, Oregon
Plate 2
Plate 2. Channel migration hazard map for the Coalbank Slough, river miles 0 through 2, Coos County, Oregon
Plate 3
Plate 3. Channel migration hazard map for the Isthmus Slough, river miles 3 through 4, Coos County, Oregon
Plate 4
Plate 4. Channel migration hazard map for the Isthmus Slough, river miles 5 through 6, Coos County, Oregon
Plate 5
Plate 5. Channel migration hazard map for the Coos River, river miles 14 through 16, Coos County, Oregon larger preview
Plate 6
Plate 6. Channel migration hazard map for the Catching Slough, river miles 0 through 2, Coos County, Oregon
Plate 7
Plate 7. Channel migration hazard map for the Catching Slough, river miles 3 through 5, Coos County, Oregon
Plate 8
Plate 8. Channel migration hazard map for the Catching Slough, river miles 4 through 6, Coos County, Oregon
Plate 9
Plate 9. Channel migration hazard map for the Coos River, river miles 16 through 17, Coos County, Oregon
Plate 10
Plate 10. Channel migration hazard map for the Coos River, river miles 18 through 19, Coos County, Oregon
Plate 11
Plate 11. Channel migration hazard map for the Coos River, river mile 19, Coos County, Oregon
Plate 12
Plate 12. Channel migration hazard map for the Coquille River, river miles 2 through 3, Coos County, Oregon
Plate 13
Plate 13. Channel migration hazard map for the Coquille River, river miles 4 through 6, Coos County, Oregon
Plate 14
Plate 14. Channel migration hazard map for the Coquille River, river miles 6 through 7, Coos County, Oregon
Plate 15
Plate 15. Channel migration hazard map for the Coquille River, river miles 8 through 10, Coos County, Oregon
Plate 16
Plate 16. Channel migration hazard map for the Coquille River, river miles 10 through 12, Coos County, Oregon
Plate 17
Plate 17. Channel migration hazard map for the Coquille River, river miles 13 through 16, Coos County, Oregon
Plate 18
Plate 18. Channel migration hazard map for the Coquille River, river miles 16 through 23, Coos County, Oregon
Plate 19
Plate 19. Channel migration hazard map for the Coquille River, river miles 22 through 28, Coos County, Oregon
Plate 20
Plate 20. Channel migration hazard map for the Coquille River, river miles 28 through 36, Coos County, Oregon
Plate 21
Plate 21. Channel migration hazard map for the Coquille River, river miles 34 through 36, Coos County, Oregon
Plate 22
Plate 22. Channel migration hazard map for the Coquille River, river miles 36 through 38, Coos County, Oregon
Plate 23
Plate 23. Channel migration hazard map for the Coquille River, river miles 38 through 40, Coos County, Oregon
Plate 24
Plate 24. Channel migration hazard map for the Coquille River, river miles 41 through 44, Coos County, Oregon
Plate 25
Plate 25. Channel migration hazard map for the Coquille River, river miles 43 through 47, Coos County, Oregon
Plate 26
Plate 26. Channel migration hazard map for the Coquille River, river miles 64 through 66, Coos County, Oregon
Plate 27
Plate 27. Channel migration hazard map for the Coquille River, river miles 66 through 69, Coos County, Oregon

 


Conventional flood hazard maps, like Federal Emergency Management Administration (FEMA) Digital Flood Insurance Rate Map (DFIRM) series maps, examine only hazards posed by standing floodwaters on a given floodplain. However, 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, this channel migration hazard study identifies areas susceptible to future channel movement and erosion. Following the methodology of Rapp and Abbe (2003) we examined light detection and ranging (lidar) derived digital elevation models and serial aerial photographs to map the positions of channels over time. From these data we calculated local erosion rates and identified potential avulsion sites, areas where infrastructure may prevent erosion, and areas where infrastructure is at risk from erosion. The resulting channel migration zone (CMZ) and its subzones represent our best estimate of the likely hazard projected 100 years into the future. The analysis is restricted to the geologic floodplain of the river, with no attempt to address hazards on valley walls.

Channel migration zone

(Above) Schematic of Historic Migration Zone (HMZ) with respect to overall Channel Migration Zone (CMZ).
DMA is Disconnected Migration Area. EHA is Erosion Hazard Area. AHZ is Avulsion Hazard Zone.

The project focused on urban areas of Coos County, Oregon, where the floodplain showed evidence of channel movement over time as well as signs of significant response to effective flows. In the lower Coos River drainage, we mapped the cities of North Bend and Coos Bay. On the Coquille River we mapped reaches that include the cities of Bandon and Myrtle Point and that extend from south of Broadbent (river mile 69) to the river mouth. A five-mile reach of the upper Coquille River at the city of Powers was also mapped.

location map locations of plates (Far left) Study location and (left) locations of individual plates in study.

The Coos River portion of the project area includes the Coos River from river mile 19 to the mouth as well as the response portions of Isthmus Slough, Coalbank Slough, and Catchings Slough. The extent of analysis along the sloughs was decided on the basis of channel width, flood plain extent, and valley width.