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ALASKA RISK MAP PROGRAM

Emmonak

Emmonak Risk MAP Study

The Risk MAP process began for the City of Emmonak on May 28, 2015 when the State and FEMA conducted a Risk MAP Interview. A Discovery Meeting was held in Emmonak on June 16, 2015 and a Discovery Report was provided to the community on September 9, 2015.

Emmonak Risk MAP Discovery Documents Emmonak Channel Migration Assessment and Mapping Study Documents Region X Service Center Quarterly Reports

During the Discovery Meeting, community members identified flood and erosion hazards on a map. This information has been developed into a Discovery map, below.

Emmonak Discovery Map

Emmonak's Discovery Map identifies critical facilities, areas of concern including erosion and flooding, environmentally sensitive areas, and mitigation needs. Click on the map image to open a full-sized version of the Discovery Map.
Emmonak Discovery Map

Emmonak Risk MAP Study Scope

Following Discovery, it was determined that detailed topography (LiDAR) would be flown in and around the City of Emmonak to enhance existing available data. Emmonak community officials did not identify areas requiring a detailed riverine study or approximate study for an updated Flood Insurance Rate Map (FIRM). The 1% chance flood elevation that is currently being used represents an elevation that exceeds the ground elevations. Thus, new topography would not change how the floodplain extents would be mapped. There also is not enough new information to justify changing the 1% chance flood elevation currently being regulated to. However, there is likely a need for a determination of a larger, rarer storm than the 1% chance flood. The intent of mapping a larger flood event would serve to identify evacuation sites located outside of areas that may become inundated.

It was also identified that Emmonak could benefit from a river-channel migration assessment to document historical trends in riverine erosion and identify areas potentially threatened by future erosion, to inform local decisions about existing and future development.

Emmonak's Risk MAP Study scope of work includes the following efforts:

  • LiDAR Acquisition: LiDAR was collected in Emmonak and used to support the Channel Migration Mapping and Change Analysis, described below.
  • Chanel Migration Mapping Study: Based on the priorities of Emmonak and the State of Alaska Risk MAP Program, the Alaska Division of Geological and Geophysical Survey (DGGS) applied for and was awarded FEMA Cooperating Technical Partner funding to conduct a channel migration study at Emmonak. To conduct the study, DGGS used moderate-resolution satellite imagery (ca. 2010) and high-resolution aerial imagery (ca. 1950) to identify regional or large-scale changes to the Yukon River channel. DGGS used high-resolution imagery and elevation data to model the potential impacts of localized erosion to help inform site planning for potential mitigation structures and community planning for relocation of infrastructure.
    • On a regional scale, the study found that major flood events, particularly from ice jams, have the potential to migrate channels and reroute Yukon River discharge across the floodplain. Changes to river morphology could result in less water flowing through Kwiguk Pass, which could impact local commercial and subsistence fishing activities as well as barge access to the community. DGGS recommended that additional studies be conducted to better understand the potential for channel migration near Emmonak. Additionally, minimal information is available on historical floods in the region. Historical information that would benefit future studies includes:
      • The type of flood event that occurred, the location of ice jams (if appropriate), and flood extent beyond the community location.
      • Future flood events should be documented by mapping flood extents and monitoring river water levels on Kwiguk Pass.
      • Studies to numerically model river dynamics would benefit from additional elevation and bathymetric data of the study area.
  • On a local scale, the study found that erosion of the Yukon River and Kwiguk Pass have the potential to significantly impact community infrastructure. Based on historical orthoimagery and lidar, rates of shoreline change on Kwiguk Pass are generally on the order of +/- 1 m/year (3.3 ft/year). Certain areas experience higher rates of erosion, including the river shoreline east of the city dock (average 2.03 m/year [6.7 ft/ year]):
    • Road infrastructure along the river to the east of the city dock is expected to
    • Erosion of infrastructure can be mitigated through constructing a hardened river bank, moving, or rebuilding infrastructure. Although hardened structures provide immediate protection from erosion events, they have limited lifetimes and can redirect river energy to cause erosion downstream.
    • Continued monitoring and reanalysis of erosion rates will improve the understanding of whether or not erosion rates are increasing or decreasing through time and whether erosion is episodic or continuous.

Project Status

FEMA coordinated through the 3DEP Process with the U.S. Geological Survey (USGS) and the U.S. Fish and Wildlife Service to collect LiDAR in Emmonak. The LiDAR data was used to support analysis FEMA funded through the DGGS to conduct a river-channel migration assessment for the City of Emmonak, complete din November 2018. The following table illustrates project status and includes major milestones with dates:

Activity Actual or Projected End Date
Discovery Interview May 28, 2015
Discovery Meeting June 16, 2015
Discovery Report completed and submitted to community September 9, 2015
LiDAR Acquisition begun August 30, 2016
Channel Migration Study November 2018

*All projected dates are subject to revision as the project progresses

FEMA Region X Risk MAP Newsletters

Contact for More Information

Sally Russell Cox
State of Alaska Risk MAP Coordinator
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