why did they change the flow of the chicago river
Chicago River The River is also noteworthy for its natural and man-made history. In 1887, the Illinois General Assembly, partly in response to concerns arising out of an extreme weather event in 1885 that threatened the city's water supply,[3] decided to reverse the flow of the Chicago River through civil engineering by taking water from Lake Michigan and discharging it into the Mississippi River watershed. In 1889, the Illinois General Assembly created the Chicago Sanitary District (now The Metropolitan Water Reclamation District) to replace the Illinois and Michigan Canal, which had become inadequate to carry the city's increasing sewage and commercial navigation needs, with the Chicago Sanitary and Ship Canal, a much larger waterway.[4] The District completed this man-made hydrologic connection between the Great Lakes and Mississippi watershed in 1900 [5] by reversing the flow of the Main Stem and South Branch of the river using a series of canal locks, and increasing the river's flow from Lake Michigan, causing it to empty into the new Canal. In 1999, this system was named a 'Civil Engineering Monument of the Millennium' by the American Society of Civil Engineers (ASCE).[6]
Mississippi River The Mississippi River is called the Lower Mississippi River from its confluence with the Ohio River to its mouth at the Gulf of Mexico, a distance of about 1,000 miles (1,600 km). At the confluence of the Ohio and the Middle Mississippi, the long-term mean discharge of the Ohio at Cairo, Illinois is 281,500 cubic feet per second (7,970 cubic metres per second),[23] while the long-term mean discharge of the Mississippi at Thebes, Illinois (just upriver from Cairo) is 208,200 cu ft/s (5,900 m3/s).[24] Thus, by volume, the main branch of the Mississippi River system at Cairo can be considered to be the Ohio River (and the Allegheny River further upstream), rather than the Middle Mississippi.