A Concrete Plan for Nature’s Way : Pacoima Wash: A $6-million project to begin next month will transform the last unimproved section of the stream bed to an efficient, if lifeless, flood control channel.

One of the last natural stream beds on the floor of the San Fernando Valley is an ugly sight.

The nearly two-mile stretch of the Pacoima Wash between the intersection of Woodman Avenue and Lassen Street south to Parthenia Street is a weedy, dusty eyesore littered with shopping carts and household trash. Apartment buildings back up to it. Graffiti mar fences along it. And in at least one place, a junkyard juts 20 feet into it.

Historically, its headwaters are in narrow, steep Pacoima Canyon. But the last time water from there flowed through the wash was probably in the 1950s, before a diversion channel was built by the U. S. Army Corps of Engineers.

Still, some will mourn when the Los Angeles County Department of Public Works begins construction next month on a $6-million project to replace the stream bed through Sepulveda with a concrete flood control channel or underground drainage pipes.

At a time when environmentalists are lobbying for the removal of the concrete linings from the Los Angeles River and the lower Arroyo Seco in Pasadena, some find it distressing that an additional channel--efficient for carrying water but nonetheless antiseptic and fenced in--is to be built.

“There are two ways to deal with flood control,” said Michael S. Anderson, a civil engineer who is head of drainage planning for the public works department. “The No. 1 way is you keep the people away from the water . . . and the other way is to keep the water away from the people.”

In the case of the Pacoima Wash, he said, houses and businesses have been built right to the stream bed’s edge, leaving no room to allow it to overflow. The only remaining option is to dig a channel so that the water flows quickly away, he said.

“There is nothing wrong with flood protection. We need flood protection,” said Denis Schure, a Sierra Club activist. “But they could take fresh looks at it that give us other uses for that investment, in addition to flood protection.”

As an example, Schure, a canoeing instructor, points to a stretch of the Los Angeles River near the Sepulveda Basin that he would like to see turned into a public white-water course. He is among a growing group of Southern Californians who believe that the region’s rivers have been treated merely as a plumbing system instead of as part of a rich natural and recreational resource.

For example, public and private studies have concluded that development, flood control, gravel mining, water projects and agriculture have wiped out as much as 95% of the riparian habitat that once existed in the state. As a result, as many as 17 of the 111 bird species that breed or forage in those areas are no longer evident.

With that record of neglect, Schure and others now say what is left must be preserved. “The people in the area have been so oblivious to the stream-side environment for so long, they’ve forgotten that there’s anything like that in the city at all,” Schure said.

Don Nichols, the public works department’s conservation and hydrology chief, patiently listens to such comments and then offers this observation:

“During prolonged periods of drought, it’s natural for all the folks around town to suspect the merit of having built all these heavy concrete structures. It takes a gully-washer every few years to wake us up and make us say, ‘Gee! I didn’t know that river could do that!’ ”

County engineers calculate that portions of the seemingly dry wash could gush with as much as 18,500 gallons of water per second in the event of a 50-year flood--one so severe that, in any one year, there is only a 2% chance of it occurring.

In its present condition, the stream is capable of carrying only 10% of that amount. The rest would flood the surrounding area, flowing through streets, inundating homes and carrying away cars. Lives, almost certainly, would be in danger.

At present, even moderate rainstorms cause Plummer, Nordhoff, Rayen and Parthenia streets to flood. Those streets have often been underwater during past storms--so much so that rickety bridges were built in the 1950s to allow pedestrians to cross. And intense development in the area has increased the flood threat by spreading concrete and asphalt over open land.

Richard Urban, who has lived in the 9000 block of Kester Avenue next to the wash since 1957, said he won’t miss the stretch of natural terrain when it’s gone.

“It’s always been a dry wash until we have a torrential rainstorm. When they get done concreting it up, we won’t have water on Rayen Street every time it rains three inches,” Urban said.

To build the channel, the county has to buy additional property in places, and Urban and some of his neighbors are unhappy with the amount of money the county wants to pay for their land. But few, if any, want to see the remnant of the wash remain as it is.

Even though it is in a relatively natural state--except for some pipe-and-wire retaining fences buried at its edges, and street crossings that cause it to be funneled underground--the wash has been isolated from its upstream and downstream drainages for decades.

The wash begins in Pacoima Canyon in the foothills of the San Gabriel Mountains northeast of Sylmar. The stream’s rocky path crosses a wide, gravelly flood plain as it heads south. Before the San Fernando Valley was developed, the wash carried intermittent flows of water and deposited sediment as it meandered across the area’s nearly flat belly, petering out near Kittridge Street east of Van Nuys Boulevard.

The lower wash began drying up in 1929, when the 365-foot-high Pacoima Dam was built. The dam was among the highest concrete dams in the world when it was completed at the mouth of the canyon by the Corps of Engineers. It created the Pacoima Reservoir, which could hold 1.2 billion gallons of water. Also that year, the county first graded part of the wash’s stream channel, near what is now Rayen Street, to improve its flow rate.

A few years later, the Pacoima Spreading Grounds were built on a 161-acre site between Woodman and Arleta avenues and Filmore and Devonshire streets.

The combination of the dam and the spreading grounds, where water from the dam was allowed to stand as it percolated into the underground water table, meant that precious little ever flowed farther down the wash.

Then, in 1953, the Corps of Engineers built the Pacoima Diversion Channel. The channel is designed to carry any water in excess of the spreading grounds’ capacity, diverting it eastward to the Tujunga Wash and the Los Angeles River.

The first project built to contain the bottom portion of the wash was completed in 1975, from Kittridge to just north of Vanowen Street. That project, essentially an underground storm drain, emptied into another drain that in turn flowed into the Los Angeles River.

Channels have been under almost continuous planning or construction ever since, with the latest--from Valerio to Raymer streets--completed only this spring.

The project due to begin next month, which will include improvements to sidewalks, streets and curbs in the area, will complete channelization of the wash from 1 1/2 miles north of the Foothill Freeway to the Los Angeles River.

Mark Caddick, who designed the last link in the system, said he is aware of the discussions regarding alternatives to flood channels--the proposals to remove parts of channels, to put in trails and to restore natural vegetation.

“You can’t do that kind of stuff when you have a limited amount of space,” Caddick said. “You design whatever you can get in the space allotted to you. As a designer, you like to design something that’s aesthetically pleasing, but you have to design things given what you have to work with.

“These are some of the last ones we need to improve,” Caddick said, referring to the wash’s natural bed. “This is like the backbone to the whole area as far as drainage is concerned.”