Lewisville Dam Flood Protection Upgrades Underway

Major upgrades to the Lewisville Dam are underway to secure the 71-year-old structure for people downstream.

The record high lake level recorded in 2015 helped cause issues at the dam that worried some people.

Those issues helped win $150 million for upgrades at the dam by the U.S. Army Corp of Engineers.

Officials hosted a tour of the work Thursday.

Around half of the money is going to upgrades at the dam spillway.

Giant anchors are being drilled 180 feet into the ground to secure the spillway area.

Stacy Gray is the dam program manager.

“We want to make sure that thing does not move,” Gray said.

A massive flow of water did rush over the spillway in 2015.

Normally dry areas around the lake were inundated.

Passengers flying over the lake to DFW Airport could see what appeared to be an alarming slide in the water side of the earthen dam.

Another part of the upgrade money has already been repaired for that area with a stronger rocky surface.

“That’s not to say we’ll never have another slide, but it is to say we mitigated the size of the slides and the extent it’s going to take to repair those slides,” Gray said.

Seepage collection areas have been upgraded with new monitoring equipment to be sure water coming from underneath is not damaging the dam.

Seepage did increase in 2015 and one seepage area was constantly muddy.

“We put in a system that would safely collect all of that seepage, get rid of that muddiness and allow us to see what was happening when it was happening,” Gray said. “Seepage is a normal occurrence in an earthen dam. We rely on the weight of the structure itself to hold back the water. So that water is going to move through that soil. This is just our way to monitor it and make sure it is performing as we want it to.”  

The normal conservation pool height of Lewisville Lake is 522 feet. The spillway top is 532 feet.

Gray said the 537-foot 2015 record topped the spillway and did cause street flooding in areas below the dam but did not enter structures.

Dam improvements are to secure the structure to withstand an even higher flood event.

“So even though it’s never happened, we want to make sure as responsible dam owners that we’re doing our part to minimize the risk,” Gray said.

The U.S. Army Corp of Engineers works with communities in the potential path of such extreme flooding.

In a worst-case flood event, an estimated 431,000 people and $24 billion worth of property are in the path.

U.S. Army Corp of Engineers Fort Worth District Operations Chief Timothy MacAllister said the 2015 events were a concern but never a threat to the dam structure.

“We were never in any imminent threat of losing anything,” he said.

But, MacAllister said, the current Lewisville work is the biggest and most needed project of the 25 dams he oversees.

“There’s a lot of comfort level that goes along with making sure that things, although they may not be of serious consequence or concern, they certainly look like that, and if you don’t address them, they can become that,” he said.

The lakes are lastly for recreation, secondly for water supply, and primarily for flood control.

“A lot of times people say, what keeps you up at night about your job? That’s one of the things that keeps us up. We take it very, very seriously,” MacAllister said.

The Lewisville Dam work is due for completion in 2026.