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Kasum, Emil (ed.) / The Wisconsin engineer
Volume 52, Number 1 (October 1947)

Moore, Sherman
Water levels of Lake Erie,   pp. 12-13


Page 12


Water
Levels of Lake Erie
by Sherman Moore c'02
-Reprint from "Shore and Beach"
T  HE St. Lawrence River is one of the great rivers of the
    world, with a length of more than 1,700 miles, drain-
ing an area of some 300,000 square miles. It is unique
among rivers of comparable size in its remarkable uni-
formity of flow and small range in stage. While the net
water supply varies from more than 800,000 c.f.s. per
month to less than zero, the flow at Ogdensburg shows a
monthly variation of less than 150,000 c.f.s. This is due
to the Great Lakes, lying near the head waters with an
area of about 95,000 square miles, which act as great
storage reservoirs, absorbing the fluctuation in the supply
with a variation in level of only about five feet.
  The upper lakes are old, possibly some sixty million
years. They were here before the Glacial Period, and
probably came into existence, although not in their pres-
ent form, in the great-orogeny which began in late Meso-
zoic time and continued into the first part of the Tertiary.
Lake Erie. on the other hand, is comparatively young,
probably less than 25,000 years. There is no evidence of
the lake before the Glacial Period, although possibly
there was a small lake occupying the extreme easterly end
of the basin. Lake Erie is the only one of the Great Lakes
whose bottom does not extend below sea-level. Its aver-
age depth is but 58 feet, its maximum depth only 210 feet.
  The source of the water supplied to the Great Lakes is
the precipitation on their drainage basins. Much of that
falling on the land areas is used by growing vegetation
but approximately one half of it finds its way ultimately
into the lakes. There a considerable proportion is lost by
evaporation. But little is known as to the evaporation from
the lake surfaces, but it seems to be approximately equal
to the mean annual rainfall.
  Of the total net supply of water to the St. Lawrence
River at Ogdensburg, approximately 29 per cent comes
from Lake Superior, 19 per cent from Lake Michigan, 27
per cent from Lake Huron, 9 per cent from Lake Erie,
and 16 per cent from Lake Ontario. The local supply to
the Erie basin is only about 12 per cent of the total supply
to that lake, and if the supply it receives from the lakes
above were cut off, its level would fall some fifteen feet.
  As the supply of water to the Lakes comes from the
precipitation, the lake stages reflect the variation in the
rainfall, but the relationship between the two is obscured
by other factors. A year of heavy precipitation following
a dry period has but little effect upon lake levels, the water
to a large extent being absorbed in filling the small lakes
and swamps and in building up the ground water level.
Ordinarily several years of large precipitation are needed
to create high lake stages. It has been found that rains
occurring in the spring have much more effect upon lake
levels than do those in late summer. The effect of precipi-
tation by snow is not predictable.
  As it has been fairly well established that there is a rela-
tionship between rainfall and the sunspot cycle, a cycle
of about 1012 years should be traceable in lake levels.
Many attempts to demonstrate such a cycle have been
made, but no satisfactory relationship has been shown. In
1929 the stages of the lakes were unusually high. In ac-
cordance with the sun spot cycle high water should have
occurred again in 1939 or 1940, but it did not occur until
1943. The lakes were high in 1918, 1908, 1886, and 1876
as they should have been, but 1897 was not high and
1865-66 were actually low. Of eight sun spot cycles cov-
ered by the record, five check and three fail. This can not
be considered conclusive.
  Lake levels are subject to a seasonal fluctuation which
is directly connected with the variation in supply to the
lake. Minimum stages usually occur in February, the sup-
ply for two or three preceding months having been stored
as snow, and the flow of the tributary streams having been
reduced by ice. With the spring break-up the levels rise,
reaching a maximum in mid-summer. The outflow then
becomes greater than the inflow and the levels fall.
  The wind causes temporary changes in level of short
duration but frequently of considerable magnitude. These
changes do not affect the mean level, but are the result
of tilting of the water surface. Other variations of very
short duration but of considerable size occur probably on
all of the lakes. These superficially resemble tidal waves.
Their cause is not definitely known. The Weather Bureau
has advanced the theory that they are due to a sharp
barometric gradient moving rapidly across the lake, push-
ing a wave of water before it. It has been demonstrated
definitely that lunar tides exist on Lake Superior and Lake
Michigan, and they probably occur on the other lakes.
Their magnitude is so small that they are obscured in other
fluctuations. The tide on Lake Michigan has amplitude of
about an inch and a half.
THE WISCONSIN ENGINEER
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