Friday, October 4, 2013



Water levels for the previous year and the current year to date are shown as a solid line on the hydrographs. A projection for the next six months is given as a dashed line. This projection is based on the present condition of the lake basin and anticipated future weather. The shaded area shows a range of possible levels over the next six months dependent upon weather variations. Current and projected levels (solid and dashed lines) can be compared with the 1918-2011 average levels (dotted line) and extreme levels (shown as bars with their year of occurrence).The legend below further identifies the information on the hydrographs.
 The levels on the hydrographs are shown in both feet and meters above (+) or below (-) Chart Datum. Chart Datum, also known as Low Water Datum, is a reference plane on each lake to which water depth and Federal navigation improvement depths on navigation charts are referred.

All elevations and plots shown in this bulletin are referenced to International Great Lakes Datum 1985 (IGLD 1985). IGLD 1985 has its zero base at Rimouski, Quebec near the mouth of the St. Lawrence River (approximate sea level).

Lakes Superior, Michigan-Huron and St. Clair were below their long-term average (1918-2012) water levels in August. Lakes Superior and Michigan-Huron continue their 14 consecutive year stretch of below average water levels, the longest in each of their recorded histories. The latest six month forecast does not call for record low levels on any lakes given any scenario. The most probable forecast shows Lake Michigan-Huron remaining 12 to 13 inches ABOVE record lows through February.
Expected impacts to navigation: The August monthly mean water levels of Lakes Superior and Michigan-Huron were both above chart datum, but both lakes remain below their long-term averages. Lake Superior is expected to remain above chart datum through December and be 1 to 3 inches below datum in January and February. Lake Michigan-Huron is forecasted to fall below chart datum by November. Low water levels on the Great Lakes will affect navigation in several ways. The first is that harbors and ports on Lakes Michigan, Huron and Superior will experience lake levels near low water datum during much of this navigation season. Shippers will have to continue to light load. Groundings will be much more likely and some harbors may close. Waukegan Harbor is currently closed to commercial navigation. Many recreational harbors have also been affected. Also, it is important to note that because the Great Lakes operate as a system with interdependent ports, problems in the upper lakes have negative impacts across all the commercial projects throughout the system, including the ports on Lakes Erie and Ontario. Light-loading caused by low levels on the upper lakes will have repercussions throughout the system with increased costs to shippers in the agricultural and manufacturing sectors. Every foot of lost depth requires a 1,000-footer to load 3,200 tons less. At 1.5 feet below datum, they are losing 8-10 percent of their carrying capacity. This causes significant economic impacts in increased shipping costs.

Recorded water levels in this bulletin are derived from a representative network of water level gages on each lake (see cover map). Providers of these data are the U.S.Department of Commerce, NOAA, National Ocean Service, and Integrated Science Data Management, Department of Fisheries and Oceans, Canada. The Detroit District, Corps of Engineers and Environment Canada derive historic and projected lake levels under the auspices of the Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data. This bulletin is produced monthly as a public service. The Corps also publishes the "Great Lakes, Connecting Channels and St. Lawrence River Water Levels and Depths,” weekly, which provides a forecast of depths in the connecting rivers between the Great Lakes and the International Section of the St. Lawrence River. This Monthly Bulletin of the lake levels for the Great Lakes may be obtained free of charge by writing to the address shown on the front cover, by calling (313) 226-6442 or emailing Notices of change of address should include the name of the publication. This information is available on the internet at

Great Lakes Basin Hydrology
September 2013
All of the Great Lakes basins received below average precipitation in September 2013, with the total precipitation ranging between 2.5 and 3 inches for all of the Great Lakes. Over the past 12 months, though, the total precipitation received for all of the Great Lakes basins was above average. In September, the net basin supply of water to Lake Superior was near average, while the net basin supplies of water to all of the other Great Lakes were below average. The tables below list September precipitation and water supply information for all Great Lakes basins. A comparison of monthly mean lake levels for September to long-term average (1918-2012) shows Lakes Superior and Michigan-Huron were 2 and 18 inches below average, respectively. Lake St. Clair was 5 inches below average in September, while Lake Erie was near average. Lake Ontario was 2 inches above average in September. Boaters should be aware of hazards to navigation due to continued below average water levels on Lakes Superior, Michigan-Huron, and St. Clair. 

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