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Region's risk of flooding is subject of rising debate ©[copyright] 2003 | St. Louis Post-Dispatch 07/30/2003
Jeff Reeves of Webster Groves jogs a path along the floodwall in St. Louis north of downtown. The wall and a levee on the north side of the city are all that exist for protecting the city from Mississippi River floods.
(Teak Phillips/P-D)
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If the Flood of 1993 were to happen again, Dennis Nadler thinks he knows where the water would end up - in his house.
The flood swamped Nadler's farm machinery repair shop and nipped at his home in Defiance, a sleepy St. Charles County hamlet of 100 that calls itself the "gateway to Missouri River wine country."
"My house and two others on this side of the street were the only ones that did not have water in them," he said. "We sandbagged around to keep it from running in the basement windows."
Next time, Nadler thinks he won't be so lucky. Just five miles downstream, the broken Chesterfield levee has been reborn as an earthen behemoth designed to withstand a much greater flood. Nadler believes that floodwater that would have spread over Chesterfield Valley will back up on him and his neighbors in the future.
"It doesn't take a rocket scientist to know that upstream from that bottleneck, there's going to be a lot of water," Nadler said.
RELATED LINKS:
Full series in our special report
Flood timeline, with links to archival photos and stories
<LI><A HREF="/stltoday/news/special/flood93.nsf/C4CCE258128EB3628625676F001EE75C#Graphics" CLASS="related">Graphics: How a levee works, riverfront development and more</A>
<LI><A HREF="/stltoday/news/special/flood93.nsf/C4CCE258128EB3628625676F001EE75C#ArchivalVideo" CLASS="related">Archival video, courtesy KTVI Fox 2</A>
<LI><A HREF="/stltoday/news/special/flood93.nsf/C4CCE258128EB3628625676F001EE75C#PhotoGalleries" CLASS="related">Photo galleries from the '93 flood (including readers' photos)</A>
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Defiance isn't the only place that could find itself under water in the next big flood.
Scientists have noted a dramatic, continuous increase in flood levels. If they are correct, a future flood could take an even greater toll than the $12 billion of destruction in 1993. The research shows that similar volumes of water are resulting in higher flood levels over time, potentially putting levee-protected areas at greater risk.
Even some of the Army Corps of Engineers' own research has detected rising flood levels on the lower Missouri River, where development has boomed in the past decade.
But the corps, which built some of the levees in question, has discounted the independent studies as scientifically flawed.
St. Louis district hydraulic engineer Dennis Stephens said he doesn't think local river communities face any greater threat of flooding now than they did in '93.
"We have a pretty stable system right now," Stephens said.
The debate affects vast areas, leaving river communities unsure of their real flood risk.
In St. Louis, a flood wall protects $3 billion worth of industrial areas north and south of downtown, and a low levee guards residential neighborhoods along River Des Peres to the south.
The 85,000-acre Metro East flood plain, with 150,000 residents and more than $2.5 billion worth of chemical plants, refineries, and other industrial development, is protected by levees and flood walls.
Arnold, Festus, Ste. Genevieve, Valley Park, St. Charles, St. Peters, Hannibal and Hermann all have people and property within the river's reach.
For these communities, the margin between salvation and disaster is just a few feet - the amount in dispute.
For example, the Corps of Engineers recently completed an $8 million study of projected flood heights on the upper Mississippi River system. The flow-frequency study shows that the level of a so-called 100-year flood - one that has a 1 percent chance of happening in any given year - is 1 foot lower today than it was 30 years ago on the Mississippi River at St. Louis.
Nicholas Pinter, a geologist at Southern Illinois University Carbondale, disagrees, saying the level has risen at least 3.3 feet in the same area.
The 4.3-foot difference is huge.
If the corps is correct, flood walls protecting the city of St. Louis and the Metro East are sufficient. Corps officials say they are confident in the 500-year flood walls on both sides of the river.
"That 500-year protection is adequate," said Deborah Rousch, a corps project manager for the east side flood wall.
If Pinter is right, parts of St. Louis would be subject to flooding in a true 100-year flood, and the Metro East area comes perilously close. Using slightly different assumptions, the East St. Louis levee would be in danger of failing, too, Pinter said.
The corps pegs the 1993 flood as a 175-year flood, meaning that, on average, a flood that size should happen only once every 175 years. But Pinter says it's slightly less than a 100-year flood. Robert Criss, a geologist at Washington University, says a flood of that size can be expected every 50 years or less.
Academics have challenged the corps' flood-control methods and predictions for years.
In 1975, St. Louis University geologist Charles Belt concluded that the then record-breaking flood levels seen in the 1973 Mississippi River flood were "man-made."
Belt wrote in the journal Science that floods carrying the same volume of water were resulting in higher flood crests over time. The 1908 flood, for example, was estimated to have the same water flow as the '73 flood, but its peak was 8.3 feet lower.
Belt's paper said that levees constricted the river, preventing water from spreading out over the natural flood plain. He also attributed increased flood heights to wing dikes and other navigation structures, which deposit sediment on river banks and stop up flood flows.
He predicted that "additional channel constriction and levee building will cause further problems."
The corps attacked Belt's methods and conclusions. But over the next three decades, Belt was joined by other scientists who found evidence that floods are getting worse - and that the problem is caused mostly by human interference.
Criss, the geologist at Washington University, has found that similar amounts of water have caused floods from 6 to 13 feet higher at many locations on the lower Missouri and middle Mississippi rivers.
For example, the 1903 flood was estimated to carry almost an identical volume of water as the Flood of 1993. But the earlier flood peaked at 38 feet in St. Louis, compared with 49.6 feet nine decades later. That's an 11.6-foot difference.
Criss found that the phenomenon of rising flood levels was limited to locations where rivers have been shoved into a corset of levees, wing dams and other structures. Relatively unchanged rivers such as the Meramec showed no increases in flood stages, according to a report published in the journal Geology in 2001 by Criss and a colleague, Everett L. Shock.
"Now it's commonplace to have river stages that were once truly acts of God," Criss said.
Pinter, the Southern Illinois University geologist, has reached similar conclusions with slightly different methods. In one study, Pinter looked at water heights on the Mississippi River from St. Louis to Thebes, Ill., just downstream of Cape Girardeau, Mo.
Pinter found that for very low flows, water heights had decreased, which he attributed to water flowing more swiftly within the channel. But under flood conditions, water levels have climbed progressively higher.
The effect appeared to be increasing over time.
"Four of the 10 highest stages measured at Thebes since 1941 now have occurred in just the past 10 years, and all 10 of the highest stages since 1973," Pinter wrote in a study published in the geophysics journal Eos in 2001.
Corps says academics
use unreliable flood data
Corps researchers dispute such studies as being overly simplistic and based on inaccurate data.
One major problem, according to the corps, is that early flood data are unreliable. Before 1931, the instruments used to measure the volume and speed of water flow overestimated the actual amount by 10 percent to 15 percent, according to corps research. And some numbers were estimates, not based on readings at all. The corps officially revised the earlier figures in a 1995 paper called "Changing History."
An 1844 flood, previously thought to be the biggest on record in St. Louis, was downgraded from a flow of 1.3 million cubic feet per second, or cfs, to 1 million cfs. The 1903 flood, which had been pegged at 1.01 million cubic feet per second, was downgraded to 875,000 cfs.
"There was no way those (old) discharges were accurate," said Stephens, the corps hydraulic engineer who worked on the changes.
Pinter has a different explanation: "The technical term for that is monkeying with the numbers," he said. He pointed to a 1979 corps study concluding that the old measurements were acceptable.
Another corps criticism is that the studies didn't account for the effects of upstream reservoirs, which hold back water during floods. The reservoirs, which came online from the 1950s through the 1980s, should be credited with decreasing flood heights, the corps says.
Without taking these factors into consideration, it's impossible to develop an accurate picture of future flood risk, corps officials say. That's what the corps did with its new study.
The flow-frequency study estimated new 100-year flood heights for the upper Mississippi, lower Missouri and Illinois rivers. The corps took historical estimates of water flow, adjusted them for the effects of reservoirs and other factors, and then projected the results into the future.
Critics immediately blasted the results and the controversial assumptions underpinning the study. While the corps assumed a positive effect from reservoirs, the agency concluded that flooding was not significantly affected by climate change, land development or the construction of levees and wing dams.
Edward J. "Ted" Heisel, senior law and policy coordinator for the Missouri Coalition for the Environment, said the corps' study should be reviewed by outside experts, such as the National Academy of Sciences.
"The implications are too large to blindly rely on a study that flatly contradicts the work of credible scientists," Heisel said.
S.K. Nanda, chief of hydrology and hydraulics for the corps' Rock Island, Ill., district, and the leader of the flow frequency study, said the corps' study already has been reviewed by an independent scientific advisory panel, as well as seven federal agencies and officials from the seven states involved.
"The methods, the concepts, the process, everything has been blessed by all," he said.
Last month, the corps announced that publication of the study had been suspended, pending funding to complete it. Some critics have questioned whether the corps might be backing away from results that have come under fire, but Nanda said the delay was for financial reasons only.
The two sides are grounded in different scientific viewpoints. Belt, Criss and Pinter are geologists, earth scientists who study long-term changes in nature. The corps is stocked with hydrologists and hydraulic engineers trained in the mechanics of water flow. Their approaches and methods are different, usually leading to conflicting results.
But in one case, a corps' study using a method similar to the academic researchers found a similar result.
Hydraulic engineer Al Swoboda, in the corps' Water Management Office in Omaha, Neb., concluded in 1998 that flood levels had risen about 3 to 5 feet on the lower Missouri since the 1930s. The bigger the flood, the greater the increase.
"It's due to the development that's occurred in the flood plain and in the channel," Swoboda said in an interview. "Deposition (of sediment), levees, roads, structures in the river. Man's influence."
Groups want corps study
of growth in flood plains
Because of the uncertainty and the high stakes involved, several groups have asked the corps to study the cumulative impact of new levees and flood plain development in the St. Louis region before authorizing any more.
The U.S. Fish and Wildlife Service, the Environmental Protection Agency and St. Louis Mayor Francis Slay all have asked the corps to look at cumulative effects.
The corps uses models to figure the "induced flooding" caused by each of its own individual levee projects. But the agency has not looked at the total impact of federal and private projects, such as the Howard Bend levee being raised from a 100-year level to a 500-year level in Maryland Heights.
"You have all these levees going in and all this land being removed from the flood plain," said Rick Hansen, a biologist with the wildlife service's office in Columbia. "Every time they (corps officials) issue a public notice, we say, 'What's the cumulative effect?' That's something we keep asking that they don't look at."
David Leake, chief of the corps' St. Louis district project management branch, said the corps would like to conduct such a study, but Congress must order it first and provide the money.
"We think it's a very important question, one that's pretty darn complicated," Leake said. "It's not something you can do in a quick study. And it's not exactly clear what people want."
Leake favors looking not just at levees, but also at upstream reservoirs and at bridge crossings such as the new Page Avenue extension.
The combined impact of many projects is "undoubtedly" greater than that caused by one project alone, he said. But he predicted that the total effect will be "not as much as you might think."
As for a potential congressional sponsor, U.S. Sen. Jim Talent, R-Chesterfield, said he would support such a study "if it was properly set up."
Meanwhile, communities must live with limited studies and conflicting reports from the corps and its critics. Flood-height projections are imprecise and subject to revision.
In the case of the Chesterfield levee, the corps initially said the new levee would cause an additional 3.4 feet of flooding a short distance upstream in a 500-year flood. The agency later revised that figure to 0.8 feet, based on newer models calibrated to recent floods.
Any increase would be devastating to Nadler, who led his town's sandbag brigade during the '93 flood.
"That eight-tenths of a foot would work on the houses that didn't get water in them," he said. "That eight-tenths of a foot would be more than we could stand."
Reporter Sara Shipley:
E-mail: sshipley@post-dispatch.com
Phone: 314-340-8215
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