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<br />u <br />u <br />u <br />u <br />n <br />o <br />H <br />U <br />n <br />ti <br />B <br />ti <br />. <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />-204- <br /> <br />~ primarily by irrigation return flows, thereby necessitating <br />en <br />~ a delineation of the components and practices. <br />~ <br />Probably no other single issue has been considered with <br />more intensity by the several research and planning groups <br />associated with the Grand Valley than the total and relative <br />sources of contributions to the net salt loading from the <br />valley. This figure is central to any salinity study <br />because it defines the boundaries within each segment that <br />the agricultural hydrology must fit. By subtracting the <br />salt carried in the irrigation water supplies from the <br />volume of subsurface and drainage return flow, the net <br />agricultural contribution can be delineated. <br />At the time of this writing, there are basically two <br />principal hydro-salinity budget estimates for the Grand <br />Valley (Table 2-1). In various meetings and conferences, <br />the differences have been noted and the essential areas of <br />disagreement identified. It should be noted that the basis <br />of the Kruse (1977) estimate has been expanded to be con- <br />gruent with the analyses of Walker et al. (1977). <br />Salinity Control-- <br />The Grand Valley is presently the site of the only <br />active salinity control program in the Upper Colorado River <br />Basin. The programs under way include water systems im- <br />provement (canal and lateral lining), irrigation management <br />services (irrigation scheduling), and the Soil Conservation <br />Service sponsored on-farm improvements. When implemented, <br />this total program is expected to reduce the salinity by <br /> <br />I <br />~ <br />