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<br />N <br />ooJ <br />eN <br />o <br /> <br />Another comparison between natural flows and flow conditions under <br />present levels of depletion and reservoir regulation c~n he derived <br />from table 3.5. As can be seen', reservoir reguli1tinn ....ll..lIlld. I"VI,r the <br />long run, uniformly reduce the percentage of [lows that would occur under <br />present levels of development in the months of May-July, while the per- <br />centage of flows in the winter months would increase to some extent. <br />This effect is, of course, most pronounced at Lees Ferry due to the cu- <br />mulative impact of Lake Powell's operation and that of upstream reser- <br />voirs. The reason for these circumstances is that. spring flows are <br />being captured for storage, with subsequent releases of water from stor- <br />age in the late summer, fall, and winter months. <br /> <br />Present Surface Water Quality <br /> <br />This section will discuss present baseline water quality conditions <br />in those subbasins of the Upper Colorado River Region most likely to be <br />influenced by EET development. Only those variables which have been des- <br />ignated as concerns, or for which water quality standards violations <br />have occurred, are discussed. Tables showing individual State water <br />qUality standards and present monitoring data are not given. Reports <br />by the Environmental Protection Agency, U.S. Geological Survey, and State <br />208 planning agencies were consulted in preparing this brief discussion, <br />as well as detailed development plans and environmental baseline reports. <br />Few footnotes are given, but the references listed at the end of this <br />section and in the bibliography may be consulted for further information and <br />documentation. Also, at the end of this section is a brief discussion <br />of present water quality planning efforts in the Upper Basin. <br /> <br />Variables of Concern. Dissolved solids (salt) concentrations and loadings <br />(DS)l have long been recognized as the most prevalent water quality prob- <br />lems in the Colorado River Basin. In general, salts are contributed pri- <br />marily by the Upper Basin2 and become a problem as they are concentrated <br />downstream in the Lower Basin. The following description of the problem and <br />of the institutional arrangements adopted by the Upper Basin States is <br />from the U.S. Water Resources Council's '75 Water Assessment, Upper Colorado <br />Region Technical Memorandum No.2, State/Regional Future, August, 1976, <br />pp. 28-29. . <br /> <br />1. The designation TDS (total dissolved solids) is more commonly used, <br />but the U.S. Geological Survey (which is performing the future water quality <br />analysis for this assessment) uses the abbreviation DS. It should be noted <br />that DS is a conservative water quality parameter as compared with non- <br />conservative pRrameters such as dissolved oxygen and temperature (see <br />following pages). <br /> <br />2. There are, however, some significant sources of salinity in the Lower <br />Basin. Among them are natural sources and agricultural return flows. <br /> <br />3-16 <br /> <br />:tk~~ <br /> <br />:~{~;~~) <br /> <br />.... '. <br />" ...~.., <br /> <br />,'.- <br />