The Mississippi flood of 1993

• the Mississippi River (Fig) is the sixth largest river in the world in terms of discharge, with a freshwater discharge onto the continental shelf of 580  km³ yr^-1
• it is 2,320 miles (3712 km) long and drains 41% of the land area of the continental United States

History

• satellite pictures of the river at Glasgow, Missouri (The Great Flood of 1993)
• flood of 1993 in the upper Mississippi River Basin was an unprecedented hydrometeorological event
• in June and July (and somewhat into the fall) of that year, the Mississippi River basin in the midwestern United States experienced anomalously high rainfall which produced record flooding.
• the cause of the high precipitation was a persistent atmospheric weather pattern consisting of a quasi-stationary jet stream positioned over the central part of the nation. As a result, moist air flowing north from the Gulf of Mexico converged with unseasonably cool, dry air moving south from Canada
• in June and July, close to 14 inches of precipitation (averaged over the upper Mississippi River Basin) was observed, significantly higher than average (approximately 8 inches)
• the fall of 1992 and spring of 1993 were already quite wet as well, subsurface was saturated
• at 45 USGS stations, the discharge rate exceeded the 100 year flood value
• flood lasted very long, many areas stayed flooded for weeks!
• estimates of total damages in the Midwest from weather events during 1993 range between
$12 and $16 billion
• Over half of these were agricultural damages, with the remaining being primarily to residences, businesses, public facilities, or transportation
  
• 100,000 home were damaged, 50% of those due to groundwater or sewer backup
• thirty-eight deaths were attributed directly to the flood
• warm, nutrient rich water resulted in hypoxic conditions in the Gulf of Mexico
• many levees broke, as evident in the satellite pictures

The Mississippi River at St. Louis, Missouri

• location of St. Louis in the upper Mississippi River Basin (Fig)
• discharge of the Mississippi at St Louis, 1934-94 (Fig), discharge in 1993 (Fig)
• Mississippi satellite images of the St Louis area (Fig)(Fig)
• Student excercise: Flood prediction for the Mississippi:
1. download the data annual peak discharge data of the Mississippi at St Louis (Mississippi River At St Louis Mo) and convert the data into an EXCEL spreadsheet.
   
2. determine minimum and maximum of the annual peak discharge rate and make a histogram
3. the data are skewed and are not normally distributed
4. calculate the natural logarithm of the annual peak discharge and determine the basic statistics of those data (MIN,MAX, AVERAGE, STDEV)
5. make a histogram of those data as well
6. what is the discharge rate equivalent to the 100 year flood (P=0.01)? Use the NORMINV function to determine this value, do not forget to reverse the transformation by using the EXP function
7. do the same for the 1000 year flood
8. how does the 1993 flood compare to these discharge rates?
9. what is the recurrence interval of the 1993 flood at St. Louis? Use the NORMDIST function
10. perform the calcluation for the 100 y flood again, this time using a period of only 20 years from anywhere in the record

Resources

• USGS 1993 flood
  
• Mississippi River At St Louis Mo
• NOAA/GFDL El Niño-Southern Oscillation Page
• Mississippi River Flood, lecture by David McConnell
• US Army Corps of Engineers 1993 Flood Home Page
• Lower Mississippi River Forecast Center - river flood forecasts rainfall data navigation
• The Great USA Flood of 1993