Morning News Responds to Dam Questions

On Wednesday, Eric put up a post that asked several questions about the DMN’s recent story on the Lewisville Dam. Doug Swanson was the editor of that story. He has sent along responses to each of Eric’s questions. I am going to repost each of those questions, along with Swanson’s responses, which I’ve indented. Swanson says that anyone with further questions is welcome to contact him at

1. The only named Army Corps person in the story who supports its thesis — basically, that we’re all gonna die in a 65-foot wall of water if we don’t do something pronto — is a former employee. Did any current employees, even on deep background, support this theory?

SWANSON: It’s true that the person quoted is identified as a former Corps employee. However, when the story was first being reported, some months back, he was  the dam safety program manager for the Corps district, as the story says. In fact, he’s wearing a shirt with a Corps logo in the video posted on the DMN website.  He left the Corps, under favorable circumstances, to work in the private sector.

He is just one of numerous Corps employees who confirmed the 65-foot wall of water figure. The Corps figure was not based on “theory.” It was based on a host of inundation studies performed by the Corps and by consultants working for the Corps.

2. The discovery of a sand boil leads the story. The story says, “[S]uch a ‘sand boil’ indicates that increasing seepage has created a passage under the base of the dam. If not stopped, it could lead to a rupture of the dam.” But that’s not true of all sand boils, is it? This Corps document suggests they’re very common, especially after area flooding. The story says there were rainstorms and flooding. Shouldn’t we note that sand boils are common in those conditions? And the document draws distinctions between sand boils that are common and mean very little and those that indicate seepage. And although the story says that a sand boil “indicates that excessive seepage is starting to erode soil material from the downstream slope or foundation of the dam through to the upstream side to form a pipe, or cavity, to the reservoir” (or “piping,” as it’s known), that’s not always true, right? For the reasons stated above. And a Corps official yesterday said the type of sand boil in Lewisville wasn’t the dangerous kind. From a story in yesterday’s Denton Record-Chronicle, we learn:

“[FW Corps chief engineer guy Tim] MacAllister said sand boils and piping are two different issues. A sand boil is just water bubbling up out of the the ground like a spring, he said. Piping, on the other hand, is similar to a sand boil, but the water that bubbles up out of the ground is muddy and loaded with material from the dam, he explained. A dam safety training document used by the Corps of Engineers says, ‘Sand boils could indicate piping is occurring.’

“But MacAllister said piping has not occurred at Lewisville Lake Dam.

“’If we had piping taking place, that’s when I call these guys [the emergency response teams] and start evacuating,’ he said.”

SWANSON: A sand boil is an indicator of possible piping — a dangerous condition where excessive seepage starts to erode soil material from the foundation of the dam to form a pipe, or cavity, to the reservoir.  Piping could cause failure. When the sand boil was spotted during the May deluge, the Corps was concerned that piping had in fact occurred — so concerned that emergency operation centers downstream were alerted, with possible evacuations planned.  It was not treated as a “common” side effect of heavy rain. As the story says, measures were taken to mitigate the sand boil, and the evacuation planning was subsequently called off.

3. The story also addressed another thing that bugged me. The lead photograph is very dramatic. But my light Googling, plus MacAllister himself in that document, says that it’s only a “surface slide,” which is very common. In fact, he says the Corps repairs “hundreds” of such slides a year. Was that context not important?

SWANSON: Though quite large, the slide in question is not yet considered a major slide. However, Corps engineers were seriously concerned that it could, without repair or with further heavy rain, develop into a deep-seated slide, a potentially catastrophic problem. The story says that.

4. The story says the Corps lists the Lewisville Dam as “the eighth-most hazardous in the country.” That sounds very bad. Just wondering where that list is, since my Google-Fu was not strong enough to find it.

SWANSON: Citing security concerns, the Corps would not provide The News with a list of its most dangerous dams.  But it did disclose that it ranked Lewisville the eighth most hazardous dam in the country.

5. At first, I suspected that information was contained in one of the “internal documents” that the story mentions. But then I easily found this online, which seems to have a lot of the information discussed here. Information that the Corps didn’t want anyone to know — at least that’s what the DMN story suggests. And yet it’s online. In fact, the Corps guy in that Denton Record-Chronicle says that all of the information mentioned in the story has been posted online since said reports were finalized. Is that true? Then should that be made clear? Should the dramatic language be scaled back? Because the story plainly says, “The public hasn’t been told the full story about the Lewisville Dam.” But I’m trying to figure out what has been kept from the public. Little help?

SWANSON: Regarding information not disclosed to the public, the writer (and his UNT students) obtained multiple documents from current and former employees, dam consultants and government officials that are not distributed publicly.

Here are a couple of examples of information not given to the public:

The Corps did not disclose the slide at the Lewisville Dam that occurred on June 23.  The Corps put out a press release about the slide after the writer, who spotted it from a boat in late September, asked about it during an interview with the Corps in early October.

The Corps has assembled an inundation map, which shows the potential damaging path of floodwater sweeping down from the lake, through the heavily populated northern suburbs and well past downtown Dallas. The DMN produced its own version of that map from information gathered by the writer. The Corps has not made its map public.

6. The dam’s “high-hazard” status certainly hasn’t been kept from the public. Because although it seems as though this story exposes the dam’s classification — “Internal documents make clear the Corps has known about its ‘high risk of failure under an extreme event’ for many years” — that’s been part of the public record. This 2010 WFAA story says the Corps calls the dam “very high risk” and says they’re working on repair options. This DMN story from 2013 says the dam was one of 94 marked “very high risk” of failure, but that it was only then being looked at for repairs because the Corps first had to fix 13 dams classified as “urgent.” So, again, what was being hidden exactly? That Fort Worth is considering moving Lewisville Dam to the “urgent” category? Given that the 2013 story said repairs were slated to start in 2017-18, that would seem to be as much an accounting/priority/budgeting move as anything. Or maybe it’s nefarious evildoing? Just curious.

SWANSON: Are you suggesting that when the Corps district HQ considered requesting that the Lewisville dam be reclassified as “critically near failure,” it was simply engaging in an accounting procedure?  We know of no one who has said that.

7. And why was your source (the ex-employee, not the fisherman) so surprised at how many people were in the path of water in the case of a catastrophic event? Dams are classified specifically by this: how many people would be in the water’s path in a worse-case scenario. That’s why this is a “high-hazard dam.” It has nothing to do with the structural integrity of the dam; the 1,600 or so dams in United States that are “high-hazard” are so designated only based on how many people are in the water’s path if the dam goes poof. (Scroll down to the chart that explains this.) So, downtown skyscrapers would all be classified “high-hazard” under such a policy, because if they collapsed a lot of people would die. Seems relevant, but maybe I’m wrong.

SWANSON: It is true that the potential damage caused by a catastrophic failure is a part of the calculation when assigning a hazard ranking for a dam. But there are additional characteristics in the rubric. Specifically, they involve the structural integrity and condition of the dam, the risks of failure, and other safety issues.  A team of engineers and analysts from outside the Fort Worth District determined in 2008 and 2009 that the “likelihood of failure” from a number of defects in the Lewisville Dam was “too high to assure public safety.” The story makes this point as well.


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