Water Watch : Carson, Gardena, Torrance Would Suffer in Major Flood, Study Says

Most of the South Bay would escape damage from a “100-year flood,” suffering only “nuisance flooding,” a recently completed study by the Army Corps of Engineers says.

That’s the good news.

The bad news is that the 100-year flood--defined as the worst flood with at least a 1% chance of occurring in any single year--would inundate about half of the city of Carson with water up to eight feet deep. Such a deluge also would flood portions of the Los Angeles city strip and outlying sections of Gardena and Torrance.

Corps officials, who released the study last week, say such a flood would overflow levees of the Los Angeles River and other parts of the Los Angeles County flood control system. The flow along the river would be a torrent of 150,000 cubic feet--enough to fill 32,000 bathtubs--every second.

Countywide, the floods would cover up to 100 square miles and cause up to $2.5 billion in damage, enough to justify a $500-million construction program to beef up flood control facilities, according to Ira Arzt, the study project manager. Damage in the South Bay could run into the millions of dollars, Arzt said.

Before formulating a final plan for improvements to the county’s flood control system--which consists of 500 miles of channels, 20 dams and 125 debris basins--the corps will hold a series of meetings with local officials and residents. A meeting for the South Bay will be held at 7 p.m. on Oct. 20 at the Carson Community Center, 801 E. Carson St.

The inability of the existing system to handle a 100-year flood results in general from increased urbanization, which leads to fast runoff from paved surfaces, in the 2,000-square-mile watershed served by the flood control system. Contributing factors include an increasingly efficient storm sewer system, which sends water to drainage ditches sooner, and increased sedimentation in reservoirs, which reduces their capacity.

But in Carson, which the study says will be the most severely affected area in the South Bay, a number of other factors make the threat even worse. According to corps and Carson officials:

The water table there is close to the surface, just several feet below ground in a low-lying former lake bed, which would probably be flooded.

The city is close enough to the Los Angeles River to be subject to flooding from breaks in the river levee.

The Dominguez Channel, which runs from the northwest corner of the city to the southeast, also would overflow.

The Dominguez Hills area, which would be above the flood, would make matters worse by blocking water flow and causing water to pile up in Carson.

The corps study says that water six to eight feet deep would flood the Carson Mall, causing an estimated $10 million in damage, and the Arco refinery, where losses of $1.5 million are predicted. Flood waters would also soak Carson’s City Hall and Community Center and the Intermodal Cargo Transfer Facility in a nearby section of Wilmington.

William Huber, Carson’s chief engineer, said the city is seeking more precise information from the corps about the extent of possible flooding. Carol Henderson, assistant project manager for the study, said detailed topographic maps will be available at the Oct. 20 hearing.

“They will show on a street-by-street basis where flooding will occur and where not,” she said.

In the Los Angeles city strip--the section of Los Angeles along the Harbor Freeway that connects the Port of Los Angeles, San Pedro and Wilmington with downtown Los Angeles--two areas are subject to flooding, according to the Corps of Engineers. One is between the San Diego Freeway and the Artesia Freeway, extending from Carson to Torrance and Gardena. The second area is an irregularly shaped section pointed southwest into the city strip a short distance south of the intersection of the Harbor and San Diego freeways.

Los Angeles City Engineer Larry Erdos said he did not have precise information on the extent of possible flooding.

In Gardena, where the southern fringe of the city is in the flood zone, City Manager Ken Landau said without elaboration that the corps report “might be a bureaucratic document” and that he was more worried about earthquakes than floods.

“The report prepared by the Army corps deals with a hypothetical situation,” Landau said. “We know the devastating effects of an earthquake. Right now we are studying the report. . . . If it means getting more federal funds to build up the Dominguez Channel, we will certainly pursue that.”

In Torrance, the flood waters are predicted to touch a small section in the northeast of the city near the intersection of Western Avenue and Artesia Boulevard. “Torrance is 99.9% out of” the flood area, said Brooks Bell Jr., a Torrance civil engineering associate.

One South Bay official, who asked not to be identified, said the report smacked of a self-serving effort to promote the corps’ budgetary goals.

‘People Forget’

Arzt said: “We always get skeptics. After floods, we get attacked for not doing anything about it. Our analysis is performed according to regulations outlined by the Corps of Engineers and Congress.” He added that skepticism is sharper in Los Angeles than in other areas because “it is dry here. . . . People forget about the storm that flooded them out.”

The worst flood in Los Angeles took place in 1868 before many people lived in the area. The flood was so severe that it redirected the Los Angeles River, shifting its mouth from what is now Marina Del Rey to Long Beach and flooding everything in between.

In 1938, when construction of the existing flood control system was beginning, another large flood cut off all rail and roads leading into the Los Angeles Basin, injured hundreds and destroyed the homes of thousands of people.

Sizable storms also afflicted the Los Angeles area in 1969, 1978, 1980 and 1983. In 1980, corps officials say a 100-year flood almost occurred when reservoirs were full and the ground saturated after six storms came in a short period of time. A feared seventh storm, which officials say probably would have broken the levees, was brewing but missed the area.

Few structures in the areas subject to flooding are insured against flood hazard, according to Arzt.

In tandem with the corps study, the Federal Emergency Management Administration is updating flood hazard maps, which are used for a federally sponsored flood insurance program. The agency makes flood insurance available to individuals in communities with a flood hazard if local officials agree to reduce future flood risks.

The maps, which provide information about the potential for flooding on a building-by-building basis, are used to determine which locations are in the 100-year flood plain.

Arzt said that federal flood insurance regulations will inhibit development in the newly defined 100-year flood plain by making it more costly.

“Anyone who buys a home from a bank will be required to get flood insurance. Anyone who wants to add on to a home will be required to buy flood insurance,” he said.

In addition, new residential development must be built above the flood depths by adding fill or building on pillars, according to Ray Lenaburg, a civil engineer for the federal agency. New commercial development must be built above the flood depths or construction at ground level will have to be flood-proofed, Lenaburg said.

The average home flood insurance policy in Los Angeles County covers losses up to $120,000 and costs $340 a year, he said. From 1974 when the current program was started to January, 1987, the program in the county has covered 2,000 flood losses totaling $15 million, he said.