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Open-File Report O-11-13, Channel migration hazard maps for the Sandy River, Multnomah and Clackamas counties, Oregon, by John T. English, Daniel E. Coe, and Robert D. Chappell.

Order publication CD-ROM, $25, from Nature of the Northwest. CD-ROM includes 12 PDF map plates.

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

Plate 1
Plate 1, Channel Migration Hazard Map for the Sandy River, River Miles 1 through 6, Multnomah County, Oregon, scale 1:12,000
Plate 2
Plate 2, Channel Migration Hazard Map for the Sandy River, River Miles 7 through 9, Multnomah County, Oregon, scale 1:6,000
Plate 3
Plate 3, Channel Migration Hazard Map for the Sandy River, River Miles 10 through 14, Multnomah County, Oregon, scale 1:6,000
Plate 4
Plate 4, Channel Migration Hazard Map for the Sandy River, River Miles 15 through 17, Multnomah and Clackamas Counties, Oregon, scale 1:6,000

Plate 5
Plate 5, Channel Migration Hazard Map for the Sandy River, River Miles 18 through 20, Clackamas County, Oregon, scale 1:6,000 larger preview
Plate 6
Plate 6, Channel Migration Hazard Map for the Sandy River, River Miles 21 through 24, Clackamas County, Oregon, scale 1:6,000
Plate 7
Plate 7, Channel Migration Hazard Map for the Sandy River, River Miles 34 through 35, Clackamas County, Oregon, scale 1:6,000
Plate 8
Plate 8, Channel Migration Hazard Map for the Sandy River, River Miles 35 through 37, Clackamas County, Oregon, scale 1:6,000
Plate 9
Plate 9, Channel Migration Hazard Map for the Sandy River, River Miles 37 through 39, Clackamas County, Oregon, scale 1:6,000
Plate 10
Plate 10, Channel Migration Hazard Map for the Sandy River, River Miles 39 through 41, Clackamas County, Oregon, scale 1:6,000
Plate 11
Plate 11, Channel Migration Hazard Map for the Sandy River, River Miles 41 through 43, Clackamas County, Oregon, scale 1:6,000
Plate 12
Plate 12, Channel Migration Hazard Map for the Sandy River, River Miles 43 through 44, Clackamas County, Oregon, scale 1:6,000

 

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.

 

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

For methodology, see English, J. T., and Coe, D. E., 2011, Channel migration hazard maps, Coos County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Report O-11-09 [preview], 18 p.