SHACKLING THE COLORADO
THE basin of the Colorado River covers approximately one-thirteenth of the area of the United States. It is half as big as the region that lies east of the Mississippi. It is equal in size to New England, plus all of the Middle Atlantic States, with Ohio and Indiana thrown in. But it has largely run to waste. It is the least developed and the most sparsely inhabited portion of the country. It has a population only equal to that of the tiny State of Rhode Island.
The remotest headwaters of the Colorado appear where the Green River taps certain crystal, ice-fed lakes in the Wind River Mountains of Wyoming, and where the main stream chooses Longs Peak, the highest in Colorado, to stand as a monument at its very source. Both streams frolic through high mountain country, their waters occasionally diverted for purposes of irrigation. They flow into the plateau region which, the geologists say, has slowly risen a perpendicular mile because of the inner pressure of the earth. But as it has come up the swift waters of the Colorado have eaten their way into it and have cut to the depth of a mile through its varying strata. The walls have tumbled in to widen the gorge. Tributaries have ripped their auxiliary, bizarre excavationsand the Grand Canyon came forth as the greatest earth-carving demonstration water ever gave.
Then the mad river becomes a sullen, clumsy, lowland stream, from the banks of which thorned desert plants get the only glimpse of water ever vouchsafed in this corner of the world. But as the mad stream, now grown morose, nears its end it performs one final fantastic feat. It builds itself a trough of silt in which to run, a trough which, strangely, looks down from its high elevationhundreds of feetupon the plain that stretches away into California. The silt which makes the Colorado muddy stops here as the waters slow down to build the land. It was thus that the stream built a dam across the Gulf of California ages ago and left its upper end (in what is now the United States) to dry out and become the Imperial Valley of to-day, with Salton Sea, 204 feet below the ocean level, at its feet.
Private enterprise has here developed an irrigation canal which, for engineering convenience, runs for 60 miles on Mexican soil. Its builders pledged certain water to Mexico for the privilege of looping this canal across its border. Then they brought their canal back to the American side and spread its waters out until they irrigated 400,000 acres, worth $100,000,000, and furnished homes for 60,000 people. The yield of this land is prodigious. Its crops are earlier and more tropical than those grown elsewhere in the United States.
But the mad river in its sand trough looks down in constant menace on these cultivators of the silt-lined valley.
Such was the situation into which, throughout the past two decades, the Government was asked to look as into a crystal ball and behold the vision. Yet it was strange that those who conjured up that vision were not medieval magicians but modern engineers with slide rules, water gages, and blue prints. The vision became definite plans which were approved by congressional action carrying appropriations to convert dreams into realities. The unprecedented features of this undertaking to which the Government has set its hand and on the details of which it has already decided may now be described.
The central feature is the great Hoover Dam, the best location for which, all aspects of the problem considered, was found at Black Canyon, 30 miles north of Needles, Ariz., and 30 miles east of Las Vegas, Nev., its nearest railroad point. This is below the Grand Canyon section of the riverupon which it will have no effectamong barren desert hills, blistering in the sun.
The job, the major portion of which is being executed under a single contract, will cost more than a hundred million dollars, including work and materials. About half of this will go to the contractor for the work, and the Government will spend the rest for the makings. The job begins with four mile-long tunnels to run around the base of the dam through the solid rock of the mountain. When these are completed a cofferdam 80 feet high must be built to turn the river, even when the floods come, to go roaring though these tunnels. Another dam must be put below the site to keep these waters from backing up. Thus will a dry stretch half a mile long, in which the dam is to rest, be created. The débris that has settled in the bottom of the river, 140 feet of it, will have to be lifted out. Power houses, elevators running to the top of the mountain, railroads up and down the canyon, are all a part of the plan.
The biggest single contract that the Reclamation Service ever let before was that for the construction of Owyhee Dam in Idaho, which cost $6,000,000. It will cost almost that much to excavate one of these four tunnels that are to run around Hoover Dam. They are to be 50 feet in diameter, drilled through hard and solid rock. Two 4-story city houses could be set in the mouth of one of these tunnels and lots of room would be left at the sides.
Driving one of these tunnels the size of a shady village street for a mile though this rock will take some time, and the big dam can not be started until the river is running though them. The contractor for each will work from both ends and from the middle, at sixteen places in all. In tackling this mountain face the contractor's chief weapon is dynamite. Its skillful use will leave walls that can readily be lined with concrete.
But blasting out the rock is but part of the job. That rock must be disposed of, and here they are in a canyon not unlike Broad Street, in which there must be no obstruction and traffic must be kept moving. It is 2 miles down the canyon before it opens out at all. It may be necessary to haul this rock 6 miles before it is dumped, and 13 miles of railway will be built in the canyon walls just to move this broken material. And there is 2,000,000 cubic yards of it, which is considerable rock.
When the tunnels are finished the upstream cofferdam will be thrown across the river to send it through these artificial courses. This dam will be built chiefly of rock and earth and will be 80 feet high. When it has taken form it will be given a rock facing 3 feet thick and an apron of reinforced concrete paving 6 inches thick will be thrown over it. Then along its toe steel sheet piling will be driven in such a way as to make a water-tight cut-off wall reaching far underground. The actual diversion of the river will be made at a time of low water and the dam will be strengthened to rebuff the floods. There is here a sporting venture, however, in which the Government assumes the risk. This cofferdam is equal to any flood that is likely to come, to any high water that has been known to the white man. Once in a thousand years, it is admitted, phenomenal situations arise. Engineers say they have a way of coming at the wrong moment. The one overwhelming flood of the centuries might occur after this cofferdam is in. The great tunnels might not be sufficient to carry off its volume. The water might sweep over this dam and destroy the mere house of cards that puny man was building in the river bed below. If it should do so, the Government and not the contractor would have to carry the burden of loss.
But taking it that the cofferdam will be in and the river diverted two years hence, the next task will be clearing out the débris that rests on bedrock. The cofferdams are half a mile apart. In the bottom of the great trough of the river is a deposit of bowlders and gravel 140 feet deep resting on bedrock. The bottom of the dam is to be 650 feet long up and down the river. With the necessary slopes for approaches and elbow room in which to work, the trough will have to be cleaned out for 1,000 feet. With all the men and machines that can be got into this space, it will take them a year, working antlike, to clean the canyon down to bedrock. When this is done the solid rock of the bottom and sides of the gorge will be worked over to insure the cleanness and soundness of every spot, much as a dentist works over a cavity in a patient's tooth before he puts in a filling. Not only this, but deep trenches will be cut into the bedrock, into which the dam may be tied to add to its strength. The whole will be gone over with brushes, water, and compressed air to insure absolute soundness.
When the foundation is thus prepared the laying of concrete for the great dam will begin. To give an idea of the size of this undertaking, it may be said that the 4,400,000 cubic yards of concrete that is to be used in the dam, power plant, and appurtenant works is more concrete than the Reclamation Bureau has used in all its other projects combined in the 29 years of its existence. The Government will buy and supply to the contractor the 5,500,000 barrels of cement needed in the manufacture of this concrete. The contractor must go up the river some 8 miles to a natural gravel deposit and get his own gravel. He must bring it to the dam site and mix his own concrete. This in itself will require a huge plant.
From there on the big job will be one of mixing and pouring concrete. Besides the bulk of the task there are such fine points in construction as so pouring this concrete that expansion and contraction due to heat will not leave cracks which might start leaks in the structure. At times the weather temperature here in the canyon may be 120 degrees. Concrete as it sets undergoes chemical action that generates heat and increases its temperature some 50 degrees. Heat expands the concrete, and it will contract as it cools and may leave cracks and open spaces. To avoid this the dam is to be refrigerated as the concrete is laid. Pipes are to be run through the 50-foot-square blocks as they take form and refrigerating fluids are to be forced though the pipes. The temperature of the concrete will be kept down so it will not expand. This concrete will occupy a space that is almost exactly equal to that it will fill when the job is done. The dam will be built up in these 50-foot blocks. If there are cracks, they will come between the blocks. They will be found and grout under high pressure will be forced into them. This grout is liquid concrete and will be made to fill every cavity in the dam.
As the dam ascends work will also be going ahead in the development of the power houses below it, which are a part of the construction, and the sale of power from which will ultimately repay the Government every cent put into this enterprise. There are to be 1,100 feet of these power houses across the base of the dam and in wings extending 500 feet down each side of the canyon. When the dam is halfway up, the cofferdam above it will be blown out and the water let in against it. Thus the reservoir may be started on its work of storing water in advance of the completion of the project. As soon as it has raised the water to a sufficient level, it may be diverted though the penstocks and the power houses and the generation of electricity for local use and even for sale to the outside world may begin. Thus a revenue from the dam may be derived for a year before it is completed.
The quantity of concrete consumed by the dam decreases rapidly as its height increases. It finally narrows to a width of 45 feet at the top, as compared to 650 feet at bedrock, 730 feet below. Thus it appears that if the Washington Monument, which is 555 feet tall, were set on bedrock beside the dam, it would reach but a little more than two-thirds of the way up its front. The Woolworth Building, 792 feet high, would barely overtop it.
At its crest the dam will be 1,180 feet long, spanning the gap between Arizona and Nevada. The whole structure arches gracefully, with its back upstream, which fact gives it enormous strength to resist the pressure of the water that will pile up back of it.
When the dam is completed two links of a transcontinental automobile highway will have been built up to its respective sides. The top of the dam will be used as a bridge over the gap of the Colorado. It is taken that, when this highway is open, the majority of the automobiles that cross these States will come by the dam, for it will constitute one of the wonders of the West.
After the dam is completed the automobile tourist coming from the East will break though low, barren desert hills on the Arizona side and come suddenly on the border of this, the largest artificial lake in all the world, stretching its tentacles away into innumerable canyons that reach into the most barren and solitary area in the United States. To his left, if the reservoir is full, he will see merely the crest of the great dam. Proceeding a bit farther he will come on the structure itself and will be given a look downstream where Black Canyon, robbed of its river, presents its solemn and precipitous walls for inspection. Looking over the edge of the dam where its skirt flares out, he will see the roof of the power house through which this stored water under pressure is roaring in the generation of electricity. This water finds its way though the inner tunnel on each side of the dam which was originally built for the diversion of the river. The second great tunnel on each side has been converted into a spillway. If it should happen at the time of the tourist's visit that the reservoir is full to overflowing, the surplus waters would be roaring down the spillways and discharging as a mighty torrent at the tunnel exits half a mile below. The rush of these waters under more than 500 feet of pressure would represent a titanic force such as man has never harnessed before.
If the tourist should pause for a visit of a day or two, he would find that he might take a boat up this lake for fifty or a hundred miles, leading through massive eroded plateaus that reach into the areas of the lower Grand Canyon of the Colorado. He might visit the dark canyons below the dam where the pent-up waters escape, yielding their power and going on their way to irrigate many desert acres and supplying water to many thirsty towns of the Southwest. Proceeding on his way across the dam and climbing to greater heights among the rock cliffs, he will be able to look back and view the entire panorama that has been unfolded here in the great solitudes and which in its completed form will present the most spectacular engineering accomplishment in the history of all the world.
There are thee units in the entire Colorado River projectthe Hoover Dam, the power houses, and the All-American Canalwith a total authorization of $165,000,000. The canal will be 200 miles down the river, will cost 500,000, and will be big enough to float a ship drawing feet of water. It will carry water to desert lands in southern California, replacing the present international ditch, and will be the biggest irrigation canal ever built. The money for all of this will be advanced by the Government. The cost of the dam, power plant, and appurtenant works will be repaid with interest from power sales, contracts for which are already signed. The cost of the All-American Canal will be repaid by the water users benefited.
These stored waters of this Government undertaking give birth to another enterprise, financed locally and not by the Federal Government, that is no less spectacular and that will cost $200,000,000, to be paid by the community. Los Angeles and that group of communities between it and San Diego will take an aqueduct full of this water 225 miles across the desert, lift it 1,400 feet over a mountain range, and offer it as an added water supply to this area which will soon be built up to its water supply and would cease to grow unless this water supply were increased.
Last Updated: 20-Jul-2009