Corps Warns that Trinity River Levees Pose a Flood Risk to Downtown, but is City Hall Listening?

Now that the truth is finally coming out about the Trinity River toll road project, it makes a difference to remember who said what two years ago. And not just as gotcha.

The Trinity River toll road is in trouble now because the basic due diligence on it never took place— not two years ago when we were voting on it in a referendum, not in the entire decade since we first authorized the Trinity River Project in an election in 1998.

These are some bad old chickens coming home.

Last week, after the U.S. Army Corps of Engineers announced that Dallas' Trinity River flood control levees are "unacceptable," meaning they are unsafe, I went back and listened to some tapes I had made to write about the issue.

One reason the Corps said the levees aren't safe is that Dallas has allowed trees to grow in and near them. Levees, the earthen berms along the sides of the river that protect downtown from catastrophic floods every spring and fall, are made of clay. Tree roots in or near levees create cuts in the clay that may allow scouring floodwaters to tear the levees apart.

In the run-up to the 2007 referendum on the Trinity River toll road, opponents of the toll road cried foul when toll road backers promised the road would be screened from view by a small forest of trees that the city would plant in the levees. City council member Angela Hunt and former member Sandy Grayson pointed out that planting trees in levees would be a violation of Corps of Engineers safety standards.

One recording I listened to was of a pre-election debate at an Oak Cliff school. Clear as a bell on my recording, Dallas Mayor Tom Leppert assured the audience that the Corps of Engineers had "signed off" on the tree issue. In fact, he promised that the Corps had signed off on all aspects of the toll road design.

"The Corps has signed off on the tree issue," Leppert told the audience. "They have signed off on the safety issue. They have signed off on the environmental issue. They are the experts. Don't take our word for it."

We know now that the U.S. Army Corps of Engineers hadn't signed off on anything. Still hasn't.

Leppert repeatedly promised Dallas voters he had an agreement with the North Texas Tollway Authority by which the authority would provide all funding for the toll road beyond the relatively nominal sum Dallas voters agreed to contribute in the original bond election in 1998. Remember? He said over and over again that he was "very comfortable" with assurances he had received from the NTTA.

We now know that the NTTA is a billion dollars short of the cost of building the road and can't come up with the money.

During the run-up to the 2007 referendum, Leppert often cited his experience as former CEO of Turner Construction, one of the world's biggest construction companies. But in fact he rose to that position from a career as a management consultant rather than as a construction engineer.

Maybe if the mayor's office had been occupied by a person who actually knew construction, someone in that office might have asked better questions about soil conditions in the Trinity River floodway where Dallas proposes to erect a major new highway, much of it on concrete piers.

If someone had insisted back then on knowing what kind of soil lies beneath the proposed road bed, they might have come up with the answer that has them all jumping out of their skins now.

Sand.

That's the concern. Sand may lie beneath the floodway. If extensive amounts of sand are down there, as tests are about to determine, then sinking a series of massive concrete piers into the floodway would be very risky, indeed.

At the end of last week, I had a detailed and helpful conversation with Kevin Craig, who is manager of the Trinity River project for the Corps of Engineers. I wanted to know more about what was wrong and why it took the Corps so long to reveal results of tests it did back in December 2007.

The answer was that the original test results sort of went out the window last year when a contractor began drilling 54-inch diameter shafts 90 feet into the soil for the Margaret Hunt-Hill "signature" bridge. The drillers hit sand.

Craig told me the Corps decided it needed to go back and review its data after the sand came up out of the bridge pier shafts. He said sand tends to occur in layers, not pockets. He said piers sunk into sand create a difficult problem and danger.

I asked him if the danger is that flood water might follow a pier down beneath the surface of the floodway and find its way to the sand. The danger then would be the water excavating the sand, hollowing out collapsible caves beneath the levees and roadway.

He said, "Yeah. Any time you have a connection of natural ground with some manmade structure, concrete or whatever, it's really hard for there to be a sealed connection there."

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