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Chicago Portage
The Chicago Portage is a water gap connecting the watersheds ''(BrE: drainage basins)'' and the navigable waterways of the Mississippi River and the Great Lakes. It cuts through the Valparaiso Moraine, crossing the continental divide that separates the Great Lakes and Gulf of St. Lawrence watersheds from the Gulf of Mexico watershed, making it one of the most strategic points in the interior of the North American continent. The saddle point of the gap is within the City of Chicago, and the Chicago Portage is a reason Chicago exists and has developed to become the immensely important city that it is,〔(【引用サイトリンク】title= The Chicago Portage National Historic Site )〕 ranking 7th in the world in the 2014 Global Cities Index. The official flag of the City of Chicago is a stylized map of the Chicago Portage, with four red stars symbolizing city history, separating two blue stripes symbolizing the two great waters that meet at the city.〔(【引用サイトリンク】title= Chicago Facts: Municipal Flag )〕
==Flow direction==
A principal feature of the Chicago Portage water gap is that water can flow through it in either direction across the continental divide. It has flowed from east to west, west to east, or not at all. There have been two long-term reversals, and short-term reversals still happen today. Initially, water flowed from east to west starting about 10,000 years ago. About 3,000 years ago, this flow mostly stopped, and the Chicago Portage became a wind gap, except during floods when it flowed from west to east. In the year 1900, it was reversed to again flow continuously from east to west, except during floods when it can be reversed to flow from west to east.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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