Posted on 02/19/2017 6:26:41 PM PST by Mariner
MAXWELL
Forecasters with the National Weather Service offered a stark warning Sunday for just about everyone living in the soggy, soaked Central Valley.
“Pretty much anybody needs to be prepared for the possibility that they may have to evacuate quickly,” said Sacramento meteorologist Brooke Bingaman.
Though most of the Valley had avoided further flooding by Sunday evening, the worst may be yet to come Monday and Tuesday, Bingaman said.
On Sunday, the weather service issued a flood warning in urban areas and along small streams through Thursday for the counties that make up the Sacramento and northern San Joaquin valleys, as well as for most of the counties that sit along the Valley’s rim.
“We may see flooding in locations which haven’t been impacted in many years,” the alert reads.
In other words, those living anywhere near a river, a slough, a levee, a creek or a canal need to be ready to flee floodwaters at a moment’s notice.
(Excerpt) Read more at sacbee.com ...
idiots
Do you think there is any way for the dam itself at Oroville to fail? Nobody says that there is a chance of that publically, and looking at the way the spillways are separated from the dam by the hillside, it doesn’t look like it could happen. I don’t think it could happen from erosion coming from the spillways. I do think that there will be tremendous erosion from the spillways which will continue, especially if the water continues around the emergency spillway and goes over the parking lot.
Thank you, very much, for that information.
Just checked the weather for that area - it’s rain today; Monday; and, Tuesday.
Hoping for the best news.
It’s not much different than New Orleans in the delta areas of California. Due to the levees, many of those areas are below sea level - yet they have the most productive agricultural areas in America. But if they breach - there could easily be many square miles under water.
Funding illegals and other waste means they couldn’t maintain them...
The magnitude of such a breach depends entirely on how far down any erodable rock veins go below the emergency spillway. The latter is 30 feet high so the least magnitude of a breach would be from its top edge (901' above sea level) to 871' above sea level. The maximum credible estimate I've seen is 100' down, which would be to 801' above sea level.
The chief moderator of the professional forum I've followed estimated the volume of reservoir water from 801' feet elevation to 901' is 1.2 million acre feet of water. That is the probable worst case. My guesstimate of a 30' breach from that is 400,000 - 500,000 acre feet.
Either volume wouldn't all go at once. IMO it would take hours for a breach to form from the time the emergency spillway overflows, more hours for the breach to erode down as far it can go, and still more hours for the reservoir to drain as much as it's going to.
My brother lives in Colusa west of the Oroville Dam and near the Sacramento River and levees. He is nervous.
Why? Because no only do you have all that runoff from the Sacramento River diverted through the Yolo Bypass (the Bypass ends northwest of Rio Vista, you also have runoff from the roaring Putah Creek, especially with the water level higher than the bell-mouth spillway at Monticello Dam, resulting in a lot more water going down Putah Creek.
That means every Sacramento-San Joaquin Delta island from Rio Vista and downstream are under threat, the cities of Antioch, Pittsburgh, and Martinez are under threat, the oil refineries east and west of Carquinez Strait are under threat, everything else along the shores of San Pablo Bay are under threat.
Your analysis is correct, unless there is a levee break further upstream on the San Joaquin or Sacramento rivers. If one of those breaks on a major river moving 250,000 - 350,000CFS, that will get a lot of people wet.
Of course their will be minor flooding at the base of every gully in the foothills, and the Consumes will flood I5 as usual.
But it’s time to worry about the big rivers now.
I really think after what happened this winter, there will now be calls to build a small flood-control dam on Consumes River just east of Rancho Murietta. Otherwise, everything on the shores of the Consumes will flood every winter we have even slightly above-normal rains.
“Now, I will concede that we do not know that it will happen. We only surmise that it may happen. I don’t think I am going to dine in one of those charming River front Restaurants on the North side of Sacramento on Wednesday or Thursday.”
Not unless they have a drive-up window and you’re in your boat!
And you’re right the 30ft of water isn’t trivial Let’s just hope that the forecasted amounts of rain don’t happen and the main spillway doesn’t fail. I think it can handle the required discharges so long as it holds together.
Lake Oroville's capacity (assuming a lake level of 850 ft. to start) is large enough that, at that time, an additional 10" of rain in the Lake Oroville "catchment basin" = emergency spillway should not be topped, but it might get dicey.
Now, note this excerpt from the current NWS forecast discussion (bold highlights are mine):
Discussion... Take this afternoon and evening to make final preparations ahead of the incoming storm with flooding, strong winds and heavy snow. If you were given less than 15 minutes to evacuate your home would you have everything you need and gas in your vehicle? If roadways are closed from flooding, downed trees, or mudslides, do you have enough supplies to last you several days? If there are widespread power outages that last more than a day would you be prepared? If you are stuck on a road, do you have supplies in your car?
Northern California has become very vulnerable after being hit continuously with storms since early January and we want all residents in our region to plan ahead and be prepared.
Another very wet pattern starts later tonight with precipitation lingering into Wednesday. However, the strongest storm will be Monday into Tuesday when we expect the greatest precipitation and strongest winds. An atmospheric river will bring another plume of intense moisture to the west coast. Models vary slightly on where this plume will hit directly, but we have good confidence that it will be somewhere in our CWA. Another concern is that this plume could stall for a period of time which would significantly increase flooding issues for wherever that stall occurs. Keep in mind that significant flooding can also occur outside of this intense moisture plume since soils are so saturated and there will be added stress to levees, rivers and streams. That`s why residents should stay tuned to social media, news and updates during the storm so they can act quickly if needed.
Specifics of the Monday-Tuesday storm: Precipitation amounts could range 1 to 3 inches in the valley with up to 10 inches along the Western Sierra Slopes. Remember that runoff from the mountains will eventually flow downstream and add impacts to the valley. Snow amounts will be heaviest above 6000 feet with a range of 2-5 feet of new snow but we could see up to a foot of snow down to 5500 feet. Snow levels will be near or slightly above Sierra pass levels on Monday, then lower below pass levels on Tuesday. Strong wind gusts in the valley and foothills are forecast to range 45-65 mph with stronger winds over mountains Monday afternoon into Monday night.
The last big rainmaker stalling, and lack of maintenance of the spillways @ Oroville, was most of what caused the 1st round of major problems...
Good analysis. This is much like the “blowing” of the Birds Point levee back in 2015. (I was close enough that the explosions sounded like heavy thunder.) Unfortunately, the media construed that as a “Cairo vs. the farmers” (racial) issue, when the real issue was “the whole flood control system” vs. the farmers. Places far upstream and downstream were saved, including industrial plants @ Calvert City, KY, the new convention center @ Paducah, much other farmland, etc.
One has to feel bad for the farmers flooded out in the “relief” area, but, they KNEW they were operating in a floodway.
Good article on the (Birds Point) floodway:
https://en.wikipedia.org/wiki/Birds_Point-New_Madrid_Floodway
Having lived very near (but not actually on) flood prone land most of my life, I can really feel for those in CA...
If the main dam suffers catastrophic failure, the flooding is not going to cover 3.5M acres, because they're not a pool table, but much less, concentrated in or near (within two, three, five, perhaps even ten miles, depending on the terrain) the river valleys, but to a much greater depth than one foot. Say, 10ft on average, or 20ft on average, a hundred miles or more down river (all that water is going to need a new home).
Pray for those folks. Many tens of thousands are at risk.
I am trying very hard to avoid any biblical references, and it’s difficult, so all I will say is “build an ark.”
Okay, good morning everyone. As one who has followed this event with interest it looks like Oroville is still holding on this morning.
Based upon Lake measurements, it appears inflow has fluctuated between 47k and 23k cubic feet per second. Operators have been holding outflow over the main spillway to 59,900 cfs or thereabouts. This has kept lake levels falling very slightly from 851.17 to 849.54 or a decline of 1’ 7 1/2”.
Rainfall in the tributary area continues with Brush Creek, Four Trees and Buck’s Lake showing 24 hour rainfall running 2.4, 2.7 and 2.9 on the main fork of the Feather. Quincy and Grizzly Ridge have received about 1.5 inches. Gauges at Buck’s Creek and Lake Davis are not reporting data but areas surrounding them are less than critical.
Beale AFB radar:
https://radar.weather.gov/radar_lite.php?rid=bbx&product=N0R&loop=yes
Shows the more intense storms in the Folsom Reservoir drainage but higher elevation hills shade out some readings east of Oroville.
Clicking the eastern link shows Reno radar showing even distribution of precipitation across the western Sierras.
San Francisco Bay radar
https://radar.weather.gov/radar_lite.php?rid=mux&product=N0R&loop=yes
Shows the storms making landfall to be heavier south of the main urban area with Flash Flood warnings south of Monterrey Bay. I believe the coast highway is still closed for the bridge problems at Pfeiffer Canyon so travel there is very limited.
A prayer is offered for the next 72 hours that the Rivers don’t rise and the dam holds.
The main spillway has been damaged. Yet it must continue to discharge massive amounts of water. If the damage to it continues & starts working its way back up the dam, its operators must slow or stop using the main spillway.
At this point the entire dam is at risk. The concrete cap on the emergency spillway is close to being undermined. Video clearly shows this. Once that collapses the entire dam is at risk & there is NOTHING anyone can do but stand by & watch.
This dam was never designed to withstand all the potential mountain runoff. CA never finished the water projects that would have built upstream dams which would have controlled what water arrived at Oroville dam as well as other dams (Shasta).
Beyond the extreme risk to life & property, much the water flooding people’s homes, flowing to the sea could have been retained by those unbuilt dams, which could have provided the water for a revival of central valley agriculture & end water usage restrictions, greening CA again & thereby absorbing tons of that evil CO2.
it’s not raining hard enough for significant flooding.
good to hear — hope it stays that way
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