Road Closed by Flooding in Canyon : Weather: Workers use between-rains respite to drain waters in an effort to reopen Laguna Canyon Road today. New storm due tonight.

Laguna Canyon Road, a major South County artery, was closed Monday by flooding and might not reopen today, as workers try to drain 18-inch-deep water covering a stretch of the highway.

The road is closed for about five miles between the San Diego Freeway and El Toro Road as crews dig trenches and operate pumping machines. The road has been flooded since Friday night, when freshwater lakes on either side of it rose with the rain and ran together.

The California Highway Patrol will assess the problem today and determine when the road might reopen, officials said.

Meanwhile, another major storm is expected to arrive today, dumping three more inches of rain by Friday and threatening to trigger mudslides of already drenched earth.

“It’s possible we can see rain off and on for several days” said Rick Dittmann, meteorologist for WeatherData Inc., which provides forecasts for The Times.

There should also be more of the intense type of showers that battered Southern California over the weekend.

“With these storms, we’ll be getting some pretty intense rain showers because they’re picking up a lot of subtropical moisture,” said Gary Neumann, a meteorologist with the National Weather Service. “That’s likely to give us some local flooding and mudslides because the ground is already fairly saturated.”

Heavy rainfall is likely today after 6 p.m. and may continue through the night and Wednesday. “That’s when the locally heavy stuff will kick in,” Dittmann said.

Up to two inches of rain are forecast for low-lying inland areas, more than two inches for the coastal areas and lower mountain elevations, and as much as three inches for higher mountains.

Santa Ana and Anaheim are expected to be pelted with two to four inches, Dittman said.

The new storm follows a battering rainfall that began Friday in Orange County, leaving more than three inches in Santa Ana, 4.7 inches in Villa Park and a mountain-drenching 10.2 inches at Santiago Peak in the Cleveland National Forest.

Rain on Sunday night closed Fullerton Airport, Roland Elder, airport director, said. At 10:30 p.m. Sunday about 400 feet of the runway was covered with up to five inches of water.

“As the sun came up, we got it open again,” he said. Flights were not affected.

The latest storm pushed rainfall totals significantly ahead of last year and above the average marks for this time of year in the county.

The year-to-date rainfall for Santa Ana is 14.7 inches, compared to only 8.5 inches last year and an average of 11.2 inches. In Costa Mesa, the year-to-date rainfall is 13.6 inches, compared to 7.8 inches last year and an average of 10.5 inches.

Crews in Laguna Beach worked into the night Monday during the respite between storms.

But John Phillips, who owns two homes south of the flooded area, feared that attempts to drain the lakes might flood his and his neighbors’ properties. He and other residents along Laguna Canyon Road stacked sandbags to ward off potential floods.

But Terry Brandt, Laguna Beach director of municipal services, said there was little likelihood of flooding.

Brandt said workmen cut a trench through a raised access road that was blocking drainage. But the trenching, even in combination with the 40,000 to 50,000 gallons an hour being drained by three pumps operated by city and Caltrans crews, should pose no flooding problems downstream, he said.

Meanwhile, on Monday county public works crews were inspecting checkpoints in preparation for the runoff.

“We don’t expect much (rain on Monday), but we’re out making sure grates and drains are cleared so water will flow smoothly when it rains,” said Thomas P. Connellie public works maintenance manager.

Monday afternoon’s blue skies briefly brought out beach-goers.

Saturating the Soil

Heavy rains can cause street flooding and minor mudslides, but a longer-term problem occurs when the soil gets over-saturated. Here is a look at what can happen during the rain season from December through March:

A) When rainfall is less than about 4 to 6 inches, there tend to be few problems.

B) When rainfall approaches 6 to 10 inches, soil begins to saturate and water becomes harder to absorb. Small mudslides, with a few feet of soil washing away, can occur.

C) With more than 10 inches, real problems begin. These include large mudslides during the storms and, later in the year, the chance of massive landslides as water undermines bedrock layers of compacted earth.

The Worst Case

The major long-term risk of saturated soil is that it will be weakened and later give way.

* In some areas of the Southland--especially in coastal places including Pacific Palisades, the Malibu Coast, Palos Verdes and Laguna Beach--the underlying bedrock is not the usual granite but compacted earth.

* Heavy rainfall during the winter months can seep into this less-stable type of bedrock.

* The seepage can loosen the soil.

* In the fall, minor rains can make the weakened area vulnerable to a big slide.

Source: Caltech