therefore, is necessary for maximum utilization of water. High spring run-off from melting snow usually ends in May or June. Low flows then continue well into the fall. Occasional freshets or floods occur in all seasons of the year; in winter and spring from heavy rain or rapidly melting snow or both, and in summer and fall from localized torrential rains.

The average annual virgin flow of the Virgin River at Littlefield, Ariz., near its mouth is estimated at 310,000 acre-feet. Recorded flows of streams at various points are shown in the following table. Unfortunately there are no discharge records of Kanab Creek and Meadow Valley Wash, the principal tributary of Muddy River.

Ground water.-Many small springs and seeps scattered through the area have been developed for stock watering and domestic purposes, and all the larger springs are utilized for irrigation. Other than the discharge of springs, ground water is of limited importance. A few small wells in alluvial-filled valleys are operated for irrigation and domestic purposes. There are no known ground-water basins having large contributing drainage areas, and the possibilities of further ground-water development for irrigation are believed to be insignificant.

Quality of water.-Waters of the upper portion of the Virgin River and of all its northern tributaries are of suitable chemical quality for irrigation use. These waters have been used for many years for irrigation, and no detrimental effects to crops have been apparent.

Below La Verkin, Utah, mineral springs contribute to the Virgin River large quantities of water which are highly charged with mineral salts, chiefly carbonates, sulphates, and chlorides of calcium, magnesium, and sodium. At Littlefield, Ariz., near the mouth of the river, mineral springs contribute an average of 60 second-feet of water, which constitutes most of the low flow of the stream. This water is unsatisfactory for domestic use. Only because a

high percentage of the mineral content is gypsum is the water at all usable for irrigation, and then only for the more salt-tolerant crops.

Waters of Kanab Creek and Meadow Valley Wash are of good chemical quality and have long been used for irrigation. Muddy River waters, derived principally from springs, are of fairly good quality for irrigation.

Silt content of streams in the Virgin division is fairly low in the headwaters at nearly all times and also in the lower reaches during ordinary low flows. Freshet and flood flows, however, are high in silt content.

PRESENT DEVELOPMENT OF WATER RESOURCES

General.--Although the total run-off during the lowflow season is now fully utilized for irrigation and some shortages are experienced, the major part of the stream flow during the nonirrigation and high spring run-off seasons escapes from the area unused. Plans for development of portions of this surplus water for irrigation have been proposed from time to time and there has been some effort toward promotion of projects, but no successful developments therefrom have as yet materialized.

Domestic water for communities is obtained for the most part from springs, and nearly all communities have municipal distribution systems. Some community domestic supplies are pumped from wells. Outlying farmsteads obtain domestic supplies from privately owned springs, irrigation ditches, small wells, or by hauling from distant sources. Many seeps and springs have been developed for stock watering, and many watering ponds have been constructed on the ranges for capture of occasional surface run-off.

Irrigation. Irrigation was early expanded to the limits of natural stream flow, and by 1905 some streams were overappropriated, with shortages resulting in low run-off seasons. The high cost of potential projects has precluded any material development of new systems by local interests for irrigation of additional lands in the area since about 1905. Present storage development is practically negligible.

Approximately 36,100 acres are irrigated in the Virgin division, of which 23,500 acres are in Utah, 2,800 acres are in Arizona, and 9,800 acres are in Nevada. These areas include 400 acres of Indian lands; the Office of Indian Affairs estimates that 700 additional acres of Indian lands in existing developments will be irrigated ultimately. Irrigated acreage varies somewhat from year to year depending upon fluctuations in stream flow as well as economic conditions. All irrigation development has been accomplished by individuals and mutual irrigation companies.

Nearly all irrigation developments are simple gravity diversions without storage regulation. Some small areas

are served by pumping. About 15,000 acres of the total irrigated area have a fairly adequate water supply. The remaining area suffers frequent water shortages of varying degree. No water is imported into the division and only one small diversion is made out of the area. This diversion is from the headwaters of Santa Clara River to Pinto Creek in the Bonneville Basin.

Power development.-Stream flow is used for power production at five hydroelectric plants in the area. One plant of 1,000-kilowatt capacity is located on the Virgin River at La Verkin, Utah, and three plants with combined capacities of 1,890 kilowatts are located on Santa Clara River near Veyo and Gunlock, Utah. These four plants are owned and operated by the Southern Utah Power Co., which supplies electric energy to most of the communities in the Utah portion of the division. The fifth plant is the recently installed St. George municipal plant located on the pipe line diverting municipal water from springs at the head of Cottonwood Creek, 15 miles northwest of St. George. This plant has a capacity of 550 kilowatts, and its output is augmented by two diesel installations at St. George, having a combined capacity of 800 kilowatts. Communities in the Nevada portion are served with power from the Boulder Dam power plant.

Summary.--Irrigated areas and estimated amounts of water consumed in the Virgin division are summarized in the following tables:

to secure a full supply for lands now inadequately irrigated and for as large an additional irrigable area as is practicable. Such development would help to stabilize irrigated agriculture, relieve the local population pressure, and enlarge the livestock feed base so as to attain more nearly a balance in industry of the area.

Kanab Creek project. Storage on the main streams of either Kanab Creek or its tributary, Johnson Creek, is impracticable because of the high silt discharge of these streams. New development is limited to offstream storage of the comparatively silt-free, nonirrigation season flows of Kanab Creek, which are derived essentially from springs emerging in the stream bed several miles above the town of Kanab. To provide such storage a reservoir of 1,400 acre-feet capacity at the offstream State Line site would be fed a water supply from Kanab Creek through a short extension of the existing Kanab canal. The stream flow thus diverted and stored would furnish a supplemental supply for 1,000 acres of land near Fredonia, Ariz.

Hurricane project.-A reservoir of 165,000 acre-feet total capacity (65,000 acre-feet active and 100,000 acrefeet reserved for silt) on Virgin River at the Virgin City site 3 miles northeast of Hurricane, Utah, together with a 27-mile canal extending southwest from the reservoir, would furnish a supplemental supply for 6,500 acres of land now insufficiently irrigated and a full supply for 14,000 acres of new land, all in the Hurricane-St. George Valley in Utah and Arizona. The existing 1,000-kilowatt power plant at La Verkin, Utah, dependent on erratic river flow, would be abandoned, and power would be developed at three new plants having a combined capacity of 4,600 kilowatts and a combined head of 800 feet. In addition to meeting power replacement and project pumping needs, these plants would produce about 15,000,000 kilowatt-hours of firm power annually. The reservoir would also have incidental value for flood control, silt retention, fishing, and recreation.

Santa Clara project. Full regulation and utilization of the flow of Santa Clara River, the principal Virgin River tributary, could be obtained by means of an 18,000acre-foot (14,000 acre-feet active capacity) reservoir at the Lower Gunlock site on that stream. A supplemental water supply for irrigating 1,700 acres of land in need of more water and a full supply for 2,000 acres of new land in Utah under existing canals would be provided. The reservoir would have incidental value for flood and silt control and for fishing and recreation.

Panaca Valley project.-Irrigation development in the Muddy River Basin is limited by available water. A 48,000-acre-foot reservoir at the Delmue site on Spring Creek near its mouth (the head of Meadow Valley Wash) 7 miles northeast of Panaca, Nev., would provide storage for irrigation water and flood control. A new 10-mile canal would carry this water to 2,000 acres of land in need of a supplemental supply and 2,000 acres

of new land. The reservoir would have incidental value for fishing and recreation.

Moapa Valley project.-A reservoir of 9,500 acre-feet capacity at the White Narrows site on Muddy River would provide water storage regulation to furnish a supplemental water supply for 2,500 acres and a full supply for 1,500 acres of new land in Moapa Valley, Ariz. This reservoir would also provide 2,500 acre-feet of storage for flood control and silt retention. Rehabilitation of the present distribution system and drainage of project lands would be included in the project development.

Moapa Valley Pumping project. This development would provide an irrigation supply for 6,000 acres of new land in the Muddy River drainage area by pumping from

Kanab Creek.. Hurricane..

Santa Clara___

Panaca Valley.

Project

Lake Mead. The first pump would lift the water 130 feet to a canal 22 miles long. A second pump would lift the water an additional 105 feet where half the flow would be diverted in a 5-mile canal. A third pump would lift the remaining flow another 80 feet to a canal 10 miles long.

Summary

The following tables summarize potential development of water resources in the Virgin divisions, including the various purposes to be served by potential projects, estimated construction costs, areas to be irrigated, and stream depletions.

Moapa Valley..

Moapa Valley pumping

Total_

1 Symbols used: I-irrigation, P-power, S-silt reteniion, and F-flood control.

2 Preliminary estimates based on construction cost of Jan. 1, 1940.

Estimated construction cost 2

$200,000 9, 200, 000 1, 700, 000. 1,300,000 700, 000

2, 800, 000

15, 900, 000

California, and Nevada. It includes not only the area which drains into the Colorado River below Lee Ferry, excluding areas tributary to the Little Colorado River above Moenkopi Wash, Kanab Creek, Virgin River, Muddy River, and the Gila River above Sentinel, but the valley containing the Salton Sea, whose drainage is not tributary to the Colorado River and whose diversions therefore constitute exports from the basin.

The Colorado River enters the division from the northeast at Lee Ferry, weaves its way west and south for 350 river miles, then flows south 358 miles emerging from the Boulder division at the Mexican border. The Williams River, formed by the confluence of Big Sandy and Santa Maria Rivers in west central Arizona and entering the Colorado just above Parker Dam, is the only major stream rising in the Boulder division.

WATER RESOURCES

Surface water.-Gage height records of the Colorado River at Yuma, Ariz., have been maintained continuously since 1878, although discharge measurements date only from 1902. During later years other measuring stations have been established on the main stream and tributaries. The average annual virgin flow of the Colorado River at Lee Ferry, based on the period 1897-1943, is estimated at 16,270,000 acre-feet. The virgin flow for the Gila River near Dome, Ariz., is estimated to be 1,270,000 acre-feet. The average annual flows of the Colorado River and two of its tributaries as recorded at various points in the Boulder division are as follows:

TABLE XCI.—Average annual stream flows in the Boulder division

Average annual flows (acrefeet)