Engineers study earthquake risk at Tuttle Creek Dam

Related Sites: • Army Corps of Engineers

By JOHN L. PETTERSON - The Kansas City Star Date: 09/07/01 22:15

TOPEKA -- Someday a strong earthquake could jolt the Manhattan area, cracking apart the dam at nearby Tuttle Creek Reservoir and freeing the huge lake behind it.

Should that occur, much of Manhattan would be flooded, as well as other downstream areas. Losses would be staggering.

The U.S. Army Corps of Engineers is studying the dam with an eye to coming up with a plan to reduce the possibility that an earthquake could take out the 11/2-mile-long earth-and-rock structure.

"Tuttle Creek Dam is at risk of significant damage or failure from seismic ground shaking," state geologist M. Lee Allison said recently at a briefing for a legislative committee. "The dam should be seismically retrofitted, (or) removed, or the reservoir drained in order to reduce or eliminate the risk."

Just when to expect an earthquake large enough to cause the dam to fail, no one knows. Experts can offer only educated guesses.

"The next big earthquake might not happen for hundreds or even thousands of years, or it might occur tomorrow," said Allison, director of the Kansas Geological Survey.

It's hard to get people excited about earthquakes in Kansas, especially when the Federal Emergency Management Agency last year ranked Kansas 45th among states in the amount of damage caused by earthquakes in an average year.

Bill Empson, the corps' dam safety project manager, said there was a 3 percent chance in the next 50 years of an earthquake registering 5.7 in the Tuttle Creek area. An earthquake of that magnitude would create the potential for significant damage to the dam.

The Corps of Engineers, which is conducting similar studies throughout the country, said the dam had been evaluated by international experts.

They found that a big earthquake could "liquefy" the sands under the dam, causing them to act like a liquid and making them unable to support the dam's weight. The dam would crack, and water running through it would cause its failure.

"Although the probability of an earthquake of the size necessary to damage the dam is very small, due to the potential consequences, this possibility is being taken with all seriousness," the Corps of Engineers said in a report on its Web site.

Tuttle Creek Reservoir is about 12 miles west of the Humboldt fault, the most active earthquake zone in Kansas. It stretches generally from Omaha, Neb., southwest to Oklahoma City.

It was just east of Manhattan near the town of Wamego that in 1867 the largest recorded quake in Kansas history occurred. Based on published reports, experts estimate it would have registered between magnitude 5.1 and 5.5.

It caused walls to crack in Manhattan and sands in the Kansas River valley to liquefy. There was minor damage in Lawrence and Kansas City, and the shaking was felt as far away as Indiana, Kentucky and Arkansas.

The Corps of Engineers already has devised a list of options for dealing with the possibility of a damaging earthquake.

For a total fix, it could remove, replace or enlarge the dam, or stabilize the soil under the dam.

To minimize the risk it could improve seepage control, restrict lake levels, manage the downstream flood plain, improve emergency planning and improve the ability to drain the lake.

Another alternative is to do nothing and accept the risk.

So far, none of those possibilities has been selected. A proposed recommendation is scheduled to be made public in the spring, Empson said.

"As far as the existing safety of the dam is concerned, we have had contingency plans in place since 1976," Empson said. "Under normal operating circumstances, the dam is safe."

It would cost about $250 million to replace the dam, $100 million to stabilize the foundation soil, and about $30 million to remove the dam and eliminate the lake.

The state, along with some cities and businesses along the Kansas River, would be obligated to pay part of the cost of any improvements.

Work costing $100 million would mean a $375,000 bill for the state and members of the Kansas River Water Assurance District. Among the district's members are Olathe, Bonner Springs, Johnson County Water District No. 1 and the Board of Public Utilities in Kansas City, Kan.

The idea of sharing the dam improvement costs does not sit well with Senate Majority Leader Lana Oleen, a Manhattan Republican: "It seems to me that common sense would be that the corps certainly would be responsible for reinforcing the dam they built."

The lake behind the dam holds back almost one-fourth of all flood storage in the Kansas River basin. At flood pool it stores 2.2 million acre-feet of water. One acre-foot would cover 1 acre to the depth of 1 foot.

Pat Collins, Riley County's emergency management director, said that if the dam were to break, the east side of Manhattan would be flooded and that about 10,000 people would be affected immediately.

So far, local officials are waiting to see what kind of proposal the corps develops.

"Administratively, we're...encouraging people to respond to the corps' request for input," said Jerry Petty, Manhattan's public works director.

To reach John L. Petterson, who covers Kansas government and politics, call (785) 354-1388 or send e-mail to jpetterson@kcstar.com.

The details

A few facts about Tuttle Creek Dam:

137 feet tall.

7,500 feet long.

Earth-and-rock structure.

(The Humboldt fault is about 12 miles away.

On the Web

For quick, easy access to the U.S. Army Corps of Engineers, go to The Star online at www.kansascity.com.

-- Anonymous, September 08, 2001

Answers

It's amazing, isn't it? We go about constructing these things like dams and *later* think about the "what if" an earthquake comes along. Well, frankly, I don't think there's one single thing we can do to stop earthquakes, and when they hit they release mind boggling energy. Sort of like Mount St. Helens. The devastation was beyond the comprehension of the best people who studied that. In fact it took the life of some of the scientists who didn't even know where it would be safe to be to even watch the darn thing. If that dam fails during an earthquake, NY is toast. Soggy toast, sure, but toast.

-- Anonymous, September 08, 2001

Is this a problem?

-- Anonymous, September 08, 2001

Um, I think that's manhattan, Kansas. Bit the following statement causes me some anxiety:

"Under normal operating circumstances, the dam is safe."

Now is it just me or do I hear you all going, "Wow! That's pro-found" and rolling yer eyes?

-- Anonymous, September 08, 2001