ALASKA RISK MAP PROGRAM

Community Risk MAP Studies

Municipality of Anchorage Risk MAP Study

FEMA and the State of Alaska are conducting a Risk MAP Study in the Municipality of Anchorage (MoA) that began in 2013.  

Project Scope of Work

The Municipality of Anchorage Risk MAP Study included a series of non-regulatory risk and exposure assessments. The results and findings of these risk and exposure assessments have been summarized in a draft Risk Report which has been made available for the Municipality of Anchorage’s review. This report is still a provisional document and is not publicly available.

A risk assessment analyzes, in detail, how flooding and earthquake hazards affect the built environment, population, and local economy, and their likelihood of occurrence. In hazard mitigation planning, risk assessments are the basis for identifying resilience strategies and actions; they define the hazard and enhance the decision-making process. The earthquake risk assessment prepared for the Municipality of Anchorage was prepared using a free FEMA risk assessment tool, Hazus, which estimates losses due to earthquakes for specific buildings.

An exposure assessment identifies areas that would be affected by a hazard. This provides an opportunity for State and local officials to prioritize mitigation actions in these areas. For the purposes of exposure assessments, economic loss is summarized for non-vacant parcels where at least one structure has been identified. Parcels with at least one structure are referred to throughout this Risk Report as “improved parcels.” Additionally, total values and economic losses consider the replacement value of the building and its contents.

Exposure assessments were conducted for the following hazards at the jurisdictional levels:

• Flood Exposure Assessment
• Avalanche Exposure Assessment
• Dam Failure Exposure Assessment
• Landslide Exposure Assessment
• Wind Exposure Assessment
• Wildfire Exposure Assessment

Earthquake Risk Assessment

Maps depicting the shaking intensity and ground motion produced by an earthquake, called ShakeMaps, can be produced in near-real time for events or created for specific scenarios by regional seismic network operators in cooperation with the U.S. Geological Survey (USGS). ShakeMaps can be used for response, land use, and emergency planning purposes. The ShakeMaps selected by FEMA, the Municipality of Anchorage, and the Alaska Division of Geological and Geophysical Surveys (DGGS) for this analysis represented the best available data at the time:

• M7.5 Castle Mountain Scenario
• M7.2 lntraplate Scenario
• M7.1 Border Ranges Fault

FEMA’s contractor incorporated individual parcel data from the Municipality of Anchorage into Hazus to allow losses to be reported at the parcel level. The team incorporated only properties with buildings (improvements) into the analysis; therefore, the team did not assess impacts to vacant land.

As noted, the ShakeMaps listed above were the best available data to run the earthquake risk assessment. Since the 2018 Cook Inlet earthquake took place, more recent ShakeMaps are available and could be used to update the earthquake risk assessment.

Flood Exposure Assessment

In 2009, FEMA created a digital Flood Insurance Rate Map for the Municipality of Anchorage using existing U.S. Army Corps of Engineers work maps to regulate and manage flood hazards in Anchorage, Chugiak, Eagle River, Girdwood, Indian, and other regions within the Municipality of Anchorage. Special Flood Hazard Areas (SFHAs) based on existing modeling were mapped for Anchorage, Chugiak, Eagle River, and Girdwood. Portions of the Municipality of Anchorage are mapped as Zone D, areas where there are possible but undetermined flood hazards, as no assessment of flood hazards has been conducted. These maps were used for the flood exposure assessment. Due to the age and the type of data used, an updated flood study with high quality LiDAR data could produce a more accurate flood risk assessment for the Municipality of Anchorage.

Avalanche Exposure Assessment

The avalanche exposure assessment was based on the 1982 Anchorage Snow Avalanche Zoning Analysis prepared by Arthur Mears. Due to the age of this information, more current data could be collected to refresh this exposure assessment.

Dam Failure Exposure Assessment

The dam failure exposure assessment performed by FEMA’s contractor measured potential impacts of dam inundation based on the failure of dams. Dam flooding was estimated based on the inundation by floodwater of a specified area being protected by a dam or levee. Dam inundation areas varied based on the type of structure, location of structural elements, and flooding source being addressed.

Landslide Exposure Assessment

To estimate where landslide hazard occurrences could potentially affect properties within the Municipality of Anchorage, the project team performed a spatial analysis to identify vulnerable structures with an estimated potential loss based on exposure. For this exposure assessment, the team compared the locations of improved parcels to the geographic extent of deep transitional landslides (Jibson and Michael, 2009). Spatial data for shallow landslide zones is not available.

Wind Exposure Assessment

Wind risk data was obtained from the Municipality of Anchorage. For this exposure assessment, the FEMA’s contractor compared locations of improved parcels to the geographic extent of high wind.

Wildfire Exposure Assessment

Wind risk data was obtained from the Municipality of Anchorage. For this exposure assessment, the FEMA’s contractor compared locations of improved parcels to the geographic extent of high wind.

Outstanding/Pending Flood Studies

In addition to the new Risk MAP study discussed above, there are two outstanding/pending flood studies in the MOA:

• A Physical Map Revision incorporating new studies for Furrow and Girdwood Creeks in 2006. This project is a legacy Map Modernization project which is currently on hold due to the change in FEMA’s levee policy.
• Under the Risk MAP Program, FEMA commenced a Physical Map Revision/LiDAR Acquisition project comprised of a mix of detailed studies and redelineations, including a detailed study of Eagle River and re-delineation of Girdwood flooding sources and of Little Campbell Creek. This project has been suspended due to numerous concerns the Municipality had with technical and procedural aspects of the project, including the vertical datum and the scope of the project study. FEMA would like to continue the project once these concerns are addressed and resolved.

FEMA Region X Risk MAP Newsletters

For more information contact:

Sally Russell Cox

Division of Community and Regional Affairs
Department of Commerce, Community, and Economic Development
550 West 7th Avenue, Suite 1640, Anchorage, AK 99501-3569
Phone (907) 269-4588 Fax (907) 269-4539
Email: sally.cox@alaska.gov

Revised 03/14/2023