Low Water Levels Expected to Continue

Water levels on all of the Great Lakes except Ontario will remain below average this summer and will probably peak lower than last summer, according to the latest forecast from the U.S. Army Corps of Engineers (USACE). 

The USACE estimates that levels on Lakes Michigan and Huron (which are always equal) will be one to two feet lower than the average over the last 80 years, but about 2 to 10 inches above the record lows set in the mid-1960s (see 2000-2001 graph).

Continued low water on the western Great Lakes is creating a need for repairs of federal harbor structures and dredging that will cost more than the available funds in the USACE budget, according to UW Sea Grant Coastal Engineer Philip Keillor.

Old timber supports of some breakwaters and piers are now subject to ice damage and, because they are exposed to air, to rotting, Corps staff said.  Wisconsin has at least 13 harbors with sections of federal breakwaters supported by timber pilings and cribs that are now partly exposed in the fall, winter, and spring.

The lake level declines of the past few years are due mainly to greater-than-average evaporation and less-than-average snowfall, Keillor said.  Evaporation increases as the air cools below the water temperature. The lakes have warmed to higher-than-average temperatures in recent years, resulting in greater evaporation when cold, dry winds blow across the lakes in the fall. The warmer waters have also inhibited ice formation, further increasing evaporation in the winter.

During the last three years of declining water levels, precipitation has actually been near average, Keillor said. In April of this year, the Lake Superior basin received record high precipitation for the month, according to the USACE. Combined with melting snows, the rainfall provided the lake with the highest net supply of water on record. Lake levels rose a record 11 inches during the month. However, this boost will not make up for the low snowfalls and high evaporation of the past several years.

While low lake levels increase the need for dredging and reduce the amount of cargo incoming ships can carry, they also allow some beach building and reduce erosion along Great Lakes shorelines, Keillor said.

For updated information on Great Lakes water levels and precipitation, see www.lre.usace.army.mil. 

Also see "Twenty Frequently Asked Questions about Great Lakes Water Levels and Coastal Erosion." 

--John Karl

Last updated 14 June 2001 by Karl
All contents copyright 2000 University of Wisconsin Sea Grant Institute

http://www.seagrant.wisc.edu/Communications/news/LD_stories/2001/LowWater.html