Quilt-like pattern putting a stop to erosion

Quilt-like pattern putting a stop to erosion

Work to combat an erosion problem at the Brazos River Authority's intake building on Lake Granger is nearly complete and should protect that shoreline for decades.

The BRA owns and operates the East Williamson County Regional Water System, currently providing the city of Taylor, Jonah Water Special Utility District, and the Lone Star Regional Water Authority in Williamson County with potable or drinking water.

The EWCRWS consists of several big components: the intake structure, the raw water pipeline, the water treatment plant, and the treated water pipeline, said Brad Brunett, BRA central and lower basin regional manager. The intake structure takes surface water out of Lake Granger, so it can be pumped through the pipeline to the water treatment plant, where the water is then treated. The newly treated drinking water is then pumped about 3.8 miles to where users have pipelines and storage tanks to access their water. 
The lakeside intake structure is a critical component in the system that provides treated water to users.
The BRA purchased the water treatment plant from the city of Taylor in 2004. At that time, the older intake structure was located further upstream on one of the tributaries of the lake, Brunett said. The location was vulnerable to low water levels, making the intake structure at times incapable of accessing the water, he said. So, the BRA build the current intake structure closer to the dam where the water is deeper.

For the first few years, everything was fine, Brunett said. 

Then consistent rain entered the picture from 2015 through 2019. 

Lake Granger is a flood control reservoir owned and operated by the US Army Corps of Engineers. They catch water in that reservoir and hold it until any flooding downstream subsides, and then they can slowly release the water, he said. 

"And what happened was we had a lot of periods where we had prolonged high-water levels, where the water was up higher on the bank and closer to our intake structure than it normally would be," he said. "And at the same time, we had a lot of wind, and the wind generates waves, and the waves generate the erosion on the bank. And so even though the intake structure was relatively new after five or six years, we noticed that we had a problem - that the slope was eroding. It was eroding much more rapidly than I think anyone had envisioned or anticipated."

The BRA initially tried several in-house attempts to address the erosion before finally hiring the engineering firm Gannett Fleming, he said. 

The company proposed a plan, which has since been implemented.

The intake structure is located on a peninsula over a giant sump, which is essentially a pit or hollow area in which liquid collects. At the bottom of that sump, pipes are drilled out horizontally into the lake.

"The way the erosion was working, it was, every year, little by little, we were losing land, or at some point, it was going to erode all the way up to the edge of our structure, into the edge of that sump and potentially threaten the integrity of all of it," Brunett said.

There are two components to the project. On the upper section, closer to the structure, crews reinforced the area with a stucco-like concrete material that is blown on the slope. Metal nails then go into the soil and affix to the concrete anchors and into the soil. 

On the lower portion of the slope toward the lake, an articulating block concrete mattress was tied down. It looks like a giant quilt that's overlaid on the surface of the land, only instead of the quilt squares having padding, there is a concrete mixture to them. All the squares are then interlaced with cables to hold them all together, Brunett said. This quilt, so to speak, can move with the soil. 

"We're very close to being complete. I think the contractor had the final walkthrough on the project earlier this month, and the contractor is in the process of now demobilizing," he said. "We're going to have to plant some trees and things for mitigation later on in the project. But in terms of the actual structural part of the work at the intake structure, we're pretty much complete."

This fix should secure the slope for several decades, he said. 

"I've been impressed with how quick we've got it all done," Brunett said. "The contractor got in there and got it done in just a few months. And it's a big project."

Learn more here about how ongoing growth in Williamson County has spurred the incorporation of a new water source as part of the East Williamson County Regional Water System.