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~' . . o lr? U') I..:.::J '--') CHAPTER I INTRODUCTION values have considerable uncertainity, but are calibrated and adjusted to meet known conditions in the drainages, and finally in the Colorado River itself. To complete this last step it is necessary to have as accurate an estimate as possible of the annual salt pickup to the Color,ado River in the Grand Valley. This report will show that considerable effort and analysis has gone into the salt pickup determination, and that considerable confidence can be placed on its utilization. In March of 1977 members of the Grand Valley Salinity Coordinat ing COlmnittee, Technical Sub-committee agreed upon a figure of B02,000 tons per year of the annual salt loading to the Colorado River as it flows through Grand Valley. This number was a consensus figure based on various studies performed independently by individuals from Colorado State University, the Soil Conservation Service, the Agricultural Research ServicE', and the Bureau of Reclamation. The consensus figure of 802,000 tons was subsequently modified to 780,000 tons, by the Bureau of Reclamation, as presented in the Stage One Definite Plan Report dated November 1978. All of the above studies were done on an internal basis determining the salt loading contribution from canal seepage, lateral seepage, on-farm ditch seepage, deep percolation, and natural runoff. These studies did not include an inflow-outflow river budget model on the Colorado River. The U.S. Geological Survey (USGS) performed river budget analyses in their 1976 report titled, "Salt Load Computations--Colorado River, Cameo, Colorado, to Cisco, Utah." USGS estimates ranged from 460,000 to 780,000 tons per year of salt pickup. The procedures outlined in thl~ following 1-3