Liveblogging the Deluge: Perspectives on the Biggest Flood in a Decade, Part One

See updates at end of post... BTW, if you are on the scene in places like Yosemite Valley, please send photos or updates! I will gladly post them here.

Printable PDF of current conditions can be found at this link 

It's clear by now that I am fascinated by the current atmospheric river storm that is blanketing the state of California with precipitation from one end of the state to the other. I'm right in the thick of it, in the Great Valley, sandwiched by mountain ranges that will be getting rain amounts measured not in inches, but in feet. On this blog, I've already talked about the last record-breaking storm, the 1997 event that caused unprecedented damage across California, but especially in Yosemite and along the Tuolumne River. I also blogged about the preparations being made in anticipation of the storm: the operators of Don Pedro Reservoir have ramped up the flow of the Tuolumne River to near flood stage to make room for storm runoff. Then, last evening, we had a spectacularly clear view of the Sierra Nevada from the valley floor, covered with snow, and seeming to wait for the coming storm event. From here on, I'll be liveblogging, sort of, the storm (it will be separate posts at times).

Radar of precipitation in Central California as of 8:00 PM Saturday. Source: Intellicast

And now the storm has arrived. Atmospheric river storms are linear streams of moisture-rich air coming northward out of the tropics (they have been called Pineapple Express storms at times). In "normal" front-related storms, the period of precipitation is fairly limited as the front sweeps through the state. Atmospheric river storms are different; they spray the state with storms that can last for days, and in some extreme examples, weeks. They are also warm storms. The snow level can reach very high elevations so that rain falls on the snowpack, melting vast amounts of ice. It all adds up to a potential for the worst kinds of floods in California.

I don't know what all is going to happen in the next few days, but I want to establish some baselines so it can be understood just what the storm means for California and our water situation. We have been in the grip of a crippling drought since 2011, and reservoirs across the state have been at historical, even catastrophic, low levels. The first diagram in this post provides a benchmark to track the changes in the next few days. It's already been a fairly good precipitation year, as some reservoirs already sit at 100% or more of their desired levels. A few are still very low, including especially New Melones Reservoir on the Stanislaus River just north of me. It is only at 27% of capacity. Lake McClure on the Merced River below Yosemite Valley is about where it is supposed to be at 47% of capacity. My special river, the Tuolumne which also flows out of Yosemite National Park, is a bit too close to full at 76% of normal. If the storm dumps too much rain in the park, it has a small chance of overflowing the floodgates in an uncontrolled manner as it did in 1997. That's the reason the dam operators ramped up flows in the last two days.

Source: California Nevada River Forecast Center

It's going to be especially interesting to see how the storm predictions pan out. The flood hydrograph above is the expected outcome in Yosemite Valley. The red dotted line is flood stage (at 10 feet, or around 7,000 cubic feet per second). Earlier predictions for the flood peak have wavered between 15,000 cfs and 24,000 cfs. The high end prediction would be of 1997 magnitude, but even the low prediction would be enough to flood valley roads and possibly close the park. The high flow history at Pohono Bridge in the valley is shown below:

Historic Crests

(1) 23.43 ft on 01/03/1997
(2) 23.43 ft on 01/02/1997
(3) 21.52 ft on 12/23/1955
(4) 20.98 ft on 11/19/1950
(5) 20.10 ft on 12/11/1937
(6) 16.96 ft on 12/23/1964
(7) 13.11 ft on 04/11/1982
(8) 13.01 ft on 01/13/1980

The current outlook is for a peak of 21,590 cfs (19.7 feet).  If it happens, it would be the 6th highest flow ever recorded. As you might expect, I'll be watching this one closely.

Flood hydrograph for Dry Creek. Source: http://www.cnrfc.noaa.gov/graphicalRVF.php?id=DCMC1

The other local river that has my undivided attention is Dry Creek. It's not a well-known waterway outside our region, but it is capable of causing some havoc at times. Although it doesn't have a vast drainage basin (it arises in the Sierra Nevada foothills in the Mother Lode), it has no dams or flood control structures. It is therefore very responsive to variations in storm intensity. I've seen it flowing at 3,000 or 4,000 cfs, but the prediction as of this evening is a bit ominous: it may peak at 8,400 cubic feet per second. Let's be clear what that means: yesterday, the Tuolumne River was flowing at 8,000 cfs, and that's considered very close to flood stage. For the Tuolumne River. A minor tributary to the Tuolumne River may be as big as the Tuolumne, but in a channel that is many times smaller. I will be out and about on Monday to get pictures, but to set a baseline of sorts, here's how the creek normally looks at the Oakdale-Waterford Highway bridge:

Dry Creek on Dec. 17, 2016 just prior to a previous high water event late last year.

So, here is where we stand with the atmospheric river storm in my backyard. We've received about a half inch of rain today, adding towards an expected 4 inches by the end of the week. If things transpire that way, it will represent about a third of the precipitation expected in my town over the course of an entire normal year. We of course are in the driest part of Central California (aside from the desert east of the Sierra Nevada), so literally everywhere else will be getting a lot more. As I've been saying in my previous blogs, be safe out there! Don't travel if you can avoid it, don't try crossing flooded bridges, and don't try walking either. If you are headed into the mountains, imagine being stranded by yourself for a few days and pack accordingly, especially with warm clothing and extra food rations. My distant relatives, the Donners, failed to do that in the Sierra Nevada in 1847, and look how they ended up. If authorities issue a flood warning, take it seriously. They're getting their advice from scientific professionals, and that still means something.

UPDATE: Officials closed Yosemite Valley roads and visitor services as of yesterday, and will reopen after the flooding subsides.
UPDATE: (although more like an addendum) For comparison's sake, here is where the reservoirs of the state were at a year ago:

A huge difference!
UPDATE (1/8, 1:52 AM): Yes, up late, listening to intensified rainfall. Gauge has picked up another .40 inches in two hours.

UPDATE  (1/8, 10:18 AM): Good morning! There was another 0.20" in the backyard gauge this morning, and now we are in a lull between major storms (most of the action is north of here at the moment). Another 2/3 inch is expected later today on valley floor. There is better news in Yosemite; the expected flood is now projected to be less than catastrophic, with a projected high flow of 9,600 cubic feet per second. Yesterday, the projection was twice that. It's still above flood level by 2 feet, but would not cover valley roads. Several more inches of warm rain is expected (~4"), but tomorrow the precipitation will turn to snow, and that is a good development.

The Difference a Year Makes: Liveblogging the "Deluge" (Hint: There isn't one)

This post is both a look back at ten years of Geotripping, but is also an update on snow and precipitation conditions in California right now, and that picture is not pretty. My backyard rain gauge had amassed a mere 1.22" of rain by the beginning of January, and while January had higher than normal precipitation, I only show 4.66" for the rain year, just a bit over 50% of normal (I think we benefited from a few isolated downpours, as Modesto, just 13 miles away is at 3.09"). During the historic drought of 2011-16, three of the dry years were wetter than this.

I walked the Tuolumne River Parkway Trail today, and for the first time in weeks I could see the Sierra Nevada, the peaks that loom high above Yosemite Valley. The sun reflected off a snowpack that was far different than it was a year ago. The snowpack is only 30% of normal (see below). It's late January and there are a few ski resorts that haven't even opened yet (if they'll even open at all).

Source: http://cdec.water.ca.gov/snowapp/sweq.action

If there is any bright spot in this dismal year it is California's reservoirs. Because of the ample rain and snow last year, most of the reservoirs are at healthy levels, more than 100% of normal (see below). One prominent exception is Oroville Reservoir, which was lowered drastically to allow repairs to the spillways that failed during the height of the storms last year. There is at least some comfort to know that we have some resources to weather another drought, at least for a few years. I would have preferred a few wet years to help replenish our depleted groundwater reservoirs. That is a lasting effect of the drought that may not be fixed any time soon.

Source: http://cdec.water.ca.gov/cgi-progs/products/rescond.pdf

The Tuolumne River Parkway is a changed place. During the deluge last year, river flows were maintained at or near flood levels through July. Much of the river floodplain was underwater for months, and hundreds of trees and shrubs were uprooted and carried downstream, in places leaving behind huge masses of dead vegetation. Riverside vegetation really never had a chance to recover and regrow once the water subsided. The hated invasive weed River Hyacinth is gone, but so are many riparian shrubs. The six month flood was necessary to protect human developments on the river, but it didn't do the habitat much good. I'm hoping that the wholesale redistribution of river gravels will do the Salmon and other river organisms some good. I have run across signs of beaver, otter, raccoon, and foxes on the floodplain in recent days.

I've been going through the Geotripper archives to select some of my favorite blog posts of the last ten years. The first half of 2017 was dominated by my observations of the extraordinarily wet year and the flooding, which I called "Liveblogging the Deluge". I wrote dozens of posts all through the first half of the year, and it was hard to pick any particular ones to illustrate here, so I settled on the one I wrote exactly one year ago. It involved the post-mortem of the first of the major atmospheric river storms that battered the state. Many more were to come...

Thursday, January 26, 2017

Liveblogging the Deluge: The Post Mortem...Storms That Made a Difference

The atmospheric river storms of January have finally subsided, and we are looking at kind of a new landscape across California. We had a couple of sunny days, so we headed up the highway to have a look at Don Pedro Reservoir on the Tuolumne River coming out of Yosemite. When we visited on January 5, the lake stood at 786 feet, which translates to 76% of capacity. That was 114% of normal for this time of year, which was a relief after five years of intense drought.

Don Pedro Reservoir on January 26 after two atmospheric river storms, elevation 813 feet (90% of capacity).

When we arrived yesterday, the lake stood at 813 feet, or 90% of capacity, which is 133% of normal. It is only 17 feet below the level of the dam. It could have been higher, but the dam operators have been maintaining constant outflows in the range of 7,000-9,000 cubic feet per second, a level that is just short of flood stage. Had they not done this, the lake could have overflowed and flooded downstream urban areas as happened in 1997.

Source: http://cdec.water.ca.gov/cgi-progs/products/rescond.pdf

It is a similar picture at the major reservoirs all around California. The monster reservoirs, Shasta and Oroville, are at more than 120% of normal for this time of year. San Luis Reservoir, the critical link in the California Water Project, is 103% of normal, and may fill for the first time in five years. A few are still low, most notably New Melones (68% of normal), and Trinity (84% of normal), but they are way up from where they stood before the storm.

Source: http://cdec.water.ca.gov/cgi-progs/products/rescond.pdf

The picture in my corner of the woods is brighter too. The Tuolumne River is running fast and cold, and in many places it covers practically the entire floodplain, and has done so for several weeks now. I believe that most areas downstream are not affected by the high flows (there is a history after all of flooding, and outflow from Don Pedro is regulated so as to prevent it). Instead the river is flushing itself of invasive hyacinth, which has been threatening numerous creatures and plants. Gravel bars are shifting and accumulated silt is being removed, providing better nesting areas for salmon and other fish species. Silt is being redistributed across the floodplain, rejuvenating the soils of the riparian areas. Groundwater aquifers in the vicinity of the river are being recharged.

Tuolumne River in Waterford, about 8,000 cubic feet per second

My rain gauge has been active. My friends in more humid regions may snicker a bit when I talk of how we've had 7.38 inches of precipitation in January. That might not seem like all that much but in 25 years of recording rainfall in Waterford, only two had greater amounts, 7.58" in 1995, and 8.60" in 2011.  We've had a year where that was the total for the entire season (7.26" in 2014). We've already passed the total rainfall normally received in an average year (14.69" so far compared to 13.92" average for the last 25 years).

But the real story? The snowpack.

At the height of the drought, we had a snowpack that was 5% of normal. 5%! It was both unbelievable and appalling.

Source: http://www.sacbee.com/news/state/california/water-and-drought/article124305504.html

This year started out with some good healthy storms, but the January events threatened to undo the progress. On the first of January, the statewide average was 70% of normal, which was an improvement over the last five years.The atmospheric rivers began as warm tropical storms that threatened to melt what snow there was. At first they did, but colder arctic are started to move in and the snowpack began to build. After the first set of storms blew through, the statewide snowpack had improved to more than 100% of normal.

And the snow kept falling! The second atmospheric river storm system brought even more snow, and as of today, the snowpack is nearly 200% of normal. If the trend continues (there is NO guarantee of this), we could be on track for a record snowpack. I don't consider it likely, but it would be nice to start recharging the groundwater aquifers that have been severely depleted in recent years.

Source: http://cdec.water.ca.gov/cgi-progs/products/swccond.pdf

The record snowpack should not be seen as evidence that global warming isn't happening. Average temperatures are defiinitely up and have been for several decades. The thing is, snow is snow whether the temperature is 15 degrees or 30 degrees. A not-at-all unusual heat wave could undo the progress in the snow levels. The sky spigot could turn off. After the record flooding of 1997, February and March both provided less than a quarter inch of rain over the entire month. And the drought will never be truly over, as demand outstrips supply even in plentiful years. And little is being done to replenish declining groundwater aquifers.

All in all, though, I'm happier to have plentiful rain rather than crippling drought!

Liveblogging the Deluge: It Ain't Over 'til the Fat River Drains...A Six Month Flood is in Process

The flooding in California hasn't been in the news all that much of late, but that doesn't mean the threat is over. The atmospheric river storms that have been hitting the state like an out-of-control fire hose have been turned off for more than two weeks, and no storms are in the ten-day forecasts, at least not in my area along the drainage of the Tuolumne River.

Our local rivers haven't received the message yet.

We were at the Merced National Wildlife Refuge yesterday, and as we were leaving we noticed that the Mariposa Slough, a usually dry watercourse, was in full flood mode, flowing over Dan MacNamera Road. Off to the west, water covered a huge area (below).

Today I was back on my own river, the Tuolumne, where it flows out of the Sierra Nevada onto the Great Valley floor. It is still flooding, and has been since January 4 when the most damaging of the atmospheric river storms began battering the state (the current flow is more than 11,000 cubic feet per second). One might think that once the rain stops, so will the flooding, but the situation is not so simple.

In the days before gigantic dams were built on Sierra rivers, huge tropical rainstorms would drop prodigious amounts of rain in the mountains, and monstrous floods would spread out across the floor of the Great Valley, looking much like the scene above, but extending for three hundred miles north, as far as Red Bluff in the north valley. The water would take weeks to flow out through the Carquinez Straits into San Francisco Bay. The last storm that did this took place in 1861-62. The vast flood caused the state to move its capitol to San Franscisco until the waters subsided. 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 have to seriously consider the possible effects.

The giant reservoirs that have been built along the major rivers of the Sierra Nevada represent our last line of defense against such floods. They are designed to capture the biggest surges in such storms, holding the water until it can be released at lower flow rates spread out over time. Most years the dams do their job well, but they can be overwhelmed, as they were in 1997 when there was widespread flooding across the valley. Which brings us to the current situation on the Tuolumne River.

Don Pedro reservoir can hold just over 2 million acre-feet of water. Because of the brutal drought of the last five years, the lake was allowed to collect and hold much of the runoff from the early season storms of November and December, and by the end of the year, the lake was beginning to fill. And then the big storms of January appeared in the long-range forecasts. Operators at the dam realized they needed to make more room in the reservoir, so they ramped up the outflow of the river to a near flood level rate of 9,000 cubic feet per second. It's not usually allowed to go higher because of a local quirk of the geology.

The Tuolumne River is trapped in a narrow channel all the way through Modesto downstream, and has little room to spread out over the valley floor. In some ways that is a good thing: downtown Modesto and other cities downstream can't be flooded by overflowing rivers the way it can happen in Stockton or Sacramento (these towns require extensive levees for flood protection). Others who live downstream are not so lucky, as higher flows translate to deep-water flooding within the narrow floodplain. The floods can also overwhelm levees downstream on the flatter parts of the valley floor around Patterson and Tracy.

The unique channel and bluffs along the Tuolumne originated in the Pleistocene ice ages. During the time of maximum ice advance the swollen river (average flow was several times what it is today) was full of silt and mud which was distributed across the Great Valley flow in a vast alluvial fan. When the glaciers receded, the rivers started flowing clear and the faster flows cut into the surface of the alluvial fan, forming the distinctive terraces that can be followed from the Mother Lode to west of Modesto.

So here's the tricky part: this wasn't just a few tropical atmospheric river storms that dumped incredible amounts of rain. Many of these storms drew in arctic air masses and tremendous amounts of snow now coat the high country of the Sierra Nevada. The snowfall has accumulated to record depths and now something like two million acre-feet of water now drapes the slopes upstream of Don Pedro. If you are keeping track of all the numbers, that's enough to completely fill the reservoir, which happens to be nearly full already.

We are facing a problem of water disposal not seen in modern times. The operators of the dam have to walk a fine line of preventing downstream flooding, but allowing for huge inflows of melting ice and snow in the coming weeks. The "fine line" included opening up the emergency spillway for the first time since 1997 and having the water rise to within an inch or two of overflowing in an uncontrolled manner. Outflow finally began exceeding inflow on the 25th of February, and the lake is now about 10 feet below the rim for the first time since January.

The threat is not so much more stormy weather (the rain season is tapering off now), but heat waves. It's going to reach 80 degrees around the valley floor next week, and the warm conditions are going to accelerate the rate of melting. So we can be sure that the water managers will be watching conditions carefully. I read that flows will continue at near flood levels for another three or four months!

My local stretch of the Tuolumne River (and the rest, of course) will be a changed place by the end of this extraordinary year. I will not be surprised if there are some new channels in a few places. Certainly the number of trees along the river will be changed. Several big ones on the Parkway Trail have already come down. A great many shrubs and thickets have been washed away as well. One very nice development is that the upstream sections of the river have been swept clean of the hated river hyacinth, an invasive species that has caused innumerable problems (I don't know the current situation with the hyacinth in the Sacramento Delta).

Learn more about the possibility of overwhelming atmospheric river storms here: USGS ARkStorm Report (PDF - 46 mb).

Liveblogging the Deluge: The Post Mortem...Storms That Made a Difference

Don Pedro Reservoir on January 5 before the storms, elevation about 786 feet (76% of capacity).

The atmospheric river storms of January have finally subsided, and we are looking at kind of a new landscape across California. We had a couple of sunny days, so we headed up the highway to have a look at Don Pedro Reservoir on the Tuolumne River coming out of Yosemite. When we visited on January 5, the lake stood at 786 feet, which translates to 76% of capacity. That was 114% of normal for this time of year, which was a relief after five years of intense drought.

Don Pedro Reservoir on January 26 after two atmospheric river storms, elevation 813 feet (90% of capacity).

When we arrived yesterday, the lake stood at 813 feet, or 90% of capacity, which is 133% of normal. It is only 17 feet below the level of the dam. It could have been higher, but the dam operators have been maintaining constant outflows in the range of 7,000-9,000 cubic feet per second, a level that is just short of flood stage. Had they not done this, the lake could have overflowed and flooded downstream urban areas as happened in 1997.

Source: http://cdec.water.ca.gov/cgi-progs/products/rescond.pdf

It is a similar picture at the major reservoirs all around California. The monster reservoirs, Shasta and Oroville, are at more than 120% of normal for this time of year. San Luis Reservoir, the critical link in the California Water Project, is 103% of normal, and may fill for the first time in five years. A few are still low, most notably New Melones (68% of normal), and Trinity (84% of normal), but they are way up from where they stood before the storm.

Source: http://cdec.water.ca.gov/cgi-progs/products/rescond.pdf

The picture in my corner of the woods is brighter too. The Tuolumne River is running fast and cold, and in many places it covers practically the entire floodplain, and has done so for several weeks now. I believe that most areas downstream are not affected by the high flows (there is a history after all of flooding, and outflow from Don Pedro is regulated so as to prevent it). Instead the river is flushing itself of invasive hyacinth, which has been threatening numerous creatures and plants. Gravel bars are shifting and accumulated silt is being removed, providing better nesting areas for salmon and other fish species. Silt is being redistributed across the floodplain, rejuvenating the soils of the riparian areas. Groundwater aquifers in the vicinity of the river are being recharged.

Tuolumne River in Waterford, about 8,000 cubic feet per second

My rain gauge has been active. My friends in more humid regions may snicker a bit when I talk of how we've had 7.38 inches of precipitation in January. That might not seem like all that much but in 25 years of recording rainfall in Waterford, only two had greater amounts, 7.58" in 1995, and 8.60" in 2011.  We've had a year where that was the total for the entire season (7.26" in 2014). We've already passed the total rainfall normally received in an average year (14.69" so far compared to 13.92" average for the last 25 years).

But the real story? The snowpack.

At the height of the drought, we had a snowpack that was 5% of normal. 5%! It was both unbelievable and appalling.

Source: http://www.sacbee.com/news/state/california/water-and-drought/article124305504.html

This year started out with some good healthy storms, but the January events threatened to undo the progress. On the first of January, the statewide average was 70% of normal, which was an improvement over the last five years.The atmospheric rivers began as warm tropical storms that threatened to melt what snow there was. At first they did, but colder arctic are started to move in and the snowpack began to build. After the first set of storms blew through, the statewide snowpack had improved to more than 100% of normal.

And the snow kept falling! The second atmospheric river storm system brought even more snow, and as of today, the snowpack is nearly 200% of normal. If the trend continues (there is NO guarantee of this), we could be on track for a record snowpack. I don't consider it likely, but it would be nice to start recharging the groundwater aquifers that have been severely depleted in recent years.

Source: http://cdec.water.ca.gov/cgi-progs/products/swccond.pdf

The record snowpack should not be seen as evidence that global warming isn't happening. Average temperatures are defiinitely up and have been for several decades. The thing is, snow is snow whether the temperature is 15 degrees or 30 degrees. A not-at-all unusual heat wave could undo the progress in the snow levels. The sky spigot could turn off. After the record flooding of 1997, February and March both provided less than a quarter inch of rain over the entire month. And the drought will never be truly over, as demand outstrips supply even in plentiful years. And little is being done to replenish declining groundwater aquifers.

All in all, though, I'm happier to have plentiful rain rather than crippling drought!

Liveblogging the Deluge: San Joaquin River National Wildlife Refuge - What a difference a few months made (and Rabbits)

The San Joaquin River at the National Wildlife Refuge in November 2017

Just a few months ago, the San Joaquin River, and its major tributary the Tuolumne River, were in big trouble. The worst drought in California's recorded history had left the rivers at a mere trickle, and many parts of the San Joaquin were dry, despite recent efforts to bring back some sort of minimal flows to stretches of river that had been dry for decades (after dam and irrigation levee construction upstream). The invasive weed River Hyacinth had choked channels, crowding out native vegetation and making life difficult for fish and other organisms.

I hiked the Pelican Nature Trail in the San Joaquin River National Wildlife Refuge back in November, and despite a few early storms, dryness was the overwhelming feeling. Volunteers have put in a vast amount of work replanting former riparian woodlands, but it felt like the river overflow areas wouldn't see water any time soon. The river was flowing at a sluggish couple of hundred cubic feet per second.

The San Joaquin River in the same exact location on February 14, 2017

I returned to the Pelican Trail yesterday to a changed world. A series of atmospheric river storms over the last six weeks have dumped record amounts of precipitation across northern and central California. Watermasters at the reservoirs upstream joyfully let their dams fill with the prodigious amounts of water, but then the storms kept coming and they realized that some of the dams were in danger of overflowing. They ramped up flows out of the reservoirs and the rivers downstream swelled. The Tuolumne River, for instance, has been flowing at near flood levels (~9,000 cubic feet per second) for the last five weeks, and this week the flows were increased to over 11,000 cubic feet per second. Don Pedro Dam is only 2-3 feet below full capacity, and has only about 30,000 acre-feet of capacity (out of 2.03 million acre feet of storage space). The Merced River has been experiencing high flows as well, and water is high in the usually dry San Joaquin riverbed. Yesterday the river at Vernalis, just downstream of my trail, reached official flood state at 34,000 cubic feet per second.

It was rather stunning to stand on one bank of the San Joaquin, the neglected trickle of water from the southern Great Valley, and not be able to discern exactly where, off in the distance, the other bank was located. And there is this: the water level is probably going to rise soon. Yet another intense storm is headed towards California, and there is going to be another week of rainfall and snow in the mountains upstream. Don Pedro Lake, for one, is just about full and it is possible they will have to let additional water through the system to keep the lake from overflowing.

More than a month ago, on January 4, I wrote the first of a series of blogs that I soon called Liveblogging the Deluge. I quite honestly thought it was going to consist of four, maybe five posts as the first atmospheric river storm passed through California. But another storm soon followed, and then another. I look back now and see that I've published 24 posts on the storms, and they keep coming. This has been an extraordinary storm event and, for some people, a scary experience. Nature cares little for human beings and our puny attempts to control it can sometimes result in failure and tragedy. Despite the evacuation of 180,000 people because of an unstable situation at Oroville Dam, we've kind of held things together in the north part of the state, but the system is presently strained to the limits. Levees are showing signs of failure in places and reservoirs are getting dangerously full. It is imperative that residents in California keep their eyes open, and when the warnings come and evacuations are ordered that they comply as quickly and orderly as possible. Making a principled stand to defend your house against a rising flood is dangerous and may be deadly.

By the way, the other strange sight on the Pelican Nature Trail was the prevalence of Desert Cottontail Rabbits. There were perhaps hundreds of them along the trail. I assumed they had been flooded out of their habitat on the flats below and had gathered on the high ground of the levee where they were nibbling at the smallest shoots of grass, or reaching for leaves on the lower branches of the shrubs.

They barely seemed to register my presence. I was stepping only two or three feet away from them before they would move into the brush along the trail. They only scattered rapidly once, when a Northern Harrier flew overhead. Human beings are not the only beings who are affected by the floods.

I'm not going to be able to liveblog the coming storm, as I will be out in the middle of it. We're headed out to the Death Valley region where we will be navigating between storms and flash floods. I expect to have some interesting observations once the storm is past and we are home again. And yes, we will be careful out there. It's not often that one gets to observe rain in the driest place in North America. See you in a few days!

Liveblogging the Deluge: Before and Almost After

Tuolumne River on Feb. 21, 2017, discharge about 16,000 cubic feet per second

There is no doubt that this has been a unique year for the rivers of California, one that could very well not be repeated in many of our lifetimes. A year ago we were in the grips of the worst drought ever recorded, five years running, and then the rains began. And continued. Month after month, one atmospheric river storm after another took aim at California like an out-of-control fire hose. The snowpack reached levels not seen in generations, in some places reaching 200% of normal.

Tuolumne River this afternoon, discharge 3,520 cubic feet per second

And then things got scary. Oroville Dam came uncomfortably close to failure, requiring the evacuation of 200,000 people downstream for a period of time. Don Pedro Dam on the Tuolumne River was not in danger of failure but it came within inches of overflowing uncontrollably, and the emergency floodgates were opened for only the second time in history (the first being in 1997). On January 4, operators at the dam ramped up flows of the river to 10,000-12,000 cubic feet per second (for a day or two, flows reached 16,000 cfs), putting it in a state of official flooding, and the water flows did not begin to recede until only a few days ago. I checked out the river a week back, and the river was down to 6,000 cfs. Today it was 3,520 cfs, and after five months of constant inundation, the floodplain was at long last reemerging. For perspective's sake, the average flow of the river during much of the drought was around 200-500 cubic feet per second.

On Feb. 21, the river was flowing into the large quarry pond on the top left of the picture.

The snowmelt has not actually slowed down, actually. The inflow into Don Pedro Reservoir has remained constantly above 12,000 cfs for much of the last month, but apparently the dam operators are feeling confidant that they can fill the dam without overflowing, and have allowed the lake level to rise slowly from 798 feet to 815 feet (it would be full at 830 feet). This is the delicate dance they must do to maintain flood protection while preserving as much water in storage as possible for irrigation and domestic use downstream.

Today, the river and the pond are separated again. The floodplain in the foreground is once again exposed.

I've been wondering ever since the floodplain was inundated how the channel of the river would be affected by the ongoing deluge. At such high flow velocity, cobbles and gravel have surely been redistributed across the floodplain. It is not yet clear whether the river will find a new channel, but I would not be surprised if that happens. I can see new sandbars that may be blocking old channels in a few places. I wondered if the slough at the base of the metal stairway on my river trail would become a new channel, but it's looking like it will not, but it may be longer than it once was.

The most apparent change will be in the riparian vegetation. There had been a great deal of growth on the floodplain since the last inundation in 1997, and much of that vegetation has been swept away. Whole mature trees are gone, and entire willow thickets. A bit of good news in that regard is the complete absence of river hyacinth. The invasive plant was well established on the upper Tuolumne, but all sign of it has been swept away in the torrent. I hope the same has happened downstream at the confluence with the San Joaquin and in the delta. The hyacinth has choked channels and blocked out native plants and wildlife. Maybe this event will be a reset, and some form of control can be achieved.

The other changes to consider are the animals. The floodplain was a rich habitat for all manner of mammals, reptiles, amphibians, fish, and creepy crawlers. Many have been displaced for months, and their former homes will be highly altered or gone. There will be large tracts of barren gravel. I'll be watching for their return.

The floodplain of the Tuolumne was not a natural river before the flood. Gold mining, dredging, and quarrying had already severely damaged the riparian environment, and altered the natural channel. There were few of the gravel bars needed by the salmon and other native fishes to spawn. I am hopeful that the flood will have made some positive changes.

The deluge is not yet over. There is still a huge amount of snow in the high country, and flows will no doubt remain high for weeks or months to come. The full extent of the changes to the floodplain will not be apparent for some time. I'll be there to report when they are!

Liveblogging the Deluge: Atmospheric River Storm Version 2.0

Intellicast radar image of January 18, 2017.

What a strange January it has been. We were hit by the strongest storms in two decades, and there was a spate of flooding and high river flows across much of northern and central California. The storms built up state reservoir levels to a healthy degree, and the snowpack is looking better than it has in many years. The storms were examples of atmospheric river storms, which tap into tropical moisture as they stream across the west coast of the United States, especially California. Such storms are historically the most important source of precipitation across the state.

We had three pulses of precipitation during the event last week, and the first was maybe the most dangerous, as it was particularly warm and dropped heavy rain on the snowpack at elevations as high as 10,000 feet in some areas. This was a recipe for disaster, but luckily the forecasts were accurate enough that most people and communities were aware of the coming floods, and were able to act accordingly. There certainly was damage, but nowhere near the scale of the floods of 1997. The remaining storms added considerably to the snowpack so that by January 14, the statewide snowpack was 150% or more of average. Many of California's reservoirs are at 100% or more of average, with just a few exceptions, including New Melones Lake (67% of normal) and Trinity Lake (82% of normal).

All of this would be a great bit of news in terms of the drought, even if no new storms materialized. But here's the thing: it's about to happen again this week! Another set of atmospheric river storms are taking aim at California, and they will be quite egalitarian, providing a big boost to rain totals in Southern California as well (which got some rain last week, but not to the extent of the north). The first storm is here, and it is raining across the entire state from the Oregon border to Baja.

On the local scene, my backyard rain gauge captured 3.69 inches during the first set of storms, and with a smaller storm earlier in the month, I'd recorded 4.58 inches. That's more than twice the average for January around here, and 0.80 inches has already fallen tonight. 5.38 inches for January makes this the seventh wettest January in the quarter century that I've been measuring. As much as 3 more inches of precipitation is expected in this latest series of storms, so we have the chance of breaking the record for the month (8.60 inches in 2011, according to my records). 

It's worth noting that in 1997, we had the record floods at the beginning of the month, and a second group of intense storms later in January. But after that, literally nothing: 0.25 inches in February, 0.09 inches in March, and 0.19 inches in April. The total precipitation for the year of worst flooding was barely higher than average at 15.43 inches (my local average for 1991-2016 is 13.92 inches).

The Tuolumne River is still running at near flood levels as Don Pedro is drained to make room for coming storms.

It's going to be interesting to see what the rest of the water year holds for us...