upr000318 119

38 WATER RESOURCES OP CALIFORNIA. / were all accumulated and confined above that acre. Conventional use, however, has resulted in dropping the unit of area, the acre; and of time, the year; and although not expressed, these are now implicitly contained in the phrase “ Duty of W ater.” Qualifying terms are in common use, such as “ N et” and “ Gross.” “ Net D uty” is the quantity of water measured at the point nearest to its entry and spreading out upon the cropped land. It thus con­tains the water required for plant growth, together with the spreading or application losses and the losses contingent to storage in the soils prior to absorption by the roots of plants. The “ Gross Duty” is this same quantity of water in lake or flowing stream, reservoir or place of storage, together with the conveyance losses and waste over spillways incident to its flow through canals or conduits from the first point of diversion at its natural source, to its point of entry on to the cropped soil. “ Net D uty” of water is best adapted to considerations of the requirements of accessory water supplies and in comparing the needs of different localities. “ Gross D uty” is a subject for consideration in canal and conduit design and in initial diversion quantities. The application of waters to large areas in the quantities tabu­lated at “ Net Duty of W ater” in Table 2, provide adequate moisture for their intensive cultivation; but in estimating the total water requirements in any locality, portions of the entire area will not need water. Contingent to an intensively developing agricultural com­munity, the rural and urban dwellings, routes o f communication and transportation, industries, and improvements, occupy an increasingly large portion of the total area. As the small farm holdings become greater in number, the land is more vigorously cultivated and the production per acre is enhanced; the farm buildings needed for this great activity occupy a larger proportion of the cultivatable area. The total value of improvements, the wealth created and the income derived from agriculture vastly increases, but the farmed area would tend to diminish except for the cultivation o f new areas previously unprofitable to farm. The inclusion of new areas among the tilled lands, however, is limited, for after the entire area is brought into use, no additions can be made without destroying improvements which themselves are essen­tial for the tilling o f the soil, and also, there are always some lands naturally unfit for cultivation, such as rocky and alkali spots, high knolls and stream beds. These will never be irrigated. Further, in each season a portion of the total area will remain fallow, other por­tions will be planted but not watered and irrigation water will not be, required for either. So, in closely settled irrigated communities, the sum total of the unirrigated lands may be a considerable part of the total area. The studies made in these investigations, indicate that the part of the gross area ultimately requiring agricultural water, is from sixty to ninety per cent in the various sections of the state. Of all the waters in use for the various purposes of civilization, that employed in agriculture is predominant. In the year 1920, with three and one-half millions of people in California and one-quarter of its arable lands under irrigation, about one-fourth of all waters that can ultimately be made available through storage within the borders of the state, were in use for domestic and industrial supply, irrigation, power generation and mining. The domestic and industrial use was about four per cent of the total, while much of the waters used for generating e ectric power and in mining, being on elevated lands, was employed a second time at lower levels in irrigating the state’s dry soils. \ WATER RESOURCES OF CALIFORNIA. 39 CHAPTER YI. COMPREHENSIVE PLAN FOR ACHIEVING THE MAXIMUM SERVICE FROM THE WATERS OF THE STATE. Plans for converting the waters of California to their greatest service in this generation and for all posterity, must give precedence among the many uses for water, to those purposes which are indispensable to man’s continued existence. Water for drinking and household use takes priority over that for growing food-stuffs, while water for growing food-stuffs is primary to that for industrial purposes. Were there abundant water for all needs, cognizance of its relative importance in domestic, agricultural and industrial service, could be disregarded. In California, however, where the waters in the streams are replenished by rains that largely occur in a few months of the year, and seasons of meager or bountiful rainfall succeed each other in all variations of sequence, there would be deficiencies of water for present needs during every season, were it not for impounding works already constructed. Only through the construction of still greater and more elaborate works to equalize the erratic stream flow and to transport waters to localities of urgent need, can California continue to enhance its wealth and increase the numbers of its people at the prevailing rate which for the past decade has exceeded that of all other states of the Union but two.(1> The combined increase of population in these two states, however, was only one-third that in California. A comprehensive plan must primarily insure a full supply of water for drinking and household purposes. But since the present needs for domestic and industrial water supplies are only a twenty-fifth the amount required for irrigation of the agricultural lands now using water; the principle constructive features of a plan for obtaining maxi­mum use of the state's waters, must revolve about its distribution for the greatly preponderant use in agriculture. Further, the magnified urban communities of the future must largely encroach upon lands, now classed as agricultural, for these farm areas Comprise all the lands that are suitable for residence, except those about the state’s seaports. Because of their harbors, commerce and strategic locations, the seaports will expand over adjacent lands now excluded from the agricultural areas on account of being scatteringly settled fringes to population centers or on account of being too rough of surface or steep of slope. But metropolitan areas in all other parts of the state will undoubtedly arise upon the flatter lands classed in this report as agricultural. As these are relinquished for city development, the total consumption, of water in any district for both domestic and irrigation supplies will not increase very much, since cities of fairly mature growth use water about WTJ. S. Census— 1920. Population of Arizona increased 63.5 per cent, Montana 46 per cent, while California increased its numbers 44 per cent during the preceding decade.