How a giant water tunnel saved downtown San Antonio during the flood of '98

$111M infrastructure project kept heart of city high and dry

By Ursula Pari - Anchor

SAN ANTONIO - Most San Antonio residents remember Saturday, Oct. 17, 1998, vividly: They recall where they were when they realized the city was underwater and would stay that way for days.

Twenty years ago, downtown San Antonio did not flood. In fact, it was business as usual along the Riverwalk as that serenely flowing tourist attraction continued its leisurely pace as it had in the days prior.

At the time, Nefi Garza was a floodwater expert working in the private sector. He was one of a small population of residents who knew something really big was happening beneath the surface of the Alamo City. He dropped what he was doing and fought his way through flooded streets down to Olmos Basin, a nearly impossible task. Then he went downtown.

He was shocked by what he saw.

“I expected to see Casa Rio, different hotels flooded. I drove up and put on my hazards, and people were having lunch on the river. I said, ‘What is going on?'" Garza, who is now the head of the city of San Antonio’s Flood Management, said. 

Instead of the catastrophe of the Great Flood of 1921, when downtown San Antonio streets turned into a series of destructive canals and 51 people lost their lives, all was calm due to the success of a $111 million infrastructure project that had been suddenly put to the test.

Garza explained the San Antonio River Tunnel works first by taking the water funneled into the Olmos Basin. 

The beautiful basin park turns into an angry drainage ditch where water stops at the dam, then is slowly released to the inlet of the tunnel at Josephine Street. Water is filtered of trash and then sucked deep underground for 3.2 miles, directly under downtown San Antonio. The 150-foot-deep pipe was drilled quietly and completed in 1995, like a giant earthworm that is 24 feet, 4 inches in diameter.

The water is pushed via natural gravity to its outlet location at Mission Road on the other side of the city right behind Brackenridge High School and Roosevelt Park.

Garza was there on the bridge watching floodwaters spurt out at such a velocity that he said he felt the heat on his face across the street. His excitement watching the tunnel pass the test in what we now know was a 500-year flood is still evident in his voice today. 

“Had the tunnel not been in place, we would have had catastrophic flooding of the downtown area. Businesses, hotels, it would have shut down the city,” he says. In doing its job so well in 1998, it’s estimated that the San Antonio River Tunnel paid for itself in one day.

Today, markers on the wall commemorate the water levels inside the flood-management infrastructure where the workers had to evacuate, letting the tunnel do its job: pushing out a volume of water three times the capacity for which it was built.

Since then more than $2 billion in flood management has been spent, not just in San Antonio, but in a coordinated effort with surrounding counties, cities and towns which meet regularly now to problem-solve together.

That is yet another side effect of the flood of 1998. The issue of flood control is no longer a problem on each individual municipality to solve.

So the next time you see Olmos Dam full, remember there is an awesome, lifesaving tunnel deep below the surface, keeping downtown high and dry.

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