The mighty power of the river: Will levees hold against the next great flood?

News-DemocratAugust 3, 2013 

Two decades after the Great Flood of 1993, scars can still be seen in the landscape along the Mississippi River.

In some places, such as the metro-east village of Valmeyer, empty foundations and farm fields stand where businesses and residential homes once did. But across the Mississippi River in Missouri, hundreds of millions of dollars of development have been added in places such as the Chesterfield Valley, where two new shopping malls are set to open.

Mike Petersen, spokesman for the U.S. Army Corps of Engineers, said the levees in the St. Louis metropolitan area were rebuilt to the standards they were before the 1993 flood. And in some places, they were built to higher standards.

"The levees in the urban areas are meant to withstand a 500-year flood," Petersen said. "We're as prepared as we can be. But no levee is ever completely flood-proof."

Petersen said in some places people have been lulled into a false sense of security because of the fact that the levees held for the last two decades. Even in 1995 when the fourth-worst flood in history at St. Louis occurred at a level of 41.89 feet, and earlier this year when the sixth-worst flood, 40.52 feet, happened, water stayed on the right side of levees.

"Although the 1993 flood was the worst we have ever experienced, it's not the worst possible," Petersen said. "It was roughly a 350-year flood. So the expectation is that a greater flood could come."

Corps of Engineers civil engineer Gerald Allen said the 1993 flood, which topped out at 49.58 feet at St. Louis, came within less than a foot from over-topping flood walls in East St. Louis. If it was only a little bit deeper, water would have gushed into areas of that city, Collinsville, Granite City and everyplace west of the bluffs on the Illinois side of the river. More than 100,000 people would have been affected on both sides of the Mississippi.

Brenda Johnson said she and her husband, Brian, helped their neighbors in Valmeyer desperately move their belongings when the levee system became compromised 20 years ago. She said they lived just outside the Federal Emergency Management Area buyout area. While her friends moved to new Valmeyer on top of the bluffs, she and a handful of her neighbors were left down below in the path of a potential future flood. She saw too much to take the river for granted.

"My son spent his 16th birthday driving the town dump truck to load sand for the many volunteers," Johnson said. "My daughter and I baked and cooked for a lot of the volunteers at the firehouse. Yet we still lost the town to the mighty power of the river.

"My mother and one sister lived in our driveway in a camper trailer," Johnson said. "My other sister and brother-in-law moved in with his parents. My husband's 94-year-old grandmother had to be relocated. I packed up so many houses during that time, I lost count.

"Yes, it was a devastating time, but, the good news is that my husband retired two years ago from Valmeyer. He will tell you that the flood was the most challenging time," Johnson said. "Yes, we were lucky that we didn't lose our home. (But) we gained a new respect for the Mississippi, and for the faith in people."

In the metro-east, the Southwestern Illinois Flood Prevention District was formed by Madison, Monroe and St. Clair counties to oversee improvement of the region's levees. The district is funded by a quarter-cent sales tax that took effect in 2009 in Madison, St. Clair and Monroe counties and generates about $11 million a year.

In New Athens along the Kaskaskia River, the levees didn't pass inspection and have lost their Corps of Engineers certification. Local officials there say they don't have the money to make needed improvements.

And, even if they did, it doesn't guarantee that the levees won't fail.

"Anything below 40 feet I don't worry about," Corps of Engineers civil engineer Dennis Gilmore said. "But a big part of the problem is that levees are made out of earth and they can only stand so much water and so much pressure."

The levees failed in 1993 not just because the water was deep but also because it stayed around for so long, Gilmore said.

Mark Alvey, chief of geotechnical engineering for the U.S. Army Corps of Engineers in St. Louis, explained how flood protection fails.

"When levees get saturated by through-seepage, the saturated soils can soften, lose strength, and make the levee unstable and more vulnerable to landslides," Alvey said. "If a levee slides and that slide is not addressed with flood fight efforts, it could progress the center of the levee and reduce the height of the flood protection."

Also, according to Alvey, saturated levees become a problem because they get too wet to drive onto the structure the equipment needed to repair and save it.

But Alvey said newer flood protection is more reliable than the levees they replaced.

"Modern levees, those designed and built after the 1950s, take this through-seepage and saturation into account," Alvey said. "These levees perform better than older levees that aren't as well designed and built."

Then there is the issue of the water just getting too high to stop.

According to the Corps of Engineers, at 44.1 feet the Chouteau Island pump station begins to flood and the Harrisonville and Columbia levees will be over-topped, exposing 50,000 people to flooding. At 48 feet, the Prairie DuPont levee is over-topped exposing 37,360 acres to flooding. At 49 feet, the Hartford public water supply is threatened and at 54 feet the East St. Louis and Fish Lake levees are over-topped exposing 71,000 acres.

Allen said one of the main improvements to levees was to try to take the pressure off in the event of major flooding.

"There were a lot of lessons learned and a lot has changed," Allen said. "There has been a lot of rehabilitation of relief wells done along the entire system. A lot of buildup of seepage berms because of sand boils. There are quite a few of those along the stretch of Chain of Rocks canal. We redid all the closure structures on the East St. Louis levee wall, painted it and put numbers on the monoliths so we can reference them. We've done everything we could to be ready. But you're never prepared for everything."

Johnson said she will never forget the lessons on 1993.

"Trust is something that is earned, right?" Johnson asked. "So far, the levees are holding, but of course the river hasn't been as high as it was in 1993.

"The levees were rebuilt, and they are supposed to be stronger than ever' Johnson said. "They probably are. However, in 1993, our course of history was changed forever. Do I think it could happen again? Maybe not in my lifetime, but, yes, I anticipate it happening again. That is the history of the river, isn't it?"

Contact reporter Scott Wuerz at swuerz@bnd.com or call 239-2626.

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