Numerical Modeling Studies Supporting Port of Anchorage Deepening and Expansion: Part IV; Numerical Sediment Transport Modeling

The US Army Engineer Alaska District is currently assessing hydrodynamic and port sedimentation issues associated with proposed phased expansion and deepening of the Port of Anchorage. A series of numerical model simulations were performed to assess the impact of the proposed expansion configurations on sedimentation rates within the port. The EFDC surface water modeling system was used to perform these simulations. The hydrodynamic model in EFDC was driven by ADCIRC simulated tides at the forelands near Nikiski, AK in Upper Cook Inlet. The sediment transport model was calibrated using a two-month average sedimentation rate in the port calculated from dredging records. EFDC was applied to represent six different expansion configurations of the port in order to assess the impact of the phased port expansion and deepening on the sedimentation rate inside the port. The ratios of dredging volumes, calculated as the ratio of the predicted sedimentation volume for each of the expansion configurations to the base configuration sedimentation volume, for the six expansion configurations vary from 3.2 to 5.2. These increases in dredging volumes are mainly due to the larger area to be dredged for the expansion configurations than for the base port configuration. Variations in dredging volume ratios among the six expansion configurations are attributed to altered gyre circulation and therefore current speeds along the dock face in the port due to 1) the phased closure of the North and South replacement areas, and 2) the deepening of the bathymetry immediately offshore of the port in the 2009 and 2013 port configurations.