LAKE MICHIGAN STUDIES
Special Report Number
TO LAKE CUBRMT STUDIES
April 1963
U. S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
Division of Water Supply and Pollution Control
Great Lakes-Illinois River Basins Project
-------
OOOR63014
-------
LAKE MICHIGAN STUDIES
Special Report Number LM7
H3TRC!DU£3a!IC8S TO LAKE CURRENT STUDIES
April 1963
U. S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
Division of Water Supply and Pollution Control
Great Lakes-Illinois River Basins Project
-------
-------
TABLE OF CONTENTS
Page
INTRODUCTION 1
DESCRIPTION OP THE LAKE 2
GENERAL CONSIDERATIONS 3
Diffusion 3
Turbulent Mixing 3
Advection 6
Meteorology 8
Possible Pate of Pollutants 8
PROCEDURES 12.
Temperature Studies 11
Tracer Methods 12
Fixed-Position Current Metering 12
REFERENCES 13
FIGURES
-------
-------
FIGURES
1 Drainage Basin of Lake Michigan
2 Current Meter Station
3 Chicago Cribs and Beaches
k The Bathythermograph Slide
-------
-------
INTRODUCTION
A study of currents in Lake Michigan is part of the overall
program of investigations undertaken by the Great Lakes-Illinois
River Basins Project. The ultimate objectives of the studies are:
to assist in predicting the fate of pollutants introduced into the
lake; to assess the effects of waste inputs on lake water quality--
effects both local and area-wide, both for now and in the future;
and to aid in the making of wise decisions for protecting this
valuable water resource.
The dispersal of waste-bearing waters from a point of input
to the lake is accomplished by some combination of three processes:
l) molecular diffusion, 2) turbulent mixing, and 3) mass transport.
The relative importance of each process will depend on physical
conditions in the lake. For example, in completely quiescent waters
the predominant process would be molecular diffusion. Turbulence
(the, existence of randomly-varied water velocities) in the vicinity
of the point of input will greatly accelerate the rate of dispersal
over that effected by molecular activity alone. If, superimposed on
this random turbulence, there is a prevailing velocity, then the
water mass as a whole, and the accompanying waste waters, will move
in that direction. Knowledge of the existence (or absence) of such
novements is essential, both for predicting the fate of pollutants
and for planning strategic locations of waste input and water takeout
points to minimize short-circuiting.
The objectives of the Lake Michigan current study are, then:
to determine the variations in physical characteristics, temperature
and density, of water within the lake; to measure the water movement
patterns over a period of time; and to develop, from considerations
of cause and effect, a theoretical basis for generalizing the
observed conditions.
-------
-------
DESCRIPTION OF THE LAKE
Lake Michigan ranks fifth in size of all the fresh water
lakes in the world and third in size of the Great Lakes of North
America. By comparison the lake is equivalent in area to the
State of West Virginia; however, its bottom is not characteristic
of a hilly or rugged terrain. The lake has a surface area of
22,400 square miles, a maximum depth of 923 feet, and an average
depth of 276 feet. The deepest portion of the lake is nearly 3^3
feet below sea level. It is 307 miles long and 118 miles wide,
measured at the wide point through Green Bay.
The shoreline length, including islands, is 1,660 miles.
The drainage basin, land and water area, covers 67,900 square
miles (Figure l). The volume of water in the lake is 1,170
cubic miles.
The mean water surface elevation of Lake Michigan is 578.80
feet above sea leval. The range of monthly means about the mean
elevation is 6.3 feet and the average seasonal (difference between
summer and winter) fluctuation is 1.0 foot.
Historically the total annual diversion from Lake Michigan
into the Illinois River Basin has varied markedly in different
periods, as shown below (l).
Average 1901-1939 (water years - Oct. 1 thru Sept. 30) 7210 cfs
1940-1961 " " 3240 cfs
1901-1961 " " 5750 cfs
Outflow through the Straits of Mackinac is 40,000 cfs
(1931-1960). This has been computed by the tributary inflow plus
precipitation minus evaporation. Tributary inflow as estimated
by the U.S. Geological Survey is 38,900 cfs (l).
The U.S. Lake Survey, Detroit, Michigan has computed the
precipitation on the lake surface from adjacent land stations.
The estimate of the average annual precipitation from 1900 to I960
is 30.4 inches (2). Evaporation from the lake as estimated by the
U.S. Weather Bureau is 27.8 inches (3).
-------
-------
GENERAL CONSIDERATIONS
In order to comprehend the details of the data on currents
it is logical to review the theoretical concepts and the terminology
of the study.
A pollutant which is a liquid or a suspension of small
particles, when introduced into a body of water, may be diffused
(molecular scale), mixed or diluted (larger scale), and advected
or moved by currents (still larger scale). All three scales
of motion are present in Lake Michigan. Each will be discussed
in turn and its significance considered. It will be evident
by the end of the discussion that there are many gaps in our
knowledge of these forces. Some of these gaps can be filled by a
field investigation; the rest await advances in theory and
instrumentation.
Diffusion
Molecular diffusion is a complex random motion directly
associated with molecular motion and accelerated by the thermal
agitation of individual molecules. It is perhaps the least
important motion for pollutants in Lake Michigan in comparison
with the effects of larger-scale movements. Other than acknowledging
its existence, molecular diffusion will not be considered further.
Turbulent Mixing
Turbulent mixing is a complex random motion not directly
associated with the agitation of individual molecules. According
to Corrsin (4), "....turbulence can be expected in a fluid whenever
there is a shearing flow and the inertia! effects are much larger
than viscous effects." These conditions are often satisfied in Lake
Michigan. Turbulence affects the dispersal rate of pollutants much
more than does molecular diffusion.
Generally speaking, "....much of the core of the turbulence
problem has yet to yield to formal theoretical attack" (4). Mathe-
matical difficulties in handling non-linear expressions have greatly
hampered progress; the non-linearity implies that there are no simple
relationships readily susceptible to mathematical treatment. Work
relating to natural waters, both salt and fresh, has been published
by Richardson and Stommel (5), Stommel (6), Joseph and Sendner (7),
Noble (8) and others. In addition, there is significant unpublished
work by Schonfeld of the Netherlands and Okubo of the Johns Hopkins
University's Chesapeake Bay Institute, among others.
-------
-------
The wind, acting both directly and indirectly, appears to be
the chief force causing water motion in Lake Michigan. It is the
chief force overcoming inertia and stability, resulting in internal
turbulence. Wind stress on the water surface can cause waves,
set-up, and currents, and if abruptly terminated after a sufficiently
long period, may result in a seiche.
If water temperatures are vertically isothermal, the wind
could stir the whole lake. Wind results in waves and orbital
particle motion to depths of at least half a wave length if thermal
stratification is not too strong. If the wind blows from the same
direction for a few hours, it will cause set-up; that is, wind
stress will drag surface water to the leeward side of the lake,
causing a measurable piling up of water against the shore. Mixing
will occur while water is moving toward the shore and while part
of the piled-up water is escaping by moving parallel to the shore
or by reverse flow as a subsurface current. In addition, when the
wind either stops blowing or shifts direction, the piled-up water
begins to return to the opposite side of the lake. Often it surges
back and forth across the lake several times with a period determined
by basin geometry and fluid density; this phenomenon is called a
"surface seiche." The seiche, of course, results in further, though
less important, mixing. To increase the complexity of the matter,
if there is significant density stratification, an "internal seiche"
may be started. The internal seiche, like the surface seiche, is
a wave form at a density interface, though in this instance there
is water above and below, while for the surface seiche air is above
and water below. Periods of internal seiches are longer and amplitudes
are very much greater (10 times and 1000 times, respectively) than
surface seiches. Because of the large amplitudes, internal seiches
can accomplish more mixing. Seiches may be uni- or multi-nodal.
The possibility of their presence makes a single temperature
observation suspect; observations should be repeated at each
location to ascertain conditions. Observations off Chicago by
Project personnel in October 196l, indicated a 23-foot vertical
movement of an isotherm within 3| hours. If such motion is typical,
attempts to estimate the volume of water available for mixing in
the epilimnion (or upper layer) without a set of simultaneous
temperature-depth measurements could be disastrously in error.
It is pertinent to insert a discussion of the Lake Michigan
temperature structure here, because temperature structure determines
density structure which in turn determines stability. The most
important published works are by Van Oosten (9), describing data
from 136 stations occupied from mid-April to mid-November in the
years 1930, 1931, and 1932; by Church (10), describing 2,000
-------
-------
bathythermograph soundings made between November 19^1 and
February 19^-; and by Ayers, et al. (ll), describing four synoptic*
studies of 50 or more temperature stations occupied in June and
August, 1958.
During early winter mouths the lake surface cools and
conveetive mixing occurs as the denser colder water sinks. This
mixing may not affect the deeper areas of the lake where water
may already be at maximum density. At some time during this
period the entire lake will reach a condition of maximum density,
about 4°C. At this time vertical convective mixing ceases. As
the surface temperature continues to drop, the less dense colder
water remains at the surfaco except for such mixing as may result
from wind or wave action. Following the winter season, the
temperature increases slowly until late spring, when the whole
lake again reaches the temperature of maximum density. During
this latter period most of the lalis is again convectively mixed.
When the lake is vertically isothermal at temperatures somewhat
higher than V"*C, the surface temperatures will increase rapidly until
early August, resulting in a very stable stratification by the
formation of a thermocline (a layer of rapid temperature decrease
10 to 50 feet thick). Ultimately, a homogeneous surface layer
with temperatures of l8°C to 22°C is separated by a thermocline
(lO)(ll) from bottom water which hac temperatures close to k°C.
During the time of high stratification it is unlikely that even
the strongest winds could cause complete nixing in the entire lake;
only the water above the thermocline (the epilimnion) is available
for thorough mixing with pollutants., Cooling of the epilimnion
begins with September storms, and the thermocline weakens as the
surface homogeneous layer cools and increases in depth until the
whole lake becomes isothermal at about 4°C to 5°C in early December.
According to Church (10), minimum surface temperatures
(between 0.5°C ani 4.0°C) are reached between tlr? middle and end
of March, at which tine the main body of the lake is vertically
isothermal. These temperatures are 3.ow2r than that producing
maximum density; if such low temperatures could be found in the
deepest part of the lake, f.isn their presence would conclusively
demonstrate complete vertical mixing of the entire lake volume
for the year (12). (Church found them in much shallower water
on the rise between Milwaukee, Wisconsin and Muskegon, Michigan.)
*A synoptic survey is a c]ata gathering operation in which a number of
ships on roughly parallel tracks take samples on the same day, thus
approximating a set of simultaneovis observations from the entire lake.
-------
-------
Dissolved oxygen (DO), for the most part, enters the water
from the atmosphere. During periods of convective overturn the DO
will tend to approach saturation values, but during periods of
stratification DO losses below the thermocline at best will not be
restored by vertical mixing. If pollutants with sufficient
Biochemical Oxygen Demand were introduced into or below the
thermocline, the DO concentration might drop rapidly to low levels.
Two points should be emphasized. First, the volume of
water available for mixing keeps changing throughout the year,
and it is not known whether the entire lake volume mixes completely;
at certain seasons of a year, only the uppermost water (50 feet)
may be available for diluting pollutants. Second, there is a stable
density stratification for a significant portion of the year. The
density of any pollutant introduced into the lake determines whether
the pollutant would stay on the bottom, at intermediate depths, or
at the surface.
Advection
Mixing as accomplished by turbulent motion is a term
describing complex random movements involving relatively little
transport of a water parcel, though a change in its pollution
distribution. Advection is roughly the opposite of turbulent
mixing, and refers to linear translation or gross motion of a
water parcel. There are a number of possible situations between
the two extremes, random turbulence and prevailing advection,
and labelling a given situation with confidence may prove difficult.
Advection theory, in part, is in a more advanced state than
turbulence theory; however, a situation often is so complex that
it is exceedingly difficult to obtain even semi-quantitative
predictions, especially in the vicinity of shore lines (13) •
In Lake Michigan the wind seems to be the chief cause of
advection (as well as internal turbulence, previously discussed).
Tides are negligible for most purposes, having a range of some 3/100
of a foot (lk). Seiches are important to advection only in restricted
areas, such as the Straits of Mackinac. Precipitation minus evapora-
tion although not known in definite detail, is small enough to be
neglected in this instance. Because of the large area of a transverse
cross-section of the lake, net flow-through produces very low
velocities of advectionj indeed, flow in the Straits of Mackinac
is often reversed by seiches and wind-tilt. Church (10) noted
that during most of the year denser water was in the center of
Lake Michigan and less dense water at the edges, implying a slow
-------
-------
counterclockwise density circulation superimposed on the net
flow-through. Project personnel found a similar distribution
off Chicago in the fall of 1962. Attempts to obtain definite
evidence of a stable circulation pattern have produced conflicting
results. The most important works were a three-year drift-bottle
study by Harrington (15), a two-year drift-bottle, study by
Johnson (l6), and the four synoptic cruises by Ayers (ll). According
to Ayers (ll), major current changes caused by the wind are often
superimposed on the more stable, slower flow, and changing winds
are responsible for the varying currents observed.
Haines and Bryson (17) find that the speed of a surface
current is 1.3$ of that of the wind producing it, provided the
wind speed is lass than 5.9 m/sec. (13 mph); above this critical
speed, the relationship is believed to be non-linear. Shulman
and Bryson (l8) find that the direction of surface transport is
about 20.6° to the right of the wind direction and that the "depth
of frictional influence" is between 1.8 and 3.3 meters. These
studies were conducted on Lake Mendota at Madison, Wisconsin and
may not be entirely applicable to Lake Michigan. In the discussion
of thermal structure it was pointed out that the thermocline separated
the homogeneous less-dense epilimnion from the denser homogeneous
bottom water. Bryson and Bunge (19) find that when the wind
suddenly drops or shifts direction after set-up is established,
a rapid increase in current velocity is observed just above the
thermocline. They consider this current to be the first swing
of an internal seiche. Accordingly, significant currents may
exist both at the top and bottom of the epilimnion. Lathbury,
et al. (20) found significant currents below the thermocline also,
which they consider attributable not to seiches but to thermally
and/or wind induced pressure gradients. Set-up causes a hydro-
dynamic pressure gradient, resulting in currents along or
perpendicular to the shore. Shoreline and bottom topography will
also influence currents. It is evident because of the multiple
forces to be considered that attempts to predict currents soon
become complicated.
Recent studies have shown that currents exist through the
entire vertical column of water at least to 120 feet. Current
velocities of 0.3 ft/sec at a depth of 120 feet were measured by
the Project about 25 miles WE of Chicago in October 196! (Figure 2).
On one occasion Project personnel found floating pollutants
in the vicinity of Chicago's beaches and water intakes (Figure 3)
for several days running (21). Generally speaking, surface currents
are weak and southbound near Lake Michigan's west shore but narrower,
-------
-------
8
stronger, and northbound near its east shore. Sometimes there is
evidence of a counterclockwise eddy in the lake's southern basin.
Again, it is to be emphasized that these conditions are variable.
Meteorology
The winds, precipitation, and evaporation over Lake Michigan
have rarely been measured. One study "Report on Wind Velocities at
the Lake Crib and at Chicago" by Hazen (1883) was one of the few
works undertaken to determine the wind differential that exists
between the land and the lake (22). Major Ira Hunt, U.S. Lake
Survey, working on Lake Erie, made some calculations on the wind
differential that exists over that lake. From this study it would
appear that winds over Lake Michigan can be 96 per cent greater
than those over the City of Chicago at certain times of the year,
according to Hunt (23).
Evaporation and precipitation over the lake surface is
limited to estimates by the U.S. Lake Survey rather than precise
observation information. Information from radar studies of
precipitation variations over the Great Lakes are still in the
experimental stage by both the U.S. and Canadian Weather Bureaus.
Verber reports that convectional type rainfall over Lake Erie
is less than at adjacent land stations (24). The U.S. Lake Survey
has embarked on a similar study in northern Lake Michigan, and
the results are now complete (25). Estimates on evaporation have
varied from 21 inches per year to more than 30 inches per year.
Estimates on precipitation have also varied in the same range.
The U.S. Lake Survey (1960) states that the average annual
precipitation over Lake Michigan (l900-196o) is 30.4 inches.
Information on precipitation aad evaporation are far from
insignificant when trying to determine the water balance of the lake.
Wind studies are an important facet of the understanding of the
currents within the lake. The meteorological factors are involved
in any consideration of transport of materials that may be returned
to the lake.
Possible Fate of Pollutants
Despite our present modicum of knowledge concerning current
and wind conditions, one or more of the following factors can
determine the fate of an effluent which is discharged into the lake.
These are: a) existing current regime, b) winds, c) topography, and
d) density difference between pollutant and lake water.
-------
-------
9
If there is a current regime, it will transport any pollutants
introduced into it. As previously noted, there may be a counterclock-
wise gyre in the entire lake or an eddy in the southern portion that
would be the prevailing circulation feature.
Wind sets up currents which can move pollutants introduced
into the lake. The wind currents may be superimposed on any previously
existing currents and may move in any direction.
Topography may determine whether a pollutant remains in an
area or not. If the pollutant is less dense than lake water, then
it may be moved by wind currents until it is trapped against a shore.
If the pollutant is denser than lake water, it may run along the
bottom to collect in depressions.
If an effluent is discharged and there is a density
difference between the effluent and the lake water the following
situations are possible:
l) If the effluent is of low density, it will rise to
the surface and under certain wind conditions may be carried along
the southern and western shores, possibly affecting adversely water
supplies that serve populations totalling several million people
as well as heavily used bathing beaches. 3uch conditions could last
for many days.
2) If the effluent is of low density, it will rise to the
surface and under certain wind conditions may be kept in the southern
end of the lake by the eddy which is sometimes there. Under such
conditions concentrations of chemical constituents well in excess
of those normally present may build up.
3) If the effluent has the same density as the lake water,
it will not move vertically very much. Under certain wind conditions
it may be carried by subsurface currents to the Chicago water intakes
or bathing beaches with little opportunity for dispersion or dilution,
or brought to the surface by upwelling.
Each of the three possible situations cited above will be
considerably more serious if it happens to follow a period of low
wind and water currents during which effluent concentration may
build up in the vicinity of diffusers. Such conditions may occur
even when no ice is present and, on the basis of existing wind
records, may be expected most frequently during summer months.
-------
-------
10
4) If the effluent is of high density, it will sink to
the "bottom and may run down to and collect in the southern basin.
Concentrations of various constituents may build up and seriously
interfere with existing aquatic life. The density of treated
effluent may be so close to that of the lake water that at different
times of year temperature changes in the lake water may result in
the occurrence of all four of the possibilities listed above.
-------
-------
11
PROCEDURES
Procedures for the study are a combination of old and new
techniques. These have been developed through consultation with
oceanographers at the various oceanographic institutes, Chesapeake
Bay Institute, Harvard University and New York University.
Included in the study period on the lake will be approximately
one year of data collection. The collection of past records,
experimental testing of equipment, purchasing equipment, and the
development of techniques preceded the actual study and required
nearly 18 months.
In order to provide the quality control of the instruments
and navigation, services are secured from other agencies. The
Project has established lines of liaison with the National
Oceanographic Instrumentation Center to provide basic calibration
of the instrumentation. Aircraft and photographic techniques used
in the study of littoral currents are provided by personnel of the
U.S. Naval Air Station at Glenview, Illinois. The precision for
water navigation is provided by the utilization of vessels and
personnel of the U.S. Corps of Engineers.
The following field procedures are now underway or are
planned as weather permits.
Temperature Studies
Temperature studies on Lake Michigan have been underway
since September of 1961. Approximately 20 cruises have been made
on the lake since that time, with more than 200 bathythermograph
(Figure **•) casts. Information gained during these studies
established the various configurations of the thermocline during
spring, summer, fall, and winter. Temperature information gained
throughout the past year can be used to determine the depth of
mixing and the variations in density layers within the lake.
In addition to securing data from bathythermographs the
Project has secured 222 temperature recorders, designed by
Woods Hole Oceanographic Institute, to be used in conjunction
with the current meters to determine the location of the thermocline.
-------
-------
12
Tracer Methods
Drogues are being used for inshore studies. A drogue is
a cloth or metal vane which is suspended in the water at any desired
depth by a line which in turn is attached to a small surface float.
The cross-section of the vane is sufficiently large to make the move-
ment of the assembly dependent on forces acting directly upon the
vane, with negligible effect by possibly countering forces on the
line and surface float. The position of the vane below the water-
surface is followed by the movements of the surface float. Drogue
studies, both from a small boat and with the use of aerial photography,
have been carried on in the Chicago area since the spring of 1962.
The first drogue studies made by the Project were for the formulation
of techniques and methods of study. Drogues will be used primarily
to study current patterns in shallow water.
Other tracer techniques include the use of dye studies.
Rhodamine B dye can be traced by use of a fluorometer and its
concentration plotted by a recorder attachment. The Project staff
has cooperated with the City of Milwaukee in making its equipment
and technical advice available to the City for studies in Milwaukee
Harbor. Dye tracing techniques are being planned in conjunction
with the drogue study.
Fixed-Position Current Metering
Since October 1961, a study and evaluation of three types
of meters have been made. These include the telemetry current meter,
the Woods Hole meter, and one devised by the Marine Advisers, Inc.
After an overall evaluation it was decided that the most economical
and reliable approach to the study would be the use of the Woods Hole
current meter. Because of a lack of testing and available information
on long-term use, the Marine Advisers' current meter system was not
considered.
The present current meter stations are located principally
in southern Lake Michigan and were set prior to the severe winter
weather. The first series of stations were set and placed in
operation during the last week of November 1962.
-------
-------
13
REFERENCES
1. Surface Water Supply of the United States. Part 5. Hudson
Bay and Upper Mississippi River Basins. U.S. Geological Survey,
Washington, B.C.
2. Average Precipitation in Inches on the Lake Surface of Lake
Michigan"(Annual Report)U.S. Lake Survey, Detroit, Michigan.
3. Evaporation Maps for the United States. Technical Report No. 37 >
U.S. Weather Bureau (1959).p. 13.
4. Corrsin, S. Turbulent Plow. .American Scientist, 49: 300-325 (l96l).
5. Richardson, L. P. and Stommel, H. Note on Eddy Diffusion in the
Sea. J. Meteorology, 5: 238-240 (19^8).
6. Stommel, H. Horizontal Diffusion Due to Oceanic Turbulence.
J. Marine Research, 8: 199-225 (1949).
7. Joseph, J. and Sendner, H. Uber die Horizontale Diffusion im
Meere. Deutsche Hydrographische Feitschrift. 11: 4-9-77 (1958).
8. Noble, V. E. Measurement of Horizontal Diffusion in the Great
Lakes. Proceedings Fourth Conference on Great Lakes Research.
Great Lakes Research Division, Publication No. 7 (1961).
9. Van Oosten, J. Temperatures of Lake Michigan, 1930-32. United
States Fish and Wildlife Service Special Scientific Report,
Fisheries No. 322 (I960).
10. Church, P. E. Annual Temperature - Cycle of Lake Michigan: Abstract.
Transactions American Geophysical Union, 27: 109-110 (1946).
11. Ayers, J. C., Chandler, D. C., Lauff, G. H., Powers, C. P. and
Benson, E. B. Currents and Water Masses of Lake Michigan.
Great Lakes Research Institute, Publication No. 3 (1958).
12. Birge, E. A. The Thermocline and its Biological Significance.
Trans American Microscopic Society, 25: 5-33 (1904).
13. Hutchinson, G. E. A Treatise on Limnology, Volume I: Geography,
Physics and Chemistry. John Wiley & Sons, Inc., New York (1957).
p. 1-1015.
-------
-------
Ik. Judson, W. V. Currents in Lake Michigan. First Report of The
Lake Michigan Water Commission. Urbana, Illinois (1909).pT~63-68.
15. Harrington, M. W. Surface Currents of The Great Lakes, as
Deduced from the Movements of Bottle Papers During The Seasons
of 1892, 1893, and 1894.U. S. Department Agric.7 Weather
Bureau.Bulletin B (rev. ed.) (1895). p. I-lk.
16. Johnson, J. H. Surface Currents in Lake Michigan, 1954 and 1955-
United States Fish and Wildlife Service Special Scientific Report,
Fisheries Wo. 338 (I960).p. 1-120.
17. Haines, D. A. and Bryson, R. A. An Empirical Study of Wind
Factor in Lake Mendota. Limnology and Oceanography, 6: 356-364 (l96l).
18. Shulman, M. D. and Bryson, R. A. The Vertical Variations of
Wind-Driven Currents in Lake Mendota. Limnology and Oceanography,
6: 347-355 (1961).
19« Bryson, R. A. and Bunge, W. W. Jr. The Stress-Drop Jet in
Lake Mendota. Limnology and Oceanography, 1: 42-46" (1956).
20. Lathbury, A., Bryson, R. and Lettau, B. Some Observations of
Currents in the Hypolimnion of Lake Mendota. Limnology and
Oceanography, 5: 409-413 (1960).
21. U. S. Public Health Service. Movements in Lake Michigan of
Water Discharged Ik September 1961 from The Chicago Sanitary
Canal System. U. S. Exhibit No. 4, Chicago Diversion Case,
Mimeo., Unpublished (1961).
22. Hazen, H. A. Report on Wind Velocities at the Lake Crib and
at Chicago. Signal Service Notes Mo. VI (1883). p. 1-20.
23. Hunt, Ira A. Winds, Wind Set-tips, and Seiches on Lake Erie.
U. S. Lake Survey. Detroit (1959). p. 59.
2k. Verber, James L. The Climates of South Bass Island, Western
Lake Erie. Ecology, 36: 388-400 (1955).
25. Bloust, F. and DeCooke, B. Comparison of Precipitation on
Islands of Lake Michigan with Precipitation on the Perimeter
of the Lake. Jour. Geophysics Res.. 65: 1565-1572 (i960).
-------
-------
JVJSC.
ILL~
GREAT LAKES 8 ILLINOIS
RIVER BASINS PROJECT
DRAINAGE BASIN
of
LAKE MICHIGAN
DEPT. OF HEALTH, EDUCATION, 8 WELFARE
PUBLIC HEALTH SERVICE
REGION V CHICAGO, ILLINOIS
FIGURE I
-------
WISCONSIN
"ILLINOIS "
N
01234
SCALE IN MILES
Subsurface Current Station
October, 1961
Subsurface
Current Station
_ May, 1962
O
GREAT LAKES 8 ILLINOIS
RIVER BASINS PROJECT
CURRENT METER STATIONS
DEPT. OF HEALTH, EDUCATION, 8 WELFARE
PUBLIC HEALTH SERVICE
REGION V CHICAGO, ILLINOIS
FIGURE 2
-------
FIGURE 3
-------
0
25
50
I-
bJ
Ul 75
U_
I JOO
X
a 125
LU
a
150
175
200
Slide No. 5
Oct. 6,1961
Time' |2|2 CST
BT No.5834
5 10 15
TEMPERATURE -°C
20
TYPICAL SUMMER THERMOCLINE IN LAKE MICHIGAN'S SOUTH BASIN
Slide No. 1-4
March .22,1962
Time; 1500 CST
BT No 1241
900
TEMPERATURE- °C
TYPICAL WINTER THERMOCLINE IN LAKE MICHIGAN^ NORTH BASIN
Reproduction Of Glass Slide From
Bathythermograph
GREAT LAKES 8 ILLINOIS
RIVER BASINS PROJECT
THE BATHYTHERMOGRAPH SLIDE
DEPT. OF HEALTH, EDUCATION, 8 WELFARE
PUBLIC HEALTH SERVICE
REGION V CHICAGO, ILLINOIS
GFO 827804
FIGURE 4
------- |