Studies on water movements and sediments in Southern Lake Michigan : part 1[-3] ... / by John C. Ayers.

to give additional information as to the direction of current
movement under different wind conditions, it has been possible
to derive two crude estimates of the dilution rate inherent
in the currents off Chicago. These estimates include error
due to the windage effect on the drogue floats and are not
considered to do more than indicate an order of magnitude.
The water off Chicago is relatively shallow and the bottom
has but a gentle slope. The surface drogues of 4-5 October and
of 9-10 October moved in relatively constant mean depths of 40
and 50 feet respectively.
If the two surface drogues farthest apart on these two
occasions (FigsQ 4 and 5) are considered to move along near
the edges of an hypothetical plume of effluent originating at
the bottom_ at the release position and extending upward through
the water column, successive tentative cross-sectional areas
of the plume can, be computed.
Assuming that the progressive increases in cross-sectional
area of the plumes are due to entrainment of diluting water
from the environment, dilution can be expressed as ratios of
plume cross-sectional areas at successive pairs of times. In
constant depths the shape of the plume cross-section need not
be known.
In the following, the width of the plume at the bottom
at the origin is taken to be ten feet; its width at the surface
at the origin is taken to be fifty feet (the distance apart of
the drogues at setting). In the successive cross-sections the
5:1 ratio of plume width at surface to plume width at bottom
is maaintained (assumption of uniform dilution along the vertical

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