Prado Dam’s Floodgates Open, River Comes Alive : Runoff: As rain pummels the Southland, Santa Ana channel receives up to 3,000 cubic feet per second.

At 8:10 a.m. Wednesday, David Riggle stood atop a dam and peered through his binoculars to the swirling, muddy water 80 feet below. It was time to raise the massive gates to allow 1,000 cubic feet per second to escape.

Three hours later, as the rain continued to fall steadily, Riggle, 48, again lifted the gates to release double the amount. By 2:30, the lone keeper of Prado Dam was releasing 3,000 cubic feet per second into the Santa Ana River, as runoff from inland rivers flowed toward the dam.

Ordinarily, Riggle’s is admittedly not a high-pressure job. This week has been very different. Working from a control tower, which rests on concrete stilts above the entrance of the dam, Riggle monitors the amount of water arriving at its wall and radios his information to the Army Corps of Engineers’ Reservoir Operation Center in downtown Los Angeles.

In the control tower with him are six hoists with cables that lift the six, 7-by-12-foot underwater gates.

Riggle adjusts the gates according to instructions he receives from the engineers downtown.

Like most people, Riggle usually works a 40-hour-week. But when a storm hits, he and his co-worker, Lester Burwell, work 12-hour alternating shifts until the rain stops.

By Wednesday evening, Riggle was allowing water to accumulate in the dam at the rate of a foot an hour. Anything less than that would have put too great a burden on the Santa Ana River channel, which runs through a highly populated area of Orange County.

In 1938, storms along the Santa Ana River washed out bridges, flooded highways and killed 19 people. Almost immediately afterward, Congress authorized funds to build Prado Dam, near the Orange County border with Riverside County.

In a few years, the Army Corps of Engineers plans to begin raising and bolstering the dam.

Despite the accumulation inside the reservoir Wednesday night, it still was only 5% full.

“We’re a long way from spilling over,” Riggle said.

Meanwhile, at Villa Park Dam in Villa Park, operator John Gietzen was also busy monitoring water levels and answering phones. That dam, built in 1963, sits astride Santiago Creek, which flows out of Irvine Lake.

Gietzen was also confident that the danger of flooding is unlikely.

“There’s very little reason to worry, because the rain event that would cause this particular dam to fill up happens every 50 years,” Gietzen said. “It’s quite rare.”

The last time the dam reached the spillway level was in 1969, he said. During that flood, which devastated houses, apartment buildings and bridges, he pumped out water at a rate of 6,000 cubic feet per second.

At Prado, Riggle said that although he enjoys his job during the quiet times for its solitude and location in the country, weeks such as this one are also fun.

“We’re in flood operation and that’s what we’re supposed to do,” Riggle said. “It’s good to get a chance to see that everything works.”