"Ten years ago, the upper Mississippi River Basin in the Midwestern United States experienced the costliest flood in the history of the United States. The flood came to be known as 'The Great Flood of 1993.' The Mississippi River drains approximately 40 percent of the continental United States (approximately 1.25 million square miles), and portions of two Canadian provinces, Ontario and Manitoba. During the summer of 1993, the Upper Midwest experienced extremely high amounts of rainfall. An abnormally stationary jet stream was positioned over the central part of the Nation during this time. Moist, unstable air moving north from the Gulf of Mexico converged with unseasonably cool, dry air moving south from Canada. Was the Great Flood of 1993 an anomalous, unique event? Was it caused by levees? Was it exacerbated by other actions of man? We'll never know without reliable data from long-term stream flow-gaging stations. Users of USGS stream flow data agree that a plan is needed to reverse the loss of stream gages and to provide for a stable and modern stream flow-monitoring network for the future."
USGS Illinois Water Science Center Publications: http://il.water.usgs.gov/pubs/