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  Great Lakes-St. Lawrence Hydrology
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Levels & Hydrology Section: Home | Levels | Hydrology | Flows

 
What's New
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Weekly Water Levels Forecast
New! Update for Friday November 6, 2009 (includes data summary)

Weather conditions: A few weak disturbances brought light rain showers and chilly temperatures to the Great Lakes basin this week. A warming trend is expected for the weekend as a high pressure center slides to the east. Temperatures in the 60s are likely across the region on Saturday and Sunday. Scattered showers are expected to return to start the workweek.

Water Level Conditions: All of the Great Lakes remain higher than their levels of a year ago. Lakes Superior, Michigan-Huron, St. Clair, Erie and Ontario are 3, 12, 8, 6, and 1 inches, respectively, higher than their levels last year at this time. The water levels of Lakes Superior, Michigan-Huron and St. Clair are expected to decline by 2 inches over the next month. Lake Erie and Ontario are expected to decline 1 and 2 inches, respectively, over the next 30 days. Over the next several months, Lake Superior, Lake Michigan-Huron and Lake St. Clair are forecasted to be above their water levels of a year ago. Lakes Erie and Ontario are forecasted to remain near or below last year's levels over the same time period. See the USACE Daily Levels web page for more water level information.

Current outflows / channel conditions: In October, the outflow from Lake Superior through the St. Mary's River and the outflow from Lake Michigan-Huron through the St. Clair River were below average. The flow in the Detroit River was also below average. The Niagara River carried near average flows during October, while the outflow from Lake Ontario through the St. Lawrence River was above average in October.

Alerts: Users of the Great Lakes, connecting channels and St. Lawrence River should keep informed of current conditions before undertaking any activities that could be affected by changing water levels. Mariners should utilize navigation charts and refer to current water level readings.

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Overview
Carved by glaciers, the Great Lakes-St. Lawrence River system is a series of steps that drains from Lake Superior in the west to the Atlantic Ocean in the east. Covering more than 94,000 square miles, the Great Lakes and their connecting channels form the largest fresh, surface water system on earth, holding about 18 percent of the world's supply.
 
Ever since the last glaciers retreated about 10,000 years ago, the system's water levels and outflows have been fluctuating, affecting the lakeshore environment and human activities. Unlike oceans, where ebbs and tides are constant and predictable, Great Lakes water level fluctuations are almost never regular, nor can their levels be predicted accurately in the long term. This is because the many factors affecting Great Lakes water levels and flows are never constant and likely can not be predicted accurately in the long term.
 
The major influences on Great Lakes hydrology are weather and climate, which affect the balance of water in the Great Lakes and their connecting channels. Water enters the system as precipitation, runoff (including snowmelt) from the surrounding land, and groundwater inflow. Water leaving the system consists of evaporation from the water's surface, groundwater outflow, consumptive uses and diversions.
 
The GLIN hydrology section discusses these factors and links to resources from many relevant agencies. We hope that an understanding of the Great Lakes system's dynamics will promote living in harmony with one of the most precious natural resources of this planet.
 
Coordinating Committee Co-chairs:
John Kangas
U.S. Army Corps of Engineers, Great Lakes and Ohio River Division
john.w.kangas@usace.army.mil
 
Peter Yee
Environment Canada, Great Lakes-St. Lawrence Regulation Office
peter_yee@pch.gc.ca

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Datums
Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data
 

Datums - explanation of datums used for water levels and navigational charts
Department of Fisheries and Oceans, Canadian Hydrographic Service

Establishment of International Great Lakes Datum 1985
Department of Fisheries and Oceans, Canadian Hydrographic Service

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Education
TEACH Great Lakes: Water Levels
Water levels are part of the ebb and flow of nature. Learn about the three types of water level fluctuations, how levels are measured on the Great Lakes, and what's causing the recent drop.

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Laws
Boundary Waters Treaty
United States and Canada, 1909

Great Lakes Charter

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References
Great Lakes Water Levels Home Page
U.S. Army Corps of Engineers (USACE), Detroit District
A regularly updated page of links to information on Great Lakes hydrology. Includes current conditions, recent water levels, forecasted levels, general news and information, multimedia, reference materials, and more!

Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data
 

Great Lakes Atlas
U.S. Environmental Protection Agency (EPA)
This Environmental Atlas and Resource Book is an excellent resource on the Great Lakes, including physical characteristics, natural processes, people, concerns, joint management and new directions (mirrored on Environment Canada's site).

Hydrologic Cycle Online Meteorology Guide
University of Illinois, Department of Atmospheric Sciences

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Related Resources
GLIN: Agencies and Organizations, Hydrology
GLIN: Environmental Research in the Great Lakes Region
GLIN: Great Lakes-St. Lawrence Water Flows
GLIN: Great Lakes-St. Lawrence Water Levels
GLIN: Weather and Climate in the Great Lakes Region

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CC Data This page was created under the guidance of the binational Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data. This symbol is used throughout the GLIN hydrology section to indicate data or references prepared under the auspices of the Coordinating Committee.

 

 
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Last Updated: June 18, 2009
Maintained by: Christine Manninen, manninen@glc.org
Selected Photos: Copyright ©John and Ann Mahan
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