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  1. StickyMockwell

    StickyMockwell New Member

    By doing a simple water balance with the observed inflows and outflows, I’ve had a look at what the reservoir water level would have been without the main spillway temporary shut down and reduced outflows through 7-9 Feb. (I must admit I needed a small fudge factor to get the predictions to closely match the observed reservoir water level.)

    In the chart below, the continuous lines show the actual observed water level (blue) and outflow (red). There are then two alternative options looking at amended reservoir outflows (the dashed lines): (1) just fills in the 7-9 Feb shutdown gap at around 60,000cfs; (2) shows a more aggressive ramp up to 100,000cfs. The results show in each case the peak reservoir level is well below the emergency spillway level (900ft): with (1) just below 890ft; or with (2) below 870ft.


    In summary, unless either (a) there is a storm with much more rainfall than experienced in early February or (b) the main spillway becomes compromised and has to be throttled back, it seems unlikely the reservoir level gets near the emergency spillway crest.

    Attached Files:

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  2. Old Peter

    Old Peter New Member

    New member here, first post. I hope this ends up at the appropriate place and is useful.

    An engineer blog ( suggested this resource:


    In spite of first appearances the author is not just another talking head blatherer - he attends the news conferences and interviews DPW staff, asking very good questions I have not previously seen raised.
    E.g. Presuming the key to keeping control is the main spillway and assuming it will suffer no more catastrophic failures, the key to its operations is its gate array. How do they run? (Answer: electric motors. ) Electricity from where? (PGE mains, but they are down.) Backup? (Some sort of generators, but here the answers became less than forthcoming).
    Immediately calls to my mind Fukushima where all would have been fine had the tsunami wall around the backup generators been sufficiently high.
    He answers another question I have not seen dealt with: the hydropower 12-16,000cfs flow cannot resume until the channel below the main spillway is cleaned out and until the generator connections to the grid have been repaired (water flow turns turbines which turn generators which must be on the grid when generating).
    Amazing how interconnected things turn out to be when they go ahoo. For want of the nail...

    Metabunk is a fine resource. Thanks Mick et al.
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  3. okcrum

    okcrum New Member

    There are several possibilities for the apparent discrepancy:

    - measurement loss or inaccuracy plus accuracy loss due to computational rounding or truncation
    - time offset of the measurements
    - time lag of measured effects (example: the lake level is not constant; it's slightly higher at the inflow areas)
    - fudge factors such as the estimates for ungaged inflow
    - combinations of any or all of these

    It's probably better to note the level at the dam face and correlate with the inflow/outflow trends.
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  4. CRM114

    CRM114 Member

    Nice work. I had to use a fudge factor as well when looking at inflows vs. outflows. Any chance that fudge factor was about 5000 cfs leaving the reservoir unaccounted for?
  5. Pablo712

    Pablo712 New Member

    I’m engineer and I work in generator business here in Argentina.

    Don’t have to worry about power; you don’t need Mains power grid, you don’t need the dam’s turbines. With just 2 or 3 small diesel generators you are ok.

    Fukushima needed a constant and reliable power to maintain the pumps that refrigerates the cores. And you needed all the pumps working 24/7 to cooled down those nuclear cores that they were not designed to go off grid in a second.

    Here you only need power when you want to move a gate position (only when you want to change the flow rate of the spillway). And those gates are moved surely by independent “small” electric motors (100-200 HP max I think). Easy manageable with diesel generators. In the hypotetical case that the 3 generators fails, you have time to move another one by truck or helicopter.
    No a matter to worry about. A side of those 100 heavy machinery and helicopters working reinforcing the emergency spillway, a couple of diesel generators are only a small dent in the emergency bill.

    But…. Below the dam, there are a very expensive 820 MW worth turbine-generators that you don’t want to lose in a flooding. And also, in a dam water is money, you are letting water go down the lake without generating any power (aprox u$s 40 million a month for that power).
    That’s why the rush work in the “dam side” to get those debris cleared, lower the river level, not damage the turbines get them working as soon as possible.
    Last edited: Feb 21, 2017
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  6. whoosh

    whoosh Member

    Key to persistent daily briefing statements that they're going to continue armoring the emergency overland flow route until they don't need it any more.

    It'll make a great medium for the paint artists for the next several years. :)
  7. whoosh

    whoosh Member

    Often this is how we can measure the error inherent (uncertainty) in our observations (measurements); something which always exists and is very important to us measurement scientists.
  8. DirtyLaundry

    DirtyLaundry New Member

    I've wondered the same.

    I've been looking all over for a description of the ORO gages and how they work (also looking for the "Flood/Water Control Manual"). As a non-expert (engineering degree with no experience in hydrology), I don't believe there exists an inflowometer. The gage locations shown on CDEC's map are at the dam or thermalito diversions, not places to directly measure inflow. Inflow could be calculated from storage changes and outflow. Storage is a reasonably straightforward calculation from measured reservoir height (or water pressure). Outflow can be calculated from river stage (height). River stage will be influenced by extra sediment in the channel. My proposed model here is a useful thought model, but likely too simple and incorrect in several details. I believe they use a more sophisticated calculation involving more actual measurements and a smoothing function (math function such as a more specialized version of rolling average).

    Seeing the variation in the inflow graph during and following use of the e-spillway, I see some inconsistencies. First, it's not clear to me that the outflow over the spillway is accounted for. There appears to be a dip below trend from Feb 12-14. Evening of the 12th shows a sudden dip in inflow. On the 13th, the inflow data is plain missing. I believe it went out of range and an algorithm (possibly a human) just excluded it until it looked 'normal' again. The inflow contains a lot of 'noise,' and the noise looks different following the e-spillway use.

    The variations in inflow noted above do not match my conception of normal streamflow behavior. They do however match the behavior seen in algorithmically derived data in the face of unexpected input conditions. I could speculate wildly about which input changed and why the change discombobulated the algorithm - e.g. the sudden big outflow change or added sediment.

    Notes about inflow this study (, indicate the complexity of calculating the inflow, and point to measurement errors of 5-10%. It also suggest errors may be worse at high flows.
    bold my emphasis.
    Quotes from page 15.

    Conclusion: It's complicated, and there is some measurement error.
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  9. BrokenLug

    BrokenLug New Member

    Well the good news is at least there won't be a lot of new precip introduced into this drainage basin over the next 6 days. Doing all the necessary repair work that needs doing is always easier to do when it's it's not pouring rain outside. :)

    02-22_6 day QPF.
  10. StickyMockwell

    StickyMockwell New Member

    As I said on the previous page (post #160), inflows are likely calculated by summing upstream gages and adjusting for ungaged areas. As to how flow gages work, the USGS website describes this quite nicely (

    Note: stage means water depth
  11. StickyMockwell

    StickyMockwell New Member

    Yes. I crudely increased the inflow by 7% to get the volume balance right (average of around 5000 cfs). As others have noted, there will always be uncertainty (margin of error) in the recorded inflow, outflow and storage volume values. Despite the number of significant figures used in the data tables, we can't expect 100% accuracy.
  12. CRM114

    CRM114 Member

    There are physical reasons as well. Some reservoirs seep to deep groundwater, and there is some evaporation. 5000 cfs is a lot of that, though. To rule out evaporation:

    For Oroville, it's around 40 mm in Feb:

    Table is mm of evaporation:


    For 15,800 acres:


    that works out to only 34 CFS. 5,000 CFS of seepage is a little frightening in my experience - I hope it's not that.

    I thought the outlet works at the dam are down, but it could be that as well.
  13. Mick West

    Mick West Administrator Staff Member

    I get my water from a well here in Shingle Springs, like most people not in town. People are always talking about their wells, and how the water here is in fracture zones, not in permeable sand, and that it's basically flowing through relatively large cracks in the rocks. As we've seen, the rocks round there (and here) are pretty prone to fractures. So maybe it's more like natural underground leakage than seepage.
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  14. Brent Loken

    Brent Loken New Member

    There was a post further up the thread regarding statistics on past rainfall data. I'd like to point out that rainfall statistics are expressed in IDF (intensity duration frequency), or point precipitation frequency, curves which can be found on the NOAA NWS website. This is what engineers use as input to models which predict design flows and flood levels.

    Below are the curves for a point just upstream of the Oroville dam. Probabilities are expressed as "recurrence interval" or return period. You can see from the curves that the maximum amount of precipitation intensity over a 7 day duration for a typical year (1 year return period) would be 10". Once in 10 years you would expect twice that, 20", and once every 100 years you would expect 30" over 7 days. Although the season totals for precipitation are high, the recent storms individually have not really been exceptional. But if the 10 year storm came through, do they really want to run the damaged spillway at more than 100,000 cfs ? Seems prudent to manage the lake level down a bit lower than they might have otherwise.

    Last edited: Feb 22, 2017
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  15. BrokenLug

    BrokenLug New Member

    It does appear that this neck of the woods is heading in the correct direction precipitation wise.

    24 hour precip.

    02-23 6 Day QPF.
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  16. harkin

    harkin New Member

    As a side note to this season's epic CA weather, Mammoth Mtn (east of Yosemite) just passed 500" of snow (510" as of yesterday).

    They've only had seven 500"+ seasons since 1970 but they weren't all decades ago, two as recent as 2009/10 (557") and 2010/11 (668") but I'm pretty sure they've not reached 500 this early in the season since they started keeping track. One thing of interest is that of the seven 500+ seasons, six were in back-to-back pairs (81/82/83, 85/86/87 and 09/10/11). Makes one wonder if 2017/18 will be another big water year.

    By contrast their worst (lowest) year was the drought of 1976/77 at 94", about 80" less than the recent drought season of 2014/15.
  17. Mick West

    Mick West Administrator Staff Member

    Yeah, they actually have too much snow

    For some perspective on the Sierra Snowpack, this is one of the ski lifts today.
    © miles weaver

    On a good year they try to stay open until 4th of July. This year they announced "maybe later" - i.e. skiing until mid-late July.

    This just shows the challenge facing Oroville. Even though the rain/snow tapers off in April-May the snow run-off can go through July-August5, and then it starts raining in Oct-Nov
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  18. whoosh

    whoosh Member

    I think the power plant can handle the melt season; leaving the spillway dry.
  19. BrokenLug

    BrokenLug New Member

    Well it still appears that the precip in the "oroville drainage" will be minimal in the 6 day near term.

    Thanks for starting all of these threads (the powers that be) and to all of the contributors.

    For me it was a very informative, level headed, non-BS and thorough discussion of this event.

    02-24 6 Day QPF.

    I'll be checking out this forum in the future. :)
  20. Anna Reynolds

    Anna Reynolds Member

    I have noticed over the past few days that the CDEC data for ORO has been especially variable and wonder if it might shed some light on what points they are actually physically measuring and what may be derived from equations. You can see from this screen shot that there are release schedule changes planned, but the outflow numbers do not change after those hours come and go. This has been the case for a couple of days now. I wonder if this is because the gates need to be opened further as water level drops to maintain the same cfs of outflow. I have also noticed that inflow records have been more erratic than usual. I don't think any of this is cause for concern, only that it may show that some of these numbers may be more precise/literal than others. Screenshot_2017-02-26-23-20-40.
  21. Anna Reynolds

    Anna Reynolds Member

  22. whoosh

    whoosh Member

    That IS the easiest and most direct and most precise way possible :)
    No complexity whatsoever. Flow rates are more complicated.
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  23. whoosh

    whoosh Member

    For those of us looking at inflow projections, CDWR publishes a monthly long term outlook, from which the 1 February report (issued on the 8th?) shows the following, inserted here now so that we can also compare it to the forthcoming March outlook. [or the actual Feb inflows, if somebody wants to go through that exercise]

    Water-Year (WY) Forecast and Monthly Distribution
                        Oct                                            Water      80%      WY
                        thru  Feb  Mar  Apr  May  Jun  Jul  Aug  Sep   Year   Probability  %
                        Jan                                                      Range    Avg
    Feather, Oroville   2756 1000 1150  890  840  420  180  115   99   7450  6035 - 10355  169
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  24. BrokenLug

    BrokenLug New Member

    It does look like it's going to get a little bit wetter in the drainage in the next 6 days anyway ..

    02-28 6 Day QPF.
  25. whoosh

    whoosh Member

    Here are the new numbers for March:
    				   Oct											Water	  80%	  WY
    				   thru  Feb  Mar  Apr  May  Jun  Jul  Aug  Sep   Year   Probability  %
    				   Jan													  Range	Avg
    Feather, Oroville   2756 2920 1025 1030 1035  540  225  130  114   9775  8905 - 11445  222
    in thousands of acre-feet unimpaired runoff forecast for each of the next several months

    More searching would be in order to see if this projects new rainfall in addition to existing snowmelt.

    With a bit of mathematical modelling, this inflow information combined with anticipated outflows would be sufficient to model future reservoir surface levels (probability ranges) through the summer in order to provide levels of confidence in anticipating the need for either spillway.

    Edit: can't get the columns to line up this time. Use the source.
  26. whoosh

    whoosh Member

    Wow. Twice a day! modelling at CDWR per
  27. Mick West

    Mick West Administrator Staff Member

    Wow what? That seems like a reasonable frequency to keep up with the weather and the inflow trends.
  28. Mick West

    Mick West Administrator Staff Member

    Snow melt is now a significant factor. The weather had been very warm here the last few days.,Longitude;+City,ST;+or+Station+ID&var=ssm_melt_48_d&dy=2017&dm=3&dd=14&dh=5&snap=1&o1=1&o5=1&o6=1&o12=1&o13=1&lbl=m&mode=pan&extents=us&min_x=-121.69166666667&min_y=39.333333333329&max_x=-120&max_y=40.633333333329&coord_x=-120.84583333333501&coord_y=39.983333333329&zbox_n=&zbox_s=&zbox_e=&zbox_w=&metric=0&lp=1&palette=1&title=1&width=1000&height=768&nw=1000&nh=768&h_o=0&font=1&js=1&uc=0

    That's a two day forecast. Looks like about 2/3 the watershed is in the 0.39 to 1.4 inches range, so let's say 0.8". So maybe 0.5" equivalent over the whole area, 0.25" per day rain equivalent. Backing up to my older calculations, that's very roughly three feet level rise per day, or, very roughly again, 20K cfs inflow.
    Last edited: Mar 11, 2017
  29. Anna Reynolds

    Anna Reynolds Member

    I emailed the CDEC helpdesk ( with an inquiry about how "Infow" at the Oroville station is calculated and received this response:

    "The inflow is primarily calculated using the change in reservoir storage, lake evaporation, and reservoir releases.

    Too difficult to measure inflow based only on upstream gages."
    Last edited: Mar 13, 2017
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  30. SR1419

    SR1419 Senior Member

    Looks like things are turning wet again next week and beyond and this doesnt take into account snow melt at 6000ft and below.

  31. Anna Reynolds

    Anna Reynolds Member

    Lake Davis is one of the resevoirs that feeds into the Middle Fork of the Feather River, and ultimately Lake Oroville. Its spillway, at the Grizzley Valley Dam, has been flowing since the 21st. This is the first time the spillway has been used since 1996, and DWR just announced that outflows are soon expected to increase.

    Not likely to cause a major change to Lake Oroville, but it will be interesting to see how this, and the next storm coming tonight, affect the delicate balance of Inflows and Outflows. I imagine the spillway will be running for at least a few more days.
    Last edited: Mar 23, 2017
  32. David Jensen

    David Jensen Closed Account

    SR1419: Built the attached .xls rough model on the weekend and used 2' [feet] of accumulated water equivalent in the Oroville Dam catchment as an estimate. Your map seems to indicate that this is approximately correct.

    The model indicates that the Oroville Dam needs to exhaust 40,000 cfs for ~ 50 days (24hr periods) this spring to pass the accumulated snowpack in the catchment when it melts. The spillway condition does not look great at this point given the initial engineer's report:

    Attached Files:

  33. David Jensen

    David Jensen Closed Account

  34. Joe Hennessey

    Joe Hennessey New Member

    There were several dry years before the great flood of 1861/1862. Afterwards there was drought. But the year following a flood need not be dry.

    There are indications that a new el Nino will develop this year. For example,
    Forecasters in the southern hemisphere seem more excited about it, but it is early yet.

    If so, next year will not be dry. During an el Nino, usually southern California gets the bulk of the precip. For planning purposes one might assume the Feather River area will get 103% of normal. Jan Null is a good source of information ( ). The column labeled 8SI is the 8 station northern Sierra Nevada Index and is the column you want to look at.
  35. harkin

    harkin New Member

    At Mammoth Mtn ski area from 1970 to 2015 they've had seven seasons of 500"+ snow.

    SIX of those seven were in back-to-back winters (81-83, 04-06 and 09-11).

    The current season is at 540" and counting......maybe this will be another set of back-to-back big winters.....?
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