An Old Dam Photo, A Great Dam Adventure

This is a history blog, not a travel blog - except today, it's both. Besides just being a story about the photo below, this is about how the pursuit of a photo's backstory can lead to a great adventure and meeting some really cool people.

So when I started researching this old dam, it became quite the rabbit hole. I was surprised to learn how many different types of dams there are, and that this one is one of the rarer kinds, the multiple-arch dam. The multiple-arch design was a controversial one, championed in the very early 20th century by a bold and forward-thinking engineer, John S. Eastwood, who built 17 multiple arch dams across the West. I became a bit obsessed with figuring out where this dam was and the story behind it. What I found was that the dam was still around almost a hundred years after it was built, and so I set out to go replicate this photo as it looks today. But I'm getting ahead of myself.

I'm not sure who that man is...a project worker? Lars Jorgensen himself? Or just someone passing by on the Rush Creek trail?

I first tracked down the country's foremost expert on Eastwood and multiple arch dams (he's written several books on the subject), Dr. Donald C. Jackson, a professor of engineering history at Lafayette University. I emailed him and was pleasantly surprised when I not only received an email back, but a phone call as well.

Dr. Jackson explained that this wasn't one of Eastwood's dams, but was one of only two multiple arch dams designed by a contemporary and sometimes competitor of Eastwood, Lars Jorgensen, and that it is still in service. It is located on Rush Creek at Agnew Lake in the eastern Sierras, not far from the June Lake Loop just north of Mammoth. Jorgensen's other multiple arch dam, a much larger one, is immediately upstream at Gem Lake. Jackson even guided me to it on the map...and what I also saw on the map were markings for the Rush Creek trail.

What that meant, for me, was that I could go see it for myself, and more, I could shoot a modern version of the old photo. The map suggested the hike would be a mere 2.5 miles or so...but the was the matter of a 1,500 foot elevation change! Undaunted, my wife and I started planning a weekend getaway, and booked a room at our favorite Mammoth Lakes B&B (the Cinnamon Bear Inn; yes, that's an unabashed plug...mainly because of the wonderful people who work there). I was also hoping to time things so that I'd have a lot of fall colors photography opportunities.

The third weekend in October was perfect, weather-wise. It had rained and snowed the week before, and though the fall colors were a bit passed their peak, they were still gorgeous. After an hour or so of huffing up the trail (starting elevation was 7,500 feet or so), we came to the Agnew Lake Dam, and it look just like the old photograph, except that the lake had been drained the year before so that some repairs to the dam could be accomplished by SoCal Edison. It was not exactly easy to get to the spot where the original photographer had stood, and I realized that if the lake had been full, it would have even been riskier. My brother later reminded me that the original photographer had probably hauled his bulky camera equipment in on horse or mule-back.

That's me, standing one arch closer than the man in the old photo, since there's now a locked gate.
Photo by my wife, Barbara.

The video below animates the old and new photos for easier comparison

Through this whole adventure, I also learned some fascinating history about how dams are designed and built - and found out that it has been quite controversial, and the subject of a lot of bitter feuds between dam engineers over the years. Dr. Jackson explained some of it, and I was fascinated enough that I rushed over the Amazon and bought his book on dams and Eastwood, Building the Ultimate Dam (you don't have to be an engineer to enjoy this book...if you like history and especially when it comes to water in the West, this is an excellent read).

It turns out that as man has tried to tame rivers with dams, two basic dam design traditions have developed. The first is the "massive" or "gravity dam": the idea is to pile up so much material - be it earth and rock, or reinforced concrete - that the dam's weight alone is sufficient to hold back the pressure of the water in the reservoir behind it. The upside of this concept is that the design engineering doesn't have to be terribly precise...just keep piling up stuff, and eventually the dam will be so heavy that it'll never move. The downside is that it's enormously expensive and uses a tremendous amount of material (when it was built - or overbuilt, critics would argue - the Grand Coulee dam was praised for being the first man-made structure in 3000 years to use more material than the Great Pyramid). This method is sort of the "work harder" approach.

The Lake Hodges Dam, designed by John Eastwood
and completed in 1918.

The second method is the "work smarter" approach, the engineered structure dam, where precision engineering design skills utilize material strength rather than material bulk to hold back the flood.The Romans discovered the an arch laid on its side can use its natural strength to hold water back just as easily as it can hold a building up. An arch dam works well in a narrow, deep ravine, where the sides of the arch can be braced to the rock walls of the canyon. Where this is not possible, the Romans realized that you can line up multiple arches side by side, and reinforce them with buttresses. They built the first multiple-arch dam at Esparragalejo, Spain in the first century BC. 

John Eastwood was the first modern engineer to utilize what the Romans had discovered. He melded practical engineering with mathematical theory and added a generous amount of artistry, resulting in an unconventional and sometimes-controversial approach to solving the problem of water storage. 

Totally by luck, a month before our adventure to find Jorgensen's dam, I found this photo of Eastwood's Lake Hodges
dam at an antique store in Ventura.

Gem Lake Dam

The engineering needed to design a successful multiple-arch dam is complex. Think of a line of half-pipes, standing next to each other and tipped 25 to 45 degrees. Where the edges of the half-pipes touch each other, a triangular buttress extends downstream to carry the stresses down into the foundation. In order to strengthen the stability of the buttresses (and reduce their thickness), reinforcing arches are added between them (Eastwood's arches are elegant because he intentionally applied his artistic talents; in comparison, Jorgensen's buttress reinforcements look extremely crude). The result is a light, airy looking design (and this can be a detriment as Eastwood later found).

Jorgensen would only design two multi-arch dams during his lifetime, the Agnew and Gem Lake dams. What he would became famous for was the constant-angle arch dam concept, which he held a patent on. He designed the world's first single-arch, constant angle dam on Salmon Creek in Alaska. But in designing these two small, out-of-the-way dams, me made a big splash in the engineering world. In 1915, Jorgensen received a commission from the Pacific Power Corporation of Bodie, California, for the two dams along Rush Creek. Agnew Lake's dam was to be 50 feet high and Gem's was to tower 112 feet. There were already lakes in both locations, and the dams were intended to increase their water storage capacity in order to provide a more constant supply of water for electrical generation.

The "rustic" style of Jorgensen's buttress supports shows the
mold of the crudely-sawn timbers used as forms.

Both dams were built using as much local material as possible. Lumber for the forms was harvested from nearby trees, cut in a temporary saw mill. Sand and gravel came from Rush Creek, which would later cause problems with the Gem Lake dam (more in a bit). For what couldn't be obtained locally, Pacific Power built a narrow-gauge cable car tramway in 1915 using track and a car purchased from a defunct operation at Bodie. The right-of-way of the tramway has the profile of a world-class roller coaster! The tramway was built in two parts, the first from Silver Lake up to Agnew Lake, and then supplies destined for the Gem dam were barged across Agnew Lake to the second portion of the tramway which climbed the steep hill to the Gem site.

Eastwood's and Jorgensen's ideas about multiple arch dams were not rousingly accepted in the larger dam engineering community. His detractors called the look "lace curtains", suggesting fragility. But the economic arguments are powerful: a multi-arch design uses 80% less material than a massive gravity dam. Eastwood claimed that, "when its merits are fully understood, [the design would become] the standard structure for all dams." He was frequently heart emphatically stating, "Bulk does not mean strength."

The concept's leading opponent (and Eastwood's arch-nemesis) was John Freeman, who was an ardent advocate of the massive gravity dam tradition. The two went head-to-head over Eastwood's design for the Big Meadows dam. When Freeman couldn't win his argument on empirical engineering terms, he argued that the massive tradition was better because of the psychological comfort that the public derived from seeing its massive and immovable bulk. Thin, delicate-looking designs do not, Freeman argued, do not engender confidence in the mathematically-ignorant public. Freeman won that battle when Eastwood's patron died, and his half-completed multiple-arch dam was replaced with a massive gravity dam. The sad reality is that the general public will never fully understand - doesn't want to fully understand - the merits of revolutionary engineering concepts. They feel better when their eyes see what they think is the strongest, and that is bulk.

Gem Lake Dam sits high above Agnew Lake.
Note the tram tracks

Despite the detractors, the multiple arch designs that did get built have, by and large, stood the test of time, and the test of earthquakes. So far, not one of Eastwood's dams has failed. The Big Bear Lake dam was subjected to a 6.8 earthquake in 1918 and a 6.5 temblor in 1992, and suffered only minor, superficial damage. There have concerns with a few of them due to the age and deterioration of the concrete, and this has led to some unwarranted criticism. One of the dams in the spotlight, unfortunately, turned out to be the Gem Lake dam. As early as the mid-1920s, the concrete in Gem's arches began to show signs of deterioration, the most likely culprit being the quality of the local sand that was used in mixing the concrete. In addition, the altitude which the dam sits at (just above 9,000 feet) along with the seasonal changes in the water height behind the dam, led to the structure experiencing a brutal freeze-thaw cycle over the years. Multi-arch opponents jumped on the problem, claiming that such a thin-walled dam concept would be especially susceptible to concrete deterioration, and a number of leading "experts" proclaimed the dam's imminent failure (the fact that it has lasted a century seems to have proven them wrong).

The geomembrane liner can be seen on the face of Agnew Dam.

While dam failure really wasn't an issue, concrete deterioration was taking its toll, and in 1966 and 1969, repairs were attempted by applying gunnite to the face of the dam. Such methodology only seemed to have about a 20-year lifespan, so in the summer of 2007, Gem Lake was partially drained and SoCal Edison had a thick vinyl "geomembrane" was installed over the face of the dam, reducing leakage but up to 90 percent. It was so successful, that the utility decided to apply it to Agnew as well.

Because the lake was drained down to its original level when we were there, I asked hiker and photographer Ted Muller for permission to use his photo of the lake when it was full. This is from his excllent review of the Rush Creek Trail hike on his Ted's Outdoor World site.

The smaller Agnew Dam has seen some concrete deterioration, but is at a lower elevation, so it has not be as pronounced. In order to perform the work, Edison took advantage of the existing cable-car tramway, refurbishing it and supplying a new car to haul men and materials to the job site (Edison's old website which announced the refurbishment project stated that the cable car was going to be replaced by a self-propelled, diesel-powered car. However, that's not what we found when we hiked the trail. At the Agnew Dam, there's a new cable car sitting outside the hoist house.

When the lake is full, the spur to the left allows material to be loaded on a boat to be taken to the upper end for the tram to Gem Lake Dam.

The failed Gleno Dam in Italy remains today as a monument.
(Wikimedia, public domain)

One multiple arch dam did fail, though not because of the design concept. Unfortunately, it failed in dramatic fashion, and cast an undeserved pall over the design concept. In 1923, while Eastwood was in the midst of working several major dam projects, disaster struck in Italy The Gleno Dam, in the Valle di Scalve, Beragmo, Italy, was not one of Eastwood's designs, but took advantage of the economies of the design concept. Gleno was originally supposed to be a gravity dam, but due to budgetary restraints, the design was changed in order to save money (the designers didn't bother amending the permit, which shows how little government oversight there was on the project). The dam's construction, at that point, had already run into problems: allegations flew that inferior cement products were being used in the dam's foundations. Problems continued, and costs were trimmed wherever possible. Instead of using proper steel reinforcement material, the builders used WWI-surplus wire mesh anti-grenade netting. The concrete itself was of poor quality, and was not allowed to properly cure before the reservoir began to fill. The construction was completed on October 22, 1923, and heavy rains quickly filled the reservoir. On December 1st, just before dawn, one of the buttresses began to crack and then failed. In mere minutes, 159 million cubic feet of water gushed from the dam flooding villages below. Over 350 people died in the disaster. Although the dam was doomed by cost-cutting and poor workmanship, the multiple-arch design concept died as collateral damage. In the end, it seems, Freeman's arguments about the psychological aspects of dam design (not to mention how such psychology influences liability issues) have won out over the technical merits of the design concept. Though a few multiple arch dams have been built in the decades since (such as the 1968 Pensacola Dam and the very graceful thick-shell Daniel Johnson Dam), Eastwood's dream of a better way never fully materialized.

What? After this loooong post you actually want to read more? Okay...

• Building the Ultimate Dam on Amazon
• Jorgensen's own paper on the building of the Rush Creek dams, which includes lots of drawings plus some photos of the Agnew dam being built.
• Detailed article about the geomembrane liner applied to the Gem Lake Dam in Hydroworld
• SoCal Edison article on the refurbishment of the tramline.
• Ted's Outdoor World profiles the Rush Creek Trail hike to Agnew Lake, and includes a great photo of Agnew Lake completely full!
• Another hiking review from The Path Less Beaten