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Determining the Facts

Reading 2: A Short Course on Dam Building

In 1938, a New York publisher put out an illustrated “cartoon guide” for tourists visiting Hoover Dam, then known as Boulder Dam.  The guide included the instructions excerpted below:

15 Minute Course in Engineering
Full (?) instructions on
HOW TO BUILD A DAM LIKE BOULDER
Complete with startling statistics

LESSON NO. 1
Take a canyon—Any canyon several blocks deep, with a good sized river running through it, will do.  In fact there are still quite a few nice canyons along the Colorado River.  You can take one of them—no one will miss it—maybe.

LESSON NO. 2
Preliminaries.—Before you can start on the dam, it will be necessary to build a town.  You are going to have 3500 men working day and night for five years, so you’ve got to have some place to put ‘em.

And you will need to build some roads and erect a power line.  At Boulder Dam they had to get the electricity from Los Angeles to build the dam which now sends electricity back to Los Angeles.

LESSON NO. 3
Materials.—The following list will give you most of what you need:
Cement—5 million barrels.  That’s 16,667 freight cars full.
Sand and gravel—get quite a bit of this to mix with the cement; enough to make 4,440,000 cubic yards of concrete.
Ice plant—you’ve got to have a plant capable of turning out about 2 million pounds of ice a day.
Pipe for ice water—581 miles of it will do.
Plate steel for making pipes—88 million pounds—when you get into pipe 30 feet in diameter, you have to make your own.
Structural steel, nuts, bolts—and other stuff like that—18 million pounds.
Assorted steam shovels, etc.—you'll have to move about 6 million cubic yards of rock and dirt, digging tunnels and whittling out the canyon walls to make room for the dam.

LESSON NO. 4
Drying up the river.—It is necessary to have the spot where you intend to build your dam as dry as possible.  To people who have not taken our engineering course, it seems pretty tough to dry out a river, but actually it’s a cinch.  Simply drill four tunnels about ¾ miles through the cliffs above the water line.  Make them each 56 feet in diameter, then line them with three feet of concrete.  When you finish you will have 3 miles of tunnel 50 feet in diameter.

When you’ve got ‘em ready, dump a bunch of rock and dirt in the river, just below the upper end of the tunnels to block off the river.  Make this “cofferdam” about a hundred feet high, two blocks thick at the base and 70 feet thick on top.

At the other end of the tunnels build another cofferdam to keep the water from backing up, pump the puddles out from between, and there you have it—a dry spot in the river, with the stream running right around it, through the tunnels.  Simple?

LESSON NO. 5
Scaling—After standing out in the weather so long, canyon walls become soft and decayed on the surface.  Before you can safely anchor a dam on ‘em, it will be necessary to scale off this unstable face.  Lower several hundred men from the top on ropes and let them drill the cliffs full of holes.  Stuff the holes with dynamite, and blast it away.  Repeat as necessary. 

LESSON NO. 6
Excavating.—Lower steam shovels into the canyon.  (We forgot to say that you’ll have to string some cables and pulleys across the canyon to let stuff down to bottom.  Better do that right now.)  Build a platform so spectators can watch, and dig down about 130 feet from the river bed to bed rock, removing all loose material as you go.  You are now ready to install the main portion of the dam.

LESSON NO. 7
Pouring the dam.—Take cement, rock and sand—mix well—add water—pour into canyon.

Concrete has a nasty habit of cracking.  The lime in cement causes it to get hot when it is mixed with water.  As it dries and cools, it shrinks and that’s what causes the cracks.  Obviously you must not allow this to happen when you are building a dam.  If cracks were to appear in your dam it might cause severe criticism from people living below the dam—or from their heirs.

It would take 150 years for all that concrete in the dam to cool under normal conditions.  To hurry it up, string two or three miles of water pipe around through each five-foot layer of concrete as you pour it.  From your ice plant, run ice cold brine through the pipes.  This will cause the mass to cool and shrink quickly.  You can then pump a very thin cement “soup” into cracks and spaces that have opened up.  Your dam will be sealed tighter than a drum—and wedged between the canyon walls.

LESSON NO. 8
Spillways.—During your spare time you can erect a spillway on each side of the canyon, on the lake side of the dam.  Drill holes connecting them with two of the tunnels constructed in Lesson 4.  Plug the upper end of the tunnels to cut off water from the lake.  At flood time, if the lake rises high enough to reach the spillways, it can be turned out through these original tunnels.

LESSON NO. 9
Intake towers and power house.—Build four intake towers on the upstream side of the dam, being sure that the top of ‘em is above the high water line.  Erect a power house below the dam.  Now drill holes through the cliffs from towers to power plant.  Connect them with pipes.  As you make each section of pipe, X-ray it for defects.

This completes our engineering course. 

Questions for Reading 2

1. This guide contains many large numbers. Can you think of ways to translate those numbers into comparisons with more familiar things, so that it would be easier to get a sense of how big the project was?

2. The diversion tunnels were among the longest in the world when they were built. Six Companies thought that building them was the most critical part of the project. Under their contract with Reclamation, they would have to pay $3,000 for every day they exceeded the deadline for finishing this part of the work. Why do you think both Reclamation and Six Companies thought the diversion tunnels were so important? Do you agree? Explain your answer.

3. Why was it important to speed up the cooling process? How long would it take for the concrete in the dam to cool by itself? (The pipes are still there, buried in the concrete.)

4. The spillways at Hoover Dam are only used when the water in the reservoir is so high that it would otherwise overflow the top of the dam. Why do you think the engineers thought they had to keep this from happening?

5. In Lesson 1, the guide suggests, possibly not quite seriously, that you could take any canyon on the Colorado you wanted—"no one will miss it, maybe." There are many canyons on the river, some almost as dramatic as the Grand Canyon, located just upstream from Hoover Dam's reservoir. What might people "miss" about these canyons if they were filled with water? Do you think anybody today would suggest that no one might notice if you flooded one of them? Why or why not?


Reading 2 is abridged from Reg Manning's Cartoon Guide of the Boulder Dam Country (Locust Valley, NY: J.J. Augustin, 1938), pages 10-17. Used by permission
.

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