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. . . ". N v) CAUSES OF SALINITY -- Table C Contribution from major springs and tributaries between Glen Canyon and Hoover Dams Source Dissolved-solids discharge in thousands of tons per year Paria River Little Colorado River above Blue Spring Springs in Lower Little Colorado River Bright Angel Creek Tapeats Creek Kanab Creek (base flow) Havasu Creek (base flow) 30 130 550 7 12 4 24 Total inflow in Colorado River (Glen Canyon Dam to Lake Mead) 757 LaVerkin Springs (inflow to Virgin River) Littlefield Springs (inflow to Virgin River) 98 16 Total inflow from major springs and tribu- taries to Colorado and Virgin Rivers 871 The minimum annual inflow of 871,000 tons from these sources results in an increase of about 62 milligrams per liter (0.08 ton per acre-foot) in the Colorado River on the basis of an average annual flow of 10.5 million acre-feet at Hoover Dam. 2. Agricultural Sources of Salinity It is anticipated that development of ne~ irrigation projects may increase the total dissolved solids in the Colorado River. Return flo~s from the irrigated lands pick trp salts from the soils and underlying shales and transport them to the river system. Studies prior to irrigation would be helpful. but they have not been made in most areas, so comparisons must be made when ne~ land is added or ne~ storage is made available. Salt balance conditions exist when the amount of dissolved solids carried off the land is equal to that amount added. Pickup of salt as used in this report represents an unbalanced condition show~ by the increase of total dissolved-solids load In the runoff over the total load in the applied water. This pickup from an area could result from natural sources. such as precipitation runoff. and/or irrigation return flows. Salt pickup chargeable to irrigation would be only that additional which occurs as a result of irrigation and should not include the amount of pickup off the land resulting from natural sources. 31