A Validation of Engineering

My little coup during our visit to Vegas was a side trip to the Hoover dam. I've always been interested in a distant sort of way, but between the enthusiasms of my dad (a retired civil engineer, remember) and of Great And Powerful Jeffy (GAP-J) along with, apparently, every other male who has ever visited the place, I decided I needed to make this happen this time around. Of course, nobody else initially was going to accompany me, but in the end Susan and her parents came around we we took the trip as a foursome.

The numbers alone give some sense of the magnitude of the project:

--4.3 million cubic yards of concrete, weighing 6.6 million tons
--a reservoire (Lake Mead) 585 feet deep and stretching back for 115 miles, holding enough water when full--9.2 trillion gallons!--to cover the entire state of Connecticut to a depth of 10 feet, or to supply 5,000 gallons to every person on the planet. It is far and away the largest man-made body of water in the world.
--water flows through the electrical power generators at 85 mph, and generates over 1.8 million horsepower, which is good for 4.3 billion kilowatt-hours of electrical power per year, enough to supply 1.3 million people.
--During peak electrical demand, enough water flows through the power plant to fill 15 average-sized swimming pools (20,000 gallons each) each second.




Prior to building Hoover Dam, the Colorado river was mostly a menacing presence to the West. It did not flow consistently enough to provide regular irrigation or water supply for much of anything, and it flooded often enough to bring havoc just when everyone thought it was safe to start building / farming in the flood plain. I suppose it's a fair question to ask whether the solution to sporadic flooding was... permanent, widespread flooding (a couple small towns lay now at the bottom of Lake Mead, their property values plummeting even still), but the dam is generally thought to have solved problems of long standing. It provides a reservoir of fresh water for desert communities and for irrigation. And it generates a shitload of power in the process, all without pollution or substantial sustaining cost.




The story of the building of the dam is mesmerizing to me. In the midst of the depression, some seven thousand workers were brought to this place in, comparatively, the middle of nowhere, where they toiled in three shifts and were paid $4 a day--considered a good wage at the time. A small town was erected a few miles away--Boulder City, which still exists--for the army of workers and support staff.

As always, I'm fascinated at how a fairly straightforward concept--damming up a major river to a depth of nearly 600 feet--was brought about in practice by a whole series of steps of which the average person would not have thought. Quite apart from the difficulty of finding a river which allows for 600 feet of elevation drop to even fill up such a reservoir, where do you find the reservoir? The site they found was, not surprisingly, remote. There were no roads at the site, no railroads, no electrical power. Hell, there wasn't anything. The river was following its millennia-old course at the bottom of a deep, inaccessible solid-rock gorge. But there's no way to stop the river without a dam and no dam could be built while the river flowed. Hmmmm. The solution was to bore four 56-foot-diameter, concrete-lined tunnels adding up to over three total miles through solid rock on either side of the dam site, and then put up a small, temporary dam to force the river to divert through these tunnels. Just getting to this point constituted an almost unfathomable engineering feat in itself--the tunnels cost as much to bore and finish as the whole rest of the project. There was no easy way to get machinery to the site, and eventually large factories for pipe manufacture and concrete plants were constructed on site.



And the concrete. The structure is 725 feet high and over 660 feet thick at the base. That's a mind-boggling amount of material. Indeed, there's enough concrete in the Hoover Dam to pave a standard two-lane road from San Francisco to New York. Or to build a sidewalk around the earth's equator. And (of course) it's nothing so simple as just building a form and filling it up with cement. Concrete doesn't fully cure for years, and so the ongoing status of the material had to be carefully studied and fully known before the project was undertaken, since a failure of this dam, and its sudden release of a nearly 10 trillion gallon tsunami, would be catastrophic. The curing of concrete generates a great deal of heat which, unmanaged, would cause the structure to crack and be structurally unsound (enough heat, one source whimsically said, to bake 500,000 loaves of bread a day for three years). Without intervention, the amount of concrete in Hoover Dam would have required 125 years to cure. And so the world's largest refrigeration facility had to be built to carry this heat away from the dam while it initially cured, the refrigerant being pumped through 582 miles of pipe laid in the concrete as it was poured. The concrete was delivered by overhead cable cranes from two onsite concrete plants via eight-cubic-yard buckets. That's a large bucket, about the capacity of a standard dump truck. This bucket brigade ran 24 hours a day for two years. At the peak, one of these buckets was delivered every 78 seconds.



If I write any more about the construction project I may be nearing the length of the little government book they sell at the site (which I haven't even looked at yet--maybe I'm writing the same words and will be found guilty of plagiarizing!). But every detail seems a bit stunning. Stopping up a major river to a depth of almost 600 feet would, it seems, create worlds of problems elsewhere, even if the difficulties at the dam site could be managed. Where will that water flow when backed up? What will be the effect on ground water reservoirs? What do we do if we find water going where it is not wanted (in untold millions of gallons)? Maybe these are senseless questions if I understood the terrain better. But still.



It's interesting how one of the great public works of the 20th Century comes upon one with so little warning. The roadway snakes through the rocks (which themselves approach rather suddenly) to round a corner and arrive at dam-top level. The opposite bank of the river is visible directly across from one; you could almost reach out and touch it, it seems. You can see a lake to one side of the curved roadway, a chasm on the other. You have no sense that the original stream bed, the bottom of that chasm, is nearly 50 stories below you. Of course, the depth and narrowness of the gorge is exactly what makes it a good site for a dam. But it makes for a grandeur that takes a little time to wrap your head around.



We toured the generating plant last, and as maybe the most mundane part of the project, it's also the most pointedly beneficial. After the initial turmoil of construction, the dam just sits there holding back water, and in exchange it provides electricity to parts of seven states. Fabulous. That so much good can come from a burst of effort like this, so much good with (near as I can tell) so little cost, seems the greatest application of the engineer's art and science.