Super-Rainy Days Get the Attention of Civil Engineers
Bob Talafus clicks off a date as easily as Carl Sagan might for the last sighting of Kahoutek.
“March 1, 1983,” Talafus says. “We came very close to a 100-year flood.”
After his wife told him Tuesday about daylong TV coverage of “Flood Watch 1995,” Talafus, a civil engineer with Wagner Pacific Inc. in Placentia, thought they might be hyping things a bit. On the other hand, he’s impressed enough with the storm to say: “It’s got the potential to be historic, especially with the rains that are dropping up north.”
If you’re an astronomer, comets turn you on.
If you’re an archeologist, there’s nothing like unearthing a lost city to spice up your life.
And if you’re a civil engineer. . . .
Well, can they help it if they’re intrigued by what these rains will do? After all, talk about the 100-year flood is their Super Bowl and 800-pound gorilla all rolled into one, so you can’t blame them if their hearts beat a little faster when rain falls relentlessly in our desert clime.
Engineers are interested in torrential rain because this business of hundred-year floods and how to prepare for them is not an exact science. It’s all about the breeding of probability and economics. That is, the engineer’s task has been to strike a reasonable balance between protecting lives and property against foreseeable flood damage and making such protections economically feasible.
To illustrate: We could be protected to the max, even against a mythical “200-year flood,” but street curbs would be two feet high instead of six inches, and storm-drain pipes would be three times their current size. The cost of building homes or making capital improvements, such as the prodigiously expensive Santa Ana River project currently underway to protect against a 100-year flood, would be exorbitant.
And, of course, the 200-year flood may never come.
On the other hand, planning on the cheap--say, not upgrading the Santa Ana River--would imperil citizens and property. So, over the years, engineers settled on the 100-year benchmark for major facilities, like river projects, that could result in widespread and catastrophic residential flooding. Smaller systems, such as channels running through neighborhoods and those for single-street drainage, are built to handle 50- or 25-year floods. (For you trivia buffs, parking lots generally are built to handle 10-year storms.)
So, that’s the bargain we’ve struck between cost and protection. Now, we all sit back and hope the calculations are correct.
Loren Sandberg, an engineer with the Tustin firm of K W Lawler & Associates, said the prospect of major rains underscores the uncertainty of the business. While professional engineers have confidence in the 100-year specifications, Sandberg conceded they’d love to have 10,000 years’ worth of rain and flood experience on which to base decisions. Adding to the mathematical puzzle is that widespread development over the years systematically removes open space that once absorbed rainfall.
But without 10,000 years of experience, engineers go with what we think will happen when the Liquid Big One hits.
Not surprisingly, Sandberg has become a weather-watcher the last couple weeks. “I like to see, especially, how systems I’ve designed are performing,” he said. “And there are certain assumptions on what water is going to do.” Builders in Orange County use a manual last updated in 1985, he said. “We’ve decided we’re going to use this manual, right or wrong, which, in theory, should protect us from these storms.”
Sampath Raghavan, with the Laguna Hills firm of Lotus Consulting Engineers Inc., doesn’t even wait each year to see if big rains come.
“Annually, we get 12 to 14 inches in any regular year, from Oct. 15 through April 15,” he said. “So what I do is, before Oct. 15, I send out hundreds of letters to my clients reminding them of the coming rainy season, what precautions they should take, what are the do’s and don’ts to protect their property structure so the site will be stable.”
In the last couple weeks, Raghavan said, his reaction to the persistent rain has been a combination of “ ‘Iinteresting,’ at the same time, ‘Oh, no.’ ”
Interesting and oh, no. That may come as close as anything to describing engineers as they wait to see when the rain will stop.
“I think there is kind of an anticipation now,” Talafus said. “I heard Santa Barbara has had 7 inches since last night. That’s significant. If this storm continues to come through and continues to dump, let’s say, that much water in the next 12 hours, there’s going to be some incredible flooding that goes on.”