SAN ANTONIO – Many people in San Antonio may have walked, biked or driven past one without even realizing it.
Dozens of dams are hidden in plain sight across the city — tucked into parks, trails and green spaces — quietly protecting neighborhoods when heavy rain hits Flash Flood Alley.
At one flood-control dam inside McAllister Park, people walk dogs and ride bikes nearby every day without realizing they are standing on critical infrastructure.
“These were built when all of this was ranch land,” said Wayne Tschirhart, a senior technical engineer with the San Antonio River Authority whose focus is dam safety.
Many of San Antonio’s dams do not look like traditional dams with large walls and reservoirs. Instead, they are mostly grassy, earthen structures designed to temporarily hold back floodwaters during major storms.
“Most of them are earthen dams with earthen auxiliary spillways,” Tschirhart said. “They are earth and grass covered, and you really don’t know they are there.”
At the dam at McAllister Park, Tschirhart said the concrete spillway almost never sees water.
“I’ve been here 19 years, I’ve never seen water go over this concrete,” he said.
The dam stretches more than a mile long through the park.
“We’re at the dam crest. This is the auxiliary spillway,” Tschirhart said. “Then the earthen part goes back into the park, and the total length is like 6,600 feet. So it’s over a mile long.”
According to Tschirhart, there are 65 dams in Bexar County listed in the National Dam Inventory. The San Antonio River Authority operates 27 of them.
Those dams quietly hold back massive amounts of water during storms before it can rush into neighborhoods downstream.
“This and seven other dams upstream hold back a lot of, you know, thousands of acre-feet of water during a flood event that would normally impact people’s homes downstream and community downstream,” Tschirhart said. “And so they don’t make any noise. They fill and there’s no sirens.”
“They just sit here and operate and do what they do,” he added.
Without the dam system, Tschirhart said neighborhoods including Terrell Hills, Alamo Heights and areas stretching to Roland Avenue could flood during major rain events.
The dams may not look impressive, but Tschirhart said they play a major role in keeping people safe.
“They are nothing fancy,” he said.
But when asked whether they save lives in the community, Tschirhart had a simple answer: “Yeah, save lives and property.”
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