Flood thy neighbor: Who stays dry and who decides?

Meramec begins to rise, the gates close and seal off Valley Park from the wall of water.

When the levee was designed in 1993, the Corps’ hydraulic modeling software demonstrated it would increase flooding upstream by less than 5 inches during a 100-year flood (a flood that has a 1 percent chance of occurring each year) and only within a few miles of Valley Park — not far enough to reach Eureka or Pacific. It had put the average yearly cost of flooding created by the levee at $7,200 in 1987, or $16,000 in 2018 dollars.

“The Army Corps of Engineers, before they built the levee, they were having meetings and telling everybody, ‘No, no, this levee’s not going to hurt anything. It’s not going to affect anything,’” Walt Wolfner said. “And they basically, in our minds, lied to us.”

In reality, the Corps could not say with certainty that the levee wouldn’t contribute to additional flooding in the future, because its calculations left out how key variables could change over time.

The first of those factors is development. The Corps built the levee tall enough to protect against a 100-year flood, a height that offered an additional perk: Valley Park residents no longer had to buy costly federal flood insurance.

With a levee to protect the city, the Corps calculated that rising land values in Valley Park and administrative savings in the flood insurance program would create nearly $100,000 in annual benefits, about $225,000 today. That number helped bolster the case for the levee in the Corps’ cost-benefit analysis.

But even though the Corps anticipated that the levee would prompt growth in the area worth $15 million per year, it didn’t expect the flood damage to grow, too.

Valley Park’s population has more than doubled since the 1980s, to 6,900. And between 1980 and 2010, the combined population of Arnold, Fenton, Valley Park, Eureka and Pacific increased nearly 50 percent.

Tim Engelmeyer, Valley Park’s city attorney, said critics in the region are unduly fixated on the levee, but any Meramec community that allowed development since 1993 has “brought