Very Simply Put, the Trinity River's Levees Keep Looking Worse With Every Corps Answer
The Corps of Engineers tells Schutze, ya know, it's not quite sure how much sand's buried in the Trinity River levees.
Well, I think I got some interesting stuff here.
The city keeps telling people they're going to "fix" the Trinity River levees. Don't much think so. Looks to me like a whole lot of the existing levee system along the Trinity is going to have be torn out and replaced.
My column in this week's paper version of Unfair Park is about the U.S. Army Corps of Engineers' report on the levee system that protects downtown Dallas from catastrophic flooding. I got to the Corps too late with my questions; they answered some right away but were not able to answer other questions by my deadline.
Just today they e-mailed me full responses to everything I asked, for which I am grateful. People have to spend time working on this stuff that we reporters ask them.
First off, a question I consider to be sort of a fun thing: Does anybody have any idea what the new Margaret Hunt Hill suspension bridge will be standing on?
This has to do with an item in the report released last week in which the Corps revealed terrible problems last year when a contractor was trying to pour concrete piers to support the bridge deck. On one of these huge piers (seven feet in diameter, about 90 feet down to bedrock), they kept pouring concrete into the hole they had drilled, finally dumping in twice the volume of concrete that the shaft should have held.
I asked the Corps, "Where did the concrete go? What kind is structure is in the ground now?"
Their answer today: "Concrete overruns can result when soil adjacent to a pier hole falls into the hole during the excavation process, leaving a void around the outside of the excavated hole which is filled with concrete as the concrete is being placed. It is believed that the reported overruns were due to this type of event."
It is believed? It is believed? I'm a-gonna drive my car on that sucker? What the heck kind of a concrete mess is down there? Are they sure it goes straight down and not sideways? Is this a finished product?
Much of the Corps report quoted in my story is about sand that liquefies or turns to syrup out there whenever anything wet hits it. I asked the Corps if they are worried that water seeping down the piers of the bridges or the toll road could turn things to soup in a big enough area that it might undermine the levees. They said no: "Based on our current understanding of conditions within the Floodway, it is unlikely that piers in the floodway will cause the sand under the levees to liquefy."
But I also asked them how much sand is out there between the levees. They said they don't know: "The location and extent of sand throughout the Floodway is unknown at this time, but will be identified as part of the additional investigations to be conducted."
It's unknown, but it's not a problem. I'm not getting comfort level here. But this is what I think the big news may be.
Sounds to me like the levees themselves are no good no matter what. The Corps report last week said, "Review of design documentation from the 1950s indicates that the levees were designed for a minimum Factor of Safety for stability of 1.3. For the Steady State Seepage condition that generally controls levee design, current criteria presented in EM 1110-2-1913 require a Factor of Safety of 1.4."
I gave them a question similar to the questions I asked all the time in my high school trigonometry class: "Uh, whudat mean?"
"Very simply put," they said, "a Factor of Safety (FS) for stability is a number that shows the relationship between resisting forces and destabilizing forces within the levee. A FS equal to 1.3 means that resisting forces (such as the weight of the levee) are 1.3 times greater than the destabilizing forces (such as water forces) acting on the levee. All things being equal, a FS of 1.4 indicates a higher level of safety than a FS of 1.3."
Did you get that "very simply put" thing? That's about me. Anyway, my reading of their answer would be this: The dirt levees "protecting" downtown were designed at a lower safety level than what is now required. So tell me: If we want downtown to be safe, according to state-of-the-art standards, doesn't that mean all the levees we have now are screwed? Jes wonderin'. That's all.
Last week's Corps report also said, "It is noted that underseepage analyses performed by others for the design of mitigations necessary for proposed projects (including bridges and pump stations) within the Floodway indicate critical gradients as high as 2.0 can be expected in some areas of the Floodway. These values are substantially greater than the 0.5 allowed under ETL 1110-2-569, and indicate that a closer look, to include extensive subsurface investigations of the Floodway and existing levees, is needed to evaluate this project under current criteria."
I asked Corps experts, "Uh, whudat mean?" They said, "Very simply put ..." Oh, man. That's twice with the "very simply put" business.
Anyway, they said: "... a critical gradient is a way of evaluating the resistance of the levee and/or its foundation to internal erosion caused by seepage forces (i.e. - loss of soil particles which is called piping). The higher the gradient, the lower the factor of safety, and the more likely that soils within the levee or its foundation will be removed during a flood. If a gradient is greater than 0.5, then implementation of remediation measures is necessary to ensure good performance at design flood levels."
Very simply put, wouldn't that mean that we have really bad gradients in "some areas of the Floodway," meaning that construction in those areas might be a bad thing? Jes wonderin'.
Hey, you know what, compadre. Every time anybody has anything to say that's real about this project, based on real data, the whole thing just keeps getting worser and worser. You know what? I'm gonna have that on my tombstone. "Jim Schutze, 1946-2009. Very simply put."
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