O.C. Soaked, Sliding in Storms’ Wake : History: January may become the wettest ever in O.C., but the mark in destruction has not yet been eclipsed.

After researching rainfall records dating back to the turn of the century, county historian Jim Sleeper predicted Monday that this month will go down as the wettest January in Orange County history.

The monthly rainfall has already exceeded the 9.25 inches of January, 1969, when floodwaters wiped out four bridges and two homes in Santiago Canyon, and Sleeper believes that it will top the record of 11.18 inches set in a 1916 “gully washer.”

Monday, WeatherData, which provides weather information for The Times, reported that Santa Ana has received 11.03 inches of rain since New Year’s Day--just .15 inches short of the 1916 record, Sleeper said. Steve Burback, WeatherData’s meteorologist, said Santa Ana could receive that much by today.

The rain “back in 1916 is what prompted us to start thinking about flood control,” Sleeper said. “Historically, in terms of water, this (month) is enormous. We are getting virtually a year’s worth of rain in one month.”

There have been several 20th-Century storms that have wrought more damage on Orange County, such as the 1969 deluge in which emergency crews stacked junked cars along the banks of the Santa Ana River to try to hold back the raging torrents.

And 24 years ago, on Jan. 26, Santiago Creek burst its banks and the roaring waters swept away four bridges and two homes. Hundreds of residents were reported stranded in the canyon area.

The Modjeska Canyon Volunteer Fire Department estimated the cost of the damage at more than $1 million.

Starting in 1936, Sleeper said, Orange County was soaked with four consecutive years of rainfall that more than doubled the county’s seasonal average. Each year, the county suffered flood damage. However, a lot of the rain fell in February and March, which historically have been wetter months than January.

In 1938, the Santa Ana River overflowed its banks. But much of the floodwater poured into agricultural areas where damage was minimized. And in 1958, Sleeper said, there were serious floods when a warm rain quickly melted a large snowpack.

To Sleeper, the county has done a remarkable job building a flood control system that has largely prevented the major problems Orange County used to suffer routinely from heavy rains. But still, he noted, the cost of storm damage has soared because of the county’s booming development.

County officials have already counted about $10 million in damage caused by this month’s storms, even though flood control channels were generally performing well. County public works officials said Monday that they will begin this week to put this month’s rainfall in historical context.

Based on a formula that includes the amount of precipitation as well as the duration of the storm, county hydrologists will determine whether the soaking qualifies as a 100-year storm, the model for which the county’s flood infrastructure is designed.

County officials said their records of rainfall were not available Monday because of the holiday. But even with a record amount for the month, they said the rain may not be considered a severe storm by flood control planners because it was not a concentrated downpour.

Tom Connelie, a county public works manager, said the county’s flood control system may have received a greater test last month when four inches of rain fell in about four hours.

“A storm that lasted just a few hours, like that one, could be more severe than this storm from a flood control standpoint, even though the amount of rain was much less,” Connelie said.

Rainfall amounts vary throughout the county, with the highest amounts recorded in the mountains. Sleeper said that Santa Ana has a history of monthly rainfall records dating back to 1908. His historical weather records are a compilation of county government sources, the county farm bureau and newspaper clippings.

Sleeper said he also records the rainfall at his house in Tustin and, as of Monday afternoon, had tallied 14.55 inches for this month.