Emergency: California’s Oroville Dam Spillway Near Failure, Evacuations Ordered

Breitbart ^ | Feb 12, 2017 | Joel B. Pollak1

[janetjanet998]

The California Department of Water Resources issued a sudden evacuation order shortly before 5 p.m. Sunday for residents near the Oroville Dam in northern California, warning that the dam’s emergency spillway would fail in the next 60 minutes.

The Oroville Dam is the highest in the nation.

[Jim W N]

DWR is more concerned with PR than with providing technically correct answers?

Seems to be the core issue with DWR and Moonbeam's government in general.

I would add, DWR appears more concerned with PR than with the safety of those living below the dam.

[EternalHope]

Are other large California dams likely to have to use their spillways during this year’s spring melt?

If so, do we know anything about the status of their spillways, and their ability to handle an unusually large spring melt when they are already nearly full?

Shasta stores more water than Oroville.

Trinity apparently has significantly less peak release capacity than needed in a major event, and is already nearly full.

Somehow I suspect neither of these dams has been properly maintained.

[EternalHope]

A link to the "current" status of major reservoirs in California:

Status of major California reservoirs

[janetjanet998]

sounds like the upper part of the spillway is on better shape then they thought..so they will start repairs at the bottom
http://www.orovillemr.com/article/NB/20170504/NEWS/170509898

also outflow down to 2000 cfs at this time

[Ray76]

excerpt of interesting article

Power industry consultant proposes dual design Oroville Dam spillway

(Apr 28, 2017) A power industry consulting firm has proposed a design for the Oroville Dam spillways which involves not repairing the current one, but building a new, wider spillway.

The designer says the structure’s capacity would handle flows of 300,000 cubic-feet per second.

Kenneth Viney, manager of CoastalGen Inc., based in Napa, filed suggestions Monday with the Federal Energy Regulatory Commission, or FERC.

Viney said based on some engineering specifications information he has provided on dams in the past, construction didn’t go through, as his firm pointed out flaws in a design like trying to build upon a limestone base.

“This is what we do — project planning,” Viney said. “We do an overview of the project and say, ‘This looks good or it doesn’t.”

CoastalGen Inc. has been a part of projects like appraising power stations for Southern California Edison and giving design input on hydroelectric plants in the James Bay Project in Quebec.

“We work all over the world and see things other people can’t see because of our experience,” Viney said

http://www.chicoer.com/article/NA/20170426/NEWS/170429806

[EarthResearcher333]

Oroville Dam History Images - Reveals Heavy soil migration from internal leakage erosion - Differential settlement Twin Columns - Potent Green Leakage area today

More discussion: This Historical sequence of Images reveals strong evidential behavior and existence of a persistent Leakage problem within Oroville Dam. This original leakage behavior of the first "settlement" phases of the dam, caused "twin columns" of strong seepage which deposited thick soil patches from internal dam soils migration. The "twin columns" of this large seepage were centered on the original "hump" layer which induced differential settlement stresses to the core region resulting in the mirrored hillside saturation. Note that there is NO greening along the other areas of the dam - as an example of the "rainfall" theory proposed by DWR. The early problem Green Wet Area was in its infancy in seepage as illustrated by the dark patches near the left abutment of the dam. Image item (1) shows NO greening or soil "patches" in the original construction.

After the significant seepage of the vertical twin columns (2), large internal soil deposition "patches" are observable that resulted from the prior "significant dam seepage" (3). These 'soils' are from within the internal dam and were migrated by a persistent leakage flow leading to a thick deposition at the surface slope. NOTE: rains would have had to concentrate, then "upwell" (not likely), to form such a collection of soils from the zone 3 shell layer, yet fluid flow physics defies how these oval formed patches could occur from an "even slope rainfall" theory. ONLY an internal flow path (inside to the outer surface layer) could form such a concentration and pattern of soil. The fact that there are twin soil patches, centered over the original "hump" toe axis layer, strongly supports a differential settlement leakage path through the core in two regions of the upper twin columns. Over years, these soil patches have been washed away as the internal seepage condition "sealed itself" (i.e. Zone 2 silts, sands, migrating into the core to reseal as designed) and the "differential settlement" over the toe axis "hump" balanced out.

Yet, there is an area that continued to experience "differential settlement". That was along the steep slope of the left abutment. Thus the internal seepage and erosion developed early and is continuing today to pipe soil material -along with the increased presence of water flow- to facilitate large vegetative growth (greening) on the dam face. (See 2nd image from April 2017). Because of the physics of the internal phreatic shelf (waterflow shelf) inside this long developing internal erosion channel (longitudinal seams leaking within), there likely is seepage flow that is "unseen" at the surface. This would be due to a seepage percolation through the erosion soil shelf that curves in a subsurface flow (parallel but under the surface of the "downhill erosion channels". What determines how much leakage and what volume reaches the Green Area Wet Spot is due to reservoir levels, how long the reservoir has increased the pore pressure within the core regions, and the hydration state of the outer zone 3 material.

These factors would affect an assessment of seasonal greening assuming the cause to be from seasonal weather. But the internals are more complex. Essentially, the phreatic line (water level) and its curvature are dependent on these factors. When the conditions are suitable, the phreatic curvature leakage upon the erosion soil migration "shelf" determines the point at which the leakage at the outer surface intensifies, then "greening" accelerates, thus giving a "seasonal" association.

Original leakage behavior of the first "settlement" phases of the dam, caused "twin columns" of strong seepage which deposited thick soil patches from internal dam soils migration. Soils were concentrated forming two "patches". ONLY internal core flows may cause this result. (not rainfall).

Heavy Greening and Leakage in 2017 (conflicts with "rainfall" theory). Unknown total flow rate and extent of internal uncertainties to the erosion channels makes this situation an unknown risk. Leakage, strong dam face erosion channels, soil base, large greening all above steep slope transition (differential settlement dam risk).

[EternalHope]

As usual, excellent information and analysis.

Key unasked question: Is there currently detectable water flowing from the dense green area through the easily visible erosion channels?

If so, how much?

If not, was there when the lake was at a higher level than it is right now?

It seems it must be one or the other, or both. Otherwise, how did the multiple obvious erosion channels form? They clearly originate in the green area, they are not visible elsewhere on the dam, and it was NOT rain.

The green area is growing, which means the water flow is increasing.

So... HOW MUCH WATER?

Presumably the DWR knows the answer and has chosen not to tell us. It’s even worse if they DON’T.

[EarthResearcher333]

"Key unasked question: Is there currently detectable water flowing from the dense green area through the easily visible erosion channels?"

A very good question. These large erosion channels are a physical displacement of fill material that is designed to have water percolate & penetrate into this zone 3 fill (sands, gravels, cobbles, boulders). So the fact that there are visible surface erosion channels in such material means that there is more water flowing that is not observable at the surface.

That is precisely why the 2014/2015 Division of Safety of Dams (DSOD) Inspection report noted that this leakage should be monitored (yet no instrumentation for monitoring is noted as emplaced over the years - other than cutting vegetation to visually observe for greening "area" changes). Deeper penetration & erosion below the surface can cause these channels to be formed by subsidence erosion. So the outside view of the channels may look somewhat dry, but the waterflow is real and its underneath.

To determine the full waterflow volume requires understanding the curvature and the extent of the undersurface erosion channel percolation dispersion passages.

This same effect is how the "greening" may vary on supplemental hydration of the hillside adding to the effect of the strength of the internal reservoir head pressure, the internal core leakage volume, and the net percolation saturation of these under surface dispersion channels.

Instead, DWR drills a test well in the hill thinking a "spring" or maybe "piping around the dam" is somehow penetrating the left abutment zone 3 fill and then "flowing uphill" (greenage pattern elevation slope away from the abutment). Yet DWR is not saying this to the public. They hold town hall meetings and say "rain falls...then grass grows".

The only way to assess an accurate risk is to quickly get answers. Assuming DWR's latest press release is what they really believe, it likely will take external engineering criticism from reputable sources before they reluctantly may take action.

Worst case, if there is a sudden change of events were water is observed to flow on the surface of the erosion channels, that would be a bad sign.

[Ray76]

I've gathered monthly precipitation and lake elevation data for the past ten years. If dated photographs of the dam can be obtained it may help determine whether it is precipitation or raised lake elevations which most closely correlate with appearance and size of the green area.

                                        Precipitation

       Jan   Feb   Mar   Apr   May   Jun   Jul   Aug   Sep   Oct   Nov   Dec
2007   0.0   5.7   0.4   1.7   0.6   0.5   0.4   0.0   0.3   1.3   0.8   4.1
2008   4.5   3.6   0.2   0.3   0.0   0.0   0.0   0.0   0.0   1.8   2.5   2.7
2009   2.2   6.6   2.1   0.4   1.9   0.2   0.0   0.0   0.6   1.7   1.4   3.8
2010   8.0   3.1   2.3   4.5   1.4   0.0   0.0   0.0   0.0   2.6   2.6   7.2   
2011   1.8   4.1   6.9   0.6   2.7   1.1   0.1   0.0   0.0   2.1   1.6   0.3
2012   4.4   1.1   5.8   2.2   0.0   0.1   0.0   0.0   0.0   1.4   4.4   7.2
2013   0.7   0.5   2.0   0.8   0.3   0.6   0.0   0.0   0.8   0.1   1.5   0.3 
2014   0.4   6.1   5.2   0.3   0.3   0.0   0.0   0.2   0.7   1.2   2.6   8.9
2015   0.1   2.5   0.4   1.5   0.0   0.0   0.0   0.1   0.1   0.2   2.7   2.9 
2016   7.2   0.7   6.8   1.1   0.4   0.1   0.0   0.0   0.0   3.2   2.2   5.5
2017   7.5   8.6   2.9   3.0   

precip inches rounded to tenths

https://www.wunderground.com/history/airport/KOVE


                                   Avg Elev Lake Oroville

       Jan   Feb   Mar   Apr   May   Jun   Jul   Aug   Sep   Oct   Nov   Dec
2007   850   858   866   871   866   852   818   782   748   730   713   699
2008   703   716   737   753   757   748   718   693   680   675   667   661
2009   661   679   758   787   804   799   760   724   712   708   695   674
2010   675   704   732   769   813   838   833   803   770   754   749   767
2011   811   830   854   869   888   897   899   892   876   860   853   838
2012   827   830   840   875   898   891   860   819   789   770   762   812
2013   834   848   857   868   859   842   813   777   751   741   724   711
2014   703   711   739   765   764   745   714   688   677   668   651   686
2015   719   744   760   763   748   729   702   679   673   670   658   656
2016   690   754   829   881   890   875   836   787   753   738   733   755
2017   834   861   851                           

lake elevation rounded to feet

https://cdec.water.ca.gov/cgi-progs/queryMM

Station ID   ORO      Sensor Number   6       Date    04/17       Span   144

[PavewayIV]

I'm confused why the DWR engineers wouldn't be more curious about anomalies in the location of the actual phreatic line, especially in cases like this. One can theorize all they want, but in the end this is something that looks like it can be determined fairly easily with readily-available instrumentation.

Peizometers are not exactly rocket science. Pneumatic ones are less than $200 apiece, and plenty of data logging or real-time electronic ones are less than $1000. For some modest investment (let's say < $275M) you could have a fairly robust, high-resolution, real-time picture of the way your dam was performing rather than relying on weeds, as-designed hopium or the blatherings of your PR spokesperson.

Laying a grid of 20 or so of these across a suspicious area shouldn't be that big of a deal to the dam operators. They could probably get a grant for a university and have it done for free, including slave labor. Is it lack of intellectual curiosity, or is there some other reason DWR wouldn't want this done at Oroville?

Has anyone ever instrumented a dam like this ER333, or is there an assumption that the phreatic line should be nearly vertical and too deep inside the dam to measure? I understand why they didn't bother doing this in 1965, but not doing it today on the tallest earth-fill dam here with 'issues' seems a little like depraved indifference.

Bravo for DWR managing a grand total of one monitoring well over what looks like a former erosion channel on the abutment to confirm their 'natural spring' theory, but really?

Maybe I'm oversimplifying this, but I don't see the need for a year-long project to install a thousand individual 300' deep monitoring wells on the downstream slope. Sinking a dozen or two drive-point piezometers into a grid on the hillside near the green spot would take a week. Two weeks if you use grad students because they're always late.

Either the water is there or it's not. If it's not, then DWR management can crow about their engineering genius. If it *IS* there, then maybe they could actually address the issue. Foisting it off on their PR spokesperson so the hostile crowd doesn't string them up on lampposts seems a bit... self-serving.

[EarthResearcher333]

"I'm confused why the DWR engineers wouldn't be more curious about anomalies in the location of the actual phreatic line, especially in cases like this. One can theorize all they want, but in the end this is something that looks like it can be determined fairly easily with readily-available instrumentation."

I'll have to answer in pieces to give the best type of a "total" answer..

1. One of the first rules: Don't touch the dam.

This is strictly regulated: FERC to DWR example quote: "3. You are reminded that you may not proceed with collection of shear wave velocity data until we authorize your proposed plan for drilling."

If DWR wants to emplace sensors anywhere in the dam embankment (especially the core) it is a significant step that has to be planned, coordinated, and mostly "explained why" in communications and authorization from FERC.

This is because if you do something stupid you can introduce a leakage path that may lead to a serious problem. I'm not saying the engineers are not intelligent, it is just that there is a very high safety protocol that has to be maintained in dam operations. ex: Any sensors into the core or other zones have to be carefully emplaced to have "filter stops" to prevent an introduction of a "guided" leakage path.

2. Who (engineer or lowly manager) wants to trigger an intense "what's going on, do you have a problem?" response from FERC if someone wants to figure out an unexplained anomaly (such as Greenage). Unless there is a collective will in "belief" that there is a real puzzle that needs to be investigated, they likely will take "heat" from upper management, directors, and the Board in triggering a FERC intensive inquiry. You can degrade your career with triggering an investigation where the starting point is "I really don't know" (re: the anomaly). In a Pro-active High Reliability Systems World -> A boldness should be encouraged by upper management to support someone who actively wants to identify problems proactively, even if it's a minor atypical anomaly in a typical dam performance expectation.

3. DSSMRs (Dam Safety and Surveillance Monitoring Reports) are the life blood of critical independently performed inspections, usually by outside contractor experts, to meet the very extensive FERC DSSMR report requirements & standards. FERC's required DSSMRs of full inspections & reviews are done less frequently than the annual CA Division of Safety of Dams (DSOD) Inspections. Look at it as a hierarchy of safety inspections.

4. Below is a 2012 DSSMR findings & response document (GEI Consultants [DSSMR inspectors for this FERC report], DWR as responders to the findings of DSSMR items, and FERC as the agency that this report & actions are filed with). There are key points in this DSSMR report that shed light on the Green Area anomaly question. (a) GEI gave a glowing report on the performance of the main dam (i.e. the Green Area was not mentioned). (b) Monument surveys were mentioned, but no information was stated as to how many of the 100 dam surface monuments are part of the regular survey. (there was mention of "threshold levels" in terms of "methods and actions" on any data - but this too was not fully detailed). (c) ONLY 3 of the original 56 Piezometers still work at the dam. So the dam mostly does not have the ability to determine reference internal water levels (phreatic line) within the dam. Thus, no mention of the Green Area, no mention of settlement issues (mainly a "glowing" report). This could very likely discourage anyone from initiating or speaking out in concerns of this Greening anomaly.

5. Somewhere buried in my mounds of documents - I ran across communications where FERC is asking DWR to determine the Phreatic line within the dam. (I'll need to keep digging to find it again). This FERC request may be linked to the fact that the dam has only 3 working Piezometers left.

6. Because of (1)(2)(3)(4) there becomes a potential significant hurdle in someone triggering an "investigation" into the atypical Greening. The "system" says that there is nothing of issue (DSSMR report), other than the DSOD Inspection reports continually repeating, "we should watch this grass". The net effect of the redundant safety procedures between FERC, DSSMR's, Independent Contractors desiring continuing business, DSOD, DWR's sensitivity to meeting "good standing with FERC" for re-licensing - creates a net environment that could greatly discourage any Green Spot "alarm" raising by engineers or managers. Worse, this Green Spot defies the typical known world of phreatic line behavior if the complexities of the prior postings - i.e. if not forensically researched with a high grade of expertise (history, stages, seasonal consolidation in construction, differential settlement sharp slope transition, phreatic line anomalies, clogged drain zone sections, seepage silt/soil "shelf forming", etc).

Original Oroville main dam sensors & instrumentation - 56 hydraulic piezometers of which only 3 function today. 100 Survey Monuments on the outside layer of the dam to measure settlement.

Glowing DSSMR report - no mention of Green Area - DWR notes only 3 piezometers work (out of the original 56) - no info on number of survey monuments tracked AND the "threshold" level to "action"

[PavewayIV]

Again, thanks for the very detailed reply, ER333. Fascinating read. I do sincerely appreciate the time you take to reply a random idiot like me - for free - in your spare time.

So given the engineering politics of all this and a broken oversight system that enables and encourages inaction, let's forget Oroville completely for a moment.

Consider an imaginary dam exactly like Oroville as it is today - let's call it Sam's dam. I wave my magic wand and make you engineering Tsar (or Tsarina) of Sam's dam. No FERC, no Army Corps of Engineers, no DWR. All the dam operators and engineers report directly to you. You have a reasonable but generous budget. Qualifications like prudent, safe and reasonable are only subject to the consideration of your peers in the profession, not politicians or lawyers or anyone else.

So what do you do today about the possibility that the impervious layer is leaking today and/or the filter layer/drains might not be working right? If it was caused by differential settlement, can it be fixed? Has that ever been done anywhere else? What's the right course of action from a purely engineering standpoint?

[jpal]

Ray76’s data shows there was a 3 month period ending in August 2011 when the lake level stayed above 891’, within 10’ of topping out. This contrasts with 2017, when the lake was above 891’ for just 4 days, and has averaged closer to 850’.

Hence, there was more elevation head on the dam for a longer period in 2011 than so far in 2017. Yet the green area (apparently, as assessed by locals) is larger now than in 2011. Had this green area had stayed “green” through August 2011, correlating with the high lake levels on the opposite side of the dam, someone would have noticed and taken pictures, as you don’t get green grass in California in the summer without irrigation.

This indicates that either the internal piping through the dam has gotten much worse recently, passing a higher flow rate now under less head; or this green area is not a function of lake level, but more of a function of the extent and duration of precipitation.

[EarthResearcher333]

"So what do you do today about the possibility that the impervious layer is leaking today and/or the filter layer/drains might not be working right? If it was caused by differential settlement, can it be fixed? Has that ever been done anywhere else? What's the right course of action from a purely engineering standpoint?"

You are going to have me give away some of my secrets... :-)

note: It is always best to first gather information from direct sources & get their viewpoints, past analysis, their opinions, any tests that have already been done, etc. Barring access to that important knowledge set....

(1) First, I would use military grade non-invasive spectral Thermal Infrared/Forward Looking Infrared TIR/FLIR camera mounted systems on a suitable aircraft to image map the thermal profile that the subsurface zone 3 layers of hydration leakage creates. I would also use concurrent digital stereo imaging to allow the overlay of the sets of TIR/FLIR captures.

(2) Second, I would contact the USGS or any group that has obtained inSAR satellite data in the past years and then arrange for an inSAR satellite data capture as soon as available. By doing an Interferometric synthesis of "two" periodic runs, you would be able to get to millimeter precision surface deformations of the entire surface of the Zone 3 embankment of the full dam downstream & crest regions.

(3) Third, I would collect samples of the Green Zone sediment and have a soils analysis performed to identify if there is a standout ratio of any marker component of the clay-clayey borrow pit area near the original pit by Oroville Airport.

(4) Fourth, I would identify if there were "clear" water flowing at locations in the green area and would capture H2O samples from the most direct flows to have analyzed for any indicative markers. Higher flow points may have better markers from deeper within.

(5) in items (3)(4) I would use a portable precision GPS units to mark the locations of sediment and H20 sample collection(s) and combine all of the collected data in an overlay map (1) through (5).

(6) I would go to the Grout Curtain Gallery Weir & collect sediment that has been present there and have it cross analyzed to any of the data to see if there are any trace minerals associated with (4)(5).

(7) I would obtain access to a group of about 3 seasoned experts who are in this unique field that I would choose myself from qualities I know what to look for. Also I would obtain access to construction experts who have experience in doing actual investigations and repairs of this specific situation. (always leverage expertise + it is the equivalent of a force multiplier, but choose carefully).

= =

At this point (1) thru (7), the data should give a good indicator to the magnitude of the hydration of the zone 3 fill, the extent, and possibly "mineral markers" to where the water source is from. There should be distinct mineral markers from the metavolcanic rock if the water source were flowing from or "porting" through the left abutment hillside. If all of the indicators point to an internal dam source path, OR, a strong hillside flow, then I would assess the possible "unknown" or unseeable phreatic percolation that may be deeper within the zone 3 fill. This "worst case" calculation would determine what actions or steps should be taken.

Earth Fill dams are fixable over any of these erosion path issues. The challenge for Oroville dam is its massive size. If there is belief that there may be a risk of a long term internal erosion flow, determining the exact location/location(s) would be take work. Differential Settlement (if proven the cause) creates "longitudinal" fracturing. To seal such a potentially wide horizontal type of region with probe injection of a clayey + bentonite mix would require knowing the origin(s) to an accurate degree.

Some dams were compromised in the core to the extent where they were excavated from the crest downward to the level of the defective layering and then they rebuilt the core with a modern clayey + bentonite mix. But that was done on smaller dams. Not as easy for the Oroville dam giant.

Perhaps the most difficult political decision (politics of engineering judgement) comes from a safety factor of unknowns. That is, making a decision to lower the reservoir below the threshold of the leaking area until an accurate assessment of the core & any suitable "fix/repair" is completed. Why would this decision be difficult? Because, in the real engineering world, you have to make decisions that are based upon a ratio of "belief verses proof". Proper engineering efforts will transition the mostly "I believe xyz" into "I now can prove xyz". The pressures when you are in the "belief" mostly side of the equation are enormous as the impact to this choice is challenged by those that demand "proof". You have to stand your ground. You also have to "build consensus" with powerful interests to get their trust that you know what you are doing.

[EarthResearcher333]

Hi jpal, one variable that is being overlooked is the internal phreatic line or curvature in a long duration summer heat condition. The surface area of the zone 3 fill and its thermal retention properties form a significant evaporative mechanism. Thus the furthest "reach" of the phreatic line (curve) to the zone 3 surface may be fluctuated by this mechanism since the greenage is a balance of a hysteresis state (hotter crosses an accelerated threshold of loss in vegetative cut-off). A deeper percolation becomes the "unseen unknown" in such a comparative experiment. (precipitation to reservoir only).

Another variable that should be included is the phreatic saturation of the core and fill zones (time at a given level). (to which you properly brought up in a "period" notation).

Another "unseen unknown" variable is if a threshold has been crossed where there may be an increase to the defect or source that has changed from in the past.

The Division of Safety of Dams have been noting this area for years in their inspection reports - for monitoring & determining flow. Only in 2016 was a piezometer sensor (water sensor) test well drilled near this area by DWR. This should have been done long ago. There is nothing like direct evidence in getting to the root cause of something that shouldn't be occurring on an earthen dam. Any "unknown" such as this, is unacceptable as this sign are known signs of a potential failure mode.

To prove the certainty of safety requires removing the uncertainty. DWR knows there is an uncertainty as they have officially requested from FERC to place this test well at 670' in the hillside to try to figure out the cause. DWR wouldn't do this if they felt it wasn't an issue.

[EarthResearcher333]

OR, if you wanted to bypass (1) through (7), get a Canadair CL-415 fire fighting water bomber to unload dark green paint on the whole backside. Then nobody would know the difference. :-) /s

[meyer]

How about a giant pool liner! :)

LOL

[EarthResearcher333]

Pool liner...lol.

When I was younger, my brothers & I dammed a small cold water mountain creek next to our camping property (family privately owned). Used round boulders to build the base then placed black plastic liner on the upstream side. We left an "overtopping control" section in the center a few feet wide.

We quickly learned that we could not safely walk through this center section. That water was near ice cold & you didn't want an instant bath. So we learned to walk/wade around it in the center area.

The trout fishing was amazing. But the yellow jackets AND hornets were pesky. The river valley was named "Twisp", which is an indian translation for "you see 'um many bees" (I forgot the exact wording but it was a name associated with bees).

The bald faced hornets are "meat bee" machines. We once forgot & left a fresh trout on the picnic table. Came back in a few hours and only a perfectly picked clean skeleton remained. Sheesh.

Our entertainment was watching the bald faced hornets attack and eat the yellow jackets. It was interesting as the yellow jackets were more maneuverable, yet smaller, but they would gang up on the hornet if it attacked a fellow yellow jacket. The hornet would hover & wait for a yellow jacket to wander by & then it would attack. We built a homemade 5 gal bucket bee trap (oil layer on water fill with a hanging piece of ham slice). The yellow jackets would gorge until they fell into the oil surface. So many bees died that the layer was almost 3 inches thick (yes there were that many ground nests all around). Once the population of the yellow jackets were greatly reduced, the hornets had the upper hand. They would capture, sting, then take the yellow jacket to a pine tree, hook one of its legs on the pine needle junction, and hang upside down as it ate the bee. You would see the yellow jacket's wings flutter down as the bee was consumed. Then the hornet would go back down a inch or so off the ground to hover and wait for another victim. Bee wars.

btw - Safety tip: You had to search out the area for any underground nests if you had to make a momentary "pit stop".

[janetjanet998]

judging by the NWS river forecast at Gridley...it looks like they are going to turn the spillway back on Tuesday....the lake will be not be as high as the start of the last spills

then I assume they will run the lake back down to 835ish then thats it for the main spillway

[Ray76]

You're way ahead of me. :)

I was working on this chart before being interrupted by a Kentucky Derby get together.

I wanted to see when there was low precipitation and high lake levels, and when there was high precipitation and low lake levels. In other words, does the occurrence and size of the green area correlate with precipitation or with raised lake elevation.

Aside from a few spikes in precipitation, between April 2011 and November 2014 there was persistently high lake levels and relatively low precipitation. This is particularly true between January 2013 and January 2014 when there was a drought and high lake levels.

It would be very interesting to examine the status of the green area during this period.