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.

Too Much Dam Hubris...Lake Powell and the Future of the Colorado River

The Colorado River is a wonder of nature. Starting from glacial cirques high in the Rocky Mountains, the river flows through one canyon after another, culminating in the grandest canyon of them all, the Grand. For 1,450 miles, the river is a corridor of life, and webs extend out in numerous directions, providing life in some unlikely locations, like Las Vegas, Los Angeles, and Phoenix. Irrigation from the Colorado grows vast amounts of crops in desert valleys throughout the southwest.

The river has exposed an incredible geological story, and has played an important part of my life in my development as a teacher and geologist. It was a catalyst in my own life as I explored a corner of it on my first geology trip, and more recently as I floated a raft through the Grand Canyon for the first time last summer. So it is that I feel a little bit of ownership of the river (along with about 35 million other people).

I first became aware of the abuse of the river system as a teen when I came into possession of a dogeared copy of On The Loose, by Terry and Renny Russell, which was in part a eulogy for the canyons that disappeared beneath the stagnant waters of Lake Powell, backed up behind Glen Canyon Dam. I had grown up learning of the giant mega-dams as the greatest achievements of mankind (did anyone else get taught "Roll on Columbia, Roll on" while in grade school?), and I was duly impressed when I saw Lake Mead and the newly completed Glen Canyon Dam when I was a child on vacation. I started to learn that there were more issues at stake in regards to these giant mega-dams. Yes, flood control. Yes, cheap renewable clean energy. But at the cost of the some of some of the most amazing scenic canyons in existence, and at the cost of an entire river ecosystem. I know that those arguments don't hold much sway in a capitalistic society that measures the value of something in dollars earned. The thing is, the main purpose of these dams is imperiled by changing climate. One has to wonder if they were a gigantic mistake in the end. Do the benefits truly outweigh the costs?

One of the most incredible stories of Glen Canyon Dam is that it came perilously close to failing during an extraordinary runoff event in 1983. I've covered this story in the past, but it bears repeating (especially if you not familiar with it). Instead of using floodgates and spillways at the top of the dam for emergency drainage, designers utilized the diversion tunnels used to channel the Colorado River around the dam site during construction. They proved woefully inadequate to the task in 1983 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. The diversion tunnels had to be shut down, and the lake threatened to flow over the crest of the dam in an uncontrolled fashion. 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. The structural integrity and survival of the dam came down to about one inch...the distance between the water level and the top of the flashboard dam in 1983.

There is an inherent conflict between water storage for irrigation and energy production, and flood control. One requires a reservoir to be mostly full; the other requires sufficient storage space for unusual events like those of 1983. The conflict requires a balancing act on the part of the water masters. Getting the balance wrong can lead to catastrophe downstream.

The scary part is that the 1983 event was not actually all that unusual. It happened because of a lack of storage space in the reservoir at the time (it had filled for the first time ever in 1980). The flooding involved flows of over 111,500 cubic feet (3,160 m³) per second. This was statistically a 25-year flood, one that has a 4% chance of occurring in any given year. Unfortunately, the statistics that guided the design of the dam have been called into question because of analysis of flood deposits upstream near Moab, Utah. New research suggests that there have been more than 40 large floods in the last 2000 years. Of these, 34 exceeded floods expected to strike once a century (20 would be expected under the old models), and 26 were larger than the so-called 500-year flood (only four of these would be expected under the prevailing models). Two of the floods were monsters that exceeded the design standards of the dam, even with the enhancements added after 1983.

At the other extreme of dismal news is the ongoing drought, 13 years and counting. The lake is hovering around 50% of capacity, and is expected to rise only modestly this year despite good snow conditions in the Rocky Mountains. We may be at the point where we are depending on the occasional El Nino event just to maintain a usable amount of water in the reservoir. There are some who think the reservoir will never have enough runoff to ever fill again.

All in all, this calls into question the wisdom of trying to control such a variable and unpredictable river. And we haven't even dealt with the question of sediment infill. The giant mega-dams are filling with silt at an astounding rate that is shortening their useful life. Ultimately our gigantic engineering projects will give way and the river will once again be in control. It's happened before with gigantic lava flow dams and blockages like Hoover Dam and Glen Canyon Dam will also give way.

Such were my thoughts as I stood on the hilltop overlooking this "mighty work of man". We hit the road again, headed towards Grand Staircase-Escalante National Monument, the largest single park on the Colorado Plateau.

Thanks to Wayne Ranney over at Earthly Musings for the heads up on the recent Colorado River research!

A Rock Outcrop, a River, and Sand flow into a Point Bar...

And the bartender said "is this some kind of joke?"

But it's not a joke of course, it's a simply stunning example of what happens when water flows over stone for a long time. What you are seeing here Horseshoe Bend on the Colorado River a few miles downstream of Glen Canyon Dam and Lake Powell outside of Page, Arizona.

A point bar is a real thing with rivers. When a river loops back and forth as a series of meanders, point bars form as sand ridges develop on the inside of the loop where the water flows more slowly. In the most technical sense, the sand bars in the picture above can be consider an example of the feature, although they are more familiar where rivers are flowing in flat floodplain.

It's obvious that Horseshoe Bend is no longer a flat floodplain! It may have been one at one time, but uplift of the Colorado Plateau (or the subsidence of the lands around the edge of the plateau) caused the river to speed up and start to erode downwards, forming an entrenched meander.

The approach to Horseshoe Bend is a sandy trail about three-quarters of a mile up from a parking lot about five miles south of Page on Highway 89. Although views are wide-ranging along the trail, there is barely a hint of the incredible view that awaits when one arrives at the brink of the cliff and looks down nearly a thousand feet to the river. Stunning is the only word for it.

My old camera couldn't show the entirety of Horseshoe Bend, so I was thrilled I was able to get these wider angle pictures with my new one. It's almost like looking at a petrified rainbow, although it should be said, this view is not entirely natural.

When Glen Canyon Dam was completed in the 1960s, the river was changed forever in terms of a human lifetime. Instead of the normal red silt-laden water, the river flows clear and cold (almost refrigerator cold, about 46 degrees; I can attest to this as I almost drowned in the river last year). As a result, green algae grows in the unnaturally blue river. It's beautiful to look at, but is kind of sad to consider what it should have been. Many of the native species of river life are in decline and cold-loving invasive species are thriving.

A trip-planning note just in case you are headed out to the region this summer: Highway 89 between Bitter Springs and Page was closed down by a serious slope failure along the Echo Cliffs Monocline. It may be years, if ever, before the highway will be repaired. In the meantime, the Arizona Department of Transportation has constructed a newly paved highway replacing Navajo Route 20. Although the detour is supposed to be temporary, I suspect it is permanent despite any feelings of the Navajo Nation about a new busy highway in a formerly isolated part of the reservation. There are far fewer engineering problems where the new highway crosses the monocline.

Into the Great Unknown: The Last Day...An Elegy for a Journey, and for a River

Elegy (from the Greek word for "lament") is a mournful, melancholic or plaintive poem, especially a funeral song or a lament for the dead.

How many ways can I describe the last day of our trip? The word "elegy" came to mind. It was the end of a long but incredible rafting trip down the Colorado River, and I was feeling sad. Sure, I was anxious to hear the news from the family and the outside world, but it was also the ending of one of the greatest experiences of my life. It was the ending of a personal journey, which ventured sometimes into terrifying darkness, but mostly it was a world of sublime beauty, even glory. And... the story was about the abuse and destruction of a river.

We packed at a leisurely pace. We only had a few miles to go, and the Hualapai Nation requested that no take-outs happen before 10 AM.

We set out down the river. We turned a corner and I saw something I hadn't seen in more than a week: a familiar sight. I've been down Diamond Creek several times, and Diamond Peak has an unmistakeable shape, even from the opposite side. To offer a sense of scale, Diamond Peak is only about 200 feet higher than the beach at the beginning of our trip in Lee's Ferry. It stands out in part because it is a fault block that has risen between two fault zones. Erosion along these faults has led to the trick of the topography that allowed a road to be constructed down to the river.

At mile 224 we passed the final rapid, a little riffle that didn't even merit a name. But it was the last one...

And then we entered the last mile or so of river, and it nearly broke my heart. It was perfect. In that moment I wanted to simply float on and on into eternity. Pete stopped rowing and we simply drifted. The river was quiet. A swallowtail butterfly landed briefly on my hand, confused by the bright colors of our clothing and luggage. Pete pulled out his harmonica and played a few tunes.

I wrote in my journal...

I was suddenly wistful, wishing to float down a serene river, at peace, but knowing that it is never truly serene. There are those perfect moments that make everything worthwhile but around the bend there can be excitement, action, and even terror. But peace returns, and we recover our sense of well being.

Such beauty in such a savage land. Without the river, life would be barely possible for a person. Too far between water sources when it is so god-awful hot. The hike yesterday across the Tapeats ledges could have been unbearable without soaking in the cold water first.

But along the string of life-giving water, the beauty is overwhelming. Every side canyon would be worthy of a national park all its own. I found myself thinking 30 Yosemite Valleys strung in a line would equal the Grand Canyon.

I don't know that I will be back. I faced the big waters twice and made it through, one time in terror, and the other less so. But I enjoyed the rapids a bit less afterwards...

...but nothing can take the place of drifting down the placid parts of the river; seeing the herons and bighorns, and I'll never forget the sounds of the canyon wrens. I would do it for that...those parts will always live on in my memories.

The cliffs would glow red in the pre-morning hours after the stars disappear. The red fades into shadow, and then the sun lights up the cliffs in blazing orange. The river was always brown but in the shadows of evening and morning, it reflected the lights of the cliffs above...wonderful moments.

I took one last video as we drifted...

 

And then, a strange sight, a big orange ball and a cable strung across the river. It was the gaging station at Diamond Creek. It was a reminder that this was a heavily utilized river that had to be measured and controlled. There was a feeling on the entire trip that the river we were traveling on was not "right". It was far too cold for a desert summer, and it ran too high for any snow-fed river in August. The disappearing beaches demonstrated that the river rarely flooded anymore.

It's hard to imagine the difference between this river and the river that was experienced by John Wesley Powell and his courageous men. And it was almost entirely due to the construction in 1963 of the monstrosity that flooded a precious gorge called Glen Canyon. And the sewage lagoon that formed behind the dam was named for Powell. I don't think he would have been pleased. He recognized sooner than most the problems that would lie ahead for the millions who would come to depend on an inherently undependable river. The lake that bears Powell's name may never again fill if the predictions of the climate scientists come to pass.

The river will return. And it probably won't take as long as it did when lava flows temporarily stopped the flows of the river. The dam is built in unstable porous rock, and it almost failed catastrophically in 1983, due in part to the arrogance of the dam engineers. It ultimately must fail, probably within a few years of being abandoned by the society that maintains it. Ultimately the river will return to something of its former self. Time is all it needs.

The gaging station also meant that our time was almost up...

A beach came into view, with trucks and giant pontoon boats. We waited until the other boats left on their journey to Lake Mead and pulled off the river for the last time.

Rigging the boats at the beginning of our trip took parts of two days. The de-rigging took an hour or less. No one wanted to hang out on the river in the growing heat of the day.

All of the material we began the trip with came off the river, although some of it had been, um, "transformed". A few items, most notably my hat, gloves and a guidebook were still in the river somewhere. Oh and a tent that blew away several days earlier.

I finally had a look at the unadorned raft that had been my home for the last two weeks. We developed a luggage line and got all our gear onto the truck; we would unscramble it in much more comfortable weather in Flagstaff at an elevation of 7,000 feet. We piled into the truck and a van and set out on the bumpy 20 mile drive to Peach Springs where we would rediscover ice cream and flush toilets. A 90 mile drive to Flagstaff followed...

...our trip was over.

I hope you have enjoyed following our journey. Thanks to all those who traveled with me, and especially my brother and his family who invited me to come along. Thanks to Pete, who was a wonderful boatman and traveling companion. They were wonderful people to travel with! Thanks to Barry, Bev and Jeff, who pulled me from the river, sometimes more than once.  And thanks to all the river runners who have clearly worked to keep the river clean and wild.

Look for one more post in this series, a compilation of all the posts on the journey, and maybe a few final thoughts.

A Dam Big Shame, and Things Lost and Gamed...

A different "Paradise Lost"...

It just doesn't get much better than this, to stand on the brink of a high cliff in the barren desert, and to see a stream of life-giving water in the depths below. Of course, if you are in trouble and dying of thirst, you are pretty well screwed, since the cliffs are pretty much unclimbable! There is a story behind the dramatic appearance of the river in the photo. It not a genuine river anymore, not exactly. It is a blunt instrument, wielded badly.

Glen Canyon Dam was built between 1957-1964 after a contentious environmental battle over whether national parks (Grand Canyon – Bridge Canyon dam) or National Monuments (Echo Park dam-Dinosaur National Monument) should have reservoirs extending into their boundaries. Glen Canyon was at the time protected by neither designation. The dam 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 lake is a popular national recreational site today, but Glen Canyon was once one of the most beautiful valleys along the Colorado River. Unfortunately, when the dam was completed, only a few hundred people had floated down the river to see the stunning canyon (and therefore explaining my title of things "lost and gamed"; the dam was built here by threatening to put dams elsewhere).

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. Instead of using floodgates and spillways at the top of the dam for emergency drainage, designers utilized the diversion tunnels used to channel the Colorado River around the dam site during construction. They proved woefully inadequate to the task in 1983 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. The diversion tunnels had to be shut down, and the lake threatened to flow over the crest of the dam in an uncontrolled fashion. 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. The structural integrity and survival of the dam came down to about one inch...the distance between the water level and the top of the flashboard dam in 1983.

Dam engineers are confident that modifications to the spillway tunnels will allow the dam to withstand future flooding events, but other concerns have become prominent. The southwest has been suffering an extended drought, and lake levels in recent years have become perilously low, threatening to turn Lake Powell into a “dead pool” incapable of producing electrical energy. In 2013 the lake was filled to less than 50% of capacity. Some water experts suggest that the lake may never be able to fill to capacity again, in part from drought, climate change, and upstream diversions of water.

Back to that photo at the top of the page...it isn't the whole story. The spot is called Horseshoe Bend, and it lies just a couple of miles downstream of Glen Canyon Dam. It is an entrenched meander, which developed when the land was uplifted, while the originally sluggish winding river started cutting downward instead of laterally. The rainbow-like pattern of red rock and green-blue water is an artifice of the reservoir. Unlike the olden days when copious amounts of silt caused the river to flow red, the water draining from the lake today is transparent and cold, in the 40-50 degree range. For a river in a hot desert, this is extraordinary. The ecosystem of the river evolved in different conditions than this, and species are sensitive to the new regime. Natural species of fish, amphibians and insects are in a difficult situation. For we humans it is ironic that river rafters have look out for hypothermia in their crews if people get dumped in the river on a day when the temperature is over 110 degrees.

So the view is just stupendous, but sobering at the same time. It can be reached by a short 3/4 mile long sandy trail from a parking lot on Highway 89 just 4-5 miles south of Page, Arizona. The highway is closed because of a serious landslide farther south but is open to the parking lot. It is well worth your time if you are ever in the region.

Accretionary Wedge #36: How does life affect geology? Surviving on the Colorado Plateau

There was a day this home was abandoned. There was a day that something happened, a decision was made. Were they under attack? Did people die? Or was it a moment that a family knew the crops had failed, and there would be no food that winter? Or no more water in the nearby streambed? Were they called away to another place by a chief, or a shaman? Lots of questions, questions that are hard to answer. But abandoned it was, along with hundreds or thousands of similar homes in the region. Abandoned for hundreds of years before others came into the region.

Tourists seek out these former homes, and many of them remark on the permanence of these structures, still standing after 800 years. I look at them and I think of the permanence of stone, maybe, but also the transitory existence of people and populations. Before the decision to leave, generations of people had lived in these structures, and throughout their lives they never thought of being anywhere else. They didn't plan on enduring whatever catastrophe or threat that led to the decision to leave. But leave they did. There are lots of hypotheses, but I feel pretty strongly that they finally exceeded the capacity of the land to support human populations. That led to whatever else happened, I suspect.

Accretionary Wedge #46, hosted this month by Knowledge Flocs asks the question: How has life or civilization been affected by geology or how has geology been affected by life? I pondered this question essentially for the whole month before sitting down tonight and writing this. I was out there on the Colorado Plateau a few weeks back, and I almost mindlessly snapped a picture that I didn't give a second thought to. It was part of the view from the Wahweap Overlook at Lake Powell on the border between Arizona and Utah, and I was snapping a series of shots to get sort of a panoramic record of the view.

Tonight it caught my eye. A coal-burning power plant on the shores of an artificial desert lake. What is the carrying capacity of this land? There are thousands of people living in the immediate vicinity, but there are lines of copper wire leading out like a web to literally millions of homes in the wider region, especially places like Phoenix or Las Vegas. Looking at the coal-burning powerplant is to realize that the present-day population is depending on sunlight that fell on plants 70 million years ago to survive. They are depending on water that used to exist only in a deep inaccessible canyon. And to propel their vehicles they import the remains of plankton and one-celled organisms that lived by trillions upon trillions 200 million years ago in oceans and seas that don't even exist on Planet Earth anymore. Their food in large part is grown in other states or other continents.

And we take for granted that we will be living here permanently. We barely ever give thought to the intricate web of connections and imported energy that keeps this civilization alive. What happens when a piece of the web breaks?

I ask in particular because of that white strip along the shoreline of Lake Powell. It's the bathtub ring of the reservoir. It doesn't look like much from my lofty perch, but that is a terrifying lake level if you are one of the watermasters responsible for providing an allotment of water needed to keep things going downstream. The Colorado is the most important source of water in this arid land except for groundwater, which is pretty much non-renewable and is being used up in many areas. The region has been suffering through a decade-long drought, and global warming is leading to changes that may intensify the droughts for the conceivable future.

There are limits.That is the effect of geology on human life in this region. There is only so much water, and there is only so much coal. And populations and societies are not stable. Some will last longer than others, but the changes will come. Will we know when the limits have been reached and act? Or will we be caught off guard, and realize we need to move someplace else? And where will we go?

I'm appalled when I hear politicians say that the most important questions facing our generation have to do with the marriage of the gays and how important it is to de-fund Planned Parenthood.