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  1. EricL

    EricL Member

    This isn't the first place I've mentioned this, but in actual fact, there is no way to stop water in the spillway from getting under the slab. There will always be cracks, In the very best of circumstances, there will only be cracks at all of those saw-cut joints (control joints). So yes, when you see water dribbling along the slab and then disappearing, so the slab is dry downhill of the crack or joint, that's perfectly normal and unavoidable.
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  2. wrorke

    wrorke New Member

    There is no flow from the drain on the right wall adjacent to where the hole opened. That would imply the pipe to the wall outlet was either blocked or disconnected. A simple blockage would merely increase flow at the other outlets. A disconnected pipe would release water in the area around the break. Such a condition could undermine the slab in that vacinity. It would be of interest to know how long ago (months or years) that outlet stopped flowing when the others were flowing.
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  3. Scott Gates

    Scott Gates Active Member

  4. Mick West

    Mick West Administrator Staff Member

    They said one reason why - to make it easier to move the debris pile at the base of the main spillway that is blocking the pool, and raising the water level at the Hyatt power station - which is in some danger of being inundated. They are staging ramps, heavy equipment, and rafts around the corner to do this.
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  5. Scott Gates

    Scott Gates Active Member

    The base of the ogee weir has drain channels cast in it. Additionally a rubber mat was specified for subgrade sections on the reservoir side of the weir in drawings.
  6. EricL

    EricL Member

  7. Jeff Semenak

    Jeff Semenak New Member

  8. Scott Gates

    Scott Gates Active Member

    Water officials also stated they have to scale back flow when level gets to the TOP of the main spillway intake cut on reservoir side. Once to that elevation they are intaking only thru the narrow spillway intake channel and high rates thru the narrow channel can cause erosion damage. I haven't checked exact - but somewhere around 860 I believe is top of intake cut
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  9. CACapitol

    CACapitol New Member

    This is a couple cropped screen shots from a DWR drone flyover at the beginning of the week which shows the damage done to the downstream face of the auxiliary spill way. I am unable to tell if the depth of the erosion in front of the concrete is greater than the 6ft design description.
    These are a couple cropped screen shots from a DWR drone flyover early in the week of the damage done to the downstream face of the auxiliary spillway. I am unable to determine if the depth of the erosion in front of the concrete is greater than the 6ft design description but if water continued to flow over the toe, eventually there would be enough of a water fall to start cutting back underneath the auxiliary spillway. Also, I don't see bed rock directly underneath/against the spillway toe but the pools of standing water in a few places could be an indication of bedrock at those depths, perhaps?

    Attached Files:

  10. Scott Gates

    Scott Gates Active Member

    Power plant intake can draw down to 640' I believe ....
  11. EricL

    EricL Member

    This is yet another post where a logical idea about how those drains work is relevant. The gist of that idea is that there will always be water forced beneath the slab during times of flow, and the drains are there remove it, as described here, from post #775:

    "After I talked with a soils and foundation engineer about the drain system, I (or we, since I agree with the engineer's idea) believe that it's a system designed to transfer water from under the slab back into the spillway. Since any volume of water tends to settle to having a level surface, fully-flooded conditions beneath the slab would result in that water, upon flooding the backfill behind the walls, being at the height of the drain outlets in the wall at some distance down the hill. The result is that each of those drains is removing water from beneath the slab which is at that same level, but higher up the slope. The conduction vessel for that water would be the backfill of the retaining walls on each side. The result of having this series of drains along the length of each wall would be a sloping, or perhaps slightly stair-step pattern of the water elevation within the retaining-wall backfill along the length of each wall. The bottom line is that it seems that a system was put in place to keep accumulated water from developing the enormous head pressure which otherwise could develop beneath the slab at greater and greater distances down the slope, since the head pressure at any given location would be only that of the height of the nearest wall drain."

    So, if this idea is correct, and I'm sure it is, there are no drain pipes present. The water flows through open-graded backfill behind the retaining walls (I'll find a picture of that. I've seen it once already). What I am certain that you are seeing, in the case where that one drain is not running, is that the water coming down the hill below and on each side of the structure, which would have flooded the wall backfill to the height of the drain at that location and exited there, simply dropped down into the void spaces beneath the floor and within the highly weathered bedrock at that location, leaving that particular drain high and dry. The next drain down the hill was flowing at that time, either because water passing beneath and alongside the part of the structure which did not initially fail was finding its way there, or because water which dropped into the weathered-rock area again found its way to an under-slab situation where its downhill flow path was intercepted by the downward-sloping slab, or both.
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  12. CACapitol

    CACapitol New Member

    A relief well discharge pipe perhaps? I watched this video a few days ago on seepage and piping in dams.

    Source: https://www.youtube.com/watch?v=AhpMyq4ZV2k
    The possible explanation is around the 28:00 minute mark.
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  13. Scott Gates

    Scott Gates Active Member

    The "toe" you see exposed at grade is not necessarily the actual cast toe of the weir. The apron or "toe" is 12' wide ... so the exposed face in this shots is clearly less than 6' in all of them.

    More importantly though as the shot below shows, the apron you can see is poured alongside the face of the weir ... rising along the weir as the land in front of the weir rises the further away you move from the main spillway.

    The toe is cast as a part of the weir and sits on the foundation bedrock. The foundation would be flat as would the toe. They then would pour concrete on top of the toe to match the ground height desired.
  14. Junkie

    Junkie New Member

    Yes, it can draw from far deeper than the spillway. However, if the spillway stops flowing the sediment will settle roughly where it is, leading to more blockage of the power plant outlet vs running the water longer at a lower flow rate (or at least that's what I seem to remember).
  15. CRB93

    CRB93 New Member

    I immediately notice no water coming from the side drain adjacent where the hole developed. Right side.
  16. CRB93

    CRB93 New Member

    My guess is those drains aren't connected to pipes. The lack of water suggests it is draining elsewhere, like into a hole under the slab.
  17. aczlan

    aczlan Member

    As I understand it, the spillways were not blasted, they were ripped with D9 Caterpillar bulldozers, then they cleaned out the loose rock:
    Aaron Z
  18. edi malinaric

    edi malinaric New Member

    Thanks Scott - missed that - makes sense

    cheers edi
  19. Mick West

    Mick West Administrator Staff Member

    You can't just let the dam rise to two feet above the emergency spillway to see what happens. That's essentially what happened here - and it was a near disaster. A test would be uncontrolled because it would take many hours to lower the level of the lake.

    Those were both emergency spillways in addition to the normal spillways
    I mislabeled the image though, the ravine is shared by both spillways. The emergency spillway at New Don Pedro is basically the same as in Oroville - a long weir next to the main spillway gates.
    This one at least has been used:

    The New Melones Dam's spillway is just an unlined and ungated overflow emergency spillway
    The spillway does not seem to have been used much, if at all.
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  20. EricL

    EricL Member

    Your reply was to this statement of mine:

    "This isn't the first place I've mentioned this, but in actual fact, there is no way to stop water in the spillway from getting under the slab. There will always be cracks, In the very best of circumstances, there will only be cracks at all of those saw-cut joints (control joints). So yes, when you see water dribbling along the slab and then disappearing, so the slab is dry downhill of the crack or joint, that's perfectly normal and unavoidable."

    In that post, I was talking about water getting beneath the slab of the normal spillway, and you are talking about the weir of the emergency spillway. These are two different structures with entirely different designs. The only relationship between your topic and mine, is that in both situations, the water beneath the structure must be given an exit path. That method of drainage in the two cases is completely different.

    I thought it best to clarify that.
    Last edited: Feb 16, 2017
  21. Clare Krishan

    Clare Krishan New Member

    Last edited: Feb 16, 2017
  22. Clare Krishan

    Clare Krishan New Member

    except for the vast horizontal separation of the exiting flow -- they're cheek by jowl at Oroville (as shown in my schematic when I can post it, thx moderator from prompt approval)
  23. Scott Gates

    Scott Gates Active Member

    Thanks ... I was prob responding to a different post ;-)
  24. Mick West

    Mick West Administrator Staff Member

  25. Last edited: Feb 16, 2017
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  26. Scott Gates

    Scott Gates Active Member

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  27. Scott Gates

    Scott Gates Active Member

    Update …

    In the 92 hours since last Sunday afternoon when they upped the outflow rate to 100,000 cfs, officials have dropped the level from 901.65 to 866.75 – a drop of 35 feet. They have released 524,312 acre feet over 92 hours …
    Total capacity 3,537,577 minus current level 3,039,414 equals 498,163 current available capacity. That number will increase as they continue outflows.

    The avg outflow last 24 hours is appx 6100 ac ft/hour – at 100,000 cfs. Operators have enacted a planned reduction to 85,0000 cfs – due to levels reaching the top of the main spillway intake channel cut – so as not to cause erosion in the intake channel.

    Flood control elevation 850
    Capacity at 850' 2,808,349
    Maximum capacity at 900' 3,537,577
    Reserve at 850 729,228

    Current Elevation 866.75
    Current capacity 3,039,414
    Current reserve 498,163

    Estimate in/hr at 85,000 cfs 4.17 inch/hour
    Est time to 850' at 85,000 cfs 48.16 hours

    (as of 1PM PST - 2/16/17)

    During the major rainfall event in early Jan 2017, I believe appx 15 inches fell in the area. During the appx 18 hour peak inflow period on 1/8 and 1/9 inflow rates averaged appx 135,000 cfs with a peak of appx 155,000 cfs.

    Significantly increased inflows (60,000 cfs and higher) ran from the morning of 1/8 thru midday 1/11 … reservoir level was appx 793′ on 1/8 and appx 842 midday 1/11 … an increase of appx 49′ … or appx 676,740 acre feet.
    There was no appreciable outflow during this entire 3 day period.

    We currently have appx 500,000 acre feet of storage available – and should have more than 700,000 by Saturday.

    There is currently enough storage to handle nearly 75% of the inflow from the current storm … and even IF it is as STRONG as the January one … in the next 48 hours there should be enough available storage capacity to handle 100% of the inflow from a 15″ January type super storm … without running the spillway at all.

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  28. SeanT

    SeanT Member

    As of 3 PM DWR has lowered it to 80,000 CFS and plan to leave it there.
  29. Scott Gates

    Scott Gates Active Member

  30. deirdre

    deirdre Moderator Staff Member

    Last edited: Feb 16, 2017
  31. yellowsubmarine

    yellowsubmarine New Member

    I don't know about the area rainfall but just over 6 inches fell at the dam from January 7-10.
  32. Clare Krishan

    Clare Krishan New Member

    I agree that the "gap" in the photo I cited corresponds to the engineered concrete lip on the image you cited. How do we known where the actual profile of the land is? Where does the legacy elevation 900' bedrock end and where does the engineered 812.6' bedrock bed of sluice begin? What is the topological difference comprised of -- rammed earth infill / concrete / cement grout ?
  33. deirdre

    deirdre Moderator Staff Member

    youre over thinking it. just find a photo of the exposed reservoir side of the spillway, taken at approximately the same angle and compare. Otherwise you are just banging your head against a wall.

    Please use modifiers here at Metabunk. Say "possible erosion", not "erosion", unless you can absolutely prove (or have statements from DWR) to teh erosion claim. We do not want to spread misinformation at Metabunk.
  34. 6850

    6850 New Member

    CK -- here's an old USGS topo map with dam fixtures superimposed. You can see where the original surface of the ridge was, and make an educated guess as to how far below the surface the bedrock lies. You can see that the south side of the main spillway is embedded in the top of a knoll that exceeds 900', while the north side is well into the saddle. But the soil surface was still at 875' at that point (on its way down to just above 850 at the bottom of the saddle).

    20170215_NewLabelsOldMap. More images like this on previous page, current thread.
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  35. Don Turner

    Don Turner New Member

    And as a corollary to that, those highway slabs were notorious for rocking under the continued repeated truck loading. Most have since been replaced with CRCP (continuously reinforced concrete pavement), or by edge doweling.
  36. wrorke

    wrorke New Member

    In a picture in the Main Thread https://www.metabunk.org/oroville-dam-main-spillway-waterfall-erosion-watch.t8402/page-2#post-200784 you can see the end of a pipe running behind the sidewall and draining. That is evidence of a pipe.

    Further, there are several pictures showing very high flows through the sidewall openings -- that indicate high pressures on the backside. Given the relatively shallow depth of burial of these openings (the backfill surface appears to be on the order of 10-15 ft above the openings) the maximum hydrostatic pressure based on the distance from the backfill surface would be perhaps 20 psi - any higher pressure would breakout on the surface. It looks like the driving pressure on the sidewall streams exceeds that -- it looks like there is way more "head" than a mere dozen feet. I dont see how this can happen without drain pipes. (Like the one in the picture I linked.)

    Flow from a broken pipe over extended times in the wrong location could easily undermine the slab.
  37. Graham2001

    Graham2001 Active Member

    Snopes.com just uploaded an article dealing with the meme claiming that California diverted money from dam repair/upgrade to supporting illegal migrants.

  38. EricL

    EricL Member

    Your link takes me not to a picture, but to a numerical table, which for some reason I can't paste here. It's in Post#47 of that erosion-watch thread.

    I looked for pictures showing the wall backfill, and I found some interesting shots on the website for the California Department of Water Projects. Unfortunately, their photos of the Oroville Dam can't be copied, downloaded, or even linked to (links are of no use because the only links you can copy are for individual pages which have a large number of photos - there's no separate link to the individual photos). In any case, what I saw made me modify my idea of how the drain system works, specifically, that it most likely does make use of pipes. What I saw indicated that the very open-graded backfill is only present at the surface, so the kind of flow I was imagining for this system would have to be through pipes. However, one remark in your post tells me that your mental image of how the pipes are arranged is much different than mine (I'll get to that difference farther below). And one other difference between your idea and mine became apparent when I saw that, at locations where ground elevation relative to the drain outlets could clearly be seen, the drain outlets are actually just barely below the top surface of the wall backfill, and though that has no bearing on my idea for drainage, it does conflict with yours (or at least my interpretation of yours, since you stated that depth below the surface matters in some way (though you didn't elaborate as to why that might be)).

    I still envision water beneath the floor being channeled downhill to a point that the hydraulic head (from the uphill location) is higher than the drain outlet in the wall. I am expecting that there's a line running along the base of the wall, likely with cross lines of perforated pipe going under the floor for water collection. The main line along the wall would have regularly-spaced vertical branches leading up to those drain outlets in the wall.

    Water collected from beneath the floor would run downhill along the main line, until at some point, it encounters one of the vertical branches which has an opening that is lower than the supplied hydraulic head of the water that is farther up the hill, and at that point, water would flow up that branch and gush out the opening, back into the spillway.

    Your comment about the drain openings being at too slight a depth beneath the ground misses my main point (and indeed, the drain outlets I saw most clearly were at an elevation just slightly below ground level), which is that the water is actually coming from farther up the slope of the spillway, not from the surrounding land. One picture that I would have loved to copy and link from the Water Projects website clearly showed that on the upper, much-flatter part of the spillway, the first set of drain outlets below the control gates was quite far from the top (photos can be deceptive, but it appeared to be about one-hundred yards or more), and the perspective also indicated that that looked to be the first available location where drain outlets at that height on the wall would be as low or lower than the floor slab at the upper end. From that point on, the outlets were closely spaced.

    Also interesting in that photo, was the fact that the first two drain outlets on the right wall (as seen when looking downstream) were considerably higher than the adjacent land (the wall backfill sloped steeply down to meet the adjacent land). Therefore, the flow from those outlets could not have originated from the surrounding land (and I can't imagine a scenario where all the drains could run that way just based on groundwater, especially on a site that is so high and dry.

    I would like to provide a diagram of how this system would effectively remove water from beneath the floor, but I lack the tools or skills (I'm a field-tech guy, not a guy with office skills). So try to picture this. There is a long sloping pipe, matching the slope of the main spillway. This pipe has regularly-spaced vertical branches which are all the same length and open at the top end. If you fill that long sloping pipe with water, water will exit the ends of every vertical pipe that has an opening which is lower than the water at the far uphill end of the main pipe. In hydraulic principle, it's actually no different than poking a bunch of holes in the side of a bucket, with a constant increment of height change from one hole to the next (all the holes will spurt water if the bucket is full).

    To finish up, the idea that a broken pipe would erode material beneath the slab is basically correct, but I'm working on the assumption that there already is a large amount of water under the slab that wants to flow downhill, and the drain system was put there to keep that water from developing severe pressure or un-contained flow. I am expecting that the designers also would have known the risks associated with flowing water, and would have provided foundation support that is immune to such damage, like placing the concrete directly on bedrock. Finally, it most likely was erosion of foundation rock by under-floor water flow which caused the floor slab to fail, but at that location the rock appeared to be highly weathered, and more erosion-prone than anyone likely realized at the time of construction.

    Sorry for the long post, but it's hard for me to accurately put this into words any other way, and I'm kind of a geek about understanding and clearly stating basic principles.
    Last edited: Feb 16, 2017
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  39. Scott Gates

    Scott Gates Active Member

    Bedrock ... which carried all the way up to the top of ridge.

  40. Scott Gates

    Scott Gates Active Member

    "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."

    Page 133
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