Characterization of a storm surge exposed arctic inlet: Shaktoolik, Alaska

The Inupiaq community of Shaktoolik, in northwestern Alaska is constructed on a low-lying barrier spit located on Norton Sound. The inhabited portion of the spit is ~200m across and vulnerable to flooding from both the open water and lagoon sides during storm events. Previously modeled storm events estimate elevated sea surfaces reaching a maximum storm surge of 6.4m (21 feet) in the Norton Sound region. Historical storm events have been documented every few years in the region, usually occurring during the fall, but storm surge heights in Shaktoolik have never been recorded. An inlet is located at the northern terminus of the barrier spit, adjacent to the community, and provides access for fishing boats to and from the sheltered lagoon. This research focuses on the responses of Shaktoolik's inlet to storm surge and subsequent flooding of the spit. Fieldwork conducted in July 2011 focused on mapping the on land and nearshore coastal morphology of the barrier system. Prior to this, limited baseline data about the Shaktoolik coastal zone was available. The research goals for this project are to understand the morphodynamics of the inlet and surrounding coastal area and to analyze impacts on the inlet by storm surge events. This study is in support of a larger geohazard mapping project with the Alaska Department of Geological and Geophysical Surveys. Onshore, beach profiles and wrackline positions were surveyed, and grain size samples were collected north and south of the inlet. These data provide insight into the longshore sediment transport patterns, past flood levels, and the extent of possible flooding and inundation in the future. In the nearshore, bathymetric data, current velocity measurements, and suspended and bedload sediment samples were obtained seaward of the spit, in the inlet, and within the lagoon. Nearshore measurements characterize the inlet channel depths and composition, and locate areas of sediment deposition. In addition, three months of fall seasonal water levels were collected hourly on the lagoon side of the inlet in order to capture tide ranges and storm surge heights. Further analysis will include historical storm surge flooding estimates for Shaktoolik, water height ranges for storm events, and inlet current velocities and discharge rates.