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<br />J <br />J <br />. <br />I <br />. <br />. <br />. <br />t <br />. <br />. <br />f <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />3771 <br /> <br />Summary <br /> <br />Relative to other subbasins in the state, salt loading <br />information on the San Juan Tributaries in Colorado is less <br />complete. McElmo Creek, under the authority of the ColoradO <br />River Salinity Control Program, and. the Mancos Valley, under the <br />authority of the Watershed Protection and Flood prevention Act <br />are scheduled for more detailed investigations. The remaining <br />tributaries do not appear to present unusual salt loading <br />problems. This is explained in part by the fact that much of the <br />tributary area in Colorado is underlain by insoluble geologic <br />formations associated with most headwater areas. <br /> <br />The EPA measurement of a 533 tons per day salt load in <br />McElmo Creek due to irrigation in the Cortez area works out to <br />about twice as much annually as the USGS and BuRec estimated for <br />this same area. The EPA also came up with a higher salt yield <br />per irrigated acre per year in the La Plata drainage area in <br />Colorado. It is important to note that the USGS estimates are <br />annual averages while the EPA study covers a one year period from <br />June 1965 to May 1966. <br /> <br />Average Annual Salt Loads for Colorado River Subbasins in <br />Colorado <br /> <br />Professional Paper 441 presents average annual dissolved <br />solids discharges for water years 1914-57 adjusted to 1957 <br />conditions. The BLM's 1977 Status Report presents average <br />annual salt yields for 1966-75. Periodic measurements of total <br />dissolved solids concentrations and continuous stream flow <br />measurements presented in Water Resources Data for COlorado <br />(water years 1969-80) were used to determine salt loading for <br /> <br />-39- <br />