EPA-660/3-73-011
September 1973
Ecological Research Series
Big Eddies And Mixing Processes
In The Great Lakes
I
55
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:e of Research and Development
U.S. Environmental Protection Agenci
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination o± traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
U. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ECOLOGICAL
RESEARCH series. This series describes research
on the effects of pollution on humans, plant and
animal species, and materials. Problems are
assessed for their long- and short-term
influences. Investigations include formation,
transport, and pathway studies to determine the
fate of pollutants and their effects. This work
provides the technical basis for setting standards
to minimize undesirable changes in living
organisms in the aquatic, terrestrial and
atmospheric environments.
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EPA-660/3-73-011
September 1973
BIG EDDIES AND MIXING PROCESSES
IN THE GREAT LAKES
By
G. T. Csanady
Project 16050 DIL
Program Element 1BA023
Project Officer
Dr. Walter M. Sanders III
Southeast Environmental Research Laboratory
National Environmental Research Center-Corvallis
U. S, Environmental Protection Agency
Athens, Georgia 30601
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price SO cents
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D. C. 20460
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EPA Review Notice
This report has been reviewed by the Environmental Protection
Agency and approved for publication. Approval does not sig-
nify that the contents necessarily reflect the views and
policies of the Environmental Protection Agency, nor does
mention of trade names or Commercial products constitute en-
dorsement or recommendation for use.
11
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ABSTRACT
Physical factors involved in the disposal of effluents in the Great
Lakes were studied. The experimental work was carried out at the
Baie du Dore research station on Lake Huron in the summer seasons of
1967 and 1968. Data evaluation and parallel theoretical work continued
into 1970.
Some direct measurements of lake turbulence intensity were obtained and
the structure of big eddies studied in a variety of ways. Some informa-
tion was obtained on the interrelationship of short internal waves and
turbulence. The turbulence intensity level could be shown to be propor-
tional to effective diffusivity.
Further studies were carried out of mean concentration and fluctuation
'distributions in dye plumes. A comprehensive review article on lake
dispersion was prepared. This also contained proposals for specific
pollution prediction models, as well as tentative estimates of quantita-
tive parameters required in the use of those models.
Coastal flow processes became recognized as being of especial importance
in pollution problems in virtue of the observed "coastal entrapment" of
pollutants discharged near shore. Theoretical models of the coastal
boundary layer were therefore studied, leading to the discovery of
"coastal jets."
This report was submitted in fulfillment of Project Number 16050 DIL,
by the University of Waterloo, Waterloo, Ontario, Canada, under the
sponsorship of the Environmental Protection Agency. Work was completed
as of August 31, 1970.
iii
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CONTENTS
Section Page
I Conclusions 1
II Recommendations 3
III Introduction 5
IV Lake Turbulence 7
V Diffusion 9
VI Coastal Currents 11
VII Publications in the Literature at Least
Partially Supported by Grant 16050 DIL 13
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SECTION I
CONCLUSIONS
A number of different results arose from this project. Some fundamental
insight was gained in regard to such diverse dynamical problems as large
scale circulation in the Great Lakes and the relationship of internal
waves to turbulence. Quantitative data characteristic of turbulent
diffusion were collected, both on the distribution of mean concentration
and on concentration fluctuations. The results of the project were sum-
marized for potential practical use and pollution prediction models were
proposed.
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SECTION II
RECOMMENDATIONS
The results of this project add up to only a beginning of an under-
standing of coastal dispersal processes. In order to provide reliable
methods of pollution prediction, much further work will be required on
coastal dynamics, transport and diffusion in the coastal zone and on
mass-exchange episodes. Major and sustained efforts in these areas
should prove very rewarding.
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SECTION III
INTRODUCTION
The broad objective of the research supported by this grant was the
elucidation of the physical factors involved in the mixing of pollutants
with the water masses of the Great Lakes. Specifically, according to
the initial application, stress was to be laid on the role played by
relatively large eddies in diffusion processes. Some of these large
eddies called "Langmuir circulations" were known to have a helical struc-
ture and to give rise to "windrows" on the surface. However, the
precise physical mechanism of Langmuir circulations and their exact
dynamical role in the structure of the surface or "mixed" layer of the
sea (or of large lakes) was and is unknown. In the course of the project
attention gradually shifted also to transport (as distinct from mixing
or diffusion) of pollutants in the coastal zone, the dynamical structure
of which proved to be quite complex. Large-scale mass exchange episodes
between coastal zone and main lake mass, in particular, became recognized
as potentially critical controlling influences in coastal pollution.
Research on mixing processes and coastal dynamics in the Great Lakes has
been pursued by the principal investigator and his associates since 1962
and is continuing. Grant 16050 DIL was awarded for the support of this
work in 1967 and continued for another year in 1968, then was extended
without additional funds into 1970. The experimental work supported by
the grant was performed at the Baie du Dore research station on Lake
Huron in the 1967 and 1968 seasons. A detailed summary of the experi-
mental results of these two seasons was given respectively in the
following two interim reports:
Dispersal processes in Lake Huron, by G. T. Csanady, I. S. F.
Jones, and B. C. Kenney, Department of Mechanical Engineering,
University of Waterloo, May 1968, 80 pp. (contains 1967 season
data).
Dynamics and Diffusion in the Great Lakes, by G. T. Csanady,
B. Pade, G. M. Bragg, M. Mekinda, and A. M. Hale, Department
of Mechanical Engineering, University of Waterloo, November
1969, 142 pp. (contains 1968 season data).
Grant funds were also used to support evaluation and assessment of the
experimental data and parallel relevant theoretical work. As a result,
a number of publications arose from the work supported; these are listed
in a later section. Particular attention is drawn to a major review
article entitled "Dispersal of Effluents in the Great Lakes" (Water
Research, 1970) which gives a comprehensive summary of findings up to
early 1970.
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The research actually performed relates to three more or less
distinctly identifiable topics: (a) lake turbulence, (b) diffusion,
and (c) coastal currents. An attempt follows to give an overview of
the work in these three categories, very briefly summarizing what
are thought to be the main scientific or engineering results. For
greater detail, reference should be made to the two previous reports,'
containing all the experimental data, and to the publications in the
literature.
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SECTION IV
LAKE TURBULENCE
In analogy with well known results in the atmospheric diffusion of
pollutants, it was expected that turbulence intensity in the surface
layer of the lakes would exert a controlling influence on the spread-
ing of any effluents. However, no suitable instrument was available
to make turbulence measurements in such a way as to include contri-
bution of the big eddies, known to be important for diffusion. Jones
(1968 report) developed a light directional vane, which measured at
least lateral (= perpendicular to the mean current, in the horizontal
plane) turbulence intensity. Bragg and Mekinda (1969 report) have
further developed this instrument.
Turbulence intensity data collected with the aid of the directional
vane showed considerable day-to-day variations (Jones, 1968 report) and
also large changes in the vertical (Mekinda, 1969 report). In addition,
it became clear that internal waves contribute to the observed velocity
fluctuations and that it may be very difficult experimentally to separate
"turbulence" from "internal waves" (Csanady and Mekinda, 1969 report).
Observed velocity spectra were complex and suggested that internal waves
feed energy to turbulent motions, establishing several "equilibrium
ranges" in the spectrum.
Another light on this problem was thrown by Hale (1969 report) who has
carried out visualization studies of water movements with the aid of an
underwater movie camera and fluorescent dye. His results illustrated
the "breaking" of internal waves, presumably leading to the formation of
turbulence.
The series of windrow observations carried out in 1968 (Csanady and Fade,
1969 report) may also be classed as "direct" turbulence observations,
emphasizing the large eddies. The windrow problem had proved elusive:
surface cooling was thought to be certainly the cause of more or less
well-defined large helical vortices on some occasions, certainly not on
others. One possible problem was that surface streaks due to causes
other than Langmuir circulations could have been labeled "windrows."
The objective identification technique evolved for the 1968 experiments
(drift bottles caught by a long net spun across the current) showed
irregularities in windrow spacings similar to those observed by others
and again demonstrated that surface cooling is not essential for the
appearance of windrows. The irregularity and ubiquitousness of windrows
finally led to the conclusion that Langmuir circulations are more or less
"ordinary" manifestations of big eddies in turbulent flow, which are not
completely irregular also in such other situations as jets or boundary
layers.
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SECTION V
DIFFUSION
Directly linked to the lake turbulence measurements were the diffusion
experiments carried out by Kenney and Jones in the 1967 season (1968
report). These experiments added to the previously existing body of
evidence on dye plume diffusion, and also tentatively demonstrated a
more or less direct proportionality between lateral turbulence intensity
and effective turbulent diffusivity. This has provided an explanation
for the relatively large day-to-day variations of previously observed
diffusivities--"good" or "bad" days for pollutant dispersion apparently
occur according to whether turbulent eddies are vigorous or not. This
connection between turbulence and diffusion was to be expected, but the
great day-to-day variability of both could not have been foreseen.
Another diffusion study was conducted in cooperation with C. R. Murthy of
the Canada Centre for Inland Waters, also at the Baie du Dore research
station in 1968. The results of this work extended earlier evidence on
the distribution of mean concentration in a dye plume and also on the
fluctuations of concentration. From a practical point of view, it is
important to note that the root mean square fluctuation is comparable to
the mean concentration in a plume, so that actual peak concentration
readings may be two or three times higher than the maximum (centreline)
mean concentration at a given plume cross section. The results of this
work were reported in the Journal of Physical Oceanography (January 1972,
the first issue of that new journal).
A considerable proportion of the principal investigator's time budgeted
under this grant was taken up by preparing the comprehensive review for
Water Research, already referred to in the Introduction. Apart from a
coherent picture of mixing processes in the Great Lakes, also some
specific pollution prediction models were proposed in this article, valid
hopefully for sewage outfalls and other pollution sources.
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SECTION VI
COASTAL CURRENTS
Some large-scale diffusion experiments in 1966 and 1967 (not supported
by Grant 16050 OIL) have indicated the crucial importance of larger
scale coastal flow processes in the dispersal of pollutants. Specifi-
cally, it was recognized that effluents discharged at the shore tend to
remain trapped in the coastal zone for periods of several days, to be
removed during large-scale mass-exchange episodes associated with
coastal current reversal. The dynamics of coastal currents, and in
particular their frequency of reversal thus becomes deeply implicated
in the disposal of effluents in the Great Lakes.
Nearshore currents, their direction in relation to winds, and particularly
their reversals of direction have been studied experimentally by Jones
(1968 report). The preliminary result was (confirmed by much subsequent
work not supported under this grant) that currents were mostly shore-
parallel and retained one direction or the other for periods of the order
of 100 hours, or the typical period of weather cycles.
With partial support from this grant, a considerable amount of effort was
also devoted to theoretical studies of coastal currents. This led to the
discovery of baroclinic "coastal jets," which are concentrated bands of
current within 10 km. or so from the shores. The direction of these
currents is determined by major wind-stress impulses (storms, in other
words) and they are accompanied by thermocline upwellings or downwellings,
one or the other according to the direction of the current. A current
reversal brings about large thermocline movements and results in the
mass-exchange episode already alluded to. The results of these theoretical
studies were reported by the principal investigator in a series of articles
in the open literature from 1967 to the present. Support from Grant 16050
DIL was involved in some of these; they are listed in the next section.
11
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SECTION VII
PUBLICATIONS IN THE LITERATURE AT LEAST
PARTIALLY SUPPORTED BY GRANT 16050 OIL
1. Csanady, G. T., "Wind-Driven Summer Circulation in the Great Lakes,"
J. Geophys. Res.. 73. pp. 2579-2589 (1968).
2. Csanady, G. T., "Simple Analytical Models of Wind-Driven Circulation
in the Great Lakes," Proc. llth Conf. on Great Lakes Res.. Int. Assoc.
for Great Lakes Res., Toronto, pp. 371-384 (1968).
3. Jones, I. S. F., "Surface Layer Currents in Lake Huron," Proc. llth
Conf. on Great Lakes Res., Int. Assoc. for Great Lakes Res., Toronto,
pp. 406-411 (1968).
4. Csanady, G. T., "Dispersal of Effluents in the Great Lakes," Water
Research. 4, pp. 79-114 (1970).
5. Csanady, G. T., and M. Mekinda, "Rapid Fluctuations of Current
Direction in Lake Huron," Proc. 13th Conf. on Great Lakes Res., Int.
Assoc. for Great Lakes Res., pp. 397-412 (1970).
6. Hale, A. M., "Dye Injection in the Vicinity of the Thermocline,"
Proc. 13th Conf. on Great Lakes Res,, Int. Assoc, for Great Lakes
Res., pp. 419-429 (1970).
7. Murthy, C. R., and G. T. Csanady, "Experimental Studies of Relative
Diffusion in Lake Huron," J. Phys. Oceano^r.. 1. pp. 17-24 (1971).
8. Kenney, B. C., and I. S. F. Jones, "Relative Diffusion as Related to
Quasi-periodic Current Structures," J. Phys. Qceanogr.. 1. pp. 224-232
(1971).
9. Csanady, G. T., "Baroclinic Boundary Currents and Edge Waves in
Basins with Sloping Shores," J. Phys. Oceanogr.. 1, pp. 92-104 (1971).
,~ *Ut GOVERNMENT PRINTING OFFICi: 1973 546-312/133 1-3
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SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
? Re-
'No.
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BIG EDDIES AND MIXING PROCESSES IN THE GREAT LAKES
.1, R oTtD,
6.
?. Prrformir.' Or gar ation
Csanady, G. T.
Waterloo University, Waterloo, Ontario, Canada
)or^r/-i< ?aw«> ">n ^ g> gnvironmentai Protection Agency
Environmental Protection Agency report number,
EPA-660/3-73-011, September 1973.
16050 DIL
13. Typet 'Repot and
Period Coveted
Final Report
Physical factors involved in the disposal of effluents in the Great Lakes were studied
The experimental work was carried out at the Baie du Dore research station on Lake
Huron in the summer seasons of 1967 and 1968. Data evaluation and parallel theoretica
work continued into 1970.
Some direct measurements of lake turbulence intensity were obtained and the structure
of big eddies studied in a variety of ways. Some information was obtained on the
interrelationship of short internal waves and turbulence. The turbulence intensity
level could be shown to be proportional to effective diffusivity.
Further studies were carried out of mean concentration and fluctuation distributions
in dye plumes. A comprehensive review article on lake dispersion was prepared. This
also contained proposals for specific pollution prediction models, as well as tenta-
tive estimates of quantitative parameters required in the use of those models.
Coastal flow processes became recognized as being of especial importance in pollution
problems in virtue of the observed "coastal entrapment" of pollutants discharged near
shore. Theoretical models of the coastal boundary layer were therefore studied,
leading to the discovery of "coastal jets."
*Turbulence, *Water circulation, Movement, Turbulent boundary layers, Lakes,
*Great Lakes, Hydraulics, *Diffusion, *Currents (Water), Eddies, Mixing, Waves (Water)
Wind Tide, Mathematical model, Transport
Lake coastal currents, Nearshore currents, coastal jets, Windrows, Helical vortex
02H
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G. T. Ctanady
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