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Show Chapter 3 Present Water Resources and Related Land Development Present Irrigation Development Lands now irrigated in the Columbia River Basin total about 3.7 million acres. Nearly 70 per- cent of the total lies in the Snake River Basin, largely on the Snake River Plain and in the broad valleys along the lower courses of the Boise, Pay- ette, Weiser, Owyhee, and Malheur Rivers. The Columbia Basin above the mouth of the Snake River embraces about 23 percent of the total, with notable concentrations in the Yakima, Wenatchee, Okanogan, Bitterroot, and Flathead Valleys. The relatively small remainder in the Columbia River Basin below the confluence of the Snake is largely found in tributary valleys, particularly those of the Walla Walla, Umatilla, John Day, Deschutes, Hood, and Willamette Rivers. The relatively deep, narrow canyons cut into the plateau by the Columbia and lower Snake Rivers preclude extensive irrigation development directly from the main stems except by high pump lifts, few of which have yet been undertaken. Water sup- plies are obtained predominantly from surface waters; ground water forms a relatively unimpor- tant source of supply at present. Development prior to entry of the Federal Gov- ernment into the irrigation field accounts for the initial development of the greater part of the area now irrigated. About 72 percent was initially put under irrigation by private, cooperative, or other agencies rather than the Federal Government. In most cases, however, it has not had the benefit of adequate storage works. The remaining 28 per- cent has been developed through Federal under- takings of the Bureau of Indian Affairs and of the Bureau of Reclamation. Another very important function of the latter agency has been the provision of supplemental water to lands in private or co- operative undertakings which were inadequately supplied. More than 40 percent of the lands ini- tially developed by agencies other than the Federal Government have been served in this manner by projects of the Bureau of Reclamation. Thus the total area developed and aided by the Federal Gov- ernment through initial construction and through provision of supplemental water represents approxi- mately 60 percent of the present irrigated area. Although the total amount of water used for irrigation purposes constitutes a small part of the total runoff of the Columbia River, large propor- tions of the inflows to a number of subbasins are so used. Assuming an average diversion of 6 acre- feet per acre and an average consumptive use of 2 acre-feet per acre, the total diversion and total depletion represent less than 14 and 5 percent, re- spectively, of the average annual discharge of the Columbia River. Great variation exists from one part of the basin to another, however, and in some the fullest practicable utilization is being ap- proached. In the Boise, Owyhee, and Malheur Basins, for example, use for irrigation and related consumptive purposes of the local economy results in a depletion of about two-thirds of total runoff. The great bulk of the irrigated area is devoted to hay, forage crops, and pasture which provide winter feed for the extensive range livestock in- dustry of the basin and support widespread dairy farming. Although a relatively small part of the total irrigated area is used for cash crops, the in- come obtained from onions, beans, potatoes, sugar beets, seed crops, and the like is of importance. Fruits, notably apples, peaches, apricots, and cherries attain major importance in a few restricted localities. |
