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.