Dam Trouble

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August West

Trad climber

Where the wind blows strange

Feb 15, 2017 - 02:14pm PT

They expressed it just fine once the state of emergency was declared. My kids live on the back side of a levee in Natomas. They were absolutely at risk because of the spillway. The Sacramento river is a few measly feet from topping its levee out near the Sacramento Weir. The weir is still open meaning that slug of water would have surged right through the city. Still might have held anyway but I wouldn't count on DWR assurances to that effect.

DMT

I actually work with guys (that have no association with DWR) that are involved in figuring out how big a flood would be caused by a given dam failing. If the comment about the emergency spillway "only" losing 30 feet or so is correct, then they tell me that Sacramento would not be at risk. Yuba city and Marrysville would get it though.

A slug of water spreads out as it goes downstream. As an example, say you have been releasing 100,000 cfs from Oroville for a long time. You then release 200,000 cfs for one hour and then go back to 100,000. By the time it gets to Sacramento (12 hours or so later), it doesn't cause a 100,000 increase for one hour. It might be something more like 33,000 for 3 hours. (Note, I'm just making these numbers up to describe a behavior).

If the emergency spillway had gone, they would have shut off all of the flow going through the main, gated spillway. They could also completely close Folsom for a few hours while the peak flow was going past Sacramento. The Sacramento river going through Sacramento can handle ~600,000 cfs without flooding. Shasta is farther away then Oroville, but they might also have shut it down for a few hours if the Oroville spillway started going.

I don't have any insight as to why they thought the spillway would only lose 30 feet.

I absolutely agree that those individuals and those institutions that are responsible should be held responsible and lessons should be learned. But neither should the danger (in this case Sacramento flooding) be overstated.

August West

Trad climber

Where the wind blows strange

Feb 15, 2017 - 02:23pm PT

Additionally, it seems, the 100 year rainfall/melt potential of California's long term climate was ignored. This dam should have been pared with another upstream to accommodate the possible fill potential, without resorting to emergency releases,
during a 100 year event. Any study this design was based on is phony science

The reason they had flow over the emergency spillway was not because the dam was too small or was operated incorrectly.

If the main gated spillway had not had the problem with the concrete ripping out (which caused them to reduce the flow down this spillway), the lake would never had filled to the emergency spillway, there would have been no evacuation and nobody would have heard anything about Oroville. It would just be a wetter then usual, but still routine spring flow.

But the fact that this spillway had damage absolutely was a problem. The fact that the emergency spillway had a problem at such a small flow is also a big deal.

There are a limit to how many dams you can build. There are only so many sites where you can put a large dam. Also there is real tradeoff. If you kept the lakes lower, floods (or the sort of problem that Oroville just had) would be reduced. But farmers would have less water if CA happened to go into a drought.

To be a cynical snark: do you want to protect the residents of Yuba city or do you want to grow almonds in dry years?

cleo

Social climber

wherever you go, there you are

Feb 15, 2017 - 02:28pm PT

According to some back-of-the envelope calcs..

Area = 15,500 acres
Loss = 30 feet
Total Loss = 465,000 acre-ft

Lets assume it takes 4 hours for all that water to spill out...
-> 1,406,000 cfs for 4 hours.

That's a lot of water. Double it for 2 hours, quadruple it for 1 hour. You get the idea.

Lots of floodplain between the dam and Sacramento, that flood would pretty much obliterate those upstream levees and the water would spread out, so I *think* Sac would be ok, but there would still be a surge in the River. I don't know if anyone knows how much, but there were some flood maps at the SacBee.

August West

Trad climber

Where the wind blows strange

Feb 15, 2017 - 02:28pm PT

In the run-up to the emergency spillway overflow, dam and DWR officials publicly vacillated about whether to use it or not.

not sure this is correct. The flood control rule book limits the flow that is allowed from the dam downstream.

I haven't gone back and calculated the release the rules required...

Once the main gated spillway was damaged, they are no longer in "normal" operations. I don't know this for a fact, but I would assume they could operate the dam in whatever manner they thought would first minimize risk and second, would minimize damage and that they wouldn't be bound by the flood control rule book.

rick sumner

Trad climber

reno, nevada/ wasilla alaska

Feb 15, 2017 - 02:34pm PT

Hey West, your all wet.

The dam has had to release beyond flood stage levels a few times already in its relatively short existence. In 1997 it reached its brim. 1862 was much worse, and what this Feather River drainage should have been designed to since it occurs regularly in the climatic record.

August West

Trad climber

Where the wind blows strange

Feb 15, 2017 - 02:35pm PT

Lots of floodplain between the dam and Sacramento, that flood would pretty much obliterate those upstream levees and the water would spread out, so I *think* Sac would be ok, but there would still be a surge in the River. I don't know if anyone knows how much, but there were some flood maps at the SacBee.

If you know (or assume) how fast the water comes out of Oroville (i.e. it is this many cfs for this many hours), then they can model this flood very accurately (with some caveats below).

They don't usually know exactly how many hours it takes for it (the emergency spillway in this case) to fully collapse (although there are some limits on the both the short and long side).

Caveats: you have to know what the downstream river looks like to model a flood surge. For a catastrophic flow that causes levees downstream to overtop, you wouldn't always know which levees would fail first. When a levee fails, it can reduce the flow in the main river which might protect other levees. So the answers could vary a little bit based on which levees fail first and which levees don't fail at all.

August West

Trad climber

Where the wind blows strange

Feb 15, 2017 - 02:39pm PT

I was referring to the folks who let the dam over-fill and kept offering reassurances all was well right up until it wasn't. I'd suppose a lot of the original engineers have passed through the veil darkly.

I think the water users / rate payers who use water from the lake should foot the bill for dam improvements, for the most part.

I kind of covered this, but the dam wasn't "over-filled". The cascade of events didn't start until the main spillway had erosion from the failed concrete.

And for those following my posts: having water supply reservoirs is a fine thing. But farming uses the lion share of water that has frequently been subsidized by tax payers. (And perhaps by resident that have less margin against flooding.)

August West

Trad climber

Where the wind blows strange

Feb 15, 2017 - 02:42pm PT

DMT,

The levee failures would all be upstream of Sacramento. If the numbers my engineering buddies are telling me are correct, Sacramento wouldn't have a flood flow. It would fill the bypass by levees wouldn't be overtopped. Yes, a levee that is in bad shape can fail without overtopping. But the flows going through Sacramento wouldn't be any larger than the sort of flows you would expect every 10 years or so.

August West

Trad climber

Where the wind blows strange

Feb 15, 2017 - 02:51pm PT

The Main SW (MSW) is damaged and no one can say if it can be used throughout the rest of this wet season...

How in hell are they going to beef up the ESW so that it can cover the MSW in the event of a true emergency which is certainly possible this year??? Acting DWR Head yesterday said CA was on track for the wettest recorded year in history if it kept raining at previously seen rates.

A wet rainstorm in March like the '97 event could easily see 150,000 CFS...

The damage on the main spillway it still a long ways downstream. Yes, the more you use, the more erosion you get. But they could still let a lot of water out before it became an emergency issue. The more you let out the more it is going to cost to repair, but that can be dealt with later.

I would presume that they are going to keep lowering the water level as fast as they dare. They aren't going to be limited by any rule book or concerns about water supply.

It wouldn't surprise me to see them drop the water level a hundred feet or more. This will dramatically reduce the chance of the reservoir filling up again (but would impact things if CA goes back into a drought).

I don't know if they can repair it in one summer (I would kind of doubt it). If they can't, I would imagine they would really drop the lake level before next winter.

I'm curious also as to the repair bill. My wild guess at the moment is $500 million.

August West

Trad climber

Where the wind blows strange

Feb 15, 2017 - 02:58pm PT

DMT,

For a collapse of the Oroville spillway, the peak flow through Sacramento might be over a time span of 6 to 12 hours. You could completely shut off the flow from Folsom during that time. I didn't find the number with a quick search, but that might be 100,000 cfs or so.

A much bigger difference could be made by reducing the flow from Shasta. Although Shasta is further upstream than Oroville, so if the spillway collapse had happened really suddenly, I'm not sure if a reduction from Shasta would help or not.

cleo

Social climber

wherever you go, there you are

Feb 15, 2017 - 03:08pm PT

I think Shasta flows are 4-5 days from the Delta*, so shutting down Shasta would not help with a sudden collapse.

Shutting down Folsom would help, however.

*probably a summer estimate, so maybe less in winter

tuolumne_tradster

Trad climber

Leading Edge of North American Plate

Feb 15, 2017 - 05:01pm PT

skcreidc said ^^^

... I used to be a hard core hydrologist and geologist ...

so then you know that most/all geologic/hydrogeologic problems are severely under sampled and the challenge is to make full use of what little information you have to interpret what is between the known data points, boreholes, outcrops, etc

green schist is notorious for being unstable due to the inconsistency of secondary alteration and consolidation as well as fracturing.

yes, exactly and according to the geologic map, the dam and the entire reservoir is underlain by this material...so, as an initial approximation, extrapolate that fractured green schist outcrop over the entire area.

Looks like there is a fault interpreted within the green schist (mv) unit on the geologic map that projects toward the southeastern end of the dam.

August West

Trad climber

Where the wind blows strange

Feb 15, 2017 - 06:02pm PT

So a correction to my earlier comments. I thought Yuba city flooding was based on the collapse of the emergency spillway stopping after 30 feet. The latest I am hearing is that it could go two or three hundred feet deep and it sill wouldn't flood Sacramento.

The flows would be somewhere in the 1 to two million cfs at the dam. But it would really spread out and slow down.

Basically, as long as the flows are below the levee, the water shoots down the channel. Once it goes over the levee it creates a giant, slow moving muddy lake that fills up and then slowly drains. So there would be a large region affected but the peak flow would be really spread out by the time it reached Sacramento. If this is the scenario, I would think that shutting off the flows from Shasta for a while, would make a big difference to the maximum flow in the Sacramento area.

bergbryce

climber

East Bay, CA

Feb 15, 2017 - 06:21pm PT

Fill 'er to the rim, with Brim.

The rain totals through Thursday look pretty damn' heavy. Where the hell was all this rain 2011-2015?

rick sumner

Trad climber

reno, nevada/ wasilla alaska

Feb 15, 2017 - 07:54pm PT

So Toprope, you are alluding to more problems for the troubled Dam? Do you have room at your place to house flood refugees? Might happen before summer.

Actually, I was talking of other facilities on the same scale as Oroville.

john hansen

climber

Feb 15, 2017 - 08:10pm PT

Having grown up around there, I am finding it very difficult to find photos of the progress they are making in fixing and protecting the bottom of the emergency spillway. I have seen many photos of trucks and helicopters and excavators and dozers working 24 / 7. I saw one boom pump,,
Where are all the concrete trucks? I wonder how much progress they made today?

The last photos I could find they were working down on the east end of the temp spillway and the rest was the helo's .

Any one have a link to the latest KCRA flyover and how much progress they have actually made today in protecting the area below the emergency spillway?

Ed Hartouni

Trad climber

Livermore, CA

Feb 16, 2017 - 12:11am PT

so from the USACE archive site I linked above you can see that 1997 was very different from 2017, here is the same plot from the site for 1997

I also downloaded the data and could use the "flood control diagram" to map out the outflow, the reservoir volume and the volume prescribed by the flood control for the years 1997 and 2017

the first thing you notice is that the reservoir was "full" in 1997. There were two storms that year in the period shown which dropped 27.57" of rain in the drainage. In 2017 there were 4 storms dropping 40.2".

The flood control diagram prescribes the reservoir volume given the average previous 6 weeks of precipitation, (in millimeters per day) ...

the green line on the plots above is the capacity prescribed by flood control, the red line is the actual reservoir level, and the blue line is the average daily outflow in cubic feet per second.

In 1997 the big storm was late Dec/early Jan and dropped 18.44". That accounts for the big spike in the outflow, but notice that the reservoir level tracked the flood control prescription. The second storm was in late January and dropped 9.13" and there was some additional outflow.

In 2017 the first storm was in December dropping 10.28" and raising the reservoir level. However, the reservoir was well below the flood control prescription.

The second storm in early January dropped 13.49" and raised the reservoir to the prescribed flood control capacity.

A mid January storm dropped an additional 4.45" and the outflow was raised to keep at the flood control level. However, the early February storm dropped 11.98" and while the outflow was increased it could not keep up with the inflow.

The current situation is that the reservoir capacity is still well over the flood control prescription, and at the current average outflow of 100000 cfs it will take another week to lower the reservoir to the prescribed level.

This year was anomalous compared to 1997.