Homeowners nervous after rains, landslide
Parts of backyards overlooking Shoal Creek were swept away.
Standing in the backyard of the Wooldridge Drive home where he was born and that he now owns, William Heyer pointed at a lofty tree below what just days ago was a gentle slope at the edge of his property and now is an abrupt drop-off.
“That big tree,” he said Wednesday, moving his pointing finger up to the open space in front of him, “was right here. Everything you can see was 40 feet, 50 feet higher last week . ... There wasn’t a view here. This was all trees.”
Just a few months ago, Heyer’s children were climbing and play- ing on a stone wall that bordered the back of his property, just as he once did at their age.
But on Saturday, after Friday’s short but torrential downpour, an out-of-town Heyer received a text message from a neighbor telling him that much of his backyard, including that stone wall, had crumbled away about 4 a.m. Saturday, moving the edge of his property to within 30 to 50 feet of the back of his house.
Heyer is one of four home- owners in an upscale neigh- borhood who saw parts of their backyards swallowed by a landslide near the 2500 block of North Lamar Boulevard and along the west bluff overlooking Shoal Creek.
“It’s enough to make you nervous,” said Heyer, 51. “It’s really sad. This house has been in my family for 55 years, and it’s going to be very difficult to fix.”
The roughly 80-foot-long landslide also caused a paved section of the Shoal Creek Trail to collapse into the creek bed, prompting officials to cordon off the trail from Shoal Creek Boulevard to 24th Street.
There were no reports of injuries, officials said, but the erosion damaged city park- land at Pease Park and about
300 feet of the hike-and-bike trail while also buckling a city wastewater line beneath the trail.
For now, crews have put in pumps that redirect wastewa
ter flow to a working part of the system until they can find a permanent solution, said Mike Kelly, Austin Watershed managing engineer.
More rain or any move- ment to the soil could trigger further erosion, so offi- cials have instructed city and private repair crews to stay away from the landslide and to refrain from removing any material for the time being, Kelly said.
In a race against time as Austin awaits sometimes heavy May rainfall, officials say their priority is safely determining in coming weeks the stability of the land and what, if anything, can be done to secure the cliff in the future.
Repairing the trail, which can still be accessed by crossing the creek and using the sidewalk along Lamar, is more of a secondary concern, Kelly said.
While Kelly said he can’t pinpoint the specific cause of the landslide, in general such mass movement of soil is caused by a combination of water, fragile geography and topography.
“Geology set us up for this situation,” he said, “and then water events are what precipitate failures like this (one).”
Though it’s easy to forget in relatively earthquake-less Austin, Kelly said, Central Texas sits within the Balcones Fault Zone.
What’s more, the bluff above Shoal Creek is made of Buda limestone over an unstable Del Rio clay forma- tion, he said. When the clay moves beneath the limestone, it causes fractures that can eventually lead to slope failures. Heavy rains Friday swelled
Shoal Creek by 11 feet. Austin’s Camp Mabry weather station recorded 3.67 inches of rain Friday, according to National Weather Service data. It came over a period of a little more than an hour, officials said.
The creek usually is in the neighborhood of 1.4 feet. Around noon Friday, however, it crested at 12.37 feet, according to Lower Colorado River Authority stream gauges.
Development atop the cliff was likely not a factor, Kelly said, as there have been buildings on Wooldridge Drive since the 1920s.
“Any activity can set this off,” he said, including digging or otherwise disturbing the soil, but “we don’t have any indication that there was an event. The rain is the event that we look towards.” The landslide could, how
ever, cause Austin to reconsider the boundaries of its erosion hazard zones, which trigger certain city requirements for what hazard mitigation one needs to do to gain per- mission to build, Kelly said.
Kelly said his department and many others, including Parks and Recreation, Pub
lic Works and Austin Water, are collaborating to study the landslide as well as working with the affected property owners.
Using drone footage and flood plain maps, Kelly said, staffers are running models of what could happen to the area in the event of more rain, which will help them come up with solutions.
Some possible fixes that have been used in the past include a sheet piling system, which consists of stiff, corrugated steel placed into a slope to keep soil in place, or earth anchors, which are engineered reinforcements.
It’s too early to say whether those fixes will be possible without knowing the soil’s threshold for more movement right now, Kelly said.
Fr i day’s lan d sl ide was not the first to occur in the area. Most recently, there was a slope failure in 1998 that affected the trail in the same spot, Kelly said.
City crews at the time repaired the trail with a boul
der retaining wall and reinforced a small portion of the lower slope, he said.
Whether residents decide to stay or move once the city has determined the level of risk to their homes will be up to them, Kelly added.
Heyer estimates he lost about 3,000 square feet of his backyard. In the past couple of years, he said, he had noticed that some of the
dirt had begun to shift a bit and a pipeline had started to tilt. “I think the rain and the flooding was just the last straw for it,” he said. “It looks like Malibu, one of their slides.”
For now, Heyer, who had recently started thinking about selling the home, said he’ll wait for the city’s analysis before deciding what to do.
“Nobody’s going to buy it right now while this gets resolved,” he said. “So, yeah, we’ll be holding on to it for a while.”