The same rocky, hilly terrain that makes Woodway scenic makes some would-be homebuyers skittish.

A ridge of layered chalk and shale runs through the suburb and into parts of West Waco, and near that ridge, soil can sometimes shift or slide downhill.

Developers say those problems only affect certain slivers of Woodway but have affected the whole city’s reputation as a place to build.

Now Baylor University geologists, working for the city of Woodway, have created a detailed map to help developers and residents sort out what’s safe to build on, what’s not, and what should be approached with caution.

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• Link: Interactive map of areas safe, unsafe to build on

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Developer Steve Sorrells stands on a foundation in the Badger Ranch subdivision in Woodway. Sorrells said the foundations are engineered to withstand expansion and contraction of the soil. Still, he said, Woodway developers face misperceptions that all of the city is geologically unstable. (Rod Aydelotte photo)

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A local foundation repair company owner said foundations on newer homes, such as these at Badger Ranch, are better reinforced than those built decades ago. (Rod Aydelotte photo)

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Sorrells scoops up a handful of red, sandy soil at Badger Ranch. (Rod Aydelotte photo)

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Baylor University geologists, working with the city of Woodway, created a map marking areas safe to build on and areas to be approached with caution. An interactive online version is available at http://maps.baylor.edu/website/woodway. (Scott Fagner graphic)

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Led by Professor Joe Yelderman, a longtime Woodway resident, the mapping identifies an “escarpment zone” along the ridge, where development is allowed only with special permission. The map, available at http://maps.baylor.edu/website/woodway, also shows “sensitive slopes” that are less risky but where developers should be cautious.

“Woodway has a lot of good area left to build on, but there appears to be some confusion,” Woodway City Manager Yost Zakhary said. “That’s why we’ve engaged one of the foremost experts in the country on this and put the map on the Web. We don’t want someone to be surprised and build something that’s a half-million-dollar investment and find out 10 years later that it’s cracking. What we’re doing is proactive.”

Zakhary said existing homeowners in the affected zones should contact the city engineer before building a fence, retaining wall or swimming pool or clearing trees from a slope.

Woodway began restricting development along the escarpment in the early 1990s, partly because of the leadership of Yelderman, who served on the planning and zoning commission. But the city has not had an official map of the affected areas until the city council adopted Yelderman’s map this month.

Yelderman had help from other Baylor geologists and students, along with Vince Cronin and Bruce Byars of Baylor’s Center for Spatial Research. Researchers used fieldwork to corroborate earlier geological data they had on Woodway.

As part of their work, they mapped slopes that were at risk of slipping or shifting because of their steepness and soil type.

Parts of Woodway lie on a base of soft Bosque shale, layered with hard Austin chalk. When it gets wet, the shale can swell and shift. When the shale lies exposed on a slope without vegetation to hold it down, big chunks of the slope face can slide away. City of Waco officials have identified a similar danger on some bluffs overlooking Lake Shore Drive.

The new Woodway map shows that many homes already lie along the escarpment, mostly in areas developed decades ago.

Yelderman said some of those homes, especially at the top of the escarpment, are on solid ground because they rest primarily on chalk instead of shale. Foundation problems are more common a little farther downhill, he said.

“Just because you’re in the escarpment zone doesn’t mean you’re destined for terrible problems,” Yelderman said, but he added: “If I’m going to buy a house in that zone, I’m definitely going to have it inspected by an engineer or a geologist.”

Waco Foundation Repair owner David Maddox said he does a lot of foundation work in older parts of Woodway.

“Typically it’s a 30- to 40-year-old home — a lot of older homes sitting on a hilly type foundation,” he said. “The biggest part of it is the soil. When we see a lot of rain like what just occurred, the soil really swells up.”

Maddox said a typical foundation job for a Woodway home of about 1,800 square feet is between $6,000 and $12,000.

But Maddox said newer homes, which tend to have better reinforcement around their foundations, have fewer problems.

Steve Sorrells, a builder and developer for the Badger Ranch subdivision in Woodway, said a modern home uses at least twice as much steel in its foundation as a home built in the 1960s. At the subdivision off of Highway 84, each home site and foundation is engineered, and the clay topsoil at the foundation footprint is replaced with a more stable red sand to prevent shifting.

Badger Ranch is far from the escarpment zone, and only a few lots are affected by the slope zone. Still, Sorrells said he has to battle perceptions that all of Woodway is shaky ground, and he hopes the map will put fears to rest.

“There have been misperceptions for a number of years,” Sorrell said. “People don’t understand it, or they misinterpret it. Wherever you build, you need to be aware of what you’re building on.”

jbsmith@wacotrib.com

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