HUGE DAM

Wairarapa Times-Age, 25 July 1938, Page 3

HUGE DAM

WORLD’S LARGEST STRUCTURE. COLUMBIA RIVER PROJECT. Boulder Dam is the largest structure ever built by man, yet it could be buried in the base alone of a concrete colossus which engineers are raising above the Columbia river in Washington, states “Popular Mechanics.” Called the “biggest thing on earth,” the Grand Coulee dam, when finished, will be three times the size of Boulder, will develop one and a half times as much power, and will provide irrigation for an area one and a half times the size of Rhode Island. The dam will be as high as a 46story building and as long as fourteen ordinary city blocks. Its bottom will be as thick as the length of a six-car train, and four vessels the size of the Queen Mary could be spaced along its top. The 23 million tons of concrete will bulk four times the volume of the Great Pyramid. The gigantic mass to be seen today is not much more than the mere foundation of the whole structure. When finished the dam will be nearly a mile long and three times as high as Niagara Falls.. It will back up a lake 151 miles long clear to the Canadian border, and its generators will develop the equivalent of 2,700,000 horse-power, more than the hydroelectric power of all seven dams of the Tennesse Valley Authority combined.

The gorge of the Columbia river is too big to permit an arch-type dam, Grand Coulee must depend upon its massive weight alone to resist the pressure of the water it will back up. At the dam site the river is 700 feet wide and at times 70 feet deep. It is estimated that potentially this one river alone, exploited under a huge ten-dam programme of which the Grand Coulee is one and the Bonneville dam now being built 300 miles down stream is another, can turn out energy amounting to more than half the total hydro-electric power developed in the United States today. ' When the engineers selected the present site' on the Columbia they took advantage of an event that happened millions of years ago. During the last great ice age a glacier flowed into the present river-bed and dammed the river as effectively as the modern concrete structure will. The impounded waters gradually filled the canyon and then overflowed the falls, cutting out a new river channel to the south. For centuries the river flowed along its new bed and then, when the ice retreated, resumed its age-old path. That left a dry river-bed, from 2 to 5 miles wide and 56 miles long; high on the canyon wall; pointing away almost in the opposite direction from the great gorge of the Columbia. At the far end of this old channel lie 1,200,000 acres of the richest arid agricultural land in the country. The present idea is to pump billions of gallons of water up from behind the new dam into the extinct river bed and use 23 miles of this trough both as a canal and a balancing reservoir to carry part of the Columbia to the arid acres of the Big Bend country. Never before has a river the size of the Columbia been dammed, and getting ready to build the dam was a major job in itself. Two towns, a “contractor’s town” and a “government town,” were built on opposite sides of the river for the nearly 6,000 workmen and engineers. A large permanent railroad bridge and a suspension bridge for carrying cement across the river had to be built as well as several pile bridges and catwalks. In drilling down to bedrock to ensure firm foundations for the dam the drillers wore away nearly 49 miles of hardened drill steel. To make sure that the foundation granite itself is as strong as possible, ten miles of grout holes were drilled into it and 12,500 tons of cement “grout” were forced down the holes under pressure to fill every crack and seam. Today the nerve centres of the dam are in the two roaring, vibrating “houses of magic” where the concrete that goes into the dam is mixed. Be-, tween them; “Eastmix” and “Westmix” digest 15,000 barrels of cement, 21,750 tons of sand and gravel, and 360,000 gallons of water every day. On an average 15,000 cubic yards of concrete are mixed and placed in a 24-hour period. Above the mixing chamber, in the comparative quiet of a glassed-in office, the chief mixer controls and regulates each batch of concrete. Flick-

dring red and green lights on a dispatch board tell him which crews far out on the dam want concrete, and the amount and type of material they need. In front of him and above his head are push button controls and valves by which the automatically measured doses of water and materials that go into the mixing machines are released, as well as time controls that .automatically stop and dump each batch at the right time. Against one wall of the chief mixer’s office a dozen electrically operated steel pens ihk jagged lines on the moving paper of a huge graph, telling the mixer, as a visual check, the exact amount of materials that go into each batch and the viscosity of the finished' concrete. The dam grows in five foot “lifts” of wet cbncrete, placed in alternate blocks measured up to 50ft square. The forms that hold each block are shaped to provide vertical keys so that when concrete is poured in the intervening blocks the adjoining masses become locked and tied to each other. 'With both mixing plants in operation a cubic yard of concrete is

added to the dam every five arid onehalf seconds; After one-tenth of the Columbia’s flow is diverted for irrigation more than enough Water will always be available tb . keep the generators in continuous operation and to maintain the river level at approximately twice its past minimum flow. A huge fish hatchery is planned below the dam to raise and distribute' young salmon, since the hordes of salmon that normally travel to the upper reaches of the river will be < unable to get by the dam.

It is estimated that the dam and power-houses will cost a total of 178,790,000 dollars and that the combined dam and irrigation project will represent a total investment of 378,631,000 dollars. It will probably require another three years, at the present rate of work, to complete.