BOTTOM CURRENTS IN LAKE ERIE
Robert P. Hartley
Chief, Surveillance Section
U. S. DEPARTMENT OF THE INTERIOR
FEDERAL WATER POLLUTION CONTROL ADMINISTRATION
GREAT LAKES REGION
CLEVELAND PROGRAM OFFICE
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ABSTRACT
In the summer of 1965, seabed drifters were released in Lake
Erie primarily along the south shore and in the western basin. Re-
turns have indicated clockwise bottom eddies in the Toledo-Detroit
area, in the island area, and in mid-lake in the west half of the
central basin. They have also indicated eastward bottom flow in a
narrow band along the south shore and in a wider band along the north
shore of the central basin. Centers of eddies may be significant
repositories for pollutants. The center of the large clockwise gyre
in the central basin may accumulate material originating all along
the south shore of the central-basin. The Toledo-Detroit eddy sug-
gests accumulation of materials therein from these cities.
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INTRODUCTI ON
Many attempts have been made to describe the circulation of water
in Lake Erie, beginning with the work of Harrington (1895). Most of
the work has been on surface currents and has been concentrated in the
western basin. Examples are the work of Verber (1955) and Olson
(1952). In all of these studies, either floating cards and bottles
,or near-surface drogues were used.
The Federal Water Pollution Control Administration, in its pol-
lution investigations, recognized the need for more adequate lake flow
data and conducted a current measurement program throughout Lake Erie.
The program was similar to that conducted in Lake Michigan by Verber
(1962), using Richardson self-recording current meters. To supplement
the Lake Erie program and to learn more about the transport of bottom
and near-bottom suspended materials, seabed drifters were utilized.
To our knowledge this was the first time that bottom drifters had been
used successfully in Lake Erie. They have been used successfully along
the Atlantic coast (Bumpus, 1965) and along the Pacific coast (Morse
et a I., 1968).
METHODS OF INVESTIGATION
The seabed drifters (Figure I) were of the type designed by
Woodhead and Lee (I960), constructed of polyethylene plastic and shaped
like an umbrella. The disc was bright yellow and the stem was red,
making them easily visible from a considerable distance. The stem was
weighted so that the entire assembly had a slight negative buoyancy In
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fresh water. The tail drags along the bottom while the disc is pushed,
parachute-1 ike, by the near-bottom current. The response to water
movement, according to the supplier, is \QQ% at speeds above 17 centi-
meters per second. At 5 centimeters per second the rate of travel is
approximately 10% of true water speed.
The drifters were marked with return-addressed adhesive-backed
labels which requested the finder to note the date and location found
and to return. The labels were sequentially numbered with a laundry
marking pen.
Ordinarily the enti% drifter was returned. Most of the drifters
survived their travels in remarkably good condition, attesting to their
durability. Nearly all were released during sampling cruises between the
first part of June and the middle of August, 1965. Most releases
(Figure 2) were near the south shore of the central basin and around
the western basin because these are the areas of the most significant
tributary inputs to the lake. In addition a few drifters were dropped
in mid-lake and near the north shore of the central basin. Two drifters
were dropped at each station. In all, 368 drifters were released—
118 in the western basin, 234 in the central basin, and 16 in the
eastern basin.
RESULTS OF INVESTIGATION
A gross summary of seabed drifter releases and returns is given in
Table I, indicating the relative success of this kind of study in each
of the lake's basins and in the entire lake.
Drifter returns began shortly after release and they were plotted
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TABLE I
SUMMARY OF SEABED DRIFTER RELEASES AND RETURNS
Place of Release
Western basin
Western basin
Central basin
Central basin
Eastern basin
Eastern basin
Tota 1 s
- Canada
- U. S.
- Canada
- U. S.
- Canada
- U. S.
Number
Releases
48
70
16
218
10
6
"368
Returns
U. S.
0
8
0
26
0
2
36
Canada
3
3
7
37
0
1
51
Total %
return
6.3
15.7
43.7
28.9
0.0
50.0
23.6
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according to shortest route. The first returns (Figure 3) indicated
a dominant eastward nearshore flow along the south shore of the cen-
tral basin and a stronger eastward flow along the north shore. Vel-
ocities are not known, but, if the shortest times are used, the flow
along the south shore netted I.I miles per day eastward, and along
the north shore 4.1 miles per day, also eastward. Along the south
shore the drifters moving eastward averaged 12 times the distance of
those moving westward.
In the western basin the first returns suggested bottom flow
5
eastward through the southern inland channels. Along the Michigan
shore a flow westward toward shore was indicated off Toledo, while
near the mouth of the Detroit River a flow away from shore was sug-
gested.
Returns during the first half of 1966 (Figure 4) correlated with
previous returns except that a westward bottom flow was indicated at
the west end of the central basin.
Drifter returns dwindled by the beginning of summer 1966 and the
project had apparently been completed. Then, in the fall of 1966,
nearly one and one-half years after the releases, a rash of drifters
from the north half of the lake was returned (Figure 5). Some of the
drifters were found on shore, but most were picked up in fishing nets.
From this time on nearly all returns were from nets and most were
forwarded to us by Dr. R. G. Ferguson of the Canada Department of Lands
and Forests. Most drifters were found in the broad bay between Pelee
Point and Pointe Aux Pins, Ontario, probably because of relatively
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Intense commercial fishing in that area.
Returns were even greater in the spring of 1967 (Figure 6) and
were essentially from the same areas. Another pause the following
summer was again followed by a similar pattern of returns in the fall
(Figure 7). For the first time a western basin drifter was also
found in the Pelee Point-Pointe Aux Pins area.
It is significant that in the last one and one-half years only
two drifters have been found in the southern half of the lake while
42 have been recovered from the northern half. All but three of those
recovered from the north side were released near the south shore.
Plotting all returns on the same chart (Figure 8) with near to
shortest paths presents a pattern of total confusion. Many of the
paths in the central basin cross at high angles which is a most un-
likely occurrence in reality.
DISCUSSION
Bottom drifters are similar to surface drifters in their limita-
tions. Only the end points of travel are known. Travel paths and
velocities cannot be determined. Minimum possible velocities can be
calculated but these have no great significance after the first few
returns. It is likely that low current velocities can exist without
drifter movement and that occasional higher velocities can indicate a
false net movement. Wave action can also have the same effect. The
type of bottom can affect velocities and number of returns. For example,
one would expect many drifters to be caught in craggy rock surfaces, to
be slowed by dragging through low-density mud, and to be most responsive
over smooth hard sand bottoms.
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Despite their limitations, it is assumed with some confidence
that the seabed drifters released in Lake Erie did respond fairly
well to important water motions. With this assumption a movement
pattern has been developed on the basis of least conflicting lines
of flow, meaning simply that lines of flow should tend to be parallel
instead of crossing at high angles.
The development of the bottom flow pattern (Figure 9) was vastly
aided by correlating the predominant directions of flow as recorded
by the lowermost meters at current metering stations. Although other
patterns have been drawn to fit the data and bottom topography, all
indicate similar major bottom flow features.
In the western basin a «MM*VFclockwise bottom flow exists be-
tween the Detroit River inflow and the western shore of Lake Erie.
A predominant flow out of the northern channel, Pelee Passage, and a
lesser flow out South Passage are indicated with perhaps a clockwise
gyre around Pelee Island and Kelleys Island. Scarcity of returns from
releases in the mid-portion of the basin indicate sluggishness of bot-
tom flow in that area.
Bottom flow from the western basin appears to be directed south-
ward toward the south shore with some turning westward but most deflected
toward the east. Some of this flow continues eastward as part of the
general eastward flow along the remainder of the south shore. Much
appears to be caught up in a huge clockwise bottom flow gyre of the
central basin. This gyre is centered about 20 miles south of Pointe
Aux Pins, Ontario in the western half of the central basin. Flow is
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strongly toward the east in the northern third of the basin while
the southern two-thirds is characterized by a slower westward flow.
The south shore eastward flow is a narrow band usually separate from
the gyre.
In the eastern basin the bottom flow is less distinct but appears
to have a central clockwise gyre in the deep part and a strong eastward
south shore flow turning toward the north shore in the eastern half
of the basin. There appears to.be a flow toward shore along most of
the north shore. The south shore flow appears to feed the Niagara
River.
The bottom flow pattern shown in Figure 9 Is caused primarily by
prevailing westerly winds and is consistent with them. In general,
westerly and northerly flowing bottom currents are the balancing
response to relatively rapid eastward currents in the upper layers.
Eastward flowing bottom currents are probably caused mainly by wind-
driven surface currents which reach to the bottom in addition to the
requirements for continuity of flow.
The flow patterns of the central and eastern basins suggest also
a vertical circulation with upwelling along almost the entire north
shore and corresponding downwelling near the south shore. This is
required to feed the eastward surface flow which is much greater than
could be fed by drainage inputs.
In the western basin the bottom currents are probably dominated
by the large Detroit River inflow. The large flow out Pelee Passage
•>
and the shoreward movement along the Michigan shore are reinforced .*
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by the prevailing winds.
CONCLUSIONS
The seabed drifter project along with other investigations of
water motion in Lake Erie have led to several conclusions important
to the studies of pollution.
Suspended materials, many of which are damaging to the lake
environment, will accumulate in areas of eddy motion. Such areas are
indicated off Toledo and near the Michigan shore, in the island area,
in the large eddy area in mid-lake in the western half of the central
basin, and in the deep part of the eastern basin.
Prime sources of suspended materials which would be expected in
bottom flow are at or near the origin of the eddies. For example,
wastes from Detroit and Toledo are fed into the eddy of that area and,
to a lesser extent, the one around the islands. Wastes from the
entire south shore of the central basin, when they escape the nearshore
flow, feed into the large eddy In that basin. It is suspected that
this becomes significant in late fall with colder tributary flow under-
running lake water and In spring with under-running of silt-laden trib-
utary water. The paucity of mid-lake drifter returns in the fall of
1965 and spring of 1966 suggests that the drifters were mainly in the
nearshore flow zone until the spring of 1966, and then were forced lake-
ward by this phenomenon.
Only the eddy in the eastern basin is remote from prime sources
of wastes, there being no large sources along the Canadian shore.
Surface currents in the central and eastern basins originate along
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the north shore and move away from it toward the south shore. This
surface water Is productive and as it nears the shore it becomes
more so. This results in large crops of algae along the south shore.
When these algae die and sink they can be carried back to the center
of the lake by bottom currents where they damage bottom water quality.
The eddies in the western basin exist top to bottom, suggesting
that productivity should be higher in these areas. The eddies in
the central and eastern basins are In bottom water only, Indicating
that productivity of surface waters would not necessarily be higher
in these areas.
The lack of returns during the summer months from mid-lake in
the central basin indicates that a definite pattern of flow may not
have existed below the thermocline and that the drifters were trapped
in the hypolimnion. Current meters have shown occasionally rapid
motion in the hypoltmnion, but it is generally to and fro. A gyre-
like motion in the hypolimnion probably does not exist, while above
the hypolimnion it does exist. In effect then the thermocline, although
flexible, acts as the summer lake bottom for the pattern of Figure 9.
Bottom flow in the central basin is strong in late fall and
spring according to returns. It is perhaps also strong in winter but
there is little Chance of retrieving drifters during that time. Many
Canadian fishermen report that drifters are most often found just after
a storm, particularly a northwester. They also report that their nets
are cluttered with debris, organic detritus, and sometimes garbage.
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This suggests rather rapid transport from waste source areas and also
that direct Inputs of man-made wastes may have a measurable pollution
effect on mid-lake waters. This has previously been considered In-
significant.
One of the more important conclusions of this investigation is
that transboundary bottom water motion exists and It Is predominantly
from the American side toward the Canadian side. If suspended pol-
lutlonal materials can be construed as similar In response- to bottom
drifters, we have strong evidence that materials originating on the
American side can be transported and deposited on the Canadian side
of Lake Erie.
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REFERENCES
Bumpus, D. F. 1965, Residual drift along the bottom of the continental
shelf in the Middle Atlantic Bight area; Limnology and Oceanography,
V.IO (Supplement): R50-R53.
Harrington, M. W. 1895, Surface currents of the Great Lakes as deduced
from the movements of bottle papers during the seasons of 1892, 1893,
and 1894; U. S. Dept. Agric., Weather Bur. Bull. B: p. IH4.
Morse, B., Gross, M. G. and C. A. Barnes 1968, Movement of seabed
drifters near the Columbia River: A.S.C.E. Jour. Waterways and Harbors
Div. V, 94, no. WWI: 93-103.
Olson, C. W. 1952, The Currents of western Lake Erie; Ohio State Univ.,
unpub. PhD dissertation.
Verber, J. L. 1955, Surface water movement in western Lake Erie; Proc.
International Assoc. of Theoretical and Applied Limnology, V. 12:
97-104.
Verber, J. L. 1962, Studies of currents in Lake Michigan and related
activities; Proc. 5th Conf. on Great Lakes Research, GLRD pub. no. 9,
p. 127.
Woodhead, P.M.J., and A. J. Lee I960, A new instrument for measuring
residual currents near the seabed; ConseiI International Exploration
Mer. Hydrog. Comm., no. 12, Moscow, USSR.
Wright, Stlllman 1955, Limnological survey of western Lake Erie; Spec.
Sc. Report, Fisheries 139, U.S.F.W.S. 341 p.
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List of figures for "Bottom Currents in Lake Erie", Hartley
Figure I - Woodhead seabed drifter used in this investigation.
Figure 2 - Locations of seabed drifter release in Lake Erie during the spring
and summer of 1965. Each circle denotes the release location of
2 drifters. Releases totalled 368.
Figure 3 - Seabed drifter returns during last half of 1965.
•0
Figure 4 - Seabed drifter returns during first half of 1966.
t
Figure 5 - Seabed drifter returns during last half of 1966.
Figure 6 - Seabed drifter returns during first half of 1967.
Figure 7 - Seabed drifter returns during last half of 1967.
Figure 8 - Seabed drifter returns .during all of period from summer 1965
through falI 1967.
Figure 9 - Prevailing bottom water circulation as inferred from seabed drifter
returns with paths plotted as near to parallel lines and correlated
with metered directions.
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YELLOW
POLYETHYLENE
RED
POLYETHYLENE
5 GRAM
BRASS WEIGHT
55 cm
FIGJ
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