As the saying goes, when it rains, it pours.
Over the last week, Murphy’s Law has been on overdrive in Northern California as Oroville dam suffered a series of mishaps, resulting from poor planning, lack of maintenance, and lack of heeding warnings years ago on the part of the state bureaucracy known as the California Department of Water Resources. The result was a badly broken regular spillway, a damaged “emergency spillway” (if you could even call it that, since they had to do emergency prep for two days to even make it usable) and finally, a several county evacuation downstream of about 180,000 people because DWR officials feared the “emergency spillway” would breach.
Given the attention paid to this worldwide, in technical parlance, it would be safe to say the DWR made a global cluster f*** out of their mismanagement of the dam. Even the White House got involved, calling the mess DWR created a “textbook example of the need for spending“.
Our local newspaper, the Enterprise Record, had a scathing editorial using less colorful wording than I have, calling it a “failure on many levels”. And, the Feds aren’t happy, and have sent them a letter demanding some immediate accountability by an independent review, something DWR isn’t used to, since they have a history of being accountable to nobody but themselves.
For example, the re-licensing process for the dam; it was started on 2002, and to be completed by 2007 but has dragged on for 15 years! It only took seven years to build the dam:
Construction was initiated in 1961, and despite numerous difficulties encountered during its construction, including multiple floods and a major train wreck on the rail line used to transport materials to the dam site, the embankment was topped out in 1967 and the entire project was ready for use in 1968.
Combined with the mismanagement under our current weather situation, it’s fair to say that DWR’s oversight of Oroville Dam is a complete and utter failure. Maintenance was deferred, warnings weren’t heeded, and there was a mindset of global warming induced “permanent drought” out of Sacramento. New dams, such as the Sites Reservoir aren’t being built, being stalled in funding, despite a doubling of Califonia’s population since 1968, and monetary focus has been on Gov. Jerry Brown’s pet boondoggles such as “Bullet Trains to Nowhere” and “Water tunnels under the Delta“. Ironically, the tunnels would rely on water from Lake Oroville, which seems to have gotten lost in political space.
People with an ounce of sense proposed killing the bullet train, and putting money towards water storage, but, sadly, it didn’t make it past the rancid political interests of Sacramento and Brown.
All of this has combined to nominate DWR is a poster child for everything that is wrong with California’s government.
So, with that in mind, we have a new challenge from mother Nature ahead: A series of 5 storms over a weeklong period that could give up to 8″ (or more) of rain in the Oroville watershed area. On the short term, NWS is forecasting the storm on Thursday could produce up to 1 to 2 inches of rain in the foothills, with more at higher elevations.
The long-term forecast has rainfall totals withing the watershed that are showing the exact spot where Lake Oroville watershed is located will get 11.62 inches of rain over the next 10 days, the most accumulated rainfall in the entire western USA:
From today’s ChicoER article, there is this quote from DWR:
In a press conference Tuesday, Department of Water Resourecs acting Director Bill Croyle said that there is room in Lake Oroville for upcoming storms and that the inflow was not expected to reach 100,000 cfs.
Given that DWR said 11 years ago that the spillway was safe in response to challenges, then last week they didn’t think there would be any problems with the storms, then kept slipping into disaster mode inch by inch, walking back all the way to “The emergency spillway might fail, therefore evacuations are needed” why should anybody believe one word these bureau-clowns utter?
I sure don’t.
UPDATE: About a half hour after publication, the missing word “spillway” was added to the headline for clarification. The dam itself is not damaged, but the dam spillway is.
.
Oh yes, the crack in the spillway should have been repaired when it was noticed in 2012, there seems to have been an oversight.
The spillway was inspected annually. And there were repairs made in 2013 (among other times) … sorry, your claim does not compute.
The experts have already admitted that the last inspection was a cursory affair. They should have understood the risk of having another winter similar to 1996/97. Now with rains that did not reach the levels of rain back 20 years ago, the risk of a catastrophic release of water still hangs in the air.
“And there were repairs made in 2013”
They should have used something better than Superglue.
What is the catchment are of the dam in relation to its current surface extent?
Two inches of rain on the catchment is far more than 2″ on the water level in the dam. For the moment they seem to be able to maintain a steady flow of c. 100,000 cfs and have gained themselves a bit of breathing space.
Maybe they should be doing some cloud seeding well up wind on the incoming weather fronts.
Here is a graph I did of the current state of play, earlier today.
The North Fork Feather Watershed is approximately 2100 square miles. I do not have elevation data that would determine runoff events for various snow lines.
Catchment is Roughly 150x size of lake.
Dave Kelly linked this radio interview with a dam engineer in the last thread. very informative
https://youtu.be/rl7Sm15unPQ
Right at the end of the podcast we have another well known saying:- “Penny wise pound foolish”.
Excellent interview, frightening but not surprising in California.
jw
A terrible interview from a pompous, fear-mongering, self-promoting jerk – alleged expert or not. He actually told people to trust him and not local officials.
“alleged expert or not. He actually told people to trust him and not local officials.”
Did you forget to add /sarc
Highly recommended! This guy (Scott Cahill) knows the specific geo-technical details associated with the Oroville dam construction, primary spillway, and emergency spillway. Combined with his training and experience, he describes the problems in terms most folks can understand.
No JMac he does not. He admits he does not have soil maps or topos. And he initially didn’t even understand the type spillway.
And no clipe, I did not forget /sarc … he actually and seriously told people not to believe the local officials and to trust him instead …
Yes, I am not sure the emergency spillway could every have functioned properly. One section emptied onto bare earth, seemingly with no foundations under it. And the waterflow for the entire length of the spillway was then directed to the right as we look at it, along the base of the spillway, and then drained downhill.
But what into? I could not see a culvert under the road. So the spillway appears to have been designed just to cross over a road and flood across some bare ground. But water will never do that, it will cut a valley, which is exactly what it did. So how did this emergency spillway ever pass any inspection?
Does anyone have any good photos of it, before it was damaged?
R
The emergency spillway if built on rock but it is weathered rock which does not resist well to the immense destructive force of falling, surging water.
It seems that they regarded having one as a mere formality and never expected to actually use it.
Here is an image after the damage. So the emergency spillway waterflow runs over the spillway, and runs away from us towards the main spillway. It then does a 90º right turn and heads towards the small road. But then what? Was there ever a culvert under the road? It seems the flow was designed to just wash the road away and gouge out a valley. Which is what it did.
And the diversion away from us, along the base of the spillway, was also inadequate. You cannot expect a soil mound to stop boiling white-water. So without anything there to stop it, the water to the left of the spillway just carried straight on, and started gouging out another valley, where it was not supposed to be at all.
And both of these erosion patterns would have eventually undermined the emergency spillway dam. Which is the same as how New Orleans was flooded. As I understand that event, the overtopping of some concrete levee walls was not a big problem, as the pumps could easily deal with that. But the overtopping water gouged out a hole at the base of the levee wall, and once deprived of its foundations the levee wall collapsed. And now there was a complete flood. And the same would happen at Oroville too, if those erosion hotspots reached the base of the spillway.
http://www.vosizneias.com/wp-content/uploads/2017/02/APTOPIX-Damaged-Dam_sham-1.jpg
The emergency spillway is designed and intended for rare emergency use. Some erosion of the hillside is considered acceptable. That said – the entire hill is very hard bedrock. Some of the top layer is weathered and is susceptible to erosion. Some topsoil will always erode.
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And we can clearly see that even with the water from the emergency spillway concentrated almost entirely in one channel – the area of hillside below the access road shows minimal damage in the channel. Larger hi-rez aerial images show the bottom of that channel is green – meaning bedrock … which did not erode.
The flat bench below the emergency spillway and the road should have been better hardened. It is most rock – with bedrock not far below. That bench should have been hardened … for several reasons.
One to minimize erosion. The area below the main spillway side of the emergency spillway WAS armored before the emergency spillway becoming active – and operated as designed – there was no erosion in this armored area.
The second reason is design related. A big part of the operation of a weir type spillway is a flat, laminar flow. That the water follows smoothly over the spillway and down its face and then spreads in a flat sheet down slope is an important consideration. Where the flow is not smooth, erosion is more likely and once erosion begins it exacerbates the situation by head cutting upstream.
The bench below the weir is stepped in height across its face. That in itself creates lateral current at the sideslopes. In particular at the parking lot end where the emergency “ogee” style (curved) weir meets the small concrete wall net to the parking lot.
That junction created a jet at an appx 20-30 degree angles to the flow over the main weir. At the same point water flowed down the sidelsope between the main weir and the parking lot weir …. again creating a lateral flow – across the laminar flow down the main weir.
It is exactly there were the erosion area of concern was created.
The bench below the main emergency weir should have been flat, the sideslopes minimized across it, and it should have been armored down to an across the road, and the roads downslope.
The Sierra club and other pushed for the entire hillside to be armored – which has been shown to be unnecessary. I believe that push took focus away from the bench area which WAS important.
This image shows those flows:
This image shows the resultant erosion and the flows that created it:
There are other issues and areas that became apparent as well – for example significant problems with the silly concrete wall along the parking lot – and the fact it does not continue to higher ground. Something that could have been seen on a topo map – IF you ever expected the emergency weir to see a 1.5 foot ‘head’ – a lake level 1 and a half feet higher than the weir …
Hindsight is always 20/20
The road was always sacrificial … it was built with small rock base. There was an outlet under it but it was designed to drain rainwater not spillway flow.
the majority of the “cut” at the road is just from the road washing away … what is left is largely bedrock. The section of the weir at that end DID have a hardened area at its base and that performed well.
They have built a new haul road closer to the weir in that same area. It is built of larger boulders and is lower.
The cement hardening has been extended in that area as well.
>>the majority of the “cut” is just from the road washing away.
Rather more than just the road washing away. The rapid erosion causing such a deep crevasse rather demonstrates that the rock upon which the entire dam complex is built is friable, and will wash away quite easily.
https://www.metabunk.org/attachments/img_7413-png.24548/
Let’s try that image again…
https://www.metabunk.org/attachments/img_7413-png.24548/
Try this one…
I have a bunch of photos before and after and historical here:
https://www.facebook.com/scott.gates.750/posts/10154887673187457
A detailed discussion with much info avail here:
https://www.metabunk.org/oroville-dam-spillway-failure.t8381/page-15
Nice pictures Scott.
In this original picture of yours, I see no provision at all for run-off from the emergency spillway. No channel at all – just the road for the water to run down. But if the emergency spillway was only ever designed for very low discharge rates, then why was it so wide? Why build a spillway 100m wide, if the ground below could never cope with that volume? And why did no subsequent inspection highlight this design flaw?
The emergency spillway water flows down the hillside unrestricted. If you understand topos and review them you can see exactly where the water will flow down the hill. And i you then pull up any of the many images during and now – you’ll see the water followed that path.
You’ll also see there was minimal erosion in that narrow path … AND you will see its all mostly green-blue in color now – after the event. Which means good hard bedrock
You can get great views of the whole thing by just typing Oroville dam into Bong r google and then clicking on tabs.
But for even better views, go to bing maps, type in Oroville dame, and then click on Birds Eye view.
This opens a page in which virtually the entire US has been photographed by low flying planes, from four angles.
As you rotate the view on the compass, you will get shots from different angles from the plane.
This are low enough and of goon enough resolution that you can see details as small as a few inches…people, cars, trailers backed up down the boat ramps…
Looks to have been done when the lake was tens of feet lower.
Since looking at this…that parking lot seems less dangerous…on the lake side it is not deep and banks very gradually down to a bunch of other parking lots and ramps for hundreds and maybe thousands of feet.
The water flowing over that parking lot would have had a lot of ground to cut through.
The lake side of the spillway seems to be made of dirt however, and if it was undercut it could be very bad.
“If Trump turns off the satellites, California will launch its own damn satellite,” roared Brown to the crowd.
Presumably he will also be shouldering the cost of his failed and decrepit damn dam. Not expecting the rest of the nation to foot the bill for their mismanagement.
So just to get this straight, they are forecasting 11 inches of RAIN in the catchment over 10 days? Or is that 11 inches of snow? If 11 inches of rain fall and some snowpack melts with it, you’d might as well be packing everything now if you’re in the valley.
11 inches of precipitation. It’ll be snow above about 7K feet, which should total several feet, and rain below that. The inflow into the lake will rise dramatically although the lower snow levels will prevent even worse flooding. The last storm had snow levels around 9K feet.
It depends on how much of that precipitation flows to Lake Oroville. With the soils in the catchment area pretty saturated, the percentage could be high. Over a 3607 square mile catchment area, and 640 acres per mile, 11.62 inches of rain is a total of around 2.25M acre feet of precipitation, or around 225K per day. If all of that flowed into the lake evenly, that would be around 113K cfs. As long as they can keep releasing 100K cfs from the main spillway, they should be OK, but that is not accounting for any snowmelt that might be added to that.
Why wasn’t there preparation to clear debris from the inflow ports for the dam? Someone here pointed out that no water is flowing through the dam’s turbines, because there is too much debris blocking them. Possibly the people in charge didn’t anticipate that the dam itself might not be contributing to draining the lake.
I read that the dirt and rock eroded when the main spillway failed has caused the water level at the base of the dam to reach a level high enough to prevent the power turbines from being used. So not only are they unable to generate electricity they also are kept from releasing another 15K cfs through the power generation facility.
The debris is the eroded mess from the failed spillway. Half shot downstream, and half shot up into the diversion channel. Now theynhave to remove that debris bar before the powerhose penstock can be opened.
Why?
@Menicholas if silt backs up into the turbines, the power plant will be destroyed and they will lose the ability to remove 15K cfs for a long time until the power plant is repaired, in addition to being without the power.
I never see any mention of the fact that they’re releasing over 60 billion gallons of water per day. Water that California needs since, according to the the experts, we’re still in a drought emergency.
This story won’t be over until June and then it’ll shift to the monumental repairs that will be necessary. I have to wonder if they’ll go ahead and line the emergency spillway with concrete as recommended 12 years ago.
Well, the erosion pattern would indicate where that might go…
The hillside has performed just fine. Even with flow concentrated in mostly one channel. The hillside is mostly bedrock and needs no hardening.
The bench from the weir to the access road DOES absolutely need hardening. They have already done that for much of the area. They need to rebuild the road and harden it, and a short section downslope of the road … the hillside will be fine.
@LoganSix – The main spillway is not “eroding the base of the dam” … and that main spillway has been running at a non-stop 100,000 cfs now for days with little or no additional damage. The fractured rock and soil has been flushed out and it is now down to bedrock (the blue/green rock) which isn’t going anywhere.
@emsnews and @logansix – the emergency spillway repairs are much more than a ‘a puny pile of rocks – dropped in the holes’ … again, the spillway is built largely on bedrock. Its location was originally a saddle in an existing hilltop. The erosion seen was the top layer of fractured rock, dirt fill, and the road base for the parking lot access road.
The erosion areas near the spillway weir were, where rock was exposed, filling with large and smaller boulders which was then filled with cement. Areas of dirt and fill were excavated, and those too are being filled with boulders and cement.
The area at the base of the emergency spillway weir near the main spillway had been similarly hardened with rock and cement before the spillway was used and those areas suffered no erosion. That area has been strengthened further, including the side slope of the roadway … and a new access road has been built, with heavy rock this time – not just compacted small rock fill. presumably that will be hardened with cement today as well.
The flow over the emergency weir is important to note … at its peak – when the lake level was 1.6 feet higher than the top of the weir – was just 12,000 cfs … about 12″ of the main spillway flow. And that was spread across 900′ of the emergency weir. During much of the release over the emergency spillway the flow was well less than 10,000 cfs.
Still significant – but not huge. It should be noted that other than in the bench area just below the emergency weir, the water caused minimal erosion of the hillside below – despite all of the flow over the weir consolidating into mostly one channel. Aerial views show that channel hit green bedrock quickly.
In no way am I saying this isn’t a typical California “clusterf***” … it certainly is. The whole emergency spillway situation – and the arrogance of those responsible for decades – is inexcusable.
But reality is important for the present as well … and that reality is the cement hardened areas performed during the release. And not only has the erosion in the bench below the weir been repaired and hardened with cement, but I believe much of the entire bench will be as well before they are done.
There are no guarantees in life, but the repairs made, along with other actions, and the forecast all point to the high likelihood the danger is minimal.
There is an excellent technical discussion here on the issue:
https://www.metabunk.org/oroville-dam-spillway-failure.t8381
https://github.com/axibase/atsd-use-cases/tree/master/OrovilleDam
Based off of our estimate, for every inch of rainfall at the Oroville dam, 136,790.5 acre-feet will be added to the reservoir. As of 5:00 am PT on February 15th, there was 307,145 af of space left in the reservoir before it reaches its threshold. The maximum outflow per day that the dam is able is push out is 142,034 afd, which was achieved on February 14th. So, if we multiply the rainfall per day by our acre-feet rate (136,790.5) and subtract the maximum outflow, we should get a storage amount added per day. If we then divide the storage added per day, we should get a answer for how many days it would take for the storage to reach threshold capacity again. Below is a table showing the amount of time for the dam storage to reach threshold capacity for a given amount of rainfall per day.
Rainfall Storage Added/Day Remaining Storage Time to Reach Threshold
1 inch per day -5,243.5 307,145 No storage gain
2 inch per day +131,547 307,145 2.334 days ~ 56 hours
3 inch per day +268,337.5 307,145 1.144 days ~ 27 hours
===================================================
So is this bunk too?
I moved out of California during Moonbeam I. I have never regretted it. Why the people of California chose to elect the idiot a second time (actually 3rd and 4th) shows that you do not need brains to live there. But while it is normal to get mad and start demanding accountability and answers, the crises is upon us. Those 200k folks have lives that may never be the same. And right now, we have a slow motion wreck descending upon them. We can only hope that the spillways hold up as they will get used.
To those on the left, stop reading, because you do not want to see what I write next.
I will pray for all those people that hopefully the dam system has enough left in it to save them from further harm, for their lives and property. I pray that those without agendas and with competency can be given a free hand to do what is necessary to safeguard all.
+1776
“resulting from poor planning, lack of maintenance”
You see these words plastered all over the news. Many here are saying that they should have never let the dam fill up and that California let it fill up do to drought concerns.
The fact is the dam this year is being operated the say way as they have been doing for 50 years. Every year they allow 4/5ths of the lake to fill and leave 1/5 of the lake unfilled for flood control. Only when the rain stops and snow melts do they allow the rest of the dam to fill. The only difference is that this year we are seeing rainfall at 200% or normal which no one was predicting. The lake has gone from almost empty to full in record time. Water inflow has been exceeding what the original designers were expecting for over a month. Clearly the dam need a bigger spillway but no one knew that until now.
In the San Francisco bay area right now there are at least 6 dams receiving earthquake retrofit. One is being completely replaced. At the time those dams were made we didn’t know that much about earthquakes. Now we do and now were are upgrading them. Some also had spillways that were too small. With the earth quake retrofits those spillways are also being upgraded. Oroville dam has not been identified as needing an earthquake retrofit. Is Oklahoma doing anything to address the increasing earthquake threat in there state? Or what about alll the other states in the central and east cost which also have earthquake faults? Clearly california is addressing infrastructure issues as quickly as it can. Yes improvements can be made but clearly we are not the worst state.
We also have repaired or replaced most bridges in the state because of the better understanding of earth quakes. The includes almost all of the freeway overpasses in the state. Thats a lot of bridges.
As to Maintenance No reports of any maintenance lapses have surfaced. They have been performing regular inspections since the dame was built. People have been saying that they should have inspected the spillway and repaired it before it failed. The trouble is that a visual inspection cannot tell you if there is anything wrong underneath the cement. No one has x-ray vision and even the best instruments available may have not detect the void that developed under the cement. In fact the void that caused the spillway damage may not have even existed until the record setting rains arrived this year. 90% of all maintenance starts with a visual inspection. Unfortunately visual inspections don’t catch 100% of all problems.
Yes the warnings about the emergency spillway were correct. However at the time all the experts said it wasn’t necessary and that the dam meet FERC design standards. Clearly the design standards were not sufficient. Now every dam in the US will need to be evaluated. That has already started in california but will it be done in every state?
Its easy to criticize the designer that designed and built the highest dam in the US with nothing more than a slide rule, pencil, and paper. Yet clearly they did very well with no long term weather data, no modern computer models and no seismic survey equipment available.
An excellent comment Steven. I have read much of the documentation and commentary on construction and design. The planning started in the early 50’s and was extensive. The accomplishments they made considering the tech then vs now is amazing.
The hindsight of fear always opens eyes to possibilities that may never have been considered …
“The only difference is that this year we are seeing rainfall at 200% or normal which no one was predicting.”, no one except me. …https://disqus.com/home/discussion/cnbc/sierra_nevada_snowpack_lowest_in_500_years/#comment-2253607967
They should have been well aware of the potential danger after the major winter of 1996/97. The emergency spillway came very close to releasing water during that huge rain storm, and that was with the turbines still flowing water and the spillway functioning properly. They were very worried at that time.
crosspatch postulated that the weir is anchored to bedrock. Much depends on the design details of that anchoring. I hypothesize that the engineers did not include the mass of the downstream hillside buttressing the weir in their calculations that the weir could withstand the hydraulic head.
I’m guessing that because they didn’t concrete line the slope below the weir. They either assumed that flows over the emergency spillway would always be gentle; or they could fully lose the downstream hillside. Apparently by TPTB reaction this last week, they don’t want to lose the hillside. TPTB are terrified of the exposure of the weir foundation to falling water forces.
Nevertheless, the engineers probably did not fully analyze the effect of scouring and undermining at the base of the exposed weir, with enhanced water fall forces.
There is probably a UC Engineering library somewhere that contains the design details, all in a big book. Then again, they might have removed those books to prevent terrorists from exploiting design vulnerabilities like “a small [hydraulic control] port, right below the main port. The shaft leads directly to the [weir control] system. A precise hit will start a [scouring] reaction which should destroy the [dam]. Only a precise hit will set off a [scouring] reaction.” The book is probably stored in the CA DWR data storage facility in Scarif (Sacramento CA Regional Information Facility).
As to the loss of the raceway. The engineers did not want any modification to the main dam left side buttress. That raceway went all the way to the riverbed and was supposed to handle 250K cuft/s. That left-side buttress has now been hydraulically modified. More design assumptions invalidated.
Good luck California. Pray for drought. Hope is not a successful survival behavior.
From that “book” which is available:
“Page 92 …
The spillway for Oroville Dam (Figure 76) is locat- ed in a natural saddle on the right abutment of the Dam. This location allows spillway discharges to enter the River, well downstream of the toe of the Dam and powerplant tailrace. The spillway consists of a combined flood control outlet and an emergency weir. The flood control outlet consists of an unlined approach channel with approach walls shaped to make a smooth transition to the outlet passage, a headworks, and a chute.
The headworks structure (Figure 77) has eight outlet bays controlled by top-seal radial gates, 17 feet – 7 inches wide by 33 feet high. A concrete chute (Figure 78), 178 feet – 8 inches wide, extends 3,050 feet from the flood control outlet down the side of the canyon to a terminal structure (chute blocks) where the water plunges into the Feather River.
The emergency spillway is an ungated, concrete, overpour weir located to the right of the flood control outlet and is made up of two sections ( Figure 79) .
The right 800-foot section is a broad-crested weir on a bench excavation.
The left 930-foot section is a gravity ogee weir up to 50 feet in height. Except for a narrow strip immediately downstream of the weir, the terrain below the weir was not cleared of trees and other natural growth because emergency spillway use will be infrequent.
The flood control outlet was sized on the basis of limiting Feather River flow to leveed channel capacity of 180,000 cfs during occurrence of the standard project flood (peak inflow 440,000 cfs).
This limitation applies at the confluence of the Feather and Yuba Rivers approximately 35 miles downstream of the Dam. It was estimated that a runoff of 30,000 cfs could be expected within this 35-mile reach of the Feather River during the standard project flood. Therefore, the flood control outlet was designed for a controlled release of 150,000 cfs.
The normal reservoir water surface previously had been set at elevation 900 feet. To meet these criteria, a flood control reservation of 750,000 acre-feet was needed. The criteria also governed the size and location of the flood control outlet gates.
The outlet must release 150,000 cfs at water surface elevation 865 feet to control the flood shown on Figure 80.
The standard project flood has a probability recurrence interval of approximately 450 years. If data received indicate a flood is developing greater than the standard project flood, release through the flood control outlet may be increased above 150,000 cfs but may not exceed 90% of the inflow.
When the reservoir fills above elevation 901 feet, flow occurs over the emergency spillway. The emergency spillway, in conjunction with the flood control outlet, has the capacity to pass the maximum probable flood release of 624,000cfs for the drainage area (peak inflow 720,000 cfs) while maintaining a freeboard of 5 feet on the embankment.
The maximum probable flood has a probability recurrence interval in excess of 10,000 years.
Hydrologic and hydraulic data are shown on Figure 80.
Various types of spillways were studied and modeled to arrive at the final structure. The original design consisted of a control structure with radial gates to pass the total spillway design flood. A short concrete apron was to extend downstream from the control structure, and then the flows were to be turned loose down the hillside in an excavated pilot channel. As the spillway would operate on the average of every other year, this plan was determined to be unacceptable based on the large quantities of debris that would be washed into the Feather River and could ultimately affect power operations. Adding a converging concrete-lined channel and chute to the original headworks structure created major standing-wave problems throughout the system.
These problems were resolved by separating the flood control structure from the spillway structure as shown on Figure 76. The rating curve for the flood control outlet (Fig- ure 81) is based on these hydraulic studies.
Concrete for the spillway chute, weir, and flood control outlet structure above elevation 865 feet was specified to obtain a strength of 3,000 psi in 28 days; concrete for the lower portions of the flood control outlet, below elevation 865 feet, was specified to obtain a strength of 4,000 psi in 28 days; and concrete immediately behind the prestressed trunnion anchorages was specified to obtain a strength of 5,000 psi in 28 days. Steel reinforcement conforms to intermediate or hard-grade billet steel as specified in ASTM Designation A15 or A408. Post-tensioned tendons for the gate trunnion anchorages have an ultimate strength of 160,000 psi. Structural steel for the main members of the radial gates and bulkhead gates conforms to ASTM Designation A441. Secondary gate members and trunnion beams are of A36.
Emergency Spillway. The grout curtain was continued under the left reach of the emergency weir near the upstream face, and formed drains are used under the downstream half. The crest of the emergency weir to the right, which is only 1 foot above the excavated channel, is keyed 2 feet into the foundation. Both weir sections were checked for overturning and shear friction safety factor and found to be satisfactory.
Pg 185:
Spillway Clearing. Approximately 115 acres, 40 in the spillway and chute and 75 in the emergency spillway area, were cleared of brush and trees. The area below the emergency spillway was not cleared.
Excavation. The three major methods used to excavate the spillway were as follows: bottom-loading scrapers and pushcats, a loader with cats feeding the belt and bottom-dump wagons hauling the material, and two large shovels. In general, the scrapers were used to strip the area to rock. The shovels were used to excavate the rock after it was drilled and shot. The loader was used similarly to the scraper operation, the main difference being that it was possible to work this operation in rougher terrain as up to eight dozers were used to push material to the feeding hopper.
A road was graded out below the hopper and the bottom-dump wagons could drive under the hopper to load. All drilling for blasting was done by percussion type drills mounted on tracks and powered by air. The patterns varied greatly from area to area. The most generally used pattern was 8 by 8 feet; however, patterns ranging all the way from 2’/2 by 2/4 feet to 15 by 15 feet were used depending on the area, type of rock, and excavation objective.
Excavation near structure lines had to be controlled to avoid damage to the rock to be left in place, and 840,000 tons of riprap for Oroville Dam had to be produced.
In part of the emergency spillway, an additional 10 feet of excavation was required to reach acceptable foundation rock, resulting in considerable additional time for excavation and placement of the backfill concrete to subgrade.
Approximately 90% of the chute foundation required blasting to reach grade.
The only extra excavation directed was removal of a few clay seams in the foundation and a few areas where slope failures occurred.
The depth of overburden in the approach channel was deeper than estimated and the slopes had to be changed from ½ to 1 to 1½ to 1 to prevent sloughing as the excavation reached the final grade.
The slopes in the flood control outlet gate section proved to be of a lower quality rock than anticipated. There were several large seams running parallel with the chute. The planned anchor bars were replaced with grouted rock bolts, pigtail anchors, and chainlink surface covering in that area.”
https://ia800302.us.archive.org/3/items/zh9californiastatew2003calirich/zh9californiastatew2003calirich_bw.pdf
Scott, thanks very much for that, exactly what I though should exist somewhere.
Design details:
1. “The crest of the emergency weir to the right, which is only 1 foot above the excavated channel, is keyed 2 feet into the foundation. Both weir sections were checked for overturning and shear friction safety factor and found to be satisfactory.”
2. “The emergency spillway is an ungated, concrete, overpour weir located to the right of the flood control outlet and is made up of two sections ( Figure 79) . The right 800-foot section is a broad-crested weir on a bench excavation. The left 930-foot section is a gravity ogee weir up to 50 feet in height. ”
Figure 81 shows the right weir with keyway. Figure 81 Section B-B does not show the key, but it talks about “grouting details”. I don’t see evidence for trunnions going from the weir into bedrock. So I can see why they are concerned about undermining. The weir is sitting on a flat bench,held in place by shear at the foundation, and mass for overturning. It can’t be allowed to be undermined.
Pray for drought, prepare for rain.
Also note the flood details. A controlled spillway release of 150K cuft/s would be required every 450 years, for a “standard project flood” peak lake inflow of 440k cuft/s. An emergency spillway release will be needed for all larger, up to a peak 10,000-year inflow of 720,000 cuft/s. I do not think the emergency spillway can be counted on for that flood. Time to steal money from the “Bullet Train to Nowhere” to retro-fix this dam. Fast trains are too hard for governments. Governments are really good at pouring concrete.
I knew a guy in the early 1970s who had worked at CA DWR. He talked about “shot duck syndrome,” people who had got as far as they wanted, and just went into glide mode for the rest of their working lives.
The damage to the spillway seems to be just below where the gradient of the spillway increases. This might have caused suction that “lifted” the concrete. Concrete has no strength in tension. You avoid this sort of thing with a dentated sill, or better still designing a spillway where the gradient is constant.
It is actually called an “incompetence syndrome”. As long as you are competent, you get promoted. Once you reach a level for which you are no longer competent, you stay there. In a sufficiently old organization, everybody sits just above the level of their competence.
“incompetence syndrome” == “The Peter Principal”; People are promoted to their level of incompetence.
The St Fransis dam failed because of geology. It was built on a fault plane. After fill, the gouge of the faultplane was eroded and it propogated upwarded, destroying the dam.
My big worry is that the Feds will pay for the fix. This is entirely California’s problem. If they have the money for a train to nowhere, they can fix these spillways themselves and leave the rest of us out of it. Until California becomes more responsible, giving them money is a total waste.
My philosophy is that if they don’t want to pay for it, there is no reason the rest of us should either. If it doesn’t matter to them, it shouldn’t matter to us.
I’m a Californian. I agree. Gerry says we are rich (despite the debt), and we blow money on bullet trains, windmills, and solar. We are able to divert money used on whimsical projects to necessary infrastructure. The Fed should not be guaranteeing our silliness. Take the money required from one of the above projects.
Frankly, the money to repair the spillway and upgrade the emergency spillway is a drop in the bucket compared to what we’re blowing on those silly projects.
let me third this comment: make Moonbeam come up with the $$$ to fix his F up…
he built it, he can fix it, and i’m a native. #HighSpeedFail can cover this tab.
How about a bullet train to Oroville. That oughta do ‘er.
IMO the Metabunk forum discussion establishes at pages 12-16 that the emergency spillway will fail when used, most likely from the west side parking lot. Look for the term “weathered bedrock”.
Overflow water will find the lowest path downhill and erode around any newly dumped rock and poured concrete. One of those paths will erode back up when it gets steep enough and undermine some part of the parking lot or even the concrete weir, resulting in structure failure. Any unexpected sideways flow someplace would greatly exacerbate this.
Scott Walker is correct that this won’t happen fast. Hopefully it will go slowly enough so that mass evacuation can take place now the Butte County Sheriff understands that outgoing traffic should be opened on both sides of all roads and highways.
The problem is that six week remain in the rainy season, plus there are snow pack melting issues.
Tom … I’m a part of that thread at Metabunk – and I don’t think it establishes anything of the sort. It discusses weathered rock as an issue but not that the emergency weir will fail.
In fact all the evidence shows it is NOT as worrying as before we knew more facts – such as that the emergency spillway IS on bedrock – and care was taken to get a good bedrock base during construction – making a failure unlikely:
“In part of the emergency spillway, an additional 10 feet of excavation was required to reach acceptable foundation rock, resulting in considerable additional time for excavation and placement of the backfill concrete to subgrade. ”
Further, while there is more than can and should be done – crews gave repaired the major erosion on the ogee spillway bench … with boulders, hardened by cement.
Your claim these repairs are aren’t sufficient is not supported by the facts and evidence.
First, it is exactly these same type repairs, boulders reinforced with cement, that worked flawlessly at the main spillway end of the emergency spillway bench …
Second, the crews oriented these hardened areas following the path flow had already identified as the path it wanted to follow. Where the water chose to flow is what they repaired and hardened.
Third, along with the information they went to extra effort t insure solid, good bedrock for the foundation is that the ogee weir section includes a 12′ apron at the down slope base – that is 6′ thick – and sits on bedrock.
Additionally a high ridge of bedrock sits between the main spillway and the dam … the dam is effectively isolated from the emergency and main spillway …
And yet the exposed bench bedrock just downstream from the weir crumbled, the first time it was exposed to a minor flow, in one spot almost to the weir apron. That wasn’t supposed to happen. When something like that happens, saying “failure unlikely” is premature. The condition of the bedrock under the weir foundation is unknown, and suspect until proven otherwise. As also the weir/bedrock contact plane.
The weathered SURFACE rock eroded.
And we do have a good idea of the condition of the bedrock condition for the ogee weir emergency spillway foundation … the builders went to significant extra time and expense to ensure they were down to high quality bedrock for the foundation. That bedrock foundation is well underground. It is not exposed to weathering.
Scott, I refer in particular to EricL’s Post No. 517, BradP”s No. 523, and Rock Whisperer’s post No. 634, at Metabunk.
Impermeable obstacles created by repairs on the slope side of the emergency spillway will cause the overflow to pool and thereby create concentrated flow points to begin erosion. See your Post No. 660.
Your reference to the main spillway is classic diversion from my point about the parking lot. “Oh look, a squirrel!”
And you could have been much more effective in criticizing the Butte County Sheriff. IMO he made the right call on the evacuation but, if the emergency spillway had failed, hundreds or thousands of people would have unnecessarily died from his emergency management failures.
There was no pre-existing evacuation plan for a reservoir breach.
No hasty evacuation plan was made when the main spillway cratered.
His office did not seem to consult any emergency managers, let alone state OES, when he decided to order evacuation.
We know this because the roads and highways out were not made all one-way to foster the evacuation. I saw incoming traffic using them on television Sunday evening.
Even New Orleans roads were made one way out for the evacuation before Hurricane Katrina.
What you should have done was point this out and suggest that the Sheriff was as professional in ordering the evacuation as he was in managing it.
Tom … I made NO comment on the Sheriff or his actions. You can feel free to denigrate and second guess his decision if you like – as I have been involved in emergency preparedness and management since I was in high school I will not use hindsight and bash someone who made a gigantically important and critical decision and erred on the safe side.
You take the data given, evaluate it to the best of your availability, and make a decision. The Sheriff was told there was erosion rapidly approaching the base of the spillway and failure could occur within 45 minutes.
What would your decision have been?
And what if they were accurate, and you dicked around for 15 or 20 minutes talking to others and people died?
And what if you are completely correct? That everything could have been better. What point does attacking as you suggest, do in any way? Clearly the Sheriff understands everything you brought up. And I guarantee his staff and others are scrambling to develop a plan and procedures.
Context and situation matters.
Everything coming over the next weeks and months is on top of a state that has been saturated unusually early.
Right now, Feb. 15th, snow/water equivalency exceeds the peak April 1st levels.
No public officials anticipated this.
Quite the contrary all of them were confident California was in the middle of a doomish persistent drought produced in part by global warming.
Because of their irrational political belief in a lingering or permanent drought their focus was on containing as much water as possible without any regard for retaining flood control capacities.,
Now the state is in a horrific situation that has little to no flood control options as the natural return to a routine wet cycle unleashes what flood control would control if it had not been sacrificed.
I do not think that this winter can be called a routine wet winter. This is very likely a cyclical flood as was the 1996/97 winter which affected the region from Marin County in California up to central Oregon. Now there is the distinct possibility that there is going to be a step up with this storm moving in as it is holding twice the water weight of any of the previous storms to make landfall. The last several storms ranged from 0.6 kg/m2 to 1.2 kg/m2. Off shore right now is a flow rated at 2.5 kg/m2. That is the biggest flow of the winter to make landfall. …https://earth.nullschool.net/#current/wind/surface/level/overlay=total_cloud_water/orthographic=-151.91,28.34,497/loc=-126.780,37.700
I meant routine as in historically been there done that regardless of how infrequent the that is.
Making things work and run safely and efficiently is some weird fetish of the right. We on the left know that making restrooms safe for everyone regardless of any residual dangly bits is where the real focus needs to be.
one upside to all this rainfall up north?
panning for gold in the various creeks, etc, this summer/fall might pay off handsomely.
they didn’t find all the gold back in the day.
Panning is back breaking. The best way to search is with a metal detector or dredging. Unfortunately the climate nizis shut down the right to dredge 7 years ago. Last year a judge ruled in favor of dredgers after a 6 year battle. Yet the current eco nizi regime still refuses to issue dredge permits. This is for recreational dredging, and despite the fact that the Mining Act of 1872 gives citizens the right to search for gold. But what does a law mean to these folks.
I found this link on cavitation :
https://www.usbr.gov/ssle/damsafety/risk/BestPractices/Chapters/VI-3-20150610.pdf
My background is developing systems requiring extremely high reliability. It seems that this dam given everything that’s been commented on here was designed with multiple levels of safety backup systems – emergency spillway etc.
When a system that has been designed for high reliability fails usually it’s some scenario that wasn’t even considered.
Watching the videos of the high pressure water tear up the concrete spillway made me wonder about cavitation effects.
If high pressure water flows down the emergency spillway we will find out if there is a complete layer of bedrock underlining that area. The cavitation process is a non linear chaotic system and results depend upon the surface which is unknown in the emergency spillway area.
I’ll bet no one in designing this structure considered long periods of cavitation effects in the emergency spillway
From the link cited above:
“For a given discharge, flow depths, velocities and cavitation indices can be determined at key stations along the spillway. The water surface profile program (ZPROF) calculates cavitation indices at identified stations along the spillway, in addition to providing the flow depth and velocity at those stations. This information along with information on offsets and irregularities on the spillway flow surface can be used to estimate probabilities for the development of this potential failure mode.”
Emergency spillways are not “designed” for use. They are a designed weakness in the structure to create a designed failure mode and path. Think of a frost plug for analogue.
A earthen gravity dam WILL fail if overtopped. To avoid using such language the weakest or lowest point is given the name “emergency” spillway. When the dam overtops, the dam HAS failed. The overflow undercuts at the desired point and the reservoir drains. That is how it is “supposed” to work. It is the design feature.
The E- spill doesn’t do much for the people downstream but it DOES save the majority of the main dam and powerhouse. No small achievement – mucho $$$ GK
“I’ll bet no one in designing this structure considered long periods of cavitation effects in the emergency spillway”
=====
I’ll bet they did, and in fact considered lots of other things.
Which is not to say they’re not sweating things out, like everybody else.
Tom,
The link you provided comes up with a “rejected” page. I would really like to view the info and calculations on that primary spillway. Thanks in advance for any help you may offer.
I like the part at the end of the article where it says “the dam spillway” is damaged.
Does anyone know the velocity of the water in the primary spillway at the current 100,000 cfs discharge? Second question : What is the slope angle of the spillway after the ‘ski jump’ where the spillway turns downward? Accurate answers and supporting links would be appreciated.
‘Moim zdaniem jebnie!’
Jebnie, who’s opinion you’re adhering ?