Basins, Dams in Mountains Contain Flow : Storm: County facilities dotting the San Gabriels are keys to controlling flooding from torrential rains.

SAN GABRIEL VALLEY —  Donald F. Nichols, the man in charge of keeping floodwaters at bay in Los Angeles County, surveyed his troop of engineers who were trying to keep track of every drop of rain falling across the 4,000-square-mile Los Angeles Basin.

“This is not a major war,” Nichols, who has seen many a storm over the decades, said Tuesday night. “But it’s a pretty good battle. None of the dams are over the spillway and nobody’s panicking.”

Nichols, however, knows how fast floodwaters can gather force in the San Gabriel Mountains. By Wednesday, as the heavy rain continued, he was less sanguine: “I’ve got a heavy storm working and I’m not sure what the results will be.”

Except for drills, it was the first time since 1983 that the county Department of Public Works had staffed its storm “war room” on the second floor of the 13-story building in Alhambra.

Still, Nichols says, the intricate system of 15 major dams, 500 miles of concrete channels, 2,370 miles of underground storm drains, acres of “spreading grounds” to shunt aside a torrent of water and football-field sized craters known as debris basins normally can control rain water and the accompanying flow of mud and sticks.

“The system works,” said Nichols, who is assistant deputy director of public works for hydrology and water conservation.

A good dozen of the county’s major dams are socked into the mountains roughly between Pasadena and the county line at Claremont.

Then there are the 130 debris basins, large troughs that catch the torrent of mud, boulders and timber that can wash down during a storm. About 90 of them dot the mountainsides roughly from Glendale to Claremont.

When a storm hits, one duty of those in the war room is to notify public agencies and residents about possible spillover from the dams that might endanger property or people. The calls were fast and furious Tuesday and Wednesday.

Other engineers electronically monitored rainfall in gauges spread across the county. By phone, they spoke with dam keepers at facilities spread across the tops and sides of the San Gabriel Mountains, where the average rainfall in wet years can reach 35 to 40 inches, or more than three times what falls in downtown Los Angeles.

On a television monitor, a color weather map of Southern California flickered, obscured by whirling wisps of storm clouds. On another television, the evening news gave reports from throughout the county: a landslide blocking California 39 north of Azusa, the flooded Sepulveda Dam area where dozens of motorists were trapped and Malibu mudslides.

“If it rains the way it’s supposed to the rest of the week, we will have flow over the spillways,” supervising engineer Ken Swanson said.

The San Gabriel River wends its way from the heart of the San Gabriel Mountains north of Azusa, passing through a series of three dams before it reaches Santa Fe Dam in Irwindale. Farther downriver is Whittier Narrows Dam.

Controlling the upstream flow keeps the reservoirs from overflowing and flooding the cities below.

By Wednesday morning, the Cogswell Dam about eight miles due north of Monrovia had recorded close to 13 inches in seven days. The average annual rainfall there is 32 inches. This year, close to 30 inches has already fallen.

Studying weather reports and charts, Swanson and others were calculating how much water they should release from the reservoirs. At Cogswell, which had been emptied for construction last summer, the reservoir was filling but was still 95 feet below the spillway Wednesday morning.

But engineers were allowing a torrent of water to be released through the dam, into the San Gabriel River: 2,000 cubic feet per second, or the equivalent every 24 hours of 4,000 acre-feet--enough water to supply the needs of 8,000 families for a year.

Downstream, at San Gabriel Dam, the water was being released at an even faster rate through two 10-foot-diameter pipes.

Even farther downstream at Morris Dam, only a small amount of water was being released into the San Gabriel River. Flood control officials so far haven’t needed to allow more water to flow out of Morris.

Two special phones are direct lines to the U.S. Army Corps of Engineers and the Los Angeles County Sheriff’s Department. In the San Gabriel Valley, the corps operates the Santa Fe Dam and Whittier Narrows, which is in unincorporated county area next to South El Monte and Rosemead. Like Sepulveda, these facilities have parks, nature and recreation areas and roadways.

“The big difference (from Sepulveda) is Santa Fe and Whittier Narrows are protected upstream by reservoirs,” Nichols said.

“Could the Sepulveda situation happen in the San Gabriel Valley?” Nichols said. “Sure, given the right weather patterns.”

Corps officials said Wednesday that Santa Fe Reservoir was filled only to 2% of its capacity and Whittier Narrows, 3%. Nichols ticked off big storms of the century: 1978, 1969, 1938, 1934. “We’re not even close to those events,” Nichols said.

Still, he said, Devil’s Gate Reservoir in Pasadena above the Rose Bowl had more water in it than it has had since it was built in 1920.

In Pasadena Glen, residents remember seeing this much water before--in the 1978 flood. Pasadena Glen is a collection of 55 houses perched along the sides of a normally dry creek bed. It is not on a county flood control channel and is not directly affected by water movement from the dams. But much flood water and destruction can swirl through the canyon.

“You learn about the rhythms of nature in this place,’ said Barbara Horton, 74, a retired ballet teacher. Horton and her husband, Mel, have lived in Pasadena Glen, in unincorporated county area just north of Pasadena, for 40 years.

As she spoke, the sound of the rushing creek filtered into her living room. In years past, the Hortons have had mud damage; other homes have been damaged by cascading boulders.

Wednesday morning, residents were anxious; a visitor’s Cadillac had already washed away.

“Of course, none of us should be living here in a flood plain.” Barbara Horton said. “But it’s been going on a century that a lot of these houses have been here. That’s longer than places where the houses just get taken down because somebody wants to build another one in its place.”

Flood Controls

A huge network of dams, basins and canals that channels most runoff water to the ocean protects the 4,000-square-mile Los Angeles County basin from major flooding during storms. The Sepulveda Dam Basin, which was flooded Monday, is one of five such facilities operated by the U.S. Army Corps of Engineers in the county. In addition, the county Department of Public Works operates 15 dams.

Water running off from mountains and canyons is trapped by the dams, then channeled into the Los Angeles, Rio Hondo and San Gabriel rivers. The Los Angeles River collects water from the northwestern portion of the county. Water from the east flows into the Rio Hondo and San Gabriel rivers. Supplementing the dams are 2,370 miles of underground storm drains that collect runoff from streets, curbs and gutters.

Despite heavy rain this week, the dam, basin and canal system is not near capacity. The 15 county dam areas have a storage capacity of 116,000 acre-feet of water. As of Tuesday--the most recent day when figures were available--about 40,000 acre-feet of water were in the dammed areas.

Officials say there also has been no danger of the Los Angeles River flooding downstream. At its peak, more than 51,000 cubic feet of water per second rushed through the lower river to the ocean; the river could have taken as much as 146,000 cubic feet.

THE SAN GABRIEL VALLEY has 12 of the 15 dams operated by the county Department of Public Works to capture water running from the San Gabriel Mountains.

The largest is the San Gabriel Dam above Glendora, which can hold 44,000 acre-feet of water. Morris Dam is the next largest, with a capacity of 22,000 acre-feet. The smallest is Puddingstone Diversion Dam, which has a capacity of 195 acre-feet. The Santa Fe Basin Dam and the Whittier Narrows Basin Dam, operated by the U.S. Army Corps of Engineers, are also in the San Gabriel Valley. The Santa Fe Dam has a capacity of 34,276 acre-feet, while Whittier Narrows’ capacity is 18,950 acre-feet. Officials said no part of the system was in danger of flooding this week.