Alaska Climate Change Impact Mitigation Program

Community Planning Grants: Kipnuk

After completing a Hazard Impact Assessment (HIA), the Kipnuk Traditional Council was awarded a $150,000 State Fiscal Year 2011 Community Planning Grant to address one or more of the recommendations from the Kipnuk HIA. The Kipnuk Traditional Council made the decision to conduct the Kipnuk Engineering Analysis and Design Study to determine the most suitable combination of solutions to mitigate riverbank erosion, flood damages, and permafrost degradation. AECOM was selected as the contractor to conduct this study.

The study found that bank stability can be achieved with installation of a sheetpile seawall and/or riprap revetment. Riprap revetment was found to be a more cost effective solutions and is recommended as the bank stability alternative moving forward. If no funding is available for the riprap alternative, the study addressed alternatives for relocation of infrastructure and buildings. Storm surge elevations were estimated for the 100-year storm. The study also provided recommendations for establishing minimum floor elevations above estimated flood levels for future construction and for ground settlement problems.

Background

The village of Kipnuk is located in the Yukon-Kuskokwim Lowlands, on the Kuguklik River about three miles from the Bering Sea coast. The community is about 100 miles southwest of Bethel. The Kuguklik River is a meandering stream that originates about 30 miles east in a flat tundra and lakes complex area. The community is located on an actively eroding bend of the river. The area around Kipnuk is flat and poorly drained with numerous lakes and small drainages that flow into the Kuguklik River.

The potential climate change-related hazards in Kipnuk include increased riverbank erosion rates, increased flooding, and permafrost degradation. Community structure that may be impacted by these hazards include homes, commercial and public buildings, power generation facilities, bulk fuel storage, boardwalks, and communication infrastructure.

Kipnuk has a history of riverbank erosion and flooding. The Alaska District Corps of Engineers (USACE) recently completed a Community Erosion Assessment of the Kuguklik River at Kipnuk. The USACE study identified three primary areas of erosion with calculated erosion rates between 6 and 9 feet per year. Most erosion is reported to occur in the fall, during storm surges. The reported fall erosion timing correlates with the deepest extent of active layer thaw, which occurs at the end of summer. Residents report that flooding affects Kipnuk on a regular basis, occurring mainly in the spring and fall. Concerns have also been raised that more homes are being affected over time.

In addition to flooding and erosion, thawing permafrost is also of concern to the village. Thawing permafrost causes the ground to subside when the ice-rich layer thaws and the soil settles to fill the void. Additional settlement can occur due to soil consolidation as the soil strength properties change from frozen to an unfrozen state. The lower ground elevation is then subject to further flooding. The thawing of permafrost can also result in a loss of foundation support, threatening structures. Foundations designed for permafrost conditions may not necessarily perform as designed under degraded permafrost conditions resulting in foundation settlement as both uniform and differential settlement. Thawing of permafrost due to increasing surface temperatures could also contribute to changes in river discharges and dynamics. River channel dynamics can be altered due to a reduction in soil strength properties of adjacent riverbank soils when compared to permafrost soil strength properties, thus, erosion rates could increase.

Bank erosion north of the village of Kipnuk. Photo: U.S. Army Corps of Engineers

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 1650,
Anchorage, AK 99501-3569
Phone (907) 269-4588
Fax (907)269-4066
Email: sally.cox@alaska.gov