The tone was serious but optimistic at a meeting hosted by the Army Corps of Engineers to discuss the state of the Lewisville Lake Dam and the measures being prepared to keep it functioning. A failure would submerge a large swath of Dallas and its suburbs.
Tuesday night’s overall message from the Corps was that the dam is working as designed but that measures to fix the dam are being taken very seriously.
When resident Jim Barnheart learned about the possibility of the dam failing, he checked to see if his home and his daughter’s home were in the flood zone. He’s attended several meetings now and seen how the plan has evolved. “The last meeting they didn’t have that solution,” Barnheart says, as he examines a display. “They seem to be on top of everything they need to be.”
The issues with the dam began about eight years ago but the severity of the situation only came to light after The Dallas Morning News published an article last December detailing the dam’s instability following 2015’s heavy rains. A landslide, the third since 1995, affected a wide section of the dam.
Several Corps members claimed that the article sensationalized the damage. Regardless, since the public became aware of the extent of the issue, the Corps has become increasingly transparent when discussing the state of the dam — and their efforts to maintain it.
More than 400,000 people live downstream from the Lewisville Dam with more than $22 billion of investments in its path. Elliot Reep is a member of the Carrollton Fire Department’s emergency management team who attends the Corps' meetings to keep his finger on the pulse of the situation. “Lewisville’s directly downstream, then I’m the first one after them,” Reep says. “Anytime there’s one of these events, we do our due diligence and make sure we come.”
The Corps and many other major dam entities changed their policies around 2009 to increase the amount of scrutiny given to dams. The new approach takes the risk associated with a dam failure into consideration when examining precautions and measures that prevent catastrophes.
“Even though we are comfortable with the [low] probability,” Gray says, “the mere idea that something could go wrong and effect all of those people and all of that investment was a substantial realization.”
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During the presentation to about 30 attendees, Gray said that seepage under the dam is not an issue as long as the water coming through is clear, even saying that seepage is natural with an earthen dam. Murky water seeping out of the dam could signify internal erosion or piping but Corps staff at the event are adamant that the seepage is clear as it should be and that there is currently no evidence of either potential source of danger.
The economic cost to reduce the risk of the 61-year-old dam is between $100 to $200 million but that’s a magnitude below previous estimates, which peaked as high as a couple billion dollars. Gray explains that the amount fluctuates so wildly because the Corps develops estimates based on measures currently under consideration. The high end estimate is if every measure is undertaken and the low end represents if the absolute minimum is carried out.
Chief Tim MacAllister from the Corps' operations division says that he sees no issue securing the funds.
Cosmetic work is currently being done to tidy up completed repairs on the slide while modifications to decrease the risk of dam failure are scheduled to begin ahead of schedule in 2018 and carry on through 2025. Currently planned modifications to stabilize the dam and reduce erosion include new berms, collection trenches, tension anchors, concrete apron slabs, a conduit filter and a crest replacement.