San Gabriel Dam valve test sends torrent down canyon

San Gabriel Dam operator Herbert Romero led 16 engineers clad in hard hats and yellow vests down a long flight of metal stairs on Wednesday to a cast-iron wheel on a ledge overlooking a stream bed a few miles above Azusa.

At 9 a.m., Romero turned the wheel, opening one of the earth-and-rock dam’s two 123-inch-diameter valves. The ground rumbled and water blasted forth with a roar in a horizontal stream more than 200 feet long, as if from a mammoth rocket engine.

The biannual release of water at a rate of up to 3,800 cubic feet a second was needed to ensure that the dam, as high as a 25-story building, would be able to control floods out of the San Gabriel Canyon’s 200-square-mile watershed.

Romero smiled as torrents of water laden with sediment exploded on the concrete spillway below. “The test results are excellent,” he said. “We’re ready for the storms.”

As he spoke, the engineers marveled at the spectacle from a railing under an austere inscription carved into the face of the dam: Los Angeles County Flood Control District. Outlet Tunnel. San Gabriel Dam No. 1. 1933.

“I’m amazed at the scale, workmanship and elegance of the technology, which was installed in an area that was remote mountain wilderness in the 1930s,” said Sterling Klippel, a civil engineer with the Los Angeles County Department of Public Works, which operates the flood control district. “All this, without electricity,” he added.

Water released during the valve tests churned a mile down the canyon to Morris Dam, a facility that President Hoover dedicated in honor of Los Angeles consulting engineer Sam Morris in 1934.

Both facilities are part of a sprawling network of 14 dams, 487 miles of flood control channels and dozens of debris basins and spreading grounds operated to prevent flooding and capture storm water for groundwater recharge in local aquifers.

Components of the aging system such as Big Tujunga Dam are undergoing extensive renovation needed to increase reservoir storage capacity and meet seismic requirements.

County flood control authorities routinely ask elected officials to attend the spectacular valve tests.

Standing on a catwalk just a few yards away from the water bursting out of the valve, Mark Pestrella, deputy director of the public works department, was only half-joking when he said, “Once they’ve seen this up close, they never vote ‘no’ on our projects.”

But Romero, 40, who was a high school student when he immigrated to the United States from El Salvador in 1990, invited a special guest.

He pointed to a woman standing on the side of a utility road several hundred yards away, waving with one hand and aiming a video camera at him with the other.

“That’s my mother,” Romero said. “She’s awfully proud of me.”

louis.sahagun@latimes.com