Vessel Quotas and Operating Requirements Vessel Quotas and ...

Example calculations of water particle velocities showed that for the wave heights and periods typical of
the wave climate in Glacier Bay proper, the velocities would be more difficult to compare in the various
sites of interest because additional input parameters are required. These include the wave speed, C, and
the period of the vessel waves. The calculations performed show that the typical particle velocities were
smaller than the design velocity of 10 feet per second (fps), which is used in aquariums to prevent marine
fouling. Velocities of less than 10 fps are inferred to be required to allow marine growth. Velocities in
the range of 10 fps do routinely occur in the shallow surf zone during wind wave events. Even in the
shallowest water, as predicted by Airy theory, the maximum horizontal water particle velocity caused by
the design boat wake is approximately 3 fps.
Water particle velocity was not as suitable a parameter for analysis of vessel wake effects in Glacier Bay
proper. The additional input information required is not readily available and would require making
additional assumptions.
6 CONCLUSIONS AND SUGGESTIONS FOR FURTHER STUDY
The purpose of this technical memorandum is to provide a method to evaluate existing and proposed
vessel quotas and operating requirements in Glacier Bay National Park and Preserve. The method detailed
in this technical memorandum will be used to classify all sites selected for full evaluation in the EIS.
Some conclusions can be drawn based on our work so far and on the information contained within this
technical memorandum. These include:
• For most of Glacier Bay proper, vessel wakes pose little threat to the coastline.
• There are specific locations where operating requirements may be necessary to prevent adverse
effect to the shoreline. This may include creating a no-wake zone near the shoreline. See the
Environmental Impact Statement for specific sites and evaluations.
• The potential effect of vessel generated internal waves to all aspects of the environment is not
known. Research indicates that internal waves have the potential to mix stratified layers of water.
This could affect stratification of pelagic organisms like algae. Further scientific study is required
to determine if they exist and their affects on the environment. It is likely that naturally occurring
internal waves occur in Glacier Bay proper and would not be affected by vessels due to the
shallow extent of influence by the vessel.
• Vessel wake disturbance occurs close to the vessel producing the wake. Wakes are essentially
dissipated within 2,000 feet of the vessel.
35