Numerical Modeling Studies Supporting Port of Anchorage Deepening and Expansion: Part II; Measuring Physical Processes

The US Army Engineer Alaska District is currently assessing hydrodynamic and port sedimentation issues associated with proposed expansion and deepening of Port of Anchorage. Port of Anchorage is located in lower Knik Arm, a macrotidal subestuary of Cook Inlet, Alaska characterized by large, seasonally variant suspended sediment loads; strong tidal currents; and dynamic eddy structure associated with headland points and shoals. Two field experiments were conducted to support numerical hydrodynamics and sediment transport modeling, quantifying physical processes from subgrid to estuary scales. Measurements include bottom- and vessel-mounted Acoustic Doppler Current Profilers (ADCPs), suspended sediment settling velocities, and cohesive sediment erosion. Analysis of tidal volume exchange indicates a strong influence of upper Knik Arm intertidal mudflats on currents at the study site. Prior to the field experiments, eddy shedding by headland points within lower Knik Arm was known, but poorly quantified. The field experiments and data analysis quantified time-dependent development and growth of these eddies. Analysis of sediment data indicates weak cohesiveness in the physically weathered sediments of Knik Arm and pronounced tidal, seasonal, and decadal variation in suspended sediment concentration. The findings from field experiments and data analysis were found to be crucial in representing the dynamic physical processes at the study site with numerical models.