Spatiotemporal patterns of bluff erosion at Goodnews Bay, Alaska

Abstract

Coastal erosion is of increasing concern to rural Alaskan communities, yet direct measurements remain absent over much of the coast. In southwestern Alaska, the village of Goodnews Bay has been repeatedly devastated by storms and flooding, events that forced the village to relocate to higher ground in the 1920s. Storm surge continues to damage property and infrastructure that is essential to their subsistence culture. This work assesses shoreline change rates at the new village site based on a 59-year time series of aerial and satellite imagery. Long-term and contemporary shoreline retreat rates were analyzed along nearly 500 meters of the village coastline. The majority of the bluff fronting the village experienced a complex history of erosion and mitigation, exhibiting a maximum erosion rate of -0.14 m/y (R2 = 0.82). Bluff erosion has been mitigated via depositing gravel and large rocks after significant storms. The unmitigated bluff just north of the village eroded at -0.10 m/y rate consistently across its length (R2 = 0.92), suggesting that measureable erosion would have also occurred at the village bluff in the absence of mitigation efforts. Projected future bluff top edge positions indicate that the main road system will be significantly eroded in the coming decades, but no buildings are projected to be directly impacted by 2050. Storm surge is the primary driver of erosion in Goodnews Bay, thus the reliability of local storm surge modeling is significant to the community. Historical storm surge and marine total water level estimates were quantified using a combination of GPS data, formal reports, anecdotal accounts, and post-storm imagery. These estimates were compared to the modeled height for the 11/11/2011 storm surge in order to assess accuracy of modeling in this area. Storms that caused significant damage had total water levels between 4.3 and 5.3 m above mean sea level. The upper limit of this estimate came from the large 2011 Bering Sea storm. Evidence for the total water level of previous storms was very limited. It is likely that the 1979 storm, which flooded four homes, reached a similar height. Damage from large storms is expected to become more prevalent with shorter land-fast sea ice seasons in Alaska. A significant portion of this research incorporated community outreach. This included educating youth about coastal science, discussing village history with elders, and installing community-based erosion monitoring sites. Through these efforts, we hope to preserve the traditional knowledge and increase local capacity to adapt to a changing climate.