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Show Colorado River salinity down at Mexican border By Helene C. Monberg Vernal Express Washington Correspondent Washington In a surprising conclusion, conclu-sion, the Bureau of Reclamation's latest progress report on quality of water in the Colorado River Basin states the salt content con-tent in the river has actually gone down at Imperial dam. Imperial dam is in Southern California near the U.S.-Mexical border, and it is the last major storage dam on the Lower Colorado River before it crosses the Mexican border. So it is the site of the last set of water quality gauging stations checked by the U.S. Geological Survey and the Bureau of Reclamation on the river in this country. The Bureau of Reclamation has a number of reasons for the decrease in salinity in the river, and the report makes it plain that experts think the reduction in salinity is only a temporary phenonemon. It notes that the reduction in salinity has occurred at a time when "transbasin diversions" such as the Colorado-Big Thompson and the Fryingpan-Arkansas in Colorado, the San Juan-Chama in New Mexico, and numerous diversions in Utah, have resulted in major depletions of water in the river over a period of about 40 years, "but no additional salt pick-up or loading occurred with these depletions." The same is true of reservoir evaporation, evapora-tion, according to the Bureau. Upper Colorado Col-orado River Basin diversions and depletions deple-tions increased from 1,712,000 acre-feet in the 1930-39 period to 3,565,000 acre-feet in the 1970-79 period, according to the Bureau. Diversions and depletions from reservoir evaporation at Flaming Gorge dam in Utah and Glen Canyon dam in Arizona, in particular, were once regarded regard-ed as the primary causes. But that's not the record being made at Imperial dam during the past decade. "Salinity concentrations at Imperial dam have decreased in an apparent steady decline from 1970-89, dropped notably in 1980, and increased sharply in 1981," the report said. The additions of more Upper Basin storage dams on the River, such as Glen Canyon, Flaming Gorge, Navajo and the Curencanti complex on the Gunnison River in Colorado, actually had a "buffering "buf-fering effect" on keeping down salinity at Imperial dam, the report said. So did the much higher flow of the Colorado River in recent years. Another factor may be the efforts being be-ing made by the technicians in the Soil Conservation Service to work with other agencies and farmers to control erosion, a pilot project on Bureau of Land Management (BLM) land in Utah showed. show-ed. The Bureau of Rec. study said, "BLM salinityerosion studies in the Price River Basin" in eastern Utah "show that at least one drainage yielded significantly significant-ly reduced salt loads where experimental experimen-tal contour plowing and gully plugs were used for erosion control. The feasibility of erosion control as a mechanism to control salinity, including snowmelt runoff, needs further investigation in-vestigation based on the BLM Price River studies," the report stated. The Bureau of Rec. clearly is of two minds about these surprising findings. It is pleased that salinity in the Colorado River basin in stabilizing for the moment, mo-ment, at least. On the other hand, it is concerned that public interest, particularly par-ticularly in the Upper Basin, to control salinity will flag due to these findings, at a time when it is trying to update the Colorado Col-orado River salinity legislation passed in 1974. The report was published last month, but it has just become available. It concludes that salinity on the river seems to be currently contained, if not licked. It gives virtually no credit to the Bureau's own work at Meeker Dome, Grand Valley and Paradox Valley in - Western Colorado primarily because it is too early for the results of such work to show up in Lake Mead at Hoover dam on the Lower Colorado River. It finds that salinity concentrations at acceptable levels, within salinity standards, stan-dards, should continue "for at least the next few years," at Lees Ferry near Glen Canyon dam, and at Hoover, Parker and Imperial dams on the Lower Colorado River. "Unless an extended drought.. .occurs, .oc-curs, salinity should remain fairly stable." With good water conditions in the Basin, "the Colorado River Reservoir Reser-voir system is currently at a high storage level. If above-average runoff occurs in 1983, additional flood control releases may be required, and any increases in flow are expected to decrease salinity levels downstream due to dilution," the report stated. "Therefore," it concluded, "salinity concentrations appear favorable over the next five years. As Upper Basin states continue to develop their apportioned appor-tioned water, salinity levels are expected to rise," it pointed out. But such developments have not proceeded as expected ex-pected and so the stabilizing effect on the river may extend for many years, not merely for the next five, Bureau sources speculate. The report gives some reasons for the obvious slowing of salinity buildup in the river, including favorable hydrologic conditions at this point, the ability of the new Upper Basin reservoirs to contain impurities including salinity, the surprising surpris-ing neutral effect of diversions and depletions, deple-tions, decreased flooding, greater state protection of aquifers, the salinity control con-trol projects, new efforts at erosion control, con-trol, chemical shifts not clearly understood in the Upper Basin reservoirs, particularly at Flaming Gorge, and a new method of measuring total dissolved solids, notably salt. |