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4 2 WATER RESOURCES OF CALIFORNIA. submerge these lands on an average four and one-half feet in annual depth; while its southerly part, the San Joaquin Valley, contains eight and one-quarter million acres of arable land, but only enough water flows in its stream to cover them a foot and a third in average depth if spread evenly over them each year. To the west and south of these landc and disposed along the coast from San Francisco to the Mexican boundary, is the South Pacific Coast region, which contains a tillable area of over three million acres, but its streams on an average, yield only water enough to cover these lands a little more than one foot in depth annually. Other agricultural lands, about a half million acres in the San Franeiseo Bay Region and four and one-half million acres easterly from the Sierra Nevada and the mountain range extending southerly from Tehachapi Pass, have water in adjacent streams that will cover them annually to less than an average depth of one and a quarter feet, excepting those areas that can receive water from the Colorado River] Areas that are irrigable from the Colorado River may obtain amounts more than double this. To evolve works by which waters may be transported to overcome this uneven geographic distribu­tion of California’s waters, so that, as nearly as possible, all these diversely situated bodies of agricultural lands may be served with their needed waters at the least expense, is the main problem to be solved in unfolding the comprehensive plan. However, other most important considerations intervene in pre­paring plans. In addition to the seventy-three million acre-feet of California ’s waters being located in geographic positions adverse for use on much of the agricultural lands, these waters course down their stream channels in capriciously erratic rates o f flow and three-fourths of them reach the lower levels at a season of the year during which they are of little use for irrigation, because the same storms that pre­cipitate the run-off on the mountain collecting areas, usually wet the lower agricultural lands as well. Thus works must be provided to detain large volumes of flood waters on their catchment areas and hold them in reserve for supplementing the diminishing summer flow of the streams at the time needed for irrigation. In holding waters in storage for later use, evaporation is continually active on their surfaces and the stored volumes are constantly depleted through loss to the atmosphere. It is revealed by these investigations that, even with unlimited storage capacity available on every stream, not more than eighty per cent of the state’s waters can be brought into use as uniform flow ; that, with maximum equalization of stream flow, one-fifth o f all the waters would be lost by evaporation while being detained in reservoirs until the time arrives for their use. Thus the four great basins deficient in waters for their agricultural lands, the San Joaquin Valley, the South Pacific Coast Basin, and the regions of San Francisco Bay and of the Great B asin drainage, within whose confines lie two-thirds of all the agricultural lands o f the state, would have their already inadequate waters, if developed in their entirety, reduced one-fifth in volume by losses of evaporation. To further complicate the problem, the waters of some streams, in their flow being less erratic, can be more easily equalized to uniform discharge than in others. To minimize the cost of the works, those streams must be most heavily drawn upon for water that require the least storage capacity to equalize their flow and upon whose drainage WATER RESOURCES OF CALIFORNIA. 43 areas cheap reservoir sites may be found. The capacities: of storage required to yield the maximum amount of uniform flow for irrigation use varies widely on the different streams. On the streams of least requirements, the maximum development may be obtained with a storage capacity whose volume is less than the annual yield of uniform flow, while on the streams of greatest requirements, a storage capacity fifteen times as large as the annual equalized flow is necessary to obtain the maximum yield. In general, the greatest storage requirements are on streams in the regions of least water production, so that the most effective use of the state’s waters may be accomplished only through a superlatively scientific plan. That the highest attainments of science could be introduced in the . preparation of a comprehensive plan, the investigations have assembled masses of data and completed intricate analyses concerning the location, the quantities and the variability of occurrence of the waters of the state. This digest of information has been all-inclusive, and is pre­sented in full in Appendix “ A ” to this report. It is summarized in Table 1, “ Water Resources of California.” This audit of California’s waters results in the first complete inventory of the waters of an entire state that has ever been assembled. In addition, data on twelve hundred and seventy reservoir sites have been examined and preliminary estimates of the reservoir capacity and of the water yield were made on nearly eight hundred of these. The field parties o f the department made reconnoissance surveys of one hundred and seventy-six reservoir sites and searched three thousand five hundred miles of stream bed for other possible locations. Further, that the amounts of water needed for irrigated agriculture might be ascertained, data were gathered on the quantities of water used on over two million acres of irrigated lands in the state, or more than half the total area irrigated in 1920. These records of water use extend over an average of four years. They are presented in Appendix “ B ” to this report. An analysis, of all this data discloses that four-fifths o f all the agri­cultural lands of the state may be watered. Additional investigation would probably result in finding means of irrigating still larger areas, but the water would be very costly. The 18,000,000 acres which it is found possible to water is an expanse greater than the entire area in all the western states irrigated in 1919, and three times as large as the area under water in California in the same year. To accomplish the irrigation of this large area will require the con­struction of reservoirs having an aggregate capacity of 50,000,000 acre feet, and many miles o f large canals to transport water from its source to the regions of need for it. Because of the inclusion of the maximum area in the estimates of cost, the average price per acre for accomplish­ing the irrigation of the 18,000,000 acres is greater than most projects that are now under construction, but additional areas to those watered at the present time can only be'irrigated at greater costs, for they are the residual lands as the more favorable areas for constructive enter­prises are selected. Quoting from the 1919 report to the Smithsonian Institution on irri­gation in the western states, ‘ ‘ The great bulk of the land west of the hundredth meridian which is not too high, cold, or rocky for agricul­ture, is arid. Of this arid portion, over 15,000,000 acres have been X