3 Idealized Cook Inlet Models
Field observations of flow patterns in upper Cook Inlet, visualized by ice
breakup in the spring, had previously indicated that large-scale flow separation
occurred at major headland features. The flow separation generated 3-D flow
structures, and it was hypothesized that this might be a mechanism responsible
for the formation of deep scour holes and sedimentation in the Port of
Overview of Idealized Models
Two idealized scale models of a portion of upper Cook Inlet, AK, were
constructed and tested on the CHL precision flow table. The purpose of these
models was to observe and identify the predominant large-scale tidal flow
patterns responsible for sediment erosion and deposition in the vicinity of the
Port of Anchorage.
These models were termed "idealized" because actual bathymetry in the
modeled region was represented by several horizontal surfaces situated at
selected depth contours. Transitions between different depths were vertical, and
the shoreline was also vertical rather than sloping. So, in essence, the bathymetry
had a "terraced" look. There were three reasons for this bathymetry compromise:
a. The models would be inexpensive and easy to build.
b. The models could be rapidly constructed based on nautical charts.
c. The horizontal surfaces constructed of clear Plexiglas would allow
velocity measurements to be obtained throughout most of the flow
It was judged that the idealized bathymetry would produce flow patterns
similar to models having actual bathymetry, but it was recognized the vertical
shoreline and vertical transitions between depths would have some impact on the
3-D flow structure, thus compromising model results.
The second major concession in the idealized models was geometric
distortion. Both idealized models had significant geometric distortion with the
horizontal scale much larger than the vertical scale. The reason for the distortion
was to be able to model a vast horizontal portion of Cook Inlet at the small size
of the flow table. In general, smooth steady and unsteady nonoscillatory flow is
not compromised by geometric distortion. However, this was not the case for
regions of the flow where vertical velocities and accelerations were significant,
Chapter 3 Idealized Cook Inlet Models