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

of the water column).
For the run of 4-5 October the separations of drogues I
and III were: 50 feet at setting, and (by scaling from Fig. 4)
5/16 mile at 1730 on 4 October, and 7/10 mile at 0900-0912 on
5 October.
Keeping a five-to-one ratio of plume widths in constant
mean depth of 40 feet, the successive plume cross-sectional
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areas are: 1200 ft2, 39600 ft2, and 88700 ft2. The successive
ratios are: 39600/1200 or 33X and 88700/39600 or 2.2X. Crude
estimate of total indicated dilution during the run: 33 x 2.2
or about 73X.
For the run of 9-10 October the distances apart of drogues
III and IV were: 50 feet at setting, and (by scaling from
Fig. 5) 1/8 mile at 1245-1255 on 9 October, and 1/2 mile at
0830-0845 on 10 October. With a five-to-one ratio of plume
widths and in constant mean depth of 50 feet, the plume crosssection areas are: 1500 ft, 19800 ft2, and 79200 ft2. The
successive ratios of areas are: 19800/1500 or 13.2X and
79200/19800 or 4X. Crude estimate of total indicated dilution
during the run: 13.2 x 4 or 52.8X.
Whether the plume cross-sections are considered to be
rectangles of equal surface and bottom widths, as trapezoids
of unequal surface and bottom widths, or as triangles with
observed surface widths and zero bottom widths makes no
difference; the same ratios of cross-sectional areas emerge.
Though crude, the indicated dilutions of less than 10OX
in a day mean a limited ability of the local currents to
dilute introduced materials.

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