Weather-Beaten: O.C. Deluge : Drainage System Fails a Major Test : Flood control: Channels could not cope with a level of rainfall expected only every 100 years or so.

The day after Orange County’s flood-control system overflowed, spewing water into streets, disrupting traffic and forcing home evacuations, officials acknowledged that the county was unprepared for the intensity of Wednesday’s downpour.

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Countywide, three to four inches of rain fell Wednesday, concentrated within three to six hours, officials said.

Herb Nakasone, the county’s flood-control manager, said that in much of the county the rain fell with an intensity expected to occur in this region only every 100 years or so. The deluge, he said, “overtaxed the storm drains and flood-control channels.”

While the county has a master plan for upgrading the countywide system of channels to handle such a situation and some improvements have been made over the years, Nakasone said, there was not enough money available to complete the job even before the county’s bankruptcy.

“It will cost probably over $1 billion to upgrade all of the flood-control system in Orange County to handle these kinds of 100-year storms,” he said. “We recognize where the deficiencies are.”

Bill Reiter, public works manager for the county Environmental Management Agency, said more than 20 flood-control channels overflowed in Wednesday’s rains. The most rain and flooding problems, he said, struck the western part of the county, from Huntington Beach to La Palma.

“Most of the channels were built in the ‘50s and ‘60s for more of a rural area than we have today. Now we are completely urbanized,” Reiter said.

Inadequate engineering of drainage channels was compounded in Buena Park, flood-control officials said, where rushing waters eroded the concrete lining of a flood-control channel, clogging the channel with concrete debris.

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In Cypress, the rain fell on trash collection day, causing trash cans to tip over in the high water, dumping trash into drains.

In Laguna Beach, where a torrent of water tore out a 100-foot stretch of beach and boardwalk, city engineer Ross Cox said the city and county for at least 13 years have been mulling ways to shore up the drainage system. That system runs down both sides of Laguna Canyon and then funnels into an underground channel along Broadway. The storm drain surfaces briefly near Beach Street and Broadway, which is where it overflowed Wednesday night, causing a four-foot wave of water, mud and debris to wash over the downtown area.

Cox said the city recently embarked on an engineering study of the feasibility of putting retention basins in the upper drainage area in hopes of retarding future flooding downtown. Every past proposal to upgrade the city’s drainage system, he said, has been scuttled by environmental or cost concerns.

Until the county’s flood-control system is up to snuff, Nakasone said, he strongly recommends that all residents living in a flood-control plain prepare for the worst by having sandbags ready to divert floodwaters and by buying flood insurance.

While the rains caused havoc to the county’s flood-control system, other government agencies in charge of sanitation, water pollution control and water supply were counting their blessings Thursday.

Officials at the Orange County Sanitation Districts reported with relief that there were no sewage overflows in its system, which collects and treats the sewage of 24 cities in central and northern Orange County. But they said the system was pushed to capacity.

Wednesday “was historical for us,” said spokesman Patrick McNelly, noting that at 9 p.m. the districts’ sanitation plants in Fountain Valley and Huntington Beach pumped an all-time record amount of treated sewage water into the ocean. The extra burden, he said, consisted of rainwater that had seeped into the sewage system through manholes.

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“Surprisingly, we had very little in the way of sewage spills out there,” said Larry Honeybourne, program chief of the water quality section of the Orange County Health Care Agency. “We had expected some major problems with those kinds of rainfall totals.”

Honeybourne said that as of late Thursday afternoon his agency had received reports of only two minor spills: a broken sewer line in Buena Park that dumped about 10,000 gallons of sewage into Fullerton Creek and a pump station overflow near the Links at Monarch Beach golf course in Dana Point that spilled almost 500 gallons of sewage into Salt Creek.

Lisa Ohlund, assistant general manager for the Aliso Water Management Agency, said that it was not certain whether the outfall the agency operates next to Aliso Pier sustained any damage.

“High waves and muddy water are making it difficult for us to detect in the ocean the dye we placed in the pipe to detect leaks,” she said.

“Luckily, there aren’t that many people at the beach right now, and it gives us a little breathing room,” she added.

Honeybourne said that so far the county has not quarantined any beaches. However, he said, county health officials are warning that swimmers should stay out of ocean waters near discharging storm drains, creeks and rivers and avoid contact with any dirt or other urban runoff on the beach.

“It could include fertilizers, road oils and animal wastes,” he said.

The rain was hailed as a gift by the Orange County Water District, which is responsible for maintaining the county’s ground-water basin, the source of about half the water used by county residents.

Jim Van Haun, executive assistant to the general manager of the Orange County Water District, said that rainfall in Riverside and San Bernardino counties created a lake containing 15,000 acre feet of water behind Prado Dam on the Santa Ana River. Before the rain, he said, the dam had been empty.

The water is being released downstream from Prado Dam into Orange County at a rate of 2,500 cubic feet per second, he said. On the way, a portion of the water will sink into sandy banks along the river to help fill the county’s underground water basin. The remainder will flow into the ocean.

One acre foot of water, Van Haun said, is enough to support two Orange County families of four for a year.

The alternative to rainwater, he said, is water purchased from the Metropolitan Water District of Southern California at a cost of $222 an acre foot. He noted that the money the district intended to use for water purchases was part of the $118 million it had placed in Orange County’s troubled investment pool.

The rainfall bonus, Van Haun said, “is all good news, definitely. It is all free water, and with the county fund crisis, this is very welcome.”

(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)

Deluge Drain Off As evidenced by this week’s rain, Orange County’s storm drains and channels are ill-equipped to handle heavy rainfall. The county’s master plan has provisions for upgrading the flood-control system, but with a $1-billion price tag, work has to be done in stages. How flooding occurs: * Street shortcomings: Some streets lack storm drains, and water collects. * Storm drains: If too small, water backs up on streets until they empty. * Earthen channels: Built to carry field runoff, they are less effective in urban areas. Water can spill over levees if channels have not been upgraded. * Concrete channels: These carry three times more water than earthen channels. Too much water can close flaps, create backup in storm drains. * Pumps: In heavy storms, they may not be able to move water fast enough from storm drains into drainage channels. Source: Times reports