A SYSTEMATIC APPROACH TO BUILDING-SCALE GEOHAZARD RISK ASSESSMENTS IN OREGON

The Risk Mapping, Assessment and Planning (Risk MAP) program is managed by FEMA and executed at the state-level in cooperation with state and local agencies. In Oregon, FEMA has partnered with DOGAMI and together are prioritizing Risk MAP program resources to acquire high quality airborne lidar data, use lidar to produce detailed geological hazard mapping, and in turn, use geohazard mapping to support building-scale risk assessments.

High quality lidar is the foundation of this work. With significant help from the Risk MAP program, DOGAMI has overseen lidar acquisition in Oregon that now covers ~45% of the land area of the state and >90% of the populated area. Primarily using lidar digital elevation models, DOGAMI has developed or is developing mapping protocols for landslides, flooding, coastal erosion, fluvial erosion, earthquake shaking and induced ground failure, and tsunami. The mapping is accurate at large scales, typically 1:8,000, reasonably supporting analysis of exposure and loss for individual buildings.

DOGAMI has employed the FEMA Hazus methodology for earthquake, flood, and tsunami damage estimation. Hazus is built on damage functions that relate building characteristics to geohazard intensity to calculate estimated loss. Hazus damage functions are based on empirical data collected in the field following geohazard disasters. For geohazards where Hazus methodology has not been developed (landslides, coastal erosion, and fluvial erosion), exposure overlays are used to determine what is at risk.

DOGAMI and FEMA have identified a systematic and cyclical approach to reach each of Oregon’s 36 counties with lidar acquisition, geohazard mapping, and risk assessments. Draft risk assessments have been completed for six counties. In Tillamook County, as an example: 27,371 total buildings valued at $2.8 billion; loss due to a magnitude 9.0 Cascadia Subduction Zone earthquake scenario is $821 million (29% of total building value); loss due to a magnitude 9.0 CSZ tsunami scenario is $561 million (20% of total building value); loss due to a 1%-annual-chance flood scenario is $26 million (0.9% of total building value); exposure to coastal erosion high hazard areas is $117 million (4.2% of total building value); exposure to landslide high hazard areas is $779 million (28% of total building value).