LAKE MICHIGAN STUDIES
Special Report Number LM 11
CURRENTS AT FIXED STATIONS- HEAR 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 OF CONTENTS
Page
INTRODUCTION 1
Period of Study 1
Purpose of Study 1
RESULTS 2
Daily Current Graphs 2
Prevalence of Movement k
ANALYSIS OF RESULTS 6
Daily Movements 6
Long Term Movements 6
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TABLES
1. Station Description
2. Maximum Hours of Consecutive Calms and Movement From One Quadrant
FIGURES
1. Location Map
2. Two-Hour Envelopes of Speed and Direction, Station k} Depth 30 ft.
311 ii ii n it ti ii u ii ii ti
•
k. " " " " " " " , Station k, Depth 50 ft.
511 n it n it it ti u u ti ti
•
6. ' , Station 3, Depth 30 ft.
7. Percent of Speed and Direction, Station k, Depth 30 ft.
8. " " " " " " " " 50 ft.
9. " " " " " , Station 3, Depth 30 ft.
10. " " " " " , Station X, Depth 30 ft.
11. " " " " " , Chicago, 111. Winds
12. " " " " " , Milwaukee, Wisconsin Winds
13. Current Vectors
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INTRODUCTION
The first detailed studies of currents using current meters
at fixed locations began in the fall of 1962. The techniques and
methods of study were based on tests conducted in the lake during
the previous six months. The study represents the first such data
ever collected from Lake Michigan.
Period of Study
Stations 3 and 4 were set on December 18, 1962 northeast
of the city of Chicago (see Figure l). The meters at these stations
were set to record information on speed and direction for 50 seconds
at intervals of 30 minutes. Each meter recorded about 4,500 readings.
The details on the make-up of each station are shown in Table 1.
One station was set on March 22, 1963, at the approximate position
of the diffuser outlet proposed by Mr. Hazen (Lakes States Exhibit
528) and recorded continuously for a six-day period. Approximately
7,200 readings were made when printing the data at a 1.25 minute
interval.
Stations 3 and k were in operation for approximately 93 days
and Station X for 6 days. The stations were set on a "U" shaped
mooring as described in Figure 6 of Special Report No. LM 9. The
instruments were the Woods Hole type current meters and temperature
recorders.
Purpose of Study
Stations 3 and k are part of the network of stations proposed
for a one-year study to provide knowledge of water motions (currents)
in Lake Michigan. This report includes data on the ranges of current
speed and direction with respect to time and depth, and relates these
generally to wind movements recorded simultaneously at the U.S. Weather
Bureau Station at Midway Airport, Chicago.
The current survey during the winter of 1962-63 provided
periods of data before, during, and after the ice cover on the Lake.
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RESULTS
At the present time, there is no backlog of studies or
published reports on large quantities of current data. Thus,
the effort here is to illustrate, by new techniques, the current
data obtained from Lake Michigan and to show movement of water
during the period of observation.
Ice of varying extent and thickness covered the southern
part of Lake Michigan during the period when stations 3 and k were
in operation. Details as to the dates of ice cover over the stations
are unknown.
After the film records were removed from the meters and
processed, they were scanned electronically by a Flying Spot-Scanner
attached to a PDP-1 computer. This is part of a new technique
developed recently. The current speed and direction were read from
the fifty second recording made each half hour and were transferred
to magnetic tape and processed at the Computer Center of Hew York
University. The data are recorded each half hour for speed and
direction and the six-hour vector averages are tabulated. The two
hour "envelopes" of speed and direction are plotted on a separate
tabulation. The data from each meter were grouped into frequencies
by class intervals - using five-degree intervals of azimuth for
direction, and speed increments of 0.03 ft./sec.
Daily Current Graphs
Figures 2, 3.» k, 5> and 6 show the envelopes of the maximum
and minimum speeds and direction for each two-hour period. When any
of the values in a two-hour period are missing, only the maximum
value shown is plotted. These graphs illustrate the possible
magnitude of variation that occurred during the time period shown.
The graphs show the stable and changing current patterns from day
to day and cover a six-day period.
Figures 2 and 3, Station 4 at 30-ft. depth, show two separate
six-day periods, January 29 to February 3, 19^3 and March Ik to
March 20, 1963- These periods were selected to show variable (Figure 2)
and stable (Figure 3) current direction and variations of speed.
On January 30 (Figure 2) the current was from the SSW (l80°-2l6°) with
speeds about 0.80 ft./sec. which were maintained for about 36 hours.
On January 31 "the speeds decreased to 0.20 ft./sec. at noon and began
to shift to the west at midnight and had shifted to the northwest by
the end of the following day. The currents remained low for nearly
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24 hours. On February 2 the current shifted again, coming from the SW;
the speed increased to a maximum of 1.20 ft./sec. at 2:00 P.M. and
remained high for 14 hours. 'Che current speed decreased to 0.12 ft./sec.
at midnight on February 3. As the current speed decreased, there was
a slight shift in direction to a movement out of the SE.
Figure 3, March Ik to 20, 1963, is an example of a steady
direction of flow for a continuous six-day period. The current, from
the south, began on March 14 and remained fairly constant in direction
until March 20. The speeds ranged from near zero to 0.77 ft./sec.
The small amount of oscillation of the direction indicates very little
fluctuation in movement or a stable current.
Figure 4 shows a six-day period for the 50-ft. depth at
station 4. It is apparent that there is more shifting and slightly
lower speeds than at the 30-ft. depth (Figure 2). The period covered
by Figure 4 is from January 30 to February 5. At noon on January 3L>
the current was from the SE and shifting to the SW. By February 3,
the current speed reached 0.90 ft./sec. at the 50-ft. level as compared
to 1.20 ft./sec. at the 30 ft. level (Figure 2). The current was
from the south, whereas it was from the southwest at the 30 ft. depth.
The current velocity decreased on February 4 and remained at approxi-
mately 0.25 ft./sec. for the next two days. The direction during
this period shifted from the SE to the west.
Figure 5, station 4 at 50 feet, February 19 to February 25,
shows a complete shift of 360° in 34 hours during which time there
was a 24-hour calm period. On February 19 the currents were from
the SE and continued from that direction until the afternoon of the
22nd. The current pattern appeared to rotate clockwise 360° until
the movement was again from the SE on the morning of the 24th.
Although speeds decreased to zero, there is enough evidence to
indicate a complete rotation. Current speeds during the period
changed from 0.10 ft./sec. to 0.70 ft./sec, from February 19 to 21
and dropped to zero early on February 23- The water began to move
again on the 24th and gradually increased in speed.
Figure 6} station 3 at 30 feet, covers the same time period
as Figure 5- The station is 15 miles west of station 4. The current
direction on February 19 was from the north along the shore through
noon of the 20th. At station 4 the flow during the same period was
from the southeast. The current at station 3 shifted abruptly about
noon of the 20th, also to a movement from the southeast, remained in
that quadrant until late on the 23rd, and began to rotate clockwise,
completing a 360° rotation by the 25th. Direction at station 4
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began to shift more than 24 hours earlier and made the complete
swing only 12 hours before the shore station. This sequence of
movement suggests that a large anticyclonic eddy current moved in
from the southeast was first detected at station h and some time
later showed up at station 3 as it moved toward the shore. The
records suggest that the eddy had a clockwise rotation and moved
around the basin in a clockwise path.
Speeds were higher at station 3 than at station U for the
same period, which is to be expected because the water is shallower
and wind stress can be impart3d to the entire mass. Speeds ranged
from near zero to 1.10 ft./sec.
Table 2 shows the number of hours of consecutive readings
for which the current speed was less than 0.1 ft./sec. and the
maximum number of hours of consecutive readings from one quadrant.
Prevalence of Movement
Figures 7, 8, and 9 show variations in speed and direction,
on a percentage-of-time basir, without regard to chronology, summarized
for the period of record. On each figure, the polar diagram is shaded
to show the percentage of time in which the direction of flow was from
each sector. It will be seen from Figures 7 and 8 that the currents
flowed from the southerly quadrant ?0p or more of the time during
the three-month period at station 4. The inshore station (No. 3)
showed a bimodal effect, as shown on Figure 9. Nearly 60$ of the
movement was from the south and kO%> from the north.
The histograms (bar graphs) on Figures J, 8, and 9 show the
percentage of time in which the speed was within a specified range,
in class intervals of 0.1 ft./sec. Speed distribution was bimodal
in all three records - exhibiting at station k a primary mode at
about 0.2 ft./sec. and a secondary mode between 0.6 and 0.7 ft./sec.
At station 3 the primary mode was a speed of about 0.3 ft./sec.,
with a secondary mode also between 0.6 and 0.7 ft./sec. Speeds
exceeding one foot per second occurred about one per cent of the
time. (Mode is a statistical term referring to the most frequently
occurring set of values in a series.)
Of a ninety-day period during the winter, speeds less than
0.08 ft./sec. were recorded on 18 days (not consecutive). Undoubtedly,
a portion of the time the stations were under an ice cover which could
be at least partly responsible for nearly calm conditions occurring
so much of the time.
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Figure 10 (station X) shows a trimodal frequency distribution
of water movement during the six-day record. Twenty-four percent of
the time the water moved from the northwest, kk-io from the southwest,
and 23$ from the northeast. The speeds were bimodal with the greatest
percent between 0.1 ft./sec. and 0.2 ft./sec., and a secondary increase
between 0.4 ft. and 0.5 ft./sec.
Figures 11 and 12 show the percent of the prevailing wind
direction and mean speeds at Chicago and Milwaukee for the period
January 1 to March 22, 1963. The records were obtained from the
official U.S. Weather Bureau offices at these stations. The
predominance of winds from the WSW to M at Chicago and west at
Milwaukee gives a fair estimation of the wind movement over the
lake during this period of time. The wind speeds were primarily
between eleven and fifteen miles per hour.
It is enlightening to calculate the hypothetical displacement
of a water particle from station 4 during the period from January 21
to 24. Assuming that velocity readings at station 4 (at the 30 ft.
depth) represent a mass water movement, and not local eddies, the
displacement of a water particle, which started at the station on
January 21, would be given by the vector sum of velocities on
succeeding days. Such a displacement is depicted on Figure 13»
Total displacement, as shown, would have been 18.T miles in a
northwesterly direction (315°).
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6
ANALYSIS OF RESULTS
pally Movements
Figures 2 to 6, and 13, graphically demonstrate that under
varied conditions water will tend to move in a particular direction
for prolonged periods of time. Present studies indicate that a
particular direction of flow may be maintained for up to six days
and perhaps longer. Table 1 of Special Report No. LM 9> Lake Currents
at a Single Station, and Table 2 of this report, show that water can
move from the northwest or southeast for 80 to 1^2 consecutive hours.
Under such conditions, an introduced effluent could move en masse
for a long period of time and be transported many miles. Calm
periods, exceeding a day or more with little or no flow, could occur
at any time of the year.
Long Term Movements
The winter study of 1962-63 shows for the first time a
clockwise rotation in a portion of the southern basin. Results
from a single station operated from May to July 1962 and previously
reported (see Special Report Wo. LM 9), indicated a prevailing flow
from the northwest at station k, and seemingly confirmed other
evidence of a counterclockwise rotation. There is apparently a
seasonal shift in current patterns in the Lake.
Because of the orientation, symmetry, and latitude of the
southern basin of the Lake, winds will tend to produce either a
clockwise or counterclockwise movement of the currents, depending
upon the direction of wind. In the northern hemisphere the
resultant force exerted by wind on the water surface will be to
the right of the wind direction. When the wind flows across the
lake at an oblique angle to the shore it will tend to pile water
against the downwind shore, and move the water laterally along
that shore. Water piled up on the east shore of the lake and
forced toward the south will produce a northward flow in the
Chicago area. This sets up a clockwise rotation. Likewise, water
piled against the west shore and forced northward will produce a
southerly flow on the eastern side of the basin to compensate for
the northerly flow and thus set up a clockwise rotation. Winds
from 240°-350° and 110°-l80° appeared to produce a clockwise
rotation in the basin for the period of record studied in December
1962 to March 1963. The winds from 350°-110° and l80°-2l|.0o would
tend to produce a counterclockwise rotation. Since, at Chicago,
the greatest fetch (over-water distance over which the wind has blown)
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7
is from the north and northeast quadrant it would indicate that the
predominant movement (strongest flow) would be from the north near
Chicago. However, the prevailing flow (greatest percentage of time)
would be from the south over the winter period in the vicinity of
Chicago.
Limits (degrees) of wind sectors favoring a particular
circulation in the lake are only approximate and vary ten or more
degrees one way or the other. Whether a shift in rotation will
occur depends upon many factors, such as the number of days a current
regime has been established, the number of hours the new stress
has been applied and the thermal structure of the lake.
The prevailing clockwise rotation of the southern basin during
the winter of 1962-63 and an apparent counterclockwise rotation earlier
in the year suggest that there are at least two major water motion
regimes near Chicago which respond to wind movements. A counterclock-
wise rotation apparently occurred during the spring and summer period
but then reversed in the winter.
An effluent discharged into the lake at the proposed diffuser
location or anywhere in the vicinity of Chicago may move in a northerly
or southerly direction depending on the direction of the currents,
which in turn depend upon the wind field over the lake and the thermal
structure of the water. Calm periods in the water can be expected
about ten to twenty percent of the time for as long as 2k hours. Data
gathered for this study as well as data collected during late spring
indicate that there is no single current regime in southern Lake
Michigan.
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TABLE 2
Maximum Hours of Consecutive Calms
and Movement From One Quadrant
Station Depth Hours of Hours from Direction
Number Ft. Calm One Quadrant
4 30 34 142 - 200°
4 50 46 136 145°
3 30 20 130 145°
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M I C H / G
L A K
Sta. 3
, A
42°OI.7-87r3l
Sta. 4 .
A42°0r-87°20' ,
Sta. X
4l°50.2'-87°29.7
Michigan
City
GREAT LAKES 8 ILLINOIS
RIVER BASINS PROJECT
LOCATION OF
CURRENT METER STATIONS
DEPT. OF HEALTH, EDUCATION, 8 WELFARE
PUBLIC HEALTH SERVICE
REGION V CHICAGO, ILLINOIS
FIGURE I
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Q
Z
o
o
UJ
V)
.66
I
O
UJ
UJ
Q.
.33
January 29 to February 4, 1963
324°
252°
UJ
UJ
o: i8o°
u)
o
I
108°
o
36°
O 0
24
12
GREAT LAKES 8 ILLINOIS
RIVER BASINS PROJECT
TWO-HOUR ENVELOPES
OF SPEED 8 DIRECTION
Station 4, Depth 30 Ft.
DEPT. OF HEALTH, EDUCATION, ft WELFARE
PUBLIC HEALTH SERVICE
REGION V
CHICAGO, ILLINOIS
FIGURE
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Less Than 1%
NOTE;
Direction is from the sector shaded,
toward the center
CURRENT
January 6, to March 22,1963
180°
GREAT LAKES 8 ILLINOIS
RIVER BASINS PROJECT
PREVAILING SPEED a DIRECTION
STATION 4— DEPTH 30 FT.
DEPT, OF HEALTH, EDUCATION, 8 WELFARE
PUBLIC HEALTH SERVICE
REGION V CHICAGO, ILLINOIS
FIGURE 7
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LessThan 1%
SPEED
FEET
(North)
0°
PER
SECOND
180°
NOTE;
Direction is from the sector shaded,
toward the center.
CURRENT
December 25,1962 to March 22,1963
GREAT LAKES 8 ILLINOIS
RIVER BASINS PROJECT
PREVAILING OF SPEED 8 DIRECTION
STATION 4- DEPTH 50 FT.
DEPT. OF HEALTH, EDUCATION, 8 WELFARE
PUBLIC HEALTH SERVICE
REGION V CHICAGO, ILLINOIS
FIGURE 8
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Less Than I %
—-.t
O.3 04
SPEED -
(North)
0°
loo
too
NOTE;
Direction is from the sector shaded,
toward the center
CURRENT
January 31 to March 22,1963
180°
GREAT LAKES 8 ILLINOIS
RIVER BASINS PROJECT
PREVAILING SPEED ft DIRECTION
STATION 3— DEPTH 50 FT.
DEPT. OF HEALTH, EDUCATION, 8 WELFARE
PUBLIC HEALTH SERVICE
REGION V CHICAGO, ILLINOIS
FIGURE 9
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02 0.3 04 0.5 0« 0.7
SPEED - FEET PER
(North)
0.8 0.9
SECOND
1.0
loo
NOTE.
Direction is from the sector snoded,
toward the center.
CURRENT
March 22 to 28, 1963
180°
GREAT LAKES 8 ILLINOIS
RIVER BASINS PROJECT
PREVAILING SPEED 8 DIRECTION
STATION X—DEPTH 30FT
DEPT. OF HEALTH, EDUCATION, 8 WELFARE
PUBLIC HEALTH SERVICE
REGION V CHICAGO, ILLINOIS
FIGURE 10
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10 SPEED,'5 KNOTS 20
(North)
NOTE:
Direction is from the sector shaded,
toward the center.
WIND
Jan. I to Mar 22,1963
GREAT LAKES 8 ILLINOIS
RIVER BASINS PROJECT
PREVAILING SPEED 8 DIRECTION
CHICAGOJLLINOIS (MIDWAY AIRPORT)
DEPT. OF HEALTH, EDUCATION, 8 WELFARE
PUBLIC HEALTH SERVICE
REGION V CHICAGO, ILLINOIS
FIGURE II
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10
is zo
SPEED KNOTS
North
0°
25
moh
30
NOTE'
Direction is from the sector shaded,
toward the center.
WIND
January I, to March 22,1963
GREAT LAKES 8 ILLINOIS
RIVER BASINS PROJECT
PREVAILING SPEED 8 DIRECTION
MILWAUKEE WISCONSIN
GENERAL MITCHELL FIELD
DEPT. OF HEALTH, EDUCATION, 8 WELFARE
PUBLIC HEALTH SERVICE
REGION V CHICAGO, ILLINOIS
FIGURE 12
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MEAN 24 HOUR WIND VELOCI -
TIES FOR INDICATED DATES AT
MIDWAY.
1/24/63
1/23/63
DATE
1/21
1/22
1/23
1/24
J
DIRECTION
W
NNW
WSW
WSW
SPEED
MILES/HR.
12
17
18
19
W
MILES
5.2
GREAT LAKES 8 ILLINOIS
RIVER BASINS PROJECT
CURRENT-VECTOR AVERAGES
STATION 4-DEPTH 30 FT.
DEPT. OF HEALTH, EDUCATION, 8 WELFARE
PUBLIC HEALTH SERVICE
REGION V CHICAGO, ILLINOIS
FIGURE 13
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