The Lake Whitney mansion that lost its clifftop footing might serve as a cautionary tale for Central Texans wanting to build for the view.
Even in Waco, where the city enforces strict rules about building on unstable slopes, some older homes overlooking Lake Waco experience foundations that shift and backyards that sometimes slide away. One slope above Lake Shore Drive is so prone to sliding that city officials fear that it could collapse and take out a section of the four-lane road.
Still, geologists and soil engineers say they doubt any homes on the escarpment, or ridge, overlooking Lake Waco would give way suddenly as the Lake Whitney house did.
It’s unclear exactly what caused the cliff to collapse under the 4,000-square-foot Lake Whitney house, leading the owner this week to have the house burned and demolished. But Scott Langerman, a Waco geotechnical engineer, said any structure built that close to the edge of a dropoff should have had extensive engineering testing first.
“I don’t want to scare people, but there is always a danger when you build on a cliff,” he said. “If they weren’t built in a manner to keep them from sliding, they’re absolutely in danger of sliding.”
The geology around Lake Waco differs significantly from that of the Lake Whitney area. The Whitney bluffs are mostly solid limestone, said Peter Allen, a Baylor University geologist whose work led to escarpment development restrictions in Waco and Dallas. As such, the bluffs should be more stable than the escarpment east of Lake Waco, which is limestone atop a shifting layer of soft South Bosque shale, which turns to clay as it weathers.
Allen said it’s rare to see a solid rock face in this area collapse, though it’s happened on a smaller scale along the river trail at Cameron Park. He said it’s possible that the stone had cracks that widened as they were exposed by wave erosion at the foot of the cliff.
Allen said he doesn’t know what kind of engineering work was done before the house was built, but given that it was in an unincorporated area, there would be no state or local rules requiring it.
“Everybody has 20/20 hindsight,” he said. “You look at a house like that and say, ‘It’s beautiful, it’s gorgeous,’ but we don’t want to worry about it until there’s a problem. That’s when ordinances are passed calling for judicious engineering.”
Allen worked with the city of Waco in the late 1980s to pass an ordinance restricting development in the Lake Waco escarpment.
Developers since then have had to submit detailed soil engineering reports and slope stability analyses to guarantee a large margin of safety. Foundations must be designed and approved by structural engineers. In addition, no one can dump, excavate or clear vegetation in the slope area without a permit.
Allen said houses built in the escarpment since the 1980s shouldn’t have problems with shifting slopes. Some older houses face complicated and expensive foundation problems, but he doesn’t foresee “catastrophic failure” like the Lake Whitney case.
“They won’t fall in the lake,” he said. “What you’ll see is a very slow failure, what we call creep, where the house will start having problems in Sheetrock and foundations.”
Langerman, the geotechnical engineer, said the escarpment ordinance is unusual in Texas but it has encouraged safer development. He said he has consulted on houses near Lake Waco that have seen their backyards slowly shrink as dirt gives way.
Tom Chase, a Waco insurance executive, lives in a home built atop the escarpment in the early 1950s. He said when he and his wife, Penny, were looking at the house in the mid-1990s, the city engineer at the time told him he’d be “stark raving mad” to buy it.
He said another expert told them that “this house is going to slide into the lake. It might be tonight, or it might be 1,000 years from now.”
“Penny said, ‘I’ll take 1,000 years,’ ” Chase said. “She really wanted it.”
Chase said he hasn’t had any geological problems with the house, though he has watched sections of rock and dirt slide down the slopes behind his neighbors’ houses.
Chase, CEO of Insurors of Texas, said his house isn’t insured for “earth movement,” which is generally excluded from standard homeowners insurance policies. He said specialized insurance against slope failure might be available but it could cost thousands of dollars a year. He said he’ll take his chances.
“We’ve known from day one that if you’re up on the fault, it might happen,” he said.
Lake Shore Drive
The slope face below the Chases’ house has had minor landslides through the years that have resulted in piles of dirt and rock stacked against the guardrail below on Lake Shore Drive.
The city hired the Kleinfelder engineering firm in 2005 to study the slope instability issues above that section of Lake Shore Drive, near Koehne Park. The firm warned of the possibility of a catastrophic failure of the slope.
“It is likely that an extensive slope failure involving destruction of portions of Lake Shore Drive will occur at some point,” the firm reported.
City officials at the time discussed ideas including elevating Lake Shore Drive on piers so that the slope would slide under it.
But Allen, who has been consulting with new City Engineer Octavio Garza on the slope issue, said he would suggest exploring less expensive and less invasive options.
“What we’re looking at is a way to make Lake Shore Drive safer,” he said.
Waco Councilman Kyle Deaver, who lives on Northridge Drive in a neighborhood between Lake Shore Drive and the lake, has asked city staff to take a new look at solutions for the road.
“I’m trying to understand for the first time what can be done to solve that,” he said. “I’m very concerned with what’s going to happen to that slope. At some point we’ve got to fix it or close the road. I don’t think closing it is an option. I just don’t want to keep putting a Band-Aid on it.”