Overview
The U.S. Army Engineer Alaska District assessed hydrodynamic and port sedimentation issues associated with the proposed phased expansion and deepening of the Port of Anchorage. A series of numerical model simulations was performed to evaluate the impact of the proposed expansion configurations on sedimentation rates within the port, using the Environmental Fluid Dynamics Code (EFDC) surface water modeling system.
Model Setup
The hydrodynamic model in EFDC was driven by ADCIRC-simulated tides at the forelands near Nikiski, Alaska, 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 then applied to represent six different expansion configurations to assess the impact of the phased port expansion and deepening on the sedimentation rate inside the port.
Key Findings
Dredging-volume ratios — the ratio of predicted sedimentation volume for each expansion configuration to that of the base configuration — varied from 3.2 to 5.2 across the six configurations. These increases are mainly due to the larger area requiring dredging in the expansion configurations. Variations among the six configurations are attributed to altered gyre circulation, and therefore current speeds along the dock face, caused by the phased closure of the North and South replacement areas and the deepening of the bathymetry immediately offshore of the port in the 2009 and 2013 configurations.