Pasadena's Devil's Gate Dam could be put to the test

Los Angeles Times ^ | November 28, 2009 | Baxter Holmes

[americanophile]

Twelve years ago, the idea of a giant mudslide barreling down the Arroyo Seco in Pasadena was considered only a distant possibility.

Nevertheless, the Devil's Gate Dam underwent a major enhancement that took two years to complete and enabled one of the oldest dams in Los Angeles County to withstand a potential massive debris flow.

At the time, engineers thought the improvements might be overkill because conditions would never be extreme enough to test the dam's strength, at least not in their lifetimes.

"Not a chance," recalled Brad Boman, engineering manager of water services at Pasadena Water and Power.

But since the Station fire burned more than 160,000 acres and nearly all of the Arroyo Seco in late August and September, making it the worst wildfire in recorded L.A. County history, the experts have changed their tune.

"Twelve years later, we're confronted with that possibility," Boman said.

L.A. County Public Works officials spent several days this month cleaning out floating debris that washed into the reservoir in mid-October during a brief rainstorm. Near the base of the dam, they also laid a "debris boom," or a connected line of floating power poles designed to keep large debris away from the concrete structure.

Devil's Gate, one of 13 dams in L.A. County, was built in 1920. The modifications made in the 1990s were needed to keep it up to code.

If a mudslide were to occur in the Arroyo Seco, the dam would take the brunt, and because of the area's geography, a flow would probably move down the canyon when heavy rains hit, said Sue Cannon, a research geologist with the U.S. Geological Survey.

There is a concern with the amount of anticipated debris flow after the Station fire,

[americanophile]

[Andyman]

The long, arching roadway on top of the dam is very attractive.

[americanophile]

Yes, as dams go, it's a very nice looking one. It was built along with the other major projects around Pasadena like the Colorado Street Bridge, Rose Bowl, etc. Here's a pic during the recent fires. One of the things that the article doesn't mention is that JPL sits within that catch basin, as you can see in the back of this photo.

[null and void]

Yeah. I parked in a lot where cars had simply vanished in a flood.

[Steely Tom]

Is that the dam Jack Nicholson visited in Chinatown?

[Lx]

[americanophile]

...you know, it’s been ages since I’ve seen that, I can’t remember. Usually for dam scenes in L.A. though they use the Sepulveda dam.

[tubebender]

The log and cable debris boom stretching across Ruth Lake formed by Matthews Dam on the Mad River in Trinity county in Northern Calif was put to the test during the torrential rains leading up to the disastrous floods of Dec 1964 in the north state. Matthews dam is a compacted earthen dam with a concrete spillway and had the boon failed the dam would have been lost as the debris would plug the spillway and they estimated the structure would have failed in 2 hours later wiping out everything in the Mad River Canyon of Humboldt County to the ocean near Arcata Ca.

There were some heroic people who went out in boats with chain saws to cut up the logs piling up, plus on shore the cable anchors were threatening to pull free. More men added extra cables to tie in to trees up hill on both side of the lake in miserable conditions.

[americanophile]

...sounds like many people are in their debt!