A Coupled Storm Surge and Wind Wave Model for the Gulf of Alaska and the Bering Chukchi and Beaufort Seas

Coastal Alaska spans over 54,000 km with highly diverse geography ranging from sharp volcanic relief in the south to low lying deltas and tundra in the west and north. This region’s complex geometry, bathymetry, coastal features, and tides in conjunction with the presence of powerful storms, leaves the Alaskan coast particularly vulnerable to storm surge and storm waves. In the Bering, Chukchi, and Beaufort Seas sea ice is present for a significant portion of the year and there is strong inter and intra annual variability in the ice coverage. The effect of ice as it relates to large scale hydrodynamic processes, such as tides and storm surges, and smaller scale processes, such as short wind waves, leads to significant uncertainty in coastal water levels during strong storm events which occur in ice covered periods.

An accurate and robust computational model of the Alaskan coastal hydrodynamics capable of simulating tides, storm surge and wind waves has been built. Particular attention has been paid to how the presence of sea ice affects these processes the effect this has on total water levels. The storm surge model uses the unstructured grid, finite element, ocean circulation code ADCIRC with a modification to the air-sea drag coefficient which accounts for the effect of sea ice on the development of storm surge. This model also computes the wind wave environment through tight coupling with the SWAN phase averaged wave model.

The model has been run and validated for a number of strong late fall and winter extra-tropical storms that led to significant high water events at the Alaskan coast. Each of these events coincided with different ice coverage extents in the Bering Sea and other neighboring bodies of water. These different ice coverages (forming coastal ice, full dense pack ice, and a highly variable coverage) have markedly different effects the development of storm surge at the coast. SWAN has been used to compute the wave conditions during these events. Future work will be done to couple the storm surge model to the Wavewatch III third generation wave model through the Earth System Modelling Framework (ESMF). Wavewatch III incorporates recent ice physics developed through an Office of Naval Research funded Directed Research Initiative, providing storm wave guidance in the nearshore and allowing for momentum to be transferred from the wind waves into the surge through dissipation of the wave energy in areas of partial ice coverage.