Volume 202: 2018 Annual Summary

Background

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

monitors 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 2018.

Lakes Superior, Michigan-Huron, St. Clair, and 

Erie remained above their average water levels in 

2018, and all have been above average their 

monthly average levels since at least November 

2015. Lake Ontario was above its monthly average 

levels in 2018 except for the three-month stretch of 

August to October when it approximated its

monthly average. 

Figure 1: Plots showing above average water 

levels on the 4 upper lakes since 2015 (2018 

water levels are provisional)

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 2017. These 

data have been coordinated between the United 

States and Canada. All 2018 water levels will be 

officially coordinated and added to the historical 

record in the spring of 2018. The elevations used 

are referenced to the International Great Lakes 

Datum of 1985. The water level of each lake is 

Great Lakes

Update
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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 from smaller, inland lakes. In general, 

Great Lakes water levels do not rise and fall with 

individual storms. Significant water level 

fluctuations require multiple months, seasons, or 

years of wet or dry conditions.

Seasonal changes in 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 liquid 

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 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 in 

the summarizing equations: 

WL: Water Level Change

 I: Connecting Channel Inflow

 O: Connecting Channel Outflow

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

 P: Precipitation falling on lake

 R: Runoff draining to lake

 E: Evaporation from lake surface

Water balance for each lake:

WL = I + D + P + R – E – O

Residual Method Net Basin Supply:

NBS = WL – I – D + O

Altogether, NBS represents the combined effects 

of precipitation over the lake, runoff to the lake, 

and evaporation off of the lake. NBS is the main 

driver of water levels, and is also discussed in more 

detail in the following sections for each lake.

Lake Superior

Figure 2: Lake Superior Water Levels

Figure 3: Lake Superior Residual Net Basin 

Supply, deviation from Long-Term Average

Figure 2 shows the 2018 water levels of Lake 

Superior compared with the 2017 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 value at zero. Chart 

datum for Lake Superior is 601.1 feet. The solid

blue line in Figure 2 represents the daily 2018 
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water levels and the solid gray line shows the 2017 

levels. The LTA levels for each month are shown 

by the circles. Figure 3 shows monthly residual 

NBS, and the NBS shown is relative to the 

monthly LTA NBS. 

In January and February 2018, Lake Superior was 

just two inches below its recorded high level for 

those two months. Lake Superior started the year 

seven inches above its 2017 water levels, but by 

May was two inches below its 2017 level. The net 

basin supply to the lake was substantially below 

average in March and April, as the lake only 

received about 35% of the precipitation it usually 

receives in those 2 months and runoff in April 

2018 was only half its April average. The NBS 

continued to be slightly below average in May and 

June, and Lake Superior remained 4 to 5 inches 

below 2017 levels from June to September. 

Lake Superior’s seasonal rise of 11 inches took 

place from April to October, when it reached its 

peak monthly average level of 602.92 feet. This 

rise was less than the 17 inch-rise in 2017, but 

nearly equal to the lake’s historical average 

seasonal rise of 12 inches. In addition, it’s typical 

from September to October for Lake Superior to 

begin its seasonal decline, but in 2018, the lake 

rose 3 inches in October. The lake received nearly 

150% of its average precipitation in October, 

leading to an NBS that was over 4 times its average 

October NBS. The period of higher than average 

NBS between September and November resulted 

in Lake Superior levels being just 1 to 3 inches 

below its 2017 Levels in October, November, and 

December. Lastly, 2018 was a particularly dry year

overall in the Lake Superior basin, as the lake only 

received 88% of its annual average precipitation.

By the end of 2018, Lake Superior had been above 

its monthly LTA levels every month since May 

2014, a period of 56 months. The lake has not 

experienced such a prolonged stretch of above 

average levels since the mid-1980s. Over the final 

3 months of 2018, Lake Superior monthly average 

levels were 10 to 11 inches above LTA and five to 

six inches below its monthly record high water 

levels

Lake Michigan-Huron

Lake Michigan-Huron’s level was 15 to 20 inches 

above its monthly LTA for every month in 2018. 

The lake’s 2018 levels are shown in Figure 4.

Figure 5 shows monthly residual net basin supply 

relative to its monthly LTA NBS. The water level 

of Lake Michigan-Huron has been above average 

every month since November 2014, a streak of 50 

consecutive months. For the first two months of 

2018, the lake was about 10 inches above its 2017 

levels, catapulted by above average net basin 

supply. Its mean monthly level in February of 

579.86 feet was its highest level in February since 

1997.

By July 2018, however, the lake’s level was at its 

2017 level, and was two inches below its August 

2017 level the following month. This relative 

decline can be attributed to the lake’s lackluster 

seasonal rise of 10 inches. Lake Michigan-Huron 

began its seasonal rise in January, one month 

earlier than it typically does, but its 2018 seasonal 

rise was less than half of its 2017 seasonal rise of 

21 inches, and was even below its historical 

average seasonal rise of 12 inches.

The lake hovered around its 2017 levels in the 

remaining 5 months of the year. Figure 5 illustrates 

there was no discernible monthly or seasonal 

pattern in the Lake Michigan-Huron’s monthly 

NBS during 2018. The lake’s NBS was 

substantially above normal in five months in 2018, 

while it was considerably below average in only 

two months last year. The water supplies to the 

lake were well above average in December 2018, 

leading to a water level of 580.15 feet. This was 

the highest December water level since the record 
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high December level in 1986, and the lake’s 

seventh highest recorded December water level.

Figure 4: Lake Michigan-Huron Water Levels

Figure 5: Lake Michigan-Huron Residual Net 

Basin Supply, difference from Long-Term 

Average

Lake St. Clair

Figure 6 shows the water levels of Lake St. Clair 

in 2018 compared to 2017 and the LTA levels. 

Lake St. Clair has been above its monthly LTA 

every month since March of 2015. Its peak level 

in 2018 of 576.51 feet, achieved in June, was its 

highest level since August of 1997. In May, the 

lake was within 6 inches of its maximum recorded 

May level.

For the first half of 2018, the level of Lake St. Clair 

was above the previous year’s levels. In July and 

August, 2018 levels approximated their levels of a 

year ago, while in the remaining four months, the 

level of Lake St. Clair ranged from two to four

inches above 2017 levels. Lake St. Clair’s seasonal 

rise in 2018 began in January, and lasted until 

June. It typically starts its seasonal rise in 

February. Lake St. Clair’s 2018 rise was 19 inches, 

higher than the previous year’s rise of 17 inches, 

and higher than its historical average rise of 16 

inches. 

The lake’s above average rise was buoyed by 

above average NBS in March, April, and June. Net 

basin supplies to Lake St. Clair were greatly above 

average in September, October, and November, 

leading to a flatter seasonal decline in the fall than 

average. The lake’s average decline from 

September to December is nine inches, but in 2018 

it only fell six inches.

Figure 6: Lake St. Clair Water Levels

Figure 7: Lake St. Clair Net Basin Supplies
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Lake Erie

2018 was another year of continued high water 

levels on Lake Erie, as displayed in Figure 8. The 

lake’s level has been above its monthly LTA since 

June 2015, a period of 43 consecutive months. The 

lake’s monthly mean level in June, 573.79 feet, 

was the highest level Lake Erie has achieved since 

July of 1997. In January, Lake Erie was 15 inches 

above its LTA level, and remained 18 to 24 inches 

above LTA for the rest of 2018.

The level of Lake Erie in 2018 was above the prior 

year’s level during the first 6 months of 2018. In 

July and August, the lake’s level was nearly equal 

to its 2017 level, but in the last 4 months of the 

year, it was three to six inches above 2017 levels.

The seasonal rise on Lake Erie in 2018 was 20 

inches, less than the lake’s previous 26-inch 

seasonal rise from December 2016 to June 2017, 

but notably larger than Lake Erie’s average water 

level climb of 14 inches. 2018’s robust seasonal 

rise can be attributed to the significant climb 

during February. The lake’s mean monthly level 

rose 9.5 inches from February to March. The 

lake’s February net basin supply was more than 2.5 

times its average February NBS, as precipitation 

received by the lake was over 50 percent above 

average. Runoff was also above average that 

month. 

Net basin supplies to Lake Erie were above 

average in 4 of the first 5 months of the year, but 

after that early part of the year, Lake Erie NBS was 

only above average in October and November. The 

lake’s monthly NBS in 2018 is shown in Figure 9. 

Concerning annual precipitation, Lake Erie’s 2018 

precipitation was slightly above average, by about 

0.5 inches. It was the only Great Lake to 

experience above average precipitation in 2018.

Figure 8: Lake Erie Water Levels

Figure 9: Lake Erie Residual Net Basin 

Supply, deviation from Long-Term Average

Lake Ontario

Figure 10 shows Lake Ontario water levels relative 

to the chart datum of 243.3 feet. The lake began 

2018 eight inches above its January 2017 level. 

The lake’s seasonal rise in 2018, including its 

ascent in December 2017, was 19 inches, 

considerably higher than Lake Ontario’s average 

seasonal rise of 14 inches. The lake’s Net Basin 

Supply, shown in Figure 11, was above average in 

four of the first five months of the year. In fact, 

March was the only month NBS to the lake was 

below average in 2018. Similar to 2017, the lake’s 

level peaked in May, although it typically peaks in 

June.
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However, in 2018, the lake did not come close to 

approaching its record-high 2017 water level 

climb of 53 inches, a historic rise which 

culminated in the setting of new record-high 

monthly levels for May, June, and July. After the 

record-high water level climb, the lake 

experienced a steep 43-inch decline in mid-to-late 

2017. This steep decline combined with the much 

lower seasonal rise in 2018 resulted in Lake 

Ontario being below its 2017 level by March 2018. 

It remained below 2017 levels for the rest of 2018. 

In fact, in the aforementioned three months in 

which record-high levels were set in 2017, the 

lake’s 2018 levels were 21, 23, and 24 inches, 

respectively, lower than they were the year before. 

Entering 2018, like the other Great Lakes, Lake 

Ontario’s monthly levels had been above average 

in every month since at least late 2015. The 2018 

seasonal decline of Lake Ontario, between May 

and October, was 23 inches, so Lake Ontario fell 

more than it rose in 2018. Although Lake Ontario 

was 11 inches above LTA in January, the lake’s 

net decline in 2018 led to the lake matching its 

monthly LTA in August, September, and October 

of 2018.

Figure 10: Lake Ontario Water Levels

Figure 11: Lake Ontario Residual Net Basin 

Supply, deviation from Long-Term Average

New Soo Lock Updated Authorization by 

Federal Government

2018 proved to be a pivotal year in the Detroit 

District’s decades-long effort to build a crucial 

new lock at its Soo Locks complex. The Soo Locks 

are a set of locks, situated on the St. Mary’s River 

at Sault Ste. Marie, Michigan that allow vessels to 

transit the 21 foot elevation change between Lake 

Superior and Lake Michigan-Huron. These locks 

are operated and maintained by the U.S. Army 

Corps of Engineers, Detroit District. The locks are 

an invaluable link in the Great Lakes/St. Lawrence 

Seaway navigation system, which supports a 

shipping industry that generates $18.1 billion in 

business revenue and nearly 130,000 jobs in the 

United States.

Only one of the locks, the Poe Lock, can handle 

the largest vessels that haul invaluable materials,

such as the iron ore, from which is produced the

high-strength steel used in the manufacture of 

automobiles and appliances. In 2017, 89% of the 

total tonnage that transited the Soo Locks Complex

was restricted to the Poe Lock due to vessel size. 

Prolonged interruption in operations of the Poe 

Lock could have a devastating impact on the 

economy and even national security of the United 

States, which underscores the importance for 

constructing a New Soo Lock with the same 

dimensions as the Poe Lock.
Vol. 202 Great Lakes Update February 2019

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In 1986, Congress authorized construction of a 

new Poe-sized lock that would be built on the site 

of the current 100-plus-year-old Sabin and Davis 

Locks. However, construction was not initiated 

until 2009 when funds were provided to construct

coffer dams at the ends of the Sabin Lock and 

deepen the downstream approach channel.

Figure 12: Current Soo Locks with inactive 

Davis and Sabin Locks on the left

Figure 13: Conceptual Rendering of New Soo

Lock replacing Davis and Sabin Locks

2018 seemed to be a turning point for the New 

Soo Lock’s construction:

• In June 2018, the Detroit District released an 

economic study that estimated a new lock 

would yield annual benefits of $77.3 million 

and a benefit-cost ratio of 2.42. The report 

also provided an updated cost estimate for the 

new lock - $922.4 million. 

• In October 2018 the President signed into law 

"America's Water Infrastructure Act of 2018," 

which authorized construction of the New 

Soo Lock at the current cost estimate of 

$922.4 million.

• In November 2018, funding in the amount of 

$32,388,000 was appropriated for the New 

Soo Lock in the fiscal year 2019 Work Plan. 

These funds were provided to completion the

design and initiate construction of the 

deepening of the upstream approach channel. 

• In December 2018, the State of Michigan and 

the U.S. Army Corps of Engineers, Detroit 

District, signed a memorandum of agreement 

allowing for the State of Michigan's 

contribution of $52 million for the New Soo 

Lock at the Soo Locks facility.

The State of Michigan’s contribution will allow for 

construction of the entire Upstream Channel 

Deepening as well as design of the Upstream 

Approach Walls and partial design of the New 

Lock Chamber. It is estimated that Michigan's 

contribution, combined with the Corps' $32 

million, will accelerate the total project's 

completion by one shipping season.

Award of a contract to begin upstream channel 

deepening is expected in the summer of 2019. 

With continued efficient funding, the next steps in 

the construction of the New Soo Lock, include:

• Complete construction of the Upstream 

Channel Deepening

• Complete design and award construction 

contract for the Upstream Approach Walls

• Continue design efforts on the New Soo Lock 

Chamber
Vol. 202 Great Lakes Update February 2019

Page 8

With efficient funding, construction of the New 

Soo Lock would be complete within 7 to 10 years 

of the start of construction. 

Learn more about the New Soo Lock project here:

https://www.lre.usace.army.mil/About/Highlighte

d-Projects/New_Soo_Lock/

More Information

Update articles are included periodically in the 

Monthly Bulletins highlighting topics and 

explanations relevant to Great Lakes water levels. 

February’s Monthly Bulletin typically includes an 

annual summary from the year before. Subsequent 

articles published this year will cover various 

topics of interest concerning the Great Lakes.

Nearly all past Update Articles dating back to 1985 

can be accessed here:

https://www.lre.usace.army.mil/Missions/Great-LakesInformation/News-and-Information/Great-Lakes-UpdateArticles/

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. Additionally, a one 

year Great Lakes Water Level Outlook is produced 

once every three months. All forecast products are 

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/USACEDetroitDistrict/

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-EHW

477 Michigan Avenue

Detroit, MI 48226