City to work on Shoal Creek flood threat after landslide stabilization negotiations fail

The City of Austin is no longer planning to stabilize a landslide along Shoal Creek. Instead, they will work to minimize the flood risk at Lamar Boulevard.

The original landslide happened in May 2018. During a rainstorm, part of the bluff slipped pushing dirt, rock, and debris into the creek. 

There was a second slide at the same spot the following year.

The Watershed Protection Department said that the second slide actually helped to somewhat stabilize the bluff.

The landslide, also known as a slope failure, threatens four properties perched high above the trail. 

“There've been these failures up and down that formation going back to the 50s that we're aware of, so, yes, it can happen. Yes, it has happened. We don't have any indication that there's an imminent threat any other place along that formation,” said Mike Kelly, managing engineer for Austin’s Watershed Protection Department.  

The initial landslide somewhat blocked the flow of water, increasing the chance of flooding on Lamar Boulevard.

“With an estimated two-foot increase in the water surface during a 100-year flood, that would come into Lamar, primarily, and endanger folks in traffic. So that has been and continues to be the safety issue,” Kelly said.  

For the past six months, the city has been negotiating with a contractor and affected homeowners to stabilize the slide, but those negotiations failed. 
Watershed said homeowners were not happy with the restrictions that would be placed on their yards and the contractor wasn't comfortable with the amount of risk involved. 
Now Watershed is moving on to Plan B. 

“Instead of looking at the significant engineering solution that would be based on stabilizing the slope, we're moving those efforts down to Shoal Creek itself, to be opening up the available area for Shoal Creek to flow to reduce that flood threat,” said Kelly.  

With stabilization off the table, the creek cannot be returned to its pre-slide state. 
“However, there is room in the adjacent park to be able to move the creek a little bit in order to open that up, such that we reduce the current threat to flooding,” Kelly said. 

Already, the creek has started to cut a new path through part of the Pease Park greenbelt, threatening heritage live oak trees and the sidewalk. Watershed hopes they can protect both by redirecting the water. However, none of that work can guarantee the fractured rock nestled above the creek will stay put. 

“We do know, however, that fractured rock that is exposed like that can fail. Is the possibility there? Yes. Can we calculate the probability? No,” said Kelly. 

Once the flood threat has been addressed, the city will work to fix a wastewater line and a segment of the trail. 
Watershed said they will have a better idea of the timeline and cost of the project this spring. 

The city already spent more than $700,000 on the project.