Mississippi river rages: the Flood Scenario: the Mississippi river system's flood protection plans and devices are overwhelmed. Thousands watch helplessly as their dreams drown in rising water levels

The Hypothetical Scenario:

The end of the previous summer had been exceptionally wet across the upper Midwest, the north central states and as far east as Pennsylvania. Torrential rain fell day after day, as a high pressure system brought cool air from Canada to mix with moisture-laden tropical air moving up from the Gulf. Above-average rainfall continued through December, so that at the start of January, water levels were already at a record in the Ohio and upper Mississippi rivers. Following heavy snowfalls over the region in January, the rains returned in February falling onto ground saturated since the end of the previous summer. Average rainfall during February and March, throughout the lower Missouri, Mississippi and Ohio River basins was 200 to 300 percent of average.

The first flooding starts in the middle of February on the smaller rivers, "affecting towns like Des Moines, Iowa; Springfield, Ill., and Indianapolis. Melting snow further to the west, combined with the heavy rainfall, means that levees fail all along the lower Missouri at Sioux City, Iowa and Omaha, Neb. And the rains continue.

Toward the end of March, with the arrival of warmer air from the Gulf, the storm systems strengthen into mesoconvective complexes which unleash intense thunderstorms bringing outbreaks of tornadoes and damaging hail.

By the end of March, levees begin to fail along the upper Mississippi, flooding Quincy, Ill., Hannibal, Mo., and vast areas of farmland. (By the time the flood is over, more than 60 percent of all the levees along the Mississippi and lower Missouri are ruined.) On April 4th, the combined flood waves of the Mississippi, Missouri and Illinois rivers arrive in St. Louis within days of one another, exceeding the 1993 record of 49.6 feet.

The flow of water approaches the previous record of 1844--at least 25 percent more than in 1993. Finally, on April 7th, the levees north of the city can't hold back the fiver, now exceeding a height of 52 feet.

A day later, the southern side of the city is under water. Although the city founders trod chosen their site carefully, and the downtown area remained dry, Riverview Drive and large adjacent industrial developments disappear under several feet of water.

Unlike the summer of 1993, when the flow of the Ohio River was low, the flood wave that now breaks through Mississippi levees south of St. Louis is destined to meet another flood wave pouring out of the Ohio River to the cast. Defenses had already been breached at Evansville, Ind. and Paducah, Ky. Flood control procedures designed to regulate flow coming from the more mountainous southeast part of the Ohio River with reservoirs on the lower Cumberland and Tennessee Rivers are unable to cope.

In early 1997, the last significant Ohio River flood, flow was 250 percent above normal. This time it is closer to 350 percent, and the flood wave of 1.5 million cusecs arrives just a few days ahead of the flood wave advancing down the Mississippi. This is a recipe for disaster. Based on the Flood Control Act of 1928, the levees at Cairo, Ill., where the Ohio and Mississippi Rivers join, had been built to withstand the combined flood volume of 2.3 million cusecs. The previous record flow on the Ohio River had been 1.8 million cusecs in the spring of 1937. The combined flows on the two rivers is now perilously close to their design limit.

As the water level approaches the tops of the flanking levees, the U.S. Army Corps of Engineers begins using explosives to divert 550,000 cusecs of flow into a relief channel to surge over unpopulated farmland that had not been inundated since the Great Flood of 1937.

The water re-enters the main channel of the Mississippi River close to New Madrid, Mo., but intense rainfall over this section of the river at the beginning of April weakens the main downstream levees. After a night of frantic sandbagging, a section, 1,000-feet long, of the western levee fails. Billions of gallons of water surge across the land carving a depression more than 100 feet deep and half a mile long. The water fans out into a flood of biblical proportions, 20 miles wide and tens of feet deep that submerges a number of towns including Caruthersville, Mo. and Blytheville, Ark.

The heavy rains over the upper Midwest are accompanied by near drought conditions over northern Texas, Oklahoma and Arkansas, so, unlike the situation in 1927, flow is not extreme along the Arkansas and White Rivers. However, to protect the City of New Orleans, the full flood management plan is put into action. Flows all down the lower Mississippi are already higher than the previous record set in 1997. Around 20 percent of the flow--some 500,000 cusecs--is diverted into the Atchafalaya River. A spillway 36 miles upstream of New Orleans is opened to divert 15 percent of the remaining flow into Lake Pontchartrain. At the end of April, the flood peak passes through New Orleans staying just below the crest of the floodwalls.

The impact of the floods is widely felt among residents living in the Mississippi, Illinois, lower Missouri and Ohio River basins.

Several major towns, including Peoria, Ill. and Des Moines, Iowa lose their water supply for more than 10 days as sewage and fuel oil clog inlets. Several blocks burn down in the center of one town after sparks ignite gasoline displaced from underground storage tanks.

In South St. Louis, Mo. three half-full liquefied propane tanks tear loose of their moorings, rupture connecting pipelines and explode--triggering further explosions in neigh boring tanks. More than 800 businesses are affected in and around the City of St. Louis. Total damage in the St. Louis District is estimated at $6 billion.

The failure of the Monarch levee floods many industrial parks and the local airport. The largest losses, however, are in Illinois and Indiana. The agricultural sector is particularly hit hard, as all the spring plantings of corn and soy were ruined.

The number of buildings destroyed or damaged in the floods is 90,000 (compared with 56,000 in 1993). The flood displaces 150,000 people and leaves 21,000 square miles submerged, about 30 percent more than in 1993, but still significantly less than the 27,000 square miles inundated in 1927. Around 60 people, unable or unwilling to evacuate from their homes, or caught in their cars, die as the floodwaters rise.

>From the beginning of February, navigation is closed on the upper Mississippi and Ohio rivers. Losses amount to around $4 million per day. From the middle of February the lower Mississippi is closed. At two large coal-fired power stations, power generation stops after floodwaters submerge a quay and ships can not supply the plants with coal for six weeks.

In early April, the rising waters set several barges free from their moorings. One of these, loaded with benzene and toluene, overturns in a bend in the river on the edge of Memphis, releasing toxic fumes. People living in neighborhoods along the river are forced to evacuate their homes. Another 40 barges in Louisiana drift through a 13-mile stretch in St. Charles Parish, home to 28 petrochemical plants. One barge collides with the intake valves of the Waterford Three nuclear power station, suspending operations. Other barges tear up wharves, intake facilities and loading platforms, rupturing a gasoline pipeline.

The spring rains trigger widespread debate about the impact of global warming. There is now evidence that average rainfall levels are rising across the United States and the Army Corps of Engineers is being challenged to re-evaluate all its flood defenses. In the state of Mississippi, lawyers serve papers in a mass-tort suit charging the principal greenhouse gas emitters--major oil companies, the steel industry and the coal-fired power generators-with recklessly endangering the livelihoods of all those living along the river.

Losses From The Hypothetical Greater Ohio and Mississippi River
Floods

Type of Loss                              Total Loss     Insured Losses

Property and infrastructure damage        $18 billion        $3 billion
Workers' compensation, life and
  health costs                           $200 million      $100 million
Direct costs of business interrup-
  tion                                    $12 billion      $1.6 billion
Other costs                                $4 billion
Total Direct Costs:                     $34.2 billion      $4.7 billion
Human Loss/Injuries
Total number of people killed:                66
Total hospitalized with serious
  injuries:                                   70
Total treated at outpatient clinics:         400

Source: Risk Management Solutions

RELATED ARTICLE: The ebb and flow--of life and death.

Flooding is the most common natural disaster in the United States.

As the biggest river system in North America, with a drainage basin of 1.25 million square miles, the 2,300-mile-long Mississippi River, fed by the Missouri and the Ohio tributaries, remains the nation's source of the biggest and most costly floods.

Floods afflicted the first settlements founded along the banks of the Mississippi and have recurred along the river throughout the past two hundred years. The most catastrophic Mississippi flood occurred in 1927. It claimed 246 lives, displaced 700,000 people, and destroyed or damaged 137,000 buildings. In all, a total of 27,000 square miles of the lower Mississippi flood plain was inundated. The loss in 1927 was assessed at $347 million at the time: inundating the same areas today would cause $28Bn in property damage alone.

The 1927 flood led to the 1928 Flood Control Act, which ushered the era of flood-protection projects: raised levees, diversionary channels and reservoirs. This was followed by the 1936 Flood Control Act authorizing the U.8. Army Corps of Engineers to construct flood control reservoirs along the Ohio River and its tributaries.

The belief that flooding had been contained--or at least could be controlled--drowned with the floods of the summer of 1993.

In St. Louis, the Mississippi surpassed flood stage for 144 days between April and September. Water levels surged beyond the previous record for more than three weeks. In all, 17,000 square miles and 56,000 homes in nine states were flooded. Thousands of miles of levees were damaged, and 400 counties were declared disaster areas. Economic loss estimates ranged from $10 billion to $20 billion. The flood submerged eight million acres of farmland. U.S. corn and soybean yields dropped by 5 percent to 9 percent

Future Mississippi floods will continue to reflect the intersection between an extreme natural event, and the limitations of a river system managed by levees, spillways and reservoirs.

Every flood defense is built to provide protection, but only out to some flood return period such as 100 years--maybe even 250 years in a city. Beyond that level of probability, the defenses will be unable to hold the waters back.

The most catastrophic floods in the United States are likely to continue on the Mississippi River system. After all, about 80 percent of wetlands along the Mississippi, the natural storage for excess rainfall, have been drained since the 1940s.

The largest risk exposure on the river is in the City of St. Louis. Researchers at the Southern Illinois University of Carbondale, and Washington University in St. Louis, found that while an 1861 flow volume of 700,000 cusecs at St. Louis meant a flood stage of 31 feet, today the same flow volume would reach 41 feet.

Flow speeds have slowed dramatically as a result of the construction of wing dams to improve navigation at times of low flow. Constricting the river with flood defenses has simply raised the height of the floods.

Flood risk is widespread in the United States and the first job of a risk manager should be to determine the flood risk of a facility. However, being outside the designated flood zone does not make a facility immune to flood damage. It is important to consider what would happen in still more extreme events, including sheet flooding associated with persistent heavy rainfall, or blocked conduits.

Where floods can occur suddenly, it is important to rehearse and update a plan to protect facilities against flood damage. For buildings at significant risk of flooding it makes sense to elevate the most sensitive equipment.

ROBERT MUIR-WOOD, PHD., is an expert on climate hazards. He heads the Research Group at Risk Management Solutions inc. He is the author of numerous books, scientific papers and articles. He also conducts insurance seminars tend runs courses on catastrophe risk for Lloyd's of London.

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