Understanding Great Lakes water levels

Fluctuations in Great Lakes water levels impact humans and the environment both directly and indirectly and are influenced by a number of factors.

Many factors can influence water levels in the Great Lakes system  including manmade diversions as shown in this diagram.
Many factors can influence water levels in the Great Lakes system including manmade diversions as shown in this diagram.

The Great Lakes watershed includes more than 94,000 square miles of water, 200,000 square miles of land and 14,000 miles of shoreline. It touches eight states and two Canadian provinces with over 40 million people living within its boundaries

Since the retreat of the glaciers that formed the Great Lakes over 10,000 years ago, the water levels in this system have gone through dramatic fluctuations of as much as hundreds of feet. In modern times, however, its levels have remained remarkably steady with normal fluctuations only ranging between 12-24 inches in a single year.

Great Lakes water levels are influenced by a variety of factors including precipitation, upstream flows, groundwater, surface water runoff, evaporation, lake water diversions and water level regulations. Great Lakes water levels are recorded using a number of water level gauges that are located throughout the Great Lakes basin.

The difference between the amount of water entering the system and the amount exiting the system is the determining factor in the increase or decrease of lake levels. Water entering the system comes in the form of precipitation on the lake, surface runoff from surrounding land, groundwater discharges into local surface water and inflow from upstream lakes. Water exits the system through evaporation from land and water surfaces, groundwater outflows, consumptive uses, diversions and outflows to downstream rivers and lakes. Evaporation can be the major factor if warm lake surfaces come into contact with dry air. Great Lakes levels also respond to climate variability.

Water levels fluctuate naturally in the short term, seasonally and long term. Short term changes in levels are due to wind and barometric changes that can occur over a few hours to days. There are annual seasonal lake fluctuations. Lake levels usually decline in winter months due to increased evaporation. Spring levels normally rise as the snow melts and spring rain and runoff occur. Long term fluctuations occur over consecutive years. Consecutive years of warm, dry weather will result in lower lake levels, while multiple wet, cool years will cause levels to rise. Winter months have more evaporation while spring and summer have the least amount of evaporation.

Changing Great Lakes water levels can impact the economy in a number of ways:

  • Low lake levels impact commercial shipping, recreational boating, hydropower facilities and drinking water filtration plants.
  • Low water levels mean less cargo per freighter to keep from hitting ground which can result in increased costs of goods.
  • Pleasure crafts break propellers on shallow lake bottoms and may not be able to get into some docks which can impact local marine purchases.
  • Hydropower facilities (using water to produce electric power) are dependent on precipitation and elevation changes. Low water levels may slow water movement to turn the turbines used in power generation.
  • Water filtration plants may need to move intake pipes out farther to insure cleaner water or may need to add additional treatment before using.

High water levels can result in coastal erosion and flooding:

  • Coastal erosion may make some buildings unsafe to occupy and adds sediment to water impacting water quality. High water can impact fisheries and other wildlife habitat.
  • Flooding has a negative economic impact in loss of property and goods while reducing disposable income to a community or region.

A number of international agencies have organized a collaborative network to assess and forecast GL water levels. These include National Oceanic and Atmospheric Administration (NOAA), U.S Army Corps of Engineers (USACE), U.S. Geological Survey (USGS), Environment Canada and Canada’s Department of Fisheries and Oceans.

The Great Lakes system is a huge interconnected ecosystem. According to Michigan State University Extension, it requires resources to manage it in ways that ensures human, environmental and economic wellbeing to the entire watershed.

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