Port of Anchorage Tidal Hydraulics Physical Model

Abstract

The Port of Anchorage is undergoing a large expansion, and the Alaska District of Corps of Engineers needed to assess how this expansion and the construction phasing might impact the Corps’ dredging and navigation missons. One of the tools used to assess Port expansion impacts was a large, geometrically-distorted physical model constructed at the Engineering Research and Development Center (ERDC) in Vicksburg, Mississippi. The spring tide cycle was simulated in the model, and the model was validated by reasonable reproduction of field-measured velocities at three locations near the Port. Flow velocities were measured in 26 model tests that included the pre-expansion configuration, three expansion phases, and the completed expansion. Velocity comparisons indicated potential shoaling problems during Port expansion, and flow visualization illustrated expected tidal flow changes at the Port. BACKGROUND The Port of Anchorage, located in the Knik Arm of upper Cook Inlet, Alaska, serves 80% of Alaska's populated area, and it claims to handle over 90% of consumer goods sold in the rail belt. Maintenance of navigation channels and berthing areas at the Port are the responsibility of the U.S. Army Corps of Engineers’ Alaska District. The tidal flow regime at the Port of Anchorage is dominated by a 30-ft tide range and by large gyres formed in the lee of prominent headlands. The Port itself is situated in a large gyre during much of the ebb tide cycle, and the lower flow velocities in this gyre promote sedimentation in the vicinity of the Port’s berthing areas. The Port is undergoing an ambitious $700M expansion that will increase substantially the Port’s footprint and relocate the dock face about 400 ft seaward. The Alaska District initiated physical and numerical model studies to examine flow modifications and changes to sedimentation likely to occur during and after the Port expansion. The purpose of these studies was to determine how the Port expansion might impact the Corps’ dredging and navigation missions. This paper focuses on the physical model study. The primary objectives of the Knik Arm and Port of Anchorage physical model study were the following: (1) examine changes to the hydrodynamic flow regime likely to occur after each Port expansion phase; (2) assess Port expansion impacts to Corps of Engineers port maintenance operations; and (3)