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Show PART X WATER RESOURCES FOR FUTURE DEVELOPMENT Present Modified Flow In order to ascertain the amount of water remaining over and above present (1965) uses, there have been reconstructed what are termed present modified flows. The reconstruction of present modified flows was accomplished in each of the three subregions for the study period 1914 to 1965, the premise being that the general hydrologic conditions of that period might reasonably be expected to reoccur in the future. The 1914-65 study period was selected as the longest period for which reliable records were generally available in the region. The procedure is one of adding to the historic annual flows at the outflow points of each subregion past annual depletions, the result being virgin annual outflows. Then, assuming that all present uses were in effect throughout the 1914-65 period, the present (1965) normalized use in the subregion was deducted from the virgin flow, the result being the present (1965) modified flow. (See "Hydrology," Part II). In each subregion the studies reflect the use of waters produced locally within the subregion. In other words the flows of the Green River and the Colorado River at their confluence are not considered a local inflow to the San Juan-Colorado Subregion. The data from the three subregions can thus be summed up to ascertain the respective results at Lee Ferry, the outlet of the total region. In the study no attempt has been made to account for changes or differences in natural losses, sometimes referred to as "salvage." A considerable amount of such salvage water, however, is accounted for in the computa- tion of reservoir losses in the Main Stem reservoirs. 46 |