Volume 194: 2015 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 summarizes the 

hydrologic conditions of the Great Lakes basin in 

2015. 

Great Lakes water levels generally remained 

above average in 2015. The Great Lakes, 

particularly Lakes Superior and Michigan-Huron, 

surged upward in 2013 and 2014, following a 

prolonged period of below average water levels 

that culminated in record and near record low 

levels in 2012 and January 2013. The levels of 

Lakes Superior and Michigan-Huron surpassed 

long term average water levels in 2014, and 

remained above average throughout all of 2015. A 

summary of 2015 Great Lakes water levels is 

discussed below in the lake-by-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 2015. These 

data have been coordinated between the United 

States and Canada through 2014. All 2015 water 

levels will be officially coordinated and added to 

the historical record in the spring of 2016. 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 large and behave differently 

from smaller, inland lakes. In general, Great Lakes 

water levels do not rise and fall dramatically with 

individual storms, but rather significant water level 

fluctuations require multiple months, seasons, or 

years of wet or dry conditions. 

Each year, the Great Lakes experience a seasonal 

rise and a seasonal decline due to changes in 

weather patterns. The seasonal rise, typically 

starting in the spring, is caused primarily by an 

increase in precipitation, increased runoff due to 

melting of accumulated snow, 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 term net basin supply (NBS) is used to 

describe the amount of water that is contributed to 

or lost from a lake within the confines of its natural 

drainage basin. 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 

Net basin supply includes water a lake receives 

from precipitation on its surface and runoff from 

land making up its drainage basin, less the 

Great Lakes

Update 
Vol. 194 Great Lakes Update February 2015 

Page 2 	 	

evaporation of water from the lake’s surface. The 

higher the quantity of precipitation and runoff, the 

higher the NBS will be. Conversely, the higher the 

quantity of evaporation, the lower the NBS will be. 

NBS is far and away the main driver of water 

levels, and is discussed in more detail in the 

following sections. 

Figure 1: Lake Superior Water Levels 

Figure 2: Lake Superior 

Residual Net Basin Supply 

Lake Superior 

Figure 1 shows the 2015 water levels of Lake 

Superior compared with the 2012 through 2014 

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. 

Lake Superior water levels remained above 

average for all of 2015. Lake Superior started the 

year at a level of 602.17 ft, 10 inches higher than 

at the beginning of 2014, 9 inches above its Long 

Term Average (LTA) in January, and 21 inches 

higher than January 2012. At the end of 2015, the 

lake was less than an inch below its level in 

December 2014, but still 10 inches above LTA. 

The lake’s seasonal climb of 11 inches in 2015 was 

near its historical average. However, this seasonal 

rise was small in comparison to the previous year’s 

rise of 23 inches, and Lake Superior did not reach 

its 2014 peak level. Nevertheless, the net basin 

supply to the lake in December 2015 was 

historically high and caused the level of the lake to 

rise from November to December for only the 3rd

time since 1918. This small rise nearly brought the 

lake to its December 2014 level. 

Figure 2 shows the Lake Superior NBS for each 

month in 2015 compared to the average of the 

monthly 2013 and 2014 NBS and the historical 

average NBS. Precipitation that fell within the 

lake’s basin was near average in 2015, with only 3 

months of above average precipitation. 

December saw particularly high precipitation at 

42% above average. The NBS to the lake was the 

highest NBS ever recorded for December dating to 

1918. December was also warmer than average, 

which allowed most of the precipitation to fall as 

rain rather than snow, which increased runoff. 

Moreover evaporation in late fall and early winter 

was 38% below average. This is because the 

temperature difference between the air and lake 

surface was less than normal due to the above 

average air temperatures. 
Vol. 194 Great Lakes Update February 2015 

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Lake Michigan-Huron 

Following record low water levels in late 2012 and 

January 2013, Lake Michigan-Huron’s level 

soared in 2013 and 2014, reaching its long term 

average in September 2014 for the first time since 

1998. Lake Michigan-Huron’s rises during 2013 

and 2014 led to levels being more than 3 feet 

higher in January 2015 than January 2013. Levels 

were also 7 inches above average in January 2015. 

Water levels in Figure 3 are relative to the Lake 

Michigan-Huron chart datum level of 577.5 ft. 

Lake Michigan-Huron declined just 2 inches in the 

winter of 2014/2015; the average fall is 11 inches. 

Because of the substantial rise in 2014 and the 

small seasonal decline in fall/winter 2014-2015, 

Lake Michigan-Huron’s level in March 2015 was 

21 inches higher than it was 12 months before. The 

lake peaked at 579.79 ft. in July, its highest level 

since August 1998. 

Lake Michigan-Huron’s seasonal rise in 2015 was 

only 8 inches, or 3 inches lower than average. The 

lake’s seasonal decline in 2015 began in July, and 

by November it had declined 7 inches. October’s 

net basin supply was particularly low due to 

extremely low precipitation. The smaller-thanaverage seasonal rise coupled with a July-toNovember decline of 7 inches resulted in the lake 

falling to its 2014 level in November. However, 

the lake level experienced a slight increase from 

November to December, only the 12th time that has 

happened since 1918. This small increase was the 

result of the highest net basin supply that the lake 

has received in December dating back to 1918. 

Figure 4 shows the 2015 NBS for Lake MichiganHuron compared to the average of the 2013 and 

2014 NBS and the historical averages. The Net 

Basin Supply to Lake Michigan-Huron was below 

average 5 of the first 7 months of 2015, but was 

above average in 4 of the last 5 months of 2015. 

Above average NBS in September, November, and 

December corresponded with below average 

evaporation. Just as with Lake Superior, the 

December 2015 NBS was a record high. 

Precipitation was 66% above average that month. 

Total precipitation to the lake was 91% of average 

in 2015. 

Figure 3: Lake Michigan-Huron Water Levels 

Figure 4: Lake Michigan-Huron 

Residual Net Basin Supply 

Lake St. Clair 

Heart-shaped and shallow Lake St. Clair is the 

smallest lake in the Great Lakes system. As seen 

in Figure 5, Lake St. Clair water levels exhibit 

more short-term fluctuations than lakes Superior, 

Michigan-Huron, Erie, or Ontario because of its 

smaller size. Because of the smaller size, the 

connecting channels (the St. Clair River upstream 
Vol. 194 Great Lakes Update February 2015 

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and the Detroit River downstream) 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. A representative example of the 

significant impact the connecting channels and ice 

have on the lake’s level is the sharp 8-inch decline 

in water level that occurred from January to 

February 2015. Ice build-up reduced flow in the 

St. Clair River, which decreased the amount of 

water discharging into Lake St. Clair. Ice 

formation began affecting the St. Clair River flow 

around January 7th. Photo 1 shows significant ice 

in the St. Clair River in January 2015. 

Daily St. Clair River flow from January 1 to 

January 7 averaged 203,299 cfs, and the daily flow 

from January 8th to January 31st averaged 143,920 

cfs, indicating a reduced amount of water 

discharging into the lake. 

Photo 1: Ice on the St. Clair River at Marine City, 

MI on 25-January-2015 

In 2015, with the exception of February, the level 

of Lake St. Clair was above average. In January 

2015, Lake St. Clair was 11 inches above its 

January 2014 monthly mean level and 5 inches 

above LTA. By year’s end, the lake was still above 

LTA by 9 inches but had dropped slightly below 

its December 2014 level. The lakes’ 2015 seasonal 

rise of 32 inches was 6 inches was higher than its 

2014 rise. The 2015 seasonal rise was buoyed by 

precipitation in June that was over 50% above 

average. Lake St. Clair peaked in July at 575.98 ft., 

its highest level since June 1998. A quicker than 

average decline occurred during the fall of 2015 

due to dry conditions, especially in October. 

Figure 5: Lake St. Clair Water Levels 

Lake Erie 

In 2015, Lake Erie’s water level was above LTA 

in 11 of 12 months. Lake Erie began 2015 by 

dropping a total of 6 inches in January and 

February, a time period in which the lake 

historically rises an average of 3 inches. Below 

average precipitation and above average 

evaporation driven by extreme cold in January and 

February contributed to the water level decline. In 

addition, the ice formation that clogged the St. 

Clair River and reduced the inflow into Lake St. 

Clair in January and February also reduced inflow 

to Lake Erie and contributed to lower its level. The 

US Geological Service’s gage on the Detroit River 

at Fort Wayne showed the average discharge in the 

river was 205,667 cfs in December, while the 

average discharge in January was 145,229 cfs and 

134,536 cfs in February. 
Vol. 194 Great Lakes Update February 2015 

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Figure 6 shows Lake Erie water levels relative to 

the chart datum of 569.2 ft. The lake’s level 

climbed 30 inches from March to July, more than 

double the lake’s average seasonal rise of 14 

inches. This was the lake’s largest seasonal rise 

since 1947 when it rose 33 inches. The lake’s July 

monthly mean level of 573.29 ft. was its highest 

since June 1998. In June, the lake was about 24 

inches higher than it was in July 2012. Lake Erie’s 

monthly mean level rose the highest, 8 inches, 

from June to July, a time period when it usually 

begins declining. This large rise was due to the 

record rainfall in June 2015. By December 2015, 

water levels had fallen to those of the previous 

December, but remained 7 inches above LTA. 

Precipitation within the Lake Erie basin was 94% 

of average in 2015. On a monthly basis, 

precipitation was below average in 9 months in 

2015. A notable exception to the below average 

precipitation in 2015 was June when Lake Erie 

received 6.75 inches of rain. This rainfall was the 

highest recorded amount of precipitation that the 

lake has received in June. The 6.75 inches was 

almost double its June average. In addition, this 

rainfall had a significant impact on the total 

amount of precipitation that Lake Erie received in 

2015. If the lake had received just an average 

amount of rainfall in June, about 3.5 inches, than 

the total precipitation to the lake in 2015 would 

have been just 84% of average. 

Corresponding with the fall in water level in 

January and February, Lake Erie NBS was below 

average the first 3 months of the year. However, 

the lake’s 30 inch seasonal rise was fed by above 

average NBS from April to July. Due to the record 

rainfall in June, NBS to Lake Erie was the highest 

on record for the lake in the month of June dating 

back to 1900. 

Figure 6 Lake Erie Water Levels 

Figure 7: Lake Erie Residual Net Basin Supply 

Lake Ontario

In December 2014, Lake Ontario was 2 inches 

below LTA. Similar to Lake Erie, Lake Ontario’s 

monthly level fell 6 inches in January and 

February. Precipitation in January and February 

was well below average. This contributed to the 

lake’s water level being below average the first 6 

months of the year. Figure 8 shows Lake Ontario 

water levels relative to the chart datum of 243.3 ft. 

The lake was more than 10 inches below average 

by March. Lake Ontario’s seasonal rise began in 

March and was 31 inches high, 8 inches higher 

than its average seasonal rise. A catalyst of the 

lake’s above average rise was the nearly 6 inches 

of rain the lake received in June. The lake’s level 

climbed to 8 inches higher than LTA in July and 
Vol. 194 Great Lakes Update February 2015 

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remained above average until December, when it 

nearly matched its December 2014 level. The 

lake’s peak level of 246.75 ft. in July was its 

highest level since June 2011. 

Figure 9 shows the average of the 2013 and 2014 

NBS and LTA NBS for Lake Ontario. Similar to 

Lake Erie, Lake Ontario experienced below 

average NBS the first 3 months of the year. The 

low NBS in January and February was the result of 

below average precipitation and above average 

evaporation. Fueled by precipitation that was 79% 

above average in June, the NBS to Lake Ontario 

was its highest in June since 1947 and the 3rd

highest since 1900 according to USACE 

calculations. Despite the considerable rainfall in 

June, precipitation was below average for 8 

months of 2015, and the total rainfall to the lake’s 

basin in 2015 was 11% below average. In 

addition, evaporation was below average the first 

2 months of 2015, but at or above average in 9 of 

the final 10 months of the year. 

Figure 8: Lake Ontario Water Levels 

Figure 9: Lake Ontario Residual 

Net Basin Supply 

Coastal erosion 

With the recent rise in water levels, coastal bluffs 

are beginning to erode again after over a decade of 

low water and apparent stability. It is important, 

however, to understand that lake levels do not 

cause erosion – waves cause erosion. The lake 

level merely concentrates the wave energy onto a 

particular section of the coastal profile. During the 

last decade plus of low water, the offshore portion 

of the coastal profile has been quietly eroding. 

This is of little immediate concern since little to 

none of society’s infrastructure is on the lake bed. 

However, with the recent rise in lake levels, the 

waves now have access to the bluffs and dunes, 

which host much infrastructure. Increased erosion 

has been observed over the last two years on the 

Great Lakes. Photo 2 shows an example of coastal 

erosion on Lake Superior. 
Vol. 194 Great Lakes Update February 2015 

Page 7 	 	

Photo 2: Coastal Erosion on 

Lake Superior at Paradise, MI 

The extent of coastal erosion in the Great Lakes is 

a delicate balance between the supply of sand to 

the beaches and the rate at which waves carry it 

away. There is currently no evidence that the wave 

climate has changed, yet erosion seems to be 

increasing. The sand supply to the beaches, 

however, has been steadily reduced over the last 

few decades due to the proliferation of coastal 

shore protection. A study is currently underway to 

assess the effects of the reduced sand supply and 

mitigation options. Expect a report highlighting 

findings of this study is to be complete later in 

2016, but it is hoped that data collection and 

analysis will continue for the foreseeable future. 

More Information 

Starting in 2016, Update Articles will be included 

in various editions of the Monthly Bulletin. Topics 

will rotate between Great Lakes hydrology and 

lake levels and other less technical pieces relevant 

to the Great Lakes as a whole. February’s Monthly 

Bulletin will typically include an annual summary 

from the year before. 

The next Update Article will likely be in June and 

will cover a unique group of Federal agencies from 

both the United States and Canada. This group, 

called the Coordinating Committee on Basic Great 

Lakes Hydraulic and Hydrology Data meets twice 

per year and will have just celebrated its 100th

meeting in May. All of our past Update Articles 

can be read online here: 

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

ation/NewsandInformation/GreatLakesUpdateArticles.aspx

Some of the past topics include: 

Water level forecasting techniques 

A Guide to the Monthly Bulletin 

Frequently Asked Questions 

Winter Work at the Soo Locks 

100th Anniversary of the Boundary Waters Treaty 
Vol. 194 Great Lakes Update February 2015 

Page 8 	 	

The Monthly Bulletin is sent by postal mail. To be 

added to the postal mailing list, 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 

A new product developed and issued by the 

USACE this year is the Great Lakes Water Level 

Outlook. It is a longer term look at potential water 

levels based on specific NBS scenarios. These 

scenarios are developed using climate projections 

and current conditions in the Great Lakes basin. 

The outlook can be found here: 

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

ation/GreatLakesWaterLevels/WaterLevelForecast/WaterL

evelOutlook.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 District plans on posting water level and other 

relevant Great Lakes information on a more 

frequent basis in 2016, so please like us on 

Facebook to keep current on the ups and downs of 

Great Lakes water levels and other Great Lakes 

gee-whiz items. 

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. 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