This article first appeared in the St. Louis Beacon: June 16, 2008 - Heartbreaking flooding is destroying thousands of homes and endangering their inhabitants, in an arching belt that extends 500 miles: from Des Moines to Milwaukee to Terre Haute. As the waters gather and flow downstream, they will affect numerous cities along the Mississippi River. Levees will be overtopped in many areas, streets are already flooded in many river cities and acre after acre of crops will be lost, too late to replant this year.
Mercifully, drier conditions are forecast for a few days, but the die is cast: The Mississippi River at many sites in eastern Iowa, western Illinois and northeast Missouri will attain record or near-record levels this year.
Fortunately for St. Louis, most of the major flooding will be upstream, north of the mouth of the Illinois River. The flood stage projected for St. Louis, about 39 feet, is only about a "5-year" flood. Indeed, this level was exceeded eight times since World War II, including 1993 and 1995. However, this unremarkable stage was never attained during the 80-year interval between the Civil War and WW II, and only twice in the century before that!
What is happening?
Historical records prove that high flood stages occur much more frequently than before, and that longstanding, "worst-ever" record levels are being recurrently broken. Clearly, either the climate has changed, or the river has changed, or both. Annual rainfall amounts at St. Louis show little or no increase since 1871, but severe precipitation events may occur more often, with huge rainfall totals being delivered in only a few days. These would cause more flooding, particularly in small basins. This effect probably explains the unimaginable flood levels that devastated Cedar Rapids, Iowa, just last week.
In contrast, river constriction is probably the single biggest cause of increased flooding of the huge Mississippi River at St. Louis.
When Robert E. Lee mapped St. Louis harbor in 1837, the river was 4,000 feet wide. Now the river is spanned by the three graceful arches of Eads Bridge, totaling only 1,520 feet.
A narrower river must attain higher flood stages to accommodate high flows -- if the river can't spread out, it must go up, at least until the levees break.
Many scientists who have examined this issue, starting with the late Professor Charles Belt (as published in Science in 1975), have concluded that the combination of levees and wing dikes along and within the river are the major cause of our increased flood stages. To accommodate a given flow, our flooding river must rise 10 feet higher than it would have a century ago.
Professor Belt was discussing the unprecedented stage of 43 feet set by the flood of 1973, yet that record was smashed by the 49.6 foot stage of the 1993 flood, water more than 6 feet deeper only 20 years later!
Sadly, Professor Belt's conclusions were not just ignored, he was publicly attacked in comments authored by the St. Louis District of the Army Corps of Engineers. Consequently, business-as-usual prevailed, until the flood of 1993 vindicated the professor's important message.
So, given that the 1973 message was lost, how did our region respond after 1993?
Well, "business as usual" prevailed again, as we did the exact opposite of what the professor would have recommended.
- The levee near Chesterfield was increased and upgraded to a federally certified "500 year" level, fostering several billion dollars of new construction, in a floodplain now renamed the "largest strip mall in the world."
- Other new levees were constructed at Earth City, walling off hundreds of acres of floodplain encouraging not only new construction, but encouraging the recent decision to retain buried radioactive waste there.
- Hundreds of additional acres were walled off by new levees at St. Peters, restricting what was already the narrowest part of the Mississippi River floodplain for 40 miles.
Less obvious are navigational structures within the Mississippi River channel, which have been likened to "speed bumps" that impede the flow of the river. These include the wing dikes decried by Belt and many other scientists, as well as their newly reconfigured forms as "bendway weirs" and the three huge "chevrons" placed in St. Louis Harbor in 2007.
On a positive note, scientists from St. Louis University, Southern Illinois University-Carbondale and Washington University met last week with Col. Setliff and others of the Army Corps of Engineers. In a productive meeting, preliminary agreement was reached that additional study of the cumulative effects of levees, navigational structures and climate change on flood stages was needed, as was a conference specifically addressing those topics.
Perhaps we are on the cusp of a period of more enlightened regional development. On the other hand, "business of usual" might prevail again, with the leaders of the "Show Me" state insisting that the floodwall at St. Louis be breached or overtopped before we even consider that there may be a problem.
Robert Criss is a professor in the department of Earth and Planetary Sciences at Washington University. He is the coauthor of the 2003 book, "At the Confluence: Rivers, Floods, and Water Quality in the St. Louis Region."