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Scientist questions flood benefits of public lands along Missouri River

Tuesday, July 5, 2011 | 12:00 a.m. CDT; updated 1:28 p.m. CDT, Tuesday, July 5, 2011
U.S. Geological Survey Hydrologist Carrie Elliott walks on the bank along the North Overton chute past the arm holding the multibeam echosounder she's using to create detailed maps of the chute floor on Friday.

COLUMBIA — Public lands along the Missouri River don't soak up nearly as much floodwater as previously believed.

At least that's the initial conclusion of Robb Jacobson, who has studied the river for two decades. The idea of publicly managed wetlands warding off big floods was "wishful thinking," he said, and couldn't be backed by science.

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Jacobson, chief of river studies for the U.S. Geological Survey in Columbia, recently began measuring the flood-reducing effect of public lands designed to let floods in rather than keep them out.

"I was hearing a lot of discussion in the press about how the conservation lands were probably contributing to decreasing flood peaks," he said. "And I said, 'Well, is that likely?'"

What he's found thus far through what he calls "back of the envelope" calculations, is that the effect of those lands was overestimated. They do have some effect on downstream flooding, but in a flood as large and as long-lasting as the one this summer, that effect will be insignificant.

After the overflowing Missouri River displaced 37,000 residents and caused $3 billion worth of damages in 1993, thousands left the floodplain; residents took buyouts to seek higher ground, and farmers sold land rather than reclaim their damaged soil.

The Army Corps of Engineers has spent $47 million on floodplain land in Missouri since 1993, acquiring 29,539 acres, such as Overton Bottoms along Interstate 70 near Rocheport. The Big Muddy Wildlife Refuge, which includes Overton Bottoms, manages just over 17,000 acres of that land along the Missouri River. The vast majority of it used to be farmland, Refuge Director Tom Bell said.

The Department of Conservation credited public lands for soaking up floodwater in 1998 and 2002 that would have damaged properties up and down the river.

The math doesn't add up, though. In a big flood, a small portion of natural wetlands can't swallow all the water from a river with levees lining most of its banks.

If all 17,000 acres of the Big Muddy Wildlife Refuge flooded to an extreme depth of 20 feet, it would store just 1 percent of all the water expected on the Missouri River this summer, Jacobson found. Even if all the authorized land of the refuge, 60,000 acres worth, could flood that high, it would store 10 percent of the floodwater, which he estimates would equate to less than a foot of river stage.

"For large floods, unless we have a lot more of these flood plains and wetlands, it's unlikely they'll store a big enough volume to attenuate the flood," Jacobson said. "Locally, they'll have an effect. But systematically, they won't."

Levee breaches in northwest Missouri illustrate that disparity.

When the river breached a levee protecting Rulo last week, the area saw a 24-hour drop in the river level, Jud Kneuvean, chief of emergency management for the corps' Kansas City District, said. Soon, though, the river filled the plain behind the breached levee and continued to add to the river level downstream.

"For all the acres we buy, the bulk of the flood plain is still protected by levees and still in agricultural production," Kneuvan said. "Folks like to believe it will relieve flood peaks, and we don't really have any data on that."

Jacobson's team is trying to change that. No one has ever studied the effects of conservation areas on Missouri River flood levels, as far as he knows.

On Thursday and Friday, Jacobson and his team took a jon boat into Overton Bottoms to study how water travels over that land and back into the main channel. Where the water enters a floodplain, where it leaves, and what vegetation it flows over all determine how quickly that water returns to the channel.

During smaller floods, flood-prone conservation lands do seem to provide some relief, Jacobson said.

Farmers John Sam Williamson of McBaine and Wayne Hilgedick of Hartsburg say they've noticed a difference. A high river level on the Boonville gauge doesn't seem to affect the river towns like it did before areas such as Overton Bottoms were set up. Brett Dufur, a bed and breakfast owner in Rocheport, also credited conservation areas for lessened flooding effects.

"You know, I didn't think they would do much, but somehow or another we don't get the full impact of the water when it's raised, so I don't know," Hilgedick said. "There's a place for the water to go, but it's hard to tell whether that's having any effect on the end results."

One of Jacobson's projects this summer is determining what severity of flood those lands help reduce, be it ones likely to happen every five years, every 10 years or the rarer, larger floods. The data collected at Overton Bottoms will go toward making river models that can help answer the question of what benefit public lands along the river pose beyond the obvious environmental gains.

"Are those lands beneficial from a socioeconomic and political standpoint? They could be if it saves flood damage every 10 years or so," Jacobson said. "That's what will come out of our analysis, hopefully."


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