News LA Times: Engineers up failure risk for dam protecting Disneyland, dozens of Orange County cities

mharrington

Well-Known Member
Original Poster
I found this on the LA Times: https://www.latimes.com/local/lanow/la-me-ln-prado-dam-flood-risk-failure-20190516-story.html:

Federal engineers are raising alarms that a “significant flood event” could compromise the spillway of Southern California’s aging Prado Dam and potentially inundate dozens of Orange County communities from Disneyland to Newport Beach.

After conducting an assessment of the 78-year-old structure earlier this month, the U.S. Army Corps of Engineers announced that it was raising the dam’s risk category from “moderate” to “high urgency."

“Our concern right now is about the concrete slab of the spillway and how well it will perform if water were to spill over the top of the dam,” said Lillian Doherty, the Army Corps’ division chief. “We will determine whether or not it is as reliable as it should be.”

Located beside the 91 Freeway on the border of Riverside and Orange counties, the dam impounds little to no water for much of the year. During periods of heavy rain, however, the structure is intended to collect water and prevent flooding along the Santa Ana River.

Doherty said her agency is working with a national team of experts to develop interim and permanent risk-reduction measures at the dam, as well as public outreach strategies to alert the estimated 1.4 million people who live and work in 29 communities downstream.

The sudden downgrade in the structure’s evaluation comes after major problems have been identified in California dams...


All of a sudden, I am very concerned for the future of Disneyland. The article says that they will retrofit the spillways, but that that won't be for another two years, which may not be enough time.
 

TP2000

Well-Known Member
I found this on the LA Times: https://www.latimes.com/local/lanow/la-me-ln-prado-dam-flood-risk-failure-20190516-story.html:

Federal engineers are raising alarms that a “significant flood event” could compromise the spillway of Southern California’s aging Prado Dam and potentially inundate dozens of Orange County communities from Disneyland to Newport Beach.

After conducting an assessment of the 78-year-old structure earlier this month, the U.S. Army Corps of Engineers announced that it was raising the dam’s risk category from “moderate” to “high urgency."

“Our concern right now is about the concrete slab of the spillway and how well it will perform if water were to spill over the top of the dam,” said Lillian Doherty, the Army Corps’ division chief. “We will determine whether or not it is as reliable as it should be.”

Located beside the 91 Freeway on the border of Riverside and Orange counties, the dam impounds little to no water for much of the year. During periods of heavy rain, however, the structure is intended to collect water and prevent flooding along the Santa Ana River.

Doherty said her agency is working with a national team of experts to develop interim and permanent risk-reduction measures at the dam, as well as public outreach strategies to alert the estimated 1.4 million people who live and work in 29 communities downstream.

The sudden downgrade in the structure’s evaluation comes after major problems have been identified in California dams...


All of a sudden, I am very concerned for the future of Disneyland. The article says that they will retrofit the spillways, but that that won't be for another two years, which may not be enough time.

Interesting. Whenever I drive out to Palm Springs and pass the Prado Dam, I always look at it suspiciously. There's just something that tells me that it's going to be a problem in the future. I'm not a New Age weirdo, but I just get bad vibes from that dam.

I wouldn't worry about Disneyland directly though. If and when the Prado Dam fails, the damage to Disneyland will be mostly aesthetic and not life threatening. It's the 100,000+ people living directly below the dam along the Santa Ana River basin in east Anaheim, Yorba Linda and Orange that would be in physical danger if the dam were to fail. By the time the surge of water reached the flatlands of Anaheim and the Disneyland Resort District, you'd just have a foot or two of standing water ruining carpets and flooding basements, not real death and destruction.

I imagine the basement levels of Disneyland would be quickly flooded though, so you could have real problems with sunken structures like the Tiki Room, Space Mountain, Pirates, Haunted Mansion, etc.
 
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TP2000

Well-Known Member
I found this image online of the inundation map when Prado Dam fails. Disneyland is about a third of the way out in the floodplain, away from the canyon walls where the real death and destruction will happen.

Hmm... having trouble linking to the image. It's in this report on page 14. https://rsccd.edu/Departments/Risk-Management/Documents/Risk Management/IV-D Dam Failure.pdf

It's going to be messy, but it's not going to wash the Matterhorn away. I don't think. :oops:
 

Darkbeer1

Well-Known Member
You have it right. The areas close to The Santa Ana River could get a l9t, such as the Honda Center and Angel Stadium. The stadium's field is lower than grade, maybe 30 to 50 feet. I walked both ramps a couple of weeks ago for a 5K.

West Anaheim has another flood control channel that goes East West next to the Dad Miller Golf Course and the Tiger Woods Learning Center. So that could impact us and close to Knott's. Goes under Beach Blvd.

Much of Disneyland is above grade. The I-5 could also become a free flowing river due to the lack of things to slow the water.

But the 91 will clearly get the water first as it flows to East Anaheim, Yorba Regional Park, etc.
 

lazyboy97o

Well-Known Member
All of a sudden, I am very concerned for the future of Disneyland. The article says that they will retrofit the spillways, but that that won't be for another two years, which may not be enough time.
Why? The concern is not that the dam itself is in danger of failing. The concerns is regarding the spillway and a spillover event. Based on the data I can find from the US Army Corps of Engineers and California Department of Water Resources, Prado Dam has so far never had a spillover event. A temporary construction dam did a few years ago along with other serious damage that was related to the construction, but not the spillway that the Corps is concerned about. Spillover will occur when the reservoir reaches 543’ NGVD (NGVD is roughly sea level). The reservoir’s highest elevation was 528’ on February 22, 1980. It reached nearly reached that level again in January 2005. More recent highs have been just under 515’ and yesterday the elevation was at 483’. Knowing that the spillway is a point of serious concern means the Corps can take action to try to prevent the reservoir from spilling over in the event of major rainfall.

Archived US Army Corp of Engineers page

California Department of Water Resources Board elevation data
 
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Darkbeer1

Well-Known Member
What I heard on the news this morning is that they want to raise the height of the dam a bit when they do the repair work.

In a state where Earthquakes are a constant worry that big one can do damage, the dam is much less of a worry.
 

TP2000

Well-Known Member
I KNEW SNL's The Californians was based on real Californians!!!


Oh my God, that's hysterical. I haven't watched Saturday Night Live in years and years, but good to know they can still be funny.

For those keeping score at home, when I drive out to Palm Springs I go down to Taft and over to Santiago Blvd and take it to the 91. I then take the 91 all the way out to the 215 and jump onto the 60 in Moreno Valley, take the 60 over the hills until it hits the 10 where the speed limit goes up to 75 (real world speed 85-ish) wave at the dinosaurs in Cabazon and then I get off on Palm Canyon Drive and head straight into town.

Without traffic and with channel 67 jazz playing on Sirius, it's exactly 95 minutes from my driveway to the valet stand at the Avalon.

Five to eight minutes later I'm checked in, a bellboy is taking my bags to my room, and I've slid into a bar stool and am ordering a cocktail at the Chi Chi. Done!
 
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Ismael Flores

Well-Known Member
that would have to be quite a bit of rain and all at the same time. It would have to be the worse possi le scenario for this to happen.

they have been saying similar things about the whittier area as well as for the coachella valley.

at this point they need to address it and see if we do get a 100 year flood.

meanwhile Orange county/ Anaheim has allowed land developers to saturate the natural creek area and surrounding wildlife corridor by building secluded villages with minimal exit roads from the natural canyons.

they have walled up natural veins and laid concrete over the natural waterflow. This destroyed the wildlife corridor for mountain lions and coyotes that those neighborhood now get upset about.

that area is now a death pit because after several fires where huge areas have burnt they still leep building. i thought they learned their lesson when during the last major rain the spillway from the damn narrowed from a natural river to a concrete channel and ended up destroying part if the golf and part if a neighborhood. the concrete did not give the area a natural escape route for the water.

i remembered the county and city trying to sue riverside county and wanting to force riverside to destroy the natural river in that part of the county by paving it. Riverside won and Anaheim had to break up the canal and revert it back to its natural state. Now the area is a lush river and flooding during rains stopped because of the bwtter water flow and because now the water natural goes i to the sediment.

it will be interesting to see now with this announcement how much more those residents will be punished by their home insurance. now that they are in a zone of red eminent danger of flooding
 

MoonRakerSCM

Well-Known Member
Just going to chime in, geotechnical consultant here... nothing seems out of the ordinary to me. Spillways will be retrofitted (they've been retrofitting Prado for a few years already), this is a reclassification due to recent work done on the facilities that show it falls within a different bracket than before as defined by the corps.

I know that right now the entire O.C. Santa Ana River levee system is under review for upcoming re-certification from FEMA.

All that aside, keep in mind (using the worst example we know of)... 1862, the central valley became an inland sea, the inland empire became an inland sea, and orange county was mostly under several feet of water. Historically the Los Angeles River has jumped around the coast and used to periodically enter the ocean at Marina Del Rey... and prior to 1862 the LA and San Gabriel rivers actually came together before entering the sea; during the flood of 1862 the San Gabriel River carved out a new path close to its current man made path...

Water is a fierce mistress.
 

Darkbeer1

Well-Known Member

 

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