Major conclusions from the study tasks are presented in this section. The
first group of itemized conclusions pertains to those tasks specific to Cook Inlet
and problems with shoaling at the Port of Anchorage. The second set of
conclusions relate to the study of turbulence scale effects in geometrically
distorted physical models.
Cook Inlet study conclusions
a. Tidal flow in upper Cook Inlet features large, 3-D, gyres formed by flow
separation at major headlands. The gyres exhibited vertical and lateral
mixing, and regions of reduced flow velocity magnitude corresponded
well with shoal areas.
b. Turbulent flow separation at Cairn Point during ebb tide was shown to be
potentially instrumental in causing shoaling of the Port of Anchorage.
This shoaling mechanism was first observed in the idealized models, but
there was concern that the terracing of bathymetry in the idealized
models might be contributing to the flow pattern. The 3-D model
confirmed this was not the case.
c. Dye injection during flood and ebb tide demonstrated that dredge
disposal practices could be improved by choice of disposal sites and
timing dump releases to correspond with tidal flow direction. This
reduces the possibility of dredged material being immediately carried
back into the harbor area.
d. Dredging along the dock face without leaving a pathway to the deeper
channel could promote trapping of suspended sediment and increased
sedimentation in the harbor region.
Upstream boundaries are very important
to the flow regime.
Consequently, natural processes such as shifting of major shoals could
have significant impact that might lead to additional maintenance
dredging requirements. Modifying the Fire Island shoals did not appear
to affect flow patterns farther upstream around Anchorage during flood
tide. However, this conclusion is based only on visual observation
without any quantifying measurements.
The smooth boundaries of the physical model might impede
development of fully turbulent flow, and thus represent a scale effect.
However, addition of surface roughness did not have any impact on the
overall flow conditions observed in the 3-D model. This may be the
result of the water passing through a perforated screen before flowing
across the table, making the flow somewhat turbulent initially.
g. Although 3-D flow structures were evident throughout the flow regime,
the turbulent vertical velocities did not seem as important as the
horizontal motion of the gyres. Therefore, 2-D, depth-averaged
numerical models might provide reasonable approximation of the overall
flow in Cook Inlet. However, details of motion within the gyres or flow
entrainment areas are best investigated using a physical modeling
approach, preferably with minimum geometric distortion.
Chapter 8 Summary and Conclusions