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."
Good.
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."
Umm.
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."