Laserfiche WebLink
<br />.i <br />/ <br /> <br />~ <br />..... <br />U'l <br />v1 <br /> <br />- <br /> <br />. <br /> <br />SPECIAL STUDIES (continued) <br /> <br />Water quality data were collected on drainage channels in the Lower <br />Gunnison Bnd Grand Valley areas thought to be yielding only irrigation <br />returnflow. The annual salt loads from these channels were subtracted <br />from salt loads estimated to be contributed by natural ground water. <br />All of the base flow salt load contributed by the Price River was believed <br />to be from irrigation return flow and was subtracted from the total. <br />An average value of 50 percent of the base flow salt load was arbitrarily <br />set for irrigation return flow on the San Rafael, Duchesne, and Blacks <br />Fork Rivers, and piceance Creek. A value of 20 percent was similarly <br />estimated for irrigation return flow salt load from the Big Sandy River. <br />These were all subtracted from computed total salt loads for the subbasins. <br />Table 1 shows the results of this exercise. <br /> <br />It is estimated that the contribution of ground water from natural <br />sources to the total salt load of the Green and Colorado Rivers above <br />their confluence is 38 percent. This is a reduction from the 55 percent <br />measured as ground water-contributed salt load. The remaining 17 percent of <br />salt load would theoretically be from irrigation returnflow during the base <br />flow period. This 38 percent from natural ground water sources is in <br />contrast to the 58 percent estimated by the EPA, 1971(26) to be from <br />natural diffuse and point sources. The EPA also estimates that the total <br />annual yield to the salt load from the irrigation returnflow is 41 percent <br />and I percent from industrial and municipal sources. BLM, 1978,(25) <br />estimated that surface runoff from the public lands yielded a total of 8 <br />percent of the total salt load of the Upper Basin. Surface runoff from <br />similar lands owned or administered by private individuals, states, Indian <br />tribes, and other Federal agencies probably yields an additional 7 percent <br />of the Upper Basin salt load. These estimates account for 95 percent of <br />the total salt load. The 5 percent unaccounted for is well within the <br />error of these calculations. Table H shows salt load contributions from <br />natural and irrigation returnflow ground water for the nine subbasin"s. <br /> <br />In summary, salt contributions from the Upper Basin can be outlined as <br />follows: <br /> <br />Natural Ground Water (diffuse & point sources) <br />Surface Runoff from Rangelands (BLM, private, & State) <br />Surface Runoff from Forest & Error in Calculations <br />Irrigation Returnflow <br />Industrial & Municipal <br /> <br />38% <br />15% <br />5% <br />41% <br />1% <br /> <br />Total <br /> <br />100 <br /> <br />This exercise gives a gross accounting of sources of salt in the <br />Upper Basin. It was done for the purpose of trying to better identify the <br />contribution of natural sources, an area that has been ignored because of <br />the difficulty in obtaining data. Hyatt et. a!., 1970, indicate that only <br />20 percent of the 1931 to 1960 average annual salt load from the Upper <br />Basin is traced to its area of origin through actual measurements. (27) <br />Therefore, most estimates of the natural salt are derived by determining <br />the salt load from agriculture, industry, municipalities, and natural point <br />sources, then attributing the remaining salt to "other natural sources. II <br />It is believed that the estimates presented in this report give a more <br />accurate value for the salt load contributed from natural diffuse sources. <br /> <br />118 <br />