ARIZONA'S MODERN IRRIGATORS-PART II

Arizona's Modern Irrigators

PART II BY ERNEST DOUGLAS YUMA VALLEY, second Arizona project undertaken by the U. S. Bureau of Reclamation, is in several respects unique among irrigated areas of the Copper State. Water shortage has never been a problem there, since the Colorado river furnishes more than enough at all seasons. The supply canal passes through another state. Its diversion dam is of the weir type, probably the only one of any consequence in the west. Climatic conditions more nearly approach the tropical than anywhere else in Arizona. Even people to whom the prodigality of Nature along the Gila, Salt and Santa Cruz is an old story, are astonished at the lushness and variety of vegetation down in the extreme southwestern corner of Yuma county. Furthermore, Yuma county's immediate prospects for agricultural expansion are greater than for all the rest of Arizona combined. At least 240,000 additional acres are certain to be placed under irrigation within the next few years, and over 600,000 acres of desert will be made to bloom if the entire Gila project is carried through as planned. When we speak of Yuma Valley we mean that broad alluvial plain which heads right at the city of Yuma, sweeps southward and westward to the Mexican border. Yuma Mesa, a flood plain of previous geological era, is a bench 60 to 80 feet above the valley floor. The first explorers found Indians growing corn, squash and beans which they planted among the "jungles" of the Colorado "bottom" after recession of the annual spring floods. Farming by white men did not begin until 1890 and proved

U. S. BUREAU OF RECLAMATION Head works of the main Gila project canal, at the east end of the Imperial dam.

extremely hazardous because of the variable flow of a large and erratic river. There was no site, no material, no capital for anything but the flimsiest of brush dams. That dark-brown water was half mud, so the problem of keeping canals and ditches clear of silt was especially acute. But worst of all were the floods that spread relentlessly over the farms and could be controlled only ineffectively by levees.

Potentialities of that rich soil were apparent, however, and soon after the passage of the National Reclamation Act, in 1902, Uncle Sam was persuaded to give Yuma Valley a real irrigation systern. The engineers went 14 miles up the Colorado and built Laguna dam, 4,470 feet from bank to bank, extending down into the sand and gravel 19 feet below the stream bed. Since there was no rockbed foundation, weight of the concrete itself was relied on to hold it firm. It was to raise the water 10 feet to the canal intake and the excess was to flow over the crest. A controversy arose as to the safety of the structure; critics asserted that it would wash out with the first freshet. Time, however, has vindicated the designers. Laguna dam has served its purpose well for 19 years and its impending abandonment is not because of any failure to function.

The canal was dug on the California side to serve the Bard district and part (Turn to Page 29)

U. S. BUREAU OF RECLAMATION