Developer’s Plan for Tujunga Wash Evokes Interest, Skepticism

Donald E. Cunningham seemed a bit abashed when reminded how he once compared a proposed levee for a business-residential development he wants to build in the Tujunga Valley to the dikes protecting the Netherlands from the pounding sea.

“I was just using that as a figure of speech,” Cunningham, a San Fernando Valley developer, said during a recent interview.

“We’re not building dikes. There are levees all over the world, from the Mississippi River to the Nile.”

But he was not embarrassed to propound his theory that, despite the doubts of environmentalists, government engineers and some local homeowners, the floods that periodically fill the Tujunga Valley’s wash in the northeast Valley can be held in check.

As visualized by Cunningham, the $100-million development would combine an industrial park, about 500 homes and three to five commercial buildings. Part of the development, including the housing, would be on the southern side of the 565-acre wash, while several commercial buildings would be built on an overpass next to the Foothill Freeway overpass.

The developers have earmarked another $5 million to $7 million for construction linked to flood control.

Proposal in Limbo

The proposal is in bureaucratic limbo while it undergoes evaluation by an independent engineering firm, as ordered by the City of Los Angeles. The plan would have to be judged feasible by that firm as well as by city engineers before it could be presented to other city agencies for input and approval.

Several government agencies and neighborhood groups view with dismay Cunningham’s controversial plan for the wash, worried over the possible environmental consequences of the project and its effect on the neighborhood. Others are openly skeptical that the levee-based flood-control system can work.

Still others, notably homeowners groups calling themselves “The YES Coalition,” are behind the project, saying it is technologically feasible and will attract new residents and bring 3,000 new jobs to the area.

Los Angeles City Councilman Howard Finn, who represents the area where the project would be built, has expressed reservations. There are similar doubts in the Los Angeles County Public Works Department, which served as a consultant to the city on the project, which is within city limits.

“Any proposal to channelize Tujunga Wash needs to be carefully reviewed, as it is an unstable, highly dynamic river capable of rapid channel shifting and transporting and/or depositing large quantities of debris,” Thomas Tidemanson, director of the Public Works Department, wrote in a report on the project.

Los Angeles city engineers have said the project has grown so complex and ambitious that they are unable to evaluate it.

“I hate to admit that we can’t analyze it, but it will take people who have experience in the mechanics of river and flow, and we don’t have that kind of system in an urban environment,” said Ralph Valenzuela, deputy engineer at the Public Works Department.

The city has appointed an independent engineering firm in Ventura County to analyze the plan, which is expected to take about six weeks. The developer will pay for the approximately $13,000 study.

Meanwhile, Cunningham and Donald D. Hoag, an engineer and land development consultant, said they have tackled concerns from the city and county with additional study and advice from consultants.

“When we’ve gone this far, you have to believe that we know what we’re doing, and we really believe in this,” Cunningham said.

The property is owned by the estate of Peter J. Akmadzich, who lived in Tujunga, and CalMat Inc., a gravel-mining operation. Developer Cunningham owns an option to buy the land but he refused to say for how much.

Just above the project site to the northwest, Tujunga Creek serves as the outlet for runoff from the western San Gabriel Mountains, also known as Big Tujunga Canyon. Runoff from rainfall in the mountains flows from the 115-square-mile canyon into the creek, which then drains into Tujunga Valley, about three miles long and half a mile wide, with many channels.

As proposed, the floodwaters leaving Tujunga Creek would hit an 11,000- to 12,000-foot-long levee, a slanted wall of thick reinforced concrete running parallel to Wentworth Street. The new levee would connect an existing levee to the east along Oro Vista Avenue to the Hansen Dam recreation area on the west.

Would Offer Protection

Cunningham said the new levee would protect the development, which lies south of it, from floodwaters and debris. He said the levee would be 10 to 20 inches thick, enough to protect the development from boulders that are washed down during the floods.

Although the wash would be narrowed significantly by the development, the level of the water would rise only slightly, Hoag said. He said the velocity of the water flow also would increase by an insignificant degree.

Cunningham said that, in any case, the development would not be built in the part of the wash where a flood would occur.

“The water does not go through the part of the valley where we’re building,” he said.

However, city officials say the course and velocity of any flooding is extremely difficult to predict.

Cunningham and Hoag said they are confident their concept can work, citing calculations they based on worst-case scenarios for major wash floods, or what officials call “capital floods.”

Capital floods are defined as those resulting from the worst storm that could theoretically be predicted in a 50-year period. That flood would consist of runoff from adjacent mountains combined with debris from a recent fire, which supposedly would have burned before the storm.

Tetra Tech, Pasadena-based engineering consultants who conducted a hydraulic study for Cunningham, said a capital storm in the Tujunga Wash would produce a flood that would be measured as flowing 64,000 cubic feet per second into the wash. The largest flow on record was during the 1937-38 rainfall season between October and April, when a Los Angeles County Flood Control gauge measured a peak flow of 50,000 cubic feet per second.

Runoff into the wash has varied greatly from year to year. Bridges, highways and part of Big Tujunga Canyon Road have been washed out, and houses along Le Berthon and other streets have been destroyed during the past 20 years, the Tetra Tech study said.

The flooding problem is aggravated by large amounts of gravel, sand, sediment and boulders coming from the mountains and eroding the wash. During storm peaks, the sediment moves along the channel beds in a “slurry-like” flow along the bottom of the channel below the clear water, the consultants said in their report.

The wash is most vulnerable in January and February, usually the wettest months, Los Angeles County Flood Control officials said.

Extra Height

In order to keep the water from overflowing, the developers said they would build the levee 8 1/2 feet higher than the level that would be required to accommodate a capital-storm flood. That would allow for additional sediment buildup.

The levee would also extend into the ground 14 to 22 1/2 feet below the surface to ensure that floodwaters would not seep under the levy into the development area.

“With these added safety factors, we’re prepared for the worst-case scenario for floods in that region,” Cunningham said.

The developer said the levee will range in height from about 20 to 30 feet above the existing ground levels.

Cunningham also wants to use 3 million cubic yards of dirt and sediment collected in Hansen Dam, which is nearly choked with debris, to elevate the site of the project several feet above the ground level, further decreasing the chance that floodwaters would flow into it.

The waters could then flow to the lake behind Hansen Dam--now reduced to a low level by sediment--which would again become a water recreation area, he said.

The Tetra Tech study said the courses of the floods historically have ranged from several hundred to 2,000 feet wide. The water splits into a north and south branch that each cross the Foothill Freeway and Foothill Boulevard before joining again and moving westerly to the Hansen Dam Flood Control Basin, the study said.

The developers had previously submitted a plan that provided only for a six-foot elevation above the levels of the projected worst-case runoff. Officials said debris, boulders and gravel from the last major storm in the wash, in January and February of 1969, eroded the wash to a depth of 14 feet in some places and deposited sediment as high as 16 feet in other locations.

“We looked at the objections the city and county had, and by raising the height, we give a greater level of protection to our development,” Cunningham said. He said his analysis showed that long-term erosion of the wash is not taking place.

sh Possible Threat

Even if the project, which would occupy less than half of the wash, is never completed, large deposits of sediment from floods in 1969 near the Oro Vista Avenue levee would have to be removed or floodwaters could endanger 165 homes near the levee, according to the Tetra Tech report.

Though Cunningham and Hoag say they believe they have prepared for the worst by charting the history of the wash, Orville McCollom, deputy director of the Public Works Department, said future events cannot be predicted because of the natural structure of the wash.

“There’s no defined water course in the wash, and the wild stream could go toward the houses, or just move back and forth, making any kind of protection potentially inadequate,” McCollom said.

William Lewis, an engineering consultant hired by the Shadow Hills Homeowners Assn., which opposes the project, said the plan for the levee is flawed because calculations for it are based only on a predictable set of wash conditions.

“Any capital-flood event occurring at a time when the wash has undergone substantial deposition will produce flow depth substantially higher than expected,” Lewis wrote in a letter to the association.

City engineer Valenzuela said it is possible that the increased height of the levee would compensate for the channel’s narrowing through the planned development.

He added: “I wish I could say whether this would fly or not. The heights are a lot better to work with, but it’s still too early to say whether it would work.”