Council OKs Emergency Procedures : Sepulveda Basin: City workers are ordered to hold practice sessions. The measures were prompted by February floods that trapped motorists.

The Los Angeles City Council, trying to prevent a repetition of the near-disaster in February when floodwaters trapped dozens of motorists in the Sepulveda Basin, Tuesday approved new emergency measures and ordered city workers to hold practice sessions to test them.

Under the new procedures, a police patrol car would be sent to the basin to observe the rising waters of the Los Angeles River well before they could inundate Burbank Boulevard and other streets in the basin.

If the procedures work as planned, police will be on the scene at least 90 minutes before floodwaters flow over the streets, even in the heaviest rainstorms, city officials said.

City streets cross the basin, which is dry most of the time but is also a federally owned flood plain. It is designed to store the waters of the Los Angeles River, which back up behind the Sepulveda Dam during heavy rains to prevent disastrous flooding downstream in central Los Angeles.

During heavy rains in February, floodwaters rose swiftly over the streets, trapping 48 motorists, many of whom had to be rescued by helicopters. In the aftermath of the emergency, city officials blamed lack of preparation and coordination by police and city streets officials and the Army Corps of Engineers, which operates the dam.

The revised plan was quietly adopted by the council with only minor comments by Councilwoman Joy Picus, who was among the city leaders who urged that improved emergency plans be developed. “Plainly there was a failure of the system in February,” Picus said in an interview.

Under the new emergency plan, a Los Angeles Police Department unit would be sent to the basin to monitor conditions after floodwaters reach a level of 680 feet above sea-level at the dam.

That is 8.2 feet below the level on the dam at which the water, spreading in a vast lake behind the dam, would inundate the intersection of Burbank Boulevard and Woodley Avenue, several hundred yards away.

Previously, the corps’ procedure had been to notify city officials of flooding in the basin when the waters were only two inches short of the flood level on the dam, said Ed Howell, Valley District engineer for the city’s Bureau of Engineering.

Even under flash-flood conditions, the new warning level will give city emergency crews 90 minutes to begin preparing for the possible closure of the roads in the basin and the evacuation of motorists, Howell said.

“There’s going to be a lot of false alarms with this system,” Howell said in an interview. “The LAPD will be put on alert, but in most cases the waters will subside before they flood the intersection.”

The plan approved Tuesday gives detailed instructions on which agencies are to be notified about conditions in the basin during rainy weather.