QUIET BEGINNING HERALDED NATION’s WORST FLOOD IN 1993

April 2, 2003 — Mark Twain once said the Mississippi River “cannot be tamed, curbed or confined...you cannot bar its path with an obstruction which it will not tear down, dance over and laugh at. The Mississippi River will always have its own way, no engineering skill can persuade it to do otherwise...” In 1993, the Mississippi River and the Missouri River provided emphatic proof of Twain’s words. (NOAA image of Iowa levee from the Great Flood of 1993.)

By the time flood waters subsided in October, the Great Flood of 1993 had inundated 20 million acres in nine states, taking 50 lives and costing about $20 billion. Approximately 54,000 people were evacuated from flooded areas, approximately 50,000 homes were destroyed or damaged and 75 towns had been completely inundated. Some riverside communities were abandoned or relocated to higher ground.

According to the U.S. Army Corps of Engineers (as noted in the NOAA National Weather Service natural disaster survey report) 40 of 229 federal levees and 1,043 of 1,347 non-federal levees were over-topped or damaged. Every breeched levee contributed to the amount of flood water flowing outside the main drainages. The flood eroded more than 600 billion tons of top soil and deposited great amounts of sand and silt on valuable farm land. In large areas inundated by the flood, the harvest of 1993 was a total loss and some farmers lost any chance for a 1994 harvest, as well.

The entire state of Iowa was declared a disaster area, as were portions of eight other states: North Dakota, South Dakota, Minnesota, Wisconsin, Illinois, Missouri, Nebraska and Kansas.

Flood Timeline
Hydrologists at two NOAA National Weather Service River Forecast Centers had warned that a wet fall 1992 and normal or above normal snowpack in the central United States were setting the table for possible serious flooding when the spring thaw hit in 1993.

Experienced personnel at the North Central River Forecast Center in Minneapolis, Minn., knew soils in the upper Mississippi River drainage basins were too saturated to absorb much more rainfall. The same situation existed for the Missouri River basin, which is monitored by the Missouri Basin River Forecast Center, located at the time in Kansas City prior to a move to a new office in Pleasant Hill, Mo. Heavy snowpack in the Dakotas, Minnesota and Wisconsin, they warned, could be released in a rush if certain weather patterns prevailed in the spring. Flood forecasters, however, had no indication they were only months and weeks away from the most costly and devastating flood to ravage the United States in modern history.

“The NOAA National Weather Service was just a few years into the modernization that brought us new radars, satellites and other weather and hydrologic tracking and forecasting tools, so, even though we knew there was strong potential for continued flooding, we didn’t know the rains would be so heavy and last for so long,” said Kenneth D. King, chief of hydrologic services at the NOAA National Weather Service Central Region Headquarters in Kansas City, Mo. “I think everyone was ready for some short-term heavy rain and serious flooding, but nobody thought it would last all summer.”

Late March rains quickened the melting rate of snow on the ground and added volume to the runoff in southern Minnesota and Wisconsin, feeding the headwaters of the Mississippi River. At the same time the northern reaches of the Missouri River were becoming saturated.

An annual weather condition termed a Bermuda High (a high-pressure system that develops in late spring off the southeastern U.S. coast and steers weather systems across the eastern part of the country) had a few surprises of its own in store for weather forecasters. The 1993 Bermuda High was of greater intensity and moved farther to the north and west than usual. The High formed an atmospheric dam over the Ohio River Valley and prevented storms from following their normal course to the eastern seaboard. Instead, storms kept re-generating over the central states, dropping record amounts of rain on a nine-state area (North Dakota, South Dakota, Minnesota, Wisconsin, Nebraska, Iowa, Illinois, Kansas and Missouri) primed for flooding.

“I think the two most important aspects of the flood of 1993 were its intensity and its duration,” King said. “That made it a historic flood. This part of the country had never seen such heavy rainfall over such a long period of time and had never experienced such heavy flooding over such an extended period. The magnitude and duration of flooding were almost overwhelming and it’s a tribute to the millions of people impacted by the flood that they continued to battle to save their homes, farms and communities. That perseverance is difficult enough to maintain when flooding lasts for several days or a few weeks. To maintain it for the duration of the flooding took incredible fortitude.”

Through the course of the Great Flood of 1993, flooding occurred at approximately 500 Weather Service flood forecast points with record flooding recorded at 93 forecast points (44 points in the upper Mississippi River drainage and 49 on the Missouri). Some forecast points were above flood stage non-stop for five months.

Producing accurate flood and flash flood forecasts through all this was especially difficult, King said, because the volume of water was so great it overwhelmed the mainstem drainages. “In many locations, there was as much water running outside the leveed river channels as there was running inside the levees,” King said. “We had sufficient gauges to help us determine the flow levels within the river basins but had to make educated estimates about how much unaccounted for runoff was flowing outside the levees.”

At St. Louis, the first spring flooding on the Mississippi River was recorded April 8, cresting at .2 feet above flood stage and lasting only that day. The Mississippi rose above flood stage again on April 11 and stayed above flood stage until May 24. The city got a respite as the Mississippi stayed below flood stage May 24 to June 26. On June 27, the Mississippi again went above flood stage and didn’t drop below flood stage for the year until October 7—a total of 146 days above flood stage. The Mississippi River was above the old record flood stage for more than three weeks at St. Louis from mid July to mid August. Prior to 1993, the historic flood of record on the Mississippi River at St. Louis had been 43.2 feet, recorded April 28, 1973. That record was broken July 21, 1993, with a level of 46.9 feet and broken again 11 days later with a record stage of 49.58 feet on Aug. 1. St. Louis is located near the confluence of the Missouri, Illinois and Mississippi rivers, all of which were in flood at the same time.

During July, central Iowa became the focus of media attention when flooding devastated Ames and Des Moines. Record rainfall July 8-9 pushed Saylorville Reservoir near Des Moines to a record level for the third time in three weeks. The Racoon River flooded the Des Moines water works, despite dikes that had been built six feet above the flood of record, and flooded several electrical plants. More than 250,000 Des Moines residents were without electricity and without water. At Ames, Squaw Creek flooding inundated Hilton Coliseum on the Iowa State University campus with 14 feet of water.

Later in July, Iowa City was impacted by the flood. The Iowa River at Iowa City reached its second highest level ever, cresting at 28.21 feet July 19. Water levels at Coralville Reservoir, about nine miles upstream from Iowa City, peaked July 24 at 716.75 feet, the highest level recorded since the reservoir was completed in 1958. Water went over the Coralville Reservoir spillway from July 5 to Aug. 1, the only time in the reservoir’s history the spillway had been topped.

Some locations on the Mississippi River were in flood for almost 200 days while locations on the Missouri neared 100 days of flooding. On the Mississippi, Grafton, Ill., recorded flooding for 195 days, Clarksville, Mo, for 187 days, Winfield, Mo., for 183 days, Hannibal, Mo., for 174 days, and Quincy, Ill., for 152 days. The Missouri River was above flood stage for 62 days in Jefferson City, Mo., 77 days at Hermann, Mo.; and for 94 days at St. Charles in the St. Louis metropolitan area.

At different times, the survey report noted, flooding closed all bridges on the Mississippi River from Davenport, Iowa, to St. Louis; and all bridges on the Missouri River from Kansas City to St. Louis. Flooding forced closure of seven of eight railroad lines in Missouri, as well as 12 commercial airports and portions of interstate highways 29, 35 and 70 across the state and of Interstate 64 to Kentucky.

In the prologue for the disaster survey report, the NOAA administrator at the time wrote: “Although the Great Flood of 1993 has caused devastating human, environmental and economic impacts, the lessons learned will guide us in providing improved services and benefits to the nation in the future.”

“Our forecasters were highly complimented by emergency managers and others for the accuracy of their weather and flood forecasts and vital information provided through the flood of 1993,” King said. “That is a great source of pride for us. Still, the Weather Service always strives to improve its services and its efficiency.”

NOAA is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of the nation’s coastal and marine resources. NOAA is part of the Department of Commerce.

Relevant Web Sites
1993 Flood Summaries

NOAA Floods Page

NOAA River Forecast Centers

NOAA National Weather Service

NOAA Office of Hydrologic Development

NOAA Hydrometeorological Prediction Center

NOAA Hydrologic Information Center

NOAA Hydrologic Information Center Daily Flood Conditions

NOAA National Weather Forecast Offices

Media Contact:
Patrick Slattery, NOAA National Weather Service central region, (816) 891-7734 ext. 621