Liveblogging the Deluge: 2018 Short Version

High water on the Tuolumne River, February 2018, about 15,000 cubic feet per second.

Why "short"? What deluge? Hasn't this been another dry year?

Tuolumne River on January 19, 2018, flow at about 300 cubic feet per second.

If you've been reading over the last year, you would know that I started what I thought would be a short blog series (Liveblogging the Deluge) on what looked like (and almost was) a record-breaking atmospheric storm that hit California last January. The storm hit, and then there was another. And another. Prodigious amounts of snow and rain fell in central and northern California through the end of April, putting an end to California's historically bad five-year drought, and filling the state's dry reservoirs. So much snow accumulated in the drainage of the Tuolumne River that the main reservoir, Don Pedro, was constantly at the edge of overflowing, so the outflow was maintained at near flood-level (averaging 9,000 cubic feet per second, briefly to 15,000 cfs) through July. We really had no chance to see the changes on the floodplain until September.

Tuolumne River on March 25, 2018, flow at about 4,500 cubic feet per second

And then...when the "storm door" was supposed to open in November, barely anything happened. My backyard gauge told the story: October, 0.07", November 1.15", December 0.0". January finally brought an almost normal amount, 3.44", but the next month was one of the driest Februarys ever recorded, with my gauge recording a mere 0.37". Statewide, the snowpack was a mere 20-25% of normal. At Don Pedro Reservoir, there was a lot of water in storage, but realizing that there would be almost no snowmelt, the operators kept the outflow into the lower Tuolumne River at very low levels, about 300 cubic feet per second. They left a minimum of space for emergency flood control.

Tuolumne River, January 19, 2018, flow at 300 cubic feet per second.

And then March happened. The storm door opened in a big way, and three major storms blew through the state raising havoc with floods and mudflows in numerous localities, including some of the areas affected by the horrific fires of last summer (and December, unfortunately). Locally, we received 3.36", but my little town was one of the driest spots in the state. The snow in the Sierra Nevada was measured in feet, including 7-8 feet in a few places.

Tuolumne River on March 25, flow at 4,500 cubic feet per second.

It wasn't a drought ending month, but it took the snowpack from disastrous to merely disappointing. Current levels range from 44% to 66% of normal. And now the operators at Don Pedro Reservoir can expect some runoff amounts that will be semi-normal. That means they'll need a bit more reservoir space....

I noticed the first ramping up of river flows about a week ago, when the discharge was tripled to about 1,000 cubic feet per second. I could hear the river again (the velocity of the water at 300 cfs is very low). But then when I walked the river trail yesterday, the river was raging along at 4,500 cubic feet per second. Not a flood, but a higher level than at almost any point during the entire run of the 2012-2017 drought. The islands and gravel bars that were being used by fisher-people and picnickers were once again underwater. The slough at the west end of the Parkway Trail where I walk was once again flowing. This is good on a number of counts: salmon and other fish will have a better chance of survival and getting to the sea, and the invasive weed river hyacinth will probably not gain root in the upper areas of the river. The river weed choked the slough and parts of the river channel during the drought, smothering out other vegetation, and making life difficult for fish and aquatic wildlife.

Farther afield, the outlook is reasonably good. Most of California's reservoirs are at or well-above normal (flood-damaged Lake Oroville is an exception at 75% of normal). Don Pedro came up at least 8 feet during the storms in March.

While good for the snowpack and reservoirs, the storms did a lot of damage. Roads were washed out in numerous places in the foothills of the Sierra Nevada. We almost lost a smaller reservoir on Moccasin Creek. In the end, the "Deluge" was a lot shorter than the one we got last year, but in a year as dry as this, it was good to have a little extra water "in the bank". With the uncertainties related to global warming, and the expectation of future extended droughts, every drop counts.

Houston's Horrific Flooding: Thank Goodness It Can't Happen Here...Eh...Right? Think Again...

What's happening in Houston is beyond belief. And tragically, horrible flooding is happening now in southeast Asia as well, with at least 1,200 people dead. Although the extent of the damage in Houston is not yet known, meteorologists are already calling it unprecedented in American history. I can't begin to imagine experiencing feet of rain in the space of days, and it isn't over yet. My heart goes out to those in the midst of the disaster. It may take weeks for the waters to subside, and years for the region to fully recover.

This isn't Houston. It is our own much more modest flood a few months ago.

(I've abridged and adapted the following from a post in 2011)

Seeing events like this unfold on television or on the computer screen can provide a certain emotional distance from the full magnitude of what has happened. Thoughts develop along the lines of "Could it happen here?" and as we realize it might, we think "Are we prepared for an event like that?" Floods occur essentially everywhere, but the Central Valley (the GREAT Valley) is notable in the magnitude and frequency of its flooding. We had a experienced a few terrifying days in the early part of the year when it seemed that one of our largest dams, Oroville, was in danger of failing, and we have become aware that almost all our dams are aging, and need maintenance or replacement.  It makes one wonder how bad it could possibly get. Pretty bad, as it turns out.

Climate experts have been analyzing the possibilities that California could be hit by a devastating storm sequence that could leave much of the Central Valley as an inland lake. It sounds unlikely, at best a hypothetical model, but it has actually already happened. In 1861-62, a storm series dropped so much precipitation that a 300 mile long lake covered the valley, and forced the state capital to move operations from Sacramento to San Francisco for a time.

I mentioned Yellowstone in a while back, and it got me thinking once again about those things that are worth worrying about, those that are not, and those that are worth preparing for. Yellowstone last had an eruption 70,000 years ago, and the last major "supervolcano" (i.e. rhyolite caldera event) was more than 600,000 years ago. So how much should we worry about Yellowstone? It could happen, but not likely any time soon. But people are freaked out about the possibility if a quick internet search is any measure. They obsess about it, and even see strange conspiracies.

But what about a "superstorm"? People don't seem to worry about flooding so much, yet huge floods are a disturbingly common occurrence. Besides 1862, evidence has been uncovered of similar intense events in 212, 440, 603, 1029, 1418, and 1605 (sediments from storm runoff are preserved in ocean basins offshore of the state). That adds up to around a 0.3% possibility in a given year; not common, but enough that emergency providers are beginning to seriously consider the possible effects. A report from the US Geological Survey talks about the potential for an atmospheric river storm they have termed an ARkStorm (Atmospheric River Storm). The possible effects make California's expected "Big One" earthquake look, well, medium in comparison. From the USGS ARkStorm Report (PDF download here - 46 mb):

The storm is estimated to produce precipitation that in many places exceeds levels only experienced on average once every 500 to 1,000 years. Extensive flooding results. In many cases flooding overwhelms the state’s flood-protection system, which is typically designed to resist 100- to 200-year runoffs. The Central Valley experiences hypothetical flooding 300 miles long and 20 or more miles wide. Serious flooding also occurs in Orange County, Los Angeles County, San Diego, the San Francisco Bay area, and other coastal communities. Windspeeds in some places reach 125 miles per hour, hurricane-force winds. Across wider areas of the state, winds reach 60 miles per hour. Hundreds of landslides damage roads, highways, and homes. Property damage exceeds $300 billion, most from flooding. Demand surge (an increase in labor rates and other repair costs after major natural disasters) could increase property losses by 20 percent. Agricultural losses and other costs to repair lifelines, dewater (drain) flooded islands, and repair damage from landslides, brings the total direct property loss to nearly $400 billion, of which $20 to $30 billion would be recoverable through public and commercial insurance. Power, water, sewer, and other lifelines experience damage that takes weeks or months to restore. Flooding evacuation could involve 1.5 million residents in the inland region and delta counties. Business interruption costs reach $325 billion in addition to the $400 billion property repair costs, meaning that an ARkStorm could cost on the order of $725 billion, which is nearly 3 times the loss deemed to be realistic by the ShakeOut authors for a severe southern California earthquake, an event with roughly the same annual occurrence probability.

If that doesn't sound like events in Houston, you haven't been paying attention. This is serious stuff.
Flooding rarely gets the epic movie treatment. Volcanic eruptions and earthquakes are so sudden and devastating; rising water just doesn't cut it as a drama setting. I haven't seen a lot of Katrina movies yet. But life isn't a movie. If you live in California, think for a moment about getting hit with a superstorm, and the delta and Central Valley ending up like this:It is a real possibility and a sobering thought....

By the way, not wanting to stir the pot (or maybe I do), if you are worried about Yellowstone erupting and you live in California, why aren't you giving more thought to our very own active rhyolite caldera, our "supervolcano"?

Maps and second photo from the USGS ARkStorm Report (PDF - 46 mb)

Liveblogging the Deluge: Reflections on the Events at Oroville Dam. What Will it Take to Change Things?

This picture is on the San Joaquin River, not the Feather. It's a metaphor for floods all around.

Let me be absolutely clear: this is a serious situation. Nearly two hundred thousand people have been evacuated as officials try to deal with two crumbling spillways at Oroville Dam as high river flows have filled the reservoir past capacity. The situation has briefly stabilized as the lake has been lowered to a level below the auxiliary ("emergency") spillway so temporary repairs can be started. But again, this is serious. If you live in the evacuation zone, follow the orders and get out.

I have a story that will seem pointless at first, but bear with me. I have a fence in the backyard. It was a nice fence at one time. But the years took their toll. Heavy storms would knock some of the slats loose, but I would nail them back in. Dry rot attacked some of the crossbeams, but chicken wire and bungee cords sort of sufficed to hold things together.

The years went by and it got worse. But there never seemed to be enough money, and there were always excuses to do other things instead. But the storms of January hit, and hit the fence hard. Whole sections just fell to pieces. The fence was totally destroyed and finally we had to act, whether we could afford it or not.

What does this small story from my life have to do with Oroville Dam?

From the Los Angeles Times

First, a recap...

Oroville Dam is the highest dam in the United States, at 770 feet, and the second largest reservoir in California with a capacity of 3.5 million acre-feet. It is a major component of the State Water Project, providing water for millions of people in central and southern California. It was completed in 1968.

California has finally ended the worst drought in the state's history with what may turn out to be the wettest year on record (there are still several months left in the season). A series of atmospheric river storms have dumped incredible amounts of rain and snow across the state, and rivers are swollen. Most of the state's reservoirs are nearly full, and operators are carefully draining what they can to avoid flooding now and in coming weeks as more storms roll through. But the big problems cropped up at Oroville Dam.

The main spillway early in the crisis. The emergency spillway is to the left.

When flows get too high, the lakes have to be drained through spillways which are supposed to be designed to accommodate the largest credible flood events. Oroville has such a spillway, but when flows ramped up earlier this week, a huge section of the concrete collapsed and water started tearing away at the adjacent hillside, threatening some of the major electrical transmission lines. It turns out that even though it was never meant to be used, a second spillway had been constructed. No effort had been made to prepare the slopes below for floodwaters, and the cement lip was never really properly reinforced.

Hard choices had to be made. The lake was filling fast, and the longer the main spillway was flowing, more and more concrete was being ripped away. The decision was made to let the lake drain over the auxiliary spillway and only yesterday morning the water started seeping over the edge. By the end of the day, the water was one or two feet deep across the entire structure, and if what I heard is accurate, the flow was around 10,000-15,000 cubic feet per second. For perspective, that's the current near-flood level flow of the Tuolumne River in my own backyard down the valley (below).

Tuolumne River flowing at 9,000 cubic feet per second

It was only a day before a big problem cropped up. A large hole had eroded from the spillway that threatened to cause its collapse. This was the event that precipitated the evacuation event, with warnings that the collapse could happen within an hour. I can't imagine what it must have been like to be living there and hearing such a warning.

What was about to happen? It wasn't a collapse of the entire dam. That's not really in the cards here. Had the spillway collapsed, the water would have starting flowing over the bedrock and loose soil beneath the concrete lip. The breach would have concentrated the flow in one spot, and even though the bedrock is solid metavolcanic rock, the smallest fissures and joints would have been exploited by the rushing water. The result would be a cut of several tens of feet, and that would have drained a significant portion of the reservoir (the top 30 feet out of the 770 feet). That would have been enough water to inundate a wide swath of the floodplain and adjacent areas downstream, and that is what prompted the evacuation order.

The operators of the dam ramped up the flow on the original spillway to around 100,000 cubic feet per second, and that was finally enough to start lowering the level of the lake. By 8 PM this evening the water dropped below the level of the auxiliary spillway, and repairs started immediately (six helicopters are dropping huge bags of boulders into the hole). The immediate crisis passed, but they are still depending on flow down a crippled spillway for the foreseeable future with a stated hope to drop the lake fifty feet beneath the emergency spillway. And we have more storms on the horizon.

What should we take from this perilous situation? My first thoughts as this event unfolded is that this dam and a great many others across the country are decades old. Concrete gets old and crumbles, steel reinforcement beams rust away deep within the concrete, and equipment suffers intense wear and tear. Congress and state legislatures are almost always generous with initial construction funds, but when the time comes for maintenance and renovation, suddenly the deficit becomes important and funds can't be found.

We have chosen to allow our population to grow beyond the capacity of our landscape to support us, and many times over we have chosen to place giant urban centers in places that make no sense (yes, I'm looking at you Las Vegas and Phoenix). We thus depend on gigantic projects bent on controlling nature to provide our water for irrigation and domestic use. We depend on them, and their failure would be catastrophic, both in lives lost, and in damaged infrastructure. And yet we refuse to provide enough funding for their upkeep.

I don't know what caused the failure of the original spillway at Oroville Dam, although I have some suspicions. I think I know the dynamics of what happened with the emergency auxiliary spillway. Whatever the reasons were, they were predictable to those knowledgeable in engineering design. They were in fact predicted in 2005 by environmental groups testifying during the relicensing of the dam according to a note by the California Water Research:

A single operational use or multiple operational uses (with failure to repair any preceding or cumulative damage) of the ungated spillway could result in a loss of crest control of Oroville Dam. A loss of crest control could not only cause additional damage to project lands and facilities but also cause damages and threaten lives in the protected floodplain downstream. An unarmored spillway is not in conformance with current FERC engineering regulations. (emphasis added.)

And that's where we are tonight. A dam in danger of spillway failure, as many as 180,000 people displaced suddenly from their homes, and a government unwilling to take care of infrastructure because it is just too expensive and inconvenient. This is a story that is going to be repeated over and over in coming years. The failure of the levees and the deaths of 1,800 people in New Orleans during Hurricane Katrina was a harbinger. I frankly don't think the events of this evening are going to be enough to convince legislatures to do the responsible thing. What will the tipping point be? The death of hundreds? The death of thousands?

Our country went collectively nuts after terrorists killed 3,000 people in the Twin Towers on 9/11 and we spent more than a trillion dollars on a useless war on terror. Fixing and investing in our failing dams and bridges makes so much more sense, and the benefits go far beyond just safety. It also means putting hundreds of thousands, maybe millions of people to work, and that will strengthen the economy immeasurably.

It's just like the way I put some people to work this week fixing my broken fence. They benefitted and so did I. And my yard is a much nicer place now.

UPDATE (2/13/17): A picture of the damage that was expected to impact the auxiliary spillway, from Peter Gleick on Twitter (@PeterGleick). I certainly looks like the jointed metamorphic rock I expected. This is similar to what happened at Don Pedro in 1997 when a 40 foot channel was carved in a few days.

Circled are people for scale.

Liveblogging the Deluge: The Concerns (Panic?) at Oroville Dam, a Story We've Seen Before

The graphic above (from the Los Angeles Times, Google Earth, and the California Dept. of Water Resources) succinctly explains the serious problem unfolding right now at Oroville Dam on the Feather River. The lake is the second largest reservoir in California backed behind the highest dam in the United States. It is very close to capacity, but the main relief valve, the spillway, has been severely damaged and is essentially crippled. Without the spillway, the operators have only two choices to get rid of the rapidly rising floodwaters. They could let the floodwaters flow over the top of the dam itself, or they open a second emergency spillway.

California Dept. of Water Resources via The Landslide Blog

The first choice is unthinkable. The structure is an earthen-fill dam, made up of a core of impermeable clay covered by other sediments and rock material. If floodwaters top the dam, they would easily cut through the loose material, and the dam could fail. Such a failure would be a catastrophe without precedent. The instantaneous release of more than 3 million acre-feet into the Sacramento River system would be a flood of Biblical proportions. Sacramento and other towns would be inundated, threatening the lives of hundreds of thousands of people. The water delivery system for California would be crippled for years or decades. Postscript: Darn it, I wasn't thinking right. The emergency spillways are below the level of the dam by 20 feet, so this is unlikely to happen, at least due to flooding. It just made such vivid narrative.  Thanks jfmiller for the clarification (see comments below). So that is not going to happen.

Source: CA Dept. of Water Resources via The Landslide Blog

The second choice is magnitudes less catastrophic, but would still be a problem. The emergency spillway would flow across slopes and hillsides that have never been exposed to fast-moving floodwaters. Trees, rocks, and mud will pour into the river downstream, complicating efforts to prevent flooding and levee breaches downstream.

We'll see where this situation resolves over the next few days. But I couldn't help but be reminded of two historical events involving dams and reservoirs that put a spotlight on the choices we've made to build such titanic structures to serve the needs of our society: Don Pedro Reservoir in 1997, and Glen Canyon Dam in 1983.

Glen Canyon Dam in Arizona

We tend to think of these huge structures as monuments to our creativity, power, and control over nature (it's an entirely different issue that I almost wrote "man's control over mother nature", which sounds very patriarchal or chauvinistic). The fact remains though, that we sometimes have flaws in our thinking and planning. Let's take Glen Canyon as an epic example.

Glen Canyon Dam was built between 1957-1964. It is 710 feet high (216 m) and 1,560 feet (475 m) wide, with a volume of 5,370,000 cubic yards (4,110,000 cubic meters) of concrete. It is anchored in Navajo Sandstone. When full the lake is 186 miles (299 km) long, with 1,960 miles (3,150 km) of shoreline, and a total capacity of 26.2 million acre feet (equivalent of two years of the average flow of the Colorado River). The main thing to notice about the picture above is that the dam has no spillway. It...has...no...spillway. If water ever came over the top of the dam, the floodwaters could destroy the power generators below, possibly "pulling the bath plug" on the dam. The sandstone that anchors the dam is relatively easy to erode, so such an event could threaten the very stability of the dam itself.

That not to say the operators have no way to deal with floods. When they built the dam, the Colorado River was diverted through tunnels in the cliffs around the dam site. The tunnels were adapted into an underground spillway within the cliffs. When floodwaters threatened to fill the reservoir, they would simply open the spillways and millions of gallons of water would shoot out of the cliffs at the base of the dam.

Which brings us to the events of 1983.

Wait a second...why is there a dam made of plywood here?

After construction was completed in 1964, the lake slowly filled (since water use downstream did not cease, only surplus water was used to fill the lake) and did not reach capacity until 1980. In 1983, the dam came perilously close to failing due to a major flood and design errors. An unexpectedly warm and wet storm caused a tremendous flood upstream of the nearly full Lake Powell. To prepare for the huge influx of water, the dam engineers opened up the underground spillways for the first time. They proved woefully inadequate to the task as cavitation caused the walls of the diversion tunnels to rip out. In places the powerful flow of water cut 32 feet (10 meters) into the soft Navajo Sandstone and threatened the structural integrity of the dam itself. People working within the dam reported rumblings and vibrations that simply shouldn't have been happening.

The diversion tunnels had to be shut down, and the lake threatened to flow over the crest of the dam in an uncontrolled fashion. As noted above, this could have led to catastrophe, as such uncontrolled flow could have eroded and weakened the sandstone abutments of the dam. Failure of Glen Canyon dam would have led to the domino-like destruction of other large dams downstream, and the decimation of the water-supply infrastructure of some thirty million people. The disaster was averted by the construction of an 8 foot high dam of wood flashboards that held back the water long enough for the flood to subside (see the picture above). The structural integrity and survival of the dam came down to less than a foot...the distance between the water level and the top of the flashboard dam in 1983.

The damaged spillway at Glen Canyon Dam in 1983

That is what came to mind as I saw pictures of the Oroville spillway yesterday. The other echo of the past was the need to open up the spillway onto new ground. Something very similar happened at Don Pedro during the floods of 1997 (and if the narrative below seems familiar, yes, I used it a couple of weeks ago as an introduction to the coming atmospheric river storms. I'm revisiting the story because of the similarity of events at Oroville Dam).

Don Pedro Reservoir on the Tuolumne River stores water for the Modesto and Turlock Irrigation Districts, and also serves as storage for Hetch Hetchy Reservoir water bound for San Francisco. The earth-fill dam stands 580 feet high and inundates 26 miles of the Tuolumne River, which flows out of Yosemite National Park. It stores just over 2 million acre-feet of water. The dam was built for irrigation storage, hydroelectric power generation, and recreation. And flood control.

The water year of 1996-1997 was unusual, but unfortunately familiar given the events of the last month in California. A series of large storms in December had built up a record or near-record snowpack in the Yosemite high country. Then a New Years Day Pineapple Express storm took aim at central California. The warm, moist atmospheric river flowed over the Central Valley dropping only a few inches of rain, but when it hit the mountains, it poured as much as three feet of rain at elevations as high as 10,000 feet and onto the record snowpack.

Don Pedro Reservoir was at the proper level for normal flash flood conditions, with about 300,000 acre feet of storage available. But the water coming downstream was not normal. At the peak, the rivers flowed into the lake at an unbelievable rate of 130,000 cubic feet per second (the Feather River, by the way, reached about 170,000 cubic feet per second this week). To put this number into perspective, the Tuolumne River is considered to be at flood stage at 9,000 cubic feet per second. The dam operators had a big problem and they knew it. They had to purposely flood the cities downstream to prevent a total catastrophe. They ramped up the power generating turbines, and for the first time in the dam's history, they opened the floodgate.

The floodgate didn't open into the Tuolumne River. It faced a meadow that had never before had a river flowing through. As can be seen from the pictures here, the meadow was hit by a flood of gigantic proportions. Ripping away soil and solid rock, the river quarried a channel forty feet deep in the space of three days. And it barely worked. At the highest point, the reservoir was flowing uncontrolled over a concrete weir that was the never supposed to be topped. The water was only a foot deep, but spread out over several hundred feet, it ripped away soil, rock, and the highway that passed below the floodgates.

The city of Modesto and others downstream experienced the greatest flood in their history, with top flows of around 60.000-70,000 cubic feet per second. But if Don Pedro Dam had not been there, the towns would have been hit with a flood twice as big.

Only one flood in recorded history could possible compare with 1997. That was the flood of 1861-62, which was so large that parts of the Great Valley turned into a lake for weeks. Sacramento was abandoned as the state capitol for months while the waters subsided. No gauges were present on any of the rivers so we don't know how the numbers compare, but considering that 1997 was considered a 250 year flood (a 1/250 chance of occurring in any one year), it must have been truly extraordinary. And in the last month, only twenty years later, we seem to have reached a similar level of flooding on many of our rivers in California.

And that's the way it is with Oroville Dam today. With a dam and a river that is larger than the Tuolumne. I can't imagine the stress levels of those who are dealing with the situation as they try to navigate their way between undesirable choices.

Since we have chosen to live together as a society in numbers totaling millions of people, we have to make many choices about how much we alter and change the landscape that supports us. Our basic needs of water, food and shelter have to be provided on a massive scale, but the infrastructure at such kinds of scale also have the potential to fail at equally high magnitude. Politicians are fond of keeping taxes low and complain endlessly about "burdensome" regulations and guidelines. They cut the budgets of agencies who provide the expertise that can allow us to avoid catastrophes. When they do this, they are setting up conditions for failure on an astronomic scale. So who will we blame in the end?

I wish the operators of Oroville Dam all the best. I assume they are talented at what they do and that they will be making the best possible decisions in coming days. I also hope that those who represent us in the halls of government will gain some kind of insight about the best ways to care for and improve the infrastructure that supports and protects us all. I hope, but I'm not all that optimistic, seeing the disdain that those in power right now hold for science and knowledge.

POSTSCRIPT: The incoming flow has declined to 120,000 cfs, with 65,000 cfs outflow. If it continues to drop, the operators might not need to use the emergency spillway.

POSTSCRIPT (2/11/17 at 8 AM): According to this Mark Finan at KCRA, this is the emergency spillway this morning at 7 AM. About to go over the edge...

The incoming flow at 8 AM is 89,276 cubic feet per second, the outflow is 55,092 cfs. The lake is still rising, with less than 2 inches of clearance before water flows through the spillway.

POSTSCRIPT (2/12/17): The inflow to Oroville Reservoir is finally dropping below the outflow, so the lake level can start dropping (hopefully enough to deal with the next storm in five days).

POSTSCRIPT (2/12/17, 6:45 PM): Gee whiz, things were quiet, so I went birding for a few hours and all hell broke loose while I was gone. First, if you are in the Oroville area, take the official announcements seriously and follow evacuation orders without delay. It's got to be serious if they take a step like that. In any case, the auxiliary spillway is in imminent danger of failing. If it does so, lake water would be surging over bedrock in an uncontrolled manner. It depends what kind of bedrock there is (I'm working on that), since the rapid flows could erode the rock channel downward (as happened at Don Pedro in 1997) which could then lead to higher flows and flooding downstream. It sounds like the operators increased flow on the other damaged spillway, so that the flow over the auxiliary spillway is down to 2 inches, rather than the 1 1/2-2 feet. That takes a lot of pressure off the auxiliary spillway, and offers hopes for some kind of repairs before the next storm hits.

Queensland's Flooding: Thank Goodness It Can't Happen Here...Eh...Right? Think Again...

Before you read anything else in this particular blog, go to the BBC news and look at 3 minutes and 46 seconds of stunning pictures of the extraordinary flooding this season in Queensland, Australia. The amount of water on the ground in the normally dry landscape is almost beyond belief. The BBC mentions a vast inland sea the size of France and Germany combined. My heart goes out to those in the midst of the disaster. This was an unusual train of meteorological events that ended a long drought, and culminated in the arrival of Cyclone Yasi, a category 5 hurricane. It will take weeks for the waters to subside, and years for the region to fully recover.

Not Australia, this is flood stage on our own San Joaquin in 2006

Seeing events like this unfold on television or on the computer screen can provide a certain emotional distance from the full magnitude of what has happened. Thoughts develop along the lines of "Could it happen here?" and as we realize it might, we think "Are we prepared for an event like that?" Floods occur essentially everywhere, but as I am based in California, my ears perk up whenever I hear about unfolding events along the Pacific coast. We had a pretty wild time of it in the last two months with serious floods in a number of areas, especially in southern California. It makes one wonder how bad it could possibly get. Pretty bad, as it turns out.

Those pesky climate experts have been analyzing the possibilities that California could be hit by a devastating storm sequence that could leave much of the Central Valley as an inland lake. It sounds unlikely, at best a hypothetical model, but it has actually already happened. In 1861-62, a storm series dropped so much precipitation that a 300 mile long lake covered the valley, and forced the state capital to move operations from Sacramento to San Francisco for a time.

I mentioned Yellowstone in a recent post, and it got me thinking once again about those things that are worth worrying about, those that are not, and those that are worth preparing for. Yellowstone last had an eruption 70,000 years ago, and the last major "supervolcano" (i.e. rhyolite caldera event) was more than 600,000 years ago. So how much should we worry about Yellowstone? It could happen, but not likely any time soon. But people are freaked out about the possibility if a quick internet search is any measure. They obsess about it, and even see strange conspiracies.

But what about a "superstorm"? People don't seem to worry about flooding so much, yet huge floods are a disturbingly common occurrence. Besides 1862, evidence has been uncovered of similar intense events in 212, 440, 603, 1029, 1418, and 1605 (sediments from storm runoff are preserved in ocean basins offshore of the state). That adds up to around a 0.3% possibility in a given year; not common, but enough that emergency providers are beginning to seriously consider the possible effects. There was a bit of a stir in the geoblogosphere a few weeks ago about a report from the US Geological Survey about the potential for an atmospheric river storm they have termed an ARkStorm (Atmospheric River Storm). The possible effects make California's expected "Big One" earthquake look, well, medium in comparison. From the USGS ARkStorm Report (PDF download here - 46 mb):

The storm is estimated to produce precipitation that in many places exceeds levels only experienced on average once every 500 to 1,000 years. Extensive flooding results. In many cases flooding overwhelms the state’s flood-protection system, which is typically designed to resist 100- to 200-year runoffs. The Central Valley experiences hypothetical flooding 300 miles long and 20 or more miles wide. Serious flooding also occurs in Orange County, Los Angeles County, San Diego, the San Francisco Bay area, and other coastal communities. Windspeeds in some places reach 125 miles per hour, hurricane-force winds. Across wider areas of the state, winds reach 60 miles per hour. Hundreds of landslides damage roads, highways, and homes. Property damage exceeds $300 billion, most from flooding. Demand surge (an increase in labor rates and other repair costs after major natural disasters) could increase property losses by 20 percent. Agricultural losses and other costs to repair lifelines, dewater (drain) flooded islands, and repair damage from landslides, brings the total direct property loss to nearly $400 billion, of which $20 to $30 billion would be recoverable through public and commercial insurance. Power, water, sewer, and other lifelines experience damage that takes weeks or months to restore. Flooding evacuation could involve 1.5 million residents in the inland region and delta counties. Business interruption costs reach $325 billion in addition to the $400 billion property repair costs, meaning that an ARkStorm could cost on the order of $725 billion, which is nearly 3 times the loss deemed to be realistic by the ShakeOut authors for a severe southern California earthquake, an event with roughly the same annual occurrence probability.

Flooding rarely gets the epic movie treatment. Volcanic eruptions and earthquakes are so sudden and devastating; rising water just doesn't cut it as a drama setting. I haven't seen a lot of Katrina movies yet. But life isn't a movie. If you live in California, think for a moment about getting hit with a superstorm, and the delta and Central Valley ending up like this:It is a real possibility and a sobering thought....

By the way, not wanting to stir the pot (or maybe I do), if you are worried about Yellowstone erupting and you live in California, why aren't you giving more thought to our very own active rhyolite caldera, our "supervolcano"?

Maps and second photo from the USGS ARkStorm Report (PDF - 46 mb)

2010, The Year of Traveling Dangerously (Storms in California)

Water in California is always a proposition of too much or too little, and sometimes those problems occur at the same time (the north-south dichotomy is striking sometimes). This week we are experiencing the biggest series of storms in five years, and some localities in the Los Angeles region have received 12 inches or more, and the storms are continuing this evening.

I had occasion to tour a large swath of California yesterday, through the southern San Joaquin Valley, over the southernmost Sierra Nevada at Tehachapi, and across the Mojave Desert to the Colorado River near Needles. On the 500 mile journey, the rain did not stop. I did not see the most intense problems (apparently the entire town of McFarland was evacuated, for instance), but I saw plenty of water where I've never seen water before. I have been over Tehachapi Pass perhaps 80 times in the last 20 years, and I have never seen water in the channel of Caliente Creek where it flows into the Central Valley near Bakersfield. That's it above...

Dry Creek near Modesto is actually rarely dry because of irrigation runoff, but it also rarely looks like a river. I've seen it worse, but then the Modesto area was one of the areas least affected by the current storms.

The desert was simply soaked. The western Mojave Desert has an internal drainage system (doesn't flow to the ocean) and is exceedingly flat. The ground was already saturated by the time we came through, and water was ponding everywhere, including our highway near Barstow. Greenery was already showing through, and the additional moisture means there is potential for a spectacular wildflower display in another month or two. I have my fingers crossed for our Death Valley trip in February!

Some pretty serious problems cropped up in western national parks. Road damage closed Sequoia National Park in California, and Zion National Park in Utah (Zion may not reopen until January). The normal flow of the Virgin River in Zion is 40-50 cubic feet per second; today it reached 5,000 cfs in the morning and was continuing to rise.

Thanks to Susan for the first and third pictures!