LAKE MICHIGAN STUDIES
Special Report Number LM 10
DROGUE SUKV1YS OP LAKE CURRENTS NEAR CHICAGO
May 1963
U. S. DEPARTMENT OP HEALTH, EDUCATION, AND WELFARE
Public Health Service
Division of Water Supply and Pollution Control
Great Lakes-Illinois River Basins Project
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LAKE MICHIGAN STUDIES
Special Report Number LM 10
DROGUE SURVEYS OF LAKE CURRENTS NEAR CHICAGO
May 1963
U. S. DEPARTMENT OP HEALTH, EDUCATION, AND WELFARE
Public Health Service
Division of Water Supply and Pollution Control
Great Lakes-Illinois River Basins Project
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TABLE OP CONTENTS
Page
INTRODUCTION 1
METHOD AND DESCRIPTION OF STUDY 2
RESULTS 4
DISCUSSION
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FIGURES
1. Reference Mgsrker Locations
2. Drogue Study Equipment
3. Drogue Field - Zero Hour
k. " " - First Hour
5. " " Second Hour
6. " " Third Hour
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INTRODUCTION
The use of floats or drogues in the shallow waters of
Lake Michigan provides detailed information on water movements
and dispersion. Current meters are usually not used in water
depths of less than 50 feet except for short periods of time.
Problems of anchoring a current meter station and the orbital
motion of storm waves in shallow water make this type of station
unsuitable over a prolonged period of time.
Studies in the area of the proposed diffuser site (Figure l)
were made by aerial photography and color coded surface floats on
April 11 and 12, 1963.
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METHOD AND DESCRIPTION OF STUDY
Figure 2 shows a typical drogue and its size. The surface
floats holding the drogues at a specified depth were coded "by shape
and color. The colors used were: green, white, orange, red, and
yellow. The shapes used were: triangle, hexagon, rectangle.
Prior to placing the drogues in the water, reference markers,
six meters long (19 feet), were set in the lake. Four rows of four
markers each were set around the proposed diffuser site at 660 foot
intervals (l/8 mile spacing). The diffuser location was marked by
a buoy colored a brilliant orange. The reference markers were
color coded for quick visual identification. The markers were
double anchored to prevent swinging (translating) in the water.
Drogues were launched next to the upwind marker field. A
drogue was set every 75-100 feet, five drogues to a pass. Twenty-
five drogues, at the thirty foot depth, were set on the first run
which was completed at 11:40. The surface floats of the five
drogues placed during the first pass had the same shape but were
of different colors. On the successive pasres the shapes were
alternated and the colors were set in the same order as the first
pass. Thus, each line of drogues had one shape and each row the
same color. The second pass or placement of drogues was made
after the first set of drogues moved out of the initial marker
field.
A twin engine Beechcraft, with an aerial camera (Zeiss
RMK 15/23 camera with a 6 inch lens) began to photograph the
drogue field at 11:40 from a height of 900 feet and a speed of
120 miles per hour. The plane made 4? passes, at approximately
five minute intervals. The photographs had a 60 percent overlap
of field for easy identification. Each photograph contained
three or more reference markers. About 900 frames, 9x9 inches,
were exposed during the two days of study.
A dye patch of Rhodamine B was laid out during the period
of the study. There was some downward diffusion of the dye but
it tended to remain at the surface.
The color film was developed by the U.S. Navy at the
Glenview Air Station photographic laboratory.
Although two days of drogue stvidies were made only the
results from the first day have been analyzed.
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The drogues were set in straight lines and every attempt
was made to form a square pattern with the 25 drogues. Figure 3,
taken seven minutes after the first flight shows the marked
distortion of the original square pattern. As the drogues were
placed in the water they settled at varying rates and were in
normal position in about five minutes. However, the drogues
sinking slowest moved downwind the fastest, since they remained
longer in the faster moving surface layers. The elongation in
the downwind direction continued over the three hour period,
as seen in Figures if- through 6.
Strong northerly winds blew for several days over the area
and began to diminish on April 11, the first day of the study,
although remaining from the north during the entire day.
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RESULTS
Thirteen of the 25 drogues were identified and plotted
on each of the figures. These drogues comprised the general
outer limit of the drogue field.
The outer perimeter of the 13 drogues was joined by
straight lines and the area covered was computed by planimetry
at the end of each hour afloat. Figures 3 to 6, made at hourly
intervals disclose several features of water motion. The
original field; at zero hour, covered an area of 111,350 square
feet. At the end of the first hour (Figure 4) the area had
increased to 113*7&0 square feet or 1.02 times the original area.
The second hour showed a slightly greater expansion of the field,
to 1.12 times the original area. At the end of the third hour
the increase was to 1.18 times the original area. These data
do not indicate a significant change in dispersal area during
the three hours of this study. In relative positions, the
distance between drogues increased downwind and laterally. The
average speed during the three hours of study was 0.055 feet
per second (O.Q miles per day).
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DISCUSSION
The first attempt to measure the mixing or dispersion rate
was made by using drogues at the 30 foot level. It is realized that
several sets of drogues placed at varying depths will give a more
accurate picture of the dispersion rate than drogues set at one
level. Surface speed, during the period of study, was 0.065 feet
per second. Since the total water depth at the study area was
approximately 50 feet, the drogue field set at 30 feet probably
represented average conditions during the study period. Speeds
at the 50 foot depth would not be significantly different from
those at the 30 foot depth as indicated in Special Report No. IM 11.
Studies of the surface water made during a reversal of flow of the
Chicago River into the Lake on September 14, 196"L, also indicated
a very slow dispersion rate because the water mass was identified
up to five days. The September 1961 study was made during a period
of high winds and still indicated that the mixing rate or dispersion
was small. During severe wind conditions and high turbulence the
mixing rate might increase.
Under the conditions found during the study period an
effluent discharged into the lake would not disperse rapidly
after its initial dilution with the lake water. During near
calm conditions an effluent field or mass could build up in the
vicinity of a diffuser. Although the initial dilution of the
effluent may be great upon its discharge, the pollutant concentra-
tion will increase in the water surrounding the diffuser unless
it is removed by water currents. Movement of the discharged
effluent by currents, will not bring about a sufficient dilution
of the water mass in a period of several hours. Rather, studies
indicate that adequate dispersion may take several days, even
during periods of high winds,
Based on the drogue studies it appears that a water mass
could not be expected to have a dilution ratio much greater than
1.2 over a period of several hours. If these conditions are
nearly typical of the average dispersion rate then an effluent
could remain, during calm periods, at its initial state of dilution
with lake water for many days.
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WILSON AVENUE
FOUR-MILE
Current Meter Station at
Proposed Diffusor Site
x» Reference Markers
A Cribs
Scale In Miles
111
14240
FIGURE I
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Drogue Float
Nylon Cord
Slits Cut for Air Escape
Aluminum Fish Net Floats
Zinc Coated Thin Wall
Electrical Conduit
Nylon Cord
ASSEMBLED DROGUE
Foam Material
Nylon Cord
Foam Material
DROGUE FLOAT ASSEMBLY
Galvanized Steel Pipe
Rope to Anchor
Plywood
Foam Material
REFERENCE MARKER
Rope to Anchor
GREAT LAKES 8 ILLINOIS
RIVER BASINS PROJECT
DROGUE STUDY EQUIPMENT
(NO SCALE)
OEPT. OF HEALTH, EDUCATION, 8 WELFARE
PUBLIC HEALTH SERVICE
REGION V CHICAGO, ILLINOIS
FIGURE 2
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LEGEND
o Drogues
X Oiffuser site
A-D Reference marker
Date: April II, 1963
Frame no. 35
Time: Ih47
SCALE-I inch = 105 feet
AREA 111,350 Square feet
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LEGEND
o Drogues
X Diffuser site
&-D Reference marker
Date^ April II, 1963
Frame no. 127
Time: 12:44
SCALE
I inch= 120 feet
Area: 113,760 square feet
FIGURE 4
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o Drogues
X Diffuser site
fr-Q Reference marker
Date: April II, 1963
Frame no. 186
Time- I3'44
SCALE
I inch =140 feet
Area' 124,460 square feet
FIGURE 5
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