Flood Levels are Becoming the New Normal

  • A swollen Ohio River engulfs a barn in Golcanda, Illinois, March 7, 2011. Photo: Newbie1982 via Flickr

July 10, 2015

You might be noticing high waters along the rivers. But they aren’t necessarily unusual, and they may be a sign of the new normal. A new study suggests the federal government has underestimated 100-year flood levels by as much as five feet on many rivers.

By definition, a 100-year flood reflects a water level that is supposed to have a one-percent chance of happening in any given year, as determined by federal agencies. But Robert Criss, a geology professor at Washington University in St. Louis, says the big 100-year floods happen much more often than that.

“The real one-percent flood is much higher than the official calculations that presume things are the same as they used to be.”

In a study published this month in the Journal of Earth Science, Criss looked at historic flood records on a dozen Midwestern rivers, including the Ohio. He says average high-water marks on these rivers are rising about an inch per year. He blames fewer trees, faster runoff and higher levees along the rivers. Climate change is also a factor.

Criss says a flood level the government anticipates every 10 years now happens nearly every year. This leads to people building houses and other structures in flood zones. Criss wants the flood levels recalculated and says it would help communities better prepare for increasing flood levels.