Understanding the 2017 Oroville Dam Crisis

Chances are likely that unless you’ve lived in or visited northern California, you’ve never heard of the Oroville Dam.

I’m one of those people.  I’ve never been to that part of the country, and that dam never popped up in any of my geography or geosciences classes in high school or college.

My awareness of the dam changed last night when I began seeing news reports of mandatory evacuations as part of the dam was expected to collapse, jeopardizing the lives of over 100,000 people living immediately downstream.  Needless to say, this grabbed my attention and I’ve been focusing on the dam’s situation, following streaming news stations along with people who live out there posting updates on Internet forums.

Oroville Dam

Located in the mountains about an hour north of Sacramento, California, the Oroville Dam is one of the biggest dams in the country.  The dam is 770 feet tall and forms Lake Oroville.  The dam and lake are situated on the Feather River.  The Feather River is one of several sources of water that continually feed into the dam.  Water flows through the hydroelectric power station and is released back into the Feather River where it flows downstream ultimately to the Sacramento River and all points beyond.

It’s an impressive structure located in an extremely scenic part of the country.  You can read more about it on its Wikipedia page.

What brings us here today is the recent development of the mandatory evacuation of parts of the town of Oroville and other communities immediately downstream of the dam.

Earlier this year, northern California received a TON of precipitation.  The area received so much rain and snow that large parts of the state were essentially brought out of what has been considered to be a never-ending drought.  The storm system was basically a giant equalizer that nullified years of dry conditions.  (Remember, folks.  Mother Nature always wins in the end.)

Anyway, the snow and rain in the mountains drained into streams and tributaries, and lots of that water ultimately flowed into Lake Oroville, causing the lake’s water level to rise higher and higher.  Ordinarily this isn’t a problem as dams have spillways to help control the height of the water level and prevent it from breaching the top of the dam.  The spillway was used and it was helping relieve the pressure as water continued to drain out of the mountains and flow into the lake.

Oroville Dam’s features

Trouble started back on February 7 when a crater was spotted in the dam’s concrete spillway.  Normally the engineers would cut off the flow of water in the spillway, make the necessary repairs, and then open the spillway again.  However, since the water was flowing into Lake Oroville at such a fast rate, the engineers were forced to keep the damaged spillway open and just wait it out and hope that the inflow would ultimately slow down long enough to close the spillway and make repairs.

Unfortunately, that reduction of inflow to the lake did not occur.  The spillway was forced to remain open to relieve pressure on the dam.  A few days later, that crater was significantly larger and the water was causing erosion and threatening to destroy the upper section of the spillway.  On February 10, workers quickly cleared the land underneath the emergency spillway in anticipation of it being needed.

Water began flowing over the top of the emergency spillway on the morning of February 11, 2017.  The emergency spillway is basically a 30-foot tall concrete wall that stands on top of a large hill.  It’s a separate feature from the Oroville Dam.  In the dam’s nearly 60-year history, this was the first time that the emergency spillway has been used.

The following day on February 12, the emergency spillway was still being used, and engineers noticed that the water flowing down the mountain was causing serious erosion.  The rapidly moving water was basically eating away at the mountain that held the emergency spillway.  If that pattern continued, then it was just a matter of time until the erosion worked its way up to the emergency spillway and caused the concrete wall to collapse, sending that upper thirty feet of water in Lake Oroville rushing downstream in a powerful and devastating flood.

Because of that imminent threat, mandatory evacuation orders were issued for people living immediately downstream from the dam on the Feather River.  That area being evacuated housed around 200,000 people.

Yesterday afternoon and evening had people pouring out of the area and heading to safety, whether that was in other towns, or simply high ground that was safe from a potential flood.  Emergency shelters opened and people, along with organizations, have been donating everything from food and water to clothing and even toys for kids.  It’s still touching to see how quickly people pull together and donate when it’s urgently needed.

As of today, February 13th, the emergency spillway is no longer being used.  That and the main spillway were able to relieve enough water so that the lake’s water level is several feet below the overflow level for the emergency spillway.  This came at a bit of a price though as erosion has cut away large areas of land.  The crater in the main spillway had grown so large that it has now cut the spillway in half.  KCRA has some great aerial footage of the damage.

What’s Going To Happen Next?

From what I understand, it’s going to be a race for engineers to repair as much of the spillway as possible before the next storm system arrives on Wednesday or Thursday, bringing significantly more rainfall to the region.  For now though they’ll have another day or two free of rain so that they can make repairs and hopefully stop the erosion occurring on the spillway.

The problem is that unless it’s repaired, erosion will continue destroying the main spillway to the point where the spillway itself is destroyed.  Without that control mechanism, water will quickly build in Lake Oroville and reach the overflow level for the emergency spillway.  This time around it’ll flow over the emergency spillway even faster, the erosion underneath it will also “eat” the land at a faster pace, and the emergency spillway will collapse, sending a thirty-foot wall of water rushing downstream.

*IF* that flooding occurs, then large areas of the Feather River downstream from the dam will be destroyed.  One can only guess how far the flood waters will overflow the river’s banks, but anything close to the water will be quickly wiped out by the rushing wall of water and all of the rocks and debris that it’ll be carrying as well.

It’s important to note that the Oroville Dam (that huge wall holding back the brunt of Lake Oroville) is NOT going to fail.  The dam will remain standing.  All of this flooding will come from the emergency spillway, and possibly the main spillway if that’s also destroyed.  It’ll ultimately be more that thirty feet of water as the rushing water will cut a notch at the top from the erosion, but it won’t be anywhere near the scale of losing the Oroville Dam itself.  That structure is not going to fail.

The next 48 hours will be critical as the engineers race around the clock to analyze the situation and repair the dam’s spillway as best as they can.  Remember that the threat from rainfall and the runoff will last through the spring and into the early summer as the snow melts in the mountains and drains into Lake Oroville.  It won’t be until after that point when the lake’s inflow is slow enough and engineers can fully repair any further damage to the dam’s spillways.

All we can do is wait and see what happens next.