UNL engineer: Stormwater management projects worked

Heavy rains in early June caused water in Salt Creek to rise to near flood stage for a second time this spring.
Heavy rains in early June caused water in Salt Creek to rise to near flood stage for a second time this spring.

During a record-breaking two months of rainfall this spring, much of Nebraska kept its eyes on the sky and its ears open for weather alerts about flooding.

While John Stansbury wasn't out chasing storms or watching radar, the University of Nebraska-Lincoln associate professor of civil engineering was paying close attention nonetheless.

"I'm more interested in the big picture and how it's going to affect our water resources than I am in any one big storm," said Stansbury, whose research includes best-management practices for stormwater management.

In the days after a May 7 storm dumped up to 11 inches of rain on parts of southeast Nebraska, many towns and cities felt the effects, including flooding in DeWitt, Fairbury and McCool Junction. The Antelope Valley project in Lincoln saw water levels in the Salt, Oak and Antelope creeks nearly spill over their banks and communities to the north and east, along the path Salt Creek takes as it flows toward the Platte River, saw some flooding.

While driving through Ashland in the days after the big storm, Stansbury couldn’t help but take a detour to see how Salt Creek and the Platte River held up. His interest, he said is in the larger meaning: Are the climate patterns changing? What effect could that have on our water resources availability? Will we have more water or less water? Will we have more floods or bigger floods we have to engineer around?

For the most part, Stansbury said, the engineering projects across the eastern Nebraska fared well, despite being overwhelmed in places by rainfall and residual runoff.

"It's really hard to take these isolated events and say too much about them because there have always been floods in these basins," Stansbury said. "We've certainly had 11-inch storms before. You want to think there’s something special about these, but it takes a lot of data collected over decades and centuries to make that determination."

Civil engineers often look at projects in terms of preparing for the "100-year flood or 100-year storm," Stansbury said. The relative paucity of data, he said, makes it difficult to know just what that means.

Across the United States, it is only in recent decades that engineers have been able to make those historical analyses with great certainty. That is because weather statistics have only been kept for a little more than the last 100 years. In Lincoln, for example, a University of Nebraska database shows temperature and precipitation records that date to the 1880s.

"When you're talking about recent, though, you're talking about a decade or a couple of decades. It's hard to know if the data you're collecting is representative of what it's going to be like or if it's just a blip in the historical record," Stansbury said. "In another 100 years, we'll be able to look back and say that what was going on in 2015 was the start of things that changed or if that just happened to be a wetter-than-normal year in a certain part of Nebraska."

In the meantime, Stansbury said, engineers have plenty of options available to help cities control flooding and diminish the potential for damage to property -- flood-control reservoirs and levees, for example. But none of them is fail-safe, as recent months of rain and the storms of 2011 showed with the flooding along the Missouri River in Nebraska, Iowa and Missouri.

"The tricky thing about those kinds of controls is they have a designed return period that they protect for," Stansbury said. "We typically design levees, although there's no such thing as typical, to protect for the 100-year flood. On average, that means that 99 years out of 100 years your town shouldn't get flooded.

"People forget that that it also means that on average one year out of 100 you will get flooded. Some get upset and say that the flood protection didn't work, when in reality it probably did work just as it was designed."

— Karl Vogel, Engineering