OCR Text |
Show 1368 CONSUMPTIVE USE OF WATEE IN IRRIGATION the total available heat termed by him the "thermal location", and that the magnitude of Vv, as computed from a known constant and the available heat, be reduced in proportion to the lack of attainment of the highest possible standard of agriculture. The dependability of such reduction in the computed valley consumptive use obviously rests on the experience and judgment of the engineer. The method proposed by Hedke, therefore, seems to give the greatest promise in those valleys where a high standard of agriculture has been attained, thus eliminating the necessity of applying the so-called "personal equation of judgment and experience". Obviously, the method may likewise be applied to the newer irrigated valleys under an assumed ultimate distribution of crops and high agricultural standard for the purpose of estimating the consumptive use of water which will occur after the agricultural development of the valley concerned has been completed, Harding's Method.-Harding has studied project and valley consumptive use on extensive areas in the San Joaquin Valley, California (4, 5). A complete report of his California investigations is beyond the scope of this report, which is restricted to a brief statement of the extent of the work, a description of his methods, and a summary of his observations. The Kings River area included about 700 000 acres of irrigated land and the Kaweah area, 184 000 acres. Harding measured the factors of water supply and run-off of Equation (5), as follows: (a) The channel inflow is based on records of current-meter rating stations. (&) The crop seasonal draft on soil moisture was not measured; in effect, however, it was reduced to a wnTnTnnm by so modifying other factors as to provide an equivalent elevation of water-table. (c) The necessity of computing the quantity of water absorbed from the ground-water was eliminated by the same method as the moisture content in Factor (6). (d) The crop-seasonal rainfall on the projects investigated is neg- ligible. (e) There were no appreciable surface run-off losses. (J) The need for measurements of deep percolation losses was eliminated by determining graphically the quantity of canal water needed to maintain the water-table at a constant normal elevation (see Fig. 1). A similar statement applies to Harding's method of determining PL, and Rv in Equation (7). Harding's Method as Applied to the Kings River Area.-The conditions in some of the areas served by the Kings River (4) are such as to furnish a basis on which the consumptive use may be estimated. These conditions are most favorable in the Fresno, Consolidated, and Alta Irrigation Districts. For these districts adequate records of ground-water fluctuation were available for 1922 to 1925, which include one year of more than normal run-off, one year of about 80%, one of about 70%, and one of about 25% run-off. The relative diversions vary even more widely than the run-off due to the later priorities of rights of the Consolidated and Alta Districts. Adequate |