It's called the "100-year flood," a deluge that officials say could cause $14 billion damage and as many as 3,000 deaths along the Santa Ana River, and it is overdue.
The normally sleepy river that runs, often at a trickle, through three Southern California counties from the San Bernardino Mountains to the Pacific Ocean could inundate as many as 500,000 homes during worst-likely weather conditions, according to the Army Corps of Engineers.
"It's the worst potential flood problem west of the Mississippi, maybe the worst in the country," said Carl Nelson, Orange County's director of public works.
The Corps of Engineers and local officials from San Bernardino, Riverside and Orange counties have joined in a push to get money for major projects along the river to contain destructive floodwaters.
Fund Bills Pending
Authorization bills are pending in both houses of Congress for a massive 20-year flood-control project, which will include raising the Prado Dam, located roughly halfway in the river's path, building new dams upstream and widening the concrete river channel running through Orange County.
Officials say the improvements are needed because of rapid development of areas along the river, especially in Orange County, which has changed in only a few years from mostly farmland to a bustling metropolitan area of 2 million people.
Until 1940, most of the land in the three counties the river runs through was planted in orchards and crops, and farmers more or less accepted and adjusted to occasional floods. After the industrialization of the area in the 1940s, population jumped 1,800% in Orange County alone.
The Corps of Engineers estimates that if the area were to be hit with the same conditions today that caused a massive flood in 1862, 100,000 acres would be covered with an average of three feet of water and some low-lying portions of Laguna Beach at the river's mouth would be under six feet of water.
Up to 3,000 deaths, massive power outages, a virtual halt to transportation and overflows of most major sewer systems would result, Nelson said.
"If the flood comes now, it would most likely flow over the Santa Ana Freeway, and places like Disneyland would certainly be inundated," he said. "You can't really tell how bad it will be, because we've never seen anything like it."
Officials are mounting a campaign to warn residents of the danger and to build support for flood-control projects with mailings and a multimedia show detailing the possibility of a major disaster.
Warnings about the danger of a deluge were sent to all homeowners in the area with their property tax bills, along with a plea for residents to protect themselves by buying flood insurance.
Since the huge 1862 flood, there have been 14 floods classified as medium to severe in the river basin, and in 1938, 1969, 1978 and 1980 the area was hit with major floods in terms of relative size and economic damage.
Could Happen Anytime
The 1938 flood devastated central Orange County and killed 45 people, prompting the construction of Prado Dam and other control measures. But officials say that while the current precautions would contain the 1938 flood, they would be almost useless if conditions similar to those in 1862 recur, and they expect that to happen at any time.
"Every year that passes brings more of a threat of severe damage and deaths," Nelson said.
Studies of tree rings to determine annual rainfall and estimates of historical weather patterns by meteorologists show that the chance of a flood the size of the 1862 deluge occurring every 100 years or so is very good.
Even if the funding for the flood-control projects is approved quickly, it could be 20 years before all the work is done, and political squabbles and other delays could push completion well past the year 2000. The earliest anticipated completion would be 1998.
"We want to get this thing cured before the flood," Nelson said. "But the problem is that until there is a flood no one believes you when you say there's a problem.
"It's just a matter of time until it happens again."