Mansfield Dam gets a $10.5M facelift, floodgate renovation

The project is the first time the dam’s 24 floodgates have ever been worked on, Hofmann said.

Dam construction began in 1937, with the floodgates built first and the concrete for the dam poured over the top of the gate structures in place, he said. However, the plans were altered following major floods on Lake Buchanan in July 1938 that heavily damaged communities downstream, he said.

“That water hit down here in the middle of construction of Mansfield Dam, which at that time was [known as] Marshall Ford,” Hofmann said. “There was a little bit of a debate as to how high the dam facility ought to be. After the 1938 flood event, they decided to add another 78 feet to this dam facility to increase its protection capabilities.”

He said the increased dam height added flood storage capability to and greater protection to Austin, Bastrop, LaGrange and downstream.

The spillway height is 714 feet, and Hofmann said the closest that water has risen to the spillway top occurred during 1991 when water rose to within 3 1/2 feet of going over the structure.

“That’s our record,” he said.

Renovation challenges

Because replacement parts for the 80-year-old floodgates and dam infrastructure are no longer available, the LCRA contracted with an independent company to recreate the intricate pieces needed to repair the broken and/or inefficient parts, he said.

“These are not parts that you can get at Home Depot,” Hofmann said. “In fact, a lot of these parts have to be manufactured specially according to the specifications that were put in place by the engineers that designed the facility in the late 1930s.”

There are about 5,500 parts that comprise a gate, which presents a logistical issue regarding accountability, he said.

Another challenge involves the narrow interior dam tunnels through which the gate structures need to be transported to be worked on, he said.

Each one of the floodgates gets entirely removed from the gate hole in which it sits, is taken apart and pulled outside, Hofmann said.

Each gate weighs about 50,000 tons, and 16-ton hoists, or chains—similar to very large bicycle chains—are located on each side of the gate to pull the structure out the gate hole, he said. A crane is used to lower the gate onto a cart, he said. Rails inside the tunnel house a cart that moves the gates once they are out of their compartments and through the tunnel to the dam entrance and then to an air-conditioned work structure constructed on-site specifically for this project, Hofmann said.

“The [chains] have a lot of very small gears due to the amount of weight they have to lift, so the lifting takes a great deal of time,” he said. “It takes about 10 minutes to go a foot. If you have both [chains] on at the same time and you lifted the gate in one continuous motion, it would take something like five hours to pull the gate completely out of the compartment.”

Hofmann said staff generally pulls up the gate in stages and works on it as it is pulled out of the gate hole.

“In some cases, there is only inches of clearance between the uppermost portion of the gate structure that you pull out and these tunnels,” he said. “There’s no locomotion associated with the carts we put them on. It takes five or six of our employees pushing like crazy to get these carts through these tunnel structures and out where we can finish taking the gate apart and work on it.”

Some work is shipped to other places, but the majority of it is done in the on-site shop, Hofmann said. Five gates are already completed, he said.

Being required to maintain the dam's flood-ready status at all times is an issue during the project, he said.

“No matter what we’re doing with the gate rehab project, we have to make sure we have sufficient capability to deal with a major flood event if it happens,” Hofmann said. “That’s true for the entire 11 years [of] the project.”

The most gates that have ever been open on this facility is six, Hofmann said. Staff initially worked on a single gate at a time but now work on two gates simultaneously, he said. It takes about six months to complete the refurbishment of each gate, he said.

Other projects

The road on top of Mansfield Dam—replaced by RR 620—will also be improved. Renovations to the dam tunnels as well will decrease the humidity inside and help preserve gate parts.

“After 70 years, it’s time,” Hofmann said of the project. “The goal is to get them as close to original condition as we can so that we can hopefully get another 50, 60, 70 years of service out of them.”