Dam Trouble

you don't have any role in this, of course, except to be a public scold...

I've been following this hour by hour for 3-days. I was there on Saturday, ok? They took the choice to use the emergency spillway. They didn't have to.

1862-It happens on average every 100 years. Nothing abnormal per the long term climate history of the west coast.

Just remember this situation the next time the water guys start talking about building yet more dams, like at Sites and Temperance Flat.

you don't have any role in this, of course, except to be a public scold...

There's only so much money for everything to go around and politics play a huge part of it especially when;

Oroville has, apparently, had listed deficiencies that went unaddressed for up to 12 years.

The rainy season commenced on the 8th of November, and for four weeks, with scarcely any intermission, the rain continued to fall very gently in San Francisco, but in heavy showers in the interior. According to the statement of a Grass Valley paper, nine inches of rain fell there in thirty-six hours on the 7th and 8th inst. Whether, it is possible that so much rain could fall in thirty-six hours I will not decide; but it is certain that, the amount was great, for the next day the river-beds were full almost to the hilltops. The North Fork of the American River at Auburn rose thirty-five feet, and in many other mountain streams the rise was almost as great. On the 9th the flood reached the low land of the Sacramento Valley.

"[1]Back to the dam, any experts here want to chime in on the subject as to why the emergency spillway has nothing but dirt underneath it...

[2]Also, if a big sinkhole collapsed under the main spillway does that mean water has been leaking under there for a while?"

2- not necessarily. Could be they used precast concrete panels without sealing joints, or had cracking that got big enough to leak through. Any of a bunch of reasons that the failure could have occurred.

1- it looks to me like the issue is the pool at the end of the spillway - the turbulence eating out under the end of the spillway. I don't know what design standards were in the 1960's when this was built, but it is possible they don't have sufficient (size & amount) rock to break up the energy from the water at the end of the emergency spillway.

Anyone know why they aren't letting people return home?

The water coming out of the power plant race is muddy and has been for a couple of days.

One of the biggest challenges engineers and work crews face is how to clear the Thermalito Diversion Pool immediately below the wrecked spillway of a large volume of concrete debris and sediment that have dammed the waterway and forced closure of the hydroelectric plant at the base of Oroville Dam.

There's nothing dumber than a news outlet

The muddy water is sediment from the erosion of the spillway.

Is the main spillway down to bedrock yet? Is there any bedrock below the emergency spillway?

Is the main spillway down to bedrock yet? Is there any bedrock below the emergency spillway?

I'm trying to draw attention to the underlying bedrock geology and all you guys want to talk about is rebar ;-(

So T Tradster what is that rock unit at the dam? Motherlode Jurassic 'slate'? Or perhaps serpentinite?

Genesis of the Smartville arc-ophiolite, Sierra Nevada foothills, California
American Journal of Science Vol 280-A, 1980, p 329-344.

Abstract
Rare earth element analyses of metavolcanic rocks from the Smartville, Calif. ophiolite divide the uniform suite of pillowed and massive lavas into the lower part consisting of massive, brecciated tholeiites, an intrusive dike-sill complex, and part of a plutonic suite. The tholeiites are light REE depleted with a (Ce)N range of 6.5 to 26.0 and (Yb)N of 6.0 to 30.0; it is suggested that the tholeiites were produced by partial melting of a LREE depleted source similar to MORB. The upper part of the volcanic pile is comprised of basaltic-andesitic flows and interbedded coarse to fine volcanic sediments; these 'calc-alkaline' rocks are light REE enriched with the (Ce)N range of 17.0-28.0 and (Yb)N of 8.0 to 12.0. Finally, petrographic investigations of volcanic sediments and sulfide ore deposits in the lava show that the ophiolite formed near a group of active submarine and subareal volcanoes.

I wonder why they are using helicopters to fill those holes near the parking area? Why not use trucks and tractors?

And I don't mean that in the millennial-praise sense.

The damage if an earthquake hit sometime in the next week to 10 days would be huge.

If the spillway fails and releases 30 feet of water then the damn dam failed. Can't parse that away with engineering double talk about how the dam was in no danger of failing.

According to a study by the China Earthquake Administration (CEA), the earthquake occurred along the Longmenshan fault, a thrust structure along the border of the Indo-Australian Plate and Eurasian Plate. Seismic activities concentrated on its mid-fracture (known as Yingxiu-Beichuan fracture). The rupture lasted close to 120 seconds, with the majority of energy released in the first 80 seconds. Starting from Wenchuan, the rupture propagated at an average speed of 3.1 kilometers per second 49° toward north east, rupturing a total of about 300 km. Maximum displacement amounted to 9 meters. The focus was deeper than 10 km

...the added weight both eased the squeeze on the fault, weakening it, and increased the stress tending to rupture the fault. The effect was 25 times that of a year's worth of natural stress loading from tectonic motions, Klose said. When the fault did finally rupture, it moved just the way the reservoir loading had encouraged it to, he noted.

An interesting question is whether after 5 years of drought, the large and rapid refilling of the Lake this winter—from 1/3 full to brim full—could set the stage for future induced earthquakes at the Lake. What this means is that both the spillway integrity and seismic resilience point to the same need for safety, strength, and vigilance.

You guys are gonna scare those poor people living below the dam with all this talk of earthquakes and sh!t going wrong .......

SO... more geology required in CA civil engineering code and licensure! That's my recommendation!

Abstract
The Late Jurassic-Early Cretaceous Bear Mountains fault zone (BMFZ) is the westernmost strand of the Foothills fault system in the Western Metamorphic belt of the Sierra Nevada. The tectonic significance of this 300-km-long fault zone has been downplayed in the past, but we contend that it is a major discontinuity within the Foothills terrane. The BMFZ is an ˜ 5-km-wide shear zone consisting of slate-metagraywacke-matrix melange that experienced intense polyphase deformation and metamorphism. Small-scale structures indicate reverse slip along most of the extent of this steeply east dipping shear zone. A host of lithologically diverse tectonic blocks are enclosed in the BMFZ. Blocks of sandstone, metavolcanic rocks, and plutonic rocks of intermediate composition have counterparts in the adjacent eastern and western zones of the Foothills terrane, whereas other block types are exotic. Exotic blocks include ultramafites that locally contain pods of gabbro, garnet amphibolite, greenschist, sedimentary breccia, and volcaniclastic rocks. The breccia is composed primarily of clasts of amphibolite and minor garnet-bearing impure quartzite (metachert?); it probably accumulated at the base of fault scarps. The exotic blocks comprise a broadly ophiolitic assemblage similar to that inferred to form basement to the Foothills terrane, and they record a deformation prior to incorporation in the slate-metagraywacke matrix. Amphibolite blocks and quartzite preserved as clasts within the breccia probably were deformed during overthrusting of oceanic lithosphere in a setting similar to that beneath the Tuolumne ophiolite east of the BMFZ. The presence of exotic blocks implies large-scale mixing and large displacements in the BMFZ, as do differences in stratigraphy across the fault zone. Metamorphic grade does not vary significantly across the BMFZ, however, suggesting that dip slip did not exceed several tens of kilometers if the fault zone originally dipped gently eastward as we propose. There is no direct evidence for major strike slip along the BMFZ as has been proposed by others; any such slip must have occurred before the reverse-slip related structures of the zone. We thus interpret the BMFZ as an intra-arc reverse fault of moderate to large displacement, with possible earlier strike slip, that incorporates ophiolitic basement showing an older, complicated history.

"This is an aggressive proactive attack to address the erosion," said Bill Croyle, acting director of the state Dept of Water Resources.

Obviously they were loathe to use it even then.

There is a good chance that the people in charge back when they were sued over this are now retired. So whose head should roll? People inherit messes.

"This is an aggressive proactive attack to address the erosion," said Bill Croyle, acting director of the state Dept of Water Resources.

Proactive? Really? Spoken like a true bureaucrat, sir.

Since the eroson of the main spillway is the key risk now water levels are under control, I've created this thread to keep track of any changes in the erosion at the "waterfall" location. Inevitably there will be some "head cutting" and the erosion will the move up the hill. However it seems to have stopped since Feb 10, and the hope is that it is now stable with the spillway spilling over a rock-bedded location.

But to me, the potential for it to be a piping problem based on placement is high.

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.

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

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...

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.

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.

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...

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

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

Can someone just explain the problem to me

The damage is to the spillway? This is on the downstream side of the dam? How does this affect the integrity of the dam itself?

"parallel erosion channel sharply cutting into the hillside directly left of the waterfall" is referring to the flow (new) that can be seen to the left side of the left wall on the main spill way. It is shown clearly in the attached photo (very high definition and very useful). Also note the small stream of water just further to the left of the wall.

If this continues it will probably just lead to a widening of the fan below the waterfall, and the continued destruction of the structure of the lower parts of the spillway (already pretty much a total loss)

there are plans to fly the towers out by chopper once there is time/availability/cooperative weather.

Officials had said they would start throttling back the releases to resume pulling debris from the river channel beneath the dam. The debris has backed up the river at a critical point, preventing the state from restarting the dam’s hydroelectric power plant. The plant would be capable of releasing up to 13,000 cfs.

This canyon is ~200 feet deep and formed in 3-4 days of ~40,000 cfs.

The concern would be with the "cliffs" in the waterfall region, the lower down ones are not too important. The most important one would be by the transmission towers (although they are going to move them anyway).

Given the pounding and spray already, I suspect that some rain isn't going to do much damage. The hillside is relatively stable and has been there for decades (if not thousands of years). Maybe a bit more surface erosion.

Read more here: http://www.sacbee.com/news/state/california/water-and-drought/article133030359.html#storylink=cpy

I think this is exactly what you were getting at when you talked about the flood procedures of the Oroville Dam earlier in this thread. Frankly I was surprised to read that the operating procedures were not updated after the '97 flood, and it turns out, the '86 flood as well.

Back to the dam, any experts here want to chime in on the subject as to why the emergency spillway has nothing but dirt underneath it...

Back to the dam, any experts here want to chime in on the subject as to why the emergency spillway has nothing but dirt underneath it...

Your last graph there from AFPS has a puzzling aspect which I could probably figure out by going there, but if you know the answer quickly, that would be dandy. The blue dots for "Dist Mean" are all well below the minimums, not to mention the range, SD, and max. Are those means for the date from the period of record?? Because they certainly can't be means of the forecast ranges. (Can they?)

The prescriptions are predicated on the idea that the "conservation pool" is sufficient to store any additional inflow and avoid what happened, and recall that what happened is that they filled the reservoir to the flood control limit but were unable to raise the outflow sufficiently high to compensate for the next storm.

Is the above in reference to what just happened or '97?

There seems to be some misunderstanding of the Sacramento releases from Keswick Dam on Lake Shasta and it's relation to the Feather River.

Currently, Keswick Dam is releasing the maximum that can be sent downstream. The Sacramento is at or near flood stage in most of Tehama County..

The Feather River joins the Sacramento near the little farm town of Nicholas, off the Garden Highway about 30 or so miles upstream of Sacramento.

This meeting of the rivers may become the new problem area if the Sunday, Monday rain event meets or exceeds precipitation predictions.

TT, the flood control diagram says they have to get the capacity down to 2780000

Rock Whisperer, and others, have reported that the bedrock in the area of both spillways is of variable quality. Some portion of it is competent rock and this appears in the images in a blue gray shade. Other portions appear to be subject to weathering or oxidation such that the rock becomes friable. This weathered rock takes on a reddish / orange hue. One poster with experience rock climbing in the the area around Chico and Oroville suggests the weathered rock will not hold the weight of a human being.

I have some experience dealing with corrosion events which are similar processes to rock weathering. Both are oxidation events. Oxidation may be accelerated by both water and heat. Since California has experienced a number of years of drought it is clear there was an extended period during which little use was made of the flood control spillway. Local rain would still have fallen and this may have passed through cracks in the spillway floor. The cement floor of the spillway would have heated during the day and this may have resulted in heat transfer to any voids beneath the spillway floor. The result may have been accelerated weathering of once competent rock.

If we now move forward in time to the present day with its high levels of rainfall then it is possible some amount of this rainfall percolated into the control joints between abutting slabs. This rainfall may have filled any existing voids and initiated a new drainage path through the weathered rock bypassing the installed drainage system and inhibiting water from exiting the "missing" drain in the image annotated by Mick presented in post 844.

Once the flood control spillway was put back in service the additional water, and the increased head, would have acted to initiate scour along any new drainage path. Over a period of time this would ultimately remove a significant amount of under-burden and enlarge the void to the point that the spillway floor suffered a collapse. Given the volume of water, and the high pressures, any incipient point of failure would quickly be enlarged, the material support for the spillway floor would be removed and the floor slabs would fail, likely collapsing into the void and then being hammered and broken by the water flow. The outcome would be something akin to what may be viewed on the images of the workers inspecting the flood control spillway after the the large void developed.

This also serves to explain why the point of failure has not "marched uphill" toward the sluice control structure. The drainage system above the damaged area is functioning as it should, the water is being drained from beneath the slab and there is no opportunity for the creation of alternate, destructive, drainage path.