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The Great Lakes

The Great Lakes - St. Lawrence Seaway commercial navigation system serves the heartland of the United States and Canada by providing a minimum 25.5 foot safe vessel draft at low water datum. The Great Lakes-St. Lawrence Seaway System extends from the western end of Lake Superior to the Gulf of St. Lawrence on the Atlantic Ocean, a distance of more than 2,000 miles. The five Great Lakes -- Superior, Michigan, Huron, Erie and Ontario -- with their connecting channels, have a water surface area of about 95,000 square miles.

The lakes lie partly in each of the two countries of Canada and the United States, except for Lake Michigan which lies wholly within the United States. The total area of the Great Lakes basin, both land and water, above the eastern end of Lake Ontario is approximately 296,000 square miles, of which 175,000 square miles are in the United States and 122,000 square miles are in Canada.

The Great Lakes, their connecting channels, and the St. Lawrence River have a controlling commercial navigation depth of 27 feet providing a maximum 25.5-foot vessel draft on the five Great Lakes and a 26-foot vessel draft on the St. Lawrence River. In general, the Great Lakes basin experiences a continental to semimaritime climate, largely determined by the prevailing winds from west to east and the modifying influences of the Great Lakes. The basin is normally humid throughout the year, with cold winters and cool summers in the north and warm sumers in the south. The average annual frost-free season is about four months at the northern extremity of the basin and about six months at the southern extremity.

Lake Superior is the largest of the upper Great Lakes. Compared with the other Great Lakes, its surface is more elevated above the Atlantic Ocean, is more irregular in outline, has deeper water, more fog, and less rain. Major United States public commercial harbors are located at Duluth and Two Harbors, Minnesota; Superior and Ashland, Wisconsin; and Marquette and Presque Isle, Michigan. Two additional private commercial harbors are located in Minnesota on the north shore of Lake Superior at Silver Bay and at Taconite Harbor. Each is used for the shipment of concentrated taconite-iron ore. In addition, there is an important Canadian harbor at Thunder Bay, Ontario.

Lakes Huron and Michigan are one lake from a navigation standpoint, since the Straits of Mackinac, which connect the two lakes, are so broad and deep there is no perceptible flow between them and their surfaces stand at the same elevation. Major harbors on Lake Huron located in the United States are at Calcite, Stoneport, Alpena, Alabaster, Bay City, and Saginaw, Michigan. Major harbors on Lake Michigan are located at Milwaukee, Wisconsin; Chicago and Calumet Harbor, Illinois; and at Burns Waterway, Buffington, Gary, and Indiana Harbor, Indiana.

Lake Erie is the shallowest of all the Great Lakes and considerably smaller than Lakes Superior, Michigan and Huron. Major harbors on Lake Erie are located at Monroe, Michigan; Toledo, Sandusky, Huron, Lorain, Cleveland, Fairport, Ashtabula, and Conneaut, Ohio; Erie, Pennsylvania; and Buffalo, New York.

Lake Ontario is the smallest of the Great Lakes with its waters flowing into the St. Lawrence River to the Atlantic Ocean. The only navigable connection from Lake Erie to Lake Ontario is by the Welland Canal which extends for about 27 miles and provides a series of locks that overcome a difference in elevation of 326 feet. The Niagara River is the natural flow of water from Lake Erie to Lake Ontario. Major U.S. harbors on Lake Ontario are located at Rochester, Sodus Bay, and Oswego, New York. Major Canadian harbors are located at Hamilton and Toronto, Ontario.

Had Nature given to Lakes Superior and Huron a common level, as she has to the oceans, the supposed obstacle at the Soo to free communication would have long since been removed by the construction of a channel clear of all obstructions, and this regardless of any cost that was within our capacity and resources. But, unfortunately, Nature made such simple treatment impossible, for Lake Huron is twenty-odd feet lower than Lake Superior. It was useless to wish for an ideal treatment of the obstacle, for it was an impossibility; and American and Canadian engineers have provided the best solution possible.

The St. Clair River-Lake St. Clair-Detroit River System connects Lake Huron and Lake Erie. The system is approximately 89 miles long and has a relatively uniform water surface profile with a fall of 8 feet from Lake Huron to Lake Erie. The St. Clair River has a length of about 39 miles. Lake St. Clair, extending between the mouth of the St. Clair River and the head of the Detroit River (a distance of about 18 miles), occupies a shallow basin having an average depth of about 10 feet, with low, marshy shores. The shallow depth requires a dredged commercial navigation channel 27.5 feet deep and 800 feet wide throughout its length. The Detroit River extends about 31 miles to Lake Erie. Major harbors located along the system are at Sarnia and Windsor, Ontario, and at Detroit, Michigan.

Lake Superior has been regulated since 1921 by means of a series of control structures including a gated dam (Compensating Works) across the St. Marys River at Sault Ste. Marie, Michigan and Ontario. Construction of the gated dam was authorized by the International Joint Commission (IJC) as a condition to approval of the water diversion for hydropower. By operation of the gates, locks, and changes in power diversions, flows specified by the adopted plan of regulation can be achieved.

The Great Lakes store great quantities of heat and tend to moderate temperatures on adjacent land areas. Thus, the interiors of Michigan's Upper and Lower Peninsulas are colder than areas nearer the lakes at the same latitude. The Great Lakes cause an increase of average annual humidity on the order of 15 percent. Short-term local variations in surface air temperatures can be extreme.

The Great Lakes basin was created by the Wisconsin Glaciation during the Pleistocene Epoch. The present Great Lakes configuration, with its outlets and existing lake levels, date back less than 3,000 years, with the subsequent processes of stream and shoreline erosion making only slight changes in the original topography.

Prior to the Pleistocene or Ice Age, the Great Lakes were nonexistent. As the ice sheet retreated northward for the final time, entrained debris was released and vast irregular deposits of overburden were laid down. The topography was changed with parts of the major preglacial valleys being deepened or filled by glacial action, thus forming the basins of the five Great Lakes.

The Superior Highlands of northern Minnesota, Wisconsin, and Michigan, range in elevation from about 600 feet to approximately 2,300 feet above mean sea level. Elevations in the interior lowlands range from 700 to 1,000 feet. In most of the basin, land surface is less than 1,000 feet above mean sea level. The highest point is the headwaters area of Lake Superior with an elevation of 2,301 feet above mean sea level at Eagle Mountain in Cook County, Minnesota, and the lowest elevation is about 570 feet above mean sea level at the lowlands adjoining Lake Erie.

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Page last modified: 01-11-2017 19:24:10 ZULU