Oroville Watershed Weather Forecast, Lake Level and Inflow Calculations

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Mick West

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Staff member
Note
This discussion is split from the main Oroville discussion thread, and should be focussed only on weather forecasts, hydrologic forecasts, and lake level forecasts

Some things to note:
  • The weather forecast, especially just loca rain forecast, don't tell you the picture. You need the hydrologic forecast - i.e. how much water is gong to reach the lake
  • The watershed (catchment area that drains into the lake) is about 3,600 square miles.
  • It's the average rainfall over the whole watershed that's important. 2" in one small spot is not as important as 1" over the whole area.
  • The snow level is very important, as the more that falls a snow, the less goes directly into the lake. But later higher snow level can melt the low lying snow
  • It takes some time for rainfall to get into the lake.

Resources:

DWR-CDEC Oroville Dam real time sensors:
http://cdec.water.ca.gov/cgi-progs/queryF?s=ORO

NOAA 6-Day precipitation accumulation
http://www.cnrfc.noaa.gov/precipForecast.php?cwa=STO&imgNum=1

Bucks Creek Powerhouse (BUP) sensor which gives daily rainfall totals.
http://cdec.water.ca.gov/cgi-progs/queryDaily?s=BUP

For a nice wide view of the incoming water vapor, try the GFS / Pacific Sector / Precipitable Water loop at http://weather.cod.edu/forecast/
Nam, Nam4k, and others, will have higher resolution maps of P.W., 6 hour, and total precip.

http://www.tropicaltidbits.com/analysis/models/ is also good. Their map even has Lake Oroville on it.


First rains have arrived in the area:
20170215-103740-krjfa.jpg

Should not be a problem in terms of rising lake levels for at least a day - and probably not at all if 100K CFS is maintained. Just might cause some operational difficulties - and less opportunities for good photos.
 
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Mick West

Administrator
Staff member
Another way of looking at the potential inflows.

Oroville watershed, based on original reservoir plans, and tweaked for ridges in Google Earth.
20170215-105936-ntaze.jpg

GE tells me this is 3672 square miles. Oroville Lake is 25 square miles. So the watershed is very roughly 150x the lake area.

Very simplistically that would mean if you get 1" of rain, then that's maximum 150" of lake rise (12.5 feet)

Looking at a weather station in the watershed, Berry Creek, that's six inches over the next 8 days, realtively evenly spread.
https://www.wunderground.com/cgi-bin/findweather/getForecast?query=Berry+Creek,+CA

20170215-110640-dxyaz.jpg


That would translate (and again, a very simplistic figure) to 100 feet rise over those 8 days at 12.5 feet per day.

Current 100K CFS is dropping the lake at 0.6 feet per hour, or 15 feet per day, 120 feet over 8 days.

So the level of the lake should continue to fall overall, with only some minor pauses to rise. It's at 877 now. After the storm is over, worst case it will be at 857 feet.

And I think this a very conservative estimate. For one thing not all the precipitation will fall as rain (some will be snow, which just stays on the hill for now), and some is lost to groundwater aquifers, and the actual streams and rivers take some time to get to the lake. So almost certainly the level of the lake will be well under 850 feet in 8 days.
 

Vicki W

New Member
This is what I was looking for yesterday. This storm is also supposed to be colder from what I understand, meaning more water stays in place as snow.
 
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Mick West

Administrator
Staff member
I saw a tweet say the waterflow intake was 3,222 sq miles, a bit lower than my measurement from GE. However he also said that this means an inch is 171,840 acre-feet flowing in, and this exceeds the 150K acre-feet flowing out.

However, at 100,000 cubic feet per second, that's 100000*60*60*24 cubic feet per 24 hours, which is actually 198K acre feet, according to google.
https://www.google.com/search?q=100000*60*60*24+cubic+feet+in+acre+feet
20170215-120901-wplyf.jpg

I suspect he was simply mistaking the 150K cfs standard release for 150K acre/feet. But perhaps this misconception is based on something else. Have there been acre-feet figures given for the releases?
 

alec

Member
from here on out (full season) storm temperature (can also be read as given storms snowfall elevation) matters. First case rain flows quickly to res, snow slowly (weeks, months), second case, rain on snowpack increases flow beyond rainfall amount.
Precip quantity also matters, high snow load eventually melts, flows downhill, later season gradual melting = better
 

yellowsubmarine

New Member
press conference now--they feel they can hold reservoir level as is with the first round of storms (i.e. it won't go back up); don't be surprised if they reduce the 100k cfs outflow when they can. Makes sense given they have to manage the downstream impacts too. of course, this is assuming their input models are correct and storms don't bring in more (Croyle said they expect 45k cfs coming in, which they can easily deal with)
 

Ethan O'Connor

New Member
Being situated hundreds of feet above the river has left this bedrock exposed to the elements for a million years more or less and has led to chemically weathered bedrock extending far below the surface in places while inches away horizontally is fresh bedrock.
...
There are many sections of the main spillway directly below the gates that were built on chemically weathered bedrock. With a 100k cfs flowing for the foreseeable future, with higher rates possible considering the long range forecasts, another blowout is a real possibility.
...
The emergency spillway is not auxiliary, and i don't believe any competent geologist present during it's construction would have considered its use as anything but a last ditch effort.

Strong agreement with the points in your entire post.
In addition to differential erosion following bedding planes, there are known vertically dipping shear zones in both abutting ridges that strike perpendicular to the plane of the dam and exhibit chemical weathering to 100':

...Weathering of rock approached 100 feet in depth in
the sheared zones...

The identified zones are "mid-height" on the abutments, but it's fairly clear that the geologic survey work in the zone below the emergency spillway was nowhere near as thorough as that in the immediate abutment zones of the embankment and there may be additional sheared/schistose zones at all scales in alignments consistent with the deep, rapid erosion we saw into bedrock in the new ravines directly below the weir.

Meanwhile, the 2000Z 7-day QPF actually looks worse than the setup at the start of precipitation on Feb. 5th. Here's now - the 10-15" zone lies right over the Lake Oroville drainage:



and here's at the start of the precipitation event that led to the weir overflow:



Compared to the 5th, inflows are nearly the same but there's now less than half as much storage below 901'.

Lower snow levels will help, of course, but this is not a bullet-dodged scenario yet.
 

Mick West

Administrator
Staff member
Meanwhile, the 2000Z 7-day QPF actually looks worse than the setup at the start of precipitation on Feb. 5th. Here's now - the 10-15" zone lies right over the Lake Oroville drainage:


Croyle was saying it would be a much smaller storm.

Here's a more local forecast with the watershed outlined
20170215-143208-0aczf.jpg

Looks like it will average under 1" per day over the whole area, which is manageable.
 

Scott Gates

Active Member
Another way of looking at the potential inflows.

Oroville watershed, based on original reservoir plans, and tweaked for ridges in Google Earth.
View attachment 24668

GE tells me this is 3672 square miles. Oroville Lake is 25 square miles. So the watershed is very roughly 150x the lake area.

Very simplistically that would mean if you get 1" of rain, then that's maximum 150" of lake rise (12.5 feet)

Looking at a weather station in the watershed, Berry Creek, that's six inches over the next 8 days, realtively evenly spread.
https://www.wunderground.com/cgi-bin/findweather/getForecast?query=Berry+Creek,+CA

View attachment 24669


That would translate (and again, a very simplistic figure) to 100 feet rise over those 8 days at 12.5 feet per day.

Current 100K CFS is dropping the lake at 0.6 feet per hour, or 15 feet per day, 120 feet over 8 days.

So the level of the lake should continue to fall overall, with only some minor pauses to rise. It's at 877 now. After the storm is over, worst case it will be at 857 feet.

And I think this a very conservative estimate. For one thing not all the precipitation will fall as rain (some will be snow, which just stays on the hill for now), and some is lost to groundwater aquifers, and the actual streams and rivers take some time to get to the lake. So almost certainly the level of the lake will be well under 850 feet in 8 days.

I posted a tweet earlier that said the 15" rain last time translated to appx 50' total increase in lake levels ...

You have to keep in mind that what falls as snow doesn't get released to the lake immediately ... and I'd heard they stirms may be colder than the prior ones
 

yellowsubmarine

New Member
Thanks,
Hmmn, guess it's time for a calculation on top 100' of reservoir capacity, just to file back in the databanks. That takes some of the uncertainty out of things.
On Jan 8, the lake level was at 805.5, 2254644 acre-feet. On Jan 9, 820.67, 2433696. So you could estimate the AF at the 813.6 level using those. When the lake level was 900.11, 3539318 AF. So it looks like that top between where spillway can empty, up to spilling over the emergency spillway, is roughly 1.2 million acre feet of water.
 

Mick West

Administrator
Staff member
On Jan 8, the lake level was at 805.5, 2254644 acre-feet. On Jan 9, 820.67, 2433696. So you could estimate the AF at the 813.6 level using those. When the lake level was 900.11, 3539318 AF. So it looks like that top between where spillway can empty, up to spilling over the emergency spillway, is roughly 1.2 million acre feet of water.

Or about 7 inches of rain over the entire watershed, (none it falling as snow)
 

Gregory

New Member
I see that almost a foot of rain is coming according to the story in this link:

/wattsupwiththat.com/2017/02/15/super-soaker-atmospheric-river-taking-aim-on-beleaguered-orovilledam/

It is a warm storm so I'm wondering if some of the snow in the watershed will be melted - creating a "perfect storm"...

Further, the levies are designed to handle a Feather River flow of 300,000 cfs.

Any comments welcome.
 

Mick West

Administrator
Staff member
Here's a more local forecast with the watershed outlined
View attachment 24675

Looks like it will average under 1" per day over the whole area, which is manageable.[/QUOTE]

http://www.cnrfc.noaa.gov/precipForecast.php?cwa=STO&imgNum=1
The forecast has got somewhat worse.

20170216-073552-jv5us.jpg

Black line is the watershed. Given that more than half the area is 6" or above, then average over the area is probably over 1". Just a simplistic visual estimate with the range going from 3" to 12" put it at 7.5" over 6 days.
 
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FishOutofWater

New Member
First post here. Retired PhD geochemist / geologist who appreciates the informative technical discussion here. My professional experience is with nuclear waste disposal safety research and regulation.

The weather forecast for Monday and Tuesday just got worse, as Mick noted in the other thread. Basically there's going to be a warm atmospheric river event with a high snow level starting on Monday. Precipitation forecast amounts just went up. Because snow levels will apparently be over 5000 feet snow that fell at lower elevations in the cooler storms over the week end could melt so there could be a pretty good inflow starting late Monday. This storm swings in a moisture fetch from north of Hawaii so it's going to be warm and wet early on. By Tuesday colder air will be moving in and the snow level will drop.

After this storm, forecasting gets difficult because the models have trouble handing blocking patterns. However, it looks like a colder drier pattern will set in so there's potentially good news after Tuesday.

20Feb1818Zgfs_mslp_pcpn_frzn_swus_17.png
 

Mick West

Administrator
Staff member
This article is from yesterday, so opinions might have changed a little.

https://www.washingtonpost.com/news...-rain-in-the-forecast/?utm_term=.05b370d26d6d
But I think a very important thing here is the snow level of the storm. Current NWS storm warning for the area (Pluma County covers most of it) has the snow level at 6,000
http://forecast.weather.gov/wwamap/wwatxtget.php?cwa=sto&wwa=winter storm watch
 

Mick West

Administrator
Staff member
this might be useful


No it's not. As mentioned above it miscalculates the acre feet from of the outflow

I saw a tweet say the waterflow intake was 3,222 sq miles, a bit lower than my measurement from GE. However he also said that this means an inch is 171,840 acre-feet flowing in, and this exceeds the 150K acre-feet flowing out.

However, at 100,000 cubic feet per second, that's 100000*60*60*24 cubic feet per 24 hours, which is actually 198K acre feet, according to google.
https://www.google.com/search?q=100000*60*60*24+cubic+feet+in+acre+feet
View attachment 24671

I suspect he was simply mistaking the 150K cfs standard release for 150K acre/feet. But perhaps this misconception is based on something else. Have there been acre-feet figures given for the releases?
 

SR1419

Senior Member.
sorry- didnt notice which tweet it was. Good point. Perhaps someone can ask him or point it out. I notice he (Jan Null) didnt really comment on his miscalculation.
 
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whoosh

Member
I see that almost a foot of rain is coming according to the story in this link:

/wattsupwiththat.com/2017/02/15/super-soaker-atmospheric-river-taking-aim-on-beleaguered-orovilledam/

It is a warm storm so I'm wondering if some of the snow in the watershed will be melted - creating a "perfect storm"...

Further, the levies are designed to handle a Feather River flow of 300,000 cfs.

Any comments welcome.

That site's no good. Atmospheric River is not observed in the 250mb jet stream. Better to use Precipitable Water (PWAT) from the models, and/or this site from UCSD
 

whoosh

Member
You can tweak around on this NWS site for recent and forecast weather, river stages, etc.
As noted earlier, since the watershed isn't overlaid, focus on the whole of Plumas County, back toward the reservoir.
 

CRM114

Member
There's a very good USGS report on this basin. A couple of notes:

About 40% of precip leaves the basin as evapotranspiration in an average water year. However in a wet year that % would go down. Just a very rough guess, maybe 2 inches would evapotranspirate this month and never reort as inflow.

Also, they report the basin as 3600 sq mi reporting to the reservoir, I believe.
 

Mick West

Administrator
Staff member
About 40% of precip leaves the basin as evapotranspiration in an average water year. However in a wet year that % would go down. Just a very rough guess, maybe 2 inches would evapotranspirate this month and never reort as inflow.

I'd think that while it's actually raining there's pretty much zero percentage loss from evaporation, as relative humidity is very high.
 

CRM114

Member
I'd think that while it's actually raining there's pretty much zero percentage loss from evaporation, as relative humidity is very high.
Yes, but plants are uptaking water, which seems to be the main mechanism in this basin, at least in the rainy season. They later lose this water.
 

JustCurious

New Member
Here's a more local forecast with the watershed outlined
View attachment 24675

Looks like it will average under 1" per day over the whole area, which is manageable.

http://www.cnrfc.noaa.gov/precipForecast.php?cwa=STO&imgNum=1
The forecast has got somewhat worse.

View attachment 24712

Black line is the watershed. Given that more than half the area is 6" or above, then average over the area is probably over 1". Just a simplistic visual estimate with the range going from 3" to 12" put it at 7.5" over 6 days.

With the current storm snowfall elevation is lower 4-5000 with the next system snow levels projected to be 6000' and above. This in mind anyway to determine the added run-off and water inflows as the air warms and snow melt begins?
 
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David T

New Member
Yes, but plants are uptaking water, which seems to be the main mechanism in this basin, at least in the rainy season. They later lose this water.

I would think that after all the earlier rain, the ground is already fairly saturated and the plants have already taken up what they want/need. So I would suggest most of the rain precipitation will make it into the lake. Key will be how much falls as snow and stays in the mountains.
 

CRM114

Member
I would think that after all the earlier rain, the ground is already fairly saturated and the plants have already taken up what they want/need. So I would suggest most of the rain precipitation will make it into the lake. Key will be how much falls as snow and stays in the mountains.

It's complicated and there are all sorts of processes involved. Don't assume 100% immediate runoff from this storm. It's probably safe to assume 》60% of the precip from this storm will eventually flow to the reservoir. The more precip it gets, the greater the runoff %.
 

Mick West

Administrator
Staff member
It's complicated and there are all sorts of processes involved. Don't assume 100% immediate runoff from this storm. It's probably safe to assume 》60% of the precip from this storm will eventually flow to the reservoir. The more precip it gets, the greater the runoff %.

Agreed, and we can do a different ballpark calculation, with 3600 square miles of catchment, what the CFS for 1" over 24 hours? It's 3600*5280*5280/12/24/60/60 = 96K cfs.
(3600 square miles which are 5280x5280, then /12 for on inch, /24 for hour /60 for minutes /60 for seconds)

So that's a real simple figure that give an upper bound. If it were raining 1" per day for weeks, and all the water went into the lake, and we ignore the effects of snow, then you've got 96K inflow all day.
 

Mick West

Administrator
Staff member
LA Times is reporting the NWS says that Sunday/Monday is going to be a warm wet storm.
http://www.latimes.com/local/lanow/la-me-ln-oroville-weather-forecast-20170216-story.html
 

CRM114

Member
Agreed, and we can do a different ballpark calculation, with 3600 square miles of catchment, what the CFS for 1" over 24 hours? It's 3600*5280*5280/12/24/60/60 = 96K cfs.
(3600 square miles which are 5280x5280, then /12 for on inch, /24 for hour /60 for minutes /60 for seconds)

So that's a real simple figure that give an upper bound. If it were raining 1" per day for weeks, and all the water went into the lake, and we ignore the effects of snow, then you've got 96K inflow all day.

Yes. 1 inch of water a day and reservoir level is static at 95 k cfs release (though that ignores evaptranspiration). Technically, its say 1.2 inches. So if next 7 days averages over 8.4 inches, reservoir goes up not down like they claim.

Snow is a big factor. Stations I have looked at are 30+ inches water equivalent. So that could be 25 days of 95 k cfs outflow alone, but I cannot find what basin average snowpack is. This will spread over several months but bulk is in next month or two I believe. Between this storm and snow, there could be a month of outflows already in the pipeline. This surely is not the last storm.
 

Mick West

Administrator
Staff member
While the average rain over the watershed is going to determine the average runoff, it's probably significant that the rain is strong loaded over the area directly adjacent to the lake:
20170216-114242-ejylj.jpg
That pink and white region next to the dam is about 1000 square miles, about 10" over six days.

700*5280*5280/12/24/60/60*10/6 = 45K cfs just from that region
 

JustCurious

New Member
CRM 114 this what your looking for?

Snow pack vs water content for Feather Valley Region

Station Name ID Elev. Date/Time Value
BUCKS LAKE BKL 5750' 02/16/2017 11:00 37.44"
FOUR TREES FOR 5150' 02/16/2017 11:00 21.48"
GOLD LAKE GOL 6750' 02/16/2017 11:00 42.84"
GRIZZLY RIDGE GRZ 6900' 02/16/2017 11:00 31.08"
HARKNESS FLAT HRK 6200' 02/16/2017 11:00 27.76"
HUMBUG HMB 6500' 02/16/2017 11:00 35.28"
KETTLE ROCK KTL 7300' 02/16/2017 11:00 34.20"
PILOT PEAK (DWR) PLP 6800' 02/16/2017 11:00 48.39"
RATTLESNAKE RTL

Source: http://cdec.water.ca.gov/cgi-progs/getAll?sens_num=3
 

whoosh

Member
Thats the one, enjoy!

Absolutely. Not only does it show that the majority of the watershed is below the 5500ft. snow line (my visual est.), but it reveals the presence of Nine!! upstream (N. fork Feather River) powerhouses (with reservoirs). Boy, I didn't see *that* coming.

That said, the document reveals an extensive network monitoring and modelling capacity for the Oroville reservoir inflow, which I trust is calibrated and functional.
 

whoosh

Member
wunderground.com Merrimac, CA (upstream, below the snow line)

upload_2017-2-16_15-10-40.png
 

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