The currents of Lakes Michigan and Huron / John C. Ayers.

4

involved in this flow appear to come mostly from the mid-lake eddy, with minor
additions received from Mississagi Strait, False Detour Channel, and Detour
Channel.
Detailed studies in Saginaw Bay were carried out by the United States Fish
and Wildlife Service in 1955. They confirmed the counterclockwise trend of
currents which Chart 5 indicates as "estimated" in the inner end of the bay.
The author greatly appreciates their permission to use this information.
Drift Bottle Studies
The drift of floating objects has provided man with both food for thought
and information about currents since he first approached a sea-faring mode of
life. Tropical woods stranded as driftwood on the coast of Ireland are cited
among the several reasons that Columbus believed the "Indies" lay west of
Europe. Few persons will pass an empty bottle on the beach without at least
a stolen glance to see if it contains a "bottle note." Interest in the paths
taken by flotsam stems from several causes. It may have a sanitation basis
(as when a public health official suspects that the sewer outfall is upcurrent
from the water intake), a more macabre undertone (the location or back-tracking
of a drowned body), or any of several other causes, but generally it is nothing
more than plain human curiosity.
For many years use has been made of the beachcomber's natural "wonder
where it came from?" to obtain information about currents. Bottle messages
released at sea are accompanied by a return postcard upon which the finder is
asked to report the date and place of discovery. The whole package of message, return card, and bottle is commonly called a "drift bottle."
Charts 6 and 7 and Tables 3 and 4 show the release points and discovery
points of 161 drift bottles released in Lake Michigan on 28 and 29 June 1955.
Chart 19 shows the stations where the bottles were released. It is of course
impossible to tell the actual path travelled by a drift bottle, but the direction
of its movement is convincing evidence of the direction of the current. Since
a drift bottle usually remains afloat for several days, its average rate of travel is an average of its movements in fast currents and in slow ones. The
average current speeds obtainable from Charts 3, 4, and 5 have been derived
from a complicated computation of the distribution of density of the water, but
they have been checked by (and are in good agreement with) the average speeds
of the drift bottles that travelled in the same regions.
When several drift bottles are released at one place, the straight lines
connecting release point to place of recovery may all run nearly side-by-side
(indicative of strong currents) or they may fan out (indicating the successive
stranding of bottles moving in a circular path). The paths of bottles released
off Manistee in Chart 6 and just off Charlevoix in Chart 7 are good examples
of the strong-current type of distribution; the movements of those released off
Manistique in both charts show the fan-shaped distribution indicative of stranding from an eddy.
Chart 8 and Table 5 give the release points and recovery points of 89
drift bottles from releases made in Lake Huron on 29 June 1954. Chart 20
shows the stations where releases were made. Strong-current distributions of
the bottles are indicated in South Channel of the Straits of Mackinac, False
Detour Channel, and at the extreme end of the lake near the mouth of the St.
Clair River. Fan-shaped distributions indicative of bottles stranding out of
eddies are shown off Goderich and along the Saugeen Peninsula.