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<br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />.,. <br />1\;., <br /> <br />e,.'J <br />C. <br /> <br />PART IV. CAUSES OF SALI~ITY <br /> <br />A. Increased Concentration from Salt Additions <br /> <br />1. Natural Sources of Salinity <br /> <br />Flow and quality records reveal that along certain reaches of the <br />Colorado River there are large increases in the dissolved-solids load <br />that cannot be attributed to irrigation or other man-related activity. <br />This increase is mainly due to natural diffused sources and saline <br />springs. <br /> <br />Natural diffused sources are those sources of salt contribution <br />which occur gradually over long reaches of the river system. Salt <br />pickup occurs over large areas of surface and underlying soils, from <br />stream channels and banks. and is difficult to identify, measure, or <br />control. This source contributes the largest overall share of the salts <br />to the Colorado RiVer. Natural point sources are mainly saline springs <br />where the contribution of salt and water is easily identified, issuing <br />from single or concentrated sources. <br /> <br />Very little information was obtained prior to irrigation, making <br />it difficult to identify the magnitude of specific natural sources of <br />salinity in the Colorado River Basin. <br /> <br />Upper Basin.--Past records indicate a substantial increase in salt <br />load in the Lake Powell area above Lees Ferry and below the Green River <br />Utah, Cisco, and Bluff stations. Iorns and others (1965, p. 20) presented <br />estimates of dissolved-solids loads in this river reach based on the <br />period 1914-57 adjusted to 1957 conditions of development. Unaccounted <br />inflow of dissolved solids in this reach amounted to about 5 percent of <br />the load at Lees Ferry. Most of this resulted from natural diffused <br />sources with the San Rafael and Dirty Devil areas fairly heavy <br />contributors. (I) <br /> <br />Other areas in the Upper Basin with large amounts of natural diffused <br />sources of salt are the Grand Valley, Uncompahgre, Lower Gunnison, and <br />McElmo Creek areas in Colorado; Price, and Uintah Basin in Utah; and Big <br />Sandy River area in ~yoming. Although a large amount of salt pickup in <br />these areas is due to natural runoff, some can be attributed to <br />irrigation. <br /> <br />Table A summarizes information about the contribution of water and <br />dissolved salts by point sources, including the springs and wells in the <br />Upper Colorado River system. Although wells are man-made and not a <br /> <br />27 <br />