Tuttle Creek Dam is in the process of being stabilized because of the possibility of a moderate to large earthquake.
In order to secure the dam, the federal government is sponsoring a project under the supervision of the Army Corps of Engineers that not only will stabilize the foundation of the dam but also create supportive walls beneath the structure.
“What they’re doing is stabilizing the dam with concrete so that it protects it from earthquakes and terrorist attacks,” said Bob Strawn, city commissioner. “It is a dam stabilization project. The dam was built in the ’50s, so it was getting some age on it, and it was time to visit the safety of the dam itself. Because we are in an earthquake area, it was important to get some concrete in.”
If significant damage did occur, the lake could wash out the dam and would affect millions of Kansas citizens, he said.
“There are two million feet of water behind it,” Strawn said. “If that dam were to spill, it would just be a catastrophic impact on eastern Manhattan – all of that area would be hit with flood water. You would have many people that would drown.”
There have been more than 25 earthquakes within the Kansas borders in the past 133 years. When Tuttle Creek Dam was completed in 1962, the intake tower was put through and passed several earthquake resistance tests. During that time, however, a specific evaluation of the dam itself was not recognized. Since that time, the dam has been evaluated by worldwide experts using state-of-the-art techniques to predict the behavior of the dam during a major earthquake, according to the U.S. Army Corps of Engineers.
“We’re designing the modifications to the dam to prevent failure from anything larger than a 5.7 magnitude earthquake,” said Brian McNulty, operations manager for Tuttle Creek Lake. “From what we have determined from the experts, the largest earthquake we could possibly see in this area is a 6.6. Anything larger is unlikely.”
An earthquake at a magnitude of 2.5 or less cannot be felt on the surface of the earth. Earthquakes ranging from 2.5 to 5.4 in magnitude are often felt but cause little to no damage. Slight damage to buildings and other structures might occur in an earthquake ranging in magnitude from 5.5 to 6.0 while earthquakes ranging from 6.1 to 6.9 might cause heavy damage in populated areas. Earthquakes of the greatest magnitude reach a level of 8.0 or more and can completely decimate communities, according to UPSeis, an educational Web site from Michigan Technological University.
The federal government is sponsoring the project that originally was budgeted at $200 million. However, it looks as though the project will come under budget due to the use of different materials and faster-paced work, Strawn said.
McNulty has been examining the project as it progresses. “(McNulty) went through and described the information they found that has led them to the conclusion that the stabilizing that was planned for the lakeside of the dam is no longer necessary,” said Bruce Snead, city commissioner. “They have concluded what measure to use that would be most effective.”
The project will include stabilization through the process of modifying the sand foundation beneath the dam and excavating trenches approximately 65 feet deep in order to construct concrete walls to support the dam, said Bill Empson, Tuttle Creek Dam project manager.
“We anticipate construction completion in 2010, which is about two years ahead of our original schedule,” Empson said. “Another thing that this project includes is that we are starting to work to modify the spillway.”
Empson estimates that the entire project will require 50 to 60 contractors for the two-year period.
According to the Army Corps of Engineers Web site, at a meeting held by the Special Committee on Energy, Natural Resources and Environment in 2001, a Corps attendee explained the likelihood of an earthquake in the Wamego area within the next 100 years and the effects it would have. The attendee described that the dam would crumble and water would spill through the cracks, causing the dam to drain in approximately six days.
“The 5.7 (magnitude) probability is a 3 percent chance within the next 50 years,” McNulty said. “The problem with earthquake frequency is that each year you do not have that kind of earthquake, the probability goes up.”
Another option addressed at the 2001 meeting examined the possibilities of removing the dam altogether. After further examination, however, the committee decided that removal was not an option. Removing the dam would result in the jeopardization of drinking water for 1.5 million Kansas residents.
“The dam serves many objectives,” Strawn said. “It provides sub control on the Missouri River, so if Missouri is in a flood stage they cut off water at the dam; it serves recreation; it keeps Manhattan from flooding every year. To drain that or take that dam down, in my view, that would not be wise at all.”
Currently, the dam is set up with an emergency system that will alert the area with sirens in case of any malfunctions. Though prior arrangements were being made to remove the system once construction is completed, the city has requested control of the sirens to serve as a tornado warning system once the project is finished.
“We installed a dam failure system so that if we were to have an earthquake and the dam were damaged, we could evacuate people,” Empson said. “Even after we’re done, that system will provide tornado siren coverage for people who did not have it before.”
Over the next few years, the dam stabilization project will continue. The project aims to create a dam that will be secure during an earthquake situation.