Foresthill Bridge

(and the late Auburn Dam)

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The Foresthill Bridge is reputed to be the 3rd highest bridge in the US and is the tallest in California. It was built to span Auburn Lake, the reservoir that would have backed up into the North and Middle Fork canyons of the American River behind the Auburn Dam, if it had ever been built. The dam project was abandoned (see below) and the bridge now spans the North Fork canyon, some 730+ feet above the river.

The bridge was built in the early 70's, from each side outward. Standing at the confluence of the North and Middle Forks, it was awesome to watch the spans progress to meet each other at the middle. That they actually did meet, closely enough to get the bolts into the holes is probably an engineering marvel! Click here and here for a couple of additional views of the bridge (about 100KB each)

Auburn Dam

(Should you be interested, and most won't be, here's a brief synopsis of the Saga of the Auburn Dam from the perspective of one engineer [me] who worked for the DOE/Bureau of Reclamation on the Central Valley Project for several years)

The Auburn Dam was originally authorized as part of the Central Valley Project (CVP), a system of dams, canals, pumping plants, tunnels, and power plants originally conceived in 1933 with construction of Shasta Dam and reservoir on the upper Sacramento River, and Friant Dam on the San Joaquin River. In addition to Shasta and Friant, the CVP now has some 30+ dams including Trinity Dam and Claire Engle Lake (Trinity River), Folsom Dam and reservoir (American River), New Melones Dam and reservoir (Stanislaus River), a number of smaller power plants, several 12' diameter tunnels bored through mountain ranges to conduct water from Claire Engle Lake to the Sacramento River, the Delta-Mendota Canal, half of the San Luis Canal and San Luis Reservoir (the other half belongs to the State), and a variety of regulating dams, pumping plants, and hydroelectric generation and transmission facilities.

In the latter half of the 20th century, the State undertook a major water project which included a dam and reservoir at Oroville (Feather River), and a joint state-federal canal, dam, and pumping plants to feed excess winter water into the San Luis Reservoir (The San Luis Reservoir has no natural inflow to speak of). Below San Luis, the canal, now called the Edmund G. Brown California Aqueduct (and wholly owned by the State), continues south through the Central Valley, and ultimately over the Tehachapis to So. Cal.

Together, the CVP and State Water Project currently comprise the world's largest water project (possibly to be overtaken by China's Three Gorges Project?). Allegedly, according to Susan Sward writing in the Santa Barbara News-Press in March, 1977, "...the astronauts who landed on the moon reported they could see the California project, the only manmade item they could identify from that distance."

(This sort of thing has also been said of the Great Wall, natural gas flares in the Gulf, and other natural and unnatural wonders. I worked on the Apollo program in Houston while in the USAF and assigned to NASA for 3 years. As a result, I knew a number of the crew members, and none of them ever mentioned this. You will have to decide for yourself.)

There is no doubt that the CVP and State Water Project together form an engineering undertaking more massive than anything in its time. Nearly all the water in California is in the watersheds of the north. The Central Valley, directly and indirectly, produces more food than any other equivalent area on the planet. That takes water. Southern California (south of the Tehachepis) has the majority of the population and they take water too. Unfortunately, they don't have enough of it. Moving all that water, and generating and using electricity in the process is incredibly complex.

The Auburn Dam was the last to be started in the CVP. It was designed as a high, thin arch, not unlike Hoover Dam (the American River Canyon is nearly 1,000' deep at this point), and was located on the American River just below the confluence of the North and Middle Forks. Foundation work continued until about 1977, when an earthquake on a fault believed to be dormant near Oroville raised seismic concerns about Auburn. This was exacerbated by circumstantial evidence that the Oroville earthquake may have actually been "induced" by the weight of the newly filled reservoir. No one really knows today if that actually was the case, however.

Construction was halted for a series of seismic studies, and ultimately, was never restarted. The studies did confirm similar faults under the Auburn site, making the thin arch design inappropriate. There really are no physical problems for which an engineering solution cannot be found, provided you have enough money ... Unfortunately, a redesigned dam that would be seismically safe was way beyond even the Federal budget, and so, economics is really what killed the Auburn Dam.

Auburn Dam Economics

The Auburn Dam was to have impounded North and Middle fork American River water in a 2 million acre-foot reservoir behind an 800' high dam. Its primary purpose was flood control for the Sacramento area, since the dam and reservoir at Folsom (1 million acre-feet) was insufficient for the rare but devastating floods that can occur from runoff in the Sierra Nevada. Auburn would also provide a "yield" of perhaps 50,000 - 75,000 acre-feet of water annually, and would generate electricity when water was released.

While construction was stopped for the seismic studies, economic analyses were also conducted, and of course, costs rose due to required design changes and inflation. It's fairly complex, of course, but the results can be pretty fairly summarized as follows:

One does not have to be a graduate engineer to sense the problem. Part of the inflow of a small river feeding a reservoir twice the size of Folsom (which gets all of the river's inflow), just doesn't seem right, and economically, it isn't. So in its wisdom, Congress has refused to re-fund construction for a seismically safe dam. As time has gone on, the construction costs have outraced any increases in investment payback. In a particularly large runoff year in the 80's, the diversion tunnel around the dam site was unable to handle the flow, water backed up behind the cofferdam flooding the areas where I stood to take the pictures of the bridge, and eventually, the cofferdam was breached. Recently, the Bureau of Reclamation has decided to close the diversion tunnel (a fairly unsafe site for local teens to raft), and restore the river to its natural streambed. Thus, for all practical purposes, the Auburn Dam is dead.

A Somewhat Bum Rap

Throughout most of this period, our local congressman has taken on, apparently as his "Life Mission," construction of the dam at Auburn despite the overwhelmingly compelling case against it. Unfortunately, in such cases of politics, polarizations often occur, and in this case, it's been the "dam backers" against the "environmentalists." Charges have flown back and forth, and many backers naively blame the environmental folks for "killing the dam." Those attuned to the environmental side accuse the backers of gross insensitivity and lack of intelligence. Neither, of course, is even remotely close to true.

Those opposed to the dam on environmental grounds have been, at the very best, an extremely minor factor in the decisions not to restart construction. Whether or not they have put forth good arguments is quite moot. Environmental issues were dealt with during dam authorization and construction of the remainder of the CVP (remember, Auburn was last on the list). The Auburn Dam was stopped by an earthquake in Oroville, and was not restarted because, when made seismically safe, it turned out to be a very bad project economically ... and in our capitalistic republic, economics always rule in the end.

Those in favor of the dam have little access to the engineering facts surrounding the project, and are forced, in most cases, to rely on emotional and political arguments. That California ("the dimly lit state") has an energy and water problem is well known to everyone, and naively, part of the solution would seem to be "build another dam." Even though the dam at Auburn will do virtually nothing to solve these twin problems, it's hard to fault the average citizen for adopting what seems to be an intuitive position in an otherwise vacuum of real information.

So, not being economically viable, it is quite unlikely that the dam will ever be funded. By law, the Federal contribution can only be for a portion (it used to be 75%, I'm not sure if it's that much now) of the portion of the dam cost that is allocatable to flood control. Everything else has to pay its own way, so to speak, and someone else (like the State, currently near bankruptcy?) has to come up with the money. The dam would likely cost somewhere in the 2 - 3 billion range, so the non-federal contribution would be a lot ... way more than the State and counties could come up with.

Cost Update [early 2007]: At a cost of several million, the Bureau was instructed to again visit the Auburn Dam with a cost/benefit analysis. The results were published at the end of Jan, 2007 and were not surprising. The water yield has declined even further (the result of water delivery agreements that have transpired since the last study), electrical production potential has declined (due mainly from operation constraints arising over the last decade or so), and cost has escalated to between 6 and 10 billion.

In early 2003, our local congressman and the congressman for Sacramento finally began discussions on alternatives to the Auburn Dam. The result was (for us who live here) an historic agreement to address Sacramento's flood control issues by:

The Bureau of Reclamation is proceeding with the closure of the diversion tunnel, restoration of the river to it's natural channel, and installation of permanent pumps to allow the Placer County Water Agency access to their American River water rights. Unfortunately, restoration of the river will eliminate a trail from Auburn to Cool that traversed the dry river bed and over the tunnel. There is a good possibility that a pedestrian bridge to alleviate this may be part of the project, however.

All in all, and although it took many years, it is probably a win for everyone. Sacramento will get it's flood protection upgraded (which it really needs), the water agency will get permanent access to its water rights for western Placer County (which is the fastest growing area in the state), and the Feds/State will not have to fork over several billion bucks which they don't have to build a dam that will never repay its cost. Those who love the canyon as it is will keep it, we'll continue to have the 3rd highest bridge in the nation, at least for awhile, and the residents of Foresthill have a shortcut to Auburn.

Should anyone be interested in the rather facinating history of water development in the West, I highly recommend "Cadillac Desert" by Marc Reisner published by Penguin Books. (Be sure to get the 1993 second edition). The Bureau of Reclamation is the focus of course, and the author's opinions about the Bureau and its leaders sometimes shows through, but it provides a detailed, factual account of projects built, some planned and not built, the economic and political forces driving reclamation law, and how seemingly totally unrelated projects thousands of miles apart are really coupled. I found the never-implemented plan to divert the Columbia River into the Colorado to make the Central Arizona Project feasible somewhat bizarre

Hydroelectric Factoids


"Yield" is a term hydrologists and hydraulic engineers use to place a value on the water impounded behind a dam. It is a very complex issue, but roughly, it goes like this:

Some of the water in any river already belongs to someone before a dam is built. It may be cities and towns that pump domestic water from the river, farmers who irrigate with it, or even a municipality that dumps its treated sewage effluent back into the river and depends on historic flows to keep it diluted. Some of it also "belongs" to wildlife ... sufficient seasonal flows to protect wetlands, fish spawning, and plants. (How much belongs to wildlife is a never ending battle of wits [and a few half-wits], sometimes called the "Attorney Full Employment Act")

When the dam is built, these rights to downstream water must be respected. Consequently, downstream flows must be maintained, and some of the water behind the dam really belongs to those rights-holders. Loosely speaking, what is left behind the dam that does not belong to anyone is the "yield." You can think of yield as saving the excess, unclaimed water that would have flowed down the river and into the ocean during runoff season, and selling it to new users. Obviously, the amount of "unclaimed" water available as yield varies greatly with annual rain and snowfall levels, and calculation of economic yield is a very complex process.

Capacity vs Energy

As consumers, we purchase electrical energy (measured in watt-hours) in a retail market. Essentially, we have an implied contract with the utility to supply us with energy at a prescribed voltage and frequency at whatever rate we want to demand it (up to the limit of the main circuit breaker on our electrical panel). Thus, we start the toaster, and our demand goes up. The A/C turns on, and it goes up further still. Someone in the house starts the dryer, and it rises again. Then the toast is done and it goes down ... the A/C shuts down and it falls again. All the while, we are getting what we demand at a steady 120 volts (well ... really it's 230 volts) and 60 Hz. Our bill at the end of the month is for the energy in watt-hours that we have consumed.

For the utility, the situation is a bit different. The generator turns (due to a steam turbine or water from the dam), and it generates energy. The rate at which it does so is measured in watts, and a characteristic of electrical generation is that, if the demand exceeds the capability of the generator or the power source driving it, it will slow down. This lowers the voltage and the frequency. Everything in our power distribution system is optimized for 60 Hz, and losses climb very rapidly with even small reductions in the frequency or voltage. Consequently, if the generator is overloaded, the frequency and voltage drop, losses increase the demand for energy, and a run-away condition develops which collapses the entire power grid, often in milliseconds. Utilities prevent this with metering and circuit breakers that can shed load very quickly, causing a blackout for users on that load.

As with most businesses, an electric utility has two broad categories of business expenses ... Operating Costs, and Capital Costs. The energy (i.e. kilowatt-hours) the utility sells to us is directly linked to its ongoing operating costs ... fuel, labor, maintenance and repair, etc. If no one wants energy, they don't consume these resources to make it, and the utility doesn't incur the costs. Well, OK, it's quite a bit more complicated that that, but you probably get the idea.

The ability to generate energy at a given rate is called "capacity," and it is directly linked to capital investment in generating plants, transmission facilities, fuel storage tanks, pipeline construction, etc. For hydroelectricity, it is the cost of building the power plant, transmission facilities, and that portion of the cost of the overall dam structure that can be imputed to the production of electricity. Since utilities must have the capacity to meet the demand for energy, "capacity" becomes a tradeable commodity ... essentially a promise from a generating plant operator to generate energy at some rate for some period of time in the future. The purchasing utility pays for this promise, whether or not its demand actually requires the seller to generate the energy. It also pays for the energy if it is actually generated. So, unlike us consumers in the retail market, the wholesale market includes the independent trading of both capacity (watts) and energy (watt-hours).

The Auburn Dam was to have had 700 megawatts of generating capability at one point in it's design process. Unfortunately, that doesn't mean that it can generate energy at a rate of 700 million watts whenever needed. First off, the maximum rate at which it can generate energy depends on the height of the reservoir behind the dam, and it falls rapidly as the lake falls (and, of course, the mere act of letting water turn the generator lowers the reservoir level and thus the instantaneous capacity). Secondly, most of the water in the reservoir already belongs to someone ... you can't just release it to make electricity because someone wants to toast some bread. Thirdly, the water released will go into Folsom Lake, which is less than half the capacity planned for Auburn, and which gets additional inflow from the South Fork of the American River. Obviously there are stringent limits on how much and when water can be released from Auburn.

There's more, however. In drought years, any dam may simply be unable to generate energy at a given rate ... there's not enough water. No rational utility is going to pay for a promise to produce energy at some rate unless they are certain that they'll get the energy at that rate when they ask for it. Consequently, for hydroelectricity, they will only pay for the capacity to generate energy at the rate the dam can do so in the worst of water years,and after all other constraints have been satisfied. This is the saleable capacity, and is often termed "firm capacity" or "dependable capacity."

The upshot of all of this electrical drivel is that, regardless of how much "nameplate capacity" would have been installed at Auburn, only around 60 - 80 megawatts of capacity was actually saleable. This is why the return on the investment for the power plant and transmission facilities is negative.

Update - June 2005

Our local utility (Pacific Gas and Electric [PG&E] -- in fact the utility that supplies power to a majority of California consumers) has recently filed with the California Public Utilities Commission to allow a demand-tiered pricing of electricity. In this scheme, the unit price a consumer pays for energy would depend on that consumers demand-rate. Now, most everyone has had usage-tiered pricing for years. A KWh costs X cents up to some total usage. Above that, each KWh costs Y cents (more than X), up to another threshold total usage. Above that, each Kwh costs Z cents, again higher than Y, etc.

The scheme proposed by PG&E however, would additionally base the rate you pay for energy (KWh) on your instantaneous demand (in KW). Under this scheme, the cost of your energy would depend on the rate at which you demanded it as well as your total usage for the billing period. For a simplistic example, let us say you have a steady demand rate of 1KW, 24/7. At the end of a 30-day billing period you will have consumed 720 KWh of energy. You will be billed for that 720KWh of total usage acording to the usage-tiered tariffs, however the unit price you pay at each usage tier will be based on your continuous 1KW demand rate. On the other hand, suppose you demand 2KW but only for 12 daylight hours each day. Your energy usage for the period is still 720 KWh, but now, the utility is required to meet your higher demand during hours when everyone else is also demanding more. In the proposed demand-tiered pricing, the unit price you pay for each of your 720 KWh will be higher, because PG&E has to provide more capacity (i.e. capital investment in generation and transmission equipment) to meet your demand.

This is all made possibly today because electric meters can be made "smart" and can record your demand rate over the period. While no one really wants to pay more for anything, the basic concept to demand-tiered pricing is more fair to all, and to our economy, than the usage-tiered only scheme. It is a bit unreasonable that we consumers can demand our energy at whatever rate we choose (A/C on at noon on a warm but not really hot day when maybe it doesn't need to be), and the utility has to assure that it has the capital capacity to meet that demand. It is likely that it will foster increased awareness of energy usage at the consumer level, and probably will increase energy conservation to some degree, which translates into fewer atmospheric emissions and less coal/oil/gas consumption.

I'm sure that PG&E has included some "wrinkles" in their proposal to help out their stockholders, and hopefully, the California PUC will examine those "wrinkles" carefully. But, in basic concept, it is probably an idea whose time has come.

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