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<br />. <br /> <br />l\) <br />en man's activities. Salt concentrating results when water is lost through <br />W <br />. ~ evaporation or transpiration within the Basin or when water of lower <br /> <br />salinity than that of downstream points is diverted from the Basin. <br /> <br />The result is an increase in downstream salinity due to the remaining <br /> <br />. <br /> <br />amount of salt being carried in less water. <br /> <br />Studies of the effects of salt loading and salt concentrating <br />within the Colorado River Basin have been conducted for about 20 <br /> <br />. <br /> <br />years. Although adequate information is lacking to accurately identify <br />all contributing sources of salinity, the studies have identified the <br /> <br />major sources of increasing salinity in the river as it flows from <br />the headwaters to the Gulf of California. However, present under- <br /> <br />. <br /> <br />standing of the cause and effect relationships is limited with <br />respect to natural and man-caused salinity in irrigated areas. <br /> <br />. <br /> <br />The relative effects of salt loading and salt concentrating <br />factors on salinity in the river at Hoover Dam for the period 1942-61, <br />as estimated by the Environmental Protection Agency in its 1971 report, <br />"The Mineral Quality Problem in the Colorado River Basin", are shown <br /> <br />. <br /> <br />in Table 1. Some of the estimates in EPA's report are being <br /> <br />investigated and brought up to date by USBR studies currently <br /> <br />underway. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />-12- <br /> <br />. <br /> <br />~,~<jj; <br />