L.A. River--Can It Still Protect Basin Against a Major Storm?

For most of the year, the Los Angeles River meanders lazily on an eastward course across the San Fernando Valley, bending south in Glendale on its way past downtown Los Angeles before emptying into the Pacific Ocean at Long Beach.

Usually, it is little more than a trickle.

But three times since 1978 it has become a torrent, clawing at its concrete sides and coming dangerously close to topping its levees. Muddy waves hurtled down its course like raised fists.

During the February-March storms of 1980, floodwaters actually overtopped the river’s concrete channel at Cedros Avenue in Van Nuys. Debris was tossed by the churning waters onto the top of a 20-foot-high levee at Wardlow Road in Long Beach.

Not Confident About Future

For the most part, however, the Los Angeles River--described by the U.S. Army Corps of Engineers as the backbone of the Los Angeles County flood control system--has withstood nature’s fury. Since major segments were completed 40 years ago, it has prevented $3.3 billion in potential flood damage, according to calculations by the Corps.

Now, however, local and federal authorities are no longer as confident that it can do the job in the future.

New calculations that take into account the basin’s explosive growth since the river was designed in the 1930s and the longer history of rainfall and runoff have led engineers to conclude that there are major deficiencies in the river’s capacity to protect the nation’s second-largest metropolitan area from a major storm.

County engineers believe that in the most severe storms, the likelihood of the river swelling over its banks into densely populated areas has increased 65% along some sections of its 43-mile-length.

Worse yet, it is feared that if the water overflows the levees, it could undermine the landward side of the levees, which are not lined with concrete, and within 30 to 60 minutes cause a catastrophic breach that would inundate thousands of homes and businesses.

These are among the findings of an as-yet-uncompleted $4.5-million Corps of Engineers study of the 2,000-square-mile Los Angeles County drainage area, which includes the Los Angeles River, its 295 miles of tributaries, the San Gabriel and Rio Hondo rivers and five major flood control dams.

The study focuses on the river channel’s ability to withstand a major storm with an intensity likely to occur statistically once every 100 years. Although officials have no record of a 100-year storm ever hitting the Los Angeles area, they note that one of the findings of the current study is that smaller storms can produce a larger runoff than previously thought.

The Corps of Engineers expects to complete its assessment of the magnitude of the threat by December. The next step will be to develop solutions, which could range from changing water release patterns at county reservoirs to raising the height of existing dams and widening the river channel.

But major flood-control improvements could take years to complete. Meanwhile, there is disturbing evidence that billions of dollars in property face a greater flood threat than previously imagined.

In testimony recently before the House subcommittee on energy and water development, Brig. Gen. Donald J. Palladino, division engineer for the Corps of Engineers’ vast South Pacific Division, warned that the flood threat along the Los Angeles River may be “as great as the neighboring Santa Ana River basin.”

The Santa Ana basin has been repeatedly described in congressional testimony as facing the worst flood threat west of the Mississippi. Flood damages there have been projected to run as high as $14 billion in a 100-year flood.

‘Seriously Concerned’

‘The levels of protection (in the Los Angeles River) . . . are far less than what were originally intended,” James L. Easton, chief deputy director of the Los Angeles County Public Works Department, told the same subcommittee. “We are seriously concerned.”

Of special concern to engineers is the river channel that begins at about Firestone Boulevard in South Gate and which is not entrenched below grade, as it is upstream. On this southern leg, the river runs on the surface and is contained only by levees.

“A levee failure during a major flood event could produce the same catastrophic results as a dam failure--a loss of life as well as significant property damage. The suddenness of the event does not allow people to get out of the way in time,” said Edward J. O’Neill, chief of program development at the Corps’ South Pacific Division headquarters in San Francisco.

However, Corps of Engineers and county officials said overtopping of a levee would not occur without efforts to shore it up, during which time residents could be evacuated. “We really think the (chance of a) big catastrophic loss of life is pretty remote,” county Public Works spokeswoman Roslyn Robson said.

But, even without a levee break and a loss of life, the magnitude of the threat from overtopping alone and slowly rising water is evident on preliminary flood-hazard scenario maps drafted by the county independent of the Corps study.

Maps Not Predictions

The new maps are not predictions that flooding will actually occur simultaneously in all the areas depicted, or that it will occur at any one of the locations.

Rather, they show what areas would be subject to flooding if all of the excess water overtopped the banks at any of the mapped points. The county cautioned that if there was an overtopping in the southern reaches, for example, the flooding depicted on the maps upstream would be less likely.

Still, the maps, shaded with blue ink in areas now considered subject to flooding, give pause.

For the first time, fringes of downtown Los Angeles, including Union Station and the County Jail, are shown as subject to flooding.

Major sections of Compton, Paramount and Lynwood are similarly subject to flooding. Long stretches of the Long Beach Freeway are shaded in blue ink on the maps.

Homes, Businesses Not Insured

The scenarios are all the more startling because most of the homes and businesses that are now being plotted on preliminary flood hazard maps are not insured against flood damage.

Indeed, a search of federal flood insurance records indicates that as of April, only 9,659 flood insurance policies were in force in a basin in which 7.7 million people live. There are only 62 flood insurance policies in effect in Compton, Paramount and Lynwood.

“We think we have a duty to advise the citizenry that lives along the river that they should take action to protect themselves. About the only action they can take to protect themselves is to buy federal flood insurance,” said James L. Easton, chief deputy director of the county Public Works Department.

To many Southern Californians, the prospect of a major flood has an air of unreality to it. To be sure, there have been severe mud slides in the foothills and canyons and localized flooding in the San Fernando Valley and elsewhere that have wreaked havoc. But, the prospect of the river overtopping its banks and threatening lives and billions of dollars in property has seemed better suited for a B-grade disaster film.

During a recent tour of the river, Stephen J. Hawkins, Los Angeles River study manager for the Corps of Engineers, said summertime appearances can be misleading. “It’s simple to come down here and stand on a bridge and say, ‘You’re kidding!’ Sometimes those concrete channels give a false sense of security.”

Several Factors Involved

The dramatic reassessment of the river’s capacity to hold back the floodwaters has been caused by several factors: intensive urbanization since the river was designed in the 1930s, additional years of rainfall and runoff records, the fact that dams have reached or exceed their design capacity to hold sediment, and more sophisticated computer modeling techniques with which to digest and analyze this data.

As recently as 1978, none of the flood-hazard maps adopted by the Federal Emergency Management Agency indicated a flood threat along the river. Those maps were based on data collected between 1943 and 1975, one of the driest periods in the basin’s history.

“Based on the numbers we had at that point, our projections of a 100-year rainfall event were that it would stay very nicely, thank you, within the Los Angeles River,” Easton said.

“Then we had heavy rainfall in ‘78, ’80 and ’83 (three of the top 10 rainfall years on record). Last fall, we made new calculations based on 52 years of records through ’83. We found that there would be substantial deficiencies in the Los Angeles River in the event of a 100-year runoff event in the river. That’s why we’re concerned now.”

The fact that neither the Corps of Engineers nor the county has a record of a 100-year storm in the Los Angeles Basin does not alleviate all of the concerns.

Smaller Storms Can Hurt

They note that smaller storms have the potential to create greater runoff now than in the past, largely because the area is far more urbanized than engineers expected when they designed the river. The effect of this paving over of the water-absorbing soil with concrete, asphalt and buildings has been telling.

“To tell you we haven’t had a 100-year runoff event doesn’t mean anything because we didn’t have urbanization this heavy 100 years ago,” Joseph Evelyn, chief of the Corps’ hydrolic section, said.

“If the same storm were to occur today that occurred in March of 1938, then we would experience a much larger flood event that might approach a 100-year flood event due to the urbanization that has occurred and the extensive storm drain system that’s in place now,” Evelyn said.

For example, during the 1980 storm, water in the Sepulveda Dam reservoir came uncomfortably close to the top of the spillways, and engineers have estimated that the inflow at the reservoir was equivalent to a 50- to-60-year event. At Wardlow Road in Long Beach, where debris was found on the top of a levee, the amount of water flowing through the river at that point was estimated to be the equivalent of a 30-year runoff event.

The river is designed to handle 140,000 cubic feet per second below the Rio Hondo. But it has exceeded 100,000 c.f.s. 10 to 12 times in any bad weather year--years that have fallen far short of the 100-year deluge.

Easton added, “Nobody foresaw the explosive growth that was going to take place here after World War II.”

In addition, dam reservoirs are filling with sediment, reducing their capacity. This means that more water must be released sooner into the river and its tributaries.

Hansen Dam, located near Lakeview Terrace, is an example. Originally, the dam restrained a 130-acre lake. Now its capacity has shrunk to 30 acres no more than a couple of feet deep. There is nearly twice as much sediment in the dam as the maximum 12.4-million cubic yards envisioned by the engineers who built it in 1941.

Although the Corps of Engineers has awarded contracts to haul out sediment, the work is barely able to keep up with each year’s new inflows, and Lakeview Terrace residents are alarmed by the possible threat of water in the sediment-choked basin backing up into their neighborhood.

The Corps is frankly embarrassed by the length of time it has taken to complete the first phase of the Los Angeles County Drainage Area study. It began 13 years ago and the first phase, which is intended to define the threat, is not expected to be completed until December. The rest of the study, including solutions to the problem, is not scheduled for completion until October, 1987.

Sociological Considerations

“There’s a tremendous number of sociological considerations that go into what the possible solutions will be. . . . God knows what impact that causes,” O’Neill said.

Corps officials decline to predict what the solutions may be. But they hint that given the billions of dollars in property at stake, a large-scale project could be justified based on the cost benefit.

“If the problem is as big as we perceive it to be, we would have to proceed on the same basis as the Santa Ana River,” Hawkins said. The Santa Ana River is one of the Corps’ biggest flood-control projects. Because of the flood threat there, the Corps has given it top priority and is looking at large-scale solutions, including controversial proposals for construction of new dams in the mountains.

The county drainage area study findings could have far-reaching implications for continued development in the threatened areas once the Federal Emergency Management Agency follows up and officially declares the areas to be in a flood hazard zone--something that could happen in two or three years.

While virtually all areas adjacent to the river are developed, such a declaration would undoubtedly have an effect on new construction and lending practices.

Law Mandates Flood Insurance

The Flood Disaster Protection Act of 1973 mandates flood insurance as a condition of receiving from any federally insured lending agency loans for the purchase or new construction of buildings in any special flood hazard area.

In addition, improvements to any structure that equal or exceed 50% of the existing structure’s market value must conform to flood-plain management measures intended to minimize the flood damage threat. Flood-plain management can include zoning restrictions and tougher building code provisions.

Because none of the areas adjacent to the river have been officially designated to be in a high-risk or “special” flood hazard zone, lower insurance rates still apply. And, for policies in effect before the new flood hazard is officially declared, the low rates will remain in effect.

If the special hazard is declared, however, the cost of new policies would be roughly double the $275-per-year price of current standard coverage of $185,000 for a structure and $60,000 on contents.

Because flood insurance is generally unavailable from insurance companies, a federally subsidized national flood insurance program has been established by Congress and is administered by the Federal Emergency Management Agency. Policies are available through participating private property insurance agents or brokers but backed by the government.

Seen as Only Protection

For the moment, buying insurance protection is viewed by engineers as the only thing property owners can do to protect themselves against flood damage.

“What we have designed and built here is not a system that will protect against any event that will ever occur in Los Angeles County,” Easton said. “We will get events that will exceed the capacity of this system. Even if this system were exactly what the designers intended, we would get storms that would exceed its capacity, and I think that sometimes people forget that.

“They think that that’s supposed to be there to protect me against everything. And it isn’t. We can’t afford systems like that.”