Draining the Valley’s Big Pool

Fifty-seven feet above the cafe au lait-colored water churning through the Sepulveda Dam’s outlet channel, Dave Manring was speaking assurances to the police lieutenant.

From where they stood in the pelting rain late Tuesday morning, two vistas were offered.

In front of the dam: a green slope, a damp concrete spillway, busy traffic on the San Diego Freeway-Ventura Freeway interchange, neighborhoods sulking in a gray mist.

Behind the dam: a new brown lake.

The thought of the former becoming the latter was what troubled Lt. Bob Tumas, watch commander of the LAPD’s Van Nuys Division.

“I had the gates raised to 4 feet,” dam keeper Manring told Tumas, “and I just raised them to 5 feet. When they get enough control downstream, we’ll probably go up to 9, and this thing’ll drop as fast as it rose.”

“So pretty much we’ve got a handle on it?” Tumas asked.

“Right.”

As the water level in the Sepulveda Basin behind the dam reached its peak of 693 1/2 feet above sea level--21 1/2 feet above the basin floor--so did the demand for Dave Manring.

Police officers, firefighters, CHP officers, a federal emergency management representative and TV news camera crews in matching rain slickers invaded the spare concrete control house where the 36-year-old Manring usually labors in solitude.

Would more water-laden clouds wheel in over the Santa Monicas and dump on the saturated 152-square-mile watershed? they wanted to know. Would the water level reach the point where it would breach the dam’s seven automatic crest gates and flow into the spillway, headed toward the freeways and the neighborhoods?

Would there be havoc? (Would there be great video footage?)

Manring, a laconic man with a clutch of keys dangling at the waist of his soiled brown uniform pants, explained that, yes, if the water reached about 714 feet above sea level, a 10-foot-high wall of water 500 feet long would be unleashed.

But there was little chance of that. Once, in 1993, it had gotten to its highest point ever, 709 feet above sea level, he said. But the higher the level, the more water it takes to raise it another increment, he added.

As to what today’s level might reach, Manring shrugged.

“I can’t predict the weather,” he told a police officer.

“Mother Nature’s Mother Nature,” he told a reporter.

Police officers bundled Manring off to Fire Station No. 88, where a task force consisting of representatives of the LAPD, L.A. County Fire Department, the CHP and others could jointly hear the prognostications of the reluctant sage of Sepulveda Dam.

While he was there, at nine minutes before noon, word came from the Army Corps of Engineers’ downtown Los Angeles office, where the holdings and releasings of the corps’ 19 L.A. dams are coordinated. Sepulveda’s four closeable outlet channel gates should be raised to their maximum 9-foot height, the central office ordered.

Dave Hamrick, an El Monte-based dam equipment repairman, turned the valves that activated the 10-horsepower electric motor, which in turn ran the pump that lifted the giant hydraulic gates, one at a time. The job was done at 12:15.

The volume of water rampaging through the outlet channel, on its semi-circuitous route via the L.A. River to the ocean off Long Beach, swelled from 8,400 cubic feet a second to 10,800.

By the time Manring had returned, the brown lake behind the dam had begun to drop. It fell to 692 1/2 feet above sea level. It dropped to 691 1/2, and 690 1/2.

“We’re draining the pool,” Manring murmured.

By late afternoon, Manring had the concrete mausoleum that is the control house, with its telephone klaxon booming, mostly to himself again.

“Now that there isn’t a panic, nobody’s here,” he said, smiling. “I guess TV doesn’t explain all this enough to people, and that’s why when it rains hard, everybody gets a heart attack.”

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Rain in Your Neighborhood

This map shows the cumulative amount of rain that fell on Valley communities from a storm system that hovered over the region from Sunday night through Tuesday evening. Most of the precipitation came Tuesday. This data was gathered by a Doppler radar unit that can measure the amount of precipitation within areas approximately 1 mile square.

Source: WeatherData Inc.

(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)

Opening the Floodgates

Water running off from a 152-square-mile area of the San Fernando Valley during Tuesday’s storm collected to a peak height of 21 1/2 feet above the basin floor behind the Sepvuleda Dam in Encino. The Army Corps. of Engineers central office in downtown Los Angeles coordinated the dam’s release of water with that of 18 other dams in L.A. County to prevent flooding.

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Releasing Water

1. Water flow from approach channel to dam. Using data from water gauges and the dam keeper, Army Corps officials downtown calculate how high gates should be opened and radio instructions to the dam keeper.

2. The dam keeper operates each gate separately, using hydraulic lifts in steel cylinders inside the control house. Each gate can be raised a maximum of 9 feet.

Sources: U.S. Army Corps. of Engineers, Times staff reports. Researched by JULIE SHEER / Los Angeles Times