Cook County Precipitation Network Water Year Reports

The volume of water diverted from Lake Michigan into the state of Illinois is monitored to ensure that the diversion does not exceed a long-term average of 3,200 cubic feet per second (cfs) as imposed by a 1967 U.S. Supreme Court Order, which was updated in 1980. This diversion has a long history, dating back to the mid-1800s with the completion of the Illinois and Michigan Canal. Over the years, it has been affected by such events as the flow reversal of the Chicago River and completion of the Chicago Sanitary and Ship Canal in 1900, and has weathered various legal proceedings that attempted to ensure that the diversion could be monitored and did not exceed certain limits. One of the key components of the monitoring procedure, administered by the U.S. Army Corps of Engineers (USACE), Chicago District, is the accurate representation of the precipitation that falls over portions of Cook County, Illinois. The Cook County Precipitation Network collects precipitation data, and reports to the USACE each Water Year (October through September).

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