Volume 190: 2013 Annual Summary 

Background 

The U.S. Army Corps of Engineers (USACE) 

tracks and forecasts the water levels of each of 

the Great Lakes. This report is primarily focused 

on summarizing the hydrologic conditions of the 

Great Lakes basin in 2013. 

At the beginning of 2013 all of the Great Lakes 

water levels were well below their long-term 

averages following dry conditions during 2012. 

Lake Michigan-Huron’s January 2013 monthly 

mean water level set an all-time record low of 

576.02 ft. At the beginning of 2014, all of the 

Great Lakes are at a higher level than at the 

beginning of 2013. A summary of 2013 Great 

Lakes water levels is discussed below in the lakeby-lake sections. 

Official water levels are based on monthly lakewide means and the period of record used for 

each of the lakes includes the years 1918 to 2012. 

This data has been coordinated between the 

United States and Canada. All 2013 water levels 

will be officially coordinated and added to the 

historical record in the spring of 2014. The 

elevations used are referenced to the 1985 

International Great Lakes Datum. The water 

level of each lake is averaged from a network of 

individual gages around each lake. Also of note is 

that Lake Michigan and Lake Huron are 

hydraulically treated as one lake due to their 

connection at the Straits of Mackinac. 

The Great Lakes are very large and behave 

differently than smaller, inland lakes. In general, 

Great Lakes water levels do not rise and fall with 

individual storms, but rather significant water 

level fluctuations require multiple months, 

seasons, or years of wet or dry conditions. 

Seasonal changes in the weather patterns 

typically cause an annual pattern of rising and 

falling of Great Lakes water levels. Each of the 

Great Lakes typically exhibits a seasonal rise in 

the spring primarily caused by an increase in 

precipitation, the melting of accumulated snow, 

an increase in runoff, and low evaporation rates. 

The typical seasonal decline of the water levels in 

the fall and winter is primarily caused by an 

increase in evaporation, a decrease in 

precipitation, and the accumulation of snowpack 

on the land area. 

The Net Basin Supply (NBS) is an important 

quantity for understanding the amount of water 

which arrives to the lake. USACE uses the 

residual method to compute NBS, shown below: 

Residual Method Net Basin Supply: 

 NBS = WL – I – D + O 

 WL: Water Level Change 

 I: Connecting Channel Inflow 

 O: Connecting Channel Outflow 

 D: Diversion into(+) or out(-) of lake 

Altogether, NBS represents the combined effects 

of precipitation, runoff, and evaporation. NBS is 

far and away the main driver of water levels, and 

is also discussed in more detail in the following 

sections for each lake. 

Great Lakes

Update 
Vol. 190 Great Lakes Update February 2014 

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Figure 1: Lake Superior Water Levels 

Figure 2: Lake Superior Residual Net Basin Supply 

Lake Superior 

Figure 1 above shows the 2013 water levels of 

Lake Superior compared with the 2012 levels and 

the monthly long-term average (LTA) levels. A 

similar figure is shown for each lake in the 

following sections. Each lake’s data has been 

plotted relative to chart datum (a.k.a. low water 

datum), which represents the horizontal line at a 

value of zero. Chart datum for Lake Superior is 

601.1 ft. The solid line in Figure 1 represents the 

2013 water levels and the dotted line shows the 

2012 levels. The LTA levels for each month are 

shown by the solid circles. Lake Superior started 
Vol. 190 Great Lakes Update February 2014 

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off 2013 well below average and also below the 

January 2012 levels. 

However, from March’s monthly mean to 

September’s monthly mean, Lake Superior had a 

2013 seasonal rise of 23 inches, compared to an 

average seasonal rise of 12 inches. During that 

time period, Lake Superior moved from 13 inches 

below LTA to only 2 inches below LTA. For the 

time period from September through December, 

Lake Superior remained 2 inches below LTA. 

The January 2014 monthly mean water level was 

601.35 ft, which represents a year-to-year rise of 

12 inches and is only 1 inch below LTA. The 

large water level rise during 2013 was caused by 

wetter than average basin conditions. The total 

precipitation and total runoff for 2013 were both 

above average. As mentioned above in the 

Background section, the net basin supply (NBS) 

is an important quantity for explaining basin 

conditions. Figure 2 shows the Lake Superior 

NBS for each month in 2013 compared to both 

the 2012 NBS and the historical average NBS. A 

negative NBS is caused by the evaporation from 

the lake surface being greater than the combined 

precipitation on the lake and runoff flowing to the 

lake. Here in Figure 2, the NBS has been 

converted to an equivalent depth of water over 

the lake surface for each month. 

Lake Superior’s NBS was the second highest ever 

for the month of May in 2013. These extremely 

wet conditions can clearly be seen in the behavior 

of the 2013 water levels for Lake Superior 

through the month of May. Since May of 2013, 

the monthly NBS has consecutively been above 

average each month. 

Lake Michigan-Huron 

For Lake Michigan-Huron, the wet conditions in 

2013 essentially caused the water level to make 

up all of the ground lost from the historic dry 

conditions of 2012. The January 2013 Lake 

Michigan-Huron water level of 576.02 ft was 

lower than any other month in the entire period of 

record, dating back to 1918. The previous alltime record low was 576.05 ft, set in March 1964. 

The Michigan-Huron water level rose 15 inches 

from January 2013 to January 2014, as shown in 

Figure 3. Water levels in Figure 3 are relative to 

the Lake Michigan-Huron chart datum level of 

577.5 ft 

The 2013 seasonal rise for Michigan-Huron was 

20 inches from January through July, compared 

to an average seasonal rise of 11 inches. In the 

short period from March to May, Lake MichiganHuron’s monthly mean water levels moved 10 

inches closer to the 2012 levels and gained 5 

inches on the LTA. 

The seasonal decline from the fall of 2013 into 

the early part of 2014 has been much less than 

average. Michigan-Huron has fallen only 5 

inches from July 2013 to January 2014, compared 

to a typical fall of 11 inches during that time 

period. This can be seen in Figure 3 by the 

relatively low slope at the end of 2013 compared 

to the steep decline in the last half of 2012 and 

the typical decline of the LTA. Despite the 

significant rise in 2013 and the relatively smaller 

decline this winter thus far, Michigan-Huron was 

still 13 inches below its LTA in January 2014. 

Figure 4 shows the 2013 NBS for Lake 

Michigan-Huron compared to the 2012 NBS and 

the historical averages. The NBS was the second 

highest ever for the month of April in 2013. 

Basin conditions for the single month of April 

supplied the equivalent of 12 inches of water to 

the lake. This high NBS in April caused a steep 

rise of the water level, as can be seen in Figure 3. 

Total precipitation over the lake and total runoff 

flowing to the lake were both above average in 

2013 for Michigan-Huron. The NBS was above 

the historical average for 9 out of 12 months in 

2013 and above the 2012 NBS for 10 out of 12 

months.
Vol. 190 Great Lakes Update February 2014 

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Figure 3: Lake Michigan-Huron Water Levels 

Figure 4: Lake Michigan-Huron Residual Net Basin Supply 

Lake St. Clair 

As seen in Figure 5 below, the Lake St. Clair 

water levels have a tendency to exhibit more 

short-term fluctuation than lakes Superior, 

Michigan-Huron, Erie, or Ontario because of the 

smaller size of Lake St. Clair. The smaller size 

causes the connecting channels (the St. Clair 

River upstream and the Detroit River 

downstream) to have a large influence on the 

Lake St. Clair water levels. Wind, ice, and other 

climate variations can cause fluctuations in the 

hydraulic behavior through the St. Clair River, 

Lake St. Clair, and Detroit River system. 
Vol. 190 Great Lakes Update February 2014 

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Figure 5: Lake St. Clair Water Levels 

The Lake St. Clair water level is starting 2014 

much higher than 2013 due to the 7 inch rise from 

January 2013 to January 2014. As seen by 

Figure 5, Lake St. Clair did not exhibit a seasonal 

rise at all in 2012. The 2013 water level gained 

rapidly on the 2012 levels in the first half of the 

year and rose above the 2012 levels in June. The 

steep rise in June was caused by the highest NBS 

on record for Lake St. Clair for the month of 

June. Monthly means since July 2013 have 

remained above 2012 levels and between 3 and 6 

inches below LTA. 

Lake Erie 

The water level behavior of 2012 was unlike any 

other year in the period of record for Lake Erie, 

because it exhibited no seasonal rise. Figure 6 

shows the Lake Erie water levels relative to the 

Lake Erie chart datum of 569.2 ft. The water 

level plummeted 22 inches from January 2012 to 

January 2013 due to extremely dry conditions 

during the year of 2012. During the first six 

months of the year, the 2013 levels gained ground 

and rose above the 2012 levels in June. 

From May through July the Lake Erie water level 

rose significantly. The monthly mean in May 

2013 was 8 inches below LTA and July’s 

monthly mean was 2 inches above LTA. The 

explanation for this large rise relative to LTA can 

be seen by the high NBS shown in Figure 7 for 

the months of June and July. The June 2013 NBS 

was the highest ever recorded for Lake Erie for 

the month of June. The amount of precipitation 

received by the Lake Erie basin in June 2013 was 

144% of the average precipitation for June. Lake 

Erie also had much larger than average NBS in 

the months of February, April, July, and 

December in 2013. Since July 2013, the Lake 

Erie monthly mean water levels have remained 

within 2 inches of LTA. 
Vol. 190 Great Lakes Update February 2014 

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Figure 6: Lake Erie Water Levels 

Figure 7: Lake Erie Residual Net Basin Supply 

Lake Ontario 

Lake Ontario water levels also rose during the 

course of 2013, as shown in Figure 8. From the 

monthly mean of January 2013 to January 2014, 

the water level rose 10 inches. Lake Ontario 

started 2013 below LTA and then rose above 

LTA in June. Since June 2013, the Lake Ontario 

monthly mean water levels have remained 0 to 6 

inches above LTA. 

Figure 9 shows the Lake Ontario NBS for 2013 in 

comparison to the 2012 NBS and the historical 

averages. The month which stands out the most 
Vol. 190 Great Lakes Update February 2014 

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is June. Lake Ontario received the fourth highest 

NBS on record for the month of June in 2013. 

During the month of June 2013, precipitation was 

152% of the average for the month. During that 

same month, the water levels climbed well above 

LTA. Overall, the Ontario NBS has been near or 

above average for 9 out of 12 months of 2013. 

Figure 8: Lake Ontario Water Levels 

Figure 9: Lake Ontario Residual Net Basin Supply 
Vol. 190 Great Lakes Update February 2014 

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Great Lakes Physical Characteristics 

The physical characteristics of the Great Lakes 

(Superior, Michigan, Huron, Erie, and Ontario) 

are enormous. The total surface area of the Great 

Lakes is over 94,000 square miles (244,000 

square kilometers) and the total volume is over 

5,400 cubic miles (22,700 cubic kilometers). 

Figures 10 and 11 show the water surface area 

and volume comparisons among the Great Lakes. 

Figure 10: Great Lakes Water Surface Areas 

Figure 11: Great Lakes Water Volumes 

More Information 

Update articles are included in the February and 

August Monthly Bulletins highlighting topics and 

explanations relevant to Great Lakes water levels. 

February’s Monthly Bulletin will typically include 

an annual summary from the year before and each 

August Monthly Bulletin will typically include a 

summary of the first six months of the year. 

The Monthly Bulletin is sent by postal mail. To 

receive it by email, please send an email to 

hhpm@usace.army.mil or call 1-888-694-8313 

and select option 1. Alternatively, the Monthly 

Bulletin can be viewed on our website. the home 

page is: http://www.lre.usace.army.mil. In 

addition to the Monthly Bulletin, the Detroit 

District issues the Weekly Great Lakes Water 

Level Update and the Weekly Great Lakes 

Connecting Channels Water Levels and Depths. 

Both products are updated each Thursday and can 

be located here: 

http://www.lre.usace.army.mil/Missions/GreatLakesInform

ation/GreatLakesWaterLevels/WaterLevelForecast.aspx

The Detroit District also has a Facebook page 

which can be found here: 

https://www.facebook.com/pages/Detroit-District-USArmy-Corps-of-Engineers/144354390916

The Detroit District welcomes comments on all of 

our forecast products. Please email questions and 

comments to hhpm@usace.army.mil. To contact 

the District by phone call toll free 1-888-694- 

8313 and select option 1. To receive the Monthly 

Bulletin by postal mail, please email us or call us 

with the contact information just mentioned. The 

Detroit District’s mailing address is: 

Department of the Army 

Detroit District Corps of Engineers 

ATTN: CELRE-HH-W 

477 Michigan Avenue 

Detroit, MI 48226