Austin is evaluating the destruction caused by a landslide last week along Shoal Creek, just downstream from Shoal Creek Boulevard. Part of a hill next to the creek collapsed after heavy rains Friday, but the full scope of the damage – including damage to private property in the posh Pemberton Heights neighborhood – is only now coming into focus.
The landslide sheared off the backyards of four homes uphill from the creek on Wooldridge Drive. On its way down the hill, the debris destroyed about 300 feet of the Shoal Creek Hike and Bike Trail, toppled power lines and broke a sewage pipe, before finally settling in the creek.
(Drone footage courtesy of the Austin Watershed Protection Department)
"What we have here is a very multidimensional issue," Mike Kelly, a managing engineer with the city's Watershed Protection Department, told reporters Wednesday.
Kelly said the sewage is being pumped out of the creek, but other recovery efforts are hindered by concerns that the land could give way again.
The first order of business, he said, is to make sure removing the debris doesn't inadvertently cause another landslide. Once the city is sure the erosion is stabilized, it may try to remove debris and "shore up" the damage.
A Race Against The Clock
One of the challenges facing the Watershed Protection Department is that much of the debris has ended up in Shoal Creek. That creates greater risk for flooding and more erosion if Austin gets another rainstorm.
More water could cause greater shifting of the earth, Kelly said, so the city is looking at flood plain models to decide how to tackle the debris' removal.
But workers need to act quickly.
"May and June are our rainiest [months] historically, therefore the urgency is even higher," Kelly said.
Erosion Hazard Zones
The landslide has also directed attention to the way Austin regulates areas with high potential for landslides.
The city keeps tabs on what Kelly calls "erosion hazard zones" – generally, places near creeks and waterways where there's a high risk the ground could give way. If people want to build in those zones, they need to show they'll mitigate that risk before receiving a permit.
The damaged Pemberton Heights properties – at least one valued at over $3.5 million – were not in an erosion hazard zone, though there had been a landslide in the area in 1998.
"This area was not in a mapped hazard zone, because it was so high up," Kelly said, "and it was so far away from the creek."
The earlier landslide prompted the city to install a boulder-retaining wall. Kelly said the city will now flag it as being in a hazard zone.
"This is not something that we have often enough that we develop a systematic process to look for landslide prone zones," he said.
The houses appear to remain on stable ground, but Kelly said more rain or activity could lead to another landslide. There is also the possibility the ground could continue to slowly give way.
When asked if the city could require residents to leave their homes, Kelly said: "That's actually not something that the city would enforce. So, we would be working collaboratively" with the property owners.
In other cases, officials have not been reluctant to force people out of homes deemed dangerous.
After the Onion Creek floods in 2013, 15 homes were found to be uninhabitable. In 2010, Austin pulled the certificate of occupancy from an East Austin home after the homeowner dug tunnels underneath it without a permit.
