Arctic Coastal Geomorphic Change Modeling with Arctic Xbeach

Abstract:

An Arctic-capable coastal geomorphic change model has been developed, based on the open-source geomorphic change model, Xbeach. The model addresses Arctic coastal configurations in which the dominant erosion mechanism is bluff face thaw/slump, followed by offshore transport of thawed sediment from the bluff and beach faces during storms. The geomorphic change is modeled as a two-step process. During the first step, which occurs during non-storm conditions, the bluff face thaws due to solar radiation and convective heat transfer, and thawed material deposits on the beach face before the bluff. During the second step, which occurs during storm conditions with elevated water levels, additional thawing of the bluff and beach occurs, and waves and currents contact the bluff and beach sediments and potentially transport them (if they are thawed), leading to geomorphic change. In a given open water period, we execute the two-step model for each inter-storm / storm sequence, arriving at a prediction of the total amount of erosion in a given year. In the current version of Arctic Xbeach, we convert the area of erosion of the bluff/beach profile following each two-step sequence to an erosion length. Then, we sum up the total erosion distance during an annual cycle and compare this distance to observations of annual shoreline change. In this presentation, we use the Arctic Xbeach model to simulate geomorphic change on the Foggy Island Bay coast on the north coast of Alaska. Once Arctic Xbeach has been validated in the historic period, we use it to forecast shoreline change into the future. Finally, in addition to its service as a tool to forecast coastal geomorphic change in Arctic settings, Arctic Xbeach also serves as a platform for designing coastal stabilizing efforts that feature control of the thermal environment.