Modeling Holocene evolution of the Colville River Delta, AK under sea ice

The Arctic Ocean has undergone seasonal sea ice coverage since the mid-Holocene, leading deltas like the Colville River Delta to develop unique fluvial sediment pathways and complex geomorphologies when compared to those in temperate regions. Little long-term morphologic modeling has been done on arctic deltas which has left a gap in the understanding of sea ice controls on delta formation. To address this, a long-term morphologic and hydrodynamic model was constructed in Delft3D to simulate the temporal evolution of the Colville River Delta, the largest river on the Alaskan North Slope. Model simulations begin at 6 ka, when Holocene transgression ended, resulting in the development of modern deltas such as the Colville. Simulations are in 2D, from the delta apex down to the shelf break, and include the dominant arctic seasonal conditions that drive coastal morphology: freeze-up, break-up/freshet, and open-water. The model uses the novel approach of a floating structure (barges) on the water surface to mimic the lid-like effect of nearshore landfast sea ice on hydrodynamics. Preliminary results show that increased sea ice thickness promotes subaqueous delta progradation, up to ~ 3 km, as well as the creation of a shallow 2 m ramp which is a characteristic present on most arctic deltas. These findings help address how certain features of arctic deltas formed and provide insight on future morphologic processes of arctic deltas as seasonal sea ice extent decreases.