Liveblogging the Deluge: Merced River in Yosemite Reaches Flood Stage

This picture is a cheat. I'm not in Yosemite, this picture is from two years ago

I was supposed to be in Yosemite right now. We had scheduled a field studies class today that would have sent us up the Merced River to Yosemite Valley and back, but nature has intruded with an unusual April atmospheric river storm that is setting some daily rainfall records across Central California. San Francisco, for instance, received rain equivalent to an average April in a single day. My backyard rain gauge in the Central Valley has recorded 2.2 inches since yesterday. In 26 years of measuring, there have only been three Aprils where we've received that much in the entire month.

I had already decided to postpone the trip by last Monday when the forecasts called for flooding on the Merced River in Yosemite Valley. In short, the river jumps its banks at the 10 foot level (about 6,000 cubic feet per second). At 12 feet (9,500 cfs), the flooding river covers some of the main roads in the valley. Today's storm is expected to result in a river that crests at 14 feet, or 14,000 cubic feet per second. Even if I had decided to go ahead with the field trip, we would not have reached our goal, because the park service closed Yosemite Valley yesterday. We're going to try and make the trip tomorrow to check out any flood damage, but if the valley floor is still closed, we'll try to see Hetch Hetchy instead.

Yosemite Valley is especially prone to flooding because it is high up in the mountains close to the headwaters of the Merced River, and when rain falls, it falls on mostly barren granite. The water flows into channels very quickly, and the channels gather into the Merced River and Tenaya Creek just as quickly. There are no reservoirs upstream for flood control (nor should there ever be).

If it drives home the point, Yosemite Valley has only been closed a few times in its history, most notably in 1997 during the unprecedented floods of that year, and during a few government shutdowns. It takes a major event to convince the park administration to shut down the iconic valley.

I hope to be back tomorrow with pictures of Yosemite Valley. We'll see what happens! I will update the flood hydrograph in the space below when the river flow peaks.

UPDATE: At 1:00 PM, the river has reached 10,800 cubic feet per second (12.85 feet). If I'm reading the data right (below), this is only the fourth time the flow has reached this level since 1996.

Here is the 1:00 PM report:

Also, here is a link to video of the main road in Yosemite Valley at the moment, courtesy of the Fresno Bee.

UPDATE 2: We've reached 12,100 cubic feet per second as of 5:00PM, and 13.68 feet (10 feet is flood  level), and the flood may be peaking. The discharge only increased by 100 cfs in the last hour.

FINAL UPDATE: It looks like the flood has peaked at 12,100 cfs, as it has been there for two hours. I expect it will now start dropping. I'm hoping the valley will reopen in time for our visit tomorrow. If not, I guess we'll check out Hetch Hetchy!

WELL, OKAY, ONE MORE UPDATE: Yosemite National Park has posted pictures of the flooding today: https://www.facebook.com/pg/YosemiteNPS/photos/?tab=album&album_id=1650167855031490

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.

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: The First Day of Fall and a River Finally Returns to Abnormal

I was mistaken. Nearly two months ago, I suggested in a post that the abnormally high flows on the Tuolumne River were finally subsiding, and that the great flood of 2017 might finally be ending. This happened because I strolled along the river on a day when the output from Don Pedro Reservoir finally fell below 5,000 cubic feet per second, to around 1,500 cfs. That lasted for an entire day or two. The inflow at Don Pedro was still several thousand cfs, and the effort to build up some emergency flood storage space in the reservoir meant that they ramped up flows to 5,000 cfs, and that level continued for another seven weeks.

Source: https://waterdata.usgs.gov/ca/nwis/uv?11289650

I walked the river again today and saw something I haven't seen in nine months: a river at very close to minimum mandated flow. A quick check of the river gauge on the USGS site confirmed that the river was flowing at a mere 339 cubic feet per second. A look at the table above shows how the flow has been declining over the last week.

The CDEC site for Don Pedro Reservoir is even more informative, showing high flows throughout August and early September. Inflow to the reservoir finally dropped below 1,000 cfs about the 12th of September, and the outflow was then also lowered (about 1,500 cfs is diverted for irrigation which accounts for the discrepancy between output from Don Pedro and the river flow below LaGrange Dam where the diversions take place).

Source: http://cdec.water.ca.gov/cgi-progs/queryDaily?s=DNP&d=22-Sep-2017+20:14

Don Pedro Reservoir remains well above normal in water storage after an extremely wet year of precipitation. It presently holds 1.7 million acre-feet, about 84% of lake capacity, and 126% of normal for this time of year.

The floodplain is a different place now, compared to what it was a year ago. The biggest change is the vegetation. Hundreds, maybe thousands of trees and shrubs have been uprooted and washed away downstream. There are huge piles of branches and tree trunks across the riverbed. Other areas along the streambed have been washed clean of any vegetation at all, leaving vast tracts of barren gravel and pebbles. The invasive and damaging water hyacinth is gone, carried downstream in the many months of flooding. One can only hope that the seeds were carried away as well, although they probably weren't. I'll be pulling any hyacinth out of the river that I see in coming months.

The river is not back to normal, because "normal" disappeared more than a century and a half ago when gold was discovered upstream. The original channel and floodplain was upended in the search for the elusive metal. Trees and shrubs were removed, and every bit of gravel was run through sieves, longtoms, or dredges. After the search for gold ended, quarrying for gravel and sand took over, further altering the floodplain, ultimately forming numerous ponds fed by groundwater seepage.

These days, efforts are being made by organizations like the Tuolumne River Trust to bring about some sort of natural balance on this badly scarred landscape. Adjustments to the channel can help expose the gravel bars that salmon need to spawn, and one can hope that the fall run will be more successful than those of the last five years during the drought. Only the Merced River has a more southerly run of Chinook Salmon. At one time 130,000 salmon cruised the Tuolumne. In the last decade, the run has exceeded 1,000 only once (1,926 in 2013).

Walking the Tuolumne River Parkway Trail in Waterford. This is my backyard.

In the meantime, the flood of 2017 seems to finally have subsided. The river is back to abnormal, and we now await the new storm season. After a monster season in 2017, one has to wonder what the coming year holds in store for the river.

Liveblogging the Deluge: Is the Big-Boned Lady Singing? The Aftermath of the 2017 Flood on the Tuolumne River

The Tuolumne in August of 2015. This was a sick river overgrown with invasive hyacinth. Flow is about 200 cfs.

Goodness sakes, are we still talking about that flood? Well, yes we are. It isn't quite done, although events this week are signaling the end, at least in some respects. In another respect, the five-year drought that we thought the floods put an end to is still with us.

I've had the privilege of seeing two great floods in my time living along the Tuolumne River where it flows into California's Great Valley. The first was the incredible flood of 1997 when the river overwhelmed Don Pedro Reservoir and rampaged through my town at around 70,000 cubic feet per second. The second was this year. The river never topped 15,000 cubic feet per second, but the flood continued for kind of a long time...it lasted for more than six months! The watermaster at Don Pedro Reservoir upstream had to do a delicate dance of balancing the inflow of storm water and snowmelt with a lake that was at more than 95% of capacity. The snow this year was around 200% of normal, and even today, on the first day of August, the inflow is still a respectable 4,000 cubic feet per second. Normal would be a few hundred cfs. I am reasonably sure that I'll never see an event like this again in my life.

The Tuolumne River in the same spot in January 2017, at about 12,000 cubic feet per second

These six months have been a stark example of geology in action. There have been real changes in the channel of the Tuolumne River that are only just beginning to become visible. At the beginning of July, the river was still running close to flood level, at 9,000 cfs, although irrigation canals were taking some of the water. In the last week, the flow dropped from around 7,000 cfs to around 1,500 cfs. Consider this: 1,500 cfs is about a seventh of flood level, where the river stayed for six months, but is about seven times the average flow of the river at this time of year!

After five years of horrific drought, the river channel was in trouble. Without the flushing action of at least a moderate flood, silt had covered many potential nesting sites for salmon and other fish, and invasive hyacinth threatened to choke the channel (the hyacinth crowds out other life and prevents light from penetrating the water; in some places the river was covered entirely by the floating mats).

The Tuolumne River this morning, at about 1,500 cfs. All of the hyacinth and many trees and willows have been swept away. 

As the river channel starts to emerge from the floodwaters, we can see that trees and willow thickets have been swept away from some areas, leaving a floodplain of barren river cobbles (above). The hyacinth is gone (although I bet seeds are hiding in the soils along the river). In other areas, the floodplain is a tangled mass of trunks, branches and root balls.

The flood took away a lot of habitat for the wide variety of animals that normally live on the floodplain, and took it for a long time (I'm wondering if homeowners on the bluff above had problems this year with raccoons and the like). It will be interesting to see how and when they come back.

For farmers and anyone who uses water, the results are spectacular. Compare where California's major reservoirs were in January of 2015 during the height of the drought to where they are today. It's almost like we have an embarrassment of riches, but not really...

There is one aspect of the drought that cannot be shown on these maps, but which will affect Californians for decades. It's the groundwater. During the drought when surface water was not available, agricultural interests went underground to meet their needs. Paradoxically, almonds became a hot crop, and despite the dry conditions, tens of thousands of acres were planted with the water-hungry trees, and the orchards were almost exclusively irrigated from new wells. After a number of years without subsidence, some areas of the Central Valley began to sink again as the water was pulled out.

The high river flows will contribution a little to the recharge of the groundwater reservoir, but for the most part the water is irreplaceable, and we went through a lot of it. It's analogous to living off of a savings account without making any deposits. In the long run it is unsustainable.

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

The problem now, of course, is trying to plan for the future health of our groundwater basins, but with the end of the drought people are thinking of other things. There are important decisions that need to be made about the future use of our groundwater resources, and when citizens aren't paying attention, the decisions end up being made by those who stand to profit from the use of the water. They won't be acting for the common good.

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: The Other Shoe Drops!

Wait...it hasn't rained in weeks. Why am I still talking about "liveblogging the deluge"? This is the case of the other shoe dropping. For months we have had storm after storm, adding up to a record year of precipitation in Northern California, and nearly a record in the central state. The snowpack a week ago was nearly 200% of normal. So the storms have stopped, but now a tremendous amount of snow is about to melt, so we have another round of possible flooding.

This was all brought home to me this last weekend when I took my class on a field trip to Yosemite Valley. We had a short heat wave during the week prior, and the river shot above flood stage on Wednesday and stayed there until Saturday when we arrived. The valley floor was flooded in many places, and the Merced was raging downstream (below).

On Thursday, the river peaked at nearly 12 feet (9,000 cubic feet per second), and was still at 10 feet (6,500 cfs) on Saturday. With a weak storm system passing through over the weekend, the flows backed off a bit, but the next heat wave will started the cycle all over again. For perspective, the average flow at this time of year is about 2,000 cubic feet per second.

Needless to say, the waterfalls were booming. Yosemite Falls were exploding and the echoes were resounding across the valley. It sounded like boulders were falling off the cliffs.

There was a change back home, but for a different reason, I suspect. The Tuolumne River was down for the first time since early January! I took my customary walk along the Parkway River Trail in Waterford, and the water had receded some 2 or 3 feet! I checked the numbers, and indeed the flow had declined in the last week from flood stage at 11,000 cubic feet per second to about 8,500 cfs. My first thought is that the dam operators finally felt confident enough about the flood capacity at Don Pedro Reservoir, and this has to be partly true, as the lake is down to 798 feet after nearly spilling over in January at 830 feet.

A check of the flow data told a different story. For months the outflow has been at 11,000 cfs or so, and inflow at the reservoir has been around 8,000-9,000 cfs. But during the heat wave last week inflows climbed to 11,000-12,000 cfs. The releases have been fairly constant at about the same level, but now the irrigation system is starting to take a fair fraction of the river at LaGrange Dam, thus the drop in river level.

The river is still astounding. The normal channel still lies hidden beneath 10-15 feet of water, and the river is filling the flood plain in a way that hasn't been seen in decades. And it will continue, according to reports, well into the summer. Extraordinary...