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44 WATER RESOURCES OP CALIFORNIA. placed under irrigation by private or public enterprise, and in carry­ing out this work, of course, the most favorable opportunities for such irrigation have been developed. It will still be possible to add many million acres to the irrigated area and perhaps to double the area now irrigated, but this must generally be done at a high cost, as the cheap opportunities have been long since exhausted. There are remaining, however, many areas which can be irrigated within feasible costs and will develop values far in excess of the necessary expenditures. ’ ’ These investigations show that it is possible to complete the irrigation of 18,000,000 acres in California alone. This would add 12,000,000 acres to the area under water in the western United States. In preparing a general plan for this attainment, the complexly involved rights and claims to rights for the use of water in this state were not considered, but rather a plan was devised which comprehends the state as a virgin territory with its waters and soils unsegregated in private ownership. However, inclusion was made of all constructed works, so that the plan does not contain proposals for discarding monu­ments of attainment of this or preceding generations. The plan would use all existant reservoirs, main canals and distribution ditches. Waters from new sources would be turned into the systems now in use on their arrival in that locality. In the estimates of cost, entries were included for expenditures made in building all existing works except distribution canals, so that the total cost estimated is for a complete system of storage works and main canals giving uniform service to all lands irrespective of their present stage o f development. It was found to be impossible in a general layout to separate the service and costs between areas now under water and those yet to be irrigated, because large areas, now classed as irrigated lands, have supplies that are deficient during the latter part of summer and many projects are short of water during the entire season in years of subnormal stream flow. To make this segregation would require a detail design of the plan in each locality, a work of great magnitude for so large an area as 18,000,000 acres. Therefore the cost estimates here given are the average cost per acre to develop a first-class water supply for all irrigable lands, whether they are now watered or not. They include all costs of construction and of rights of way, for storing waters and transporting them into the regions of use, but do not include the cost of constructing distributing canals or of operating the works, or the costs of acquiring water-rights, of litigation over claims to water-rights, or of damage suits. Neither have credit allowances for power that might be developed at or in the vicinity of the many dams for storing water been deducted in the cost estimates. The average cost of storage works necessary to develop a full supply for the entire 18,000,000 acres, through all seasons without shortage, is twenty-five dollars per acre-foot of water developed, while the cost to the land for adequate amounts would be forty-five dollars per acre. The cost of canals with appurtenant structures to transport this water to the regions of use would average thirty-five dollars per acre. The total average cost per acre to deliver a first-class supply to the region of use is, therefore, eighty dollars. These costs vary greatly in the different localities. WATER RESOURCES OF CALIFORNIA. 45 To effect the watering of so large an area at these costs, it is neces­sary over the bulk o f California’s lands to adopt a coordinated scheme of development and distribution of water, that comprise very large areas in interrelated works. To store the waters at the cheapest loca­tions of abundant1 supply and transport them long distances to the localities of use requires inter-service works of great dimensions. Areas greater than are now under irrigation may be watered without coordi­nated development and distribution, but a limit is being approached t whereby united endeavors almost statewide in extent will be necessary to secure greater service from the state’s waters at reasonable costs. The plan herein set forth requires Complete coordination of the dis­tribution of water over large areas, as well as in the construction of the works. This is necessary in order to utilize the inexpensive storage sites to the greatest advantage.: Dam sites of low cost often have lim­ited Catchment areas draining into their reservoirs that do not yield enough water to warrant the construction of high dams when the draft on them is uniform. But under the coordinated scheme of oper­ation of the comprehensive plan, these dams may be erected to their full height and the cheap storage capacity thus created, utilized to the same advantages as the capacities behind other more expensive dams. To secure this advantage requires that the draft on all reservoirs be pooled so that in apportioning the total draft between the reservoirs in each season, the largest amounts may be taken from the reservoirs that are filling the quickest. In this way, the draft may- be appor­tioned to small reservoirs situated on large drainage areas so as to empty them more than once, a season and thus? use excess water that otherwise would flow over their spillways ; similarly, reservoirs with watersheds of small yield may be left to fill with accumulating waters during the seasons of plenteous run-off and may be drawn on only dur­ing the drier seasons. In so apportioning the draft, exactly the same results are attained in irrigating the land as by the customs in present use whereby the waters from each reservoir become attached to a particular tract of land and the reservoir is drawn on regularly each year at its maximum rate of yield. Under this prevailing system of individual reservoir-draft it would be useless to build dams to greater heights than is required to equalize the flow of their tributary drainage area for a uniform draft, because no greater yield would be obtained with the higher dams. But when their waters are utilized for over year storage only, for hold­ing over the surplus of wet seasons to dispense it for use in the dry ones that may come several years later, these cheap reservoirs answer just as well as the more expensive Ones with larger drainage areas. In either ease the same amount of water must be held in storage some­where for the same length of time, but a great advantage in cost is gained over the customary system of individual reservoir-draft, by the selection of the.cheapest sites for Storing this water under the sys­tem of pooled draft. The scheme of pooled draft of the comprehensive plan, allots the total draft to the various reservoirs so that the greatest efficiency is attained in operating the works. To obtain equal yield to that of the customary system of individual draft on reservoirs, the coordinated scheme of pooling the draft contained in the comprehensive plan, would result in an average construction cost of storage works only slightly more than half that of the individual reservoir-draft system.