Sunday, December 28, 2008

North County: the greatest flood hazard west of the Mississippi?

It's amazing how you can live somewhere for decades and not know some of the most basic things about it. 

Take geography. How many of us in "the OC" realize that, geographically, our county comprises part of a mountain range and two valleys? (Click on the map to enlarge it.)

Yep. Naturally, there are the Santa Ana Mountains—home to Silverado, Modjeska, and Trabuco canyons, among others—which come up from San Diego County and end with the Peralta Hills in the tiny city of Olive. That's a nice little town. Still has some old buildings. It was founded in 1812!



North of the Santa Anas, the Santa Ana River flows (ultimately from San Gorgonio Mt., 11,499 feet) westward past Corona, through Santa Ana Canyon to Anaheim and then southward, through Santa Ana Valley, to the ocean on the border between Newport Beach and Huntington Beach.

Naturally, on the south side of the Santa Anas, there's Saddleback Valley, which extends more or less from Lake Forest down to San Juan Capistrano. "Saddleback," as most of you know, is a reference to the appearance of the Santa Anas, which, in OC, are dominated by two peaks (Modjeska Pk. and Santiago Pk.), which from a distance look, well, like the back of a saddle.


Those hills just northeast of Irvine are called the "Loma Ridge," which is the portion of the Santa Anas set off by Santiago Creek, which starts in Modjeska Canyon and runs northwest to Villa Park and then to the Santa Ana River.

Here's something I'll bet you didn't know: according to Wikipedia, the Santa Ana Valley, site of such cities as Anaheim and Santa Ana, is a highly worrisome flood zone (See Register graphic (pdf):

[T]he Santa Ana River is prone to flooding in wet seasons. The Army Corps of Engineers considers it to be the greatest flood hazard west of the Mississippi River. It produced devastating floods in 1862, 1938, and 1969.

The 1938 flood was caused by heavy rains in the area that started on February 27, 1938. The river spilled over its banks on March 3, sweeping away cars, homes, and bridges, including Pacific Coast Highway. A total of 2000 people were left homeless and 19 people perished. As a result of this flood, the Prado Dam was built near Corona in 1941. Officials in Orange County felt further protection was needed. The Seven Oaks Dam was completed in 1999, located a few miles north of Redlands.

In early 2005, Southern California experienced one of its wettest periods in recent history, which placed unusual stress on the Santa Ana River system. Prado Dam, which was under construction for expansion at the time, seeped water, and residents of the local communities of Corona and Yorba Linda were evacuated as a precaution. The dam was damaged, but there was no major flooding as a result, and evacuated people were soon allowed to return.

The flood of '38.

SEE ALSO
The Flood of 1938, part 1
Part 2
Part 3



SEE:

3 comments:

Anonymous said...

Tsunamis? Really?

Anonymous said...

My first ex could have told us we lived on a coastal flood plain. In fact, I learned that in his geology class when I was a sophmore. Folks, if the ocean disappears one day, don't run out to see where it went....run the other way!

Anonymous said...

And of equal concern (or it should be) is the problem of "liquification" in the coastal flood plain areas. Water soaks in beneath the surface and causes collapses of structures, much like what happens to children's sand castles built near the shoreline. Many of us remember these facts in association with the naming of IVC--some joked it should be called "Irvine Tidal Flood Plain College," since there is no true valley. Thanks for the reminders, Roy.

Roy's obituary in LA Times and Register: "we were lucky to have you while we did"

  This ran in the Sunday December 24, 2023 edition of the Los Angeles Times and the Orange County Register : July 14, 1955 - November 20, 2...