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Open-File Report O-13-08, Landslide hazard and risk study of northwestern Clackamas County, Oregon, by William J. Burns, Katherine A. Mickelson, Cullen B. Jones, Sean G. Pickner, Kaleena L. B. Hughes, and Rachel Sleeter

YouTube Video Presentation: Landslide hazard and risk of northwestern Clackamas County, narrated by William J. Burns

Order publication DVD, $30, from Nature of the Northwest.

Publication includes:

—from the report summary:

Northwestern Clackamas County has significant landslide hazards in some of the most developed land in Oregon. The intersection of landslide hazard and dense development result in a relatively high level of risk. We performed this study to increase understanding of the landslide hazard and risk, so that targeted risk reduction could be continued and accelerated.

A major part of this study was developing the lidar-based landslide inventory and shallow- and deep-landslide susceptibility maps. We mapped 2,885 existing landslides, which cover roughly 7% of the study area. Many of these are prehistoric or ancient landslides (that is, older than 150 years); however, these landslides should be considered just barely stable and in most cases would require only a small change in stability to reactivate. We found the large, deep landslides are a primary threat in the study area. Asset exposure to these large, deep landslides is significant—more than 7,000 residents and more than 3,000 buildings with a combined land and building value of $832 million are located on large, deep landslides. Damage and losses alone from landslides induced by a local large crustal earthquake may be in the range of $1 billion with ~4,500 buildings moderately to completely destroyed.

The next step after identifying hazard and risk is to work on landslide risk reduction. The three primary actions are 1) awareness, 2) regulation, and 3) planning. Making everyone aware of the hazard and associated risk is the first step, so that everyone can work on risk reduction.

The landslide inventory and susceptibility maps produced as part of this project show areas of low, moderate, and high potential for landslides in the future and are suited for use in connection with landslide ordinances or building code regulation. The maps could also be used in short- and long-term development planning, comprehensive planning, and maintenance planning.

O-13-08 study area O-13-08 Study Area

Map plate thumbnails:

Assets Overview: Primary Infrastructure and Critical Facilities, Population Distribution, and Generalized Land-Use (actual plate scale 1:50,000, 42 x 72 inches) Landslide Inventory and Shallow- and Deep Landslide Susceptibility Overview (actual plate scale 1:50,000, 42 x 72 inches)
Assets overview susceptibility overview

 

Lake Oswego 7.5-minute quadrangle:
Shallow Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches) Deep Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches)
shallow landslide susceptibility map

 

Gladstone 7.5-minute quadrangle:
Shallow Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches) Deep Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches)

 

Damascus 7.5-minute quadrangle:
Shallow Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches) Deep Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches)
shallow landslide susceptibility map

 

Sandy 7.5-minute quadrangle:
Shallow Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches) Deep Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches)

 

Sherwood 7.5-minute quadrangle:
Shallow Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches) Deep Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches)

 

Canby 7.5-minute quadrangle:
Shallow Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches) Deep Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches)

 

Oregon Cit 7.5-minute quadrangle:
Shallow Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches) Deep Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches)
shallow landslide susceptibility map

 

Redland 7.5-minute quadrangle:
Shallow Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches) Deep Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches)
shallow landslide susceptibility map

 

Estacada 7.5-minute quadrangle:
Shallow Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches) Deep Landslide Susceptibility (NW, NW, SW, SE quarter quads, actual plate scale 1:8,000; 34 x 36 inches)
shallow landslide susceptibility map