OCR Text |
Show "The ground water factor over large areas is difficult of determination. It may be either positive or negative yearly, but if irrigation has reached a stabilized condition and drainage is effective, it may be assumed that over a series of years there is no final change. This term may, therefore, be dropped. "It may also be assumed that the precipitation will continue in average amount in the future as in the past; hence that term may be dropped when considering the change in consumptive use from virgin to cultural conditions. This leaves only the term I-R which becomes not true consumptive use but stream depletion by man's cultural activities, which, of course, is the quantity with which we are concerned. In this sense the inflow, I, becomes the amount diverted for agricultural and other purposes and the return flow, R, is the amount returning to the stream from those diversions. Diversions may be by canals, by closed conduits, or by flooding with check dams in streams or by any other method of applying water to lands or of transporting it. "The total inflow to a valley, including precipitation, less the outflow therefrom, represents the depletion not only by man's cultural activities, but by native vegetation, evaporation from non-irrigated soils, natural water surfaces, swamps, etc. This latter natural consumption must be eliminated in order to arrive at the depletion caused by man. The best measure of the latter is 'diversions less returns', which is the meaning often given 'consumptive use'. "In order to restrict this loss to stream depletion caused by irrigation, we have used the term 'depletion by irrigation' to mean the diversions less returns, exclusive of pre- |
Source |
Original book: [State of Arizona, complainant v. State of California, Palo Verde Irrigation District, Coachella Valley County Water District, Metropolitan Water District of Southern California, City of Los Angeles, California, City of San Diego, California, and County of San Diego, California, defendants, United States of America, State of Nevada, State of New Mexico, State of Utah, interveners] : California exhibits. |