"During the 3 months in 2011 that lake was at this 890’(+) stage, thousands of people drove over the dam to get to the boat ramp."..."No one registered much concern about it at the time."...."This (apparently) wasn’t an issue at the time."
Why are you making these inferred assumptions? (thousands driving over & no one registered much concern about it at the time) & (This (apparently wasn't an issue at the time)?
I'm not intending to be adverse, but just curious. What documentation do you have that supports these statements? Or is this just discussion "what if's" context of a form of speculation?
First - "hysteresis", as used in the prior upthread discussion was strictly in the greening or death of the plant itself. Perhaps I could have made that distinction more specific in my writing as it was "greening" - could be interpreted as specific or in general. The greening or death of the plant, I was intending to describe, is based on the localized state of hydration, soil nutrition, sunlight, and including summer heat (infrared absorption of zone fill region surface temperatures + direct spectral light to plant + atmospheric temperatures + aridity). At a certain threshold, the plant will degrade and turn brown.
As far as "890'(+) 3 month stage" and "thousands" and "no one registered much concern".
IN fact DWR DID note the most documentation I have run across to date during this exact 3 month window in DSOD documents: "Lush grass and weeds covered this area", "The ground remains wet..". They even revealed that they were trying to figure out the "water source".
DWR/DSOD's two leading theories in their discussions were (1) possible mechanism causing "perched rain water" to gather in this localized area, (2) a possible "abutment seepage source" (aka "natural spring" theory). They even researched construction archives and found that during original construction it was noticed that there was some seepage "wetting" in the left abutment.
But their words are revealing, they say "Another possible source could be an abutment seepage..". They didn't know, but they were surely trying to figure this out. DWR - DSOD's 2011 documents have had the most revealed information than the other remaining years regarding the wet area notation & engineering discussion.
If you read carefully, (docs below), DSOD showed their concern of the risk factor this posed in noting that they need to "monitor the area for unexpected changes in the seepage pattern or flow quantity". This is the very first valid "alarm", albeit low key, of the risk they knew an "unexpected change" could mean - a failure mode may be developing.
Yet none of the posited theories has been able to explain the uphill angle away from the abutment in a highly linear longitudinal structure. Source water speculation is one thing, but fluid flow hydraulics does not operate in a highly linear longitudinal alignment structure, besides the fact of an upward elevation formation away from the abutment.
DSOD Feb 2011 Inspection report - "damp to wet".."no moving water was observed" - "cause".."yet to be determined" - "could be an abutment seepage".
DSOD May 2011 Inspection report 1 of 2 - "Lush grass and weeds cover this area" - "The ground remains wet, but no active flow was observed".
DSOD May 2011 Inspection report 2 of 2 - ""staff should continue to monitor the area for unexpected changes in the seepage pattern or flow quantity" - KEY POINT: 100% of Piezometers are admitted to be non-functional as the last 3 are considered useless.
Good tidings EarthResearcher333. Thanks for your many thoughtful and well documented posts.
In regard to my post 3574, you ask:
“Why are you making these inferred assumptions? (thousands driving over & no one registered much concern about it at the time) & (This (apparently wasn’t an issue at the time)?”
Admittedly, these are just assumptions. However, I’d classify them as more “informed” assumptions than “inferred” assumptions. Either descriptor applies.
I’ve done a lot of boating in California and have been on many lakes, although I avoided Oroville, partly because I’ve always heard it was too crowded. The day use boat ramp north of the dam is 13 lanes wide with hundreds of parking spaces. If they had just 20 boat launches a day during this 3 month period in 2011 when the lake was higher than its ever been, at 2 people per boat, that translates to “thousands” of potential dam observers. I don’t have the actual traffic counts though.
Northern California is generally green in February, drys out by May, and is universally brown by August. A wet or green spot would definitely stand out in August, but not so much in February or May. I have never known fellow boaters to take notice of a green area on any dam in August, or heard of it on social media. It is my assumption that they would have taken notice of this, and records of this would have come out by now. But that is a rather speculative assumption.
If the “green spot” water is originating from the reservoir, then the flow rate into it must be a function of the reservoir level. As Ray76 pointed out, this is key to assessing where this water originates.
The DSOD report from 2/2/11 you cited says “the area ranged from damp to wet”. On that date, the lake level was about 826’ according to DWR. The lake level didn’t get down that low again until January the following year, so the same flow rate or more should have been sustained across this period.
The DSOD report from 5/18/11 you cite says “the ground remains wet” with “lush grass and weeds”. At this time, the reservoir was about 887’, 60’ higher than the February report. The green spot would have had quite a bit more head on it, but significantly greater flow was not apparently observed.
Now if we had a report from August through October 2011, that still said this area remained wet and green, then it would be reasonable to conclude the only plausible source of water would be the lake.
Another key thing to assess is how the vertical channels below the wet spot got formed.
At some point in time, this wet spot must have been flowing sufficiently to generate these multiple erosion channels, many of which (I’m assuming) would be flowing concurrently rather than sequentially. It takes a lot of flow to push a steep cobble embankment aside rather than perk back into it. That peak flow event must have been at peak lake level, if the water originated from the lake. The longest sustained peak lake level (+890’) was the summer of 2011, when (I’m assuming) no one noticed these channels being formed.
Now it could be a plausible assumption that this peak wet spot flow, associated with peak lake level, might have evaporated away when perking out on to the hot SouthWest face of the dam in the summer. However, even in the summer, it can get kind of chilly at night. I find it hard to believe that a flow rate sufficient to erode multiple channels down the face of a cobble embankment would just evaporate away through the night every night for months on end. That doesn’t seem plausible to me, but I could be wrong.
If those erosion channels were initiated by high lake levels, then why would they stop eroding as long as the lake was high? Once there is sufficient pressure and flow to push the surface materials aside, wouldn’t that process cascade until the dam collapsed? Unless that flow originated from a much more limited source, like a rain fed groundwater channel.
Upthread, a thousand or so post ago, I thought it seemed plausible that the wet spot water was originating from the reservoir. However, upon reasoning this out, it now seems more reasonable to me that this water originates from some underground channel or other rain induced source. Obviously, no one, including DWR knows what that source is at this time. It is an issue that should be investigated, and then mitigated. But I think the imminent threat of a Teton Dam style failure seems minimal, at least until the next rainy season. I’m downstream of the dam, so I do care about these things.