Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5

2010

OCT

1945

NOV

1945

DEC

1945

2011

JAN

1946

FEB

1952

MAR

1952

APR

1973

MAY

1973

JUN

1952

JUL

1947

AUG

1947

SEP

1947

OCT

19451934

NOV

19451934

DEC

19451934

2012

JAN

1946

1935

FEB

1952

1936

MAR

19521935

APR

19731935

MAY

19731935

JUN

19521935

JUL

19471934

AUG

19471934

SEP

19471934

OCT

19451934

NOV

19451934

DEC

19451934

2013

JAN

1946

1935

FEB

1952

1936

MAR

19521935

CHART DATUM 243.3 FEET (74.2 METERS)

Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

+ 6

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5+ 1.8

2010

OCT

1986

NOV

1986

DEC

1986

2011

JAN

1987

FEB

1987

MAR

1986

APR

1985

MAY

1986

JUN

1986

JUL

1986

AUG

1986

SEP

1986

OCT

1986

1934

NOV

1986

1934

DEC

1986

1934

2012

JAN

19871935

FEB

1987

1936

MAR

1986

1934

APR

19851934

MAY

1986

1934

JUN

1986

1934

JUL

1986

1934

AUG

1986

1934

SEP

1986

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1934

2013

JAN

19871935

FEB

1987

1936

MAR

1986

1934

CHART DATUM 569.2 FEET (173.5 METERS)

Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5

2010

OCT

1986

NOV

1986

DEC

1986

2011

JAN

1986

FEB

1986

MAR

1986

APR

1986

MAY

1986

JUN

1986

JUL

1986

AUG

1986

SEP

1986

OCT

1986

1934

NOV

1986

1934

DEC

1986

1964

2012

JAN

19861936

FEB

19861926

MAR

1986

1934

APR

19861926

MAY

1986

1934

JUN

1986

1934

JUL

1986

1934

AUG

1986

1934

SEP

1986

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1964

2013

JAN

19861936

FEB

19861926

MAR

1986

1934

CHART DATUM 572.3 FEET (174.4 METERS)

ELEVATIONS REFERENCED TO THE CHART DATUM OF EACH 

Superior

601.05

183.20

601.15183.23603.22

183.86

1985

600.46

183.02

2007

602.13183.53

MichHuron

576.97

175.86

577.85176.13

581.96

177.38

1986

576.64

175.76

1964

579.10

176.51

St.

Clair

573.33174.75

574.41

175.08

576.90

175.84

1986

571.98174.34

1934

574.41

175.08

Erie

570.70

173.95571.85

174.30

573.59174.83

1986

568.83173.38

1934

571.39

174.16

Ontario

244.42

74.50

245.28

74.76

247.41

75.41

1947

242.49

73.91

1934

245.21

74.74

SEPTEMBER MEAN LAKE LEVELS

(IGLD 1985)

* 2012 Ft.

M.

2011 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional** Average, Maximum and Minimum for period 1918-2011

1985

1985

1973 1973

1936

1934

1926 1934

LAKE ONTARIO

LAKE ERIE

LAKE ST. CLAIR

LEGEND

LAKE LEVELS

RECORDEDPROJECTEDAVERAGE **MAXIMUM **MINIMUM **

The levels on the hydrographs are shown inboth feet and meters above (+) or below (-) Chart Datum. Chart Datum, also known as Low Water Datum, is a reference plane on each lake to which water depth and Federal navigation improvement depths on navigation charts are referred.All elevations and plots shown in this bulletin are referenced to International Great Lakes Datum 1985 (IGLD 1985). IGLD 1985 has its zero base at Rimouski, Quebec near the mouth of the St. Lawrence River (approximate sea level).
 Information 

Recorded water levels in this bulletin are derived from a representative network of water level gages on each lake 

(see cover map). Providers of these data are the U.S. Department of Commerce, NOAA, National Ocean Service, 

and Integrated Science Data Management, Department of Fisheries and Oceans, Canada. The Detroit District, 

Corps of Engineers and Environment Canada derive historic and projected lake levels under the auspices of the 

Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data. 

This bulletin is produced monthly as a public service. Tables of possible storm-induced rises at key locations on 

the Great Lakes are available on request. The Corps also publishes the "Great Lakes, Connecting Channels and 

St. Lawrence River Water Levels and Depths,” weekly, which provides a forecast of depths in the connecting rivers 

between the Great Lakes and the International Section of the St. Lawrence River. This information is available on 

the internet at http://www.lre.usace.army.mil/glhh. 

Great Lakes Basin Hydrology

September 2012

Much of the Great Lakes basin continued to receive below average precipitation for the month of September. The 

Lake Superior basin received 46% of average precipitation, which was 1.9 inches less than it typically gets during 

the month. The Lake Michigan-Huron basin received 74% of average precipitation last month and 92% of average 

over the past 12 months. Lake Erie received 118% of average precipitation in September and slightly above 

average precipitation over the past 12 months. Lake Ontario saw 116% of average precipitation last month but 

has received below average precipitation over the past 12 months. Combined precipitation over the entire Great 

Lakes basin was below average last month and below average over the past 12 months. The provisional water 

supply for Lake Superior was the driest on record for September and it was the second driest on record for Lake 

Michigan-Huron for September. Lake Erie’s water supply was above average, but Lake Ontario was below 

average. The tables below list September precipitation and water supply information for all Great Lakes basins. 

A comparison of monthly mean lake levels for September to long-term average (1918-2011) shows Lakes Superior 

and Michigan-Huron were 13 and 26 inches below average, respectively. Lake St. Clair was 13 inches below 

average in September, and Lakes Erie and Ontario were 8 and 9 inches, respectively, below average. Boaters 

should be aware of hazards to navigation due to continued below average water levels on all lakes. 

 

PRECIPITATION (INCHES) 

BASIN 

September 12-Month Comparison 

2012 Average Diff. % of 

Average 

Last 12 

months 

Average Diff. % of 

(1900-2008) (1900-2008) Average 

Superior 1.62 3.52 -1.90 46 26.16 30.51 -4.35 86 

Michigan-Huron 2.55 3.45 -0.90 74 29.73 32.44 -2.71 92 

Erie 3.79 3.20 0.59 118 36.31 35.40 0.91 103 

Ontario 3.78 3.27 0.51 116 30.25 35.71 -5.46 85 

Great Lakes 2.61 3.41 -0.80 77 29.92 32.64 -2.72 92 

 

 LAKE September WATER SUPPLIES1

 (cfs) September OUTFLOW2 (cfs) 

2012 Average3

(1900-2008) 2012 Average3(1900-2008)

Superior -61,000 70,000 66,000 83,000 

Michigan-Huron -131,000 27,000 168,000 195,000 

Erie -13,000 -17,000 183,000 204,000 

Ontario 2,000 5,000 229,000 249,000 

Notes: Values (excluding averages) are based on preliminary computations; cfs denotes cubic feet per second. 1

 Water supply is the net result of precipitation falling on the lake, runoff from precipitation falling on the land which flows to 

the lake, and evaporation from the lake. Negative water supply denotes evaporation exceeded runoff and precipitation. 2

 Does not include diversions. 

3

 Lake Ontario average water supplies and average outflows are based on period of record 1900-2005