Lake Lewisville Dam Repairs Nearly Complete, But More is Needed

Eight months have passed since the U.S. Army Corps of Engineers announced plans to repair a 161-footlong slide affecting the upstream side of the Lewisville Lake Dam. As heavy rains fall across the region, sources tell the Observer  that the repairs are still a month away from completion. 
 
The slide collapsed part of a roadway crossing over the top of the dam and caused officials to stretch black tarps across the earthen dam to protect it from the elements. Fishermen took notice and alerted The Dallas Morning News.
 
The newspaper broke the story about the slide in December 2015. Upon hearing the news, many North Texans worried that a 95-foot wall of water would be thundering downstream at any moment to flood their properties. City officials in places such as Lewisville were bombarded with phone calls from concerned residents. Congressional officials felt the threat was significant enough to come up with millions of dollars in taxpayer money to repair the slide.  

Corps officials made appearances at county commissioners courts, downplaying the threat to the dam. “I just want to reiterate that we do not have imminent dam failure going on,” Tim MacAllister, the chief of the operations division of the U.S. Army Corps of Engineers Fort Worth District, told the Denton County Commissioners Court in early December 2015. 

Good thing, because the repairs won't be done until late September, Corps spokesman Clayton Church told the Observer on Wednesday. 

Church didn’t give too many specifics about why it’s taken so long to finish the repairs. But he did say weather was partially to blame for the delay. It’s been wet so far this year, but not nearly as wet as it was last year, according to the National Weather Service. 

In the article, a former Corps dam safety coordinator claimed the Lewisville Lake Dam said that a sand boil did not indicate there was excessive seepage. Such leaks, called piping, lead to an erosion of the dam’s foundation and often lead to complete dam failure. One symptom of piping is a sand boil, a collection of ejected material where the dam's foundation's vomits water. 

A sand boil has been spotted on Lewisville Lake Dam. McAllister told the Observer that sand boils were a common occurrence affecting the old earthen dams.

Church pointed out that in the May/June 2015 floods, one area of the dam did have a “small sand boil.” To stop it, Corps workers placed a ring of sandbags around the area. It wasn’t part of the repairs, he says, but it’s routinely observed by Lake staff.

A more permanent fix is coming. Since the sand boil was part of the Dam Safety Modification Study, he says construction on the area, and other repairs identified by the study, should begin in 2018. Until then, he said, “the dam continues to function as designed.”