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Feb. 14, 2017
   

Here's why the Oroville evacuation order HAS NOT been lifted - Is the dam expected

 

The only variable is how much rain the area will get.

The Oroville dam may fail, and here is the reason why. The top layer of rock is "rotten," and will be quickly eroded and washed away if water tops the emergency spillway again. The dam could be breached to about 100 feet down, releasing a flood of catastrophic proportions. People who have returned to the town of Oroville are also reporting that workers are not allowed to speak to the public.

 


Butte County's 900-foot tall Oroville Dam spillway is broken.

LOS ANGELES, CA - There is a reason why the evacuation order for Oroville and elsewhere has not been lifted. The odds of the Oroville dam failing are likely much higher than what is being discussed between authorities and the public.

One Monday, it was predicted the evacuation order would be lifted as water levels dipped below the level of the emergency spillway and a dry spell approached. Yet despite a few solid days without rain, the evacuation order has not been lifted. People have not been allowed to return to retrieve pets, keepsakes or other important possessions. Many people still have just what was in their pockets in Sunday night.

There is a major issue with the dam. The top 100 feet of rock is considered "rotten." This means it is fractured and shattered by natural forces. When it meets with the force of water, it can break apart. The fractured rock has been blatantly exposed by the water flowing over the emergency spillway. That water, which did not have a smooth flow over the spillway, tore apart the uneven ground and removed chunks of earth and rock. A gash, estimated to be about 40 feet deep, was quickly carved in the rock within just a few hours.

 


How erosion may undermine the Oroville dam.

If water tops the spillway again, it will widen the gash. If it widens it enough, the top 100 feet of the dam in front of the emergency spillway will fail, and a significant portion of water from Oroville reservoir will cascade into the Feather River and fan out in the valley below. The town of Oroville will be the first destroyed.


A close up of the damage caused by the erosion in front of the emergency spillway. If more water crests the spillway, the dam could fail entirely.

There is also evidence water is percolating into the rock under the spillway. Bubbles are visible in the water behind the emergency spillway. The bubbles are large, frequent and visible from the air.

Now for the grim calculus.

Officials have wanted to drain the dam by 50 feet before new rains begin on Wednesday. The water crests the dam at 902 feet. Since Sunday's crest, the water level has only fallen by 14 feet to 888 feet. In the next 24 hours, the water level may drop another 15 feet, give or take. The water will be about 20-25 feet above the goal set by engineers for safety.

The fracture in the earth reveals the shattered nature of the 'rotten' rock below. This is the source of the problems for the dam, along with the fact water cannot flow smoothly over the emergency spillway to the Feather River below.

The only variable now is the rain. How much will the area get? How much runoff will enter the reservoir in the coming days? This is difficult to predict, but the reservoir is intentionally designed to capture as much water as possible from the surrounding mountains.

While the surrounding area will receive at least three to five inches of rain, those few inches end up as several feet of water in the reservoir. Needless to say, the math is close enough that authorities have refused to lift the evacuation order at all.

 


A view from above the spillway towards Oroville in the distance.

Despite the order, which applies to nearly 200,000 people, some residents have sneaked back into Oroville. These residents have initiated rumors, which remain unconfirmed, that they attempted to speak to workers. Workers have privately expressed serious concerns, but have admonished they are not allowed to speak to the public. We cannot give these rumors any credence as we have no way of fact checking that such conversations have taken place. However, if such rumors are true the suggests that authorities are very pessimistic about their chances for saving the dam.

If Oroville dam fails, it will be one of the largest engineering disasters in American history. It will be on par with Chernobyl and Fukushima, although the long-term consequences will not be as deadly.

People thinking about returning to evacuation zones should think twice. The most likely time of failure for the structure will be around Friday, when the greatest rains will impact the area.

 

California Network