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Show PART II PRESENT STATUS OF IRRIGATION In the Green River Subregion, for example, Big Sandy Creek below Farson, Wyo., reaching to its confluence with the Green River, has total dissolved solids varying from 1,000 to over ^,000 mg./l. and a sodium adsorption ratio as great as 10. The Duchesne River between Myton, Utah, and its confluence with the Green River at Ouray, Utah, often contains in excess of 2,000 mg./l. dissolved solids. The Price River from Welling- ton, Utah, to its confluence with the Green River has dissolved solids ranging from 1,000 to 5,000 mg./l. Total dissolved solids reach *l,000 mg./l. in the lower reach of the San Rafael River, another tributary of the Green River. Some of the northward-flowing tributaries of the Du- chesne River have boron concentrations which reach 10 mg./l. on occasion, well above the critical point. These streams are considered to have a high to very high salinity hazard and low to medium sodium hazard for irrigation. In the Upper Main Stem Subregion, dissolved solids in the lower reaches of the Uncompahgre River vary between 2,000 and 3>000 mg./l. Cedar Creek upstream from its confluence with the Uncompahgre River and the Uncompahgre River below Montrose, Colo., have sodium adsorption ratios approaching 10. These waters are considered to have a very high salinity hazard and low to medium sodium hazard for irrigation. In the San Juan-Colorado Subregion below irrigated areas, dissolved solids of the Mancos and La Plata Rivers vary between 500 and 1,200 mg./l. Dissolved solids vary between 2,000 and ^,000 mg./l. in McElmo Creek, a tributary of the San Juan River, since the streamflow is principally re- turn flow from irrigated lands in the vicinity of Cortez, Colo. The former has a medium to high salinity hazard and the latter has a very high salinity hazard for irrigation. Both have a low sodium hazard. Suspended sediment concentrations vary widely throughout the region. The sediment load is normally light in the upper reaches of major streams but increases in the middle and lower reaches. Prior to construction of Colorado River Storage Project dams, the average annual suspended sediment concentration measured on a long-term basis at Lees Ferry was about 6,000 parts per million. Since 1965, as a result of the closure of Glen Canyon Dam above Lees Ferry and storage in Lake Powell, weighted average concen- trations of sediment have been reduced to less than 100 parts per million. Construction of Glen Canyon and similar storage reservoirs has had a bene- ficial effect on the quality of the water for irrigation. 35 |