As more people claimed the Colorado River Basin for their home, they came to realize that the extent of the ultimate habitable area was determined by the limitations of the dependable water supply and that the Colorado River was increasingly important as a national re

source.

How to divide the waters of the Colorado River for beneficial use presented complications. Because the watershed reached into seven States in this country interstate problems required solution before any comprehensive development could be undertaken. Since the river's lower delta and its mouth extend into Mexico international problems also were presented.

In the history of the development of the Colorado River the early 1920's was a significant period. By that time the use of water in the lower river area had reached the maximum possible without extensive storage regulation, and demands for additional water had created a critical situation which finally resulted in the Colorado River Compact, the Boulder Canyon Project Act, and subsequent acts pertaining thereto.

In this chapter the history of irrigation development is traced to this critical period and problems are presented that pressed for solution in the development and use of the Colorado River for irrigation, flood control, power production, and other beneficial uses. The Colorado River Compact which divided the water between the upper and lower Basins, other legislative acts pertaining to the development of the Colorado River, and the Mexican treaty allocating certain of the waters of the Colorado River to the sister republic are briefly outlined with no attempt at legal interpretation.

Fundamental to a division of the water is a knowledge of the quantity, quality, and flow characteristics of the water available. Virgin conditions of the Colorado River are considered for this purpose.

Virgin Conditions

The Colorado River, draining 242,000 square miles in this country, has the largest watershed of any stream

in the United States outside of the Mississippi River Basin. Beginning high on the Continental Divide it empties into the Gulf of California at sea level.

Rain and snow fall in abundance on the Rocky Mountains rimming the upper part of the Colorado River Basin, but great expanses in the lower areas are comparatively dry. The average annual precipitation for the entire drainage area of less than 15 inches is near the lowest for the major river basins of America. Nearly 90 percent of the moisture that falls returns again to the atmosphere through evaporation, and only about 10 percent flows in the river channel. Yet about 10 percent of the scanty precipitation on so vast an area makes up the flow of the mighty Colorado River. The river grows almost to its full size from contributions of tributaries in the upper half of its drainage area, above Lee Ferry in Arizona. Below that only minor contributions are made by the Little Colorado and Virgin Rivers, and between Black Canyon (site of Boulder Dam) and the entry of the Gila River near the Mexican border inflow is insufficient to offset evaporation losses in the desert region. From an analysis of all available data, average virgin flows at various points are estimated as follows:

snow was a mighty, raging torrent, reaching flood peaks of 250,000 second-feet or more. Below the canyon section it overflowed its banks and inundated the country for miles around. In summer in years of low run-off its flow became a mere trickle by comparison, sometimes dropping to 2,500 second-feet. The only sustained summer flow of most tributaries was the outflow from numerous mountain lakes fed by the melting of perpetual snow banks. The northern tributaries had greater sustained flows than those in the southern region, but they too were subject to great fluctuations.

The flow of the river also fluctuated greatly from year to year. At Lee Ferry, under virgin conditions, annual flows probably ranged from as little as 5,500,000 acrefeet to as much as 25,000,000 acre-feet. Flows of tributary streams were characterized by even greater variations, especially those of the lower region. Under virgin conditions the average annual flow of the Gila near Phoenix is estimated to have been 2,282,000 acre-feet, of which probably only about 1,270,000 acre-feet reached the Colorado because of losses in the lower river area.

The creeks and streams at higher elevations generally bring clear, pure water into the main Colorado River, although they become roily during the spring run-off. Soluble salts in quantities damaging to plant growth occur in isolated tributaries but the injurious effects are local and generally unimportant. Diluted by larger streams of the system, these soluble salts of tributary streams cease to be harmful. Water of the main river becomes progressively more saline as it moves downstream and receives return flows from irrigation and drainage from basin lands but is considered suitable for irrigation at the lowest diversion. (See Ch. VIII, Geological Survey "Quantity and Quality of Water.")

Tributaries entering the middle and lower sections of the Colorado River, notably the San Juan, Little Colorado, and Virgin Rivers, have highly erosive watersheds and hence contribute great quantities of silt to the main stream. At normal flow stages little silt is carried, but more is picked up in spring and early summer when flows become high and turbulent. Occasional summer cloudbursts cut into unstable earth sections, flushing large amounts of mud and silt into the streams.

Early Development of the River

IRRIGATION

The first white irrigators in the Colorado River Basin were the Jesuits who established themselves at the old missions of Cuevavi and San Xavier in Arizona in 1732. In the period 1768 to 1822, considerable irrigation was practiced along the Santa Cruz River near the missions and the Spanish presidios of Tubac and Tucson.

After the Gadsden Purchase in 1854, a number of Americans military followers, stragglers from the immigrant stream to California, and others, pioneers by instinct-began to settle and develop irrigation in Arizona. Thomas H. Blythe moved to the Palo Verde Valley in 1856 and commenced the first recorded use of the Colorado River in California. In 1877 he made the first filing on Colorado River water in California. About the same time the first modern irrigation works were being constructed in Wyoming, Utah, and Colorado. In 1854 Mormon pioneers began to irrigate from Blacks Fork, a tributary of Green River, in Wyoming. Irrigation in the basin in Colorado began in the 1860's and 1870's when prospectors and miners came over the Continental Divide from the older mining districts on the eastern slope of the Rockies. The Federal Government first attempted to reclaim arid lands on the Colorado River Indian Reservation in 1867. In 1883 the Grand Valley Canal, a private development, was started to irrigate a relatively large area in Grand Valley on the western slope of the Rockies in west-central Colorado.

The possibility of exporting water from the Colorado River to the Imperial Valley of California by a simple diversion canal passing in part through Mexico was recognized even before the Civil War. In 1876 Lt. Eric Bergland made surveys on the lower river for the War Department for the purpose of investigating flood conditions and to determine the feasibility of diverting water from the Colorado River to the Imperial Valley through a canal wholly within the United States. He reported unfavorably on such a canal but efforts continued for a water supply to the Imperial Valley. Despite the difficulties and undesirability of a canal through Mexico for the irrigation of Imperial Valley from the Colorado River, construction of an international canal was finally begun in 1902 by the California Development Co. By September 1904 nearly 8,000 people had settled in the valley; 700 miles of canal were in operation; and 75,000 acres of land were cropped.

After passage of the Reclamation Act by Congress in 1902, the Reclamation Service (Bureau of Reclamation since 1923) of the United States Department of the Interior began investigations to determine the feasibility of constructing large irrigation works in the West. Some of the early projects constructed in the Colorado River Basin by the Reclamation Service were the Uncompahgre and Grand Valley projects in Colorado, the Strawberry Valley project in Utah, and the Yuma and Salt River projects in Arizona.

Irrigation continued to expand in both the Upper and Lower Basins. In 1922 the approximate irrigation development in the entire Colorado River Basin, according to a report by F. E. Weymouth, then Chief Engineer of the Reclamation Service, was as follows: