‘50-Year Storm’ Might Swamp L.A. River Basin, Engineers Warn

Storms of much less severity than previously thought could overwhelm the capacity of some segments of the Los Angeles River and cause widespread flooding, the U.S. Army Corps of Engineers said Thursday.

Only last July, the agency, which has been conducting a study of the Los Angeles area drainage basin, said it was concerned that portions of the river would not be able to withstand a so-called 100-year flood, a storm of a severity that statistically occurs only every 100 years.

Now, the Corps of Engineers has concluded that portions of the river could be overcome by a 50-year storm, officials said. That conclusion is based on the continuing study, not on any problems caused by the past week’s heavy rainfall, which was far less severe than a 50-year storm, officials said. The river had no trouble handling the nearly six inches of rain recorded since Feb. 13.

“There’s a tremendous message there, to say that in an area like Los Angeles,” said Edward J. O’Neill, chief of program development at the corps’ South Pacific Division headquarters in San Francisco. “It cannot even fully control a 50-year flood.”

At the same time, O’Neill said the corps is wrestling with the issue of which urbanized areas may be intentionally subjected to a flood threat in the event that heavy runoff must be diverted into channels or rivers that run through populated areas. Most property owners in the area do not carry flood insurance.

Among the major decisions to be resolved by the study is whether to send heavy runoff from the Whittier Narrows Dam in South El Monte into the Rio Hondo or San Gabriel rivers.

The Rio Hondo River flows southwesterly from the dam through Pico Rivera, Montebello, Downey, Bell Gardens and South Gate before it empties into the Los Angeles River near Imperial Highway.

The San Gabriel River runs southwesterly through Pico Rivera and Santa Fe Springs and then juts south through Downey, Norwalk, Bellflower, Cerritos, Lakewood and Long Beach.

In either case, high runoff could mean subjecting the urbanized area adjacent to those two rivers to increased flood threats.

“What we don’t know on an extremely complex system is who gets wet and in what order they get wet. . . , O’Neill said in a telephone interview. “It certainly has political consequences. . . . The issues in all their varied complexity--environmental, political, economic--are pretty darn tough.”

However, the Corps of Engineers has also said that it will be considering numerous options to minimize any flood threat, including construction projects to increase the capacity of the rivers and dams.

The 43-mile-long Los Angeles River, which flows easterly across the San Fernando Valley, bends south in Glendale, runs past downtown Los Angeles and empties into the Pacific Ocean at Long Beach, is the backbone of Los Angeles County’s flood control system. Since the Corps of Engineers began shoring up its sides and diverting its course in the 1930s to control flooding, extensive urbanization has greatly increased runoff into the river.

The new findings come at a time when the Army has fallen behind schedule in completing the river study, which began 14 years ago. The first phase of the study, which was to define the extent of flooding under various scenarios, will not be completed until at least next October and possibly later.

Last July, the Corps of Engineers said that phase would be completed by December, 1985. Completion of the entire study, including subsequent phases, is not expected until September, 1988--a six-month delay.

Congress appropriated $370,000 in the current budget year for the study and the proposed federal budget calls for an increase to $1.15 million in the new fiscal year beginning Oct. 1.

Carl Enson, chief of the Corps of Engineers’ planning division in Los Angeles, said the delay was caused by a decision to expand the scope of the study to gather more data “due to the severity of the flood problem.”

The study covers the 2,000-square-mile Los Angeles County drainage area, which includes the Los Angeles River, its 295 miles of tributaries, and the San Gabriel and Rio Hondo rivers.

County Concerned

The delay has concerned the Los Angeles County Public Works Department, which operates dams and flood-control channels that empty into the Los Angeles River.

James L. Easton, chief deputy director of the county department, said: “I’m disappointed because I had hoped the information the corps was going to come up with would help us to graphically demonstrate to Congress the magnitude of the problem. We’ll go with what we had last year, which is graphic enough.”

O’Neill responded: “I understand his concern. But I’m not at all uncomfortable with our position. Last year we had $370,000 in the budget. This year it’s $1.15 million. We have no qualms about justifying that to Congress.”